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Sample records for aragonite

  1. Enrichment of lanthanides in aragonite

    Institute of Scientific and Technical Information of China (English)

    瞿成利; 路波; 刘刚

    2009-01-01

    Using the constant addition technique,the coprecipitation of lanthanum,gadolinium,and lutetium with aragonite in seawater was experimentally investigated at 25 ℃.Their concentrations in aragonite overgrowths were determined by inductive coupled plasma mass spectrometer.All these lanthanides were strongly enriched in aragonite overgrowths.The amount of lanthanum,gadolinium,and lutetium incorporated into aragonite accounted for 57%-99%,50%-89%,and 40%-91% of their initial total amount,respectively.With the in...

  2. Aragonite twinning in gastropod nacre

    Science.gov (United States)

    Mukai, Hiroki; Saruwatari, Kazuko; Nagasawa, Hiromichi; Kogure, Toshihiro

    2010-10-01

    Aragonite twinning in gastropod nacre has been investigated using scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM) with the focused ion beam (FIB) sample preparation technique. At the growth front of nacre, Haliotis discus hannai and Omphalius rusticus form a "stack-of-coins" structures, which consist of pseudo-hexagonal and elliptical aragonite tablets, respectively. SEM, EBSD, and TEM analyses revealed that these tablets are monolithic single crystal and almost free of the {1 1 0} twins that are common in aragonite of biotic or abiotic origin. The longest diagonal of the hexagon and the longer axis of the ellipse are parallel to the a-axis of aragonite. The crystal orientation of each tablet in a stack, measured by TEM-Kikuchi pattern analysis, is almost the same but there is occasionally {1 1 0} twin-like relationship between adjacent tablets along the stacking. On the other hand, the fibrous aragonite layer formed prior to the nacreous structure is composed of polycrystalline aragonite with high density of {1 1 0} twins. TEM observation suggests that the interlamellar organic sheet prevents the inheritance of the twins, by selecting only single domain of the twins, through the mineral bridge.

  3. Determination of aragonite trace element distribution coefficients from speleothem calcite-aragonite transitions

    Science.gov (United States)

    Wassenburg, J. A.; Scholz, D.; Jochum, K. P.; Cheng, H.; Oster, J.; Immenhauser, A.; Richter, D. K.; Häger, T.; Jamieson, R. A.; Baldini, J. U. L.; Hoffmann, D.; Breitenbach, S. F. M.

    2016-10-01

    The processes that govern the incorporation of (trace) elements into speleothems can often be linked to environmental changes. Although element incorporation into speleothem calcite is now reasonably well understood, current knowledge regarding trace element variability in speleothem aragonite is very limited. Of particular interest is whether trace element distribution coefficients are above or below one in order to assess the extent to which prior aragonite precipitation has affected speleothem aragonite trace element records. This study uses nine calcite-to-aragonite transitions in seven speleothems from diverse environmental settings to derive the first quantitative estimates of the distribution coefficients for several elements in speleothem aragonite: DMg(Ar) = 9.7E-5 ± 9.01E-5, DBa(Ar) = 0.91 ± 0.88, DSr(Ar) = 1.38 ± 0.53, and DU(Ar) = 6.26 ± 4.54 (1σ SD). For one speleothem from western Germany, the distribution coefficients are generally higher, which is potentially related to the very low growth rates (negative correlation with growth rate when growth rate is below 20 μm/year. In summary, our results demonstrate that speleothem aragonite DMg(Ar) is below one, DU(Ar) is considerably above one, and DSr(Ar) is above one or close to unity. For DBa(Ar), reaching a similar conclusion is difficult due to the relatively high uncertainty. Enhanced prior aragonite precipitation will thus result in lower U and higher Mg concentrations in speleothem aragonite, although in many cases Mg in speleothem aragonite is most likely dominated by other processes. This result suggests that U concentrations in aragonitic stalagmites could serve as a very effective proxy for palaeo-rainfall.

  4. Determination of aragonite trace element partition coefficients from speleothem calcite-aragonite transitions

    Science.gov (United States)

    Wassenburg, Jasper A.; Scholz, Denis; Jochum, Klaus Peter; Cheng, Hai; Oster, Jessica; Immenhauser, Adrian; Richter, Detlev K.; Haeger, Tobias; Hoffmann, Dirk; Breitenbach, Sebastian F. M.

    2016-04-01

    Speleothem trace element variability has often been linked to environmental changes. While research has focused on element incorporation into speleothem calcite, our current knowledge of trace element variability in speleothem aragonite is limited to a few studies only. Here we present, to our knowledge, for the first time quantitative estimates of distribution coefficients for speleothem aragonite (DMg, DBa, DSr, and DU). These were derived from ten calcite-to-aragonite transitions from seven speleothems from Morocco, Germany, Spain, France and India. Our calculations indicate the following distribution coefficients: DMg = 1.01E-04 ± 9.0E-05, DBa(Ar) = 0.91 ± 0.53, DSr(Ar) = 1.38 ± 0.53, and DU(Ar) = 6.26 ± 4.53. These results are discussed in the context of speleothem growth rates, Rayleigh distillation effects, temperature, drip water elemental composition and drip water pH. We conclude that speleothem aragonite DMg(Ar) is below one, DSr(Ar) is close to unity, and DU(Ar) is above one. For DBa(Ar), such a conclusion is difficult. Speleothem growth rate may affect aragonite DSr in samples forming at a growth rate lower than 20 μm/a. Our results also indicate that calcite DSr and calcite DBa are affected by the Mg content of calcite. This has important implications for studies attempting to quantify processes like prior calcite precipitation. In particular, DSr and DBa cannot be transferred from caves developed within a limestone host rock to caves developed within a dolostone host rock.

  5. Synthesis and characterization of lamellar aragonite with hydrophobic property

    International Nuclear Information System (INIS)

    A novel and simple synthetic method for the preparation of hydrophobic lamellar aragonite has been developed. The crystallization of aragonite was conducted by the reaction of sodium carbonate with calcium chloride in the presence of sodium stearate. The resulting products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and the contact angle. The results revealed that sodium stearate plays an important role in determining the structure and morphology of the sample. Besides, we have succeeded in surface modification of particles in situ at the same time. The contact angle of the modified aragonite reached 108.59 deg.

  6. Synthesis and characterization of lamellar aragonite with hydrophobic property

    Energy Technology Data Exchange (ETDEWEB)

    Wang Chengyu, E-mail: wangcy@nefu.edu.cn [College of Materials Science and Engineering, Northeast Forestry University, 150040 (China); Xu Yang [China Nation Center for Quality Supervision and Test of Woodworking Machinery, Northeast Forestry University, 150040 (China); Liu Yalan; Li Jian [College of Materials Science and Engineering, Northeast Forestry University, 150040 (China)

    2009-04-30

    A novel and simple synthetic method for the preparation of hydrophobic lamellar aragonite has been developed. The crystallization of aragonite was conducted by the reaction of sodium carbonate with calcium chloride in the presence of sodium stearate. The resulting products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and the contact angle. The results revealed that sodium stearate plays an important role in determining the structure and morphology of the sample. Besides, we have succeeded in surface modification of particles in situ at the same time. The contact angle of the modified aragonite reached 108.59 deg.

  7. Aragonite coating solutions (ACS) based on artificial seawater

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Developed completely inorganic solutions for the deposition of monolayers of aragonite spherules (or ooids). • Solutions mimicked the artificial seawater. • Biomimetic crystallization was performed at the tropical sea surface temperature of 30 °C. - Abstract: Aragonite (CaCO3, calcium carbonate) is an abundant biomaterial of marine life. It is the dominant inorganic phase of coral reefs, mollusc bivalve shells and the stalactites or stalagmites of geological sediments. Inorganic and initially precipitate-free aragonite coating solutions (ACS) of pH 7.4 were developed in this study to deposit monolayers of aragonite spherules or ooids on biomaterial (e.g., UHMWPE, ultrahigh molecular weight polyethylene) surfaces soaked in ACS at 30 °C. The ACS solutions of this study have been developed for the surface engineering of synthetic biomaterials. The abiotic ACS solutions, enriched with calcium and bicarbonate ions at different concentrations, essentially mimicked the artificial seawater composition and started to deposit aragonite after a long (4 h) incubation period at the tropical sea surface temperature of 30 °C. While numerous techniques for the solution deposition of calcium hydroxyapatite (Ca10(PO4)6(OH)2), of low thermodynamic solubility, on synthetic biomaterials have been demonstrated, procedures related to the solution-based surface deposition of high solubility aragonite remained uncommon. Monolayers of aragonite ooids deposited at 30 °C on UHMWPE substrates soaked in organic-free ACS solutions were found to possess nano-structures similar to the mortar-and-brick-type botryoids observed in biogenic marine shells. Samples were characterized using SEM, XRD, FTIR, ICP-AES and contact angle goniometry

  8. Aragonite coating solutions (ACS) based on artificial seawater

    Energy Technology Data Exchange (ETDEWEB)

    Tas, A. Cuneyt, E-mail: c_tas@hotmail.com

    2015-03-01

    Graphical abstract: - Highlights: • Developed completely inorganic solutions for the deposition of monolayers of aragonite spherules (or ooids). • Solutions mimicked the artificial seawater. • Biomimetic crystallization was performed at the tropical sea surface temperature of 30 °C. - Abstract: Aragonite (CaCO{sub 3}, calcium carbonate) is an abundant biomaterial of marine life. It is the dominant inorganic phase of coral reefs, mollusc bivalve shells and the stalactites or stalagmites of geological sediments. Inorganic and initially precipitate-free aragonite coating solutions (ACS) of pH 7.4 were developed in this study to deposit monolayers of aragonite spherules or ooids on biomaterial (e.g., UHMWPE, ultrahigh molecular weight polyethylene) surfaces soaked in ACS at 30 °C. The ACS solutions of this study have been developed for the surface engineering of synthetic biomaterials. The abiotic ACS solutions, enriched with calcium and bicarbonate ions at different concentrations, essentially mimicked the artificial seawater composition and started to deposit aragonite after a long (4 h) incubation period at the tropical sea surface temperature of 30 °C. While numerous techniques for the solution deposition of calcium hydroxyapatite (Ca{sub 10}(PO{sub 4}){sub 6}(OH){sub 2}), of low thermodynamic solubility, on synthetic biomaterials have been demonstrated, procedures related to the solution-based surface deposition of high solubility aragonite remained uncommon. Monolayers of aragonite ooids deposited at 30 °C on UHMWPE substrates soaked in organic-free ACS solutions were found to possess nano-structures similar to the mortar-and-brick-type botryoids observed in biogenic marine shells. Samples were characterized using SEM, XRD, FTIR, ICP-AES and contact angle goniometry.

  9. Uranyl incorporation into calcite and aragonite: XAFS and luminescence studies

    International Nuclear Information System (INIS)

    X-ray absorption, luminescence, and Raman spectroscopic studies of U(VI)-containing calcite and aragonite show that the UO22+ ion, the dominant and mobile form of dissolved uranium in near-surface waters, has a disordered and apparently less stable coordination environment when incorporated into calcite in comparison to aragonite, both common polymorphs of CaCO3. Their findings suggest that calcite, a widely distributed authigenic mineral in soils and near-surface sediments and a principal weathering product of concrete-based containment structures, is not likely to be a suitable host for the long-term sequestration of U(VI). The more stable coordination provided by aragonite suggests that its long-term retention should be favored in this phase, until it inverts to calcite. Consequently, future remobilization of U(VI) coprecipitated with calcium carbonate minerals should not be ruled out in assessments of contaminated sites. Their observation of a similar equatorial coordination of UO22+ in aragonite and the dominant aqueous species [UO2(CO3)34-] but a different coordination in calcite indicates that a change in UO22+ coordination is required for its incorporation into calcite. This may explain the observed preferential uptake of U(VI) by aragonite relative to calcite

  10. High-pressure compressibility and thermal expansion of aragonite

    Science.gov (United States)

    Palaich, S.; Heffern, R. A.; Kavner, A.; Manning, C. E.; Merlini, M.; Hanfland, M.

    2015-12-01

    An important component of Earth's deep carbon cycle is the return of surficial carbon to the planet's interior. Most recycled carbon is bound in CaCO3 minerals, of which aragonite is the most significant at upper mantle pressures. It is therefore essential to understand the phase stability and compressibility of aragonite at high pressures and temperatures. Aragonite has an orthorhombic 2/m 2/m 2/m structure and a Z of 4. The high-pressure behavior of aragonite has been studied under dynamic and static compression using both X-ray diffraction and spectroscopic techniques, but these results have been contradictory and inconclusive. To address these issues, a single-crystal synchrotron X-ray diffraction study of aragonite under hydrostatic compression was performed to 40 GPa in a diamond anvil cell at ambient temperature. To supplement the compressional experiment, thermal expansion was also measured via powder X-ray diffraction at ambient pressure between 298-673 K. Ambient-pressure single-crystal measurements confirm the orthorhombic 2/m 2/m 2/m structure and yield a unit cell volume of 226.932(5) Å3. At room temperature, aragonite is stable in the orthorhombic structure to 40 GPa, with an isothermal bulk modulus of 66.5(7) GPa and K' = 5.0(1). The a-axis is most compressible and the c-axis is the least compressible. The b-axis is intermediate, but starts to decrease in compressibility at ~15 GPa. Between 25-30 GPa the aragonite unit cell distorts due to the stiffening of the b-axis, which is controlled by the orientation and distortion of the carbonate groups, layered in the aragonite structure parallel to the a-axis. The carbonate groups elongate and deform from equilateral to isosceles between 15 and 30 GPa, thus influencing the compressibility of the b-axis. The thermal expansion measurements yield expansion coefficients a0 = 4.9(2) x 10-5 and a1 =3.7(5) x 10-8, in agreement with previous data. The combination of the isothermal and isobaric studies allows the

  11. Growth rate controlled barium partitioning in calcite and aragonite

    Science.gov (United States)

    Goetschl, Katja Elisabeth; Mavromatis, Vasileios; Baldermann, Andre; Purgstaller, Bettina; Dietzel, Martin

    2016-04-01

    The barium (Ba) content and the Ba/Ca molar ratios in biogenic and abiotic carbonates have been widely used from the scientific community as a geochemical proxy especially in marine and early diagenetic settings. The Ba content of carbonate minerals has been earlier associated to changes in oceanic circulation that may have been caused by upwelling, changes in weathering regimes and river-runoff as well as melt water discharge. The physicochemical controls of Ba ion incorporation in the two most abundant CaCO3 polymorphs found in Earth's surface environments, i.e. calcite and aragonite, have adequately been studied only for calcite. These earlier studies (i.e. [1]) suggest that at increasing growth rate, Ba partitioning in calcite is increasing as well. In contrast, to date the effect of growth rate on the partitioning of Ba in aragonite remains questionable, despite the fact that this mineral phase is the predominant carbonate-forming polymorph in shallow marine environments. To shed light on the mechanisms controlling Ba ion uptake in carbonates in this study we performed steady-state Ba co-precipitation experiments with calcite and aragonite at 25°C. The obtained results for the partitioning of Ba in calcite are in good agreement with those reported earlier by [1], whereas those for aragonite indicate a reduction of Ba partitioning at elevated aragonite growth rates, with the partitioning coefficient value between solid and fluid to be approaching the unity. This finding is good agreement with the formation of a solid solution in the aragonite-witherite system, owing to the isostructural crystallography of the two mineral phases. Moreover, our data set provides new insights that are required for reconstructing the evolution of the Ba content of pristine marine versus diagenetically altered carbonate minerals commonly occurring in marine subfloor settings, as the thermodynamically less stable aragonite will transform to calcite enriched in Ba, whilst affecting

  12. Intra- and inter-annual uranium concentration variability in a Belizean stalagmite controlled by prior aragonite precipitation: A new tool for reconstructing hydro-climate using aragonitic speleothems

    Science.gov (United States)

    Jamieson, Robert A.; Baldini, James U. L.; Brett, Marianne J.; Taylor, Jessica; Ridley, Harriet E.; Ottley, Chris J.; Prufer, Keith M.; Wassenburg, Jasper A.; Scholz, Denis; Breitenbach, Sebastian F. M.

    2016-10-01

    Aragonitic speleothems are increasingly utilised as palaeoclimate archives due to their amenability to high precision U-Th dating. Proxy records from fast-growing aragonitic stalagmites, precisely dated to annual timescales, can allow investigation of climatic events occurring on annual or even sub-annual timescales with minimal chronological uncertainty. However, the behaviour of many trace elements, such as uranium, in aragonitic speleothems has not thus far been as well constrained as in calcitic speleothems. Here, we use uranium concentration shifts measured across primary calcite-to-aragonite mineralogical transitions in speleothems to calculate the distribution coefficient of uranium in aragonitic speleothems (derived DU = 3.74 ± 1.13). Because our calculated DU is considerably above 1 increased prior aragonite precipitation due to increased karst water residence time should strongly control stalagmite aragonite U/Ca values. Consequently, uranium concentrations in aragonitic speleothems should act as excellent proxies for effective rainfall. We test this using a high-resolution ICP-MS derived trace element dataset from a Belizean stalagmite. YOK-G is an aragonitic stalagmite from Yok Balum cave in Belize with an extremely robust monthly-resolved chronology built using annual δ13C cycles. We interpret seasonal U/Ca variations in YOK-G as reflecting changes in the amount and seasonality of prior aragonite precipitation driven by variable rainfall amounts. The U/Ca record strongly suggests that modern drying has occurred in Belize, and that this drying was primarily caused by a reduction in wet season rainfall. This is consistent with published stable isotope data from YOK-G also very strongly suggesting modern rainfall reductions, previously interpreted as the result of southward ITCZ displacement. Our results strongly suggest that U/Ca values in aragonitic speleothems are excellent proxies for rainfall variability. This new tool, combined with the

  13. Visualization of newt aragonitic otoconial matrices using transmission electron microscopy

    Science.gov (United States)

    Steyger, P. S.; Wiederhold, M. L.

    1995-01-01

    Otoconia are calcified protein matrices within the gravity-sensing organs of the vertebrate vestibular system. These protein matrices are thought to originate from the supporting or hair cells in the macula during development. Previous studies of mammalian calcitic, barrel-shaped otoconia revealed an organized protein matrix consisting of a thin peripheral layer, a well-defined organic core and a flocculent matrix inbetween. No studies have reported the microscopic organization of the aragonitic otoconial matrix, despite its protein characterization. Pote et al. (1993b) used densitometric methods and inferred that prismatic (aragonitic) otoconia have a peripheral protein distribution, compared to that described for the barrel-shaped, calcitic otoconia of birds, mammals, and the amphibian utricle. By using tannic acid as a negative stain, we observed three kinds of organic matrices in preparations of fixed, decalcified saccular otoconia from the adult newt: (1) fusiform shapes with a homogenous electron-dense matrix; (2) singular and multiple strands of matrix; and (3) more significantly, prismatic shapes outlined by a peripheral organic matrix. These prismatic shapes remain following removal of the gelatinous matrix, revealing an internal array of organic matter. We conclude that prismatic otoconia have a largely peripheral otoconial matrix, as inferred by densitometry.

  14. Magnesium stable isotope fractionation in marine biogenic calcite and aragonite

    Science.gov (United States)

    Wombacher, F.; Eisenhauer, A.; Böhm, F.; Gussone, N.; Regenberg, M.; Dullo, W.-Chr.; Rüggeberg, A.

    2011-10-01

    This survey of magnesium stable isotope compositions in marine biogenic aragonite and calcite includes samples from corals, sclerosponges, benthic porcelaneous and planktonic perforate foraminifera, coccolith oozes, red algae, and an echinoid and brachiopod test. The analyses were carried out using MC-ICP-MS with an external repeatability of ±0.22‰ (2SD for δ 26Mg; n = 37), obtained from a coral reference sample (JCp-1). Magnesium isotope fractionation in calcitic corals and sclerosponges agrees with published data for calcitic speleothems with an average Δ 26Mg calcite-seawater = -2.6 ± 0.3‰ that appears to be weakly related to temperature. With one exception ( Vaceletia spp.), aragonitic corals and sclerosponges also display uniform Mg isotope fractionations relative to seawater with Δ 26Mg biogenic aragonite-seawater = -0.9 ± 0.2. Magnesium isotopes in high-Mg calcites from red algae, echinoids and perhaps some porcelaneous foraminifera as well as in all low-Mg calcites (perforate foraminifera, coccoliths and brachiopods) display significant biological influences. For planktonic foraminifera, the Mg isotope data is consistent with the fixation of Mg by organic material under equilibrium conditions, but appears to be inconsistent with Mg removal from vacuoles. Our preferred model, however, suggests that planktonic foraminifera synthesize biomolecules that increase the energetic barrier for Mg incorporation. In this model, the need to remove large quantities of Mg from vacuole solutions is avoided. For the high-Mg calcites from echinoids, the precipitation of amorphous calcium carbonate may be responsible for their weaker Mg isotope fractionation. Disregarding superimposed biological effects, it appears that cation light isotope enrichments in CaCO 3 principally result from a chemical kinetic isotope effect, related to the incorporation of cations at kink sites. In this model, the systematics of cation isotope fractionations in CaCO 3 relate to the

  15. Uranium isotope fractionation during coprecipitation with aragonite and calcite

    Science.gov (United States)

    Chen, Xinming; Romaniello, Stephen J.; Herrmann, Achim D.; Wasylenki, Laura E.; Anbar, Ariel D.

    2016-09-01

    Natural variations in 238U/235U of marine calcium carbonates might provide a useful way of constraining redox conditions of ancient environments. In order to evaluate the reliability of this proxy, we conducted aragonite and calcite coprecipitation experiments at pH ∼7.5 and ∼8.5 to study possible U isotope fractionation during incorporation into these minerals. Small but significant U isotope fractionation was observed in aragonite experiments at pH ∼8.5, with heavier U isotopes preferentially enriched in the solid phase. 238U/235U of dissolved U in these experiments can be fit by Rayleigh fractionation curves with fractionation factors of 1.00007 + 0.00002/-0.00003, 1.00005 ± 0.00001, and 1.00003 ± 0.00001. In contrast, no resolvable U isotope fractionation was observed in an aragonite experiment at pH ∼7.5 or in calcite experiments at either pH. Equilibrium isotope fractionation among different aqueous U species is the most likely explanation for these findings. Certain charged U species are preferentially incorporated into calcium carbonate relative to the uncharged U species Ca2UO2(CO3)3(aq), which we hypothesize has a lighter equilibrium U isotope composition than most of the charged species. According to this hypothesis, the magnitude of U isotope fractionation should scale with the fraction of dissolved U that is present as Ca2UO2(CO3)3(aq). This expectation is confirmed by equilibrium speciation modeling of our experiments. Theoretical calculation of the U isotope fractionation factors between different U species could further test this hypothesis and our proposed fractionation mechanism. These findings suggest that U isotope variations in ancient carbonates could be controlled by changes in the aqueous speciation of seawater U, particularly changes in seawater pH, PCO2 , Ca2+, or Mg2+ concentrations. In general, these effects are likely to be small (<0.13‰), but are nevertheless potentially significant because of the small natural range of

  16. Towards an Understanding of the Role of Aragonite in the Mechanical Properties of Nacre

    Energy Technology Data Exchange (ETDEWEB)

    2010-08-25

    Nacre, also known as mother-of-pearl, is a biocomposite material that exhibits higher strength and fracture toughness than its component materials. It derives its strength from the brick-and-mortar layering of aragonite (CaCO{sub 3}) platelets and organic binder. It is believed that the protein binder helps redistribute the stress throughout all tablets for optimal mechanical performance. In this study, we attempt to measure the mechanical properties of aragonite within nacre and compare them to bulk aragonite and bulk nacre and understand the redistribution of stresses. Here we show that x-ray diffraction techniques are useful for isolating and measuring strain of crystallites within a composite material. Our results show that the apparent stiffness of aragonite varies with crystallographic directions and is higher than the stiffness of bulk nacre in all cases, meaning that aragonite tablets are exposed to less than the average bulk stress. The average force applied to the bulk sample is partitioned between the aragonite and the binder, so that the protein layer bears as much as 27.2% of the total applied force. Different crystallographic directions exhibit behaviors different than bulk aragonite or bulk nacre. These are related to texture of aragonite platelets (i.e. preferred orientations within nacre). By examining nacre, we can obtain a better understanding of the mechanical relationship between the ceramic and polymer in composite materials. We expect that x-ray diffraction will become the standard method for probing the mechanical properties of composite materials.

  17. Aragonite saturation state dynamics in a coastal upwelling zone

    Science.gov (United States)

    Harris, Katherine E.; Degrandpre, Michael D.; Hales, Burke

    2013-06-01

    upwelling zones may be at enhanced risk from ocean acidification as upwelling brings low aragonite saturation state (ΩAr) waters to the surface that are further suppressed by anthropogenic CO2. ΩAr was calculated with pH, pCO2, and salinity-derived alkalinity time series data from autonomous pH and pCO2 instruments moored on the Oregon shelf and shelf break during different seasons from 2007 to 2011. Surface ΩAr values ranged between 0.66 ± 0.04 and 3.9 ± 0.04 compared to an estimated pre-industrial range of 1.0 ± 0.1 to 4.7 ± 0.1. Upwelling of high-CO2 water and subsequent removal of CO2 by phytoplankton imparts a dynamic range to ΩAr from ~1.0 to ~4.0 between spring and autumn. Freshwater input also suppresses saturation states during the spring. Winter ΩAr is less variable than during other seasons and is controlled primarily by mixing of the water column.

  18. Study of Binding Interaction between Pif80 Protein Fragment and Aragonite

    Science.gov (United States)

    Du, Yuan-Peng; Chang, Hsun-Hui; Yang, Sheng-Yu; Huang, Shing-Jong; Tsai, Yu-Ju; Huang, Joseph Jen-Tse; Chan, Jerry Chun Chung

    2016-08-01

    Pif is a crucial protein for the formation of the nacreous layer in Pinctada fucata. Three non-acidic peptide fragments of the aragonite-binding domain (Pif80) are selected, which contain multiple copies of the repeat sequence DDRK, to study the interaction between non-acidic peptides and aragonite. The polypeptides DDRKDDRKGGK (Pif80-11) and DDRKDDRKGGKDDRKDDRKGGK (Pif80-22) have similar binding affinity to aragonite. Solid-state NMR data indicate that the backbones of Pif80-11 and Pif80-22 peptides bound on aragonite adopt a random-coil conformation. Pif80-11 is a lot more effective than Pif80-22 in promoting the nucleation of aragonite on the substrate of β-chitin. Our results suggest that the structural arrangement at a protein-mineral interface depends on the surface structure of the mineral substrate and the protein sequence. The side chains of the basic residues, which function as anchors to the aragonite surface, have uniform structures. The role of basic residues as anchors in protein-mineral interaction may play an important role in biomineralization.

  19. Study of Binding Interaction between Pif80 Protein Fragment and Aragonite.

    Science.gov (United States)

    Du, Yuan-Peng; Chang, Hsun-Hui; Yang, Sheng-Yu; Huang, Shing-Jong; Tsai, Yu-Ju; Huang, Joseph Jen-Tse; Chan, Jerry Chun Chung

    2016-01-01

    Pif is a crucial protein for the formation of the nacreous layer in Pinctada fucata. Three non-acidic peptide fragments of the aragonite-binding domain (Pif80) are selected, which contain multiple copies of the repeat sequence DDRK, to study the interaction between non-acidic peptides and aragonite. The polypeptides DDRKDDRKGGK (Pif80-11) and DDRKDDRKGGKDDRKDDRKGGK (Pif80-22) have similar binding affinity to aragonite. Solid-state NMR data indicate that the backbones of Pif80-11 and Pif80-22 peptides bound on aragonite adopt a random-coil conformation. Pif80-11 is a lot more effective than Pif80-22 in promoting the nucleation of aragonite on the substrate of β-chitin. Our results suggest that the structural arrangement at a protein-mineral interface depends on the surface structure of the mineral substrate and the protein sequence. The side chains of the basic residues, which function as anchors to the aragonite surface, have uniform structures. The role of basic residues as anchors in protein-mineral interaction may play an important role in biomineralization. PMID:27484975

  20. Skeletal aragonite neomorphism — quantitative modelling of a two-water diagenetic system

    Science.gov (United States)

    Maliva, Robert G.

    1998-11-01

    The neomorphism of skeletal aragonite occurs by the simultaneous dissolution of aragonite and precipitation of calcite along thin solution films, which may have an associated zone of partly dissolved aragonite (chalky zone). It has been proposed that pore waters at neomorphic calcite-aragonite contact zones (neomorphic fronts) may be partly isolated from bulk pore waters and thus retain primary geochemical signatures to varying degrees. Iterative computer programs were developed that simulate aragonite neomorphism in two-water diagenetic systems using stable isotope and trace element data. Neomorphism of aragonitic mollusks from the Purbeck Group of southern England (Late Jurassic to Early Cretaceous) was associated with a decrease in strontium concentration from approximately 5100 ppm to 500 ppm. Modelling results indicate a high bulk water/rock ratio and minimal, if any, isolation of the neomorphic front waters for the Purbeck Group mollusks and also for some Pleistocene corals. Partial isolation of neomorphic front waters from bulk pore waters is uncommon, based on published data on the geochemistry of neomorphic calcites. However, partial isolation does occur in some thick, low porosity shells, such as the gastropod Strombus gigas (Pleistocene). Process-based modelling of fluid-rock interaction provides a means for better interpreting trace element and stable isotope data in diagenetic carbonates. Sensitivity analysis results indicate that water/rock ratios cannot be determined at much better than order of magnitude accuracies, because of uncertainties over initial pore water composition, fractionation factors and distribution coefficients.

  1. 88Sr/86Sr fractionation in inorganic aragonite and in corals

    Science.gov (United States)

    Fruchter, Noa; Eisenhauer, Anton; Dietzel, Martin; Fietzke, Jan; Böhm, Florian; Montagna, Paolo; Stein, Moti; Lazar, Boaz; Rodolfo-Metalpa, Riccardo; Erez, Jonathan

    2016-04-01

    Conflicting results have been reported for the stable Sr isotope fractionation, specifically with respect to the influence of temperature. In an experimental study we have investigated the stable Sr isotope systematics for inorganically precipitated and biogenic (coral) aragonite (natural and laboratory-cultured). Inorganic aragonite precipitation experiments were performed from natural seawater using the CO2 diffusion technique. The experiments were performed at different temperatures and different carbonate ion concentrations. 88Sr/86Sr of the inorganic aragonite precipitated in the experiments are 0.2‰ lighter than seawater, but showed no correlation to the water temperature or to CO32- concentration. Similar observations are made in different coral species (Cladocora caespitosa, Porites sp. and Acropora sp.), with identical fractionation from the bulk solution and no correlation to temperature or CO32- concentration. The lack of 88Sr/86Sr variability in corals at different environmental parameters and the similarity to the 88Sr/86Sr fractionation in inorganic aragonite may indicate a similar Sr incorporation mechanism in corals skeleton and inorganic aragonite, and therefore the previously proposed Rayleigh-based multi element model (Gaetani et al., 2011) cannot explain the process of Sr incorporation in the coral skeletal material. It is proposed that the relatively constant 88Sr/86Sr fractionation in aragonite can be used for paleo reconstruction of seawater 88Sr/86Sr composition. The seawater 88Sr/86Sr ratio reconstruction can be further used in calcite samples to reconstruct paleo precipitation rates.

  2. Biotic control of skeletal growth by scleractinian corals in aragonite-calcite seas.

    Directory of Open Access Journals (Sweden)

    Tomihiko Higuchi

    Full Text Available Modern scleractinian coral skeletons are commonly composed of aragonite, the orthorhombic form of CaCO3. Under certain conditions, modern corals produce calcite as a secondary precipitate to fill pore space. However, coral construction of primary skeletons from calcite has yet to be demonstrated. We report a calcitic primary skeleton produced by the modern scleractinian coral Acropora tenuis. When uncalcified juveniles were incubated from the larval stage in seawater with low mMg/Ca levels, the juveniles constructed calcitic crystals in parts of the primary skeleton such as the septa; the deposits were observable under Raman microscopy. Using scanning electron microscopy, we observed different crystal morphologies of aragonite and calcite in a single juvenile skeleton. Quantitative analysis using X-ray diffraction showed that the majority of the skeleton was composed of aragonite even though we had exposed the juveniles to manipulated seawater before their initial crystal nucleation and growth processes. Our results indicate that the modern scleractinian coral Acropora mainly produces aragonite skeletons in both aragonite and calcite seas, but also has the ability to use calcite for part of its skeletal growth when incubated in calcite seas.

  3. Abrupt onset and prolongation of aragonite undersaturation events in the Southern Ocean

    Science.gov (United States)

    Hauri, Claudine; Friedrich, Tobias; Timmermann, Axel

    2016-02-01

    Ocean acidification may lead to seasonal aragonite undersaturation in surface waters of the Southern Ocean as early as 2030 (ref. ). These conditions are harmful to key organisms such as pteropods, which contribute significantly to the pelagic foodweb and carbon export fluxes in this region. Although the severity of ocean acidification impacts is mainly determined by the duration, intensity and spatial extent of aragonite undersaturation events, little is known about the nature of these events, their evolving attributes and the timing of their onset in the Southern Ocean. Using an ensemble of ten Earth system models, we show that starting around 2030, aragonite undersaturation events will spread rapidly, affecting ~30% of Southern Ocean surface waters by 2060 and >70% by 2100, including the Patagonian Shelf. On their onset, the duration of these events will increase abruptly from 1 month to 6 months per year in less than 20 years in >75% of the area affected by end-of-century aragonite undersaturation. This is likely to decrease the ability of organisms to adapt to a quickly evolving environment. The rapid equatorward progression of surface aragonite undersaturation can be explained by the uptake of anthropogenic CO2, whereas climate-driven physical or biological changes will play a minor role.

  4. Phase transformation of Mg-calcite to aragonite in active-forming hot spring travertines

    Science.gov (United States)

    Greer, Heather F.; Zhou, Wuzong; Guo, Li

    2015-08-01

    A travertine specimen collected from the western part of Yunnan Province of China was subjected to microstructural analysis by powder X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. A new formation mechanism was proposed whereby polycrystalline rhombohedral particles of magnesium-containing calcite underwent a phase transformation into sheaf-like clusters of aragonite microrods. It is proposed that a high concentration of magnesium ions and embedded biological matter poisoned the growth of calcite and therefore instigated the phase transformation of the core of the rhombohedral calcite particles to an aragonite phase with a higher crystallinity. The single crystalline aragonite microrods with a higher density than the Mg-calcite nanocrystallites grew at the expense of the latter to generate sheaf-like clusters. This newly discovered formation mechanism is expected to enhance previous knowledge on this geologically important phase transformation from a morphology point of view.

  5. Preserved aragonite cements in Miocene coral reefs: a record of Messinian salinity crises in Mediterranean

    Energy Technology Data Exchange (ETDEWEB)

    Esteban, M.; Prezbindowski, D.R.

    1985-02-01

    Layers of fibrous aragonite cement up to 2 cm thick, developed on aragonitic corals and micritic cements, occur in outcrops of Miocene coral reefs in western Sicily. These aragonitic fabrics show only minor amounts of corrosion after subaerial exposure for at least 3 m.y. Their preservation is attributed to encasement by subsequent gypsum cements. Although these botryoidal, banded aragonite cements are strontium-rich (7000 ppm) and resemble modern marine examples, they were precipitated in secondarily enlarged pores that formed during erosional episodes. Multiple cycles of enrichment in oxygen and carbon stable isotopes are recorded in the aragonite cement layers. The delta/sup 18/O values of these cycles range from -0.9 to +6.8 per thousand, whereas the delta/sup 13/C values range from +0.6 to +3.8 per thousand (PDB). These cyclic variations, indicated by isotopic data together with the petrology of the cements, are believed to record major changes in salinity, temperature, and organic productivity of the Mediterranean waters during the Miocene-Pliocene transition. These Messinian reefs were subaerially exposed and later onlapped by the upper evaporite unit with multiple cycles of marine hypersaline carbonate and evaporite deposition separated by periods of erosion. Aragonite cements formed in the enlarged cavities of the lower Messinian reefs during time of deposition of the upper evaporite and recorded the changes in Mediterranean water chemistry. This cementation is believed to have continued into the early Pliocene when colder Atlantic waters invaded the Mediterranean, ending reef growth and evaporite deposition.

  6. Limpets counteract ocean acidification induced shell corrosion by thickening of aragonitic shell layers

    Directory of Open Access Journals (Sweden)

    G. Langer

    2014-08-01

    Full Text Available Specimens of the patellogastropod limpet Patella caerulea were collected within (pHlow-shells and outside (pHn-shells a CO2 vent site at Ischia, Italy. Four pHlow-shells and four pHn-shells were sectioned transversally and scanned for polymorph distribution by means of confocal Raman microscopy. The pHlow-shells displayed a twofold increase in aragonite area fraction and size normalised aragonite area. Size normalised calcite area was halved in pHlow-shells. Taken together with the increased apical and the decreased flank size normalised thickness of the pHlow-shells, these data led us to conclude that low pH exposed P. caerulea specimens counteract shell dissolution by enhanced shell production. The latter is different from normal elongation growth and proceeds through addition of aragonitic layers only, while the production of calcitic layers is confined to elongation growth. Therefore aragonite cannot be regarded as a per se disadvantageous polymorph under ocean acidification conditions.

  7. Limpets counteract ocean acidification induced shell corrosion by thickening of aragonitic shell layers

    Science.gov (United States)

    Langer, G.; Nehrke, G.; Baggini, C.; Rodolfo-Metalpa, R.; Hall-Spencer, J. M.; Bijma, J.

    2014-12-01

    Specimens of the patellogastropod limpet Patella caerulea were collected within (pHlow-shells) and outside (pHn-shells) a CO2 vent site at Ischia, Italy. Four pHlow-shells and four pHn-shells were sectioned transversally and scanned for polymorph distribution by means of confocal Raman microscopy. The pHlow-shells displayed a twofold increase in aragonite area fraction and size-normalised aragonite area. Size-normalised calcite area was halved in pHlow-shells. Taken together with the increased apical and the decreased flank size-normalised thickness of the pHlow-shells, these data led us to conclude that low-pH-exposed P. caerulea specimens counteract shell dissolution by enhanced shell production. This is different from normal elongation growth and proceeds through addition of aragonitic parts only, while the production of calcitic parts is confined to elongation growth. Therefore, aragonite cannot be regarded as a disadvantageous polymorph per se under ocean acidification conditions.

  8. Aragonite saturation states and nutrient fluxes in coral reef sediments in Biscayne National Park, FL, USA

    Science.gov (United States)

    Lisle, John T.; Reich, Christopher D.; Halley, Robert B.

    2014-01-01

    Some coral reefs, such as patch reefs along the Florida Keys reef tract, are not showing significant reductions in calcification rates in response to ocean acidification. It has been hypothesized that this recalcitrance is due to local buffering effects from biogeochemical processes driven by seagrasses. We investigated the influence that pore water nutrients, dissolved inorganic carbon (DIC) and total alkalinity (TA) have on aragonite saturation states (Ωaragonite) in the sediments and waters overlying the sediment surfaces of sand halos and seagrass beds that encircle Alinas and Anniversary reefs in Biscayne National Park. Throughout the sampling period, sediment pore waters from both bottom types had lower oxidation/reduction potentials (ORP), with lower pH relative to the sediment surface waters. The majority (86.5%) of flux rates (n = 96) for ΣNOx–, PO43–, NH4+, SiO2, DIC and TA were positive, sometimes contributing significant concentrations of the respective constituents to the sediment surface waters. The Ωaragonite values in the pore waters (range: 0.18 to 4.78) were always lower than those in the overlying waters (2.40 to 4.46), and 52% (n = 48) of the values were aragonite in 75% (n = 16) of the samples, but increased it in the remainder. The elevated fluxes of nutrients, DIC and TA into the sediment–water interface layer negatively alters the suitability of this zone for the settlement and development of calcifying larvae, while enhancing the establishment of algal communities.

  9. Dissolution dominating calcification process in polar pteropods close to the point of aragonite undersaturation.

    Science.gov (United States)

    Bednaršek, Nina; Tarling, Geraint A; Bakker, Dorothee C E; Fielding, Sophie; Feely, Richard A

    2014-01-01

    Thecosome pteropods are abundant upper-ocean zooplankton that build aragonite shells. Ocean acidification results in the lowering of aragonite saturation levels in the surface layers, and several incubation studies have shown that rates of calcification in these organisms decrease as a result. This study provides a weight-specific net calcification rate function for thecosome pteropods that includes both rates of dissolution and calcification over a range of plausible future aragonite saturation states (Ω(ar)). We measured gross dissolution in the pteropod Limacina helicina antarctica in the Scotia Sea (Southern Ocean) by incubating living specimens across a range of aragonite saturation states for a maximum of 14 days. Specimens started dissolving almost immediately upon exposure to undersaturated conditions (Ω(ar) ∼ 0.8), losing 1.4% of shell mass per day. The observed rate of gross dissolution was different from that predicted by rate law kinetics of aragonite dissolution, in being higher at Ω(ar) levels slightly above 1 and lower at Ω(ar) levels of between 1 and 0.8. This indicates that shell mass is affected by even transitional levels of saturation, but there is, nevertheless, some partial means of protection for shells when in undersaturated conditions. A function for gross dissolution against Ω(ar) derived from the present observations was compared to a function for gross calcification derived by a different study, and showed that dissolution became the dominating process even at Ω(ar) levels close to 1, with net shell growth ceasing at an Ω(ar) of 1.03. Gross dissolution increasingly dominated net change in shell mass as saturation levels decreased below 1. As well as influencing their viability, such dissolution of pteropod shells in the surface layers will result in slower sinking velocities and decreased carbon and carbonate fluxes to the deep ocean.

  10. Synthesis of vaterite and aragonite crystals using biomolecules of tomato and capsicum

    Science.gov (United States)

    Chen, Long; Xu, Wang-Hua; Zhao, Ying-Guo; Kang, Yan; Liu, Shao-Hua; Zhang, Zai-Yong

    2012-12-01

    In this paper, biomimetic synthesis of calcium carbonate (CaCO3) in the presence of biomolecules of two vegetables-tomato and capsicum is investigated. Scanning electron microscopy and X-ray powder diffractometry were used to characterize the CaCO3 obtained. The biomolecules in the extracts of two vegetables are determined by UV-vis or FTIR. The results indicate that a mixture of calcite and vaterite spheres constructed from small particles is produced with the extract of tomato, while aragonite rods or ellipsoids are formed in the presence of extract of capsicum. The possible formation mechanism of the CaCO3 crystals with tomato biomolecules can be interpreted by particle-aggregation based non-classical crystallization laws. The proteins and/or other biomolecules in tomato and capsicum may control the formation of vaterite and aragonite crystals by adsorbing onto facets of them.

  11. The intensity, duration, and severity of low aragonite saturation state events on the California continental shelf

    Science.gov (United States)

    Hauri, C.; Gruber, N.; McDonnell, A. M. P.; Vogt, M.

    2013-07-01

    Ocean acidification will progress in an episodic manner, yet this has rarely been considered. Here, we investigate how the intensity, duration, and severity of episodic low aragonite saturation state events along the California continental shelf have changed since ~1750, and how they might change up to 2050 under the A2 scenario from the Special Report on Emissions Scenarios by the Intergovernmental Panel on Climate Change. Our model-based results suggest that between 1750 and 2010, aragonite undersaturation events along the shelf have quadrupled in their number and lengthened in duration, but that even larger changes are bound to occur within the next 20 to 40 years. Undersaturation will become very likely the norm near the seafloor by 2030, and if atmospheric CO2 increases beyond ~500 ppm, this layer will become permanently undersaturated. Combined with a fourfold increase in intensity, the resulting increase in severity of low aragonite saturation state events will substantially affect the viability of calcifying organisms and will alter ecosystem structure.

  12. Influences of organic matter and calcification rate on trace elements in aragonitic estuarine bivalve shells

    Science.gov (United States)

    Takesue, R.K.; Bacon, C.R.; Thompson, J.K.

    2008-01-01

    A suite of elements (B, Na, Mg, S, K, Ca, V, Mn, Cr, Sr, and Ba) was measured in aragonitic shells of the estuarine bivalve Corbula amurensis, the Asian clam, using the Sensitive High-Resolution Ion MicroProbe with Reverse Geometry (SHRIMP RG). Our initial intent was to explore potential geochemical proxy relationships between shell chemistry and salinity (freshwater inflow) in northern San Francisco Bay (SFB). In the course of this study we observed variations in shell trace element to calcium ([M]/Ca) ratios that could only be attributed to internal biological processes. This paper discusses the nature and sources of internal trace element variability in C. amurensis shells related to the shell organic fraction and shell calcification rates. The average organic content of whole C. amurensis shells is 19%. After treating whole powdered shells with an oxidative cleaning procedure to remove organic matter, shells contained on average 33% less total Mg and 78% less total Mn. Within our analytical uncertainty, Sr and Ba contents were unchanged by the removal of organic matter. These results show that aragonitic C. amurensis shells have a large component of non-lattice-bound Mg and Mn that probably contribute to the dissimilarity of [M]/Ca profiles among five same-sized shells. Non-lattice-bound trace elements could complicate the development and application of geochemical proxy relationships in bivalve shells. Because B, Ba and Sr occur exclusively in shell aragonite, they are good candidates for external proxy relationships. [M]/Ca ratios were significantly different in prismatic and nacreous aragonite and in two valves of the same shell that had different crystal growth rates. Some part of these differences can be attributed to non-lattice-bound trace elements associated with the organic fraction. The differences in [M]/Ca ratios were also consistent with the calcification rate-dependent ion transport model developed by Carr?? et al. [Carr?? M., Bentaleb I

  13. Influences of organic matter and calcification rate on trace elements in aragonitic estuarine bivalve shells

    Science.gov (United States)

    Takesue, Renee K.; Bacon, Charles R.; Thompson, Janet K.

    2008-11-01

    A suite of elements (B, Na, Mg, S, K, Ca, V, Mn, Cr, Sr, and Ba) was measured in aragonitic shells of the estuarine bivalve Corbula amurensis, the Asian clam, using the Sensitive High-Resolution Ion MicroProbe with Reverse Geometry (SHRIMP RG). Our initial intent was to explore potential geochemical proxy relationships between shell chemistry and salinity (freshwater inflow) in northern San Francisco Bay (SFB). In the course of this study we observed variations in shell trace element to calcium ([M]/Ca) ratios that could only be attributed to internal biological processes. This paper discusses the nature and sources of internal trace element variability in C. amurensis shells related to the shell organic fraction and shell calcification rates. The average organic content of whole C. amurensis shells is 19%. After treating whole powdered shells with an oxidative cleaning procedure to remove organic matter, shells contained on average 33% less total Mg and 78% less total Mn. Within our analytical uncertainty, Sr and Ba contents were unchanged by the removal of organic matter. These results show that aragonitic C. amurensis shells have a large component of non-lattice-bound Mg and Mn that probably contribute to the dissimilarity of [M]/Ca profiles among five same-sized shells. Non-lattice-bound trace elements could complicate the development and application of geochemical proxy relationships in bivalve shells. Because B, Ba and Sr occur exclusively in shell aragonite, they are good candidates for external proxy relationships. [M]/Ca ratios were significantly different in prismatic and nacreous aragonite and in two valves of the same shell that had different crystal growth rates. Some part of these differences can be attributed to non-lattice-bound trace elements associated with the organic fraction. The differences in [M]/Ca ratios were also consistent with the calcification rate-dependent ion transport model developed by Carré et al. [Carré M., Bentaleb I

  14. Strong biological controls on Sr/Ca ratios in aragonitic marine bivalve shells

    Science.gov (United States)

    Gillikin, David Paul; Lorrain, Anne; Navez, Jacques; Taylor, James W.; André, Luc; Keppens, Eddy; Baeyens, Willy; Dehairs, Frank

    2005-05-01

    It is well known that skeletal remains of carbonate secreting organisms can provide a wealth of information about past environments. Sr/Ca ratios have been successfully used as a temperature proxy in corals and sclerosponges. Previous work on aragonitic bivalve shells has not been conclusive but suggests a major control of growth rate on Sr/Ca ratios. As many studies have used bivalve growth rates to determine temperature, we tested if Sr/Ca ratios could predict temperature through its relationship with growth rate. Shells from the two species of clams from the same family (veneroidea) studied here, Saxidomus giganteus and Mercenaria mercenaria, show vastly different seasonal Sr/Ca profiles. A strong relationship between average annual Sr/Ca ratios and annual growth rate was found in S. giganteus shells from both Washington (R2 = 0.87) and Alaska (R2 = 0.64), USA, but not in M. mercenaria shells from North Carolina, USA. Furthermore, the Sr/Ca-growth rate relationship was also evident upon a more detailed inspection of subannual growth rates in S. giganteus (R2 = 0.73). Although there were significant positive correlations between Sr/Ca ratios and temperature in S. giganteus shells, the correlations were weak (0.09 control in either clam species, since thermodynamics predict a negative correlation between Sr/Ca ratios and temperature in aragonite. This points toward dominance of biological processes in the regulation of Sr2+. This is also reflected by the largely differing Sr/Ca partition coefficients (DSr) in these shells (DSr ≈ 0.25), when compared to inorganic, coral, and sclerosponge studies (DSr ≈ 1), all of which show a negative dependence of Sr/Ca on temperature. We suggest that caution be taken when using Sr/Ca in any biogenic aragonite as a temperature proxy when the DSr greatly deviates from one, as this indicates the dominance of biological controls on Sr/Ca ratios.

  15. Biosorption of divalent Pb, Cd and Zn on aragonite and calcite mollusk shells

    Energy Technology Data Exchange (ETDEWEB)

    Du Yang; Lian Fei [Key Laboratory of Pollution Process and Environmental Criteria, Ministry of Education, Tianjin Key Laboratory of Urban Ecology Environmental Remediation and Pollution Control, College of Environmental Science and Engineering, Nankai University, Tianjin 300071 (China); Zhu Lingyan, E-mail: zhuly@nankai.edu.cn [Key Laboratory of Pollution Process and Environmental Criteria, Ministry of Education, Tianjin Key Laboratory of Urban Ecology Environmental Remediation and Pollution Control, College of Environmental Science and Engineering, Nankai University, Tianjin 300071 (China)

    2011-07-15

    The potential of using mollusk shell powder in aragonite (razor clam shells, RCS) and calcite phase (oyster shells, OS) to remove Pb{sup 2+}, Cd{sup 2+} and Zn{sup 2+} from contaminated water was investigated. Both biogenic sorbents displayed very high sorption capacities for the three metals except for Cd on OS. XRD, SEM and XPS results demonstrated that surface precipitation leading to crystal growth took place during sorption. Calcite OS displayed a remarkably higher sorption capacity to Pb than aragonite RCS, while the opposite was observed for Cd. However, both sorbents displayed similar sorption capacities to Zn. These could be due to the different extent of matching in crystal lattice between the metal bearing precipitate and the substrates. The initial pH of the solution, sorbent's dosage and grain size affected the removal efficiency of the heavy meals significantly, while the organic matter in mollusk shells affected the removal efficiency to a lesser extent. - Highlights: > Mollusk shells display high removal efficiency to heavy metals in contaminated water. > Surface precipitation leading to crystal growth takes place during the sorption. > Crystal structure similarity between precipitates and substrates affects the sorption. > pH, sorbent dosage and grain size of adsorbent affects the removal efficiency. > Organic matter in mollusk shells affects the removal efficiency to a less extent. - Mollusk shells display high sorption ability to heavy metals and crystal structure similarity between precipitates and substrates affects the sorption.

  16. Dating of aragonite and dolomite from Devil's cave - SP, by dosimetric thermoluminescent method (DTL) and ESR

    International Nuclear Information System (INIS)

    We have investigated TL (Thermoluminescence) and ESR (electron spin resonance) properties of aragonite and dolomite found at ''Caverna do Diabo (Devil's cave)'' in the state of Sao Paulo to determine the ages of these geological materials. The aragonite, which is not a thermoluminescent material, shows one ESR signal whit g = 2.003. We obtained the age of 1.1 x 105 years and the growth rate of 1 μ m/year by the sample calibration with additional Y irradiation. The dolomite gives a TL glow curve with three distinct peaks at 261, 334 and 395 0C. We found that the fit for the TL glow curve to second-order kinetics can be considerered as very acceptable. Using the second TL peak we obtained the age of 9.4 x 10 5 years and the compatible values of the activation energy (1.90 ± 0,07 eV) by the following methods: Hyperbolic heating, isothermal decay and fractional glow technique. We observed many ESR absorption signals in the dolomite. Three principal signal com g = 2.002, 2.003 and 2.005 were studied. We found that the first and second ESR signals were atributed to the CO2- and/or CO33- centers and the last to the CO3- centers, and observed that the first ESR signal might related with the second TL peak and the TL sensitivity were associated with the concentration of Mn2+

  17. Carbonate "clumped" isotope signatures in aragonitic scleractinian and calcitic gorgonian deep-sea corals

    Science.gov (United States)

    Kimball, J.; Tripati, R. E.; Dunbar, R.

    2015-12-01

    Deep-sea corals are a potentially valuable archive of the temperature and ocean chemistry of intermediate and deep waters. Living in near constant temperature, salinity and pH, and having amongst the slowest calcification rates observed in carbonate-precipitating biological organisms, deep-sea corals can provide valuable constraints on processes driving mineral equilibrium and disequilibrium isotope signatures. Here we report new data to further develop "clumped" isotopes as a paleothermometer in deep-sea corals as well as to investigate mineral-specific, taxon-specific, and growth-rate related effects. Carbonate clumped isotope thermometry is based on measurements of the abundance of the doubly-substituted isotopologue 13C18O16O2 in carbonate minerals, analyzed in CO2 gas liberated on phosphoric acid digestion of carbonates and reported as Δ47 values. We analyzed Δ47 in live-collected aragonitic scleractinian (Enallopsammia sp.) and calcitic gorgonian (Isididae and Coralliidae) deep-sea corals, and compared results to published data for other aragonitic scleractinian taxa. Measured Δ47 values were compared to in situ temperatures and the relationship between Δ47 and temperature was determined for each group to investigate taxon-specific effects. We find that aragonitic scleractinian deep-sea corals exhibit higher values than calcitic gorgonian corals and the two groups of coral produce statistically different relationship between Δ47-temperature calibrations. These data are significant in the interpretation of all carbonate "clumped" isotope calibration data as they show that distinct Δ47-temperature calibrations can be observed in different materials recovered from the same environment and analyzed using the same instrumentation, phosphoric acid composition, digestion temperature and technique, CO2 gas purification apparatus, and data handling. There are three possible explanations for the origin of these different calibrations. The offset between the

  18. First-principles study of boron speciation in calcite and aragonite

    Science.gov (United States)

    Balan, Etienne; Pietrucci, Fabio; Gervais, Christel; Blanchard, Marc; Schott, Jacques; Gaillardet, Jérome

    2016-11-01

    Despite the importance of boron as a proxy of past ocean pH, the crystal-chemical factors controlling its incorporation in the structure of calcium carbonates are still poorly understood. This is partly linked to an imperfect knowledge of the coordination, protonation state and local environment of boron species in these minerals. In the present study, we use first-principles quantum mechanical tools to model selected trigonal and tetragonal boron species in calcite and aragonite. The stable geometry of the models is obtained from standard energy minimization schemes or using a more advanced metadynamics exploration of their configurational space. The computation of 11B NMR chemical shifts and quadrupolar coupling parameters enables a straightforward comparison of the models to existing experimental NMR data. The results show that B in calcium carbonates does occur as structural species substituted for CO32- anions. The B speciation depends on the polymorph considered. In calcite, structural boron is present as partially deprotonated trigonal BO2(OH)2- species coexisting with a fraction of substituted B(OH)4- groups. In aragonite, the B(OH)4- substitution for CO32- anions is dominant. Different species, including entrapped B(OH)3 molecules and substituted BO33- groups also occur in biogenic samples. The diversity of B speciation reflects a diversity of B incorporation mechanisms and sheds light on previous studies confronting B isotopic composition determination with NMR observations. The mechanisms of boron incorporation in calcium carbonates are probably more complex than usually assumed in the literature using boron isotopes as a proxy of paleo-atmospheric CO2 reconstructions. Although not invalidating the empirical paleo-pH proxy, these results call for a better understanding of the fundamental mechanisms of boron incorporation in carbonates.

  19. Heterogeneous growth of calcite at aragonite {001}- and vaterite {001}-melt interfaces: A molecular dynamics simulation study

    Science.gov (United States)

    Nada, Hiroki; Nishimura, Tatsuya; Sakamoto, Takeshi; Kato, Takashi

    2016-09-01

    Crystal growth at the interface between a calcium carbonate (CaCO3) crystal and its melt at a high temperature of 1500 K is investigated by means of a molecular dynamics simulation. The simulation is performed for the interfaces of a calcite {104} plane, aragonite {001}, {100}, and {010} planes, and vaterite {001}, {110}, and {100} planes. The growth from a pure melt and that from a melt containing Mg2+ are examined. Calcite growth occurs on the calcite {104} plane, aragonite growth occurs on the aragonite {100}, and {010} planes, and vaterite growth occurs on the vaterite {110} and {100} planes. However, the heterogeneous growth of calcite occurs on the {001} plane of aragonite and vaterite, irrespective of the presence of Mg2+. The results advance our understanding of geological processes that occur at high temperature, such as the formation of CaCO3 crystals from carbonatite magma and the formation of marble. Moreover, the results provide useful information for the control of CaCO3 crystal formation in material design.

  20. Assignment of polarization-dependent peaks in carbon K-edge spectra from biogenic and geologic aragonite.

    Science.gov (United States)

    Zhou, Dong; Metzler, Rebecca A; Tyliszczak, Tolek; Guo, Jinghua; Abrecht, Mike; Coppersmith, Susan N; Gilbert, P U P A

    2008-10-16

    Many biominerals, including mollusk and echinoderm shells, avian eggshells, modern and fossil bacterial sediments, planktonic coccolithophores, and foraminifera, contain carbonates in the form of biogenic aragonite or calcite. Here we analyze biogenic and geologic aragonite using different kinds of surface- and bulk-sensitive X-ray absorption near-edge structure (XANES) spectroscopy at the carbon K-edge, as well as high-resolution scanning transmission X-ray microscopy (STXM). Besides the well-known main pi* and sigma* carbonate peaks, we observed and fully characterized four minor peaks, at energies between the main pi* and sigma* peaks. As expected, the main peaks are similar in geologic and biogenic aragonite, while the minor peaks differ in relative intensity. In this and previous work, the minor peaks appear to be the ones most affected in biomineralization processes, hence the interest in characterizing them. Peak assignment was achieved by correlation of polarization-dependent behavior of the minor peaks with that of the main pi* and sigma* peaks. The present characterization provides the background for future studies of aragonitic biominerals.

  1. Development of nanoantibiotic delivery system using cockle shell-derived aragonite nanoparticles for treatment of osteomyelitis

    Directory of Open Access Journals (Sweden)

    Saidykhan L

    2016-02-01

    Full Text Available Lamin Saidykhan,1 Md Zuki Bin Abu Bakar,2 Yaya Rukayadi,1,3 Aminu Umar Kura,4 Saiful Yazan Latifah5 1Microbiology Unit, Laboratory of Natural Products, Institute of Bioscience, 2Laboratory of Anatomy and Histology, Department of Veterinary Preclinical Sciences, Faculty of Veterinary Medicine, 3Department of Food Science, Faculty of Food Science and Technology, 4Vaccine and Immunotherapeutics Laboratory Unit, Institute of Bioscience, 5Department of Biomedical Science, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Selangor Darul Ehsan, Malaysia Abstract: A local antibiotic delivery system (LADS with biodegradable drug vehicles is recognized as the most effective therapeutic approach for the treatment of osteomyelitis. However, the design of a biodegradable LADS with high therapeutic efficacy is too costly and demanding. In this research, a low-cost, facile method was used to design vancomycin-loaded aragonite nanoparticles (VANPs with the aim of understanding its potency in developing a nanoantibiotic bone implant for the treatment of osteomyelitis. The aragonite nanoparticles (ANPs were synthesized from cockle shells by a hydrothermal approach using a zwitterionic surfactant. VANPs were prepared using antibiotic ratios of several nanoparticles, and the formulation (1:4 with the highest drug-loading efficiency (54.05% was used for physicochemical, in vitro drug release, and biological evaluation. Physiochemical characterization of VANP was performed by using transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, and Zetasizer. No significant differences were observed between VANP and ANP in terms of size and morphology as both samples were cubic shaped with sizes of approximately 35 nm. The Fourier transform infrared spectroscopy of VANP indicated a weak noncovalent interaction between ANP and vancomycin, while the zeta potential values were slightly increased from -19

  2. Aragonite saturation state in a monsoonal upwelling system off Java, Indonesia

    Science.gov (United States)

    Xue, Liang; Wang, Huiwu; Jiang, Li-Qing; Cai, Wei-Jun; Wei, Qinsheng; Song, Hongjun; Kuswardani, Rita Tisiana Dwi; Pranowo, Widodo S.; Beck, Brian; Liu, Lin; Yu, Weidong

    2016-01-01

    Aragonite saturation state (Ωarag) and its influence from upwelling along the southern coast of Java, Indonesia were examined using carbonate and hydrographic data collected from 22 September to 2 October 2013. Results showed that sea surface Ωarag was lower in the upwelling area (2.97-3.44) than in the nonupwelling area (3.45-3.57), with the lowest value in the eastern part of the study area. We used a two end-member mixing model to separate contributions on Ωarag from two processes associated with upwelling: physical transport vs. biological production. Results indicated that physical transport induced at least a Ωarag decrease of 0.8, whereas biological production caused Ωarag to increase by up to 0.6. Additionally, the influence on Ωarag of interannual upwelling variability modulated by the Indian Ocean Dipole (IOD), a unique climate phenomenon in the Indian Ocean, was roughly estimated. We argue that the effect of interannual upwelling variability modulated by IOD events was possibly larger than what was imposed on Ωarag by increasing atmospheric CO2 levels over the past decade.

  3. Large-Scale Growth of Tubular Aragonite Whiskers through a MgCl2-Assisted Hydrothermal Process

    Directory of Open Access Journals (Sweden)

    Changyin Dong

    2011-08-01

    Full Text Available In this paper, we have developed a facile MgCl2-assissted hydrothermal synthesis route to grow tubular aragonite whiskers on a large scale. The products have been characterized by powder X-ray diffraction (XRD, optical microscopy, and scanning electronic microscopy (SEM. The results show the as-grown product is pure tubular aragonite crystalline whiskers with a diameter of 5–10 mm and a length of 100–200 mm, respectively. The concentration of Mg2+ plays an important role in determining the quality and purity of the products. Furthermore, the method can be extended to fabricate CaSO4 fibers. The high quality of the product and the mild conditions used mean that the present route has good prospects for the growth of inorganic crystalline whiskers.

  4. Baseline monitoring of the western Arctic Ocean estimates 20% of Canadian basin surface waters are undersaturated with respect to aragonite.

    Directory of Open Access Journals (Sweden)

    Lisa L Robbins

    Full Text Available Marine surface waters are being acidified due to uptake of anthropogenic carbon dioxide, resulting in surface ocean areas of undersaturation with respect to carbonate minerals, including aragonite. In the Arctic Ocean, acidification is expected to occur at an accelerated rate with respect to the global oceans, but a paucity of baseline data has limited our understanding of the extent of Arctic undersaturation and of regional variations in rates and causes. The lack of data has also hindered refinement of models aimed at projecting future trends of ocean acidification. Here, based on more than 34,000 data records collected in 2010 and 2011, we establish a baseline of inorganic carbon data (pH, total alkalinity, dissolved inorganic carbon, partial pressure of carbon dioxide, and aragonite saturation index for the western Arctic Ocean. This data set documents aragonite undersaturation in ≈ 20% of the surface waters of the combined Canada and Makarov basins, an area characterized by recent acceleration of sea ice loss. Conservative tracer studies using stable oxygen isotopic data from 307 sites show that while the entire surface of this area receives abundant freshwater from meteoric sources, freshwater from sea ice melt is most closely linked to the areas of carbonate mineral undersaturation. These data link the Arctic Ocean's largest area of aragonite undersaturation to sea ice melt and atmospheric CO2 absorption in areas of low buffering capacity. Some relatively supersaturated areas can be linked to localized biological activity. Collectively, these observations can be used to project trends of ocean acidification in higher latitude marine surface waters where inorganic carbon chemistry is largely influenced by sea ice meltwater.

  5. The Raman spectrum of CaCO{sub 3} polymorphs calcite and aragonite: A combined experimental and computational study

    Energy Technology Data Exchange (ETDEWEB)

    De La Pierre, Marco, E-mail: cedric.carteret@univ-lorraine.fr, E-mail: marco.delapierre@unito.it; Maschio, Lorenzo; Orlando, Roberto; Dovesi, Roberto [Dipartimento di Chimica, Università di Torino and NIS (Nanostructured Interfaces and Surfaces) Centre of Excellence, Via P. Giuria 7, 10125 Torino (Italy); Carteret, Cédric, E-mail: cedric.carteret@univ-lorraine.fr, E-mail: marco.delapierre@unito.it; André, Erwan [Laboratoire de Chimie Physique et Microbiologie pour l’Environnement (LCPME), UMR 7564, Université de Lorraine-CNRS, 405 rue de Vandoeuvre, 54601 Villers-lès-Nancy (France)

    2014-04-28

    Powder and single crystal Raman spectra of the two most common phases of calcium carbonate are calculated with ab initio techniques (using a “hybrid” functional and a Gaussian-type basis set) and measured both at 80 K and room temperature. Frequencies of the Raman modes are in very good agreement between calculations and experiments: the mean absolute deviation at 80 K is 4 and 8 cm{sup −1} for calcite and aragonite, respectively. As regards intensities, the agreement is in general good, although the computed values overestimate the measured ones in many cases. The combined analysis permits to identify almost all the fundamental experimental Raman peaks of the two compounds, with the exception of either modes with zero computed intensity or modes overlapping with more intense peaks. Additional peaks have been identified in both calcite and aragonite, which have been assigned to {sup 18}O satellite modes or overtones. The agreement between the computed and measured spectra is quite satisfactory; in particular, simulation permits to clearly distinguish between calcite and aragonite in the case of powder spectra, and among different polarization directions of each compound in the case of single crystal spectra.

  6. Proteomic and profile analysis of the proteins laced with aragonite and vaterite in the freshwater mussel Hyriopsis cumingii shell biominerals.

    Science.gov (United States)

    Berland, Sophie; Ma, Yufei; Marie, Arul; Andrieu, Jean-Pierre; Bedouet, Laurent; Feng, Qingling

    2013-10-01

    Hyriopsis cumingii (Lea, Unionidae), a freshwater bivalve species widely distributed in China and commercially exploited for freshwater pearl production, was chosen as the reference model to investigate the protein signature in the organic scaffold matching calcium carbonate crystallization mode. This study takes advantage of different calcium carbonate habits production by the organism: aragonite in shell and pearl and vaterite in alternative pearl formation. Amino acid global composition and proteomics analysis have been undertaken to study the amino acid imbalance with respect to biominerals and microstructures. Forty peptides sequences were obtained by proteomics, of which ten are shared by all the different samples, nine are laced with aragonite; another nine with vaterite and twelve are related to pearls. Bioinformatics analysis allowed the peptides to be matched to the deduced protein sequences from EST databases and allowed functional assignment (e.g. scaffolding, strain strength, chitin binding or carbonic anhydrase function) to the proteins found in the different materials. Such panel of motifs tailored in vaterite and aragonite habits produced in a freshwater mollusk gives food for thought about organic control of the biomineralization processes.

  7. Effects of episodic low aragonite saturation and elevated temperature on the physiology of Stylophora pistillata

    Science.gov (United States)

    Lürig, M.; Kunzmann, A.

    2015-05-01

    As global climate change is predicted to gradually alter the oceans' carbonate system and water temperature, knowledge about the effects an altered marine environment has on the physiology of reef building (hermatypic) coral species is more widely established. However, although it is recognized that seawater temperature and the carbonate system of a coral reef can change rapidly and with great amplitude, little is known about how the interaction of these natural fluctuations with long term effects of climate change may affect the metabolism and productivity of hermatypic corals. To investigate this, we acclimated the hermatypic coral Stylophora pistillata to a "worst case" scenario for carbon dioxide emissions (aragonite saturation state [ΩARAG] = 1.6), and tested how exposure to short term (24 h) elevated temperature (+ 3 °C) and further lowered ΩARAG (-1 unit) affected its photosynthesis and respiration. While episodic exposure to very low ΩARAG had only little effect on S. pistillata's physiology, short term heat stress caused a shift from net oxygen production to consumption and partial coral bleaching. Higher gross coral respiration, and lowered photosynthetic activity under episodically elevated temperature may have been the result of photoinhibition and partial coral bleaching. These findings suggest that fluctuating environmental conditions in combination with a low ΩARAG background signal may impair basic metabolic processes in calcifying corals. In a future high-CO2 world short term stress could be relevant for reef ecosystem processes, and may affect the resilience of coral reefs to other external influences and effects of climate change.

  8. Factors determining δ13C and δ18O fractionation in aragonitic otoliths of marine fish

    Science.gov (United States)

    Thorrold, Simon R.; Campana, Steven E.; Jones, Cynthia M.; Swart, Peter K.

    1997-07-01

    Fish otoliths are aragonitic accretions located within the inner ear of teleost fish. The acellular nature of otoliths, along with taxon-specific shapes, chronological growth increments, and abundance in the fossil record suggest that the stable isotope chemistry of these structures may be unique recorders of environmental conditions experienced by fish in both modern and ancient water masses. To assess the factors determining δ 13C and δ 18O fractionation in fish otoliths, we reared Atlantic croaker ( Micropogonias undulatus) larvae under controlled environmental conditions. Metabolic effects apparently generated large isotopic disequilibria in the δ 13C values of M. undulatus otoliths. We found evidence of a negative regression between δ 13C- carbonate-δ 13C water (δ 13C) and temperature: δ 13C = -1.78 - 0.18 T °C However, this relationship was aliased to a degree by a positive correlation between δ 13C and somatic growth and otolith precipitation rates. Oxygen isotopes were deposited close to equilibrium with the ambient water. The relationship between temperature and the 18O/ 16O fractionation factor (α) was determined empirically to be: 1000 ln α = 18.56(10 3T K -1) - 32.54 The fractionation factor was not affected by either otolith precipitation or fish growth rates. Reconstruction of water temperature histories should, therefore, be possible from the δ 18O values of M. undulatus otoliths with a precision of 1°C, providing the δ 18O of the ambient water can be estimated.

  9. Variations in Cenozoic seawater uranium reconstructed from well preserved aragonitic fossil corals

    Science.gov (United States)

    Gothmann, A. O.; Higgins, J. A.; Bender, M. L.; Stolarski, J.; Adkins, J. F.; McKeon, R. E.; Farley, K. A.; Wang, X.; Planavsky, N.

    2015-12-01

    U/Ca ratios were measured in a subset (n ≈ 30) of well preserved scleractinian fossil corals previously described by Gothmann et al. (2015) in order to investigate Cenozoic changes in seawater [U]. He/U dating studies and measurements of 234U/238U and δ238/235U provide constraints on fossil coral U preservation. He/U ages also demonstrate the ability of well preserved coral aragonite to retain most of its radiogenic He over million year timescales. We find that fossil coral U/Ca has increased by a factor of ~4 between the Early Cenozoic and today. This number is calculated from the change in seawater [Ca2+] implied by brine inclusions and other proxies, and the assumption that the U/Ca in shallow water corals equals the seawater ratio. The change cannot be attributed to a dependence of coral U uptake on seawater pH or [CO32-] (e.g., Inoue et al., 2011), which would lead to a decrease in U/Ca going forward in time. Instead, we suggest that seawater [U] has increased since the Early Cenozoic. Possible explanations for the inferred change include: (1) a small decrease in uranium uptake in suboxic and anoxic sediments over the Cenozoic, (2) a decrease in the rate of low-temperature hydrothermal alteration, and associated U uptake, over the Cenozoic, and (3) a decrease in U removal from seawater resulting from an increase in UO2-CO3 complexation, as originally suggested by Broecker (1971). References: Broecker, W. S. (1971) A Kinetic Model for the Chemical Composition of Sea Water. Quaternary Research, 1, 188-207. Gothmann, A.M., Stolarski, J., Adkins, J.F., Dennis, K.J., Schrag, D.P., Schoene, B., Bender, M.L. (2015) Fossil corals as an archive of secular variations in seawater chemistry. Geochimica et Cosmochimica Acta, 160, 188-208. Inoue, M., Suwa, R., Suzuki, A., Sakai, K., and Kawahata, H., (2011) Effects of seawater pH on growth and skeletal U/Ca ratios of Acropora digitifera coral polyps. Geophysical Research Letters 38, 12801-12804.

  10. Aragonite crystals grown on bones by reaction of CO2 with nanostructured Ca(OH)2 in the presence of collagen. Implications in archaeology and paleontology.

    Science.gov (United States)

    Natali, Irene; Tempesti, Paolo; Carretti, Emiliano; Potenza, Mariangela; Sansoni, Stefania; Baglioni, Piero; Dei, Luigi

    2014-01-21

    The loss of mechanical properties affecting archeological or paleontological bones is often caused by demineralization processes that are similar to those driving the mechanisms leading to osteoporosis. One simple way to harden and to strengthen demineralized bone remains could be the in situ growth of CaCO3 crystals in the aragonite polymorph - metastable at atmospheric pressure -which is known to have very strong mechanical strength in comparison with the stable calcite. In the present study the controlled growth of aragonite crystals was achieved by reaction between atmospheric CO2 and calcium hydroxide nanoparticles in the presence of collagen within the deteriorated bones. In a few days the carbonation of Ca(OH)2 particles led to a mixture of calcite and aragonite, increasing the strength of the mineral network of the bone. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) and Fourier transform infrared (FT-IR) spectrometry showed that aragonite crystallization was achieved. The effect of the aragonite crystal formation on the mechanical properties of the deteriorated bones was investigated by means of X-rays microtomography, helium porosimetry, atomic force microscopy (AFM), and Vickers microhardness techniques. All these data enabled to conclude that the strength of the bones increased of a factor of 50-70% with respect to the untreated bone. These results could have immediate impact for preserving archeological and paleontological bone remains.

  11. Early and late lithification of aragonitic bivalve beds in the Purbeck Formation (upper jurassic-lower cretaceous) of Southern England

    Science.gov (United States)

    El-Shahat, Adam; West, Ian

    1983-05-01

    Beds of euryhaline bivalves alternating with shales constitute much of the middle Purbeck Formation. They originated on "tidal" flats at the western margin of an extensive brackish lagoon. When these shell beds are thin and enclosed in shale they are often still preserved as aragonite and are associated with "beef", fibrous calcite formed during compaction. In most cases, however, the shell debris has been converted by diagenesis into calcitic biosparrudite limestones. A compacted type has been lithified at a late stage, after deep burial. In this, pyrite is abundant and most of the shell aragonite has been replaced neomorphically by ferroan pseudopleochroic calcite. A contrasting uncompacted type of biosparrudite is characterised by bivalve fragments with micrite envelopes. Shells and former pores are occupied by non-ferroan sparry calcite cement, and there is little pyrite. These limestones frequently contain dinosaur footprints and originated in "supratidal" environments where they were cemented early, mainly in meteoric water. Once lithified they were unaffected by compaction. This uncompacted type indicates phases of mild uplift or halts in subsidence. These shell-bed lithologies, and also intermediate types described here, will probably be recognised in other lagoonal formations.

  12. Thermodynamics of aragonite-strontianite solid solutions: Results from stoichiometric solubility at 25 and 76°C

    Science.gov (United States)

    Plummer, L.N.; Busenberg, E.

    1987-01-01

    Dissolution of synthetic strontianite-aragonite solid solutions was followed analytically to stoichiometric saturation using large solid to solution ratios in CO2-H2O solution at 25 and 76°C. The compositional dependence of the equilibrium constant was calculated from the composition of saturated (stoichiometric) solutions and used to calculate the activities and activity coefficients of CaCO3 and SrCO3 in the solid Ca(1−x)SrxCO3 at 25 and 76°C. The results show that the solid-solution is not regular but unsymmetrical. The excess free energy of mixing is closely modeled for all compositions by the relation where A0 is 8.49 ± 0.30 and 7.71 ± 0.20 KJ/mole and A1 is −4.51 ± 0.20 and −3.36 ± 0.40 KJ/mole at 25 and 76°C, respectively. The equilibrium constant is denned as a function of the SrCO3 mole fraction, x, by the relation where R is the gas constant, T is in Kelvins and KA and KS are the aragonite and strontianite equilibrium constants.

  13. Origin of authigenic calcite and aragonite in pelagic sediments of the Mendeleev Ridge (Arctic Ocean) and their paleoceanographicimplications

    Science.gov (United States)

    Woo, K. S.; Ji, H. S.; Nam, S.; Stein, R. H.; Mackensen, A.; Matthiessen, J. J.

    2013-12-01

    Carbonate minerals were discovered from the giant box core (PS72/410-1) of the pelagic sediments recovered from the Canadian Arctic across the central Mendeleev Ridge (Station location= Lat. 80°30.37"N, Long. 175°44.38"W) during the Arctic cruise by Polarstern in 2008. The core was 39 cm long and was collected from the water depth of 1802 meters. The sediments show various colours from grey to brown as previously reported in other Arctic pelagic sediments. The sediments include planktonic foraminifers together with carbonate minerals. The contents of planktonic foraminifers and carbonate minerals vary with core depth, however these carbonate minerals are present through the whole sequence except for a few centimetres. After wet sieving, coarse fractions were texturally examined with binocular microscope and SEM, and stable isotope and trace element contents were obtained. Mineralogy of carbonate minerals were determined using crystal shapes and qualitative Sr contents by EDAX together with trace element analysis. The carbonates are composed of high Mg-calcite, low Mg-calcite and aragonite. Aragonite crystals show (1) radiating fibrous texture, (2) randomly oriented fibrous texture, (3) spherulitic fibrous texture, and (4) bladed texture, and calcite crystals show (1) foliated texture, (2) randomly bladed texture, (3) spherulitic fibrous texture, and (4) equant texture. Various crystal shapes of aragonite and calcite together with clear growth shapes of the crystals suggest that they are inorganic in origin. Highly enriched carbon isotope compositions (δ13C = 0 ~ +5‰ vs. PDB) strongly indicate that they formed in methanogenic zone below sediment/water interface by the reaction between anoxic pore fluids and host sediments induced by methanogenic bacteria. However, a wide range of oxygen isotope values (δ18O = -5 ~ +5‰ vs. PDB) may indicate that porewater has been changed due to reaction between residual seawater and volcanic sediments. Four types of stable

  14. Characteristics of the Aragonitic Layer in Adult Oyster Shells, Crassostrea gigas: Structural Study of Myostracum including the Adductor Muscle Scar

    Directory of Open Access Journals (Sweden)

    Seung-Woo Lee

    2011-01-01

    Full Text Available Myostracum, which is connected from the umbo to the edge of a scar, is not a single layer composed of prismatic layers, but a hierarchically complex multilayered shape composed of minerals and an organic matrix. Through the analysis of the secondary structure, the results revealed that a β-antiparallel structure was predominant in the mineral phase interface between the myostracum (aragonite and bottom folia (calcite. After the complete decalcification and deproteinization, the membrane obtained from the interface between the myostracum buried in upper folia, and the bottom folia was identified as chitin. The transitional zone in the interface between the adductor muscle scar and folia are verified. The myostracum disappeared at the edge of the scar of the posterior side. From this study, the entire structure of the myostracum from the adult oyster shell of Crassostrea gigas could be proposed.

  15. Evidence of prolonged aragonite undersaturations in the bottom waters of the southern Bering Sea shelf from autonomous sensors

    Science.gov (United States)

    Mathis, Jeremy T.; Cross, Jessica N.; Monacci, Natalie; Feely, Richard A.; Stabeno, Phyllis

    2014-11-01

    The southeastern shelf of the Bering Sea is a dynamic area that experiences seasonal variability in primary production and remineralization of organic matter, both of which control the carbon biogeochemistry of the water column. Surface-water partial pressure of carbon dioxide (pCO2) is greatly reduced in summer by biological production, which increases carbonate mineral saturation states (Ω). In contrast, the export of large quantities of organic matter from surface blooms drives an active remineralization loop that sharply increases pCO2 near the bottom, lowering pH and suppressing Ω. New observations from moored biogeochemical sensors in 2011 showed that seasonal net community production lowers surface-water pCO2, causing large gradients between the ocean and atmosphere that are sustained throughout the summer, confirming that these waters likely remain supersaturated with respect to aragonite throughout the open water season. On the other hand, moored sensors deployed near the bottom showed that pCO2 levels exceed 500 μatm by early June and remain at these high levels well into the autumn months, indicating that the bottom waters are likely continuously undersaturated in aragonite for at least several months during each year. Only a small fraction of the increased pCO2 can currently be attributed to the intrusion of anthropogenic CO2 from the atmosphere, while the majority is due to natural respiration processes. The biological impacts, along with the timing and duration of these undersaturation events, could play a role in the development of larval and juvenile calcifiers in the region and will change as anthropogenic CO2 concentrations continue to rise.

  16. Effect of carbonation temperature on CO2 adsorption capacity of CaO derived from micro/nanostructured aragonite CaCO3

    Science.gov (United States)

    Hlaing, Nwe Ni; Sreekantan, Srimala; Hinode, Hirofumi; Kurniawan, Winarto; Thant, Aye Aye; Othman, Radzali; Mohamed, Abdul Rahman; Salime, Chris

    2016-07-01

    Recent years, CaO-based synthetic materials have been attracted attention as potential adsorbents for CO2 capture mainly due to their high CO2 adsorption capacity. In this study, micro/nanostructured aragonite CaCO3 was synthesized by a simple hydrothermal method with using polyacrylamide (PAM). The structural, morphological and thermal properties of the synthesized sample were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and thermogravimetry analysis (TG-DTA). The XRD and FESEM results showed that the obtained sample was aragonite CaCO3 with aggregated nanorods and microspheres composed of nanorods. A TG-DTA apparatus with Thermoplus 2 software was used to investigate the effect of carbonation temperature on the CO2 adsorption capacity of CaO derived from aragonite CaCO3 sample. At 300 °C, the sample reached the CO2 adsorption capacity of 0.098 g-CO2/g-adsorbent, whereas the sample achieved the highest capacity of 0.682 g-CO2/g-adsorbent at 700 °C. The results showed that the carbonation temperature significantly influenced on the CO2 adsorption capacity of the CaO derived from aragonite CaCO3.

  17. Attempt of absolute dating and reconstitutions of climate changes in the Caribbean Sea: multi-proxy approaches to planktonic foraminifera and fine aragonitic fraction

    OpenAIRE

    Sepulcre, Sophie

    2008-01-01

    Absolute dating of climate archives is essential to better understand climate mechanisms. A marine sediment core from the Caribbean Sea enriched in fine-grained aragonite (suitable to U/Th dating) has been studied for both planktonic foraminiferal tests (>150 μm) and fine fraction (

  18. Trace element and stable isotope data from a flowstone in a natural cave of the mining district of SW Sardinia (Italy: evidence for Zn2+-induced aragonite precipitation in comparatively wet climatic conditions

    Directory of Open Access Journals (Sweden)

    Caddeo Guglielmo Angelo

    2011-07-01

    Full Text Available A speleothem from Crovassa Azzurra, a mine cave in SW Sardinia (Italy, has been analysed for mineralogy, minor and traceelements and stable isotopes. It is composed of layers of primary calcite and aragonite, with a region of secondary calcite. The primarycarbonate is strikingly rich in Zn and Pb, presumably as the result of transport in solution from overlying Pb-Zn deposits. Immediatelybelow the transition between calcite and aragonite, concentrations of Zn, Cd and P increase. At the transition between aragonite andPb-rich aragonite, concentrations of Pb and P increase. Stable isotopes do not indicate an evolution toward drier periods for thesetwo transitions, conversely to what is normally observed in calcite-aragonite speleothems. On the contrary the combined observationof increase in P and metals derived from oxidation of sulphides and the variation of isotopic composition of aragonite and calcitesuggests that in this mine cave aragonite was deposited with increasing flowrate and thus more humid conditions. In addition, theeffect of Zn2+ or Pb2+ in inhibiting precipitation of calcite appears to have been more important than that of Mg2+.

  19. Self-Assembly of Nano Hydroxyapatite or Aragonite Induced by Molecular Recognition to Soy Globulin 7S or 11S.

    Science.gov (United States)

    Liu, Dagang; Tian, Huafeng; Kumar, Rakesh; Zhang, Lina

    2009-09-01

    Molecular self-assembly is emerging as a viable 'bottom-up' approach to build stable organic/inorganic nanometer-scale blocks. Herein, under the conditions of appropriate pH and ionic strength, soy globulin 7S or 11S were coprecipitated with hydroxyapatite (HAp) or aragonite (Arag), respectively, to fabricate two organic/inorganic hybrids: 7S/HAp and 11S/Arag. Results from high-resolution transmission electron microscopy show that the hybrids exhibit a nanosized core-shell structure with globulin monomer 7S or 11S as core and HAp or Arag as shells. 7S/HAp and 11S/Arag present a disk and hexagon shape, respectively. After calcinations, monodispersed HAp without support from globulins existed as nanospheres. It was revealed that the globulin as host induces the self-assembly and growth layer by layer of HAp or Arag nanocrystals. The factors of molecular recognition and surface potential definitely affected the size and shape of the hierarchical blocks. This work provided a novel pathway to controllably synthesize a wide variety of precise plant protein/biomineral hybrid biomaterials.

