Sample records for mg isotope composition

  1. Magnesium isotopic composition of the oceanic mantle and oceanic Mg cycling

    Liu, Ping-Ping; Teng, Fang-Zhen; Dick, Henry J. B.; Zhou, Mei-Fu; Chung, Sun-Lin


    To constrain the Mg isotopic composition of the oceanic mantle, investigate Mg isotope fractionation of abyssal peridotites during seafloor alteration, and assess Mg budget in the oceans, a suite of 32 abyssal peridotite samples from the Gakkel Ridge and Southwest Indian Ridge (SWIR) was, for the first time, selected for high-precision Mg isotope analyses. Although most of these samples are extensively altered, largely by serpentinization and weathering, primary olivine, diopside and enstatite grains are preserved in some samples. Olivine grains from the least altered samples have δ26Mg varying from -0.30 to -0.12‰ (n = 7), whereas enstatite and diopside have δ26Mg varying from -0.27 to -0.16‰ (n = 7), and from -0.23 to -0.09‰ (n = 6), respectively. Whole-rock δ26Mg values range from -0.24 to 0.03‰ with an average of -0.12 ± 0.13‰ (2SD, n = 32). Strongly serpentinized peridotites have lower average δ26Mg values (δ26Mg = -0.19 ± 0.07‰, 2SD, n = 7) than weathering-dominated ones (δ26Mg = -0.10 ± 0.12‰, 2SD, n = 25). Calculated Mg isotopic compositions of fresh mantle peridotites vary from -0.29 to -0.13‰, beyond the previously reported range of the subcontinental lithospheric mantle (-0.25 ± 0.04‰) and the analytical uncertainty (±0.07‰, 2SD). Our study therefore indicates that the oceanic mantle may have similar but slightly heterogeneous Mg isotopic compositions to that of subcontinental lithospheric mantle. Secondary serpentinization does not fractionate Mg isotopes of abyssal peridotites, whereas low-T weathering and formation of clay can result in the enrichment of heavy Mg isotopes in abyssal peridotites. This study also demonstrates that fluid-rock interaction does not necessarily produce rocks with intermediate Mg isotopic compositions. Magnesium isotopes of the rocks thereafter are dependent on the secondary minerals formed. We also conclude that the release of light Mg isotopes into the ocean during alteration of abyssal

  2. Is my C isotope excursion global, local, or both? Insights from the Mg and Ca isotopic composition of primary, diagenetic, and authigenic carbonates

    Higgins, J. A.; Blättler, C. L.; Husson, J. M.


    The C isotopic composition of ancient limestones and dolomites is a widely used proxy for the global geochemical cycles of carbon and oxygen in the ocean-atmosphere system and a critical tool for chemostratigraphy in Precambrian rocks. Although relatively robust to diagenesis, the C isotopic composition of bulk carbonates can be reset when conditions favor high water-to-rock ratios or fluids with high C concentrations and distinct isotopic compositions. Authigenic carbonates and different pools of primary carbonate (e.g. calcite vs. aragonite) may also bias the C isotopic composition of bulk carbonates if they are both abundant and isotopically distinct. New approaches to quantifying contributions from diagenesis, authigenesis, and mixing of primary carbonates to the C isotopic composition of bulk sedimentary carbonates are needed. Here we present preliminary Mg and Ca isotope data sets of primary, diagenetic, and authigenic carbonates, both modern and ancient. We show that recrystallization, dolomitization, and authigenesis produce Mg and Ca isotope fingerprints that may be used to identify and characterize these processes in ancient carbonate sediments.

  3. High-precision Mg isotope measurements of terrestrial and extraterrestrial material by HR-MC-ICPMS—implications for the relative and absolute Mg isotope composition of the bulk silicate Earth

    Bizzarro, Martin; Paton, Chad; Larsen, Kirsten Kolbjørn


    shergottite and sea water samples. Repeated analyses of terrestrial and extraterrestrial samples demonstrate that it is possible to routinely measure the relative Mg-isotope composition of silicate materials with an external reproducibility of 2.5 and 20 ppm for the m26Mg* and m25Mg values, respectively (m......-isotope composition for Earth’s mantle – and hence that of the bulk silicate Earth – to be 25Mg/24Mg 1/4 0.126896 ¿ 0.000025 and 26Mg/24Mg 1/4 0.139652 ¿ 0.000033. Given the restricted range of m25Mg obtained for bulk planetary material by the sample-standard bracketing technique and the excellent agreement between...

  4. The effect of permafrost, vegetation, and lithology on Mg and Si isotope composition of the Yenisey River and its tributaries at the end of the spring flood

    Mavromatis, Vasileios; Rinder, Thomas; Prokushkin, Anatoly S.; Pokrovsky, Oleg S.; Korets, Mikhail A.; Chmeleff, Jérôme; Oelkers, Eric H.


    This work focuses on the behavior of the stable Mg and Si isotope compositions of the largest Arctic river, the Yenisey River and 28 of its major and minor tributaries during the spring flood period. Samples were collected along a 1500 km latitudinal profile covering a wide range of permafrost, lithology, and vegetation. Despite significant contrasts in the main physico-geographical, climate, and lithological parameters of the watersheds, the isotope composition of both dissolved Mg and Si was found to be only weakly influenced by the degree of the permafrost coverage, type of vegetation (forest vs. tundra), and lithology (granites, basalts, carbonates or terrigenous rocks). This observation is generally consistent with the lack of chemical uptake of Mg and Si by soil mineral formation and vegetation during the early spring. The radiogenic Sr isotope composition of the Yenisey and its tributaries varied within a narrow range (0.708 ⩽ 87Sr/86Sr ⩽ 0.711) reflecting the dominance of Phanerozoic rock weathering and/or atmospheric deposition on these compositions. The Mg and Si isotopic compositions of riverine samples reflect two main processes with distinct isotopic signatures. First, isotopically heavier Mg (δ26Mg = -1.0 ± 0.2‰) and isotopically lighter Si (δ30Si = 1.0 ± 0.25‰) are added to the waters by river suspended matter dissolution and leaching from vegetation biomass/topsoil litter. Second, isotopically lighter Mg (δ26Mg = -1.5 to -1.75‰) and isotopically heavier Si (δ30Si = 1.75-2.0‰) are delivered to the Yenisey's tributaries from deep underground water feeding the rivers via taliks. This lighter Mg and heavier Si isotopic composition is interpreted to originate from Precambrian dolomite dissolution and aluminosilicate dissolution coupled with authigenic mineral precipitation, respectively, in deep underground water reservoirs. Taking account of the isotopic composition evolution over the course of the year established earlier on mono

  5. Resetting of Mg isotopes between calcite and dolomite during burial metamorphism: Outlook of Mg isotopes as geothermometer and seawater proxy

    Hu, Zhongya; Hu, Wenxuan; Wang, Xiaomin; Lu, Yizhou; Wang, Lichao; Liao, Zhiwei; Li, Weiqiang


    Magnesium isotopes are an emerging tool to study the geological processes recorded in carbonates. Calcite, due to its ubiquitous occurrence and the large Mg isotope fractionation associated with the mineral, has attracted great interests in applications of Mg isotope geochemistry. However, the fidelity of Mg isotopes in geological records of carbonate minerals (e.g., calcite and dolomite) against burial metamorphism remains poorly constrained. Here we report our investigation on the Mg isotope systematics of a dolomitized Middle Triassic Geshan carbonate section in eastern China. Magnesium isotope analysis was complemented by analyses of Sr-C-O isotopic compositions, major and trace element concentrations, and petrographic and mineralogical features. Multiple lines of evidence consistently indicated that post-depositional diagenesis of carbonate minerals occurred to the carbonate rocks. Magnesium isotope compositions of the carbonate rocks closely follow a mixing trend between a high δ26Mg dolomite end member and a low δ26Mg calcite end member, irrespective of sample positions in the section and calcite/dolomite ratio in the samples. By fitting the measured Mg isotope data using a two-end member mixing model, an inter-mineral Δ26Mgdolomite-calcite fractionation of 0.72‰ was obtained. Based on the experimentally derived Mg isotope fractionation factors for dolomite and calcite, a temperature of 150-190 °C was calculated to correspond to the 0.72‰ Δ26Mgdolomite-calcite fractionation. Such temperature range matches with the burial-thermal history of the local strata, making a successful case of Mg isotope geothermometry. Our results indicate that both calcite and dolomite had been re-equilibrated during burial metamorphism, and based on isotope mass balance of Mg, the system was buffered by dolomite in the section. Therefore, burial metamorphism may reset Mg isotope signature of calcite, and Mg isotope compositions in calcite should be dealt with caution in

  6. Mg isotope fractionation during microbe-mineral interactions

    Kim, Insu; Ryu, Jong-sik; Lee, Kwang-sik; Lee, Dongho


    Magnesium is involved in various biogeochemical processes important to the global climate change over geological time-scale. Mg isotopes allow us to directly trace the Mg cycle in the Earth's surface but the factors controlling Mg isotopic compositions have not fully understood yet. Here, we conducted a batch experiment using two bacterial species (Shewanella putrefaciens and Burkholderia fungorum) and three major Mg-bearing minerals (biotite, dolomite and hornblende). All elemental concentrations increased by 336 h and then reached to steady-state values, of which Mg concentrations varied depending on minerals and bacterial species. This result indicates that the mineral dissolution is affect by the presence of microbes, which either provide organic acids or attach onto mineral surface. The Mg isotopic compositions of initial minerals biotite, dolomite and hornblende are -0.35o of biotite, -0.99o of dolomite, and -0.24o of hornblende, in δ26Mg. Similarly, δ26Mg values increased by 336 h and reached to steady-state values, which also varied with minerals and microbes. During dissolution of three minerals, the light isotope of Mg is preferentially incorporated into the dissolved phases and then the dissolved δ26Mg values become consistent with those of minerals with the time.

  7. Preparation of Metallic Isotope 26Mg

    WuXiaolei; ZhangFuming; GanZaiguo; GuoJunsheng; QinZhi


    Some special isotope material is usually used in nuclear experiments. It can be served as ion beam or target. When new superheavy nuclide 265Bh (Z=107) is synthesized, a reaction of 243Am target with 26Mg ion beamis selected to produce new isotope 265Bh. The preparation and production of this rare and extremely expensive isotope 26 Mg used for ion beam substance will be a key problem in synthesizing experiment of 265Bh. Theavailable chemical form of isotope 26Mg in commercial product usually is oxide or other compound, which are not required in our experiment. They need to be transformed to metal form as a proper working substance in ion source.

  8. Atomic Weights and Isotopic Compositions

    SRD 144 Atomic Weights and Isotopic Compositions (Web, free access)   The atomic weights are available for elements 1 through 111, and isotopic compositions or abundances are given when appropriate.

  9. Mg Isotope Fractionation Between E. coli and Growth Medium

    Basset, R.; Lemelle, L.; Albalat, E.; Telouk, P.; Albarède, F.


    Magnesium is a major element in both microbial cells and minerals, immune to redox conditions and atmospheric interactions. In organic cells, Mg can be associated with membranes, with cytoplasm (either as an isolated ion or bound to proteins). Its isotope composition can be used to constrain the contribution of organic material to carbonate fluxes and the overall cycle of this element in the exogenous environment [1, 2]. Cells of DH5α E. coli strain were grown in Luria Broth medium and the Mg isotope fractionation between the cells and their growth medium determined after calcination in Pt crucibles, chemical purification by cation exchange chemistry in HCl medium [3] and isotopic analysis on a Nu HR MC-ICPMS. The yield is better than 96%. The Mg contents of 2.19 ± 0.08 mg per g DW in cells and 0.117 ± 0.001 mg per g DW in Luria Broth medium are consistent with literature data [4]. About half of the Mg initially present in the LB medium is taken up by the growing cells. At high cellular concentrations (OD600 = 3.5), cells are enriched in 26Mg by 0.97 ± 0.14 ‰ with respect to the culture medium. Although E. coli may not be a good proxy for oceanic plankton, such a substantial fractionation of Mg isotopes suggests that incorporation of even a few percent organic matter into oceanic oozes depletes oceanic Mg in its heavy isotopes and therefore accounts for the isotopic difference between riverine and marine Mg. [1] Drever, The Sea 5 (1974) 337-357 [2] Tipper et al., EPSL 250 (2006) 241-253 [3] Chang et al., JAAS 18 (2003) 296-301 [4] Outten et al., Science 292 (2001), 2488-2492

  10. High-precision Mg isotopic systematics of bulk chondrites

    Schiller, Martin; Handler, Monica R.; Baker, Joel A.


    Variations of the mass-independent abundance of 26Mg ( δ26Mg*) and stable Mg ( δ25Mg) isotope composition of chondrites are important because they constrain the homogeneity of 26Al and Mg isotopes in the proto-planetary disc and the validity of the short-lived 26Al-to- 26Mg chronometer applied to meteorites. We present high-precision Mg isotope data and Al/Mg ratios of chondrites representing nearly all major chondrite classes, including a step-leaching experiment on the CM2 chondrite Murchison. δ26Mg* variations in leachates of Murchison representing acid soluble material are ≤ 30 times smaller than reported for neutron-rich isotopes of Ti and Cr and do not reveal resolvable deficits in δ26Mg* (-0.002 to + 0.118‰). Very small variations in δ26Mg* anomalies in bulk chondrites (-0.006 to + 0.019‰) correlate with increasing 27Al/ 24Mg ratios and δ50Ti, reflecting the variable presence of calcium-aluminium-rich inclusions (CAIs) in some types of carbonaceous chondrites. Similarly, release of radiogenic 26Mg produced by 26Al decay from CAI material in the step-leaching of Murchison best explains the high δ26Mg* observed in the last, aggressive, leaching steps of this experiment. Overall, the observed variations in δ26Mg* are small and potential differences beyond that which result from the presence of CAI-like material cannot be detected within the analytical uncertainties of this study (± 0.004‰). The results do not allow radical heterogeneity of 26Al (≥±30%) or measurable Mg nucleosynthetic heterogeneity (≥±0.005‰) to have existed on a planetesimal scale in the proto-planetary disc. Combined with published δ26Mg* data for CAIs, the bulk chondrite data yield a precise initial ( 26Al/ 27Al) 0 = (5.21 ± 0.06) × 10 -5 and δ26Mg* = -0.0340 ± 0.0016‰ for the Solar System. However, it is not possible with the currently available data to determine with certainty whether CAIs and the material from which planetesimals accreted including

  11. Resolving the stellar sources of isotopically rare presolar silicate grains through Mg and Fe isotopic analyses

    Nguyen, Ann N.; Messenger, Scott, E-mail: [Robert M. Walker Laboratory for Space Science, Astromaterials Research and Exploration Science Directorate, NASA Johnson Space Center, Houston, TX 77058 (United States)


    We conducted multi-element isotopic analyses of 11 presolar silicate grains from the Acfer 094 meteorite having unusual O isotopic compositions. Eight grains are {sup 18}O-rich, one is {sup 16}O-rich, and two are extremely {sup 17}O-rich. We constrained the grains' stellar sources by measuring their Si and Mg isotopic ratios, and also the {sup 54}Fe/{sup 56}Fe and {sup 57}Fe/{sup 56}Fe ratios for five grains. The Mg and Fe isotopic measurements were conducted after surrounding matrix grains were removed for more accurate ratios. Most of the {sup 18}O-rich silicates had anomalous Mg isotopic ratios, and their combined isotopic constraints are consistent with origins in low-mass Type II supernovae (SNe II) rather than high-metallicity stars. The isotopic ratios of the {sup 16}O-rich silicate are also consistent with an SN origin. Mixing small amounts of interior stellar material with the stellar envelope replicated all measured isotopic ratios except for {sup 29}Si/{sup 28}Si and {sup 54}Fe/{sup 56}Fe in some grains. The {sup 29}Si/{sup 28}Si ratios of all SN-derived grains are matched by doubling the {sup 29}Si yield in the Ne- and Si-burning zones. The {sup 54}Fe/{sup 56}Fe ratios of the grains imply elemental fractionation in the Si/S zone, or introduction of isotopically solar Fe by secondary processing. The two highly {sup 17}O-rich silicates exhibited significant {sup 25}Mg and/or {sup 26}Mg enrichments and their isotopic ratios are best explained by strong dilution of 1.15 M {sub ☉} CO nova matter. We estimate that ∼12% and 1% of presolar silicates have SN and nova origins, respectively, similar to presolar SiC and oxides. This implies that asymptotic giant branch stars are the dominant dust producers in the galaxy.

  12. Magnesium Isotopic Composition of Subducting Marine Sediments

    Hu, Y.; Teng, F. Z.; Plank, T. A.; Huang, K. J.


    Subducted marine sediments have recently been called upon to explain the heterogeneous Mg isotopic composition (δ26Mg, ‰) found in mantle wehrlites (-0.39 to +0.09 [1]) in the context of a homogeneous mantle (-0.25 ± 0.07 [2]). However, no systematic measurements of δ26Mg on marine sediments are currently available to provide direct support to this model. To characterize the Mg inputs to global subduction zones, we measured δ26Mg data for a total of 90 marine sediments collected from 12 drill sites outboard of the world's major subduction zones. These sediments span a 1.73‰ range in δ26Mg. The detritus-dominated sediments have δ26Mg (-0.59 to +0.53) comparable to those of weathered materials on continents (e.g. -0.52 to +0.92 [3]), while the calcareous oozes yield δ26Mg (as light as -1.20) more similar to the seawater value (-0.83 [4]). The negative correlation between δ26Mg and CaO/Al2O3 in these sediments indicates the primary control of mineralogy over the Mg isotopic distribution among different sediment types, as carbonates are enriched in light Mg isotopes (-5.10 to -0.40 [5]) whereas clay-rich weathering residues generally have heavier δ26Mg (e.g. up to +0.65 in saprolite [6]). In addition, chemical weathering and grain-size sorting drive sediments to a heavier δ26Mg, as indicated by the broad positive trends between δ26Mg with CIA (Chemical Index of Alteration [7]) and Al2O3/SiO2, respectively. Collectively, the arc systems sampled in this study represent ~30% of global arc length and the extrapolated global Mg flux of subducting marine sediments accounts for ~9% of the yearly Mg riverine input with a flux-weighted average δ26Mg at -0.26. Subduction of these heterogeneous sediments may not cause significant mantle heterogeneity on a global scale, but the highly variable Mg fluxes and δ26Mg of sediments delivered to different trenches are capable of producing local mantle variations. Volcanic rocks sourced from these mantle domains are thus

  13. Boron isotope effect in superconducting MgB2.

    Bud'ko, S L; Lapertot, G; Petrovic, C; Cunningham, C E; Anderson, N; Canfield, P C


    We report the preparation method of and boron isotope effect for MgB2, a new binary intermetallic superconductor with a remarkably high superconducting transition temperature T(c)(10B) = 40.2 K. Measurements of both temperature dependent magnetization and specific heat reveal a 1.0 K shift in T(c) between Mg11B2 and Mg10B2. Whereas such a high transition temperature might imply exotic coupling mechanisms, the boron isotope effect in MgB2 is consistent with the material being a phonon-mediated BCS superconductor.

  14. Mg Isotope Evolution During Water-Rock Interaction in a Carbonate Aquifer

    Zhang, Z.; Jacobson, A. D.; Lundstrom, C. C.; Huang, F.


    To better understand how Mg isotopes behave during weathering and aqueous transport, we used a Nu Plasma MC-ICP-MS to measure δ26Mg values (relative to DSM-3) in water samples along a 236 km flow path in the Madison aquifer of South Dakota, a confined carbonate aquifer recharging in the igneous Black Hills. We also analyzed local granite and dolomite samples to characterize the Mg isotope composition of source rocks constituting the recharge zone and aquifer, respectively. Repeated analyses of Mg standard solutions yielded external precisions (2σ) better than 0.1 permil for δ26Mg(CAM-1, - 2.584±0.071, n=13; UIMg-1, -2.217±0.087, n=9.). The Madison aquifer provides a unique opportunity to quantify Mg isotope effects during water-rock interaction because (1) fluids and rock have chemically equilibrated over a much longer timescale (up to ~15 kyr) than can be simulated in laboratory experiments and (2) previous studies have determined the rates and mass-balances of de- dolomitization and other geochemical reactions controlling solute evolution along the flow path. Reactions important for changing the concentration and isotope composition of Mg include dolomite dissolution, Mg-for- Na ion exchange, calcite precipitation, and isotope exchange. δ26Mg values within the recharge region (0-17 km along flow path) vary between -1.08 and -1.63 permil, and then remain essentially constant at -1.408±0.010 permil(1σ, 5 samples) from 17 to 189 km. A final sample at 236 km shows an increase to -1.09 permil. Either mixing between different recharge waters or rapid isotope exchange between infiltrating waters and dolomite could control δ26Mg variability between 0 and 17 km. Likewise, reactive transport modeling suggests that preferential uptake of 24Mg during Mg-for-Na ion exchange might cause an increase in δ26Mg between 189 and 236 km. However, unchanging δ26Mg values observed throughout most of the aquifer clearly demonstrate that Mg isotopes are not fractionated during

  15. Zinc isotopic compositions of breast cancer tissue.

    Larner, Fiona; Woodley, Laura N; Shousha, Sami; Moyes, Ashley; Humphreys-Williams, Emma; Strekopytov, Stanislav; Halliday, Alex N; Rehkämper, Mark; Coombes, R Charles


    An early diagnostic biomarker for breast cancer is essential to improve outcome. High precision isotopic analysis, originating in Earth sciences, can detect very small shifts in metal pathways. For the first time, the natural intrinsic Zn isotopic compositions of various tissues in breast cancer patients and controls were determined. Breast cancer tumours were found to have a significantly lighter Zn isotopic composition than the blood, serum and healthy breast tissue in both groups. The Zn isotopic lightness in tumours suggests that sulphur rich metallothionein dominates the isotopic selectivity of a breast tissue cell, rather than Zn-specific proteins. This reveals a possible mechanism of Zn delivery to Zn-sequestering vesicles by metallothionein, and is supported by a similar signature observed in the copper isotopic compositions of one breast cancer patient. This change in intrinsic isotopic compositions due to cancer has the potential to provide a novel early biomarker for breast cancer.

  16. Modern and Cenozoic records of seawater magnesium from foraminiferal Mg isotopes

    Pogge von Strandmann, P. A. E.; Forshaw, J.; Schmidt, D. N.


    Magnesium is an element critically involved in the carbon cycle, because weathering of Ca-Mg silicates removes atmospheric CO2 into rivers, and formation of Ca-Mg carbonates in the oceans removes carbon from the ocean-atmosphere system. Hence the Mg cycle holds the potential to provide valuable insights into Cenozoic climate-system history, and the shift during this time from a greenhouse to icehouse state. We present Mg isotope ratios for the past 40 Myr using planktic foraminifers as an archive. Modern foraminifera, which discriminate against elemental and isotopically heavy Mg during calcification, show no correlation between the Mg isotope composition (δ26Mg, relative to DSM-3) and temperature, Mg / Ca or other parameters such as carbonate saturation (ΔCO3). However, inter-species isotopic differences imply that only well-calibrated single species should be used for reconstruction of past seawater. Seawater δ26Mg inferred from the foraminiferal record decreased from ~0‰ at 15 Ma, to -0.83‰ at the present day, which coincides with increases in seawater lithium and oxygen isotope ratios. It strongly suggests that neither Mg concentrations nor isotope ratios are at steady state in modern oceans, given its ~10 Myr residence time. From these data, we have developed a dynamic box model to understand and constrain changes in Mg sources to the oceans (rivers) and Mg sinks (dolomitisation and hydrothermal alteration). Our estimates of seawater Mg concentrations through time are similar to those independently determined by pore waters and fluid inclusions. Modelling suggests that dolomite formation and the riverine Mg flux are the primary controls on the δ26Mg of seawater, while hydrothermal Mg removal and the δ26Mg of rivers are more minor controls. Using Mg riverine flux and isotope ratios inferred from the 87Sr / 86Sr record, the modelled Mg removal by dolomite formation shows minima in the Oligocene and at the present day (with decreasing trends from 15 Ma

  17. Modern and Cenozoic records of magnesium behaviour from foraminiferal Mg isotopes

    P. A. E. Pogge von Strandmann


    Full Text Available Magnesium is an element critically involved in the carbon cycle, because weathering of Ca–Mg silicates removes atmospheric CO2 into rivers, and formation of Ca–Mg carbonates in the oceans removes carbon from the ocean–atmosphere system. Hence the Mg cycle holds the potential to provide valuable insights into Cenozoic climate-system history, and the shift during this time from a greenhouse to icehouse state. We present Mg isotope ratios for the past 40 Myr using planktic foraminifers as an archive. Modern foraminifera, which discriminate against elemental and isotopically heavy Mg during calcification, show no correlation between the Mg isotope composition (δ26Mg and temperature, Mg / Ca or other parameters such as carbonate saturation (Δ CO3. However, inter-species isotopic differences imply that only well-calibrated single species should be used for reconstruction of past seawater. Seawater δ26Mg inferred from the foraminiferal record decreased from ~ 0‰ at 15 Ma, to −0.83‰ at the present day, which coincides with increases in seawater lithium and oxygen isotope ratios. It strongly suggests that neither Mg concentrations nor isotope ratios are at steady-state in modern oceans, given its ~ 10 Myr residence time. From these data, we have developed a dynamic box model to understand and constrain changes in Mg sources to the oceans (rivers and Mg sinks (dolomitisation and hydrothermal alteration. Our estimates of seawater Mg concentrations through time are similar to those independently determined by pore waters and fluid inclusions. Modelling suggests that dolomite formation and the riverine Mg flux are the primary controls on the δ26Mg of seawater, while hydrothermal Mg removal and the δ26Mg of rivers are more minor controls. Using riverine flux and isotope ratios inferred from the 87Sr / 86Sr record, the modelled Mg removal by dolomite formation shows minima in the Oligocene and at the present day (with decreasing trends from 15

  18. Magnesium stable isotope composition of Earth's upper mantle

    Handler, Monica R.; Baker, Joel A.; Schiller, Martin; Bennett, Vickie C.; Yaxley, Gregory M.


    The mantle is Earth's largest reservoir of Mg containing > 99% of Earth's Mg inventory. However, no consensus exists on the stable Mg isotope composition of the Earth's mantle or how variable it is and, in particular, whether the mantle has the same stable Mg isotope composition as chondrite meteorites. We have determined the Mg isotope composition of olivine from 22 mantle peridotites from eastern Australia, west Antarctica, Jordan, Yemen and southwest Greenland by pseudo-high-resolution MC-ICP-MS on Mg purified to > 99%. The samples include fertile lherzolites, depleted harzburgites and dunites, cryptically metasomatised ('dry') peridotites and modally metasomatised apatite ± amphibole-bearing harzburgites and wehrlites. Olivine from these samples of early Archaean through to Permian lithospheric mantle have δ25Mg DSM-3 = - 0.22 to - 0.08‰. These data indicate the bulk upper mantle as represented by peridotite olivine is homogeneous within current analytical uncertainties (external reproducibility ≤ ± 0.07‰ [2 sd]). We find no systematic δ25Mg variations with location, lithospheric age, peridotite fertility, or degree or nature of mantle metasomatism. Although pyroxene may have slightly heavier δ25Mg than coexisting olivine, any fractionation between mantle pyroxene and olivine is also within current analytical uncertainties with a mean Δ25Mg pyr-ol = +0.06 ± 0.10‰ (2 sd; n = 5). Our average mantle olivine δ25Mg DSM-3 = - 0.14 ± 0.07‰ and δ26Mg DSM-3 = - 0.27 ± 0.14‰ (2 sd) are indistinguishable from the average of data previously reported for terrestrial basalts, confirming that basalts have stable Mg isotope compositions representative of the mantle. Olivine from five pallasite meteorites have δ25Mg DSM-3 = - 0.16 to - 0.11‰ that are identical to terrestrial olivine and indistinguishable from the average δ25Mg previously reported for chondrites. These data provide no evidence for measurable heterogeneity in the stable Mg isotope

  19. Ground-state properties of neutron-rich Mg isotopes

    Watanabe, Shin; Shimada, Mitsuhiro; Tagami, Shingo; Kimura, Masaaki; Takechi, Maya; Fukuda, Mitsunori; Nishimura, Daiki; Suzuki, Takeshi; Matsumoto, Takuma; Shimizu, Yoshifumi R; Yahiro, Masanobu


    We analyze recently-measured total reaction cross sections for 24-38Mg isotopes incident on 12C targets at 240 MeV/nucleon by using the folding model and antisymmetrized molecular dynamics(AMD). The folding model well reproduces the measured reaction cross sections, when the projectile densities are evaluated by the deformed Woods-Saxon (def-WS) model with AMD deformation. Matter radii of 24-38Mg are then deduced from the measured reaction cross sections by ?ne-tuning the parameters of the def-WS model. The deduced matter radii are largely enhanced by nuclear deformation. Fully-microscopic AMD calculations with no free parameter well reproduce the deduced matter radii for 24-36Mg, but still considerably underestimate them for 37,38Mg. The large matter radii suggest that 37,38Mg are candidates for deformed halo nucleus. AMD also reproduces other existing measured ground-state properties (spin-parity, total binding energy, and one-neutron separation energy) of Mg isotopes. Neutron-number (N) dependence of defor...

  20. Mg isotopes in biocarbonates: new insight into vital effects associated to echinoderms and bivalves calcification

    Planchon, F.; Hermans, J.; Borremans, C.; Dubois, P.; Poulain, C.; Paulet, Y.; Andre, L.


    Mg isotopes can be helpful tracers to reveal the fundamental pathways of Mg incorporation during biomineralisation. We report in this study a detailed characterisation of the Mg isotopic signatures of different biominerals: high magnesium calcitic skeletons of selected echinoderms (sea urchins and starfish) and low magnesium aragonitic shells of a bivalve species (clam). State of the art analytical procedures were applied including sample purification step followed by high precision measurements using MC-ICP-MS (Nu instrument) in dry plasma conditions. 26Mg/24Mg and 25Mg/24Mg are expressed as per mil deviations from the DSM3 (Dead Sea Metal 3) reference standard in delta notation (d26Mg and d25Mg). For echinoderms, we considered: (a) adult specimens of six starfish species (Asteria r., Marthasterias g., Anseropoda p., Asterina g., Echinaster s. and Henricia o.), sampled in Brittany (France); (b) a sea urchin species (Paracentrotus lividus) with field samples (Mediterranean Sea, Marseille, France) and culture specimen under T and S controlled conditions. In vivo endoskeletons display negative, but different d26Mg values of -3.06 for starfish (with uniform interspecies signatures) and -2.65 for sea urchin. Relative to seawater signature (-0.82), all echinoderms favour the incorporation of light isotopes during biocalcification. The d26Mg depletion is lower than theoretically expected from a inorganic calcite precipitation from seawater (at -3.5). These differences suggest that on its route from seawater to the shell, Mg isotopes are partly biologically fractionationated through "vital effects" leaving heavier Mg isotopic signatures. Taken into account that calcification in echinoderms is an intra- cellular process involving transient amorphous calcium carbonate (ACC) phase, the observed bio-fractionation factors can be related to: (1) changes in the isotopic composition of the precipitating intracellular fluids due to active pumping in and out of the cell; (2) a

  1. Effect of organic ligands on Mg partitioning and Mg isotope fractionation during low-temperature precipitation of calcite

    Mavromatis, Vasileios; Immenhauser, Adrian; Buhl, Dieter; Purgstaller, Bettina; Baldermann, Andre; Dietzel, Martin


    characterized by low dissolved organic carbon levels, the presence of organic ligands is rather unlikely to significantly affect the Mg isotope composition of precipitated calcite.

  2. Constraining dolomitization by Mg isotopes: A case study from partially dolomitized limestones of the middle Cambrian Xuzhuang Formation, North China

    Peng, Yang; Shen, Bing; Lang, Xian-Guo; Huang, Kang-Jun; Chen, Ji-Tao; Yan, Zhen; Tang, Wen-bo; Ke, Shan; Ma, Hao-Ran; Li, Fang-Bing


    The "dolomite problem" refers to the rare dolomite formation in modern oceans that is in sharp contrast to the widespread ancient dolostone in rock record, as well as failure of laboratory inorganic dolomite precipitation at near Earth-surface temperature. Novel Mg isotope systematics provides a promising tool in resolving the "dolomite problem". Here, we develop a protocol to place constraints on the dolomitization process by using Mg isotopes. In this study, we measured Mg isotopic compositions (δ26Mg) of two batches of partially dolomitized limestone samples from the middle Cambrian Xuzhuang Formation in North China. δ26Mg varies between -0.55‰ and -3.18‰, and shows a negative linear correlation with 1>/[Mg>], suggesting that δ26Mg can be described by a binary mixing between the calcite and dolomite components. Mg isotopic composition of the dolomite component (δ26Mgdol) for the lower sample set that is collected from a 4 m stratigraphic interval containing three high-frequency ribbon rock-packstone cycles is -1.6‰, while δ26Mgdol for the upper sample set (from a thick sequence of ribbon rock) is significantly higher (-0.3‰). However, neither mineralogical and elemental compositions, carbon and oxygen isotopes, nor crystal morphologies of dolomite provides diagnostic criteria to differentiate these two batches of samples. δ26Mgdol of the Xuzhuang limestone is simulated by the Advective Flow (AF) and the Diffusion-Advection-Reaction (DAR) models. The AF model assumes that Mg is transported by advective fluid flows, while the DAR model simulates a contemporaneous seawater dolomitization process, in which Mg is delivered by diffusion. The AF modeling result indicates that δ26Mg of the dolomitization fluid is +0.4‰ and +1.7‰ for the lower and upper sample sets, respectively. These values are significantly higher than modern and Cenozoic seawater Mg isotopic composition, suggesting that the dolomitization fluid is not contemporaneous seawater. The

  3. Calcium isotopic compositions of mid-ocean ridge basalts

    Zhu, H.; Zhang, Z.; Sun, W.; Wang, G. Q.


    Previous studies have demonstrated that Earth's mantle has heterogeneous calcium isotopic compositions. But the reason why mantle has its heterogeneity remains uncertain. In general, δ44/40Ca values of mantle xenolith samples have a variation of >0.45‰. While ultramafic rocks, especially dunites, have higher δ44/40Ca values than volcanic rocks, and there is a positive correlation between δ44/40Ca and Ca/Mg. These phenomena imply that the heterogeneity of Ca isotopic compositions of mantle xenolith samples might result from different degrees of melt extraction, as indicated by large Ca isotopic fractionation between co-existing clinopyroxene and orthopyroxene. However, because ancient marine carbonate has its own unique calcium isotopic characteristics, recycling of even a small amount of ancient marine carbonates into the mantle could also cause the heterogeneity of Ca isotopes in Earth's mantle. This could be the reason why oceanic island basalts (OIB) have lighter Ca isotopic compositions than the mantle xenolith. Thus, the lighter Ca isotopic compositions in the mantle source cannot only be ascribed to magmatic processes. Therefore, it is more important to know calcium isotopic characteristics during partial melting and oceanic crust contamination.Mid-ocean ridge basalts (MORB) are formed from the partial melts of the upper mantle and are rarely affected by crustal contamination. Different types of MORB, including D-MORB, N-MORB and E-MORB, have experienced different degrees of partial melting and contamination of enriched end-members. Here we report calcium isotopic characteristic of different types of MORB, we believe it will be very helpful to understand the behaviors of Ca isotopes during partial melting and it is possible to provide further information to discover the reason why calcium isotopic compositions is heterogeneous in Earth's mantle. This work was supported by Natural Science Foundation of China (No. 41373007, No. 41490632 and No. 91328204

  4. The effects of diagenesis and dolomitization on Ca and Mg isotopes in marine platform carbonates: Implications for the geochemical cycles of Ca and Mg

    Fantle, Matthew S.; Higgins, John


    The Ca, Mg, O, and C isotopic and trace elemental compositions of marine limestones and dolostones from ODP Site 1196A, which range in depth (∼58 to 627 mbsf) and in depositional age (∼5 and 23 Ma), are presented. The objectives of the study are to explore the potential for non-traditional isotope systems to fingerprint diagenesis, to quantify the extent to which geochemical proxies are altered during diagenesis, and to investigate the importance of diagenesis within the global Ca and Mg geochemical cycles. The data suggest that Ca, which has a relatively high solid to fluid mass ratio, can be isotopically altered during diagenesis. In addition, the alteration of Ca correlates with the alteration of Mg in such a way that both can serve as useful tools for deciphering diagenesis in ancient rocks. Bulk carbonate δ44Ca values vary between 0.60 and 1.31‰ (SRM-915a scale); the average limestone δ44Ca is 0.97 ± 0.24‰ (1SD), identical within error to the average dolostone (1.03 ± 0.15 1SD ‰). Magnesium isotopic compositions (δ26Mg, DSM-3 scale) range between -2.59‰ and -3.91‰, and limestones (-3.60 ± 0.25‰) and dolostones (-2.68 ± 0.07‰) are isotopically distinct. Carbon isotopic compositions (δ13C, PDB scale) vary between 0.86‰ and 2.47‰, with average limestone (1.96 ± 0.31‰) marginally offset relative to average dolostone (1.68 ± 0.57‰). The oxygen isotopic compositions (δ18O, PDB scale) of limestones (-1.22 ± 0.94‰) are substantially lower than the dolostones measured (2.72 ± 1.07‰). The isotopic data from 1196A suggest distinct and coherent trends in isotopic and elemental compositions that are interpreted in terms of diagenetic trajectories. Numerical modeling supports the contention that such trends can be interpreted as diagenetic, and suggests that the appropriate distribution coefficient (KMg) associated with limestone diagenesis is ∼1 to 5 × 10-3, distinctly lower than those values (>0.015) reported in laboratory

  5. Nickel isotopic composition of the mantle

    Gall, Louise; Williams, Helen M.; Halliday, Alex N.; Kerr, Andrew C.


    This paper presents a detailed high-precision study of Ni isotope variations in mantle peridotites and their minerals, komatiites as well as chondritic and iron meteorites. Ultramafic rocks display a relatively large range in δ60 Ni (permil deviation in 60 Ni /58 Ni relative to the NIST SRM 986 Ni isotope standard) for this environment, from 0.15 ± 0.07‰ to 0.36 ± 0.08‰, with olivine-rich rocks such as dunite and olivine cumulates showing lighter isotope compositions than komatiite, lherzolite and pyroxenite samples. The data for the mineral separates shed light on the origin of these variations. Olivine and orthopyroxene display light δ60 Ni whereas clinopyroxene and garnet are isotopically heavy. This indicates that peridotite whole-rock δ60 Ni may be controlled by variations in modal mineralogy, with the prediction that mantle melts will display variable δ60 Ni values due to variations in residual mantle and cumulate mineralogy. Based on fertile peridotite xenoliths and Phanerozoic komatiite samples it is concluded that the upper mantle has a relatively homogeneous Ni isotope composition, with the best estimate of δ60Nimantle being 0.23 ± 0.06‰ (2 s.d.). Given that >99% of the Ni in the silicate Earth is located in the mantle, this also defines the Ni isotope composition of the Bulk Silicate Earth (BSE). This value is nearly identical to the results obtained for a suite of chondrites and iron meteorites (mean δ60 Ni 0.26 ± 0.12‰ and 0.29 ± 0.10‰, respectively) showing that the BSE is chondritic with respect to its Ni isotope composition, with little to no Ni mass-dependent isotope fractionation resulting from core formation.

  6. A Review of Mg Isotope Analytical Methods by MC-ICP-MS

    Yajun An; Fang Huang


    Application of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has led to big breakthrough of analytical methods for metal stable isotopes, resulting in rapid progresses in non-traditional stable isotope geochemistry. As a new geological tracer, Mg isotopes have been widely applied in studies of almost all important disciplines of geochemistry. High precision Mg isotope data measured by MC-ICP-MS are now available with precision about 0.05‰ amu-1 (2SD) or better. Because mass bias caused by chemical procedure and instrument can easily cause significant analytical error, it is still a challenge to obtain accurate Mg isotope data for natural samples. In this paper, we systematically review the development of analytical technique of Mg isotopes, with a detailed description of a series of important techniques used in the measurement process, including calibration of instrumental mass-bias, chemical purification process, matrix effect, and pitfalls for high precision isotope analyses. We compare standard data from different labs and establish a guideline for Mg iso-tope analysis procedure. Additionally, we briefly discuss the behaviors of Mg isotopes during geological processes including equilibrium and kinetic Mg isotope fractionations, such as magma differentiation, chemical and thermal diffusion, and continental weathering. Finally, we propose some future prospects for Mg isotope geochemistry in both high and low temperature geological processes.

  7. Ca and Mg isotope constraints on the origin of Earth's deepest δ13 C excursion

    Husson, Jon M.; Higgins, John A.; Maloof, Adam C.; Schoene, Blair


    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

  8. The influence of critical zone processes on the Mg isotope budget in a tropical, highly weathered andesitic catchment

    Chapela Lara, María; Buss, Heather L.; Pogge von Strandmann, Philip A. E.; Schuessler, Jan A.; Moore, Oliver W.


    In order to assess the effects of critical zone processes on Mg concentrations and isotopic signatures of tropical streams, we studied a well constrained, highly weathered andesitic volcaniclastic catchment in the Luquillo Critical Zone Observatory, Puerto Rico. Our results indicate that dissolved Mg concentrations and isotope ratios in the regolith pore water are mainly controlled by rain input, with weathering inputs being more important at sites with thinner regolith (2.7-0.9 m deep) and at depth (>8 m) on a thick ridgetop regolith (∼10 m). In addition to mixing of precipitation and weathering-sourced Mg, an isotopic fractionation process is taking place between dissolved Mg and the regolith, likely during dissolution or recrystallisation of Fe(III)-(hydro)oxides under alternating redox conditions. Bulk regolith is isotopically heavier than both the bedrock and the exchangeable fraction (δ26Mgregolith-bedrock = +0.03 to +0.47‰), consistent with the preferential incorporation of heavy 26Mg into secondary minerals with some exchange of sorbed Mg with isotopically lighter pore water. Magnesium concentrations in the stream show a typical dilution behaviour during a storm event, but the [Mg] - δ26Mg pattern cannot be explained by mixing of rain and pore water; the data are best explained by a steady-state fractionation model with α = 1.00115. During baseflow the stream has δ26Mg = +0.01‰, higher than any of the water samples or the bedrock. In-situ analysis of the Mg isotopic composition of bedrock minerals points at the dissolution of Mg-rich chlorite (δ26Mg = +0.19‰) as the most likely source of this isotopically heavy Mg, with mass balance calculations indicating chlorite dissolution is also the main source of Mg to the stream. Overall, our study highlights the importance of atmospheric input of nutrients to the vegetation in tropical areas covered by thick, highly leached regolith, whereas the Mg flux and Mg isotopic signature of watershed exports

  9. Oxygen isotopic constraints on the origin of Mg-rich olivines from chondritic meteorites

    Libourel, Guy; Chaussidon, Marc


    Chondrules are the major high temperature components of chondritic meteorites which accreted a few millions years after the oldest solids of the solar system, the calcium-aluminum-rich inclusions, were condensed from the nebula gas. Chondrules formed during brief heating events by incomplete melting of solid dust precursors in the protoplanetary disk. Petrographic, compositional and isotopic arguments allowed the identification of metal-bearing Mg-rich olivine aggregates among the precursors of magnesian type I chondrules. Two very different settings can be considered for the formation of these Mg-rich olivines: either a nebular setting corresponding mostly to condensation-evaporation processes in the nebular gas or a planetary setting corresponding mostly to differentiation processes in a planetesimal. An ion microprobe survey of Mg-rich olivines of a set of type I chondrules and isolated olivines from unequilibrated ordinary chondrites and carbonaceous chondrites revealed the existence of several modes in the distribution of the ∆17O values and the presence of a large range of mass fractionation (several ‰) within each mode. The chemistry and the oxygen isotopic compositions indicate that Mg-rich olivines are unlikely to be of nebular origin (i.e., solar nebula condensates) but are more likely debris of broken differentiated planetesimals (each of them being characterized by a given ∆17O). Mg-rich olivines could have crystallized from magma ocean-like environments on partially molten planetesimals undergoing metal-silicate differentiation processes. Considering the very old age of chondrules, Mg-rich olivine grains or aggregates might be considered as millimeter-sized fragments from disrupted first-generation differentiated planetesimals. Finally, the finding of only a small number of discrete ∆17O modes for Mg-rich olivines grains or aggregates in a given chondrite suggests that these shattered fragments have not been efficiently mixed in the disk and

  10. Triple oxygen isotope composition of the Campi Flegrei magma systems

    Iovine, Raffaella Silvia; Wörner, Gerhard; Pack, Andreas; Sengupta, Sukanya; Carmine Mazzeo, Fabio; Arienzo, Ilenia; D'Antonio, Massimo


    Sr-O isotope relationships in igneous rocks are a powerful tool to distinguish magma sources and quantify assimilation processes in magmatic rocks. Isotopic (87Sr/86Sr and 18O/16O-17O/16O) data have been acquired on whole rocks and separated minerals (feldspar, Fe-cpx, Mg-cpx, olivine phenocrysts) from pyroclastic products of the Campi Flegrei volcanic complex (Gulf of Naples, Southern Italy). Oxygen isotope ratios were measured by infrared laser fluorination using a Thermo MAT253 gas source isotope ratio mass spectrometer in dual inlet mode, on ˜2 mg of hand-picked phenocrysts. Variations in triple oxygen isotope ratios (17O/16O, 18O/16O) are expressed as the δ notation relative to VSMOW. Sr isotopic compositions were determined by thermal ionization mass spectrometry after standard cation-exchange methods on separated hand-picked phenocrysts (˜300 mg), and on whole rocks, in case of insufficient sample size to separate crystals. Sr-isotopes in Campi Flegrei minerals range from 0.707305 to 0.707605 and δ18O varies from 6.5 to 8.3‰ . Recalculated δ18Omelt values accordingly show a large range between 7.2 and 8.6‰ . Our data, compared with published δ18O-isotope data from other Italian volcanic centers (Alban Hills, Mts. Ernici, Ischia, Mt. Vesuvius, Aeolian Islands, Tuscany and Sardinia) and from subduction zones worldwide (Kamchatka, Lesser Antilles, Indonesia and Central Andean ignimbrites), show compositions that are very different from typical mantle values. Distinct trends and sources are recognized in our compilation from global data: (1) serpentinized mantle (Kamchatka), (2) sediment-enrichment in the mantle source (Indonesia, Lesser Antilles, Eolian arc), (3) assimilation of old radiogenic continental crust affecting magmas derived from sediment-modified mantle sources (Tuscany, Sardinia), (4) assimilation of lower crustal lithologies (Central Andes, Alban Hills, Mts. Ernici, Ischia). Sr-O-isotope values of Campi Flegrei and Vesuvius magmas

  11. Impact of amorphous precursor phases on magnesium isotope signatures of Mg-calcite

    Mavromatis, Vasileios; Purgstaller, Bettina; Dietzel, Martin; Buhl, Dieter; Immenhauser, Adrian; Schott, Jacques


    Various marine calcifiers form exoskeletons via an amorphous calcium carbonate (ACC) precursor phase and magnesium plays an important role in the temporary stabilization of this metastable phase. Thus, the use of Mg isotope ratios of marine biogenic carbonates as a proxy to reconstruct past seawater chemistry calls for a detailed understanding of the mechanisms controlling Mg isotope signatures during the formation and transformation of ACC to the final crystalline carbonate mineral. For this purpose we have investigated the Mg isotope fractionation between (Ca,Mg)CO3 solids and aqueous fluids at 25 °C and pH = 8.3 during (i) the direct precipitation of crystalline Mg-calcite and (ii) the formation of Mg-rich ACC (Mg-ACC) and its transformation to Mg-calcite. The outcome documents that the small Mg isotope fractionation between Mg-ACC and reactive fluid (ΔMg26ACC-fluid = - 1.0 ± 0.1 ‰) is not preserved during the transformation of the ACCs into Mg-calcite. Following a pronounced isotopic shift accompanying the transformation of Mg-ACC into Mg-calcite, Δ26Mgcalcite-fluid progressively decreases with reaction progress from ∼ - 3.0 ‰ to - 3.6 ‰, reflecting both the approach of isotopic equilibrium and the increase of calcite Mg content (to near 20 mol % Mg). In contrast the crystalline Mg-calcite precipitated directly from the reacting fluid, i.e. lacking a discernable formation of an amorphous precursor, exhibits only small temporal variations in Δ26Mgcalcite-fluid which overall is affected by the precipitation kinetics. The values found in this study at the onset of Mg-ACC precipitation for Mg isotope fractionation between Mg-ACC and the fluid (ΔMg26ACC-fluid = - 1.0 ‰) and between Mg-ACC and Mg2+(aq) (Δ(aq) 26 Mg ACC-Mg2+ = + 2.0 ‰) are consistent with the formation of a hydrated Ca nanoporous solid accommodating Mg bicarbonate/carbonate species in combination with hydrated magnesium. This material crossed by percolating channels filled with the


    Pizzarello, Sandra, E-mail: [Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85018-1604 (United States)


    HCN is ubiquitous in extraterrestrial environments and is central to current theories on the origin of early solar system organic compounds such as amino acids. These compounds, observed in carbonaceous meteorites, were likely important in the origin and/or evolution of early life. As part of our attempts to understand the origin(s) of meteoritic CN{sup –}, we have analyzed the {sup 15}N/{sup 14}N isotopic composition of HCN gas released from water extracts of the Murchison meteorite and found its value to be near those of the terrestrial atmosphere. The findings, when evaluated viz-a-viz molecular abundances and isotopic data of meteoritic organic compounds, suggest that HCN formation could have occurred during the protracted water alteration processes known to have affected the mineralogy of many asteroidal bodies during their solar residence. This was an active synthetic stage, which likely involved simple gasses, organic molecules, their presolar precursors, as well as mineral catalysts and would have lead to the formation of molecules of differing isotopic composition, including some with solar values.

  13. Elevated temperature properties of Mg- 12Li-Al-MgO composites

    WEI Xiao-wei; HUANG Qing-min


    The compressive creep of Mg-12Li-Al-MgO particulate composites was investigated, which were produced by the reaction of reinforcement materials (B2O3) with Mg-12Li-Al alloy melt in the temperature range of 100-190 ℃ and under different compressive stress in the range of 40-70 MPa with special apparatus. The content of MgO particulates is about 0, 5%, 10%,15%(volume fraction) in Mg-12Li-Al alloy respectively. The results reveal that the creep resistance of the particulate composites is increased with increasing the content of MgO particulates and considerable improvementin creep resistance is observed in Mg-12Li-Al-MgO composites. However, over all range of temperatures and stresses, the creep data for these composites can be correlated using an empirical equation εs =Aσnexp(-Q/RT), where n is 4.93 and Q is about 78.1 kJ/mol for Mg-14Li-Al alloy and n is between 7.48 and 9.47 and Q is 111.2-137.3 kJ/mol for Mg-12Li-Al-MgO composites. The different compressive creep behavior of the composites is associated with the different material constant A. The compressive creep rate is controlled by the lattice diffusion of Li and dislocation climb.

  14. The isotopic composition of CO in vehicle exhaust

    Naus, Stijn; Röckmann, Thomas; Popa, Elena


    The isotopic composition of atmospheric carbon monoxide (CO) and its sources can be a powerful tool to help constrain the CO budget, but data on the isotopic composition of CO sources is sparse. We investigated the isotopic composition (13C16O and 12C18O) of one of the main sources of CO in urban areas: traffic emissions. Samples from individual passenger cars and atmospheric samples from polluted areas were measured. The results show strong indications that CO emissions from traffic are dominated by a small subset of cars or driving conditions, which, in this study, were cold petrol cars. The spread in isotopic composition of the full dataset was large, but this dominant subset showed a relatively stable isotopic composition. Therefore, the individual car samples result in a well-defined overall traffic signature, which was in agreement with the atmospheric isotopic signature derived from the atmospheric samples.

  15. Chemical and isotopic kinship of iron in the Earth and Moon deduced from the lunar Mg-Suite

    Sossi, Paolo A.; Moynier, Frédéric


    The Moon and the Earth's mantle share many chemical and isotopic traits, leading to the prevailing theory that they were formed from similar material. Iron is one element that shows apparent differences between the two bodies, with models for the composition of the Moon having ≈1.5 times more FeO (12-14 wt.%), relative to the Earth's mantle (8 wt.%). This difference is mirrored in their isotope compositions, where lunar mare basalts have δ57Fe (per mille deviation of the 57Fe/54Fe ratio from the IRMM-014 standard) 0.1-0.2‰ higher than peridotitic rocks representative of Earth's mantle, a feature initially attributed to loss of isotopically light Fe following a giant impact. However, whether basaltic rocks are suitable analogues for the Moon's composition is debatable in the light of their distinct source regions that reflect the extensive lithological stratification of the lunar mantle. Here, we evaluate the iron isotope composition of the bulk Moon through the study of igneous cumulate rocks of the lunar highlands Magnesium Suite (Mg Suite). The δ57Fe of Mg Suite rocks spans a limited range, from 0.05‰ to 0.10‰, with an average (+ 0.07 ± 0.02 ‰) that overlaps with Earth's mantle (+ 0.05 ± 0.01 ‰), similarities that extend to their Mg#s, where both reach 0.9. Numerical modelling of iron isotope fractionation during lunar magma ocean crystallisation shows that the Mg Suite should accurately reflect the composition of the bulk Moon, which is therefore + 0.07 ± 0.02 ‰, indistinguishable from Earth's mantle but heavier than chondrites (- 0.01 ± 0.01 ‰). Iron thus behaves coherently with other elements that condense at temperatures higher than Li in showing no isotopic difference between the Earth and Moon, suggesting element depletion on the Moon affected only the more volatile elements. Therefore, there is no cosmochemical basis for iron enrichment or depletion in the bulk Moon relative to the Earth's mantle, whose composition is an analogue for

  16. Mg isotope ratios in giant stars of the globular clusters M 13 and M 71

    Yong, D; Lambert, D L; Yong, David; Aoki, Wako; Lambert, David L.


    We present Mg isotope ratios in 4 red giants of the globular cluster M 13 and 1 red giant of the globular cluster M 71 based on spectra obtained with HDS on the Subaru Telescope. We confirm earlier results by Shetrone that for M 13, the ratio varies from (25+26)Mg/24Mg = 1 in stars with the highest Al abundance to (25+26)Mg/24Mg = 0.2 in stars with the lowest Al abundance. However, we separate the contributions of all three isotopes and find a spread in the ratio 24Mg:25Mg:26Mg with values ranging from 48:13:39 to 78:11:11. As in NGC 6752, we find a positive correlation between 26Mg and Al, an anticorrelation between 24Mg and Al, and no correlation between 25Mg and Al. In M 71, our one star has a ratio 70:13:17. For both clusters, the lowest ratios of 25Mg/24Mg and 26Mg/24Mg exceed those observed in field stars at the same metallicity, a result also found in NGC 6752. The contribution of 25Mg to the total Mg abundance is constant within a given cluster and between clusters with 25Mg/(24+25+26)Mg = 0.13. For M...

  17. The behaviour of Li and Mg isotopes during primary phase dissolution and secondary mineral formation in basalt

    Wimpenny, Josh; Gíslason, Sigurður R.; James, Rachael H.; Gannoun, Abdelmouhcine; Pogge Von Strandmann, Philip A. E.; Burton, Kevin W.


    This study presents lithium (Li) and magnesium (Mg) isotope data from experiments designed to assess the effects of dissolution of primary phases and the formation of secondary minerals during the weathering of basalt. Basalt glass and olivine dissolution experiments were performed in mixed through-flow reactors under controlled equilibrium conditions, at low pH (2-4) in order to keep solutions undersaturated (i.e. far-from equilibrium) and inhibit the formation of secondary minerals. Combined dissolution-precipitation experiments were performed at high pH (10 and 11) increasing the saturation state of the solutions (moving the system closer to equilibrium) and thereby promoting the formation of secondary minerals. At conditions far from equilibrium saturation state modelling and solution stoichiometry suggest that little secondary mineral formation has occurred. This is supported by the similarity of the dissolution rates of basalt glass and olivine obtained here compared to those of previous experiments. The δ 7Li isotope composition of the experimental solution is indistinguishable from that of the initial basalt glass or olivine indicating that little fractionation has occurred. In contrast, the same experimental solutions have light Mg isotope compositions relative to the primary phases, and the solution becomes progressively lighter with time. In the absence of any evidence for secondary mineral formation the most likely explanation for these light Mg isotope compositions is that there has been preferential loss of light Mg during primary phase dissolution. For the experiments undertaken at close to equilibrium conditions the results of saturation state modelling and changes in solution chemistry suggest that secondary mineral formation has occurred. X-ray diffraction (XRD) measurements of the reacted mineral products from these experiments confirm that the principal secondary phase that has formed is chrysotile. Lithium isotope ratios of the experimental

  18. Isotope Effect on Electron-Phonon Coupling in Multiband Superconductor MgB2

    Mou, Daixiang; Taufour, Valentin; Wu, Yun; Huang, Lunan; Bud'Ko, Serguei; Canfield, Paul; Kaminski, Adam

    We systematically investigate the isotope effect of electron-phonon coupling in multi-band superconductor MgB2 by laser based Angle Resolved Photoemission Spectroscopy. The kink structure around 70 meV on two σ bands, which is caused by electron coupling to E2 g phonon mode, is shifted to higher binding energy in Mg10B2 than that in Mg11B2. The measured shifting energy of 3.5 meV is consistent with theoretical calculation based on harmonic phonon in MgB2. Our temperature dependent measurement also indicates the isotope effect of kink structure is not dependent on superconducting transition.

  19. Coherent phonon decay and the boron isotope effect for MgB2.

    Alarco, Jose A; Talbot, Peter C; Mackinnon, Ian D R


    Ab initio DFT calculations for the phonon dispersion (PD) and the phonon density of states (PDOS) of the two isotopic forms ((10)B and (11)B) of MgB2 demonstrate that use of a reduced symmetry super-lattice provides an improved approximation to the dynamical, phonon-distorted P6/mmm crystal structure. Construction of phonon frequency plots using calculated values for these isotopic forms gives linear trends with integer multiples of a base frequency that change in slope in a manner consistent with the isotope effect (IE). Spectral parameters inferred from this method are similar to that determined experimentally for the pure isotopic forms of MgB2. Comparison with AlB2 demonstrates that a coherent phonon decay down to acoustic modes is not possible for this metal. Coherent acoustic phonon decay may be an important contributor to superconductivity for MgB2.

  20. Experimental study of the Mg and Sr isotopic evolution of seawater interacting with basalt between 150 and 300 ° C.

    Voigt, Martin; Pearce, Christopher R.; Oelkers, Eric H.


    The chemical exchange of material between seawater and the oceanic crust plays a major role in marine geochemical cycles [1]. Isotopic signatures provide an important means of tracing elemental transfer in hydrothermal environments, yet only a limited amount of experimental data on the extent of isotopic fractionation under these conditions is currently available. This study consequently investigated the extent of δ26/24Mg and 87Sr/86Sr isotopic variation during a seawater-basalt interaction experiments at 150, 250 and 290 ° C. A suite of closed system experiments were run for several months at each temperature under saturated water pressure, using either crystalline or glassy basalt as the starting material and a water/rock ratio of 10 or 25. Our results demonstrate that the dissolution of basaltic material in hydrothermal environments occurs at the same time as the precipitation of alteration minerals (mainly smectite and anhydrite), which is consistent with results from similar studies in the past (e.g. [2]). As expected, the rate of reaction using crystalline basalt was slower than with basaltic glass, and both sample types reacted faster at higher temperatures. The 87Sr/86Sr composition of the experimental fluids decreased from the initial seawater value (0.70916) towards the lower basaltic signature during the experiments (0.70317), demonstrating the progressive release of Sr during basalt dissolution. Magnesium was steadily removed from the fluid via the precipitation of clay minerals, with the residual fluids having progressively lighter δ26/24Mg compositions. The mean Mg isotope fractionation factor (αsolid-solution) observed at 250 oC was 1.0005±0.0002, supporting low-temperature evidence that clay minerals preferentially incorporate isotopically heavy magnesium [3]. These experiments provide quantitative information on the extent of Mg isotopic fractionation between fluids and secondary silicate minerals in hydrothermal systems, and demonstrate the

  1. Isotopic compositional Characteristics of Terrigenous Natural Gases in China

    沈平; 徐永昌


    The C and H isotopic compositions of the methane in more than 160 gas samples from 10 basins in China are presented in this paper.The natural gases are classified as four types: biogenic gas ,bio-thermocatalytic transitional gas, gas associated with condensate oil ,and coal-type gas. The isotopic compositions of these gases closely related to the depositional basins, the types of organic matter,the stages of thermal evolution and the genetic characteristics of different gas reservoirs.Studies of the C and H isotopic compositions of terrigenous natural gases will provide valua-ble information on the prospecting and development of natural gases of different genetic types.

  2. Isotope composition and volume of Earth’s early oceans

    Pope, Emily C.; Bird, Dennis K.; Rosing, Minik T.


    Oxygen and hydrogen isotope compositions of Earth’s seawater are controlled by volatile fluxes among mantle, lithospheric (oceanic and continental crust), and atmospheric reservoirs. Throughout geologic time the oxygen mass budget was likely conserved within these Earth system reservoirs, but hydrogen’s was not, as it can escape to space. Isotopic properties of serpentine from the approximately 3.8 Ga Isua Supracrustal Belt in West Greenland are used to characterize hydrogen and oxygen isotop...

  3. Effect of interband interaction on isotope effect exponent of MgB2 superconductors

    P Udomsamuthirun; C Kumvongsa; A Burakorn; P Changkanarth


    The exact formula of c's equation and the isotope effect exponent of two-band s-wave superconductors in the weak-coupling limit are derived by considering the influence of interband interaction. In each band, our model consists of two pairing interactions: the electron-phonon interaction and non-electron-phonon interaction. We find that the isotope effect exponent of MgB2, = 0.3 with c ≈ 40 K can be found in the weak coupling regime and interband interaction of electron-phonon shows more effect on the isotope effect exponent than on the interband interaction of non-phonon.

  4. The Late Quaternary Oxygen Isotope Composition of Lake Michigan

    MacDonald, R. A.; Longstaffe, F. J.; Crowe, A. S.


    We present stable isotope records for porewater (oxygen, hydrogen) and biogenic carbonates (oxygen, carbon; ostracode and clam shells) in sediment cores from the Chippewa, Milwaukee and South Chippewa Basins of Lake Michigan. The oxygen and hydrogen isotope compositions of porewater from the South Chippewa Basin core showed very little variation with depth. At the maximum depth of 16.6m, δ18O values were within 2‰ and δD values were within 12‰ of modern Lake Michigan water (average δ18O = -5.9‰; average δD = -45‰); original porewater compositions have not been preserved. The oxygen isotope results for the biogenic carbonates, by comparison, provide a record of the isotopic composition of Lake Michigan over the last ~11,000 years, including significant incursions of very low-18O water, as first reported by Colman et al. (1990) and Forester et al. (1994). The low-18O waters originated from the retreating Laurentide ice sheet and may have been routed through Lakes Agassiz and Superior and discharged as large volumes over very short intervals of time. Periods characterized by much higher oxygen isotope compositions likely record the isotopic composition of regional precipitation over the catchment area. In summary, the large variations in the oxygen isotope composition of early Lake Michigan water arose from regional climate change and changing water sources during the times of ice-sheet retreat.

  5. Isotopic composition of precipitation in Ljubljana (Slovenia

    Polona Vreča


    Full Text Available The stable isotopic composition of hydrogen and oxygen (δ2H and δ18O and tritium activity (3H are monitored in monthly precipitation at Ljubljana since 1981. Here we present complete set of numerical data and the statistical analysis for period 1981–2006. Seasonal variations of δ2H and δ18O are observed and are typical for continental stations of the Northern Hemisphere. The weighted mean δ2H and δ18O values are –59 ‰ and –8.6 ‰, respectively.The orthogonal Local Meteoric Water Line is δ2H = (8.06 ± 0.08δ18O + (9.84 ± 0.71, and the temperature coefficient of δ18O is 0.29 ‰/°C. Deuterium excess weighted mean value is 9.5 ‰ and indicates the prevailing influence of the Atlantic air masses. Tritium activity in monthly precipitation shows also seasonal variations which are superposed to the decreasing trend of mean annual activity.

  6. Can Mg isotopes be used to trace cyanobacteria-mediated magnesium carbonate precipitation in alkaline lakes?

    Shirokova, L. S.; Mavromatis, V.; Bundeleva, I.; Pokrovsky, O. S.; Bénézeth, P.; Pearce, C.; Gérard, E.; Balor, S.; Oelkers, E. H.


    The fractionation of Mg isotopes was determined during the cyanobacterial mediated precipitation of hydrous magnesium carbonate precipitation in both natural environments and in the laboratory. Natural samples were obtained from Lake Salda (SE Turkey), one of the few modern environments on the Earth's surface where hydrous Mg-carbonates are the dominant precipitating minerals. This precipitation was associated with cyanobacterial stromatolites which were abundant in this aquatic ecosystem. Mg isotope analyses were performed on samples of incoming streams, groundwaters, lake waters, stromatolites, and hydromagnesite-rich sediments. Laboratory Mg carbonate precipitation experiments were conducted in the presence of purified Synechococcus sp cyanobacteria that were isolated from the lake water and stromatolites. The hydrous magnesium carbonates nesquehonite (MgCO3·3H2O) and dypingite (Mg5(CO3)4(OH)25(H2O)) were precipitated in these batch reactor experiments from aqueous solutions containing either synthetic NaHCO3/MgCl2 mixtures or natural Lake Salda water, in the presence and absence of live photosynthesizing Synechococcus sp. Bulk precipitation rates were not to affected by the presence of bacteria when air was bubbled through the system. In the stirred non-bubbled reactors, conditions similar to natural settings, bacterial photosynthesis provoked nesquehonite precipitation, whilst no precipitation occurred in bacteria-free systems in the absence of air bubbling, despite the fluids achieving a similar or higher degree of supersaturation. The extent of Mg isotope fractionation (Δ26Mgsolid-solution) between the mineral and solution in the abiotic experiments was found to be identical, within uncertainty, to that measured in cyanobacteria-bearing experiments, and ranges from -1.4 to -0.7 ‰. This similarity refutes the use of Mg isotopes to validate microbial mediated precipitation of hydrous Mg carbonates.

  7. Isotope effect on electron-phonon interaction in the multiband superconductor MgB2

    Mou, Daixiang; Manni, Soham; Taufour, Valentin; Wu, Yun; Huang, Lunan; Bud'ko, S. L.; Canfield, P. C.; Kaminski, Adam


    We investigate the effect of isotope substitution on the electron-phonon interaction in the multiband superconductor MgB2 using tunable laser-based angle-resolved photoemission spectroscopy. The kink structure around 70 meV in the σ band, which is caused by electron coupling to the E2 g phonon mode, is shifted to higher binding energy by ˜3.5 meV in Mg 10B2 and the shift is not affected by superconducting transition. These results serve as the benchmark for investigations of isotope effects in known, unconventional superconductors and newly discovered superconductors where the origin of pairing is unknown.

  8. Isotopic compositions of boron in sediments and their implications

    Shirodkar, P.V.; Yingkai, X.

    of sediments are mostly closer to the boron isotopic composition of minerals. Such low delta sup(11)B values are attributed to the presence of borates, ulexite and other carbonate minerals in sediments of the salt lakes of Qaidam Basin....

  9. Isotopic compositions of the elements 2013 (IUPAC Technical Report)

    Meija, Juris; Coplen, Tyler B.; Berglund, Michael; Brand, Willi A.; De Bièvre, Paul; Gröning, Manfred; Holden, Norman E.; Irrgeher, Johanna; Loss, Robert D.; Walczyk, Thomas; Prohaska, Thomas


    The Commission on Isotopic Abundances and Atomic Weights ( of the International Union of Pure and Applied Chemistry ( has revised the Table of Isotopic Compositions of the Elements (TICE). The update involved a critical evaluation of the recent published literature. The new TICE 2013 includes evaluated data from the “best measurement” of the isotopic abundances in a single sample, along with a set of representative isotopic abundances and uncertainties that accommodate known variations in normal terrestrial materials.

  10. Oxygen isotopic composition of carbon dioxide in the middle atmosphere

    Liang, Mao-Chang; Blake, Geoffrey A.; Lewis, Brenton R.; Yung, Yuk L.


    The isotopic composition of long-lived trace molecules provides a window into atmospheric transport and chemistry. Carbon dioxide is a particularly powerful tracer, because its abundance remains >100 parts per million by volume (ppmv) in the mesosphere. Here, we successfully reproduce the isotopic composition of CO2 in the middle atmosphere, which has not been previously reported. The mass-independent fractionation of oxygen in CO2 can be satisfactorily explained by the exchange reaction with...

  11. Porous Ceramic Composite ZrO2(MgO)-MgO for Osteoimplantology

    Buyakov, A. S.; Kulkov, S. N.


    Pore and crystalline structure, biocompatibility of ceramic composite ZrO2(MgO)-MgO were studied. The main mechanical characteristics were determined and it has been shown that compression strength directly depends on microstresses obtained from X-ray data. In-vitro studies of mesenchymal stromal stem cells (MMSC), cultivated on material surface are shown that cell proliferation and differentiation of MMSC goes throw osteogenic type.

  12. Porous composite materials ZrO{sub 2}(MgO)-MgO for osteoimplantology

    Buyakov, Ales, E-mail: [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); National Research Tomsk State University, Tomsk, 634050 (Russian Federation); Litvinova, Larisa, E-mail:; Shupletsova, Valeria, E-mail: [Immanuel Kant Baltic Federal University, Kaliningrad (Russian Federation); Kulbakin, Denis, E-mail: [Tomsk Cancer Research Institute, Tomsk, 634050 (Russian Federation); Kulkov, Sergey, E-mail: [Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation); National Research Tomsk State University, Tomsk, 634050 (Russian Federation); National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation)


    The pore structure and phase composition of ceramic composite material ZrO{sub 2}(Mg)-MgO at different sintering temperatures were studied. The main mechanical characteristics of the material were determined and it was shown that they are close to the characteristics of natural bone tissues. It was shown that material structure has a positive effect on the pre-osteoblast cells proliferation. In-vitro studies of pre-osteoblast cells, cultivation on material surface showed a good cell adhesion, proliferation and differentiation of MMSC by osteogenic type.

  13. New candidate for deformed halo nucleus in Mg isotopes through analysis of reaction cross sections

    Watanabe S.


    Full Text Available The total reaction cross sections of Mg isotopes on a 12C target at 240 MeV/nucleon have been analyzed with a fully microscopic framework, i.e., the double folding model with the density calculated by antisymmetrized molecular dynamics. Our results well reproduce the latest experimental data except 37Mg as a new candidate for a deformed halo nucleus.

  14. Microstructure and hardness of Mg-based composites reinforced with Mg2Si particles

    Mustafa Aydin; Cem Ozgür; Osman San


    Magnesium powders were mechanically alloyed with SiO2 powder particles having different particle sizes using high-energy ball milling techniques under Ar atmosphere for 1 h. The powders were consolidated with cold pressing under 560 Mpa. They were then sintered at 550℃ for 45 min under Ar atmosphere. The composites obtained on the Mg-SiO2 system were investigated using the Archimedes principle, a differential scanning calorimeter, X-ray diffraction, optic microscopy, and scanning electron microscopy. For the mechanically alloyed powders, the solid-state reaction of the synthesis of Mg2Si and MgO progressed further during sintering of the materials. The results showed that the strengthening mechanisms were dependent on dispersion hardening of fine Mg2Si and MgO particulates dispersed homogeneously in the matrix.

  15. Nuclear Structure and Reaction Properties of Ne, Mg and Si Isotopes with RMF Densities

    Panda, R N; Patra, S K


    We have studied nuclear structure and reaction properties of Ne, Mg and Si isotopes, using relativistic mean field densities, in the frame work of Glauber model. Total reaction cross section $\\sigma_R$ for Ne isotopes on 12C target have been calculated at incident energy 240 MeV. The results are compared with the experimental data and with the recent theoretical study [W. Horiuchi et al., Phys. Rev. C, 86, 024614 (2012)]. Study of $\\sigma_R$ using deformed densities have shown a good agreement with the data. We have also predicted total reaction cross section $\\sigma_R$ for Ne, Mg and Si isotopes as projectiles and 12C as target at different incident energies.

  16. Core correlation effects in multiconfiguration calculations of isotope shifts in Mg I

    Filippin, Livio; Ekman, Jörgen; Jönsson, Per


    The present work reports results from systematic multiconfiguration Dirac-Hartree-Fock calculations of isotope shifts for several well-known transitions in neutral magnesium. Relativistic normal and specific mass shift factors as well as the electronic probability density at the origin are calculated. Combining these electronic quantities with available nuclear data, energy and transition level shifts are determined for the $^{26}$Mg$-^{24}$Mg pair of isotopes. Different models for electron correlation are adopted. It is shown that although valence and core-valence models provide accurate values for the isotope shifts, the inclusion of core-core excitations in the computational strategy significantly improves the accuracy of the transition energies and normal mass shift factors.

  17. A first roadmap for kryptology. [isotopic composition from supernovae

    Heymann, D.; Dziczkaniec, M.


    Studies of the complex variations of the isotopic composition of xenon in the solar system have been christened 'xenology'. In the title of the present investigation, the word 'kryptology' is employed to indicate the primary objective of the reported studies. This objective is related to the prediction of the isotopic composition of krypton which comes from a number of specific locations of a supernova in association with the isotopic compositions of xenon from these locations. Krypton is a logical candidate for testing the stellar theory on geochemical grounds, taking into account also the point of view of nucleosynthesis, because the isotopes of xenon and krypton are formed by the same thermonuclear processes in stars. The data and arguments presented in the investigation show that the treatment by Heymann and Dziczkaniec (1979), although not wrong, is too simplistic, because it has ignored the possibility of holdup and arrest in Xe network.

  18. Investigation of magnesium isotope fractionation during basalt differentiation: Implications for a chondritic composition of the terrestrial mantle

    Teng, F.-Z.; Wadhwa, M.; Helz, R.T.


    To investigate whether magnesium isotopes are fractionated during basalt differentiation, we have performed high-precision Mg isotopic analyses by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) on a set of well-characterized samples from Kilauea Iki lava lake, Hawaii, USA. Samples from the Kilauea Iki lava lake, produced by closed-system crystal-melt fractionation, range from olivine-rich cumulates to highly differentiated basalts with MgO content ranging from 2.37 to 26.87??wt.%. Our results demonstrate that although these basalts have diverse chemical compositions, mineralogies, crystallization temperatures and degrees of differentiation, their Mg isotopic compositions display no measurable variation within the limits of our external precision (average ??26Mg = - 0.36 ?? 0.10 and ??25Mg = - 0.20 ?? 0.07; uncertainties are 2SD). This indicates that Mg isotopic fractionation during crystal-melt fractionation at temperatures of ??? 1055????C is undetectable at the level of precision of the current investigation. Calculations based on our data suggest that at near-magmatic temperatures the maximum fractionation in the 26Mg/24Mg ratio between olivine and melt is 0.07???. Two additional oceanic basalts, two continental basalts (BCR-1 and BCR-2), and two primitive carbonaceous chondrites (Allende and Murchison) analyzed in this study have Mg isotopic compositions similar to the Kilauea Iki lava lake samples. In contrast to a recent report [U. Wiechert, A.N. Halliday, Non-chondritic magnesium and the origins of the inner terrestrial planets, Earth and Planetary Science Letters 256 (2007) 360-371], the results presented here suggest that the Bulk Silicate Earth has a chondritic Mg isotopic composition. ?? 2007.

  19. Triple sulfur isotope composition of Late Archean seawater sulfate

    Paris, G.; Fischer, W. W.; Sessions, A. L.; Adkins, J. F.


    Multiple sulfur isotope ratios in Archean sedimentary rocks have provided powerful insights into the behavior of the ancient sulfur cycle, the redox state of fluid Earth, and the timing of the rise of atmospheric oxygen [1]. Most processes fractionate sulfur isotopes in proportion to their mass differences, but the Archean sulfur isotope record is marked by pronounced mass-independent fractionation (MIF, Δ33S≠0). The origin of these signatures has been traditionally interpreted as the result of photolysis of SO2 from short wavelength UV light, with positive Δ33S values recorded in pyrite and negative Δ33S values in sulfate-bearing phases [2]. This long-held hypothesis rests on observations of negative Δ33S from enigmatic barite occurrences from mixed volcanic sedimentary strata in Mesoarchean greenstone terrains. Despite forming the framework for understanding Archean sulfur cycle processes [3], it is largely untested [3]. It is largely untested. Consequently, the biggest challenge to our current understanding of the early sulfur cycle is a poor understanding of the isotopic composition of seawater sulfate. Sulfate evaporite minerals are absent from Archean strata and the sulfur isotope record is written entirely by measurements of pyrite. Carbonate associated sulfate (CAS) provides an important archive for assaying the isotopic composition of ancient seawater sulfate It has been exploited in many studies of Phanerozoic and Proterozoic sulfate but have been only marginally used thus far for Archean samples because of the extremely low concentration of CAS in limestones and dolomites from this era. We have developed a novel MC-ICP-MS approach to solve this problem [4]. This new method lowers the detection limit by up to three orders of magnitude for δ34S and Δ33S measurements, enabling to work on a few nmols of sulfate which represent only tens of mg of sample powders micromilled from specific carbonate textures. Two stratigraphic sections from the 2

  20. Hydrogen reversibility of LiBH₄-MgH₂-Al composites.

    Hansen, Bjarne R S; Ravnsbæk, Dorthe B; Skibsted, Jørgen; Jensen, Torben R


    The detailed mechanism of hydrogen release in LiBH4-MgH2-Al composites of molar ratios 4 : 1 : 1 and 4 : 1 : 5 are investigated during multiple cycles of hydrogen release and uptake. This study combines information from several methods, i.e., in situ synchrotron radiation powder X-ray diffraction, (11)B magic-angle spinning (MAS) NMR, Sievert's measurements, Fourier transform infrared spectroscopy and simultaneous thermogravimetric analysis, differential scanning calorimetry and mass spectroscopy. The composites of LiBH4-MgH2-Al are compared with the behavior of the LiBH4-Al and LiBH4-MgH2 systems. The decomposition pathway of the LiBH4-MgH2-Al system is different for the two investigated molar ratios, although it ultimately results in the formation of LiAl, Mg(x)Al(1-x)B2 and Li2B12H12 in both cases. For the 4 : 1 : 1-molar ratio, Mg(0.9)Al(0.1) and Mg17Al12 are observed as intermediates. However, only Mg is observed as an intermediate in the 4 : 1 : 5-sample, which may be due to an earlier formation of Mg(x)Al(1-x)B2, reflecting the complex chemistry of Al-Mg phases. Hydrogen release and uptake reveals a decrease in the hydrogen storage capacity upon cycling. This loss reflects the formation of Li2B12H12 as observed by (11)B NMR and infrared spectroscopy for the cycled samples. Furthermore, it is shown that the Li2B12H12 formation can be limited significantly by applying moderate hydrogen partial pressure during decomposition.

  1. The ruthenium isotopic composition of the oceanic mantle

    Bermingham, K. R.; Walker, R. J.


    The approximately chondritic relative, and comparatively high absolute mantle abundances of the highly siderophile elements (HSE), suggest that their concentrations in the bulk silicate Earth were primarily established during a final ∼0.5 to 1% of ;late accretion; to the mantle, following the cessation of core segregation. Consequently, the isotopic composition of the HSE Ru in the mantle reflects an amalgamation of the isotopic compositions of late accretionary contributions to the silicate portion of the Earth. Among cosmochemical materials, Ru is characterized by considerable mass-independent isotopic variability, making it a powerful genetic tracer of Earth's late accretionary building blocks. To define the Ru isotopic composition of the oceanic mantle, the largest portion of the accessible mantle, we report Ru isotopic data for materials from one Archean and seven Phanerozoic oceanic mantle domains. A sample from a continental lithospheric mantle domain is also examined. All samples have identical Ru isotopic compositions, within analytical uncertainties, indicating that Ru isotopes are well mixed in the oceanic mantle, defining a μ100Ru value of 1.2 ± 7.2 (2SD). The only known meteorites with the same Ru isotopic composition are enstatite chondrites and, when corrected for the effects of cosmic ray exposure, members of the Main Group and sLL subgroup of the IAB iron meteorite complex which have a collective CRE corrected μ100Ru value of 0.9 ± 3.0. This suggests that materials from the region(s) of the solar nebula sampled by these meteorites likely contributed the dominant portion of late accreted materials to Earth's mantle.

  2. Can Mg isotopes be used to trace cyanobacteria-mediated magnesium carbonate precipitation in alkaline lakes?

    L. S. Shirokova


    Full Text Available The fractionation of Mg isotopes was determined during the cyanobacterial mediated precipitation of hydrous magnesium carbonate precipitation in both natural environments and in the laboratory. Natural samples were obtained from Lake Salda (SE Turkey, one of the few modern environments on the Earth's surface where hydrous Mg-carbonates are the dominant precipitating minerals. This precipitation was associated with cyanobacterial stromatolites which were abundant in this aquatic ecosystem. Mg isotope analyses were performed on samples of incoming streams, groundwaters, lake waters, stromatolites, and hydromagnesite-rich sediments. Laboratory Mg carbonate precipitation experiments were conducted in the presence of purified Synechococcus sp cyanobacteria that were isolated from the lake water and stromatolites. The hydrous magnesium carbonates nesquehonite (MgCO3·3H2O and dypingite (Mg5(CO34(OH25(H2O were precipitated in these batch reactor experiments from aqueous solutions containing either synthetic NaHCO3/MgCl2 mixtures or natural Lake Salda water, in the presence and absence of live photosynthesizing Synechococcus sp. Bulk precipitation rates were not to affected by the presence of bacteria when air was bubbled through the system. In the stirred non-bubbled reactors, conditions similar to natural settings, bacterial photosynthesis provoked nesquehonite precipitation, whilst no precipitation occurred in bacteria-free systems in the absence of air bubbling, despite the fluids achieving a similar or higher degree of supersaturation. The extent of Mg isotope fractionation (Δ26Mgsolid-solution between the mineral and solution in the abiotic experiments was found to be identical, within uncertainty, to that measured in cyanobacteria-bearing experiments, and ranges from −1.4 to −0.7 ‰. This similarity refutes

  3. Isotopic compositions of cometary matter returned by Stardust.

    McKeegan, Kevin D; Aléon, Jerome; Bradley, John; Brownlee, Donald; Busemann, Henner; Butterworth, Anna; Chaussidon, Marc; Fallon, Stewart; Floss, Christine; Gilmour, Jamie; Gounelle, Matthieu; Graham, Giles; Guan, Yunbin; Heck, Philipp R; Hoppe, Peter; Hutcheon, Ian D; Huth, Joachim; Ishii, Hope; Ito, Motoo; Jacobsen, Stein B; Kearsley, Anton; Leshin, Laurie A; Liu, Ming-Chang; Lyon, Ian; Marhas, Kuljeet; Marty, Bernard; Matrajt, Graciela; Meibom, Anders; Messenger, Scott; Mostefaoui, Smail; Mukhopadhyay, Sujoy; Nakamura-Messenger, Keiko; Nittler, Larry; Palma, Russ; Pepin, Robert O; Papanastassiou, Dimitri A; Robert, François; Schlutter, Dennis; Snead, Christopher J; Stadermann, Frank J; Stroud, Rhonda; Tsou, Peter; Westphal, Andrew; Young, Edward D; Ziegler, Karen; Zimmermann, Laurent; Zinner, Ernst


    Hydrogen, carbon, nitrogen, and oxygen isotopic compositions are heterogeneous among comet 81P/Wild 2 particle fragments; however, extreme isotopic anomalies are rare, indicating that the comet is not a pristine aggregate of presolar materials. Nonterrestrial nitrogen and neon isotope ratios suggest that indigenous organic matter and highly volatile materials were successfully collected. Except for a single (17)O-enriched circumstellar stardust grain, silicate and oxide minerals have oxygen isotopic compositions consistent with solar system origin. One refractory grain is (16)O-enriched, like refractory inclusions in meteorites, suggesting that Wild 2 contains material formed at high temperature in the inner solar system and transported to the Kuiper belt before comet accretion.

  4. Study on in-situ Mg2Si/Al-Si composites with different compositions

    Jing Qingxiu; Zhang Caixia; Huang Xiaodong


    Effects of chemical composition and heat treatment on microstructures and mechanical properties of in-situ Mg2Si/Al-Si composites were investigated. It was found that, in the microstructure of an Al-5.7wt% Mg2Si composite with 8.2wt% extra Si, the binary eutectic Mg2Si locates at the grain boundaries with an undeveloped Chinese script-like morphology, and the primary α-Al is formed into a cell structure due to the selective modification effect of the modifiers of mischmetal and Strontium salt; whereas in the composite with a near Al-Mg2Si eutectic composition and little extra Si content, the intercrescence eutectic Mg2Si formed with the binary eutectic a-Al grows into integrated Chinese script-like shape. As Si content increases, the eutectic Mg2Si dendrite becomes coarser in morphology but less in volum e fraction. Hardness and tensile strength of the cast Mg2Si/Al-Si composites do not increase with increasing of Mg content, but they are related to the size and morphology of the eutectic and primary Mg2Si phases. Heat treatment with optimal parameters is an effective way to improve the properties of the in-situ composites.

  5. Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth

    Chen, Heng; Savage, Paul S.; Teng, Fang-Zehn; Helz, Rosalind T.; Moynier, Frédéric


    he zinc stable isotope system has been successfully applied to many and varied fields in geochemistry, but to date it is still not completely clear how this isotope system is affected by igneous processes. In order to evaluate the potential application of Zn isotopes as a proxy for planetary differentiation and volatile history, it is important to constrain the magnitude of Zn isotopic fractionation induced by magmatic differentiation. In this study we present high-precision Zn isotope analyses of two sets of chemically diverse, cogenetic samples from Kilauea Iki lava lake, Hawaii, and Hekla volcano, Iceland, which both show clear evidence of having undergone variable and significant degrees of magmatic differentiation. The Kilauea Iki samples display small but resolvable variations in Zn isotope composition (0.26‰66Zn66Zn defined as the per mille deviation of a sample's 66Zn/64Zn compositional ratio from the JMC-Lyon standard), with the most differentiated lithologies exhibiting more positive δ66Zn values. This fractionation is likely a result of the crystallization of olivine and/or Fe–Ti oxides, which can both host Zn in their crystal structures. Samples from Hekla have a similar range of isotopic variation (0.22‰66Zn66Zn=0.28±0.05‰ (2s.d.).

  6. Iron isotope composition of some Archean and Proterozoic iron formations

    Planavsky, Noah; Rouxel, Olivier J.; Bekker, Andrey; Hofmann, Axel; Little, Crispin T. S.; Lyons, Timothy W.