  20. Uranium concentrations from an aragonite speleothem as a proxy for Mesoamerican Monsoon Variability over the last 2,250 years

    Science.gov (United States)

    Crotty, C.; Lachniet, M. S.; Asmerom, Y.; Polyak, V. J.; Bernal, J. P.

    2015-12-01

    Trace element concentrations (Mg and U) were measured in an aragonite stalagmite (JX-6) from Juxtlahuaca Cave ("JX Cave"), in southwestern Mexico, using an inductively coupled plasma mass spectrometer (ICP-MS). These trace element concentrations were compared to previously analyzed δ18O and δ13C values from JX-6, and to the results of previous studies comparing U concentrations in speleothems to paleoclimate. U concentrations of JX-6 correlate well with δ13C and δ18O values, and we interpret them to be a proxy for soil moisture above Juxtlahuaca Cave. This study concludes that U concentrations in JX-6 may be controlled by changes in the pCO2 of overlying soils in relation to plant respiration possibly linked to the consistency of wet season (May - November) rainfall and temperature between 240 BCE to 1800 CE. Comparison to previous studies suggests that speleothem U concentrations are controlled by local cave conditions and are best used with the support of additional trace element and stable isotope data. Anomalous spikes in trace element concentrations were also observed in JX-6 at ~1862, 1871, 1904, and 1933 CE. These spikes were interpreted to be caused by increased U mobilization in overlying soils related to multiple deforestation events in association with the clearing of land above Juxtlahuaca Cave for agricultural use.

  1. Baseline monitoring of the western Arctic Ocean estimates 20% of the Canadian Basin surface waters are undersaturated with respect to aragonite

    Science.gov (United States)

    Robbins, Lisa L.; Wynn, Jonathan G.; Lisle, John T.; Yates, Kimberly K.; Knorr, Paul O.; Byrne, Robert H.; Liu, Xuewu; Patsavas, Mark C.; Azetsu-Scott, Kumiko; Takahashi, Taro

    2013-01-01

    Marine surface waters are being acidified due to uptake of anthropogenic carbon dioxide, resulting in surface ocean areas of undersaturation with respect to carbonate minerals, including aragonite. In the Arctic Ocean, acidification is expected to occur at an accelerated rate with respect to the global oceans, but a paucity of baseline data has limited our understanding of the extent of Arctic undersaturation and of regional variations in rates and causes. The lack of data has also hindered refinement of models aimed at projecting future trends of ocean acidification. Here, based on more than 34,000 data records collected in 2010 and 2011, we establish a baseline of inorganic carbon data (pH, total alkalinity, dissolved inorganic carbon, partial pressure of carbon dioxide, and aragonite saturation index) for the western Arctic Ocean. This data set documents aragonite undersaturation in ~20% of the surface waters of the combined Canada and Makarov basins, an area characterized by recent acceleration of sea ice loss. Conservative tracer studies using stable oxygen isotopic data from 307 sites show that while the entire surface of this area receives abundant freshwater from meteoric sources, freshwater from sea ice melt is most closely linked to the areas of carbonate mineral undersaturation. These data link the Arctic Ocean’s largest area of aragonite undersaturation to sea ice melt and atmospheric CO2 absorption in areas of low buffering capacity. Some relatively supersaturated areas can be linked to localized biological activity. Collectively, these observations can be used to project trends of ocean acidification in higher latitude marine surface waters where inorganic carbon chemistry is largely influenced by sea ice meltwater.

  2. Application of a fluidized bed reactor charged with aragonite for control of alkalinity, pH and carbon dioxide in marine recirculating aquaculture systems

    Science.gov (United States)

    Paul S Wills, PhD; Pfeiffer, Timothy; Baptiste, Richard; Watten, Barnaby J.

    2016-01-01

    Control of alkalinity, dissolved carbon dioxide (dCO2), and pH are critical in marine recirculating aquaculture systems (RAS) in order to maintain health and maximize growth. A small-scale prototype aragonite sand filled fluidized bed reactor was tested under varying conditions of alkalinity and dCO2 to develop and model the response of dCO2 across the reactor. A large-scale reactor was then incorporated into an operating marine recirculating aquaculture system to observe the reactor as the system moved toward equilibrium. The relationship between alkalinity dCO2, and pH across the reactor are described by multiple regression equations. The change in dCO2 across the small-scale reactor indicated a strong likelihood that an equilibrium alkalinity would be maintained by using a fluidized bed aragonite reactor. The large-scale reactor verified this observation and established equilibrium at an alkalinity of approximately 135 mg/L as CaCO3, dCO2 of 9 mg/L, and a pH of 7.0 within 4 days that was stable during a 14 day test period. The fluidized bed aragonite reactor has the potential to simplify alkalinity and pH control, and aid in dCO2 control in RAS design and operation. Aragonite sand, purchased in bulk, is less expensive than sodium bicarbonate and could reduce overall operating production costs.

  3. Aragonite saturation state gridded to 1x1 degree latitude and longitude at depth levels of 0, 50, 100, 200, 500, 1000, 2000, 3000, and 4000 meters in the global oceans (NCEI Accession 0139360)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This archival package contains gridded data of aragonite saturation state across the global oceans (spatial distributions with a resolution of 1x1 degree latitude...

  4. Review: geological and experimental evidence for secular variation in seawater Mg/Ca (calcite-aragonite seas and its effects on marine biological calcification

    Directory of Open Access Journals (Sweden)

    J. B. Ries

    2010-09-01

    Full Text Available Synchronized transitions in the polymorph mineralogy of the major reef-building and sediment-producing calcareous marine organisms and abiotic CaCO3 precipitates (ooids, marine cements throughout Phanerozoic time are believed to have been caused by tectonically induced variations in the Mg/Ca ratio of seawater (molar Mg/Ca>2="aragonite seas", <2="calcite seas". Here, I assess the geological evidence in support of secular variation in seawater Mg/Ca and its effects on marine calcifiers, and review a series of recent experiments that investigate the effects of seawater Mg/Ca (1.0–5.2 on extant representatives of calcifying taxa that have experienced variations in this ionic ratio of seawater throughout the geologic past.

    Secular variation in seawater Mg/Ca is supported by synchronized secular variations in (1 the ionic composition of fluid inclusions in primary marine halite, (2 the mineralogies of late stage marine evaporites, abiogenic carbonates, and reef- and sediment-forming marine calcifiers, (3 the Mg/Ca ratios of fossil echinoderms, molluscs, rugose corals, and abiogenic carbonates, (4 global rates of tectonism that drive the exchange of Mg2+ and Ca2+ along zones of ocean crust production, and (5 additional proxies of seawater Mg/Ca including Sr/Mg ratios of abiogenic carbonates, Sr/Ca ratios of biogenic carbonates, and Br concentrations in marine halite.

    Laboratory experiments have revealed that aragonite-secreting bryopsidalean algae and scleractinian corals and calcite-secreting coccolithophores exhibit higher rates of calcification and growth in experimental seawaters formulated with seawater Mg/Ca ratios that favor their skeletal mineral. These results support the assertion that seawater Mg/Ca played an important role in determining which hypercalcifying marine organisms were the major reef-builders and sediment-producers throughout Earth history. The observation that primary

  5. Aragonite saturation states and pH in western Norwegian fjords: seasonal cycles and controlling factors, 2005-2009

    Science.gov (United States)

    Omar, Abdirahman M.; Skjelvan, Ingunn; Rune Erga, Svein; Olsen, Are

    2016-07-01

    The uptake of anthropogenic carbon dioxide (CO2) by the ocean leads to a process known as ocean acidification (OA), which lowers the aragonite saturation state (ΩAr) and pH, and this is poorly documented in coastal environments including fjords due to lack of appropriate observations.Here we use weekly underway data from the Voluntary Observing Ships (VOS) program covering the period 2005-2009 combined with data from research cruises to estimate ΩAr and pH values in several adjacent western Norwegian fjords, and to evaluate how seawater CO2 chemistry drives their variations in response to physical and biological factors.The OA parameters in the surface waters of the fjords are subject to strong seasonal and spatially coherent variations. These changes are governed by the seasonal changes in temperature, salinity, formation and decay of organic matter, and vertical mixing with deeper, carbon-rich coastal water. Annual mean pH and ΩAr values were 8.13 and 2.21, respectively. The former varies from minimum values ( ≈ 8.05) in late December - early January to maximum values of around 8.2 during early spring (March-April) as a consequence of the phytoplankton spring bloom, which reduces dissolved inorganic carbon (DIC). In the following months, pH decreases in response to warming. This thermodynamic decrease in pH is reinforced by the deepening of the mixed layer, which enables carbon-rich coastal water to reach the surface, and this trend continues until the low winter values of pH are reached again. ΩAr, on the other hand, reaches its seasonal maximum (> 2.5) in mid- to late summer (July-September), when the spring bloom is over and pH is decreasing. The lowest ΩAr values ( ≈ 1.3-1.6) occur during winter (January-March), when both pH and sea surface temperature (SST) are low and DIC is its highest. Consequently, seasonal ΩAr variations align with those of SST and salinity normalized DIC (nDIC).We demonstrate that underway measurements of fugacity of CO2 in

  6. Response of Acropora digitifera to ocean acidification: constraints from δ11B, Sr, Mg, and Ba compositions of aragonitic skeletons cultured under variable seawater pH

    Science.gov (United States)

    Tanaka, Kentaro; Holcomb, Michael; Takahashi, Asami; Kurihara, Haruko; Asami, Ryuji; Shinjo, Ryuichi; Sowa, Kohki; Rankenburg, Kai; Watanabe, Tsuyoshi; McCulloch, Malcolm

    2015-12-01

    The response of Acropora digitifera to ocean acidification is determined using geochemical proxy measurements of the skeletal composition of A. digitifera cultured under a range of pH levels. We show that the chemical composition (δ11B, Sr/Ca, Mg/Ca, and Ba/Ca) of the coral skeletons can provide quantitative constraints on the effects of seawater pH on the pH in the calcification fluid (pHCF) and the mechanisms controlling the incorporation of trace elements into coral aragonite. With the decline of seawater pH, the skeletal δ11B value decreased, while the Sr/Ca ratio showed an increasing trend. The relationship between Mg/Ca and Ba/Ca versus seawater pH was not significant. Inter-colony variation of δ11B was insignificant, although inter-colony variation was observed for Ba/Ca. The decreasing trend of pHCF calculated from δ11B was from ~8.5, 8.4, and 8.3 for seawater pH of ~8.1, 7.8, and 7.4, respectively. Model calculations based on Sr/Ca and pHCF suggest that upregulation of pHCF occurs via exchange of H+ with Ca2+ with kinetic effects (Rayleigh fractionation), reducing Sr/Ca relative to inorganic deposition of aragonite from seawater. We show that it is possible to constrain the overall carbonate chemistry of the calcifying fluid with estimates of the carbonate saturation of the calcifying fluid ( Ω CF) being derived from skeletal Sr/Ca and pHCF (from δ11B). These estimates suggest that the aragonite saturation state of the calcifying fluid Ω CF is elevated by a factor of 5-10 relative to ambient seawater under all treatment conditions.

  7. Marine biogeochemistries of Be and Al: A study based on cosmogenic 10Be, Be and Al in marine calcite, aragonite, and opal

    Indian Academy of Sciences (India)

    Weiquan Dong; Devendra Lal; Barbara Ransom; Wolfgang Berger; Marc W Caffee

    2001-06-01

    The geochemical behaviors of Be and Al in ocean waters have been successfully studied in recent years using natural, cosmogenic, radioactive 10Be and 26Al as tracers. The present day dissolved concentrations and distribution of the stable and radioactive isotopes of Be and Al in ocean waters have revealed their short residence times and appreciable effects of exchange uxes at the coastal and ocean-sediment interfaces. It follows that concentrations of these particle-active elements must have varied in the past with temporal changes in climate, biological productivity and aeolian ux of continental detritus to the oceans. We therefore investigated the feasibility of extending the measurements of Be and Al isotope concentrations in marine systems to the 103-106 BP time scale. We report here the discovery of significant amounts of intrinsic Be and Al in marine foraminiferal calcite and coral aragonite, and of Al in opal (radiolarians) and aragonite (coral), which makes it possible to determine 10Be/Be and 26Al/Al in oceans in the past. We also report measured 10Be/9Be in foraminiferal calcite in Pacific Ocean cores, which reveal that the concentrations and ratios of the stable and cosmogenic isotopes of Be and Al have varied significantly in the past 30 ky. The implications of these results are discussed.

  8. Chemical and physical evolution of dolomite precipitation at 180°C and 220°C from calcite and aragonite seeds

    Science.gov (United States)

    Kell-Duivestein, Isaac; Dietzel, Martin; Mavromatis, Vasileios

    2016-04-01

    In this present study an experimental approach is taken to gain a better understanding of secondary dolomite formation under diagenetic hydrothermal conditions. A series of 60 experiments were set up in closed bomb reactors with Teflon inserts to simulate exposure of calcium carbonate materials of (i) aragonite and (ii) calcite to hydrothermal conditions. 30 reactors were prepared using calcite as a seed material and 30 using aragonite. In each experiment 330mg of the seed calcium carbonate was placed in 30mL of 0.2M MgCl2 solution along with 252mg NaHCO3 to balance charges. 15 of each the calcite and aragonite prepared reactors were placed in an oven at 180°C and 15 of each at 220°C. Samples were then progressively removed from the ovens beginning in short time intervals and increasing the time apart as the phase transformations became less rapid (ie. after 3, 6, 13, 21, 31, 56 days *ongoing*). Samples were separated into fluid and solid phases by filtration for separate analysis. Fluids were analysed by titration for alkalinity and ICP-OES for elemental concentrations of major cations to determine the migration of major cations between the calcium carbonate seed material and the reaction fluid. Solid samples were analysed with FTIR-spectroscopy and X-ray diffraction of powdered smears on glass loading slides to identify the present mineral phases. Rietveld analysis was conducted on the XRD patterns to quantify the mineral phases and to determine the stoichiometry and the superstructure of the formed magnesite and dolomite. Although experiments are still running, several trends have been identified. Transformation of the aragonite seed material occurs at a much faster rate than transformation of the calcite seed material, with each precursor material first transforming into a Ca-rich magnesite. With increased reaction time the Ca-rich magnesite recrystallizes to purer phases of magnesite, the Ca concentration of the fluid increases as the Ca is liberated into

  9. Dissolution of aragonite-strontianite solid solutions in nonstoichiometric Sr (HCO3)2-Ca (HCO3)2-CO2-H2O solutions

    Science.gov (United States)

    Plummer, L.N.; Busenberg, E.; Glynn, P.D.; Blum, A.E.

    1992-01-01

    Synthetic strontianite-aragonite solid-solution minerals were dissolved in CO2-saturated non-stoichiometric solutions of Sr(HCO3)2 and Ca(HCO3)2 at 25??C. The results show that none of the dissolution reactions reach thermodynamic equilibrium. Congruent dissolution in Ca(HCO3)2 solutions either attains or closely approaches stoichiometric saturation with respect to the dissolving solid. In Sr(HCO3)2 solutions the reactions usually become incongruent, precipitating a Sr-rich phase before reaching stoichiometric saturation. Dissolution of mechanical mixtures of solids approaches stoichiometric saturation with respect to the least stable solid in the mixture. Surface uptake from subsaturated bulk solutions was observed in the initial minutes of dissolution. This surficial phase is 0-10 atomic layers thick in Sr(HCO3)2 solutions and 0-4 layers thick in Ca(HCO3)2 solutions, and subsequently dissolves and/or recrystallizes, usually within 6 min of reaction. The initial transient surface precipitation (recrystallization) process is followed by congruent dissolution of the original solid which proceeds to stoichiometric saturation, or until the precipitation of a more stable Sr-rich solid. The compositions of secondary precipitates do not correspond to thermodynamic equilibrium or stoichiometric saturation states. X-ray photoelectron spectroscopy (XPS) measurements indicate the formation of solid solutions on surfaces of aragonite and strontianite single crystals immersed in Sr(HCO3)2 and Ca(HCO3)2 solutions, respectively. In Sr(HCO3)2 solutions, the XPS signal from the outer ~ 60 A?? on aragonite indicates a composition of 16 mol% SrCO3 after only 2 min of contact, and 14-18 mol% SrCO3 after 3 weeks of contact. The strontianite surface averages approximately 22 mol% CaCO3 after 2 min of contact with Ca(HCO3)2 solution, and is 34-39 mol% CaCO3 after 3 weeks of contact. XPS analysis suggests the surface composition is zoned with somewhat greater enrichment in the outer ~25

  10. Attempt of absolute dating and reconstitutions of climate changes in the Caribbean Sea: multi-proxy approaches to planktonic foraminifera and fine aragonitic fraction

    International Nuclear Information System (INIS)

    Absolute dating of climate archives is essential to better understand climate mechanisms. A marine sediment core from the Caribbean Sea enriched in fine-grained aragonite (suitable to U/Th dating) has been studied for both planktonic foraminifera tests (≥150 μm) and fine fraction (≤63 μm) over the last one million years using mineralogical and geochemical approaches. This study aims at i) examining lead/lag of δ18O and radiometric ages of the different-size fractions and ii) reconstructing paleo-environment in the area. The fine fraction mineralogy is strongly influenced by glacial-interglacial sea level changes. The offset of δ18O and 14C ages between the fine and foraminifera fractions during Termination I is partly explained by a bioturbation model. Attempt of U/Th dating to Termination II and V reveals that the fine fraction contains non-radiogenic Th, which needs further analytical development. Reconstructed surface water δ18O changes suggest a decrease in surface water salinity at the end of Mid-Pleistocene Transition related to ITCZ position over the Caribbean Sea. (author)

  11. Two-dimensional X-ray diffraction as a tool for the rapid, nondestructive detection of low calcite quantities in aragonitic corals

    Science.gov (United States)

    Smodej, Jörg; Reuning, Lars; Wollenberg, Uwe; Zinke, Jens; Pfeiffer, Miriam; Kukla, Peter A.

    2015-10-01

    Paleoclimate reconstructions based on reef corals require precise detection of diagenetic alteration. Secondary calcite can significantly affect paleotemperature reconstructions at very low amounts of ˜1%. X-ray powder diffraction is routinely used to detect diagenetic calcite in aragonitic corals. This procedure has its limitations as single powder samples might not represent the entire coral heterogeneity. A conventional and a 2-D X-ray diffractometer were calibrated with gravimetric powder standards of high and low magnesium calcite (0.3% to 25% calcite). Calcite contents analysis showed very similar results. This enables spot measurements with diameters of ˜4 mm, as well as systematic line scans along potential tracks previous to geochemical proxy sampling. In this way, areas affected by diagenetic calcite can be avoided and alternative sampling tracks can be defined. Alternatively, individual sampling positions that show dubious proxy results can later be checked for the presence of calcite. The presented calibration and quantification method can be transferred to any 2-D X-ray diffractometer.

  12. Two-dimensional X-ray diffraction as a tool for the rapid, nondestructive detection of low calcite quantities in aragonitic corals

    Science.gov (United States)

    Smodej, Jörg; Reuning, Lars; Wollenberg, Uwe; Zinke, Jens; Pfeiffer, Miriam; Kukla, Peter A.

    2015-10-01

    Paleoclimate reconstructions based on reef corals require precise detection of diagenetic alteration. Secondary calcite can significantly affect paleotemperature reconstructions at very low amounts of ˜1%. X-ray powder diffraction is routinely used to detect diagenetic calcite in aragonitic corals. This procedure has its limitations as single powder samples might not represent the entire coral heterogeneity. A conventional and a 2-D X-ray diffractometer were calibrated with gravimetric powder standards of high and low magnesium calcite (0.3% to 25% calcite). Calcite contents advantage of 2-D-XRD over convenient 1-D-XRD methods is the nondestructive and rapid detection of calcite with relatively high spatial resolution directly on coral slabs. The calcite detection performance of the 2-D-XRD setup was tested on thin sections from fossil Porites sp. samples that, based on powder XRD measurements, showed sampling. In this way, areas affected by diagenetic calcite can be avoided and alternative sampling tracks can be defined. Alternatively, individual sampling positions that show dubious proxy results can later be checked for the presence of calcite. The presented calibration and quantification method can be transferred to any 2-D X-ray diffractometer.

  13. Total individual ion activity coefficients of calcium and carbonate in seawater at 25°C and 35%. salinity, and implications to the agreement between apparent and thermodynamic constants of calcite and aragonite

    Science.gov (United States)

    Plummer, L. Neil; Sundquist, Eric T.

    1982-01-01

    We have calculated the total individual ion activity coefficients of carbonate and calcium,  and , in seawater. Using the ratios of stoichiometric and thermodynamic constants of carbonic acid dissociation and total mean activity coefficient data measured in seawater, we have obtained values which differ significantly from those widely accepted in the literature. In seawater at 25°C and 35%. salinity the (molal) values of  and  are 0.038 ± 0.002 and 0.173 ± 0.010, respectively. These values of  and  are independent of liquid junction errors and internally consistent with the value . By defining  and  on a common scale (), the product  is independent of the assigned value of  and may be determined directly from thermodynamic measurements in seawater. Using the value  and new thermodynamic equilibrium constants for calcite and aragonite, we show that the apparent constants of calcite and aragonite are consistent with the thermodynamic equilibrium constants at 25°C and 35%. salinity. The demonstrated consistency between thermodynamic and apparent constants of calcite and aragonite does not support a hypothesis of stable Mg-calcite coatings on calcite or aragonite surfaces in seawater, and suggests that the calcite critical carbonate ion curve of Broecker and Takahashi (1978,Deep-Sea Research25, 65–95) defines the calcite equilibrium boundary in the oceans, within the uncertainty of the data.

  14. The solubilities of calcite, aragonite and vaterite in CO2-H2O solutions between 0 and 90°C, and an evaluation of the aqueous model for the system CaCO3-CO2-H2O

    Science.gov (United States)

    Plummer, L. Niel; Busenberg, Eurybiades

    1982-01-01

    Calculations based on approximately 350 new measurements (CaT-PCO2) of the solubilities of calcite, aragonite and vaterite in CO2-H2O solutions between 0 and 90°C indicate the following values for the log of the equilibrium constants KC, KA, and KV respectively, for the reaction CaCO3(s) = Ca2+ + CO2−3: 

  15. Rare earth elements in the aragonitic shell of freshwater mussel Corbicula fluminea and the bioavailability of anthropogenic lanthanum, samarium and gadolinium in river water.

    Science.gov (United States)

    Merschel, Gila; Bau, Michael

    2015-11-15

    High-technology metals - such as the rare earth elements (REE) - have become emerging contaminants in the hydrosphere, yet little is known about their bioavailability. The Rhine River and the Weser River in Germany are two prime examples of rivers that are subjected to anthropogenic REE input. While both rivers carry significant loads of anthropogenic Gd, originating from contrast agents used for magnetic resonance imaging, the Rhine River also carries large amounts of anthropogenic La and lately Sm which are discharged into the river from an industrial point source. Here, we assess the bioavailability of these anthropogenic microcontaminants in these rivers by analyzing the aragonitic shells of the freshwater bivalve Corbicula fluminea. Concentrations of purely geogenic REE in shells of comparable size cover a wide range of about one order of magnitude between different sampling sites. At a given sampling site, geogenic REE concentrations depend on shell size, i.e. mussel age. Although both rivers show large positive Gd anomalies in their dissolved loads, no anomalous enrichment of Gd relative to the geogenic REE can be observed in any of the analyzed shells. This indicates that the speciations of geogenic and anthropogenic Gd in the river water differ from each other and that the geogenic, but not the anthropogenic Gd is incorporated into the shells. In contrast, all shells sampled at sites downstream of the industrial point source of anthropogenic La and Sm in the Rhine River show positive La and Sm anomalies, revealing that these anthropogenic REE are bioavailable. Only little is known about the effects of long-term exposure to dissolved REE and their general ecotoxicity, but considering that anthropogenic Gd and even La have already been identified in German tap water and that anthropogenic La and Sm are bioavailable, this should be monitored and investigated further. PMID:26151653

  16. pH up-regulation as a potential mechanism for the cold-water coral Lophelia pertusa to sustain growth in aragonite undersaturated conditions

    Science.gov (United States)

    Wall, M.; Ragazzola, F.; Foster, L. C.; Form, A.; Schmidt, D. N.

    2015-12-01

    Cold-water corals are important habitat formers in deep-water ecosystems and at high latitudes. Ocean acidification and the resulting change in aragonite saturation are expected to affect these habitats and impact coral growth. Counter to expectations, the deep water coral Lophelia pertusa has been found to be able to sustain growth even in undersaturated conditions. However, it is important to know whether such undersaturation modifies the skeleton and thus its ecosystem functioning. Here we used Synchrotron X-Ray Tomography and Raman spectroscopy to examine changes in skeleton morphology and fibre orientation. We combined the morphological assessment with boron isotope analysis to determine if changes in growth are related to changes in control of calcification pH. We compared the isotopic composition and structure formed in their natural environment to material grown in culture at lower pH conditions. Skeletal morphology is highly variable but shows no distinctive differences between natural and low pH conditions. Raman investigations found no difference in macromorphological skeletal arrangement of early mineralization zones and secondary thickening between the treatments. The δ11B analyses show that L. pertusa up-regulates the internal calcifying fluid pH (pHcf) during calcification compared to ambient seawater pH and maintains a similar elevated pHcf at increased pCO2 conditions. We suggest that as long as the energy is available to sustain the up-regulation, i.e. individuals are well fed, there is no detrimental effect to the skeletal morphology.

  17. Rare earth elements in the aragonitic shell of freshwater mussel Corbicula fluminea and the bioavailability of anthropogenic lanthanum, samarium and gadolinium in river water.

    Science.gov (United States)

    Merschel, Gila; Bau, Michael

    2015-11-15

    High-technology metals - such as the rare earth elements (REE) - have become emerging contaminants in the hydrosphere, yet little is known about their bioavailability. The Rhine River and the Weser River in Germany are two prime examples of rivers that are subjected to anthropogenic REE input. While both rivers carry significant loads of anthropogenic Gd, originating from contrast agents used for magnetic resonance imaging, the Rhine River also carries large amounts of anthropogenic La and lately Sm which are discharged into the river from an industrial point source. Here, we assess the bioavailability of these anthropogenic microcontaminants in these rivers by analyzing the aragonitic shells of the freshwater bivalve Corbicula fluminea. Concentrations of purely geogenic REE in shells of comparable size cover a wide range of about one order of magnitude between different sampling sites. At a given sampling site, geogenic REE concentrations depend on shell size, i.e. mussel age. Although both rivers show large positive Gd anomalies in their dissolved loads, no anomalous enrichment of Gd relative to the geogenic REE can be observed in any of the analyzed shells. This indicates that the speciations of geogenic and anthropogenic Gd in the river water differ from each other and that the geogenic, but not the anthropogenic Gd is incorporated into the shells. In contrast, all shells sampled at sites downstream of the industrial point source of anthropogenic La and Sm in the Rhine River show positive La and Sm anomalies, revealing that these anthropogenic REE are bioavailable. Only little is known about the effects of long-term exposure to dissolved REE and their general ecotoxicity, but considering that anthropogenic Gd and even La have already been identified in German tap water and that anthropogenic La and Sm are bioavailable, this should be monitored and investigated further.

  18. Rare earth elements in the aragonitic shell of freshwater mussel Corbicula fluminea and the bioavailability of anthropogenic lanthanum, samarium and gadolinium in river water

    Energy Technology Data Exchange (ETDEWEB)

    Merschel, Gila, E-mail: g.merschel@jacobs-university.de; Bau, Michael

    2015-11-15

    High-technology metals — such as the rare earth elements (REE) — have become emerging contaminants in the hydrosphere, yet little is known about their bioavailability. The Rhine River and the Weser River in Germany are two prime examples of rivers that are subjected to anthropogenic REE input. While both rivers carry significant loads of anthropogenic Gd, originating from contrast agents used for magnetic resonance imaging, the Rhine River also carries large amounts of anthropogenic La and lately Sm which are discharged into the river from an industrial point source. Here, we assess the bioavailability of these anthropogenic microcontaminants in these rivers by analyzing the aragonitic shells of the freshwater bivalve Corbicula fluminea. Concentrations of purely geogenic REE in shells of comparable size cover a wide range of about one order of magnitude between different sampling sites. At a given sampling site, geogenic REE concentrations depend on shell size, i.e. mussel age. Although both rivers show large positive Gd anomalies in their dissolved loads, no anomalous enrichment of Gd relative to the geogenic REE can be observed in any of the analyzed shells. This indicates that the speciations of geogenic and anthropogenic Gd in the river water differ from each other and that the geogenic, but not the anthropogenic Gd is incorporated into the shells. In contrast, all shells sampled at sites downstream of the industrial point source of anthropogenic La and Sm in the Rhine River show positive La and Sm anomalies, revealing that these anthropogenic REE are bioavailable. Only little is known about the effects of long-term exposure to dissolved REE and their general ecotoxicity, but considering that anthropogenic Gd and even La have already been identified in German tap water and that anthropogenic La and Sm are bioavailable, this should be monitored and investigated further. - Highlights: • Corbicula fluminea shells are bioarchives of dissolved geogenic REE in

  19. 洞穴文石石笋古气候环境变化研究进展、存在问题及研究方向%Aragonite stalagmite use in paleoclimate and environmental change research:Progress,disadvantages and further research directions

    Institute of Scientific and Technical Information of China (English)

    殷建军; 林玉石; 唐伟

    2014-01-01

    Due to global warming,extreme climate events have increased in frequency and intensity.Thus,it is important to use the geologic record to reconstruct climate change during the past 2 000 years,including the warm period (Medieval Warm Period),cold period (Little Ice Age)and the human-activity-influenced Current Warm Period,to better understand the mechanisms of climate change and extreme climate events. This paper focuses on aragonite stalagmites with high levels of uranium,allowing for high precision dating. The high precision dating enables study of the relationship between climate and cultural changes (such as the development and disintegration of the Mayan political systems),differences in regional climate (such as dry-wet conditions in the Asian monsoon area),and reconstruction of extreme climate events (such as the mech-anism of drought events in the Asian monsoon area). When aragonite stalagmites are used in paleoclimate reconstruction,it is very important to know both the aragonite formation conditions and the aragonite-to-calcite transition conditions.To address these issues, the following techniques may be used,First,87 Sr/86 Sr,δ26 Mg,δ18 O andδ13 C should be integrated into anal-ysis of the stalagmite provenance,to determine if the stalagmite Mg comes from bedrock dolomite or is due to the hydrologic process.Second,synthetically analyze the aragonite formation environment and the hydro-logic process using Mg/Ca,Sr/Ca,δ13 C and △47 to determine if changes in temperature or hydrologic process may have caused PCP (Prior Calcite Precipitation)or PAP (Prior Aragonite Precipitation).Third, use crystallography and physical chemistry in aragonite-to-calcite transition analysis.The aragonite-to-calcite transition is not progressive in some aragonite stalagmites,and this may be due to pore water between crys-tals and infiltration water from the surface of the stalagmite.This is very important for crystallography and physical chemistry research in the

  20. THE ORIENTATION OF CaCO3 ARAGONITE CRYSTALS FROM SEVERAL ORGANISMS%几种生物CaCO3霰石结晶的取向性

    Institute of Scientific and Technical Information of China (English)

    蒋新农; 李敬之; 徐学红

    2001-01-01

    The CaCO3 crystals are widely distributed in organisms. Thecalcite, aragonite and vaterite are the main crystal polymorphisms of CaCO3. In this paper, CaCO3 crystals were obtained from the nacreous layers of Hyriopsis cumingii Lea and Pinctada martensii Dunker, the internal shell of a cuttlefish and the otolith of Pseudosciaena crocea. X-ray diffraction measurement was used to analyze the crystal orientation of CaCO3 crystals: The results showed that each kind of natural CaCO3 crystal has an orientation on specific plane. In detail, the crystal orientations of the nacreous layers are higher than the internal shell, and the orientation of the otolith is the lowest. Except the nacreous layers of Pinctada martensii, whose highest peak is on the crystal plane (312), all the other three natural samples have the highest peak on the crystal plane (012). As to ground CaCO3 crystals, the differences between their corresponding d values are very small, so each ground sample has the CaCO3 aragonite structure characterized by the JCPDS card (5-0453).%CaCO3结晶广泛分布于生物界,其主要结晶形式为方解石、霰石及球霰石。用X-射线衍射法对三角帆蚌及合浦珍珠母贝的珍珠层、墨鱼骨和大黄鱼耳石的CaCO3结晶进行测定,发现各样品均有一定取向性,以三角帆蚌和合浦珍珠母贝珍珠层的取向性为最强,墨鱼骨的取向性次之,大黄鱼耳石的取向性最小,以上材料粉末样的衍射分析表明,各样品对应d值间差异极小,均为X射线衍射卡(5-0453)所表征的CaCO3霰石结构。

  1. The impact of low pH, low aragonite saturation state on calcifying corals: an in-situ study of ocean acidification from the "ojos" of Puerto Morelos, Mexico

    Science.gov (United States)

    Crook, E. D.; Paytan, A.; Potts, D. C.; Hernandez Terrones, L.; Rebolledo-Vieyra, M.

    2010-12-01

    Recent increases in atmospheric carbon dioxide have resulted in rising aqueous CO2 concentrations that lower the pH of the oceans (Caldeira and Wickett 2003, 2005, Doney et al., 2009). It is estimated that over the next 100 years, the pH of the surface oceans will decrease by ~0.4 pH units (Orr et al., 2005), which is expected to hinder the calcifying capabilities of numerous marine organisms. Previous field work (Hall-Spencer et al., 2008) indicates that ocean acidification will negatively impact calcifying species; however, to date, very little is known about the long-term impacts of ocean acidification from the in-situ study of coral reef ecosystems. The Yucatán Peninsula of Quintana Roo, Mexico, represents an ecosystem where naturally low pH groundwater (7.14-8.07) has been discharging offshore at highly localized points (called ojos) for millennia. We present preliminary chemical and biological data on a selection of ojos from lagoon sites in Puerto Morelos, Mexico. Our findings indicate a decrease in species richness and size with proximity to the low pH waters. We address the potential long-term implications of low pH, low aragonite saturation state on coral reef ecosystems.

  2. Subsurface low pH and carbonate saturation state of aragonite on China side of the North Yellow Sea: combined effects of global atmospheric CO2 increase, regional environmental changes, and local biogeochemical processes

    Directory of Open Access Journals (Sweden)

    J.-Y. Wang

    2013-02-01

    Full Text Available Based upon seven field surveys conducted between May 2011 and January 2012, we investigated pH, carbonate saturation state of aragonite (Ωarag, and ancillary parameters on the Chinese side of the North Yellow Sea, a western North Pacific continental margin of major economic importance. Subsurface waters were nearly in equilibrium with air in May and June. From July to October, the fugacity of CO2 (fCO2 of bottom water gradually increased to 697 ± 103 μatm and pH decreased to 7.83 ± 0.07 due to respiration/remineralization processes of primary production induced biogenic particles. In November and January, bottom water fCO2 decreased and pH gradually returned to an air-equilibrated level due to cooling enhanced vertical mixing. The corresponding bottom water Ωarag was 1.74 ± 0.17 (May, 1.77 ± 0.26 (June, 1.70 ± 0.26 (July, 1.72 ± 0.33 (August, 1.32 ± 0.31 (October, 1.50 ± 0.28 (November, and 1.41 ± 0.12 (January. Critically low Ωarag values of 1.0 to 1.2 were mainly observed in subsurface waters in a salinity range of 31.5–32.5 psu in October and November, accounting for ~ 10% of the North Yellow Sea area. Water mass derived from the adjacent Bohai Sea had a typical water salinity of 30.5–31.5 psu, and bottom water Ωarag values ranged mostly between 1.6 and 2.4. This study showed that the carbonate system in the North Yellow Sea was substantially influenced by global atmospheric CO2 increase. The community respiration/remineralization rates in typical North Yellow Sea bottom water mass were estimated at 0.55–1.0 μmol O2 kg−1 d−1 in warm seasons, leading to seasonal drops in subsurface pH and Ωarag. Outflow of the Bohai Sea water mass counteracted the subsurface Ωarag reduction in the North Yellow Sea.

  3. Spectral luminescence and geochemistry of coral aragonite: Effects of whole-core treatment

    NARCIS (Netherlands)

    Nagtegaal, R.; Grove, C.A.; Kasper, S.; Zinke, J.; Brummer, G.J.A.

    2012-01-01

    Luminescent and geochemical properties of coral skeletons are increasingly used for time-series analysis to resolve past and ongoing changes in environmental and climatic conditions. Corals also contain non-skeletal matter which not only quenches luminescence but is also reported to compromise stabl

  4. Spectral luminescence and geochemistry of coral aragonite: Effects of whole-core treatment

    OpenAIRE

    Nagtegaal, R.; Grove, C.A.; Kasper, S.; J. Zinke; Brummer, G.J.A.

    2012-01-01

    Luminescent and geochemical properties of coral skeletons are increasingly used for time-series analysis to resolve past and ongoing changes in environmental and climatic conditions. Corals also contain non-skeletal matter which not only quenches luminescence but is also reported to compromise stable isotope and trace element composition. In order to understand the origin and magnitude of these potential sources of error we tested whether three commonly used cleaning treatments (NaOCl, H2O2 a...

  5. A Large Metabolic Carbon Ccontribution to the δ13C Record in Marine Aragonitic Bivalve Shells

    Science.gov (United States)

    Gillikin, D. P.; Lorrain, A.; Dehairs, F.

    2006-12-01

    The stable carbon isotopic signature archived in bivalve shells was originally thought to record the δ13C of seawater dissolved inorganic carbon (δ13C-DIC). However, more recent studies have shown that the incorporation of isotopically light metabolic carbon (M) significantly affects the δ13C signal recorded in biogenic carbonates. To assess the M contribution to Mercenaria mercenaria shells collected in North Carolina, USA, we sampled seawater δ13C-DIC, tissue, hemolymph and shell δ13C. We found up to a 4‰ decrease through ontogeny in shell δ13C in a 23 year old individual. There was no correlation between shell height or age and tissue δ13C. Thus, the ontogenic decrease observed in the shell δ13C could not be attributed to changes in food sources as the animal ages leading to more negative metabolic CO2, since this would require a negative relationship between tissue δ13C and shell height. Hemolymph δ13C, on the other hand, did exhibit a negative relationship with height, but the δ13C values were more positive than expected, indicating that hemolymph may not be a good proxy of extrapallial fluid δ13C. Nevertheless, the hemolymph data indicate that respired CO2 does influence the δ13C of internal fluids and that the amount of respired CO2 is related to the age of the bivalve. The percent metabolic C incorporated into the shell (%M) was significantly higher (up to 37%) than has been found in other bivalve shells, which usually contain less than 10 %M. Attempts to use shell biometrics to predict %M could not explain more than ~60% of the observed variability. Moreover, there were large differences in the %M between different sites. Thus, the metabolic effect on shell δ13C cannot easily be accounted for to allow reliable δ13C-DIC reconstructions. However, there does seem to be a common effect of size, as all sites had indistinguishable slopes between the %M and shell height (+0.19% per mm of shell height).

  6. Relationship between Late Pleistocene sea-level variations, carbonate platform morphology and aragonite production (Maldives, Indian Ocean)

    DEFF Research Database (Denmark)

    Paul, A.; Reijmer, J.J.G.; Fürstenau, J.;

    2012-01-01

    A piston core from the Maldives carbonate platform was investigated for carbonate mineralogy, grain-size distributions, calcium carbonate content and organic carbon. The sedimentary record was linked to Late Pleistocene sea-level variations, using an age model based on oxygen isotopes obtained fr...

  7. Chemical Composition of Micrometer-Sized Filaments in an Aragonite Host by a Miniature Laser Ablation/Ionization Mass Spectrometer.

    Science.gov (United States)

    Tulej, Marek; Neubeck, Anna; Ivarsson, Magnus; Riedo, Andreas; Neuland, Maike B; Meyer, Stefan; Wurz, Peter

    2015-08-01

    Detection of extraterrestrial life is an ongoing goal in space exploration, and there is a need for advanced instruments and methods for the detection of signatures of life based on chemical and isotopic composition. Here, we present the first investigation of chemical composition of putative microfossils in natural samples using a miniature laser ablation/ionization time-of-flight mass spectrometer (LMS). The studies were conducted with high lateral (∼15 μm) and vertical (∼20-200 nm) resolution. The primary aim of the study was to investigate the instrument performance on micrometer-sized samples both in terms of isotope abundance and element composition. The following objectives had to be achieved: (1) Consider the detection and calculation of single stable isotope ratios in natural rock samples with techniques compatible with their employment of space instrumentation for biomarker detection in future planetary missions. (2) Achieve a highly accurate chemical compositional map of rock samples with embedded structures at the micrometer scale in which the rock matrix is easily distinguished from the micrometer structures. Our results indicate that chemical mapping of strongly heterogeneous rock samples can be obtained with a high accuracy, whereas the requirements for isotope ratios need to be improved to reach sufficiently large signal-to-noise ratio (SNR). PMID:26247475

  8. The use of external micro-PIXE to investigate the factors determining the Sr:Ca ratio in the shells of fossil aragonitic molluscs

    Energy Technology Data Exchange (ETDEWEB)

    Purton-Hildebrand, Louise M.A.; Grime, Geoff W. E-mail: geoff.grime@materials.ox.ac.uk; Shields, Graham A.; Brasier, Martin D

    2001-07-01

    The ratio of strontium to calcium in the shells of fossil marine molluscs has been proposed as an indicator of seawater temperature in past epochs, since this is less affected by other environmental conditions (such as variation of salinity) than the more conventional seawater palaeotemperature proxy {delta}{sup 18}O. However, in this paper, we demonstrate that the Sr:Ca ratio is influenced by several factors including temperature and growth rate. Two fossil molluscs, a large spiral gastropod, Clavilithes macrospira, and a large bivalve, Venericarda planicosta, from the Eocene-aged deposits of Southern England were selected for study. The variation of the Sr:Ca ratio as a function of distance along the growth direction was measured using PIXE in the Oxford external microbeam facility and the {delta}{sup 18}O was measured using small samples removed by drilling at points along the same direction. The Sr:Ca profiles show a significant increase of Sr with age, as well as seasonal, possibly temperature-related variations. Comparison of the Sr:Ca profiles with those for {delta}{sup 18}O and the spacing of the dark annual growth bands suggests that Sr incorporation is controlled primarily by metabolic activity, which in turn is influenced by factors such as temperature, salinity, age and growth rate.

  9. In vivo transformation of a calcium carbonate (aragonite based implant's biomaterial to bone. A histological, chemical and FT-IR study

    Directory of Open Access Journals (Sweden)

    Ramón González

    2004-01-01

    Full Text Available Se estudió la respuesta del tejido óseo a implantes de carbonato de calcio aragonito (CCA. Se utilizaron implantes de Hidroxiapatita Coralina (HA en la misma forma y proceder quirúrgico como biomaterial de control comparativo. Se investigó el efecto de la composición química sobre la capacidad de curación y la velocidad de reabsorción de ambos biomateriales implantados en el fémur de ratas. Los animales fueron sacrificados a los 3, 7, 15, 21 y 60 d y los implantes fueron recuperados para los análisis posteriores. La evaluación se realiz ó mediante técnicas de microscopia óptica, estudios histológicos y radiográficos, análisis químico cuantitativo de calcio y fósforo y espectroscopia IR de Transformada de Fourier (FT-IR. Se encontró que ambos biomateriales fueron bien asimilados y se integraron al tejido óseo circundante. En el caso de la Hidroxiapatita se observó que a los 60 d el defecto óseo fue reparado, pero el biomaterial mantuvo la misma apariencia inicial. Por el contrario, en ese mismo período, el implante de coral (CCA disminuyó su tamaño y su apariencia resultó más parecida a la del tejido circundante. Los estudios histológicos mostraron la misma capacidad osteogénica en ambos biomateriales en los primeros 7 d de implantados, pero a los 15 d se aprecia una mayor velocidad de sustitución del tejido fibrovascular por hueso en el caso del CCA. La cinética de biodegradación calculada a partir de los análisis químicos (relación Ca/P y de los espectros IR coincide con las observaciones histológicas y muestra una mayor velocidad de reabsorción de los implantes de carbonato de calcio (CCA. Se encontró que la transformación del CCA produce una fase similar a la del hueso debido a la pérdida paulatina del anión carbonato y la incorporación del fosfato correspondiente. El CCA también presentó una mayor capacidad osteogénica en comparación con la HA. A los 60 d el (42,5 ± 3,2 % del CCA originalmente implantado se transformó en fosfato de calcio y la velocidad de este proceso se incrementó de (0,22 ± 0,08 %/d a los 7 d hasta (0,7 ± 0,1 %/d a los 60 d de implantado. Los implantes de HA no experimentaron cambios en el período analizado (60 d. En conclusión, igual que la hidroxiapatita porosa, el biomaterial de aragonito estimula la proliferación de tejido vivo hacia el interior de los poros, pero con una mayor velocidad de reabsorción y de generación de nuevo hueso. Estos resultados sugieren que la velocidad de reabsorción de este tipo de biomaterial de implante puede ser controlada en dependencia de la relación fosfato/carbonato en su composición química inicial.

  10. Differential dissolution of a Pleistocene reef in the groundwater mixing zone of coastal Yucatan, Mexico.

    Science.gov (United States)

    Back, W.; Hanshaw, B.B.; Herman, J.S.; Van Driel, J. N.

    1986-01-01

    Mixing of fresh groundwater with subterranean Caribbean seawater generates a highly reactive geochemical zone that enhances aragonite and calcite dissolution and permits neomorphism of aragonite.-from Authors

  11. 利用原位沉积生成的文石型碳酸钙改善旧报纸脱墨浆性能%Improving Recycled Fiber by Applying In-situ Aragonite Calcium Carbonate Formation Process

    Institute of Scientific and Technical Information of China (English)

    陈军伟

    2015-01-01

    在旧报纸(ONP)脱墨浆中通过碳酸化法进行了原位沉积生成针状的文石型沉淀碳酸钙(PCC)的实验。结果表明,与未处理的ONP脱墨浆相比,经文石型PCC原位沉积生成工艺处理ONP脱墨浆所抄造手抄片的白度提高了20.4%(从56.8%增至68.4%),ERIC降低55.4%(从292.1 mg/kg降至130.4 mg/kg)。原位沉积生成文石型PCC不仅可改善成纸光学性能,同时还可保留手抄片的强度性能,这归因于文石型PCC的针状形态。

  12. Late Quaternary sea level and environmental changes from relic carbonate deposits of the western margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Rajagopalan, G.; Vora, K.H.; Almeida, F.

    Relic carbonate deposits along the western margin of India occur as dolomite crusts, aragonite sands (pelletal / oolitic) and aragonite-cemented limestones, oyster shells, corals, encrusted coralline algal and foraminiferal-dominated nodules...

  13. Abrupt climate-induced changes in carbonate burial in the Arabian Sea: Causes and consequences.

    Digital Repository Service at National Institute of Oceanography (India)

    Naidu, P.D.; Singh, A.D.; Ganeshram, R.S.; Bharti, S.K.

    glacial and particularly during stadials (Heinrich Events). Using aragonite content, pteropods abundance, organic carbon percentage, and abundance of fertile (eutrophic) species of planktonic foraminifer, we demonstrate that aragonite contents...

  14. Review on Researches of Aragonite Saturation State in the Arctic Ocean: A Key Parameter of Arctic Ocean Acidification%北冰洋酸化指标——海水文石饱和度变异的研究进展

    Institute of Scientific and Technical Information of China (English)

    祁第; 陈立奇

    2014-01-01

    文石饱和度(Ω文石)是评估海洋酸化及对海洋钙质生物影响的重要指标之一.海洋吸收CO2引起海洋酸化,导致Ω文石显著下降.模式研究预测表明北冰洋表层海水将成为最先出现Ω文石<1的世界大洋.通过对北冰洋Ω文石有关研究进行归纳总结,重点阐述了北冰洋Ω文石的分布特征,讨论海—气CO2交换过程、融冰过程以及生物过程等因素对北冰洋Ω文石分布的影响,展望未来的变化趋势并提出一些关键的科学问题.

  15. Relic carbonate deposits along the western margin of India: Sea level and environmental changes during the Late Quaternary

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.

    sands (pelletal/oolitic sediments) and aragonite-cemented limestones, oyster shells, corals, coralline-algal and foraminiferal-dominated nodules. The petrology and mineralogy of the deposits indicate that except for aragonite sands and foraminiferal... pellets while others are ooilte- dominated. The age of the sands ranges between 14.3 ka to 7.6 cal kaBP. The limestones associated with the platform exhibit acicular aragonite cements and their ages lie between 11 ka and 13.3 kaBP. Large oyster shells...

  16. Crystal nucleation and near-epitaxial growth in nacre

    CERN Document Server

    Olson, Ian C; Tamura, Nobumichi; Kunz, Martin; Gilbert, Pupa U P A

    2013-01-01

    Nacre, the iridescent inner lining of many mollusk shells, interests materials scientists because of its unique brick-and-mortar periodic structure at the sub-micron scale and its remarkable resistance to fracture. However, it remains unclear how nacre forms. Here we present 20-nm, 2{\\deg}-resolution Polarization-dependent Imaging Contrast (PIC) images of shells from 15 species, mapping nacre tablets and their orientation patterns, showing where crystals nucleate and how they grow in nacre. In all shells we found stacks of co-oriented aragonite (CaCO3) tablets arranged into vertical columns or staggered diagonally. Only near the nacre-prismatic boundary are disordered crystals nucleated, as spherulitic aragonite. Overgrowing nacre tablet crystals are most frequently co-oriented with the underlying spherulitic aragonite or with another tablet, connected by mineral bridges. Therefore aragonite crystal growth in nacre is epitaxial or near-epitaxial, with abrupt or gradual changes in orientation, with c-axes with...

  17. Coral Cores for selected locations in the Pacific Ocean obtained to determine calcification and extension rates of Porites spp. corals

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Laboratory experiments reveal calcification and extension rates of corals are strongly correlated to seawater aragonite saturation state. Predictions of reduced...

  18. Studies on structure and organization of calcium carbonate deposits in algae

    Digital Repository Service at National Institute of Oceanography (India)

    Kerkar, V.; Untawale, A.G.

    The structure and organization of calcium carbonate deposits is studied in species of Halimeda, Udotea, Neomeris (Chlorophyta) and Padina (Phaeophyta). It was found that in Halimeda aragonite deposition takes place outside the cell wall...

  19. Calcification Rates of Crustose Coralline Algae derived from Calcification Accretion Units (CAUs) deployed across U.S. Pacific Reefs since 2010 (NCEI Accession 0137093)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Laboratory experiments reveal calcification rates of crustose coralline algae are strongly correlated to seawater aragonite saturation state. Predictions of reduced...

  20. Calcite Formation in Soft Coral Sclerites Is Determined by a Single Reactive Extracellular Protein*

    OpenAIRE

    Rahman, M. Azizur; Oomori, Tamotsu; Wörheide, Gert

    2011-01-01

    Calcium carbonate exists in two main forms, calcite and aragonite, in the skeletons of marine organisms. The primary mineralogy of marine carbonates has changed over the history of the earth depending on the magnesium/calcium ratio in seawater during the periods of the so-called “calcite and aragonite seas.” Organisms that prefer certain mineralogy appear to flourish when their preferred mineralogy is favored by seawater chemistry. However, this rule is not without exceptions. For example, so...

  1. Ordering in red abalone nacre

    OpenAIRE

    Metzler, Rebecca A.; Zhou, Dong; Abrecht, Mike; Coppersmith, Susan N.; P.U.P.A. Gilbert

    2007-01-01

    Red abalone nacre is an intensely studied biomineral, and yet its formation mechanism remains poorly understood. Here we report quantitative measurements probing the degree of order of the aragonite tablets in nacre, and show that order develops over a distance of about 50 microns. These observations indicate that the orientational order of aragonite tablets in nacre is established gradually and dynamically, and we show that a model of controlled assembly based on suppression of the crystal g...

  2. Skeletal growth phases of the cold-water coral Lophelia pertusa shown by scanning electron microscope and electron backscatter diffraction

    Science.gov (United States)

    Mouchi, Vincent; Vonlanthen, Pierre; Verrecchia, Eric P.; Crowley, Quentin G.

    2016-04-01

    Lophelia pertusa is a cold-water coral, which may form reefs by the association of multiple coralites within which a polyp lives. Each individual polyp builds an aragonite skeleton by an initial phase of early mineralization (traditionally referred to as centres of calcification) from which aragonite fibres grow in thickening deposits. The skeleton wall features successive optically opaque and translucent bands previously attributed to different regimes of growth as either uniform in crystal orientation (translucent bands) or with a chaotic organization (opaque bands). The processes involved in any organizational changes are still unknown. Microlayers in the coral wall, which represent separate periods of skeletal growth, have been recently identified and described. These growth patterns are readily visible under scanning electron microscope (SEM) after etching in dilute formic acid, but they do not necessarily form continuously visible structures. Here we present high quality SEM images and electron backscatter diffraction (EBSD) maps to study aragonite fibre orientation across the wall of L. pertusa. Both microlayers and opaque and translucent bands are compared to the crystallographic orientation of the aragonite fibres. EBSD maps and SEM images indicate that aragonite fibres do not exhibit a chaotic orientation, even in opaque bands. The absence of continuity of microlayers is partially explained by an association of multiple crystallographic preferred orientations of aragonite fibres. In the case of L. pertusa, careful textural characterisation is necessary prior to elemental or isotope analysis in order to select a skeletal transect representing a linear and continuous time period.

  3. Hydrological Controls on Water Chemistry that Supports Freshwater Mussel Populations

    Science.gov (United States)

    Prestegaard, K. L.

    2012-12-01

    Native freshwater mussel species ranges and population sizes have been declining throughout N. America. Due to their sedentary nature, adult mussels are vulnerable to both local habitat changes (often associated with land-use changes, contaminants, and biological invaders) and to climate changes that can alter river flow regimes, bed stability, and water chemistry. The purpose of this study is to examine the relationship between water chemistry and hydrological events in rivers that support native mussel populations. USGS ion concentration and water quality (pH, temperature, conductivity) data were used to calculate saturation indices for aragonite. For some sites, electrical conductivity was highly correlated with calcium and bicarbonate concentrations and could be used to estimate concentrations when ion chemistry was not measured. Continuous water quality data from datasondes could thus be used to evaluate saturation indices for aragonite on a daily basis for 10-15 year periods. For the Delaware River, which has relatively few carbonate rocks in its watershed, tributary aragonite saturation tended to reflect local geological conditions. The lower main stem of the river integrates the water chemistry of the basin and also responds to climatic conditions. The lower Delaware supports aragonite precipitation approximately 50 days per year, with considerable inter-annual variability. During most years, aragonite precipitation could occur during both the spring and late summer periods, but years with heavy spring rains rather than snowmelt shifts aragonite precipitation to late summer periods. In 2011 when several major tropical storms hit the Delaware basin, streamflow was too dilute for aragonite precipitation for most of the summer period. These data suggest that hydrological changes associated with climatic changes may influence the water chemistry and affect the suitability of some rivers as mussel habitat.

  4. Miniaturized biosignature analysis reveals implications for the formation of cold seep carbonates at Hydrate Ridge (off Oregon, USA

    Directory of Open Access Journals (Sweden)

    T. Leefmann

    2007-11-01

    Full Text Available Methane-related carbonates from Hydrate Ridge typically show several macroscopically distinguishable phases, namely whitish aragonite, lucent aragonite, and gray micrite. The relationship of these phases to particular microorganisms or biogeochemical processes is as yet unclear. We used a miniaturized biomarker technique on mg samples, combined with factor analysis and subsequent electron microprobe analysis, to study lipid biomarkers and chemical compositions of the individual phases. This allows us to identify particular mechanisms involved in the formation of the different carbonate precipitates. Our combined analysis of biomarkers and petrographic traits shows that most of the lipids related to the anaerobic oxidation of methane (>90% by weight are concentrated within only a minor compartment (~20% by volume of the Hydrate Ridge carbonates (whitish aragonite. The patterns indicate that the whitish aragonite represents fossilized biofilms of methanotrophic consortia, whereas the precipitation of the lucent aragonite does not seem to be directly controlled by microorganisms. The gray micrite shows a partly Mg-calcitic mineralogy, higher pyrite contents, and a much higher proportion of allochthonous biomarkers. The formation of these precipitates is interpreted to reflect periodic methane-rich fluid pulses that disrupted the sediments and promoted the growth of the respective methanotrophic consortia along fluid pathways.

  5. Miniaturized biosignature analysis reveals implications for the formation of cold seep carbonates at Hydrate Ridge (off Oregon, USA

    Directory of Open Access Journals (Sweden)

    T. Leefmann

    2008-05-01

    Full Text Available Methane-related carbonates from Hydrate Ridge typically show several macroscopically distinguishable mineral phases, namely whitish aragonite, lucent aragonite, and gray micrite. The relationship of these phases to particular microorganisms or biogeochemical processes is as yet unclear. We used a miniaturized biomarker technique on mg samples, combined with factor analysis and subsequent electron microprobe analysis, to study lipid biomarkers and chemical compositions of the individual phases. This allows us to identify particular mechanisms involved in the formation of the different carbonate precipitates. Our combined analysis of biomarkers and petrographic traits shows that most of the lipids related to the anaerobic oxidation of methane (>90% by weight are concentrated within only a minor compartment (~20% by volume of the Hydrate Ridge carbonates, the whitish aragonite. The patterns indicate that the whitish aragonite represents fossilized biofilms of methanotrophic consortia containing mainly archaea of the ANME-2 group and sulfate reducing bacteria, whereas the precipitation of the lucent aragonite may have lacked the immediate proximity of microorganisms during formation. By contrast, the gray micrite formed by incorporation of allochthonous organic and inorganic matter during carbonate precipitation induced by the anaerobic oxidation of methane involving ANME-1 archaea.

  6. The structure-function relationship of MSI7, a matrix protein from pearl oyster Pinctada fucata

    Institute of Scientific and Technical Information of China (English)

    Qiaoli Feng; Zi Fang; Zhenguang Yan; Rui Xing; Liping Xie; Rongqing Zhang

    2009-01-01

    We previously identified a matrix protein, MSI7, from pearl oyster Pinctada fucata. According to the struc-tural analysis, the DGD site in the N-terminal of MSI7 is crucial for its role in the shell formation. In this study, we expressed a series of recombinant MSI7 pro-teins, including the wild-type and several mutants directed at the DGD site, using an Escherichia coli expression system to reveal the structure-function relationship of MSI7. Furthermore, in vitro crystalliza-tion, crystallization speed assay, and circular dichroism spectrometry were carried out. Results indicated that wild-type MSI7 could induce the nucleation of arago-nite and inhibit the crystallization of calcite. However, none of the mutants could induce the nucleation of ara-gonite, but all of them could inhibit the crystallization of calcite to some extent. And all the proteins acceler-ated the crystallization process. Taken together, the results indicated that MSI7 could contribute to arago-nite crystallization by inducing the nucleation of arago-nite and inhibiting the crystallization of calcite, which agrees with our prediction about its role in the nacr-eous layer formation of the shell. The DGD site was critical for the induction of the nucleation of aragonite.

  7. Disparate acidification and calcium carbonate desaturation of deep and shallow waters of the Arctic Ocean

    Science.gov (United States)

    Luo, Yiming; Boudreau, Bernard P.; Mucci, Alfonso

    2016-01-01

    The Arctic Ocean is acidifying from absorption of man-made CO2. Current predictive models of that acidification focus on surface waters, and their results argue that deep waters will acidify by downward penetration from the surface. Here we show, with an alternative model, the rapid, near simultaneous, acidification of both surface and deep waters, a prediction supported by current, but limited, saturation data. Whereas Arctic surface water responds directly by atmospheric CO2 uptake, deeper waters will be influenced strongly by intrusion of mid-depth, pre-acidified, Atlantic Ocean water. With unabated CO2 emissions, surface waters will become undersaturated with respect to aragonite by 2105 AD and could remain so for ∼600 years. In deep waters, the aragonite saturation horizon will rise, reaching the base of the surface mixed layer by 2140 AD and likely remaining there for over a millennium. The survival of aragonite-secreting organisms is consequently threatened on long timescales. PMID:27659188

  8. Surface Modification and Planar Defects of Calcium Carbonates by Magnetic Water Treatment

    Directory of Open Access Journals (Sweden)

    Yeh MS

    2010-01-01

    Full Text Available Abstract Powdery calcium carbonates, predominantly calcite and aragonite, with planar defects and cation–anion mixed surfaces as deposited on low-carbon steel by magnetic water treatment (MWT were characterized by X-ray diffraction, electron microscopy, and vibration spectroscopy. Calcite were found to form faceted nanoparticles having 3x ( commensurate superstructure and with well-developed { } and { } surfaces to exhibit preferred orientations. Aragonite occurred as laths having 3x ( commensurate superstructure and with well-developed ( surface extending along [100] direction up to micrometers in length. The (hkil-specific coalescence of calcite and rapid lath growth of aragonite under the combined effects of Lorentz force and a precondensation event account for a beneficial larger particulate/colony size for the removal of the carbonate scale from the steel substrate. The coexisting magnetite particles have well-developed {011} surfaces regardless of MWT.

  9. Molecular approaches to understand biomineralization of shell nacreous layer.

    Science.gov (United States)

    Xie, Li-Ping; Zhu, Fang-Jie; Zhou, Yu-Juan; Yang, Chao; Zhang, Rong-Qing

    2011-01-01

    The nacreous layer of molluskan shells, which consists of highly oriented aragonitic crystals and an organic matrix (including chitin and proteins), is a product of biomineralization. This paper briefly introduces the recent research advances on nacre biomineralization of shells from bivalves and gastropods, which mainly focus on analysis of the micro- and nano-structure and components of shell nacreous layers, and investigations of the characteristics and functions of matrix proteins from nacre. Matrix proteins not only participate in construction of the organic nacre framework, but also control the nucleation and growth of aragonitic crystals, as well as determine the polymorph specificity of calcium carbonate in nacre. Moreover, the inorganic aragonite phase also plays an active role in organizing nacre microstructure. Based on these studies, several models to illustrate the formation mechanism related to lamellar nacre in bivalves, and columnar nacre in gastropods are introduced.

  10. Isotopic characteristics of shells Mytilus galloprovincialis from eastern coastal area of Adriatic Sea

    Directory of Open Access Journals (Sweden)

    Tjaša Kanduč

    2006-06-01

    Full Text Available Samples of Mytilus galloprovincialis were collected from entire Eastern Adriatic coast to determine δ18O and δ13C performed on calcite and aragonite shell layers. The aim of this work was to check whether shells of M. galloprovincialis are good environmental indicators (water temperature, salinity. Based on measured isotopic composition of oxygen in shell layers and assumed isotopic composition in water temperatures of calcite and aragonite of shell layers were calculated. The calculated temperatures for M. galloprovincialis shell growth of calcite and aragonite shell layer are in good agreement with measured temperatures of sea water. According to our results of δ18O and δ13C in shell layers we canseparate the locations of the investigated area into three groups: those with more influence of fresh water, those with less influence of fresh water and those of marine environments.

  11. A high-pressure study of PbCO3 by XRD and Raman spectroscopy

    Science.gov (United States)

    Zhang, Yu-Feng; Liu, Jing; Qin, Zhen-Xing; Lin, Chuan-Long; Xiong, Lun; Li, Rui; Bai, Li-Gang

    2013-03-01

    The pressure-induced phase transitions of PbCO3 are studied using synchrotron radiation in a diamond anvil cell at room temperature. The XRD measurement indicates that PbCO3 with an initial phase of aragonite-type structure undergoes two phase transitions at ~7.8 GPa and ~15.7 GPa, respectively. The higher-pressure phase appearing at ~15.7 GPa is stable up to 51.8 GPa. The two phase transitions are further confirmed by Raman scattering up to 23.3 GPa. During the decompression process, the high-pressure phases of PbCO3 are gradually recovered to the starting aragonite-type structure, but exhibit some hysteresis. The bulk modulus B0 of the aragonite-type structure is obtained to be 63±(3) GPa by fitting the volume-pressure data to the Birch—Murnaghan equation of states with B'0 fixed to 4.

  12. Calcite formation in soft coral sclerites is determined by a single reactive extracellular protein.

    Science.gov (United States)

    Rahman, M Azizur; Oomori, Tamotsu; Wörheide, Gert

    2011-09-01

    Calcium carbonate exists in two main forms, calcite and aragonite, in the skeletons of marine organisms. The primary mineralogy of marine carbonates has changed over the history of the earth depending on the magnesium/calcium ratio in seawater during the periods of the so-called "calcite and aragonite seas." Organisms that prefer certain mineralogy appear to flourish when their preferred mineralogy is favored by seawater chemistry. However, this rule is not without exceptions. For example, some octocorals produce calcite despite living in an aragonite sea. Here, we address the unresolved question of how organisms such as soft corals are able to form calcitic skeletal elements in an aragonite sea. We show that an extracellular protein called ECMP-67 isolated from soft coral sclerites induces calcite formation in vitro even when the composition of the calcifying solution favors aragonite precipitation. Structural details of both the surface and the interior of single crystals generated upon interaction with ECMP-67 were analyzed with an apertureless-type near-field IR microscope with high spatial resolution. The results show that this protein is the main determining factor for driving the production of calcite instead of aragonite in the biocalcification process and that -OH, secondary structures (e.g. α-helices and amides), and other necessary chemical groups are distributed over the center of the calcite crystals. Using an atomic force microscope, we also explored how this extracellular protein significantly affects the molecular-scale kinetics of crystal formation. We anticipate that a more thorough investigation of the proteinaceous skeleton content of different calcite-producing marine organisms will reveal similar components that determine the mineralogy of the organisms. These findings have significant implications for future models of the crystal structure of calcite in nature. PMID:21768106

  13. In-vitro study on calcium carbonate crystal growth mediated by organic matrix extracted from fresh water pearls

    International Nuclear Information System (INIS)

    For the purpose of studying the mediation of organic matrix on the crystallization of calcium carbonate, water soluble matrix (WSM), acid soluble matrix (ASM) and acid insoluble matrix (AIM) were extracted from aragonite pearls and vaterite pearls respectively. Then, in-vitro calcium carbonate crystallization experiments under the control of these six organic matrices were carried out in the present study. Scanning electron microscopy (SEM) was utilized to observe the morphology of CaCO3 and Raman spectroscopy as a powerful technique was used to distinguish the crystal polymorph. Influences of the six kinds of organic matrices on the calcium carbonate crystal growth are proposed. ASM of vaterite pearls can induce vaterite to crystallize and WSM of aragonite pearls mediates to produce aragonite crystals. The single AIM membranes of the two pearls have no pronounced effect on the CaCO3 crystallization. Additionally, the crystal size obtained with the additive of WSM of the two kinds of pearls is smaller than that with the additive of ASM. Moreover, self-assembly phenomenon in the biomineralization process and the distorted morphology calcite are observed. Current results demonstrate important aspects of matrix protein-controlled crystallization, which is beneficial to the understanding of nacre biomineralization mechanism. Further study of the precise control of these matrix proteins on CaCO3 crystal growth is being processed. - Highlights: ► WSM, ASM and AIM are extracted from aragonite pearls and vaterite pearls. ► ASM of vaterite pearl induces vaterite. ► WSM of aragonite pearl mediates to produce aragonite. ► WSM can fine control crystal size smaller than that with the additive of ASM. ► Self-assembly and the distorted calcite existed in the mineralization process.

  14. Historical reconstruction of ocean acidification in the Australian region

    Directory of Open Access Journals (Sweden)

    A. Lenton

    2015-06-01

    Full Text Available The increase in atmospheric greenhouse gases over the last 200 years has caused an increase in ocean acidity levels. Documenting how the ocean has changed is critical for assessing how these changes could impact marine ecosystems and for the management of marine resources. We use present day ocean carbon observations from shelf and offshore waters around Australia, combined with neural network mapping of CO2, to estimate the current seasonal and regional distributions of carbonate chemistry (pH and aragonite saturation state. These predicted changes in carbonate chemistry are combined with atmospheric CO2 concentration changes since to reconstruct pH and aragonite saturation state changes over the last 140 years (1870–2013. The comparison with data collected at Integrated Marine Observing System National Reference Station sites located on the shelf around Australia shows both the mean state and seasonality for the present day is well represented by our reconstruction, with the exception of sites such as the Great Barrier Reef. Our reconstruction predicts that since 1870 an average decrease in aragonite saturation state of 0.48 and of 0.09 in pH has occurred in response to increasing oceanic uptake of atmospheric CO2. Our reconstruction shows that seasonality is the dominant mode of variability, with only small interannual variability present. Large seasonal variability in pH and aragonite saturation state occur in Southwestern Australia driven by ocean dynamics (mixing and in the Tasman Sea by seasonal warming (in the case of aragonite saturation state. The seasonal and historical changes in aragonite saturation state and pH have different spatial patterns and suggest that the biological responses to ocean acidification are likely to be non-uniform depending on the relative sensitivity of organisms to shifts in pH and saturation state. This new historical reconstruction provides an important to link to biological observations to help elucidate

  15. Summertime calcium carbonate undersaturation in shelf waters of the western Arctic Ocean – how biological processes exacerbate the impact of ocean acidification

    Directory of Open Access Journals (Sweden)

    N. R. Bates

    2013-08-01

    Full Text Available The Arctic Ocean accounts for only 4% of the global ocean area, but it contributes significantly to the global carbon cycle. Recent observations of seawater CO2-carbonate chemistry in shelf waters of the western Arctic Ocean, primarily in the Chukchi Sea, from 2009 to 2011 indicate that bottom waters are seasonally undersaturated with respect to calcium carbonate (CaCO3 minerals, particularly aragonite. Nearly 40% of sampled bottom waters on the shelf have saturation states less than one for aragonite (i.e., Ωaragonite 3-secreting organisms, while 80% of bottom waters present had Ωaragonite values less than 1.5. Our observations indicate seasonal reduction of saturation states (Ω for calcite (Ωcalcite and aragonitearagonite in the subsurface in the western Arctic by as much as 0.8 and 0.5, respectively. Such data indicate that bottom waters of the western Arctic shelves were already potentially corrosive for biogenic and sedimentary CaCO3 for several months each year. Seasonal changes in Ω are imparted by a variety of factors such as phytoplankton photosynthesis, respiration/remineralization of organic matter and air–sea gas exchange of CO2. Combined, these processes either increase or enhance in surface and subsurface waters, respectively. These seasonal physical and biological processes also act to mitigate or enhance the impact of Anthropocene ocean acidification (OA on Ω in surface and subsurface waters, respectively. Future monitoring of the western Arctic shelves is warranted to assess the present and future impact of ocean acidification and seasonal physico-biogeochemical processes on Ω values and Arctic marine ecosystems.

  16. Historical reconstruction of ocean acidification in the Australian region

    Science.gov (United States)

    Lenton, Andrew; Tilbrook, Bronte; Matear, Richard J.; Sasse, Tristan P.; Nojiri, Yukihiro

    2016-03-01

    The ocean has become more acidic over the last 200 years in response increasing atmospheric carbon dioxide (CO2) levels. Documenting how the ocean has changed is critical for assessing how these changes impact marine ecosystems and for the management of marine resources. Here we use present-day ocean carbon observations, from shelf and offshore waters around Australia, combined with neural network mapping of CO2, sea surface temperature, and salinity to estimate the current seasonal and regional distributions of carbonate chemistry (pH and aragonite saturation state). The observed changes in atmospheric CO2 and sea surface temperature (SST) and climatological salinity are then used to reconstruct pH and aragonite saturation state changes over the last 140 years (1870-2013). The comparison with data collected at Integrated Marine Observing System National Reference Station sites located on the shelf around Australia shows that both the mean state and seasonality in the present day are well represented, with the exception of sites such as the Great Barrier Reef. Our reconstruction predicts that since 1870 decrease in aragonite saturation state of 0.48 and of 0.09 in pH has occurred in response to increasing oceanic uptake of atmospheric CO2. Large seasonal variability in pH and aragonite saturation state occur in southwestern Australia driven by ocean dynamics (mixing) and in the Tasman Sea by seasonal warming (in the case of the aragonite saturation state). The seasonal and historical changes in aragonite saturation state and pH have different spatial patterns and suggest that the biological responses to ocean acidification are likely to be non-uniform depending on the relative sensitivity of organisms to shifts in pH and saturation state. This new historical reconstruction provides an important link to biological observations that will help to elucidate the consequences of ocean acidification.

  17. The carbonate mineralogy and distribution of habitat-forming deep-sea corals in the southwest pacific region

    Science.gov (United States)

    Bostock, Helen C.; Tracey, Dianne M.; Currie, Kim I.; Dunbar, Gavin B.; Handler, Monica R.; Mikaloff Fletcher, Sara E.; Smith, Abigail M.; Williams, Michael J. M.

    2015-06-01

    Habitat-forming deep-sea scleractinian and alcyonacean corals from around the southwest Pacific were analysed for their calcium carbonate mineralogy. Scleractinian coral species Solenosmilia variabilis, Enallopsammia rostrata, Goniocorella dumosa, Madrepora oculata and Oculina virgosa were all found to be 100% aragonitic, while some members of the alcyonacean taxa Keratoisis spp., Lepidisis spp., and Paragorgia spp. were determined to be high magnesium (Mg) calcite (with 8-11 mol% MgCO3) and Primnoa sp. is bimineralic with both aragonite and Mg calcite. The majority of these habitat-forming deep-sea corals are found at intermediate depths (800-1200 m) in the Antarctic Intermediate Waters (AAIW) with low salinities (~34.5), temperatures of 4-8 °C and high oxygen concentrations (>180 μmol/kg) and currently sitting above the aragonite saturation horizon (ASH). However, habitat-forming corals have been recorded from greater depths, in cooler waters (2-4 °C) that are undersaturated with respect to aragonitearagonite160 μmol/kg. To address the sampling depth bias the coral records were normalised by the number of benthic stations (sampling effort) in the same depth range. This shows that the highest number of corals per sampling effort is between 1000 and 1400 m with corals present in over 5% of the stations at these depths. The normalised records and Boot Strap analyses suggests that scleractinian corals, especially S. variabilis should be present in >1% of stations down to 1800 m water depth, with E. rostrata, M. oculata and G. dumosa slightly shallower. While alcyonacean corals are found in >1% down to 2600 m, with Keratoisis spp. the deepest down to 2600 m, while Lepidisis spp. and Paragorgia spp. found down to 1800 m. This suggests that most species can probably tolerate some undersaturation of aragonitearagonite=0.8-0.9), with several species/genera (S. variabilis; Keratoisis spp.) even more tolerant of lower carbonate concentrations ([CO3 2 -]), down

  18. Hydrocalcite (CaCO3 * H2O) and Nesquehonite (MgCO3 * 3H2O) in Carbonate Scales.

    Science.gov (United States)

    Marschner, H

    1969-09-12

    Hydrocalcite (CaCO(3) * H(2)O) with exactly one molecule of hydrate water is the main component of carbonate scales deposited from cold water in contact with air. When the magnesium content of the water is high, the hydrocalcite occurs together with MgCO(3) * 3H(2)O (nesquehonite). From the conditions under which hydrocalcite is transformed into calcite and aragonite, it appears that in some cases aragonite in nature may be formed by way of an intermediary of CaCO(3) * H(2)O. PMID:17779803

  19. Structures and stability of calcium and magnesium carbonates at mantle pressures

    OpenAIRE

    Pickard, Chris J.; Needs, Richard J.

    2014-01-01

    Ab initio random structure searching (AIRSS) and density functional theory methods are used to predict structures of calcium and magnesium carbonate (CaCO$_3$ and MgCO$_3$) at high pressures. We find a previously unknown CaCO$_3$ structure which is more stable than the aragonite and "post aragonite" phases in the range 32--48 GPa. At pressures from 67 GPa to well over 100 GPa the most stable phase is a previously unknown CaCO$_3$ structure of the pyroxene type with fourfold coordinated carbon...

  20. Mechanism of unusual polymorph transformations in calcium carbonate: Dissolution-recrystallization vs additive-mediated nucleation

    Indian Academy of Sciences (India)

    Arpita Sarkar; Samiran Mahapatra

    2012-11-01

    Unusual transformation of one CaCO3 phase to another has been reported by the process of dissolution-recrystallization and under the influence of additive. In one case, while metastable vaterite transforms to another metastable phase aragonite by simple refluxing in distilled water, it instead transforms thermodynamically stable phase calcite upon refluxing in its `mother-liquor’. This is explained by the process of dissolution-recrystallization. In another case, aragonite is preferentially synthesized over calcite in the presence of molten lauric acid as an additive.

  1. U-Th dating of calcitic corals from the Red Sea

    Science.gov (United States)

    Stein, M.; Yehudai, M.; Kohn, N.; Shaked, Y.; Agnon, A.; Lazar, B.

    2013-12-01

    Pristine aragonite skeletons of reef building corals can be rapidly recrystallized to calcite by the interaction of the corals with freshwater in coastal aquifers. The aragonite/calcite transformation is accompanied by opening the coral's U-Th isotope system in which uranium is partly lost while Th remains adsorbed and reincorporates into the newly formed calcite. Depending on the geological setting of the reef, the corals may incorporate secondary aragonite with higher U and 234U/238U isotope ratio, while still submerged, before the recrystallization process. Recrystallization to calcite occurs during sea level drop or coast tectonic uplift and later may follow a subaerial closed system decay scheme. In this study we examine the behavior of the U and Th in calcitic corals from the last interglacial reefs at the northern Gulf of Aqaba. We analyzed several subsamples from selected reef coral skeletons in an attempt to follow the recrystallization scheme of the corals and find a reliable method to estimate the age of these heavily altered corals. The main assumptions were that all subsamples from the same coral have identical deposition age and the sub-samples Th (and hence 230Th) was fully preserved during recrystallization to calcite (increasing the 230Th/238U isotope ratio). Diagenesis to calcite occurred several thousand years after the initial precipitation of the aragonitic skeleton. This calls for wetter (than present) conditions during the last interglacial in the currently hyperarid northern Red Sea.

  2. Methane seepage intensities traced by biomarker patterns in authigenic carbonates from the South China Sea

    Science.gov (United States)

    Guan, H.; Feng, D.

    2015-12-01

    Authigenic carbonate rocks from an active seep (Site F) at 1120 m water depth of the South China Sea (SCS) were studied using mineralogical and lipid biomarker analyses. Carbonate mineral compositions, in specific samples, were predominantly aragonite, high-Mg calcite (HMC), or a mixture of both. Abundant 13C-depleted lipid biomarkers (various isoprenoids) diagnostic for archaea provide evidence that anaerobic oxidation of methane (AOM) mediated by anaerobic methane oxidizing archaea (ANME) and their bacterial partners is the major process leading to formation of the carbonates. Nearly a pure suite of AOM biomarkers was preserved in aragonitic carbonate in which predominant consortia were most likely ANME-2/Desulfosarcina & Desulfococcus (DSS) assemblages and a mixture of ANME-2/DSS and ANME-1/DSS consortia in the mixed mineral sample, the predominant consortia are in good accordance with the point that the relative higher methane seepage intensity favors the precipitation of aragonite over HMC. In contrast, the completely different biomarker patterns in HMC sample were mainly composed terrestrial organic matter and marine Thaumarchaea, which most likely originally within sediments accompanied with high organic matter input and low methane supply. This environment is known to be favored for archaea of ANME-1 and precipitation of HMC. High concentrations of 13C-depleted hopanoids, including diplopterol, hopanoic acids and hopanols were observed in the aragonite sample that may be sourced by the intermittent presence of oxic conditions in an overall anoxic condition, which was possibly induced by changing seepage intensities.

  3. Polymorphism of CaCO3 and microstructure of the shell of a Brazilian invasive Mollusc (Limnoperna fortunei)

    International Nuclear Information System (INIS)

    Applying the theories of Materials Science and Engineering to describe the composition and hierarchy of microstructures that comprise biological systems could help the search for new materials and results in a deeper insight into evolutionary processes. The layered microstructure that makes up the freshwater bivalve Limnoperna fortunei shell, an invasive specie in Brazil, was investigated utilizing SEM and AFM for the determination of the morphology and organization of the layers; and XRD was used to determine the crystalline phases of the calcium carbonate (CaCO3) present in the shell. The presence of the polymorphs calcite and aragonite were confirmed and the calcite is present only on the external side of the shell. The shell of L. fortunei is composed of two layers of aragonite with distinct microstructures (the aragonite prismatic layer and the aragonite sheet nacreous layer) and the periostracum (a protein layer that covers and protects the ceramic part of the shell). A new morphology of the calcite layer was found, below the periostracum, without defined form, albeit crystal (author)

  4. Threshold of carbonate saturation state determined by CO2 control experiment

    Directory of Open Access Journals (Sweden)

    A. Negishi

    2012-04-01

    Full Text Available Acidification of the oceans by increasing anthropogenic CO2 emissions will cause a decrease in biogenic calcification and an increase in carbonate dissolution. Previous studies have suggested that carbonate dissolution will occur in polar regions and in the deep sea where saturation state with respect to carbonate minerals (Ω will be a (aragonite saturation state value of >1. This is probably related to the dissolution of reef carbonate (Mg-calcite, which is more soluble than aragonite. However, the threshold of Ω for the dissolution of natural sediments has not been clearly determined. We designed an experimental dissolution system with conditions mimicking those of a natural coral reef, and measured the dissolution rates of aragonite in corals, and of Mg-calcite excreted by other marine organisms, under conditions of Ωa > 1, with controlled seawater pCO2. The experimental data show that dissolution of bulk carbonate sediments sampled from a coral reef occurs at Ωa values of 3.7 to 3.8. Mg-calcite derived from foraminifera and coralline algae dissolves at Ωa values between 3.0 and 3.2, and coralline aragonite starts to dissolve when Ωa = 1.0. We show that nocturnal carbonate dissolution of coral reefs occurs mainly by the dissolution of foraminiferans and coralline algae in reef sediments.

  5. Characterization of organic matrix extracted from fresh water pearls

    International Nuclear Information System (INIS)

    Aragonite pearl and vaterite pearl from cultured Hyriopsis cumingii in Zhuji (Zhejiang province, China) were chosen for the study. The matrix proteins were extracted using water and weak acid, and classified as water soluble matrix (WSM), acid soluble matrix (ASM) and acid insoluble matrix (AIM). The proteins from both pearls were characterized by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), X-ray diffraction (XRD) and Fourier transformation infrared spectra (FTIR). The results showed that, AIM of aragonite pearl and vaterite pearl had an ordered structure of α-helix. ASM conformations of these two pearls were different from each other. WSM differed the most between these two pearls. - Research Highlights: → We use a specific method for extracting matrix proteins from aragonite pearl and vaterite pearl respectively. → The matrix proteins are extracted by water and weak acid, and classified as water soluble matrix (WSM), acid soluble matrix (ASM) and acid insoluble matrix (AIM). → AIM of aragonite pearl and vaterite pearl have an ordered structure. ASM conformations of the two pearls are different from each other. WSM differ the most between these two pearls.

  6. Tectonic forcing of early to middle jurassic seawater Sr/Ca

    DEFF Research Database (Denmark)

    Ullmann, Clemens Vinzenz; Hesselbo, Stephen P.; Korte, Christoph

    2013-01-01

    The Jurassic Period (ca. 201–145 Ma) is marked by fundamental reorganizations of paleogeography, paleoceanography, ecosystems, and the progressive shift from aragonite to calcite as the favored marine biogenic carbonate polymorph. Sr/Ca ratios of well-preserved Jurassic oysters and belemnites fro...

  7. Oxygen and carbon isotopic composition of limestones and dolomites, bikini and eniwetok atolls

    Science.gov (United States)

    Grant, Gross M.; Tracey, J.I., Jr.

    1966-01-01

    Aragonitic, unconxolidated sediments from the borings on the Eniwetok and Bikini atolls are isotopically identical with unaltered skeletal fragments, whereas the recrystallized limestones exhibit isotopic variations resulting from alteration in meteoric waters during periods of emergence. Dolomites and associated calcites are enriched in O18, perhaps because of interaction with hypersaline brines.

  8. Petrosraphic and geochemical characterization of seep carbonate from Alaminos Canyon, Gulf of Mexico

    Institute of Scientific and Technical Information of China (English)

    FENG Dong; CHEN DuoFu; QI Liang; Harry H.ROBERTS

    2008-01-01

    Seep carbonates were collected from the Alaminos Canyon lease area, Gulf of Mexico. The carbonates are present as slabs and blocks. Bivalve shell and foraminifer are the dominant bioclasts in carbonate. Pores are common and usually filled with acicular aragonite crystals. XRD investigation shows that aragonite is the dominate mineral (98%). Peloids, clotted microfabirc and botryoidal aragonite are developed in carbonate and suggest a genesis linked with bacterial degradation of the hydrocarbons. The δ13C value of bioclasts in carbonate is from -4.9‰ to -0.6‰, indicating that the carbon source is mainly from sea water as well as the small portion incorporation of the seep hydrocarbon. The microcrystalline and sparite aragonite shows the δ13C value from -31.3‰, to -23.4‰, suggesting that their carbon is derived mainly from microbial degradation of crude oil. 14C analyses give the radiocarbon age of about 10 ka. Rare earth elements (REE) analyses of the 5% HNO3-treated solution of the carbonates show that the total REE content of the carbonates is low, that is from 0.752 to 12.725 ug·g-1. The shale-normalized REE patterns show significantly negative Ce anomalies. This suggests that cold seep carbonate is most likely formed in a relatively aerobic environment.

  9. Thermally induced phase transformation of pearl powder

    International Nuclear Information System (INIS)

    The polymorphic phase transformation of thermally treated pearl powder was investigated by X-ray diffraction and thermoanalytical techniques. The phase transformation was based on quantification of the calcite content at various temperatures using Rietveld refinement analysis. The results show that the phase transformation of pearl aragonite occurred within a temperature range of 360–410 °C, which is 50–100 °C lower than the range for non-biomineralized aragonite. These thermoanalytical results suggest that the phase transformation of pearl aragonite may occur immediately after the thermal decomposition of the organic matrix in the pearl powder. An important finding is that decomposition of the organic matrix may greatly facilitate such transformation by releasing additional space for an easier structural reconstruction during the phase transformation process. - Highlights: ► Providing a new method to describe the polymorphic transition of pearl powder ► The phase transition sketch was exhibited by XRD phase quantitative analysis. ► There are dozens of degrees in advance comparing to natural aragonite. ► The phase transition occurs following the thermal decomposition of organism

  10. ESEM-BSE coupled with rapid nano-scratching for micro-physicochemical analysis of marine exposed concrete

    NARCIS (Netherlands)

    Palin, D.; Thijssen, A.; Wiktor, V.; Jonkers, H.M.; Schlangen, H.E.J.G.

    2015-01-01

    Ordinary Portland cement (OPC) mortar specimens submerged in sea-water were analysed through environmental scanning electron microscopy (ESEM) in back scattered electron (BSE) mode and nano-scratching. Results from both sets of analysis show the presence of distinct phases associated with aragonite,

  11. Planetary Boundaries: Exploring the Safe Operating Space for Humanity

    DEFF Research Database (Denmark)

    Richardson, Katherine; Rockström, Johan; Steffen, Will;

    2009-01-01

    understanding, we propose quantifications for seven of them. These seven are climate change (CO2 concentration in the atmosphere ocean acidification (mean surface seawater saturation state with respect to aragonite = 80% of pre......-industrial levels); stratospheric ozone (oceans not to exceed 10 times the natural...

  12. Electron Spin Resonance Studies of Mn2+ in Freshwater Snail Shells: Pomacea Canaliculata Lamarck and Fossilized Snail Shell

    Institute of Scientific and Technical Information of China (English)

    N. Udomkan; S. Meejoo; P. Limsuwan; P. Winotai; Y. Chaimanee

    2005-01-01

    @@ We study paramagnetic Mn2+ ions present in the nowadays shells of univalve freshwater snails of Pomacea canaliculata lamarck (PCL) and the fossilized freshwater snail (FFS), Viviparus. All these shells are abundant in Thailand. The PCL shells were ground into fine powder. A set of seven samples were then separately annealed for 2 h in air atmosphere at different annealing temperatures while the FFS powder was characterized as-received.The PCL shells mainly consist of aragonite and a fraction of calcite. The heat treatments of the PCL powder samples at temperature higher than 450 ℃ resulted in an irreversible phase transformation from aragonite to calcite. However, it is found that the FFS shell is mainly made of calcite, with a minor fraction of aragonite. The crystal structure of the high-temperature-annealed PCL samples are quite similar to that of FFS, which indicates that the metamorphosis (aragonite → calcite) in the FFS shell had occurred but was not yet completed, although it had remained under the pressure and temperature of the Earth's crusts over millions of years. Our detailed ESR spectral analyses of PCL and FFS show that Mn2+ ions enter the Ca2+ sites during a biomineralization process. Simulated ESR parameters of PCL-500 of Mn2+ at a uniaxial site of calcite are reported. It is surprising to find that the ratio of Mn2+ concentration present in FFS to those in PCL shells evaluated from ESR spectra is as much as 10:1.

  13. Isotopic fractionation between seawater and the shell of

    NARCIS (Netherlands)

    Santos, S.; Cardoso, J.F.M.F.; Borges, V.; Luttikhuizen, P.C.; van der Veer, H.W.

    2012-01-01

    This study analyzed the isotopic profiles of four aragonitic shells of Scrobicularia plana in conjunction with measured seawater temperatures and salinities. Comparison of delta O-18(SHELL) with expected values revealed fractionation of delta O-18 in near equilibrium with the ambient environment. Gr

  14. Initial formation stage and succedent biomineralization of pearls

    Energy Technology Data Exchange (ETDEWEB)

    Fu, Fen [State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Tian, Liangguang [Shandong Institute of Supervision and Inspection on Product Quality, Jinan 250100 (China); Xu, Xiangang [State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China); Hu, Xiaobo, E-mail: xbhu@sdu.edu.cn [State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100 (China)

    2014-04-01

    The initial formation stage and succedent biomineralization of pearls were studied using scanning electron microscopy, Raman spectroscopy, transmission electron microscopy and atomic force microscopy. A new initial formation phase with needle-like structure which is found to be nanocrystallites of aragonite was discovered. As a result, two possible formation modes are proposed to describe the initial formation stage of pearls. As for the succedent mineralization of “brick and mortar” structure, nanostripes were first discovered inside the “brick” (aragonite platelet), compared with the foregoing finding of nanograins. The various nanostructures of aragonite platelet allow us to reconsider the role of the inter- and intracrystalline organic material surrounding CaCO{sub 3}, and a possible biomineralization mechanism was proposed. - Highlights: • A new initial formation mineral phase was discovered in pearl. • Nanograins and nanostripes inside aragonite platelets were found in pearl. • Two possible initial formation stages were proposed for pearl. • A possible biomineralization mechanism of nacre in pearl was proposed.

  15. Mineralogical analyses in Peştera Polovragi (Olteţului Gorges and Peştera Muierii (Galbenului Gorges, Gorj County

    Directory of Open Access Journals (Sweden)

    Ştefan Marincea

    2008-01-01

    Full Text Available Following a series of cave mineralogy researches in Peştera Polovragi and Peştera Muierii, Gorj county, we evidence an association made up of hydroxylapatite, taranakite, calcite and secondarily of quartz and illite and respectively, of hydroxylapatite, brushite, calcite and aragonite, and secondarily of α-quartz and illite.

  16. Polymorphism of CaCO{sub 3} and microstructure of the shell of a Brazilian invasive Mollusc (Limnoperna fortunei)

    Energy Technology Data Exchange (ETDEWEB)

    Nakamura Filho, Arnaldo; Almeida, Arthur Correa de; Riera, Hernan Espinoza; Cardoso, Antonio Valadao, E-mail: nakamuraaf@gmail.com [Rede Tematica em Engenharia de Materiais (REDEMAT), Ouro Preto, MG (Brazil); Araujo, Joao Locke Ferreira de [Centro de Bioengenharia de Especies Invasoras de Hidreletricas(CBEIH), Belo Horizonte, MG (Brazil); Gouveia, Vitor Jose Pinto [Fundacao Centro Tecnologico de Minas Gerais (CETEC), Belo Horizonte, MG (Brazil); Carvalho, Marcela David de [Companhia Energetica de Minas Gerais (CEMIG), Belo Horizonte, MG (Brazil)

    2014-08-15

    Applying the theories of Materials Science and Engineering to describe the composition and hierarchy of microstructures that comprise biological systems could help the search for new materials and results in a deeper insight into evolutionary processes. The layered microstructure that makes up the freshwater bivalve Limnoperna fortunei shell, an invasive specie in Brazil, was investigated utilizing SEM and AFM for the determination of the morphology and organization of the layers; and XRD was used to determine the crystalline phases of the calcium carbonate (CaCO{sub 3}) present in the shell. The presence of the polymorphs calcite and aragonite were confirmed and the calcite is present only on the external side of the shell. The shell of L. fortunei is composed of two layers of aragonite with distinct microstructures (the aragonite prismatic layer and the aragonite sheet nacreous layer) and the periostracum (a protein layer that covers and protects the ceramic part of the shell). A new morphology of the calcite layer was found, below the periostracum, without defined form, albeit crystal (author)

  17. Physical and chemical constraints limit the habitat window for an endangered mussel

    Science.gov (United States)

    Campbell, Cara; Prestegaard, Karen L.

    2016-01-01

    Development of effective conservation and restoration strategies for freshwater pearly mussels requires identification of environmental constraints on the distributions of individual mussel species. We examined whether the spatial distribution of the endangered Alasmidonta heterodon in Flat Brook, a tributary of the upper Delaware River, was constrained by water chemistry (i.e., calcium availability), bed mobility, or both. Alasmidonta heterodon populations were bracketed between upstream reaches that were under-saturated with respect to aragonite and downstream reaches that were saturated for aragonite during summer baseflow but had steep channels with high bed mobility. Variability in bed mobility and water chemistry along the length of Flat Brook create a “habitat window” for A. heterodon defined by bed stability (mobility index ≤1) and aragonite saturation (saturation index ≥1). We suggest the species may exist in a narrow biogeochemical window that is seasonally near saturation. Alasmidonta heterodon populations may be susceptible to climate change or anthropogenic disturbances that increase discharge, decrease groundwater inflow or chemistry, and thus affect either bed mobility or aragonite saturation. Identifying the biogeochemical microhabitats and requirements of individual mussel species and incorporating this knowledge into management decisions should enhance the conservation and restoration of endangered mussel species.

  18. A Simplified Model to Predict the Effect of Increasing Atmospheric CO[subscript 2] on Carbonate Chemistry in the Ocean

    Science.gov (United States)

    Bozlee, Brian J.; Janebo, Maria; Jahn, Ginger

    2008-01-01

    The chemistry of dissolved inorganic carbon in seawater is reviewed and used to predict the potential effect of rising levels of carbon dioxide in the atmosphere. In agreement with more detailed treatments, we find that calcium carbonate (aragonite) may become unsaturated in cold surface seawater by the year 2100 C.E., resulting in the destruction…

  19. Unhatched and Hatched Eggshells of the Chinese CobraNaja atra

    Institute of Scientific and Technical Information of China (English)

    Zheng WANG; Longhui LIN; Xiang JI

    2014-01-01

    Changes in structure and composition of the eggshell resulting from embryonic mobilization of minerals from the eggshell are found in all oviparous reptiles studied thus far. In this study, we measured samples of unhatched and hatched eggshells of the Chinese cobraNaja atrato determine the percentage of ash and the phase composition of calcium carbonate. The mean percentage of ash was signiifcantly higher in unhatched eggshells (24.6%) than in hatched eggshells (22.3%). The dominant phase in unhatched eggshells was the calcite form of calcium carbonate. In addition to the peaks of calcite, a few small peaks were found to be caused by the aragonite and vaterite phases of calcium carbonate, implying that there are small amounts of aragonite and vaterite in the eggshell. The concentration of the various phases calculated from the intensity of the X-ray diffraction spectra allowed the estimation that percentages of calcite, aragonite and vaterite were about 92%, 4% and 4%, respectively. Hatched eggshells produced similar spectral characteristics as unhatched eggshells, with one exception. The dominant phase composition in the hatched eggshell was also calcite, but the amount of the aragonite phase had a marked increase. Our study adds evidence that embryonic mobilization of minerals from the eggshell may result in changes in structure of the eggshell.

  20. Characterization of calcareous deposits in artificial seawater by impedance techniques 3--Deposit of CaCO{sub 3} in the presence of Mg(II)

    Energy Technology Data Exchange (ETDEWEB)

    Barchiche, Ch.; Deslouis, C.; Festy, D.; Gil, O.; Refait, Ph.; Touzain, S.; Tribollet, B

    2003-05-30

    Calcareous deposits were formed on steel under cathodic protection conditions in artificial seawater at various potentials from -0.9 to -1.4 V/SCE. The deposition kinetics was analysed by chronoamperometry measurements and the calcareous layers were characterized by electrochemical and electrohydrodynamical impedance spectroscopies, scanning electron microscopy observations and X-ray diffraction analyses. At 20 deg. C, the deposits were composed of aragonite CaCO{sub 3} when formed at potentials E comprised between -0.9 and -1.1 V/SCE, of brucite Mg(OH){sub 2} and aragonite when formed at -1.2 V/SCE, and only of brucite when formed at potentials E{<=}-1.3 V/SCE. However, the in situ impedance techniques demonstrated the presence of a Mg(II)-containing porous layer along with the aragonite deposit at E{>=}-1.1 V/SCE. In seawater enriched with Mg{sup 2+}, the deposition of aragonite was almost totally inhibited, and the behavior of the film containing Mg(II) could be described.

  1. Characterization of calcareous deposits in artificial seawater by impedance techniques 3--Deposit of CaCO3 in the presence of Mg(II)

    International Nuclear Information System (INIS)

    Calcareous deposits were formed on steel under cathodic protection conditions in artificial seawater at various potentials from -0.9 to -1.4 V/SCE. The deposition kinetics was analysed by chronoamperometry measurements and the calcareous layers were characterized by electrochemical and electrohydrodynamical impedance spectroscopies, scanning electron microscopy observations and X-ray diffraction analyses. At 20 deg. C, the deposits were composed of aragonite CaCO3 when formed at potentials E comprised between -0.9 and -1.1 V/SCE, of brucite Mg(OH)2 and aragonite when formed at -1.2 V/SCE, and only of brucite when formed at potentials E≤-1.3 V/SCE. However, the in situ impedance techniques demonstrated the presence of a Mg(II)-containing porous layer along with the aragonite deposit at E≥-1.1 V/SCE. In seawater enriched with Mg2+, the deposition of aragonite was almost totally inhibited, and the behavior of the film containing Mg(II) could be described

  2. Complementary microstructural and chemical analyses of Sepia officinalis endoskeleton

    Energy Technology Data Exchange (ETDEWEB)

    Florek, Marek, E-mail: mflorek@kul.lublin.pl [Department of Chemistry, John Paul II Catholic University of Lublin, al. Krasnicka 102, 20-718 Lublin (Poland); Fornal, Emilia [Department of Chemistry, John Paul II Catholic University of Lublin, al. Krasnicka 102, 20-718 Lublin (Poland); Gomez-Romero, Pedro [Institut de Ciencia de Materials de Barcelona (CSIC), Campus UAB, E-08193 Bellaterra, Barcelona (Spain); Zieba, Emil [Department of Chemistry, John Paul II Catholic University of Lublin, al. Krasnicka 102, 20-718 Lublin (Poland); Paszkowicz, Wojciech [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland); Lekki, Janusz [Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, ul. Radzikowskiego 152, 31-342 Krakow (Poland); Nowak, Jakub; Kuczumow, Andrzej [Department of Chemistry, John Paul II Catholic University of Lublin, al. Krasnicka 102, 20-718 Lublin (Poland)

    2009-05-05

    Cuttlebone exhibiting high compressive strength is a very interesting material from the biomimetic materials' technology point of view. Its microstructure and chemical composition were characterized by complementary analytical techniques. Structural features of the skeleton were revealed by SEM, micro-Raman, FT-IR and XRD measurements. XRD analyses showed that the only mineral phase present in the samples is aragonite. 2D-maps obtained from micro-Raman analyses for peaks attributed to aragonite (1100 cm{sup -1}) and chitin (1660 cm{sup -1}) revealed that the septa are richer in chitin and pillars in aragonite. 2D-distributions of elements detected by a electron microprobe showed that Ca-rich locations are poor in Mg, Na, and Br. Ca is mainly present at those locations where aragonite prevails. Bromine, sodium and magnesium are most likely located in the organic matrix. The average content of the elements, as determined by ICP-OES, was: Na - 1.0%, Mg - 0.133%, K - 0.26%, Fe - 0.03% and Sr - 0.28%. Using the elemental CHN analysis the following amounts of nitrogen, carbon and hydrogen were detected: 1.42%, 15.36% and 0.68%, respectively. The elemental analysis together with TGA measurements allowed evaluating the approximate concentration of organic matter in the cuttlebone at the level of 10%.

  3. Macroalgae contribute to nested mosaics of pH variability in a subarctic fjord

    NARCIS (Netherlands)

    Krause-Jensen, D.; Duarte, C.M.; Hendriks, I.E.; Meire, L.; Blicher, M.E.; Marba, N.; Sejr, M.K.

    2015-01-01

    The Arctic Ocean is considered the most vulnerable ecosystem to ocean acidification, and large-scale assessments of pH and the saturation state for aragonite (Oarag) have led to the notion that the Arctic Ocean is already close to a corrosive state. In high-latitude coastal waters the reg

  4. Study of the crystallographic architecture of corals at the nanoscale by scanning transmission X-ray microscopy and transmission electron microscopy.

    Science.gov (United States)

    Benzerara, Karim; Menguy, Nicolas; Obst, Martin; Stolarski, Jarosław; Mazur, Maciej; Tylisczak, Tolek; Brown, Gordon E; Meibom, Anders

    2011-07-01

    We have investigated the nanotexture and crystallographic orientation of aragonite in a coral skeleton using synchrotron-based scanning transmission X-ray microscopy (STXM) and transmission electron microscopy (TEM). Polarization-dependent STXM imaging at 40-nm spatial resolution was used to obtain an orientation map of the c-axis of aragonite on a focused ion beam milled ultrathin section of a Porites coral. This imaging showed that one of the basic units of coral skeletons, referred to as the center of calcification (COC), consists of a cluster of 100-nm aragonite globules crystallographically aligned over several micrometers with a fan-like distribution and with the properties of single crystals at the mesoscale. The remainder of the skeleton consists of aragonite single-crystal fibers in crystallographic continuity with the nanoglobules comprising the COC. Our observation provides information on the nm-scale processes that led to biomineral formation in this sample. Importantly, the present study illustrates how the methodology described here, which combines HRTEM and polarization-dependent synchrotron-based STXM imaging, offers an interesting new approach for investigating biomineralizing systems at the nm-scale.

  5. Endolith microborings and their preservation in Holocene-Pleistocene (Bahama-Florida) ooids

    Science.gov (United States)

    Harris, Paul M.; Halley, Robert B.; Lukas, Karen J.

    1979-01-01

    Holocene ooids from Joulters Ooid Shoal (Bahamas) are bored in various ways by blue-green algae that groove along the grain surface, reside just beneath the grain surface, and tunnel extensively a few tens of microns within the grain. The microborings, morphologically distinctive, are documented with scanning electron micrographs of open borings and resin casts. Gentle dissolution of ooid aragonite permits identification of several algal genera by light microscopy and enables comparison with the microboring casts. Pleistocene ooids from the Miami Limestone (Florida) contain natural casts of microborings, some of which are similar in form to Holocene examples. Significantly, these aragonite casts are more resistant to solution than surrounding ooid aragonite. They remain after most of the ooid is leached away and survive replacement of the ooid by low-Mg calcite. Dissolution or precipitation may occur along the walls of microborings, causing morphological alteration during their preservation. This points out a difficulty in the specific identification of endoliths on the basis of fossilized microborings in ancient rocks composed of original aragonite grains.

  6. Depositional facies and aqueous-solid geochemistry of travertine-depositing hot springs (Angel Terrace, Mammoth Hot Springs, Yellowstone National Park, U.S.A.)

    Science.gov (United States)

    Fouke, B. W.; Farmer, J. D.; Des Marais, D. J.; Pratt, L.; Sturchio, N. C.; Burns, P. C.; Discipulo, M. K.

    2000-01-01

    Petrographic and geochemical analyses of travertine-depositing hot springs at Angel Terrace, Mammoth Hot Springs, Yellowstone National Park, have been used to define five depositional facies along the spring drainage system. Spring waters are expelled in the vent facies at 71 to 73 degrees C and precipitate mounded travertine composed of aragonite needle botryoids. The apron and channel facies (43-72 degrees C) is floored by hollow tubes composed of aragonite needle botryoids that encrust sulfide-oxidizing Aquificales bacteria. The travertine of the pond facies (30-62 degrees C) varies in composition from aragonite needle shrubs formed at higher temperatures to ridged networks of calcite and aragonite at lower temperatures. Calcite "ice sheets", calcified bubbles, and aggregates of aragonite needles ("fuzzy dumbbells") precipitate at the air-water interface and settle to pond floors. The proximal-slope facies (28-54 degrees C), which forms the margins of terracette pools, is composed of arcuate aragonite needle shrubs that create small microterracettes on the steep slope face. Finally, the distal-slope facies (28-30 degrees C) is composed of calcite spherules and calcite "feather" crystals. Despite the presence of abundant microbial mat communities and their observed role in providing substrates for mineralization, the compositions of spring-water and travertine predominantly reflect abiotic physical and chemical processes. Vigorous CO2 degassing causes a +2 unit increase in spring water pH, as well as Rayleigh-type covariations between the concentration of dissolved inorganic carbon and corresponding delta 13C. Travertine delta 13C and delta 18O are nearly equivalent to aragonite and calcite equilibrium values calculated from spring water in the higher-temperature (approximately 50-73 degrees C) depositional facies. Conversely, travertine precipitating in the lower-temperature (travertine crystals. Despite the production of H2S and the abundance of sulfide

  7. Shell condition and survival of Puget Sound pteropods are impaired by ocean acidification conditions.

    Directory of Open Access Journals (Sweden)

    D Shallin Busch

    Full Text Available We tested whether the thecosome pteropod Limacina helicina from Puget Sound, an urbanized estuary in the northwest continental US, experiences shell dissolution and altered mortality rates when exposed to the high CO2, low aragonite saturation state (Ωa conditions that occur in Puget Sound and the northeast Pacific Ocean. Five, week-long experiments were conducted in which we incubated pteropods collected from Puget Sound in four carbon chemistry conditions: current summer surface (∼460-500 µatm CO2, Ωa≈1.59, current deep water or surface conditions during upwelling (∼760 and ∼1600-1700 µatm CO2, Ωa≈1.17 and 0.56, and future deep water or surface conditions during upwelling (∼2800-3400 µatm CO2, Ωa≈0.28. We measured shell condition using a scoring regime of five shell characteristics that capture different aspects of shell dissolution. We characterized carbon chemistry conditions in statistical analyses with Ωa, and conducted analyses considering Ωa both as a continuous dataset and as discrete treatments. Shell dissolution increased linearly as aragonite saturation state decreased. Discrete treatment comparisons indicate that shell dissolution was greater in undersaturated treatments compared to oversaturated treatments. Survival increased linearly with aragonite saturation state, though discrete treatment comparisons indicated that survival was similar in all but the lowest saturation state treatment. These results indicate that, under starvation conditions, pteropod survival may not be greatly affected by current and expected near-future aragonite saturation state in the NE Pacific, but shell dissolution may. Given that subsurface waters in Puget Sound's main basin are undersaturated with respect to aragonite in the winter and can be undersaturated in the summer, the condition and persistence of the species in this estuary warrants further study.

  8. Using palynology to re-assess the Dead Sea laminated sediments - Indeed varves?

    Science.gov (United States)

    López-Merino, Lourdes; Leroy, Suzanne A. G.; Eshel, Amram; Epshtein, Valentina; Belmaker, Reuven; Bookman, Revital

    2016-05-01

    Lacustrine laminated sediments are often varves representing annual rhythmic deposition. The Dead Sea high-stand laminated sections consist of mm-scale alternating detrital and authigenic aragonite laminae. Previous studies assumed these laminae were varves deposited seasonally. However, this assumption has never been robustly validated. Here we report an examination of the seasonal deposition of detrital-aragonite couplets from two well-known Late Holocene laminated sections at the Ze'elim fan-delta using palynology and grain-size distribution analyses. These analyses are complemented by the study of contemporary flash-flood samples and multivariate statistical analysis. Because transport affects the pollen preservation state, well-preserved (mostly) air-borne transported pollen was analysed separately from badly-preserved pollen and fungal spores, which are more indicative of water transport and reworking from soils. Our results indicate that (i) both detrital and aragonite laminae were deposited during the rainy season; (ii) aragonite laminae have significantly lower reworked and fungal spore concentrations than detrital and flash-flood samples; and (iii) detrital laminae are composed of recycling of local and distal sources, with coarser particles that were initially deposited in the Dead Sea watershed and later transported via run-off to the lake. This is in line with previous carbon balance studies that showed that aragonite precipitation occurs after the massive input of TCO2 associated with run-off episodes. Consequently, at least for the Holocene Ze'elim Formation, laminated sediments cannot be considered as varves. Older Quaternary laminated sequences should be re-evaluated.

  9. Ocean acidification reduces the crystallographic control in juvenile mussel shells.

    Science.gov (United States)

    Fitzer, Susan C; Cusack, Maggie; Phoenix, Vernon R; Kamenos, Nicholas A

    2014-10-01

    Global climate change threatens the oceans as anthropogenic carbon dioxide causes ocean acidification and reduced carbonate saturation. Future projections indicate under saturation of aragonite, and potentially calcite, in the oceans by 2100. Calcifying organisms are those most at risk from such ocean acidification, as carbonate is vital in the biomineralisation of their calcium carbonate protective shells. This study highlights the importance of multi-generational studies to investigate how marine organisms can potentially adapt to future projected global climate change. Mytilus edulis is an economically important marine calcifier vulnerable to decreasing carbonate saturation as their shells comprise two calcium carbonate polymorphs: aragonite and calcite. M. edulis specimens were cultured under current and projected pCO2 (380, 550, 750 and 1000μatm), following 6months of experimental culture, adults produced second generation juvenile mussels. Juvenile mussel shells were examined for structural and crystallographic orientation of aragonite and calcite. At 1000μatm pCO2, juvenile mussels spawned and grown under this high pCO2 do not produce aragonite which is more vulnerable to carbonate under-saturation than calcite. Calcite and aragonite were produced at 380, 550 and 750μatm pCO2. Electron back scatter diffraction analyses reveal less constraint in crystallographic orientation with increased pCO2. Shell formation is maintained, although the nacre crystals appear corroded and crystals are not so closely layered together. The differences in ultrastructure and crystallography in shells formed by juveniles spawned from adults in high pCO2 conditions may prove instrumental in their ability to survive ocean acidification.

  10. Effect of Additives and pH on the Formation of Carbonate Mineral by CO2 Sequestration of Cement Paste

    Science.gov (United States)

    Lee, J. H.; Hwang, J.; Lee, H.; Son, B. S.; Oh, J.

    2015-12-01

    CO2 in the atmosphere causes a global warming that is a big issue nowadays. Many studies of CO2 capture and storage (CCS) technologies have been studied all over the world. Waste cement is a good source for aqueous carbonation because it is rich in calcium. Therefore, this study was performed to develop the aqueous carbonation method for waste cement powder. Cement paste was made with water/cement ratio of 6:4 and cured for 28 days in water bath. The cement paste was pulverized into a fine powder sizing less than 0.15 mm. To study effect of additives and pH on the formation of carbonate minerals, aqueous carbonation experiments were conducted. The mineral compositions and morphology of carbonate mineral were identified by XRD and SEM/EDS analysis. 1.0 M NaCl and 0.25 M MgCl2 were applied as additives. Aqueous carbonation experiment was conducted with injecting pure CO2 gas (99.9%) to a reactor containing 200 ㎖ of reacting solution. The pH of reacting solution was controled to determine formational condition of carbonate minerals. In 0.25 M MgCl2 solution, calcite was dominant mineral at high pH. More aragonite, however, formed as decreasing pH of solution with injection of CO2. The presence of Mg2+ in solution makes aragonite more dominant than calcite. Aragonite was mainly formed at the high pH of solution with 1.0 M NaCl additive, whereas calcite was more preponderant mineral than aragonite as falling pH. It show that unstable aragonite transformed to calcite as decreasing pH. In no additive solution, vaterite was dominantly formed at the initial stage of experiement, but unstable vaterite transformed to well crystallized calcite with further carbonation.

  11. CO(2-driven ocean acidification alters and weakens integrity of the calcareous tubes produced by the serpulid tubeworm, Hydroides elegans.

    Directory of Open Access Journals (Sweden)

    Vera Bin San Chan

    Full Text Available As a consequence of anthropogenic CO(2-driven ocean acidification (OA, coastal waters are becoming increasingly challenging for calcifiers due to reductions in saturation states of calcium carbonate (CaCO(3 minerals. The response of calcification rate is one of the most frequently investigated symptoms of OA. However, OA may also result in poor quality calcareous products through impaired calcification processes despite there being no observed change in calcification rate. The mineralogy and ultrastructure of the calcareous products under OA conditions may be altered, resulting in changes to the mechanical properties of calcified structures. Here, the warm water biofouling tubeworm, Hydroides elegans, was reared from larva to early juvenile stage at the aragonite saturation state (Ω(A for the current pCO(2 level (ambient and those predicted for the years 2050, 2100 and 2300. Composition, ultrastructure and mechanical strength of the calcareous tubes produced by those early juvenile tubeworms were examined using X-ray diffraction (XRD, Fourier transform infrared spectroscopy (FT-IR, scanning electron microscopy (SEM and nanoindentation. Juvenile tubes were composed primarily of the highly soluble CaCO(3 mineral form, aragonite. Tubes produced in seawater with aragonite saturation states near or below one had significantly higher proportions of the crystalline precursor, amorphous calcium carbonate (ACC and the calcite/aragonite ratio dramatically increased. These alterations in tube mineralogy resulted in a holistic deterioration of the tube hardness and elasticity. Thus, in conditions where Ω(A is near or below one, the aragonite-producing juvenile tubeworms may no longer be able to maintain the integrity of their calcification products, and may result in reduced survivorship due to the weakened tube protection.

  12. Identification of genes directly involved in shell formation and their functions in pearl oyster, Pinctada fucata.

    Directory of Open Access Journals (Sweden)

    Dong Fang

    Full Text Available Mollusk shell formation is a fascinating aspect of biomineralization research. Shell matrix proteins play crucial roles in the control of calcium carbonate crystallization during shell formation in the pearl oyster, Pinctada fucata. Characterization of biomineralization-related genes during larval development could enhance our understanding of shell formation. Genes involved in shell biomineralization were isolated by constructing three suppression subtractive hybridization (SSH libraries that represented genes expressed at key points during larval shell formation. A total of 2,923 ESTs from these libraries were sequenced and gave 990 unigenes. Unigenes coding for secreted proteins and proteins with tandem-arranged repeat units were screened in the three SSH libraries. A set of sequences coding for genes involved in shell formation was obtained. RT-PCR and in situ hybridization assays were carried out on five genes to investigate their spatial expression in several tissues, especially the mantle tissue. They all showed a different expression pattern from known biomineralization-related genes. Inhibition of the five genes by RNA interference resulted in different defects of the nacreous layer, indicating that they all were involved in aragonite crystallization. Intriguingly, one gene (UD_Cluster94.seq.Singlet1 was restricted to the 'aragonitic line'. The current data has yielded for the first time, to our knowledge, a suite of biomineralization-related genes active during the developmental stages of P. fucata, five of which were responsible for nacreous layer formation. This provides a useful starting point for isolating new genes involved in shell formation. The effects of genes on the formation of the 'aragonitic line', and other areas of the nacreous layer, suggests a different control mechanism for aragonite crystallization initiation from that of mature aragonite growth.

  13. Coupling Physics, Biology and Terrestrial Runoff to Ocean Acidification and Carbonate Mineral Suppression in the Pacific-Arctic Region (Invited)

    Science.gov (United States)

    Mathis, J. T.; Cross, J. N.; Shake, K. L.

    2010-12-01

    Rising CO2 levels in the atmosphere and ocean have lead to an anthropogenically induced acidification phenomenon in high latitude seas. These areas are projected to become persistently undersaturated with respect to important carbonate minerals as early as mid-century and seasonal aragonite undersaturations have already been observed in surface and shallow subsurface waters over of the continental shelf seas surrounding Alaska. Some calcifying marine organisms, including pteropods, foraminifers, mollusks, and coralline algae that could be susceptible to reduced calcification rates under increasing ocean acidity are keystone species in the Pacific-Arctic region. Recent observations along the only long term time-series in the northern Gulf of Alaska found that the high seasonal and spatial variability of the carbonate parameters are largely controlled by physical circulation and glacial discharge. In general, surface DIC and TA concentrations decreased between May and September due to primary production and dilution from the region’s numerous glacial sources. Conversely, concentrations of DIC and TA increased in the bottom waters of the inner shelf between May and September likely due to a combination of remineralization of exported organic matter and seasonally induced upwelling. Analysis of the calcite and aragonite saturation states (Ω) showed an increase in the surface layer from May to September. However, in the bottom waters over the inner shelf the Ω of calcite and aragonite was suppressed and aragonite undersaturations were observed within 50 m of the surface. In the Bering Sea, prior to sea ice retreat in 2008, calcite and aragonite Ω ranged from 1.3 to 3.2 and 0.8 to 2.0 respectively in the upper 30 m over the shelf. Two inshore stations likely impacted by the outflows of the Yukon and Kuskokwim Rivers showed aragonite undersaturation (0.91 - 0.84) from the surface to the bottom. In summer, DIC concentrations in the upper 30 m were drawn down by

  14. Calibration of the carbonate `clumped isotope' paleotemperature proxy using mollusc shells and benthic foraminiferal tests

    Science.gov (United States)

    Came, R. E.; Curry, W. B.; Weidman, C. R.; Eiler, J. M.

    2007-12-01

    It has recently been shown that the carbonate `clumped isotope' thermometer can provide temperature constraints that depend only on the isotopic composition of carbonate (in particular, on the proportion of 13C and 18O that form bonds with each other), and that do not require assumptions about the isotopic composition of the water in which the carbonate formed (Ghosh et al., 2006). Furthermore, this novel method permits the calculation of seawater δ18O based on the clumped isotope temperature estimates and the simultaneously obtained δ18O of carbonate, thereby enabling the extraction of global ice volume estimates for both the recent and distant geologic past. Here we present clumped isotope analyses of several naturally occurring marine carbonates that calcified at known temperatures in the modern ocean. First, we analyzed benthic foraminiferal tests from six high-quality multicore tops collected in the Florida Strait, spanning a temperature range of 9.3-20.2 degrees C. Second, we analyzed shallow-water mollusc shells from a variety of different climate regimes, spanning a temperature range of 2.5-26.0 degrees C. We find that the calcitic foraminiferal species Cibicidoides spp. agrees well with the inorganic calcite precipitation experiments of Ghosh et al. (2006), while the aragonitic species Hoeglundina elegans is significantly offset. Similarly, clumped isotope results obtained from aragonitic mollusc shells also reveal an offset from the Ghosh et al. (2006) trend, although the offset observed in mollusc aragonite is quite different in nature from that observed in foraminiferal aragonite. Assuming our estimates of the growth temperatures of these naturally occurring organisms are correct, these results suggest that there are vital effects associated with the stable isotope compositions of the aragonite-precipitating organisms examined in this study; further work will be required to determine their cause. Nevertheless, the internal coherence of trends for

  15. Evidences of microbial mediation in the formation of MDAC in the Gulf of Cadiz

    Science.gov (United States)

    Magalhaes, V. H.; Pinheiro, L. M.; Birguel, D.; Peckmann, J.; Niemann, H.; Santos, L.; Vasconcelos, C.; McKenzie, J.; Ivanov, M.

    2006-12-01

    The study of methane-derived authigenic carbonates (MDAC) in the Gulf of Cadiz allowed the identification and collection of different types of authigenic carbonates: (I) dolomite crusts, dolomite nodules, chimneys or filled burrows and (II) aragonitic slabs or pavements. Both correspond to the cementation of sediments by the precipitation of authigenic carbonates, and the different lithologic types correspond to different geochemical environment of formation. Authigenic carbonates yielded 13C values indicating methane as the major carbon source with ratios as low as -46.9(per mil PDB). Likewise, the crusts and chimneys can be interpreted as a record of extensive methane seepage in this particular area of the Gulf of Cadiz. SEM observations revealed large amounts of structures and textures that clearly indicate microbial activity. In the cement of the dolomite chimneys, which consists of minor aggregates of rhombohedric calcite, high-Mg calcite and dolomite, SEM observations allowed the identification of a large variety of microbial-induced fabrics, such as: (1) microbial filaments; (2) high Mg-calcite and dolomite crystal aggregates calcifying and mimetizing filaments and flattening themselves against dolomite and calcite minerals; (3) rods with brush-like terminations; (4) dumbbell-like and cauliflower structures. The identification of microbial and mucous biofilms is frequent in aragonite pavements, occurring as a coating, draped between the aragonite fibres and needles of the stromatolitic layers. Also, aragonite batons, ball-capped batons and nanograins are observed. Specific 13C-depleted biomarkers indicators of archaea involved in the anaerobic oxidation of methane (AOM) as PMI, squalane, crocetane/phytane have been identified in dolomite chimney samples. The aragonite crusts showed even better preserved biomarkers. PMI is accompanied by unsaturated derivatives with 1 to 3 double bonds. Several bacterial lipid biomarkers, also with 13C-depleted compositions

  16. Changing carbonate chemistry in ocean waters surrounding coral reefs in the CMIP5 ensemble

    Science.gov (United States)

    Ricke, K.; Schneider, K.; Cao, L.; Caldeira, K.

    2012-12-01

    Coral reefs comprise some of the most biodiverse ecosystems in the world. Today they are threatened by a number of stressors, including pollution, bleaching from global warming and ocean acidification. In this study, we focus on the implications of ocean acidification for the open ocean chemistry surrounding coral reefs. We use results from 13 Earth System Models included in the Coupled Model Intercomparison Project 5 (CMIP5) to examine the changing aragonite saturations (Ωa) of open ocean waters surrounding approximately 6,000 coral reefs. These 13 Earth System Models participating in CMIP5 each have interactive ocean biogeochemistry models that output state variables including DIC, alkalinity, SST, and salinity. Variation in these values were combined with values from the GLODAP database to calculate aragonite, the form of calcium carbonate that corals use to make their skeletons. We used reef locations from ReefBase that were within one degree (in latitude or longitude) of water masses represented both in the GLODAP database and in the climate models. Carbonate chemistry calculations were performed by Dr. James C. Orr (IPSL) as part of a separate study. We find that in preindustrial times, 99.9 % of coral reefs were located in regions of the ocean with aragonite saturations of 3.5 or more. The saturation threshold for viable reef ecosystems in uncertain, but the pre-industrial distribution of water chemistry surrounding coral reefs may nevertheless provide some indication of viability. We examine the fate of coral reefs in the context of several potential aragonite saturation thresholds, i.e., when Ωa_crit equals 3, 3.25, or 3.5. We show that under a business-as-usual scenario Representative Concentration Pathway (RCP) 8.5, the specific value of Ωa_crit does not affect the long-term fate of coral reefs -- by the end of the 21st century, no coral reef considered is surrounded by water with Ωa> 3. However, under scenarios with significant CO2 emissions

  17. Behaviour of calcium carbonate in sea water

    Science.gov (United States)

    Cloud, P.E.

    1962-01-01

    Anomalies in the behaviour of calcium carbonate in natural solutions diminish when considered in context. Best values found by traditional oceanographie methods for the apparent solubility product constant K'CaCO3 in sea water at atmospheric pressure are consistent mineralogically-at 36 parts per thousand salinity and T-25??C, K'aragonlte is estimated as 1.12 ?? 10-6 and K'calcite as 0.61 ?? 10-6. At 30??C the corresponding values are 0.98 ?? 10-6 for aragonite and 0.53 ?? 10-6 for calcite. Because the K' computations do not compensate for ionic activity, however, they cannot give thermodynamically satisfactory results. It is of interest, therefore, that approximate methods and information now available permit the estimation from the same basic data of an activity product constant KCaCO3 close to that found in solutions to which Debye-Hu??ckel theory applies. Such methods indicate approximate Karagonite 7.8 ?? 10-9 for surface sea water at 29??C; Kcalcite would be proportionately lower. Field data and experimental results indicate that the mineralogy of precipitated CaCO3 depends primarily on degree of supersaturation, thus also on kinetic or biologic factors that facilitate or inhibit a high degree of supersaturation. The shallow, generally hypersaline bank waters west of Andros Island yield aragonitic sediments with O18 O16 ratios that imply precipitation mainly during the warmer months, when the combination of a high rate of evaporation, increasing salinity (and ionic strength), maximal temperatures and photosynthetic removal of CO2 result in high apparent supersaturation. The usual precipitate from solutions of low ionic strength is calcite, except where the aragonite level of supersaturation is reached as a result of diffusion phenomena (e.g. dripstones), gradual and marked evaporation, or biologic intervention. Published data also suggest the possibility of distinct chemical milieus for crystallographic variations in skeletal calcium carbonate. It appears

  18. Feedbacks and responses of coral calcification on the Bermuda reef system to seasonal changes in biological processes and ocean acidification

    Directory of Open Access Journals (Sweden)

    N. R. Bates

    2010-08-01

    Full Text Available Despite the potential impact of ocean acidification on ecosystems such as coral reefs, surprisingly, there is very limited field data on the relationships between calcification and seawater carbonate chemistry. In this study, contemporaneous in situ datasets of seawater carbonate chemistry and calcification rates from the high-latitude coral reef of Bermuda over annual timescales provide a framework for investigating the present and future potential impact of rising carbon dioxide (CO2 levels and ocean acidification on coral reef ecosystems in their natural environment. A strong correlation was found between the in situ rates of calcification for the major framework building coral species Diploria labyrinthiformis and the seasonal variability of [CO32-] and aragonite saturation state Ωaragonite, rather than other environmental factors such as light and temperature. These field observations provide sufficient data to hypothesize that there is a seasonal "Carbonate Chemistry Coral Reef Ecosystem Feedback" (CREF hypothesis between the primary components of the reef ecosystem (i.e., scleractinian hard corals and macroalgae and seawater carbonate chemistry. In early summer, strong net autotrophy from benthic components of the reef system enhance [CO32-] and Ωaragonite conditions, and rates of coral calcification due to the photosynthetic uptake of CO2. In late summer, rates of coral calcification are suppressed by release of CO2 from reef metabolism during a period of strong net heterotrophy. It is likely that this seasonal CREF mechanism is present in other tropical reefs although attenuated compared to high-latitude reefs such as Bermuda. Due to lower annual mean surface seawater [CO32-] and Ωaragonite in Bermuda compared to tropical regions, we anticipate that Bermuda corals will experience seasonal periods

  19. Interaction of ions in water system containing copper-zinc alloy for boiler energy saving

    Institute of Scientific and Technical Information of China (English)

    MING Xing; LIANG Jinsheng; OU Xiuqin; TANG Qingguo; DING Yan

    2006-01-01

    Copper-zinc alloy element for boiler energy saving was put in the intake of simulated boiler system to investigate the interaction and transfer of ions in water system both theoretically and experimentally. The fouling was analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray detector (EDX). The results show that the transfer of calcium and magnesium ions in heat-transfer-surface-water system is affected by zinc ions dissolved from the alloy because of primary battery reaction. Some calcium ions of calcium carbonate crystal are replaced by zinc ions, the growth of aragonite crystal nucleus is retarded, and the transition of calcium carbonate from aragonite to calcite is hampered.

  20. Polymorph selection and nanocrystallite rearrangement of calcium carbonate in carboxymethyl chitosan aqueous solution: Thermodynamic and kinetic analysis

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Donghui [Key Lab For Special Functional Materials Ministry of Education, Henan University, Kaifeng 475004 (China); Key Lab of Inorganic Coating Materials, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi, Changning, Shanghai 200050 (China); Zhu, Yingchun, E-mail: yzhu@mail.sic.ac.cn [Key Lab of Inorganic Coating Materials, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi, Changning, Shanghai 200050 (China); Li, Fang; Ruan, Qichao [Key Lab of Inorganic Coating Materials, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi, Changning, Shanghai 200050 (China); Zhang, Shengmao [Key Lab For Special Functional Materials Ministry of Education, Henan University, Kaifeng 475004 (China); Zhang, Linlin; Xu, Fangfang [Key Lab of Inorganic Coating Materials, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi, Changning, Shanghai 200050 (China)

    2010-01-15

    In this article, the polymorph selection of calcium carbonate has been successfully achieved in water-soluble carboxymethyl chitosan aqueous solution at different temperatures (25-95 {sup o}C). Vaterite is formed in carboxymethyl chitosan solution 25 {sup o}C accompanied with trace of calcite, whereas pure aragonite is obtained at 95 {sup o}C. Scanning electron microscopy and transmission electron microscopy analyses show that the products are formed from the recrystallization of nanometer crystallites. Thermodynamic and kinetic analyses reveal that the polymorph of calcium carbonate is controlled and selected by kinetics in various temperatures. As a heterogeneous nucleator and stabilizing agent, carboxymethyl chitosan changes the nucleation and growth of calcium carbonate from thermodynamic into kinetic control. Under kinetic limitation, the reaction rate of aragonite increases along with the elevating of temperature and surpasses the rate of vaterite above 327 K.

  1. Fluctuations of sulfate, S-bearing amino acids and magnesium in a giant clam shell

    Directory of Open Access Journals (Sweden)

    T. Yoshimura

    2014-01-01

    Full Text Available We used micro-X-ray fluorescence combined with X-ray photoabsorption spectroscopy to investigate speciation-specific sulfur profiles in the inner shell layer of a giant clam (Hippopus hippopus. The sulfate, S-bearing amino acids, and total sulfur profiles indicated that inorganic sulfate was the dominant component in the shell of this bivalve. Sulfur profiles in the inner shell layer showed clear annual fluctuations that varied by more than one order of magnitude, from K-edge XANES and comparison of Mg and S-bearing amino acids profiles indicated that a pronounced effect of the organic fraction or disordered phases were observed in aragonitic shell of H. hippopus rather than regulated substitution into the aragonite crystal lattice.

  2. Texture and nano-scale internal microstructure of otoliths in the Atlantic molly, Poecilia mexicana: a high-resolution EBSD study.

    Science.gov (United States)

    Schulz-Mirbach, T; Götz, A; Griesshaber, E; Plath, M; Schmahl, W W

    2013-08-01

    Otoliths of modern bony fishes are massive polycrystalline structures consisting mainly of calcium carbonate (primarily aragonite), and 1-10% organic residuals. Unlike other biomineralisates like shells, teeth and bones, they are not optimized for mechanical loads but serve the senses of hearing and balance in the inner ear. We examined internal structural variation of otoliths through microstructural and texture analyses. Our study applied the electron backscattered diffraction technique (EBSD) to whole sections of saccular otoliths on cave- and surface-dwelling fish. Application of high spatial resolution EBSD on otoliths of the livebearing fish Poecilia mexicana allowed for an investigation of crystal orientation despite the small size (<150 nm) of aragonite crystallites. Crystallites at the rims of otoliths had a higher structural organization than those situated near the center, where no dominant orientation pattern was discernible. Moreover, the medial (sulcal) face of otoliths, which makes contact with the sensory epithelium, was more structured than the lateral (antisulcal) face.

  3. The long-term impact of magnesium in seawater on foraminiferal mineralogy: Mechanism and consequences

    Science.gov (United States)

    Dijk, I.; Nooijer, L. J.; Hart, M. B.; Reichart, G.-J.

    2016-03-01

    Foraminifera are unicellular protists, primarily known for their calcium carbonate shells that provide an extensive fossil record. This record, ranging from Cambrian to present shows both major shifts and gradual changes in the relative occurrence of taxa producing different polymorphs of carbonate. Here we present evidence for coupling between shifts in calcite- versus aragonite-producing species and periods with, respectively, low and high seawater Mg/Ca throughout the Phanerozoic. During periods when seawater Mg/Ca is extinction rates of species producing the mineral phase not favored by the seawater Mg/Ca of that time may be responsible for this alteration. These results imply that the current high seawater Mg/Ca will, in the long term, favor prevalence of high-Mg and aragonite-producing foraminifera over calcite-producing taxa, possibly shifting the balance toward a community in which calcite production is less dominant.

  4. Scanning electron microscopic structure of the prismatic layer in the Bivalvia

    Institute of Scientific and Technical Information of China (English)

    Iwao KOBAYASHI

    2008-01-01

    The shell structure of the Bivalvia has been observed with the use of optical and electron microscopes since the early 1900's. The prismatic structure is one of the more attractive shell structures in bivalved mollusks. This structure is composed of the aggregation of polygonal prisms arranged densely. Each prism is made of small calcite crystallites arranged perpendicular to a growth shell surface. Organic materials, named organic sheaths, accumulate around prisms and stain well with heamatox-ylin-eosin.The Bivalvia, which make prismatic structures, are divided into two groups. One group has the inner shell layer made up of a nacreous structure, and the other has the inner shell layer made up of a foliated structure. The aragonite prismatic layer and the prismatic layer are clo-sely related to each other, as is the aragonite prismatic layer to the composite prismatic one.

  5. Multi-decadal variations in calcareous holozooplankton in the California Current System: Thecosome pteropods, heteropods, and foraminifera

    Science.gov (United States)

    Ohman, Mark D.; Lavaniegos, Bertha E.; Townsend, Annie W.

    2009-09-01

    We examine long-term (1951-2008) variability of three major taxa of calcareous holozooplankton (aragonite-secreting thecosome pteropods and heteropods, and calcite-secreting large planktonic foraminifera) in light of recent interest in the impingement of waters undersaturated with respect to aragonite onto continental shelf depths in the California Current System. We assess interannual variability in springtime abundances of zooplankton sampled in the epipelagic layer, using CalCOFI (California Cooperative Oceanic Fisheries Investigations) zooplankton samples from two regions: Southern California (SC) and Central California (CC). Thecosome pteropods show no evidence of recent declines in abundance in SC or CC waters. In SC, sampling was sufficient to conclude that heteropods and large foraminifera also show no evidence of declines in abundance in recent years. These results do not preclude as-yet undetected changes in vertical distributions or shell morphology, and underscore the importance of sustained in situ measurement programs in order to detect and understand changes to pelagic ecosystems.

  6. [Calcium carbide of different crystal formation synthesized by calcium carbide residue].

    Science.gov (United States)

    Lu, Zhong-yuan; Kang, Ming; Jiang, Cai-rong; Tu, Ming-jing

    2006-04-01

    To recycle calcium carbide residue effectively, calcium carbide of different crystal form, including global aragonite, calcite and acicular calcium carbide was synthesized. Both the influence of pretreatment in the purity of calcium carbide, and the influence of temperatures of carbonization reaction, release velocity of carbon dioxide in the apparition of calcium carbide of different crystal form were studied with DTA-TG and SEM. The result shows that calcium carbide residue can take place chemistry reaction with ammonia chlorinate straight. Under the condition that pH was above 7, the purity of calcium carbide was above 97%, and the whiteness was above 98. Once provided the different temperatures of carbonization reaction and the proper release velocity of carbon dioxide, global aragonite, calcite and acicular calcium carbide were obtained.

  7. Diagenesis of Isla de Mona, Puerto Rico

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez, L.A. (Univ. of Iowa, Iowa City (USA)); Ruiz, H.; Monell, V. (Univ. of Puerto Rico, Mayaguez (Puerto Rico))

    1990-05-01

    Isla de Mona is a carbonate plateau, 50 mi west of Puerto Rico. The plateau is composed mostly of two Miocene carbonate units, the Isla de Mona Dolomite overlain by Lirio Limestone. These two units consist primarily of back-reef sands with a reefal sequence present in the Lirio Limestone to the southwest. The Lirio Limestone is heavily karstified with numerous sinkholes in the central part of the island resembling present-day cenotes of the Yucatan peninsula. Numerous large cave openings are exposed along cliffs surrounding the island, with cavern size rapidly decreasing toward the interior. Within the Isla de Mona Dolomite, three different soil development episodes can be identified in the central part of the island, and on the periphery of the island several episodes of vadose diagenesis are identified by the presence of vadose silts and paleotravertine. Both units exhibit selective dissolution of aragonitic skeletal grains with fabric retentive replacement of former high magnesium calcite skeletal components, by calcite in the Lirio Limestone, and by dolomite in the Isla de Mona Dolomite. Petrographic relationships suggest early diagenetic modification by fluids that were substantially undersaturated with respect to aragonite, which preferentially dissolved aragonitic components, near saturation with respect to calcite/high magnesian calcite during dolomitization, and saturated with respect to calcite during calcitization. Stable isotopic composition of individual dolomitized components and dolomite microspar in the Isla de Mona Dolomite define a hyperbolic trend characteristic of composition produced by fluid mixing. The similarity of the karstified Lirio Limestone to present-day Yucatan, the nature and fluid chemistry requirement of the aragonite dissolution and calcite replacement process, the isotopic composition of the dolomite suggest diagenetic modification under meteoric-marine fluid mixing.

  8. Skeletal mineralogy of coral recruits under high temperature and pCO2

    Directory of Open Access Journals (Sweden)

    T. Foster

    2016-03-01

    Our results show that elevated pCO2 alone is unlikely to drive changes in the skeletal mineralogy of young corals. Not having an ability to switch from aragonite to calcite precipitation may leave corals and ultimately coral reef ecosystems more susceptible to predicted ocean acidification. An important area for prospective research would be the investigation of the combined impact of high pCO2 and reduced Mg ∕ Ca ratio on coral skeletal mineralogy.

  9. Skeletal mineralogy of coral recruits under high temperature and pCO2

    Directory of Open Access Journals (Sweden)

    T. Foster

    2015-08-01

    Full Text Available Aragonite, which is the polymorph of CaCO3 precipitated by modern corals during skeletal formation, has a higher solubility than the more stable polymorph calcite. This higher solubility leaves animals that produce aragonitic skeletons more vulnerable to anthropogenic ocean acidification. It is therefore, important to determine whether scleractinian corals have the plasticity to adapt and produce calcite in their skeletons in response to changing environmental conditions. Both high pCO2 and lower Mg / Ca ratios in seawater are thought to have driven changes in the skeletal mineralogy of major marine calcifiers in the past ∼540 myr. Experimentally reduced Mg / Ca ratios in ambient seawater have been shown to induce some calcite precipitation in both adult and newly settled modern corals, however, the impact of high pCO2 on the mineralogy of recruits is unknown. Here we determined the skeletal mineralogy of one-month old Acropora spicifera coral recruits grown under high temperature (+3 °C and pCO2 (∼900 μatm conditions, using X-ray diffraction and Raman spectroscopy. We found that newly settled coral recruits produced entirely aragonitic skeletons regardless of the treatment. Our results show that elevated pCO2 alone is unlikely to drive changes in the skeletal mineralogy of young corals. Not having an ability to switch from aragonite to calcite precipitation may leave corals and ultimately coral reef ecosystems more susceptible to predicted ocean acidification. An important area for prospective research would be to investigate the combined impact of high pCO2 and reduced Mg / Ca ratio on coral skeletal mineralogy.

  10. Recruitment and Succession in a Tropical Benthic Community in Response to In-Situ Ocean Acidification

    OpenAIRE

    Elizabeth Derse Crook; Kristy J Kroeker; Potts, Donald C.; Mario Rebolledo-Vieyra; Hernandez-Terrones, Laura M.; Adina Paytan

    2016-01-01

    Ocean acidification is a pervasive threat to coral reef ecosystems, and our understanding of the ecological processes driving patterns in tropical benthic community development in conditions of acidification is limited. We deployed limestone recruitment tiles in low aragonite saturation (Ωarag) waters during an in-situ field experiment at Puerto Morelos, Mexico, and compared them to tiles placed in control zones over a 14-month investigation. The early stages of succession showed relatively l...

  11. Buffer Capacity, Ecosystem Feedbacks, and Seawater Chemistry under Global Change

    OpenAIRE

    Robert J. Toonen; Atkinson, Marlin J; Thomas, Florence I. M.; Jury, Christopher P.

    2013-01-01

    Ocean acidification (OA) results in reduced seawater pH and aragonite saturation state (Ωarag), but also reduced seawater buffer capacity. As buffer capacity decreases, diel variation in seawater chemistry increases. However, a variety of ecosystem feedbacks can modulate changes in both average seawater chemistry and diel seawater chemistry variation. Here we model these effects for a coastal, reef flat ecosystem. We show that an increase in offshore pCO2 and temperature (to 900 µatm and + 3 ...

  12. Trace elements in speleothems. A short review of the state of the art.

    OpenAIRE

    Verheyden Sophie

    2004-01-01

    A state of the art of the research on trace elements of speleothems is given. First studies focussed on problems such as the colour of speleothems and the aragonite problem. Insitu studies and studies oriented towards a better understanding of vadose hydrology brought new insights in the controls on trace elemental composition of speleothems. Recent studies deal with microscale analyses and annual and intra-annual chemistry changes. Further in-situ studies should be performed to further diffe...

  13. Annually laminated speleotherms : a review

    OpenAIRE

    Baker, Andy; Smith, Claire; Jex, Catherine; Fairchild, I. J.; Genty, Dominique; Fuller, Lisa

    2008-01-01

    This review of annually laminated speleothems firstly considers the four types of annual laminae found within speleothems: fluorescent laminae formed by annual variations in organic matter flux; visible or petrographic laminae, formed by annual variations in calcite texture or fabric; calcite-aragonite couplets; and finally trace element laminae. The methods available to confirm the annual nature, or otherwise, of lamina deposition are reviewed. We consider the use of annual laminae ...

  14. Diagenesis and Geochemistry of Upper Muschelkalk (Triassic) Buildups and Associated Facies in Catalonia (NE Spain): a paper dedicated to Francesc Calvet

    OpenAIRE

    Tucker, M.; Marshall, J

    2004-01-01

    Carbonate buildups are well developed in the Triassic Upper Muschelkalk of eastern Spain in the La Riba Unit, but they are completely dolomitised. These mud-mounds with reefal caps have well-developed fibrous and botryoidal marine cements which were probably high-Mg calcite and aragonite originally. The dolomite is fabric retentive indicating an early origin, but the d18O values are quite negative (average -3.‰), interpreted as indicating recrystallisation during shallow burial, but without f...

  15. Use of nanoindentation technique for a better understanding of the fracture toughness of Strombus gigas conch shell

    Energy Technology Data Exchange (ETDEWEB)

    Romana, L., E-mail: laurence.romana@univ-ag.fr [Groupe de Technologie des Surfaces et des Interfaces, Université des Antilles et de la Guyane, 97 159 Pointe à Pitre, French West Indies, Guadeloupe (France); Thomas, P.; Bilas, P. [Groupe de Technologie des Surfaces et des Interfaces, Université des Antilles et de la Guyane, 97 159 Pointe à Pitre, French West Indies, Guadeloupe (France); Mansot, J.L. [Groupe de Technologie des Surfaces et des Interfaces, Université des Antilles et de la Guyane, 97 159 Pointe à Pitre, French West Indies, Guadeloupe (France); Centre Commun de Caractérisation des Matériaux, 97 159 Pointe à Pitre, French West Indies, Guadeloupe (France); Merrifiels, M. [Groupe de Technologie des Surfaces et des Interfaces, Université des Antilles et de la Guyane, 97 159 Pointe à Pitre, French West Indies, Guadeloupe (France); Bercion, Y. [Centre Commun de Caractérisation des Matériaux, 97 159 Pointe à Pitre, French West Indies, Guadeloupe (France); Aranda, D. Aldana [CINVESTAV IPN Unidad Merida, Recursos del Mar, Laboratorio de Biología y Acuacultura de Moluscos, Km 6 antigua Carretera a Progreso, Cp 97310 Cordemex (Mexico)

    2013-02-15

    In this work the nanochemical properties of the composite organomineral biomaterial constituting Strombus gigas conch shell are studied by means of dynamic mechanical analyses associated to nanoidentation technique. The measurements are performed on shell samples presenting different surface orientations relative to the growth axis of the conch shell. The influence of the organic component of the biomaterial on its nanomechanical properties is also investigated by studying fresh and dried S. gigas conch shells. Monocrystalline aragonite is used as a reference. For the understanding of nanochemical behaviour, special attention is paid to the pop in events observed on the load/displacement curves which results from nanofractures' initiation and propagation occuring during the load process. In order to better understand the mechanical properties systematic studies of the structure and morphology are performed using scanning electron microscopy, atomic force microscopy and X-ray diffractometry. The hardness and Young's modulus values measured on bio aragonite samples are close to those of the aragonite mineral standard. This surprising result shows that, H and E values are not related to the bio composition and lamellar structure of the bio aragonite. However, it was found that the organic layer and the micro architecture strongly influence the nanofracture initiation and propagation processes in the samples. Statistic study of the pop-in events can help to predict the macroscopic mechanical behaviour of the material. - Highlights: ► Nanomechanical properties of Strombus gigas conch shell ► Low influence of the crossed lamellar structure on H and E values at the nano scale ► Strong influence of the crossed lamellar on nanocracks initiation ► Correlation between mechanical behaviors at the macro and nano scales.

  16. Low Florida coral calcification rates in the Plio-Pleistocene

    OpenAIRE

    T. C. Brachert; Reuter, M.; Krüger, S; Klaus, J. S.; K. Helmle; Lough, J.M.

    2015-01-01

    In geological outcrops and drill cores from reef frameworks, the skeletons of scleractinian corals are usually leached and more or less completely transformed into sparry calcite because the highly porous skeletons formed of metastable aragonite (CaCO3) undergo rapid diagenetic alteration. Upon alteration, ghost structures of the distinct annual growth bands may be retained allowing for reconstructions of annual extension (= growth) rates, but information on skeletal density...

  17. Transition of microbiological and sedimentological features associated with the geochemical gradient in a travertine mound in northern Sumatra, Indonesia

    Science.gov (United States)

    Sugihara, Chiya; Yanagawa, Katsunori; Okumura, Tomoyo; Takashima, Chizuru; Harijoko, Agung; Kano, Akihiro

    2016-08-01

    Modern travertines, carbonate deposits in Ca-rich hydrothermal water with high pCO2, often display a changing environment along the water path, with corresponding variability in the microbial communities. We investigated a travertine-bearing hot spring at the Blue Pool in northern Sumatra, Indonesia. The thermal water of ~ 62 °C with high H2S (200 μM) and pCO2 (~ 1 atm) developed a travertine mound ~ 70 m wide. The concentrations of the gas components H2S and CO2, decrease immediately after the water is discharged, while the dissolved oxygen, pH, and aragonite saturation increase in the downstream direction. Responding to the geochemical gradient in the water, the surface biofilms change color from white to pink, light-green, dark-green, and brown as the water flows from the vent; this corresponds to microbial communities characterized by chemolithoautotrophs (Halothiobacillaceae), purple sulfur bacteria (Chromatiaceae), Anaerolineaceae, and co-occurrence of green non-sulfur bacteria (Chloroflexales)-Cyanobacteria, and green sulfur bacteria (Chlorobiales), respectively. In an environment with a certain level of H2S (> 1 μM), sulfur digestion and anoxygenic photosynthesis can be more profitable than oxygenic photosynthesis by Cyanobacteria. The precipitated carbonate mineral consists of aragonite and calcite, with the proportion of aragonite increasing downstream due to the larger Mg2 +/Ca2 + ratio in the water or the development of thicker biofilm. Where the biofilm is well developed, the aragonite travertines often exhibit laminated structures that were likely associated with the daily metabolism of these bacteria. The microbiological and sedimentological features at the Blue Pool may be the modern analogs of geomicrobiological products in the early Earth. Biofilm of anoxygenic photosynthetic bacteria had the potential to form ancient stromatolites that existed before the appearance of cyanobacteria.

  18. Biomineral repair of Abalone shell apertures

    OpenAIRE

    Cusack, M.; Guo, D.; Chung, P.; Kamenos, N. A.

    2013-01-01

    The shell of the gastropod mollusc, abalone, is comprised of nacre with an outer prismatic layer that is composed of either calcite or aragonite or both, depending on the species. A striking characteristic of the abalone shell is the row of apertures along the dorsal margin. As the organism and shell grow, new apertures are formed and the preceding ones are filled in. Detailed investigations, using electron backscatter diffraction, of the infill in three species of abalone: Haliotis asinina, ...

  19. Effect of carbonate chemistry alteration on the early embryonic development of the Pacific oyster (Crassostrea gigas.

    Directory of Open Access Journals (Sweden)

    Frédéric Gazeau

    Full Text Available Ocean acidification, due to anthropogenic CO₂ absorption by the ocean, may have profound impacts on marine biota. Calcareous organisms are expected to be particularly sensitive due to the decreasing availability of carbonate ions driven by decreasing pH levels. Recently, some studies focused on the early life stages of mollusks that are supposedly more sensitive to environmental disturbances than adult stages. Although these studies have shown decreased growth rates and increased proportions of abnormal development under low pH conditions, they did not allow attribution to pH induced changes in physiology or changes due to a decrease in aragonite saturation state. This study aims to assess the impact of several carbonate-system perturbations on the growth of Pacific oyster (Crassostrea gigas larvae during the first 3 days of development (until shelled D-veliger larvae. Seawater with five different chemistries was obtained by separately manipulating pH, total alkalinity and aragonite saturation state (calcium addition. Results showed that the developmental success and growth rates were not directly affected by changes in pH or aragonite saturation state but were highly correlated with the availability of carbonate ions. In contrast to previous studies, both developmental success into viable D-shaped larvae and growth rates were not significantly altered as long as carbonate ion concentrations were above aragonite saturation levels, but they strongly decreased below saturation levels. These results suggest that the mechanisms used by these organisms to regulate calcification rates are not efficient enough to compensate for the low availability of carbonate ions under corrosive conditions.

  20. Ocean acidification limits temperature-induced poleward expansion of coral habitats around Japan

    OpenAIRE

    Yara, Y.; M. Vogt; Fujii, M.; Yamano, H; Hauri, C; Steinacher, M.; Gruber, N.; Yamanaka, Y.

    2012-01-01

    Using results from four coupled global carbon cycle-climate models combined with in situ observations, we estimate the effects of future global warming and ocean acidification on potential habitats for tropical/subtropical and temperate coral communities in the seas around Japan. The suitability of coral habitats is classified on the basis of the currently observed regional ranges for temperature and saturation states with regard to aragonitearag). We find ...

  1. Ocean acidification limits temperature-induced poleward expansion of coral habitats around Japan

    OpenAIRE

    Yara, Y.; M. Vogt; Fujii, M.; Yamano, H; Hauri, C; Steinacher, M.; Gruber, N.; Yamanaka, Y.

    2012-01-01

    Using results from four coupled global carbon cycle-climate models combined with in situ observations, we estimate the effects of future global warming and ocean acidification on potential habitats for tropical/subtropical and temperate coral communities in the seas around Japan. The suitability of coral habitats is classified on the basis of the currently observed regional ranges for temperature and saturation states with regard to aragonite (Ωarag). We find that, under the "business as usua...

  2. Ocean acidification limits temperature-induced poleward expansion of coral habitats around Japan

    OpenAIRE

    Yara, Y.; M. Vogt; Fujii, M.; Yamano, H; Hauri, C; Steinacher, M.; Gruber, N.; Yamanaka, Y.

    2012-01-01

    Using results from four coupled global carbon cycle-climate models combined with in situ observations, we estimate the combined effects of future global warming and ocean acidification on potential habitats for tropical/subtropical and temperate coral communities in the seas around Japan. The suitability of the coral habitats are identified primarily on the basis of the currently observed ranges for temperature and saturation states Ω with regard to aragonitearag<...

  3. Groundwater geochemistry observations in littoral caves of Mallorca (western Mediterranean: implications for deposition of phreatic overgrowths on speleothems

    Directory of Open Access Journals (Sweden)

    Bogdan P. Onac

    2014-05-01

    Full Text Available Phreatic overgrowths on speleothems (POS precipitate at the air-water interface in the littoral caves of Mallorca, Spain. Mainly composed of calcite, aragonite POS are also observed in specific locations. To characterize the geochemical environment of the brackish upper water column, water samples and salinity values were collected from water profiles (0-2.9 m in April 2012 and March 2013 near aragonite POS in Cova des Pas de Vallgornera and calcite POS in Coves del Drac (hereafter, Vallgornera and Drac. Degassing of CO2 from the water was evidenced by the existence of lower dissolved inorganic carbon (DIC concentration and enriched δ13CDIC values in a thin surface layer (the uppermost 0.4 m, which was observed in both profiles from Drac. This process is facilitated by the efficient exchange of cave air with the atmosphere, creating a CO2 partial pressure (pCO2 disparity between the cave water and air, resulting in the precipitation of calcite POS as CO2 degasses from the water. The degassed upper layer was not observed in either profile from Vallgornera, suggesting that less efficient cave ventilation restricts outgassing of CO2, which also results in accumulation of CO2 in the cave atmosphere. The presence of an existing uncorroded POS horizon, as well as higher concentrations and large amplitude fluctuations of cave air pCO2, may indicate that aragonite POS deposition is currently episodic in Vallgornera. Ion concentration data from monthly water samples collected in each cave between October 2012 and March 2013 indicate higher Mg:Ca, Sr:Ca, Ba:Ca and Sr:Mg ratios in Vallgornera. Salinity alone does not appear to be a viable proxy for ions that may promote aragonite precipitation or inhibit calcite precipitation. Instead, these ions may be contributed by more intense bedrock weathering or deep groundwater flow.

  4. Optics and remote sensing of Bahamian carbonate sediment whitings and potential relationship to wind-driven Langmuir circulation

    OpenAIRE

    H. M. Dierssen; R. C. Zimmerman; Burdige, D. J.

    2008-01-01

    Regions of milky white seas or "whitings" periodically occur to the west of Andros Island along the Great Bahama Bank where the bottom sediment consists of fine-grained aragonite mud. We present comprehensive measurements of inherent optical properties within a whiting patch and discuss the potential for monitoring the frequency, extent, and quantity of suspended matter from ocean colour satellite imagery. Sea spectral reflectance measured in situ and remotely from space revealed hi...

  5. Biominerals at the nanoscale: transmission electron microscopy methods for studying the special properties of biominerals

    DEFF Research Database (Denmark)

    Posfai, Mihaly; Kasama, Takeshi; Dunin-Borkowski, Rafal E.

    2013-01-01

    Biominerals have important functions in living organisms: apatite crystals are responsible for the strength of our bones and the hardness of our teeth, calcite and aragonite are used by many organisms for making shells, and magnetite and greigite help bacteria and birds to navigate in magnetic...... fields. In order to fulfill their roles in organisms, biominerals have strictly controlled physical and chemical properties. Transmission electron microscopy (TEM) is ideally suited for the study of the structures, arrangements, compositions, morphologies, crystallographic orientations, crystallographic...

  6. Skeletal mineralogy of coral recruits under high temperature and pCO2

    Science.gov (United States)

    Foster, T.; Clode, P. L.

    2016-03-01

    Aragonite, which is the polymorph of CaCO3 precipitated by modern corals during skeletal formation, has a higher solubility than the more stable polymorph calcite. This higher solubility may leave animals that produce aragonitic skeletons more vulnerable to anthropogenic ocean acidification. It is therefore important to determine whether scleractinian corals have the plasticity to adapt and produce calcite in their skeletons in response to changing environmental conditions. Both high pCO2 and lower Mg / Ca ratios in seawater are thought to have driven changes in the skeletal mineralogy of major marine calcifiers in the past ˜ 540 Ma. Experimentally reduced Mg / Ca ratios in ambient seawater have been shown to induce some calcite precipitation in both adult and newly settled modern corals; however, the impact of high pCO2 on the mineralogy of recruits is unknown. Here we determined the skeletal mineralogy of 1-month-old Acropora spicifera coral recruits grown under high temperature (+3 °C) and pCO2 (˜ 900 µatm) conditions, using X-ray diffraction and Raman spectroscopy. We found that newly settled coral recruits produced entirely aragonitic skeletons regardless of the treatment. Our results show that elevated pCO2 alone is unlikely to drive changes in the skeletal mineralogy of young corals. Not having an ability to switch from aragonite to calcite precipitation may leave corals and ultimately coral reef ecosystems more susceptible to predicted ocean acidification. An important area for prospective research would be the investigation of the combined impact of high pCO2 and reduced Mg / Ca ratio on coral skeletal mineralogy.

  7. Simulation of global ocean acidification and chemical habitats of shallow- and cold-water coral reefs

    Directory of Open Access Journals (Sweden)

    Mei-Di Zheng

    2014-12-01

    Full Text Available Using the UVic Earth System Model, this study simulated the change of seawater chemistry and analyzed the chemical habitat surrounding shallow- and cold-water coral reefs from the year 1800 to 2300 employing RCP2.6, RCP4.5, RCP6.0, and RCP8.5 scenarios. The model results showed that the global ocean will continue to absorb atmospheric CO2. Global mean surface ocean temperature will rise 1.1–2.8 K at the end of the 21st century across RCP scenarios. Meanwhile, the global mean surface ocean pH will drop 0.14–0.42 and the ocean surface mean concentration of carbonate will decrease 20%–51% across the RCP scenarios. The saturated state of sea water with respect to calcite carbonate minerals (Ω will decrease rapidly. During the pre-industrial period, 99% of the shallow-water coral reefs were surrounded by seawater with Ω > 3.5 and 87% of the deep-sea coral reefs were surrounded by seawater with aragonite supersaturation. Within the 21st century, except for the high mitigation scenario of RCP2.6, almost none shallow-water coral reefs will be surrounded by seawater with Ω > 3.5. Under the intensive emission scenario of RCP8.5, by the year 2100, the aragonite saturation horizon will rise to 308 m under the sea surface from 1138 m at the pre-industrial period, thus 73% of the cold-water coral reefs will be surrounded by seawater with aragonite undersaturation. By the year 2300, only 5% of the cold-water coral reefs will be surrounded by seawater with aragonite supersaturation.

  8. Reassessing the dissolution of marine carbonates: I. Solubility

    Science.gov (United States)

    Gehlen, M.; Bassinot, F. C.; Chou, L.; McCorkle, D.

    2005-08-01

    We studied the solubility of the [63-150 μm] and the greater than 150 μm size fractions of sediments from two bathymetric transects in the eastern tropical Atlantic (Sierra Leone rise and Cape Verde Plateau). Both fractions are made mainly of foraminiferal shells and fragments. We determined the calcite crystallinity (full width at half maximum of XRD (104) calcite peak) of the >150 μm size fraction. Equilibration experiments were carried out in artificial seawater (20 °C, pCO 2=3100 ppm) for up to 57 days starting from undersaturation with respect to calcite and supersaturation with respect to aragonite. Experiments starting from supersaturation yielded concentration products close to aragonite solubility for sediments from the shallowest stations, suggesting the presence of trace levels of aragonite in these samples. Concentration products computed for the deeper stations were intermediate between aragonite and calcite solubility. Our results indicate the formation of a high-Mg coating. The equilibration period was too short to allow the complete recrystallization of these Mg-rich overgrowths. Experiments initiated from undersaturation yield concentration products that are between 4% and 24% higher than the reported stoichiometric concentration product of synthetic calcite. These differences between estimates of calcite stoichiometric solubility products are explained in terms of variations in experimental conditions (artificial versus natural seawater) and related choices of carbonic acid dissociation constants. They do not reflect a true difference in solubility between biogenic and synthetic calcite. The thinning of the foraminiferal calcite (104) XRD peak from 0.168°( 2θ) to 0.148°( 2θ) along the depth transects is interpreted as reflecting an improvement in calcite crystallinity. This and the change in specific surface area are consistent with the progressive change of the carbonate assemblage. The evolution of the bulk composition of the carbonate

  9. Palaeomagnetism of greigite bearing sediments from the Dead Sea, Israel

    OpenAIRE

    Ute Frank; Norbert Nowaczyk; Jörg F.W. Negendank

    2007-01-01

    Detailed magnetostratigraphic investigations were carried out on five sediment cores obtained from three sites on the northwestern shore of the Dead Sea, Israel. The sediments are heterogeneous, composed of fine clastic layers alternating with authigenic aragonite. The magnetic remanence is carried by Ti-magnetite and greigite, reflecting a detrital as well as an authigenic phase. Directions of the characteristic remanent magnetization were obtained from stepwise AF-demagnetization of the nat...

  10. Natural variability in the surface ocean carbonate ion concentration

    Directory of Open Access Journals (Sweden)

    N. S. Lovenduski

    2015-11-01

    Full Text Available We investigate variability in the surface ocean carbonate ion concentration ([CO32−] on the basis of a~long control simulation with an Earth System Model. The simulation is run with a prescribed, pre-industrial atmospheric CO2 concentration for 1000 years, permitting investigation of natural [CO32−] variability on interannual to multi-decadal timescales. We find high interannual variability in surface [CO32−] in the tropical Pacific and at the boundaries between the subtropical and subpolar gyres in the Northern Hemisphere, and relatively low interannual variability in the centers of the subtropical gyres and in the Southern Ocean. Statistical analysis of modeled [CO32−] variance and autocorrelation suggests that significant anthropogenic trends in the saturation state of aragonitearagonite are already or nearly detectable at the sustained, open-ocean time series sites, whereas several decades of observations are required to detect anthropogenic trends in Ωaragonite in the tropical Pacific, North Pacific, and North Atlantic. The detection timescale for anthropogenic trends in pH is shorter than that for Ωaragonite, due to smaller noise-to-signal ratios and lower autocorrelation in pH. In the tropical Pacific, the leading mode of surface [CO32−] variability is primarily driven by variations in the vertical advection of dissolved inorganic carbon (DIC in association with El Niño–Southern Oscillation. In the North Pacific, surface [CO32−] variability is caused by circulation-driven variations in surface DIC and strongly correlated with the Pacific Decadal Oscillation, with peak spectral power at 20–30-year periods. North Atlantic [CO32−] variability is also driven by variations in surface DIC, and exhibits weak correlations with both the North Atlantic Oscillation and the Atlantic Multidecadal Oscillation. As the scientific community seeks to detect the anthropogenic influence on ocean carbonate chemistry, these results

  11. Atomic force microscope observations of otoconia in the newt

    Science.gov (United States)

    Hallworth, R.; Wiederhold, M. L.; Campbell, J. B.; Steyger, P. S.

    1995-01-01

    Calcitic and aragonitic otoconia from the Japanese red-bellied newt, Cynops pyrrhogaster, were examined using an atomic force microscope. The surface structure of both otoconial polymorphs consisted of arrays of elements approximately 50 nm in diameter. Elements were generally round and were separated by shallow depressions of no more than 20 nm. The elements are suggested to be single crystals of calcium carbonate. The relationship of these observations to theories of otoconial genesis is discussed.

  12. Evidence of compositional and ultrastructural shifts during the development of calcareous tubes in the biofouling tubeworm, Hydroides elegans.

    Science.gov (United States)

    Chan, Vera Bin San; Vinn, Olev; Li, Chaoyi; Lu, Xingwen; Kudryavtsev, Anatoliy B; Schopf, J William; Shih, Kaimin; Zhang, Tong; Thiyagarajan, Vengatesen

    2015-03-01

    The serpulid tubeworm, Hydroides elegans, is an ecologically and economically important species whose biology has been fairly well studied, especially in the context of larval development and settlement on man-made objects (biofouling). Nevertheless, ontogenetic changes associated with calcareous tube composition and structures have not yet been studied. Here, the ultrastructure and composition of the calcareous tubes built by H. elegans was examined in the three early calcifying juvenile stages and in the adult using XRD, FTIR, ICP-OES, SEM and Raman spectroscopy. Ontogenetic shifts in carbonate mineralogy were observed, for example, juvenile tubes contained more amorphous calcium carbonate and were predominantly aragonitic whereas adult tubes were bimineralic with considerably more calcite. The mineral composition gradually shifted during the tube development as shown by a decrease in Sr/Ca and an increase of Mg/Ca ratios with the tubeworm's age. The inner tube layer contained calcite, whereas the outer layer contained aragonite. Similarly, the tube complexity in terms of ultrastructure was associated with development. The sequential appearance of unoriented ultrastructures followed by oriented ultrastructures may reflect the evolutionary history of serpulid tube biominerals. As aragonitic structures are more susceptible to dissolution under ocean acidification (OA) conditions but are more difficult to be removed by anti-fouling treatments, the early developmental stages of the tubeworms may be vulnerable to OA but act as the important target for biofouling control. PMID:25600412

  13. Fresh-water cementation of a 1,000-year-old oolite

    Science.gov (United States)

    Halley, R. B.; Harris, P. M.

    1979-01-01

    Calcite cementation of aragonite ooid sand is producing oolite on Joulters Cays, Bahamas. During the last 1,000 years, calcite cement has formed at an average rate of between 27 and 55 cm3 /m3 /yr and is derived from dissolution of ooid aragonite in fresh water. The dissolution-reprecipitation of carbonate minerals in the aquifer results in ground waters of unusually high Sr content. Sea water and mixtures of fresh and sea water appear to inhibit cementation. A pronounced cement fabric change occurs across the water table and has produced an obvious petrographic record of fresh-water diagenesis. Above the water table, cement is typically near grain contact positions, where water is held by capillarity; below the water table, cement is more randomly distributed around grains. At the water table a transition zone, 1 meter thick, marks the boundary between cement textures. No porosity reduction is associated with cementation; calcite cement precipitation is apparently compensated by an equal or greater amount of aragonite dissolution in the interval undergoing cementation. Permeability is more variable above the water table than below it, reflecting early channelling of flow patterns in the vadose zone. Effective permeability below the water table is one to two orders of magnitude higher than above the water table because of entrained gas in the vadose zone. This permeability difference promotes preservation of unstable minerals above the water table and continued diagenetic alteration below the water table.

  14. Threshold of carbonate saturation state determined by a CO2 control experiment

    Directory of Open Access Journals (Sweden)

    A. Negishi

    2011-08-01

    Full Text Available Acidification of the oceans by increasing anthropogenic CO2 emissions will cause a decrease in biogenic calcification and an increase in carbonate dissolution. Previous studies suggest that carbonate dissolution will occur in polar regions and in the deep-sea oceans where saturation state with respect to carbonate minerals (Ω will be 1. Recent reports demonstrated nocturnal carbonate dissolution reefs, despite Ω_a > 1, probably relate to the dissolution of the minor reef carbonate (Mg-calcite, which is more soluble than aragonite. However, the threshold of Ω for the dissolution of natural sediments has not been clearly determined, and it is unknown whether these dissolution processes actually occur under natural conditions. This work describes the measurement of the dissolution rates of coral aragonite and Mg calcite excreted by marine organisms under conditions of Ω_a > 1 with controlled seawater pCO2. Laboratory experimental data of the present study show that bulk carbonate sediments sampled from a coral reef start to dissolve when Ω_a = 3.7, and dissolution rates increase with falling Ω_a. Mg-calcite derived from foraminifera and coralline algae dissolved when Ω_a reached 3.4, whereas coralline aragonite started to dissolve when Ω_a was almost 1.0. We show that nocturnal carbonate dissolution of coral reefs occurs mainly by the dissolution of foraminifera and coralline algae in reef sediment.

  15. Drastic Aridification Caused the Decline of Oasis Civilizations on the Silk Route during the Eighth Century

    Science.gov (United States)

    Wei, K.; Song, S.; Huang, C.

    2003-12-01

    Availability of water, and response to shortage of it, plays an important role in shaping human history. Near a century ago, Ellsworth Huntington (1907) suggested that the developments of ancient civilizations in Inner Asian and their invasions into China and Europe were pulsed by climatic changes. In revisiting this proposition, here we present a paleoclimatic record of the past 5000 years deduced from carbon isotopic ratio of organic carbon and percentage of aragonite in bulk sediments of a radiometrically dated sedimentary core of Lake Bosten, Xinjiang, China. Together the two proxies of aridity provide a detailed record of climatic fluctuation of the Inner Asia. The arid periods are well characterized by high content of authigenic aragonite and heavier values of carbon isotopic ratio of organic carbon in the bulk sediments (implying dominance of C4 plants which thrived under arid condition). Conversely, the humid/wet periods are marked by lighter carbon isotopic values (indicating presence of C3 plants of humid climateœcand absence of aragonite. The Western Region (Xi-Y"1) area of China enjoyed a long period of stable and humid condition from 2nd century B.C. to the 8th century when many oasis city-states were established and Buddhism spread from India. A drastic deterioration of climate during the eighth century appears to cause the decline of those once strived ancient civilizations in the eastern side of the Tarim Basin along the Silk Routes.

  16. Adverse effects of ocean acidification on early development of squid (Doryteuthis pealeii.

    Directory of Open Access Journals (Sweden)

    Maxwell B Kaplan

    Full Text Available Anthropogenic carbon dioxide (CO2 is being absorbed into the ocean, altering seawater chemistry, with potentially negative impacts on a wide range of marine organisms. The early life stages of invertebrates with internal and external aragonite structures may be particularly vulnerable to this ocean acidification. Impacts to cephalopods, which form aragonite cuttlebones and statoliths, are of concern because of the central role they play in many ocean ecosystems and because of their importance to global fisheries. Atlantic longfin squid (Doryteuthis pealeii, an ecologically and economically valuable taxon, were reared from eggs to hatchlings (paralarvae under ambient and elevated CO2 concentrations in replicated experimental trials. Animals raised under elevated pCO2 demonstrated significant developmental changes including increased time to hatching and shorter mantle lengths, although differences were small. Aragonite statoliths, critical for balance and detecting movement, had significantly reduced surface area and were abnormally shaped with increased porosity and altered crystal structure in elevated pCO2-reared paralarvae. These developmental and physiological effects could alter squid paralarvae behavior and survival in the wild, directly and indirectly impacting marine food webs and commercial fisheries.