    Fe isotopes can provide new insight into redox-dependent biogeochemical processes. Precambrian iron formations (IF) are deserving targets for Fe isotope studies because they are composed predominantly of authigenic Fe phases and record a period of unprecedented iron deposition in Earth's history. We present Fe isotope data for bulk samples from 24 Archean and Proterozoic IF and eight Phanerozoic Fe oxide-rich deposits. These data reveal that many Archean and early Paleoproterozoic iron formations were a sink for isotopically heavy Fe, in contrast to later Proterozoic and Phanerozoic Fe oxide-rich rocks. The positive δ56Fe values in IF are best explained by delivery of particulate ferric oxides formed in the water column to the sediment-water interface. Because IF are a net sink for isotopically heavy Fe, there must be a corresponding pool of isotopically light Fe in the sedimentary record. Earlier work suggested that Archean pyritic black shales were an important part of this light sink before 2.35 billion years ago (Ga). It is therefore likely that the persistently and anomalously low δ56Fe values in shales are linked with the deposition of isotopically heavy Fe in IF in the deeper parts of basins. IF deposition produced a residual isotopically light dissolved Fe pool that was captured by pyritic Fe in shales. Local dissimilatory Fe reduction in porewater and associated diagenetic reactions resulting in pyrite and carbonate precipitation may have further enhanced Fe isotope heterogeneity in marine sediments, and an 'iron shuttle' may have transported isotopically light Fe from shelf sediments to the basin. Nevertheless, water-column processing of hydrothermally delivered Fe likely had the strongest influence on the bulk iron isotope composition of Archean and Paleoproterozoic iron formations and other marine sediments.

  7. Soil Carbon: Compositional and Isotopic Analysis

    Moran, James J.; Alexander, M. L.; Laskin, Alexander


    This is a short chapter to be included in the next edition of the Encyclopedia of Soil Science. The work here describes techniques being developed at PNNL for investigating organic carbon in soils. Techniques discussed include: laser ablation isotope ratio mass spectrometry, laser ablation aerosol mass spectrometry, and nanospray desorption electrospray ionization mass spectrometry.

  8. Composition Range of Amorphous Mg-Ni-Y Alloys

    陈红梅; 钟夏平; 欧阳义芳


    Based on the thermodynamic point of view, a method for predication of the composition range of amorphous ternary alloys was proposed. The composition range of amorphous ternary alloys is determined by the comparison of the excess free energy of the amorphous alloy and the free energy of competing crystalline states. The free energy is extrapolated from the data of three binary alloys by using Toop′s model. The method was applied to predict the composition range of amorphous Mg-Ni-Y alloys. The theoretical results are in good agreement with the available experimental results. It indicates that the present method can be used to predict the composition range for amorphous ternary alloys.

  9. Stable isotope composition of human fingernails from Slovakia

    Grolmusová, Zuzana, E-mail: [Comenius University in Bratislava, Faculty of Mathematics, Physics and Informatics, Department of Experimental Physics, Mlynská dolina F2, 842 48 Bratislava (Slovakia); State Geological Institute of Dionýz Štúr, Laboratory of Isotope Geology, Mlynská dolina 1, 817 04 Bratislava (Slovakia); Rapčanová, Anna [Comenius University in Bratislava, Faculty of Mathematics, Physics and Informatics, Department of Experimental Physics, Mlynská dolina F2, 842 48 Bratislava (Slovakia); Michalko, Juraj; Čech, Peter [State Geological Institute of Dionýz Štúr, Laboratory of Isotope Geology, Mlynská dolina 1, 817 04 Bratislava (Slovakia); Veis, Pavel [Comenius University in Bratislava, Faculty of Mathematics, Physics and Informatics, Department of Experimental Physics, Mlynská dolina F2, 842 48 Bratislava (Slovakia); State Geological Institute of Dionýz Štúr, Laboratory of Isotope Geology, Mlynská dolina 1, 817 04 Bratislava (Slovakia)


    Stable isotope composition of human fingernails has proven to be useful for documenting human dietary information and geographical patterns in archeological, forensic, anthropological and biological studies. Therefore, it is of interest to detect all factors influencing the stable isotopic composition in the certain regions in the world. Carbon and nitrogen isotope data of human fingernail keratin from 52 individuals from Slovakia were reported in this study. The online combustion and continuous flow isotope-ratio mass spectrometer Delta V Advantage was used for δ{sup 13}C and δ{sup 15}N analysis of fingernail keratin samples from 24 vegetarian and 28 omnivorous individuals. A group of people with frequent meat consumption showed enrichment in {sup 13}C and {sup 15}N isotopes in fingernails. A similar trend was observed with increasing seafood in an individual's diet. Moreover a significant difference was revealed between smokers and nonsmokers for both δ{sup 13}C and δ{sup 15}N values. These data were compared to previously published δ{sup 13}C and δ{sup 15}N fingernail values from across the globe. This study brings new information on the stable isotope signature of individuals from Slovakia and characterizes the Central European region for the first time. The stable isotope composition of fingernails is influenced by the frequency of meat and seafood consumption as well as smoking. - Highlights: • This study deals with stable isotope analyses of fingernails from Slovak volunteers. • δ{sup 13}C and δ{sup 15}N values of vegetarian and omnivore fingernails were compared. • Influence of sex, diet and smoking was studied.


    Poitrasson, F.; Zambardi, T.; Magna, T.; Neal, C. R.


    responsible for this peculiar isotopic effect observed in the high-Ti basalts that are unknown on Earth. It might be linked to armalcolite, a Fe- and Ti-oxide specific to the Moon. Estimating the bulk Moon Fe isotope composition remains difficult. The now clarified Fe isotope difference between high- and low-Ti basalts shows that a high temperature process generates a planetary-scale Fe isotope fractionation. Hence, these basalts cannot be easily taken as the direct proxies of the Fe isotope composition of the deep Moon. On the other hand, highland rocks, both anorthosites and rocks from the Mg-suite that are older than the mare basalts, display the same Fe isotope composition whatever their petrology. They may well yield a more pristine iron isotope composition of the bulk Moon. The value obtained here (δ57Fe = 0.177±0.036‰) is undistinguishable from our previous estimate for the Moon (0.206±0.029‰). It must be recognized, however, that this conclusion is based on a limited number of samples (n = 6) and more highland bulk rock data are required to assess whether the Moon is isotopically similar to or different from the Earth.

  11. Aerosol carbon isotope composition over Baltic Sea

    Garbaras, Andrius; Pabedinskas, Algirdas; Masalaite, Agne; Petelski, Tomasz; Gorokhova, Elena; Sapolaite, Justina; Ezerinskis, Zilvinas; Remeikis, Vidmantas


    Particulate carbonaceous matter is significant contributor to ambient particulate matter originating from intervening sources which contribution is difficult to quantify due to source diversity, chemical complexity and processes during atmospheric transport. Carbon isotope analysis can be extremely useful in source apportionment of organic matter due to the unique isotopic signatures associated with anthropocentric (fossil fuel), continental (terrestrial plants) and marine sources, and is particularly effective when these sources are mixed (Ceburnis et al., 2011;Ceburnis et al., 2016). We will present the isotope ratio measurement results of aerosol collected during the cruise in the Baltic Sea. Sampling campaign of PM10 and size segregated aerosol particles was performed on the R/V "Oceania" in October 2015. Air mass back trajectories were prevailing both from the continental and marine areas during the sampling period. The total carbon concentration varied from 1 µg/m3 to 8 µg/m3. Two end members (δ13C = -25‰ and δ13C = -28 ‰ ) were established from the total stable carbon isotope analysis in PM10 fraction. δ13C analysis in size segregated aerosol particles revealed δ13C values being highest in the 1 - 2.5 µm range (δ13C = -24.9 ‰ ) during continental transport, while lowest TC δ13C values (δ13C ≈ -27 ‰ ) were detected in the size range D50 dual carbon pools contributing to organic matter enrichment in marine aerosol, Scientific Reports, 6, 2016. Masalaite, A., Remeikis, V., Garbaras, A., Dudoitis, V., Ulevicius, V., and Ceburnis, D.: Elucidating carbonaceous aerosol sources by the stable carbon δ13C TC ratio in size-segregated particles, Atmospheric Research, 158, 1-12, 2015.

  12. Carbon isotopic composition of individual Precambrian microfossils.

    House, C H; Schopf, J W; McKeegan, K D; Coath, C D; Harrison, T M; Stetter, K O


    Ion microprobe measurements of carbon isotope ratios were made in 30 specimens representing six fossil genera of microorganisms petrified in stromatolitic chert from the approximately 850 Ma Bitter Springs Formation, Australia, and the approximately 2100 Ma Gunflint Formation, Canada. The delta 13C(PDB) values from individual microfossils of the Bitter Springs Formation ranged from -21.3 +/- 1.7% to -31.9 +/- 1.2% and the delta 13C(PDB) values from microfossils of the Gunflint Formation ranged from -32.4 +/- 0.7% to -45.4 +/- 1.2%. With the exception of two highly 13C-depleted Gunflint microfossils, the results generally yield values consistent with carbon fixation via either the Calvin cycle or the acetyl-CoA pathway. However, the isotopic results are not consistent with the degree of fractionation expected from either the 3-hydroxypropionate cycle or the reductive tricarboxylic acid cycle, suggesting that the microfossils studied did not use either of these pathways for carbon fixation. The morphologies of the microfossils suggest an affinity to the cyanobacteria, and our carbon isotopic data are consistent with this assignment.

  13. What controls the isotopic composition of Greenland surface snow?

    H. C. Steen-Larsen


    Full Text Available Water stable isotopes in Greenland ice core data provide key paleoclimatic information, and have been compared with precipitation isotopic composition simulated by isotopically-enabled atmospheric models. However, post-deposition processes linked with snow metamorphism remain poorly documented. For this purpose, a monitoring of the isotopic composition (δ18O, δD of surface water vapor, precipitation and samples of top (0.5 cm snow surface has been conducted during two summers (2011–2012 at NEEM, NW Greenland. The measurements also include a subset of 17O-excess measurements over 4 days, and the measurements span the 2012 Greenland heat wave. Our observations are consistent with calculations assuming isotopic equilibrium between surface snow and water vapor. We observe a strong correlation between surface vapor δ18O and air temperature (0.85 ± 0.11 ‰ °C−1 (R = 0.76 for 2012. The correlation with air temperature is not observed in precipitation data or surface snow data. Deuterium excess (d-excess is strongly anti-correlated with δ18O with a stronger slope for vapor than for precipitation and snow surface data. During nine 1–5 days periods between precipitation events, our data demonstrate parallel changes of δ18O and d-excess in surface snow and surface vapor. The changes in δ18O of the vapor are similar or larger than those of the snow δ18O. It is estimated that 6 to 20% of the surface snow mass is exchanged with the atmosphere using the CROCUS snow model. In our data, the sign of surface snow isotopic changes is not related to the sign or magnitude of sublimation or condensation. Comparisons with atmospheric models show that day-to-day variations in surface vapor isotopic composition are driven by synoptic weather and changes in air mass trajectories and distillation histories. We suggest that, in-between precipitation events, changes in the surface snow isotopic composition are driven by these changes in surface vapor isotopic

  14. What controls the isotopic composition of Greenland surface snow?

    H. C. Steen-Larsen


    Full Text Available Water stable isotopes in Greenland ice core data provide key paleoclimatic information, and have been compared with precipitation isotopic composition simulated by isotopically enabled atmospheric models. However, post-depositional processes linked with snow metamorphism remain poorly documented. For this purpose, monitoring of the isotopic composition (δ18O, δD of near-surface water vapor, precipitation and samples of the top (0.5 cm snow surface has been conducted during two summers (2011–2012 at NEEM, NW Greenland. The samples also include a subset of 17O-excess measurements over 4 days, and the measurements span the 2012 Greenland heat wave. Our observations are consistent with calculations assuming isotopic equilibrium between surface snow and water vapor. We observe a strong correlation between near-surface vapor δ18O and air temperature (0.85 ± 0.11‰ °C−1 (R = 0.76 for 2012. The correlation with air temperature is not observed in precipitation data or surface snow data. Deuterium excess (d-excess is strongly anti-correlated with δ18O with a stronger slope for vapor than for precipitation and snow surface data. During nine 1–5-day periods between precipitation events, our data demonstrate parallel changes of δ18O and d-excess in surface snow and near-surface vapor. The changes in δ18O of the vapor are similar or larger than those of the snow δ18O. It is estimated using the CROCUS snow model that 6 to 20% of the surface snow mass is exchanged with the atmosphere. In our data, the sign of surface snow isotopic changes is not related to the sign or magnitude of sublimation or deposition. Comparisons with atmospheric models show that day-to-day variations in near-surface vapor isotopic composition are driven by synoptic variations and changes in air mass trajectories and distillation histories. We suggest that, in between precipitation events, changes in the surface snow isotopic composition are driven by these changes in near

  15. What controls the isotopic composition of Greenland surface snow?

    Steen-Larsen, H. C.; Masson-Delmotte, V.; Hirabayashi, M.; Winkler, R.; Satow, K.; Prié, F.; Bayou, N.; Brun, E.; Cuffey, K. M.; Dahl-Jensen, D.; Dumont, M.; Guillevic, M.; Kipfstuhl, S.; Landais, A.; Popp, T.; Risi, C.; Steffen, K.; Stenni, B.; Sveinbjörnsdottír, A. E.


    Water stable isotopes in Greenland ice core data provide key paleoclimatic information, and have been compared with precipitation isotopic composition simulated by isotopically enabled atmospheric models. However, post-depositional processes linked with snow metamorphism remain poorly documented. For this purpose, monitoring of the isotopic composition (δ18O, δD) of near-surface water vapor, precipitation and samples of the top (0.5 cm) snow surface has been conducted during two summers (2011-2012) at NEEM, NW Greenland. The samples also include a subset of 17O-excess measurements over 4 days, and the measurements span the 2012 Greenland heat wave. Our observations are consistent with calculations assuming isotopic equilibrium between surface snow and water vapor. We observe a strong correlation between near-surface vapor δ18O and air temperature (0.85 ± 0.11‰ °C-1 (R = 0.76) for 2012). The correlation with air temperature is not observed in precipitation data or surface snow data. Deuterium excess (d-excess) is strongly anti-correlated with δ18O with a stronger slope for vapor than for precipitation and snow surface data. During nine 1-5-day periods between precipitation events, our data demonstrate parallel changes of δ18O and d-excess in surface snow and near-surface vapor. The changes in δ18O of the vapor are similar or larger than those of the snow δ18O. It is estimated using the CROCUS snow model that 6 to 20% of the surface snow mass is exchanged with the atmosphere. In our data, the sign of surface snow isotopic changes is not related to the sign or magnitude of sublimation or deposition. Comparisons with atmospheric models show that day-to-day variations in near-surface vapor isotopic composition are driven by synoptic variations and changes in air mass trajectories and distillation histories. We suggest that, in between precipitation events, changes in the surface snow isotopic composition are driven by these changes in near-surface vapor

  16. Australian atmospheric lead deposition reconstructed using lead concentrations and isotopic compositions of archival lichen and fungi.

    Wu, Liqin; Taylor, Mark Patrick; Handley, Heather K; Wu, Michael


    Lead concentrations and their isotopic compositions were measured in lichen genera Cladonia and Usnea and fungi genus Trametes from the Greater Sydney region (New South Wales, Australia) that had been collected and archived over the past 120 years. The median lead contents were elevated in lichens and fungi prior to the introduction of leaded petrol (Cladonia 12.5 mg/kg; Usnea 15.6 mg/kg; Trametes 1.85 mg/kg) corresponding to early industrial development. During the use of leaded petrol for automobiles in Australia from 1932 to 2002, total median lead concentrations rose: Cladonia 18.8 mg/kg; Usnea 21.5 mg/kg; Trametes 4.3 mg/kg. Following the cessation of leaded petrol use, median total lead concentrations decreased sharply in the 2000s: Cladonia 4.8 mg/kg; Usnea 1.7 mg/kg. The lichen and fungi isotopic compositions reveal a significant decrease in (206)Pb/(207)Pb values from the end of 19th century to the 1970s. The following decades were characterised by lower allowable levels of lead additive in fuel and the introduction of unleaded petrol in 1985. The environmental response to these regulatory changes was that lichen and fungi (206)Pb/(207)Pb values increased, particularly from 1995 onwards. Although the lead isotope ratios of lichens continued to increase in the 2000s they do not return to pre-leaded petrol values. This demonstrates that historic leaded petrol emissions, inter alia other sources, remain a persistent source of anthropogenic contamination in the Greater Sydney region.

  17. Oxygen Isotope Composition of Nitrate Produced by Freshwater Nitrification

    Boshers, D.; Granger, J.; Bohlke, J. K.


    Measurements of the naturally occurring nitrogen and oxygen stable isotope ratios of nitrate (NO3-), δ15N and δ18O, can be used to determine the source, dispersal, and fate of natural and contaminant NO3- in aquatic environments. To this end, it is necessary to know the extent to which NO3- isotopologues are modified by biological reactions, as heavy and light isotopes have different reaction rates. The purpose of this study was to determine the influence of the δ18O of ambient water on the isotope composition of NO3- produced during nitrification, the biological oxidation of ammonium (NH4+) to nitrite (NO2-) and then NO3-, which is poorly constrained in freshwater systems. To determine the δ18O of NO3- produced by nitrification in freshwater, we collected water from a stream in New England, which we amended with NH4+ and with increments of 18O-enriched water, to monitor the isotope composition of NO3- produced by a natural consortium of nitrifiers. Added NH4+ was completely oxidized to NO3- over 26 days. The final δ18O of nitrified NO3- revealed sensitivity to the δ18O of water mediated by (a) isotopic equilibration between water and NO2- and (b) kinetic isotope fractionation during O-atom incorporation from water into NO2- and NO3-. Our results concur with nitrifying culture experiments that have demonstrated analogous sensitivity of the δ18O of nitrified NO3- to equilibrium and kinetic O isotope effects (Buchwald et al. 2012), as well as show that these dynamics need to be considered to interpret NO3- isotope distribution in freshwater environments.

  18. Measurement of Plutonium Isotopic Composition - MGA

    Vo, Duc Ta [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)


    In this module, we will use the Canberra InSpector-2000 Multichannel Analyzer with a high-purity germanium detector (HPGe) and the MGA isotopic anlysis software to assay a variety of plutonium samples. The module provides an understanding of the MGA method, its attributes and limitations. You will assess the system performance by measuring a range of materials similar to those you may assay in your work. During the final verification exercise, the results from MGA will be combined with the 240Pueff results from neutron coincidence or multiplicity counters so that measurements of the plutonium mass can be compared with the operator-declared (certified) values.

  19. Isotopic fractionation of Mg 2+(aq), Ca 2+(aq), and Fe 2+(aq) with carbonate minerals

    Rustad, James R.; Casey, William H.; Yin, Qing-Zhu; Bylaska, Eric J.; Felmy, Andrew R.; Bogatko, Stuart A.; Jackson, Virgil E.; Dixon, David A.


    Density-functional electronic structure calculations are used to compute the equilibrium constants for 26Mg/ 24Mg and 44Ca/ 40Ca isotope exchange between carbonate minerals and uncomplexed divalent aquo ions. The most reliable calculations at the B3LYP/6-311++G(2d,2p) level predict equilibrium constants K, reported as 10 3ln ( K) at 25 °C, of -5.3, -1.1, and +1.2 for 26Mg/ 24Mg exchange between calcite (CaCO 3), magnesite (MgCO 3), and dolomite (Ca 0.5Mg 0.5CO 3), respectively, and Mg 2+(aq), with positive values indicating enrichment of the heavy isotope in the mineral phase. For 44Ca/ 40Ca exchange between calcite and Ca 2+(aq) at 25 °C, the calculations predict values of +1.5 for Ca 2+(aq) in 6-fold coordination and +4.1 for Ca 2+(aq) in 7-fold coordination. We find that the reduced partition function ratios can be reliably computed from systems as small as M(CO)610- and M(HO)62+ embedded in a set of fixed atoms representing the second-shell (and greater) coordination environment. We find that the aqueous cluster representing the aquo ion is much more sensitive to improvements in the basis set than the calculations on the mineral systems, and that fractionation factors should be computed using the best possible basis set for the aquo complex, even if the reduced partition function ratio calculated with the same basis set is not available for the mineral system. The new calculations show that the previous discrepancies between theory and experiment for Fe 3+-hematite and Fe 2+-siderite fractionations arise from an insufficiently accurate reduced partition function ratio for the Fe 3+(aq) and Fe 2+(aq) species.

  20. Isotopic Fractionation of Mg2+(aq), Ca2+(aq), and Fe2+(aq) with Carbonate Minerals

    Rustad, James R.; Casey, William H.; Yin, Qing-Zhu; Bylaska, Eric J.; Felmy, Andrew R.; Bogatko, Stuart A.; Jackson, Virgil E.; Dixon, David A.


    Density functional electronic structure calculations are used to compute the equilibrium constant (the isotope fractionation factor) for 26Mg/24Mg and 44Ca/40Ca isotope exchange between carbonate minerals and uncomplexed divalent aquo ions. The most reliable calculations at the B3LYP/6-311++G(2d,2p) level predict equilibrium constants K, reported as 103ln(K) at 25 °C, of -5.3, -1.1, and +1.1 for 26Mg/24Mg exchange between calcite (CaCO3), magnesite (MgCO3), and dolomite (Ca0.5Mg0.5CO3), respectively, and Mg2+(aq), with positive values indicating enrichment in the mineral phase. For 44Ca/40Ca exchange between calcite and Ca2+(aq), the calculations predict values of +1.5 for Ca2+(aq) in six-fold coordination and +4.1 for Ca2+(aq) in seven-fold coordination. We find that the reduced partition function ratios can be reliably computed from systems as small as M(CO3)610- and M2+(H2O)6 embedded in a set of fixed atoms representing the 2nd shell (and greater) coordination environment. We find that the aqueous cluster representing the aquo ion is much more sensitive to improvements in the basis set than the calculations on the mineral systems, and that fractionation factors should be computed using 2 the best possible basis set for the aquo complex, even if the reduced partition function ratio calculated with the same basis set is not available for the mineral system. The new calculations show that the previous discrepancies between theory and experiment for Fe3+-hematite and Fe2+-siderite fractionations arise from an insufficiently accurate reduced partition function ratio for the Fe3+(aq) and Fe2+(aq) species.

  1. Lead isotope and trace element composition of urban soils in Mongolia

    Tserenpil, Sh.; Sapkota, A.; Liu, C.-Q.; Peng, J.-H.; Liu, B.; Segebade, P. Chr.


    Lead (Pb) pollution in and around Ulaanbaatar is of national concern, given that the Mongolian capital is home to nearly half of the country's entire population. By comparison, Mongolian countryside is a pristine environment because of its sparse population and low industrial activity. The concentration of Pb in urban soils (average of 39.1 mg kg-1) was twice the values found (average 18.6 mg kg-1) in background territories (i.e., Mongolian rural sites). Furthermore, Pb contamination was examined by using Pb stable isotopic composition, and covariance of Pb isotopic ratios showed two groups between rural and urban soils as pristine and disturbed sites. The 206Pb/207Pb ratio, the most prominent fingerprint for Pb pollution, was 1.163-1.185 for the urban whereas values for rural soils (1.186-1.207) were analogue to the regional Pb isotopic signatures. Local coal sources and their combustion products, one of the potential Pb pollution sources in Ulaanbaatar, have significant radiogenic properties in terms of Pb isotopic composition and revealed an average of 1.25 for 206Pb/207Pb and 19.551 for 206Pb/204Pb ratios. Thus, contributions from coal firing activity to Pb pollution lower than it was assumed, and smaller range of these values measured in urban soils may be attributed to the mixing of less radiogenic Pb as a constituent of the leaded gasolines.

  2. Authentication of bell peppers using boron and strontium isotope compositions

    Rosner, Martin; Pritzkow, Wolfgang; Vogl, Jochen; Voerkelius, Susanne


    The wrong declaration of food in terms of geographical origin and production method is a major problem for the individual consumer and public regulatory authorities. The authentication of food matrices using H-C-N-O-S isotopic compositions is already well established. However, specific questions require additional isotopic systems, which are more diagonstic for the source reservoires involved or production methods used. Here we present B and Sr isotopic compositions of bell peppers from Europe (Germany, Austria, Netherlands, Spain) and Israel to verfiy their origin. The bell peppers' B isotopic compositions between different locations are highly variable (d11BNISTSRM951 -8 to +35 ‰), whereas the 87Sr/86Sr ratios are all close to modern seawater Sr isotopic composition of about 0.7092 (0.7078 to 0.7107), but still can reliably be distinguished. Distinct isotopically heavy and light B isotopic fingerprints are obtained for bell peppers from Israel and the Netherlands. Samples from Germany, Austria, and Spain display overlapping d11B values between 0 and +12 ‰. Bell peppers from Israel show high d11B values (+28 to +35 ‰) combined with 87Sr/86Sr ratios slightly more unradiogenic than modern seawater (ca 0.7079). Bell peppers from the Netherlands, however, show low d11B values (-8 ‰) combinded with 87Sr/86Sr ratios of modern seawater (approx. 0.7085). Mainly based on diagnostic B isotopic compositions bell peppers from Israel and the Netherlands can be related to a specific geographical growing environment (Israel) or production method (Netherlands). The isotope fingerprints of bell peppers from the Netherlands are consistent with growing conditions in greenhouses typical for the Netherlands vegetable farming. Using optimized production methods crops in greenhouses were supplied with nutritients by liquid fertilizers on artificial substrates. As most fertilizers derive from non-marine salt deposits, fertilization typically imprints invariant d11B values close

  3. Evolution of Single Particle and Collective properties in the Neutron-Rich Mg Isotopes

    Reiter, P; Wiens, A; Fitting, J; Lauer, M; Van duppen, P L E; Finke, F


    We propose to study the single particle and collective properties of the neutron-rich Mg isotopes in transfer reactions and Coulomb excitation using REX-ISOLDE and MINIBALL. From the Coulomb excitation measurement precise and largely model independent B( E2 ; 0$^{+}_{g.s.}\\rightarrow$ 2$^{+}_{1}$ ) will be determined for the even-even isotopes. For the odd isotopes the distribution of the E2 strength over a few low-lying states will be measured. The sign of the M1/E2 mixing ratio, extracted from angular distributions, is characteristic of the sign of the deformation, as is the resulting level scheme. The neutron-pickup channel in the transfer reactions will allow for a determination of the single particle properties (spin, parity, spectroscopic factors) of these nuclei. This information will give new insights in changes of nuclear structure in the vicinity of the island of deformation around $^{32}$Mg. A total of 24 shifts of REX beam time is requested.

  4. Isotope composition and volume of Earth's early oceans.

    Pope, Emily C; Bird, Dennis K; Rosing, Minik T


    Oxygen and hydrogen isotope compositions of Earth's seawater are controlled by volatile fluxes among mantle, lithospheric (oceanic and continental crust), and atmospheric reservoirs. Throughout geologic time the oxygen mass budget was likely conserved within these Earth system reservoirs, but hydrogen's was not, as it can escape to space. Isotopic properties of serpentine from the approximately 3.8 Ga Isua Supracrustal Belt in West Greenland are used to characterize hydrogen and oxygen isotope compositions of ancient seawater. Archaean oceans were depleted in deuterium [expressed as δD relative to Vienna standard mean ocean water (VSMOW)] by at most 25 ± 5‰, but oxygen isotope ratios were comparable to modern oceans. Mass balance of the global hydrogen budget constrains the contribution of continental growth and planetary hydrogen loss to the secular evolution of hydrogen isotope ratios in Earth's oceans. Our calculations predict that the oceans of early Earth were up to 26% more voluminous, and atmospheric CH(4) and CO(2) concentrations determined from limits on hydrogen escape to space are consistent with clement conditions on Archaean Earth.

  5. Tracing anthropogenic thallium in soil using stable isotope compositions.

    Kersten, Michael; Xiao, Tangfu; Kreissig, Katharina; Brett, Alex; Coles, Barry J; Rehkämper, Mark


    Thallium stable isotope data are used in this study, for the first time, to apportion Tl contamination in soils. In the late 1970s, a cement plant near Lengerich, Germany, emitted cement kiln dust (CKD) with high Tl contents, due to cocombustion of Tl-enriched pyrite roasting waste. Locally contaminated soil profiles were obtained down to 1 m depth and the samples are in accord with a binary mixing relationship in a diagram of Tl isotope compositions (expressed as ε(205)Tl, the deviation of the (205)Tl/(203)Tl ratio of a sample from the NIST SRM 997 Tl isotope standard in parts per 10(4)) versus 1/[Tl]. The inferred mixing endmembers are the geogenic background, as defined by isotopically light soils at depth (ε(205)Tl ≈ -4), and the Tl emissions, which produce Tl-enriched topsoils with ε(205)Tl as high as ±0. The latter interpretation is supported by analyses of the CKD, which is also characterized by ε(205)Tl ≈ ± 0, and the same ε(205)Tl value was found for a pyrite from the deposit that produced the cocombusted pyrite roasting waste. Additional measurements for samples from a locality in China, with outcrops of Tl sulfide mineralization and associated high natural Tl backgrounds, reveal significant isotope fractionation between soils (ε(205)Tl ≈ +0.4) and locally grown green cabbage (ε(205)Tl between -2.5 and -5.4). This demonstrates that biological isotope fractionation cannot explain the isotopically heavy Tl in the Lengerich topsoils and the latter are therefore clearly due to anthropogenic Tl emissions from cement processing. Our results thus establish that isotopic data can reinforce receptor modeling for the toxic trace metal Tl.

  6. Characteristics of carbon and hydrogen isotopic compositions of light hydrocarbons



    Light hydrocarbons named in the present paper refer to the natural gas-associated light oil and condensate 46 light oil and condensate samples from 11 oil-bearing basins of China were collected and their carbon and hydrogen isotopic compositions were analysed in terms of their total hydrocarbons, saturated hydrocarbons and a part of aromatic fractions, and gas-source materials and their sedimentary environments were discussed based on the above-mentioned data and the geological background of each area. From the view of carbon and hydrogen isotopic composition of total hydrocarbons and saturated hydrocarbons, it is revealed that the condensate related to coal-bearing strata is enriched in 13C and D while that related to the source material of type I-II is enriched in 12C. In general, the isotopic composition of carbon is mainly attributed to the inheriting effect of their source materials, whereas that of hydrogen principally reflects the correlationship between hydrogen isotopes and the sedimentary envi

  7. The isotopic composition of solar flare accelerated neon

    Mewaldt, R. A.; Spalding, J. D.; Stone, E. C.; Vogt, R. E.


    The individual isotopes of neon in energetic solar-flare particles have been clearly resolved with a rms mass resolution of 0.20 amu. The ratios found are Ne-20/Ne-22 = 7.6 (+2.0, -1.8) and Ne-21/Ne-22 of no more than about 0.11 in the 11-26 MeV per nucleon interval. This isotopic composition is essentially the same as that of meteoritic planetary neon-A and is significantly different from that of the solar wind.

  8. Stable isotope composition and volume of Early Archaean oceans

    Pope, Emily Catherine; Rosing, Minik Thorleif; Bird, Dennis K.

    Oxygen and hydrogen isotope compositions of seawater are controlled by volatile fluxes between mantle, lithospheric (oceanic and continental crust) and atmospheric reservoirs. Throughout geologic time oxygen was likely conserved within these Earth system reservoirs, but hydrogen was not, as it can...... escape to space [1]. Hydrogen isotope ratios of serpentinites from the ~3.8Ga Isua Supracrustal Belt in West Greenland are between -53 and -99‰; the highest values are in antigorite ± lizardite serpentinites from a low-strain lithologic domain where hydrothermal reaction of Archaean seawater with oceanic...

  9. New approach to global barium cycle understanding: barium isotopic composition of marine carbonates and seawater.

    Pretet, Chloé; Nägler, Thomas F.; Reynaud, Stéphanie; de Lange, Gert J.; Turpin, Mélanie; Immenhauser, Adrian; Böttcher, Michael E.; Samankassou, Elias


    In this communication we present the Ba isotope fractionation (delta137/134Ba) study on marine carbonates and seawater, initiated to gain a first order view of the marine Ba isotope cycle. A special focus is the question whether the nutrient type distribution of Ba in the water column, as well as different Ba sources, are reflected in Ba isotope ratios of carbonate archives. The approach ultimately aims to provide an improved Ba based paleonutrient proxy. The data set is composed of carbonates (micrites and limestone standard), coral skeleton and seawater (IAPSO standard and Mediterranean seawater). Part of the corals were cultured in monitored environments (CSM, Monaco) others originate from natural environments (shallow and warm water corals from the Bahamas/Florida and cold water corals from the Norwegian shelf). The analytical procedure includes the application of a 130Ba/135Ba double spike, a cation exchange column followed by isotope measurements on a Nu Instruments Multicollector ICP-MS. The Ba fractionation of the samples is compared to a Ba nitrate standard solution and a standard natural limestone BSC-CRM 393 (0.05 ± 0.04 ‰, 2SEM). No isotopic fractionation has been observed in the limestone standard and micrites (N=8) (-0.01 ± 0.04 ‰, 2SEM) compared to the Ba nitrate standard. On the contrary, coral skeletons show a significant positive fractionation (mean = 0.4 ± 0.05 ‰, 2 SEM). No significant difference was found between different cultured coral species. Thus no species-specific fractionation is identified within the same environmental conditions. Diagenetic influence on Ba isotopic composition was further tested on 5 natural samples with varying calcite to aragonite ratios (0 to 0.3). No significant effect was observed. Moreover, the Ba isotope composition seems independant from the Ba concentration in the studied coral skeleton, within our measurement resolution. Seawater isotopic composition (-0.05 ± 0.07 ‰, 2SD) is lighter than coral

  10. Do foraminifera accurately record seawater neodymium isotope composition?

    Scrivner, Adam; Skinner, Luke; Vance, Derek


    Palaeoclimate studies involving the reconstruction of past Atlantic meridional overturning circulation increasingly employ isotopes of neodymium (Nd), measured on a variety of sample media (Frank, 2002). In the open ocean, Nd isotopes are a conservative tracer of water mass mixing and are unaffected by biological and low-temperature fractionation processes (Piepgras and Wasserburg, 1987; Lacan and Jeandel, 2005). For decades, benthic foraminifera have been widely utilised in stable isotope and geochemical studies, but have only recently begun to be exploited as a widely distributed, high-resolution Nd isotope archive (Klevenz et al., 2008), potentially circumventing the difficulties associated with other methods used to recover past deep-water Nd isotopes (Klevenz et al., 2008; Rutberg et al., 2000; Tachikawa et al., 2004). Thus far, a single pilot study (Klevenz et al., 2008) has indicated that core-top sedimentary benthic foraminifera record a Nd isotope composition in agreement with the nearest available bottom seawater data, and has suggested that this archive is potentially useful on both millennial and million-year timescales. Here we present seawater and proximal core-top foraminifer Nd isotope data for samples recovered during the 2008 "RETRO" cruise of the Marion Dufresne. The foraminifer samples comprise a depth-transect spanning 3000m of the water column in the Angola Basin and permit a direct comparison between high-resolution water column and core-top foraminiferal Nd isotope data. We use these data to assess the reliability of both planktonic and benthic foraminifera as recorders of water column neodymium isotope composition. Frank, M., 2002. Radiogenic isotopes: Tracers of past ocean circulation and erosional input, Rev. Geophys., 40 (1), 1001, doi:10.1029/2000RG000094. Klevenz, V., Vance, D., Schmidt, D.N., and Mezger, K., 2008. Neodymium isotopes in benthic foraminifera: Core-top systematics and a down-core record from the Neogene south Atlantic

  11. C-isotope composition of fossil sedges and grasses

    Kurschner, Wolfram M.


    C4 plants differ from C3 plants regarding their anatomy and their C-isotope composition. Both features can be used in the geological record to determine the presence of C4 plants. Yet, the evolution of the C4 pathway in the fossil record is enigmatic as palaeobotanical and geological evidence for C4 plants is sparse. The oldest structural evidence for Kranz anatomy has been found in Late Miocene permineralized grass leaf remains. But studies on the C-isotope composition of sedimentary organic matter indicate that abundant C4 biomass was present in N-America and Asia throughout the Miocene in expanding savannahs and grasslands. The success of C4 plants appears to be related also to an increasing seasonal aridity in the tropical climate belts and the co-evolution of grazers. However, C- isotope composition of palaeosols or vertebrate teeth only allows to estimate the abundance of C4 plant biomass in the vegetation or in the diet without further taxonomical specification which plant groups would have had C4 metabolism. In this contribution the first extensive C-isotope analysis of fossil seeds of sedges and a few grasses are presented. The age of the carpological material ranges from Late Eocene to Pliocene and was collected from several central European brown coal deposits. The 52 different taxa studied include several species of Carex, Cladiocarya, Eriopherum, Eleocharis, Scirpus, Sparganium. Most of them representing herbaceous elements of a (sub)tropical vegetation growing near the edge of a lake. The C-isotope composition of the fossil seeds varies between -30 and -23 o/oo indicating C3 photosynthesis. This first systematic inventory shows that C4 plants were absent in the European (sub)tropical brown coal forming wetland vegetation during the Tertiary. These preliminary data are in agreement with phylogenetic studies which predict the origin of C4 plants outside the European realm.

  12. Magnesium and 54Cr isotope compositions of carbonaceous chondrite chondrules – Insights into early disk processes

    Olsen, Mia Bjørg Stolberg; Wielandt, Daniel Kim Peel; Schiller, Martin


    .04–0.27) and display little or no evidence for secondary alteration processes. The CV and CR chondrules show variable 25Mg/24Mg and 26Mg/24Mg values corresponding to a range of mass-dependent fractionation of ∼500 ppm (parts per million) per atomic mass unit. This mass-dependent Mg isotope fractionation is interpreted......We report on the petrology, magnesium isotopes and mass-independent 54Cr/52Cr compositions (μ54Cr) of 42 chondrules from CV (Vigarano and NWA 3118) and CR (NWA 6043, NWA 801 and LAP 02342) chondrites. All sampled chondrules are classified as type IA or type IAB, have low 27Al/24Mg ratios (0...

  13. The nucleosynthesis of heavy elements in Stars: the key isotope 25Mg

    Massimi C.


    Full Text Available We have measured the radiative neutron-capture cross section and the total neutron-induced cross section of one of the most important isotopes for the s process, the 25Mg. The measurements have been carried out at the neutron time-of-flight facilities n_TOF at CERN (Switzerland and GELINA installed at the EC-JRC-IRMM (Belgium. The cross sections as a function of neutron energy have been measured up to approximately 300 keV, covering the energy region of interest to the s process. The data analysis is ongoing and preliminary results show the potential relevance for the s process.

  14. Boron isotopic compositions of some boron minerals

    Oi, Takao; Musashi, Masaaki; Ossaka, Tomoko; Kakihana, Hidetake (Sophia Univ., Tokyo (Japan)); Nomura, Masao; Okamoto, Makoto (Tokyo Institute of Technology (Japan))


    Boron minerals that have different structural formulae but are supposed to have the same geologic origin have been collected and analyzed for the {sup 11}B/{sup 10}B isotopic ratio. It has been reconfirmed that minerals of marine origin have higher {sup 11}B/{sup 10}B ratios than those of nonmarine origin. It has been found that the sequence of decreasing {sup 11}B/{sup 10}B values among the minerals with the same geologic origin is; borax, tincal, kernite (Na borates) > ulexite (Na/Ca borate) > colemanite, iyoite, meyerhofferite (Ca borates). This sequence is explainable on the basis of the difference in crystal structure among the minerals. That is, minerals with high BO{sub 3}/BO{sub 4} ratios, (the ratio of the number of the BO{sub 3} triangle units to the number of the BO{sub 4} tetrahedron units in the structural formula of a mineral) have higher {sup 11}B/{sup 10}B ratios.

  15. Stable isotope composition and volume of Early Archaean oceans

    Pope, Emily Catherine; Rosing, Minik Thorleif; Bird, Dennis K.

    Oxygen and hydrogen isotope compositions of seawater are controlled by volatile fluxes between mantle, lithospheric (oceanic and continental crust) and atmospheric reservoirs. Throughout geologic time oxygen was likely conserved within these Earth system reservoirs, but hydrogen was not, as it can...... escape to space [1]. Hydrogen isotope ratios of serpentinites from the ~3.8Ga Isua Supracrustal Belt in West Greenland are between -53 and -99‰; the highest values are in antigorite ± lizardite serpentinites from a low-strain lithologic domain where hydrothermal reaction of Archaean seawater with oceanic...... of continents present at that time), and the mass of Early Archaean oceans to ~109 to 126% of present day oceans. Oxygen isotope analyses from these Isua serpentinites (δ18O = +0.1 to 5.6‰ relative to VSMOW) indicate that early Archaean δ18OSEAWATER similar to modern oceans. Our observations suggest...

  16. Stable isotopic composition of bottled mineral waters from Romania

    Bădăluţă, Carmen; Nagavciuc, Viorica; Perșoiu, Aurel


    Romania has a high potential of mineral waters resources, featuring one of the largest mineral resources at European and global level. In the last decade, due to increased in consumption of bottled water, numerous brands have appeared on the market, with equally numerous and variable sources of provenance. In this study we have analyzed the isotopic composition of bottled mineral waters from Romania in order to determine their source and authenticity. We have analysed 32 carbonated and 24 non-carbonated mineral waters from Romania. and the results were analysed in comparison with stable isotope data from precipitation and river waters. Generally, the isotopic values of the mineral waters follow those in precipitation; however, differences occur in former volcanic regions (due to deep circulation of meteoric waters and increased exchange with host rock and volcanic CO2), as well as in mountainous regions, where high-altitude recharge occurs.

  17. The chromium isotope composition of reducing and oxic marine sediments

    Gueguen, Bleuenn; Reinhard, Christopher T.; Algeo, Thomas J.; Peterson, Larry C.; Nielsen, Sune G.; Wang, Xiangli; Rowe, Harry; Planavsky, Noah J.


    The chromium (Cr) isotope composition of marine sediments has the potential to provide new insights into the evolution of Earth-surface redox conditions. There are significant but poorly constrained isotope fractionations associated with oxidative subaerial weathering and riverine transport, the major source of seawater Cr, and with partial Cr reduction during burial in marine sediments, the major sink for seawater Cr. A more comprehensive understanding of these processes is needed to establish global Cr isotope mass balance and to gauge the utility of Cr isotopes as a paleoredox proxy. For these purposes, we investigated the Cr isotope composition of reducing sediments from the upwelling zone of the Peru Margin and the deep Cariaco Basin. Chromium is present in marine sediments in both detrital and authigenic phases, and to estimate the isotopic composition of the authigenic fraction, we measured δ53Cr on a weakly acid-leached fraction in addition to the bulk sediment. In an effort to examine potential variability in the Cr isotope composition of the detrital fraction, we also measured δ53Cr on a variety of oxic marine sediments that contain minimal authigenic Cr. The average δ53Cr value of the oxic sediments examined here is -0.05 ± 0.10‰ (2σ, n = 25), which is within the range of δ53Cr values characteristic of the bulk silicate Earth. This implies that uncertainty in estimates of authigenic δ53Cr values based on bulk sediment analyses is mainly linked to estimation of the ratio of Cr in detrital versus authigenic phases, rather than to the Cr-isotopic composition of the detrital pool. Leaches of Cariaco Basin sediments have an average δ53Cr value of +0.38 ± 0.10‰ (2σ, n = 7), which shows no dependency on sample location within the basin and is close to that of Atlantic deepwater Cr (∼+0.5‰). This suggests that authigenic Cr in anoxic sediments may reliably reflect the first-order Cr isotope composition of deepwaters. For Peru Margin samples

  18. Interlaboratory comparison of magnesium isotopic compositions of 12 felsic to ultramafic igneous rock standards analyzed by MC-ICPMS

    Teng, Fang-Zhen; Yin, Qing-Zhu; Ullmann, Clemens V.; Chakrabarti, Ramananda; Pogge von Strandmann, Philip A. E.; Yang, Wei; Li, Wang-Ye; Ke, Shan; Sedaghatpour, Fatemeh; Wimpenny, Joshua; Meixner, Anette; Romer, Rolf L.; Wiechert, Uwe; Jacobsen, Stein B.