  17. Adverse effects of ocean acidification on early development of squid (Doryteuthis pealeii).

    Science.gov (United States)

    Kaplan, Maxwell B; Mooney, T Aran; McCorkle, Daniel C; Cohen, Anne L

    2013-01-01

    Anthropogenic carbon dioxide (CO2) is being absorbed into the ocean, altering seawater chemistry, with potentially negative impacts on a wide range of marine organisms. The early life stages of invertebrates with internal and external aragonite structures may be particularly vulnerable to this ocean acidification. Impacts to cephalopods, which form aragonite cuttlebones and statoliths, are of concern because of the central role they play in many ocean ecosystems and because of their importance to global fisheries. Atlantic longfin squid (Doryteuthis pealeii), an ecologically and economically valuable taxon, were reared from eggs to hatchlings (paralarvae) under ambient and elevated CO2 concentrations in replicated experimental trials. Animals raised under elevated pCO2 demonstrated significant developmental changes including increased time to hatching and shorter mantle lengths, although differences were small. Aragonite statoliths, critical for balance and detecting movement, had significantly reduced surface area and were abnormally shaped with increased porosity and altered crystal structure in elevated pCO2-reared paralarvae. These developmental and physiological effects could alter squid paralarvae behavior and survival in the wild, directly and indirectly impacting marine food webs and commercial fisheries.

  18. Final report for grant number DE-FG02-06ER64244 to the University of Idaho (RW Smith)-coupling between flow and precipitation in heterogeneous subsurface environments and effects on contaminant fate and transport

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Robert W. [Univ. of Idaho, Idaho Falls, ID (United States); Beig, Mikala S. [Univ. of Idaho, Idaho Falls, ID (United States); Gebrehiwet, Tsigabu [Univ. of Idaho, Idaho Falls, ID (United States); Corriveau, Catherine E. [Univ. of Idaho, Idaho Falls, ID (United States); Redden, George [Idaho National Lab. (INL), Idaho Falls, ID (United States); Fujita, Yoshiko [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2010-06-18

    Engineered remediation strategies for inducing mineral precipitation in the subsurface typically involve the introduction of at least one reactant either by direct injection or by in situ generation. The localization of reactant sources means a wide range of saturation states and ion ratios will be created as reactants are mixed: These conditions together can result in a wide range of precipitation rates, as well as impact which mineral phase precipitates. This is potentially important for the capacity of the precipitates to take up of trace metal contaminants, for their long term stability. Aragonite, for example, is able to sequester a larger amount of Sr than calcite. However, aragonite is less stable under typical groundwater conditions, and so may release sequestered Sr over time as the aragonite transforms to a more stable phase. In addition, previous experimental studies have indicated that other system constituents may influence calcium carbonate precipitation and consequently the Sr uptake potential of a system. For example, dissolved organic carbon (at levels typical of groundwaters) can suppress crystal growth. As a result, the continuous nucleation of small crystals, rather than growth of existing crystals, may be the dominant mode of precipitation. This has the potential for greater uptake of Sr because the smaller crystal sizes associated with nucleated calcite may more readily accommodate the distortion resulting from substitution of the larger Sr ion for Ca ions than can larger crystals. However, these smaller crystals may also be less stable and over the long term release Sr as a result of Ostwald ripening. To better understand the formation and composition of relevant calcium carbonate mineral phases two related series of mineral precipitation experiments were conducted. The first series of experiments, conducted using a Continuously Stirred Tank Reactor (CSTR) operated at steady state rates of precipitation was focused on understanding the

  19. Carbonate replacement of lacustrine gypsum deposits in two Neogene continental basins, eastern Spain

    Science.gov (United States)

    Anadón, P.; Rosell, L.; Talbot, M. R.

    1992-07-01

    Bedded nonmarine gypsum deposits in the Miocene Teruel and Cabriel basins, eastern Spain, are partly replaced by carbonate. The Libros gypsum (Teruel Graben) is associated with fossiliferous carbonate wackestones and finely laminated, organic matter-rich mudstones which accumulated under anoxic conditions in a meromictic, permanent lake. The gypsum is locally pseudomorphed by aragonite or, less commonly, replaced by calcite. Low δ 13C values indicate that sulphate replacement resulted from bacterial sulphate reduction processes that were favoured by anacrobic conditions and abundant labile organic matter in the sediments. Petrographic evidence and oxygen isotopic composition suggest that gypsum replacement by aragonite occurred soon after deposition. A subsequent return to oxidising conditions caused some aragonite to be replaced by diagenetic gypsum. Native sulphur is associated with some of these secondary gypsum occurrences. The Los Ruices sulphate deposits (Cabriel Basin) contain beds of clastic and selenitic gypsum which are associated with limestones and red beds indicating accumulation in a shallow lake. Calcite is the principal replacement mineral. Bacterial sulphate reduction was insignificant in this basin because of a scarcity of organic matter. Stable isotope composition of diagenetic carbonate indicates that gypsum replacement occurred at shallow burial depths due to contact with dilute groundwaters of meteoric origin. Depositional environment evidently has a major influence upon the diagenetic history of primary sulphate deposits. The quantity of preserved organic matter degradable by sulphate-reducing bacteria is of particular importance and, along with groundwater composition, is the main factor controlling the mechanism of gypsum replacement by carbonate.

  20. SEM observation of structural (non-mineralogical) alteration inside the previously crystallized nacreous layer of Crenomytilus grayanus (Bivalvia: Mytilidae).

    Science.gov (United States)

    Zuykov, Michael; Pelletier, Emilien; Kolyuchkina, Galina

    2013-01-01

    A microstructural and mineralogical study shows the transition of aragonitic nacreous tablets to aragonitic prisms inside previously secreted nacre, i.e. without contact with the mantle or extrapallial fluid, in a field-collected mytilid bivalve Crenomytilus grayanus (D.). The intermediate zone between nacre and new prisms is represented by nacre tablets "stuck together" or by disordered calcium carbonate material. The modified nacre forms aragonitic lenses of prisms (ALPs). These lenses may reach 500 μm in thickness below the tunnels excavated by the shell borers. ALPs are similar to myostracal prisms in mineralogy, morphology, and orientation, but differ from those in the outer shell layer. The process of ALPs formation is different to that of normal shell formation (e.g. nacre-prisms transition between prismatic and nacreous layers), remote biomineralization, extra shell thickening, as well as, shell repair, erosion, deformation or disease. Response to shell excavation by boring organisms is discussed as the reason for the appearance of ALPs.

  1. Life, Decay and Biosignatures of Lithobiontic Extremophiles

    Science.gov (United States)

    Souza-Egipsy, V.; Sun, H.; Nealson, K.

    2002-12-01

    Current knowledge of fossils of microorganisms as traces of microbial activity once present within terrestrial rocks is extremely scarce. The principal aim of this study is to improve the knowledge of endolithic tufa pinnacles microbial communities from Mono Lake, California. Futhermore, we study their death processes in situ to be able to find sign of past life in the mineral deposits. The study of microorganisms colonising the inside of lithic materials has been confronted with enormous difficulties. However, the advent of new scanning microscopy techniques with backscattered electron imaging (SEM-BSE) combined with an auxiliary X-ray energy dispersive spectroscopy (EDS) has implemented the methods for the study of lithobiontic microbial communities. This technique permits the chemical characterization of mineral features, and the observation of the ultrastructural characteristic of the cells without the need to remove them from their environment. The living endolithic biofilm of cyanobacteria serves as a nucleation site for aragonite crystals. After the decay of the filaments the growth of the crystals continues without the preservation of the organic material. Finally the aragonite crystals became embedded in a calcite matrix during the growth of the tufa pinnacle. In this ecosystem the formation of aragonite crystals surrounded by calcite is a biosignature not predicted to occur by abiotic process. The application of in situ microscopy methods permitted describe the relationship between biomineralization processes happening in the living biofilm and detecting traces of the past presence of the biofilm in geological materials.

  2. Facile Synthesis of Calcium Carbonate Nanoparticles from Cockle Shells

    Directory of Open Access Journals (Sweden)

    Kh. Nurul Islam

    2012-01-01

    Full Text Available A simple and low-cost method for the synthesis of calcium carbonate nanoparticles from cockle shells was described. Polymorphically, the synthesized nanoparticles were aragonites which are biocompatible and thus frequently used in the repair of fractured bone and development of advanced drug delivery systems, tissue scaffolds and anticarcinogenic drugs. The rod-shaped and pure aragonite particles of 30±5 nm in diameter were reproducibly synthesized when micron-sized cockle shells powders were mechanically stirred for 90 min at room temperature in presence of a nontoxic and nonhazardous biomineralization catalyst, dodecyl dimethyl betaine (BS-12. The findings were verified using a combination of analytical techniques such as variable pressure scanning electron microscopy (VPSEM, transmission electron microscopy (TEM, Fourier transmission infrared spectroscopy (FT-IR, X-ray diffraction spectroscopy (XRD, and energy dispersive X-ray analyser (EDX. The reproducibility and low cost of the method suggested that it could be used in industry for the large scale synthesis of aragonite nanoparticles from cockle shells, a low cost and easily available natural resource.

  3. Chemical-mechanical stability of the hierarchical structure of shell nacre

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The hierarchical structure and mechanical property of shell nacre are experimentally investigated from the new aspects of chemical stability and chemistry-mechanics coupling. Through chemical deproteinization or demineralization methods together with characterization techniques at micro/nano scales,it is found that the nacre of abalone,haliotis discus hannai,contains a hierarchical structure stacked with irregular aragonite platelets and interplatelet organic matrix thin layers. Yet the aragonite platelet itself is a nanocomposite consisting of nanoparticles and intraplatelet organic matrix framework. The mean diameter of the nanoparticles and the distribution of framework are quite different for different platelets. Though the interplatelet and in-traplatelet organic matrix can be both decomposed by sodium hydroxide solution,the chemical stability of individual aragonite platelets is much higher than that of the microstructure stacked with them. Further,macroscopic bending test or nanoindentation experiment is performed on the micro/nanostructure of nacre after sodium hydroxide treatment. It is found that the Young’s modulus of both the stacked microstructure and nanocomposite platelet reduced. The reduction of the microstructure is more remark than that of the platelet. Therefore the chemical-mechanical stability of the nanocomposite platelet itself is much higher than that of the stacked microstructure of nacre.

  4. Evidence of compositional and ultrastructural shifts during the development of calcareous tubes in the biofouling tubeworm, Hydroides elegans.

    Science.gov (United States)

    Chan, Vera Bin San; Vinn, Olev; Li, Chaoyi; Lu, Xingwen; Kudryavtsev, Anatoliy B; Schopf, J William; Shih, Kaimin; Zhang, Tong; Thiyagarajan, Vengatesen

    2015-03-01

    The serpulid tubeworm, Hydroides elegans, is an ecologically and economically important species whose biology has been fairly well studied, especially in the context of larval development and settlement on man-made objects (biofouling). Nevertheless, ontogenetic changes associated with calcareous tube composition and structures have not yet been studied. Here, the ultrastructure and composition of the calcareous tubes built by H. elegans was examined in the three early calcifying juvenile stages and in the adult using XRD, FTIR, ICP-OES, SEM and Raman spectroscopy. Ontogenetic shifts in carbonate mineralogy were observed, for example, juvenile tubes contained more amorphous calcium carbonate and were predominantly aragonitic whereas adult tubes were bimineralic with considerably more calcite. The mineral composition gradually shifted during the tube development as shown by a decrease in Sr/Ca and an increase of Mg/Ca ratios with the tubeworm's age. The inner tube layer contained calcite, whereas the outer layer contained aragonite. Similarly, the tube complexity in terms of ultrastructure was associated with development. The sequential appearance of unoriented ultrastructures followed by oriented ultrastructures may reflect the evolutionary history of serpulid tube biominerals. As aragonitic structures are more susceptible to dissolution under ocean acidification (OA) conditions but are more difficult to be removed by anti-fouling treatments, the early developmental stages of the tubeworms may be vulnerable to OA but act as the important target for biofouling control.

  5. A comparative study on effects of heterotrophic microbial activity on the stability of bivalve and coral carbonate during early diagenesis.

    Science.gov (United States)

    Lange, Skadi M.; Krause, Stefan; Immenhauser, Adrian; Ritter, Ann-Christin; Gorb, Stanislav N.; Kleinteich, Thomas; Treude, Tina

    2016-04-01

    Following deposition and shallow burial, marine biogenic carbonates are exposed to an environment that is geochemically affected by a manifold of bacterial metabolic redox processes. To allow for comparison of potential microbe-mediated alteration effects on carbonates, we used aragonitic bivalve shell samples and porous aragonitic coral fragments for incubation experiments in oxic- and anoxic seawater media. The media contained marine sediment slurries or bacterial cultures to mimic the natural processes in vitro. The results for anoxic experimental media containing bivalve shell samples or coral fragments displayed considerable changes in carbonate-system parameters (pH, AT, CA, DIC) and divalent-cation ratios (Mg/Ca, Mg/Sr, Sr/Ca) over time. Furthermore, incubated bivalve shell samples were altered in morphology, elemental composition and isotopic signature. Coral-fragment bearing oxic incubations were run at two temperature regimes and divalent-cation ratios of the high-temperature bacterial medium displayed withdrawal of Ca2+ and Sr2+ from the medium, thus indicating microbe-induced secondary aragonite precipitation. Analyses of coral fragments include electron-microprobe mapping and X-ray microtomography to resolve elemental sample composition and pore-space alteration features, respectively. Up to this point our results indicate that heterotrophic bacterial activity has the potential to affect surficial or open pore space in carbonate archives by increasing rates of alteration relative to sterile environments.

  6. The influence of Pacific Equatorial Water on fish diversity in the southern California Current System

    Science.gov (United States)

    McClatchie, Sam; Thompson, Andrew R.; Alin, Simone R.; Siedlecki, Samantha; Watson, William; Bograd, Steven J.

    2016-08-01

    The California Undercurrent transports Pacific Equatorial Water (PEW) into the Southern California Bight from the eastern tropical Pacific Ocean. PEW is characterized by higher temperatures and salinities, with lower pH, representing a source of potentially corrosive (aragonite,Ωfish diversity. We use hydrographic data to characterize the interannual and seasonal variability of estimated pH and aragonite saturation with depth. Although there is substantial variability in PEW presence as measured by spice on the 26.25-26.75 isopycnal layer, as well as in pH and aragonite saturation, we found fish diversity to be stable over the decades 1985-1996 and 1999-2011. We detected significant difference in species structure during the 1998 La Niña period, due to reduced species evenness. Species richness due to rare species was higher during the 1997/1998 El Niño compared to the La Niña but the effect on species structure was undetectable. Lack of difference in the species abundance structure in the decade before and after the 1997/1999 ENSO event showed that the assemblage reverted to its former structure following the ENSO perturbation, indicating resilience. While the interdecadal species structure remained stable, the long tail of the distributions shows that species richness increased between the decades consistent with intrusion of warm water with more diverse assemblages into the southern California region.

  7. Radon health hazards of some rocks of Iranian origin, frequently used as building stones

    International Nuclear Information System (INIS)

    Radon exhalation rate from various types of stones, used inside the living buildings, is a major factor for evaluation of the environmental radon level. To verify the significance and lethal impacts of this unknown and obscure source of radiation upon the people around the world, the exhaled radon gas concentrations from the rocks, granodiorite, granite, limestone and aragonite, and the effect of their block sizes on the exhalation rate, have been studied. The block samples, collected from their ores, were transferred to plastic containers in which the CR-39 detectors could properly be placed and air tightened, for concentration measurements. The results show the radon concentration of 7.4 ± 0.8, 6.6 ± 0.6, 0.08 ± 0.02 and 0.09 ± 0.02 kBq m-3 for granodiorite, granite, limestone and aragonite, respectively. The corresponding annual dose values in a closed environment are: 186 ± 20, 166 ± 15, 2.5 ± 1 and 2 ± 1 mSv y-1. These absorbed dose values indicate that granodiorite and granite when used inside the buildings could increase the risk of various cancers while aragonite and limestone have much lower risks and are recommended for use inside the buildings. The former ones when used in the closure areas remedial action should be implemented. The results do not show obvious dependence between the rock size of the samples and their radon exhalation rate. (author)

  8. The Impact of Seawater Saturation State on Early Skeletal Development in Larval Corals: Insights into Scleractinian Biomineralization

    Science.gov (United States)

    Cohen, A. L.; McCorkle, D. C.; de Putron, S.

    2007-12-01

    Understanding the response of coral calcification to changes in seawater saturation state (ocean acidification) could provide important insights into the fundamental processes of scleractinian biomineralization. In particular, larval calcification, which involves initiation of skeletogenesis by a previously non-calcifying planktonic planula, offers a unique opportunity to examine the role and limitations of biological control over an essentially physicochemical process. Larvae of the brooding Atlantic coral Favia fragum were settled in unmodified seawater onto clay tiles within 12h of spawning, and placed into non-through flow 30 L aquaria prior to initiation of calcification. Seawater chemistry was pre-adjusted via HCl addition and continuous bubbling with laboratory air, yielding four aragonite saturation states: Omega(aragonite) = 3.71 (unmodified), 2.4, 1.04, and 0.22. The aquaria were held at 25 °C on a 12h/12h light/dark cycle, and sets of tiles harvested at 1, 5 and 8 days post-spawning. Accretion of aragonite (confirmed by Raman spectroscopy) in all treatments indicates that the settled larvae were able to elevate the saturation state of aquarium seawater sequestered within their calcifying space. However, external aqueous carbonate chemistry had a striking effect on larval mortality, on the nature and timing of basal plate formation, on skeletal growth rates (based on the length and cross-sectional area of septa), and on the structure and organization of aragonite crystals within the septa (imaged using SEM). Larval survival rates at the two lower saturation states was only 40% of that in the control and Omega = 2.35 treatments, and skeletal growth decreased by 30 % (relative to the control) in seawater with saturation state comparable to that predicted for the mid-latitude surface ocean by 2100 AD. SEM imaging of the larval skeletons revealed significant differences in the morphology of aragonite crystals accreted under different conditions. In stark

  9. Red Sea isolation history suggested by Plio-Pleistocene seismic reflection sequences

    Science.gov (United States)

    Mitchell, Neil C.; Ligi, Marco; Rohling, Eelco J.

    2015-11-01

    High evaporation rates in the desert climate of the Red Sea ensure that, during glacial sea level lowstands when water exchange with the Indian Ocean was more restricted, water salinity and δ18 O became unusually extreme. Modeling of the effect on Red Sea sedimentary δ18 O has been used previously to reconstruct relative sea level to 500 ka and now poses the question of whether that sea-level model could be extended if continuous core material of older sediment became available. We attempt to address this question here by examining seismic reflection data. The upper Pleistocene hemipelagic sediments in the Red Sea contain intervals of inorganic aragonite precipitated during supersaturated conditions of sea-level lowstands. Seismic impedance changes associated with boundaries to those aragonite-rich layers appear to explain seismic reflection sequences. A segment of Chirp sediment profiler data from the central Red Sea reveals prominent reflections at ∼1, ∼5, ∼23, ∼26 and ∼36 ms two-way travel time (TWT) from the seabed. Based on depths to the glacial marine isotope stages (MIS) in cores, we relate the upper three reflections to the tops of aragonite-rich layers and hence the sea level rises immediately following MIS 2, 6 and 12. The reflection at 26 ms is related to an unusually rapid fall into MIS 12 predicted by one sea level reconstruction, which may have created an abrupt lower boundary to the MIS 12 aragonite-rich layer. With the aid of seismogram modeling, we tentatively associate the ∼36 ms reflection with the top of an aragonite-rich layer formed during MIS 16. Furthermore, some segments of lower frequency (airgun and sparker) seismic data from the central and southern Red Sea show a lower (earlier) Plio-Pleistocene (PP) interval that is less reflective than the upper (late) PP interval. This implies less variability in sediment impedance and that extreme variability in water salinity did not develop; water exchange with the Indian Ocean

  10. Strontium isotopes and rare-earth element geochemistry of hydrothermal carbonate deposits from Lake Tanganyika, East Africa

    Energy Technology Data Exchange (ETDEWEB)

    Barrat, J.A.; Boulegue, J.; Tiercelin, J.J.; Lesourd, M.

    2000-01-01

    At Cape Banza (North Tanganyika Lake), fluids and aragonite chimneys have been collected many times since the discovery of this sublacustrine field in 1987. This sampling has been investigated here for the Sr isotopic compositions and the rare-earth element features of the carbonates and a few fluid samples. The {sup 87}Sr/{sup 86}Sr ratios of the chimneys indicate that they have precipitated from a mixture of lake water (more than 95%) and hydrothermal fluids. No zoning in the chimneys was detected with the Sr data. For the rare-earth elements, the situation is more complex. The external walls of the chimneys are rare-earth-element-poor (La {approx} 500 ppb, Yb {approx} 200 ppb, La/Yb = 2 to 3.4). Their shale normalized rare-earth element patterns suggest that they are in equilibrium with the inferred carbonate-depositing fluids. The rare-earth element concentrations of the internal walls of the chimneys are significantly light rare earth elements (LREE)-enriched with La contents sometimes up to 5 ppm. The authors suggest that they contain more vent-fluid rare-earth elements than the external wall samples, possibly adsorbed on the surface of growing crystals or simply hosted by impurities. It was not possible to constrain the nature of these phases, but the variations of the compositions of the internal wall materials of the active chimneys with time, as well as data obtained on an inactive chimney indicate that this rare-earth element excess is mobile. Partition coefficients were calculated between the external wall aragonite and carbonate-depositing fluid. The results are strikingly similar to the values obtained by Sholkovitz and Shen (1995) on coral aragonite, and suggest that there is no significant biologic effect on the incorporation of rare-earth elements into coral aragonite and that the various carbonate complexes involved Me(CO{sub 3}{sup +}) complexes are the main LREE carriers in seawater instead of Me(CO{sub 3}){sub 2}{sup {minus}} in Banza fluids

  11. Bony fish and their contribution to marine inorganic carbon cycling

    Science.gov (United States)

    Salter, Michael; Perry, Chris; Wilson, Rod; Harborne, Alistair

    2016-04-01

    Conventional understanding of the marine inorganic carbon cycle holds that CaCO3 (mostly as low Mg-calcite and aragonite) precipitates in the upper reaches of the ocean and sinks to a point where it either dissolves or is deposited as sediment. Thus, it plays a key role controlling the distribution of DIC in the oceans and in regulating their capacity to absorb atmospheric CO2. However, several aspects of this cycle remain poorly understood and have long perplexed oceanographers, such as the positive alkalinity anomaly observed in the upper water column of many of the world's oceans, above the aragonite and calcite saturation horizons. This anomaly would be explained by extensive dissolution of a carbonate phase more soluble than low Mg-calcite or aragonite, but major sources for such phases remain elusive. Here we highlight marine bony fish as a potentially important primary source of this 'missing' high-solubility CaCO3. Precipitation of CaCO3 takes place within the intestines of all marine bony fish as part of their normal physiological functioning, and global production models suggest it could account for up to 45 % of total new marine CaCO3 production. Moreover, high Mg-calcite containing >25 % mol% MgCO3 - a more soluble phase than aragonite - is a major component of these precipitates. Thus, fish CaCO3 may at least partially explain the alkalinity anomaly in the upper water column. However, the issue is complicated by the fact that carbonate mineralogy actually varies among fish species, with high Mg-calcite (HMC), low Mg-calcite (LMC), aragonite, and amorphous calcium carbonate (ACC) all being common products. Using data from 22 Caribbean fish species, we have generated a novel production model that resolves phase proportions. We evaluate the preservation/dissolution potential of these phases and consider potential implications for marine inorganic carbon cycling. In addition, we consider the dramatic changes in fish biomass structure that have resulted

  12. Calcium Carbonate Formation by Genetically Engineered Inorganic Binding Peptides

    Science.gov (United States)

    Gresswell, Carolyn Gayle

    Understanding how organisms are capable of forming (synthesize, crystallize, and organize) solid minerals into complex architectures has been a fundamental question of biomimetic materials chemistry and biomineralization for decades. This study utilizes short peptides selected using a cell surface display library for the specific polymorphs of calcium carbonate, i.e., aragonite and calcite, to identify two sets of sequences which can then be used to examine their effects in the formation, crystal structure, morphology of the CaCO3 minerals. A procedure of counter selection, along with fluorescence microscopy (FM) characterization, was adapted to insure that the sequences on the cells were specific to their respective substrate, i.e., aragonite or calcite. From the resulting two sets of sequences selected, five distinct strong binders were identified with a variety of biochemical characteristics and synthesized for further study. Protein derived peptides, using the known sequences of the proteins that are associated with calcite or aragonite, were also designed using a bioinformatics-based similarity analysis of the two sets of binders. In particular, an aragonite binding protein segment, AP7, a protein found in nacre, was chosen for this design and the resulting effects of the designed peptides and the AP7 were examined. Specifically, the binding affinities of the selected and the protein derived peptides off the cells were then tested using FM; these studies resulted in different binding characteristics of the synthesized and cellular bound peptides. Two of the peptides that displayed strong binding on the cells bound to neither of the CaCO 3 substrates and both the high and low similarity protein-derived peptides bound to both polymorphs. However, two of the peptides were found to only bind to their respective polymorph showing; these results are significant in that with this study it is demonstrated that the designed peptides based on experimental library

  13. Resilience of cold-water scleractinian corals to ocean acidification: Boron isotopic systematics of pH and saturation state up-regulation

    Science.gov (United States)

    McCulloch, Malcolm; Trotter, Julie; Montagna, Paolo; Falter, Jim; Dunbar, Robert; Freiwald, André; Försterra, Günter; López Correa, Matthias; Maier, Cornelia; Rüggeberg, Andres; Taviani, Marco

    2012-06-01

    The boron isotope systematics has been determined for azooxanthellate scleractinian corals from a wide range of both deep-sea and shallow-water environments. The aragonitic coral species, Caryophyllia smithii, Desmophyllum dianthus, Enallopsammia rostrata, Lophelia pertusa, and Madrepora oculata, are all found to have relatively high δ11B compositions ranging from 23.2‰ to 28.7‰. These values lie substantially above the pH-dependent inorganic seawater borate equilibrium curve, indicative of strong up-regulation of pH of the internal calcifying fluid (pHcf), being elevated by ˜0.6-0.8 units (ΔpH) relative to ambient seawater. In contrast, the deep-sea calcitic coral Corallium sp. has a significantly lower δ11B composition of 15.5‰, with a corresponding lower ΔpH value of ˜0.3 units, reflecting the importance of mineralogical control on biological pH up-regulation. The solitary coral D. dianthus was sampled over a wide range of seawater pHT and shows an approximate linear correlation with ΔpHDesmo = 6.43 - 0.71pHT (r2 = 0.79). An improved correlation is however found with the closely related parameter of seawater aragonite saturation state, where ΔpHDesmo = 1.09 - 0.14Ωarag (r2 = 0.95), indicating the important control that carbonate saturation state has on calcification. The ability to up-regulate internal pHcf, and consequently Ωcf, of the calcifying fluid is therefore a process present in both azooxanthellate and zooxanthellate aragonitic corals, and is attributed to the action of Ca2+-ATPase in modulating the proton gradient between seawater and the site of calcification. These findings also show that the boron isotopic compositions (δ11Bcarb) of aragonitic corals are highly systematic and consistent with direct uptake of the borate species within the biologically controlled extracellular calcifying medium. We also show that the relatively strong up-regulation of pH and consequent elevation of the internal carbonate saturation state (Ωcf ˜8

  14. Gamma densitometry for the measurement of skeletal density

    Science.gov (United States)

    Chalker, B. E.; Barnes, D. J.

    1990-03-01

    A method is described for the measurement of the density of calcium carbonate materials from the attenuation of a narrow, collimated beam of gamma photons. For the measurement of density for slices, approximately 0.5 to 1.0 cm thick, from the skeletons of reef building corals, the optimum beam energy is 30 34 keV; and measurement is practical from approximately 22 to 100 keV. The potential utilities of five commercially available isotopic sources (109Cd,125I,253Gd,210Pb and241Am) are evaluated. Methods and results are presented for gamma densitometry using210Pb and241Am. The210Pb point source had its principal gamma emission at 46.5 keV. Bremsstrahlung and high energy (800 keV) gamma emissions associated with the210Pb decay grand-daughter were detected, and procedures were developed to accommodate the contribution of these emissions to the overall count rate. The attenuation of count rate by aluminium and aragonite absorbers closely followed simple theoretical considerations provided that narrow energy window settings were used at the radiation monitor. These theoretical considerations take account of the density of the material absorbing the radiation, and hence the density could be determined from the attenuation of the gamma beam. Increased accuracy was achieved by the use of241Am and high speed counting equipment.241Am has its principal gamma emission at 59.6 keV. The attenuation of this gamma beam follows simple theoretical considerations for targets with mass thicknesses from 0 to 6 g cm-2. Aragonite from the shell of a giant clam was found to have slightly different properties in the absorption of gamma photons to aragonite from a coral skeleton. The differences were small but statistically significant.

  15. Response of the Arctic pteropod Limacina helicina to projected future environmental conditions.

    Directory of Open Access Journals (Sweden)

    Steeve Comeau

    Full Text Available Thecosome pteropods (pelagic mollusks can play a key role in the food web of various marine ecosystems. They are a food source for zooplankton or higher predators such as fishes, whales and birds that is particularly important in high latitude areas. Since they harbor a highly soluble aragonitic shell, they could be very sensitive to ocean acidification driven by the increase of anthropogenic CO(2 emissions. The effect of changes in the seawater chemistry was investigated on Limacina helicina, a key species of Arctic pelagic ecosystems. Individuals were kept in the laboratory under controlled pCO(2 levels of 280, 380, 550, 760 and 1020 microatm and at control (0 degrees C and elevated (4 degrees C temperatures. The respiration rate was unaffected by pCO(2 at control temperature, but significantly increased as a function of the pCO(2 level at elevated temperature. pCO(2 had no effect on the gut clearance rate at either temperature. Precipitation of CaCO(3, measured as the incorporation of (45Ca, significantly declined as a function of pCO(2 at both temperatures. The decrease in calcium carbonate precipitation was highly correlated to the aragonite saturation state. Even though this study demonstrates that pteropods are able to precipitate calcium carbonate at low aragonite saturation state, the results support the current concern for the future of Arctic pteropods, as the production of their shell appears to be very sensitive to decreased pH. A decline of pteropod populations would likely cause dramatic changes to various pelagic ecosystems.

  16. Compositional variations at ultra-structure length scales in coral skeleton

    Science.gov (United States)

    Meibom, Anders; Cuif, Jean-Pierre; Houlbreque, Fanny; Mostefaoui, Smail; Dauphin, Yannicke; Meibom, Karin L.; Dunbar, Robert

    2008-03-01

    Distributions of Mg and Sr in the skeletons of a deep-sea coral ( Caryophyllia ambrosia) and a shallow-water, reef-building coral ( Pavona clavus) have been obtained with a spatial resolution of 150 nm, using the NanoSIMS ion microprobe at the Muséum National d'Histoire Naturelle in Paris. These trace element analyses focus on the two primary ultra-structural components in the skeleton: centers of calcification (COC) and fibrous aragonite. In fibrous aragonite, the trace element variations are typically on the order of 10% or more, on length scales on the order of 1-10 μm. Sr/Ca and Mg/Ca variations are not correlated. However, Mg/Ca variations in Pavona are strongly correlated with the layered organization of the skeleton. These data allow for a direct comparison of trace element variations in zooxanthellate and non-zooxanthellate corals. In both corals, all trace elements show variations far beyond what can be attributed to variations in the marine environment. Furthermore, the observed trace element variations in the fibrous (bulk) part of the skeletons are not related to the activity of zooxanthellae, but result from other biological activity in the coral organism. To a large degree, this biological forcing is independent of the ambient marine environment, which is essentially constant on the growth timescales considered here. Finally, we discuss the possible detection of a new high-Mg calcium carbonate phase, which appears to be present in both deep-sea and reef-building corals and is neither aragonite nor calcite.

  17. Late Quaternary sea level and environmental changes from relic carbonate deposits of the western margin of India

    Indian Academy of Sciences (India)

    V Purnachandra Rao; G Rajagopalan; K H Vora; F Almeida

    2003-03-01

    Relic carbonate deposits along the western margin of India occur as dolomite crusts, aragonite sands (pelletal / oolitic) and aragonite-cemented limestones, oyster shells, corals, encrusted coralline algal and foraminiferal-dominated nodules. The petrology and mineralogy of the deposits indicate that except for aragonite sands and foraminiferal nodules, the others were formed in shallow marine conditions and serve as sea level indicators. Radiocarbon dates were measured for 62 relic deposits covering the entire margin. The age of these deposits on the continental shelf off Cape Comorin and Mangalore, between 110 and 18m depth, ranges between 12, 610 14C yr BP and 6,390 14C yr BP. On the northwestern margin of India, especially on the carbonate platform (between 64 and 100 m), the age ranges from 17,250 to 6,730 14C yr BP. The relic deposits of the Gulf of Kachchh at depths between 35 and 25m are dated at 12,550-9,630 14C yr BP. The age vs. depth plot of the relic deposits further indicates that the Gulf of Kachchh was inundated much early, atleast by 15 ka, after the Last Glacial Maximum, and was subjected to uplift and subsidence during the Holocene. The carbonate platform subsided during the early Holocene. Some of the relic deposits between Cape Comorin and Mangalore plot on or, closely follow the glacio-eustatic sea level curve. Despite abundant siliciclastic flux discharged by the Narmada and Tapti during the early Holocene, the platform off these rivers is largely devoid of this flux and carbonate sedimentation continued until 6,700 14C yr BP. We suggest that the river-derived ediment flux diverted southwards under the influence of the SW monsoon current and, thereby, increased the turbidity on the shelf and slope southeast of the carbonate platform and facilitated the formation of deeper water foraminiferal nodules off Vengurla-Goa.

  18. New Climate Reconstruction Method Well Suited To The Last Centuries: The Coral Exemple

    Science.gov (United States)

    Juillet-Leclerc, A.

    2005-12-01

    Reconstructions of environmental parameters conducted to elucidate the climatic changes of the last centuries obey to specific constraints leading to specific methodology. These investigations essentially require high resolution (from seasonal to interannual resolution), quantitative and well dated records. It supposes the improvement and the development of several proxies, based on non-empirical transfer functions and examined with new statistical approaches. The tool that I developed derived from coral skeleton responds to these conditions. First, coral aragonite offers natural features: growth bands visible on X-ray pictures allow an easy and rapid chronology, the mean annual growth of Porites (species commonly used for paleoclimatic purpose) of more than 1 cm per year insures at least a monthly sampling, the geochemical tracers of aragonite are used for a long time. By combining biological, bio-crystallization and geochemical understanding, I can demonstrate that in opposite with the interpretation commonly used, the coral skeleton deposit is essentially governed by kinetic processes. In addition, following time and space scales, coral presents successive growth units driving to different significance for monthly and annual proxies. On the other hand, this understanding highlights the limits of the tool: for example, the highest resolution is limited to monthly sample. Up to now, the interpretation is restricted to interannual signals. Future experiments conducted on cultured corals are planned to provide evidences to identify the factors forcing the seasonal variability. Since the aragonite deposition is more complex than it was earlier supposed, the proxy signals are not linear versus time. The neural network approach, well suited to non-linear records, applied on several stable isotopes and trace elements provided realistic SST and SSS reconstructions in Fiji Island during the last century. This cross-disciplinary investigation may be achieved only through

  19. Nanometric inclusions of carbonates in Kokchetav diamonds from Kazakhstan: A new constraint for the depth of metamorphic diamond crystallization

    Science.gov (United States)

    Dobrzhinetskaya, Larissa F.; Wirth, Richard; Green, Harry W.

    2006-03-01

    Previous studies have revealed that microdiamonds from the Kokchetav ultra-high pressure metamorphic terrane of Kazakhstan contain nanometric scale inclusions of Si-, Fe-, Ti-, and Cr-oxides. Because the structure of SiO 2 inclusions was not confirmed to be coesite or stishovite due to their very small size, such diamonds formerly served only as an indicator of a minimum pressure, ca. 4 GPa. Geothermobarometry applied to Kokchetav diamond-bearing rocks yielded a wide range of conditions: T = 700 °C-1250 °C, and P = 4-9 GPa. Our paper presents transmission electron microscopy studies with focused ion beam assistance that indicate that diamonds from marbles contain inclusions of aragonite (CaCO 3) and magnesite (MgCO 3), and that aragonite and nitrogen-bearing nanometric particles are associated with dislocations reflecting diamond growth at relatively high-temperature conditions. We determined the boundary of dolomite stability using the reaction CaMg(CO 3) 2 (dolomite) = CaCO 3 (aragonite) + MgCO 3. This allowed us to utilize available experimental data to evaluate the pressure at which diamond was crystallized. Taking into consideration uncertainties existing between experimental data produced in different laboratories, we propose the pressure for Kokchetav diamond crystallization to be ˜ 6 to 9 GPa. This evaluation is based on the assumption that temperature was determined correctly as 980 °C (minimum) and 1250 °C (maximum) for diamond-grade dolomitic marbles. Our data provide strong evidence that the metasedimentary rocks of the Kokchetav massif containing diamonds were subducted to the depth of ˜ 190-280 km.

  20. Ca-Mg inter-diffusion in synthetic polycrystalline dolomite-calcite aggregate at elevated temperatures and pressure

    Science.gov (United States)

    Huang, Wuu-Liang; Liu, Teh-Ching; Shen, Pouyan; Hsu, Allen

    2009-03-01

    This study measures the reaction rate of dolomite and aragonite (calcite) into Mg-calcite at 800, 850, and 900°C and 1.6 GPa. The dry synthetic dolomite-aragonite aggregate transformed very rapidly into dolomite-calcite polycrystalline aggregate while Mg-calcites formed at a relatively slow rate, becoming progressively richer in Mg with run time. We modeled the reaction progress semi-empirically by the first-order rate law. The temperature dependence of the overall transport rate of MgCO3 into calcite can be described by the kinetic parameters ( E = 231.7 kJ/mol and A o = 22.69 h-1). Extrapolation using the Arrhenius equation to the conditions during exhumation of UHPM rocks indicates that the reaction of dolomite with aragonite into Mg-saturated calcite can be completed as the P-T path enters the Mg-calcite stability field in a geologically short time period (340°C and >10 My). SEM-EDS analysis of individual calcite grains shows compositional gradients of Mg in the calcite grains. The Mg-Ca inter-diffusion coefficient at 850°C is around 1.68 × 10-14 m2/sec if diffusion is the major control of the reaction. The calculated closure temperatures for Ca-Mg inter-diffusion as a function of cooling rate and grain size reveal that Ca/Mg resetting in calcite in a dry polycrystalline carbonate aggregate (with grain size around 1 mm) may not occur at temperatures below 480°C at a geological cooling rate around 10°C/My, unless other processes, such as short-circuit interdiffusion along grain boundaries and dislocations, are involved.

  1. Bivalves build their shells from amorphous calcium carbonate

    Science.gov (United States)

    Jacob, D. E.; Wirth, R.; Soldati, A. L.; Wehrmeister, U.

    2012-04-01

    One of the most common shell structures in the bivalve class is the prism and nacre structure. It is widely distributed amongst both freshwater and marine species and gives cultured pearls their sought-after lustre. In freshwater bivalves, both shell structures (prism and nacre) consist of aragonite. Formation of the shell form an amorphous precursor phase is a wide-spread strategy in biomineralization and presents a number of advantages for the organisms in the handling of the CaCO3 material. While there is already evidence that larval shells of some mollusk species use amorphous calcium carbonate (ACC) as a transient precursor phase for aragonite, the use of this strategy by adult animals was only speculated upon. We present results from in-situ geochemistry, Raman spectroscopy and focused-ion beam assisted TEM on three species from two different bivalve families that show that remnants of ACC can be found in shells from adult species. We show that the amorphous phase is not randomly distributed, but is systematically found in a narrow zone at the interface between periostracum and prism layer. This zone is the area where spherulitic CaCO3- structures protrude from the inner periostracum to form the initial prisms. These observations are in accordance with our earlier results on equivalent structures in freshwater cultured pearls (Jacob et al., 2008) and show that the original building material for the prisms is amorphous calcium carbonate, secreted in vesicles at the inner periostracum layer. Quantitative temperature calibrations for paleoclimate applications using bivalve shells are based on the Mg-Ca exchange between inorganic aragonite (or calcite) and water. These calibrations, thus, do not take into account the biomineral crystallization path via an amorphous calcium carbonate precursor and are therefore likely to introduce a bias (a so-called vital effect) which currently is not accounted for. Jacob et al. (2008) Geochim. Cosmochim. Acta 72, 5401-5415

  2. Unique morphology and gradient arrangement of nacre's platelets in green mussel shells

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Jun; Zhang, Gangsheng, E-mail: zhanggs@gxu.edu.cn

    2015-07-01

    Nacre has long served as a classic model in biomineralization and the synthesis of biomimetic materials. However, the morphology and arrangement of its basic building blocks, the aragonite platelets, are still under hot debate. In this study, using a field emission scanning electron microscope (SEM), a high-resolution transmission electron microscope (HRTEM), and an X-ray diffractometer (XRD), we investigate the platelets at the edges and centers of green mussel shells. We find that 1) flat and curved platelets coexist in green mussel shells; 2) the immature platelets at the shell edge are aggregates of aragonite nanoparticles, whereas the immature ones at the shell center are single crystals; and 3) the morphology and thickness of the platelets exhibit a gradient arrangement. Based on these findings, we hypothesize that the gradient in the thickness and curvature of the platelets may probably result from the difference in growth rate between the edge and the center of the shell and from the gradient in compressive stress imposed by the closing of the shells by the adductor muscles or the withdrawal of the periostracum by the mantle. We expect that the presented results will shed new light on the formation mechanisms of natural composite materials. - Highlights: • Flat and curved platelets coexist in green mussel shells. • The immature platelets at the shell edge consist of aragonite nanoparticles. • The immature platelets at the shell center are single crystals. • The morphology and thickness of platelets exhibit a gradient arrangement. • The gradient arrangement of platelets may result from the stress gradient.

  3. Unique morphology and gradient arrangement of nacre's platelets in green mussel shells

    International Nuclear Information System (INIS)

    Nacre has long served as a classic model in biomineralization and the synthesis of biomimetic materials. However, the morphology and arrangement of its basic building blocks, the aragonite platelets, are still under hot debate. In this study, using a field emission scanning electron microscope (SEM), a high-resolution transmission electron microscope (HRTEM), and an X-ray diffractometer (XRD), we investigate the platelets at the edges and centers of green mussel shells. We find that 1) flat and curved platelets coexist in green mussel shells; 2) the immature platelets at the shell edge are aggregates of aragonite nanoparticles, whereas the immature ones at the shell center are single crystals; and 3) the morphology and thickness of the platelets exhibit a gradient arrangement. Based on these findings, we hypothesize that the gradient in the thickness and curvature of the platelets may probably result from the difference in growth rate between the edge and the center of the shell and from the gradient in compressive stress imposed by the closing of the shells by the adductor muscles or the withdrawal of the periostracum by the mantle. We expect that the presented results will shed new light on the formation mechanisms of natural composite materials. - Highlights: • Flat and curved platelets coexist in green mussel shells. • The immature platelets at the shell edge consist of aragonite nanoparticles. • The immature platelets at the shell center are single crystals. • The morphology and thickness of platelets exhibit a gradient arrangement. • The gradient arrangement of platelets may result from the stress gradient

  4. Distribution of total alkalinity and pH in the Ross Sea (Antarctica waters during austral summer 2008

    Directory of Open Access Journals (Sweden)

    Paola Rivaro

    2014-10-01

    Full Text Available Measurements of total alkalinity (AT and pH were made in the Ross Sea in January–February 2008 in order to characterize the carbonate system in the Ross Sea and to evaluate the variability associated with different water masses. The main water masses of the Ross Sea, Antarctic Surface Water, High Salinity Shelf Water (HSSW, Deep Ice Shelf Water, Circumpolar Deep Water (CDW and Antarctic Bottom Water, were identified on the basis of the physical and chemical data. In particular, the AT ranged between 2275 and 2374 µmol kg−1 with the lowest values in the surface waters (2275–2346 µmol kg−1, where the influence of the sea-ice melting and of the variability of the physical properties was significant. In the deep layers of the water column, the AT maxima were measured in correspondence to the preferential pathways of the spreading HSSW. The pH had variable values in the surface layer (7.890–8.033 with the highest values in Terra Nova Bay and Ross Sea polynyas. A low pH (7.969±0.025 traced the intrusion of the CDW in the Ross Sea shelf area. All samples revealed waters that were oversaturated with respect to both calcite and aragonite, but near corrosive levels of aragonite saturation state (Ω ca. 1.1–1.2 were associated with the entrainment of CDW over the slope. Aragonite undersaturation is of particular concern for the zooplankton species comprising to calcifying organisms such as pteropods. The partial pressure of CO2 at the sea surface was undersaturated with respect to the atmospheric value, particularly in Terra Nova Bay and the Ross Sea polynyas, but a large variability in the sea–air CO2 fluxes was observed associated with different responses in the strength of the biological and physical processes.

  5. Black Mn-Fe crusts as markers of abrupt palaeoenvironmental changes in El Soplao Cave (Cantabria, Spain

    Directory of Open Access Journals (Sweden)

    Gazquez Fernando

    2011-07-01

    Full Text Available Peculiar iron and manganese deposits coating walls, floors and ceilings of many galleries are one of the special features of the ElSoplao Cave (Cantabria, Spain. These speleothems appear to have been deposited over wall clay deposits, as well as formingpart of flowstones. Structure of crusts is essentially amorphous but several manganese and iron oxides were identified like goethiteand birnessite, though all occur with a low degree of crystallinity. In the outer layer of the crusts, alteration iron minerals appear thatderive from previous minerals in a process probably mediated by microorganisms. EDX microanalyses report fairly high values of Feand Mn in the crusts, though the Mn/Fe ratio varies considerably as a function of distance from the substrate/bedrock. The presentstudy proposes a genetic model for crust speleothems in El Soplao, based on oscillations of the phreatic level. The origin of thesedeposits is related to mobilization, under phreatic conditions, of polymetallic sulfides in the host rock. Metal ions (including Fe²+ andMn²+ released into the cave under reducing conditions, are oxidized and fixed in a process mediated by bacteria, giving rise to oxidesand hydroxides of low crystallinity. The presence of various black intercalated layers in aragonite flowstones indicate periods whencave conditions suddenly changed from vadose, when aragonite is precipitated, to phreatic and epiphreatic conditions, when theMn-Fe deposits are precipitated. Subsequently, vadose conditions were re-established, leading to the final stages of precipitation ofaragonite recorded in the flowstone and recent aragonite helictites on the surface of the Mn-Fe crusts.

  6. The influence of temperature and seawater carbonate saturation state on 13C–18O bond ordering in bivalve mollusks

    Directory of Open Access Journals (Sweden)

    R. A. Eagle

    2013-07-01

    Full Text Available The shells of marine mollusks are widely used archives of past climate and ocean chemistry. Whilst the measurement of mollusk δ18O to develop records of past climate change is a commonly used approach, it has proven challenging to develop reliable independent paleothermometers that can be used to deconvolve the contributions of temperature and fluid composition on molluscan oxygen isotope compositions. Here we investigate the temperature dependence of 13C–18O bond abundance, denoted by the measured parameter Δ47, in shell carbonates of bivalve mollusks and assess its potential to be a useful paleothermometer. We report measurements on cultured specimens spanning a range in water temperatures of 5 to 25 °C, and field collected specimens spanning a range of −1 to 29 °C. In addition we investigate the potential influence of carbonate saturation state on bivalve stable isotope compositions by making measurements on both calcitic and aragonitic specimens that have been cultured in seawater that is either supersaturated or undersaturated with respect to aragonite. We find a robust relationship between Δ47 and growth temperature. We also find that the slope of a linear regression through all the Δ47 data for bivalves plotted against seawater temperature is significantly shallower than previously published inorganic and biogenic carbonate calibration studies produced in our laboratory and go on to discuss the possible sources of this difference. We find that changing seawater saturation state does not have significant effect on the Δ47 of bivalve shell carbonate in two taxa that we examined, and we do not observe significant differences between Δ47-temperature relationships between calcitic and aragonitic taxa.

  7. Imminent ocean acidification projected with the NCAR global coupled carbon cycle-climate model

    Directory of Open Access Journals (Sweden)

    M. Steinacher

    2008-11-01

    Full Text Available Ocean acidification from the uptake of anthropogenic carbon is simulated for the industrial period and IPCC SRES emission scenarios A2 and B1 with a global coupled carbon cycle-climate model. Earlier studies identified seawater saturation state with respect to aragonite, a mineral phase of calcium carbonate, as a key variable governing impacts on corals and other shell-forming organisms. Globally in the A2 scenario, water saturated by more than 300%, considered suitable for coral growth, vanishes by 2070 AD (CO2≈630 ppm, and the ocean volume fraction occupied by saturated water decreases from 42% to 25% over this century. The largest simulated pH changes worldwide occur in Arctic surface waters, where hydrogen ion concentration increases by up to 185%. Projected climate change amplifies the decrease in Arctic surface mean saturation and pH by more than 20%, mainly due to freshening and increased carbon uptake in response to sea ice retreat. Modeled saturation compares well with observation-based estimates along an Arctic transect and simulated changes have been corrected for remaining model-data differences in this region. Aragonite undersaturation in Arctic surface waters is projected to occur locally soon and to become more widespread as atmospheric CO2 continues to grow. The results imply that surface waters in the Arctic Ocean will become corrosive to aragonite, with potentially large implications for the marine ecosystem, if anthropogenic carbon emissions are not reduced and atmospheric CO2 not kept below 450 ppm.

  8. Imminent ocean acidification in the Arctic projected with the NCAR global coupled carbon cycle-climate model

    Directory of Open Access Journals (Sweden)

    M. Steinacher

    2009-04-01

    Full Text Available Ocean acidification from the uptake of anthropogenic carbon is simulated for the industrial period and IPCC SRES emission scenarios A2 and B1 with a global coupled carbon cycle-climate model. Earlier studies identified seawater saturation state with respect to aragonite, a mineral phase of calcium carbonate, as a key variable governing impacts on corals and other shell-forming organisms. Globally in the A2 scenario, water saturated by more than 300%, considered suitable for coral growth, vanishes by 2070 AD (CO2≈630 ppm, and the ocean volume fraction occupied by saturated water decreases from 42% to 25% over this century. The largest simulated pH changes worldwide occur in Arctic surface waters, where hydrogen ion concentration increases by up to 185% (ΔpH=−0.45. Projected climate change amplifies the decrease in Arctic surface mean saturation and pH by more than 20%, mainly due to freshening and increased carbon uptake in response to sea ice retreat. Modeled saturation compares well with observation-based estimates along an Arctic transect and simulated changes have been corrected for remaining model-data differences in this region. Aragonite undersaturation in Arctic surface waters is projected to occur locally within a decade and to become more widespread as atmospheric CO2 continues to grow. The results imply that surface waters in the Arctic Ocean will become corrosive to aragonite, with potentially large implications for the marine ecosystem, if anthropogenic carbon emissions are not reduced and atmospheric CO2 not kept below 450 ppm.

  9. Coral resilience to ocean acidification and global warming through pH up-regulation

    OpenAIRE

    McCulloch, Malcolm; Falter, Jim; Trotter, Julie; Montagna, Paolo

    2012-01-01

    Rapidly rising levels of atmospheric CO2 are not only causing ocean warming, but also lowering seawater pH hence the carbonate saturation state of the oceans, on which many marine organisms depend to calcify their skeletons(1,2). Using boron isotope systematics(3), we show how scleractinian corals up-regulate pH at their site of calcification such that internal changes are approximately one-half of those in ambient seawater. This species-dependent pH-buffering capacity enables aragonitic cora...

  10. Minor element partitioning and mineralogy in limpets from the Ischia CO2 vent site

    Science.gov (United States)

    Langer, Gerald; Sadekov, Aleksey; Nehrke, Gernot; Baggini, Cecilia; Rodolfo-Metalpa, Riccardo; Hall-Spencer, Jason; Bijma, Jelle; Elderfield, Henry

    2015-04-01

    Specimens of the patellogastropod limpet Patella caerulea were collected within and outside a CO2 vent site at Ischia, Italy. The shells were sectioned transversally and scanned for polymorph distribution by means of confocal Raman microscopy. Minor element to calcium ratios were measured using laser-ablation-inductively-coupled-plasma-mass-spectroscopy (LA-ICPMS). Mg/Ca, Sr/Ca, and Li/Ca ratios were determined in calcitic as well as aragonitic parts of the shells. This approach allows for investigating the effects of the polymorph and the seawater carbonate chemistry on minor element partitioning separately.

  11. Microbial dolomite crusts from the carbonate platform off western India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Kessarkar, P.M.; Krumbein, W.E.; Krajewski, K.P.; Schneider, R.J.

    up to a water depth of 110 m. The inner shelf is a clastic depocentre - the Dahanu depression - in which Narmada and Tapti River-derived sediments have been deposited since the Eocene. The sediments on the platform are largely faecal pellet... of the platform (see Fig. 1). Aragonite faecal pellets, fragments of corals, bivalves and bryozoans compose the coarse fraction of the sediments (Rao et aI., 1994). Dark-grey clayey sands were recovered at 64 ill water depth in a seaward depression of the fringing...

  12. Lime muds and their genesis off-Northwestern India during the late Quaternary

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; AnilKumar, A.; Naqvi, S.W.A.; Chivas, A.R.; Sekar, B.; Kessarkar, P.M.

    . ‘drowned platform’. The relic deposits on the plat- form consist of abundant aragonite faecal pellets, ooids, Halimeda grains and a few bivalves, benthic and planktic foraminifers (Rao and Wagle 1997; Rao et al 1994). Also present are indurated arag- onite... muds, Halimeda- and pelletal limestones, coralline algal nodules, minor coral fragments, oys- ter shells and dolomite encrustations (Nair 1971; Nair et al 1979; Rao et al 1994, 2003). The radio- carbon ages of the above largely range between 12,940 14 C...

  13. Monitoring of heavy metal partitioning in reef corals of Lakshadweep Archipelago, Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Anu, G.; Kumar, N.C.; Jayalakshmy, K.V.; Nair, S.M.

    of St. John (1974) is used here to describe various forms of corals selected for this study. (1). Massive corals: - They form more or less thick masses or heads. In this study, P. andrewsi, be- longing to family Poritidae comes under this classification..., which supports the idea that corals discriminate against metals in their bio- genic precipitation of the aragonite skeleton (St. John, 1974). The trend was exactly reversed in the massive form (P. andrewsi) where K D values for all the met- als were less...

  14. Speleothem microstructure/speleothem ontogeny: a review of Western contributions

    Directory of Open Access Journals (Sweden)

    White William B.

    2012-07-01

    Full Text Available Mineral ontogeny is the study of the growth and development of mineral deposits in general and, in the present context, speleothems in particular. Previous researchers, mainly in Russia, have developed a nomenclatural hierarchy based on the forms and habits of individual crystals and the assembly of individual crystals into both monomineralic and polymineralic aggegates (i.e. speleothems. Although investigations of the growth processes of speleothems are sparse, there is a large literature on growth processes of speleothem minerals and related crystals in the geochemical and materials science literature. The purpose of the present paper is to sort through the various concepts of crystal growth and attempt to relate these to observations on speleothems and to the Russian conceptual framework of mineral ontogeny. For calcite, the most common mineral in speleothems, the activation energy for two dimensional nucleation (required for the growth of large single crystals is almost the same as the activation energy for three- dimensional nucleation (which would result in the growth of many small crystals. Calcite growth is highly sensitive to minor impurities that may poison growth in certain crystallographic directions or may poison growth altogether. Extensive recent research using the atomic force microscope (AFM provides many details of calcite growth including the transition from growth on screw dislocations to growth by two-dimensional nucleation. The deposition of aragonite speleothems requires metastable supersaturation curve and is usually ascribed to the impurities Mg2+ and Sr2+. AFM studies reveal that Mg2+ poisons calcite growth by blocking deposition sites on dislocations, thus allowing supersaturation to build up past the aragonite solubility curve. Sr2+ precipitates as a Sr-rich nucleus with the aragonite structure which acts as a template for aragonite growth. The different morphology of gypsum speleothems can be explained by the

  15. Spatiotemporal variability and long-term trends of ocean acidification in the California Current System

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    C. Hauri

    2012-08-01

    Full Text Available Due to seasonal upwelling, the upper ocean waters of the California Current System (CCS have a naturally low pH and aragonite saturation state (Ωarag, making this region particularly prone to the effects of ocean acidification. Here, we use the Regional Oceanic Modeling System (ROMS to conduct preindustrial and transient (1995–2050 simulations of ocean biogeochemistry in the CCS. The transient simulations were forced with increasing atmospheric pCO2 as projected by the NCAR CSM 1.4 model run under either the IPCC SRES A2 or B1 scenarios. Using ROMS, we investigate the timing of transition decades during which pH and Ωarag depart from their modeled preindustrial (1750 and present-day (2011 variability envelopes. We report these transition decades by noting the midpoint of the ten-year transition periods. In addition, we also analyze the timing of near permanent aragonite undersaturation in the upper 100 m of the water column. Our results show that an interplay of physical and biogeochemical processes create large seasonal variability in pH (∼ 0.14 and Ωarag (∼ 0.2. Despite this large variability, we find that present-day pH and Ωarag have already moved out of their preindustrial variability envelopes due to the rapidly increasing concentrations of atmospheric CO2. The simulations following the A2 emissions scenario suggest that nearshore surface pH of the northern and central CCS will move out of their present-day variability envelopes by 2045 and 2037, respectively. However, surface Ωarag of the northern and central CCS subregions are projected to depart from their present-day variability envelopes sooner, by 2030 and 2035, respectively. By 2025, the aragonite saturation horizon of the central CCS is projected to shoal into the upper 75 m for the duration of the annual cycle, causing near permanent undersaturation in subsurface waters. Overall, our

  16. Centuries of marine radiocarbon reservoir age variation within archaeological Mesodesma Donacium shells from Southern Peru

    Science.gov (United States)

    Jones, K.B.; Hodgins, G.W.L.; Etayo-Cadavid, M. F.; Andrus, C.F.T.; Sandweiss, D.H.

    2010-01-01

    Mollusk shells provide brief (Peru. The ranges in marine 14C ages (and thus R) from the 2 shells are 530 and 170 14C yr; R from individual aragonite samples spans 130 ?? 60 to 730 ?? 170 14C yr. This intrashell 14C variability suggests that 14C dating of small (time-slice much less than 1 yr) marine samples from a variable-R (i.e. variable-upwelling) environment may introduce centuries of chronometric uncertainty. ?? 2010 by the Arizona Board of Regents on behalf of the University of Arizona.

  17. Observations on the Solubility of Skeletal Carbonates in Aqueous Solutions.

    Science.gov (United States)

    Chave, K E; Deffeyes, K S; Weyl, P K; Garrels, R M; Thompson, M E

    1962-07-01

    Carbonate skeletal materials of marine organisms exhibit a wide range of solubilities in aqueous solutions. In most cases, the dissolution of the carbonate mineral is irreversible and therefore the material can have no true equilibrium solubility. Relative solubilities have been measured in distilled water and in sea water. The least soluble mineral appears to be calcite with low magnesium content; the most soluble is calcite containing 20 to 30 percent MgCO(3) in solid solution. Aragonite has an intermediate solubility. PMID:17774123

  18. Minerals from Macedonia IV.Discrimination between some carbonate minerals by FTIR spectroscopy

    OpenAIRE

    Jovanovski, Gligor; Stefov, Viktor; Shoptrajanov, Bojan; Boev, Blazo

    2002-01-01

    The use of FTIR spectroscopy to distinguish between some geologically im­portant carbonate minerals (calcite - CaCO3), aragonite - CaCO3, siderite - FeCO3, magnesite - MgCO3, and dolomite - CaMg(CO3)2 originating from Macedonia and to detect mineral impurities in them is considered. 1t was shown that the series of the studied isomorphous calcite type minerals is an ideal test case for the evaluating the in­fluence of the corresponding cation upon the band frequencies or the carbonate ...

  19. Coral Skeleton Density Banding: Biotic Response to Changes in Sea Surface Temperature

    Science.gov (United States)

    Hill, C. A.; Sivaguru, M.; Fried, G. A.; Fouke, B. W.

    2010-12-01

    Density bands in the CaCO3 (aragonite) skeleton of scleractinian corals are commonly used as chronometers, where crystalline couplets of high and low density bands represent the span of one year. Isotopic analysis of these density bands provides a sensitive reconstructive tool for paleoclimatology and paleoecology. However, the detailed biotic mechanisms controlling coral skeleton aragonite nucleation and crystallization events and resulting skeletal growth rate remain uncertain. The coral tissue organic matrix, composed of macromolecules secreted by the calicoblastic ectoderm, is closely associated with skeletal precipitation and is itself incorporated into the skeleton. We postulate that density banding is primarily controlled by changes in the rate of aragonite crystal precipitation mediated by the coral holobiont response to changes in sea surface temperature (SST). To test this hypothesis, data were collected from coral skeleton-tissue biopsies (2.5 cm in diameter) extracted from four species of Montastraea growing on the fringing reef tract of Curacao, Netherlands Antilles. Annual mean variation in SST on Curacao range from 29o in mid-September to 26o C in late February. Samples were collected at strategic time periods spanning the 3o C annual variations in SST. Our nanometer-scale optical analyses of skeletal morphology have revealed consistent changes between high- and low-skeletal density bands, resulting in an 11% increase in the volume of aragonite precipitated in high-density skeletal bands. The re-localization and/or change in abundance of mucus, carbonic anhydrase (a molecule that catalyzes the hydration of carbon dioxide), calmodulin (a calcium-binding protein) and the change in density of gastrodermal symbiotic dinoflagellates has permitted estimates of seasonally-fluctuating carbon allocation by the coral holobiont in response to changing environmental conditions. This digital reconstruction of over 2000 images of one-micron-thick histological

  20. Photothermal characterization of thermally treated shells of Strombus Gigas

    Science.gov (United States)

    Hernández-Ayala, A.; Quintana, P.; Alvarado-Gil, J. J.; Aldana, D.

    2005-06-01

    The thermal properties of the marine shells of the mollusk Strombus gigas are studied using photoacoustic techniques. In order to generate changes in the layered structure of the shells, they were thermally treated in the range from ambient temperature up to 400ºC. Our results show that the thermal diffusivity and conductivity have a maximum at 200ºC due to the degradation of the organic matrix. At higher temperatures the thermal diffusivity and conductivity decrease due to the calcium carbonate structural phase transition from aragonite to calcite.

  1. Mesures conjointes des rapports Sr/Ca et δ 18O effectuées sur Acropora nobilis et Pontes lutea: le paléothermomètre Sr/Ca est-il toujours fiable?

    Science.gov (United States)

    Boiseau, Muriel; Cornu, Hélène; Turpin, Laurent; Juillet-Leclerc, Anne

    1997-11-01

    We measured the Sr/Ca and 18O/ 16O ratios in Acropora nobilis and Porites lutea, from the Mayotte lagoon. As the variations of δ 18O seawater are negligible, coral δ 18O aragonite reflects only seasonal temperature variations. While there is a good agreement between the Sr/Ca ratio and δ 18O for Acropora nobilis, it is not the case for Porites lutea. Coral biological and environmental parameters cannot explain the discrepancies between Sr/Ca ratios and isotopic measurements. However, transport mechanisms of Sr 2+ and Ca 2+ and the presence of two mineralogical structures of strontium may affect the Sr/Ca ratio.

  2. Ediacaran Seepage-related Cloudina-Microbialites from Southern Namibia

    Science.gov (United States)

    Reitner, Joachim, , Dr

    2015-04-01

    Little is known about the lifestyle of the calcified tube organisms of the Cloudina group. This late Proterozoic group, whose overall morphology slightly resembles modern calcified worm tubes, were the first animals with calcified skeletons. The modern seep-related vestimentiferan worm tubes of Escarpia are composed of chitin; in few cases we note the beginning of CaCO3 (aragonite) mineralisation on the chitin surfaces. The calcified skeleton of C. hartmannae exhibits a more complicated microstructure. The calcareous skeleton, which was probably originally aragonitic, appears to be produced by a probably enzymatically controlled biomineralisation. Seilacher (1999) reconstructed the Cloudina group as typical soft bottom dwellers. Some millimeter-sized C. riemkeae specimens are indeed common in soft micritic, lagoonal carbonates. However, we have observed large C. hartmannae tubes inside very large (5-8 meters high, 30-50 cm in diameter) pillar-like microbialites ("organ-pipes") from the Zaris Mountains/Zebra River (Omkyk Member, Kuibis Subgroup, Nama Group). These microbialiates have a complex structure. The inner portions of these microbialites are formed by large, cm-sized recrystallized aragonitic spherulites covered by calcified microbial matter exhibiting a typical thrombolitic structure. The outer portions of the microbialites exhibit a typical stromatolitic structure. These "organ-pipe" microbialites strongly resemble the modern ones known from Lake Van and Mono Lake. In both modern cases the microbialites grow in extremely alkaline water located at sites where Ca2+-rich ground water is seeping in the lake water. Geochemical data, from the still Sr-rich neomorphic former aragonitic spherulites and all other noted carbonate phases, suggest that the microbialites from the Zaris Mountains in Namibia formed under comparable conditions. Cloudina is very common within the thrombolitic portion of the microbialites and the occurrence is definitely autochthonous

  3. Carbonate system in the water masses of the Southeast Atlantic sector of the Southern Ocean during February and March 2008

    Directory of Open Access Journals (Sweden)

    M. González-Dávila

    2011-05-01

    Full Text Available Carbonate system variables were measured in the South Atlantic sector of the Southern Ocean along a transect from South Africa to the southern limit of the Antarctic Circumpolar Current (ACC from February to March 2008. Eddies detached from the retroflection of the Agulhas Current increased the gradients observed along the fronts. Minima in the fugacity of CO2, fCO2, and maxima in pH on either side of the frontal zone were observed, noting that within the frontal zone fCO2 reached maximum values and pH was at a minimum.

    Vertical distributions of water masses were described by their carbonate system properties and their relationship to CFC concentrations. Upper Circumpolar Deep Water (UCDW and Lower Circumpolar Deep Water (LCDW offered pHT,25 values of 7.56 and 7.61, respectively. The UCDW also had higher concentrations of CFC-12 (>0.2 pmol kg−1 as compared to deeper waters, revealing that UCDW was mixed with recently ventilated waters. Calcite and aragonite saturation states (Ω were also affected by the presence of these two water masses with high carbonate concentrations. The aragonite saturation horizon was observed at 1000 m in the subtropical area and north of the Subantarctic Front. At the position of the Polar Front, and under the influence of UCDW and LCDW, the aragonite saturation horizon deepened from 800 m to 1500 m at 50.37° S, and reached 700 m south of 57.5° S. High latitudes proved to be the most sensitive areas to predicted anthropogenic carbon increase. Buffer coefficients related to changes in [CO2], [H+] and Ω with changes in dissolved inorganic carbon (CT and total alkalinity (AT offered minima values in the Antarctic Intermediate Water and UCDW layers. These coefficients suggest that a small increase in CT will sharply decrease the status of pH and carbonate saturation

  4. Inclined-cross Microstructure of Conch Shell

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    The microstructures of conch shell were observed with scanning electronic microscope (SEM),and a kind of inclined-cross microstructure of aragonite sheets was found. The maximal pull-out force of the inclined-cross microstructure was analyzed based on its representative model and compared with that of a conventional0°-structure. The experimental result indicates that the maximal pull-out force of the inclined-cross microstructure is markedly larger than that of the 0 °-structure.

  5. Methane Derived Authigenic Carbonates from the Upper Continental Margin of the Bay of Biscay (France)

    Science.gov (United States)

    Pierre, C.; Blanc-Valleron, M. M.; Dupré, S.

    2014-12-01

    Extensive seafloor carbonate pavements are present at water depth from 140 to 180 meters on the upper continental margin of the Bay of Biscay, 50 to 60 km away from the present-day coastline. They form at the seafloor meter-high sub-circular reliefs with a diameter from 10 m to 100 m that are surrounded by light brown silto-sandy unconsolidated sediments. All these structures are associated with active methane seeps that cover an area of 80km from N to S and up to 8km from W to E. These carbonates were sampled during the two cruises GAZCOGNE 1 (july-august 2013) and GAZCOGNE 2 (september 2013). The carbonate crusts are porous sandstones, dark brown to black by impregnation with Fe-Mn oxides/hydroxides. Subseafloor concretions are homogenous light to medium grey fine-grained sandstones. The bulk carbonate content varies in the range 36-42 weight %. The carbonate mineralogy is dominated by aragonite that cements the detrital grains whereas calcite comes from the biogenic carbonates. Dolomite occurs in significant amount in a few samples. Circular cavities of 5 to 10 µm of diameter in the carbonate cement represent traces of gas bubbles; smaller holes in the aragonite crystals are due to carbonate dissolution by CO2 issued from aerobic oxidation of methane. The oxygen isotopic compositions of the bulk carbonate (+1.7 to +4.5‰) and aragonite cement (-0.2 to +1.4‰) are lower than the values in equilibrium with the present-day temperature and salinity conditions. This indicates that the carbonate precipitated in mixtures of seawater and continental water, i.e. in a context of submarine groundwater discharge. The carbon isotopic compositions of the bulk carbonate (-51.9 to -38.2‰) and aragonite cement (-49.9 to -29.3‰) demonstrate that most carbon derived from methane oxidized as bicarbonate during microbial anaerobic oxidation of methane. The GAZCOGNE study is co-funded by TOTAL and IFREMER as part of the PAMELA (Passive Margin Exploration Laboratories

  6. Authigenic carbonate mineral formation in a latest Pleistocene palaeolake, Greece

    Science.gov (United States)

    Karageorgis, A. P.; Kanellopoulos, T. D.; Mavromatis, V.; Anagnostou, C. L.; Koutsopoulou, E.; Schmidt, M.; Pavlopoulos, K.; Tripsanas, E. K.; Hallberg, R. O.

    2012-12-01

    The Pagassitikos Gulf in Greece, is a semi-enclosed bay with maximum depth 102 m. According to the present-day bathymetric configuration and the sea level during the latest Pleistocene, the gulf would have been isolated from the open sea, forming a palaeolake since ~32 cal. ka B.P.. Initial visual inspection of sediment core B-4 (length, 258 cm), recovered from the deepest sector of the Pagassitikos Gulf, revealed evidence of a totally different depositional environment in the lowest part of the core: this contained light grey-coloured sediments, contrasting strongly with the overlain olive grey muds of the upper part. Multi-proxy analyses (mineralogy, geochemistry and scanning electron microscopy) showed the predominance of carbonate minerals (aragonite, dolomite and calcite) together with gypsum in the lowest part of the core. Additional evidence (δ18O and δ13C isotopes, and AMS 14C datings) suggest that carbonate mineral deposition can be attributed to autochthonous precipitation that took place in a saline palaeolake during the last glacial-early deglacial period. High δ18O values recorded in the lowest part of the core were associated with hypersaline and evaporative depositional environment. The most plausible explanation for the formation of the observed carbonate minerals directs to dolomite precipitation from hypersaline evaporating water bodies at low precipitation rates. Under varying weather conditions the precipitation of aragonite is favoured. Alternatively, high evaporation rates and gypsum formation, favouring an increase in Mg/Ca ratio, is proposed as a possible mechanism supporting authigenic dolomite precipitation. The lowest core sample to be AMS 14C dated provided an age of 19.53 cal. ka B.P. The palaeolake was presumably reconnected to the open sea at ~13.2 cal. ka B.P. during the last sea-level rise, marking the commencement of marine sedimentation characterised by the predominance of terrigenous aluminosilicates and fairly homogeneous

  7. XANES in Nanobiology

    Science.gov (United States)

    Metzler, Rebecca A.; Olabisi, Ronke M.; Abrecht, Mike; Ariosa, Daniel; Johnson, Christopher J.; Gilbert, Benjamin; Frazer, Bradley H.; Coppersmith, Susan N.; Gilbert, P. U. P. A.

    2007-02-01

    The combination of spectroscopy and microscopy enables unprecedented insights into the molecular and crystal structures of organic and inorganic materials, and their interfaces. This is relevant to the field of biomaterials in general and biominerals in particular. In this framework, we extensively analyzed various proteins, minerals and biominerals. Here we present two novel observations: x-ray absorption near-edge structure (XANES) spectroscopy at the carbon K-edge is sensitive to protein misfolding and aggregation into amyloid fibrils, and to the polar and azimuthal rotation of the CaCO3 polymorph aragonite.

  8. Outer organic layer and internal repair mechanism protects pteropod Limacina helicina from ocean acidification

    Science.gov (United States)

    Peck, Victoria L.; Tarling, Geraint A.; Manno, Clara; Harper, Elizabeth M.; Tynan, Eithne

    2016-05-01

    Scarred shells of polar pteropod Limacina helicina collected from the Greenland Sea in June 2012 reveal a history of damage, most likely failed predation, in earlier life stages. Evidence of shell fracture and subsequent re-growth is commonly observed in specimens recovered from the sub-Arctic and further afield. However, at one site within sea-ice on the Greenland shelf, shells that had been subject to mechanical damage were also found to exhibit considerable dissolution. It was evident that shell dissolution was localised to areas where the organic, periostracal sheet that covers the outer shell had been damaged at some earlier stage during the animal's life. Where the periostracum remained intact, the shell appeared pristine with no sign of dissolution. Specimens which appeared to be pristine following collection were incubated for four days. Scarring of shells that received periostracal damage during collection only became evident in specimens that were incubated in waters undersaturated with respect to aragonite, ΩAr≤1. While the waters from which the damaged specimens were collected at the Greenland Sea sea-ice margin were not ΩAr≤1, the water column did exhibit the lowest ΩAr values observed in the Greenland and Barents Seas, and was likely to have approached ΩAr≤1 during the winter months. We demonstrate that L. helicina shells are only susceptible to dissolution where both the periostracum has been breached and the aragonite beneath the breach is exposed to waters of ΩAr≤1. Exposure of multiple layers of aragonite in areas of deep dissolution indicate that, as with many molluscs, L. helicina is able to patch up dissolution damage to the shell by secreting additional aragonite internally and maintain their shell. We conclude that, unless breached, the periostracum provides an effective shield for pteropod shells against dissolution in waters ΩAr≤1, and when dissolution does occur the animal has an effective means of self-repair. We suggest

  9. Annually Laminated Speleothems: a Review

    Directory of Open Access Journals (Sweden)

    Baker Andy

    2008-10-01

    Full Text Available This review of annually laminated speleothems firstly considers the four types of annual laminae found within speleothems: fluorescentlaminae formed by annual variations in organic matter flux; visible or petrographic laminae, formed by annual variations in calcitetexture or fabric; calcite-aragonite couplets; and finally trace element laminae. The methods available to confirm the annual nature, or otherwise, of lamina deposition are reviewed. We consider the use of annual laminae in chronology building, with particular relevanceto palaeoclimate reconstructions. Finally, the use of annual lamina width as a palaeoclimate proxy is reviewed.

  10. Carbon and Oxygen Isotopic Composition of Surface-Sediment Carbonate in Bosten Lake (Xinjiang, China) and its Controlling Factors

    Institute of Scientific and Technical Information of China (English)

    ZHANG Chengjun; Steffen MISCHKE; ZHENG Mianping; Alexander PROKOPENKO; GUO Fangqin; FENG Zhaodong

    2009-01-01

    Bosten Lake is a mid-latitude lake with water mainly supplied by melting ice and snow in the Tianshan Mountains. The depositional environment of the lake is spatially not uniform due to the proximity of the major inlet and the single outlet in the western part of the lake. The analytical results show that the carbon and oxygen isotopic composition of recent lake sediments is related to this specific lacustrine depositional environment and to the resulting carbonate mineralogy. In the southwestern lake region between the Kaidu River inlet and the Kongqi River outlet, carbon isotope composition (δ13C) values of the carbonate sediment (-1‰ to -2‰) have no relation to the oxygen isotope composition of the carbonate (δ18O) values (-7‰ to -8‰), with both isotopes showing a low variability. The carbonate content is low (<20%). Carbonate minerals analyzed by X-ray diffraction are mainly composed of calcite, while aragonite was not recorded. The salinity of the lake water is low in the estuary region as a result of the Kaidu River inflow. In comparison, the carbon and oxygen isotope values are higher in the middle and eastern parts of the lake, with δ13C values between approximately +0.5‰ and +3‰, and δ18O values between -1‰ and -5‰. There is a moderate correlation between the stable oxygen and carbon isotopes, with a coefficient of correlation r of approximately 0.63. This implies that the lake water has a relatively short residence time. Carbonate minerals constitute calcite and aragonite in the middle and eastern region of the lake. Aragonite and Mg-calcite are formed at higher lake water salinity and temperatures, and larger evaporation effects. More saline lake water in the middle and eastern region of the lake and the enhanced isotopic equilibrium between water and atmospheric CO2 cause the correlating carbon and oxygen isotope values determined for aragonite and Mg-calcite. Evaporation and biological processes are the main reasons for the salinity

  11. Bioinspired Design of Building Materials for Blast and Ballistic Protection

    Directory of Open Access Journals (Sweden)

    Yu-Yan Sun

    2016-01-01

    Full Text Available Nacre in abalone shell exhibits high toughness despite the brittle nature of its major constituent (i.e., aragonite. Its specific structure is a major contributor to the energy absorption capacity of nacre. This paper reviews the mechanisms behind the performance of nacre under shear, uniaxial tension, compression, and bending conditions. The remarkable combination of stiffness and toughness on nacre can motivate the development of bioinspired building materials for impact resistance applications, and the possible toughness designs of cement-based and clay-based composite materials with a layered and staggered structure were discussed.

  12. Lake Qinghai, China

    OpenAIRE

    Yu, Junqing

    2006-01-01

    Lake Qinghai lies on the northeast corner of the Tibet-Qinghai Plateau. It is a closed-basin lake and the largest water body in China with an area of about 4437 km2. Aragonite and calcite are precipitating from the brackish (TDS 12-14 g/l) and alkaline water (pH 9.1-9.4). Summer rainfall exerts an important control on changes in both lake level and water chemistry. As the lake today is situated at the outer margin of the Asian summer monsoon, past climate changes were sensitively documented i...

  13. Ocean biogeochemistry and atmospheric composition: Significance of the Arabian Sea

    Digital Repository Service at National Institute of Oceanography (India)

    Naqvi, S.W.A.; Jayakumar, D.A.

    are mainly of biogenic origin 1 . Many organisms secrete CaCO 3 to build their hard skeletal parts either in the form of aragonite (e.g. corals) or calcite (e.g. foramini fera ). The oceanic surface waters are supersaturated with respect to both... these polymorphs, especially in the tropical regions, facilitating biological CaCO 3 production. The most important pathway through which the biota affects the carbon cycle is the fixation of inorganic carbon by organisms to build soft tissues. This is done...

  14. Effects of pore-scale precipitation on permeability and flow

    Science.gov (United States)

    Noiriel, Catherine; Steefel, Carl I.; Yang, Li; Bernard, Dominique

    2016-09-01

    The effects of calcite precipitation on porous media permeability and flow were evaluated with a combined experimental and modeling approach. X-ray microtomography images of two columns packed with glass beads and calcite (spar crystals) or aragonite (Bahamas ooids) injected with a supersaturated solution (log Ω = 1.42) were processed in order to calculate rates of calcite precipitation with a spatial resolution of 4.46 μm. Identification and localization of the newly precipitated crystals on the 3D images was performed and results used to calculate the crystal growth rates and velocities. The effects of carbonate precipitation were also evaluated in terms of the integrated precipitation rate over the length of the column, crystal shape, surface area and pore roughness changes. While growth was epitaxial on calcite spar, calcite rhombohedra formed on glass beads and clusters of polyhedrons formed on aragonite ooids. Near the column inlet, calcite precipitation occurred preferentially on carbonate grains compared to glass beads, with almost 100% of calcite spar surface area covered by new crystals versus 92% in the case of aragonite and 11% in the case of glass beads. Although the experimental chemistry and flow boundary conditions in the two columns were similar, their porosity-permeability evolution was different because the nucleation and subsequent crystal growth on the two substrates (i.e., calcite spar and aragonite ooids) was very different. The impact of mineral precipitation on pore-scale flow and permeability was evaluated using a pore-scale Stokes solver that accounted for the changes in pore geometry. For similar magnitude reductions in porosity, the decrease in permeability was highest within the sample that experienced the greatest increase in pore roughness. Various porous media models were generated to show the impact of different crystal growth patterns and pore roughness changes on flow and permeability-porosity relationship. Under constant flow

  15. The Li isotope composition of modern biogenic carbonates

    Science.gov (United States)

    Dellinger, M.; West, A. J.; Adkins, J. F.; Paris, G.; Eagle, R.; Freitas, P. S.; Bagard, M. L.; Ries, J. B.; Corsetti, F. A.; Pogge von Strandmann, P.; Ullmann, C. V.

    2015-12-01

    The lithium stable isotope composition (δ7Li) of sedimentary carbonates has great potential to unravel weathering rates and intensity in the past, with implications for understanding the carbon cycle over geologic time. However, so far very little is known about the potential influence of fractionation of the stable Li isotope composition of biogenic carbonates. Here, we investigate the δ7Li of various organisms (particularly mollusks, echinoderms and brachiopods) abundant in the Phanerozoic record, in order to understand which geologic archives might provide the best targets for reconstructing past seawater composition. The range of measured samples includes (i) modern calcite and aragonite shells from variable natural environments, (ii) shells from organisms grown under controlled conditions (temperature, salinity, pCO2), and (iii) fossil shells from a range of species collected from Miocene deposits. When possible, both the inner and outer layers of bivalves were micro-sampled to assess the intra-shell heterogeneity. For calcitic shells, the measured δ7Li of bivalve species range from +32 to +41‰ and is systematically enriched in the heavy isotope relative to seawater (31 ‰) and to inorganic calcite, which is characterized by Δ7Licalcite-seawater = -2 to -5‰ [1]. The Li isotope composition of aragonitic bivalves, ranging from +16 to +22‰, is slightly fractionated to both high and low δ7Li relative to inorganic aragonite. The largest intra-shell Li isotope variability is observed for mixed calcite-aragonite shells (more than 20‰) whereas in single mineralogy shells, intra-shell δ7Li variability is generally less than 3‰. Overall, these results suggest a strong influence of vital effects on Li isotopes during bio-calcification of bivalve shells. On the contrary, measured brachiopods systematically exhibit fractionation that is very similar to inorganic calcite, with a mean δ7Li of 27.0±1.5‰, suggesting that brachiopods may provide good

  16. Influences of riverine and upwelling waters on the coastal carbonate system off Central Chile and their ocean acidification implications

    Science.gov (United States)

    Vargas, Cristian A.; Contreras, Paulina Y.; Pérez, Claudia A.; Sobarzo, Marcus; Saldías, Gonzalo S.; Salisbury, Joe

    2016-06-01

    A combined data set, combining data from field campaigns and oceanographic cruises, was used to ascertain the influence of both river discharges and upwelling processes, covering spatial and temporal variation in dissolved inorganic carbon (DIC) and aragonite saturation state. This work was conducted in one of the most productive river-influenced upwelling areas in the South Pacific coasts (36°S). Additionally, further work was also conducted to ascertain the contribution of different DIC sources, influencing the dynamics of DIC along the land-ocean range. Six sampling campaigns were conducted across seven stations at the Biobío River basin, covering approximately 200 km. Three research cruises were undertaken simultaneously, covering the adjacent continental shelf, including 12 sampling stations for hydrographic measurements. Additionally, six stations were also sampled for chemical analyses, covering summer, winter, and spring conditions over 2010 and 2011. Our results evidenced that seaward extent of the river plume was more evident during the winter field campaign, when highest riverine DIC fluxes were observed. The carbonate system along the river-ocean continuum was very heterogeneous varying over spatial and temporal scales. High DIC and pCO2 were observed in river areas with larger anthropogenic effects. CO2 supersaturation at the river plume was observed during all campaigns due to the influence of low pH river waters in winter/spring and high-pCO2 upwelling waters in summer. δ13CDIC evidenced that main DIC sources along the river and river plume corresponded to the respiration of terrestrial organic matter. We have linked this natural process to the carbonate saturation on the adjacent river-influenced coastal area, suggesting that Ωaragonite undersaturation in surface/subsurface waters is largely modulated by the influence of both river discharge and coastal upwelling events in this productive coastal area. Conditions of low Ωaragonite might impact

  17. Cyanobacterial calcification in modern microbialites at the submicrometer-scale

    Directory of Open Access Journals (Sweden)

    E. Couradeau

    2013-02-01

    Full Text Available The search for microfossils in the geological record has been a long-term challenge. Part of the problem comes from the difficulty of identifying such microfossils unambiguously, since they can be morphologically confused with abiotic biomorphs. One route to improve our ability to correctly identify microfossils consists in studying fossilization processes affecting bacteria in modern settings. We studied the initial stages of fossilization of cyanobacterial cells in modern microbialites from Lake Alchichica (Mexico, a Mg-rich hyperalkaline crater lake (pH 8.9 hosting currently growing stromatolites composed of aragonite [CaCO3] and hydromagnesite [Mg5(CO34(OH2 × 4(H2O]. Most of the biomass associated with the microbialites is composed of cyanobacteria. Scanning electron microscopy analyses coupled with confocal laser scanning microscopy observations were conducted to co-localize cyanobacterial cells and associated minerals. These observations showed that cyanobacterial cells affiliating to the order Pleurocapsales become specifically encrusted within aragonite with an apparent preservation of cell morphology. Encrustation gradients from non-encrusted to totally encrusted cells spanning distances of a few hundred micrometers were observed. Cells exhibiting increased levels of encrustation along this gradient were studied down to the nm-scale using a combination of focused ion beam (FIB milling, transmission electron microscopy (TEM and scanning transmission X-ray microscopy (STXM at the C, O and N K-edges. Two different types of aragonite crystals were observed: one type was composed of needle-shaped nano-crystals growing outward from the cell body with a crystallographic orientation perpendicular to the cell wall, and another type was composed of larger crystals that progressively filled the cell interior. Organic matter (OM, initially co-localized with the cell, decreased in concentration

  18. Cyanobacterial calcification in modern microbialites at the submicrometer scale

    Directory of Open Access Journals (Sweden)

    E. Couradeau

    2013-08-01

    Full Text Available The search for microfossils in the geological record has been a long-term challenge. Part of the problem comes from the difficulty of identifying such microfossils unambiguously, since they can be morphologically confused with abiotic biomorphs. One route to improve our ability to correctly identify microfossils involves studying fossilization processes affecting bacteria in modern settings. We studied the initial stages of fossilization of cyanobacterial cells in modern microbialites from Lake Alchichica (Mexico, a Mg-rich hyperalkaline crater lake (pH 8.9 hosting currently growing stromatolites composed of aragonite [CaCO3] and hydromagnesite [Mg5(CO34(OH2 · 4(H2O]. Most of the biomass associated with the microbialites is composed of cyanobacteria. Scanning electron microscopy analyses coupled with confocal laser scanning microscopy observations were conducted to co-localize cyanobacterial cells and associated minerals. These observations showed that cyanobacterial cells affiliated with the order Pleurocapsales become specifically encrusted within aragonite with an apparent preservation of cell morphology. Encrustation gradients from non-encrusted to totally encrusted cells spanning distances of a few hundred micrometers were observed. Cells exhibiting increased levels of encrustation along this gradient were studied down to the nm scale using a combination of focused ion beam (FIB milling, transmission electron microscopy (TEM and scanning transmission x-ray microscopy (STXM at the C, O and N K-edges. Two different types of aragonite crystals were observed: one type was composed of needle-shaped nano-crystals growing outward from the cell body with a crystallographic orientation perpendicular to the cell wall, and another type was composed of larger crystals that progressively filled the cell interior. Exopolymeric substances (EPS, initially co-localized with the cells, decreased in concentration and dispersed away from the cells while

  19. Synthesis of CaCO3 crystals using hydroxypropylmethyl cellulose hydrogel as template

    Institute of Scientific and Technical Information of China (English)

    ZHAO Jin; LI YanJun; CHENG GuoXiang

    2007-01-01

    Calcium carbonate crystallization was performed in hydrogel of hydroxypropylmethyl cellulose (HPMC). Results showed that the polyhydroxy functionalities in HPMC gel network facilitated the nucleation of aragonite which was not found in experiment without HPMC hydrogel and in experiment using methylcellulose (MC) hydrogel as template. On the other hand,due to the unique assembly of the macromolecules in HPMC hydrogel network,which was different from other hydrogels used in some previous reports,particular crystal morphology,corncob-like CaCO3,was obtained for the first time.

  20. Natural variability in the surface ocean carbonate ion concentration

    Directory of Open Access Journals (Sweden)

    N. S. Lovenduski

    2015-08-01

    Full Text Available We investigate variability in the surface ocean carbonate ion concentration ([CO32−] on the basis of a long control simulation with a fully-coupled Earth System Model. The simulation is run with a prescribed, pre-industrial atmospheric CO2 concentration for 1000 years, permitting investigation of natural [CO32−] variability on interannual to multi-decadal timescales. We find high interannual variability in surface [CO32−] in the tropical Pacific and at the boundaries between the subtropical and subpolar gyres in the Northern Hemisphere, and relatively low interannual variability in the centers of the subtropical gyres and in the Southern Ocean. Statistical analysis of modeled [CO32−] variance and autocorrelation suggests that significant anthropogenic trends in the saturation state of aragonitearagonite are already or nearly detectable at the sustained, open-ocean timeseries sites, whereas several decades of observations are required to detect anthropogenic trends in Ωaragonite in the tropical Pacific, North Pacific, and North Atlantic. The detection timescale for anthropogenic trends in pH is shorter than that for Ωaragonite, due to smaller noise-to-signal ratios and lower autocorrelation in pH. In the tropical Pacific, the leading mode of surface [CO32−] variability is primarily driven by variations in the vertical advection of dissolved inorganic carbon (DIC in association with El Niño–Southern Oscillation. In the North Pacific, surface [CO32−] variability is caused by circulation-driven variations in surface DIC and strongly correlated with the Pacific Decadal Oscillation, with peak spectral power at 20–30 year periods. North Atlantic [CO32−] variability is also driven by variations in surface DIC, and exhibits weak correlations with both the North Atlantic Oscillation and the Atlantic Multidecadal Oscillation. As the scientific community seeks to detect the anthropogenic influence on ocean carbonate chemistry, these

  1. Microbial composition of biofilms associated with lithifying rubble of Acropora palmata branches.

    Science.gov (United States)

    Beltrán, Yislem; Cerqueda-García, Daniel; Taş, Neslihan; Thomé, Patricia E; Iglesias-Prieto, Roberto; Falcón, Luisa I

    2016-01-01

    Coral reefs are among the most productive ecosystems on the planet, but are rapidly declining due to global-warming-mediated changes in the oceans. Particularly for the Caribbean region, Acropora sp. stony corals have lost ∼80% of their original coverage, resulting in vast extensions of dead coral rubble. We analyzed the microbial composition of biofilms that colonize and lithify dead Acropora palmata rubble in the Mexican Caribbean and identified the microbial assemblages that can persist under scenarios of global change, including high temperature and low pH. Lithifying biofilms have a mineral composition that includes aragonite and magnesium calcite (16 mole% MgCO(3)) and calcite, while the mineral phase corresponding to coral skeleton is basically aragonite. Microbial composition of the lithifying biofilms are different in comparison to surrounding biotopes, including a microbial mat, water column, sediments and live A. palmata microbiome. Significant shifts in biofilm composition were detected in samples incubated in mesocosms. The combined effect of low pH and increased temperature showed a strong effect after two-week incubations for biofilm composition. Findings suggest that lithifying biofilms could remain as a secondary structure on reef rubble possibly impacting the functional role of coral reefs.

  2. Identifying vital effects in Halimeda algae with Ca isotopes

    Directory of Open Access Journals (Sweden)

    C. L. Blättler

    2014-03-01

    Full Text Available Geochemical records of biogenic carbonates provide some of the most valuable records of the geological past, but are often difficult to interpret without a mechanistic understanding of growth processes. In this experimental study, Halimeda algae are used as a test organism to untangle some of the specific factors that influence their skeletal composition, in particular their Ca-isotope composition. Algae were stimulated to precipitate both calcite and aragonite by growth in artificial Cretaceous seawater. The Ca-isotope fractionation of the algal calcite is much smaller than that for the algal aragonite, similar to the behaviour observed in inorganic precipitates. However, the carbonate from Halimeda is isotopically heavier than inorganic forms, likely due to Rayleigh distillation within the algal intercellular space. In identifying specific vital effects and the magnitude of their influence on Ca-isotope ratios, this study suggests that mineralogy has a first-order control on the Ca-isotope budget of the carbonate sink and the Ca-isotope composition of seawater.

  3. Identifying vital effects in Halimeda algae with Ca isotopes

    Science.gov (United States)

    Blättler, C. L.; Stanley, S. M.; Henderson, G. M.; Jenkyns, H. C.

    2014-12-01

    Geochemical records of biogenic carbonates provide some of the most valuable records of the geological past, but are often difficult to interpret without a mechanistic understanding of growth processes. In this experimental study, Halimeda algae are used as a test organism to untangle some of the specific factors that influence their skeletal composition, in particular their Ca-isotope composition. Algae were stimulated to precipitate both calcite and aragonite by growth in artificial Cretaceous seawater, resulting in experimental samples with somewhat malformed skeletons. The Ca-isotope fractionation of the algal calcite (-0.6‰) appears to be much smaller than that for the algal aragonite (-1.4‰), similar to the behaviour observed in inorganic precipitates. However, the carbonate from Halimeda has higher Ca-isotope ratios than inorganic forms by approximately 0.25‰, likely because of Rayleigh distillation within the algal intercellular space. In identifying specific vital effects and the magnitude of their influence on Ca-isotope ratios, this study suggests that mineralogy has a first-order control on the marine Ca-isotope cycle.

  4. Calcium distribution in the subtropical Atlantic Ocean: Implications for calcium excess and saturation horizons

    Science.gov (United States)

    Rosón, Gabriel; Guallart, Elisa F.; Pérez, Fiz F.; Ríos, Aida F.

    2016-06-01

    This study constituted the first attempt to measure dissolved calcium ([Ca2 +]meas) in the subtropical North Atlantic, during a zonal transoceanic cruise along 24.5°N (WOCE A05 section), in summer 1992. [Ca2 +]meas was obtained in 20 full-depth equidistant stations along the section, showing that their gradients are rather sensitive to horizontal and vertical water mass distribution. Deep waters along 24.5°N systematically show a positive calcium excess of 20 ± 14 μmol·kg- 1, i.e., more [Ca2 +] than expected by CaCO3 dissolution and organic matter oxidation (estimated by total alkalinity and nitrate). CaCO3 settling and benthic dissolution accounts for 70% and the North Atlantic plus Arctic riverine inputs of HCO3- for the remaining 30%. Combining [Ca2 +]meas and CO2 data sets, carbonate mineral saturation states distributions for aragonite and calcite can be obtained. The two solubility ratios resulted, on average, 0.5% smaller than if conservative behavior for Ca2 + was assumed (an approach widely followed when [Ca2 +]meas is unknown). As a result, shallower saturation horizon depths for both carbonate states (19 dbar for aragonite and 10 dbar for calcite) are yielded if [Ca2 +]meas is taken into account instead than estimated from salinity.

  5. Calcite as a bone substitute. Comparison with hydroxyapatite and tricalcium phosphate with regard to the osteoblastic activity

    Energy Technology Data Exchange (ETDEWEB)

    Monchau, F., E-mail: Francine.monchau@univ-artois.fr [Laboratoire Genie Civil et geo-Environnement (EA 4515, Universite Lille Nord de France), Equipe Biomateriaux Artois (Universite d' Artois), IUT/GMP, 1230, rue de l' Universite, BP 819, 62408 Bethune cedex (France); Hivart, Ph.; Genestie, B. [Laboratoire Genie Civil et geo-Environnement (EA 4515, Universite Lille Nord de France), Equipe Biomateriaux Artois (Universite d' Artois), IUT/GMP, 1230, rue de l' Universite, BP 819, 62408 Bethune cedex (France); Chai, F. [Laboratoire Medicaments et Biomateriaux a Liberation Controlee (INSERM U 1008, Universite Lille Nord de France), Groupe de Recherche sur les Biomateriaux (Universite Lille-2), Faculte de Medecine, 1, place de Verdun, 59045 Lille cedex (France); and others

    2013-01-01

    Close to the bone mineral phase, the calcic bioceramics, such as hydroxyapatite (HA) and {beta}-tricalcium phosphate ({beta}-TCP), are commonly used as substitutes or filling materials in bone surgery. Besides, calcium carbonate (CaCO{sub 3}) is also used for their excellent biocompatibility and bioactivity. However, the problem with the animal-origin aragonite demands the new technique to synthesize pure calcite capable of forming 3D bone implant. This study aims to manufacture and evaluate a highly-pure synthetic crystalline calcite with good cytocompatibility regarding to the osteoblasts, comparing to that of HA and {beta}-TCP. After the manufacture of macroporous bioceramic scaffolds with the identical internal architecture, their cytocompatibility is studied through MC3T3-E1 osteoblasts with the tests of cell viability, proliferation, vitality, etc. The results confirmed that the studied process is able to form a macroporous material with a controlled internal architecture, and this synthesized calcite is non-cytotoxic and facilitate the cell proliferation. Indeed requiring further improvement, the studied calcite is definitely an interesting alternative not only to coralline aragonite but also to calcium phosphate ceramics, particularly in bone sites with the large bone remodelling. Highlights: Black-Right-Pointing-Pointer Macroporous calcite manufacturing with controlled architecture as bone substitute Black-Right-Pointing-Pointer Cytotoxicity: adaptation of the colony-forming method with the target cells: MC3T3-E1 osteoblasts Black-Right-Pointing-Pointer Study of osteoblast proliferation and activity on calcite, HA and TCP.

  6. Ca-rich carbonates associated with ultrabasic-ultramafic melts: Carbonatite or limestone xenoliths? A case study from the late Miocene Morron de Villamayor volcano (Calatrava Volcanic Field, central Spain)

    Science.gov (United States)

    Lustrino, Michele; Prelević, Dejan; Agostini, Samuele; Gaeta, Mario; Di Rocco, Tommaso; Stagno, Vincenzo; Capizzi, Luca Samuele

    2016-07-01

    The volcanic products of the late Miocene Morron de Villamayor volcano (Calatrava Volcanic Field, central Spain) are known for being one of the few outcrops of leucitites in the entire circum-Mediterranean area. These rocks are important because aragonite of mantle origin has been reported as inclusion in olivine macrocrysts. We use petrographic observations, mineral compositions, as well as oxygen and carbon isotope ratios coupled with experimental petrology to understand the origin of carbonate phase in these olivine-phyric rocks. Groundmass and macrocryst olivines range from δ18OVSMOW of +4.8‰, typical of mantle olivine values, to +7.4‰, indicating contamination by sedimentary carbonate. Carbonates are characterized by heavy oxygen isotope compositions (δ18OVSMOW >+24‰), and relatively light carbon isotopes (δ13CPDB <-11‰), resembling skarn values, and distinct from typical mantle carbonatite compositions. Petrography, mineral compositions such as low Mg# of clinopyroxene and biotite, low Ca# and low incompatible element abundance of the carbonate, and isotopic ratios of O and C, do not support a mantle origin for the carbonate. Rather, the carbonate inclusions found in the olivine macrocrysts are interpreted as basement limestone fragments entrapped by the rising crystallizing magma. Comparison with experimental carbonatitic and silicate-carbonatitic melts indicates that low-degree partial melts of a carbonated peridotite must have a dolomitic rather than the aragonitic/calcitic composition as those found trapped in the Morron de Villamayor olivine macrocrysts.

  7. Diet control on carbon isotopic composition of land snail shell carbonate

    Institute of Scientific and Technical Information of China (English)

    LIU ZongXiu; GU ZhaoYan; WU NaiQin; XU Bing

    2007-01-01

    Carbon isotope compositions for both the carbonate shells and soft bodies (organic tissue) of living land snails collected mostly from the Loess Plateau, China have been measured. The result shows that δ13C values range from -13.1‰ to -4.3‰ for the aragonite shell samples and from -26.8‰ to -18.0‰ for the soft body samples. Although the shells are enriched in 13C relative to the bodies averagely by 14.2(±0.8)‰, the shell δ13Ca values are closely correlated to the body δ13Corg values, expressed as δ13Ca = 1.021 δ13Corg + 14.38 (R = 0.965; N = 31). This relationship indicates that δ13Ca is primarily a function of the isotopic composition of the snail diets since previous studies have proved that the snail body is the same as their food in carbon isotope composition. In other words, carbon isotope compo-sition of the carbonate shell can be used as a proxy to estimate the dietary 13C abundance of the land snails. The data also support that the 13C enrichment of the carbonate shells results mainly from the equilibrium fractionations between the metabolic CO2, HCO3- in the hemolymph and shell aragonite, and partially from kinetic fractionations when snail shells form during their activity.

  8. Microbial and diagenetic steps leading to the mineralisation of Great Salt Lake microbialites

    Science.gov (United States)

    Pace, Aurélie; Bourillot, Raphaël; Bouton, Anthony; Vennin, Emmanuelle; Galaup, Serge; Bundeleva, Irina; Patrier, Patricia; Dupraz, Christophe; Thomazo, Christophe; Sansjofre, Pierre; Yokoyama, Yusuke; Franceschi, Michel; Anguy, Yannick; Pigot, Léa; Virgone, Aurélien; Visscher, Pieter T.

    2016-08-01

    Microbialites are widespread in modern and fossil hypersaline environments, where they provide a unique sedimentary archive. Authigenic mineral precipitation in modern microbialites results from a complex interplay between microbial metabolisms, organic matrices and environmental parameters. Here, we combined mineralogical and microscopic analyses with measurements of metabolic activity in order to characterise the mineralisation of microbial mats forming microbialites in the Great Salt Lake (Utah, USA). Our results show that the mineralisation process takes place in three steps progressing along geochemical gradients produced through microbial activity. First, a poorly crystallized Mg-Si phase precipitates on alveolar extracellular organic matrix due to a rise of the pH in the zone of active oxygenic photosynthesis. Second, aragonite patches nucleate in close proximity to sulfate reduction hotspots, as a result of the degradation of cyanobacteria and extracellular organic matrix mediated by, among others, sulfate reducing bacteria. A final step consists of partial replacement of aragonite by dolomite, possibly in neutral to slightly acidic porewater. This might occur due to dissolution-precipitation reactions when the most recalcitrant part of the organic matrix is degraded. The mineralisation pathways proposed here provide pivotal insight for the interpretation of microbial processes in past hypersaline environments.

  9. Identifying vital effects in Halimeda algae with Ca isotopes

    Directory of Open Access Journals (Sweden)

    C. L. Blättler

    2014-12-01

    Full Text Available Geochemical records of biogenic carbonates provide some of the most valuable records of the geological past, but are often difficult to interpret without a mechanistic understanding of growth processes. In this experimental study, Halimeda algae are used as a test organism to untangle some of the specific factors that influence their skeletal composition, in particular their Ca-isotope composition. Algae were stimulated to precipitate both calcite and aragonite by growth in artificial Cretaceous seawater, resulting in experimental samples with somewhat malformed skeletons. The Ca-isotope fractionation of the algal calcite (−0.6‰ appears to be much smaller than that for the algal aragonite (−1.4‰, similar to the behaviour observed in inorganic precipitates. However, the carbonate from Halimeda has higher Ca-isotope ratios than inorganic forms by approximately 0.25‰, likely because of Rayleigh distillation within the algal intercellular space. In identifying specific vital effects and the magnitude of their influence on Ca-isotope ratios, this study suggests that mineralogy has a first-order control on the marine Ca-isotope cycle.

  10. The exposure of the Great Barrier Reef to ocean acidification.

    Science.gov (United States)

    Mongin, Mathieu; Baird, Mark E; Tilbrook, Bronte; Matear, Richard J; Lenton, Andrew; Herzfeld, Mike; Wild-Allen, Karen; Skerratt, Jenny; Margvelashvili, Nugzar; Robson, Barbara J; Duarte, Carlos M; Gustafsson, Malin S M; Ralph, Peter J; Steven, Andrew D L

    2016-02-23

    The Great Barrier Reef (GBR) is founded on reef-building corals. Corals build their exoskeleton with aragonite, but ocean acidification is lowering the aragonite saturation state of seawater (Ωa). The downscaling of ocean acidification projections from global to GBR scales requires the set of regional drivers controlling Ωa to be resolved. Here we use a regional coupled circulation-biogeochemical model and observations to estimate the Ωa experienced by the 3,581 reefs of the GBR, and to apportion the contributions of the hydrological cycle, regional hydrodynamics and metabolism on Ωa variability. We find more detail, and a greater range (1.43), than previously compiled coarse maps of Ωa of the region (0.4), or in observations (1.0). Most of the variability in Ωa is due to processes upstream of the reef in question. As a result, future decline in Ωa is likely to be steeper on the GBR than currently projected by the IPCC assessment report.

  11. Atlanta ariejansseni, a new species of shelled heteropod from the Southern Subtropical Convergence Zone (Gastropoda, Pterotracheoidea)

    Science.gov (United States)

    Wall-Palmer, Deborah; Burridge, Alice K.; Peijnenburg, Katja T.C.A.

    2016-01-01

    Abstract The Atlantidae (shelled heteropods) is a family of microscopic aragonite shelled holoplanktonic gastropods with a wide biogeographical distribution in tropical, sub-tropical and temperate waters. The aragonite shell and surface ocean habitat of the atlantids makes them particularly susceptible to ocean acidification and ocean warming, and atlantids are likely to be useful indicators of these changes. However, we still lack fundamental information on their taxonomy and biogeography, which is essential for monitoring the effects of a changing ocean. Integrated morphological and molecular approaches to taxonomy have been employed to improve the assessment of species boundaries, which give a more accurate picture of species distributions. Here a new species of atlantid heteropod is described based on shell morphology, DNA barcoding of the Cytochrome Oxidase I gene, and biogeography. All specimens of Atlanta ariejansseni sp. n. were collected from the Southern Subtropical Convergence Zone of the Atlantic and Indo-Pacific oceans suggesting that this species has a very narrow latitudinal distribution (37–48°S). Atlanta ariejansseni sp. n. was found to be relatively abundant (up to 2.3 specimens per 1000 m3 water) within this narrow latitudinal range, implying that this species has adapted to the specific conditions of the Southern Subtropical Convergence Zone and has a high tolerance to the varying ocean parameters in this region. PMID:27551204

  12. The exposure of the Great Barrier Reef to ocean acidification

    Science.gov (United States)

    Mongin, Mathieu; Baird, Mark E.; Tilbrook, Bronte; Matear, Richard J.; Lenton, Andrew; Herzfeld, Mike; Wild-Allen, Karen; Skerratt, Jenny; Margvelashvili, Nugzar; Robson, Barbara J.; Duarte, Carlos M.; Gustafsson, Malin S. M.; Ralph, Peter J.; Steven, Andrew D. L.

    2016-01-01

    The Great Barrier Reef (GBR) is founded on reef-building corals. Corals build their exoskeleton with aragonite, but ocean acidification is lowering the aragonite saturation state of seawater (Ωa). The downscaling of ocean acidification projections from global to GBR scales requires the set of regional drivers controlling Ωa to be resolved. Here we use a regional coupled circulation–biogeochemical model and observations to estimate the Ωa experienced by the 3,581 reefs of the GBR, and to apportion the contributions of the hydrological cycle, regional hydrodynamics and metabolism on Ωa variability. We find more detail, and a greater range (1.43), than previously compiled coarse maps of Ωa of the region (0.4), or in observations (1.0). Most of the variability in Ωa is due to processes upstream of the reef in question. As a result, future decline in Ωa is likely to be steeper on the GBR than currently projected by the IPCC assessment report. PMID:26907171

  13. Could artificial ocean alkalinization protect tropical coral ecosystems from ocean acidification?

    Science.gov (United States)

    Feng, Ellias Y.; Keller, David P.; Koeve, Wolfgang; Oschlies, Andreas

    2016-07-01

    Artificial ocean alkalinization (AOA) is investigated as a method to mitigate local ocean acidification and protect tropical coral ecosystems during a 21st century high CO2 emission scenario. Employing an Earth system model of intermediate complexity, our implementation of AOA in the Great Barrier Reef, Caribbean Sea and South China Sea regions, shows that alkalinization has the potential to counteract expected 21st century local acidification in regard to both oceanic surface aragonite saturation Ω and surface pCO2. Beyond preventing local acidification, regional AOA, however, results in locally elevated aragonite oversaturation and pCO2 decline. A notable consequence of stopping regional AOA is a rapid shift back to the acidified conditions of the target regions. We conclude that AOA may be a method that could help to keep regional coral ecosystems within saturation states and pCO2 values close to present-day values even in a high-emission scenario and thereby might ‘buy some time’ against the ocean acidification threat, even though regional AOA does not significantly mitigate the warming threat.

  14. Preservation state of metastable magnesian calcite in periplatform sediments from the Caribbean Sea over the last million years

    Science.gov (United States)

    Sepulcre, Sophie; Tachikawa, Kazuyo; Vidal, Laurence; Thouveny, Nicolas; Bard, Edouard

    2009-11-01

    Carbonate-rich periplatform sediments represent an active carbon reservoir containing metastable aragonite and magnesian calcite (Mg-calcite, > 4 mol % MgCO3). Since Mg-calcite is highly soluble, the preservation state of this mineral provides information on past carbonate systems at water depths shallower than the lysocline. The mineralogy and geochemistry of the carbonate-rich fine fraction (MgCO3) during interglacials. Glacial Mg/Ca ratios were approximately 8 mol % MgCO3 for the period from 940 ka to 400 ka, and approximately 10 mol % MgCO3 for the last 400 ka. The Mg/Ca shift is concomitant with a preferential loss of Mg-calcite relative to aragonite. The preservation state of Mg-calcite revealed that the bottom water mass of the studied site was slightly more corrosive for the earlier period, possibly relating to a composition change in intermediate water and/or to the ventilation rate in the Atlantic Ocean.

  15. Microbial composition of biofilms associated with lithifying rubble of Acropora palmata branches.

    Science.gov (United States)

    Beltrán, Yislem; Cerqueda-García, Daniel; Taş, Neslihan; Thomé, Patricia E; Iglesias-Prieto, Roberto; Falcón, Luisa I

    2016-01-01

    Coral reefs are among the most productive ecosystems on the planet, but are rapidly declining due to global-warming-mediated changes in the oceans. Particularly for the Caribbean region, Acropora sp. stony corals have lost ∼80% of their original coverage, resulting in vast extensions of dead coral rubble. We analyzed the microbial composition of biofilms that colonize and lithify dead Acropora palmata rubble in the Mexican Caribbean and identified the microbial assemblages that can persist under scenarios of global change, including high temperature and low pH. Lithifying biofilms have a mineral composition that includes aragonite and magnesium calcite (16 mole% MgCO(3)) and calcite, while the mineral phase corresponding to coral skeleton is basically aragonite. Microbial composition of the lithifying biofilms are different in comparison to surrounding biotopes, including a microbial mat, water column, sediments and live A. palmata microbiome. Significant shifts in biofilm composition were detected in samples incubated in mesocosms. The combined effect of low pH and increased temperature showed a strong effect after two-week incubations for biofilm composition. Findings suggest that lithifying biofilms could remain as a secondary structure on reef rubble possibly impacting the functional role of coral reefs. PMID:26705570

  16. Phase transitions of natural corals monitored by ESR spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Vongsavat, V. [Department of Chemistry, Faculty of Science, Mahidol University, Rama VI Road, Rajathevi, Bangkok 10400 (Thailand); Winotai, P. [Department of Chemistry, Faculty of Science, Mahidol University, Rama VI Road, Rajathevi, Bangkok 10400 (Thailand); Meejoo, S. [Department of Chemistry, Faculty of Science, Mahidol University, Rama VI Road, Rajathevi, Bangkok 10400 (Thailand)]. E-mail: scsmj@mahidol.ac.th

    2006-01-15

    The main purpose of this work is to present a systematic study of structure of marine exoskeletons, Acropora coral and its structural transformation upon heat treatments. The coralline sample was ground and characterized as powder throughout this work. Structural identifications of all samples have been confirmed using X-ray diffraction and IR spectroscopy. It was clearly found that the fresh specimen is made of aragonite, a common phase of the mineral CaCO{sub 3}. Thermal analyses, DSC and TGA were used to monitor structural and thermal decompositions and an irreversible solid-state phase transition from aragonite to calcite of the marine carbonate. Next, the coral powder was annealed at specific temperatures over the range 350-900 deg. C, and the effects of heat treatment on the structure of coralline samples were carefully studied by Rietveld refinement method. In addition, we have examined Mn{sup 2+} paramagnetic ions and free radicals present in the coral and changes of those upon heating by using ESR spectroscopy. The local environments of Mn{sup 2+} ions were verified from the calculated ESR spectra using appropriate spin Hamiltonian parameters, i.e. gyromagnetic tensor g , zero-field splitting D and hyperfine tensor A . This work reported structures and compositions as well as physical, chemical and thermal properties of the coralline material upon heat treatments qualitatively and quantitatively.

  17. The exposure of the Great Barrier Reef to ocean acidification.

    Science.gov (United States)

    Mongin, Mathieu; Baird, Mark E; Tilbrook, Bronte; Matear, Richard J; Lenton, Andrew; Herzfeld, Mike; Wild-Allen, Karen; Skerratt, Jenny; Margvelashvili, Nugzar; Robson, Barbara J; Duarte, Carlos M; Gustafsson, Malin S M; Ralph, Peter J; Steven, Andrew D L

    2016-01-01

    The Great Barrier Reef (GBR) is founded on reef-building corals. Corals build their exoskeleton with aragonite, but ocean acidification is lowering the aragonite saturation state of seawater (Ωa). The downscaling of ocean acidification projections from global to GBR scales requires the set of regional drivers controlling Ωa to be resolved. Here we use a regional coupled circulation-biogeochemical model and observations to estimate the Ωa experienced by the 3,581 reefs of the GBR, and to apportion the contributions of the hydrological cycle, regional hydrodynamics and metabolism on Ωa variability. We find more detail, and a greater range (1.43), than previously compiled coarse maps of Ωa of the region (0.4), or in observations (1.0). Most of the variability in Ωa is due to processes upstream of the reef in question. As a result, future decline in Ωa is likely to be steeper on the GBR than currently projected by the IPCC assessment report. PMID:26907171

  18. The relationship between the ratio of strontium to calcium and sea-surface temperature in a modern Porites astreoides coral: Implications for using P. astreoides as a paleoclimate archive

    Science.gov (United States)

    Tess E. Busch,; Flannery, Jennifer A.; Richey, Julie N.; Stathakopoulos, Anastasios

    2015-11-13

    An inverse relationship has been demonstrated between water temperature and the ratio of strontium to calcium (Sr/Ca) in coral aragonite for a number of Pacific species of the genus Porites. This empirically determined relationship has been used to reconstruct past sea-surface temperature (SST) from modern and Holocene age coral archives. A study was conducted to investigate this relationship for Porites astreoides to determine the potential for using these corals as a paleotemperature archive in the Caribbean and western tropical Atlantic Ocean. Skeletal aragonite from a P. astreoides colony growing offshore of the southeast coast of Florida was subsampled with a mean temporal resolution of 14 samples per year and analyzed for Sr/Ca. The resulting Sr/Ca time series yielded well-defined annual cycles that correspond to annual growth bands in the coral. Sr/Ca was regressed against a monthly SST record from C-MAN buoy station FWYF1 (located at Fowey Rocks, Florida), resulting in the following Sr/Ca-SST relationship: Sr/Ca = –0.040*SST + 10.128 (R = –0.77). A 10-year time series of Sr/Ca-derived SST yields annual cycles with a 10–12 degree Celsius seasonal amplitude, consistent with available local instrumental records. We conclude that Sr/Ca in Porites astreoides from the Caribbean/Atlantic region has high potential for developing subannually resolved modern and recent Holocene SST records.

  19. The exposure of the Great Barrier Reef to ocean acidification

    KAUST Repository

    Mongin, Mathieu

    2016-02-23

    The Great Barrier Reef (GBR) is founded on reef-building corals. Corals build their exoskeleton with aragonite, but ocean acidification is lowering the aragonite saturation state of seawater (Ωa). The downscaling of ocean acidification projections from global to GBR scales requires the set of regional drivers controlling Ωa to be resolved. Here we use a regional coupled circulation–biogeochemical model and observations to estimate the Ωa experienced by the 3,581 reefs of the GBR, and to apportion the contributions of the hydrological cycle, regional hydrodynamics and metabolism on Ωa variability. We find more detail, and a greater range (1.43), than previously compiled coarse maps of Ωa of the region (0.4), or in observations (1.0). Most of the variability in Ωa is due to processes upstream of the reef in question. As a result, future decline in Ωa is likely to be steeper on the GBR than currently projected by the IPCC assessment report.

  20. Abrupt climate change and the decline of Indus urbanism

    Science.gov (United States)

    Hodell, D. A.; Dixit, Y.; Petrie, C. A.

    2012-12-01

    Climate change has been suggested as a cause for the decline of the cities of the Indus Civilization, which is believed to have begun ~4.0 to 3.9 ky B.P. Previous studies have centered on paleoclimatic records obtained from areas outside the geographic limits of the Indus Civilization, raising questions about their suitability for evaluating past climate-cultural linkages. Here we report a detailed climate record from paleolake Kotla Dahar, Haryana (28°00'095'' N, 76°57'173'' E), located at the eastern edge of the distribution of Indus settlements and ~100km to the east of the city-site of Rakhigarhi in NW India. Regional hydrologic changes are inferred using oxygen-isotope measurements of gastropod aragonite from a 2.88-m sediment section. A permanent ~4‰ increase in δ18O of shell aragonite occurred at ~4.1±0.1 ky B.P., marking an abrupt increase in evaporation/precipitation in the lake catchment. These data provide evidence for a weakening of the monsoon and shift toward drier climate on the plains of northwest (NW) India at ~4.1±0.1 ky B.P. Decreased monsoon rainfall at this time may have been linked to increased ENSO variability, and supports a possible role of climate in the transformation of the Indus Civilization from an urbanized (mature or urban Indus) to a rural (post-urban) society.

  1. Inorganic carbon in a high latitude estuary-fjord system in Canada's eastern Arctic

    Science.gov (United States)

    Turk, D.; Bedard, J. M.; Burt, W. J.; Vagle, S.; Thomas, H.; Azetsu-Scott, K.; McGillis, W. R.; Iverson, S. J.; Wallace, D. W. R.

    2016-09-01

    Rapidly changing conditions in the Arctic can have a significant impact on biogeochemical cycles and can be particularly important in high latitude estuary-fjord systems with abundant and diverse freshwater sources. This study provides a first look into the inorganic carbon system and its relation to freshwater sources in Cumberland Sound in the east coast of Baffin Island, Nunavut, Canada. These data contribute to the very limited set of inorganic carbon measurements in high latitude estuary-fjord systems. During the ice-free conditions in August 2011, the meteoric freshwater fractions (MW) in the upper 40 m ranged from 11 to 21% and no sea ice melt (SIM) was present in the Sound. Surface waters were undersaturated with pCO2 (260 and 300 μatm), and DIC and TA ranged between 1779 and 1966 μmol DIC kg-1, and 1922 and 2140 μmol TA kg-1, respectively. Aragonite saturation (ΩAr) state ranged from 1.9 in the surface to 1.4 in the subsurface waters. Data show decreasing TA and ΩAr with increasing MW fraction and suggest that Cumberland Sound waters would become aragonite undersaturated (ΩAr water and glacial melt. In August 2012, MW fractions at the surface were between 8 and 11.5%, and SIM between 7 and 23%. Significant interannual variability of summertime SIM could potentially result in ΩAr undersaturation.

  2. Influence of the Mg-content on ESR-signals in synthetic calcium carbonate

    Energy Technology Data Exchange (ETDEWEB)

    Barabas, M.; Bach, A.; Mudelsee, M.; Mangini, A. (Akademie der Wissenschaften, Heidelberg (Germany, F.R.))

    1989-01-01

    Carbonate crystals doped with various concentrations of Mg{sup 2+}-ions have been grown by a gel-diffusion method. An increase of the Mg/Ca-ratio to more than about 1 caused a phase change in the crystal lattice from calcite to aragonite. The properties of the ESR-signals of the synthetic carbonates were studied and compared with natural marine carbonates. The following results were derived: (a) In the presence of Mg{sup 2+}-ions the synthetic carbonates display the same ESR-signals as natural calcites of marine origin with similar properties (thermal stability, radiation sensitivity). (b) The saturation value of the signal at g=2.0006 in synthetic calcites was found to be strongly related with the Mg-content in the crystals. (c) The signal at g=2.0036 (axial symmetry) which is present in calcite was not influenced by the Mg-concentration. Its saturation value decreases when the crystal phase changed from calcite to aragonite and in complement the signal at g=2.0031 appeared. (d) The signals at g=2.0057 and g=2.0031 are most probably not of organic origin. (author).

  3. Plastic deformation in nano-scale multilayer materials — A biomimetic approach based on nacre

    International Nuclear Information System (INIS)

    The paper reports about a biomimetic based comparison of deformation in magnetron sputtered multilayer coatings based on titanium (Ti), titanium nitride (TiN) and diamond-like carbon (DLC) layers and the deformation mechanisms in nacre of mollusc shells. Nacre as highly mineralized tissue combines high stiffness and hardness with high toughness, enabling resistance to fracture and crack propagation during tensile loading. Such behaviour is based on a combination of load transmission by tensile stressed aragonite tablets and shearing in layers between the tablets. Shearing in these polysaccharide and protein interlayers demands hydrated conditions. Otherwise, nacre has similar brittle behaviour to aragonite. To prevent shear failure, shear hardening occurs by progressive tablet locking due to wavy dovetail-like surface geometry of the tablets. Similar effects by shearing and strain hardening mechanisms were found for Ti interlayers between TiN and DLC layers in high-resolution transmission electron microscopy studies, performed in deformed zones beneath spherical indentations. 7 nm thin Ti films are sufficient for strong toughening of the whole multi-layered coating structure, providing a barrier for propagation of cracks, starting from tensile-stressed, hard, brittle TiN or DLC layers. - Highlights: • Biomimetic approach to TiN-diamond-like carbon (DLC) multilayers by sputtering • Investigation of deformation in/around hardness indents by HR-TEM • Plastic deformation with shearing in 7-nm thick Ti interlayers in TiN–DLC multilayers • Biomimetically comparable to nacre deformation

  4. Biomineral repair of abalone shell apertures.

    Science.gov (United States)

    Cusack, Maggie; Guo, Dujiao; Chung, Peter; Kamenos, Nicholas A

    2013-08-01

    The shell of the gastropod mollusc, abalone, is comprised of nacre with an outer prismatic layer that is composed of either calcite or aragonite or both, depending on the species. A striking characteristic of the abalone shell is the row of apertures along the dorsal margin. As the organism and shell grow, new apertures are formed and the preceding ones are filled in. Detailed investigations, using electron backscatter diffraction, of the infill in three species of abalone: Haliotis asinina, Haliotis gigantea and Haliotis rufescens reveals that, like the shell, the infill is composed mainly of nacre with an outer prismatic layer. The infill prismatic layer has identical mineralogy as the original shell prismatic layer. In H. asinina and H. gigantea, the prismatic layer of the shell and infill are made of aragonite while in H. rufescens both are composed of calcite. Abalone builds the infill material with the same high level of biological control, replicating the structure, mineralogy and crystallographic orientation as for the shell. The infill of abalone apertures presents us with insight into what is, effectively, shell repair.

  5. Mineralogy of Holocene Sediments from the Southwestern Black Sea Shelf (Turkey) in Relation to Provenance, Sea-level and Current Regimes

    Institute of Scientific and Technical Information of China (English)

    Emel BAYHAN; Mustafa ERG(I)N; Abidin TEMEL; Seref KESK(I)N

    2005-01-01

    Grain size and mineral composition of core sediments were used to investigate influences of various terrestrial and marine conditions,which have prevailed on the southwestern Black Sea shelf during the Holocene.Siliciclastic mud with small amounts of sand and gravel from nearby coastal hinterland is the principal sediment type,whereas sediments deposited near the shelf edge and the (I)stanbul Strait and off the Duru Lake (a paleo-river mouth)constitued large quantities of sand and gravel of both biogenic and terrigenic origin.Variable amounts of aragonite,1 nm-micas,quartz,feldspars,calcite and dolomite constitute the dominant non-clay minerals in bulk sediments.The clay mineral assemblage in the < 2 μm fraction is made up of smectite,illite,kaolinite and chlorite.Aragonite and calcite are mainly derived from benthic accumulations,whereas feldspars (mainly plagioclase) and smectite reflect magmaticvolcanic provenance and the distribution of 1 nm-micas and chlorite correlate with nearby metamorphic sources onland.Nevertheless,grain size and mineral distribution generally indicate a combination of effects of wind and wave climate,longshore and offshore cyclonic currents,changing sea-level stands and nearby source rock and morphological conditions.It is also suggested that at least part of clay minerals could be derived from the northwesterly Danube River input.

  6. Ooid mineralogy and diagenesis of upper Mississippian Pitkin Formation, Arkansas

    Energy Technology Data Exchange (ETDEWEB)

    Heydari, E.; Snelling, R.D.; Dawson, W.C.; Machain, M.L. (Louisiana State Univ., Baton Rouge (USA))

    1989-08-01

    The Pitkin formation is a marine oolitic-bioclastic limestone exhibiting shoal, lagoonal, beach, and tidal-channel facies. Ooids formed on the Pitkin carbonate shelf show lateral and vertical variations in original mineralogy. In a section south of Mountain View, Arkansas, the lower marine shoal and shoreface facies are composed of originally aragonitic ooids. These ooids are replaced by neomorphic calcite and exhibit elevated strontium and low magnesium concentrations. The overlying lagoonal facies are composed of originally calcite ooids that have retained their original radial fabrics. These ooids exhibit low strontium and high magnesium concentration. Ooids in sections to the west of Mountain View are all calcitic. Early diagenesis of the formation is dominated by marine cementation. Postdepositional diagenesis encompasses extensive dissolution of originally aragonite and magnesian calcite components, precipitation of a late unzoned ferroan calcite, and minor amounts of saddle dolomite. Grainstone units lack any intergranular porosity. Pressure solution contacts among grains in grainstones are generally uncommon. Cementation alone is responsible for destruction of all of the original porosity in these rocks. Intensive pressure solution is observed only in packstone units not affected by early marine cementation.

  7. Extraction and Purification of Matrix Protein from the Nacre of Pearl Oyster Pinctada fucata

    Institute of Scientific and Technical Information of China (English)

    MA Caiping; ZHANG Cen; NIE Yancheng; XIE Liping; ZHANG Rongqing

    2005-01-01

    A soluble matrix protein P14 with an apparent molecular mass of 14.5 kDa was isolated from fragmented nacre of pearl oysters (Pinctada fucata) treated with 10% NaOH solution to investigate the nacre matrix proteins and their effect on the CaCO3 crystal. The protein was characterized by gel exclusion chromatography and reversed-phase high performance liquid chromatography after demineralization by 10% acetic acid. The X-ray diffraction pattern of P14 crystals indicates that P14 plays an important role in nacre biomineralization. P14 can induce aragonite formation, stimulate CaCO3 crystal formation, and accelerate aragonite precipitation. Heating of the acid insoluble nacre residue, which was named conchiolin, in 10% sodium dodecyl sulfate solution supplemented with 10% β-mercaptoethanol solution for 10-20 min at about 100(C gave two other soluble proteins having molecular masses of 19.4 kDa and 25.0 kDa. The present study suggests that these two proteins are linked to the insoluble organic matrix by disulfide bridges because the extraction yield increases when β-mercaptoethanol is added to the medium.

  8. Mineral and Protein-Bound Water and Latching Action Control Mechanical Behavior at Protein-Mineral Interfaces in Biological Nanocomposites

    Directory of Open Access Journals (Sweden)

    Pijush Ghosh

    2008-01-01

    Full Text Available The nacre structure consists of laminated interlocked mineral platelets separated by nanoscale organic layers. Here, the role of close proximity of mineral to the proteins on mechanical behavior of the protein is investigated through steered molecular dynamics simulations. Our simulations indicate that energy required for unfolding protein in the proximity of mineral aragonite is several times higher than that for isolated protein in the absence of the mineral. Here, we present details of specific mechanisms which result in higher energy for protein unfolding in the proximity of mineral. At the early stage of pulling, peaks in the load-displacement (LD plot at mineral proximity are quantitatively correlated to the interaction energy between atoms involved in the latching phenomenon of amino acid side chain to aragonite surface. Water plays an important role during mineral and protein interaction and water molecules closer to the mineral surface are highly oriented and remain rigidly attached as the protein strand is pulled. Also, the high magnitude of load for a given displacement originates from attractive interactions between the protein, protein-bound water, and mineral. This study provides an insight into mineral-protein interactions that are predominant in biological nanocomposites and also provides guidelines towards design of biomimetic nanocomposites.

  9. Marine Biogenic Minerals Hold Clues About Changes in Ocean Chemistry and Climate: Some Important Lessons Learned from Studies of Stable and Radioactive Isotopes of Be and Al

    Directory of Open Access Journals (Sweden)

    Devendra Lal

    2002-01-01

    Full Text Available The elements Be and Al exhibit very short residence time in ocean waters, and therefore serve as useful tracers for the study of biogeochemical processes in seawater. A unique feature of these tracers is that nuclear interactions of cosmic rays in the atmosphere produce appreciable amounts of two radioactive isotopes, 10Be (with a half-life of 1.5 my and 26Al (with a half-life of 0.7 my, which are introduced in the hydrosphere, cryosphere, and lithosphere via precipitation. Thus, these elements are labeled by their respective radioactive isotopes, which help quantitative tagging of their biogeochemical cycles. Finally, as we report here, several marine organisms incorporate them in their skeletal shells in certain fixed proportions to their concentrations in the seawater, so that it seems possible to study changes in the ocean chemistry and climate over the past several million years. We summarize here the recent discovery by Dong et al.[9] of significant enrichments of intrinsic Be and Al in marine foraminiferal calcite and coral aragonite, and of Al in opal (radiolarians and aragonite (corals, which should make it possible to determine 10Be/Be and 26Al/Al in oceans in the past. We also summarize their measured 10Be/9Be in foraminiferal calcite in Pacific Ocean cores, which reveal that the concentrations and ratios of the stable and cosmogenic isotopes of Be and Al have varied significantly in the past 30 ky. The implications of these results are discussed.

  10. Carbonate inclusions in Lower Cretaceous picrites from the Hončova hůrka Hill (Czech Republic, Outer Western Carpathians): Evidence for primary magmatic carbonates?

    Science.gov (United States)

    Kropáč, Kamil; Dolníček, Zdeněk; Buriánek, David; Urubek, Tomáš; Mašek, Vlastimil

    2015-07-01

    Porphyritic picrites from the Hončova hůrka site in the Silesian Unit (Western Carpathians) are composed mostly of olivine phenocrysts enclosed in a black fine-grained groundmass, which consists of clinopyroxene, biotite, magnetite, chlorite, feldspars, and zeolites. The rocks are variably affected by hydrothermal alteration. The freshest samples contain potentially primary igneous calcite and aragonite, which occur as globular inclusions hosted by olivine phenocrysts, or as fillings of the miarolitic cavities in the picrite groundmass. In this paper, we try to clarify the nature of investigated carbonates using the combination of several petrological methods. Based on the texture, mineral composition, and relationship to the alteration patterns of the host mineral, we distinguished three basic types of inclusions: carbonate inclusions, silicate inclusions, and a combined type consisting of both carbonate and silicate domains. Only the fresh olivine-hosted round carbonate globules can contain the primary igneous calcite. These globules cannot represent immiscible carbonatite melt since they lack Si, alkalis, and other essential components (e.g. P, F, Cl, and S) present in natural carbonate melts. Instead, they can be interpreted as product of equilibrium crystallization of calcite from carbonated silicate melt (i.e. crystal cumulates). In contrast, the calcite-aragonite assemblage in inclusions hosted by altered olivine and in miaroles most probably originated during recrystallization of primary calcite during late-magmatic or post-magmatic stages or is related to the superimposed hydrothermal alteration.

  11. Freshwater on the route of hominids "out of Africa" during the last interglacial revealed by U-Th in northern Red Sea fossil reefs

    Science.gov (United States)

    Lazar, B.; Stein, M.; Agnon, A.; Shaked, Y.

    2012-04-01

    The migration of Anatomically Modern Hominids (AMH) "out of Africa" is a fundamental problem in the study of human culture concerning that the route passed through the presently hyperarid deserts surrounding the Red Sea. Here, we outline the evidence for significant presence of freshwater in a well developed phreatic coastal aquifer along the Red Sea shores during the last interglacial period. The fringing coral reefs were tectonically uplifted through the freshwater lens resulting in extensive recrystallization of reef framework from the primary aragonite into calcite. We developed a novel open-system U-Th dating methodology that enabled us estimating two ages for the calcitic reef terrace: 1. The original age of the reef terrace, deposited at ~190 ka BP; and 2. the time of freshwater recrystallization (from the primary aragonite into calcite) at ~140 ka BP. The age of freshwater recrystallization is consistent with other geological lines of evidence placing the time of AMH migration "out of Africa" at the onset of the last interglacial. It is likely therefore that during that time the hyperarid Red Sea area was wetter than today facilitating the migration of AMH to Europe and Asia.

  12. 16,000 Years of Tropical Eastern Ocean Climate Variability Recorded in a Speleothem From Sumatra, Indonesia

    Science.gov (United States)

    Wurtzel, J. B.; Abram, N.; Hantoro, W. S.; Rifai, H.; Hellstrom, J. C.; Heslop, D.; Troitzsch, U.; Eggins, S.

    2015-12-01

    Holocene climate variability in the Indo-Pacific has largely been inferred from sediment cores primarily from the central and eastern Warm Pool region. A limited number of speleothem oxygen-isotope records have provided decadally-resolved time-series of past rainfall variability over the central Indo-Pacific Warm Pool region, however no records currently exist for the Indian Ocean sector of the IPWP. Here we present the first continuous, high-resolution (~15year) speleothem record from the eastern tropical Indian Ocean, collected from central western Sumatra, Indonesia. Petrographic and geochemical analysis reveals that the sample is primarily composed of aragonite but is punctuated by intervals of primary calcite growth. In addition to Raman spectroscopy, trace element analysis by laser ablation ICP-MS reveals strongly antiphased behaviour between magnesium and strontium, attributed to the strong preference of those elements for the calcite and aragonite lattices, respectively. This relationship is utilized to develop a quantitative correction for the stable isotope fractionation offset between the two calcium carbonate polymorphs identified in the speleothem. The corrected oxygen isotope record shows a rapid transition from drier conditions during the Younger Dryas (YD) into a wetter Holocene, similar in timing and pattern to that recorded in Dongge Cave, China. This is strikingly different from other IPWP speleothem records, which show no YD or a wetter YD, suggesting that different mechanisms may be controlling rainfall amount in the eastern tropical Indian Ocean. These disparate responses are further explored through proxy-model comparison.

  13. Vertical and horizontal distribution of Desmophyllum dianthus in Comau Fjord, Chile: a cold-water coral thriving at low pH.

    Science.gov (United States)

    Fillinger, Laura; Richter, Claudio

    2013-01-01

    Cold-water corals provide an important habitat for a rich fauna along the continental margins and slopes. Although these azooxanthellate corals are considered particularly sensitive to ocean acidification, their responses to natural variations in pH and aragonite saturation are largely unknown due to the difficulty of studying their ecology in deep waters. Previous SCUBA investigations have shown an exceptionally shallow population of the cold-water coral Desmophyllum dianthus in near-surface waters of Comau Fjord, a stratified 480 m deep basin in northern Chilean Patagonia with suboxic deep waters. Here, we use a remotely operated vehicle to quantitatively investigate the distribution of D. dianthus and its physico-chemical drivers in so far uncharted naturally acidified waters. Remarkably, D. dianthus was ubiquitous throughout the fjord, but particularly abundant between 20 and 280 m depth in a pH range of 8.4 to 7.4. The persistence of individuals in aragonite-undersaturated waters suggests that present-day D. dianthus in Comau Fjord may show pre-acclimation or pre-adaptation to conditions of ocean acidification predicted to reach over 70% of the known deep-sea coral locations by the end of the century.

  14. Vertical and horizontal distribution of Desmophyllum dianthus in Comau Fjord, Chile: a cold-water coral thriving at low pH

    Directory of Open Access Journals (Sweden)

    Laura Fillinger

    2013-10-01

    Full Text Available Cold-water corals provide an important habitat for a rich fauna along the continental margins and slopes. Although these azooxanthellate corals are considered particularly sensitive to ocean acidification, their responses to natural variations in pH and aragonite saturation are largely unknown due to the difficulty of studying their ecology in deep waters. Previous SCUBA investigations have shown an exceptionally shallow population of the cold-water coral Desmophyllum dianthus in near-surface waters of Comau Fjord, a stratified 480 m deep basin in northern Chilean Patagonia with suboxic deep waters. Here, we use a remotely operated vehicle to quantitatively investigate the distribution of D. dianthus and its physico-chemical drivers in so far uncharted naturally acidified waters. Remarkably, D. dianthus was ubiquitous throughout the fjord, but particularly abundant between 20 and 280 m depth in a pH range of 8.4 to 7.4. The persistence of individuals in aragonite-undersaturated waters suggests that present-day D. dianthus in Comau Fjord may show pre-acclimation or pre-adaptation to conditions of ocean acidification predicted to reach over 70% of the known deep-sea coral locations by the end of the century.

  15. Cementing mussels to oysters in the pteriomorphian tree: a phylogenomic approach

    Science.gov (United States)

    González, Vanessa L.; Bieler, Rüdiger; Giribet, Gonzalo

    2016-01-01

    Mussels (Mytilida) are a group of bivalves with ancient origins and some of the most important commercial shellfish worldwide. Mytilida consists of approximately 400 species found in various littoral and deep-sea environments, and are part of the higher clade Pteriomorphia, but their exact position within the group has been unstable. The multiple adaptive radiations that occurred within Pteriomorphia have rendered phylogenetic classifications difficult and uncertainty remains regarding the relationships among most families. To address this phylogenetic uncertainty, novel transcriptomic data were generated to include all five orders of Pteriomorphia. Our results, derived from complex analyses of large datasets from 41 transcriptomes and evaluating possible pitfalls affecting phylogenetic reconstruction (matrix occupancy, heterogeneity, evolutionary rates, evolutionary models), consistently recover a well-supported phylogeny of Pteriomorphia, with the only exception of the most complete but smallest data matrix (Matrix 3: 51 genes, 90% gene occupancy). Maximum-likelihood and Bayesian mixture model analyses retrieve strong support for: (i) the monophyly of Pteriomorphia, (ii) Mytilida as a sister group to Ostreida, and (iii) Arcida as sister group to all other pteriomorphians. The basal position of Arcida is congruent with its shell microstructure (solely composed of aragonitic crystals), whereas Mytilida and Ostreida display a combination of a calcitic outer layer with an aragonitic inner layer composed of nacre tablets, the latter being secondarily lost in Ostreoidea. PMID:27358369

  16. Influence of acid-soluble proteins from bivalve Siliqua radiata ligaments on calcium carbonate crystal growth

    Science.gov (United States)

    Huang, Zeng-Qiong; Zhang, Gang-Sheng

    2016-08-01

    In vitro biomimetic synthesis of calcium carbonate (CaCO3) in the presence of shell proteins is a heavily researched topic in biomineralization. However, little is known regarding the function of bivalve ligament proteins in the growth of CaCO3 crystals. In this study, using fibrous protein K58 from Siliqua radiata ligaments or coverslips as substrates, we report the results of our study of CaCO3 precipitation in the presence or absence of acid-soluble proteins (ASP) from inner ligament layers. ASP can disturb the controlling function of K58 or a coverslip on the crystalline phase, resulting in the formation of aragonite, calcite, and vaterite. In addition, we identified the following four primary components from ASP by mass spectroscopy: alkaline phosphatase (ALP), ABC transporter, keratin type II cytoskeletal 1 (KRT 1), and phosphate ABC transporter, phosphate-binding protein (PstS). Further analysis revealed that the first three proteins and especially ALP, which is important in bone mineralisation, could affect the polymorphism and morphology of CaCO3 crystals by trapping calcium ions in their domains. Our results indicate that ALP may play an important role in the formation of aragonite in S. radiata ligaments. This paper may facilitate our understanding of the biomineralization process.

  17. Upwelling of Acidified Water: Not Just an Issue for Shellfish Hatcheries on the West Coast of the US

    Science.gov (United States)

    Poach, M.; Munroe, D.; Abrahamsen, I.

    2014-12-01

    Periodic upwelling events are known to occur off the coast of New Jersey during the summer. As with upwelling off the US West Coast, these events can transport acidified water to the surface and shoreward. To determine if upwelling events have the potential to impact shellfish hatcheries in New Jersey, a monitoring study was conducted at the Aquaculture Innovation Center (AIC) of Rutgers University. The AIC is an important hatchery supporting the New Jersey oyster aquaculture industry through the production of disease resistant seed oysters. Starting in June of 2014, temperature, salinity, dissolved oxygen and pH were continuously monitored at the AIC's intake pipe. Periodic grab samples were also collected at the intake and at locations within the facility. Grab samples were preserved and analyzed for pH and dissolved inorganic carbon (DIC). DIC and pH were used to calculate the aragonite saturation state of the sampled water. During an upwelling event in early July a drop in pH was measured at the intake. Grab samples showed that water of lower pH and aragonite saturation was entering the facility. These results show that hatcheries along the NJ coast need to be aware that upwelling events may bring conditions detrimental for shellfish production.

  18. Variability of the carbonate chemistry in a shallow, seagrass-dominated ecosystem: implications for ocean acidification experiments

    Science.gov (United States)

    Challener, Roberta; Robbins, Lisa L.; Mcclintock, James B.

    2016-01-01

    Open ocean observations have shown that increasing levels of anthropogenically derived atmospheric CO2 are causing acidification of the world's oceans. Yet little is known about coastal acidification and studies are just beginning to characterise the carbonate chemistry of shallow, nearshore zones where many ecologically and economically important organisms occur. We characterised the carbonate chemistry of seawater within an area dominated by seagrass beds (Saint Joseph Bay, Florida) to determine the extent of variation in pH and pCO2 over monthly and daily timescales. Distinct diel and seasonal fluctuations were observed at daily and monthly timescales respectively, indicating the influence of photosynthetic and respiratory processes on the local carbonate chemistry. Over the course of a year, the range in monthly values of pH (7.36-8.28), aragonite saturation state (0.65-5.63), and calculated pCO2 (195-2537 μatm) were significant. When sampled on a daily basis the range in pH (7.70-8.06), aragonite saturation state (1.86-3.85), and calculated pCO2 (379-1019 μatm) also exhibited significant range and indicated variation between timescales. The results of this study have significant implications for the design of ocean acidification experiments where nearshore species are utilised and indicate that coastal species are experiencing far greater fluctuations in carbonate chemistry than previously thought.

  19. Pteropods from the Caribbean Sea: dissolution as an indicator of past ocean acidification

    Directory of Open Access Journals (Sweden)

    D. Wall-Palmer

    2011-07-01

    Full Text Available The aragonite shell–bearing thecosome pteropods are an important component of the oceanic plankton. However, with increasing pCO2 and the associated reduction in oceanic pH (ocean acidification, thecosome pteropods are thought to be particularly vulnerable to shell dissolution. The distribution and preservation of pteropods over the last 250,000 years have been investigated in marine sediment cores from the Caribbean Sea close to the island of Montserrat. Using the Limacina Dissolution Index (LDX, fluctuations in pteropod dissolution through the most recent glacial/interglacial cycles is documented. By comparison to the oxygen isotope record (global sea ice volume, we show that pteropod dissolution is closely linked to global changes in pCO2 and pH and is, therefore, a global signal. These data are in agreement with the findings of experiments upon living pteropods, which show that variations in pH can greatly affect aragonitic shells. The results of this study provide information which may be useful in the prediction of future changes to the pteropod assemblage caused by ocean acidification.

  20. Lime muds and their genesis off-Northwestern India during the late Quaternary

    Indian Academy of Sciences (India)

    V Purnachandra Rao; A Anil Kumar; S W A Naqvi; Allan R Chivas; B Sekar; Pratima M Kessarkar

    2012-06-01

    Two sediment types were found in five gravity cores collected from water depths between 56 m and 121 m along the northwestern continental margin of India: lime muds were abundant in the lower section while siliciclastic sediments dominated the upper section. Lime mud-dominated sediments in shelf cores contained 60%–75% carbonate, 0.3%–0.6% Sr and terrigenous minerals, whereas those at the shelf break were found to have < 90% carbonate, 0.6%–0.8% Sr and traces of terrigenous minerals. Aragonite needles showing blunt edges, jointed needles and needles wrapped in smooth aragonite cement were found to be common. Stable (O and C) isotopes of lime mud indicate a potentially freshwater contribution for shelf cores and purely marine contribution for those at the shelf break. Calibrated radiocarbon ages of the lime muds ranged from 17.6–11.9 ka in different cores. The results reported here suggest that the lime muds in the shallow shelf are probably reworked from the Gulf of Kachchh, whereas those at the shelf break were biodetrital, initially formed on the carbonate platform during low stands of sea level and then exported. The change in lime mud-dominated to siliciclastic-dominated sediments in the cores may be due to climate change and rapid rise in sea level during the early Holocene.

  1. Reef coral δ18O thermometer in Hainan island waters, south China sea

    International Nuclear Information System (INIS)

    An 18-year-long (1981-1998) study was conducted in Hainan Island waters (22 degree 22'N, 110 degree 39'E) to determine the relationship between δ18O in skeletal aragonite carbonate and sea surface temperature (SST) in porites lutea of reef-building corals. δ18O values in skeletal aragonite carbonate were measured by means of mass spectrometry. Coral samples grew at 5 m depth at Longwan Bay. Monthly measurements of the SST from 1960 to 1998 were taken at Qinglan Bay adjacent to the place of the collected samples. The thermometer shows that SST = -4.16 δ18OPDB + 4.9 (r = 0.80) and dδ18O/dT = -0.24 per mil/degree C. The δ18O thermometer is strongly influenced by the rainfall and runoff. Using the thermometer, the SST in the past hundred years with monthly resolution will be reconstructed and the climatic change in the northern area of South China Sea will be hind cast

  2. Naked Stony Corals: Skeleton Loss in Scleractinia

    Energy Technology Data Exchange (ETDEWEB)

    Medina, Monica; Collins, Allen G.; Takaoka, Tori L.; Kuehl,Jennifer; Boore, Jeffrey L.

    2005-12-01

    Hexacorallia includes the Scleractinia, or stony corals, characterized by having an external calcareous skeleton made of aragonite, and the Corallimorpharia, or mushroom corals, that lack such a skeleton. Although each group has traditionally been considered monophyletic, some molecular phylogenetic analyses have challenged this, suggesting that skeletal features are evolutionarily plastic, and reviving notions that the scleractinian skeleton may be ephemeral and that the group itself may be polyphyletic. Nevertheless, the most comprehensive phylogenetic study of Hexacorallia supported scleractinian monophyly (REF), and so this remains controversial. In order to resolve this contentious issue, we sequenced the complete mitochondrial genome sequences of nine scleractinians and four corallimorpharians and performed phylogenetic analysis that also included three outgroups (an octocoral and two sea anemones). Our data provide the first strong evidence that Scleractinia is paraphyletic and that the Corallimorpharia is derived from within the group, from which we conclude that skeletal loss has occurred in the latter group secondarily. It is possible that a driving force in such skeletal loss could be the high levels of CO{sub 2} in the ocean during the mid-Cretaceous, which would have impacted aragonite solubility. We estimate from molecular divergence measures that the Corallimorpharia arose in the mid-Cretaceous, approximately 87 million years ago (Ma), supporting this view. These data also permit us to date the origin of Scleractinia to 265 Ma, narrowing the gap between the group's phylogenetic origin and its earliest fossil record.

  3. Comment on Peck et al: Vulnerability of pteropod (Limacina helicina) to ocean acidification: shell dissolution occurs despite an intact organic layer

    Science.gov (United States)

    Bednaršek, N.; Johnson, J.; Feely, R. A.

    2016-05-01

    Pteropods have been recognized as one of the most sensitive marine organisms to ocean acidification (OA). Their susceptibility is mostly related to rapid shell dissolution, which is correlated with exposure to waters undersaturated with respect to aragonite (Ωar≤ 1) (e.g., Lischka et al., 2011; Bednaršek et al., 2012a,b, 2014a,b; Busch et al., 2014). Increased dissolution weakens the shell, increases vulnerability to predation and infection, and imposes an energetic cost. The rapidity of shell dissolution is attributed to the combination of metastable aragonitic crystal structure of shells that are among the thinnest known for calcifying organisms, and an extremely thin outer organic layer (i.e. periostracum <1 μm thick), suggesting insufficient protection against shell dissolution at Ωar≤1 (Bednaršek et al., 2014b). The periostracum generally consists of polysaccharide and proteinaceous components (Gaffey and Bronnimann, 1993) but varies significantly in its structure and composition amongst taxa.

  4. Gradual Ordering in Red Abalone Nacre

    Energy Technology Data Exchange (ETDEWEB)

    Gilbert, P. U. P. A.; Metzler, Rebecca A.; Zhou, Dong; Scholl, Andreas; Doran, Andrew; Young, Anthony; Kunz, Martin; Tamura, Nobumichi; Coppersmith, Susan N.

    2008-09-03

    Red abalone (Haliotis rufescens) nacre is a layered composite biomineral that contains crystalline aragonite tablets confined by organic layers. Nacre is intensely studied because its biologically controlled microarchitecture gives rise to remarkable strength and toughness, but the mechanisms leading to its formation are not well understood. Here we present synchrotron spectromicroscopy experiments revealing that stacks of aragonite tablet crystals in nacre are misoriented with respect to each other. Quantitative measurements of crystal orientation, tablet size, and tablet stacking direction show that orientational ordering occurs not abruptly but gradually over a distance of 50 {micro}m. Several lines of evidence indicate that different crystal orientations imply different tablet growth rates during nacre formation. A theoretical model based on kinetic and gradual selection of the fastest growth rates produces results in qualitative and quantitative agreement with the experimental data and therefore demonstrates that ordering in nacre is a result of crystal growth kinetics and competition either in addition or to the exclusion of templation by acidic proteins as previously assumed. As in other natural evolving kinetic systems, selection of the fastest-growing stacks of tablets occurs gradually in space and time. These results suggest that the self-ordering of the mineral phase, which may occur completely independently of biological or organic-molecule control, is fundamental in nacre formation.

  5. The influence of solution stoichiometry on surface-controlled Ca isotope fractionation during Ca carbonate precipitation from Mono Lake, California

    Science.gov (United States)

    Nielsen, L. C.; Depaolo, D. J.

    2010-12-01

    Precipitation of calcite and aragonite from aqueous solution causes kinetic stable Ca isotope fractionation under conditions where Ca2+ is greatly in excess of CO32-. Research on carbonate mineral growth from low Ca2+:CO32- activity ratio solutions is lacking. Mono Lake, California is a highly alkaline lake with a Ca2+:CO32- activity ratio of 9.6 x 10-4, over five orders of magnitude lower than typical terrestrial fresh and ocean water. Aragonitic tufa towers grow along the lakeshore due to the mixing of lake water and Ca-rich spring water, while fine aragonite particles precipitate directly from the lake water, accumulating on the lake bottom. Variations in the Ca2+:CO32- activity ratio affect calcite growth kinetics and could affect the partitioning of Ca isotopes during carbonate precipitation. However, the relationship between solution stoichiometry, microscopic mineral growth mechanisms and calcium isotope fractionation is poorly understood. We analyzed the Sr and Ca isotopic compositions of a suite of lake water, spring, tufa and lake bottom sediment samples from the Mono Basin. Using the Sr isotope signatures of endmember water sources (pure lake water and shoreline spring water), we determined the compositions of carbonate mineral growth solutions, associated isotope separations (Δ44/40Cas-f = δ44/40Casolid - δ44/40Cafluid) and precipitation rates. While lake bottom aragonite precipitates directly from lake water (Ca2+:CO32- ≈ 10-3), tufa grows from mixed solutions with Ca2+:CO32- activity ratios approaching 10, so carbonate precipitation in Mono Lake spans a four order of magnitude range in solution stoichiometry. At Mono Lake, Δ44/40Cas-f and calculated precipitation rates vary between -0.6±0.15‰ at 1.5×10-9 mol m-2 s-1 for aragonite precipitating from lake water and ~ -1.0±0.15‰ at up to 4×10-8 mol m-2 s-1 for tufa growing from mixed spring and lake water. These values are consistent with fractionation observed during CaCO3 precipitation at

  6. Mg-isotopic fractionation in the manila clam (Ruditapes philippinarum): New insights into Mg incorporation pathway and calcification process of bivalves

    Science.gov (United States)

    Planchon, Frédéric; Poulain, Céline; Langlet, Denis; Paulet, Yves-Marie; André, Luc

    2013-11-01

    We estimate the magnesium stable isotopic composition (δ26Mg) of the major compartments involved in the biomineralisation process of euryhaline bivalve, the manila clam Ruditapes philippinarum. Our aim is to identify the fractionation processes associated with Mg uptake and its cycling/transport in the bivalve organism, in order to better assess the controlling factors of the Mg isotopic records in bivalve shells. δ26Mg were determined in seawater, in hemolymph, extrapallial fluid (EPF), soft tissues and aragonitic shell of adult clams collected along the Auray River estuary (Gulf of Morbihan, France) at two sites showing contrasted salinity regimes. The large overall δ26Mg variations (4.16‰) demonstrate that significant mass-dependent Mg isotopic fractionations occur during Mg transfer from seawater to the aragonitic shell. Soft tissues span a range of fractionation factors relative to seawater (Δ26Mgsoft tissue-seawater) of 0.42 ± 0.12‰ to 0.76 ± 0.12‰, and show evidence for biological isotopic fractionation of Mg. Hemolymph and EPF are on average isotopically close to seawater (Δ26Mghemolymph-seawater = -0.20 ± 0.27‰; 2 sd; n = 5 and Δ26MgEPF-seawater = -0.23 ± 0.25‰; 2 sd; n = 5) indicating (1) a predominant seawater origin for Mg in the intercellular medium and (2) a relatively passive transfer route through the bivalve organism into the calcifying fluid. The lightest isotopic composition is found in shell, with δ26Mg ranging from -1.89 ± 0.07‰ to -4.22 ± 0.06‰. This range is the largest in the dataset and is proposed to result from a combination of abiotic and biologically-driven fractionation processes. Abiotic control includes fractionation during precipitation of aragonite and accounts for Δ26Mgaragonite-seawater ≈ 1000 ln αaragonite-seawater = -1.13 ± 0.28‰ at 20 °C based on literature data. Deviations from inorganic precipitate (expressed as Δ26MgPhysiol) appear particularly variable in the clam shell, ranging from 0

  7. Biomineralization in bryozoans: present, past and future.

    Science.gov (United States)

    Taylor, Paul D; Lombardi, Chiara; Cocito, Silvia

    2015-11-01

    Many animal phyla have the physiological ability to produce biomineralized skeletons with functional roles that have been shaped by natural selection for more than 500 million years. Among these are bryozoans, a moderately diverse phylum of aquatic invertebrates with a rich fossil record and importance today as bioconstructors in some shallow-water marine habitats. Biomineralizational patterns and, especially, processes are poorly understood in bryozoans but are conventionally believed to be similar to those of the related lophotrochozoan phyla Brachiopoda and Mollusca. However, bryozoan skeletons are more intricate than those of these two phyla. Calcareous skeletons have been acquired independently in two bryozoan clades - Stenolaemata in the Ordovician and Cheilostomata in the Jurassic - providing an evolutionary replicate. This review aims to highlight the importance of biomineralization in bryozoans and focuses on their skeletal ultrastructures, mineralogy and chemistry, the roles of organic components, the evolutionary history of bimineralization in bryozoans with respect to changes in seawater chemistry, and the impact of contemporary global changes, especially ocean acidification, on bryozoan skeletons. Bryozoan skeletons are constructed from three different wall types (exterior, interior and compound) differing in the presence/absence and location of organic cuticular layers. Skeletal ultrastructures can be classified into wall-parallel (i.e. laminated) and wall-perpendicular (i.e. prismatic) fabrics, the latter apparently found in only one of the two biomineralizing clades (Cheilostomata), which is also the only clade to biomineralize aragonite. A plethora of ultrastructural fabrics can be recognized and most occur in combination with other fabrics to constitute a fabric suite. The proportion of aragonitic and bimineralic bryozoans, as well as the Mg content of bryozoan skeletons, show a latitudinal increase into the warmer waters of the tropics. Responses

  8. Experimental approaches to marine and meteoric dissolution-to-repreciptiation cycles of fine-grained marine carbonate sediments

    Science.gov (United States)

    Immenhauser, Adrian; Buhl, Dieter; Riechelmann, Sylvia; Kwiecien, Ola; Lokier, Stephen; Neuser, Rolf

    2016-04-01

    Fine-grained carbonate (carbonate ooze), or microcrystalline carbonate (micrite), its lithified counterpart, forms a main constituent of limestones throughout much of Earth's history. Fine-grained carbonates are deposited below the permanent fair-weather wave base in neritic lagoonal environments or below the storm-wave base in basinal settings. The origin of components forming these fine-grained carbonates often remains poorly understood and represents a major challenge in carbonate sedimentology, particularly when these materials are used as carbonate archives (bulk micrite geochemistry). Here we present a novel experimental approach exposing natural, fine-grained carbonate sediments to dissolution-reprecipitation cycles under non-sterile conditions that mimick earth-surface conditions. In a first stage, the experiment simulated subaerial exposure of an ooid (aragonite) shoal and leaching and carbonate dissolution under meteoric phreatic conditions. In a second stage, CO2 was added to the experimental fluid (natural rainwater) representing soil-zone activity. In a third stage, partly dissolved (micro-karstified) sediments were exposed to marine phreatic conditions simulating renewed flooding of the shoal carbonates. During the third stage, precipitation was induced by degassing the CO2 in the fluid with N2. Degassing induced nucleation and growth of a diagenetic inorganic aragonite (and subordinate calcite) phase upon the surface of carbonate particles. The outcome of these first experiments is promising. The CO2 concentration of the fluid and the air are low under atmospheric conditions and increase as expected due to adding CO2 to the experiment resulting in a lower pH. Carbonate dissolution increases conductivity, alkalinity, and calcium concentration reaching a plateau at the end of the first experimental phase. Small surficial damages to ooids represent zones of weakness and form the preferred sites of dissolution leading to a deepening and widening of these

  9. Estimates of ikaite export from sea ice to the underlying seawater in a sea ice-seawater mesocosm

    Science.gov (United States)

    Geilfus, Nicolas-Xavier; Galley, Ryan J.; Else, Brent G. T.; Campbell, Karley; Papakyriakou, Tim; Crabeck, Odile; Lemes, Marcos; Delille, Bruno; Rysgaard, Søren

    2016-09-01

    the effect of oceanic acidification on the aragonite saturation state (Ωaragonite) in fall and in winter in ice-covered areas, at the time when Ωaragonite is smallest.

  10. Spatiotemporal variability and long-term trends of ocean acidification in the California Current System

    Directory of Open Access Journals (Sweden)

    C. Hauri

    2013-01-01

    Full Text Available Due to seasonal upwelling, the upper ocean waters of the California Current System (CCS have a naturally low pH and aragonite saturation state (Ωarag, making this region particularly prone to the effects of ocean acidification. Here, we use the Regional Oceanic Modeling System (ROMS to conduct preindustrial and transient (1995–2050 simulations of ocean biogeochemistry in the CCS. The transient simulations were forced with increasing atmospheric pCO2 and increasing oceanic dissolved inorganic carbon concentrations at the lateral boundaries, as projected by the NCAR CSM 1.4 model for the IPCC SRES A2 scenario. Our results show a large seasonal variability in pH (range of ~ 0.14 and Ωarag (~ 0.2 for the nearshore areas (50 km from shore. This variability is created by the interplay of physical and biogeochemical processes. Despite this large variability, we find that present-day pH and Ωarag have already moved outside of their simulated preindustrial variability envelopes (defined by ±1 temporal standard deviation due to the rapidly increasing concentrations of atmospheric CO2. The nearshore surface pH of the northern and central CCS are simulated to move outside of their present-day variability envelopes by the mid-2040s and late 2030s, respectively. This transition may occur even earlier for nearshore surface Ωarag, which is projected to depart from its present-day variability envelope by the early- to mid-2030s. The aragonite saturation horizon of the central CCS is projected to shoal into the upper 75 m within the next 25 yr, causing near-permanent undersaturation in subsurface waters. Due to the model's overestimation of Ωarag, this transition may occur even earlier than simulated by the model. Overall, our study shows that the CCS joins the Arctic and Southern oceans as one of only a few known ocean regions presently approaching the dual threshold of

  11. Will Coral Islands maintain their growth over the next century? A deterministic model of sediment availability at Lady Elliot Island, Great Barrier Reef.

    Science.gov (United States)

    Hamylton, Sarah

    2014-01-01

    A geomorphic assessment of reef system calcification is conducted for past (3200 Ka to present), present and future (2010-2100) time periods. Reef platform sediment production is estimated at 569 m3 yr-1 using rate laws that express gross community carbonate production as a function of seawater aragonite saturation, community composition and rugosity and incorporating estimates of carbonate removal from the reef system. Key carbonate producers including hard coral, crustose coralline algae and Halimeda are mapped accurately (mean R2 = 0.81). Community net production estimates correspond closely to independent census-based estimates made in-situ (R2 = 0.86). Reef-scale outputs are compared with historic rates of production generated from (i) radiocarbon evidence of island deposition initiation around 3200 years ago, and (ii) island volume calculated from a high resolution island digital elevation model. Contemporary carbonate production rates appear to be remarkably similar to historical values of 573 m3 yr-1. Anticipated future seawater chemistry parameters associated with an RCP8.5 emissions scenario are employed to model rates of net community calcification for the period 2000-2100 on the basis of an inorganic aragonite precipitation law, under the assumption of constant benthic community character. Simulations indicate that carbonate production will decrease linearly to a level of 118 m3 yr-1 by 2100 and that by 2150 aragonite saturation levels may no longer support the positive budgetary status necessary to sustain island accretion. Novel aspects of this assessment include the development of rate law parameters to realistically represent the variable composition of coral reef benthic carbonate producers, incorporation of three dimensional rugosity of the entire reef platform and the coupling of model outputs with both historical radiocarbon dating evidence and forward hydrochemical projections to conduct an assessment of island evolution through time

  12. Experiments on different materials (polyamide, stainless & galvanized steel) influencing geothermal CaCO3 scaling formation: Polymorphs & elemental incorporation

    Science.gov (United States)

    Wedenig, Michael; Dietzel, Martin; Boch, Ronny; Hippler, Dorothee

    2016-04-01

    Thermal water is increasingly used for heat and electric power production providing base-load capable renewable and virtually unlimited geothermal energy. Compared to other energy sources geothermal facilities are less harmful to the environment, i.e. chemically and visually. In order to promote the economic viability of these systems compared to other traditional and renewable energy sources, production hindering processes such as corrosion and scaling of components arising from the typically high salinity thermal waters have to be considered as important economic factors. In this context, using proper materials being in contact with the thermal water is crucial and a playground for further improvements. Aim of the study presented, are basic experiments and observations of scaling and corrosive effects from hydrothermal water interacting with different materials and surfaces (stainless steel, polyamide, galvanized steel) and in particular the nucleation and growth effects of these materials regarding the precipitation of solid carbonate phases. The incorporation of Mg, Sr and Ba cations into the carbonate scalings are investigated as environmental proxy. For this purpose, hydrothermal carbonate precipitating experiments were initialized by mixing NaHCO3 and Ca-Mg-Sr-Ba-chloride solutions at temperatures ranging from 40 to 80 °C in glass reactors hosting artificial substrates of the above mentioned materials. The experiments show a strong dependence of the precipitation behaviour of calcium carbonate polymorphs on the particular material being present. Stainless steel and polyamide seem to restrict aragonite formation, whereas galvanized steel supports aragonite nucleation. Vaterite formation is promoted by polyamide surfaces. Importantly, vaterite is more soluble (less stable) compared to the other anhydrous calcium carbonate polymorphs, i.e. vaterite can be more easily re-dissolved. Thus, the use of polyamide components might reduce the amount and durability of

  13. Towards the kinetics of diagenetic overprint processes deduced from laboratory-based hydrothermal alteration of modern Arctica islandica shell material

    Science.gov (United States)

    Casella, Laura A.; Griesshaber, Erika; Mavromatis, Vasileios; Dietzel, Martin; Immenhauser, Adrian; Schmahl, Wolfgang W.

    2016-04-01

    Benthic and nektonic marine biogenic carbonate archives represent the foundation of numerous studies aiming at paleo-environment reconstructions. However, living organisms are not in thermodynamic equilibrium as they form local chemical environments for physiologic processes such as biological mineralization of their hard tissues. This disequilibrium is not sustained after death and all biological tissues are altered by equilibration with the surrounding environment: diagenesis. To understand transformation during diagenesis we performed laboratory-based hydrothermal alteration experiments on Arctica islandica shells at four different temperatures between 100 °C and 175 °C treated in simulated meteoric and burial waters, respectively. We investigated, relative to unaltered shells, the kinetics of Arctica islandica bioaragonite to calcite transition as well as microstructural- and nanostructural characteristics of the altered shells with X-ray diffraction, micro-Raman, high-resolution SEM and EBSD. At hydrothermal treatment at 100 °C bioaragonite - although metastable at 1 bar - does not transform to calcite, even in meteoric fluids and over a time period of 28 days. We noted a drastic recrystallization from the initial fine-grained fractal microstructure and pronounced axial texture to a new and still fine-grained microstructure with an almost randomized orientation distribution. At 175 °C the transformation to coarse-grained calcite is complete after 8 days. Calcite formation starts after a passive incubation period of 4 days; after 6 days the aragonite is almost completely transformed. In solutions simulating meteoric water the grain size of the newly formed calcite reaches 100-150 μm, while in burial fluids the calcite reaches sizes in the 1mm range during 28 days of alteration. Phase transformation proceeds where the hydrothermal fluid is in contact with the aragonite: at shell surfaces, around pores and in growth lines. Our observations lead us to the

  14. Timing of methane efflux along the Norwegian and US Atlantic margin

    Science.gov (United States)

    Sahy, Diana; Condon, Daniel; Lepland, Aivo; Crémière, Antoine; Noble, Stephen; Ruppel, Carolyn

    2016-04-01

    Methane-related authigenic carbonates (MDAC) provide a robust archive of past methane emissions from cold seeps located along continental margins. MDAC are amenable to U-Th geochronology which can be used to assess the timing and drivers of fluid flow (Teichert et al., 2003; Bayon et al., 2013). The difficulty of sourcing MDAC typically precludes the assembly of datasets with sufficient geographic coverage and resolution to investigate the processes triggering and sustaining methane seeps on a regional scale. To address this, two collaborative projects led by the British, Norwegian and US geological surveys are currently underway, targeting methane seeps located along the Norwegian and US Atlantic margins (Skarke et al., 2014). MDAC samples collected for the two projects come from a range of depths (300-2000 m), and are linked to a variety of processes (e.g. collapse of grounded ice sheet, salt diapirism, dissociation of upper slope gas hydrates, emissions from deep reservoirs through fault networks). MDAC typically present as matrix-supported conglomerate /sandstone/ siltstone, and consist of detrital material of variable grainsize (depending on locality) encased in an aragonite and/or calcite cement. Interconnected voids within the MDAC, which likely represent fluid conduits, are often at least partially filled with clean (>90%), layered aragonite. The latter are ideal materials for U-Th geochronology, and can yield U-Th dates with precision approaching 0.5 % (2σ), with thicker (ca. 2 cm) layered cavity fills showing resolvable growth histories on the order of 1 kyr. While measurements on cavity-filling aragonite give a snapshot of seep activity, quantifying the entire methane emission history of a sample, and crucially, the timing of the onset of emissions, requires the analysis of MDAC groundmass. Such analyses are more challenging as initial detrital 230Th included in the samples must be accounted for. While precise dating of the onset of methane emissions at

  15. Spatiotemporal variability and long-term trends of ocean acidification in the California Current System

    Science.gov (United States)

    Hauri, C.; Gruber, N.; Vogt, M.; Doney, S. C.; Feely, R. A.; Lachkar, Z.; Leinweber, A.; McDonnell, A. M. P.; Munnich, M.; Plattner, G.-K.

    2013-01-01

    Due to seasonal upwelling, the upper ocean waters of the California Current System (CCS) have a naturally low pH and aragonite saturation state (Ωarag), making this region particularly prone to the effects of ocean acidification. Here, we use the Regional Oceanic Modeling System (ROMS) to conduct preindustrial and transient (1995-2050) simulations of ocean biogeochemistry in the CCS. The transient simulations were forced with increasing atmospheric pCO2 and increasing oceanic dissolved inorganic carbon concentrations at the lateral boundaries, as projected by the NCAR CSM 1.4 model for the IPCC SRES A2 scenario. Our results show a large seasonal variability in pH (range of ~ 0.14) and Ωarag (~ 0.2) for the nearshore areas (50 km from shore). This variability is created by the interplay of physical and biogeochemical processes. Despite this large variability, we find that present-day pH and Ωarag have already moved outside of their simulated preindustrial variability envelopes (defined by ±1 temporal standard deviation) due to the rapidly increasing concentrations of atmospheric CO2. The nearshore surface pH of the northern and central CCS are simulated to move outside of their present-day variability envelopes by the mid-2040s and late 2030s, respectively. This transition may occur even earlier for nearshore surface Ωarag, which is projected to depart from its present-day variability envelope by the early- to mid-2030s. The aragonite saturation horizon of the central CCS is projected to shoal into the upper 75 m within the next 25 yr, causing near-permanent undersaturation in subsurface waters. Due to the model's overestimation of Ωarag, this transition may occur even earlier than simulated by the model. Overall, our study shows that the CCS joins the Arctic and Southern oceans as one of only a few known ocean regions presently approaching the dual threshold of widespread and near-permanent undersaturation with respect to aragonite and a departure from its

  16. Sr/Ca and Mg/Ca vital effects correlated with skeletal architecture in a scleractinian deep-sea coral and the role of Rayleigh fractionation

    Science.gov (United States)

    Gagnon, Alexander C.; Adkins, Jess F.; Fernandez, Diego P.; Robinson, Laura F.