    To evaluate the interlaboratory mass bias for high-precision stable Mg isotopic analysis of natural materials, a suite of silicate standards ranging in composition from felsic to ultramafic were analyzed in five laboratories by using three types of multicollector inductively coupled plasma mass spectrometer (MC-ICPMS). Magnesium isotopic compositions from all labs are in agreement for most rocks within quoted uncertainties but are significantly (up to 0.3‰ in 26Mg/24Mg, >4 times of uncertainties) different for some mafic samples. The interlaboratory mass bias does not correlate with matrix element/Mg ratios, and the mechanism for producing it is uncertain but very likely arises from column chemistry. Our results suggest that standards with different matrices are needed to calibrate the efficiency of column chemistry and caution should be taken when dealing with samples with complicated matrices. Well-calibrated standards with matrix elements matching samples should be used to reduce the interlaboratory mass bias.

  19. Modeling the carbon isotope composition of bivalve shells (Invited)

    Romanek, C.


    The stable carbon isotope composition of bivalve shells is a valuable archive of paleobiological and paleoenvironmental information. Previous work has shown that the carbon isotope composition of the shell is related to the carbon isotope composition of dissolved inorganic carbon (DIC) in the ambient water in which a bivalve lives, as well as metabolic carbon derived from bivalve respiration. The contribution of metabolic carbon varies among organisms, but it is generally thought to be relatively low (e.g., organism and high (>90%) in the shells from terrestrial organisms. Because metabolic carbon contains significantly more C-12 than DIC, negative excursions from the expected environmental (DIC) signal are interpreted to reflect an increased contribution of metabolic carbon in the shell. This observation contrasts sharply with modeled carbon isotope compositions for shell layers deposited from the inner extrapallial fluid (EPF). Previous studies have shown that growth lines within the inner shell layer of bivalves are produced during periods of anaerobiosis when acidic metabolic byproducts (e.g., succinic acid) are neutralized (or buffered) by shell dissolution. This requires the pH of EPF to decrease below ambient levels (~7.5) until a state of undersaturation is achieved that promotes shell dissolution. This condition may occur when aquatic bivalves are subjected to external stressors originating from ecological (predation) or environmental (exposure to atm; low dissolved oxygen; contaminant release) pressures; normal physiological processes will restore the pH of EPF when the pressure is removed. As a consequence of this process, a temporal window should also exist in EPF at relatively low pH where shell carbonate is deposited at a reduced saturation state and precipitation rate. For example, EPF chemistry should remain slightly supersaturated with respect to aragonite given a drop of one pH unit (6.5), but under closed conditions, equilibrium carbon isotope

  20. U and Th Concentration and Isotopic Composition of Hydrothermal Fluids at the Lost City Hydrothermal Field

    Ludwig, K. A.; Shen, C.; Cheng, H.; Edwards, R.; Kelley, D. S.; Butterfield, D. A.


    Uranium and Th concentration and isotopic composition of hydrothermal fluids at the Lost City Hydrothermal Field (LCHF) were determined using multi-collector inductively coupled plasma mass spectrometry (MC-ICP- MS). The LCHF is an off-axis, serpentinite-hosted hydrothermal system located at 30°N near the Mid- Atlantic Ridge. Carbonate chimneys reaching 60 m in height vent alkaline (pH~10), calcium-rich fluids at 40- 91°C and the towers are home to dense microbial communities. Vent fluid and seawater U and Th concentration and isotopic composition data provide critical information for constraining U-Th chimney ages. The increased sensitivity (1-2%) of MC-ICP-MS combined with an Aridus nebulization system allows the precise measurement of small quantities of sample (~150 ml) with low concentrations (ICP-MS techniques to measure the U and Th concentration and isotopic composition (234U, 238U, 230Th, and 232Th) of eight hydrothermal fluid samples. Endmember fluids with ~1mmol/kg Mg have ~0.02 ng/g U, confirming that end-member fluids contain near-zero values of both Mg and U. Thorium concentrations of fluids are close to deep seawater values. U and Th isotopic compositions are reported at the permil level. These data may provide new insights into the role of serpentinite-hosted hydrothermal systems in the budgets of U and Th in the ocean. Techniques presented in this study may be applied to other hydrothermal and seep environments.

  1. Mg/Ca and isotopic high resolution record of deep-sea hydrothermal barnacles

    Bojar, A.-V.; Bojar, H.-P.; Tufar, W.


    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

  2. Doping-Induced Isotopic Mg11B2 Bulk Superconductor for Fusion Application

    Qi Cai


    Full Text Available Superconducting wires are widely used for fabricating magnetic coils in fusion reactors. Superconducting magnet system represents a key determinant of the thermal efficiency and the construction/operating costs of such a reactor. In consideration of the stability of 11B against fast neutron irradiation and its lower induced radioactivation properties, MgB2 superconductor with 11B serving as the boron source is an alternative candidate for use in fusion reactors with a severe high neutron flux environment. In the present work, the glycine-doped Mg11B2 bulk superconductor was synthesized from isotopic 11B powder to enhance the high field properties. The critical current density was enhanced (103 A·cm−2 at 20 K and 5 T over the entire field in contrast with the sample prepared from natural boron.

  3. Photodissociation spectroscopy of the Mg + -CO2 complex and its isotopic analogs

    Yeh, C. S.; Willey, K. F.; Robbins, D. L.; Pilgrim, J. S.; Duncan, M. A.


    Mg+-CO2 ion-molecule cluster complexes are produced by laser vaporization in a pulsed nozzle cluster source. The vibronic spectroscopy in these complexes is studied with mass-selected photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer. Two excited electronic states are observed (2) 2Σ+ and 2Π. The 2Π state has a vibrational progression in the metal-CO2 stretching mode (ωe'=381.8 cm-1). The complexes are linear (Mg+-OCO) and are bound by the charge-quadrupole interaction. The dissociation energy (D0`) is 14.7 kcal/mol. Corresponding spectra are measured for each of the 24, 25, and 26 isotopes of magnesium. These results are compared to theoretical predictions made by Bauschlicher and co-workers.

  4. Clustering effects in 48Cr composite nuclei produced via 24Mg + 24Mg reaction

    Cinausero M.


    Full Text Available In the framework of studying clustering effects in N=Z light nuclei, an experiment was carried out to get information on the properties of the 48Cr composite nuclei produced via the 24Mg +24Mg reaction. In particular, the study regards the 48Cr at 60 MeV of excitation energy where a resonance with a narrow width (170 KeV has been found by measuring the elastic and anelastic channels. To determine the deformation of this state, evaporative Light Charged Particles (LCP are measured and compared to the Statistical Model (SM predictions, which are very sensitive to nuclear deformation. The experiment was performed at LNL using the 8ĒLP apparatus to select LCPs and a Parallel Plate Avalanche Counter (PPAC system to detect the Evaporation Residues (ER. Preliminary results on the measurements of ER – LCP and LCP – LCP angular correlations are presented which indicate the presence of a very large deformation.The analysis will proceed with the extraction of the LCP energy spectra and with the angular correlations for high multiplicity channels to determine the deformation.

  5. The complex nature of superconductivity in MgB2 as revealed by the reduced total isotope effect.

    Hinks, D G; Claus, H; Jorgensen, J D


    Magnesium diboride, MgB2, was recently observed to become superconducting at 39 K, which is the highest known transition temperature for a non-copper-oxide bulk material. Isotope-effect measurements, in which atoms are substituted by isotopes of different mass to systematically change the phonon frequencies, are one of the fundamental tests of the nature of the superconducting mechanism in a material. In a conventional Bardeen-Cooper-Schrieffer (BCS) superconductor, where the mechanism is mediated by electron-phonon coupling, the total isotope-effect coefficient (in this case, the sum of both the Mg and B coefficients) should be about 0.5. The boron isotope effect was previously shown to be large and that was sufficient to establish that MgB2 is a conventional superconductor, but the Mg effect has not hitherto been measured. Here we report the determination of the Mg isotope effect, which is small but measurable. The total reduced isotope-effect coefficient is 0.32, which is much lower than the value expected for a typical BCS superconductor. The low value could be due to complex materials properties, and would seem to require both a large electron-phonon coupling constant and a value of mu* (the repulsive electron-electron interaction) larger than found for most simple metals.

  6. Stable isotopes, Sr/Ca, and Mg/Ca in biogenic carbonates from Petaluma Marsh, northern California, USA

    Ingram, B.L.; De Deckker, P.; Chivas, A.R.; Conrad, M.E.; Byrne, A.R.


    Stable isotope ({sup 18}O/{sup 16}O and {sup 13}C/{sup 12}C) and minor-element compositions (Sr/Ca and Mg/Ca ratios) of ostracodes and gastropods separated from marsh sediments from San Francisco Bay, Northern California, were used to reconstruct paleoenvironmental changes in Petaluma Marsh over the past 700 yr. The value of {delta}{sup 18}O in the marsh carbonates reflects changes in freshwater inflow, evaporation, and temperature. Mg/Ca and Sr/Ca in ostracode calcite reflect changes in both freshwater inflow and temperature, although primarily reflect temperature changes in the salinity range of about 10-35 {per_thousand}. Ostracode {delta}{sup 18}O values show a gradual increase by 5 {per_thousand} between 500 yr BR and the present, probably reflecting rising sea level and increased evaporation in the marsh. Superimposed on this trend are higher frequency Mg/Ca and {delta}{sup 18}O variations (3-4 {per_thousand}), probably reflecting changes in freshwater inflow and evaporation. A period of low Mg/Ca occurred between about 100-300 cal yr BP, suggesting wetter and cooler conditions during the Little Ice Age. Higher Mg/Ca ratios occurred 600-700 cal yr BP, indicating drier and warmer conditions during the end of the Medieval Warm Period. Both ostracode and gastropod {delta}{sup 13}C values decrease up-core, reflecting decomposition of marsh vegetation, which changes from C{sub 4} ({delta}{sup 13}C {approx} -12{per_thousand}) to CAM ({delta}{sup 13}C = -26 {per_thousand})-type vegetation over time.

  7. On the iron isotope composition of Mars and volatile depletion in the terrestrial planets

    Sossi, Paolo A.; Nebel, Oliver; Anand, Mahesh; Poitrasson, Franck


    Iron is the most abundant multivalent element in planetary reservoirs, meaning its isotope composition (expressed as δ57Fe) may record signatures of processes that occurred during the formation and subsequent differentiation of the terrestrial planets. Chondritic meteorites, putative constituents of the planets and remnants of undifferentiated inner solar system bodies, have δ57Fe ≈ 0 ‰; an isotopic signature shared with the Martian Shergottite-Nakhlite-Chassignite (SNC) suite of meteorites. The silicate Earth and Moon, as represented by basaltic rocks, are distinctly heavier, δ57Fe ≈ + 0.1 ‰. However, some authors have recently argued, on the basis of iron isotope measurements of abyssal peridotites, that the composition of the Earth's mantle is δ57Fe = + 0.04 ± 0.04 ‰, indistinguishable from the mean Martian value. To provide a more robust estimate for Mars, we present new high-precision iron isotope data on 17 SNC meteorites and 5 mineral separates. We find that the iron isotope compositions of Martian meteorites reflect igneous processes, with nakhlites and evolved shergottites displaying heavier δ57Fe (+ 0.05 ± 0.03 ‰), whereas MgO-rich rocks are lighter (δ57Fe ≈ - 0.01 ± 0.02 ‰). These systematics are controlled by the fractionation of olivine and pyroxene, attested to by the lighter isotope composition of pyroxene compared to whole rock nakhlites. Extrapolation of the δ57Fe SNC liquid line of descent to a putative Martian mantle yields a δ57Fe value lighter than its terrestrial counterpart, but indistinguishable from chondrites. Iron isotopes in planetary basalts of the inner solar system correlate positively with Fe/Mn and silicon isotopes. While Mars and IV-Vesta are undepleted in iron and accordingly have chondritic δ57Fe, the Earth experienced volatile depletion at low (1300 K) temperatures, likely at an early stage in the solar nebula, whereas additional post-nebular Fe loss is possible for the Moon and angrites.

  8. Magnesium and Titanium Isotopic Compositions of an Unusual Hibonite-Perovskite Refractory Inclusion from Allende: It Is Fun

    Liu, M.-C.; Keller, L. P.; McKeegan, K. D.


    Introduction: Hibonite-rich refractory inclusions are among the first solids that formed in the solar nebula, and thus provide constraints on the earliest environment in the Solar System. An unusual hibonite-perovskite inclusion from Allende, SHAL, consists of a large (approximately 500 by 200 microns) single hibonite crystal and coexisting blocky perovskite (approximately 200 microns in size). The hibonite is characterized by chemical and oxygen isotopic compositions similar to those in the FUN (Fractionated and Unknown Nuclear anomalies) inclusion HAL. However, the rare earth element (REE) patterns measured at different spots of SHAL hibonite are highly variable, ranging from Group II-like (light REEs enriched relative to heavy REEs) to Group III-like (relatively flat with slight Eu depletions), but overall contrast largely with that of HAL, especially in the Ce and Yb abundances. This implies that SHAL hibonite formed and underwent distillation processes under more reducing conditions. Interestingly, the accompanying perovskite has uniform, unfractionated oxygen isotopic compositions (averaging delta (sup 17) O equals delta (sup 18) O equals -7 per mille) and REE abundances that are completely different from those of SHAL hibonite. This has been interpreted that perovskite and hibonite may not be co-genetic. Here we performed Al-Mg and Ti isotopic measurements of SHAL hibonite and perovskite to determine if the FUN characteristics are observed in these two isotope systems, and to further constrain the origin and evolution of SHAL. Results: Isotopic measurements of Al-Mg and Ti in SHAL were performed on the UCLA CAMECA ims-1290 ion microprobe by following the analytical protocols described in [1]. The Al-Mg and Ti data obtained in both terrestrial standards and SHAL hibonite and perovskite are shown below. Both SHAL hibonite and perovskite, despite very high (sup 27) Al to (sup 24) Mg ratios, are devoid of (sup 26) Mg excesses that can be attributed to the decay

  9. Alkali elemental and potassium isotopic compositions of Semarkona chondrules

    Alexander, C.M. O'D.; Grossman, J.N.


    We report measurements of K isotope ratios in 28 Semarkona chondrules with a wide range of petrologic types and bulk compositions as well as the compositions of CPX-mesostasis pairs in 17 type I Semarkona chondrules, including two chondrules with radial alkali zonation and 19 type II chondrules. Despite the wide range in K/Al ratios, no systematic variations in K isotopic compositions were found. Semarkona chondrules do not record a simple history of Rayleigh-type loss of K. Experimentally determined evaporation rates suggest that considerable alkali evaporation would have occurred during chondrule formation. Nevertheless, based on Na CPX-mesostasis distribution coefficients, the alkali contents of the cores of most chondrules in Semarkona were probably established at the time of final crystallization. However, Na CPX-mesostasis distribution coefficients also show that alkali zonation in type I Semarkona chondrules was produced by entry of alkalis after solidification, probably during parent body alteration. This alkali metasomatism may have gone to completion in some chondrules. Our preferred explanation for the lack of systematic isotopic enrichments, even in alkali depleted type I chondrule cores, is that they exchanged with the ambient gas as they cooled. ?? The Meteoritical Society, 2005.

  10. Where Did the Ureilite Parent Body Accrete? Constraints from Chemical and Isotopic Compositions

    Goodrich, Cyrena; O'Brien, David P.


    Almahata Sitta and other polymict ureilites contain a remarkable diversity of materials, including EH, EL, OC, R- and CB chondrites, in addition to the dominant ureilitic material [1]. These materials represent at least 6 different parent asteroids and a wide range of chemical and isotopic environments in the early Solar System. To understand the origin of this diversity it is critical to know where (heliocentric distance) the ureilite parent body (UPB) accreted. The chemical and isotopic compositions of ureilite precursors (inferred from the compositions of ureilites) can provide clues. Lithophile element ratios such as Si/Mg and Mn/Mg [2,3], and deficits in neutron-rich Cr, Ti and Ni isotopes [3], indicate that ureilite precursors were similar to ordinary or enstatite chondrites (OC or EC), not carbonaceous chondrites (CC). In contrast, high carbon contents, carbon isotopes and oxygen isotopes suggest a genetic link to CC. This poses a conundrum considering the variation of asteroid types, which suggests that EC and OC dominate the inner asteroid belt and CC the outer belt. However, the CC-like oxygen isotopes of ureilites strongly suggest the effects of parent-body aqueous alteration [4,5], which clearly implies that the UPB accreted beyond the ice line. Lithophile element properties of ureilites compared with chondrites may not be a reliable indicator of location of accretion, because lithophile elements in chondrites are sited mainly in chondrules and the UPB accreted before most chondrules formed [6]. Ureilite Cr, Ti and Ni isotopes may indicate late introduction of the neutron rich isotopes of these elements to the CC-formation region [7]. We conclude that the UPB accreted in the outer belt, like CC. The UPB or one of its offspring must have migrated to the inner belt to acquire OC, EC and R-chondrite materials.[1] Horstmann M. & Bischoff A. [2014] Chemie der Erde 74, 149.[2] Goodrich C. [1999] MAPS 34, 109.[3] Warren P. [2011] GCA 46, 53.[4] Young E. [1999

  11. Petrologic and Al-Mg isotopic clues to the accretion of two refractory inclusions onto the Leoville parent body - One was hot, the other wasn't

    Caillet, Catherine; MacPherson, Glenn J.; Zinner, Ernst K.


    A detailed petrologic and magnesium isotopic study of two Ca-Al-rich inclusions from the foliated Leoville meteorite is presented. The two type B refractory inclusions found within several centimeters of each other differ greatly in their styles of deformation, textures, and Mg-Al isotopic characteristics. One is a subspheroidal type B1 with textures similar to those observed previously in many type B1s from other CV3 meteorites, and whose deformation (fracturing, some granulation) has been almost entirely brittle in nature. Its isotopic composition shows Mg-26/Mg-24 correlated with Al-27/Mg-24 which, although disturbed, indicates a lower limit for initial Al-26/Al-27 of around 4.9 x 10 to the -5. The other inclusion is a highly elongate object whose long axis lies in the plane of foliation. It has a predominantly metamorphic texture, but relict islands of an earlier and more 'normal' type B precursor are preserved in its core. The most likely origin for the deformed and recrystallized features of the elongate inclusion is that it accreted onto the Leoville parent body while still very hot, and deformed into its present state at the moment of impact.

  12. Light and heavy element isotopic compositions of mainstream SiC grains.

    Amari, S.; Clayton, R. N.; Davis, A. M.; Lewis, R. S.; Pellin, M. J.


    Although a variety of types of pre-solar SiC grains have been classified by their C, N, and Si isotopic composition, the majority of such grains are so-called mainstream grains and are believed to have come from asymptotic giant branch stars [1]. We have previously reported the Mo isotopic compositions of presolar SiC grains whose C, N, and Si isotopic compositions were not known [2]. Since most presolar SiC grains fall in the mainstream group, we assumed that these grains were mainstream. The excellent match of the Mo isotopic data with expectations for nucleosynthesis in AGB stars was consistent with this identification. In order to better understand the distribution of isotopic compositions in presolar grains, we have begun to measure heavy element isotopic compositions of presolar SiC grains of known C, N and Si isotopic composition.

  13. Clumped-isotope geochemistry of carbonates: A new tool for the reconstruction of temperature and oxygen isotope composition of seawater

    Bernasconi, Stefano M., E-mail: [Geological Institute, ETH Zuerich, Sonneggstrasse 5, 8092 Zuerich (Switzerland); Schmid, Thomas W.; Grauel, Anna-Lena [Geological Institute, ETH Zuerich, Sonneggstrasse 5, 8092 Zuerich (Switzerland); Mutterlose, Joerg [Institut fuer Geologie, Mineralogie und Geophysik, Ruhr Universitaet Bochum, Universitaetsstr. 150, 44801 Bochum (Germany)


    Highlights: > Clumped-isotope thermometry of carbonates is discussed. > Clumped isotopes of Belemnites show higher sea surface temperatures than commonly assumed for the lower Cretaceous. > The potential of clumped-isotope measurement on foraminifera is discussed. - Abstract: Clumped-isotope geochemistry deals with State of ordering of rare isotopes in molecules, in particular with their tendency to form bonds with other rare isotopes rather than with the most abundant ones. Among its possible applications, carbonate clumped-isotope thermometry is the one that has gained most attention because of the wide potential of applications in many disciplines of the earth sciences. In particular, it allows reconstructing the temperature of formation of carbonate minerals without knowledge of the isotopic composition of the water from which they were formed. In addition, the O isotope composition of the waters from which they were formed can be calculated using the {delta}{sup 18}O of the same carbonate sample. This feature offers new approaches in paleoclimatology for reconstructing past global geochemical cycles. In this contribution two applications of this method are presented. First the potential of a new analytical method of measurement of clumped isotopes on small samples of foraminifera, for high-resolution SST and seawater {delta}{sup 18}O reconstructions from marine sediments is shown. Furthermore the potential of clumped isotope analysis of belemnites, for reconstructing seawater {delta}{sup 18}O and temperatures in the Cretaceous is shown.

  14. The triple isotopic composition of oxygen in leaf water

    Landais, A.; Barkan, E.; Yakir, D.; Luz, B.


    The isotopic composition of atmospheric O 2 depends on the rates of oxygen cycling in photosynthesis, respiration, photochemical reactions in the stratosphere and on δ17O and δ18O of ocean and leaf water. While most of the factors affecting δ17O and δ18O of air O 2 have been studied extensively in recent years, δ17O of leaf water—the substrate for all terrestrial photosynthesis—remained unknown. In order to understand the isotopic composition of atmospheric O 2 at present and in fossil air in ice cores, we studied leaf water in field experiments in Israel and in a European survey. We measured the difference in δ17O and δ18O between stem and leaf water, which is the result of isotope enrichment during transpiration. We calculated the slopes of the lines linking the isotopic compositions of stem and leaf water. The obtained slopes in ln( δ17O + 1) vs. ln( δ18O + 1) plots are characterized by very high precision (˜0.001) despite of relatively large differences between duplicates in both δ17O and δ18O (0.02-0.05‰). This is so because the errors in δ18O and δ17O are mass-dependent. The slope of the leaf transpiration process varied between 0.5111 ± 0.0013 and 0.5204 ± 0.0005, which is considerably smaller than the slope linking liquid water and vapor at equilibrium (0.529). We further found that the slope of the transpiration process decreases with atmospheric relative humidity ( h) as 0.522-0.008 × h, for h in the range 0.3-1. This slope is neither influenced by the plant species, nor by the environmental conditions where plants grow nor does it show strong variations along long leaves.

  15. A Record of Oceanic Lithium Isotope Composition for the Last 7Ma

    Marriott, C. S.; Henderson, G. M.


    measurement of hand picked and fully-reductively cleaned G. menardii. G. menardii was chosen because of its abundance throughout the core enabling the required 30-40mg of carbonate to be readily picked. Lithium isotope composition will be measured using a well established MC-ICP-MS technique [2,3] with a precision of better than +/-1 per mil to provide a record of the Li isotope composition of seawater for the last 7Ma and to identify changes in continental weathering during this period. 1. Huh Y. et al. (2001) EPSL 194, 189-199. 2. Pistiner J. S. & Henderson G. M. (In press) EPSL. 3. Marriott C. S. et al. (2002) GCA S1 66, A485.

  16. A method for determining the nitrogen isotopic composition of porphyrins.

    Higgins, Meytal B; Robinson, Rebecca S; Casciotti, Karen L; McIlvin, Matthew R; Pearson, Ann


    We describe a new method for analysis of the nitrogen isotopic composition of sedimentary porphyrins. This method involves separation and purification of geoporphyrins from sediment samples using liquid chromatography and HPLC, oxidation of the nitrogen within porphyrin-enriched fractions using a two-step process, and isotopic analysis of the resulting nitrate using the denitrifier method. By analysis of these degradation products of chlorophylls, we are able to measure an isotopic signature that reflects the nitrogen utilized by primary producers. The high sensitivity of the denitrifier method allows measurement of small samples that contain low concentrations of porphyrins. Extraction of only 50 nmol of nitrogen (nmol N) allows the following five analyses to be made (each on approximately 10 nmol N): nitrogen concentration, an assessment of potential contamination by nonporphyrin N, and three replicate isotopic measurements. The measured values of delta15N have an average analytical precision of +/-0.5 per thousand (1sigma) and an average contribution from Rayleigh fractionation of 0.7 per thousand from incomplete oxidation of porphyrin N to nitrate. The overall method will enable high-resolution records of delta15N values to be obtained for geological and ecological applications.

  17. Hydrogen generation via hydrolysis of nanocrystalline MgH2 and MgH2-based composites

    HU Lian-xi; WANG Er-de


    Nanocrystalline MgH2 and MgH2-based composites with 25% (mass fraction) of Al, Ca, or CaH2 as an individual additive respectively were prepared by ball milling. The crystallite size and morphology of the as-milled powders were characterized and their hydrolysis behaviours were investigated in comparison with commercial polycrystalline MgH2. The results show that the crystallite size of both MgH2 and MgH2-based composites is reduced to less than 13 nm after milling for 15 h. Due to its enhanced specific surface area and unique nanocrystalline structure, the as-milled MgH2 shows much better hydrolysis kinetics than the commercial polycrystalline MgH2, with the hydrolysed fraction upon hydrolysing for 70 min enhances from 7.5% to about 25%. As compared with the as-milled MgH2, the MgH2-based composites with either CaH2 or Ca as an additive present further greatly improved hydrolysis kinetics, with the hydrolysed fraction for 80 min achieving about 76% and 62% respectively.However, the addition of Al doesn't show any positive effect on the improvement of the hydrolysis kinetics of MgH2.

  18. Pygmy dipole mode in deformed neutron-rich Mg isotopes close to the drip line

    Yoshida, Kenichi


    We investigate the microscopic structure of the low-lying isovector-dipole excitation mode in neutron-rich Mg36,38,40 close to the drip line by means of the deformed quasiparticle random-phase approximation employing the Skyrme and the local pairing energy-density functionals. It is found that the low-lying bump structure above the neutron emission-threshold energy develops when the drip line is approached, and that the isovector dipole strength at ExThomas-Reiche-Kuhn dipole sum rule in Mg40. We obtained the collective dipole modes at around 8-10 MeV in Mg isotopes, that consist of many two-quasiparticle excitations of the neutron. The transition density clearly shows an oscillation of the neutron skin against the isoscalar core. We found significant coupling effects between the dipole and octupole excitation modes due to the nuclear deformation. It is also found that the responses for the compressional dipole and isoscalar octupole excitations are much enhanced in the lower energy region.

  19. Weathering of the black limestone of historical monuments (Ljubljana, Slovenia): Oxygen and sulfur isotope composition of sulfate salts

    Kramar, Sabina, E-mail: [Institute for the Protection of Cultural Heritage of Slovenia, Conservation Centre, Restoration Centre, Poljanska 40, 1000 Ljubljana (Slovenia); Mirtic, Breda [University of Ljubljana, Faculty of Natural Sciences and Engineering, Department of Geology, Askerceva 12, 1000 Ljubljana (Slovenia); Knoeller, Kay [UFZ Helmholtz-Centre for Environmental Research, Department of Isotope Hydrology, Theodor-Lieser-Str. 4, 06120 Halle (Germany); Rogan-Smuc, Nastja [University of Ljubljana, Faculty of Natural Sciences and Engineering, Department of Geology, Askerceva 12, 1000 Ljubljana (Slovenia)


    Highlights: > Weathering of the black limestone on historical monuments. > Oxygen and sulfur isotope composition of sulfate salts (outdoors and indoors). > A data exhibit more scattered {delta}{sup 34}S values with respect to {delta}{sup 18}O values. - Abstract: The black limestone widely used in Slovenian monuments, particularly in the baroque architecture, is deteriorating extensively due to salt crystallization. Samples of soluble salts from two important historical monuments (in Ljubljana, Slovenia) were investigated in terms of their mineral and isotopic (S and O) compositions. Results revealed the presence of gypsum and soluble salts of the MgSO{sub 4}.nH{sub 2}O series, such as starkeyite (MgSO{sub 4}.4H{sub 2}O), pentahydrite (MgSO{sub 4}.5H{sub 2}O) and hexahydrite (MgSO{sub 4}.6H{sub 2}O). Whereas black crusts and subflorescences consisted of gypsum, efflorescences appeared to be an assemblage of gypsum and MgSO{sub 4} hydrates. Sample {delta}{sup 18}O{sub sulfate} values varied from -1.9 per mille to +5.5 per mille vs. V-SMOW and {delta}{sup 34}S{sub sulfate} values from -19.8 per mille to +3.2 per mille vs. V-CDT. The respective isotopic composition of analysed outdoor and indoor monument samples indicated different sources of contamination.

  20. Tellurium isotope compositions of calcium-aluminum-rich inclusions

    Fehr, M. A.; Rehkämper, M.; Halliday, A. N.; Hattendorf, B.; Günther, D.


    A method for the precise and accurate determination of the tellurium (Te) isotope compositions of calcium-aluminum-rich inclusions (CAIs) has been developed. The technique utilizes multiple-collector inductively coupled plasma-mass spectrometry (MC-ICPMS) with either Faraday detectors or a dual ion-counting system. The external reproducibility (2σ) for 126Te/125Te was ~15‰ and ~2‰ when 3 pg and 65 pg of Te were analyzed with the electron multipliers. Measurements performed on 200 pg of Te using Faraday detectors and time-resolved software displayed an external reproducibility of ~8‰ for 126Te/124Te, whereas 3 ng Te could be measured to a precision of about 0.6‰. Analyses of five CAIs from the Allende chondrite yielded Te concentrations that range from 12 to 537 ppb and the inclusions are therefore depleted in Te relative to bulk Allende by factors of about 2 to 86. The Sn/Te ratios of the CAIs are also fractionated compared to bulk Allende (which displays 124Sn/128Te ≍ 0.1) with 124Sn/128Te ratios of about 0.1 to 2.5. The Te isotope measurements for these refractory inclusions yielded no 126Te excesses from the decay of the short-lived radionuclide 126Sn (τ½ = 234,500 years) and the most precise analysis provided a ɛ126Te value of 1 ± 6 (ɛ126Te = 126Te/ 124Te normalized to 122Te/124Te = 0.53594 and reported relative to the JMC Te standard). Minor differences in the Te isotope composition of the CAIs relative to the terrestrial standard and bulk Allende hint at the presence of small deficits in r-process Te isotopes or excess of s-process Te, but these nucleosynthetic anomalies are barely resolvable given the analytical uncertainties. Hence, it is also conceivable that these effects reflect small unresolved analytical artifacts.

  1. Oxygen isotope composition of mafic magmas at Vesuvius

    Dallai, L.; Cioni, R.; Boschi, C.; D'Oriano, C.


    The oxygen isotope composition of olivine and clinopyroxene from four plinian (AD 79 Pompeii, 3960 BP Avellino), subplinian (AD 472 Pollena) and violent strombolian (Middle Age activity) eruptions were measured to constrain the nature and evolution of the primary magmas of the last 4000 years of Mt. Vesuvius activity. A large set of mm-sized crystals was accurately separated from selected juvenile material of the four eruptions. Crystals were analyzed for their major and trace element compositions (EPMA, Laser Ablation ICP-MS), and for 18O/16O ratios. As oxygen isotope composition of uncontaminated mantle rocks on world-wide scale is well constrained (δ18Oolivine = 5.2 ± 0.3; δ18Ocpx = 5.6 ± 0.3 ‰), the measured values can be conveniently used to monitor the effects of assimilation/contamination of crustal rocks in the evolution of the primary magmas. Instead, typically uncontaminated mantle values are hardly recovered in Italian Quaternary magmas, mostly due to the widespread occurrence of crustal contamination of the primary magmas during their ascent to the surface (e.g. Alban Hills, Ernici Mts., and Aeolian Islands). Low δ18O values have been measured in olivine from Pompeii eruption (δ18Oolivine = 5.54 ± 0.03‰), whereas higher O-compositions are recorded in mafic minerals from pumices or scoria of the other three eruptions. Measured olivine and clinopyroxene share quite homogeneous chemical compositions (Olivine Fo 85-90 ; Diopside En 45-48, respectively), and represent phases crystallized in near primary mafic magmas, as also constrained by their trace element compositions. Data on melt inclusions hosted in crystals of these compositions have been largely collected in the past demonstrating that they crystallized from mafic melt, basaltic to tephritic in composition. Published data on volatile content of these melt inclusions reveal the coexistence of dissolved water and carbon dioxide, and a minimum trapping pressure around 200-300 MPa, suggesting

  2. Isotopic Composition of Cosmic Rays:. Results from the Cosmic Ray Isotope Spectrometer on the Ace Spacecraft

    Israel, M. H.

    Over the past seven years the Cosmic Ray Isotope Spectrometer (CRIS) on the ACE spacecraft has returned data with an unprecedented combination of excellent mass resolution and high statistics, describing the isotopic composition of elements from lithium through nickel in the energy interval ~ 50 to 500 MeV/nucleon. These data have demonstrated: * The time between nucleosynthesis and acceleration of the cosmic-ray nuclei is at least 105 years. The supernova in which nucleosynthesis takes place is thus not the same supernova that accelerates a heavy nucleus to cosmic-ray energy. * The mean confinement time of cosmic rays in the Galaxy is 15 Myr. * The isotopic composition of the cosmic-ray source is remarkably similar to that of solar system. The deviations that are observed, particularly at 22Ne and 58Fe, are consistent with a model in which the cosmic-ray source is OB associations in which the interstellar medium has solar-system composition enriched by roughly 20% admixture of ejecta from Wolf-Rayet stars and supernovae. * Cosmic-ray secondaries that decay only by electron capture provide direct evidence for energy loss of cosmic rays as they penetrate the solar system. This invited overview paper at ECRS 19 was largely the same as an invited paper presented a month earlier at the 8th Nuclei in the Cosmos Conference in Vancouver. The proceedings of that conference will be published shortly by Elsevier as a special edition of Nuclear Physics A. For further summary of results from CRIS, the reader is referred to URL and links on that page to CRIS and to Science News.

  3. Isotopic composition and origin of the precipitation in Northern Chile

    Aravena, R. [Department of Earth Sciences, University of Waterloo, Waterloo (Canada); Suzuki, O. [Exploracion y Desarrollo de Recursos Hidricos, Santiago (Chile); Pena, H. [Direccion General de Aguas, Ministerio de Obras Publicas, Santiago (Chile); Pollastri, A. [Comision Chilena de Energia Nuclear, Santiago (Chile); Fuenzalida, H. [Departamento de Geofisica, Universidad of Chile, Santiago (Chile); Grilli, A. [Empresa Metropolitana de Obras Sanitarias, Santiago (Chile)


    A 3 a data set of isotopes in precipitation from northern Chile show a very distinct pattern, with {delta}{sup 18}O values ranging between -18 and -15per thousand at high altitude stations, compared to {delta}{sup 18}O values between -10 and -6per thousand at the lower altitude areas. The {sup 18}O-depleted values observed in the high altitude area, the Altiplano, are related to processes that affect the air masses that originated over the Atlantic, cross the Amazon Basin (continental effect), ascend the Andes (altitude effect) and precipitated (convective effect) in the Altiplano. It is postulated that a second source of moisture, associated with air masses from the Pacific, may contribute to the {sup 18}O-enriched values observed in the lower altitude areas. Similar isotopic patterns are documented in springs and groundwater indicating that the data presented in this paper are an accurate representation of the long term behavior isotopic composition of rain in northern Chile. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

  4. On the isotopic composition of magmatic carbon in SNC meteorites

    Wright, I. P.; Grady, M. M.; Pillinger, C. T.


    SNC meteorites are thought, from many lines of evidence, to come from Mars. A line of investigation which has been pursued in our laboratory over the years involves measurement of the stable isotopic composition of carbon, in its various forms, in SNC meteorites. In order to establish a firm basis for studying the isotopic systematics of carbon in the martian surface environment, it is first necessary to try and constrain the delta C-13 of bulk Mars. Taking all of the available information, it would seem that the delta C-13 of the Earth's mantle lies somewhere in the range of -5 to -7 percent. Preliminary assessment of magnetic carbon in SNC meteorites, would tend to suggest a delta C-13 of 20 to 30 percent, which is conspicuously different from that of the terrestrial mantle. It is not obvious why there should be such a difference between the two planets, although many explanations are possible. One of these possibilities, that previous delta C-13 measurements for magnetic carbon in SNC meteorites are in error to some degree, is being actively investigated. The most recent results seem to constrain the theta C-13 of the magnetic carbon in SNC meteorites to about -20 percent, which is not at odds with previous estimates. As such, it is considered that a detailed investigation of the carbon isotopic systematics of martian surface materials does have the necessary information with which to proceed.

  5. Stable carbon isotopic composition of gasolines determined by isotope ratio monitoring gas chromatography mass spectrometry

    Smallwood, B.J.; Philp, R.P.; Allen, J.D. [University of Oklahoma, Norman, OK (United States). School of Geology and Geophysics


    A large number of underground gasoline storage facilities in the United States continuously leak gasoline into the subsurface, which makes gasoline a major groundwater contaminant. Gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) are used currently to characterize contaminated groundwater and soils. Correlations of contaminants with suspected source(s) are extremely difficult by these techniques because many gasolines have similar hydrocarbon distributions. The present study applied the technique of isotope ratio monitoring gas chromatography-mass spectrometry (irmGC-MS) to 19 gasoline samples from different areas of the USA. This allows a much better correlation of gasoline contaminants to source. Data obtained indicate a wide range of {sup {delta}}{sup 13}C values for 16 ubiquitous compounds in the gasolines. The majority of samples could be distinguished from each other on the basis of {sup {delta}}{sup 13}C hydrocarbon composition. The oxygenated additive methyl tertiary butyl ether (MTBE) was present in ten of the gasolines analyzed, and had a relatively narrow range of {sup {delta}}{sup 13}C values (-30.4 to -28.3 per mille). Preliminary investigations were also made to determine the extent of carbon isotopic fractionation after simple water washing and evaporation experiments. Results indicate that the majority of compounds did not undergo significant carbon isotopic fractionation as a result of these processes. (author)

  6. A method for combined Sr-Nd-Hf isotopic analysis of <10 mg dust samples: implication for ice core science

    Ujvari, Gabor; Wegner, Wencke; Klötzli, Urs


    Aeolian mineral dust particles below the size of 10-20 μm often experience longer distance transport in the atmosphere, and thus Aeolian dust is considered an important tracer of large-scale atmospheric circulation. Since ice core dust is purely Aeolian in origin, discrimination of its potential source region(s) can contribute to a better understanding of past dust activity and climatic/environmental causes. Furthermore, ice core dust source information provides critical experimental constraints for model simulations of past atmospheric circulation patterns [1,2]. However, to identify dust sources in past dust archives such as ice cores, the mineralogy and geochemistry of the wind-blown dust material must be characterized. While the amount of dust in marine cores or common terrestrial archives is sufficient for different types of analyses and even for multiple repeat measurements, dust content in ice cores is usually extremely low even for the peak dusty periods such as the Last Glacial Maximum (LGM) (5-8 mg dust/kg ice; [3]). Since the most powerful dust fingerprinting methods, such as REE composition and Sr-Nd-Pb isotopic analyses are destructive there is a clear need to establish sequential separation techniques of Sr, Nd, Pb and other REEs to get the most information out of small (5-10 mg) dust samples recovered from ice cores. Although Hf isotopes have recently been added as a robust tool of aerosol/dust source discrimination (e.g. [4,5,6,7]), precise Hf isotopic measurements of small (Central Europe (NUS), China (BEI) and the US (JUD) were processed (all acetic acid treated for carbonate removal, i.e. aluminosilicate fractions were analysed). Sr isotopic compositions varied between the aliquots within a range of ˜0.00007 for the three samples. Comparison of these values with previously obtained 87Sr/86Sr isotopic ratios from the same samples (different acid/sample amounts) reveals that these values are very sensitive to the acetic acid treatment (acid

  7. Recent insights into intramolecular 13C isotope composition of biomolecules

    Gilbert, A.; Yamada, K.; Julien, M.; Yoshida, N.; Remaud, G.; Robins, R.


    In 1961 Abelson & Hoering shown that the intramolecular 13C distribution in amino acids was not homogeneous, namely the carboxylic acid positions were 13C-enriched compared with the mean of the remaining C-atoms in the molecule [1]. Nearly 20 years later, Monson & Hayes were able to demonstrate that even and odd positions in acetogenic fatty acids also showed non-statistical 13C isotope distributions, and that the pattern varied depending on the organism [2]. It took a further decade for the intramolecular 13C distribution in the key metabolite, glucose, to be defined [3]. Although informative, much of this work was incomplete, a number of positions having to be deduced by difference. This limitation arose mainly due to the lack of techniques enabling the separation and quantification of 13C isotopomers of the target molecule. In the past decade, quantitative 13C NMR has been developed for the determination of the intramolecular isotope composition of a given molecule with a precision of 1‰ or better [4]. This breakthrough has made possible a comprehensive view of the determinants governing intramolecular isotope composition of biological molecules. In particular, it can be shown that intramolecular pattern in sugars is influenced by the C-assimilation pathway and by post-photosynthetic fractionation associated with carbohydrate metabolism [5]. In addition, analysis by NMR of the alkyl chain of acetogenic lipids (fatty acids, n-alkanes) shows an alternation between odd and even C-atom positions, as observed by Monson& Hayes [2], throughout the molecule [6]. Overall, it is becoming apparent that this pattern is influenced by two principal metabolic factors: (i) the 13C pattern extant in the starting compounds; (ii) isotope fractionation associated with the enzymes involved in the biosynthetic pathway. On the whole, the determination of intramolecular isotope patterns in biomolecules allows better insights into the conditions and pathways by which they are formed

  8. Isotope composition of bicarbonate carbon in bed waters of oil and gas deposits

    Golyshev, S.I.; Cherepnin, A.V.; Ivanov, V.G.; Manylova, L.S.


    A study is made of the isotope composition of bicarbonate carbon in bed waters of the Jurassic water complex in southeast West Siberia. It has been established that waters of empty and transcontour structures have isotope composition of carbon 5/sup 0//oo, while in waters which contact the hydrocarbon formations, the isotope composition of carbon is lighter on the average by 5-8/sup 0//oo. The isotope composition of bicarbonate carbon in bed waters reflects both the conditions for primary sedimentation, and secondary processes associated with organic matter transformation.