    2007-09-01

    Deep-sea corals are a new tool in paleoceanography with the potential to provide century long records of deep ocean change at sub-decadal resolution. Complicating the reconstruction of past deep-sea temperatures, Mg/Ca and Sr/Ca paleothermometers in corals are also influenced by non-environmental factors, termed vital effects. To determine the magnitude, pattern and mechanism of vital effects we measure detailed collocated Sr/Ca and Mg/Ca ratios, using a combination of micromilling and isotope-dilution ICP-MS across skeletal features in recent samples of Desmophyllum dianthus, a scleractinian coral that grows in the near constant environment of the deep-sea. Sr/Ca variability across skeletal features is less than 5% (2σ relative standard deviation) and variability of Sr/Ca within the optically dense central band, composed of small and irregular aragonite crystals, is significantly less than the surrounding skeleton. The mean Sr/Ca of the central band, 10.6 ± 0.1 mmol/mol (2σ standard error), and that of the surrounding skeleton, 10.58±0.09 mmol/mol, are statistically similar, and agree well with the inorganic aragonite Sr/Ca-temperature relationship at the temperature of coral growth. In the central band, Mg/Ca is greater than 3 mmol/mol, more than twice that of the surrounding skeleton, a general result observed in the relative Mg/Ca ratios of D. dianthus collected from separate oceanographic locations. This large vital effect corresponds to a ˜ 10 °C signal, when calibrated via surface coral Mg/Ca-temperature relationships, and has the potential to complicate paleoreconstructions. Outside the central band, Mg/Ca ratios increase with decreasing Sr/Ca. We explain the correlated behavior of Mg/Ca and Sr/Ca outside the central band by Rayleigh fractionation from a closed pool, an explanation that has been proposed elsewhere, but which is tested in this study by a simple and general relationship. We constrain the initial solution and effective partition

  17. Investigation of Bio-Inspired Hybrid Materials through Polymer Infiltration of Thermal Spray Formed Ceramic Templates

    Science.gov (United States)

    Flynn, Katherine Claire

    High strength and toughness are often mutually exclusive in engineered materials. This is especially true of ceramics and polymers. Ceramics exhibit high strength and stiffness, but are brittle while polymers are flaw tolerant but prone to deformation at low stresses. Nature overcomes this restriction in materials by strategically combining brittle components with tough organics, leading to materials with both a high strength and toughness. One of the most impressive natural composites is nacre consisting of mainly a brittle mineral phase, 95vol% calcium carbonate (aragonite), and 5vol% biopolymer (a combination of proteins and polysaccahrides). Nature combines constituents with poor macroscale properties and achieves levels that surpass those expected despite being formed of mostly mineral CaCO3 tablets. Interestingly, nacreous assemblies can display a toughness 3,000 times higher than their major constituent, aragonite. Similarities have been observed between nacre and sprayed ceramics in terms of their microstructures and mechanical behavior. Both assemblies follow a design hierarchy and layered organization over several length scales. The mineral phase in nacre has evolved on the microscale and nanometer interlayers of biopolymer bond neighboring tablets. In addition, these tablets have a certain degree of waviness, nanoscale roughness, and mineral bridges thereby further enhancing linkages to one another. These inherent microstructural features significantly improve the mechanical properties of nacreous assemblies. On the other hand, sprayed ceramics are formed from micron sized splats, larger than aragonite nacreous tablets, with comparable (nanoscale) roughness, resulting from grain termination sites. Together these features of sprayed ceramics respond similarly to nacre, showing a great extent of mechanical nonlinearity and hysteresis, which is mostly absent in structural ceramics. Due to the splat-by-splat deposition process, sprayed ceramics contain a

  18. Discovery of authigenic carbonates in the Canada Basin (Arctic Ocean) and its implications

    Science.gov (United States)

    Woo, K.; Nam, S.; Ji, H.; Kim, J.; Kabir, E.; Heo, N.; Stein, R. H.; Matthiessen, J. J.

    2011-12-01

    Carbonate minerals were discovered from the giant box core (PS72/410-1) of the pelagic sediments recovered from the Canadian Arctic across the central Mendeleev Ridge (Station location= Lat. 80°30.37"N, Long. 175°44.38"W) during the Arctic cruise by Polarstern in 2008. The core was 39 cm in depth and was collected from the water depth of 1802 meters. The sediments show various colors from grey to brown as previously reported in other Arctic pelagic sediments. The sediments include planktonic foraminifers together with carbonate minerals. The contents of planktonic foraminifers and carbonate minerals vary with core depth, however these carbonate minerals are present through the whole sequence except for a few centimeters. After wet sieving, coarse fractions were texturally examined with binocular microscope and SEM, and stable isotope compositions were obtained. Mineralogy of carbonate minerals were determined using crystal shapes and qualitative Sr contents by EDAX. The carbonates are composed of calcite, aragonite or a combination of both. Aragonite crystals show radiating fibrous texture, randomly oriented fibrous texture, spherulitic fibrous texture and bladed texture, and calcite crystals show foliated texture, spirally stacked foliated texture, randomly bladed texture, spherulitic fibrous texture, equant texture, and spherulitic equant texture. Various shapes of aragonite and calcite crystals are randomly distributed throughout the core. Highly enriched carbon isotope compositions (δ13C = 0 ~ +5% vs. PDB) strongly indicate that they formed in methanogenic zone below sediment/water interface by the reaction between anoxic pore fluids and host sediments induced by methanogenic bacteria. However, a wide range of oxygen isotope values (δ18O = -5 ~ +5% vs. PDB) still need more scrutiny. Various shapes of carbonate crystals together with highly positive carbon isotope values indicate that these carbonates are authigenic in origin. Because the host sediments

  19. Carbonate mineral saturation states in the East China Sea: present conditions and future scenarios

    Directory of Open Access Journals (Sweden)

    W.-C. Chou

    2013-10-01

    Full Text Available To assess the impact of rising atmospheric CO2 and eutrophication on the carbonate chemistry of the East China Sea shelf waters, saturation states (Ω for two important biologically relevant carbonate minerals – calcite (Ωc and aragonite (Ωa – were calculated throughout the water column from dissolved inorganic carbon (DIC and total alkalinity (TA data collected in spring and summer of 2009. Results show that the highest Ωc (∼9.0 and Ωa (∼5.8 values were found in surface water of the Changjiang plume area in summer, whereas the lowest values (Ωc = ∼2.7 and Ωa = ∼1.7 were concurrently observed in the bottom water of the same area. This divergent behavior of saturation states in surface and bottom waters was driven by intensive biological production and strong stratification of the water column. The high rate of phytoplankton production, stimulated by the enormous nutrient discharge from the Changjiang, acts to decrease the ratio of DIC to TA, and thereby increases Ω values. In contrast, remineralization of organic matter in the bottom water acts to increase the DIC to TA ratio, and thus decreases Ω values. The projected result shows that continued increases of atmospheric CO2 under the IS92a emission scenario will decrease Ω values by 40–50% by the end of this century, but both the surface and bottom waters will remain supersaturated with respect to calcite and aragonite. Nevertheless, superimposed on such Ω decrease is the increasing eutrophication, which would mitigate or enhance the Ω decline caused by anthropogenic CO2 uptake in surface and bottom waters, respectively. Our simulation reveals that, under the combined impact of eutrophication and augmentation of atmospheric CO2, the bottom water of the Changjiang plume area will become undersaturated with respect to aragonite (Ωa = ∼0.8 by the end of this century, which would threaten the health of the benthic ecosystem.

  20. Impacts of seawater saturation state (ΩA = 0.4-4.6) and temperature (10, 25 °C) on the dissolution kinetics of whole-shell biogenic carbonates

    Science.gov (United States)

    Ries, Justin B.; Ghazaleh, Maite N.; Connolly, Brian; Westfield, Isaac; Castillo, Karl D.

    2016-11-01

    Anthropogenic increase of atmospheric pCO2 since the Industrial Revolution has caused seawater pH to decrease and seawater temperatures to increase-trends that are expected to continue into the foreseeable future. Myriad experimental studies have investigated the impacts of ocean acidification and warming on marine calcifiers' ability to build protective shells and skeletons. No studies, however, have investigated the combined impacts of ocean acidification and warming on the whole-shell dissolution kinetics of biogenic carbonates. Here, we present the results of experiments designed to investigate the effects of seawater saturation state (ΩA = 0.4-4.6) and temperature (10, 25 °C) on gross rates of whole-shell dissolution for ten species of benthic marine calcifiers: the oyster Crassostrea virginica, the ivory barnacle Balanus eburneus, the blue mussel Mytilus edulis, the conch Strombus alatus, the tropical coral Siderastrea siderea, the temperate coral Oculina arbuscula, the hard clam Mercenaria mercenaria, the soft clam Mya arenaria, the branching bryozoan Schizoporella errata, and the coralline red alga Neogoniolithon sp. These experiments confirm that dissolution rates of whole-shell biogenic carbonates decrease with calcium carbonate (CaCO3) saturation state, increase with temperature, and vary predictably with respect to the relative solubility of the calcifiers' polymorph mineralogy [high-Mg calcite (mol% Mg > 4) ≥ aragonite > low-Mg calcite (mol% Mg 1) with respect to both aragonite and calcite reveals fundamental differences between the dissolution kinetics of whole-shell biogenic CaCO3 and inorganic CaCO3. Thus, applying stoichiometric solubility products derived for inorganic CaCO3 to model gross dissolution of biogenic carbonates may substantially underestimate the impacts of ocean acidification on net calcification (gross calcification minus gross dissolution) of systems ranging in scale from individual organisms to entire ecosystems (e.g., net

  1. Investigation of the chemistry of calcium carbonate scale nucleation and growth from seawater on OTEC heat exchangers

    Energy Technology Data Exchange (ETDEWEB)

    Morse, J.W.; Brass, G.W.; Walter, L.M.; Van Valin, R.

    1979-08-01

    The potential for calcium carbonate scale formation, from supersaturated seawater on candidate Ocean Thermal Energy Conversion heat exchanger tubes, has been tested under flowing and stagnant seawater, and leaking liquid ammonia conditions. It was not possible to confirm the existence of calcium carbonate in any of the deposits formed. However, the presence of calcium in the deposits, generally as a minor component, indicates that microcrystalline calcium carbonate may be formed. Tests performed on growth rates of calcite and aragonite powders in seawater indicate that the maximum thickening rate of a calcium carbonate scale, under conditions which are likely to be encountered in heat exchanger tubes, is less than 20 ..mu..m per month.

  2. Geochemistry of Precambrian carbonates - 3-shelf seas and non-marine environments of the Archean

    Science.gov (United States)

    Veizer, Jan; Clayton, R. N.; Hinton, R. W.; Von Brunn, Victor; Mason, T. R.

    1990-01-01

    Samples from the Pangola and Ventersdorp Supergroups (Kaapvaal Craton, South Africa) and from the Fortescue and Hamersley Groups (Pilbara Block, Australia) were analyzed, using XRF, AAS, and isotope-analysis techniques to investigate the mineralogical, chemical, and isotopic features of these representatives of contemporary shelf carbonates (Pangola and Hamersley samples) and nonmarine carbonates (the Ventersdorp and Fortescue samples). Results show that, mineralogically, the shelf carbonates are almost exclusively dolostones, while the lacustrine facies are predominantly limestones. Geological, trace-element, and oxygen-isotope results of the shelf carbonates suggest that their original mineralogy may have been aragonite, and that the Pangola dolostones may represent a direct dolomitization product of this precursor. By contrast, the stabilization of the Hamersley carbonates may have involved an additional step of transformation of a metastable precursor into limestone.

  3. The metabolic response of pteropods to acidification reflects natural CO2-exposure in oxygen minimum zones

    Directory of Open Access Journals (Sweden)

    K. F. Wishner

    2012-02-01

    Full Text Available Shelled pteropods (Thecosomata are a group of holoplanktonic mollusks that are believed to be especially sensitive to ocean acidification because their aragonitic shells are highly soluble. Despite this concern, there is very little known about the physiological response of these animals to conditions of elevated carbon dioxide. This study examines the oxygen consumption and ammonia excretion of five pteropod species, collected from tropical regions of the Pacific Ocean, to elevated levels of carbon dioxide (0.10%, 1000 ppm. Our results show that pteropods that naturally migrate into oxygen minimum zones, such as Hyalocylis striata, Clio pyramidata, Cavolinia longirostris and Creseis virgula, were not affected by carbon dioxide at the levels and duration tested. Diacria quadridentata, which does not migrate, responds to high carbon dioxide conditions with reduced oxygen consumption and ammonia excretion. This indicates that the natural chemical environment of individual species may influence their resilience to ocean acidification.

  4. Organic matter of fossil origin in the amberine speleothems from El Soplao Cave (Cantabria, Northern Spain

    Directory of Open Access Journals (Sweden)

    Gázquez Fernando

    2012-01-01

    Full Text Available Unusual amberine-coloured speleothems were recently found in El Soplao Cave (Cantabria, Spain. Chromophore elements such as Fe, Mn, Cd, Co or Ti were not present in significant quantities. Rather, our data show that their colour comes from leachates of fossilized organic material hosted in the carbonaceous Urgonian facies of the host rock. These leachates are related to the Cretaceous amber deposit that has been recently discovered in the vicinity of El Soplao Cave. The presence of humic and fulvic acids of fossil origin were confirmed by IR and Raman spectroscopic analysis of the carbonaceous strata and the speleothems. In addition, the mineralogy of the amberine speleothems was studied. Alternating bands made of calcite and aragonite reveal that periods of humidity and aridity occurred within the cave during the speleothem genesis.

  5. Dolomitization in a mixing zone of near-seawater composition, Late Pleistocene, northeastern Yucatan Peninsula

    Science.gov (United States)

    Ward, W. C.; Halley, Robert B.

    1985-01-01

    Patches of dolomite occur in cores of reefal limestone from the shallow subsurface on the northeastern coast of the Yucatan Peninsula. This limestone accumulated during an interglacial high stand of sea level about 200,000 years ago. Dolomitization was preceded by freshwater diagenesis, including precipitation of sparry calcite cement, stabilization of Mg-calcitic skeletal fragments, and partial dissolution of aragonitic components. This suggests a predolomitization lowering of sea level with the consequent freshening of pore water. The subsequent precipitation of dolomite indicates a return to high sea level with the consequent increase in Mg/Ca ratio of pore water. Dolomitization took place during a brief high stand of sea level, either shortly after deposition about 200,000 yr BP, r, more likely, about 125,000 yr BP.

  6. Cave breakdown by vadose weathering.

    Directory of Open Access Journals (Sweden)

    Osborne R. Armstrong L.

    2002-01-01

    Full Text Available Vadose weathering is a significant mechanism for initiating breakdown in caves. Vadose weathering of ore bodies, mineral veins, palaeokarst deposits, non-carbonate keystones and impure, altered or fractured bedrock, which is intersected by caves, will frequently result in breakdown. Breakdown is an active, ongoing process. Breakdown occurs throughout the vadose zone, and is not restricted to large diameter passages, or to cave ceilings. The surfaces of disarticulated blocks are commonly coated, rather than having fresh broken faces, and blocks continue to disintegrate after separating from the bedrock. Not only gypsum, but also hydromagnesite and aragonite are responsible for crystal wedging. It is impossible to study or identify potential breakdown foci by surface surveys alone, in-cave observation and mapping are essential.

  7. CO{sub 2} mineral trapping: an experimental study on the carbonation of basalts from the eastern Deccan Volcanic Province, India

    Energy Technology Data Exchange (ETDEWEB)

    Rani, Nishi; Pathak, Vamdev; Shrivastava, J.P. [Department of Geology, University of Delhi, Delhi 110007 (India)

    2013-07-01

    Rock specimens from Deccan flood basalts have been reacted in the laboratory under high pCO{sub 2} (5 and 10 bars), total pressure (vessel pressure between 10 and 20 bars), and temperature (100 and 200 deg. C) conditions for 50, 60, 70, and 80 hours. XRD and SEM-EDS analyses show that calcite, aragonite, siderite and magnesite, and clays are derived from the alteration of Deccan basalts under water-saturated, hydrothermal-like conditions. Alteration reactions were accompanied by significant variation in the pH of the reacting aqueous solution, dependent upon time, pCO{sub 2}, and temperature variables of the experiment. Neo-formed secondary products also include significant amounts of smectite, chlorite, and smectite/chlorite mixed layer clays. (authors)

  8. Analysis by Sem, EDS and XRD of mineral and soil belonging to a Colonial oven from Jalenton Chiapas

    International Nuclear Information System (INIS)

    Analytical techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD) have been applied in the study of ancient materials. The results from the study of several samples belonging to a colonial oven are present in this work. There were found sets of slides, acicular and tubular shapes as well as porous surfaces and rose-like structures. EDS revealed high concentrations of O, C, Pb, Ca, Fe and Al, and minor quantities of Si, Zn, Mg, Na, S, K, Ti and Ni. Were identified the crystalline phases such as calcite, aragonite, albite; as well some phases associated with iron and lead compounds like: iron oxides, magnetite, hematite, goethite, kirschtanite, lead oxides, litargite, wititte, and cerusite. According to the obtained results that it is considered a kiln of oxygenated mineral to lead smelting. (Author)

  9. Analysis by Sem, EDS and XRD of mineral and soil belonging to a Colonial oven from Jalenton Chiapas

    Energy Technology Data Exchange (ETDEWEB)

    Mendoza A, D.; Carapia M, L.; Rodriguez L, V. [Instituto Nacional de Investigaciones Nucleares, Salazar, Estado de Mexico C.P. 52045 (Mexico); Torres, L.; Lee, T. [Instituto de Investigaciones Antropologicas, Ciudad Universitaria C.P. 04500 Mexico D.F. (Mexico); Franco, F. [Departamento de Materiales. Area de Materiales. UAM Azcapotzalco, Mexico D.F. (Mexico)

    1999-07-01

    Analytical techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD) have been applied in the study of ancient materials. The results from the study of several samples belonging to a colonial oven are present in this work. There were found sets of slides, acicular and tubular shapes as well as porous surfaces and rose-likestructures. EDS revealed high concentrations of O, C, Pb, Ca, Fe and Al, and minor quantities of Si, Zn, Mg, Na, S, K, Ti and Ni. Were identified the crystalline phases such as calcite, aragonite, albite; as well some phases associated with iron and lead compounds like: iron oxides, magnetite, hematite, goethite, kirschtanite, lead oxides, litargite, wititte, and cerusite. According to the obtained results that it is considered a kiln of oxygenated mineral to lead smelting. (Author)

  10. Hydrogeochemical Simulation of Water-Rock Interaction Under Water Flood Recovery in Renqiu Oilfield, Hebei Province, China

    Institute of Scientific and Technical Information of China (English)

    冯启言; 韩宝平

    2002-01-01

    Hydrogeochemical simulation is an effective method to study water-rock interaction.In this paper, PHREEQM was used for the simulation of water-rock interaction under water flooding in the Renqiu Oilfield. Calculated results revealed that when fresh water was injected into the reservoir, Cl- and Na+ would decrease without involvement in water-rock interaction.Erosion to dolomite will lead to an increase in Ca2 + , Mg2 + and CaHCO3+. Saturation index of calcite and aragonite decreased first and then increased. With fresh water accounting for up to 70 %, mixed water has the strongest erosion ability. Deoiled water has erosion ability under high temperature and high partial pressure of CO2. Pyrite and gypsum were sensitive to deoiled water, which can cause the dissolution of pyrite and the precipitation of gypsum. Micrographs revealed a great deal of information about water-rock interaction.

  11. [Study on the mechanism of liesegang pattern development during carbonating of traditional sticky rice-lime mortar].

    Science.gov (United States)

    Wei, Guo-feng; Fang, Shi-qiang; Zhang, Bing-jian; Wang, Xiao-qi; Li, Zu-guang

    2012-08-01

    Liesegang patterns in traditional sticky rice-lime mortar undergoing carbonation were investigated by means of FTIR, XRD and SEM. Results indicate that well-developed Liesegang patterns only occur in the mortar prepared with aged lime and sticky rice. The smaller Ca(OH)2 particle size in aged lime and the control of the sticky rice for the crystallization of calcium carbonate lead to the small pores in this mortar. These small pores can make Ca2+ and CO3(2-) highly supersaturated, which explains the reason why Liesegang pattern developed in the sticky rice-aged lime mortar. The formed metastable aragonite proves that Liesegang pattern could be explained based on the post-nucleation theory.

  12. Radon, carbon dioxide and fault displacements in central Europe related to the Tōhoku Earthquake.

    Science.gov (United States)

    Briestenský, M; Thinová, L; Praksová, R; Stemberk, J; Rowberry, M D; Knejflová, Z

    2014-07-01

    Tectonic instability may be measured directly using extensometers installed across active faults or it may be indicated by anomalous natural gas concentrations in the vicinity of active faults. This paper presents the results of fault displacement monitoring at two sites in the Bohemian Massif and Western Carpathians. These data have been supplemented by radon monitoring in the Mladeč Caves and by carbon dioxide monitoring in the Zbrašov Aragonite Caves. A significant period of tectonic instability is indicated by changes in the fault displacement trends and by anomalous radon and carbon dioxide concentrations. This was recorded around the time of the catastrophic MW=9.0 Tōhoku Earthquake, which hit eastern Japan on 11 March 2011. It is tentatively suggested that the Tōhoku Earthquake in the Pacific Ocean and the unusual geodynamic activity recorded in the Bohemian Massif and Western Carpathians both reflect contemporaneous global tectonic changes.

  13. Synthetic nacre by predesigned matrix-directed mineralization

    Science.gov (United States)

    Mao, Li-Bo; Gao, Huai-Ling; Yao, Hong-Bin; Liu, Lei; Cölfen, Helmut; Liu, Gang; Chen, Si-Ming; Li, Shi-Kuo; Yan, You-Xian; Liu, Yang-Yi; Yu, Shu-Hong

    2016-10-01

    Although biomimetic designs are expected to play a key role in exploring future structural materials, facile fabrication of bulk biomimetic materials under ambient conditions remains a major challenge. Here, we describe a mesoscale “assembly-and-mineralization” approach inspired by the natural process in mollusks to fabricate bulk synthetic nacre that highly resembles both the chemical composition and the hierarchical structure of natural nacre. The millimeter-thick synthetic nacre consists of alternating organic layers and aragonite platelet layers (91 weight percent) and exhibits good ultimate strength and fracture toughness. This predesigned matrix-directed mineralization method represents a rational strategy for the preparation of robust composite materials with hierarchically ordered structures, where various constituents are adaptable, including brittle and heat-labile materials.

  14. MINERAL BRIDGES OF NACRE AND ITS EFFECTS

    Institute of Scientific and Technical Information of China (English)

    宋凡; 白以龙

    2001-01-01

    Nacre, or mother-of-pearl, is a kind of composites of aragonite platelets sandwiched between organic materials. Its excellent mechanical properties are thought to stem from the microarchitecture that is traditionally described as a "brick and mortar" arrangement. In this paper, a new microstructure, referred to as mineral bridge in the biomineralization, is directly observed in the organic matrix layers (mortar) of nacre. This is an indication that the organic matrix layer of nacre should be treated as a three-dimensional interface and the microarchitecture of nacre ought to be considered as a "brick-bridge-mortar" structure rather than the traditional one. Experiments and analyses show that the mineral bridges not only improve the mechanical properties of the organic matrix layers but also play an important role in the pattern of the crack extension in nacre.

  15. Dolomitic marbles from the ultrahigh-pressure metamorphic Kimi complex in Rhodope, N.E. Greece

    Science.gov (United States)

    Mposkos, E.; Baziotis, I.; Proyer, A.; Hoinkes, G.

    2006-09-01

    Dolomitic marbles from the Organi and Pandrosos areas of the ultrahigh-pressure (UHP) metamorphic Kimi complex in East Rhodope, N.E. Greece have the mineral assemblage: Cal + Dol + Ol + Phl ± Di ± Hbl ± Spl ± Ti Chu + retrograde Srp and Chl. Several generations of calcite and dolomite with variable composition and texture represent different stages of the P T evolution: The first stage is represented by matrix dolomite (X_MgCO_3 = 0.48) and relic domains of homogenous composition in matrix calcite (X_MgCO_3 = 0.11 0.13); the second stage is evident from precipitation of lath-shaped and vermicular dolomite in matrix calcite. The third stage is represented by veinlets of almost pure CaCO3 and domainal replacement of prior calcite by nearly pure CaCO3 + Ca-rich dolomite (X_MgCO_3 = 0.34 0.43). Matrix dolomite adjacent to CaCO3 veinlets also becomes Ca-rich (X_MgCO_3 = 0.42). In fact, Ca-rich dolomites with X_MgCO_3 in the range of 0.40 0.34 are reported for the first time from metamorphic marbles. Coexisting Ca-rich dolomite and Mg-poor calcite cannot be explained by the calcite-dolomite miscibility gap. This assemblage rather suggests that Mg-poor calcite was aragonite originally, which formed together with Ca-rich dolomite according to the reaction Mg Cal → Arg + Dol (1) at ultrahigh pressures and temperatures above at least 850 °C, when dolomite becomes disordered and incorporates more Ca than coexisting aragonite does in terms of Mg. The simplest explanation of these observations probably is to suggest two metamorphic events: The first one represented by relic matrix carbonates at relatively low to moderate pressures and temperatures of ca. 750 °C, and the second one limited by the minimum temperatures for dolomite disorder (ca. 850 °C) and in the aragonite + dolomite stability field, i.e. at a minimum pressure of 3 GPa and, if the presence of diamond-bearing metapelites nearby is considered, at conditions of at least 850 °C and 4.3 GPa in the diamond

  16. Stable isotope compositions of a late Jurassic ammonite shell. A record of seasonal surface water temperatures in the southern hemisphere?

    Energy Technology Data Exchange (ETDEWEB)

    Lecuyer, C. [Claude Bernard Lyon I Univ. et Institut Universitaire de France, 69 - Villeurbanne (France). Lab. ' ' Paleoenvironnements et Paleobiosphere' ' ; Bucher, H. [Zuerich Univ. (Switzerland). Palaeontologisches Inst. und Museum

    2006-07-01

    Exceptional preservation of aragonite secreted by ammonites offers an opportunity to determine the seasonal temperature variations of Mesozoic surface waters. Ontogenetic profiles of carbon and oxygen isotope compositions have been obtained from the nacreous layer of a well-preserved Late Jurassic (Oxfordian) ammonite (Perisphinctes) from Madagascar. A similar range of oxygen isotope compositions was also obtained from an associated benthic bivalve (Astarte) which suggests the absence of sampling bias. Late Jurassic seasonal variations in the southern hemisphere were close to 2.5 C and relatively weak when compared to the 2.5-6.5 C temperature range prevailing in the present-day Indian Ocean at a paleolatitude of 40{+-}1 S. According to the hypothesis of an ice cap-free Late Jurassic Earth, average sea surface temperatures may have been up to 7 C higher than now. (orig.)

  17. Mn seasonal upwellings recorded in Lake Tanganyika mussels

    Directory of Open Access Journals (Sweden)

    D. Langlet

    2006-09-01

    Full Text Available Biogenic productivity of Lake Tanganyika is highly dependent on seasonal upwellings of anoxic deep waters. We investigated the shell of freshwater bivalve Pleiodon spekii as a geochemical archive of these periodic hydrological changes tuned by the monsoon regime. The results of a 2-years-long geochemical survey of the coastal waters performed on the dissolved and particulate fractions were put in perspective against laser ablation ICP-MS profiles of Mn in five aragonitic shells from the same lake location. Skeletal Mn profiles in 3 shells are very similar and dominated by episodic peaks that matched the Mn increase recorded in surface waters during the 2002 upwelling, while a shell collected during 2003 dry season detect both 2002 and 2003 upwelling events. Larger shells showing an extremely reduced growth display more than 8Mn peaks suggesting at least an 8 years record of seasonal changes in water composition.

  18. Caracterização físico-química e microestrutural de conchas de moluscos bivalves provenientes de cultivos da região litorânea da ilha de Santa Catarina Physical chemistry and micro structural characterization of shells of bivalve mollusks from sea farmer around the Santa Catarina island

    Directory of Open Access Journals (Sweden)

    Denyo Silva

    2010-01-01

    Full Text Available Samples of shells of oysters and mussels from sea farm around the Santa Catarina Island in south Brazil were collected and analyzed by DRX, FRX, SEM, CHN-S, FTIR, TG, AAS/Flame and AAS /GF. The results showed that the crystalline structure of mussel's shells is mainly formed by aragonite and the oyster's shells by calcite. The calcium percentage in both shells species was in the range of 33 to 35% and also 850 and 1200 mg/kg of strontium was detected in the shells of oysters and mussels, respectively. The content of organic matter was larger in the mussel's shells and the thermal degradation of both shells species occurred by three events at different temperatures from 250 to 830 ºC.

  19. Corals concentrate dissolved inorganic carbon to facilitate calcification.

    Science.gov (United States)

    Allison, Nicola; Cohen, Itay; Finch, Adrian A; Erez, Jonathan; Tudhope, Alexander W

    2014-01-01

    The sources of dissolved inorganic carbon (DIC) used to produce scleractinian coral skeletons are not understood. Yet this knowledge is essential for understanding coral biomineralization and assessing the potential impacts of ocean acidification on coral reefs. Here we use skeletal boron geochemistry to reconstruct the DIC chemistry of the fluid used for coral calcification. We show that corals concentrate DIC at the calcification site substantially above seawater values and that bicarbonate contributes a significant amount of the DIC pool used to build the skeleton. Corals actively increase the pH of the calcification fluid, decreasing the proportion of DIC present as CO2 and creating a diffusion gradient favouring the transport of molecular CO2 from the overlying coral tissue into the calcification site. Coupling the increases in calcification fluid pH and [DIC] yields high calcification fluid [CO3(2-)] and induces high aragonite saturation states, favourable to the precipitation of the skeleton.

  20. Activators of Luminescence in Speleothems as Source of Major Mistakes in Interpretation of Luminescent Paleoclimatic Records

    CERN Document Server

    Shopov, Y Y

    2009-01-01

    This work summarizes the main results of the operation of the International Program Luminescence of Cave Minerals of the commission on Physical Chemistry and Hydrogeology of Karst of UIS of UNESCO in the field of activators of speleothem luminescence. It discusses Activators of Luminescence in Speleothems as a source of major mistakes in the interpretation of luminescent paleoclimatic records. It demonstrates the existence of 6 types of luminescence of speleothems and cave minerals in dependence of the type of the luminescence center and its incorporation in the mineral. 24 different activators of photoluminescence of speleothem calcite and 11 of aragonite are studied. This paper demonstrates that it is impossible to produce reliable Paleotemperature or Past Precipitation records from luminescence of speleothems without establishing the organic origin of the entire luminescence of the particular sample.

  1. The microindentation behavior of several mollusk shells

    Energy Technology Data Exchange (ETDEWEB)

    Laraia, V.J.; Heuer, A.H. (Case Western Reserve Univ., Cleveland, OH (USA). Dept. of Materials Science and Engineering)

    1990-01-01

    An investigation of the relationship between structure and mechanical behavior is reported for mollusk shells employing foliated, nacreous, and crossed-lamellar structures by microindentation in the Knoop and Vickers geometries. Indentation damage zones develop crack systems that reflect the micro-architecture. For the crosed-lamellar structure, the system of cracks about the indentation normally developed in a brittle material is suppressed. Previous reports that shells are harder than the corresponding minerals, calcite and aragonite, are confirmed, but it is found that this effect can be strongly dependent on orientation. This anomalous hardness is not an artifact of the indentation test technique, since scratch tests confirm the relative hardness of shell over the mineral. It is suggested that microstructural organization is of central importance in producing this hardness, as opposed to intrinsic properties of the mineral or matrix phases. 17 refs., 6 figs., 1 tab.

  2. An electron microscopy study of the microstructure and microarchitecture of the Strombus gigas shell

    Energy Technology Data Exchange (ETDEWEB)

    Rieke, P.C.; Laraia, V.J. (Pacific Northwest Lab., Richland, WA (USA)); Heuer, A.H. (Case Western Reserve Univ., Cleveland, OH (USA)); Aindow, M. (Ohio State Univ., Columbus, OH (USA))

    1989-11-01

    A scanning and transmission electron microscopy study is presented of the microstructure of the Strombus gigas shell. The hierarchical nature of this crossed-lamellar structure and the defect content of the mineral component are described. The mineral component consists of small single crystal grains of aragonite, the metastable orthorhombic polymorph of CaCO{sub 3}. The habit and morphology of the grains discussed here have not been determined previously. The observed habit and defect structure suggest that the organic matrix exerts a high degree of control over the crystal growth of the mineral phase and is responsible for the long range order in the microarhitecture. Electron beam heating of the mineral component leads to certain phase changes and these are discussed. 15 refs., 6 figs.

  3. Purification and functional analysis of a 40 kD protein extracted from the Strombus decorus persicus mollusk shells.

    Science.gov (United States)

    Pokroy, Boaz; Zolotoyabko, Emil; Adir, Noam

    2006-02-01

    A 40 kD protein has been extracted from the biomineral matrix of the calcium carbonate gastropod shell of Strombus decorus persicus. The protein was isolated by decalcification and ion exchange HPLC. We have named this protein ACLS40, i.e., aragonite crossed-lamellar structure protein. A partial sequence of the isolated ACLS40 and amino acid analysis both indicate that it does not belong to the family of very acidic proteins, i.e., rich in aspartic and glutamic residues. The shell-extracted protein shows the ability to stabilize calcium carbonate in vitro, in the form of thermodynamically unstable vaterite polymorph, and to inhibit the growth of calcite. PMID:16471929

  4. Study and characterization of ceramic materials from natural origin for application in jewellery design using laser texturing as innovation; Estudo e caracterizacao de materiais ceramicos de origem natural para aplicacao no design de joias utilizando a texturizacao a laser como diferencial de inovacao

    Energy Technology Data Exchange (ETDEWEB)

    Elesbao, T.R.; Carus, L.A.; Tabarelli, A.C.; Vieira, R.P.; Takimi, A.S., E-mail: taianeelesbao@hotmail.com [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS (Brazil). Departamento de Materiais

    2012-07-01

    Technological development has been largely responsible for changes in the jewelry market. Seeking to contribute to the development of new products, this study analyzed the technique of laser texturing, aiming to add commercial and aesthetic values to the mother of pearl, material used in the jewelry field. The methodology was divided into physico-chemical characterization of the mother-of-pearl and of the resulting residue of laser texturing and analysis of the interaction of laser with the surface of the mother-of-pearl. The characterizations carried out were: Infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. Results indicate that the studied material is composed mainly by the aragonite crystal phase, different from that resulting residue from texturing process. Although the process remove some of the gem material, the effect water characteristic of the mother-of-pearl is maintained, suggesting that technology combined with research and design can increase the value of this material. (author)

  5. Combining µXANES and µXRD mapping to analyse the heterogeneity in calcium carbonate granules excreted by the earthworm Lumbricus terrestris.

    Science.gov (United States)

    Brinza, Loredana; Schofield, Paul F; Hodson, Mark E; Weller, Sophie; Ignatyev, Konstantin; Geraki, Kalotina; Quinn, Paul D; Mosselmans, J Frederick W

    2014-01-01

    The use of fluorescence full spectral micro-X-ray absorption near-edge structure (µXANES) mapping is becoming more widespread in the hard energy regime. This experimental method using the Ca K-edge combined with micro-X-ray diffraction (µXRD) mapping of the same sample has been enabled on beamline I18 at Diamond Light Source. This combined approach has been used to probe both long- and short-range order in calcium carbonate granules produced by the earthworm Lumbricus terrestris. In granules produced by earthworms cultured in a control artificial soil, calcite and vaterite are observed in the granules. However, granules produced by earthworms cultivated in the same artificial soil amended with 500 p.p.m. Mg also contain an aragonite. The two techniques, µXRD and µXANES, probe different sample volumes but there is good agreement in the phase maps produced. PMID:24365942

  6. Three-dimensional distribution of polymorphs and magnesium in a calcified underwater attachment system by diffraction tomography.

    Science.gov (United States)

    Leemreize, Hanna; Almer, Jonathan D; Stock, Stuart R; Birkedal, Henrik

    2013-09-01

    Biological materials display complicated three-dimensional hierarchical structures. Determining these structures is essential in understanding the link between material design and properties. Herein, we show how diffraction tomography can be used to determine the relative placement of the calcium carbonate polymorphs calcite and aragonite in the highly mineralized holdfast system of the bivalve Anomia simplex. In addition to high fidelity and non-destructive mapping of polymorphs, we use detailed analysis of X-ray diffraction peak positions in reconstructed powder diffraction data to determine the local degree of Mg substitution in the calcite phase. These data show how diffraction tomography can provide detailed multi-length scale information on complex materials in general and of biomineralized tissues in particular.

  7. Dynamics of sheet nacre formation in bivalves.

    Science.gov (United States)

    Rousseau, Marthe; Meibom, Anders; Gèze, Marc; Bourrat, Xavier; Angellier, Martine; Lopez, Evelyne

    2009-03-01

    Formation of nacre (mother-of-pearl) is a biomineralization process of fundamental scientific as well as industrial importance. However, the dynamics of the formation process is still not understood. Here, we use scanning electron microscopy and high spatial resolution ion microprobe depth-profiling to image the full three-dimensional distribution of organic materials around individual tablets in the top-most layer of forming nacre in bivalves. Nacre formation proceeds by lateral, symmetric growth of individual tablets mediated by a growth-ring rich in organics, in which aragonite crystallizes from amorphous precursors. The pivotal role in nacre formation played by the growth-ring structure documented in this study adds further complexity to a highly dynamical biomineralization process.

  8. Reconstruction of deglacial sea surface temperature in the tropical Pacific from selective analysis of a fossil coral

    Energy Technology Data Exchange (ETDEWEB)

    Allison, N.; Finch, A.A.; Tudhope, A.W.; Newville, M.; Sutton, S.R.; Ellam, R.M. (St Andrews); (Edinburgh); (Scottish); (UC); (St Andrews)

    2010-07-13

    The Sr/Ca of coral skeletons demonstrates potential as an indicator of sea surface temperatures (SSTs). However, the glacial-interglacial SST ranges predicted from Sr/Ca of fossil corals are usually higher than from other marine proxies. We observed infilling of secondary aragonite, characterized by high Sr/Ca ratios, along intraskeletal pores of a fossil coral from Papua New Guinea that grew during the penultimate deglaciation (130 {+-} 2 ka). Selective microanalysis of unaltered areas of the fossil coral indicates that SSTs at {approx}130 ka were {le} 1 C cooler than at present in contrast with bulk measurements (combining infilled and unaltered areas) which indicate a difference of 6-7 C. The analysis of unaltered areas of fossil skeletons by microprobe techniques may offer a route to more accurate reconstruction of past SSTs.

  9. The early Holocene humid period in the Tayma palaeolake, NW Arabian Peninsula -- A high-resolution micro-facies and geochemical approach

    Science.gov (United States)

    Neugebauer, Ina; Plessen, Birgit; Dinies, Michèle; Engel, Max; Tjallingii, Rik; Brauer, Achim

    2016-04-01

    The Tayma palaeolake is a rare archive of the early Holocene humid period in northern Arabia (Dinies et al. 2015; Engel et al. 2012). Here we present a ca. 1 m thick and 500 years spanning annually laminated sediment section that was deposited in the centre of the former lake from ca. 8500 to 8000 calibrated years (cal. yrs) BP, as determined by AMS 14C dating of pollen concentrates (Dinies et al. 2015). High-resolution micro-facies analyses based on thin section microscopy, μXRF element scanning, δ18Ocarb and δ13Ccarb measurements on single carbonate laminae, as well as geochemical measurements on bulk samples for TOC, CaCO3, C/N ratio, δ18Ocarb, δ13Ccarb, δ13Corg and δ15N determination were performed in order to investigate the sedimentological and geochemical changes along the varved sequence in great detail. The finely laminated marl sediments are mainly composed of sub-mm thick laminae of endogenic aragonite, organic matter and diatoms, as well as occasional, often graded silt-clay layers. Following an early lake phase from ca. 8700 to 8500 cal. yrs BP characterized by coarsely laminated, presumably non-annual marl sediments that are rich in ostracods, three main varved phases can be distinguished within the investigated section: (1) aragonitic-organic varves from ca. 8500 to 8300 cal. yrs BP, (2) diatom-organic varves from ca. 8300 to 8100 cal. yrs BP that frequently include aragonite laminae and occasionally gastropod and ostracod shells, and (3) organic varves from ca. 8100 to 8000 cal. yrs BP with decreasing diatom and aragonite laminae and an increasing frequency of gypsum layers. After this period, gypsum becomes abundant and fine lamination appears only sporadically. In addition, we observe increasing trends of TOC, C/N and δ13Ccarb and decreasing δ18Ocarb during phase 1 and excess δ18Ocarb, δ13Ccarb and TOC values during phase 2, pointing towards the maximum lake productivity and increased seasonal precipitation. We interpret this

  10. Coral symbiotic algae calcify ex hospite in partnership with bacteria

    Science.gov (United States)

    Frommlet, Jörg C.; Sousa, Maria L.; Alves, Artur; Vieira, Sandra I.; Suggett, David J.; Serôdio, João

    2015-01-01

    Dinoflagellates of the genus Symbiodinium are commonly recognized as invertebrate endosymbionts that are of central importance for the functioning of coral reef ecosystems. However, the endosymbiotic phase within Symbiodinium life history is inherently tied to a more cryptic free-living (ex hospite) phase that remains largely unexplored. Here we show that free-living Symbiodinium spp. in culture commonly form calcifying bacterial–algal communities that produce aragonitic spherulites and encase the dinoflagellates as endolithic cells. This process is driven by Symbiodinium photosynthesis but occurs only in partnership with bacteria. Our findings not only place dinoflagellates on the map of microbial–algal organomineralization processes but also point toward an endolithic phase in the Symbiodinium life history, a phenomenon that may provide new perspectives on the biology and ecology of Symbiodinium spp. and the evolutionary history of the coral–dinoflagellate symbiosis. PMID:25918367

  11. Radon, carbon dioxide and fault displacements in central Europe related to the Tohoku earthquake

    International Nuclear Information System (INIS)

    Tectonic instability may be measured directly using extensometers installed across active faults or it may be indicated by anomalous natural gas concentrations in the vicinity of active faults. This paper presents the results of fault displacement monitoring at two sites in the Bohemian Massif and Western Carpathians. These data have been supplemented by radon monitoring in the Mladec Caves and by carbon dioxide monitoring in the Zbrasov Aragonite Caves. A significant period of tectonic instability is indicated by changes in the fault displacement trends and by anomalous radon and carbon dioxide concentrations. This was recorded around the time of the catastrophic MW = 9.0 Tohoku Earthquake, which hit eastern Japan on 11 March 2011. It is tentatively suggested that the Tohoku Earthquake in the Pacific Ocean and the unusual geodynamic activity recorded in the Bohemian Massif and Western Carpathians both reflect contemporaneous global tectonic changes. (authors)

  12. Shell microstructure of the late Carboniferous rostroconch mollusc Apotocardium lanterna (Branson, 1965)

    Science.gov (United States)

    Rogalla, N.S.; Carter, J.G.; Pojeta, J.

    2003-01-01

    The Late Carboniferous bransoniid conocardioidean Apotocardium lanterna (Branson, 1965) had an entirely aragonitic shell with a finely prismatic outer shell layer, a predominantly crossed lamellar to complex crossed lamellar middle shell layer, and an "inner" shell layer of finely textured porcelaneous and/or matted structure. This "inner" layer is probably homologous with the inner part of the middle shell layer and the inner layer sensu stricto of bivalved molluscs. Shell morphological and microstructural convergences between conocardioids and living heart cockles suggest that at least some conocardioids may have farmed algal endosymbionts in their posterior mantle margins. This symbiosis may have helped conocardioids compete with the biomechanically more efficient bivalves during the latter part of the Paleozoic.

  13. Comparative genomics explains the evolutionary success of reef-forming corals.

    Science.gov (United States)

    Bhattacharya, Debashish; Agrawal, Shobhit; Aranda, Manuel; Baumgarten, Sebastian; Belcaid, Mahdi; Drake, Jeana L; Erwin, Douglas; Foret, Sylvian; Gates, Ruth D; Gruber, David F; Kamel, Bishoy; Lesser, Michael P; Levy, Oren; Liew, Yi Jin; MacManes, Matthew; Mass, Tali; Medina, Monica; Mehr, Shaadi; Meyer, Eli; Price, Dana C; Putnam, Hollie M; Qiu, Huan; Shinzato, Chuya; Shoguchi, Eiichi; Stokes, Alexander J; Tambutté, Sylvie; Tchernov, Dan; Voolstra, Christian R; Wagner, Nicole; Walker, Charles W; Weber, Andreas Pm; Weis, Virginia; Zelzion, Ehud; Zoccola, Didier; Falkowski, Paul G

    2016-01-01

    Transcriptome and genome data from twenty stony coral species and a selection of reference bilaterians were studied to elucidate coral evolutionary history. We identified genes that encode the proteins responsible for the precipitation and aggregation of the aragonite skeleton on which the organisms live, and revealed a network of environmental sensors that coordinate responses of the host animals to temperature, light, and pH. Furthermore, we describe a variety of stress-related pathways, including apoptotic pathways that allow the host animals to detoxify reactive oxygen and nitrogen species that are generated by their intracellular photosynthetic symbionts, and determine the fate of corals under environmental stress. Some of these genes arose through horizontal gene transfer and comprise at least 0.2% of the animal gene inventory. Our analysis elucidates the evolutionary strategies that have allowed symbiotic corals to adapt and thrive for hundreds of millions of years.

  14. Cryogenic Origin for Mars Analog Carbonates in the Bockfjord Volcanic Complex Svalbard (Norway)

    Science.gov (United States)

    Amundsen, H. E. F.; Benning, L.; Blake, D. F.; Fogel, M.; Ming, D.; Skidmore, M.; Steele, A.

    2011-01-01

    The Sverrefjell and Sigurdfjell eruptive centers in the Bockfjord Volcanic Complex (BVC) on Svalbard (Norway) formed by subglacial eruptions ca. 1 Ma ago. These eruptive centers carry ubiquitous magnesian carbonate deposits including dolomitemagnesite globules similar to those in the Martian meteorite ALH84001. Carbonates in mantle xenoliths are dominated by ALH84001 type carbonate globules that formed during quenching of CO2-rich mantle fluids. Lava hosted carbonates include ALH84001 type carbonate globules occurring throughout lava vesicles and microfractures and massive carbonate deposits associated with vertical volcanic vents. Massive carbonates include cemented lava breccias associated with volcanic vents. Carbonate cements comprise layered deposits of calcite, dolomite, huntite, magnesite and aragonite associated with ALH84001 type carbonate globules lining lava vesicles. Combined Mossbauer, XRD and VNIR data show that breccia carbonate cements at Sverrefjell are analog to Comanche carbonates at Gusev crater.

  15. Stable isotopes (δ 18O and δ 13C), trace and minor element compositions of Recent scleractinians and Last Glacial bivalves at the Santa Maria di Leuca deep-water coral province, Ionian Sea

    Science.gov (United States)

    Correa, Matthias López; Montagna, Paolo; Vendrell-Simón, Begoña; McCulloch, Malcolm; Taviani, Marco

    2010-03-01

    The aragonitic skeletons of bathyal cold-water corals have a high potential as geochemical in situ archives for paleoceanography. Oxygen isotopes and stable carbon isotopes (δ 18O and δ 13C) have been analyzed, as well as trace and minor element compositions (e.g. Mg/Ca, Sr/Ca, U/Ca, B/Ca and P/Ca) in Lophelia pertusa, one of the most important frame-builders at the Santa Maria di Leuca (SML) deep-water coral hotspot in the Central Mediterranean. The Apulian Bank is swept by strong currents of the Adriatic Deep Water Outflow. The temperature of 13.9 °C is the highest temperature recorded for L. pertusa and provides an important end-member of environmental conditions for geochemical analyses on living Atlantic and Mediterranean cold-water corals. Temperature and salinity (38.77 PSU) are stable throughout the year, and thus virtually no changes should be observed in the stable oxygen isotope signal—if the coral precipitates its skeleton in equilibrium with seawater. We measured various marine properties, such as the seawater oxygen isotope composition (δ 18O sw), stable carbon isotope composition (δ 13C DIC) of dissolved inorganic carbon (DIC), and dissolved inorganic nutrient concentrations (PO 4, NO 3, NO 2, NH 3 and SiO 2). Bottom water at the coral sites shows a mean oxygen isotope composition of 1.47‰ δ 18O sw-VSMOW, and δ 13C DIC showed a mean of 1.1‰ VPDB. A section of a living L. pertusa with a thick theca calcification was probed with a Merchantek MicroMill at a high spatial sampling resolution with 10 samples per 1 mm. This reduced the signal-smoothing inherent to conventional sampling. The δ 18O ag of coral aragonite ranges between -2.0‰ and +2.8‰ VPDB and the δ 13C ag ranges between -7.77‰ and +1.47‰ VPDB. The Gaussian data distribution for both parameters, including heavy equilibrium values, suggests the completeness of the captured isotopic variability. The strict linear correlation of δ 13C and δ 18O displays a strong 'kinetic

  16. Polarization-dependent imaging contrast in abalone shells

    Science.gov (United States)

    Metzler, Rebecca A.; Zhou, Dong; Abrecht, Mike; Chiou, Jau-Wern; Guo, Jinghua; Ariosa, Daniel; Coppersmith, Susan N.; Gilbert, P. U. P. A.

    2008-02-01

    Many biominerals contain micro- or nanocrystalline mineral components, organized accurately into architectures that confer the material with improved mechanical performance at the macroscopic scale. We present here an effect which enables us to observe the relative orientation of individual crystals at the submicron scale. We call it polarization-dependent imaging contrast (PIC), as it is an imaging development of the well-known x-ray linear dichroism. Most importantly, PIC is obtained in situ, in biominerals. We present here PIC in the prismatic and nacreous layers of Haliotis rufescens (red abalone), confirm it in geologic calcite and aragonite, and corroborate the experimental data with theoretical simulated spectra. PIC reveals different and unexpected aspects of nacre architecture that have inspired theoretical models for nacre formation.

  17. Arc-parallel extension and fluid flow in an ancient accretionary wedge: The San Juan Islands, Washington

    Science.gov (United States)

    Schermer, E.R.; Gillaspy, J.R.; Lamb, R.

    2007-01-01

    Structural analysis of the Lopez Structural Complex, a major Late Cretaceous terrane-bounding fault zone in the San Juan thrust system, reveals a sequence of events that provides insight into accretionary wedge mechanics and regional tectonics. After formation of regional ductile flattening and shear-related fabrics, the area was crosscut by brittle structures including: (1) southwest-vergent thrusts, (2) extension veins and normal faults related to northwest-southeast extension, and (3) conjugate strike-slip structures that record northwest-southeast extension and northeast-southwest shortening. Aragonite-bearing veins are associated with thrust and normal faults, but only rarely with strike-slip faults. High-pressure, low-temperature (HP-LT) minerals constrain the conditions for brittle deformation to ???20 km and fluid flow suggest a link between these structures and the silent earthquake process. ?? 2007 Geological Society of America.

  18. Mn seasonal upwellings recorded in Lake Tanganyika mussels

    Science.gov (United States)

    Langlet, D.; Alleman, L. Y.; Plisnier, P.-D.; Hughes, H.; André, L.

    2006-09-01

    Biogenic productivity of Lake Tanganyika is highly dependent on seasonal upwellings of anoxic deep waters. We investigated the shell of freshwater bivalve Pleiodon spekii as a geochemical archive of these periodic hydrological changes tuned by the monsoon regime. The results of a 2-years-long geochemical survey of the coastal waters performed on the dissolved and particulate fractions were put in perspective against laser ablation ICP-MS profiles of Mn in five aragonitic shells from the same lake location. Skeletal Mn profiles in 3 shells are very similar and dominated by episodic peaks that matched the Mn increase recorded in surface waters during the 2002 upwelling, while a shell collected during 2003 dry season detect both 2002 and 2003 upwelling events. Larger shells showing an extremely reduced growth display more than 8Mn peaks suggesting at least an 8 years record of seasonal changes in water composition.

  19. Monthly sea surface temperature records reconstructed by δ18O of reef-building coral in the east of Hainan Island,South China Sea

    Institute of Scientific and Technical Information of China (English)

    HE; Xuexian(何学贤); LIU; Dunyi(刘敦一); PENG; Zicheng(彭子成); LIU; Weiguo(刘卫国)

    2002-01-01

    Stable oxygen isotopic compositions of a coral colony of Porites lutea obtained on a core allowed the reconstruction of a 56-a (1943-1998) proxy record of the sea surface temperatures. This coral δ18O data are from the east of Hainan Island water (22°20′N, 110°39′E), South China Sea. The relationship between δ18O in the skeletal aragonite carbonate and the sea surface temperature (SST) is SST = -5.36 δ18OPDB-3.51 (r = 0.73, n = 470), dδ18O/d(SST) = -0.187‰/ ℃; and the thermometer was set at monthly resolution. The 56-a (1943-1998) proxy record of the sea surface temperatures reflected the same change trend in the northern part of South China Sea as the air temperature change trend in China.

  20. Electron microscopy study of red mud after seawater neutralisation; Estudo por microscopia eletronica de transmissao de lama vermelha tratada com agua do mar

    Energy Technology Data Exchange (ETDEWEB)

    Toledo, S.P.; Kiyohara, P.K. [Universidade de Sao Paulo (IF/LME/USP), SP (Brazil); Antunes, M.L.P., E-mail: malu@sorocaba.unesp.br [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Sorocaba, SP (Brazil); Frost, Ray [Queensland University of Technology (United States)

    2012-07-01

    Red Mud, residue of Bayer process for extracting alumina from bauxite, is produced in large quantity. This residue is very alkaline and can cause damage to health and the environment. One way to minimize the environmental impact of this residue is neutralization by sea water. The Brazilian Red Mud was treated with sea water. It appears that the initial pH of the samples is reduced to 8. The analysis by x-ray diffraction allows to identify the formation of hydrotalcite and aragonite. The transmission electron microscopy images show that this consists of particles with dimensions between 0.02 to 2 μm. It was possible to identify by EDS/MET particles of magnesium, confirming the formation of hydrotalcite. (author)

  1. Decadal trends in air-sea CO2 exchange in the Ross Sea (Antarctica)

    Science.gov (United States)

    Tagliabue, Alessandro; Arrigo, Kevin R.

    2016-05-01

    Highly productive Antarctic shelf systems, like the Ross Sea, play important roles in regional carbon budgets, but the drivers of local variations are poorly quantified. We assess the variability in the Ross Sea carbon cycle using a regional physical-biogeochemical model. Regionally, total partial pressure of CO2 (pCO2) increases are largely controlled by the biological pump and broadly similar to those in the offshore Southern Ocean. However, this masks substantial local variability within the Ross Sea, where interannual fluctuations in total pCO2 are driven by the biological pump and alkalinity, whereas those for anthropogenic pCO2 are related to physical processes. Overall, the high degree of spatial variability in the Ross Sea carbon cycle causes extremes in aragonite saturation that can be as large as long-term trends. Therefore, Antarctic shelf polynya systems like the Ross Sea will be strongly affected by local processes in addition to larger-scale phenomena.

  2. Major geochemical processes in the evolution of carbonate-Aquifer systems

    Science.gov (United States)

    Hanshaw, B.B.; Back, W.

    1979-01-01

    As a result of recent advances by carbonate petrologists and geochemists, hydrologists are provided with new insights into the origin and explanation of many aquifer characteristics and hydrologic phenomena. Some major advances include the recognition that: (1) most carbonate sediments are of biological origin; (2) they have a strong bimodal size-distribution; and (3) they originate in warm shallow seas. Although near-surface ocean water is oversaturated with respect to calcite, aragonite, dolomite and magnesite, the magnesium-hydration barrier effectively prevents either the organic or inorganic formation of dolomite and magnesite. Therefore, calcareous plants and animals produce only calcite and aragonite in hard parts of their bodies. Most carbonate aquifers that are composed of sand-size material have a high initial porosity; the sand grains that formed these aquifers originated primarily as small shells, broken shell fragments of larger invertebrates, or as chemically precipitated oolites. Carbonate rocks that originated as fine-grained muds were initially composed primarily of aragonite needles precipitated by algae and have extremely low permeability that requires fracturing and dissolution to develop into aquifers. Upon first emergence, most sand beds and reefs are good aquifers; on the other hand, the clay-sized carbonate material initially has high porosity but low permeability, a poor aquifer property. Without early fracture development in response to influences of tectonic activity these calcilutites would not begin to develop into aquifers. As a result of selective dissolution, inversion of the metastable aragonite to calcite, and recrystallization, the porosity is collected into larger void spaces, which may not change the overall porosity, but greatly increases permeability. Another major process which redistributes porosity and permeability in carbonates is dolomitization, which occurs in a variety of environments. These environments include back

  3. Coral symbiotic algae calcify ex hospite in partnership with bacteria.

    Science.gov (United States)

    Frommlet, Jörg C; Sousa, Maria L; Alves, Artur; Vieira, Sandra I; Suggett, David J; Serôdio, João

    2015-05-12

    Dinoflagellates of the genus Symbiodinium are commonly recognized as invertebrate endosymbionts that are of central importance for the functioning of coral reef ecosystems. However, the endosymbiotic phase within Symbiodinium life history is inherently tied to a more cryptic free-living (ex hospite) phase that remains largely unexplored. Here we show that free-living Symbiodinium spp. in culture commonly form calcifying bacterial-algal communities that produce aragonitic spherulites and encase the dinoflagellates as endolithic cells. This process is driven by Symbiodinium photosynthesis but occurs only in partnership with bacteria. Our findings not only place dinoflagellates on the map of microbial-algal organomineralization processes but also point toward an endolithic phase in the Symbiodinium life history, a phenomenon that may provide new perspectives on the biology and ecology of Symbiodinium spp. and the evolutionary history of the coral-dinoflagellate symbiosis. PMID:25918367

  4. High-precision uranium-series dating of lacustrine carbon-ates from Daihai Lake

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Ages of small aragonite samples retrieved from sediments from the Daihai Lake are determined by using the Thermal Ionization Mass Spectrometry (TIMS) technique. The ages of the samples range from (8740±601) to (10446±489) a, with a precision of 2%-3% for non-corrected dating ages and 4.7%-9.8% for corrected ages respectively, and are consistent within the deviation range. At about 10.5 ka BP, the grain-size of the sediments coarsens sharply, the frequency curves of grain-size distribution show coarse grain dominated single-double kurtosis, indicating cooling, de-creased hydrodynamic conditions and increased wind influ-ence procedure. This is in good agreement with previous results obtained from the Daihai Lake, which suggests that the climate was cold and the lake surface was shrinking. The TIMS ages of the sediments are therefore believed to be credible.

  5. Physical basis for materials synthesis using biomineralization

    Energy Technology Data Exchange (ETDEWEB)

    De Yoreo, J; Orme, C; Dove, P; Teng, H

    2000-05-16

    -structured materials, the fundamental physical controls on carbonate biomineral formation remain poorly understood. Carbonates are formed in diverse environments almost exclusively by living organisms. These naturally occurring marine and fresh water minerals most commonly occur as the polymorphs of calcite, aragonite and vaterite which are nucleated and grown in the exoskeletons and tissues of marine and freshwater organisms ranging from simple bacteria and algae to crustaceans, molluscs, or sponges. It is known that the soluble fraction associated with mineralizing parts of organisms plays a primary role in crystal formation. In the formation of molluscan shells, this fraction is distinguished by the common presence of aspartic acid rich amino acid mixtures. It is also known that carbonates exposed to different polyamino acids exhibit different crystal habits. Belcher et al. showed that exposing growing CaCO{sub 3} crystals alternately to solutions containing polyanionic proteins associated with the aragonitic and calcitic layers of mollusc shells led to sequential switching of the crystal structure of the newly grown material between that of aragonite and calcite. Further work has demonstrated that these protein mixtures alter the morphology of the calcite growth surface and that they contain two fractions effecting growth: a step-binding fraction that inhibits step advancement on calcite surfaces, and a surface binding fraction that appears to lead to the subsequent nucleation of aragonite. Wierzbicki et al. found that polyaspartate molecules (ASP{sub 20}) bind to calcite surfaces. Finally, modeling of ASP{sub 15} binding to calcite planes predicts large binding energies for well defined orientations. This and related evidence shows that systematic relationships between crystal morphology and surface interactions with the reactive groups of the organic molecules must exist. However, the interplay between surface chemistry and the physical processes of nucleation and crystal growth

  6. Enhancing the Accuracy of Carbonate δ18O and δ13C Measurements by SIMS

    Science.gov (United States)

    Orland, I. J.; Kozdon, R.; Linzmeier, B.; Wycech, J.; Sliwinski, M.; Kitajima, K.; Kita, N.; Valley, J. W.

    2015-12-01

    The precision and accuracy of carbonate δ18O & δ13C analysis by multicollector SIMS is well established if standards match samples in structure and major/minor element chemistry. However, low-T- and bio-carbonates used to construct paleoclimate archives can include complex internal structures and some samples analyzed at WiscSIMS (and other SIMS labs) have a consistent, sample-dependent offset between average SIMS δ18O measurements and bulk δ18O analyses by phosphoric-acid digestion. The offset is typically hydrogen peroxide), for which there is no agreed procedure in conventional bulk analyses. For SIMS analyses, pre-treatments had varied influence on the δ18O value, [16O1H], the concentration of "organic markers" like 12C14N and 31P, and mineralogy (of aragonite samples).

  7. Microwave-assisted synthesis of spheroidal vaterite CaCO 3 in ethylene glycol-water mixed solvents without surfactants

    Science.gov (United States)

    Chen, Yinxia; Ji, Xianbing; Wang, Xiaobo

    2010-10-01

    Spheroidal vaterite CaCO 3 composed of irregular nanoparticals have been synthesized by a fast microwave-assisted method. The structures are fabricated by the reaction of Ca(CH 3COO) 2 with (NH 4) 2CO 3 at 90 °C in ethylene glycol-water mixed solvents without any surfactants. The diameters of the spheroidal vaterite CaCO 3 range from 1 to 2 μm, and the average size of the nanoparticals is about 70 nm. Bundle-shaped aragonite and rhombohedral calcite are also obtained by adjusting the experimental parameters. Our experiments show that the ratio of ethylene glycol to water, microwave power, reaction time, and two sources of ammonium ions and acetate anions are key parameters for the fabrication of spheroidal vaterite CaCO 3. A possible growth mechanism for the spheroidal structures has been proposed, which suggests that the spheroidal vaterite CaCO 3 is formed by an aggregation mechanism.

  8. Comparative genomics explains the evolutionary success of reef-forming corals

    KAUST Repository

    Bhattacharya, Debashish

    2016-05-24

    Transcriptome and genome data from twenty stony coral species and a selection of reference bilaterians were studied to elucidate coral evolutionary history. We identified genes that encode the proteins responsible for the precipitation and aggregation of the aragonite skeleton on which the organisms live, and revealed a network of environmental sensors that coordinate responses of the host animals to temperature, light, and pH. Furthermore, we describe a variety of stress-related pathways, including apoptotic pathways that allow the host animals to detoxify reactive oxygen and nitrogen species that are generated by their intracellular photosynthetic symbionts, and determine the fate of corals under environmental stress. Some of these genes arose through horizontal gene transfer and comprise at least 0.2% of the animal gene inventory. Our analysis elucidates the evolutionary strategies that have allowed symbiotic corals to adapt and thrive for hundreds of millions of years.

  9. Electron microscopy study of red mud after seawater neutralisation

    International Nuclear Information System (INIS)

    Red Mud, residue of Bayer process for extracting alumina from bauxite, is produced in large quantity. This residue is very alkaline and can cause damage to health and the environment. One way to minimize the environmental impact of this residue is neutralization by sea water. The Brazilian Red Mud was treated with sea water. It appears that the initial pH of the samples is reduced to 8. The analysis by x-ray diffraction allows to identify the formation of hydrotalcite and aragonite. The transmission electron microscopy images show that this consists of particles with dimensions between 0.02 to 2 μm. It was possible to identify by EDS/MET particles of magnesium, confirming the formation of hydrotalcite. (author)

  10. Effect of permethrin, anthracene and mixture exposure on shell components, enzymatic activities and proteins status in the Mediterranean clam Venerupis decussata

    Energy Technology Data Exchange (ETDEWEB)

    Sellami, Badreddine, E-mail: sellamibadreddine@gmail.com [Laboratory of Environment Biomonitoring, Coastal Ecology Unit, Faculty of Sciences of Bizerta, University of Carthage, 7021 Zarzouna (Tunisia); Khazri, Abdelhafidh [Laboratory of Environment Biomonitoring, Coastal Ecology Unit, Faculty of Sciences of Bizerta, University of Carthage, 7021 Zarzouna (Tunisia); Mezni, Amine [Unit of Research 99/UR12-30, Department of Chemistry, Faculty of Sciences of Bizerte, 7021 Jarzouna (Tunisia); Louati, Héla; Dellali, Mohamed; Aissa, Patricia; Mahmoudi, Ezzeddine; Beyrem, Hamouda [Laboratory of Environment Biomonitoring, Coastal Ecology Unit, Faculty of Sciences of Bizerta, University of Carthage, 7021 Zarzouna (Tunisia); Sheehan, David, E-mail: d.sheehan@ucc.ie [Environmental Research Institute and Department of Biochemistry, University College Cork, Western Gateway Building, Western Road, Cork (Ireland)

    2015-01-15

    Highlights: • We assessed toxicity of anthracene, permethrin and their mixture on clams. • Tissue and stressor-dependent changes were observed in biochemical responses. • Permethrin induces phase transition from aragonite to calcite in shell structure. • Interactive effects were observed on digestive gland and gill biomarkers. • Both approaches give new vision to risk assessment of organic pollution. - Abstract: Anthracene (ANT) and permethrin (PER) are two of the more toxic compounds reaching the marine environment. This study aimed to determine the impact of these molecules on Venerupis decussata, an economically important species cultured on the Tunisian coast. Shell structure and its possible transformation upon exposure to the two contaminants were studied by X-ray diffraction and gravimetric analyses. Results revealed a phase transition in shell composition from aragonite to calcite after PER exposure, to a mixture of PER and ANT (Mix) but not for ANT alone. Catalase (CAT), superoxide dismutase (SOD) and glutathione transferase (GST) activities were determined in digestive gland and gills after exposure to ANT, PER and Mix to assess the impact of the contamination on the oxidative status of V. decussata. Enzyme activities increased in the digestive gland after PER treatment and in the gills after ANT treatment. PER exposure significantly reduced the levels of free thiols and increased levels of carbonylated proteins in the digestive gland, as compared to controls. In contrast, ANT exposure significantly reduced free thiols and increased the number of carbonylated proteins in the gills. Mix induced additive effects as measured by both enzymatic and proteomic approaches. The present study suggests that PER has a strong effect on shell structure; that PER and ANT exposure generate compound-dependent oxidative stress in the tissues of V. decussata and that a mixture of the two compounds has synergistic effects on biochemical response.

  11. Diagenetic Pattern in the Citarate Carbonate Rocks, Cilograng Area, Lebak Regency, Banten Province

    Directory of Open Access Journals (Sweden)

    N. I. Basuki

    2014-06-01

    Full Text Available DOI: 10.17014/ijog.v7i3.142The carbonate sequence overlies conformably the tuffaceous sandstone unit, and in turn is conformably underlain by the tuff-sandstone unit, both of which are members of the Citarate Formation. The Citarate carbonate rocks were deposited in an open platform back reef environment, which was temporarily drowned by local sea level rise. Regional Middle Miocene deformation formed NNE-WSW trend faults and E-W trend folds in the researched area. This paper discusses the nature of diagenetic alteration of the Citarate carbonate rocks based on petrographic analyses of twenty surface samples. Carbonate rocks from bottom to top comprise algae packstone, packstone-grainstone, coral-algae packstone, and foraminifer wackestone-packstone. Fragments of coral, coralline red algae, and large foraminifera are the dominant bioclasts in most of the observed samples, whereas echinoids and bivalves are less abundant; they are set in a recrystallized micrite matrix. Planktonic foraminifera are abundant only in few samples. Fragments of plagioclase, igneous volcanic rocks, pyroclastic rocks (tuff, and much less abundant quartz are commonly present in all the studied samples. A generalized diagenesis includes early marine cementation by fibrous aragonite, compaction, aragonite dissolution and/or neomorphism, precipitation of equant-grained calcite cement in a phreatic environment, dissolution to form moldic porosities, dolomitization, the formation of stylolites and fractures, and precipitation of late ferroan calcite during burial. Multiple carbonate cements occur as pore-filling phases, with ferroan calcite cementation taking place during later-stage burial. Secondary porosities were formed during different stages in diagenetic processes, such as dissolution, dolomitization, and stylolite and fracture formations. Although precipitation of nonferroan and ferroan calcite cement occluded porosities, porosity enhancement during early selective

  12. Quantifying the influence of CO2 seasonality on future ocean acidification

    Directory of Open Access Journals (Sweden)

    T. P. Sasse

    2015-04-01

    Full Text Available Ocean acidification is a predictable consequence of rising atmospheric carbon dioxide (CO2, and is highly likely to impact the entire marine ecosystem – from plankton at the base to fish at the top. Factors which are expected to be impacted include reproductive health, organism growth and species composition and distribution. Predicting when critical threshold values will be reached is crucial for projecting the future health of marine ecosystems and for marine resources planning and management. The impacts of ocean acidification will be first felt at the seasonal scale, however our understanding how seasonal variability will influence rates of future ocean acidification remains poorly constrained due to current model and data limitations. To address this issue, we first quantified the seasonal cycle of aragonite saturation state utilizing new data-based estimates of global ocean surface dissolved inorganic carbon and alkalinity. This seasonality was then combined with earth system model projections under different emissions scenarios (RCPs 2.6, 4.5 and 8.5 to provide new insights into future aragonite under-saturation onset. Under a high emissions scenario (RCP 8.5, our results suggest accounting for seasonality will bring forward the initial onset of month-long under-saturation by 17 years compared to annual-mean estimates, with differences extending up to 35 ± 17 years in the North Pacific due to strong regional seasonality. Our results also show large-scale under-saturation once atmospheric CO2 reaches 486 ppm in the North Pacific and 511 ppm in the Southern Ocean independent of emission scenario. Our results suggest that accounting for seasonality is critical to projecting the future impacts of ocean acidification on the marine environment.

  13. Ocean acidification and temperature increase impact mussel shell shape and thickness: problematic for protection?

    Science.gov (United States)

    Fitzer, Susan C; Vittert, Liberty; Bowman, Adrian; Kamenos, Nicholas A; Phoenix, Vernon R; Cusack, Maggie

    2015-11-01

    Ocean acidification threatens organisms that produce calcium carbonate shells by potentially generating an under-saturated carbonate environment. Resultant reduced calcification and growth, and subsequent dissolution of exoskeletons, would raise concerns over the ability of the shell to provide protection for the marine organism under ocean acidification and increased temperatures. We examined the impact of combined ocean acidification and temperature increase on shell formation of the economically important edible mussel Mytilus edulis. Shell growth and thickness along with a shell thickness index and shape analysis were determined. The ability of M. edulis to produce a functional protective shell after 9 months of experimental culture under ocean acidification and increasing temperatures (380, 550, 750, 1000 μatm pCO 2, and 750, 1000 μatm pCO 2 + 2°C) was assessed. Mussel shells grown under ocean acidification conditions displayed significant reductions in shell aragonite thickness, shell thickness index, and changes to shell shape (750, 1000 μatm pCO 2) compared to those shells grown under ambient conditions (380 μatm pCO 2). Ocean acidification resulted in rounder, flatter mussel shells with thinner aragonite layers likely to be more vulnerable to fracture under changing environments and predation. The changes in shape presented here could present a compensatory mechanism to enhance protection against predators and changing environments under ocean acidification when mussels are unable to grow thicker shells. Here, we present the first assessment of mussel shell shape to determine implications for functional protection under ocean acidification.

  14. Earth system commitments due to delayed mitigation

    International Nuclear Information System (INIS)

    As long as global CO2 emissions continue to increase annually, long-term committed Earth system changes grow much faster than current observations. A novel metric linking this future growth to policy decisions today is the mitigation delay sensitivity (MDS), but MDS estimates for Earth system variables other than peak temperature (ΔT max) are missing. Using an Earth System Model of Intermediate Complexity, we show that the current emission increase rate causes a ΔT max increase roughly 3–7.5 times as fast as observed warming, and a millenial steric sea level rise (SSLR) 7–25 times as fast as observed SSLR, depending on the achievable rate of emission reductions after the peak of emissions. These ranges are only slightly affected by the uncertainty range in equilibrium climate sensitivity, which is included in the above values. The extent of ocean acidification at the end of the century is also strongly dependent on the starting time and rate of emission reductions. The preservable surface ocean area with sufficient aragonite supersaturation for coral reef growth is diminished globally at an MDS of roughly 25%–80% per decade. A near-complete loss of this area becomes unavoidable if mitigation is delayed for a few years to decades. Also with respect to aragonite, 12%–18% of the Southern Ocean surface become undersaturated per decade, if emission reductions are delayed beyond 2015–2040. We conclude that the consequences of delaying global emission reductions are much better captured if the MDS of relevant Earth system variables is communicated in addition to current trends and total projected future changes. (letter)

  15. Physicochemical and pharmacological assessment of a traditional biomedicine: Mukta shouktic bhasma

    Directory of Open Access Journals (Sweden)

    Nitin Dubey

    2009-11-01

    Full Text Available Mukta shouktic bhasma (MSB is a traditional Ayurvedic medicinal preparation. This biomedicine is synthesized through special calcination of mother of pearl as mentioned in the classical Ayurvedic text. Physicochemical characterization of MSB was carried out using modern techniques such as transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction analysis, Fourier transform infra-red spectroscopy, inductively coupled plasma analysis, energy dispersive X-ray analysis, and thermogravimetric analysis. The study showed that the raw material mukta shouktic (mother of pearl is an organo-mineral matrix containing calcium carbonate in aragonite form. The aragonite form of calcium carbonatetransforms to a stable calcite form during the process of bhasma formation and forms the main crystalline component of MSB. The heat treatment does result in partial conversion of calcite to calcium oxide, which appears as calcium hydroxide(not more than 2% w/w in the final product. The organic content of processed material degraded gradually. Physical evaluation revealed that MSB is a fine grayish white powder having a poor flow property with narrow particle size distribution of 1.22 to 22.52 m having a mean particle size of 10.20±0.45 m. A clearly identifiable fraction of MSB particles was below 50 nanometer. The presence of nanosized particles in MSB might impart the therapeutic property of this medicine. Trace element analysis of MSB revealed the presence of metals, like arsenic, lead, chromium, cadmium, mercury, and tin under regulatory acceptable limits at the prescribed dose of MSB. Energy dispersive X-ray analysis revealed calcium as the major element (40.22 wt % in MSB. Microbial load for the formulation was found to be within limits. Animals were found to be safe up to a maximum dose of 2000 mg/kg body weight in acute toxicity studies. A significant (P<0.05 reduction in hyperpyrexia in rat was produced by MSB.

  16. Linking mineral deposits to speleogenetic processes in Cova des Pas de Vallgornera (Mallorca, Spain

    Directory of Open Access Journals (Sweden)

    Bogdan P. Onac

    2014-05-01

    Full Text Available Cova des Pas de Vallgornera (CPV is the premier cave of the Balearic Archipelago. Over 74 km of passages develop within two carbonate lithofacies (reef front and back reef, which ultimately control the patterns of the cave and to some degree its mineral infilling. The diversity of speleothem-forming minerals is four times greater around or within hypogene-related features (vents, rims, cupolas, compared to any other vadose passages in the cave. The mineralogy of speleothems (crusts, nodules, crystals, earthy masses associated with hypogene features in the seaward upper maze of Sector F is characterized by the presence of aragonite, ankerite, huntite, clay minerals, and quartz. In the Tragus and Nord sectors, however, the dominant mineral is dolomite, along with aragonite, celestine, huntite, clay minerals, and quartz. Calcite is by far the most ubiquitous mineral throughout the cave. Detailed macroscopic and scanning electron microanalysis and imaging have permitted the investigation of textural relationships between the minerals associated with vents, rims, and vent’s roof and walls. These studies along with morphological and stable isotope analyses confirm that not all minerals are connected with a hypogene stage in the cave evolution, and furthermore, none of them appears to be sulfuric acid by-products. Instead, the mineral assemblages documented in speleothems from CPV clearly support at least three speleogenetic pathways, namely seacoast mixing, ascending of warm groundwaters, and meteoric recharge (vadose. Thus, cave minerals in Cova des Pas de Vallgornera hold the keys to reconstruction and understanding of processes and conditions under which they precipitated, allowing to establish their relationship with various speleogenetic pathways.

  17. The effects of artificial alteration on sulfur in Arctica islandica shells

    Science.gov (United States)

    Fichtner, Vanessa; Huthwelker, Thomas; Borca, Camelia N.; Göttlicher, Jörg; Griesshaber, Erika; Yin, Xiaofei; Schmahl, Wolfgang W.; Mavromatis, Vasileios; Immenhauser, Adrian; Strauss, Harald

    2016-04-01

    Carbonate associated sulfate (CAS) is an important proxy for reconstructing redox conditions in former oceans. Especially for biogenic carbonates it is not fully understood where exactly the CAS is incorporated, how much is incorporated in respect to ambient sulfate concentrations, and how CAS is affected by diagenetic alteration. By combining sulfur K μ-XANES and μ-XRF analyses with geochemical methods (CAS-extraction, sulfur isotope measurements), this study aims at specifying the location of incorporation of CAS. Moreover, the effects of diagenetic alteration on sulfur abundance, speciation and distribution in shells of the marine bivalve Arctica islandica will be assessed through alteration experiments. Hereby, shell pieces were hydrothermally altered at two different temperatures (100°C and 175°C) for different times (one to twelve weeks) with sulfate-free artificial seawater. Our results show that the samples altered at 100°C retain the original/primary sulfur distribution and concentration, similar to a non-altered Arctica islandica shell. In contrast, μ-XRF maps of the shells altered at 175°C exhibit a significant change in the sulfur distribution and a decrease in sulfur concentration. The respective incubation solutions, in turn, show an increase in sulfate concentration with longer alteration times at 175°C. Furthermore, μ-XRF maps of sulfur not only record the growth of calcite crystals with longer alteration times at 175°C but also indicate that newly formed crystals are characterized by a near complete absence of sulfur. We propose that the process of recrystallization from aragonite to calcite between 100°C and 175°C causes the loss of sulfur from the bivalve shell. This is consistent with S K XANES analyses which indicate that the majority of sulfur in the Arctica islandica shell is present as sulfate integrated into the inorganic, aragonitic part, where the spectra resemble sulfate in aqueous solution.

  18. Coral records of reef-water pH across the central Great Barrier Reef, Australia: assessing the influence of river runoff on inshore reefs

    Science.gov (United States)

    D'Olivo, J. P.; McCulloch, M. T.; Eggins, S. M.; Trotter, J.

    2015-02-01

    The boron isotopic (δ11Bcarb) compositions of long-lived Porites coral are used to reconstruct reef-water pH across the central Great Barrier Reef (GBR) and assess the impact of river runoff on inshore reefs. For the period from 1940 to 2009, corals from both inner- and mid-shelf sites exhibit the same overall decrease in δ11Bcarb of 0.086 ± 0.033‰ per decade, equivalent to a decline in seawater pH (pHsw) of ~0.017 ± 0.007 pH units per decade. This decline is consistent with the long-term effects of ocean acidification based on estimates of CO2 uptake by surface waters due to rising atmospheric levels. We also find that, compared to the mid-shelf corals, the δ11Bcarb compositions of inner-shelf corals subject to river discharge events have higher and more variable values, and hence higher inferred pHsw values. These higher δ11Bcarb values of inner-shelf corals are particularly evident during wet years, despite river waters having lower pH. The main effect of river discharge on reef-water carbonate chemistry thus appears to be from reduced aragonite saturation state and higher nutrients driving increased phytoplankton productivity, resulting in the drawdown of pCO2 and increase in pHsw. Increased primary production therefore has the potential to counter the more transient effects of low-pH river water (pHrw) discharged into near-shore environments. Importantly, however, inshore reefs also show a consistent pattern of sharply declining coral growth that coincides with periods of high river discharge. This occurs despite these reefs having higher pHsw, demonstrating the overriding importance of local reef-water quality and reduced aragonite saturation state on coral reef health.

  19. Out of their depth? Isolated deep populations of the cosmopolitan coral Desmophyllum dianthus may be highly vulnerable to environmental change.

    Science.gov (United States)

    Miller, Karen J; Rowden, Ashley A; Williams, Alan; Häussermann, Vreni

    2011-01-01

    Deep sea scleractinian corals will be particularly vulnerable to the effects of climate change, facing loss of up to 70% of their habitat as the Aragonite Saturation Horizon (below which corals are unable to form calcium carbonate skeletons) rises. Persistence of deep sea scleractinian corals will therefore rely on the ability of larvae to disperse to, and colonise, suitable shallow-water habitat. We used DNA sequence data of the internal transcribed spacer (ITS), the mitochondrial ribosomal subunit (16S) and mitochondrial control region (MtC) to determine levels of gene flow both within and among populations of the deep sea coral Desmophyllum dianthus in SE Australia, New Zealand and Chile to assess the ability of corals to disperse into different regions and habitats. We found significant genetic subdivision among the three widely separated geographic regions consistent with isolation and limited contemporary gene flow. Furthermore, corals from different depth strata (shallow 1500 m) even on the same or nearby seamounts were strongly differentiated, indicating limited vertical larval dispersal. Genetic differentiation with depth is consistent with the stratification of the Subantarctic Mode Water, Antarctic Intermediate Water, the Circumpolar Deep and North Pacific Deep Waters in the Southern Ocean, and we propose that coral larvae will be retained within, and rarely migrate among, these water masses. The apparent absence of vertical larval dispersal suggests deep populations of D. dianthus are unlikely to colonise shallow water as the aragonite saturation horizon rises and deep waters become uninhabitable. Similarly, assumptions that deep populations will act as refuges for shallow populations that are impacted by activities such as fishing or mining are also unlikely to hold true. Clearly future environmental management strategies must consider both regional and depth-related isolation of deep-sea coral populations. PMID:21611159

  20. Phylomineralogy of the coralline red algae: correlation of skeletal mineralogy with molecular phylogeny.

    Science.gov (United States)

    Smith, A M; Sutherland, J E; Kregting, L; Farr, T J; Winter, D J

    2012-09-01

    The coralline algae in the orders Corallinales and Sporolithales (subclass Corallinophycidae), with their high degree of mineralogical variability, pose a challenge to projections regarding mineralogy and response to ocean acidification. Here we relate skeletal carbonate mineralogy to a well-established phylogenetic framework and draw inferences about the effects of future changes in sea-water chemistry on these calcified red algae. A collection of 191 coralline algal specimens from New Zealand, representing 13 genera and 28 species, included members of three families: Corallinaceae, Hapalidiaceae, and Sporolithaceae. While most skeletal specimens were entirely calcitic (range: 73-100 wt.% calcite, mean 97 wt.% calcite, std dev=5, n=172), a considerable number contained at least some aragonite. Mg in calcite ranged from 10.5 to 16.4 wt.% MgCO(3), with a mean of 13.1 wt.% MgCO(3) (std dev=1.1, n=172). The genera Mesophyllum and Lithophyllum were especially variable. Growth habit, too, was related to mineralogy: geniculate coralline algae do not generally contain any aragonite. Mg content varied among coralline families: the Corallinaceae had the highest Mg content, followed by the Sporolithaceae and the Hapalidiaceae. Despite the significant differences among families, variation and overlap prevent the use of carbonate mineralogy as a taxonomic character in the coralline algae. Latitude (as a proxy for water temperature) had only a slight relationship to Mg content in coralline algae, contrary to trends observed in other biomineralising taxa. Temperate magnesium calcites, like those produced by coralline algae, are particularly vulnerable to ocean acidification. Changes in biomineralisation or species distribution may occur over the next few decades, particularly to species producing high-Mg calcite, as pH and CO(2) dynamics change in coastal temperate oceans. PMID:22795764

  1. Response of C3 and C4 plants to middle-Holocene climatic variation near the prairie-forest ecotone of Minnesota, U.S.A.