  9. Sulfur Isotopic Compositions of Submicrometer SiC Grains from the Murchison Meteorite

    Xu, Yuchen; Zinner, Ernst; Gallino, Roberto; Heger, Alexander; Pignatari, Marco; Lin, Yangting


    We report C, Si, N, S, Mg-Al, and Ca-Ti isotopic compositions of presolar silicon carbide (SiC) grains from the SiC-rich KJE size fraction (0.5-0.8 μm) of the Murchison meteorite. One thousand one hundred thirteen SiC grains were identified based on their C and Si isotopic ratios. Mainstream, AB, C, X, Y, and Z subtypes of SiC, and X-type silicon nitride (Si3N4) account for 81.4%, 5.7%, 0.1%, 1.5%, 5.8%, 4.9%, and 0.4%, respectively. Twenty-five grains with unusual Si isotopic ratios, including one C grain, 16 X grains, 1 Y grain, 5 Z grains, and 2 X-type Si3N4 grains were selected for N, S, Mg-Al, and Ca-Ti isotopic analysis. The C grain is highly enriched in 29Si and 30Si (δ29Si = 1345‰ ± 19‰, δ30Si = 1272‰ ± 19‰). It has a huge 32S excess, larger than any seen before, and larger than that predicted for the Si/S supernova (SN) zone, providing evidence against the elemental fractionation model by Hoppe et al. Two SN models investigated here present a more satisfying explanation in terms of a radiogenic origin of 32S from the decay of short-lived 32Si (τ1/2 = 153 yr). Silicon-32 as well as 29Si and 30Si can be produced in SNe by short neutron bursts; evidence for initial 44Ti (τ1/2 = 60 yr) in the C grain is additional evidence for an SN origin. The X grains have marginal 32S excesses, much smaller than expected from their large 28Si excesses. Similarly, the Y and Z grains do not show the S-isotopic anomalies expected from their large Si isotopic anomalies. Low intrinsic S contents and contamination with isotopically normal S are the most likely explanations.


    Xu, Yuchen [Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002 (China); Zinner, Ernst [Laboratory for Space Sciences and Physics Department, Washington University, St. Louis, MO 63130 (United States); Gallino, Roberto [Dipartimento di Fisica, Università di Torino, I-10125 Torino (Italy); Heger, Alexander [Monash Centre for Astrophysics, School of Mathematical Sciences, Monash University, Vic 3800 (Australia); Pignatari, Marco [Department of Physics, University of Basel, CH-4056 Basel (Switzerland); Lin, Yangting, E-mail: [Key Laboratory of Earth' s Deep Interior, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029 (China)


    We report C, Si, N, S, Mg-Al, and Ca-Ti isotopic compositions of presolar silicon carbide (SiC) grains from the SiC-rich KJE size fraction (0.5-0.8 μm) of the Murchison meteorite. One thousand one hundred thirteen SiC grains were identified based on their C and Si isotopic ratios. Mainstream, AB, C, X, Y, and Z subtypes of SiC, and X-type silicon nitride (Si{sub 3}N{sub 4}) account for 81.4%, 5.7%, 0.1%, 1.5%, 5.8%, 4.9%, and 0.4%, respectively. Twenty-five grains with unusual Si isotopic ratios, including one C grain, 16 X grains, 1 Y grain, 5 Z grains, and 2 X-type Si{sub 3}N{sub 4} grains were selected for N, S, Mg-Al, and Ca-Ti isotopic analysis. The C grain is highly enriched in {sup 29}Si and {sup 30}Si (δ{sup 29}Si = 1345‰ ± 19‰, δ{sup 30}Si = 1272‰ ± 19‰). It has a huge {sup 32}S excess, larger than any seen before, and larger than that predicted for the Si/S supernova (SN) zone, providing evidence against the elemental fractionation model by Hoppe et al. Two SN models investigated here present a more satisfying explanation in terms of a radiogenic origin of {sup 32}S from the decay of short-lived {sup 32}Si (τ{sub 1/2} = 153 yr). Silicon-32 as well as {sup 29}Si and {sup 30}Si can be produced in SNe by short neutron bursts; evidence for initial {sup 44}Ti (τ{sub 1/2} = 60 yr) in the C grain is additional evidence for an SN origin. The X grains have marginal {sup 32}S excesses, much smaller than expected from their large {sup 28}Si excesses. Similarly, the Y and Z grains do not show the S-isotopic anomalies expected from their large Si isotopic anomalies. Low intrinsic S contents and contamination with isotopically normal S are the most likely explanations.

  11. Corrosion behavior of Mg/graphene composite in aqueous electrolyte

    Selvam, M. [Centre for Nano Science and Technology, KS Rangasamy College of Technology, Tiruchengode, 637215, Tamil Nadu (India); Saminathan, K., E-mail: [Centre for Nano Science and Technology, KS Rangasamy College of Technology, Tiruchengode, 637215, Tamil Nadu (India); Siva, P. [Centre for Nano Science and Technology, KS Rangasamy College of Technology, Tiruchengode, 637215, Tamil Nadu (India); Saha, P. [Department of Ceramic Engineering, National Institute of Technology, Rourkela, India-769008 (India); Rajendran, V. [Centre for Nano Science and Technology, KS Rangasamy College of Technology, Tiruchengode, 637215, Tamil Nadu (India)


    In the present work, the electrochemical corrosion behavior of magnesium (Mg) and thin layer graphene coated Mg (Mg/graphene) are studied in different salt electrolyte such as NaCl, KCl and Na{sub 2}SO{sub 4}. The phase structure, crystallinity, and surface morphology of the samples are investigated using X-ray diffraction (XRD) analysis, scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDAX), and Raman spectroscopy techniques. The electrochemical corrosion behavior of the Mg and graphene coated Mg are also investigated using Electrochemical Impedance Spectroscopy (EIS) analysis. The tafel plot reveals that the corrosion of Mg drastically drops when coated with thin layer graphene (Mg/graphene) compared to Mg in KCl electrolyte. Moreover, the EIS confirms that Mg/graphene sample shows improve corrosion resistance and lower corrosion rate in KCl solution compare to all other electrolytes studied in the present system. - Highlights: • The corrosion behavior of magnesium alloy (AZ91) was investigated in three different electrolyte solution. • To study the anti-corrosion behavior of graphene coated with magnesium alloy. • To improve the corrosion resistance for magnesium alloy. • Nyquist plots confirms that MgG shows better corrosion resistance and lower corrosion rate in KCl solution.

  12. The chlorine isotopic composition of Martian meteorites 1: Chlorine isotope composition of Martian mantle and crustal reservoirs and their interactions

    Williams, J. T.; Shearer, C. K.; Sharp, Z. D.; Burger, P. V.; McCubbin, F. M.; Santos, A. R.; Agee, C. B.; McKeegan, K. D.


    The Martian meteorites record a wide diversity of environments, processes, and ages. Much work has been done to decipher potential mantle sources for Martian magmas and their interactions with crustal and surface environments. Chlorine isotopes provide a unique opportunity to assess interactions between Martian mantle-derived magmas and the crust. We have measured the Cl-isotopic composition of 17 samples that span the range of known ages, Martian environments, and mantle reservoirs. The 37Cl of the Martian mantle, as represented by the olivine-phyric shergottites, NWA 2737 (chassignite), and Shergotty (basaltic shergottite), has a low value of approximately -3.8‰. This value is lower than that of all other planetary bodies measured thus far. The Martian crust, as represented by regolith breccia NWA 7034, is variably enriched in the heavy isotope of Cl. This enrichment is reflective of preferential loss of 35Cl to space. Most basaltic shergottites (less Shergotty), nakhlites, Chassigny, and Allan Hills 84001 lie on a continuum between the Martian mantle and crust. This intermediate range is explained by mechanical mixing through impact, fluid interaction, and assimilation-fractional crystallization.

  13. Continuous measurements of isotopic composition of water vapour on the East Antarctic Plateau

    Casado, Mathieu; Landais, Amaelle; Masson-Delmotte, Valérie; Genthon, Christophe; Kerstel, Erik; Kassi, Samir; Arnaud, Laurent; Picard, Ghislain; Prie, Frederic; Cattani, Olivier; Steen-Larsen, Hans-Christian; Vignon, Etienne; Cermak, Peter


    Water stable isotopes in central Antarctic ice cores are critical to quantify past temperature changes. Accurate temperature reconstructions require one to understand the processes controlling surface snow isotopic composition. Isotopic fractionation processes occurring in the atmosphere and controlling snowfall isotopic composition are well understood theoretically and implemented in atmospheric models. However, post-deposition processes are poorly documented and understood. To quantitatively interpret the isotopic composition of water archived in ice cores, it is thus essential to study the continuum between surface water vapour, precipitation, surface snow and buried snow. Here, we target the isotopic composition of water vapour at Concordia Station, where the oldest EPICA Dome C ice cores have been retrieved. While snowfall and surface snow sampling is routinely performed, accurate measurements of surface water vapour are challenging in such cold and dry conditions. New developments in infrared spectroscopy enable now the measurement of isotopic composition in water vapour traces. Two infrared spectrometers have been deployed at Concordia, allowing continuous, in situ measurements for 1 month in December 2014-January 2015. Comparison of the results from infrared spectroscopy with laboratory measurements of discrete samples trapped using cryogenic sampling validates the relevance of the method to measure isotopic composition in dry conditions. We observe very large diurnal cycles in isotopic composition well correlated with temperature diurnal cycles. Identification of different behaviours of isotopic composition in the water vapour associated with turbulent or stratified regime indicates a strong impact of meteorological processes in local vapour/snow interaction. Even if the vapour isotopic composition seems to be, at least part of the time, at equilibrium with the local snow, the slope of δD against δ18O prevents us from identifying a unique origin leading

  14. Ground-state properties and symmetry energy of neutron-rich and neutron-deficient Mg isotopes

    Gaidarov, M K; Antonov, A N; de Guerra, E Moya


    A comprehensive study of various ground-state properties of neutron-rich and neutron-deficient Mg isotopes with $A$=20-36 is performed in the framework of the self-consistent deformed Skyrme-Hartree-Fock plus BCS method. The correlation between the skin thickness and the characteristics related with the density dependence of the nuclear symmetry energy is investigated for this isotopic chain following the theoretical approach based on the coherent density fluctuation model and using the Brueckner energy-density functional. The results of the calculations show that the behavior of the nuclear charge radii and the nuclear symmetry energy in the Mg isotopic chain is closely related to the nuclear deformation. We also study, within our theoretical scheme, the emergence of an "island of inversion" at neutron-rich $^{32}$Mg nucleus, that was recently proposed from the analyses of spectroscopic measurements of $^{32}$Mg low-lying energy spectrum and the charge rms radii of all magnesium isotopes in the $sd$ shell.

  15. Perchlorate in The Great Lakes: Distribution, Isotopic Composition and Origin

    Poghosyan, A.; Sturchio, N. C.; Jackson, W. A.; Guan, Y.; Eiler, J. M.; Hatzinger, P. B.


    Concentrations, stable chlorine and oxygen isotopic compositions, and 36Cl abundances of perchlorate were investigated in the five Laurentian Great Lakes. Samples were collected during monitoring cruises in 2007 and 2008 of the U.S. EPA's RV Lake Guardian and in 2010 at the water supply intake of Marquette, MI on the southern shore of Lake Superior. Concentrations of perchlorate were measured by IC/MS/MS at 24 locations, including one or two depth profiles in each lake. Mean concentrations (μg/L) are: Superior, 0.06 × 0.01; Michigan, 0.10 × 0.01; Huron, 0.11 × 0.01; Erie, 0.08 × 0.01, and Ontario, 0.09 × 0.01. Concentration vs. depth is nearly constant in each lake, indicating well-mixed conditions. Perchlorate was extracted from near-surface water by passing 15,000 to 80,000 L of water through 1-L cartridges containing Purolite A530E bifunctional anion-exchange resin. In the laboratory, perchlorate was eluted from the resin, purified, and precipitated as a >99% pure crystalline phase. Milligram amounts were recovered from each lake. Chlorine and oxygen isotopic analyses were performed at Caltech using the Cameca 7f-GEO SIMS instrument, following validation of the SIMS method with analyses of USGS-37 and USGS-38 isotopic reference materials. Results indicate a relatively narrow range in δ37Cl values (+2.9 to +3.9 ‰) and a wider range in δ18O values (-4.0 to +4.1 ‰), with a general geographic trend of increasing δ18O from west to east. Oxygen-17 was measured at UIC using dual-inlet IRMS of O2 produced by decomposition of KClO4. Great Lakes perchlorate has mass-independent oxygen isotopic variations with positive Δ17O values (+1.6 ‰ to +2.7 ‰) divided into two distinct groups: Lake Superior (+2.7 ‰) and the other four lakes (~ +1.7 ‰). The isotopic data indicate that perchlorate is dominantly of natural origin, having stable isotopic compositions resembling those of perchlorate from pre-industrial groundwaters in the western USA. The 36Cl

  16. Spectroscopic metrology for isotope composition measurements and transfer standards

    Anyangwe Nwaboh, Javis; Balslev-Harder, David; Kääriäinen, Teemu; Richmond, Craig; Manninen, Albert; Mohn, Joachim; Kiseleva, Maria; Petersen, Jan C.; Werhahn, Olav; Ebert, Volker


    The World Meteorological Organization (WMO) has identified greenhouse gases such as CO2, CH4 and N2O as critical for global climate monitoring. Other molecules such as CO that has an indirect effect of enhancing global warming are also monitored. WMO has stated compatibility goals for atmospheric concentration and isotope ratio measurements of these gases, e.g. 0.1 ppm for CO2 concentration measurements in the northern hemisphere and 0.01 ‰ for δ13C-CO2. For measurements of the concentration of greenhouse gases, gas analysers are typically calibrated with static gas standards e.g. traceable to the WMO scale or to the International System of Units (SI) through a national metrology institute. However, concentrations of target components, e.g. CO, in static gas standards have been observed to drift, and typically the gas matrix as well as the isotopic composition of the target component does not always reflect field gas composition, leading to deviations of the analyser response, even after calibration. The deviations are dependent on the measurement technique. To address this issue, part of the HIGHGAS (Metrology for high-impact greenhouse gases) project [1] focused on the development of optical transfer standards (OTSs) for greenhouse gases, e.g. CO2 and CO, potentially complementing gas standards. Isotope ratio mass spectrometry (IRMS) [2] is currently used to provide state-of-the-art high precision (in the 0.01 ‰ range) measurements for the isotopic composition of greenhouse gases. However, there is a need for field-deployable techniques such as optical isotope ratio spectroscopy (OIRS) that can be combined with metrological measurement methods. Within the HIGHGAS project, OIRS methods and procedures based on e.g. cavity enhanced spectroscopy (CES) and tunable diode laser absorption spectroscopy (TDLAS), matched to metrological principles have been established for the measurement of 13C/12C and 18O/16O ratios in CO2, 15N/14N ratios in N2O, and 13C/12C and 2H

  17. Boron contents and isotopic compositions of hog manure, selected fertilizers, and water in Minnesota

    Komor, S.C.


    Boron-isotope (δ11B) values may be useful as surrogate tracers of contaminants and indicators of water mixing in agricultural settings. This paper characterizes the B contents and isotopic compositions of hog manure and selected fertilizers, and presents δ11B data for ground and surface water from two agricultural areas. Boron concentrations in dry hog manure averaged 61 mg/kg and in commercial fertilizers ranged from below detection limits in some brands of ammonium nitrate and urea to 382 mg/kg in magnesium sulfate. Values of δ11B of untreated hog manure ranged from 7.2 to 11.2o/oo and of N fertilizers were −2.0 to 0.7o/oo. In 22 groundwater samples from a sand-plain aquifer in east-central Minnesota, B concentrations averaged 0.04 mg/L and δ11B values ranged from 2.3 to 41.5o/oo. Groundwater beneath a hog feedlot and a cultivated field where hog manure was applied had B-isotope compositions consistent with the water containing hog-manure leachate. In a 775-km2 watershed with silty-loam soils in southcentral Minnesota: 18 samples of subsurface drainage from corn (Zea mays L.) and soybean (Glycine max L. Merr.) fields had average B concentrations of 0.06 mg/L and δ11B values of 5.3 to 15.1o/oo; 27 stream samples had average B concentrations of 0.05 mg/L and δ11B values of 1.0 to 19.0o/oo; and eight groundwater samples had average B concentrations of 0.09 mg/L and δ11B values of −0.3 to 23.0o/oo. Values of δ11B and B concentrations, when plotted against one another, define a curved mixing trend that suggests subsurface drainage and stream water contain mixtures of B from shallow and deep groundwater.

  18. A model composition for Mars derived from the oxygen isotopic ratios of martian/SNC meteorites. [Abstract only

    Delaney, J. S.


    Oxygen is the most abundant element in most meteorites, yet the ratios of its isotopes are seldom used to constrain the compositional history of achondrites. The two major achondrite groups have O isotope signatures that differ from any plausible chondritic precursors and lie between the ordinary and carbonaceous chondrite domains. If the assumption is made that the present global sampling of chondritic meteorites reflects the variability of O reservoirs at the time of planetessimal/planet aggregation in the early nebula, then the O in these groups must reflect mixing between known chondritic reservoirs. This approach, in combination with constraints based on Fe-Mn-Mg systematics, has been used previously to model the composition of the basaltic achondrite parent body (BAP) and provides a model precursor composition that is generally consistent with previous eucrite parent body (EPB) estimates. The same approach is applied to Mars exploiting the assumption that the SNC and related meteorites sample the martian lithosphere. Model planet and planetesimal compositions can be derived by mixing of known chondritic components using O isotope ratios as the fundamental compositional constraint. The major- and minor-element composition for Mars derived here and that derived previously for the basaltic achondrite parent body are, in many respects, compatible with model compositions generated using completely independent constraints. The role of volatile elements and alkalis in particular remains a major difficulty in applying such models.

  19. Evaluating Foraminifera as an Archive for Seawater Chromium Isotopic Composition

    Wang, X.; Planavsky, N.; Hull, P. M.; Tripati, A.; Reinhard, C.; Zou, H.; Elder, L. E.; Henehan, M. J.


    In recent years there has been growing interest in using chromium isotopes (δ53Cr) as a proxy to investigate the redox evolution of Earth's ocean-atmosphere system throughout geological history. Potential archives for seawater δ53Cr that have been identified to date include iron formations and organic-rich siliciclastic sediments. However, these types of sediments are not common and they are discontinuous over geologic time. As a result, alternative types of archives are needed. Here we evaluate the utility of foraminifera tests as a recorder of seawater δ53Cr. Core-tops used were from different ocean basins. Mono-specific samples of Globigerinoides sacculifer, Orbulina universa, Pulleniatina obliquiloculata, Globoratalia crassula-crassaformis, Globoratalia truncatulinoides, and Globigerinella siphonifera were isolated to investigate inter-species isotope fractionation. Chromium concentrations were measured by isotope dilution method to be 0.1-0.3 μg/g. The δ53Cr values of these species range from 0.2‰ to 2.4‰, with an analytical uncertainty of 0.3‰ (95% confidence). Despite the high analytical uncertainty due to the extremely low levels of Cr present, there is still large detectable variation in foraminiferal δ53Cr values, which overlap presently available seawater values (Bonnand et al., 2013; Scheiderich et al., 2015). Possible explanations for such variations in foraminiferal δ53Cr values include heterogeneity of seawater δ53Cr in the modern oceans, and/or photobiochemical redox cycling of Cr in the surface oceans. Therefore, care should be taken when using foraminifera to reconstruct past seawater δ53Cr values. ReferencesBonnand, P., James, R., Parkinson, I., Connelly, D., Fairchild, I., 2013. The chromium isotopic composition of seawater and marine carbonates. Earth and Planetary Science Letters, 382: 10-20. Scheiderich, K., Amini, M., Holmden, C., Francois, R., 2015. Global variability of chromium isotopes in seawater demonstrated by Pacific

  20. Mineral composition control on inter-mineral iron isotopic fractionation in granitoids

    Wu, Hongjie; He, Yongsheng; Bao, Leier; Zhu, Chuanwei; Li, Shuguang


    This study reports elemental and iron isotopic compositions of feldspar and its coexisting minerals from four Dabie I-type granitoids to evaluate the factors that control inter-mineral Fe isotopic fractionation in granitoids. The order of heavy iron isotope enrichment is feldspar > pyrite > magnetite > biotite ≈ hornblende. Feldspar has heavier iron isotopic compositions than its co-existing magnetite (Δ56Feplagioclase-magnetite = +0.376‰ to +1.084‰, Δ56Fealkali-feldspar-magnetite = +0.516‰ to +0.846‰), which can be attributed to its high Fe3+/Fetot ratio and low coordination number (tetrahedrally-coordinated) of Fe3+. Δ56Femagnetite-biotite of coexisting magnetite and biotite ranges from 0.090‰ to 0.246‰. Based on homogeneous major and iron isotopic compositions of mineral replicates, the inter-mineral fractionation in this study should reflect equilibrium fractionation. The large variations of inter-mineral fractionation among feldspar, magnetite and biotite cannot be simply explained by temperature variation, but strongly depend on mineral compositions. The Δ56Feplagioclase-magnetite and Δ56Fealkali-feldspar-magnetite are positively correlated with albite mode in plagioclase and orthoclase mode in alkali-feldspar, respectively. This could be explained by different Fe-O bond strength in feldspar due to different Fe3+/∑Fe or different crystal parameters. The Δ56Femagnetite-biotite increases with decreasing Fe3+/∑Febiotite and increasing mole (Na + K)/Mgbiotite, indicating a decrease of β factor in low Fe3+/∑Fe and high (Na + K)/Mg biotite. High-silica leucosomes from Dabie migmatites with a feldspar accumulation petrogenesis have higher δ56Fe values (δ56Fe = 0.42-0.567‰) than leucosome that represents pristine partial melt (δ56Fe = 0.117 ± 0.016‰), indicating that accumulation of feldspar could account for high δ56Fe values of these rocks. High δ56Fe values are also predicted for other igneous rocks that are mainly composed of

  1. Isotopic composition of the ice cores obtained on the Western Plateau of the Mt Elbrus

    A. V. Kozachek


    Full Text Available The results of the isotopic investigations of several ice cores obtained at the Western Plateau of Mt. Elbrus (the Caucasus are presented. There is a distinct seasonal cycle in the isotopic composition record in these cores. Mean annual and seasonal values of the isotopic composition and accumulation rate were reconstructed for 89 years (1924–2012. These values were compared with the available regional meteorological data and the atmospheric circulation characteristics. It was shown that in the summer season the isotopic composition reflects the local temperature while in winter it depends on the atmospheric circulation.

  2. Effect of Wood Aging on Wine Mineral Composition and (87)Sr/(86)Sr Isotopic Ratio.

    Kaya, Ayse D; Bruno de Sousa, Raúl; Curvelo-Garcia, António S; Ricardo-da-Silva, Jorge M; Catarino, Sofia


    The evolution of mineral composition and wine strontium isotopic ratio (87)Sr/(86)Sr (Sr IR) during wood aging were investigated. A red wine was aged in stainless steel tanks with French oak staves (Quercus sessiliflora Salisb.), with three industrial scale replicates. Sampling was carried out after 30, 60, and 90 days of aging, and the wines were evaluated in terms of general analysis, phenolic composition, total polysaccharides, multielement composition, and Sr IR. Li, Be, Mg, Al, Sc, Ti, V, Mn, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Mo, Sb, Cs, Ba, Pr, Nd, Sm, Eu, Dy, Ho, Er, Yb, Lu, Tl, and Pb elements and (87)Sr/(86)Sr were determined by quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) and Na, K, Ca, and Fe by flame atomic absorption spectrometry (FAAS). Two-way ANOVA was applied to assess wood aging and time effect on Sr IR and mineral composition. Wood aging resulted in significantly higher concentrations of Mg, V, Co, Ni, and Sr. At the end of the aging period, wine exhibited statistically identical Sr IR compared to control. Study suggests that wood aging does not affect (87)Sr/(86)Sr, not precluding the use of this parameter for wine traceability purposes.

  3. Porous MgO material with ultrahigh surface area as the matrix for phase change composite

    Hao, Yonggan; Shao, Xiankun; Liu, Tongxuan [School of Materials Science and Engineering, Anhui University of Science and Technology, Huainan, Anhui 232001 (China); Li, Benxia, E-mail: [School of Materials Science and Engineering, Anhui University of Science and Technology, Huainan, Anhui 232001 (China); Nie, Shibin, E-mail: [School of Energy Resources and Safety, Anhui University of Science and Technology, Huainan, Anhui 232001 (China)


    Highlights: • Porous MgO material with ultrahigh surface area was synthesized. • A composite PCM was prepared from PEG-1000 and the porous MgO. • The phase change temperatures and enthalpy of the composite were measured. • The composite PCM performed good shape-stabilized property. - Abstract: Mesoporous magnesium oxide (MgO) material was synthesized using an integration of the evaporation-induced surfactant assembly and magnesium nitrate pyrolysis. The as-prepared MgO material is well crystalline, and possesses three-dimensional interconnected mesopores and a surface area as high as 596 m{sup 2}/g. Using the porous MgO as a matrix and polyethylene glycol (PEG-1000) as the functional phase for heat energy storage, a shape-stabilized phase change composite of PEG/MgO was fabricated by an easy impregnation method. In the composite, mesoporous MgO material provides structural strength and prevents the leakage of the molten PEG during the phase change process. The compositions and microstructures of the PEG/MgO composite were determined by Fourier transformation infrared spectroscope (FT-IR), X-ray diffractometer (XRD), scanning electronic microscope (SEM) and thermogravimetric analyzer (TGA), respectively. The phase change properties of the PEG/MgO composite were determined by differential scanning calorimeter (DSC). The high heat-energy storage capability and good thermal stability of the composite enable it extensive applications in the future.

  4. Preparation of novel functional Mg/O/PCL/ZnO composite biomaterials and their corrosion resistance

    Xi, Zhongxian; Tan, Cui; Xu, Lan; Yang, Na; Li, Qing, E-mail:


    Highlights: • Novel functional Mg/O/PCL/ZnO composite biomaterials were prepared. • The biomaterials were prepared by anodization treatment and dip-coating technique. • The composite biomaterials were smooth and with low porosity. • The prepared biomaterials have good corrosion resistance in SBF. • The composite biomaterials can release zinc ion to promote bone formation. - Abstract: In this study, novel and functional Mg/O/PCL/ZnO (magnesium/anodic film/poly(ε-caprolactone)/zinc oxide) composite biomaterials for enhancing the bioactivity and biocompatibility of the implant was prepared by using anodization treatment and dip-coating technique. The surface morphology, microstructure, adhesion strength and corrosion resistance of the composite biomaterials were investigated using scanning electron microscopy (SEM), adhesion measurements, electrochemical tests and immersion tests respectively. In addition, the biocompatible properties of Mg (magnesium), Mg/PCL (magnesium/poly(ε-caprolactone)) and Mg/O/PCL (magnesium/anodic film/poly(ε-caprolactone)) samples were also investigated. The results show that the Mg/O/PCL/ZnO composite biomaterials were with low porosity and with the ZnO powders dispersed in PCL uniformly. The adhesion tests suggested that Mg/O/PCL/ZnO composite biomaterials had better adhesion strength than that of Mg/PCL composite biomaterials obviously. Besides, an in vitro test for corrosion demonstrated that the Mg/O/PCL/ZnO composite biomaterials had good corrosion resistance and zinc ion was released obviously in SBF.

  5. Osmium Isotopic Composition of the Sumbar Cretaceous- Tertiary Boundary, Turkmenia

    Meisel, T.; Krahenbuhl, U.; Nazarov, M. A.


    Turekian (1982) propagated the use of the osmium isotopic composition as a cosmic indicator for the origin of the high osmium (and iridium) layers at the K/T boundaries. He did not consider the osmium isotopic signature of the terrestrial mantle, which also has a chondritic evolution of the Re-Os system. Osmium cannot serve alone as an infallible indicator of the impact theory, but interesting results can be obtained from their investigation. Different K/T boundary section have been analyzed so far for ^187Os/^186Os. An overview of the values is presented in the table. Boundary Clay layer Os ratio Reference Stevns Klint fish clay 1.66 Luck and Turekian, 1983 Woodside Creek 1.12 Lichte et al., 1986 Raton Basin 1.23 Kraehenbuehl et al., 1988 Raton Basin (several) 1.15-1.23 Esser and Turekian, 1989 Sumbar (0-1 cm) 1.16 This work We obtained a complete marine section of the K/T boundary in southern Turkmenia (decribed by Alekseyev, 1988). It shows a very high Ir concentration (66 ppb) at the boundary layer and a remarkable Ir enrichment over crustal rocks continuing up to 30 cm above the boundary. Our aim of this investigation is to analyze several samples from above and below the boundary for the ^187Os/^186Os ratio to obtain a complete picture of the isotopic evolution of the section. We want to evaluate mixing of Os with chondritic ratios with Os from upper crustal rocks. Another goal is to investigate a mobilization of Os. So far only one sample has been analyzed with NTI-MS after fire assay digestion of the sample. The sample 0 to 1 cm has an ^187Os/^186Os ratio of 1.162 +- 13, which is quite low. We expect an even lower value for the boundary clay (0 cm) itself not taking into account a contribution of radiogenic osmium from the decay of terrestrial rhenium. This might put this K/T boundary section closest of all to the present day chondritic value (approx. 1.05). Further analysis will be presented at the meeting. References Alekseyev A. S., Nazarov M. A

  6. Isotopic composition of sulfate accumulations, Northern Calcareous Alps, Austria

    Bojar, Ana-Voica; Halas, Stanislaw; Bojar, Hans-Peter; Trembaczowski, Andrzej


    The Eastern Alps are characterised by the presence of three main tectonic units, such as the Lower, Middle and Upper Austroalpine, which overlie the Penninicum (Tollmann, 1977). The Upper Austroalpine unit consists of the Northern Calcareous Alps (NCA) overlying the Greywacke zone and corresponding to the Graz Paleozoic, Murau Paleozoic and the Gurktal Nappe. Evaporitic rocks are lacking in the later ones. The Northern Calcareous Alps are a detached fold and thrust belt. The sedimentation started in the Late Carboniferous or Early Permian, the age of the youngest sediments being Eocene. The NCA are divided into the Bajuvaric, Tirolic and Juvavic nappe complexes. The evaporitic Haselgebirge Formation occurs in connection with the Juvavic nappe complex at the base of the Tirolic units (Leitner et al., 2013). The Haselgebirge Formation consists mainly of salt, shales, gypsum and anhydrite and includes the oldest sediments of the NCA. The age of the Haselgebirge Formation, established by using spors and geochronological data, is Permian to Lower Triassic. For the Northern Calcareous Alps, the mineralogy of sulphate accumulations consists mainly of gypsum and anhydrite and subordonates of carbonates. The carbonates as magnesite, dolomite and calcite can be found either as singular crystals or as small accumulations within the hosting gypsum. Sulfides (sphalerite, galena, pyrite), sulfarsenides (enargite, baumhauerite) and native sulphur enrichments are known from several deposits (Kirchner, 1987; Postl, 1990). The investigated samples were selected from various gypsum and halite rich deposits of the Northern Calcareous Alps. A total of over 20 samples were investigated, and both oxygen and sulfur isotopic composition were determined for anhydrite, gyps, polyhalite, blödite and langbeinite. The sulfur isotopic values vary between 10.1 to 14 ‰ (CDT), with three values higher than 14 ‰. The Oxygen isotopic values show a range from 9 to 23 ‰ (SMOW). The sulfur

  7. Equilibrium magnesium isotope fractionation between aqueous Mg2+ and carbonate minerals: Insights from path integral molecular dynamics

    Pinilla, Carlos; Blanchard, Marc; Balan, Etienne; Natarajan, Suresh K.; Vuilleumier, Rodolphe; Mauri, Francesco


    The theoretical determination of the isotopic fractionation between an aqueous solution and a mineral is of utmost importance in Earth sciences. While for crystals, it is well established that equilibrium isotopic fractionation factors can be calculated using a statistical thermodynamic approach based on the vibrational properties, several theoretical methods are currently used to model ions in aqueous solution. In this work, we present a systematic study to determine the reduced partition function ratio (β-factor) of aqueous Mg2+ using several levels of theory within the simulations. In particular, using an empirical force field, we compare and discuss the performance of the exact results obtained from path integral molecular dynamics (PIMD) simulations, with respect to the more traditional methods based on vibrational properties and the cluster approximation. The results show the importance of including configurational disorder for the estimation of the equilibrium isotope fractionation factor. We also show that using the vibrational frequencies computed from snapshots taken from equilibrated classical molecular dynamics represents a good approximation for the study of aqueous ions. Based on these conclusions, the β-factor of aqueous Mg2+ have been estimated from a Car-Parrinello molecular dynamics (CPMD) simulation with an ab initio force field, and combined with the β-factors of carbonate minerals (magnesite, dolomite, calcite and aragonite). Mg β-factor of Mg-bearing aragonite, calculated here for the first time, displays a lower value than the three other carbonate minerals. This is explained by a strong distortion of the cationic site leading to a decrease of the coordination number during Ca-Mg substitution. Overall, the equilibrium magnesium isotope fractionation factors between aqueous Mg2+ and carbonate minerals that derive from this methodological study support the previous theoretical results obtained from embedded cluster models.

  8. In vitro degradation and cytotoxicity of Mg/Ca composites produced by powder metallurgy.

    Zheng, Y F; Gu, X N; Xi, Y L; Chai, D L


    Mg/Ca (1 wt.%, 5 wt.%, 10 wt.% Ca) composites were prepared from pure magnesium and calcium powders using the powder metallurgy method, aiming to enlarge the addition of Ca content without the formation of Mg(2)Ca. The microstructures, mechanical properties and cytotoxicities of Mg/Ca composite samples were investigated. The corrosion of Mg/Ca composites in Dulbecco's modified Eagle's medium (DMEM) for various immersion intervals was studied by electrochemical impedance spectroscopy measurements and environmental scanning electron microscope, with the concentrations of released Mg and Ca ions in DMEM for various immersion time intervals being measured. It was shown that the main constitutional phases were Mg and Ca, which were uniformly distributed in the Mg matrix. The ultimate tensile strength (UTS) and elongation of experimental composites decreased with increasing Ca content, and the UTS of Mg/1Ca composite was comparable with that of as-extruded Mg-1Ca alloy. The corrosion potential increased with increasing Ca content, whereas the current density and the impedance decreased. It was found that the protective surface film formed quickly at the initial immersion stage. With increasing immersion time, the surface film became compact, and the corrosion rate of Mg/Ca composites slowed down. The surface film consisted mainly of CaCO(3), MgCO(3)x3H(2)O, HA and Mg(OH)(2) after 72 h immersion in DMEM. Mg/1Ca and Mg/5Ca composite extracts had no significant toxicity (p>0.05) to L-929 cells, whereas Mg/10Ca composite extract induced approximately 40% reduced cell viability.

  9. Microstructures and Mechanical Properties of Al/Mg Alloy Multilayered Composites Produced by Accumulative Roll Bonding

    H.S.Liu; B.Zhang; G.P.Zhang


    Al/Mg alloy multilayered composites were produced successfully at the lower temperature (280℃) by accumulative roll bonding (ARB) processing technique. The microstructures of Al and Mg alloy layers were characterized by scanning electron microscopy and transmission electron microscopy. Vickers hardness and three-point bending tests were conducted to investigate mechanical properties of the composites. It is found that Vickers hardness, bending strength and stiffness modulus of the Al/Mg alloy multilayered composite increase with increasing the ARB pass. Delamination and crack propagation along the interface are the two main failure modes of the multilayered composite subjected to bending load. Strengthening and fracture mechanisms of the composite are analyzed.

  10. Calcium isotopic composition of mantle xenoliths and minerals from Eastern China

    Kang, Jin-Ting; Zhu, Hong-Li; Liu, Yu-Fei; Liu, Fang; Wu, Fei; Hao, Yan-Tao; Zhi, Xia-Chen; Zhang, Zhao-Feng; Huang, Fang


    This study presents calcium isotope data for co-existing clinopyroxenes (cpx), orthopyroxenes (opx), and olivine (ol) in mantle xenoliths to investigate Ca isotopic fractionation in the upper mantle. δ44/40Ca (δ44/40Ca (‰) = (44Ca/40Ca)SAMPLE/(44Ca/40Ca)SRM915a - 1) in opx varies from 0.95 ± 0.05‰ to 1.82 ± 0.01‰ and cpx from 0.71 ± 0.06‰ to 1.03 ± 0.12‰ (2se). δ44/40Ca in ol (P-15) is 1.16 ± 0.08‰, identical to δ44/40Ca of the co-existing opx (1.12 ± 0.09‰, 2se). The Δ44/40Caopx-cpx (Δ44/40Caopx-cpx = δ44/40Caopx-δ44/40Cacpx) shows a large variation ranging from -0.01‰ to 1.11‰ and it dramatically increases with decreasing of Ca/Mg (atomic ratio) in opx. These observations may reflect the effect of opx composition on the inter-mineral equilibrium fractionation of Ca isotopes, consistent with the theoretical prediction by first-principles theory calculations (Feng et al., 2014). Furthermore, Δ44/40Caopx-cpx decreases when temperature slightly increases from 1196 to 1267 K. However, the magnitude of such inter-mineral isotopic fractionation (1.12‰) is not consistent with the value calculated by the well-known correlation between inter-mineral isotope fractionation factors and 1/T2 (Urey, 1947). Instead, it may reflect the temperature control on crystal chemistry of opx (i.e., Ca content), which further affects Δ44/40Caopx-cpx. The calculated δ44/40Ca of bulk peridotites and pyroxenites range from 0.76 ± 0.06‰ to 1.04 ± 0.12‰ (2se). Notably, δ44/40Ca of bulk peridotites are positively correlated with CaO and negatively with MgO content. Such correlations can be explained by mixing between a fertile mantle end-member and a depleted one with low δ44/40Ca, indicating that Ca isotopes could be a useful tool in studying mantle evolution.

  11. Chemical characterization and stable carbon isotopic composition of particulate polycyclic aromatic hydrocarbons issued from combustion of 10 Mediterranean woods

    A. Guillon


    Full Text Available The objectives of this study were to characterize polycyclic aromatic hydrocarbons from particulate matter emitted during wood combustion and to determine, for the first time, the isotopic signature of PAHs from nine wood species and Moroccan coal from the Mediterranean Basin. In order to differentiate sources of particulate-PAHs, molecular and isotopic measurements of PAHs were performed on the set of wood samples for a large panel of compounds. Molecular profiles and diagnostic ratios were measured by gas chromatography coupled with a mass spectrometer (GC/MS and molecular isotopic compositions13C of particulate-PAHs were determined by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS. Wood species present similar molecular profiles with benz(aanthracene and chrysene as dominant PAHs, whereas levels of concentrations range from 1.8 to 11.4 mg g−1 OC (sum of PAHs. Diagnostic ratios are consistent with reference ratios from literature but are not sufficient to differentiate the different species of woods. Concerning isotopic methodology, PAH molecular isotopic compositions are specific for each species and contrary to molecular fingerprints, significant variations of δ13C are observed for the panel of PAHs. This work allows differentiating wood combustion from others origins of particulate matter (vehicular exhaust using isotopic measurements (with δ13CPAH = −28.7 to −26.6‰ but also confirms the necessity to investigate source characterisation at the emission in order to help and complete source assessment models. These first results on woodburnings will be useful for the isotopic approach of source tracking.

  12. Chemical characterization and stable carbon isotopic composition of particulate Polycyclic Aromatic Hydrocarbons issued from combustion of 10 Mediterranean woods

    A. Guillon


    Full Text Available The objectives of this study were to characterize polycyclic aromatic hydrocarbons from particulate matter emitted during wood combustion and to determine, for the first time, the isotopic signature of PAHs from nine wood species and Moroccan coal from the Mediterranean Basin. In order to differentiate sources of particulate-PAHs, molecular and isotopic measurements of PAHs were performed on the set of wood samples for a large panel of compounds. Molecular profiles and diagnostic ratios were measured by gas chromatography/mass spectrometry (GC/MS and molecular isotopic compositions (δ13C of particulate-PAHs were determined by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS. Wood species present similar molecular profiles with benz(aanthracene and chrysene as dominant PAHs, whereas levels of concentrations range from 1.8 to 11.4 mg g−1 OC (sum of PAHs. Diagnostic ratios are consistent with reference ratios from literature but are not sufficient to differentiate the species of woods. Concerning isotopic methodology, PAH molecular isotopic compositions are specific for each species and contrary to molecular fingerprints, significant variations of δ13C are observed for the panel of PAHs. This work allows differentiating wood combustion (with δ13CPAH = −28.7 to −26.6‰ from others origins of particulate matter (like vehicular exhaust using isotopic measurements but also confirms the necessity to investigate source characterisation at the emission in order to help and complete source assessment models. These first results on woodburnings will be useful for the isotopic approach to source tracking.

  13. Oxygen Isotopic Composition of Carbon Dioxide in the Middle Atmosphere

    Liang, M.; Blake, G. A.; Lewis, B. R.; Yung, Y. L.


    The isotopic composition of long-lived trace gases provides a window into atmospheric transport and chemistry. Carbon dioxide is a particularly powerful tracer, because its abundance remains >100 ppmv in the mesosphere. Current models consider O3 as the main source of O(1D) in the mesosphere, but we note that the photolysis of 16O17O and 16O18O by solar Lyman-α radiation yields O(1D) 10-100 times more enriched in 17O and 18O than that from ozone photodissociation. We therefore incorporate both photochemical sources into stratospheric and mesospheric chemical transport models that quantitatively predict the unusual enhancement of 17O in CO2 from the middle atmosphere. New laboratory and atmospheric measurements are proposed to test our model and validate the use of CO2 isotopic fractionation as a tracer of atmospheric chemical and dynamical processes. Once fully understood the `anomalous' oxygen signature in CO2 can be used in turn to study biogeochemical cycles, in particular to constrain the gross carbon fluxes between the atmosphere and terrestrial biosphere.

  14. Volatile Concentrations and H-Isotope Composition of Unequilibrated Eucrites

    Sarafian, Adam R.; Nielsen, Sune G.; Marschall, Horst R.; Gaetani, Glenn A.; Hauri, Erik H.; Righter, Kevin; Berger, Eve L.


    Eucrites are among the oldest and best studied asteroidal basalts (1). They represent magmatism that occurred on their parent asteroid, likely 4-Vesta, starting at 4563 Ma and continuing for approx. 30 Myr. Two hypotheses are debated for the genesis of eucrites, a magma ocean model (2), and a mantle partial melting model. In general, volatiles (H, C, F, Cl) have been ignored for eucrites and 4-Vesta, but solubility of wt% levels of H2O are possible at Vestan interior PT conditions. Targeted measurements on samples could aid our understanding considerably. Recent studies have found evidence of volatile elements in eucrites, but quantifying the abundance of volatiles remains problematic (6). Volatile elements have a disproportionately large effect on melt properties and phase stability, relative to their low abundance. The source of volatile elements can be elucidated by examining the hydrogen isotope ratio (D/H), as different H reservoirs have drastically different H isotope compositions. Recent studies of apatite in eucrites have shown that the D/H of 4-Vesta matches that of Earth and carbonaceous chondrites, however, the D/H of apatites may not represent the D/H of a primitive 4-Vesta melt due to the possibility of degassing prior to the crystallization of apatite. Therefore, the D/H of early crystallizing phases must be measured to determine if the D/H of 4-Vesta is equal to that of the Earth and carbonaceous chondrites.

  15. Electrochemical deposition of Mg(OH2/GO composite films for corrosion protection of magnesium alloys

    Fengxia Wu


    Full Text Available Mg(OH2/graphene oxide (GO composite film was electrochemical deposited on AZ91D magnesium alloys at constant potential. The characteristics of the Mg(OH2/GO composite film were investigated by scanning electron microscope (SEM, energy-dispersive X-ray spectrometry (EDS, X-ray diffractometer (XRD and Raman spectroscopy. It was shown that the flaky GO randomly distributed in the composite film. Compared with the Mg(OH2 film, the Mg(OH2/GO composite film exhibited more uniform and compact structure. Potentiodynamic polarization tests revealed that the Mg(OH2/GO composite film could significantly improve the corrosion resistance of Mg(OH2 film with an obvious positive shift of corrosion potential by 0.19 V and a dramatic reduction of corrosion current density by more than one order of magnitude.

  16. Abnormal lithium isotope composition from the ancient lithospheric mantle beneath the North China Craton.

    Tang, Yan-Jie; Zhang, Hong-Fu; Deloule, Etienne; Su, Ben-Xun; Ying, Ji-Feng; Santosh, M; Xiao, Yan


    Lithium elemental and isotopic compositions of olivines in peridotite xenoliths from Hebi in the North China Craton provide direct evidence for the highly variable δ(7)Li in Archean lithospheric mantle. The δ(7)Li in the cores of olivines from the Hebi high-Mg# peridotites (Fo > 91) show extreme variation from -27 to +21, in marked deviation from the δ(7)Li range of fresh MORB (+1.6 to +5.6) although the Li abundances of the olivines are within the range of normal mantle (1-2 ppm). The Li abundances and δ(7)Li characteristics of the Hebi olivines could not have been produced by recent diffusive-driven isotopic fractionation of Li and therefore the δ(7)Li in the cores of these olivines record the isotopic signature of the subcontinental lithospheric mantle. Our data demonstrate that abnormal δ(7)Li may be preserved in the ancient lithospheric mantle as observed in our study from the central North China Craton, which suggest that the subcontinental lithospheric mantle has experienced modification of fluid/melt derived from recycled oceanic crust.

  17. Isotopic compositions of strontium in river water of Guizhou karst areas, China

    韩贵琳; 刘丛强


    We have carried out a study on the variation of strontium isotope composition of river waters, Wujiang and Yuangjiang River, in karst areas of Guizhou Province, China. The results obtained permit us to characterize the geochemistry of the river draining karst terrain and obtain a better understanding of main controls of catchment geology, chemical weathering of different rocks, and evaluate impact of human activities on the environment. The isotopic ratios of dissolved Sr in all rivers are between 87Sr/86Sr =0.7077 and 0.7110, totally lower than the weighted average of 87Sr/86Sr =0.7119 for the world large rivers. The Wujiang River waters have Sr concentrations from 1.0 to 6.1 μmol/L, while the Yuanjiang River waters have much lower Sr concentrations ranging from 0.28 to 1.3 μmol/L. Most of the river waters from the Wujiang river are characterized by low Ca/Sr and Mg/Sr, and 87Sr/86Sr ratios, in which a majority of river waters are of 87Sr/86Sr ratios lower than the average Sr isotope ratio (87Sr/86Sr

  18. Effect of organic ligands on Mg partitioning and Mg isotope fractionation during low-temperature precipitation of calcite in the absence of growth rate effects

    Mavromatis, Vasileios; Immenhauser, Adrian; Buhl, Dieter; Purgstaller, Bettina; Baldermann, Andre; Dietzel, Martin


    Calcite growth rate has been previously shown to be the dominating parameter controlling both Mg partitioning and Mg isotope fractionation during calcite growth. In natural calcite precipitation environments - characterized by abundant organic material - the presence of dissolved organic molecules may affect these two parameters. In order to assess the role of organic molecules, steady state calcite growth experiments have been performed at 25 °C, 1 bar pCO2 and constant, within analytical uncertainty growth rate (rp = 10-7.4 mol m-2 s-1) in the presence of aqueous Mg and six organic ligands in the concentration range from 0.01 to 10 mM. The organic ligands used in this study are: (i) acetic acid, (ii) citric acid, (iii) glutamic acid, (iv) salycilic acid, (v) glycine, and (vi) ethylenediaminetetraacetic acid (EDTA). These contain one or more carboxyl- and amino-groups that are commonly present in natural organic substances found in lacustrine, fluvial, soil, cave, as well as in marine and earliest diagenetic porewater environments. Results shown here indicate that the presence of these carboxyl- and amino-groups promotes an increase in the partition coefficient of Mg in calcite (DMg = (Mg/Ca)calcite/(Mg/Ca)fluid) that can be attributed to their adsorption onto the calcite surfaces and the subsequent reduction of the active sites of growth. This increase of DMg values as a function of the supersaturation degree of calcite in the fluid phase can be described by the linear equation:

  19. A combined Sm-Nd, Rb-Sr, and U-Pb isotopic study of Mg-suite norite 78238: Further evidence for early differentiation of the Moon

    Edmunson, J; E.Borg, L; Nyquist, L E; Asmerom, Y


    Lunar Mg-suite norite 78238 was dated using the Sm-Nd, Rb-Sr, and U-Pb isotopic systems in order to constrain the age of lunar magma ocean solidification and the beginning of Mg-suite magmatism, as well as to provide a direct comparison between the three isotopic systems. The Sm-Nd isotopic system yields a crystallization age for 78238 of 4334 {+-} 37 Ma and an initial {var_epsilon}{sub Nd}{sup 143} value of -0.27 {+-} 0.74. The age-initial {var_epsilon}{sub Nd}{sup 143} (T-I) systematics of a variety of KREEP-rich samples, including 78238 and other Mg-suite rocks, KREEP basalts, and olivine cumulate NWA 773, suggest that lunar differentiation was completed by 4492 {+-} 61 Ma assuming a Chondritic Uniform Reservoir bulk composition for the Moon. The Rb-Sr isotopic systematics of 78238 were disturbed by post-crystallization processes. Nevertheless, selected data points yield two Rb-Sr isochrons. One is concordant with the Sm-Nd crystallization age, 4366 {+-} 53 Ma. The other is 4003 {+-} 95 Ma and is concordant with an Ar-Ar age for 78236. The {sup 207}Pb-{sup 206}Pb age of 4333 {+-} 59 Ma is concordant with the Sm-Nd age. The U-Pb isotopic systematics of 78238 yield linear arrays equivalent to younger ages than the Pb-Pb system, and may reflect fractionation of U and Pb during sample handling. Despite the disturbed nature of the U-Pb systems, a time-averaged {mu} ({sup 238}U/{sup 204}Pb) value of the source can be estimated at 27 {+-} 30 from the Pb-Pb isotopic systematics. Because KREEP-rich samples are likely to be derived from source regions with the highest U/Pb ratios, the relatively low {mu} value calculated for the 78238 source suggests the bulk Moon does not have an exceedingly high {mu} value.

  20. Formation of Mg$_2$C$_3$ phase in N220 nanocarbon containing low carbon MgO-C composition



    This paper reports a non-conventional microstructurewith sequicarbide (Mg$_2$C$_3$) formation in N220 nanocarboncontaining low carbon magnesia carbon composition having magnesium metal powder as antioxidant. 5 wt% graphitecontaining MgO-C refractory with and without 1 wt% N220 nanocarbon is studied and 2 wt% magnesium metal powder isused as the lone antioxidant. The compositions were mixed with powder and liquid resin binder, pressed uniaxially at 150MPa and cured at 220$^{\\circ}$C. Cured samples were coked at 1000$^{\\circ}$C for 2 h. Matrix of the coked samples was studied in detail for microstructural analysis phase content and formation of nail-shaped sequicarbide was found in the nanocarbon containing compositions. The in-situ sequicarbide formation has resulted in the strength of the batch.

  1. Magnesium and 54Cr isotope compositions of carbonaceous chondrite chondrules – Insights into early disk processes

    Olsen, Mia B.; Wielandt, Daniel; Schiller, Martin; Van Kooten, Elishevah M.M.E.; Bizzarro, Martin


    We report on the petrology, magnesium isotopes and mass-independent 54Cr/52Cr compositions (μ54Cr) of 42 chondrules from CV (Vigarano and NWA 3118) and CR (NWA 6043, NWA 801 and LAP 02342) chondrites. All sampled chondrules are classified as type IA or type IAB, have low 27Al/24Mg ratios (0.04–0.27) and display little or no evidence for secondary alteration processes. The CV and CR chondrules show variable 25Mg/24Mg and 26Mg/24Mg values corresponding to a range of mass-dependent fractionation of ~500 ppm (parts per million) per atomic mass unit. This mass-dependent Mg isotope fractionation is interpreted as reflecting Mg isotope heterogeneity of the chondrule precursors and not the result of secondary alteration or volatility-controlled processes during chondrule formation. The CV and CR chondrule populations studied here are characterized by systematic deficits in the mass-independent component of 26Mg (μ26Mg*) relative to the solar value defined by CI chondrites, which we interpret as reflecting formation from precursor material with a reduced initial abundance of 26Al compared to the canonical 26Al/27Al of ~5 × 10−5. Model initial 26Al/27Al values of CV and CR chondrules vary from (1.5 ± 4.0) × 10−6 to (2.2 ± 0.4) × 10−5. The CV chondrules display significant μ54Cr variability, defining a range of compositions that is comparable to that observed for inner Solar System primitive and differentiated meteorites. In contrast, CR chondrites are characterized by a narrower range of μ54Cr values restricted to compositions typically observed for bulk carbonaceous chondrites. Collectively, these observations suggest that the CV chondrules formed from precursors that originated in various regions of the protoplanetary disk and were then transported to the accretion region of the CV parent asteroid whereas CR chondrule predominantly formed from precursor with carbonaceous chondrite-like μ54Cr signatures. The observed μ54Cr variability in chondrules from

  2. Nitrate isotopic composition and ancillary variables (land use, redox, excess N2, age, water isotopics) in California groundwater

    Veale, Nathan; Moran, Jean; Visser, Ate; Singleton, Michael; Esser, Bradley


    Nitrate is a critical water quality issue in California, the United States and the world. Lawrence Livermore National Laboratory (LLNL) has compiled a large, unique database of California groundwater nitrate isotopic compositions (δ15N-NO3 and δ18O-NO3), acquired largely through more than a decade of coordination with the State of California Groundwater Ambient Monitoring and Assessment (GAMA) program. The water samples are predominantly from shallow aquifers accessed by domestic and monitoring wells. The database of >1,300 nitrate isotopic compositions includes a number of important ancillary parameters: DO, ORP and DOC (measured for 18% of samples); excess air and dissolved N2 (24%); water isotopic composition (δ18O-H2O and δD-H2O) (43%); and tritium/3He groundwater age (27%). Methods used at LLNL include sample preparation by the denitrifier method (for δ15N-NO3 and δ18O-NO3) and Isotope Ratio Mass Spectrometry with (δ15N-NO3 and δ18O-NO3 and δ18O-H2O and δD-H2O), Noble Gas Mass Spectrometry (NGMS; for excess air and groundwater age), and Membrane Inlet Mass Spectrometry (MIMS; for major dissolved gases and excess N2). Redox indicators (DO, ORP and DOC) in conjunction with excess N2, groundwater age, and nitrate isotopic composition are used to assess the presence or absence, and potentially the rate of, saturated-zone denitrification. Comparison of δ18O-NO3 to δ18O-H2O isotopic composition is used to distinguish synthetic nitrate from nitrification of reduced forms of nitrogen as a source of groundwater nitrate. Groundwater age is used to discern timing and temporal trends in groundwater nitrate isotopic composition. The relationship of nitrate isotopic composition to ancillary parameters (redox, excess N2, water isotopic composition and groundwater age) is explored, along with its relationship to well location, screened interval, and land use, with a focus on the extent of saturated-zone denitrification and the significance of synthetic nitrate as

  3. Sr and Nd isotopic and trace element compositions of Quaternary volcanic centers of the Southern Andes

    Futa, K.; Stern, C.R.


    Isotopic compositions of samples from six Quaternary volcanoes located in the northern and southern extremities of the Southern Volcanic Zone (SVZ, 33-46??S) of the Andes and from four centers in the Austral Volcanic Zone (AVZ, 49-54??S) range for 87Sr 86Sr from 0.70280 to 0.70591 and for 143Nd 144Nd from 0.51314 to 0.51255. The ranges are significantly greater than previously reported from the southern Andes but are different from the isotopic compositions of volcanoes in the central and northern Andes. Basalts and basaltic andesites from three centers just north of the Chile Rise-Trench triple junction have 87Sr 86Sr, 143Nd 144Nd, La Yb, Ba La, and Hf Lu that lie within the relatively restricted ranges of the basic magmas erupted from the volcanic centers as far north as 35??S in the SVZ of the Andes. The trace element and Sr and Nd isotopic characteristics of these magmas may be explained by source region contamination of subarc asthenosphere, with contaminants derived from subducted pelagic sediments and seawater-altered basalts by dehydration of subducted oceanic lithosphere. In the northern extremity of the SVZ between 33?? and 34??S, basaltic andesites and andesites have higher 87Sr 86Sr, Rb Cs, and Hf Lu, and lower 143Nd 144Nd than basalts and basaltic andesites erupted farther south in the SVZ, which suggests involvement of components derived from the continental crust. In the AVZ, the most primitive sample, high-Mg andesite from the southernmost volcanic center in the Andes (54??S) has Sr and Nd isotopic compositions and K Rb and Ba La similar to MORB. The high La Yb of this sample suggests formation by small degrees of partial melting of subducted MORB with garnet as a residue. Samples from centers farther north in the AVZ show a regionally regular northward increase in SiO2, K2O, Rb, Ba, Ba La, and 87Sr 86Sr and decrease in MgO, Sr, K Rb, Rb Cs, and 143Nd 144Nd, suggesting increasingly greater degrees of fractional crystallization and associated intra

  4. Stable isotope composition of atmospheric carbon monoxide. A modelling study

    Gromov, Sergey S.


    This study aims at an improved understanding of the stable carbon and oxygen isotope composition of the carbon monoxide (CO) in the global atmosphere by means of numerical simulations. At first, a new kinetic chemistry tagging technique for the most complete parameterisation of isotope effects has been introduced into the Modular Earth Submodel System (MESSy) framework. Incorporated into the ECHAM/MESSy Atmospheric Chemistry (EMAC) general circulation model, an explicit treatment of the isotope effects on the global scale is now possible. The expanded model system has been applied to simulate the chemical system containing up to five isotopologues of all carbon- and oxygen-bearing species, which ultimately determine the δ{sup 13}C, δ{sup 18}O and Δ{sup 17}O isotopic signatures of atmospheric CO. As model input, a new stable isotope-inclusive emission inventory for the relevant trace gases has been compiled. The uncertainties of the emission estimates and of the resulting simulated mixing and isotope ratios have been analysed. The simulated CO mixing and stable isotope ratios have been compared to in-situ measurements from ground-based observatories and from the civil-aircraft-mounted CARIBIC-1 measurement platform. The systematically underestimated {sup 13}CO/{sup 12}CO ratios of earlier, simplified modelling studies can now be partly explained. The EMAC simulations do not support the inferences of those studies, which suggest for CO a reduced input of the highly depleted in {sup 13}C methane oxidation source. In particular, a high average yield of 0.94 CO per reacted methane (CH{sub 4}) molecule is simulated in the troposphere, to a large extent due to the competition between the deposition and convective transport processes affecting the CH{sub 4} to CO reaction chain intermediates. None of the other factors, assumed or disregarded in previous studies, however hypothesised to have the potential in enriching tropospheric CO in {sup 13}C, were found significant

  5. Tooth enamel maturation reequilibrates oxygen isotope compositions and supports simple sampling methods

    Trayler, Robin B.; Kohn, Matthew J.


    Oxygen isotope and major element zoning patterns of several disparate ungulate teeth were collected to evaluate the timing and geometry of enamel formation, records of isotope zoning, and tooth enamel sampling strategies. Isotopic zoning in mammalian tooth enamel encodes a sub-annual time series of isotopic variation of an animal's body water composition, with a damping factor that depends on the specifics of how enamel mineralizes. Enamel formation comprises two stages: precipitation of appositional enamel with a high CO3:PO4 ratio, followed by precipitation of maturational enamel with a lower CO3:PO4. If appositional and maturational enamel both contribute to isotope compositions (but with different CO3:PO4), and if isotope compositions vary seasonally, paired δ18O values from CO3 and PO4 profiles should show a spatial separation. CO3 isotope patterns should be shifted earlier seasonally than PO4 isotope patterns. Such paired profiles for new and published data show no resolvable shifts, i.e. CO3 and PO4 δ18O profiles show coincident maxima and minima. This coincidence suggests that enamel maturation reequilibrates appositional isotope compositions. If enamel maturation establishes enamel isotope compositions, the geometry of maturation, not apposition, should be considered when devising sampling protocols. X-ray maps of Ca zoning show that the majority of enamel (inner and middle layers) mineralizes heavily at a high angle to the external tooth surface and the enamel-dentine junction over length scales of 2-4 mm, while the outer enamel surface mineralizes more slowly. These data suggest that isotopic sampling strategies should parallel maturational geometry and focus on interior enamel to improve data fidelity. The magnitude of isotopic damping is also smaller than implied in previous studies, so tooth enamel zoning more closely reflects original body water isotopic variations than previously assumed.

  6. Geochemistry and oxygen isotope composition of main-group pallasites and olivine-rich clasts in mesosiderites

    Greenwood, Richard C.; Barrat, Jean-Alix; Scott, Edward R. D.


    they are not. To investigate this "Great DuniteShortage" we have undertaken a geochemical and oxygen isotope study of main-group pallasites and dunitic rocks from mesosiderites.Oxygen isotope analysis of 24 main-group pallasites (103 replicates) yielded a mean Δ17O value of -0.187 ±0.016‰ (2σ), which is fully...... origin. Although the Dawn mission did not detect mesosiderite-like material on Vesta, evidence linking the mesosiderites and HEDs includes: (i) theirnearly identical oxygen isotope compositions; (ii) the presence in both of coarse-grained Mg-rich olivines; (iii) both have synchronous Lu-Hf and Mn-Cr ages...... asteroidsand meteorites results from a range of factors. However, evidence from pallasites and mesosiderites indicates that the most important reason for this olivine shortage lies in the early, catastrophic destruction ofplanetesimals in the terrestrial planet-forming region and the subsequent preferential...

  7. Oxygen- and magnesium-isotope compositions of calcium-aluminum-rich inclusions from CR2 carbonaceous chondrites

    Makide, Kentaro; Nagashima, Kazuhide; Krot, Alexander N.; Huss, Gary R.; Hutcheon, Ian D.; Bischoff, Addi


    We report both oxygen- and magnesium-isotope compositions measured in situ using a Cameca ims-1280 ion microprobe in 20 of 166 CAIs identified in 47 polished sections of 15 CR2 (Renazzo-type) carbonaceous chondrites. Two additional CAIs were measured for oxygen isotopes only. Most CR2 CAIs are mineralogically pristine; only few contain secondary phyllosilicates, sodalite, and carbonates - most likely products of aqueous alteration on the CR2 chondrite parent asteroid. Spinel, hibonite, grossite, anorthite, and melilite in 18 CAIs have 16O-rich (Δ 17O = -23.3 ± 1.9‰, 2 σ error) compositions and show no evidence for postcrystallization isotopic exchange commonly observed in CAIs from metamorphosed CV carbonaceous chondrites. The inferred initial 26Al/ 27Al ratios, ( 26Al/ 27Al) 0, in 15 of 16 16O-rich CAIs measured are consistent with the canonical value of (4.5-5) × 10 -5 and a short duration (oxygen- and magnesium-isotope compositions (˜11 and 23‰/amu, respectively), a deficit of 26Mg, and a relatively low ( 26Al/ 27Al) 0 = (2.0 ± 1.7) × 10 -5. This could be the first FUN ( Fractionation and Unidentified Nuclear effects) CAI found in CR2 chondrites. Because this inclusion is slightly 16O-depleted compared to most CR2 CAIs and has lower than the canonical ( 26Al/ 27Al) 0, it may have experienced multistage formation from precursors with nonsolar magnesium-isotope composition and recorded evolution of oxygen-isotope composition in the early solar nebula over 0.9+2.2-0.7 My. Eight of the 166 CR2 CAIs identified are associated with chondrule materials, indicating that they experienced late-stage, incomplete melting during chondrule formation. Three of these CAIs show large variations in oxygen-isotope compositions (Δ 17O ranges from -23.5‰ to -1.7‰), suggesting dilution by 16O-depleted chondrule material and possibly exchange with an 16O-poor (Δ 17O > -5‰) nebular gas. The low inferred ( 26Al/ 27Al) 0 ratios of these CAIs (2 My after crystallization

  8. Using trace element content and lead isotopic composition to assess sources of PM in Tijuana, Mexico

    Salcedo, D.; Castro, T.; Bernal, J. P.; Almanza-Veloz, V.; Zavala, M.; González-Castillo, E.; Saavedra, M. I.; Perez-Arvízu, O.; Díaz-Trujillo, G. C.; Molina, L. T.


    PM2.5 samples were collected at two urban sites (Parque Morelos (PQM) and CECyTE (CEC)) in Tijuana during the Cal-Mex campaign from May 24 to June 5, 2010. Concentration of trace elements (Mg, Al, Ti, V, Mn, Fe, Co, Ni, Zn, Cu, Ga, As, Se, Rb, Sr, Mo, Cd, Sn, Sb, Ba, La, Ce, and Pb), and Pb isotopic composition were determined in order to study the sources of PM impacting each site. Other chemical analysis (gravimetric, elemental and organic carbon (EC/OC), and polycyclic aromatic hydrocarbons (PAHs)), were also performed. Finally, back-trajectories were calculated to facilitate the interpretation of the chemical data. Trace elements results show that CEC is a receptor site affected by mixed regional sources: sea salt, mineral, urban, and industrial. On the other hand, PQM seems to be impacted mainly by local sources. In particular, Pb at CEC is of anthropogenic, as well as crustal origin. This conclusion is supported by the lead isotopic composition, whose values are consistent with a combination of lead extracted from US mines, and lead from bedrocks in the Mexican Sierras. Some of the time variability observed can be explained using the back-trajectories.

  9. Hydrogenation/Dehydrogenation Performances of the MgH2-WS2 Composites

    WANG Jiasheng; ZHANG Wei; CHENG Ying; KE Dandan; HAN Shumin


    The hydrogenation/dehydrogenation kinetics and thermodynamic behaviors of the MgH2-WS2 composites were investigated. The TPD (Temperature-Programmed-Desorption) curves showed that the onset dehydrogenation temperature of the MgH2 + 20wt% WS2 composite was 615 K, 58 K lower than that of the pristine MgH2. The kinetic measurements showed that within 21 min, the MgH2 + 20wt% WS2 composite could absorb 2.818wt% at 423 K, and release 4.244 wt% of hydrogen at 623 K, while the hydriding/dehydriding capacity of MgH2 reached only 0.979wt% and 2.319wt% respectively under identical conditions. The improvement of hydrogenation/dehydrogenation performances for the composite was attributed to the co-catalytic effect between the new phases W and MgS which formed during the ball-milling process.

  10. Humidity sensing behaviour of polyaniline/magnesium chromate (MgCrO4) composite

    T Machappa; M V N Ambika Prasad


    ‘in situ’ polymerization of polyaniline (PANI) was carried out in the presence of magnesium chromate (MgCrO4) to synthesize PANI/ceramic (MgCrO4) composite. These prepared composites were characterized by XRD, FTIR and SEM, which confirm the presence of MgCrO4 in polyaniline matrix. The temperature dependent conductivity measurement shows the thermally activated exponential behaviour of PANI /MgCrO4 composites. The decrease in electrical resistance was observed when the polymer composites were exposed to the broad range of relative humidity (ranging between 20 and 95% RH). This decrease is due to increase in surface electrical conductivity resulting from moisture absorption and due to capillary condensation of water causing change in conductivity within the sensing materials. PANI / MgCrO4 composites are found to be sensitive to low humidity ranging from 20 to 50% RH.

  11. Isotopic and Elemental Composition of Roasted Coffee as a Guide to Authenticity and Origin.

    Carter, James F; Yates, Hans S A; Tinggi, Ujang


    This study presents the stable isotopic and elemental compositions of single-origin, roasted coffees available to retail consumers. The δ(13)C, δ(15)N, and δ(18)O compositions were in agreement with those previously reported for green coffee beans. The δ(15)N composition was seen to be related to organic cultivation, reflected in both δ(2)H and δ(18)O compositions. The δ(13)C composition of extracted caffeine differed little from that of the bulk coffee. Stepwise discriminant analysis with jackknife tests, using isotopic and elemental data, provided up to 77% correct classification of regions of production. Samples from Africa and India were readily classified. The wide range in both isotopic and elemental compositions of samples from other regions, specifically Central/South America, resulted in poor discrimination between or within these regions. Simpler X-Y and geo-spatial plots of the isotopic data provided effective visual means to distinguish between coffees from different regions.

  12. Light element isotopic compositions of cometary matter returned by the STARDUST mission

    McKeegan, K D; Aleon, J; Bradley, J; Brownlee, D; Busemann, H; Butterworth, A; Chaussidon, M; Fallon, S; Floss, C; Gilmour, J; Gounelle, M; Graham, G; Guan, Y; Heck, P R; Hoppe, P; Hutcheon, I D; Huth, J; Ishii, H; Ito, M; Jacobsen, S B; Kearsley, A; Leshin, L A; Liu, M; Lyon, I; Marhas, K; Marty, B; Matrajt, G; Meibom, A; Messenger, S; Mostefaoui, S; Nakamura-Messenger, K; Nittler, L; Palma, R; Pepin, R O; Papanastassiou, D A; Robert, F; Schlutter, D; Snead, C J; Stadermann, F J; Stroud, R; Tsou, P; Westphal, A; Young, E D; Ziegler, K; Zimmermann, L; Zinner, E


    Hydrogen, carbon, nitrogen, and oxygen isotopic compositions are heterogeneous among comet 81P/Wild2 particle fragments, however extreme isotopic anomalies are rare, indicating that the comet is not a pristine aggregate of presolar materials. Non-terrestrial nitrogen and neon isotope ratios suggest that indigenous organic matter and highly volatile materials were successfully collected. Except for a single circumstellar stardust grain, silicate and oxide minerals have oxygen isotopic compositions consistent with solar system origin. One refractory grain is {sup 16}O-enriched like refractory inclusions in meteorites, suggesting formation in the hot inner solar nebula and large-scale radial transport prior to comet accretion in the outer solar system.

  13. The chemical composition of red giants in 47 Tucanae. II. Magnesium isotopes and pollution scenarios

    Thygesen, A O; Ludwig, H -G; Ventura, P; Yong, D; Collet, R; Christlieb, N; Melendez, J; Zaggia, S


    The phenomenon of multiple populations in globular clusters is still far from understood, with several proposed mechanisms to explain the observed behaviour. The study of elemental and isotopic abundance patterns are crucial for investigating the differences among candidate pollution mechanisms. We derive magnesium isotopic ratios for 13 stars in the globular cluster 47 Tucanae (NGC 104) to provide new, detailed information about the nucleosynthesis that has occurred within the cluster. For the first time, the impact of 3D model stellar atmospheres on the derived Mg isotopic ratios is investigated. Using both tailored 1D atmospheric models and 3D hydrodynamical models, we derive magnesium isotopic ratios from four features of MgH near 5135{\\AA} in 13 giants near the tip of the RGB, using high signal-to-noise, high-resolution spectra. We derive the magnesium isotopic ratios for all stars and find no significant offset of the isotopic distribution between the pristine and the polluted populations. Furthermore, ...

  14. Magnesium and 54Cr isotope compositions of carbonaceous chondrite chondrules - Insights into early disk processes

    Olsen, Mia B.; Wielandt, Daniel; Schiller, Martin; Van Kooten, Elishevah M. M. E.; Bizzarro, Martin


    We report on the petrology, magnesium isotopes and mass-independent 54Cr/52Cr compositions (μ54Cr) of 42 chondrules from CV (Vigarano and NWA 3118) and CR (NWA 6043, NWA 801 and LAP 02342) chondrites. All sampled chondrules are classified as type IA or type IAB, have low 27Al/24Mg ratios (0.04-0.27) and display little or no evidence for secondary alteration processes. The CV and CR chondrules show variable 25Mg/24Mg and 26Mg/24Mg values corresponding to a range of mass-dependent fractionation of ∼500 ppm (parts per million) per atomic mass unit. This mass-dependent Mg isotope fractionation is interpreted as reflecting Mg isotope heterogeneity of the chondrule precursors and not the result of secondary alteration or volatility-controlled processes during chondrule formation. The CV and CR chondrule populations studied here are characterized by systematic deficits in the mass-independent component of 26Mg (μ26Mg∗) relative to the solar value defined by CI chondrites, which we interpret as reflecting formation from precursor material with a reduced initial abundance of 26Al compared to the canonical 26Al/27Al of ∼5 × 10-5. Model initial 26Al/27Al values of CV and CR chondrules vary from (1.5 ± 4.0) × 10-6 to (2.2 ± 0.4) × 10-5. The CV chondrules display significant μ54Cr variability, defining a range of compositions that is comparable to that observed for inner Solar System primitive and differentiated meteorites. In contrast, CR chondrites are characterized by a narrower range of μ54Cr values restricted to compositions typically observed for bulk carbonaceous chondrites. Collectively, these observations suggest that the CV chondrules formed from precursors that originated in various regions of the protoplanetary disk and were then transported to the accretion region of the CV parent asteroid whereas CR chondrule predominantly formed from precursor with carbonaceous chondrite-like μ54Cr signatures. The observed μ54Cr variability in chondrules from CV

  15. Strengthening and toughening of poly(L-lactide) composites by surface modified MgO whiskers

    Wen, Wei [Biomaterial Research Laboratory, Department of Material Science and Engineering, College of Science and Engineering, Jinan University, Guangzhou 510632 (China); Luo, Binghong, E-mail: [Biomaterial Research Laboratory, Department of Material Science and Engineering, College of Science and Engineering, Jinan University, Guangzhou 510632 (China); Engineering Research Center of Artificial Organs and Materials, Ministry of Education, Guangzhou 510632 (China); Qin, Xiaopeng; Li, Cairong [Biomaterial Research Laboratory, Department of Material Science and Engineering, College of Science and Engineering, Jinan University, Guangzhou 510632 (China); Liu, Mingxian; Ding, Shan [Biomaterial Research Laboratory, Department of Material Science and Engineering, College of Science and Engineering, Jinan University, Guangzhou 510632 (China); Engineering Research Center of Artificial Organs and Materials, Ministry of Education, Guangzhou 510632 (China); Zhou, Changren, E-mail: [Biomaterial Research Laboratory, Department of Material Science and Engineering, College of Science and Engineering, Jinan University, Guangzhou 510632 (China); Engineering Research Center of Artificial Organs and Materials, Ministry of Education, Guangzhou 510632 (China)


    Highlights: • The grafted PLLA chain on the surface of g-MgO whisker was ruled out by FTIR spectroscopy and TG/DTG analyses. • The excellent dispersion of g-MgO whiskers and the strong interfacial adhesion of g-MgO whiskers/PLLA composite were proved by FSEM. • Comparing to MgO particles and MgO whiskers, fibrous-like g-MgO whiskers are the most effective reinforcing and toughening fillers for PLLA. - Abstract: To improve both the strength and toughness of poly(L-lactide) (PLLA), fibrous-like MgO whiskers with diameters of 0.15–1 μm and lengths of 15–110 μm were prepared, and subsequently surface modified with L-lactide to obtain grafted MgO whiskers (g-MgO whiskers). The structures and properties of MgO whiskers and g-MgO whiskers were studied. Then, a series of MgO whiskers/PLLA and g-MgO whiskers/PLLA composites were prepared by solution casting method, for comparison, MgO particles/PLLA composite was prepared too. The resulting composites were evaluated in terms of hydrophilicity, crystallinity, dispersion of whiskers, interfacial adhesion and mechanical performance by means of polarized optical microscopy (POM), contact angle measurement, field emission scanning electron microscope (FSEM), transmission electron microscopy (TEM) and tensile testing. The results revealed that the crystallization rate and hydrophilicity of PLLA were improved by the introduction of MgO whiskers and g-MgO whiskers. The g-MgO whiskers can disperse more uniformly in and show stronger interfacial adhesion with the matrix than MgO whiskers as a result of the surface modification. Due to the bridge effect of the whiskers and the excellent interfacial adhesion between g-MgO whiskers and PLLA, g-MgO whiskers/PLLA composites exhibited remarkably higher strength, modulus and toughness compared to the pristine PLLA, MgO particles/PLLA and MgO whiskers/PLLA composites.

  16. Enhanced Mechanical Properties and Corrosion Behavior of Biodegradable Mg-Zn/HA Composite

    Salleh, Emee Marina; Zuhailawati, Hussain; Ramakrishnan, Sivakumar; Dhindaw, Brij Kumar


    Magnesium (Mg) and its alloys have shown potential for use in the biomedical industry due to their excellent biological performance and biodegradability in the bioenvironment. Thus, the aim of the present study was to develop a reliable biodegradable hard tissue substituent. Biodegradable and bioactive Mg-Zinc (Zn) reinforced by hydroxyapatite (HA) composite was prepared using mechanically alloyed Mg-6.5 wt pct Zn and pure HA powders as starting materials. Various HA contents (i.e., 5, 10, 15, and 20 wt pct) were introduced in forming the Mg-Zn/HA composite. The effect of bioactive HA incorporation in biodegradable Mg-6.5 wt pct Zn alloy matrix on mechanical and biodegradation properties as well as microstructural observation was investigated. As measured by the Williamson-Hall formula, the Mg crystallite size of the sintered composites containing 5, 10, 15, and 20 wt pct HA were 36.76, 29.08, 27.93, and 27.31 nm, respectively. According to X-ray diffraction (XRD) analysis, there was no new crystalline phase formed during milling, indicating that no mechanochemical reactions between Mg-Zn alloy and HA occurred. The -1.70 V shifted significantly toward the passive position of the plain Mg-6.5 wt pct Zn alloy and Mg-Zn/10 wt pct HA composite, which were -1.50 and -1.46 V, respectively, indicating that the Mg-Zn/10 wt pct HA composite was least susceptible to corrosion in the bioenvironment.

  17. Enhanced Mechanical Properties and Corrosion Behavior of Biodegradable Mg-Zn/HA Composite

    Salleh, Emee Marina; Zuhailawati, Hussain; Ramakrishnan, Sivakumar; Dhindaw, Brij Kumar


    Magnesium (Mg) and its alloys have shown potential for use in the biomedical industry due to their excellent biological performance and biodegradability in the bioenvironment. Thus, the aim of the present study was to develop a reliable biodegradable hard tissue substituent. Biodegradable and bioactive Mg-Zinc (Zn) reinforced by hydroxyapatite (HA) composite was prepared using mechanically alloyed Mg-6.5 wt pct Zn and pure HA powders as starting materials. Various HA contents ( i.e., 5, 10, 15, and 20 wt pct) were introduced in forming the Mg-Zn/HA composite. The effect of bioactive HA incorporation in biodegradable Mg-6.5 wt pct Zn alloy matrix on mechanical and biodegradation properties as well as microstructural observation was investigated. As measured by the Williamson-Hall formula, the Mg crystallite size of the sintered composites containing 5, 10, 15, and 20 wt pct HA were 36.76, 29.08, 27.93, and 27.31 nm, respectively. According to X-ray diffraction (XRD) analysis, there was no new crystalline phase formed during milling, indicating that no mechanochemical reactions between Mg-Zn alloy and HA occurred. The -1.70 V shifted significantly toward the passive position of the plain Mg-6.5 wt pct Zn alloy and Mg-Zn/10 wt pct HA composite, which were -1.50 and -1.46 V, respectively, indicating that the Mg-Zn/10 wt pct HA composite was least susceptible to corrosion in the bioenvironment.

  18. Modelling and interpreting the isotopic composition of water vapour in convective updrafts

    M. Bolot


    Full Text Available The isotopic compositions of water vapour and its condensates have long been used as tracers of the global hydrological cycle, but may also be useful for understanding processes within individual convective clouds. We review here the representation of processes that alter water isotopic compositions during processing of air in convective updrafts and present a unified model for water vapour isotopic evolution within undiluted deep convective cores, with a special focus on the out-of-equilibrium conditions of mixed-phase zones where metastable liquid water and ice coexist. We use our model to show that a combination of water isotopologue measurements can constrain critical convective parameters, including degree of supersaturation, supercooled water content and glaciation temperature. Important isotopic processes in updrafts include kinetic effects that are a consequence of diffusive growth or decay of cloud particles within a supersaturated or subsaturated environment; isotopic re-equilibration between vapour and supercooled droplets, which buffers isotopic distillation; and differing mechanisms of glaciation (droplet freezing vs. the Wegener–Bergeron–Findeisen process. As all of these processes are related to updraft strength, particle size distribution and the retention of supercooled water, isotopic measurements can serve as a probe of in-cloud conditions of importance to convective processes. We study the sensitivity of the profile of water vapour isotopic composition to differing model assumptions and show how measurements of isotopic composition at cloud base and cloud top alone may be sufficient to retrieve key cloud parameters.

  19. Controls on the stable isotope compositions of travertine from hyperalkaline springs in Oman: Insights from clumped isotope measurements

    Falk, E. S.; Guo, W.; Paukert, A. N.; Matter, J. M.; Mervine, E. M.; Kelemen, P. B.


    Carbonate formation at hyperalkaline springs is typical of serpentinization in peridotite massifs worldwide. These travertines have long been known to exhibit large variations in their carbon and oxygen isotope compositions, extending from apparent equilibrium values to highly depleted values. However, the exact causes of these variations are not well constrained. We analyzed a suite of well-characterized fresh carbonate precipitates and travertines associated with hyperalkaline springs in the peridotite section of the Samail ophiolite, Sultanate of Oman, and found their clumped isotope compositions vary systematically with formation environments. Based on these findings, we identified four main processes controlling the stable isotope compositions of these carbonates. These include hydroxylation of CO2, partial isotope equilibration of dissolved inorganic carbon, mixing between isotopically distinct carbonate end-members, and post-depositional recrystallization. Most notably, in fresh crystalline films on the surface of hyperalkaline springs and in some fresh carbonate precipitates from the bottom of hyperalkaline pools, we observed large enrichments in Δ47 (up to ∼0.2‰ above expected equilibrium values) which accompany depletions in δ18O and δ13C, yielding about 0.01‰ increase in Δ47 and 1.1‰ decrease in δ13C for every 1‰ decrease in δ18O, relative to expected equilibrium values. This disequilibrium trend, also reflected in preserved travertines ranging in age from modern to ∼40,000 years old, is interpreted to arise mainly from the isotope effects associated with the hydroxylation of CO2 in high-pH fluids and agrees with our first-order theoretical estimation. In addition, in some fresh carbonate precipitates from the bottom of hyperalkaline pools and in subsamples of one preserved travertine terrace, we observed additional enrichments in Δ47 at intermediate δ13C and δ18O, consistent with mixing between isotopically distinct carbonate end

  20. Seasonality of Oxygen isotope composition in cow (Bos taurus) hair and its model interpretation

    Chen, Guo; Schnyder, Hans; Auerswald, Karl


    Oxygen isotopes in animal and human tissues are expected to be good recorders of geographical origin and migration histories based on the isotopic relationship between hair oxygen and annual precipitation and the well-known spatial pattern of oxygen isotope composition in meteoric water. However, seasonal variation of oxygen isotope composition may diminish the origin information in the tissues. Here the seasonality of oxygen isotope composition in tail hair was investigated in a domestic suckler cow (Bos taurus) that underwent different ambient conditions, physiological states, and keeping and feeding strategies during five years. A detailed mechanistic model involving in ambient conditions, soil properties and animal physiology was built to explain this variation. The measured oxygen isotope composition in hair was significantly related (pwater in a regression analysis. Modelling suggested that this relation was only partly derived from the direct influence of feed moisture. Ambient conditions (temperature, moisture) did not only influence the isotopic signal of precipitation but also affected the animal itself (drinking water demand, transcutaneous vapor etc.). The clear temporal variation thus resulted from complex interactions with multiple influences. The twofold influence of ambient conditions via the feed and via the animal itself is advantageous for tracing the geographic origin because the oxygen isotope composition is then less influenced by variations in moisture uptake; however, it is unfavorable for indicating the production system, e.g. to distinguish between milk produced from fresh grass or from silage.

  1. Clumped Isotope Composition of Cold-Water Corals: A Role for Vital Effects?

    Spooner, P.; Guo, W.; Robinson, L. F.


    Measurements on a set of cold-water corals (mainly Desmophyllum dianthus) have suggested that their clumped isotope composition could serve as a promising proxy for reconstructing paleocean temperatures. Such measurements have also offered support for certain isotope models of coral calcification. However, there are differences in the clumped isotope compositions between warm-water and cold-water corals, suggesting that different kinds of corals could have differences in their biocalcification processes. In order to understand the systematics of clumped isotope variations in cold-water corals more fully, we present clumped isotope data from a range of cold-water coral species from the tropical Atlantic and the Southern Ocean.Our samples were either collected live or recently dead (14C ages biocalcification may not apply equally well to all corals. Clumped isotope vital effects may be present in certain cold-water corals as they are in warm-water corals, complicating the use of this paleoclimate proxy.

  2. Structural characterization and property of in-situ synthesized AZ91-Mg2Si composite

    DONG Long-xiang; WU Yao-ming; DOU Chuan-guo; XU Guo-gen; WANG Li-min


    A new-type Mg2Si composite was prepared with Mg-9Al-1Zn (AZ91) alloy and vermiculite as raw materials by melt infiltration method. The results show that the microstructure of composite consists of a large amount of Mg2Si precipitates and a little amount of MgO embedded in α-Mg matrix. The Vickers hardness of the composite is obviously higher than that of matrix of AZ91 alloy. Moreover, the composite exhibits excellent compressive property. The ultimate compressive strength of the material is 290 MPa, the yield strength is 175 MPa, and the elongation is about 5%, which are higher than those of AZ91alloy.

  3. Hydrogen storage properties of nano-composites of Mg and Zr-Ni-Cr alloys

    Yang, J.; Ciureanu, M.; Roberge, R. [H Power Enterprises of Canada, 1069 Begin Street, St. Laurent, Quebec (Canada)


    Mg and Zr-Ni-Cr alloy nano-composite hydrogen storage materials have been prepared by high energy mechanical milling (MM) of Mg powders with either crystalline ZrNiCr and ZrNi{sub 1.6}Cr{sub 0.4} powders or mechanically milled amorphous ZrNiCr and ZrNi{sub 1.6}Cr{sub 0.4} powders. Nano-composites of amorphous Zr-Ni-Cr alloy and Mg have better desorption kinetics compared to crystalline Zr-Ni-Cr alloy and Mg nano-composites. Amorphous ZrNi{sub 1.6}Cr{sub 0.4} and Mg nano-composites desorb larger amount of H{sub 2} much faster than amorphous ZrNiCr and Mg nano-composites. The nano-composite of 35 wt.% amorphous ZrNi{sub 1.6}Cr{sub 0.4} and Mg releases 4.3 wt.% H{sub 2} at 300C in 30 min. X-ray diffraction revealed that there are no reactions between Mg and Zr-Ni-Cr alloys in the milling, activation, and subsequent cycling processes, proving that amorphous ZrNi{sub 1.6}Cr{sub 0.4} is an effective hydrogen absorption and desorption catalyst.

  4. Electron beam irradiated HDPE/EVA/Mg(OH)2 composites for flame-retardant electric cables

    Hui LIU; Nabil A. Noman ALKADASI; Yan ZHU; Li-fang TONG; Zheng-ping FANG; Yong-chang WANG


    The mechanical properties and flammability of high-density polyethylene (HDPE)/ethylene vinyl acetate (EVA) mixed with various amounts of magnesium hydroxide (Mg(OH)2) as the filler in composites, irra-diated with electron beam at an irradiation dose of 150 kGy, have been studied. It is found that high-energy electron beam irradiation has significant effects on the mechanical properties of the HDPE/EVA/Mg(OH)2 com-posites. The tensile strength and elastic modulus increased greater than in the unirradiated ones. Meanwhile, with increasing the content of Mg(OH)2 in the composites, the limiting oxygen index (LOI) value increased sharply. The microstructure of the caves of the unirradiated HDPE/EVA/Mg(OH)2 composites show poor interface of composites compared with the irradiated ones, as observed in SEM micrographs.