    Energy Technology Data Exchange (ETDEWEB)

    Tian, J; Brown, T A; Hu, F S; Stefanova, I; Nelson, D M

    2003-12-24

    Paleorecords of the middle Holocene (MH) from the North American midcontinent can offer insights into ecological responses to pervasive drought that may accompany future climatic warming. We analyzed MH sediments from West Olaf Lake (WOL) and Steel Lake (SL) in Minnesota to examine the effects of warm/dry climatic conditions on prairie-woodland ecosystems. Mineral composition and carbonate {delta}{sup 18}O were used to determine climatic variations, whereas pollen assemblages, charcoal {delta}{sup 13}C, and charcoal accumulation rates were used to reconstruct vegetation composition, C{sub 3} and C{sub 4} plant abundance, and fire. The ratio of aragonite:calcite at WOL and {delta}{sup 18}O at SL suggest that pronounced droughts occurred during the MH but that drought severity decreased with time. From charcoal {delta}{sup 13}C data we estimated that the MH abundance of C{sub 4} plants averaged 50% at WOL and 43% at SL. At WOL C{sub 4} abundance was negatively correlated with aragonite:calcite, suggesting that severe moisture deficits suppressed C{sub 4} plants in favor of weedy C{sub 3} plants (e.g., Ambrosia). As climate ameliorated C{sub 4} abundance increased (from {approx}33 to 66%) at the expense of weedy species, enhancing fuel availability and fire occurrence. In contrast, farther east at SL climate was cooler and wetter than at WOL, and C{sub 4} abundance showed no correlation with {delta}{sup 18}O-inferred aridity. Woody C{sub 3} plants (e.g., Quercus) were more abundant, biomass flammability lower, and fires less important at SL than at WOL. Our results suggest that C{sub 4} plants are adapted to warm/dry climatic conditions, but not to extreme droughts, and that the fire regime is controlled by biomass-climate interactions.

  2. Effect of precipitation procedure and detection technique on particle size distribution of CaCO 3

    Science.gov (United States)

    Martos, C.; Coto, B.; Peña, J. L.; Rodríguez, R.; Merino-Garcia, D.; Pastor, G.

    2010-09-01

    The deposition of inorganic salts ("scales") such as calcium carbonate is an important flow assurance problem during crude oil production. The knowledge of the features of the precipitated solids, mainly the particle size and morphology, is crucial to understand the nature of the solids and to avoid or reduce the effect of their deposition. For instance, the use of additives is one of the most usual procedures to mitigate this problem. Additives interact with scale-forming substances either by increasing the induction time, or by inhibiting crystal growth, changing the morphology of solids. In this work, CaCO 3 was precipitated by two different experimental methods: by mixing sodium carbonate and calcium chloride at 25 °C (method 1), and by changing the pH (method 2). Precipitated solids were analyzed by means of the following techniques: laser diffraction (LD), focused-beam reflectance measurement (FBRM), scanning electron microscopy (SEM), and X-ray diffraction (XRD), in order to select a method for the determination of particle size of solids similar to scales, in order to study these deposits at the beginning of their formation and to evaluate the effect of additives in the scales particle size. Results were compared to those of scale deposits extracted from crude oil pipelines. SEM and XRD characterization showed that both the precipitation methods lead to calcium carbonate as a mixture of calcite, aragonite and vaterite, with rhombohedral morphology for method 1 and spherical for method 2. The effects of temperature, kinetics and Mg 2+ presence in the morphology of CaCO 3 were evaluated. Thus, the solids obtained by static bottle test and real scales are mainly formed by long needle-shaped aragonite. The comparison of the several particle size characterization methods determinates that an LD is a fast and sensitive technique for spherical and non-spherical solids, and it is a convenient technique for the analysis of scales extracted from oil pipelines.

  3. Calcification is not the Achilles' heel of cold-water corals in an acidifying ocean.

    Science.gov (United States)

    Rodolfo-Metalpa, Riccardo; Montagna, Paolo; Aliani, Stefano; Borghini, Mireno; Canese, Simonepietro; Hall-Spencer, Jason M; Foggo, Andy; Milazzo, Marco; Taviani, Marco; Houlbrèque, Fanny

    2015-06-01

    Ocean acidification is thought to be a major threat to coral reefs: laboratory evidence and CO2 seep research has shown adverse effects on many coral species, although a few are resilient. There are concerns that cold-water corals are even more vulnerable as they live in areas where aragonite saturation (Ωara ) is lower than in the tropics and is falling rapidly due to CO2 emissions. Here, we provide laboratory evidence that net (gross calcification minus dissolution) and gross calcification rates of three common cold-water corals, Caryophyllia smithii, Dendrophyllia cornigera, and Desmophyllum dianthus, are not affected by pCO2 levels expected for 2100 (pCO2  1058 μatm, Ωara 1.29), and nor are the rates of skeletal dissolution in D. dianthus. We transplanted D. dianthus to 350 m depth (pHT 8.02; pCO2  448 μatm, Ωara 2.58) and to a 3 m depth CO2 seep in oligotrophic waters (pHT 7.35; pCO2  2879 μatm, Ωara 0.76) and found that the transplants calcified at the same rates regardless of the pCO2 confirming their resilience to acidification, but at significantly lower rates than corals that were fed in aquaria. Our combination of field and laboratory evidence suggests that ocean acidification will not disrupt cold-water coral calcification although falling aragonite levels may affect other organismal physiological and/or reef community processes.

  4. Petrofabrics of high-pressure rocks exhumed at the slab-mantle interface from the "point of no return" in a subduction zone (Sivrihisar, Turkey)

    Science.gov (United States)

    Whitney, Donna L.; Teyssier, Christian; Seaton, Nicholas C. A.; Fornash, Katherine F.

    2014-12-01

    The highest pressure recorded by metamorphic rocks exhumed from oceanic subduction zones is ~2.5 GPa, corresponding to the maximum decoupling depth (MDD) (80 ± 10 km) identified in active subduction zones; beyond the MDD (the "point of no return") exhumation is unlikely. The Sivrihisar massif (Turkey) is a coherent terrane of lawsonite eclogite and blueschist facies rocks in which assemblages and fabrics record P-T-fluid-deformation conditions during exhumation from ~80 to 45 km. Crystallographic fabrics and other features of high-pressure metasedimentary and metabasaltic rocks record transitions during exhumation. In quartzite, microstructures and crystallographic fabrics record deformation in the dislocation creep regime, including dynamic recrystallization during decompression, and a transition from prism slip to activation of rhomb and basal slip that may be related to a decrease in water fugacity during decompression (~2.5 to ~1.5 GPa). Phengite, lawsonite, and omphacite or glaucophane in quartzite and metabasalt remained stable during deformation, and omphacite developed an L-type crystallographic fabric. In marble, aragonite developed columnar textures with strong crystallographic fabrics that persisted during partial to complete dynamic recrystallization that was likely achieved in the stability field of aragonite (P > ~1.2 GPa). Results of kinematic vorticity analysis based on lawsonite shape fabrics are consistent with shear criteria in quartzite and metabasalt and indicate a large component of coaxial deformation in the exhuming channel beneath a simple shear dominated interface. This large coaxial component may have multiplied the exhuming power of the subduction channel and forced deeply subducted rocks to flow back from the point of no return.

  5. Petrofabrics of High-Pressure Rocks Exhumed at the Slab-Mantle Interface from the 'Point of No Return'

    Science.gov (United States)

    Whitney, D. L.; Teyssier, C. P.; Seaton, N. C.; Fornash, K.

    2014-12-01

    The highest pressure typically recorded by metamorphic rocks exhumed from oceanic subduction zones is ~2.5±1 GPa, corresponding to the maximum decoupling depth (MDD) (80±10 km) identified in active subduction zones; beyond the MDD (the 'point of no return') exhumation is unlikely. One of the few places where rocks returned from the MDD largely unaltered is Sivrihisar, Turkey: a structurally coherent terrane of lawsonite eclogite and blueschist facies rocks in which assemblages and fabrics record P-T-fluid-deformation conditions during exhumation from ~80 to 45 km. Crystallographic fabrics and other structural features of high-pressure metasedimentary and metabasaltic rocks record transitions during exhumation. In quartzite, heterogeneous microstructures and crystallographic fabrics record deformation and dynamic recrystallization from ~2.6 GPa to ~1.5 GPa, as expressed by transition from prism c-axis patterns through progressive overprinting and activation of rhomb and basal slip. Omphacite, glaucophane, phengite, and lawsonite in quartzite remained stable during deformation. In marble, CaCO3 deformed in dislocation creep as aragonite, producing strong crystallographic fabrics. This fabric persisted through formation of calcite and destruction of the shape-preferred orientation, indicating the strength of aragonite marble. Omphacite in metabasalt and quartzite displays an L-type crystallographic fabric. Lawsonite kinematic vorticity data and other fabrics in metabasalt are consistent with exhumation involving increasing amounts of pure shear relative to simple shear and indicate strain localization and simple shear near the fault contact between the high-pressure unit and a serpentinite body. This large coaxial component multiplied the exhuming power of the subduction channel and forced rocks to return from the MDD.

  6. Toughening mechanisms in laminated composites: A biomimetic study in mollusk shells

    Science.gov (United States)

    Kamat, Shekhar Shripad

    2000-10-01

    Mollusk shells can be described as structural biocomposite materials composed of a mineral (aragonite) and a continuous, albeit minor, organic (protein) component. The conch shell, Strombus Gigas, has intermediate strength and high fracture toughness. The high fracture toughness is a result of enhanced energy dissipation during crack propagation due to delamination, crack bridging, frictional sliding etc. A theoretical and experimental study was conducted on the crack bridging mechanisms operative in the shell. Four-point bend tests were conducted. Acoustic emission and post-mortem dye penetrants were used to characterize the crack propagation, together with conventional fractography. A two layer composite configuration is seen in the shells, with the tough and weak layers having a toughness ratio of ˜4 (Ktough = 2.2MPam1/2). This toughness ratio is a requisite for multiple cracking in the weak layer. A theoretical shear lag analysis of the crack bridging phenomena in the tough layer is shown to lead to a bridging law for the crack wake of the form of p = betau1/2 (p is the bridging traction for a crack opening u, with beta, being a constant of proportionality). Finite element analysis yielded a value of beta = 630 Nmm-5/2 and ucritical = 5 mum for the bridging law parameters. In a nonlinear fracture mechanics phenomenology, these values are relevant material parameters, rather than a critical stress intensity factor. The work of fracture for unnotched specimens is three orders of magnitude higher than mineral aragonite, and is demonstrated numerically incorporating the toughening mechanisms in the shell. Similar structural adaptations have been observed and studied in the red abalone shell, haliotis rufescens and the spines of the sea urchin, Heterocentrotus trigonarius. The toughening mechanisms seen in these shells give insight into structural design needs of brittle matrix composites (BMC) as well as conventional structural ceramics.

  7. Establishing criteria to distinguish oil- from methane-seep carbonates

    Science.gov (United States)

    Smrzka, Daniel; Zwicker, Jennifer; Bach, Wolfgang; Bohrmann, Gerhard; Peckmann, Jörn

    2016-04-01

    Hydrocarbon seeps harbor biota depending on chemosynthesis that is preserved in the fossil record as part of authigenic carbonate deposits. Seep environments are characterized by emanation of methane-rich fluids, yet an increasing number of seeps have been discovered in recent years that are typified by seepage of crude oil. Fluid composition is an important factor governing the composition and diversity of seep-dwelling fauna at modern seeps, as different species have differing tolerances and requirements with regard to the emitted compounds. In this regard, oil seepage has a profound influence on the diversity and distribution of seep-endemic macrofauna and microbial communities. Despite current efforts to better understand oil seeps and their ecology, the confident identification of oil seeps in the geologic record still poses fundamental problems. We present new geochemical data that allow for a more reliable identification of oil seepage during the Phanerozoic. Clear, fibrous aragonite cements of modern and putative ancient oil- and methane-seep deposits were analyzed for their rare earth element (REE) content. This cement is common in seep limestones and represents a product of the anaerobic oxidation of methane and higher hydrocarbons. Clear aragonite is particularly pure and virtually free of detrital inclusions, making it an ideal mineral for comparative geochemical analyses. Its REE composition reveals that oil-seep deposits are significantly enriched in REEs compared to methane- seep deposits. Furthermore, bulk total organic carbon (TOC) measurements suggest that modern and putative ancient oil seep carbonates are enriched in organic carbon. The combined data serve as a promising tool for identifying oil seepage in the fossil record. Our results provide the foundation for an improved understanding of the adaptation of chemosynthesis-based life to oil as an energy source.

  8. Effect of ocean acidification on the early life stages of the blue mussel (Mytilus edulis

    Directory of Open Access Journals (Sweden)

    C. H. R. Heip

    2010-04-01

    Full Text Available Several experiments have shown a decrease of growth and calcification of organisms at decreased pH levels but relatively few studies have focused on early life stages which are believed to be more sensitive to environmental disturbances such as hypercapnia. Here, we present experimental data demonstrating that the growth of planktonic mussel (Mytilus edulis larvae is significantly affected by a decrease of pH to a level expected for the end of the century. Even though there was no significant effect of a 0.25–0.34 pH unit decrease on hatching and mortality rates during the first 2 days of development nor during the following 13-day period prior to settlement, final shells were, respectively, 4.5±1.3 and 6.0±2.3% smaller at pHNBS~7.8 than at a control pHNBS of ~8.1. Moreover, a decrease of 12.0±5.4% of shell thickness was observed. More severe impacts were found with a decrease of ~0.5 pHNBS unit during the first 2 days of development which could be attributed to a decrease of calcification due toslight undersaturation of seawater with respect to aragonite. Indeed, important effects on both hatching and D-veliger shell growth were found. Hatching rates were 24±4% lower while D-veliger shells were 12.7±0.9% smaller at pHNBS~7.6 than at a control pHNBS of ~8.1. Although these results show that blue mussel larvae are still able to develop a shell in seawater undersaturated with respect to aragonite, decreases of hatching rates and shell growth suggest a negative impact of ocean acidification on the future survival of bivalve populations potentially leading to significant ecological and economical losses.

  9. Tropical Cyclones Cause CaCO3 Undersaturation of Coral Reef Seawater in a High-CO2 World

    Science.gov (United States)

    Manzello, D.; Enochs, I.; Carlton, R.; Musielewicz, S.; Gledhill, D. K.

    2013-12-01

    Ocean acidification is the global decline in seawater pH and calcium carbonate (CaCO3) saturation state (Ω) due to the uptake of anthropogenic CO2 by the world's oceans. Acidification impairs CaCO3 shell and skeleton construction by marine organisms. Coral reefs are particularly vulnerable, as they are constructed by the CaCO3 skeletons of corals and other calcifiers. We understand relatively little about how coral reefs will respond to ocean acidification in combination with other disturbances, such as tropical cyclones. Seawater carbonate chemistry data collected from two reefs in the Florida Keys before, during, and after Tropical Storm Isaac provide the most thorough data to-date on how tropical cyclones affect the seawater CO2-system of coral reefs. Tropical Storm Isaac caused both an immediate and prolonged decline in seawater pH. Aragonite saturation state was depressed by 1.0 for a full week after the storm impact. Based on current 'business-as-usual' CO2 emissions scenarios, we show that tropical cyclones with high rainfall and runoff can cause periods of undersaturation (Ω < 1.0) for high-Mg calcite and aragonite mineral phases at acidification levels before the end of this century. Week-long periods of undersaturation occur for 18 mol% high-Mg calcite after storms by the end of the century. In a high-CO2 world, CaCO3 undersaturation of coral reef seawater can occur as a result of even modest tropical cyclones. The expected increase in the strength, frequency, and rainfall of the most severe tropical cyclones with climate change in combination with ocean acidification will negatively impact the structural persistence of coral reefs over this century.

  10. Out of their depth? Isolated deep populations of the cosmopolitan coral Desmophyllum dianthus may be highly vulnerable to environmental change.

    Directory of Open Access Journals (Sweden)

    Karen J Miller

    Full Text Available Deep sea scleractinian corals will be particularly vulnerable to the effects of climate change, facing loss of up to 70% of their habitat as the Aragonite Saturation Horizon (below which corals are unable to form calcium carbonate skeletons rises. Persistence of deep sea scleractinian corals will therefore rely on the ability of larvae to disperse to, and colonise, suitable shallow-water habitat. We used DNA sequence data of the internal transcribed spacer (ITS, the mitochondrial ribosomal subunit (16S and mitochondrial control region (MtC to determine levels of gene flow both within and among populations of the deep sea coral Desmophyllum dianthus in SE Australia, New Zealand and Chile to assess the ability of corals to disperse into different regions and habitats. We found significant genetic subdivision among the three widely separated geographic regions consistent with isolation and limited contemporary gene flow. Furthermore, corals from different depth strata (shallow 1500 m even on the same or nearby seamounts were strongly differentiated, indicating limited vertical larval dispersal. Genetic differentiation with depth is consistent with the stratification of the Subantarctic Mode Water, Antarctic Intermediate Water, the Circumpolar Deep and North Pacific Deep Waters in the Southern Ocean, and we propose that coral larvae will be retained within, and rarely migrate among, these water masses. The apparent absence of vertical larval dispersal suggests deep populations of D. dianthus are unlikely to colonise shallow water as the aragonite saturation horizon rises and deep waters become uninhabitable. Similarly, assumptions that deep populations will act as refuges for shallow populations that are impacted by activities such as fishing or mining are also unlikely to hold true. Clearly future environmental management strategies must consider both regional and depth-related isolation of deep-sea coral populations.

  11. Geochemical and Mineralogical Characteristics of Pleistocene Lignites and Associated Sediments of Marathousa Coal Field,Central Peloponnese,Greece

    Institute of Scientific and Technical Information of China (English)

    A.E.KELEPERTSIS; E.KONTIS

    1997-01-01

    The mineralogy and geochemistry data are presented for thirty-seven shales,four concretions,two carbonate sediments and seven lignites from the Marathousa coal field of the Megalopolis Basin in Greece.The argillaceous rocks consist of chlorite,illite,kaolinte,albite,quartz.opal-A,calcite and dolomite;the concretions of aragonite,gypsum and pyrite;and the carbonate rocks of calcite,quartz and illite.The mineral matter in the lignites consists of gypsum,quartz,albite,chlorite,illite,opal-A,dolomite,pyrite,and rarely calcite and kaolinite Athree-factor model explains the total variaition of major and trace elements in the argillaceous sediments.The first factor is an aluminosilicate factor and involves the following elements:Al,Si,Mg,Na,K,Ti,Mn,Nb,Y,Rb,Zn,Cu,Ni,Cr,Nband V,associated with chlorite,albite and illite.The second factor involves the elements Ca,Sr,Ba,Znand Sc and is related to carbonate lithology and mainly the carbonate concretions with gypsum.The third factor involves Fe and Ce with a weak association with Mn.The diagenesis of the Marathousa sediments and lignites was not very advanced as indicated by (a) the total thickness of the sequence (500m),(b) the presence of biogenic silica(opal-A) and (c) the age of the deposit(Pleistocene).FOr these reasons the rpresence of chlorite,illite and kaolinite in the sediments and lignite is due not to diagenetic reactions but to weathering of the flysch and metamorphic rocks at the edges of the Megalopolis Basin and transport of the weathering products(illite,chlorite,kaolinite)into the basin of deposition.The diagenetic minerals of the Marathousa sequence include pyrite,gypsum,dolomite and aragonite.

  12. Optics and remote sensing of Bahamian carbonate sediment whitings and potential relationship to wind-driven Langmuir circulation

    Directory of Open Access Journals (Sweden)

    H. M. Dierssen

    2009-03-01

    Full Text Available Regions of milky white seas or "whitings" periodically occur to the west of Andros Island along the Great Bahama Bank where the bottom sediment consists of fine-grained aragonite mud. We present measurements of inherent optical properties within a sediment whiting patch and discuss the potential for monitoring the frequency, extent, and quantity of suspended matter from ocean colour satellite imagery. Sea spectral reflectance measured in situ and remotely from space revealed highly reflective waters elevated across the visible spectrum (i.e., "whitened" with a peak at 490 nm. Particulate backscattering was an order of magnitude higher than that measured at other stations throughout the region. The whiting also had one of the highest backscattering ratios measured in natural waters (0.05–0.06 consistent with water dominated by aragonite particles with a high index of refraction. Regular periodicity of 40 and 212 s evident in the light attenuation coefficient over the sampling period indicated patches of fluctuating turbidity on spatial scales that could be produced from regular rows of Langmuir cells penetrating the 5-m water column. We suggest that previously described mechanisms for sediment resuspension in whitings, such as tidal bursting and fish activity, are not fully consistent with these data and propose that wind-driven Langmuir cells reaching the full-depth of the water column may represent a plausible mechanism for sediment resuspension and subsequent whiting formation. Optics and remote sensing provide important tools for quantifying the linkages between physical and biogeochemical processes in these dynamic shallow water ecosystems.

  13. Optics and remote sensing of Bahamian carbonate sediment whitings and potential relationship to wind-driven Langmuir circulation

    Directory of Open Access Journals (Sweden)

    H. M. Dierssen

    2008-12-01

    Full Text Available Regions of milky white seas or "whitings" periodically occur to the west of Andros Island along the Great Bahama Bank where the bottom sediment consists of fine-grained aragonite mud. We present comprehensive measurements of inherent optical properties within a whiting patch and discuss the potential for monitoring the frequency, extent, and quantity of suspended matter from ocean colour satellite imagery. Sea spectral reflectance measured in situ and remotely from space revealed highly reflective waters elevated across the visible spectrum (i.e., "whitened" with a peak at 490 nm. Particulate backscattering was an order of magnitude higher than that measured at other stations throughout the region. The whiting also had one of the highest backscattering ratios measured in natural waters (0.05–0.06 consistent with water dominated by aragonite particles with a high index of refraction. Regular periodicity of 40 and 212 s evident in the light attenuation coefficient over the sampling period indicated patches of fluctuating turbidity on spatial scales that could be produced from regular rows of Langmuir cells penetrating the 5-m water column. We suggest that previously described mechanisms for sediment resuspension in whitings, such as tidal bursting and fish activity, are not fully consistent with these data and propose that wind-driven Langmuir cells reaching the full-depth of the water column may represent a plausible mechanism for sediment resuspension and subsequent whiting formation. Optics and remote sensing provide important tools for quantifying the linkages between physical and biogeochemical processes in these dynamic shallow water ecosystems.

  14. Shellfish face uncertain future in high CO2 world: influence of acidification on oyster larvae calcification and growth in estuaries.

    Directory of Open Access Journals (Sweden)

    A Whitman Miller

    Full Text Available BACKGROUND: Human activities have increased atmospheric concentrations of carbon dioxide by 36% during the past 200 years. One third of all anthropogenic CO(2 has been absorbed by the oceans, reducing pH by about 0.1 of a unit and significantly altering their carbonate chemistry. There is widespread concern that these changes are altering marine habitats severely, but little or no attention has been given to the biota of estuarine and coastal settings, ecosystems that are less pH buffered because of naturally reduced alkalinity. METHODOLOGY/PRINCIPAL FINDINGS: To address CO(2-induced changes to estuarine calcification, veliger larvae of two oyster species, the Eastern oyster (Crassostrea virginica, and the Suminoe oyster (Crassostrea ariakensis were grown in estuarine water under four pCO(2 regimes, 280, 380, 560 and 800 microatm, to simulate atmospheric conditions in the pre-industrial era, present, and projected future concentrations in 50 and 100 years respectively. CO(2 manipulations were made using an automated negative feedback control system that allowed continuous and precise control over the pCO(2 in experimental aquaria. Larval growth was measured using image analysis, and calcification was measured by chemical analysis of calcium in their shells. C. virginica experienced a 16% decrease in shell area and a 42% reduction in calcium content when pre-industrial and end of 21(st century pCO(2 treatments were compared. C. ariakensis showed no change to either growth or calcification. Both species demonstrated net calcification and growth, even when aragonite was undersaturated, a result that runs counter to previous expectations for invertebrate larvae that produce aragonite shells. CONCLUSIONS AND SIGNIFICANCE: Our results suggest that temperate estuarine and coastal ecosystems are vulnerable to the expected changes in water chemistry due to elevated atmospheric CO(2 and that biological responses to acidification, especially calcifying

  15. Earth system commitments due to delayed mitigation

    Science.gov (United States)

    Pfister, Patrik L.; Stocker, Thomas F.

    2016-01-01

    As long as global CO2 emissions continue to increase annually, long-term committed Earth system changes grow much faster than current observations. A novel metric linking this future growth to policy decisions today is the mitigation delay sensitivity (MDS), but MDS estimates for Earth system variables other than peak temperature (ΔT max) are missing. Using an Earth System Model of Intermediate Complexity, we show that the current emission increase rate causes a ΔT max increase roughly 3-7.5 times as fast as observed warming, and a millenial steric sea level rise (SSLR) 7-25 times as fast as observed SSLR, depending on the achievable rate of emission reductions after the peak of emissions. These ranges are only slightly affected by the uncertainty range in equilibrium climate sensitivity, which is included in the above values. The extent of ocean acidification at the end of the century is also strongly dependent on the starting time and rate of emission reductions. The preservable surface ocean area with sufficient aragonite supersaturation for coral reef growth is diminished globally at an MDS of roughly 25%-80% per decade. A near-complete loss of this area becomes unavoidable if mitigation is delayed for a few years to decades. Also with respect to aragonite, 12%-18% of the Southern Ocean surface become undersaturated per decade, if emission reductions are delayed beyond 2015-2040. We conclude that the consequences of delaying global emission reductions are much better captured if the MDS of relevant Earth system variables is communicated in addition to current trends and total projected future changes.

  16. Climatic modulation of recent trends in ocean acidification in the California Current System

    Science.gov (United States)

    Turi, G.; Lachkar, Z.; Gruber, N.; Münnich, M.

    2016-01-01

    We reconstruct the evolution of ocean acidification in the California Current System (CalCS) from 1979 through 2012 using hindcast simulations with an eddy-resolving ocean biogeochemical model forced with observation-based variations of wind and fluxes of heat and freshwater. We find that domain-wide pH and {{{Ω }}}{arag} in the top 60 m of the water column decreased significantly over these three decades by about -0.02 decade-1 and -0.12 decade-1, respectively. In the nearshore areas of northern California and Oregon, ocean acidification is reconstructed to have progressed much more rapidly, with rates up to 30% higher than the domain-wide trends. Furthermore, ocean acidification penetrated substantially into the thermocline, causing a significant domain-wide shoaling of the aragonite saturation depth of on average -33 m decade-1 and up to -50 m decade-1 in the nearshore area of northern California. This resulted in a coast-wide increase in nearly undersaturated waters and the appearance of waters with {{{Ω }}}{arag}\\lt 1, leading to a substantial reduction of habitat suitability. Averaged over the whole domain, the main driver of these trends is the oceanic uptake of anthropogenic CO2 from the atmosphere. However, recent changes in the climatic forcing have substantially modulated these trends regionally. This is particularly evident in the nearshore regions, where the total trends in pH are up to 50% larger and trends in {{{Ω }}}{arag} and in the aragonite saturation depth are even twice to three times larger than the purely atmospheric CO2-driven trends. This modulation in the nearshore regions is a result of the recent marked increase in alongshore wind stress, which brought elevated levels of dissolved inorganic carbon to the surface via upwelling. Our results demonstrate that changes in the climatic forcing need to be taken into consideration in future projections of the progression of ocean acidification in coastal upwelling regions.

  17. Projections of ocean acidification over the next three centuries using a simple global climate carbon-cycle model

    Science.gov (United States)

    Hartin, C. A.; Bond-Lamberty, B.; Patel, P.; Mundra, A.

    2015-12-01

    Continued oceanic uptake of anthropogenic CO2 is projected to significantly alter the chemistry of the upper oceans, potentially having serious consequences for the marine ecosystems. Projections of ocean acidification are primarily determined from prescribed emission pathways within large scale earth system models. Rather than running the cumbersome earth system models, we can use a reduced-form model to quickly emulate the CMIP5 models for projection studies under arbitrary emission pathways and for uncertainty analyses of the marine carbonate system. In this study we highlight the capability of Hector v1.1, a reduced-form model, to project changes in the upper ocean carbonate system over the next three centuries. Hector is run under historical emissions and a high emissions scenario (Representative Concentration Pathway 8.5), comparing its output to observations and CMIP5 models that contain ocean biogeochemical cycles. Ocean acidification changes are already taking place, with significant changes projected to occur over the next 300 years. We project a low latitude (> 55°) surface ocean pH decrease from preindustrial conditions by 0.4 units to 7.77 at 2100, and an additional 0.27 units to 7.50 at 2300. Aragonite saturations decrease by 1.85 units to 2.21 at 2100 and an additional 0.80 units to 1.42 at 2300. Under a high emissions scenario, for every 1 °C of future warming we find a 0.107 unit pH decrease and a 0.438 unit decrease in aragonite saturations. Hector reproduces the global historical trends, and future projections with equivalent rates of change over time compared to observations and CMIP5 models. Hector is a robust tool that can be used for quick ocean acidification projections, accurately emulating large scale climate models under multiple emission pathways.

  18. Inorganic carbon in a high latitude estuary-fjord system in Canada's eastern Arctic

    Science.gov (United States)

    Turk, D.; Bedard, J. M.; Burt, W. J.; Vagle, S.; Thomas, H.; Azetsu-Scott, K.; McGillis, W. R.; Iverson, S. J.; Wallace, D. W. R.

    2016-09-01

    Rapidly changing conditions in the Arctic can have a significant impact on biogeochemical cycles and can be particularly important in high latitude estuary-fjord systems with abundant and diverse freshwater sources. This study provides a first look into the inorganic carbon system and its relation to freshwater sources in Cumberland Sound in the east coast of Baffin Island, Nunavut, Canada. These data contribute to the very limited set of inorganic carbon measurements in high latitude estuary-fjord systems. During the ice-free conditions in August 2011, the meteoric freshwater fractions (MW) in the upper 40 m ranged from 11 to 21% and no sea ice melt (SIM) was present in the Sound. Surface waters were undersaturated with pCO2 (260 and 300 μatm), and DIC and TA ranged between 1779 and 1966 μmol DIC kg-1, and 1922 and 2140 μmol TA kg-1, respectively. Aragonite saturation (ΩAr) state ranged from 1.9 in the surface to 1.4 in the subsurface waters. Data show decreasing TA and ΩAr with increasing MW fraction and suggest that Cumberland Sound waters would become aragonite undersaturated (ΩAr < 1) at MW = 0.37 (95% CI: 0.29 to 0.56). Estimated local δ18O (-19.2‰) and TA (174 μmol TA kg-1) end-members indicate MW was most likely a mixture of river water and glacial melt. In August 2012, MW fractions at the surface were between 8 and 11.5%, and SIM between 7 and 23%. Significant interannual variability of summertime SIM could potentially result in ΩAr undersaturation.

  19. The discovery of stromatolites developing at 3570 m above sea level in a high-altitude volcanic lake Socompa, Argentinean Andes.

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    María E Farías

    Full Text Available We describe stromatolites forming at an altitude of 3570 m at the shore of a volcanic lake Socompa, Argentinean Andes. The water at the site of stromatolites formation is alkaline, hypersaline, rich in inorganic nutrients, very rich in arsenic, and warm (20-24°C due to a hydrothermal input. The stromatolites do not lithify, but form broad, rounded and low-domed bioherms dominated by diatom frustules and aragonite micro-crystals agglutinated by extracellular substances. In comparison to other modern stromatolites, they harbour an atypical microbial community characterized by highly abundant representatives of Deinococcus-Thermus, Rhodobacteraceae, Desulfobacterales and Spirochaetes. Additionally, a high proportion of the sequences that could not be classified at phylum level showed less than 80% identity to the best hit in the NCBI database, suggesting the presence of novel distant lineages. The primary production in the stromatolites is generally high and likely dominated by Microcoleus sp. Through negative phototaxis, the location of these cyanobacteria in the stromatolites is controlled by UV light, which greatly influences their photosynthetic activity. Diatoms, dominated by Amphora sp., are abundant in the anoxic, sulfidic and essentially dark parts of the stromatolites. Although their origin in the stromatolites is unclear, they are possibly an important source of anaerobically degraded organic matter that induces in situ aragonite precipitation. To the best of our knowledge, this is so far the highest altitude with documented actively forming stromatolites. Their generally rich, diverse and to a large extent novel microbial community likely harbours valuable genetic and proteomic reserves, and thus deserves active protection. Furthermore, since the stromatolites flourish in an environment characterized by a multitude of extremes, including high exposure to UV radiation, they can be an excellent model system for studying microbial

  20. Temperature dependence of oxygen- and clumped isotope fractionation in carbonates: A study of travertines and tufas in the 6-95 °C temperature range

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    Kele, Sándor; Breitenbach, Sebastian F. M.; Capezzuoli, Enrico; Meckler, A. Nele; Ziegler, Martin; Millan, Isabel M.; Kluge, Tobias; Deák, József; Hanselmann, Kurt; John, Cédric M.; Yan, Hao; Liu, Zaihua; Bernasconi, Stefano M.

    2015-11-01

    Conventional carbonate-water oxygen isotope thermometry and the more recently developed clumped isotope thermometer have been widely used for the reconstruction of paleotemperatures from a variety of carbonate materials. In spite of a large number of studies, however, there are still large uncertainties in both δ18O- and Δ47-based temperature calibrations. For this reason there is a need to better understand the controls on isotope fractionation especially on natural carbonates. In this study we analyzed oxygen, carbon and clumped isotopes of a unique set of modern calcitic and aragonitic travertines, tufa and cave deposits from natural springs and wells. Together these samples cover a temperature range from 6 to 95 °C. Travertine samples were collected close to the vents of the springs and from pools, and tufa samples were collected from karstic creeks and a cave. The majority of our vent and pool travertines and tufa samples show a carbonate-water oxygen isotope fractionation comparable to the one of Tremaine et al. (2011) with some samples showing higher fractionations. No significant difference between the calcite-water and aragonite-water oxygen isotope fractionation could be observed. The Δ47 data from the travertines show a strong relationship with temperature and define the regression Δ47 = (0.044 ± 0.005 × 106)/T2 + (0.205 ± 0.047). The pH of the parent solution, mineralogy and precipitation rate do not appear to significantly affect the Δ47-signature of carbonates, compared to the temperature effect and the analytical error. The tufa samples and three biogenic calcites show an excellent fit with the travertine calibration, indicating that this regression can be used for other carbonates as well. This work extends the calibration range of the clumped isotope thermometer to travertine and tufa deposits in the temperature range from 6 °C to 95 °C.

  1. Metagenome-based diversity analyses suggest a significant contribution of non-cyanobacterial lineages to carbonate precipitation in modern microbialites

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    Purificacion eLopez-Garcia

    2015-08-01

    Full Text Available Cyanobacteria are thought to play a key role in carbonate formation due to their metabolic activity, but other organisms carrying out oxygenic photosynthesis (photosynthetic eukaryotes or other metabolisms (e.g. anoxygenic photosynthesis, sulfate reduction, may also contribute to carbonate formation. To obtain more quantitative information than that provided by more classical PCR-dependent methods, we studied the microbial diversity of microbialites from the Alchichica crater lake (Mexico by mining for 16S/18S rRNA genes in metagenomes obtained by direct sequencing of environmental DNA. We studied samples collected at the Western (AL-W and Northern (AL-N shores of the lake and, at the latter site, along a depth gradient (1, 5, 10 and 15 m depth. The associated microbial communities were mainly composed of bacteria, most of which seemed heterotrophic, whereas archaea were negligible. Eukaryotes composed a relatively minor fraction dominated by photosynthetic lineages, diatoms in AL-W, influenced by Si-rich seepage waters, and green algae in AL-N samples. Members of the Gammaproteobacteria and Alphaproteobacteria classes of Proteobacteria, Cyanobacteria and Bacteroidetes were the most abundant bacterial taxa, followed by Planctomycetes, Deltaproteobacteria (Proteobacteria, Verrucomicrobia, Actinobacteria, Firmicutes and Chloroflexi. Community composition varied among sites and with depth. Although cyanobacteria were the most important bacterial group contributing to the carbonate precipitation potential, photosynthetic eukaryotes, anoxygenic photosynthesizers and sulfate reducers were also very abundant. Cyanobacteria affiliated to Pleurocapsales largely increased with depth. Scanning electron microscopy (SEM observations showed considerable areas of aragonite-encrusted Pleurocapsa-like cyanobacteria at microscale. Multivariate statistical analyses showed a strong positive correlation of Pleurocapsales and Chroococcales with aragonite formation at

  2. Mineral parageneses, regional architecture, and tectonic evolution of Franciscan metagraywackes, Cape Mendocino-Garberville-Covelo 30' x 60' quadrangles, northwest California

    Science.gov (United States)

    Ernst, W.G.; McLaughlin, R.J.

    2012-01-01

    The Franciscan Complex is a classic subduction-zone assemblage. In northwest California, it comprises a stack of west vergent thrust sheets: westernmost Eastern Belt outliers; Central Belt mélange; Coastal Belt Yager terrane; Coastal Belt Coastal terrane; Coastal Belt King Range/False Cape terranes. We collected samples and determined P-T conditions of recrystallization for 88 medium-fine-grained metasandstones to assess their subduction-exhumation histories and assembly of the host allochthons. Feebly recrystallized Yager, Coastal, and King Range strata retain clear detrital features. Scattered neoblastic prehnite occurs in several Coastal terrane metasandstones; traces of possible pumpellyite are present in three Yager metaclastic rocks. Pumpellyite ± lawsonite ± aragonite-bearing Central Belt metasandstones are moderately deformed and reconstituted. Intensely contorted, thoroughly recrystallized Eastern Belt affinity quartzose metagraywackes contain lawsonite + jadeitic pyroxene ± aragonite ± glaucophane. We microprobed neoblastic phases in 23 rocks, documenting mineral parageneses that constrain the tectonic accretion and metamorphic P-T evolution of these sheets. Quasi-stable mineral assemblages typify Eastern Belt metasandstones, but mm-sized domains in the Central and Coastal belt rocks failed to achieve chemical equilibrium. Eastern Belt slabs rose from subduction depths approaching 25–30 km, whereas structurally lower Central Belt mélanges returned from ∼15–18 km. Coastal Belt assemblages suggest burial depths less than 5–8 km. Eastern and Central belt allochthons sequentially decoupled from the downgoing oceanic lithosphere and ascended into the accretionary margin; K-feldspar-rich Coastal Belt rocks were stranded along the continental edge without undergoing appreciable subduction, probably during Paleogene unroofing of the older, deeply subducted units of the Franciscan Complex in east-vergent crustal wedges.

  3. Aberrant otoliths in juvenile flounder Platichthys flesus (L.

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    Vanessa Neves

    2015-11-01

    Full Text Available Anomalous otolith formation has been reported in freshwater and marine fish species. The prevailing anomaly is the deposition of vaterite instead of aragonite, resulting in different otolith shape and transparency. In this study we report high occurrence rates of anomalous otoliths in juvenile flounder collected in the river Minho estuary (NW Portugal. Several pairs of otoliths were randomly selected from juvenile fish collected between 2013 and 2015, in two estuarine areas, and visually inspected on both sides for the presence of anomalies. Most anomalies consisted of depressions, projections or holes in different parts of the otolith. Distribution of irregularities was examined in relation to site of collection and fish total length. At the site with higher salinity, most otolith pairs were normal. In contrast, at the tidal freshwater station, 43% of the pairs examined were abnormal. In general, both otoliths were affected but the left one presented more extreme changes. The occurrence of anomalies seems to be related to fish size since these were only found in fish smaller than 7.5 cm. Preliminary morphometric analyses indicate that abnormal otoliths have the same proportions as normal ones, but the former seem heavier, for the same sized fish. It is presently unclear how these anomalies affect fish growth or survival. Raman microspectroscopy was used to determine the mineral phases (i.e. type of CaCO3 polymorph in one normal and one abnormal otolith, revealing crystals of aragonitic-type in both cases. SEM-EDS analysis corroborated Raman results and did not reveal differences in chemical composition between abnormal and normal zones but further studies are needed.

  4. Carbon isotope effects in carbonate systems

    Science.gov (United States)

    Deines, Peter

    2004-06-01

    Global carbon cycle models require a complete understanding of the δ 13C variability of the Earth's C reservoirs as well as the C isotope effects in the transfer of the element among them. An assessment of δ 13C changes during CO 2 loss from degassing magmas requires knowledge of the melt-CO 2 carbon isotope fractionation. In order to examine the potential size of this effect for silicate melts of varying composition, 13C reduced partition functions were computed in the temperature range 275 to 4000 K for carbonates of varying bond strengths (Mg, Fe, Mn, Sr, Ba, Pb, Zn, Cd, Li, and Na) and the polymorphs of calcite. For a given cation and a given pressure the 13C content increases with the density of the carbonate structure. For a given structure the tendency to concentrate 13C increases with pressure. The effect of pressure (‰/10 kbar) on the size of the reduced partition function of aragonite varies with temperature; in the pressure range 1 to 10 5 bars the change is given by: Δ 13C p average=-0.01796+0.06635∗ 10 3/T+0.006875∗ 10 6/T2 For calcite III the pressure effect is on average 1.4× larger than that for aragonite at all temperatures. The nature of the cation in a given structure type has a significant effect on the carbon isotope fractionation properties. The tendency to concentrate 13C declines in the series magnesite, aragonite, dolomite, strontianite, siderite, calcite, smithonite, witherite, rhodochrosite, otavite, cerrusite. For divalent cations a general expression for an estimation of the reduced partition function (β) from the reduced mass (μ = [M Cation × M Carbonate]/[M Cation + M Carbonate]) is: 1000 lnβ=(0.032367-0.072563∗ 10 3/T-0.01073∗ 10 6/T2)∗μ-14.003+29.953∗ 10 3/T+9.4610∗ 10 6/T2 For Mg-calcite the 13C content varies with the Mg concentration. The fractionation between Mg-calcite (X = mole fraction of MgCO 3) and calcite is given by: 1000 ln(α MgCalite- Calcite)=[0.013702-0.10957× 10 3/T+1.35940× 10 6/T2

  5. Low Florida coral calcification rates in the Plio-Pleistocene

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    Brachert, Thomas C.; Reuter, Markus; Krüger, Stefan; Klaus, James S.; Helmle, Kevin; Lough, Janice M.

    2016-08-01

    In geological outcrops and drill cores from reef frameworks, the skeletons of scleractinian corals are usually leached and more or less completely transformed into sparry calcite because the highly porous skeletons formed of metastable aragonite (CaCO3) undergo rapid diagenetic alteration. Upon alteration, ghost structures of the distinct annual growth bands often allow for reconstructions of annual extension ( = growth) rates, but information on skeletal density needed for reconstructions of calcification rates is invariably lost. This report presents the bulk density, extension rates and calcification rates of fossil reef corals which underwent minor diagenetic alteration only. The corals derive from unlithified shallow water carbonates of the Florida platform (south-eastern USA), which formed during four interglacial sea level highstands dated approximately 3.2, 2.9, 1.8, and 1.2 Ma in the mid-Pliocene to early Pleistocene. With regard to the preservation, the coral skeletons display smooth growth surfaces with minor volumes of marine aragonite cement within intra-skeletal porosity. Within the skeletal structures, voids are commonly present along centres of calcification which lack secondary cements. Mean extension rates were 0.44 ± 0.19 cm yr-1 (range 0.16 to 0.86 cm yr-1), mean bulk density was 0.96 ± 0.36 g cm-3 (range 0.55 to 1.83 g cm-3) and calcification rates ranged from 0.18 to 0.82 g cm-2 yr-1 (mean 0.38 ± 0.16 g cm-2 yr-1), values which are 50 % of modern shallow-water reef corals. To understand the possible mechanisms behind these low calcification rates, we compared the fossil calcification rates with those of modern zooxanthellate corals (z corals) from the Western Atlantic (WA) and Indo-Pacific calibrated against sea surface temperature (SST). In the fossil data, we found a widely analogous relationship with SST in z corals from the WA, i.e. density increases and extension rate decreases with increasing SST, but over a significantly larger

  6. Low Florida coral calcification rates in the Plio-Pleistocene

    Science.gov (United States)

    Brachert, T. C.; Reuter, M.; Krüger, S.; Klaus, J. S.; Helmle, K.; Lough, J. M.

    2015-12-01

    In geological outcrops and drill cores from reef frameworks, the skeletons of scleractinian corals are usually leached and more or less completely transformed into sparry calcite because the highly porous skeletons formed of metastable aragonite (CaCO3) undergo rapid diagenetic alteration. Upon alteration, ghost structures of the distinct annual growth bands may be retained allowing for reconstructions of annual extension (= growth) rates, but information on skeletal density needed for reconstructions of calcification rates is invariably lost. Here we report the first data of calcification rates of fossil reef corals which escaped diagenetic alteration. The corals derive from unlithified shallow water carbonates of the Florida platform (southeastern USA), which formed during four interglacial sea level highstands dated 3.2, 2.9, 1.8, and 1.2 Ma in the mid Pliocene to early Pleistocene. With regard to the preservation, the coral skeletons display smooth growth surfaces with minor volumes of marine aragonite cement within intra-skeletal porosity. Within the skeletal structures, dissolution is minor along centers of calcification. Mean extension rates were 0.44 ± 0.19 cm yr-1 (range 0.16 to 0.86 cm yr-1) and mean bulk density was 0.86 ± 0.36 g cm-3 (range 0.55 to 1.22 g cm-3). Correspondingly, calcification rates ranged from 0.18 to 0.82 g cm-2 yr-1 (mean 0.38 ± 0.16 g cm-2 yr-1), values which are 50 % of modern shallow-water reef corals. To understand the possible mechanisms behind these low calcification rates, we compared the fossil calcification with modern zooxanthellate-coral (z-coral) rates from the Western Atlantic (WA) and Indo-Pacific (IP) calibrated against sea surface temperature (SST). In the fossil data, we found an analogous relationship with SST in z-corals from the WA, i.e. density increases and extension rate decreases with increasing SST, but over a significantly larger temperature window during the Plio-Pleistocene. With regard to the

  7. Underground electromagnetic activity in two regions with contrasting seismicity: a case study from the Eastern Alps and Bohemian Massif

    Science.gov (United States)

    Baroň, Ivo; Koktavý, Pavel; Stemberk, Josef; Macků, Robert; Trčka, Tomáš; Škarvada, Pavel; Lenhardt, Wolfgang; Meurers, Bruno; Rowberry, Mattew; Marti, Xavi; Plan, Lukas; Grasemann, Berhnard; Mitrovic, Ivanka

    2016-04-01

    Electromagnetic emissions (EME) occur during the fracturing of solid materials under laboratory conditions and may represent potential earthquake precursors. We recorded EME from May 2015 to October 2015 in two caves situated in contrasting seismotectonic settings. Zbrašov Aragonite Caves are located close to the seismically quiescent contact between the Bohemian Massif and the Outer Western Carpathians while Obir Caves are located near the seismically active Periadriatic Fault on the southern margin of the Eastern Alps. The specific monitoring points are located at depths of tens of metres below the ground surface as such places are assumed to represent favourably shielded environments. The EME signals were continuously monitored by two custom-made Emission Data Loggers (EDLOG), comprising both analogue and digital parts. The crucial analogue component within the EDLOG is a wideband shielded magnetic loop antenna. To be able to observe EME related rock deformation and microfracturing we recorded signals between 10 and 200 kHz with a sampling frequency of 500 kHz. An ultralow noise preamplifier placed close to the antenna increases the signal-to-noise ratio. Further signal processing consisted of filtering, such as antialiasing and interference rejection, and additional amplification to fit the signal to the full scale range of the AD convertor. The digital part of the EDLOG comprises a range of PC components such as high-capacity replaceable data storage and unbuffered RAM, high-speed multichannel DAQ cards, and custom made control software in the programming environment LabVIEW. During our EME monitoring all the raw data were stored. This has allowed us to perform advanced data processing and detailed analysis. During the study period some artificial EME signals were observed in Zbrašov Aragonite Caves. This artificial noise may have overprinted any natural signals and is most likely to relate to the pumping of CO2. In contrast, markedly different signals were

  8. The role of crystal structure and fabrics in early diagenesis: examples from continental and marine settings

    Science.gov (United States)

    Frisia, Silvia; Borsato, Andrea; Bajo, Petra; Hellstrom, John

    2015-04-01

    Palaeoclimate research based on geological archives relies on the assumption that the system has remained closed to phase transformation and re-mobilization of chemical species, the extent of which depends on the crystallization pathways. Early diagenesis, in fact, encompasses processes that occur soon after deposition, from a few hours to centuries. In the last decade, speleothems-based palaeoclimate research has gained momentum. Speleothems (cave secondary mineral deposits) have provided geochemical records of climate, pollution, volcanism, land use and vegetation changes at seasonal to millennial scale for the past million year. Critically, the accuracy of their records relies on the absence of diagenetic modifications. Yet, contrary to late diagenetic dissolution and re-precipitation, early diagenesis is difficult to detect in stalagmites and flowstones. A striking example is a Holocene stalagmite from Corchia cave, whose fabrics appear compact and of primary origin. Nevertheless, U-Th dating by mass spectrometry of 5 out of 47 samples shows offset from neighboring samples of up to 40%. Careful petrographic observations reveal that elongated columnar fabric contains microstructural defects, expressed by irregular crystal boundaries, which allow for the percolation of diagenetic fluids and U loss. Speleothem allow for the precise dating of diagenetic processes. Aggradation of micrite into microsparite may occur in less than a hundred year. Similar aggrading neomorphism of micrite has been documented for subglacial carbonates, where aggradation occurred at secular scale. Aggradation can be fingerprinted by the stable isotope ratio values, commonly more positive than in the columnar fabrics. In speleothems, aragonite may be transformed into calcite in less than 100 years. The phase transformation may partially preserve the original fabric, and appears to commence from calcite nucleated on organic compounds at twin boundaries, taking advantage of crystal defects as

  9. Microbial bio-mineralization processes in hydrothermal travertine: the case study of two active travertine systems (Tuscany, Italy).

    Science.gov (United States)

    Barilaro, Federica; Bontognali, Tomaso R. R.; Mc Kenzie, Judith A.; Vasconcelos, Crisogono

    2015-04-01

    Modern hydrothermal travertine deposits, occurring today at Bagni San Filippo (Radicofani Basin) and at Bagni di Saturnia (Albegna Valley) in Tuscany, Central Italy, have been investigated with the main purpose to improve the understanding of the processes that control calcium carbonate precipitation in hydrothermal-spring settings. Present-day thermal activity at Bagni di Saturnia is characterized by a 37.5°C thermal spring with a rate of about 800 l/s, with a pH of ca. 6.4. Thermal water discharges at Bagni San Filippo reach a rate of 20 litres per second at a maximum temperature of 50°C and a pH of ca. 7. The springs expel water enriched in H2S-CO2-SO42- and HCO3- and divalent cations (Ca and Mg). In the studied areas, travertine precipitation occurs in association with living microbial mats and biofilms, composed of a heterogeneous community of green algae, filamentous cyanobacteria and other types of prokaryotes, anoxygenic photosynthetic bacteria and heterotrophic heat-tolerant bacteria, with a variable amount of extracellular polymeric substances (EPS). Nine categories of fabric types, dominantly calcite and aragonite in composition, showing a wide range of macro- and micro-porosity, have been identified. High magnification analysis of dendritic and laminated boundstone, crystalline crust cementstone, raft boundstone, coated bubble boundstone, micrite mudstone and coated reed boundstone fabric types, suggests that precipitation occurs in association with organic matter. Diatoms, cyanobacteria filaments and other bacteria are then associated with the EPS and often appear totally or partially entombed (passively or actively) in it. Organic extracellular polymeric substances (EPS) and often the external surface of cyanobacterial sheaths are the location where the calcite minerals nucleate and grow. Precipitation begins with organomineral nano-globules consisting of nanometre-size, from sub-spherical to globular-like, raised structures (5 to 80 nm diameter

  10. In situ Raman study of dissolved CaCO3 minerals under subduction zone conditions

    Science.gov (United States)

    Facq, S.; Daniel, I.; Sverjensky, D. A.

    2012-12-01

    The fate and the characteristics of the Earth's deep carbon reservoirs are still not well understood [1]. The connection between the surficial and the deep-Earth carbon cycles occurs at subduction zones where carbon is transported into the mantle and where hydrous silicates and carbonate minerals break down releasing H2O and C-species in fluids associated with mantle metasomatism and the generation of arc volcanism [2]. In order to obtain mass balance between recycling and burial in the deep mantle, the study of the dissolution of CaCO3 minerals in equilibrium with aqueous fluids under mantle conditions is crucial. We report a novel integrated experimental and theoretical study of the equilibration of CaCO3 minerals with aqueous solutions (pure water or NaCl solutions) at high pressures and temperatures (0.5 to 8 GPa and 250 to 500 °C). The fluid speciation was studied using in situ Raman spectroscopy coupled to an externally heated membrane type DAC equipped with 500 μm pure synthetic diamond anvils. In a typical experiment, the aqueous fluid and a calcite crystal [3] were loaded in a rhenium gasket. The pressure was determined from the calibrated shift of the carbonate υ1 symmetric stretching mode of aragonite and the temperature measured with a K-type thermocouple. Raman spectra were recorded using a Labram HR800 Raman spectrometer (Horiba Jobin-Yvon) coupled to a Spectra Physics Ar+ laser. At equilibrium with an aragonite crystal, the Raman data show that bicarbonate is the most abundant species in low-pressure fluids (below 4 GPa) whereas carbonate becomes progressively dominant at higher pressure. After correction from their Raman cross-sections [4], the relative amounts of dissolved carbonate and bicarbonate were estimated from the areas of the Raman bands of the carbonate and bicarbonate ions (υ1 and υ5 symmetric stretching modes, respectively). The presence of sodium chloride influences the speciation by extending the pressure field where the

  11. Review: the effects of secular variation in seawater Mg/Ca on marine biocalcification

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    J. B. Ries

    2009-07-01

    Full Text Available Synchronized transitions in the polymorph mineralogy of the major reef-building and sediment-producing calcareous marine organisms and abiotic CaCO3 precipitates (ooids, marine cements throughout Phanerozoic time is believed to have been caused by tectonically-induced variations in seawater molar Mg/Ca (>2="aragonite seas"; <2="calcite seas". Here, I review a series of experiments in which extant calcifying taxa were reared in experimental seawater formulated over the range of mMg/Ca ratios (1.0 to 5.2 that occurred throughout their geologic history.

    Aragonite-secreting bryopsidalean algae and scleractinian corals and calcite-secreting coccolithophores exhibited higher rates of calcification and growth in the experimental seawaters that favored their skeletal mineral. These results support the assertion that seawater Mg/Ca played an important role in determining which hypercalcifying marine organisms were the major reef-builders and sediment-producers throughout Earth history. The observation that primary production increased along with calcification in mineralogically-favorable seawater is consistent with the hypothesis that calcification promotes photosynthesis within autotrophs through the liberation of CO2.

    The Mg/Ca ratio of calcite secreted by the coccolithophores, coralline algae and reef-dwelling animals (crustacea, urchins, calcareous tube worms declined with reductions in seawater Mg/Ca. Calcifying microbial biofilms varied their mineral polymorph with seawater Mg/Ca (mMg/Ca<2=low Mg calc; mMg/Ca>2=arag+high Mg calc, suggesting a nearly abiotic mode of calcification. These results indicate that biomineralogical control can be partially overridden by ambient seawater Mg/Ca and suggests that modern high Mg calcite organisms probably secreted low Mg calcite in calcite seas of the past. Notably, Mg fractionation in autotrophic organisms was more strongly influenced by changes in

  12. Scleractinian Fossil Corals as Archives of Seawater δ26Mg

    Science.gov (United States)

    Gothmann, A. O.; Higgins, J. A.; Adkins, J. F.; Stolarski, J.; Bender, M. L.

    2014-12-01

    The recovery of environmental signatures from coral skeletons is often made difficult by 'vital effects', which cause skeletal chemistry to deviate from the expected composition of aragonite in equilibrium with seawater. Recent studies show that Mg isotopes in scleractinian corals are subject to vital effects, which appear as a departure of the δ26Mg coral temperature dependence from that of inorganic aragonite [1]. However, different from the case for Mg/Ca or δ44Ca in coral, the magnitude of the observed Mg-isotope vital effect is small (on the order of 0.1 ‰ or less). In addition, measurements of different species of modern coral show similar fractionations, suggesting that coral δ26Mg is not species dependent [2]. Together, these observations indicate that corals should faithfully record the seawater Mg-isotope composition, and that vital effects will not bias reconstructions. We measured Mg isotopes in a set of extremely well-preserved fossil scleractinian corals, ranging in age from Jurassic through Recent, to reconstruct past seawater δ26Mg. Well-preserved fossil corals of similar age show a range in δ26Mg of ~0.2 ‰, pointing to the presence of vital effects. However, our results show little variability in the δ26Mg of fossil corals across different geologic ages, suggesting that seawater δ26Mg has remained relatively constant throughout the Cenozoic and Mesozoic. This pattern has implications for our understanding of the mechanisms driving secular variations in seawater Mg/Ca. In particular, our data imply that dolomitization rates have not changed enough during the Mesozoic and Cenozoic to account for secular variations in seawater Mg/Ca. Our coral δ26Mg record agrees with a Cenozoic record from bulk foraminifera, further supporting the faithfulness of the coral archive. However, both of these records disagree with a third Cenozoic Mg-isotope record, derived from species-specific planktic forams [3]. [1] Saenger, C. et al. (2014) Chem. Geol

  13. Hydroclimatic variability in the Levant during the early last glacial (∼ 117–75 ka derived from micro-facies analyses of deep Dead Sea sediments

    Directory of Open Access Journals (Sweden)

    I. Neugebauer

    2015-08-01

    Full Text Available The new sediment record from the deep Dead Sea basin (ICDP core 5017-1 provides a unique archive for hydroclimatic variability in the Levant. Here, we present high-resolution sediment facies analysis and elemental composition by μXRF scanning of core 5017-1 to trace lake levels and responses of the regional hydroclimatology during the time interval from ca 117–75 ka, i.e. the transition between the last interglacial and the onset of the last glaciation. We distinguished six major micro-facies types and interpreted these and their alterations in the core in terms of relative lake level changes. The two end-member facies for highest and lowest lake levels are (a up to several meters thick, greenish sediments of alternating aragonite and detrital marl laminae (aad and (b thick halite facies, respectively. Intermediate lake levels are characterised by detrital marls with varying amounts of aragonite, gypsum or halite, reflecting lower-amplitude, shorter-term variability. Two intervals of pronounced lake level drops occurred at ∼110–108 ± 5 and ∼93–87 ± 7 ka. They likely coincide with stadial conditions in the central Mediterranean (Melisey I and II pollen zones in Monticchio and low global sea levels during MIS 5d and 5b. However, our data do not support the current hypothesis of an almost complete desiccation of the Dead Sea during the earlier of these lake level low stands based on a recovered gravel layer. Based on new petrographic analyses, we propose that, although it was a low stand, this well-sorted gravel layer may be a vestige of a thick turbidite that has been washed out during drilling rather than an in-situ beach deposit. Two intervals of higher lake stands at ∼108–93 ± 6 and ∼87–75 ± 7 ka correspond to interstadial conditions in the central Mediterranean, i.e. pollen zones St. Germain I and II in Monticchio, and GI 24 + 23 and 21 in Greenland, as well as to sapropels S4 and S3 in the Mediterranean Sea. These

  14. Kinetics and Mechanisms of Calcite Reactions with Saline Waters

    Energy Technology Data Exchange (ETDEWEB)

    Gorman, Brian P [Colorado School of Mines, Golden, CO (United States)

    2015-09-02

    Project Description: The general objective of the proposed research is to determine the kinetics and mechanisms of calcite reactions with saline waters over a wide range of saline water composition, pCO2, and modest ranges in T and P. This will be accomplished by studying both reaction rates and solubility from changes in solution chemistry, and making nanoscale observations of calcite precipitate surface morphology and composition at the micro-to-nano-scale to provide an understanding of controlling reaction mechanisms and pathways. The specific objectives necessary to reach the general objective are: a) determination of how pCO2, Ca2+, ionic strength and “foreign” ions influence reaction rates; and b) investigate the influence of these parameters on apparent kinetic solubility from dissolution and precipitation reactions. This information will clearly be central to the construction of reliable reaction-transport models to predict reservoir and formation response to increased CO2 in saline waters. This program was initially collaborative with John Morse at Texas A&M, however his passing shortly after the beginning of this program resulted in abbreviated research time and effort. Summary of Results: Early studies using electron microscopy and spectroscopy indicated that carbonate precipitation from natural seawater (NSW) conditions onto aragonite substrates was mediated by a surface amorphous calcium carbonate layer. It was hypothesized that this ACC layer (observed after < 5days reaction time) was responsible for the abnormal reaction kinetics and also served as a metastable seed layer for growth of epitaxial aragonite. Further studies of the ACC formation mechanism indicated a strong dependence on the Mg concentration in solution. Subsequent studies at shorter times (10 hrs) on calcite substrates and in a wide range of supersaturation conditions did not indicate any ACC layer. Instead, an epitaxial layer by layer

  15. Coral Reef Habitat Suitability in Future Climate Scenarios from NCAR CESM1 considering a Suite of Biogeochemical Variables

    Science.gov (United States)

    Freeman, L. A.; Kleypas, J. A.; Miller, A. J.

    2013-12-01

    A maximum entropy species distribution model (Maxent) is used to describe coral reef habitat in current climate conditions and to predict changes to that habitat during the 21st century. Two climate change scenarios (RCP4.5 and RCP8.5) from the National Center for Atmospheric Research's Community Earth System Model version 1 (CESM1) were used with Maxent to determine environmental suitability for the family of corals Scleractina in 1° by 1° cells. Input environmental variables most suitable for representing coral habitat limitation are isolated using a principal component analysis and include cumulative thermal stress, salinity, light availability, current speed, phosphate levels and aragonite saturation state. Considering a suite of environmental variables allows for a more synergistic view of future habitat suitability, although individual variables are found to be limiting in certain areas- for example, aragonite saturation state is limiting at higher latitudes. Climate-driven coral reef habitat changes depend strongly on the oceanic region of interest and the region of corals used to train the niche model. Increased global coral habitat loss occurred in both RCP4.5 and RCP8.5 climate projections as time progressed through the 21th century. Maximum suitable habitat loss was 82% by 2100 for RCP8.5. When only Caribbean/Atlantic coral reef environmental data is applied globally, 88% of global habitat was lost by 2100 for RCP8.5. The global runs utilizing only Pacific Ocean reefs' ability to survive showed the most significant worldwide loss, 90% by 2100 for RCP8.5. When Maxent was trained with Indian Ocean reefs, an increase in suitable habitat worldwide was estimated. Habitat suitability was found to increase by 38% in RCP4.5 by 2100 and 28% in RCP8.5 by 2050. This suggests that shallow tropical sites in the Indian Ocean basin experience conditions today that are most similar to future worldwide climate projections. Indian Ocean reefs may be ideal candidate

  16. The Modern Marine Ca-isotope Budget and its Application to the Phanerozoic Ca-isotope Record

    Science.gov (United States)

    Blattler, C. L.; Jenkyns, H. C.; Henderson, G. M.

    2011-12-01

    Variations in the calcium-isotope ratio (δ44/40Ca) of ancient seawater have been recorded in several studies using marine carbonate, barite, or apatite, but the causes of these variations have not been explored quantitatively. Seawater Ca-isotope ratios are affected by the average fractionation factor between seawater and the carbonate that precipitates from it, which is defined by the composition of the marine carbonate sink. To investigate possible changes in the fractionation factor of marine carbonate over the Phanerozoic, a Ca-isotope budget has been constructed for the modern oceans. Over 250 Ca-isotope measurements have been compiled from a wide variety of carbonate sources to describe the modern marine Ca-isotope budget. This dataset includes over 50 new measurements to characterize several components of the carbonate system, such as coral reefs, which are quantitatively important but have been undersampled, for example, relative to planktic foraminifera. δ44/40Ca values have been temperature-normalized using the relationship of +0.02% per °C, which permits observations and comparisons based on mineralogy, taxonomy, and locus of carbonate precipitation. A general offset of ~0.25%, increasing up to ~0.8% for certain taxa, is observed between subsets of aragonite and calcite samples; no statistical difference is observed between high-Mg calcite and low-Mg calcite. Additionally, within the data for calcite skeletons, two broad groups appear based on taxonomic patterns. Taxa with generally weak control over their biomineralization, such as sclerosponges, brachiopods, and calcareous red algae, are 0.4-0.5% heavier than organisms with more controlled calcification mechanisms, such as coccolithophores and planktic foraminifera. The patterns that emerge from this dataset for different clades demonstrate the usefulness of fossil carbonate for reconstructing the Ca-isotope ratio of ancient seawater. The composition of the modern Ca-isotope budget provides a basis

  17. Mg/Ca and isotopic high resolution record of deep-sea hydrothermal barnacles

    Science.gov (United States)

    Bojar, A.-V.; Bojar, H.-P.; Tufar, W.

    2012-04-01

    Barnacles are crustaceans adapted to a sessile existence and cemented to a substrate by a protein complex. Most of the known species inhabit shallow marine environment, less than 2% of the species are found at depths between 100 and 2500 m. The shell of barnacles has a great adaptive significance, the shell of some barnacle species have been already investigated for microstructure. In this study we investigated the shell microstructure as well as the Mg/Ca and stable isotope distribution of barnacles found at a depth of around 2500m at a black smoker from the Manus Spreading centre, north-east of Papua New Guinea. The shell consists of three substructures: an outer layer with pores and aragonite crystals, a massive interior mass and an inner layer with pores. The shell shows grown lines and the outer layer exhibits longitudinal striation from base to apex. The pores have a medium size of 0.8 microns. The size of the calcitic microcrystals are in the range of 0.2 to 0.5 microns, beside, larger aragonite crystals, with size of c. 10 microns are present. The massive interior mass has a compact structure, no pores or channels could be observed. Oxygen stable isotope data of barnacle shell were performed from the centre to the border of the calcitic shells, along profiles. Within one shell, the isotope values show variations of max. 0.6 ‰. The calculated temperatures from the stable isotope data consistently indicate that the barnacles populate sites with low temperature values, up to a few °C. The calculated temperatures from the isotope data are also in agreement with the reported habitat from the North Fiji and Lau Basins, where temperatures of max. 6°C were measured at sites populated by barnacles. Both calculated and measured temperatures of a few degrees indicate that at the sites where barnacles live, hydrothermal fluid input is present, as ambient temperature is around 1.5°C. Electron-microbeam analyses were done along the interior layer of the shell. The

  18. Cenozoic Seawater Sr/Ca ratios: Implications for coral reef development through ocean de-acidification

    Science.gov (United States)

    Sosdian, S. M.; Grossman, E. L.; Lear, C. H.; Tao, K.; Rosenthal, Y.

    2010-12-01

    Records of seawater chemistry help constrain the temporal variation in geochemical processes that impact the global carbon cycle and global climate across Earth’s history. To date, various attempts to reconstruct Cenozoic seawater Sr/Ca ratios have produced markedly different results, with estimated Paleogene seawater Sr/Ca ranging from ~50% higher than today to 70% lower. We reconstruct seawater Sr/Ca using Eocene to Pliocene fossil mollusks collected from US Gulf Coast (Mississippi, Alabama, and Florida). We use Conus spp. and Turritella, taxa for which the Sr/Ca distribution coefficients have been determined as a function of temperature in modern specimens [1, 2]. Specimens were serially sampled perpendicular to growth to produce seasonal records of Sr/Ca. Fossil Conus shells show pronounced seasonal Sr/Ca cycles with a strong inverse correlation between Sr/Ca and δ18O, similar to those observed in modern specimens [1]. The fossil Turritella also show similar Sr/Ca cyclicity as modern specimens [2]. We calculate seawater Sr/Ca ratios using our Sr/Ca record, modern Sr/Ca-temperature calibrations for Conus and Turritella [1, 2], and a paleotemperature record based on oxygen isotopes from the same samples [3]. Seawater Sr/Ca increased from ~11.5 to 13.9 mmol/mol between the mid-Eocene (42 Ma) and early Oligocene (33 Ma) and decreased substantially from the mid-Miocene (11 mmol/mol) to the Pliocene (9 mmol/mol) and modern (8.5 mmol/mol). A mass balance model of variations in seawater Sr concentrations suggests a long-term decrease through the Neogene, which we attribute to a significant increase in the proportion of aragonite versus calcite deposition in shallow waters. The largest change is coincident with the proliferation of coral reefs, which occurred after the calcite-aragonite sea transition, and was likely ultimately driven by ocean de-acidification. [1] Sosdian et al. (2006) Geochemistry, Geophysics, Geosystems (G3) 7, Q11023, doi:10.1029/2005GC001233; [2

  19. Seasonality and long term trends in dissolved carbon export from large rivers to the Arctic Ocean, and potential effects on coastal ocean acidification (Invited)

    Science.gov (United States)

    Tank, S. E.; Kokelj, S. V.; Raymond, P. A.; Striegl, R. G.; McClelland, J. W.; Holmes, R. M.; Spencer, R. G.

    2013-12-01

    Large Arctic rivers show marked seasonality in constituent flux as a result of variations in flowpath throughout the yearly cycle. Here, we use measurements collected from the mouths of the six largest rivers draining to the Arctic Ocean to explore seasonal variation in dissolved inorganic and dissolved organic carbon (DIC, DOC) flux, and the effect of this flux on nearshore ocean processes. This work uses data from the Yukon and Mackenzie Rivers in North America, and the Kolyma, Lena, Yenisey, and Ob' in Siberia. Mean monthly concentrations of riverine DIC vary synchronously across all rivers, peaking under ice and reaching a low point immediately after the spring freshet. Monthly climatologies for DIC, in addition to similarly constructed climatologies for Ca2+, show that the input of riverwater universally causes aragonite to be undersaturated in riverine-influenced nearshore regions, with an effect that is greater for the Siberian coast than for western North America, and greater in the spring-winter than in the late summer and fall. Because seasonal trends and geographic variation in DOC concentration are opposite to that for DIC in these large rivers, degradation of DOC to CO2 in the nearshore Arctic should accentuate seasonal and spatial patterns in aragonite undersaturation in Arctic coastal regions. Datasets that extend DIC and DOC concentration measurements back to the early 1970's (DIC) and early 1980's (DOC) near the mouth of the Mackenzie River in the western Canadian Arctic indicate that the summertime concentration and flux of these constituents has been increasing over time in this region. While evidence from other regions of the pan-Arctic, and data gathered from smaller sub-catchment studies indicate that this trend is not universal for DOC, there is growing evidence for a consistent increase in summertime DIC flux across both time and gradients of decreasing permafrost extent. These changes, in turn, could have broad implications for both

  20. Current Travertines Precipitation from CO2-rich Groundwaters as an alert of CO2 Leakages from a Natural CO2 Storage at Ganuelas-Mazarron Tertiary Basin (Murcia, Spain)

    International Nuclear Information System (INIS)

    Carbon capture and storage technologies represent the most suitable solutions related to the high anthropogenic CO2 emissions to the atmosphere. As a consequence, monitoring of the possible CO2 leakages from an artificial deep geological CO2 storage is indispensable to guarantee its safety. Fast surficial travertine precipitation related to these CO2 leakages can be used as an alert for these escapes. Since few studies exist focusing on the long-term behaviour of an artificial CO2 DGS, natural CO2 storage affected by natural or artificial escapes must be studied as natural analogues for predicting the long-term behaviour of an artificial CO2 storage. In this context, a natural CO2 reservoir affected by artificial CO2 escapes has been studied in this work. This study has mainly focused on the current travertines precipitation associated with the upwelling CO2-rich waters from several hydrogeological wells drilled in the Ganuelas-Mazarron Tertiary basin (SE Spain), and consists of a comprehensive characterisation of parent-waters and their associated carbonates, including elemental and isotopic geochemistry, mineralogy and petrography. Geochemical characterisation of groundwaters has led to recognise 4 hydrofacies from 3 different aquifers. These groundwaters have very high salinity and electrical conductivity; are slightly acid; present high dissolved inorganic carbon (DIC) and free CO2; are oversaturated in both aragonite and calcite; and dissolve, mobilize and transport low quantities of heavy and/or toxic elements. Isotopic values indicate that: i) the origin of parent-waters is related to rainfalls from clouds originated in the Mediterranean Sea or continental areas; ii) the origin of C is mainly inorganic; and iii) sulphate anions come mainly from the dissolution of the Messinian gypsum from the Tertiary Basin sediments. Current travertines precipitation seems to be controlled by a combination of several factors, such as: i) a fast decrease of the hydrostatic

  1. Coral reefs on the edge? Carbon chemistry on inshore reefs of the great barrier reef.

    Science.gov (United States)

    Uthicke, Sven; Furnas, Miles; Lønborg, Christian

    2014-01-01

    While increasing atmospheric carbon dioxide (CO2) concentration alters global water chemistry (Ocean Acidification; OA), the degree of changes vary on local and regional spatial scales. Inshore fringing coral reefs of the Great Barrier Reef (GBR) are subjected to a variety of local pressures, and some sites may already be marginal habitats for corals. The spatial and temporal variation in directly measured parameters: Total Alkalinity (TA) and dissolved inorganic carbon (DIC) concentration, and derived parameters: partial pressure of CO2 (pCO2); pH and aragonite saturation state (Ωar) were measured at 14 inshore reefs over a two year period in the GBR region. Total Alkalinity varied between 2069 and 2364 µmol kg-1 and DIC concentrations ranged from 1846 to 2099 µmol kg-1. This resulted in pCO2 concentrations from 340 to 554 µatm, with higher values during the wet seasons and pCO2 on inshore reefs distinctly above atmospheric values. However, due to temperature effects, Ωar was not further reduced in the wet season. Aragonite saturation on inshore reefs was consistently lower and pCO2 higher than on GBR reefs further offshore. Thermodynamic effects contribute to this, and anthropogenic runoff may also contribute by altering productivity (P), respiration (R) and P/R ratios. Compared to surveys 18 and 30 years ago, pCO2 on GBR mid- and outer-shelf reefs has risen at the same rate as atmospheric values (∼1.7 µatm yr-1) over 30 years. By contrast, values on inshore reefs have increased at 2.5 to 3 times higher rates. Thus, pCO2 levels on inshore reefs have disproportionately increased compared to atmospheric levels. Our study suggests that inshore GBR reefs are more vulnerable to OA and have less buffering capacity compared to offshore reefs. This may be caused by anthropogenically induced trophic changes in the water column and benthos of inshore reefs subjected to land runoff.

  2. Skeletal mineralogy of bryozoans: Taxonomic and temporal patterns

    Science.gov (United States)

    Smith, Abigail M.; Key, Marcus M., Jr.; Gordon, Dennis P.

    2006-10-01

    Skeletal carbonate mineralogy of 1183 specimens of marine bryozoans from the literature was examined for phylogenetic patterns in order to elucidate the effects of bryozoan mineralogy on geochemical and paleoenvironmental analysis. Colonies are composed of calcite (66% of specimens), aragonite (17% of specimens) or various mixtures of the two (17% specimens) (phylum mean = 72.9 wt.% calcite, n = 1051). When calcite is present, it ranges from 0.0 to 13.7 wt.% MgCO 3 (mean = 5.0 wt.% MgCO 3, n = 873). Most (61%) calcitic specimens are formed of intermediate-Mg calcite (4 to 8 wt.% MgCO 3), others (28%) of low-Mg calcite (0 to 4 wt.% MgCO 3), and few of high-Mg calcite (> 8 wt.% MgCO 3). The phylum occupies at least 63% of the theoretical mineralogical "space" available to biomineralisation. Most of this variation occurs in the class Gymnolaemata, order Cheilostomata, suborder Neocheilostomata. Fossil and Recent stenolaemate taxa are generally low- to intermediate-Mg calcite (mean = 99.7 wt.% calcite, 2.6 wt.% MgCO 3, 17% of available biomineral space). Variability among families is related in a general way to first appearance datum: families younger than 100 Ma display greater mineralogical complexity than older ones. The cheilostome infraorder Flustrina includes unusual free-living aragonitic families, dual-calcite skeletons (mainly low-Mg calcite, but with secondary high-Mg calcite), and some genera with considerable mineralogical variability. Families (e.g., Membraniporidae and Phidoloporidae) and species (e.g., Schizoporella unicornis) with the highest degree of variability have potential for environmental correlations with mineralogy, paleoenvironmental interpretation, and possibly molecular investigation for potential cryptic species. Stenolaemate families, genera and species with low variability, on the other hand, are well-suited for geochemical work such as stable isotope analysis. Variability in the skeletal mineralogy of bryozoans suggests that they may be

  3. Trace Elements in Calcifying Marine Invertebrates Indicate Diverse Sensitivities to the Seawater Carbonate System

    Science.gov (United States)

    Doss, W. C.

    2015-12-01

    Surface ocean absorption of anthropogenic CO2 emissions resulting in ocean acidification may interfere with the ability of calcifying marine organisms to biomineralize, since the drop in pH is accompanied by reductions in CaCO3 saturation state. However, recent experiments show that net calcification rates of cultured benthic invertebrate taxa exhibit diverse responses to pCO2-induced changes in saturation state (Ries et al., 2009). Advancement of geochemical tools as biomineralization indicators will enable us to better understand these results and therefore help predict the impacts of ongoing and future decrease in seawater pH on marine organisms. Here we build upon previous work on these specimens by measuring the elemental composition of biogenic calcite and aragonite precipitated in four pCO2 treatments (400; 600; 900; and 2850 ppm). Element ratios (including Sr/Ca, Mg/Ca, Li/Ca, B/Ca, U/Ca, Ba/Ca, Cd/Ca, and Zn/Ca) were analyzed in 18 macro-invertebrate species representing seven phyla (crustacea, cnidaria, echinoidea, rhodophyta, chlorophyta, gastropoda, bivalvia, annelida), then compared to growth rate data and experimental seawater carbonate system parameters: [CO32-], [HCO3-], pH, saturation state, and DIC. Correlations between calcite or aragonite composition and seawater carbonate chemistry are highly taxa-specific, but do not resemble trends observed in growth rate for all species. Apparent carbonate system sensitivities vary widely by element, ranging from strongly correlated to no significant response. Interpretation of these results is guided by mounting evidence for the capacity of individual species to modulate pH and/or saturation state at the site of calcification in response to ambient seawater chemistry. Such biomineralization pathways and strategies in turn likely influence elemental fractionation during CaCO3 precipitation. Ries, J.B., A.L. Cohen, A.L., and D.C. McCorkle (2009), Marine calcifiers exhibit mixed responses to CO2-induced ocean

  4. Permeability Reduction in Passively Degassing Seawater-dominated Volcanic-hydrothermal systems: Processes and Perils on Raoul Island, Kermadecs (NZ)

    Science.gov (United States)

    Christenson, B. W.; Reyes, A. G.

    2014-12-01

    The 2006 eruption from Raoul Island occurred apparently in response to local tectonic swarm activity, but without any precursory indication of volcanic unrest within the hydrothermal system on the island. The eruption released some 200 T of SO2, implicating the involvement of a deep magmatic vapor input into the system during/prior to the event. In the absence of any recognized juvenile material in the eruption products, previous explanations for this eruptive event focused on this vapor being a driving force for the eruption. In 2004, at least 80 T/d of CO2 was escaping from the hydrothermal system, but mainly through areas that did not correspond to the 2006 eruption vents. The lack of a pre-eruptive hydrothermal system response related to the seismic event in 2006 can be explained by the presence of a hydrothermal mineralogic seal in the vent area of the volcano. Evidence for the existence of such a seal was found in eruption deposits in the form of massive fracture fillings of aragonite, calcite and anhydrite. Fluid inclusion homogenization temperatures in these phases range from ca. 140 °C to 220 °C which, for pure water indicate boiling point depths of between 40 and 230 m assuming a cold hydrostatic pressure constraint. Elevated pressures behind this seal are consistent with the occurrence of CO2 clathrates in some inclusion fluids, indicating CO2 concentrations approaching 1 molal in the parent fluids. Reactive transport modeling of magmatic volatile inputs into what is effectively a seawater-dominated hydrothermal system provide valuable insights into seal formation. Carbonate mineral phases ultimately come to saturation along this flow path, but we suggest that focused deposition of the observed massive carbonate seal is facilitated by near-surface boiling of these CO2-enriched altered seawaters, leading to large degrees of supersaturation which are required for the formation of aragonite. As the seal grew and permeability declined, pore pressures

  5. Late Quaternary changes in surface productivity and oxygen minimum zone (OMZ) in the northwestern Arabian Sea: Micropaleontologic and sedimentary record at ODP site 728A

    Indian Academy of Sciences (India)

    Ajai K Rai; S S Das

    2011-02-01

    Changes in the abundance of selected planktic foraminiferal species and some sedimentological parameters at ODP site 728A were examined to understand the fluctuations in the surface productivity and deep sea oxygenation in the NW Arabian Sea during last ∼540 kyr. The increased relative abundances of high fertility taxa, i.e., Globigerinita glutinata and Globigerina bulloides mainly during interglacial intervals indicate intense upwelling. Strong SW summer monsoon probably increased the upwelling in the western Arabian Sea during interglacial intervals and caused high surface productivities due to the lateral transport of eutrophic waters. Most of the glacial periods (i.e., MIS 2, 4, 6, 8 and 12) are characterized by higher relative abundances of Neogloboquadrina pachyderma and Neogloboquadrina dutertrei associated with Globigerinoides ruber. The more stratified condition and deep mixed layer due to increased NE winter monsoon are mainly responsible for the higher relative abundances of N. pachyderma during glacial periods. Some of the glacial intervals (i.e., MIS 6 and 8) are also characterized by pteropod spikes reflecting deepening of aragonite compensation depth (ACD) and relatively less intense oxygen minimum zone (OMZ) in this region due to deep sea mixing and thermocline ventilation, and relatively less intense surface productivity during winter monsoon. The interglacial periods are largely devoid of pteropod shells indicating more aragonite dissolution due to increased intensity of OMZ in the northwestern Arabian Sea. In general, the interglacial periods are characterized by low sediment accumulation rates than the glacial intervals. On an average, the total biogenic carbonate percentages were higher during interglacial and during periods of higher surface productivity. Most terrigenous material was trapped on shelf during intervals of high sea level stands of interglacial, whereas more erosion of shelf increased the sedimentation rates during glacial

  6. Polygenetic Karsted Hardground Omission Surfaces in Lower Silurian Neritic Limestones: a Signature of Early Paleozoic Calcite Seas

    Science.gov (United States)

    James, Noel P.; Desrochers, André; Kyser, Kurt T.

    2015-04-01

    Exquisitely preserved and well-exposed rocky paleoshoreline omission surfaces in Lower Silurian Chicotte Formation limestones on Anticosti Island, Quebec, are interpreted to be the product of combined marine and meteoric diagenesis. The different omission features include; 1) planar erosional bedding tops, 2) scalloped erosional surfaces, 3) knobs, ridges, and swales at bedding contacts, and 4) paleoscarps. An interpretation is proposed that relates specific omission surface styles to different diagenetic-depositional processes that took place in separate terrestrial-peritidal-shallow neritic zones. Such processes were linked to fluctuations in relative sea level with specific zones of diagenesis such as; 1) karst corrosion, 2) peritidal erosion, 3) subtidal seawater flushing and cementation, and 4) shallow subtidal deposition. Most surfaces are interpreted to have been the result of initial extensive shallow-water synsedimentary lithification that were, as sea level fell, altered by exposure and subaerial corrosion, only to be buried by sediments as sea level rose again. This succession was repeated several times resulting in a suite of recurring polyphase omission surfaces through many meters of stratigraphic section. Synsedimentary cloudy marine cements are well preserved and are thus interpreted to have been calcitic originally. Aragonite components are rare and thought to have to have been dissolved just below the Silurian seafloor. Large molluscs that survived such seafloor removal were nonetheless leached and the resultant megamoulds were filled with synsedimentary calcite cement. These Silurian inner neritic-strandline omission surfaces are temporally unique. They are part of a suite of marine omission surfaces that are mostly found in early Paleozoic neritic carbonate sedimentary rocks. These karsted hardgrounds formed during a calcite-sea time of elevated marine carbonate saturation and extensive marine cement precipitation. The contemporaneous greenhouse

  7. Strontium/lithium ratios in shells of Cerastoderma edule - A potential temperature proxy for brackish environments

    Science.gov (United States)

    Füllenbach, Christoph S.; Schöne, Bernd R.; Mertz-Kraus, Regina

    2015-04-01

    Bivalve shells provide high-resolution records of climate variability. However, the number of suitable proxies to quantify environmental variables is still limited. The most frequently used and well-accepted tool for environmental reconstructions from shell carbonate, δ18Oshell, is a dual proxy that simultaneously informs about water temperature and the oxygen isotope signature of the water. Reconstruction of water temperature requires knowledge of δ18Owater and reconstruction of the latter requires knowledge of salinity. Element-to-calcium ratios that are frequently used in other biological carbonates as tools for temperature reconstructions such as Sr/Cashell or Mg/Cashell are strongly biologically controlled in bivalves and show only a weak correlation to temperature. Here, we present Sr/Lishell ratios as a new temperature proxy that can complement δ18Oshell-based environmental reconstructions. In seawater, strontium and lithium have long residence times of 1.5Ma and 2Ma, respectively. Furthermore, salinity changes do not appear to affect the incorporation of Sr2+ and Li+ into the shells. Sr and Li concentrations were determined via LA-ICP-MS (line-scan method) in aragonitic shells of four Cerastoderma edule specimens collected alive from the intertidal zone of the North Sea. Geochemical data from the ontogenetic year three (growing season: April - September) were placed in precise temporal context by using tidal growth patterns and then compared to instrumental water temperature and water chemistry data. Sr/Lishell values (15 to 287 mmol/mmol) are significantly above Sr/Liwater (1.9 to 3.3 mmol/mmol) suggesting the presence of vital effects. However, all shells revealed similar Sr/Lishell patterns that are strongly negatively correlated to water temperature (r2 = 0.65 to 0.74; p perfectly resembled with an average absolute difference of 1.9°C. Considering that Sr2+ and Li+ can substitute Ca2+ in the crystal lattice of aragonite, the Sr/Lishell ratio is a

  8. Authigenic carbonate crusts and chimneys along the North Anatolian Fault in the Sea of Marmara, Turkey

    Science.gov (United States)

    Yıldız, Güliz; Namık Çaǧatay, M.