  5. Hydrogen and oxygen in brine shrimp chitin reflect environmental water and dietary isotopic composition

    Nielson, Kristine E.; Bowen, Gabriel J.


    Hydrogen and oxygen isotope ratios of the common structural biopolymer chitin are a potential recorder of ecological and environmental information, but our understanding of the mechanisms of incorporation of H and O from environmental substrates into chitin is limited. We report the results of a set of experiments in which the isotopic compositions of environmental water and diet were varied independently in order to assess the contribution of these variables to the H and O isotopic composition of Artemia franciscana chitin. Hydrogen isotope ratios of chitin were strongly linearly correlated with both food and water, with approximately 26% of the hydrogen signal reflecting food and approximately 38% reflecting water. Oxygen isotopes were also strongly correlated with the isotopic composition of water and food, but whereas 69% of oxygen in chitin exchanged with environmental water, only 10% was derived from food. We propose that these observations reflect the position-specific, partial exchange of H and O atoms with brine shrimp body water during the processes of digestion and chitin biosynthesis. Comparison of culture experiments with a set of natural samples collected from the Great Salt Lake, UT in 2006 shows that, with some exceptions, oxygen isotope compositions of chitin track those of water, whereas hydrogen isotopes vary inversely with those of lake water. The different behavior of the two isotopic systems can be explained in terms of a dietary shift from allochthonous particulate matter with relatively higher δ 2H values in the early spring to autochthonous particulate matter with significantly lower δ 2H values in the late summer to autumn. These results suggest oxygen in chitin may be a valuable proxy for the oxygen isotopic composition of environmental water, whereas hydrogen isotope values from the same molecule may reveal ecological and biogeochemical changes within lakes.

  6. The iron isotope composition of enstatite meteorites: Implications for their origin and the metal/sulfide Fe isotopic fractionation factor

    Wang, Kun; Savage, Paul S.; Moynier, Frédéric


    Despite their unusual chemical composition, it is often proposed that the enstatite chondrites represent a significant component of Earth’s building materials, based on their terrestrial similarity for numerous isotope systems. In order to investigate a possible genetic relationship between the Fe isotope composition of enstatite chondrites and the Earth, we have analyzed 22 samples from different subgroups of the enstatite meteorites, including EH and EL chondrites, aubrites (main group and Shallowater) and the Happy Canyon impact melt. We have also analyzed the Fe isotopic compositions of separated (magnetic and non-magnetic) phases from both enstatite chondrites and achondrites. On average, EH3-5 chondrites (δ56Fe = 0.003 ± 0.042‰; 2 standard deviation; n = 9; including previous literature data) as well as EL3 chondrites (δ56Fe = 0.030 ± 0.038‰; 2 SD; n = 2) have identical and homogeneous Fe isotopic compositions, indistinguishable from those of the carbonaceous chondrites and average terrestrial peridotite. In contrast, EL6 chondrites display a larger range of isotopic compositions (-0.180‰ < δ56Fe < 0.181‰; n = 11), a result of mixing between isotopically distinct mineral phases (metal, sulfide and silicate). The large Fe isotopic heterogeneity of EL6 is best explained by chemical/mineralogical fragmentation and brecciation during the complex impact history of the EL parent body. Enstatite achondrites (aubrites) also exhibit a relatively large range of Fe isotope compositions: all main group aubrites are enriched in the light Fe isotopes (δ56Fe = -0.170 ± 0.189‰; 2 SD; n = 6), while Shallowater is, isotopically, relatively heavy (δ56Fe = 0.045 ± 0.101‰; 2 SD; n = 4; number of chips). We take this variation to suggest that the main group aubrite parent body formed a discreet heavy Fe isotope-enriched core, whilst the Shallowater meteorite is most likely from a different parent body where core and silicate material remixed. This could be

  7. A continuous flow isotope ratio mass spectrometry method for high precision determination of dissolved gas ratios and isotopic composition

    Charoenpong, C. N.; Bristow, L. A.; Altabet, M. A.


    Dissolved gas ratios and isotopic compositions provide essential information about the biological and physical mechanisms influencing N-2, O-2, and Ar in aquatic systems. Current methods available are either limited by overall cost, labor-intensive sample collection and analysis, or insufficient ...

  8. Mechanism of pore formation and structural characterization for mesoporous Mg-Al composite oxides

    赵芸; 矫庆泽; 段雪


    Mg-AI layered double hydroxides (LDH) with different particle sizes were prepared using different aging times at high supersaturation by a new method developed in our laboratory. The key features of this method are a very rapid mixing and nucleation process followed by a separate aging process. By calcination of LDH at 500癈, mesoporous Mg-AI composite oxides with an extremely narrow pore size distribution were produced. The crystal structure of the Mg-AI composite oxides was a multiphasic one consisting of MgO-like crystals and a layered material.

  9. Mechanism of pore formation and structural characterization for mesoporous Mg-Al composite oxides


    Mg-Al layered double hydroxides(LDH) with different particle sizes were prepared using different aging times at high supersaturation by a new method developed in our laboratory. The key features of this method are a very rapid mixing and nucleation process followed by a separate aging process. By calcination of LDH at 500℃, mesoporous Mg-Al composite oxides with an ex-tremely narrow pore size distribution were produced. The crystal structure of the Mg-Al composite oxides was a multiphasic one consisting of MgO-like crystals and a layered material.

  10. Compound Specific Hydrogen Isotope Composition of Type II and III Kerogen Extracted by Pyrolysis-GC-MS-IRMS

    Socki, Richard A.; Pernia, Denet; Evans, Michael; Fu, Qi; Bissada, Kadry K.; Curiale, Joseph A.; Niles, Paul B.


    The use of Hydrogen (H) isotopes in understanding oil and gas resource plays is in its infancy. Described here is a technique for H isotope analysis of organic compounds pyrolyzed from oil and gas shale-derived kerogen. Application of this technique will progress our understanding. This work complements that of Pernia et al. (2013, this meeting) by providing a novel method for the H isotope analysis of specific compounds in the characterization of kerogen extracted by analytically diverse techniques. Hydrogen isotope analyses were carried out entirely "on-line" utilizing a CDS 5000 Pyroprobe connected to a Thermo Trace GC Ultra interfaced with a Thermo MAT 253 IRMS. Also, a split of GC-separated products was sent to a DSQ II quadrupole MS to make semi-quantitative compositional measurements of the extracted compounds. Kerogen samples from five different basins (type II and III) were dehydrated (heated to 80 C overnight in vacuum) and analyzed for their H isotope compositions by Pyrolysis-GC-MS-TC-IRMS. This technique takes pyrolysis products separated via GC and reacts them in a high temperature conversion furnace (1450 C) which quantitatively forms H2, following a modified method of Burgoyne and Hayes, (1998, Anal. Chem., 70, 5136-5141). Samples ranging from approximately 0.5 to 1.0mg in size, were pyrolyzed at 800 C for 30s. Compounds were separated on a Poraplot Q GC column. Hydrogen isotope data from all kerogen samples typically show enrichment in D from low to high molecular weight compounds. Water (H2O) average deltaD = -215.2 (V-SMOW), ranging from -271.8 for the Marcellus Shale to -51.9 for the Polish Shale. Higher molecular weight compounds like toluene (C7H8) have an average deltaD of -89.7 0/00, ranging from -156.0 for the Barnett Shale to -50.0 for the Monterey Shale. We interpret these data as representative of potential H isotope exchange between hydrocarbons and sediment pore water during formation within each basin. Since hydrocarbon H isotopes

  11. Near Surface CO2 Triple Oxygen Isotope Composition

    Sasadhar Mahata


    Full Text Available The isotopic composition of carbon dioxide in the atmosphere is a powerful tool for constraining its sources and sinks. In particular, the 17O oxygen anomaly [Δ17O = 1000 × ln(1 + δ17O/1000 - 0.516 × 1000 × ln(1 + δ18O/1000], with a value > 0.5‰ produced in the middle atmosphere, provides an ideal tool for probing the exchange of carbon dioxide between the biosphere/hydrosphere and atmosphere. The biosphere/hydrosphere and anthropogenic emissions give values ≤ 0.3‰. Therefore, any anomaly in near surface CO2 would reflect the balance between stratospheric input and exchange with the aforementioned surface sources. We have analyzed Δ17O values of CO2 separated from air samples collected in Taipei, Taiwan, located in the western Pacific region. The obtained mean anomaly is 0.42 ± 0.14‰ (1-σ standard deviation, in good agreement with model prediction and a published decadal record. Apart from typically used δ13C and δ18O values, the Δ17O value could provide an additional tracer for constraining the carbon cycle.

  12. The He isotope composition of the earliest picrites erupted by the Ethiopia plume, implications for mantle plume source

    Stuart, Finlay; Rogers, Nick; Davies, Marc


    The earliest basalts erupted by mantle plumes are Mg-rich, and typically derived from mantle with higher potential temperature than those derived from the convecting upper mantle at mid-ocean ridges and ocean islands. The chemistry and isotopic composition of picrites from CFB provide constraints on the composition of deep Earth and thus the origin and differentiation history. We report new He-Sr-Nd-Pb isotopic composition of the picrites from the Ethiopian flood basalt province from the Dilb (Chinese Road) section. They are characterized by high Fe and Ti contents for MgO = 10-22 wt. % implying that the parent magma was derived from a high temperature low melt fraction, most probably from the Afar plume head. The picrite 3He/4He does not exceed 21 Ra, and there is a negative correlation with MgO, the highest 3He/4He corresponding to MgO = 15.4 wt. %. Age-corrected 87Sr/86Sr (0.70392-0.70408) and 143Nd/144Nd (0.512912-0.512987) display little variation and are distinct from MORB and OIB. Age-corrected Pb isotopes display a significant range (e.g. 206Pb/204Pb = 18.70-19.04) and plot above the NHRL. These values contrast with estimates of the modern Afar mantle plume which has lower 3He/4He and Sr, Nd and Pb isotope ratios that are more comparable with typical OIB. These results imply either interaction between melts derived from the Afar mantle plume and a lithospheric component, or that the original Afar mantle plume had a rather unique radiogenic isotope composition. Regardless of the details of the origins of this unusual signal, our observations place a minimum 3He/4He value of 21 Ra for the Afar mantle plume, significantly greater than the present day value of 16 Ra, implying a significant reduction over 30 Myr. In addition the Afar source was less degassed than convecting mantle but more degassed than mantle sampled by the proto-Iceland plume (3He/4He ~50 Ra). This suggests that the largest mantle plumes are not sourced in a single deep mantle domain with a

  13. Magnesium isotope composition of the altered upper oceanic crust at ODP Holes 504B and 896A, Costa Rica Rift

    Beaumais, Aurélien; Teagle, Damon A. H.; James, Rachael H.; Harris, Michelle; Pearce, Christopher R.; Milton, James A.; Cooper, Matthew J.; Alt, Jeffrey C.


    Chemical reactions between the oceanic crust and seawater play a major role in regulating the composition of the oceans that, in turn, influence important geochemical cycles (e.g., C, S, Mg). It is well established that alteration of the oceanic crust is the principal sink of Mg in seawater, but the effect of this process on the Mg isotope composition of the oceans remains unclear. Here we present the first measurements of Mg isotopes in altered oceanic crust from ODP Holes 504B and 896A. These holes are located in 5.9 Ma crust located 200 km south of the intermediate spreading rate Costa Rica Rift. Hole 504B penetrates: (i) A volcanic section, consisting of primitive to moderately altered mid-ocean ridge basalt (MORB) that was open to seawater alteration under oxic-suboxic conditions at temperatures rocks altered under low temperature (rock scale. [1] Teng et al., (2010) GCA 74, 4150-4166. [2] Huang et al., (2015) Lithos 231, 53-61.

  14. Tensile and Compressive Responses of Ceramic and Metallic Nanoparticle Reinforced Mg Composites

    Quy Bau Nguyen


    Full Text Available In the present study, room temperature mechanical properties of pure magnesium, Mg/ZrO2 and Mg/(ZrO2 + Cu composites with various compositions are investigated. Results revealed that the use of hybrid (ZrO2 + Cu reinforcements in Mg led to enhanced mechanical properties when compared to that of single reinforcement (ZrO2. Marginal reduction in mechanical properties of Mg/ZrO2 composites were observed mainly due to clustering of ZrO2 particles in Mg matrix and lack of matrix grain refinement. Addition of hybrid reinforcements led to grain size reduction and uniform distribution of hybrid reinforcements, globally and locally, in the hybrid composites. Macro- and micro- hardness, tensile strengths and compressive strengths were all significantly increased in the hybrid composites. With respect to unreinforced magnesium, failure strain was almost unchanged under tensile loading while it was reduced under compressive loading for both Mg/ZrO2 and Mg/(ZrO2 + Cu composites.

  15. Monitoring the water vapor isotopic composition in the temperate North Atlantic

    Sveinbjörnsdottir, Arny E.; Steen-Larsen, Hans Christian; Jonsson, Thorsteinn; Johnsen, Sigfus J.


    Water stable isotopes have during many decades been used as climate proxies and indicators for variations in the hydrological cycle. However we are to a great extent still using simple empirical relationships without any deeper theoretical understanding. In order to properly relate changes in the climate and hydrological cycle to changes in the observed stable water isotopic signal we must understand the underlying physical processes. Furthermore it is a challenge for General Climate Models to adequately represent the isotopes in the hydrological cycle because of lack of in-situ measurements of the atmospheric water-vapor composition in the source regions. During the fall of 2010 we installed an autonomous water vapor spectroscopy laser (from Los Gatos Research) in a lighthouse on the South Coast of Iceland (63.83 N 21.47W) with the plan to be operational for several years. The purpose of this installation was through monitoring of the water vapor isotopic composition to understand the physical processes governing the isotopic composition of the water vapor evaporated from the ocean as well as the processes of mixing between the free troposphere and marine boundary layer. Because of the remoteness of the monitoring site and simple topography we are able to isolate the 'fingerprint' on the isotopic signal in the water vapor from respectively the ocean and the interior highland leading to a near perfect case-study area. Using back-trajectories we find a strong influence of the origin of the air masses on the measured isotopic composition. The mixing of the marine-boundary layer is found to strongly influence the measured isotopic composition. The second order isotopic parameter, d-excess, is contrary to theory and previous observations found not to depend on the relative humidity. However we do find a good correlation between the d-excess and the measured isotopic composition. We speculate that the lack of correlation between d-excess and relative humidity can be

  16. Isotopic composition of Pb and Th in interplinian volcanics from Somma-Vesuvius volcano, Italy

    Cortini, M.; Ayuso, R.A.; de Vivo, B.; Holden, P.; Somma, R.


    We present a detailed isotopic study of volcanic rocks emitted from Somma-Vesuvius volcano during three periods of interplinian activity: "Protohistoric" (3550 y B.P. to 79 A.D.), "Ancient Historic" (79 to 472 A.D.) and "Medieval" (472 to 1631 A.D.). Pb isotopic compositions of two acid leached fractions and whole rock residues of 37 whole rock samples (determined by Somma et al., 2001) show that each of the three interplinian periods is distinguished by small, systematic, and unique uranogenic and thorogenic Pb isotopic trends. This key and novel feature is compatible with the notion that the Pb isotopic data reflect small-scale source heterogeneity operating over relatively short periods of time. From this representative group of samples, a selected set of nine whole rocks were analysed for Th isotopes. 232Th/238U ratios in the source can be obtained independently from Pb and from Th isotopes. Those obtained from Pb isotopes represent source ratios, time-integrated over the whole age of the Earth; they range from 3.9 to 4.1. 232Th/238U obtained from Th isotopes are those of the present source. They are lower, and cluster around 3.5; this difference probably indicates recent U enrichment of the present source. The behaviour of Pb, as inferred by its isotopic ratios, is quite distinct from that of Sr and Nd isotopes: Pb isotope variations are not correlated to Sr or Nd isotope variations. The isotopic contrast is compatible with the idea that the isotopes were decoupled during magmatic production, evolution, and ascent through the crust. Thus, the Pb isotopes do not reflect the effects of the same processes as in the case of the Sr and Nd isotopes, or, as we also favor, they do not necessarily reflect the same source contributions into the magmas. Moreover, the Pb isotopic evolution of the interplinian rocks chiefly reflects mixing, driven by processes that are superimposed on, and independent of, other source contributions that determine the isotopic compositions

  17. Natural isotopic composition of nitrogen in suspended particulate matter in the Bay of Bengal

    Kumar, S.; Ramesh, R.; Bhosle, N.B.; Sardessai, S.; Sheshshayee, M.S.

    The first measurements of nitrogen isotopic composition (delta sup(15) N) in suspended particulate matter (SPM) of the surface Bay of Bengal (BOB) at 24 different locations during pre- (April-May 2003) and post- (September-October 2002) monsoon...

  18. Evolution of Organic Molecules in Space: Characterization and Isotope Composition of Experimental Analogues

    Piani, L.; Tachibana, S.; Hama, T.; Endo, Y.; Fujita, K.; Nakatsubo, S.; Fukushi, H.; Mori, S.; Chigai, T.; Yurimoto, H.; Kouchi, A.


    Laboratory experiments are conducted to investigate the organic compound formation in molecular cloud conditions and its evolution through UV irradiation and heating. A particular attention is given to the isotope composition of the organic residue.

  19. Usage of burnt fuel isotopic compositions from engineering codes in Monte-Carlo code calculations

    Aleshin, Sergey S.; Gorodkov, Sergey S.; Shcherenko, Anna I. [Nuclear Research Centre ' ' Kurchatov Institute' ' , Moscow (Russian Federation)


    A burn-up calculation of VVER's cores by Monte-Carlo code is complex process and requires large computational costs. This fact makes Monte-Carlo codes usage complicated for project and operating calculations. Previously prepared isotopic compositions are proposed to use for the Monte-Carlo code (MCU) calculations of different states of VVER's core with burnt fuel. Isotopic compositions are proposed to calculate by an approximation method. The approximation method is based on usage of a spectral functionality and reference isotopic compositions, that are calculated by engineering codes (TVS-M, PERMAK-A). The multiplication factors and power distributions of FA and VVER with infinite height are calculated in this work by the Monte-Carlo code MCU using earlier prepared isotopic compositions. The MCU calculation data were compared with the data which were obtained by engineering codes.

  20. Deposition of nitrogen and phosphorus on the Baltic Sea: seasonal patterns and nitrogen isotope composition

    C. Rolff


    Full Text Available Atmospheric deposition of nitrogen and phosphorus on the central Baltic Sea (Baltic Proper was estimated monthly at two coastal stations and two isolated islands in 2001 and 2002. Yearly nitrogen deposition ranged between 387 and 727 mg N m−2 yr−1 (average 617 and was composed of ~10% organic N and approximately equal amounts of ammonium and nitrate. Winter nitrate peaks at the isolated islands possibly indicated ship emissions. Load weighted δ15N of deposited N was 3.7‰ and 0.35‰ at the coastal stations and the isolated islands respectively. Winter δ15N was ~3‰ lighter than in summer, reflecting winter dominance of nitrate. The light isotopic composition of deposited nitrogen may cause overestimates of nitrogen fixation in basin-wide isotopic budgeting, whereas relatively heavy deposition of ammonium during summer instead may cause underestimates of fixation in budgets of the upper mixed layer. δ15N in atmospherically deposited nitrate and ammonium was estimated by regression to −7.9 and 13.5‰ respectively. Phosphorus deposition showed no clear seasonal pattern and was considerably lower at the isolated islands. Organic P constituted 20–40% of annual P deposition. P deposition is unlikely to be a major source for cyanobacterial blooms but may potentially prolong an ongoing bloom.

  1. Determining the geographical origin of Chinese cabbages using multielement composition and strontium isotope ratio analyses.

    Bong, Yeon-Sik; Shin, Woo-Jin; Gautam, Mukesh Kumar; Jeong, Youn-Joong; Lee, A-Reum; Jang, Chang-Soon; Lim, Yong-Pyo; Chung, Gong-Soo; Lee, Kwang-Sik


    Recently, the Korean market has seen many cases of Chinese cabbage (Brassica rapa ssp. pekinensis) that have been imported from China, yet are sold as a Korean product to illegally benefit from the price difference between the two products. This study aims to establish a method of distinguishing the geographical origin of Chinese cabbage. One hundred Chinese cabbage heads from Korea and 60 cabbage heads from China were subjected to multielement composition and strontium isotope ratio ((87)Sr/(86)Sr) analyses. The (87)Sr/(86)Sr ratio differed, based on the geological characteristics of their district of production. In addition, the content of many elements differed between cabbages from Korea and China. In particular, the difference in the content of Sr and Ti alone and the combination of Sr, Ca, and Mg allowed us to distinguish relatively well between Korea and China as the country of origin. The present study demonstrates that the chemical and Sr isotopic analyses exactly reflect the geology of the production areas of Chinese cabbage.

  2. Determining the geographical origin of Chinese cabbages using multielement composition and strontium isotope ratio analyses

    BONG, Y.; Shin, W.; Gautam, M. K.; Jeong, Y.; Lee, A.; Jang, C.; Lim, Y.; Chung, G.; Lee, K.


    Recently, the Korean market has seen many cases of Chinese cabbage (Brassica rapa ssp. pekinensis) that have been imported from China, yet are sold as a Korean product to illegally benefit from the price difference between the two products. This study aims to establish a method of distinguishing the geographical origin of Chinese cabbage. One hundred Chinese cabbage heads from Korea and 60 cabbage heads from China were subjected to multielement composition and strontium isotope ratio (87Sr/86Sr) analyses. The 87Sr/86Sr ratio differed, based on the geological characteristics of their district of production. In addition, the content of many elements differed between cabbages from Korea and China. In particular, the difference in the content of Sr and Ti alone and the combination of Sr, Ca, and Mg allowed us to distinguish relatively well between Korea and China as the country of origin. The present study demonstrates that the chemical and Sr isotopic analyses exactly reflect the geology of the production areas of Chinese cabbage. Also, multivariate statistical analyses of multiple elements were found to be very effective in distinguishing the geographical origin of Chinese cabbages.

  3. Carbon and hydrogen isotopic composition and generation pathway of biogenic gas in China

    SHEN Ping; WANG Xiaofeng; XU Yin; SHI Baoguang; XU Yongchang


    The carbon and hydrogen isotopic composition of biogenic gas is of great importance for the study of its generation pathway and reservoiring characteristics. In this paper, the formation pathways and reservoiring characteristics of biogenic gas reservoirs in China are described in terms of the carbon and hydrogen isotopic compositions of 31 gas samples from 10 biogenic gas reservoirs. The study shows that the hydrogen isotopic compositions of these biogenic gas reservoirs can be divided into three intervals:δDCH4>-200‰,-250‰<δDCH4<-200‰ and δDCH4<-250‰. The forerunners believed that the main generation pathway of biogenic gas under the condition of continental fresh water is acetic fermentation. Our research results showed that the generation pathway of biogenic gas under the condition of marine facies is typical CO2- reduction, the biogenic gas has heavy hydrogen isotopic composition: its δDCH4 values are higher than -200‰; that the biogenic gas under the condition of continental facies also was generated by the same way, but its hydrogen isotopic composition is lighter than that of biogenetic gas generated under typical marine facies condition: -250‰<δDCH4<-200‰, the δDCH4 values may be related to the salinity of the water medium in ancient lakes. From the relevant data of the Qaidam Basin, it can be seen that the hydrogen isotopic composition of biogenic methane has the same variation trend with increasing salinity of water medium. There are biogenic gas reservoirs formed in transitional regions under the condition of continental facies. These gas reservoirs resulted from both CO2- reduction and acetic fermentation, the formation of which may be related to the non-variant salinity of ancient water medium and the relatively high geothermal gradient, as is the case encountered in the Baoshan Basin. The biogenic gas generating in these regions has light hydrogen isotopic composition: δDCH4<-250‰, and relatively heavy carbon isotopic

  4. Effect of CaO composition on oxidation and burning behaviors of AM50 Mg alloy

    Jin-Kyu LEE; Shae K. KIM


    Oxidation and burning behaviors were studied for CaO added AM50 Mg composites which were manufactured by conventional melting and casting processes without SF6 protective gas. CaO added AM50 Mg composites show the stable oxidation resistance. while AM50 Mg alloys show the poor oxidation resistance. The effects of CaO addition on the burning resistance under ambient, nitrogen and dry air atmospheres were examined for CaO added AM50 Mg composites. With increasing CaO addition, the burning temperature increases under ambient, nitrogen and dry air atmospheres. The burning temperatures of small test specimen under all conditions greatly increase even by 0.3% CaO (mass fraction) addition into AM50 Mg alloys.

  5. Non-destructive measurement of carbonic anhydrase activity and the oxygen isotope composition of soil water

    Jones, Sam; Sauze, Joana; Ogée, Jérôme; Wohl, Steven; Bosc, Alexandre; Wingate, Lisa


    Carbonic anhydrases are a group of metalloenzymes that catalyse the hydration of aqueous carbon dioxide (CO2). The expression of carbonic anhydrase by bacteria, archaea and eukarya has been linked to a variety of important biological processes including pH regulation, substrate supply and biomineralisation. As oxygen isotopes are exchanged between CO2 and water during hydration, the presence of carbonic anhydrase in plants and soil organisms also influences the oxygen isotope budget of atmospheric CO2. Leaf and soil water pools have distinct oxygen isotope compositions, owing to differences in pool sizes and evaporation rates, which are imparted on CO2during hydration. These differences in the isotopic signature of CO2 interacting with leaves and soil can be used to partition the contribution of photosynthesis and soil respiration to net terrestrial CO2 exchange. However, this relies on our knowledge of soil carbonic anhydrase activity and currently, the prevalence and function of these enzymes in soils is poorly understood. Isotopic approaches used to estimate soil carbonic anhydrase activity typically involve the inversion of models describing the oxygen isotope composition of CO2 fluxes to solve for the apparent, potentially catalysed, rate of oxygen exchange during hydration. This requires information about the composition of CO2 in isotopic equilibrium with soil water obtained from destructive, depth-resolved soil water sampling. This can represent a significant challenge in data collection given the considerable potential for spatial and temporal variability in the isotopic composition of soil water and limited a priori information with respect to the appropriate sampling resolution and depth. We investigated whether we could circumvent this requirement by constraining carbonic anhydrase activity and the composition of soil water in isotopic equilibrium with CO2 by solving simultaneously the mass balance for two soil CO2 steady states differing only in the

  6. Development and validation of a single collector ICPMS procedure to determine boron isotopeic compositions of water and food samples

    Vogl, Jochen; Rosner, Martin; Pritzkow, Wolfgang


    Authenticity and provenance studies as well as issues in environmental- and geo-sciences are hot topics in nowadays isotope research. Elements being known for their natural isotopic variation, such as lead and strontium, are being used to assign the provenance of artefacts, food and other products. A recent study revealed the potential of boron (B) isotopes for delivering information on the provenance of crop plants. To offer alternative analytical instrumentations beside the classical TIMS procedures a single collector ICPMS procedure for B isotope analyses has been developed and validated. This procedure should enable more B isotope studies, as single collector ICPMS intruments are more widepread in the relevant laboratories compared to TIMS. The developed procedures for the determination of B isotopic compositions use a magnetic sector ICPMS and consist of one low resolution (LR) and one medium resolution (MR) procedure. The absolute standard deviation for the δ11B determination in three independently measured samples lies between 0.2 and 0.8 ‰ for the LR and between 0.3 and 1.5 ‰ for the MR. The expanded uncertainties with a coverage factor of k=2 range between 1.4 and 1.6 ‰ for the LR and between 2.9 and 3.2 ‰ for the MR. The trueness, expressed as average deviation from the reference values, is less than 1.1 ‰ for LR and 0.8 ‰ for MR. To test the practicability of the procedure the matrix tolerance has been investigated. Using a measurement solution containing 100 µg/kg boron a matrix of 2 mg/kg of alkaline and earth alkaline elements was found as a limit for stable instrumental mass discrimination. Thus a highly efficient matrix separation is required, similar to TIMS. The developed procedure is well suited for the for B isotope studies of various matrices and especially the LR procedure offers relatively small uncertainties combined with high sample throughput.

  7. Spatiotemporal variation of stable isotopic composition in precipitation

    Müller, Sascha; Stumpp, Christine; Sørensen, Jens Havskov


    gradient and predominant westerly winds. Data showed the local meteoric water line for this region is expressed by the equation δ2H = 7.4δ18O + 5.4‰. A significant trend correlating enriched isotopic values to humidities around 70% during dry season and more depleted isotopic values to humidities around 90...

  8. Sr and Nd isotopic and trace element compositions of Quaternary volcanic centers of the southern Andes

    Futa, Kiyoto; Stern, C.R.


    Isotopic compositions of samples from six Quaternary volcanoes located in the northern and southern extremities of the Southern Volcanic Zone (SVZ, 33-46/sup 0/S) of the Andes and from four centers in the Austral Volcanic Zone (AVZ, 49-54/sup 0/S) range for /sup 87/Sr//sup 86/Sr from 0.70280 to 0.70591 and for /sup 143/Nd//sup 144/Nd from 0.51314 to 0.51255. Basalts and basaltic andesites from three centers just north of the Chile Rise-Trench triple junction have /sup 87/Sr//sup 86/Sr, /sup 143/Nd//sup 144/Nd, La/Yb, Ba/La and Hf/Lu that lie within the relatively restricted ranges of the basic magmas erupted from the volcanic centers as far north as 35/sup 0/S in the SVZ of the Andes. The trace element and Sr and Nd isotopic characteristics of these magmas may be explained by source region contamination of subarc asthenosphere, with contaminants derived from subducted pelagic sediments and seawater-altered basalts by dehydration of subducted oceanic lithosphere. In the northern extremity of the SVZ between 33/sup 0/ and 34/sup 0/S, basaltic andesites and andesites have higher /sup 87/Sr//sup 86/Sr, Rb/Cs, and Hf/Lu, and lower /sup 143/Nd//sup 144/Nd than basalts and basaltic andesites erupted farther south in the SVZ, which suggests involvement of components derived from the continental crust. In the AVZ, the most primitive sample, high-Mg andesite from the southernmost volcanic center in the Andes (54/sup 0/S) has Sr and Nd isotopic compositions and K/Rb and Ba/La similar to MORB. The high La/Yb of this sample suggests formation by small degrees of partial melting of subducted MORB with garnet as a residue. Samples from centers farther north in the AVZ show a regionally regular northward increase in SiO/sub 2/, K/sub 2/O, Rb, Ba, Ba/La, and /sup 87/Sr//sup 86/Sr and decrease in MgO, Sr, K/Rb, Rb/Cs, and /sup 143/Nd//sup 144/Nd, suggesting increasingly greater degrees of fractional crystallization and associated intra-crustal contamination. (orig./SHOE).

  9. Evaluation of hydrogenation properties on MgHx-transition metal fluoride composites by planetary ball milling

    Jang, Min-Hyuk; Park, So-Hyun; Kim, Whan-Gi; Hong, Tae-Whan


    To improve the disadvantages of Mg hydrides, a few studies were conducted for MgHx intermixed with transition metal fluorides. MgF2 formed from the MgHx-transition metal fluoride system can be replaces the initial surface oxide layer and provides a reactive and protective fluorinated surface for for hydrogen uptake. Thus, the absorption/desorption kinetics will be enhanced. In this research, MgHx-transition metal fluoride composites mixture has been prepared by hydrogen induced planetary ball milling. The synthesized powders were characterized by X-ray diffraction analysis, scanning electron microscopy and simultaneous thermogravimetric, differential scanning calorimetric analysis. The hydrogenation behaviors were evaluated by using a sievert's type automatic pressure-composition-temperature apparatus without any activation treatment. From the characteristics of the absorption kinetics and curves observed, the role of transition metal fluoride was catalyst in hydrogen absorption. The results of Pressure-Composition Isotherm curve, available hydrogen storage amount for MgHx-5 vol% CoF2 composites were 4.85 wt%, for MgHx-5 vol%TiF3 composites were 4.88 wt%. at 623K in the 5th cycle.

  10. Spatial gradients in the isotopic composition of paleoprecipitation for terrestrial climate and altimetry studies

    Chamberlain, C. P.; Winnick, M.; Ibarra, D. E.; Caves, J. K.; Ritch, A. J.


    The oxygen and hydrogen isotopic composition of authigenic minerals in terrestrial sediments provides one of the critical measures of past climate change. Frequently, these measurements are made at single sites to determine how climate and/or topography have changed over specific time intervals of interest. We argue here that spatial gradients in the oxygen and hydrogen isotope of precipitation along specific storm tracks provide a more powerful method to determine changes in paleoclimate and paleotopography. We use a nondimensional isotopic vapor transport model coupled with a soil water isotope model to evaluate how moisture recycling and the relative role of eddy diffusion and advective transport of water vapor affect horizontal isotopic gradients on continents. Relatively large changes in the isotopic composition of precipitation can occur by changes in water balance and the transport mechanism of water vapor - certainly as high as can be induced by the uplift of major mountain belts and large changes in global/regional temperature. As an example, we point to Miocene to Recent oxygen isotopic records of paleo-mid latitude sediments that tend to increase with time, globally. We suggest that this increase in the oxygen isotope of precipitation is the result of increased aridity and the expansion of grasslands during the Miocene. Further, we suggest that many of the Miocene to Recent isotopic records collected in the mountainous regions of Central Asia, Western North America, and South America reflect changes in water balance that are, in part, independent of changes in surface topography.

  11. Microstructural characteristics of in situ Mg2Si/Al-Si composite by low superheat pouring

    Wu Xiaofeng


    Full Text Available To control the morphology and size of the primary and eutectic Mg2Si phases in in situ Mg2Si/Al-Si composite and achieve a feasible and reliable technique to produce appropriate feedstock for the thixo-casting and rheo-casting of this type of material, three Al-Si matrix composites reinforced by 5wt.%, 9wt.% and 17wt.% Mg2Si with hypoeutectic, eutectic and hypereutectic compositions were prepared by the low superheat pouring (LSP process. The effects of the pouring temperature (superheat on the morphology and size distribution of primary phases (primary α-Al and Mg2Si, binary (α-Al + Mg2Si eutectic cell and eutectic Mg2Si were investigated. The experimental results show that low pouring temperature (superheat not only refines the grain structure of the primary α-Al and binary (α-Al + Mg2Si eutectic cell in three composites and promotes the formation of more non-dendritic structural semi-solid metal (SSM slurry of these phases; but also refines the primary and eutectic Mg2Si phases, which seems to be attributed to the creation of an ideal condition for the nucleation and the acquisition of a high survival of nuclei caused by the LSP process.

  12. Long-term data set analysis of stable isotopic composition in German rivers

    Reckerth, Anne; Stichler, Willibald; Schmidt, Axel; Stumpp, Christine


    Stable isotopes oxygen-18 (18O) and deuterium (2H) are commonly used to investigate hydrological processes in catchments. However, only a few isotope studies have been conducted on a large scale and rarely over long time periods. The objective of this study was to identify the spatial and seasonal variability of isotopic composition in river water and how it is affected by geographical and hydrological factors. The stable isotopic composition of river water has been measured in nine large river catchments in Germany for a time period of 12 years or 26 years. We conducted time series and correlation analyses to identify spatial and temporal patterns of the isotopic composition in the rivers. Further, we compared it to isotopic composition in local precipitation and catchments characteristics. In the majority of the rivers, the spatial and temporal patterns of precipitation were directly reflected in river water. The isotopic signals of the river water were time shifted and show attenuated amplitudes. Further deviations from isotopic compositions in local precipitation were observed in catchments with complex flow systems. These deviations were attributed to catchment processes and influences like evaporation, damming and storage. The seasonality of the isotopic composition was mainly determined by the discharge regimes of the rivers. We found correlations between isotopic long-term averages and catchment altitude as well as latitude and longitude, resulting in a northwest-southeast gradient. Furthermore, it was shown that long-term averages of d-excess were inversely related to flow length and catchment size, which indicates that evaporation enrichment has an impact on the isotopic composition even in catchments of humid climates. This study showed that isotopic composition in rivers can serve as a proxy for the local precipitation and can be utilized as an indicator for hydrological processes even in large river basins. In future, such long time series will help to

  13. Elemental and iron isotopic composition of aerosols collected in a parking structure.

    Majestic, Brian J; Anbar, Ariel D; Herckes, Pierre


    The trace metal contents and iron isotope composition of size-resolved aerosols were determined in a parking structure in Tempe, AZ, USA. Particulate matter (PM)2.5 microm were collected. Several air toxics (e.g., arsenic, cadmium, and antimony) were enriched above the crustal average, implicating automobiles as an important source. Extremely high levels of fine copper (up to 1000 ng m(-3)) were also observed in the parking garage, likely from brake wear. The iron isotope composition of the aerosols were found to be +0.15+/-0.03 per thousand and +0.18+/-0.03 per thousand for the PM2.5 microm fractions, respectively. The similarity of isotope composition indicates a common source for each size fraction. To better understand the source of iron in the parking garage, the elemental composition in four brake pads (two semi-metallic and two ceramic), two tire tread samples, and two waste oil samples were determined. Striking differences in the metallic and ceramic brake pads were observed. The ceramic brake pads contained 10-20% copper by mass, while the metallic brake pads contained about 70% iron, with very little copper. Both waste oil samples contained significant amounts of calcium, phosphorous, and zinc, consistent with the composition of some engine oil additives. Differences in iron isotope composition were observed between the source materials; most notably between the tire tread (average=+0.02 per thousand) and the ceramic brake linings (average=+0.65 per thousand). Differences in isotopic composition were also observed between the metallic (average=+0.18 per thousand) and ceramic brake pads, implying that iron isotope composition may be used to resolve these sources. The iron isotope composition of the metallic brake pads was found to be identical to the aerosols, implying that brake dust is the dominant source of iron in a parking garage.

  14. The oxygen isotope composition of dissolved anthropogenic phosphates: a new tool for eutrophication research?

    Gruau, Gérard; Legeas, Michèle; Riou, Christine; Gallacier, Eve; Martineau, François; Hénin, O


    High-precision oxygen isotope analyses were carried out on dissolved phosphate extracted from discharge waters from three wastewater treatment plants (WTP) located in western France, as well as on the different phosphate-based fertilizers applied by farmers in the same region. Measured delta(18)O values of phosphate from chemical fertilizers range from 19.6 to 23.1 per thousand, while those of phosphate from WTP discharge waters are more tightly grouped between 17.7 and 18.1 per thousand. The variability in delta(18)O values of phosphate fertilizers is attributed to oxygen isotope variations of the phosphorite deposits from which France's fertilizers are manufactured. The significance of the delta(18)O values of phosphate from WTP discharge waters is less straightforward. At present, it is not clear whether these values are primary isotopic compositions corresponding, e.g., to the oxygen isotope composition of phosphate builders included in detergents (delta(18)O(P)=17.9 per thousand), or represent secondary values reflecting biological recycling of the phosphate in equilibrium with ambient WTP water The restricted difference in isotopic composition obtained between phosphate from fertilizers and phosphate from WTP discharge waters (isotopic variability observed in both end-members (>/=1.5 per thousand), cast doubt about the possibility that the oxygen isotope composition could serve as a tracer for the source of anthropogenic phosphates in waters.

  15. Carbon and oxygen isotope compositions of the carbonate facies in the Vindhyan Supergroup, central India

    S Banerjee; S K Bhattacharya; S Sarkar


    The Vindhyan sedimentary succession in central India spans a wide time bracket from the Paleopro- terozoic to the Neoproterozoic period.Chronostratigraphic significance of stable carbon and oxygen isotope ratios of the carbonate phase in Vindhyan sediments has been discussed in some recent studies.However,the subtle controls of facies variation,depositional setting and post-depositional diagenesis on stable isotope compositions are not yet clearly understood.The Vindhyan Super- group hosts four carbonate units,exhibiting a wide variability in depositional processes and paleogeography.A detailed facies-specific carbon and oxygen isotope study of the carbonate units was undertaken by us to investigate the effect of these processes and to identify the least altered isotope values.It is seen that both carbon and oxygen isotope compositions have been affected by early meteoric water diagenesis.The effect of diagenetic alteration is,however,more pronounced in case of oxygen isotopes than carbon isotopes.Stable isotope compositions remained insensitive to facies only when sediments accumulated in a shallow shelf setting without being exposed.Major alteration of original isotope ratios was observed in case of shallow marine carbonates,which became exposed to meteoric fluids during early diagenetic stage.Duration of exposure possibly determined the magnitude of alteration and shift from the original values.Moreover,dolomitization is found to be accompanied by appreciable alteration of isotope compositions in some of the carbonates.The present study suggests that variations in sediment depositional settings,in particular the possibility of subaerial exposure,need to be considered while extracting chronostratigraphic signi ficance from 13C data.

  16. Variations in isotopic compositions of chlorine in evaporation-controlled salt lake brines of Qaidam Basin, China

    Xiao, Ying-kai; Liu, Wei-guo; Zhou, Y.M.; Wang, Yun-hui; Shirodkar, P.V.

    The variations in the isotopic compositions of chlorine in evaporation-controlled saline lake brines were determined by using an improved procedure for precise measurement of chlorine isotopes based on Cs sub(2) Cl sup(+) ion by thermal ionization...

  17. Oxygen isotopic composition of low-temperature authigenic clinoptilolite

    Nähr, T.; Botz, R.; Bohrmann, G.; Schmidt, M.


    Oxygen isotope ratios were obtained from authigenic clinoptilolites from Barbados Accretionary Complex, Yamato Basin, and Exmouth Plateau sediments (ODP Sites 672, 797, and 762) in order to investigate the isotopic fractionation between clinoptilolite and pore water at early diagenetic stages and low temperatures. Dehydrated clinoptilolites display isotopic ratios for the zeolite framework ( δ18O f) that extend from +18.7‰ to +32.8‰ (vs. SMOW). In combination with associated pore water isotope data, the oxygen isotopic fractionation between clinoptilolite and pore fluids could be assessed in the temperature range from 25°C to 40°C. The resulting fractionation factors of 1.032 at 25°C and 1.027 at 40°C are in good agreement with the theoretically determined oxygen isotope fractionation between clinoptilolite and water. Calculations of isotopic temperatures illustrate that clinoptilolite formation occurred at relatively low temperatures of 17°C to 29°C in Barbados Ridge sediments and at 33°C to 62°C in the Yamato Basin. These data support a low-temperature origin of clinoptilolite and contradict the assumption that elevated temperatures are the main controlling factor for authigenic clinoptilolite formation. Increasing clinoptilolite δ18O f values with depth indicate that clinoptilolites which are now in the deeper parts of the zeolite-bearing intervals had either formed at lower temperatures (17-20°C) or under closed system conditions.

  18. Phase Structure and Electrochemical Properties of RE-Mg Based Composite Hydrogen Storage Alloys

    韩树民; 刘宝忠; 张忠; 朱惜林; 王晓铁; 荆天辅


    A new type of AB5-x%LaMg3(x=2, 3, 4, 5, 6, 7, 8)composite hydrogen storage alloys were prepared by sintering the powder mixtures of a commercial AB5 alloy and LaMg3 alloy. The phase structure and electrochemical characteristics of the composite hydrogen storage alloys were also studied. It is shown that AB5-x%LaMg3(x=2, 3, 4, 5, 6, 7, 8)composites have mult; phase structure. The matrix phase has CaCu5 structure, the second phase is LaNi3 phase. The maximum discharge capacity, discharge capacity at low temperature and HRD of AB5 alloy electrodes are greatly improved after the composite. The maximum discharge capacity of the composite electrodes increases from 325 mAh·g-1 for x=0 to 358 mAh·g-1 for x=5, and the HRD of the composites for x=5 at the current density of 1200 mA·g-130% of that of the alloy at 60 mA·g-1. The discharge capacity of AB5-x%LaMg3 composite alloy electrode at 233 K is up to 174 mAh·g-1. The improvement of the electrochemical characteristics of the composite electrodes seems to be related with formation of the LaNi3 second phase.