    2016-04-01

    The Sea of Marmara is located on the North Anatolian Fault (NAF) fault zone that is a major continental transform plate boundary. It has ca. 1250 m-deep Tekirdag, Central and Cinarcik basins that are separated by two NE-SW trending Central and Western Highs. Extensive cold seeps occur along the active fault segments of the NAF in the deep basins and highs, which are associated with authigenic carbonate crusts, carbonate chimneys and mounds, black sulphidic sediments, and local gas hydrates and oil seepage. The cold seep sites were observed and sampled during the Nautile submersible and Victor 6000 Remotely Operated Vehicle (ROV) dives carried out during MARNAUT and MARSITE cruises in 2007 and 2014, respectively. Here, we report the mineralogical and stable isotopic composition of the authigenic carbonates and discuss their environmental conditions and mechanisms of formation. The carbonate crusts range up to 5 cm in thickness and the chimneys and mounds are up to 2 m high. Some chimneys are active emitting fresh to brackish water at ambient bottom water temperatures (˜ 14° C). The carbonate crusts occur as a pavements, and are commonly covered with black sulphidic sediments and bacterial mats that accommodate a rich chemosynthetic community of bivalves, sea urchins and marine annelid worms (Polychaeta). The authigenic carbonates commonly consist mainly of aragonite, but in a few instances contain subequal amounts of aragonite and calcite. High Mg-calcite is usually a minor to trace component, except in one sample in which it is present as a cement of mudstone. In the active methane emission zones, the sulphate/methane boundary occurs at or close to the seafloor, whereas elsewhere in the Sea of Marmara, the same boundary is located at 2-5 m below the seafloor. This, together with very light stable carbon isotope values (δ13C=-29.8 to - 46.3 ‰ V-PDB), indicates that the anaerobic oxidation of high methane flux emitted from the active faults is the major process

  9. Deciphering the Chemical and Physical Basis for the CaCO3 Polymorphs that Form by an Amorphous Pathway

    Science.gov (United States)

    Dove, P. M.; Blue, C.; Mergelsberg, S. T.; De Yoreo, J. J.; Han, N.

    2015-12-01

    The formation of calcite and aragonite biominerals by pathways involving metastable intermediates is increasingly recognized. Initial precipitates evolve along a multistep pathway that is not well understood. Previous studies of amorphous calcium carbonate (ACC) provide important insights, but relationships between ACC composition and the subsequent crystalline polymorphs are not yet established. This experimental study quantified control of initial solution composition on the polymorphs that transform from ACC. Using a flow-through reactor to regulate solution chemistry without organic additives, ACC was synthesized with variable Mg contents by tuning input solution Mg/Ca ratio, total carbonate concentration, and pH (Blue and Dove, 2015, GCA). This ACC was transformed to crystalline products under stirred or quiescent conditions while monitoring solution and solid compositions. By quantifying solution chemistry throughout the transformation, we find pH and Mg/Ca evolve along polymorph-specific trajectories. The relations predict the initial crystalline phase to form and suggest incipient differences in the initial ACC. The first crystalline polymorph appears controlled by fast kinetics and determined by a systematic relationship to solution Mg2+/Ca2+ and CO3=/Ca2+ ratios. Stirring versus quiescent conditions further direct the initial crystalline polymorph to form. Over longer time periods, thermodynamic factors can drive the initial phase to transform again. The results suggest a quantitative framework for predicting the products to transform from ACC that is based on the interplay of chemistry and physical conditions. Organic additives and extreme pH are not required. The findings reconcile apparent discrepancies between previous studies of ACC and suggest monohydrocalcite may be an overlooked transient phase in forming some deposits of aragonite and calcite. They also 1) support the idea that calcite composition is determined by local Mg2+/Ca2+ and isotope

  10. Pseudomorphs of Neotethyan Evaporites in Anatolia's HP/LT belts - Aptian basin-wide pelagic gypsum deposits

    Science.gov (United States)

    Scheffler, Franziska; Oberhänsli, Roland; Pourteau, Amaury; Immenhauser, Adrian; Candan, Osman

    2015-04-01

    Rosetta Marble was defined in SW Anatolia as 3D-radiating textures of dm-to-m-long calcite rods in the HP/LT metamorphosed Mid-Cretaceous pelagic carbonate sequence of the Ören Unit. Rosetta Marble in the type locality are interbedded with meta-chert beds, and may constitute entire carbonate beds. Rare aragonite relicts and Sr-rich, fibrous calcite pseudomorphs after aragonite witness the HP metamorphic imprint of this sequence during the closure of a Neotethyan oceanic domain during latest Cretaceous-Palaeocene times. We investigated the Rosetta Marble of the Ören Unit, as well as other known and newly found localities in the Tavşanlı and Afyon zones, and the Alanya Massif and Malatya area, to decipher the metamorphic, diagenetic and sedimentologic significance of these uncommon textures. Based on field, petrographic and geochemical investigations, we document a wide variety of Rosetta-type textures. A striking resemblance with well-known gypsum morphologies (e.g. shallow-tail, palm-tree textures) leads us to argue that Rosetta Marble was initially composed of giant gypsum crystals (selenite). The absence of anhydrite relicts of pseudomorphs indicate that gypsum transformed into calcite soon after the deposition by the mean of a sulphate reduction reaction. The gypsum-to-calcite transformation requires that organic matter intervened as a reactant phase. Mid Cretaceous oceanic domains in the Tethyan realm are characterised by overall anoxic conditions that allowed the preservation of organic material. Rosetta Marble exposures are widely distributed over 600 km along the Neotethyan suture zone. During deepening of the Neotethyan ocean in Mid Cretaceous times, basin-wide and cyclic sedimentation of gypsum and radiolarite occurred. The origin of high-salinity waters needed for gypsum precipitation was located at shelf levels. Density and gravity effects forced the brines to cascade downwards into the deep ocean. Favorable climatic conditions trigger the formation

  11. Coral reefs on the edge? Carbon chemistry on inshore reefs of the great barrier reef.

    Directory of Open Access Journals (Sweden)

    Sven Uthicke

    Full Text Available While increasing atmospheric carbon dioxide (CO2 concentration alters global water chemistry (Ocean Acidification; OA, the degree of changes vary on local and regional spatial scales. Inshore fringing coral reefs of the Great Barrier Reef (GBR are subjected to a variety of local pressures, and some sites may already be marginal habitats for corals. The spatial and temporal variation in directly measured parameters: Total Alkalinity (TA and dissolved inorganic carbon (DIC concentration, and derived parameters: partial pressure of CO2 (pCO2; pH and aragonite saturation state (Ωar were measured at 14 inshore reefs over a two year period in the GBR region. Total Alkalinity varied between 2069 and 2364 µmol kg-1 and DIC concentrations ranged from 1846 to 2099 µmol kg-1. This resulted in pCO2 concentrations from 340 to 554 µatm, with higher values during the wet seasons and pCO2 on inshore reefs distinctly above atmospheric values. However, due to temperature effects, Ωar was not further reduced in the wet season. Aragonite saturation on inshore reefs was consistently lower and pCO2 higher than on GBR reefs further offshore. Thermodynamic effects contribute to this, and anthropogenic runoff may also contribute by altering productivity (P, respiration (R and P/R ratios. Compared to surveys 18 and 30 years ago, pCO2 on GBR mid- and outer-shelf reefs has risen at the same rate as atmospheric values (∼1.7 µatm yr-1 over 30 years. By contrast, values on inshore reefs have increased at 2.5 to 3 times higher rates. Thus, pCO2 levels on inshore reefs have disproportionately increased compared to atmospheric levels. Our study suggests that inshore GBR reefs are more vulnerable to OA and have less buffering capacity compared to offshore reefs. This may be caused by anthropogenically induced trophic changes in the water column and benthos of inshore reefs subjected to land runoff.

  12. Cold-seep carbonates of the middle and lower continental slope, northern Gulf of Mexico

    Science.gov (United States)

    Roberts, Harry H.; Feng, Dong; Joye, Samantha B.

    2010-11-01

    Authigenic carbonates from cold seeps on the middle and lower continental slope of the northern Gulf of Mexico (GOM) exhibit a wide range of mineralogical and stable isotopic compositions. These carbonates consist of concretions and nodules in surface sediments, hardgrounds of crusts and isolated slabs, and mounded buildups of blocks and slabs of up to over 10 meters in relief above the surrounding seafloor. Mineralogically, the carbonates are dominated by high-Mg calcite (HMC) and aragonite. However, low levels (present in most samples. Petrographically, Mg-calcite peloidal matrix and acicular to botryoidal aragonitic void-filling cements are the most frequent associations. The carbon isotopic compositions of the carbonates range from -60.8 to 14.0‰ PDB, indicating complex carbon sources that include 13C-depleted biogenic and thermogenic methane, biodegraded crude oil, seawater CO2, and 13C-enriched residual CO2 from methanogenesis. A similarly large variability in δ18O values (2.5 to 6.7‰ PDB) demonstrates the geochemical complexity of the slope, with some samples pointing toward an 18O-enriched oxygen source that is possibly related to advection of 18O-enriched formation water and/or to the decomposition of gas hydrate. A considerable range of mineralogical and isotopic variations in cold-seep carbonate composition was noted even within individual study sites. However, common trends occur across multiple geographic areas. This situation suggests that local controls on fluid and gas flux, types of seep hydrocarbons, the presence or absence of gas hydrate in the near-surface sediment, and chemosynthetic communities, as well as the temporal evolution of the local hydrocarbon reservoir, all may play a part in determining carbonate mineralogy and isotope geochemistry. The carbon isotope data clearly indicate that between-site variation is greater than within-site variation. Seep carbonates formed on the middle and lower continental slope of the GOM do not appear

  13. Calcium carbonate saturation in the surface water of the Arctic Ocean: undersaturation in freshwater influenced shelves

    Directory of Open Access Journals (Sweden)

    M. Chierici

    2009-05-01

    Full Text Available In the summer of 2005, we sampled surface water and measured pH and total alkalinity (AT underway aboard IB Oden along the Northwest Passage from Cape Farwell (South Greenland to the Chukchi Sea. We investigated variability of carbonate system parameters, focusing particularly on carbonate concentration [CO32−] and calcium carbonate saturation states, as related to freshwater addition, biological processes and physical upwelling. Measurements on AT, pH at 15°C, salinity (S and sea surface temperature (SST, were used to calculate total dissolved inorganic carbon (DIC, [CO32−] and saturation of aragonite (ΩAr and calcite (ΩCa in the surface water. The same parameters were measured in the water column of the Bering Strait. Some surface waters in the Canadian Arctic Archipelago (CAA and on the Mackenzie shelf (MS were found to be undersaturated with respect to aragonite (ΩAr<1. In these areas, surface water was low in AT and DIC (<1500 μmol kg−1 relative to seawater and showed low [CO32−]. The low saturation states were probably due to the effect of dilution due from freshwater addition by sea ice melt (CAA and river runoff (MS. High AT and DIC and low pH, corresponded with the lowest [CO32−], ΩAr and ΩCa, observed near Cape Bathurst and along the South Chukchi Peninsula. This was linked to physical upwelling of subsurface water with elevated CO2. Highest surface ΩAr and ΩCa of 3.0 and 4.5, respectively, were found on the Chukchi Sea shelf and in the cold water north of Wrangel Island, which is heavily influenced by high CO2 drawdown and lower DIC from intense biological production. In the western Bering Strait, the cold and saline Anadyr Current carries water that is enriched in AT and DIC from enhanced organic matter remineralization, resulting in

  14. Neodymium isotopes in biogenic carbonates: reliable archives of ɛNd

    Science.gov (United States)

    Montagna, P.; Goldstein, S. L.; Taviani, M.; Frank, N.; McCulloch, M. T.

    2010-12-01

    Neodymium isotope (143Nd/144Nd) compositions from dispersed authigenic ferromanganese oxide fraction in marine sediments, ferromanganese crusts, foraminiferal shells and fossil fish teeth are employed to trace provenance and water mass mixing in the past, having the advantage of not being fractionated by biological processes in the water column. In the modern ocean the different water masses ultimately derive their ɛNd values through continental weathering, erosion and particle-seawater interactions. This geochemical tracer has been only recently applied to scleractinian deep-water coral skeletons sourced from various sites and depths in the Atlantic ocean. Aragonitic corals can be precisely dated by U-series, potentially providing century-long records of intermediate and bathyal zone variability at sub-decadal resolution. Motivated by these recent findings we have investigated the Nd isotopic compositions of living specimens of various calcifying organisms collected in two key locations of the Mediterranean Sea and in the Southern Ocean. In particular, we analyzed several specimens of the aragonitic deep-water corals Desmophyllum dianthus, Lophelia pertusa, Madrepora oculata, Flabellum impensum, the temperate coral Cladocora caespitosa, the calcitic gorgonian coral Corallium rubrum, the bivalves Glans aculeata and Karnekampia bruei and the polychate Serpula vermicularis. Most of the samples were retrieved from the Strait of Sicily and the Southern Adriatic Sea at different water depths. Ten seawater samples from three new profiles in the Mediterranean were also collected at the same locations and depths, offering a unique opportunity to compare the Nd isotopic composition of biogenic carbonates directly with the surrounding ambient seawater. The Mediterranean Sea is particularly suited for this comparison exercise since it is characterized by water masses displaying a large range of ɛNd values, from -10.5 in the Western Mediterranean to -4.8 in the Eastern

  15. Groundtruthing the Neodymium Isotope Proxy in Deep-Sea Corals

    Science.gov (United States)

    van de Flierdt, T.; Robinson, L. F.; Adkins, J. F.

    2007-12-01

    The Nd isotopic composition of marine precipitates is increasingly recognized as a powerful tool in paleoceanography. Unlike nutrient proxies such as δ13C or Cd/Ca, Nd isotopes are not thought to be altered by biological processes, and thus may serve as a quasi-conservative water mass mixing tracer. However, any archive, which is used to extract authigenic Nd isotopes, needs careful examination, to test the integrity of the inferred seawater signal. Here we present first data on cleaning experiments and modern calibration experiments on different species of deep-sea corals. Seven different coral samples ranging in age from modern to ~220ka were selected for experiments designed to remove ferromanganese crusts and / or organic residues that may contain high concentrations of Nd and Th. The aim was to determine whether the rigorous chemical procedure we use to remove Th associated with these crusts is effective at removing Nd, and whether it causes any fractionation in the Nd isotopic composition of the coral aragonite. Crusts were found to contain Th-232 concentrations of up to ~160ppm, with 232Th/230Th ratios dependent on the oceanic location of the coral. Un-cleaned corals had Th-232 concentrations of up to 8ppb and the cleaning procedure reduced these values to less than 0.2ppb in both modern and fossil specimens. Neodymium isotopic compositions reveal that for modern corals, with no visible coating, a pre-cleaning step is sufficient to yield the isotopic composition of ambient seawater. The ferromanganese coating around fossil corals however may have a very different isotopic composition than the coral aragonite since it may be a time-integrated signal biased towards modern values. This bias is observed for intermediate water depth D. dianthus corals from stage 3 in the northwest Atlantic. Modern D. dianthus skeletons from the northwest Atlantic and the Drake Passage reflect the seawater Nd isotopic composition, and we are extending this modern calibration to

  16. Nutrient and carbonate ion proxy calibrations in the deep sea coral D. dianthus (Invited)

    Science.gov (United States)

    Anagnostou, E.; Lavigne, M.; Gagnon, A. C.; Adkins, J. F.; McDonough, W. F.; Sherrell, R. M.

    2009-12-01

    Marine carbonates are among the most successful and reliable substrates for chemical paleoceanographic studies. Deep-sea corals are especially useful because they allow measurement of both 14C and U-Th dates in a single coral. Tracers, however, are needed to derive ventilation rates in the past from the mixing ratio of distinct endmember water masses. Reconstruction of nutrient abundances and carbonate ion distributions, even in regions where deep mixing is sluggish and regeneration is significant, could provide clues about basin-scale variations in export production, changes in whole-ocean nutrient inventory, and carbonate system equilibria on geological timescales. To fill this gap, we present modern calibrations of two paleo-nutrient proxies and a carbonate ion proxy in the deep sea coral D. dianthus. We demonstrate that P/Ca, Ba/Ca and U/Ca are direct proxies for phosphate (remineralized at shallow depths), dissolved barium (a deep-remineralized element with silicate-type distribution) and seawater carbonate ion, respectively. We analyzed 20, globally distributed, D. dianthus specimens using a 193nm excimer laser ablation HR-ICP-MS, along growth axis-oriented septal thick sections, which reveals the internal structure. Using an 80-100 μm spot size, data are collected from within the fibrous aragonite avoiding central band material as well as contamination and altered aragonite on the exterior of the septa. All seawater data used are derived from nearby WOCE/GEOSECS/CLIVAR stations. Plotting the coralline P/Ca against ambient seawater phosphate resulted in a calibration with an apparent partition coefficient (D= Element/Cacoral / Element/Caseawater) of 0.5 ± 0.1 (r=0.8, P<0.05, n=17). Similarly, the Ba/Ca in the coral versus dissolved seawater barium gave a DBa= 1.3 ± 0.3 (r= 0.8, P<0.05, n=15), and coralline U/Ca (µmol/mol) versus seawater carbonate ion (µmol/kg) gave a regression slope of -0.098 ± 0.002 (r=0.8, P<0.05, n=13). We tested potential

  17. Evaluation of boron isotope ratio as a pH proxy in the deep sea coral Desmophyllum dianthus: Evidence of physiological pH adjustment

    Science.gov (United States)

    Anagnostou, E.; Huang, K.-F.; You, C.-F.; Sikes, E. L.; Sherrell, R. M.

    2012-10-01

    The boron isotope ratio (δ11B) of foraminifers and tropical corals has been proposed to record seawater pH. To test the veracity and practicality of this potential paleo-pH proxy in deep sea corals, samples of skeletal material from twelve archived modern Desmophyllum dianthus (D. dianthus) corals from a depth range of 274-1470 m in the Atlantic, Pacific, and Southern Oceans, ambient pH range 7.57-8.05, were analyzed for δ11B. The δ11B values for these corals, spanning a range from 23.56 to 27.88, are found to be related to seawater borate δ11B by the linear regression: δ11Bcoral=(0.76±0.28) δ11Bborate+(14.67±4.19) (1 standard error (SE)). The D. dianthus δ11B values are greater than those measured in tropical corals, and suggest substantial physiological modification of pH in the calcifying space by a value that is an inverse function of seawater pH. This mechanism partially compensates for the range of ocean pH and aragonite saturation at which this species grows, enhancing aragonite precipitation and suggesting an adaptation mechanism to low pH environments in intermediate and deep waters. Consistent with the findings of Trotter et al. (2011) for tropical surface corals, the data suggest an inverse correlation between the magnitude of a biologically driven pH offset recorded in the coral skeleton, and the seawater pH, described by the equation: ΔpH=pH recorded by coral-seawater pH=-(0.75±0.12) pHw+(6.88±0.93) (1 SE). Error analysis based on 95% confidence interval(CI) and the standard deviation of the regression residuals suggests that the uncertainty of seawater pH reconstructed from δ11Bcoral is ±0.07 to 0.12 pH units. This study demonstrates the applicability of δ11B in D. dianthus to record ambient seawater pH and holds promise for reconstructing oceanic pH distribution and history using fossil corals.

  18. The calibration of clumped-isotope thermometry on modern marine mollusk

    Science.gov (United States)

    Canavan, R. R.; Affek, H. P.; Zaarur, S.; Douglas, P. M.; Wang, Z.

    2013-12-01

    Clumped-isotope (Δ47) thermometry is a novel method to reconstruct paleotemperatures that can be applied to studying past coastal and marine environments using marine mollusk shells. Macrofossil mollusk shells are common in the fossil record and provide enough material to satisfy the relatively large-sample requirement for Δ47 analysis, making them ideal for clumped-isotope paleothermometry. If consistent with the clumped isotope thermometer, mollusk Δ47 derived temperatures should record local water temperatures during shell growth season. Recent studies, however, show strong deviations from the empirical Δ47-T calibration derived from synthetic calcite in some modern mollusk shells (cephalopods, gastropods and bivalves; Dennis et al., 2013; Henkes et al., 2013; Eagle et al., 2013) but not in others (bivalves; Douglas et al., submitted; Came et al., 2007). The source of these discrepancies has been hypothesized to be related to 1) different laboratory techniques (including sample preparation and instrument standardization), 2) growth of CaCO3 polymorphs (calcite, aragonite or vaterite) in shells, and 3) variable environmental growth conditions such as salinity and pH. We test the effect of CaCO3 polymorph, taxonomy, and mollusk growth conditions by comparing among Δ47 values of calcitic shells from eastern oysters (Crassostrea virginica), those of clam shells that are mostly aragonitic (collected along the United States' Atlantic coast), and published calibrations of the clumped isotope thermometer. Atlantic oysters were collected from 37°N to 43°N latitude, with temperatures ranging between ~ 10-25°C, and brackish to marine salinities ranging from 14.5 - 34 PSU. Clam genera were similarly collected along the coast between Florida up north to Maine with growth temperatures ranging from ~ 10-22 °C. We further examine whether the deviation from the calibration is related to the relatively low reproducibility observed in modern mollusk Δ47 measurements, and

  19. Ca and Mg isotope constraints on the origin of Earth's deepest δ13 C excursion

    Science.gov (United States)

    Husson, Jon M.; Higgins, John A.; Maloof, Adam C.; Schoene, Blair

    2015-07-01

    Understanding the extreme carbon isotope excursions found in carbonate rocks of the Ediacaran Period (635-541 Ma), where δ13 C of marine carbonates (δ13 Ccarb) reach their minimum (- 12 ‰) for Earth history, is one of the most vexing problems in Precambrian geology. Known colloquially as the 'Shuram' excursion, the event has been interpreted by many as a product of a profoundly different Ediacaran carbon cycle. More recently, diagenetic processes have been invoked, with the very negative δ13 C values of Ediacaran carbonates explained via meteoric alteration, late-stage burial diagenesis or growth of authigenic carbonates in the sediment column, thus challenging models which rely upon a dramatically changing redox state of the Ediacaran oceans. Here we present 257 δ 44 / 40 Ca and 131 δ26 Mg measurements, along with [Mg], [Mn] and [Sr] data, from carbonates of the Ediacaran-aged Wonoka Formation (Fm.) of South Australia to bring new isotope systems to bear on understanding the 'Shuram' excursion. Data from four measured sections spanning the basin reveal stratigraphically coherent trends, with variability of ∼1.5‰ in δ26 Mg and ∼1.2‰ in δ 44 / 40 Ca. This Ca isotope variability dwarfs the 0.2-0.3 ‰ change seen coeval with the Permian-Triassic mass extinction, the largest recorded in the rock record, and is on par with putative changes in the δ 44 / 40 Ca value of seawater seen over the Phanerozoic Eon. Changes in both isotopic systems are too large to explain with changes in the isotopic composition of Ca and Mg in global seawater given modern budgets and residence times, and thus must be products of alternative processes. Relationships between δ 44 / 40 Ca and [Sr] and δ26 Mg and [Mg] are consistent with mineralogical control (e.g., aragonite vs. calcite, limestone vs. dolostone) on calcium and magnesium isotope variability. The most pristine samples in the Wonoka dataset, preserving Sr concentrations (in the 1000s of ppm range) and δ 44 / 40

  20. Calcium carbonate saturation in the surface water of the Arctic Ocean: undersaturation in freshwater influenced shelves

    Directory of Open Access Journals (Sweden)

    A. Fransson

    2009-11-01

    Full Text Available In the summer of 2005, we sampled surface water and measured pH and total alkalinity (AT underway aboard IB Oden along the Northwest Passage from Cape Farewell (South Greenland to the Chukchi Sea. We investigated the variability of carbonate system parameters, focusing particularly on carbonate concentration [CO32−] and calcium carbonate saturation states, as related to freshwater addition, biological processes and physical upwelling. Measurements on AT, pH at 15°C, salinity (S and sea surface temperature (SST, were used to calculate total dissolved inorganic carbon (CT, [CO32−] and the saturation of aragonite (ΩAr and calcite (ΩCa in the surface water. The same parameters were measured in the water column of the Bering Strait. Some surface waters in the Canadian Arctic Archipelago (CAA and on the Mackenzie shelf (MS were found to be undersaturated with respect to aragonite (ΩAr<1. In these areas, surface water was low in AT and CT (<1500 μmol kg−1 relative to seawater and showed low [CO32−]. The low saturation states were probably due to the likely the effect of dilution due to freshwater addition by sea ice melt (CAA and river runoff (MS. High AT and CT and low pH, corresponded with the lowest [CO32−], ΩAr and ΩCa, observed near Cape Bathurst and along the South Chukchi Peninsula. This was linked to the physical upwelling of subsurface water with elevated CO2. The highest surface ΩAr and ΩCa of 3.0 and 4.5, respectively, were found on the Chukchi Sea shelf and in the cold water north of Wrangel Island, which is heavily influenced by high CO2 drawdown and lower CT from intense biological production. In the western Bering Strait, the cold and saline Anadyr Current carries water that is enriched in AT and

  1. Pteropods in Southern Ocean ecosystems

    Science.gov (United States)

    Hunt, B. P. V.; Pakhomov, E. A.; Hosie, G. W.; Siegel, V.; Ward, P.; Bernard, K.

    2008-09-01

    To date, little research has been carried out on pelagic gastropod molluscs (pteropods) in Southern Ocean ecosystems. However, recent predictions are that, due to acidification resulting from a business as usual approach to CO 2 emissions (IS92a), Southern Ocean surface waters may begin to become uninhabitable for aragonite shelled thecosome pteropods by 2050. To gain insight into the potential impact that this would have on Southern Ocean ecosystems, we have here synthesized available data on pteropod distributions and densities, assessed current knowledge of pteropod ecology, and highlighted knowledge gaps and directions for future research on this zooplankton group. Six species of pteropod are typical of the Southern Ocean south of the Sub-Tropical Convergence, including the four Thecosomes Limacina helicina antarctica, Limacina retroversa australis, Clio pyramidata, and Clio piatkowskii, and two Gymnosomes Clione limacina antarctica and Spongiobranchaea australis. Limacina retroversa australis dominated pteropod densities north of the Polar Front (PF), averaging 60 ind m -3 (max = 800 ind m -3) and 11% of total zooplankton at the Prince Edward Islands. South of the PF L. helicina antarctica predominated, averaging 165 ind m -3 (max = 2681 ind m -3) and up to >35% of total zooplankton at South Georgia, and up to 1397 ind m -3 and 63% of total zooplankton in the Ross Sea. Combined pteropods contributed 40% of community grazing impact. Further research is required to quantify diet selectivity, the effect of phytoplankton composition on growth and reproductive success, and the role of carnivory in thecosomes. Life histories are a significant knowledge gap for Southern Ocean pteropods, a single study having been completed for L. retroversa australis, making population studies a priority for this group. Pteropods appear to be important in biogeochemical cycling, thecosome shells contributing >50% to carbonate flux in the deep ocean south of the PF. Pteropods may also

  2. Regional variability of acidification in the Arctic: a sea of contrasts

    Directory of Open Access Journals (Sweden)

    E. E. Popova

    2014-01-01

    Full Text Available The Arctic Ocean is a region that is particularly vulnerable to the impact of ocean acidification driven by rising atmospheric CO2, with potentially negative consequences for calcifying organisms such as coccolithophorids and foraminiferans. In this study, we use an ocean-only general circulation model, with embedded biogeochemistry and a comprehensive description of the ocean carbon cycle, to study the response of pH and saturation states of calcite and aragonite to rising atmospheric pCO2 and changing climate in the Arctic Ocean. Particular attention is paid to the strong regional variability within the Arctic, and, for comparison, simulation results are contrasted with those for the global ocean. Simulations were run to year 2099 using the RCP8.5 (an Intergovernmental Panel on Climate Change (IPCC Fifth Assessment Report (AR5 scenario with the highest concentrations of atmospheric CO2. The separate impacts of the direct increase in atmospheric CO2 and indirect effects via impact of climate change (changing temperature, stratification, primary production and freshwater fluxes were examined by undertaking two simulations, one with the full system and the other in which atmospheric CO2 was prevented from increasing beyond its preindustrial level (year 1860. Results indicate that the impact of climate change, and spatial heterogeneity thereof, plays a strong role in the declines in pH and carbonate saturation (Ω seen in the Arctic. The central Arctic, Canadian Arctic Archipelago and Baffin Bay show greatest rates of acidification and Ω decline as a result of melting sea ice. In contrast, areas affected by Atlantic inflow including the Greenland Sea and outer shelves of the Barents, Kara and Laptev seas, had minimal decreases in pH and Ω because diminishing ice cover led to greater vertical mixing and primary production. As a consequence, the projected onset of undersaturation in respect to aragonite is highly variable regionally within the

  3. Deep-seated gravitational slope deformations in the Vinschgau (northern Italy) and their association with springs and speleothems

    Science.gov (United States)

    Ostermann, Marc; Koltai, Gabriella; Spötl, Christoph; Cheng, Hai

    2016-04-01

    Several springs along the lower section of the south-facing slope (Sonnenberg) of the central Vinschgau (Val Venosta) are supersaturated with respect to calcite/aragonite and/or iron oxyhydroxides, and carbonate precipitation occurs locally as tufas and flowstones. These springs occur along the toe of a deep-seated gravitational slope deformation (DSGSD) showing characteristic morphological features including double-ridges, trenches and counterscarps in its upper section. The Sonnenberg DSGSD developed in a complex structural setting, involving the low-angle Schlinig normal fault. Strongly fractured orthogneisses and intercalated paragneisses constitute the host rock whose foliation dips into the slope (20-40°) and strikes NNE-SSW to E-W. Secondary carbonate deposition is strongly connected to the presence of open fractures near the toe of the slope where calcite and aragonite flowstones formed as a result of strong evaporation (Spötl et al. 2002). These waters have mean residence times up to several decades, profoundly interacted with the strongly fractured basement rocks and are part of a large groundwater flow system controlled by the DSGSD. Recharge occurs in the uppermost area of the mass movement above ˜1900 m a.s.l. and discharges near the toe of the slope and/or directly into the extensive alluvial valley fill. Recent seismic investigations show a significant displacement of the bedrock and an interdigitation with alluvial sediments up to 100 m below the surface (Maraio et al. unpublished). U-Th dating of flowstone samples was carried out to constrain the chronology of these mass movements. Flowstone deposition along the toe of the slope started during the Late Glacial period (from ca. 14.2 ka BP) and occurred continuously throughout the Holocene. Thus, gravitational displacements likely commenced soon after the deglaciation. This is consistent with observations from the nearby Mt. Watles DSGSD, where radiocarbon dates suggest a similar timing of the

  4. Comparisons of the ecology and stable isotopic compositions of living (stained) benthic foraminifera from the Sulu and South China Seas

    Science.gov (United States)

    Rathburn, A. E.; Corliss, B. H.; Tappa, K. D.; Lohmann, K. C.

    1996-10-01

    Significant differences are observed between living (Rose Bengal stained) deep-sea benthic foraminifera found in 14 box cores (510-4515 m) from the thermospheric (> 10°C) environments of the Sulu Sea and the psychrospheric ( 2‰ range and are similar to those presented by previous workers, but have no consistent relationship with microhabitat preferences. Vertical distribution patterns and carbon isotope compositions of species, however, reflect microhabitat preferences and are consistent with previous observations from other regions. Epifaunal species (0-1 cm interval) such as Cibicidoides pachyderma, Cibicidoides wuellerstorfi, Hoeglundina elegans and Anomalinoides colligera, have higher δ13C values than taxa which have the ability to live deeper within the sediments. Infaunal taxa that live in the upper 2-3 cm, including Uvigerina peregrina, Uvigerina proboscidea, and Bulimina mexicana, have lower δ13C values than epifaunal species, and the deep infaunal species, Chilostomella oolina, has the lowest δ13C. Cibicidoides bradyi and Oridorsalis umbonatus are found between 0 and ˜ 4 cm and have lower carbon isotope values (by > 1.4‰ in some cores) than epifaunal Cibicidoides species. Exceptions to this pattern include the aragonitic species, Gavelinopsis lobatulus, (0-4 cm) which produces significantly lower δ13C values than deep infaunal taxa, and the shallow infaunal species, Ceratobulimina pacifica (also aragonitic) and Bolivinopsis cubensis (deep infaunal), which yield higher carbon isotopic values than epifaunal taxa. These exceptions are found primarily in only one core, and additional samples are needed to confirm the relationship between their distribution patterns and isotopic compositions. Each of the species examined has a relatively consistent δ13C value throughout its distribution within the sediments that may result from heterogeneity of microhabitats within the intervals sampled. Intrageneric differences in δ13C of Cibicidoides, and possibly

  5. Ocean acidification state in western Antarctic surface waters: drivers and interannual variability

    Directory of Open Access Journals (Sweden)

    M. Mattsdotter Björk

    2013-05-01

    Full Text Available Each December during four years from 2006 to 2010, the surface water carbonate system was measured and investigated in the Amundsen Sea and Ross Sea, western Antarctica as part of the Oden Southern Ocean expeditions (OSO. The I/B Oden started in Punta Arenas in Chile and sailed southwest, passing through different regimes such as, the marginal/seasonal ice zone, fronts, coastal shelves, and polynyas. Discrete surface water was sampled underway for analysis of total alkalinity (AT, total dissolved inorganic carbon (CT and pH. Two of these parameters were used together with sea-surface temperature (SST, and salinity to obtain a full description of the surface water carbonate system, including pH in situ and calcium carbonate saturation state of aragonite (ΩAr and calcite (ΩCa. Multivariate analysis was used to investigate interannual variability and the major controls (sea-ice concentration, SST, salinity and chlorophyll a on the variability in the carbonate system and Ω. This analysis showed that SST and chlorophyll a were the major drivers of the Ω variability in both the Amundsen and Ross seas. In 2007, the sea-ice edge was located further south and the area of the open polynya was relatively small compared to 2010. We found the lowest pH in situ (7.932 and Ω = 1 values in the sea-ice zone and in the coastal Amundsen Sea, nearby marine out flowing glaciers. In 2010, the sea-ice coverage was the largest and the areas of the open polynyas were the largest for the whole period. This year we found the lowest salinity and AT, coinciding with highest chl a. This implies that the highest ΩAr in 2010 was likely an effect of biological CO2 drawdown, which out-competed the dilution of carbonate ion concentration due to large melt water volumes. We predict and discuss future Ω values, using our data and reported rates of oceanic uptake of anthropogenic CO2, suggesting that the Amundsen Sea will become undersaturated with regard to aragonite about

  6. Meltwater history inferred from authigenic carbonates and fine grained glaciomarine sediments from the Mendeleev Ridge in the Arctic Ocean

    Science.gov (United States)

    Nam, Seung-Il; Woo, Kyung Sik; Ji, Hyo Seon; Stein, Ruediger; Mackensen, Andreas; Matthiessen, Jens

    2015-04-01

    Authigenic carbonates and mud fractions of the glaciomarine sediments were investigated texturally and geochemically. The sediment core (PS72/410-1) was retrieved using a giant box corer from the central Mendeleev Ridge of the western Arctic Ocean (Station location= Lat. 80°30.37"N, Long. 175°44.38"W) during the Polarstern Arctic expedition (PS72) in 2008. The core is 39 cm long with age of ca. 76 ka BP and was collected from the water depth of 1,802 meters. The sediments show various colours from grey to brown as previously reported in other Arctic deep sea sediments, reflecting glacial-interglacial and/or stadial-interstadial cycles. Authigenic carbonate minerals are present through the whole sequence except for a few centimetres. These authigenic carbonates are composed of high Mg-calcite, low Mg-calcite and aragonite. Various crystal shapes of aragonite and calcite together with clear growth shapes of the crystals suggest that they are inorganic in origin. Highly enriched carbon isotope compositions (δ13C = 0 ~ +5‰ vs. PDB) strongly indicate that they formed in methanogenic zone below sediment/water interface by the reaction between anoxic pore fluids and host sediments induced by methanogenic bacteria. However, a wide range of oxygen isotope values (δ18O = -5 ~ +5‰ vs. PDB) may indicate that porewater has been changed due to reaction between residual seawater and volcanic sediments. Relatively higher contents of K, Al, Fe and Be values from muddy sediments as well as low δ18O compositions of authigenic carbonates may imply strong input of meltwater from volcanic region (Eastern Arctic region) whereas higher oxygen isotope compositions of authigenic carbonates and higher Sr and K contents of mud sediments may reflect stronger influence from carbonate-rich region (Canadian Arctic region). Mineralogical changes form low to high Mg-calcite together with decrease in Mg, Sr and Fe contents strongly support less freshwater input from glacial mode to

  7. Formation of low-T hydrated silicates in modern microbialites from Mexico and implications for microbial fossilization

    Directory of Open Access Journals (Sweden)

    Nina eZeyen

    2015-10-01

    Full Text Available Microbialites are organo-sedimentary rocks found in abundance throughout the geological record back to ~3.5 Ga. Interpretations of the biological and environmental conditions under which they formed rely on comparisons with modern microbialites. Therefore, a better characterization of diverse modern microbialites is crucial to improve such interpretations. Here, we studied modern microbialites from three Mexican alkaline crater lakes: Quechulac, La Preciosa and Atexcac. The geochemical analyses of water solutions showed that they were supersaturated to varying extents with several mineral phases, including aragonite, calcite, hydromagnesite, as well as hydrated Mg-silicates. Consistently, X-ray diffraction and Fourier transform infrared spectroscopy analyses revealed that microbialites are composed of a diversity of mineral phases including aragonite and sometimes calcite, hydromagnesite, and more interestingly, a poorly-crystalline hydrated silicate phase. Coupling of scanning electron microscopy with energy dispersive X-ray spectrometry microanalyses on polished sections showed that this latter phase is abundant, authigenic, magnesium-rich and sometimes associated with iron and manganese. This mineral phase is similar to kerolite, a hydrated poorly crystalline talc-like phase (Mg3Si4O10(OH2·nH2O. Diverse microfossils were permineralized by this silicate phase. Some of them were imaged in 3D by FIB-tomography showing that their morphologically was exquisitely preserved down to the few nm-scale. The structural and chemical features of these fossils were further studied using a combination of transmission electron microscopy and scanning transmission X-ray microscopy at the carbon and magnesium K-edges and iron L2,3-edges. These results showed that organic carbon is pervasively associated with kerolite. Overall, it is suggested that the poorly-crystalline hydrated magnesium-rich silicate forms in many alkaline lakes and has a strong potential

  8. Calibration of fossil scleraxonian Southern Ocean deep-sea corals for U-series dating

    Science.gov (United States)

    Gutjahr, M.; Vance, D.; Hoffmann, D.; Hillenbrand, C.; Kuhn, G.

    2008-12-01

    The deep Southern Ocean has been pinpointed as candidate reservoir capable of storing the additional respired carbon that was drawn from the atmosphere during the Last Glacial Maximum compared with the present-day. In this context the determination of deep ocean ventilation ages is a commonly applied tool, potentially identifying radiocarbon depletion in glacial deep water and enhanced ocean stratification. In order to derive deep-sea ventilation ages most studies to date have used either radiocarbon age differences between paired planktic and benthic foraminifera samples or coupled U-Th and radiocarbon dates obtained from aragonitic deep-sea corals. Results from both these approaches are, however, as yet very scarce for the Southern Ocean. We present calendar ages for a set of deep-sea scleraxonian corals from the Marie Byrd Seamounts in the Amundsen Sea sector of the Southern Ocean (~123°W, ~69°S, 2500 m to 1430 m water depth) employing the 230Th/U-dating method. The aim of our study is to evaluate whether these calcitic octocorals can be used for ventilation age determinations. Our corals have significantly lower uranium concentrations than aragonitic deep-sea corals, ranging from 80 to 250 ng/g. Most corals of Holocene age reproduced the present-day seawater 234U/238U. Pre-Holocene corals, however, show a systematic enrichment of 234U, leading to slightly elevated deglacial initial 234U/238U and significantly higher 234U/238U for ~MIS5 sub-samples. These corals also appear to grow very slowly, on the order of only few μm/year, making it essential to sample as little coral material as possible for combined 230Th/U- and radiocarbon dating purposes. One coral, sampled at high-resolution in various sections returned ages that scatter around 10 ka BP and the early deglaciation, though several significantly older ages were obtained as well. The present-day (234U/238U) ACT in different sections of this coral is very homogenous (1.155 ± 0.003) and more or less

  9. Current Travertines Precipitation from CO{sub 2}-rich Groundwaters as an alert of CO{sub 2} Leakages from a Natural CO{sub 2} Storage at Ganuelas-Mazarron Tertiary Basin (Murcia, Spain)

    Energy Technology Data Exchange (ETDEWEB)

    Rodrigo-Naharro, J.; Delgado, A.; Herrero, M. J.; Granados, A.; Perez del Villar, L.

    2013-02-01

    Carbon capture and storage technologies (CCS) represent the most suitable solutions related to the high anthropogenic CO{sub 2} emissions to the atmosphere. As a consequence, monitoring of the possible CO{sub 2} leakages from an artificial deep geological CO{sub 2} storage (DGS) is indispensable to guarantee its safety. Fast surficial travertine precipitation related to these CO{sub 2} leakages can be used as an alert for these escapes. Since few studies exist focusing on the long-term behaviour of an artificial CO{sub 2} DGS, natural CO{sub 2} storage affected by natural or artificial escapes must be studied as natural analogues for predicting the long-term behaviour of an artificial CO{sub 2} storage. In this context, a natural CO{sub 2} reservoir affected by artificial CO{sub 2} escapes has been studied in this work. This study has mainly focused on the current travertines precipitation associated with the upwelling CO{sub 2}-rich waters from several hydrogeological wells drilled in the Ganuelas-Mazarron Tertiary basin (SE Spain), and consists of a comprehensive characterisation of parent-waters and their associated carbonates, including elemental and isotopic geochemistry, mineralogy and petrography. Geochemical characterisation of groundwaters has led to recognise 4 hydrofacies from 3 different aquifers. These groundwaters have very high salinity and electrical conductivity; are slightly acid; present high dissolved inorganic carbon (DIC) and free CO{sub 2}; are oversaturated in both aragonite and calcite; and dissolve, mobilize and transport low quantities of heavy and/or toxic elements. Isotopic values indicate that: i) the origin of parent-waters is related to rainfalls from clouds originated in the Mediterranean Sea or continental areas; ii) the origin of C is mainly inorganic; and iii) sulphate anions come mainly from the dissolution of the Messinian gypsum from the Tertiary Basin sediments. Current travertines precipitation seems to be controlled by a

  10. The Characterisation of Residual Strain in Ensis siliqua Shells

    Institute of Scientific and Technical Information of China (English)

    D. J. Scurr; R. J. Cernik; S. P. Thompson; P. M. Mummery; S. J. Eichhorn

    2006-01-01

    This study reports the variation of residual strains within the posterior ventral area of the Ensis siliqua mollusc shell, as determined using glancing incidence synchrotron X-ray diffraction. The outer layer of this structure exhibits a tensile strain, in contrast to a compressive strain observed within the inner layer. Fluctuations in unit cell parameters for the inner layer have been determined, showing that the microscopic prismatic layer of the structure exhibits a compressive strain orientated parallel to the surface of the shell. This is thought to enhance the crack deflection properties of this layer, and aid in resisting catastrophic failure. Further analysis of residual strains has been performed using the same method, throughout several stages of compressive testing of the anterior dorsal region of the shell. This identified no variation in residual strains at various levels of loading, and it is therefore proposed that load may be transferred via the organic matrix of mollusc shell structures. A Raman spectroscopic investigation, comparing whole and powdered shell with non-biogenic aragonite, has shown that residual strains are also present in this analagous material which is devoid of organic content. This indicates that the observed strain is not entirely due to the organic matrix.

  11. Li/Mg systematics in scleractinian corals: Calibration of the thermometer

    Science.gov (United States)

    Montagna, Paolo; McCulloch, Malcolm; Douville, Eric; López Correa, Matthias; Trotter, Julie; Rodolfo-Metalpa, Riccardo; Dissard, Delphine; Ferrier-Pagès, Christine; Frank, Norbert; Freiwald, André; Goldstein, Steve; Mazzoli, Claudio; Reynaud, Stephanie; Rüggeberg, Andres; Russo, Simone; Taviani, Marco

    2014-05-01

    We show that the Li/Mg systematics of a large suite of aragonitic coral skeletons, representing a wide range of species inhabiting disparate environments, provides a robust proxy for ambient seawater temperature. The corals encompass both zooxanthellate and azooxanthellate species (Acropora sp., Porites sp., Cladocora caespitosa, Lophelia pertusa, Madrepora oculata and Flabellum impensum) collected from shallow, intermediate, and deep-water habitats, as well as specimens cultured in tanks under temperature-controlled conditions. The Li/Mg ratios observed in corals from these diverse tropical, temperate, and deep-water environments are shown to be highly correlated with temperature, giving an exponential temperature relationship of: Li/Mg (mmol/mol) = 5.41 exp (-0.049 * T) (r2 = 0.975, n = 49). Based on the standard error of the Li/Mg versus temperature correlation, we obtain a typical precision of ±0.9 °C for the wide range of species analysed, similar or better than that of other less robust coral temperature proxies such as Sr/Ca ratios.

  12. Coral skeletal tin and copper concentrations at Pohnpei, Micronesia: possible index for marine pollution by toxic anti-biofouling paints

    Energy Technology Data Exchange (ETDEWEB)

    Inoue, Mayuri; Suzuki, Atsushi; Nohara, Masato; Kan, Hironobu; Edward, Ahser; Kawahata, Hodaka

    2004-06-01

    We present 40 year-long skeletal chronologies of tin (Sn) and copper (Cu) from an annually-banded coral (Porites sp.) collected from Pohnpei Island, Micronesia (western equatorial Pacific). Both the elements are present in antifouling marine paints and are released inadvertently into ambient seawater. Especially, Sn has often been used in the form of tributyltin (TBT). Based on a stepwise pretreatment examination, Sn and Cu both inside and outside the aragonite lattice of the coral skeleton show a potential for providing marine pollution indicators. High values of extra-skeletal Cu/Ca and Sn/Ca atomic ratios were found between late 1960s and late 1980s during a period of active use of TBT-based antifouling paints worldwide. However, a significant decrease in both the ratios in the beginning of 1990s can be attributed to regulation of the use of TBT on cargo ships by countries such as the USA, Japan and Australia. - A new index of coral marine pollution is proposed.

  13. Molecular Cloning and Characterization of Full-Length cDNA of Calmodulin Gene from Pacific Oyster Crassostrea gigas

    Science.gov (United States)

    Li, Xing-Xia; Yu, Wen-Chao; Cai, Zhong-Qiang; He, Cheng; Wei, Na

    2016-01-01

    The shell of the pearl oyster (Pinctada fucata) mainly comprises aragonite whereas that of the Pacific oyster (Crassostrea gigas) is mainly calcite, thereby suggesting the different mechanisms of shell formation between above two mollusks. Calmodulin (CaM) is an important gene for regulating the uptake, transport, and secretion of calcium during the process of shell formation in pearl oyster. It is interesting to characterize the CaM in oysters, which could facilitate the understanding of the different shell formation mechanisms among mollusks. We cloned the full-length cDNA of Pacific oyster CaM (cgCaM) and found that the cgCaM ORF encoded a peptide of 113 amino acids containing three EF-hand calcium-binding domains, its expression level was highest in the mantle, hinting that the cgCaM gene is probably involved in shell formation of Pacific oyster, and the common ancestor of Gastropoda and Bivalvia may possess at least three CaM genes. We also found that the numbers of some EF hand family members in highly calcified species were higher than those in lowly calcified species and the numbers of these motifs in oyster genome were the highest among the mollusk species with whole genome sequence, further hinting the correlation between CaM and biomineralization. PMID:27703977

  14. Effect of permethrin, anthracene and mixture exposure on shell components, enzymatic activities and proteins status in the Mediterranean clam Venerupis decussata.

    Science.gov (United States)

    Sellami, Badreddine; Khazri, Abdelhafidh; Mezni, Amine; Louati, Héla; Dellali, Mohamed; Aissa, Patricia; Mahmoudi, Ezzeddine; Beyrem, Hamouda; Sheehan, David

    2015-01-01

    Anthracene (ANT) and permethrin (PER) are two of the more toxic compounds reaching the marine environment. This study aimed to determine the impact of these molecules on Venerupis decussata, an economically important species cultured on the Tunisian coast. Shell structure and its possible transformation upon exposure to the two contaminants were studied by X-ray diffraction and gravimetric analyses. Results revealed a phase transition in shell composition from aragonite to calcite after PER exposure, to a mixture of PER and ANT (Mix) but not for ANT alone. Catalase (CAT), superoxide dismutase (SOD) and glutathione transferase (GST) activities were determined in digestive gland and gills after exposure to ANT, PER and Mix to assess the impact of the contamination on the oxidative status of V. decussata. Enzyme activities increased in the digestive gland after PER treatment and in the gills after ANT treatment. PER exposure significantly reduced the levels of free thiols and increased levels of carbonylated proteins in the digestive gland, as compared to controls. In contrast, ANT exposure significantly reduced free thiols and increased the number of carbonylated proteins in the gills. Mix induced additive effects as measured by both enzymatic and proteomic approaches. The present study suggests that PER has a strong effect on shell structure; that PER and ANT exposure generate compound-dependent oxidative stress in the tissues of V. decussata and that a mixture of the two compounds has synergistic effects on biochemical response. PMID:25461742

  15. Risks to coral reefs from ocean carbonate chemistry changes in recent earth system model projections

    International Nuclear Information System (INIS)

    Coral reefs are among the most biodiverse ecosystems in the world. Today they are threatened by numerous stressors, including warming ocean waters and coastal pollution. Here we focus on the implications of ocean acidification for the open ocean chemistry surrounding coral reefs, as estimated from earth system models participating in the Coupled Model Intercomparison Project, Phase 5 (CMIP5). We project risks to reefs in the context of three potential aragonite saturation (Ωa) thresholds. We find that in preindustrial times, 99.9% of reefs adjacent to open ocean in the CMIP5 ensemble were located in regions with Ωa > 3.5. Under a business-as-usual scenario (RCP 8.5), every coral reef considered will be surrounded by water with Ωa 2 emissions abatement, the Ωa threshold for reefs is critical to projecting their fate. Our results indicate that to maintain a majority of reefs surrounded by waters with Ωa > 3.5 to the end of the century, very aggressive reductions in emissions are required. The spread of Ωa projections across models in the CMIP5 ensemble is narrow, justifying a high level of confidence in these results. (letter)

  16. Siderite 'clumped' isotope thermometry: A new paleoclimate proxy for humid continental environments

    Science.gov (United States)

    Fernandez, Alvaro; Tang, Jianwu; Rosenheim, Brad E.

    2014-02-01

    Clumped isotope measurements can be used to exploit the paleoclimatic potential of pedogenic siderite (FeCO3); however, the applicability of this method is held back by the lack of clumped isotope calibrations of mineralogies other than calcite and aragonite. Here we present an inorganic calibration of siderites grown in the laboratory between 21 and 51 °C. Linear regression of Δ47 values and temperature (106/T2, K) yields the following relationship (r2 = 0.997): Δ={(0.0356±0.0018)×106}/{T}+(0.172±0.019) We demonstrate that this calibration is indistinguishable from calcite at current levels of analytical precision. Our observations suggest that there is likely no large systematic bias in the clumped isotope acid fractionation factors between the two different carbonate minerals. We also present clumped isotope measurements of a natural siderite collected from Holocene sediments of the Mississippi River Delta. We find that siderites record warm season marsh water temperatures instead of mean annual temperatures as it has long been presumed. This finding has important implications for the accuracy of siderite stable isotope and clumped isotope based climate reconstructions.

  17. Skeletal growth, ultrastructure and composition of the azooxanthellate scleractinian coral Balanophyllia regia

    Science.gov (United States)

    Brahmi, C.; Meibom, A.; Smith, D. C.; Stolarski, J.; Auzoux-Bordenave, S.; Nouet, J.; Doumenc, D.; Djediat, C.; Domart-Coulon, I.

    2010-03-01

    The biomineralization process and skeletal growth dynamics of azooxanthellate corals are poorly known. Here, the growth rate of the shallow-water dendrophyllid scleractinian coral Balanophyllia regia was evaluated with calcein-labeling experiments that showed higher lateral than vertical extension. The structure, mineralogy and trace element composition of the skeleton were characterized at high spatial resolution. The epitheca and basal floor had the same ultrastructural organization as septa, indicating a common biological control over their formation. In all of these aragonitic skeletal structures, two main ultrastructural components were present: “centers of calcification” (COC) also called rapid accretion deposits (RAD) and “fibers” (thickening deposits, TD). Heterogeneity in the trace element composition, i.e., the Sr/Ca and Mg/Ca ratios, was correlated with the ultrastructural organization: magnesium was enriched by a factor three in the rapid accretion deposits compared with the thickening deposits. At the interface with the skeleton, the skeletogenic tissue (calicoblastic epithelium) was characterized by heterogeneity of cell types, with chromophile cells distributed in clusters regularly spaced between calicoblasts. Cytoplasmic extensions at the apical surface of the calicoblastic epithelium created a three-dimensional organization that could be related to the skeletal surface microarchitecture. Combined measurements of growth rate and skeletal ultrastructural increments suggest that azooxanthellate shallow-water corals produce well-defined daily growth steps.

  18. Determination of the mineral stability field of evolving groundwater in the Lake Bosumtwi impact crater and surrounding areas

    Science.gov (United States)

    Loh, Yvonne Sena Akosua; Yidana, Sandow Mark; Banoeng-Yakubo, Bruce; Sakyi, Patrick Asamoah; Addai, Millicent Obeng; Asiedu, Daniel Kwadwo

    2016-09-01

    Conventional graphical techniques, mass balance geochemical modelling, and multivariate statistical methods were jointly applied to hydrogeochemical data of groundwater from the fractured rock aquifer system, and surface water in the Bosumtwi and surrounding areas to reveal evolutionary trends and the characteristics of evolving groundwater in the area. Four clusters distinguished from the Q-mode hierarchical cluster analysis (HCA) comprised three main groundwater associations and one surface water group (lake water). Although both water resources are of low mineralization (TDS < 1000 mg/l), it was observed that the groundwater from the upper catchment with hydrochemical facies dominated by Nasbnd Mgsbnd HCO3-, evolves to Casbnd Mgsbnd and mixed cations HCO3- water types at the lower reaches. The lake water on the other hand is Nasbnd HCO3- water type. Results from principal component analyses (PCA) and other geochemical interpretations distinguished three sources of variations in the hydrochemistry. Saturation indices of possible reactive mineral phases show groundwater undersaturation relative to albite, anorthite, aragonite, barite, calcite, chlorite, chrysotile, dolomite, gypsum, k-felspar and talc, and supersaturation with respect to gibbsite, kaolinite, Ca-montmorillonite and k-mica in the area. The PCA and other geochemical interpretation identify weathering of feldspars and carbonate mineral dissolution as predominantly influencing the hydrochemistry of the groundwater. Hydrolysis of the aluminosilicates causes the groundwater to reach equilibrium with kaolinite. In addition to dissolution of silicates, the chemical composition of the lake water has been influenced by evaporation and consequent carbonate saturation.

  19. Mesozoic (Lower Jurassic) red stromatactis limestones from the Southern Alps (Arzo, Switzerland): calcite mineral authigenesis and syneresis-type deformation

    Science.gov (United States)

    Neuweiler, Fritz; Bernoulli, Daniel

    2005-02-01

    The Broccatello lithological unit (Lower Jurassic, Hettangian to lower parts of Upper Sinemurian) near the village of Arzo (southern Alps, southern Switzerland) is a mound-shaped carbonate deposit that contains patches of red stromatactis limestone. Within the largely bioclastic Broccatello unit, the stromatactis limestone is distinguished by its early-diagenetic cavity system, a relatively fine-grained texture, and an in-situ assemblage of calcified siliceous sponges (various demosponges and hexactinellids). A complex shallow subsurface diagenetic pathway can be reconstructed from sediment petrography in combination with comparative geochemical analysis (carbon and oxygen isotopes; trace and rare earth elements, REE + Y). This pathway includes organic matter transformation, aragonite and skeletal opal dissolution, patchy calcification and lithification, sediment shrinkage, sagging and collapse, partial REE remobilization, and multiple sediment infiltration. These processes occurred under normal-marine, essentially oxic conditions and were independent from local, recurring syn-sedimentary faulting. It is concluded that the stromatactis results from a combination of calcite mineral authigenesis and syneresis-type deformation. The natural stromatactis phenomenon may thus be best explained by maturation processes of particulate polymer gels expected to form in fine-grained carbonate sediments in the shallow subsurface. Conditions favorable for the evolution of stromatactis appear to be particularly frequent during drowning of tropical or subtropical carbonate platforms.

  20. Experiments with Seasonal Forecasts of ocean conditions for the Northern region of the California Current upwelling system

    Science.gov (United States)

    Siedlecki, Samantha A.; Kaplan, Isaac C.; Hermann, Albert J.; Nguyen, Thanh Tam; Bond, Nicholas A.; Newton, Jan A.; Williams, Gregory D.; Peterson, William T.; Alin, Simone R.; Feely, Richard A.

    2016-01-01

    Resource managers at the state, federal, and tribal levels make decisions on a weekly to quarterly basis, and fishers operate on a similar timeframe. To determine the potential of a support tool for these efforts, a seasonal forecast system is experimented with here. JISAO’s Seasonal Coastal Ocean Prediction of the Ecosystem (J-SCOPE) features dynamical downscaling of regional ocean conditions in Washington and Oregon waters using a combination of a high-resolution regional model with biogeochemistry and forecasts from NOAA’s Climate Forecast System (CFS). Model performance and predictability were examined for sea surface temperature (SST), bottom temperature, bottom oxygen, pH, and aragonite saturation state through model hindcasts, reforecast, and forecast comparisons with observations. Results indicate J-SCOPE forecasts have measurable skill on seasonal timescales. Experiments suggest that seasonal forecasting of ocean conditions important for fisheries is possible with the right combination of components. Those components include regional predictability on seasonal timescales of the physical environment from a large-scale model, a high-resolution regional model with biogeochemistry that simulates seasonal conditions in hindcasts, a relationship with local stakeholders, and a real-time observational network. Multiple efforts and approaches in different regions would advance knowledge to provide additional tools to fishers and other stakeholders. PMID:27273473

  1. Hydrogeochemical investigations and groundwater quality assessment of Torbat-Zaveh plain, Khorasan Razavi, Iran.

    Science.gov (United States)

    Nematollahi, M J; Ebrahimi, P; Razmara, M; Ghasemi, A

    2016-01-01

    Hydrogeochemical investigations of groundwater in Torbat-Zaveh plain have been carried out to assess the water quality for drinking and irrigation purposes. In this study, 190 groundwater samples were collected and analyzed for physicochemical parameters and major ion concentrations. The abundance of major cations and anions was in the following order: Na(+) > Mg(2+) > Ca(2+) > K(+), and Cl(-) > [Formula: see text] > [Formula: see text] > [Formula: see text]. As a result, alkaline element (Na(+)) exceeds alkaline earth elements (Mg(2+) and Ca(2+)), and strong acids (Cl(-) and [Formula: see text]) dominate weak acids ([Formula: see text] and [Formula: see text]) in majority of the groundwater samples. Statistical analyses including Spearman correlation coefficients and factor analysis display good correlation between physicochemical parameters (EC, TDS and TH) and Na(+), Mg(2+), Ca(2+), Cl(-) and [Formula: see text]. The results display that rock-weathering interactions and ion-exchange processes play important role in controlling groundwater chemistry. Saturation index values also indicate that water chemistry is significantly affected by carbonate minerals such as calcite, aragonite and dolomite. US Salinity Laboratory(USSL) and Wilcox diagrams together with permeability index values reveal that most of the groundwater samples are suitable for irrigation purpose. However, in some regions, the water samples do not indicate required irrigational quality.

  2. Panigarh cave stalagmite evidence of climate change in the Indian Central Himalaya since AD 1256: Monsoon breaks and winter southern jet depressions

    Science.gov (United States)

    Liang, Fuyuan; Brook, George A.; Kotlia, Bahadur S.; Railsback, L. Bruce; Hardt, Benjamin; Cheng, Hai; Edwards, R. Lawrence; Kandasamy, Selvaraj

    2015-09-01

    Variations in petrography, stable isotopes, reflectance, and luminescence along the central growth axis of a 14.5 cm stalagmite from Panigarh cave indicate cooler and slightly wetter conditions in the Himalayan foothills of northern India during the Little Ice Age (LIA), which lasted from ˜AD 1489-1889 based on deposition of calcite, and AD 1450-1820 based on rapid changes in δ18O values. Conditions were warmer and drier during the preceding Medieval Climate Anomaly (MCA) and also in the post-LIA periods, as evidenced by deposition of aragonite. A review of currently existing stalagmite and other proxy data from south and east Asia reveals a broad spatial pattern in precipitation over south and east Asia during the LIA, with northern areas showing generally increased precipitation and southern areas reduced precipitation. During the MCA and after the LIA, the records suggest this pattern was reversed. Weaker ISM during the LIA brought drought conditions to the core ISM area but triggered more monsoon 'breaks' that brought higher precipitation to the Himalayas. At the same time, the weaker ISM may also have pushed more depressions along the path of the southern winter jet which brought more winter precipitation to the Himalayas and therefore a LIA wetter in our study area.

  3. Discovery of seep carbonate nodules as new evidence for gas venting on the northern continental slope of South China Sea

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jianxin; CHEN Zhong; GU Senchang; MENG Fancong; YAN Wen; CHEN Muhong; WANG Shuhong; LU Jun; ZHANG Fan; XIANG Rong; XIAO Shangbin; YAN Pin

    2006-01-01

    Seep carbonate nodules were firstlycollected from the southwestern Dongsha area on northern continental slope of South China Sea for mineralogical and geochemical studies. The results of X-ray diffraction show that carbonate nodules are composed of Fe-rich domolite,siderite and a few cal cite and aragonite, as well as a small quantity of non-carbonate minerals such as goethite, quartz and clay minerals. Fe-rich dolomite and siderite characterized by euhedral microcrystalline structure were directly precipitated at cold seeps. The δ13C values for Fe-rich dolomite and siderite in the bulk nodules vary from -18.24‰ to -36.07‰, and the δ18O values range from 0.42 to 2.76‰. Their moderate depleted 13C reflects that carbon origin is possibly thermoge netic gas or mixed gas, which is evidence of gas ventings in the seafloor. Moreover, massive worm tube fossils related to cold seeps were found on the surfaces of carbonate nodules, and the conduits and/or channels in semi-solidified nodules which were not filled by carbonate or sediment were also observed. A preliminary conclusion is that active micro gas venting with a conduit/channel diameter range from 200 μm to 600 μm possibly exists in modern seafloor of the carbonate nodule area.

  4. Fracture mechanics of mollusc shells

    Energy Technology Data Exchange (ETDEWEB)

    Cortie, Michael B. [Institute for Nanoscale Technology, University of Technology, Sydney (Australia)]. E-mail: michael.cortie@uts.edu.au; McBean, Katie E. [Microstructural Analysis Unit, University of Technology, Sydney (Australia); Elcombe, Margaret M. [Bragg Institute, Australian Nuclear Science and Technology Organisation, PMB 1, NSW (Australia)

    2006-11-15

    The shape and structure of the shells of molluscs has attracted considerable attention. One aspect of interest is the comparatively high resistance to fracture of these shells. It is known that they are composite structures of aragonite, other calcereous materials, and up to 5% by volume of protein 'glue'. A large component of their toughening derives from crack tip blunting, deflection and closure, concepts well-known from the field of fracture mechanics. However, the possibility that they might also derive a measure of toughening from a residual stress distribution has been generally overlooked, although Illert first raised this over a decade ago. The optimum situation would be when the inner surface of the shell is maintained in a state of tensile stress, while the outer layers are in the necessarily counter-balancing compressive state. We have examined this hypothesis using a combination of neutron diffraction and scanning electron microscopy and find that it is certainly feasible. However, a definitive proof will require a diffraction study at higher resolution.

  5. A new method to reconstruct fish diet and movement patterns from δ 13 C values in otolith amino acids

    KAUST Repository

    McMahon, Kelton W.

    2011-08-01

    Fish ecologists have used geochemical values in otoliths to examine habitat use, migration, and population connectivity for decades. However, it remains difficult to determine an unambiguous dietary δ 13C signature from bulk analysis of otolith. Studies to date have focused on the aragonite component of otoliths with less attention paid to the organic fraction. We describe the application of compound-specific stable isotope analysis (SIA) to analyze amino acid (AA) δ 13C values from small amounts (<1 mg) of otolith powder. We examined δ 13C values of otolith and muscle AAs from a reef-associated snapper (Lutjanus ehrenbergii (Peters, 1869)) collected along a carbon isotope gradient (isoscape) from seagrass beds to coral reefs. Carbon isotope values in otolith and muscle samples were highly correlated within and among coastal habitats. Moreover, δ 13C values of otolith AAs provided a purely dietary record that avoided dilution from dissolved inorganic carbon. Otolith AAs served as a robust tracer of δ 13C values at the base of the food web, making compound-specific SIA a powerful tool for dietary reconstructions and tracking the movement of fishes across isoscapes.

  6. Characteristics of pulsed photo-stimulated luminescence and thermoluminescence for the identification of gamma irradiated poultry eggs

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Pulsed photo-stimulated luminescence (PPSL) is a simple screening method that can be employed qualitatively at the spot for the detection of eggs treated with ionizing radiation. Due to the variations in the results during storage, the eggs of ostrich, duck, hen, and quail were irradiated to doses of 0, 1, 2, and 3 kGy. Most of the samples were incorrectly identified during storage after four months of irradiation. Thermoluminescence (TL)technique was also tried by using egg shells in order to confirm the irradiation treatment in eggs. TL glow curves were recorded between the temperatures 50℃ to 400℃ at the rate of 5°/s for all the control and irradiated samples. On the basis of integrated areas of first glow curves (TL1), the glow curve ratios (TL1/TL2) and the shapes of maxima of TL1,the irradiation treatment of all the eggs was confirmed. Furthermore, the presence of calcite and aragonite minerals that cause the TL signal in the egg shells were studied using X-ray diffraction spectrometry.

  7. Wet season upwelling and dry season chlorophyll-a describe interannual growth rates of Porites in southern China.

    Directory of Open Access Journals (Sweden)

    Teng Teng Yang

    Full Text Available Southern China hosts coral communities in marginal environments that are characterized by low linear extension rates, low coral cover and/or no reef formation, thus providing natural laboratories to study coral communities with below average growth rates. Here we compare the annual linear extension rates over 10 years (range 1.2 to 11.4 mm yr-1 of six Porites sp. coral cores collected from Hong Kong with monthly hydrographic data from the Hong Kong Environmental Protection Department. At all sites, low-density, dry season extension were more variable than high-density, wet season extension and on average, was lower at two of the three sites. We applied multi-variate linear regressions that revealed high-density, wet season band extension to inversely correlate most significantly to temperature (r = -0.39, p<0.01. In contrast, low-density, dry season band extension was more variable and correlated most significantly with dry season chlorophyll-a (Chl-a (r = 0.64, p<0.001. Additionally, we find that corals at the site with highest dry season Chl-a have the highest dry season extension lengths. Our findings indicate that relative mixing of fresh and salt water in the wet season and primary productivity in the dry season, and their influences on aragonite saturation, are likely to impact interannual coral extension variability in marginal environments.

  8. Mineralogical and sedimentological study of gypsiferous sands from the Saharian Desert

    Science.gov (United States)

    Somma, Roberta; Bella, Francesca

    2016-04-01

    A mineralogical and sedimentological study was carried out in Quaternary aeolian sands from the Sahara Desert (Tunisia and Libya). Gypsum resulted to be the dominant mineral (65%), whereas quartz resulted to be in significant amount (25%) in all samples. Aragonite and calcite, related to marine organisms, was found especially in the Libyan sands. Gypsum grains appear in euhedral crystals or as polycrystalline twinned crystals. Crystal habitus is pseudo-octahedric or tabular. Due to the euhedral habitus, the forms of the grains is discoid or bladed but with a low roundness. Quartz grains are mostly ialin or orange as the grain surfaces are coated with thin hematite films. Quartz grains dominantly appear as subhedral crystals. Habitus is prismatic or hexagonal. Due to the subhedral habitus, quartz grain forms can be classified as bladed with a low roundness. A minor amount of quartz grains is formed by well rounded and spherical grains showing frosted and pitted surfaces. The particle size analysis indicated that the studied sediments consist of well sorted very fine sands. The studied Quaternary aeolian sands can be classified as gypsiferous sands. Notwithstanding sands are well sorted, they are immature under a mineralogical and textural point of view. Particularly, gypsum formed in present or past sabkha and the amount of marine bioclasts should suggest that the source area of the Lybian gypsum grains could be a sabkha near the sea.

  9. Microscopic and Spectroscopic Characterization of Calcified Microorganisms at the Nanometer-Scale in Experimental and Field Samples.

    Science.gov (United States)

    Benzerara, K.; Yoon, T.; Menguy, N.; Tyliszczak, T.; Brown, G. E.

    2004-12-01

    Calcium phosphates and calcium carbonates are the most prevalent minerals involved in microbial fossilization. Structural characterization of both the organic and mineral components in such samples is, however, usually difficult at the appropriate spatial resolution, i.e., at the submicrometer scale. We have used a combination of Scanning Transmission X-ray microscopy (STXM), a synchrotron-based technique, and High-Resolution Transmission Electron Microscopy (HRTEM) to characterize both the Ca-containing biominerals and the functional groups present in the organic components associated with them (STXM). These data, in turn, provide a better understanding of the mechanisms, products, and biomolecules involved in microbial calcification. We have studied the experimental biomineralization of the model strain Caulobacter crescentus by calcium phosphates, and the calcification of natural biofilms by aragonite in an alkaline lake in Turkey. The precipitation of calcium phosphate and calcium carbonate by microorganisms likely involves different mechanisms. The resulting biominerals were found to have unique features with dimensions in the nanometer-range, preferential crystallographic orientations or unusual morphologies, which provide potential biosignatures. By using C K-edge NEXAFS spectroscopy at a submicrometer scale, we were also able to document the evolution of the organic molecules during the fossilization process and to characterize those involved as templates in the formation of calcium phosphate and carbonate minerals.

  10. Hydrothermal synthesis and thermal evolution of carbonate-fluorhydroxyapatite scaffold from cuttlefish bones.

    Science.gov (United States)

    Tkalčec, Emilija; Popović, Jasminka; Orlić, Sebastijan; Milardović, Stjepan; Ivanković, Hrvoje

    2014-09-01

    Phase composition, crystal structure and morphology of carbonated fluor/hydroxyapatite synthesized hydrothermally from aragonitic cuttlefish bones were studied by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS). The product of synthesis has been characterized as carbonated fluor/hydroxyapatite with carbonate incorporated inside channel (A-type) and substituted for the PO4(3-) group (B-type). The vibration band at 874 cm(-1) assigned to bending (ν2) mode undoubtedly confirmed carbonate substituted for PO4(3-) group, while the band at 880 cm(-1) was attributed to A-type carbonate substitution. The additional sharp and intense band at 865 cm(-1) considered as "non-apatitic" carbonate substitution is not assigned with certainty so far. Evolution of CO2 from tetrahedral (PO4(3-)) sites with the increase in heat-treatment temperature is evident by the changes in tetrahedral bond lengths and angles, as obtained by the Rietveld structure refinement. Also, changes in the isotropic temperature parameters for the 2a site point to A-type carbonate incorporation as well.

  11. Biological coupling anti-wear properties of three typical molluscan shells—Scapharca subcrenata, Rapana venosa and Acanthochiton rubrolineatus

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Molluscan shells are fascinating examples of highly ordered hierarchical structure and complex organic-inorganic biocomposite material. However, their anti-wear properties were rarely studied especially in the perspective of biological coupling. So in the current study three typical shells, Scapharca subcrenata, Rapana venosa and Acanthochiton rubrolineatus, were selected as coupling models to further study their anti-wear properties. Stereomicroscope and scanning electron microscopic observations showed that all these three shells had specific surface morphologies and complicated section microstructures. Importantly, a special structure, pore canal tubules, was discovered in the shells of Scapharca subcrenata and Acanthochiton rubrolineatus, which probably contributed most to their anti-wear properties. X-ray diffraction and micro-Vikers hardness tester were further adopted to analyze the phase compositions and micro-hardness of the shells. The measured results demonstrated that aragonite was the most extensive phase present in the shell, and possesed a relatively high micro-hardness. In this paper, the shells were described in details in morphology, structure and material with emphasis on the relationship with anti-wear property. The study revealed that the selected seashells possess distinct anti-wear properties by complicated mechanisms involving the integrated functions of multiple biological coupling elements, and this would provide inspiration to the design of new bionic wear resistance components.

  12. Comparative genomics explains the evolutionary success of reef-forming corals

    Science.gov (United States)

    Bhattacharya, Debashish; Agrawal, Shobhit; Aranda, Manuel; Baumgarten, Sebastian; Belcaid, Mahdi; Drake, Jeana L; Erwin, Douglas; Foret, Sylvian; Gates, Ruth D; Gruber, David F; Kamel, Bishoy; Lesser, Michael P; Levy, Oren; Liew, Yi Jin; MacManes, Matthew; Mass, Tali; Medina, Monica; Mehr, Shaadi; Meyer, Eli; Price, Dana C; Putnam, Hollie M; Qiu, Huan; Shinzato, Chuya; Shoguchi, Eiichi; Stokes, Alexander J; Tambutté, Sylvie; Tchernov, Dan; Voolstra, Christian R; Wagner, Nicole; Walker, Charles W; Weber, Andreas PM; Weis, Virginia; Zelzion, Ehud; Zoccola, Didier; Falkowski, Paul G

    2016-01-01

    Transcriptome and genome data from twenty stony coral species and a selection of reference bilaterians were studied to elucidate coral evolutionary history. We identified genes that encode the proteins responsible for the precipitation and aggregation of the aragonite skeleton on which the organisms live, and revealed a network of environmental sensors that coordinate responses of the host animals to temperature, light, and pH. Furthermore, we describe a variety of stress-related pathways, including apoptotic pathways that allow the host animals to detoxify reactive oxygen and nitrogen species that are generated by their intracellular photosynthetic symbionts, and determine the fate of corals under environmental stress. Some of these genes arose through horizontal gene transfer and comprise at least 0.2% of the animal gene inventory. Our analysis elucidates the evolutionary strategies that have allowed symbiotic corals to adapt and thrive for hundreds of millions of years. DOI: http://dx.doi.org/10.7554/eLife.13288.001 PMID:27218454

  13. Phylogenetic analysis of a microbialite-forming microbial mat from a hypersaline lake of the Kiritimati atoll, Central Pacific.

    Directory of Open Access Journals (Sweden)

    Dominik Schneider

    Full Text Available On the Kiritimati atoll, several lakes exhibit microbial mat-formation under different hydrochemical conditions. Some of these lakes trigger microbialite formation such as Lake 21, which is an evaporitic, hypersaline lake (salinity of approximately 170‰. Lake 21 is completely covered with a thick multilayered microbial mat. This mat is associated with the formation of decimeter-thick highly porous microbialites, which are composed of aragonite and gypsum crystals. We assessed the bacterial and archaeal community composition and its alteration along the vertical stratification by large-scale analysis of 16S rRNA gene sequences of the nine different mat layers. The surface layers are dominated by aerobic, phototrophic, and halotolerant microbes. The bacterial community of these layers harbored Cyanobacteria (Halothece cluster, which were accompanied with known phototrophic members of the Bacteroidetes and Alphaproteobacteria. In deeper anaerobic layers more diverse communities than in the upper layers were present. The deeper layers were dominated by Spirochaetes, sulfate-reducing bacteria (Deltaproteobacteria, Chloroflexi (Anaerolineae and Caldilineae, purple non-sulfur bacteria (Alphaproteobacteria, purple sulfur bacteria (Chromatiales, anaerobic Bacteroidetes (Marinilabiacae, Nitrospirae (OPB95, Planctomycetes and several candidate divisions. The archaeal community, including numerous uncultured taxonomic lineages, generally changed from Euryarchaeota (mainly Halobacteria and Thermoplasmata to uncultured members of the Thaumarchaeota (mainly Marine Benthic Group B with increasing depth.

  14. Petrographical Study of Ewekoro Carbonate Rocks, in Ibese, South Western Nigeria

    Directory of Open Access Journals (Sweden)

    Osinowo O.O.

    2010-12-01

    Full Text Available

    Limestone deposits can be found in every system of the geologic column since the Precambrian. In classifying this rock, various attempts have been made and notable among them is the classification scheme based on three components: allochems, cements and matrix. Another classification divided limestoneonthe basis of texture into grainstone, packstone, mudstone, wackestone and boundstone. Texturally, limestone ranges from fine to coarse grained with aragonite and calcite as the most common minerals. This work was aimed at identifying and describing both the allochemical and orthochemical components of the limestone deposits in order to classify and deduce their depositional environment.

    Eight core samples of limestone deposits representing the Ewekoro Formation of the Dahomey Basin were studied petrographically.

    The result of the analysis carried out on the samples showed that the Ibese limestone is composed of the following allochems: sponges, echinoids, bivalves, coralline algae, and pelecypod which represent the skeletal content and intraclasts, pellets and ooids which represent the non skeletal grains. The orthochemical constituents include the carbonate mud matrix and the sparry calcite cement.

    These constituents observed from the slides indicate that the Ibese limestone belongs to the class of wackestone and could have been deposited in a quiet and low energy environment.

  15. A change in coral extension rates and stable isotopes after El Niño-induced coral bleaching and regional stress events

    Science.gov (United States)

    Hetzinger, S.; Pfeiffer, M.; Dullo, W.-Chr.; Zinke, J.; Garbe-Schönberg, D.

    2016-09-01

    Coral reefs are biologically diverse ecosystems threatened with effective collapse under rapid climate change, in particular by recent increases in ocean temperatures. Coral bleaching has occurred during major El Niño warming events, at times leading to the die-off of entire coral reefs. Here we present records of stable isotopic composition, Sr/Ca ratios and extension rate (1940–2004) in coral aragonite from a northern Venezuelan site, where reefs were strongly impacted by bleaching following the 1997–98 El Niño. We assess the impact of past warming events on coral extension rates and geochemical proxies. A marked decrease in coral (Pseudodiploria strigosa) extension rates coincides with a baseline shift to more negative values in oxygen and carbon isotopic composition after 1997–98, while a neighboring coral (Siderastrea siderea) recovered to pre-bleaching extension rates simultaneously. However, other stressors, besides high temperature, might also have influenced coral physiology and geochemistry. Coastal Venezuelan reefs were exposed to a series of extreme environmental fluctuations since the mid-1990s, i.e. upwelling, extreme rainfall and sediment input from landslides. This work provides important new data on the potential impacts of multiple regional stress events on coral isotopic compositions and raises questions about the long-term influence on coral-based paleoclimate reconstructions.

  16. Calcium carbonate-calcium phosphate mixed cement compositions for bone reconstruction.

    Science.gov (United States)

    Combes, C; Bareille, R; Rey, C

    2006-11-01

    The feasibility of making calcium carbonate-calcium phosphate (CaCO(3)-CaP) mixed cements, comprising at least 40% (w/w) CaCO(3) in the dry powder ingredients, has been demonstrated. Several original cement compositions were obtained by mixing metastable crystalline CaCO(3) phases with metastable amorphous or crystalline CaP powders in aqueous medium. The cements set within at most 1 h at 37 degrees C in atmosphere saturated with water. The hardened cement is microporous and exhibits weak compressive strength. The setting reaction appeared to be essentially related to the formation of a highly carbonated nanocrystalline apatite phase by reaction of the metastable CaP phase with part or almost all of the metastable CaCO(3) phase. The recrystallization of metastable CaP varieties led to a final cement consisting of a highly carbonated poorly crystalline apatite analogous to bone mineral associated with various amounts of vaterite and/or aragonite. The presence of controlled amounts of CaCO(3) with a higher solubility than that of the apatite formed in the well-developed CaP cements might be of interest to increase resorption rates in biomedical cement and favors its replacement by bone tissue. Cytotoxicity testing revealed excellent cytocompatibility of CaCO(3)-CaP mixed cement compositions.

  17. Diffusion-reaction compromise the polymorphs of precipitated calcium carbonate

    Institute of Scientific and Technical Information of China (English)

    Han Wang; Wenlai Huang; Yongsheng Han

    2013-01-01

    Diffusion is seldom considered by chemists and materialists in the preparation of materials while it plays an important role in the field of chemical engineering.If we look at crystallization at the atomic level,crystal growth in a solution starts from the diffusion of ions to the growing surface followed by the incorporation of ions into its lattice.Diffusion can be a rate determining step for the growth of crystals.In this paper,we take the crystallization of calcium carbonate as an example to illustrate the microscopic processes of diffusion and reaction and their compromising influence on the morphology of the crystals produced.The diffusion effect is studied in a specially designed three-cell reactor.Experiments show that a decrease of diffusion leads to retardation of supersaturation and the formation of a continuous concentration gradient in the reaction cell,thus promoting the formation of cubic calcite particles.The reaction rate is regulated by temperature.Increase of reaction rate favors the formation of needle-like aragonite particles.When diffusion and reaction play joint roles in the reaction system,their compromise dominates the formation of products,leading to a mixture of cubic and needle-like particles with a controllable ratio.Since diffusion and reaction are universal factors in the preparation of materials,the finding of this paper could be helpful in the controlled synthesis of other materials.

  18. Ocean acidification and coral reefs: effects on breakdown, dissolution, and net ecosystem calcification.

    Science.gov (United States)

    Andersson, Andreas J; Gledhill, Dwight

    2013-01-01

    The persistence of carbonate structures on coral reefs is essential in providing habitats for a large number of species and maintaining the extraordinary biodiversity associated with these ecosystems. As a consequence of ocean acidification (OA), the ability of marine calcifiers to produce calcium carbonate (CaCO(3)) and their rate of CaCO(3) production could decrease while rates of bioerosion and CaCO(3) dissolution could increase, resulting in a transition from a condition of net accretion to one of net erosion. This would have negative consequences for the role and function of coral reefs and the eco-services they provide to dependent human communities. In this article, we review estimates of bioerosion, CaCO(3) dissolution, and net ecosystem calcification (NEC) and how these processes will change in response to OA. Furthermore, we critically evaluate the observed relationships between NEC and seawater aragonite saturation state (Ω(a)). Finally, we propose that standardized NEC rates combined with observed changes in the ratios of dissolved inorganic carbon to total alkalinity owing to net reef metabolism may provide a biogeochemical tool to monitor the effects of OA in coral reef environments. PMID:22881351

  19. Stratigraphy, temperature profiles, and flow test data from the PLTG-1 and PLTG-2 coreholes, platanares geothermal system, Honduras

    Energy Technology Data Exchange (ETDEWEB)

    Goff, F.; Shevenell, L.; Kelkar, S.; Smith, D.; Meert, J.; Heiken, G.; Bargar, K.; Ramos, N.; Truesdell, A.H.; Stallard, M..

    1987-01-01

    Stratigraphy, temperature profiles, and flow test data from the PLTG-1 and PLTG-2 coreholes in Platanares, Honduras, have been used to determine production characteristics from a 160/sup 0/C fluid zone at 625 to 640 m depth and to estimate depth to the source geothermal reservoir. The two coreholes penetrate thin Quaternary deposits and several hundred meters of Miocene volcanics and Cretaceous to Eocene sedimentary rocks. Extrapolation of the deep thermal gradient of 139/sup 0/C/km in PLTG-2 (depth 401 m) indicates the source reservoir of 220 to 240/sup 0/C fluid occurs at 1.2 to 1.5 km depth. Flow tests of PLTG-1 from the 625 to 640 m zone show that 160/sup 0/C geothermal fluids similar in composition to ''end-member'' hot springs originate from fractured meta-conglomerates of the Valle de Angeles Group. Pressure transient analysis indicates this flow zone taps a localized reservoir having a volume on the order of 0.065 km/sup 3/. Maximum thermal power of PLTG-1 is roughly 3 MW/sub t/. Scaling of aragonite results from flashing of the dilute, high pH, high HCO/sub 3/ fluid. Use of the shallow, 160/sup 0/C resource will require binary cycle power plants and, possibly, downhole pumps to successfully extract heat from the fluids for electrical applications.

  20. Ocean acidification alters the material properties of Mytilus edulis shells.

    Science.gov (United States)

    Fitzer, Susan C; Zhu, Wenzhong; Tanner, K Elizabeth; Phoenix, Vernon R; Kamenos, Nicholas A; Cusack, Maggie

    2015-02-01

    Ocean acidification (OA) and the resultant changing carbonate saturation states is threatening the formation of calcium carbonate shells and exoskeletons of marine organisms. The production of