  19. Abyssal peridotites reveal the near-chondritic Fe isotopic composition of the Earth

    Craddock, Paul R.; Warren, Jessica M.; Dauphas, Nicolas


    Terrestrial oceanic and continental basalts are enriched by approximately +0.1‰ in 56Fe/54Fe ratio relative to primitive, undifferentiated meteorites (chondrites). The δ56Fe values of terrestrial basalts are also distinct from those of basalts from Mars and asteroid Vesta, which have chondritic Fe isotopic compositions. The processes responsible for the isotopic enrichment of terrestrial basalts are debated, in part because the Fe isotopic composition of the mantle source of terrestrial basalts is unknown. Here we report Fe isotopic measurements of abyssal peridotites, which are the residues of limited melting at oceanic ridges and are thus the best proxies for the composition of the convective portion of the mantle. Our data show that abyssal peridotites have a mean δ56Fe value of +0.010±0.007‰ (relative to IRMM-014), which is indistinguishable from chondrites. After correcting this data for seafloor weathering and mantle melting, we estimate the average Fe isotopic composition of the terrestrial mantle to be δ56Fe=+0.025±0.025‰, which is also indistinguishable from chondrites, within current analytical precision. We determine that the maximum shift in δ56Fe for peridotite residues during partial mantle melting is 0.01‰. Our results argue against isotopic fractionation during core-mantle differentiation or iron vaporization during the Moon-forming giant impact, because both processes would yield a bulk mantle δ56Fe value that is non-chondritic. In addition, our results suggest that disproportionation of mantle Fe2+-Fe3+ in perovskite and Fe0 metal and segregation of metal to the core could not have been a driver for Fe isotopic fractionation in the silicate mantle. Instead, the different iron isotopic compositions of abyssal peridotites and MORBs support mounting evidence for iron isotopic fractionation of melts but not residues during the formation of oceanic and continental crust.

  20. Isotopic composition of Lake Agassiz-Ojibway water just prior to final drainage

    Hillaire-Marcel, C.; Helie, J.; McKay, J.; Lalonde, A.


    Controversies persist with respect to the impact of the final drainage of Lake Agassiz-Ojibway on the thermohaline circulation of the North Atlantic, some 8.4 ka ago. The lack of response of planktic foraminifer isotope records, off Hudson Strait (i.e., at the outlet of the drainage channel) constitutes one of the most puzzling elements in this debate. However, data on the isotopic composition of drainage waters are needed to estimate the response of the 18-O-salinity relationship in NW Atlantic surface waters. In the literature, a large array of isotopic compositions have been suggested, notably for modeling experiment purposes. Scattered information about the isotopic composition of Lake Agassiz water does exist. It includes isotopic measurements of pore waters of lacustrine sediments [1], analyses of oxygen isotopes in cellulose from algal or plant remains [2], and stable isotope compositions of concretions from varves [3]. Whereas, relatively low oxygen isotope values (apx. -25 per mil vs. VSMOW) are inferred for Lake Agassiz waters during cold pulses of the deglaciation, most data suggest much higher values during the final stages of Lake Agassiz-Ojiway, just prior to its drainage. Calcareous concretions from Lake Ojibway varves (not necessarily contemporaneous to the lacustrine stage) yielded oxygen isotope compositions of about -10 per mil (vs. VPDB), suggesting values as high as -14 per mil (vs. VSMOW) for pore waters (assuming a 0-4 degrees C temperature range). Similar high values (as high as -8 per mil vs. VSMOW [1]) were also estimated from pore water analyses of contemporaneous Lake Agassiz sediments. Here, we used a core raised from Eastern Hudson Bay, off Great Whale River, to further document isotopic compositions of the lake waters prior to their drainage into the North Atlantic. The 7.40 m long core has an apx. 1.3 m-thick lacustrine layer at its base, including the drainage sub- layer. It is overlain by Tyrrell Sea clays. Scarce valves of Candona

  1. Threshold character of temperatures on deuterium desorption from the Mg-Zr composite

    Neklyudov, I. M.; Morozov, O. M.; Kulish, V. G.; Zhurba, V. I.; Lomino, N. S.; Ovcharenko, V. D.; Kuprin, O. S.


    The plasma evaporation-sputtering method was used to manufacture composite materials of the Mg-Zr system. The ion-implanted deuterium desorption temperature variations depending on the component concentrations were studied. It has been established that the introduction of a Zr impurity to magnesium leads to the significant decrease of the deuterium desorption temperature (~400K) as compared to the release from Mg samples. A step-like form of the curve of the deuterium desorption temperature testifies to presence of two various structural conditions at composite Mg-Zr depending on the relation of components. The hydrogen desorption data obtained using Mg-Zr composites can be used for the further invrstigations into the hydrogen storage materials containing chemical elements with a low solubility in the alloy components.

  2. Threshold character of temperatures on deuterium desorption from the Mg-Zr composite

    Neklyudov, I M; Morozov, O M; Kulish, V G; Zhurba, V I; Lomino, N S; Ovcharenko, V D; Kuprin, O S, E-mail: [National Science Center ' Kharkov Institute of Physics and Technology' , 61108 Kharkov (Ukraine)


    The plasma evaporation-sputtering method was used to manufacture composite materials of the Mg-Zr system. The ion-implanted deuterium desorption temperature variations depending on the component concentrations were studied. It has been established that the introduction of a Zr impurity to magnesium leads to the significant decrease of the deuterium desorption temperature ({approx}400K) as compared to the release from Mg samples. A step-like form of the curve of the deuterium desorption temperature testifies to presence of two various structural conditions at composite Mg-Zr depending on the relation of components. The hydrogen desorption data obtained using Mg-Zr composites can be used for the further invrstigations into the hydrogen storage materials containing chemical elements with a low solubility in the alloy components.

  3. Stable isotopic composition of cryptocrystalline magnesite from deposits in Turkey and Austria

    Horkel, K.; Ebner, F.; Spötl, Ch


    ). The results show that each of the deposits is characterized by a characteristic C isotopic composition. Furthermore, network and vein mineralizations in the magnesite district of Eskişehir (Tutluca/Koçbal, Günaydin, Çırçır) can be distinguished by their isotopic pattern: Tutluca/Koçbal (network mineralization) - low δ13C values (-11,0‰ to -8,3‰), Günaydin (vein mineralization) - intermediate δ13C values (- 8,9‰ to -3,1‰), and Çırçır, (Bela Stena-type CM in weathered serpentinite at the bottom of lacustrine sediments) - high δ13C values (+2,3‰ to +3,1‰). The δ18O values are very similar at all deposits (+25,5‰ to +27,3‰). References: ECE Ö.I., MATSUBAYA O. ÇOBAN F. (2005): Genesis of hydrothermal stockwork-type Magnesite deposits associated with ophiolite complexes in the Kütahya - Eskişehir region, Turkey. - N. Jb. Miner. Abh., 181, 191-205. JURKOVIĆ I. & PAMIĆ J. (2003): Carbon and oxygen composition of the Dinaridic ophiolite related magnesites. - In: Eliopoulos D. G. et al. (eds.) Mineral Exploration and Sustainable Development, 2, Millpress Rotterdam, 883-886. KRALIK, M., AHARON, P., SCHROLL, E. & ZACHMANN, D. (1989): Carbon and oxygen isotope systematics of magnesites. - In: Möller, P. (ed.) Magnesite - Geology, Mineralogy, Geochemistry, Formation of Mg-Carbonates. - Monogr. Series on Miner. Depos., 28, 197-223. POHL W. (1990): Genesis of magnesite deposits - models and trends. - Geol. Rundschau, 79, 291-299. PROCHASKA, W. (2000): Siderite and magnesite mineralizations formed during initial rifting of the Alpine cycle.- In: F. Ebner et al. (2000): Mineral Resources in the Eastern Alps and Adjoining Areas.- Mitt. Österr. Geol. Ges., 92, 157-184. WILSON, I. & EBNER, F. (2006): The World of Magnesite. - Industrial Minerals, 2006/March, 54-61. ZEDEF, V., RUSSEL, M. J., FALLICK, E. & HALL, A. J.; (2000): Genesis of Vein Stockwork and Sedimentary Magnesite Hydromagnesit Deposits in the Ultramafic Terranes of Southwestern Turkey

  4. Stable isotopic composition of perchlorate and nitrate accumulated in plants: Hydroponic experiments and field data

    Estrada, Nubia Luz; Böhlke, John Karl; Sturchio, Neil C.; Gu, Baohua; Harvey, Greg; Burkey, Kent O.; Grantz, David A.; McGrath, Margaret T.; Anderson, Todd A.; Rao, Balaji; Sevanthi, Ritesh; Hatzinger, Paul B.; Jackson, W. Andrew


    Natural perchlorate (ClO4−) in soil and groundwater exhibits a wide range in stable isotopic compositions (δ37Cl, δ18O, and Δ17O), indicating that ClO4− may be formed through more than one pathway and/or undergoes post-depositional isotopic alteration. Plants are known to accumulate ClO4−, but little is known about their ability to alter its isotopic composition. We examined the potential for plants to alter the isotopic composition of ClO4− in hydroponic and field experiments conducted with snap beans (Phaseolus vulgaris L.). In hydroponic studies, anion ratios indicated that ClO4− was transported from solutions into plants similarly to NO3− but preferentially to Cl− (4-fold). The ClO4− isotopic compositions of initial ClO4− reagents, final growth solutions, and aqueous extracts from plant tissues were essentially indistinguishable, indicating no significant isotope effects during ClO4− uptake or accumulation. The ClO4− isotopic composition of field-grown snap beans was also consistent with that of ClO4− in varying proportions from irrigation water and precipitation. NO3− uptake had little or no effect on NO3− isotopic compositions in hydroponic solutions. However, a large fractionation effect with an apparent ε (15N/18O) ratio of 1.05 was observed between NO3− in hydroponic solutions and leaf extracts, consistent with partial NO3− reduction during assimilation within plant tissue. We also explored the feasibility of evaluating sources of ClO4− in commercial produce, as illustrated by spinach, for which the ClO4− isotopic composition was similar to that of indigenous natural ClO4−. Our results indicate that some types of plants can accumulate and (presumably) release ClO4− to soil and groundwater without altering its isotopic characteristics. Concentrations and isotopic compositions of ClO4−and NO3− in plants may be useful for determining sources of fertilizers and sources of ClO4− in their growth environments and

  5. Fast hydrogen sorption from MgH2-VO2(B) composite materials

    Milošević, Sanja; Kurko, Sandra; Pasquini, Luca; Matović, Ljiljana; Vujasin, Radojka; Novaković, Nikola; Novaković, Jasmina Grbović


    The hydrogen sorption kinetics of MgH2‒VO2(B) composites synthesised by mechanical milling have been studied. The microstructural properties of composites were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM), Particle size analysis (PSD), while sorption behaviour was followed by differential scanning calorimetry (DSC) and Sievert measurements. Results have shown that although desorption temperature reduction is moderate; there is a substantial improvement in hydrogen sorption kinetics. The complete desorption of pure MgH2 at elevated temperature takes place in more than 30 min while the composite fully desorbs in less than 2 min even at lower temperatures. It has been shown that the metastable γ-MgH2 phase and the point defects have a decisive role in desorption process only in the first sorption cycle, while the second and the subsequent sorption cycles are affected by microstructural and morphological characteristics of the composite.

  6. Lead and zinc dust depositions from ore trains characterised using lead isotopic compositions.

    Kristensen, L J; Taylor, M P; Morrison, A L


    This study investigates an unusual source of environmental lead contamination - the emission and deposition of lead and zinc concentrates along train lines into and out of Australia's oldest silver-lead-zinc mine at Broken Hill, Australia. Transport of lead and zinc ore concentrates from the Broken Hill mines has occurred for more than 125 years, during which time the majority was moved in uncovered rail wagons. A significant amount of ore was lost to the adjoining environments, resulting in soil immediately adjacent to train lines elevated with concentrations of lead (695 mg kg(-1)) and zinc (2230 mg kg(-1)). Concentrations of lead and zinc decreased away from the train line and also with depth shown in soil profiles. Lead isotopic compositions demonstrated the soil lead contained Broken Hill ore in increasing percentages closer to the train line, with up to 97% apportioned to the mined Broken Hill ore body. SEM examination showed ceiling dusts collected from houses along the train line were composed of unweathered galena particles, characteristic of the concentrate transported in the rail wagons. The loss of ore from the uncovered wagons has significantly extended the environmental footprint of contamination from local mining operations over an area extending hundreds of kilometres along each of the three train lines.

  7. Normal variations in the isotopic composition of metabolically relevant transition metals in human blood

    Van Heghe, L.; Cloquet, C.; Vanhaecke, F.


    Cu, Fe and Zn are transition metals with great catalytic, structural and regulating importance in the human body. Hence, an aberrant metabolism of these elements can have serious implications on the health of a person. It is assumed that, due to differences in isotope fractionation, the isotopic composition of these elements in whole blood of patients can be different from that in blood of healthy subjects. Therefore, isotopic analysis of the element affected by the disease can be a promising approach for early diagnosis. A method for isotopic analysis of Cu, Fe and Zn in human whole blood was developed. The simultaneous chromatographic isolation of these elements and the conditions for isotope ratio measurement via multi-collector ICP - mass spectrometry (MC-ICP-MS) were optimized. So far, only whole blood of supposedly healthy volunteers (reference population) was analyzed. Results for Fe confirmed the known differences in isotopic composition between male and female blood. It is also shown that other parameters can have influence as well, e.g., the isotopic composition of Zn seems to be governed by the diet.

  8. Petrology and oxygen isotope compositions of chondrules in E3 chondrites

    Weisberg, Michael K.; Ebel, Denton S.; Connolly, Harold C.; Kita, Noriko T.; Ushikubo, Takayuki


    Chondrules in E3 chondrites differ from those in other chondrite groups. Many contain near-pure endmember enstatite (Fs metal, Cr-bearing troilite, and, in some cases Mg, Mn- and Ca-sulfides. Olivine and more FeO-rich pyroxene grains are present but much less common than in ordinary or carbonaceous chondrite chondrules. In some cases, the FeO-rich grains contain dusty inclusions of metal. The oxygen three-isotope ratios (δ 18O, δ 17O) of olivine and pyroxene in chondrules from E3 chondrites, which are measured using a multi-collection SIMS, show a wide range of values. Most enstatite data plots on the terrestrial fractionation (TF) line near whole rock values and some plot near the ordinary chondrite region on the 3-isotope diagram. Pyroxene with higher FeO contents (˜2-10 wt.% FeO) generally plots on the TF line similar to enstatite, suggesting it formed locally in the EC (enstatite chondrite) region and that oxidation/reduction conditions varied within the E3 chondrite chondrule-forming region. Olivine shows a wide range of correlated δ 18O and δ 17O values and data from two olivine-bearing chondrules form a slope ˜1 mixing line, which is approximately parallel to but distinct from the CCAM (carbonaceous chondrite anhydrous mixing) line. We refer to this as the ECM (enstatite chondrite mixing) line but it also may coincide with a line defined by chondrules from Acfer 094 referred to as the PCM (Primitive Chondrite Mineral) line ( Ushikubo et al., 2011). The range of O isotope compositions and mixing behavior in E3 chondrules is similar to that in O and C chondrite groups, indicating similar chondrule-forming processes, solid-gas mixing and possibly similar 16O-rich precursors solids. However, E3 chondrules formed in a distinct oxygen reservoir. Internal oxygen isotope heterogeneity was found among minerals from some of the chondrules in E3 chondrites suggesting incomplete melting of the chondrules, survival of minerals from previous generations of

  9. Early Paleozoic ridge subduction in the Chinese Altai: Insight from the abrupt change in zircon Hf isotopic compositions


    Zircons were separated from granitoids, gneisses, and sedimentary rocks of the Chinese Altai. Those with igneous characteristics yielded U-Pb ages of 280-2800 Ma, recording a long history of magmatic activity in the region. Zircon Hf isotopic compositions show an abrupt change at ~420 Ma, indicating that prior to that time the magmas came from both ancient and juvenile sources, whereas younger magmas were derived mainly from juvenile material. This may imply that the lithosphere was signifi- cantly modified in composition by a rapid addition of melt from the mantle. We suggest that this dramatic change was due to the onset of ridge subduction, which can account not only for the formation of voluminous granitoids, mafic rocks with complex compositions, and the association of adakite + high-Mg andesite + boninite + Nb-enriched basalt, but also for the coeval high-T, low-P metamorphism.

  10. Early Paleozoic ridge subduction in the Chinese Altai:Insight from the abrupt change in zircon Hf isotopic compositions

    SUN Min; LONG XiaoPing; CAI KeDa; JIANG YingDe; WANG BuYun; YUAN Chao; ZHAO GuoChun; XIAO WenJiao; WU FuYuan


    Zircons were separated from granitoids,gneisses,and sedimentary rocks of the Chinese Altai.Those with igneous characteristics yielded U-Pb ages of 280-2800 Ma,recording a long history of magmatic activity in the region.Zircon Hf isotopic compositions show an abrupt change at ~420 Ma,indicating that prior to that time the magmas came from both ancient and juvenile sources,whereas younger magmas were derived mainly from juvenile material.This may imply that the lithosphere was significantly modified in composition by a rapid addition of melt from the mantle.We suggest that this dramatic change was due to the onset of ridge subduction,which can account not only for the formation of voluminous granitoids,mafic rocks with complex compositions,and the association of adakite + high-Mg andesite+boninite + Nb-enriched basalt,but also for the coeval high-T,Iow-P metamorphism.

  11. The stable Cr isotopic compositions of chondrites and silicate planetary reservoirs

    Schoenberg, Ronny; Merdian, Alexandra; Holmden, Chris; Kleinhanns, Ilka C.; Haßler, Kathrin; Wille, Martin; Reitter, Elmar


    The depletion of chromium in Earth's mantle (∼2700 ppm) in comparison to chondrites (∼4400 ppm) indicates significant incorporation of chromium into the core during our planet's metal-silicate differentiation, assuming that there was no significant escape of the moderately volatile element chromium during the accretionary phase of Earth. Stable Cr isotope compositions - expressed as the ‰-difference in 53Cr/52Cr from the terrestrial reference material SRM979 (δ53/52CrSRM979 values) - of planetary silicate reservoirs might thus yield information about the conditions of planetary metal segregation processes when compared to chondrites. The stable Cr isotopic compositions of 7 carbonaceous chondrites, 11 ordinary chondrites, 5 HED achondrites and 2 martian meteorites determined by a double spike MC-ICP-MS method are within uncertainties indistinguishable from each other and from the previously determined δ53/52CrSRM979 value of -0.124 ± 0.101‰ for the igneous silicate Earth. Extensive quality tests support the accuracy of the stable Cr isotope determinations of various meteorites and terrestrial silicates reported here. The uniformity in stable Cr isotope compositions of samples from planetary silicate mantles and undifferentiated meteorites indicates that metal-silicate differentiation of Earth, Mars and the HED parent body did not cause measurable stable Cr isotope fractionation between these two reservoirs. Our results also imply that the accretionary disc, at least in the inner solar system, was homogeneous in its stable Cr isotopic composition and that potential volatility loss of chromium during accretion of the terrestrial planets was not accompanied by measurable stable isotopic fractionation. Small but reproducible variations in δ53/52CrSRM979 values of terrestrial magmatic rocks point to natural stable Cr isotope variations within Earth's silicate reservoirs. Further and more detailed studies are required to investigate whether silicate

  12. Compositional variations of chromiferous spinel in Mg-rich rocks of the Deccan Traps, India

    Leone Melluso; Roberto De’ Gennaro; Ivana Rocco


    Composition of chromiferous spinel included in olivines of Mg-rich basalts and gabbros of the Deccan Traps (Gujarat and Western Ghats) are reported here. They vary from Al-rich compositions [Al2O3 = 53wt.%; Cr#, 100Cr/(Cr + Al) = 12] to Cr-rich compositions [Cr2O3 = 51wt.%; Cr#= 84], and from Cr-Al rich compositions towards Cr-rich Ti-magnetite (TiO2 up to 23 wt.%, ulvöspinel up to 67mol.%). The Mg#[100Mg/(Mg + Fe2+)] of spinel decreases from 81 to nearly zero. The highest Cr#has been found in the Bushe Fm., Thakurvadi Fm., and some high-Ti basalts of the Pavagadh section, whereas some of the low-Ti basalts of Saurashtra have Al-rich compositions typical of spinels found in mid-ocean ridge basalts. The chemical composition of the Deccan Trap spinels is completely different compared to that observed in mantle spinel suites, with very few exceptions. The decreasing Al and increasing Fe and Ti of spinel seems to be mainly the result of decrease of Mg in the locally coexisting melts and favourable cationic substitutions in the lattice. There is barely any evidence of general relationships between the composition of the Deccan spinels and inferred mantle sources of the host magmas. Pyroxene inclusions in spinels may witness a high-pressure stage of crystallization, but the possibility of non-equilibrium crystallization, or even magma mixing, cannot be ruled out. Overall, the compositional ranges of chromiferous spinel in the Deccan Traps closely match those observed in the other Large Igneous Provinces having mafic/ultramafic intrusions and mafic magma compositions (e.g., Siberian Traps, Karoo, Emeishan).

  13. Magnesium and 54Cr isotope compositions of carbonaceous chondrite chondrules – Insights into early disk processes

    Olsen, Mia Bjørg Stolberg; Wielandt, Daniel; Schiller, Martin;


    We report on the petrology, magnesium isotopes and mass-independent 54Cr/52Cr compositions (μ54Cr) of 42 chondrules from CV (Vigarano and NWA 3118) and CR (NWA 6043, NWA 801 and LAP 02342) chondrites. All sampled chondrules are classified as type IA or type IAB, have low 27Al/24Mg ratios (0......∗) relative to the solar value defined by CI chondrites, which we interpret as reflecting formation from precursor material with a reduced initial abundance of 26Al compared to the canonical 26Al/27Al of ∼5 × 10−5. Model initial 26Al/27Al values of CV and CR chondrules vary from (1.5 ± 4.0) × 10−6 to (2.2 ± 0.......4) × 10−5. The CV chondrules display significant μ54Cr variability, defining a range of compositions that is comparable to that observed for inner Solar System primitive and differentiated meteorites. In contrast, CR chondrites are characterized by a narrower range of μ54Cr values restricted...

  14. Composition and size dependent brittle-to-malleable transitions of Mg-based bulk metallic glasses

    Yin, Jian, E-mail:; Ma, Xiujun; Zhou, Zhijian


    Mg-based bulk metallic glasses (BMGs) were often treated as brittle materials. However, some Mg-based BMGs were recently reported to show malleability. In order to identify the reasons for the achievement of the brittle-to-malleable transitions in the Mg-based BMGs, we systematically investigated the mechanical properties of four Mg-based BMGs (Mg{sub 65}Cu{sub 25}Gd{sub 10}, Mg{sub 65}Cu{sub 20}Ni{sub 5}Gd{sub 10}, Mg{sub 75}Ni{sub 15}Gd{sub 10}, and Mg{sub 75}Ni{sub 15}Gd{sub 5}Nd{sub 5} BMGs) using the uniaxial compression tests on the samples with sizes of ∅1×2 mm{sup 2} and ∅2×4 mm{sup 2}. The corresponding fracture morphology was observed by scanning electron microscopy (SEM). These Mg-based BMGs displayed the composition or size dependent brittle-to-malleable transitions, accompanied by the fracture mode transition from the cleavage fracture to the shear fracture. It appeared that the Mg-based BMGs were sensitive to cleavage cracks upon loading. The brittle-to-malleable transitions of the Mg-based BMGs were related to not only the stability of shear banding but also the nucleation and propagation of cleavage cracks. It was demonstrated that the suppression of the nucleation and propagation of cleavage cracks could favor the transition from the cleavage fracture to the shear fracture and encourage the brittle-to-malleable transition for the Mg-based BMGs. The underlying mechanism for the brittle-to-malleable transitions of the Mg-based BMGs was discussed with respect to both the composition and size effects.

  15. Microwave Dielectric Properties of Polystyrene-Forsterite (Mg2SiO4) Composite

    Sasikala, T. S.; Sebastian, M. T.


    Polystyrene-Mg2SiO4 ceramic composites have been prepared by kneading followed by hot pressing. The dielectric properties of the composites have been investigated at both radio and microwave frequency ranges as a function of filler loading up to 50 vol.%. The dielectric constant and loss tangent increased with the ceramic filler content. The composite with 50 vol.% filler had a dielectric constant of 4.0 and loss tangent of 0.006 at 5 GHz, with Vickers microhardness of 35 HV. The coefficient of thermal expansion of the composite decreased and the thermal conductivity increased with the filler loading. PS-Mg2SiO4 composites are possible candidates for microwave substrate applications.

  16. Interface reactions and stability of a hydride composite (NaBH4 + MgH2).

    Kato, Shunsuke; Borgschulte, Andreas; Bielmann, Michael; Züttel, Andreas


    The use of the interaction of two hydrides is a well-known concept used to increase the hydrogen equilibrium pressure of composite mixtures in comparison to that of pure systems. The thermodynamics and reaction kinetics of such hydride composites are reviewed and experimentally verified using the example NaBH(4) + MgH(2). Particular emphasis is placed on the measurement of the kinetics and stability using thermodesorption experiments and measurements of pressure-composition isotherms, respectively. The interface reactions in the composite reaction were analysed by in situ X-ray photoelectron spectroscopy and by simultaneously probing D(2) desorption from NaBD(4) and H(2) desorption from MgH(2). The observed destabilisation is in quantitative agreement with the calculated thermodynamic properties, including enthalpy and entropy. The results are discussed with respect to kinetic limitations of the hydrogen desorption mechanism at interfaces. General aspects of modifying hydrogen sorption properties via hydride composites are given.

  17. Analysis of in situ Reaction and Pressureless Infiltration Process in Fabricating TiC/Mg Composites

    Qun DONG; Liqing CHEN; Mingjiu ZHAO; Jing BI


    An innovative processing route, in situ reaction combined with pressureless infiltration, was adopted to fabricate magnesium matrix composites, where the reinforcement TiC formed in situ from elemental Ti and C powders and molten Mg spontaneously infiltrated the preform of Ti and C. The influences of primarily elemental particle sizes,synthesizing temperature, holding time etc on in situ reactive infiltration for Mg-Ti-C system were systematically investigated in order to explore the mechanism of this process. In fabricating TiC/Mg composites, Mg can not only spontaneously infiltrate the preform of reinforcement and thus densify the as fabricated composites as matrix metal, but also it can accelerate the in situ reaction process and lower the synthesizing temperature of Ti and C as well. In situ reaction of Ti and C and Mg infiltration processes are essentially overlapping and interacting during fabrication of TiC/Mg composites. The mechanism proposed in this paper can be used to explain the formation and morphologies of the reinforcement phase TiC.

  18. The effect of small scale variablity in isotopic composition of precipitation on hydrograph separation results

    Fischer, Benjamin; van Meerveld, Ilja; Seibert, Jan


    Understanding runoff processes is important for predictions of streamflow quantity and quality. The two-component isotope hydrograph separation (IHS) method is a valuable tool to study how catchments transform rainfall into runoff. IHS allows the stormflow hydrograph to be separated into rainfall (event water) and water that was stored in the catchment before the event (pre-event water). To be able to perform an IHS, water samples of baseflow (pre-event water) and stormflow are collected at the stream outlet. Rainfall is usually collected at one location by hand as an event total or sampled sequentially during the event. It is usually assumed that the spatial variability in rainfall and the isotopic composition of rainfall are negligible for small (area of 0.15, 0.23, and 0.7 km2). The isotopic composition of rainfall and streamflow were sampled for 10 different rain events (P: 5 mm intervals, Q: 12 to 51 samples per events). This dataset was used to perform a two-component isotope hydrograph separation. The results show that for some events the spatial variability in total rainfall, mean and maximum rainfall intensity and stable isotope composition of rainfall was high. There was no relation between the stable isotope composition of rainfall and the rainfall sum, rainfall intensity or altitude. The spatial variability of the isotopic composition of rainfall was for 4 out of the 10 events as large as the temporal variability in the isotopic composition. Different rainfall weighing methods resulted in different minimum pre-event water fractions in streamflow. For small events with a small mean temporal range in stable isotope composition of rainfall, the different rainfall weighing methods had little effect on the calculated minimum pre-event water fractions. However with increasing temporal variability in stable isotope composition of rainfall, the range in the minimum pre-event water fractions increased and therefore the choice of the rainfall weighing method

  19. Chromium isotope composition of reducing and anoxic sediments from the Peru Margin and Cariaco Basin

    Gueguen, B.; Planavsky, N.; Wang, X.; Algeo, T. J.; Peterson, L. C.; Reinhard, C. T.


    Chromium isotope systematics in marine sediments are now being used as a new redox proxy of the modern and ancient Earth's surface. Chromium is primarily delivered to the oceans by riverine inputs through weathering of Cr(III)-rich minerals present in the continental crust and oxidation of insoluble Cr(III) to soluble Cr(VI) species. Since oxidation-reduction reactions fractionate Cr isotopes whereby oxidized Cr(VI) species are preferentially enriched in heavy Cr isotopes, the Cr isotope composition of marine sediments may be useful tracers of redox conditions at the Earth's surface through geological time. Chromium is quantitatively removed in organic-rich sediments where reducing conditions prevail and promote reduction of Cr(VI) to Cr(III), and thus, these sediments should capture the ambient seawater Cr isotope composition. However, the isotopic composition of modern organic-rich sediments is poorly documented so far, and this step is essential for further modeling the global oceanic Cr isotope mass balance and assessing the effects of sedimentation and post-depositional processes on the marine Cr isotopes archive. In this study, we have characterized modern marine organic-rich sediments for their Cr isotope composition (δ53/52Cr) from two different settings, the Peru margin upwelling zone and the anoxic Cariaco Basin (Venezuela). Chromium isotopes were measured on a MC-ICP-MS (Nu Plasma) using a double-spike correction method. The authigenic fraction of shallow samples from the Peru margin sedimentary sequence with a high Total Organic Carbon (TOC) content (>10 wt%) yield an average δ53/52Crauthigenic value of +0.67 ±0.05 ‰ (2sd). However, although this value is close to the seawater value (Atlantic Ocean) and to Cariaco basin sediments (~ +0.6 ‰), reducing sediments from the Peru margin are on average isotopically slightly heavier, especially in samples having a low authigenic fraction and a low TOC content (δ53/52Crauthigenic values up to +1.30

  20. Geometric and Chemical Composition Effects on Healing Kinetics of Voids in Mg-bearing Al Alloys

    Song, Miao; Du, Kui; Wang, Chunyang; Wen, Shengping; Huang, Hui; Nie, Zuoren; Ye, Hengqiang


    The healing kinetics of nanometer-scale voids in Al-Mg-Er and Al-Mg-Zn-Er alloy systems were investigated with a combination of in situ transmission electron microscopy and electron tomography at different temperatures. Mg was observed completely healing the voids, which were then rejuvenated to the alloy composition with further aging, in the Al-Mg-Er alloy. On the contrary, Mg51Zn20 intermetallic compound was formed in voids in the Al-Mg-Zn-Er alloy, which leads to complete filling of the voids but not rejuvenation for the material. For voids with different geometrical aspects, different evolution processes were observed, which are related to the competition between bulk and surface diffusion of the alloys. For voids with a large size difference in their two ends, a viscous flow of surface atoms can be directly observed with in situ electron microscopy, when the size of one end becomes less than tens of nanometers.

  1. Mechanical properties and microstructural analysis of Al–Si–Mg/carbonized maize stalk waste particulate composites

    J.E. Oghenevweta


    Full Text Available The mechanical properties and morphological analysis of Al–Si–Mg/carbonized maize stalk particulate composites was investigated. The compositions of the composite include a matrix of Al–Si–Mg and the carbonized maize stalk particulates as reinforcement ranging from 2% to 10% at an interval of 2%. Properties such as mechanical behaviour of the composites were examined and these include tensile strength, tensile modulus, hardness value, impact energy, percentage elongation and percentage reduction in area. Besides, the microstructures of the developed Al–Si–Mg/carbonized maize stalk particulate composites were investigated. The results of the microstructures of the composite show a uniform dispersion of the reinforcement along the grain boundaries of the alloy. The tensile strength and hardness values increase to 85.60 N/mm2 and 24HRB at 8 and 10 wt% of carbonized maize stalk respectively, but there is a slight decrease in the impact energy values, values of percentage elongation and percentage reduction in area as the reinforcement increases. From these results of investigation, we concluded that the carbonized reinforcing maize particulates can be used to enhance the properties of Al–Si–Mg alloy for engineering applications.

  2. A novel biodegradable nicotinic acid/calcium phosphate composite coating on Mg-3Zn alloy

    Song, Yingwei, E-mail:; Shan, Dayong; Han, En-Hou


    A novel biodegradable composite coating is prepared to reduce the biodegradation rate of Mg-3Zn alloy. The Mg-3Zn substrate is first immersed into 0.02 mol L{sup -1} nicotinic acid (NA) solution, named as vitamin B{sub 3}, to obtain a pretreatment film, and then the electrodeposition of calcium phosphate coating with ultrasonic agitation is carried out on the NA pretreatment film to obtain a NA/calcium phosphate composite coating. Surface morphology is observed by scanning electron microscopy (SEM). Chemical composition is determined by X-ray diffraction (XRD) and EDX. Protection property of the coatings is evaluated by electrochemical tests. The biodegradable behavior is investigated by immersion tests. The results indicate that a thin but compact bottom layer can be obtained by NA pretreatment. The electrodeposition calcium phosphate coating consists of many flake particles and ultrasonic agitation can greatly improve the compactness of the coating. The composite coating is biodegradable and can reduce the biodegradation rate of Mg alloys in stimulated body fluid (SBF) for twenty times. The biodegradation process of the composite coating can be attributed to the gradual dissolution of the flake particles into chippings. - Highlights: Black-Right-Pointing-Pointer NA/calcium phosphate composite coating is prepared to protect Mg-3Zn alloy implant. Black-Right-Pointing-Pointer Nicotinic acid (vitamin B{sub 3}) is available to obtain a protective bottom film. Black-Right-Pointing-Pointer Ultrasonic agitation greatly improves the compactness of calcium phosphate coating. Black-Right-Pointing-Pointer The composite coating can reduce the biodegradation rate of Mg-3Zn twenty times. Black-Right-Pointing-Pointer The composite coating is biodegraded by the dissolution of flakes into chippings.

  3. The isotopic composition of dissolved cadmium in the water column of the West Philippine Sea

    Shun-Chung eYang


    Full Text Available The dissolved concentration and isotopic compositions of cadmium (Cd in the seawater of the West Philippine Sea were determined. In general, Cd isotopic composition in the water column decreased with depth, with ε114/110Cd (ε114/110Cd = [(114Cd/110Cdsample / (114Cd/110CdNIST 3108 - 1]×10000 ranging from +7.2 to +10.1 in the top 60 m, from +4.8 to +5.1 between 100 and 150 m, peaking at +8.2 at 200 m, decreasing from +4.5 to +3.3 from 400 to 1000 m, and remaining constant at +3.0 from 1000 m and deeper. Different to a Rayleigh fractionation model, the isotopic composition and log scale concentrations of Cd do not exhibit a linear relationship. However, from the deep water to thermocline, the variations in Cd concentration and ε114/110Cd are relevant to the variations of temperature and salinity, indicating that water mixing is the dominant processes determining the concentration and isotopic composition in the interval. At 200 m where North Pacific Tropic Water dominates the water mass, the elevated ε114/110Cd could be linked to the composition in the upper portions of the water mass. In the top 150 m, the ε114/110Cd varies similarly to the phytoplankton community structures, implying that Cd uptake by various phytoplankton species may be associated with the isotopic variation. However, the effects of atmospheric inputs to the ε114/110Cd in the surface water cannot be excluded. A box model calculation is used to constrain the contributions of various processes to the Cd isotopes of surface water, and the results indicate that the Cd concentration and isotopic composition in most of the water body of the region are controlled by physical mixing, while the effects of biological fractionation and atmospheric inputs are limited in the euphotic zone.

  4. The minor sulfur isotope composition of Cretaceous and Cenozoic seawater sulfate

    Masterson, A. L.; Wing, Boswell A.; Paytan, Adina; Farquhar, James; Johnston, David T.


    The last 125 Myr capture major changes in the chemical composition of the ocean and associated geochemical and biogeochemical cycling. The sulfur isotopic composition of seawater sulfate, as proxied in marine barite, is one of the more perplexing geochemical records through this interval. Numerous analytical and geochemical modeling approaches have targeted this record. In this study we extend the empirical isotope record of seawater sulfate to therefore include the two minor sulfur isotopes, 33S and 36S. These data record a distribution of values around means of Δ33S and Δ36S of 0.043 ± 0.016‰ and -0.39 ± 0.15‰, which regardless of δ34S-based binning strategy is consistent with a signal population of values throughout this interval. We demonstrate with simple box modeling that substantial changes in pyrite burial and evaporite sulfate weathering can be accommodated within the range of our observed isotopic values.

  5. The atomic weight and isotopic composition of nitrogen and their variation in nature

    Holden, N.E.


    Two stable isotopes of nitrogen exist in nature, /sup 14/N and /sup 15/N. The less abundant isotope, /sup 15/N, was discovered in 1929 by Naude, who studied the band spectra of nitric oxide, NO. However, the main source of a standard for this element is the air in the atmosphere, which is made up of approximately 78% N/sub 2/. Reviewed in this paper is the measurements of the isotopic composition in air and its variation around the world. Also investigated is the variation of the isotopic composition in the various compounds or sources of nitrogen compared to the value in air. Data on the atomic weight and non-terrestrial data for nitrogen is also reviewed.

  6. On the isotopic composition of precipitation; Sur la composition isotopique des precipitations

    Gonfiantini, R. [Paris-11 Univ., 91 - Orsay (France). Laboratoire d`Hydrologie et de Geochimie Isotopique


    The paper discusses some aspects of the isotopic composition (tritium and stable isotopes) of global precipitation which is being monitored since the late fifties through the network established by the International Atomic Energy Agency. Three quarters of the tritium formed during the atmospheric thermonuclear tests were released in the biennium 1961-1962. The successive five years of the test moratorium provide a unique information on the tritium transfer rate from the stratosphere to the troposphere. The tritium concentration decreased steadily, and the decrease rate appears to be greater at high latitude. This fact can possibly be explained by precipitation recycling by evapotranspiration, which is more important at low latitudes, and tritium concentration ratio between two successive years, is close to 0.68 {+-} 0.02, with the exception of the year 1965, when the tritium content dropped to 0.50 {+-} 0.02 with respect to the previous year. At latitudes between 30 and 60 deg C, the correlations between {delta}{sup 2}H and {delta}{sup 18}O show almost identical slopes in winter and summer precipitation, but different intercepts. The correlations are: {delta}{sup 2}H (8.36{+-}0.13) {delta}{sup 18}O+(14.2{+-}4.2) for January and {delta}{sup 2}H 8.33{+-}0.013) {delta}{sup 18}O+(8.2{+-}3.9) for July. This reflects a different seasonal deuterium excess (defined as d {delta}{sup 2}H - 8{delta}{sup 18}O), which has a mean value of 10.7{+-} 0.6 %0 in July, and a higher average value of 10.7 {+-} 0.6%0 in January and 5.8{+-} 0.5%0 in July, and a higher average value in stations with prevailing winter rains. Also, the slope becomes about 8 when summer and winter precipitation are considered all together. The altitude effect on the isotopic composition of precipitation on Mount Cameroon is re-examined. The model which best fits the data is based on the adiabatic condensation of the atmospheric vapour with a liquid/vapor ratio increasing from 0.15 at sea level to 0.45 at 4

  7. Natural variations in the rhenium isotopic composition of meteorites

    Liu, R.; Hu, L.; Humayun, M.


    Rhenium is an important element with which to test hypotheses of isotope variation. Historically, it has been difficult to precisely correct the instrumental mass bias in thermal ionization mass spectrometry. We used W as an internal standard to correct mass bias on the MC-ICP-MS, and obtained the first precise δ187Re values ( ±0.02‰, 2SE) for iron meteorites and chondritic metal. Relative to metal from H chondrites, IVB irons are systematically higher in δ187Re by 0.14 ‰. δ187Re for other irons are similar to H chondritic metal, although some individual samples show significant isotope fractionation. Since 185Re has a high neutron capture cross section, the effect of galactic cosmic-ray (GCR) irradiation on δ187Re was examined using correlations with Pt isotopes. The pre-GCR irradiation δ187Re for IVB irons is lower, but the difference in δ187Re between IVB irons and other meteoritic metal remains. Nuclear volume-dependent fractionation for Re is about the right magnitude near the melting point of iron, but because of the refractory and compatible character of Re, a compelling explanation in terms of mass-dependent fractionation is elusive. The magnitude of a nucleosynthetic s-process deficit for Re estimated from Mo and Ru isotopes is essentially unresolvable. Since thermal processing reduced nucleosynthetic effects in Pd, it is conceivable that Re isotopic variations larger than those in Mo and Ru may be present in IVBs since Re is more refractory than Mo and Ru. Thus, the Re isotopic difference between IVBs and other irons or chondritic metal remains unexplained.

  8. Magmatic recharge buffers the isotopic compositions against crustal contamination in formation of continental flood basalts

    Yu, Xun; Chen, Li-Hui; Zeng, Gang


    Isotopic compositions of continental flood basalts are essential to understand their genesis and to constrain the character of their mantle sources. Because of potential crustal contamination, it needs to be evaluated if and to which degree these basalts record original isotopic signals of their mantle sources and/or crustal signatures. This study examines the Sr, Nd, Hf, and Pb isotopic compositions of the late Cenozoic Xinchang-Shengzhou (XS) flood basalts, a small-scale continental flood basalt field in eastern China. The basalts show positive correlations between 87Sr/86Sr and 143Nd/144Nd, and negative correlations between 143Nd/144Nd and 176Hf/177Hf, which deviate from compositional arrays of crustal contamination and instead highlight variations in magmatic recharge intensity and mantle source compositions. The lava samples formed by high-volume magmatic recharge recorded signals of recycled sediments in the mantle source, which are characterized by moderate Ba/Th (91.9-106.5), excess 208Pb/204Pb relative to 206Pb/204Pb, and excess 176Hf/177Hf relative to 143Nd/144Nd. Thus, we propose that magmatic recharge buffers the original isotopic compositions of magmas against crustal contamination. Identifying and utilizing the isotope systematics of continental flood basalts generated by high volumes of magmatic recharge are thus crucial to trace their mantle sources.

  9. Corrosion Behavior of Mg-Al/TiC Composites in NaCl Solution

    L. A. Falcon


    Full Text Available The corrosion behavior of TiC particles reinforced Mg-Al alloy in 3.5% NaCl solution has been evaluated using electrochemical techniques. Tested alloys included an Mg-9Al (Mg AZ91E alloy with and without 56 wt. % TiC particles. Electrochemical techniques included potentiodynamic polarization curves, linear polarization resistance, electrochemical noise, and electrochemical impedance spectroscopy measurements. All techniques showed that the composite exhibited a lower corrosion rate than the base alloy. Evidence of galvanic effects that increased the composite corrosion rate was found between the matrix and the TiC particles. Additionally, the tendency to suffer from pitting corrosion was higher for the base alloy than that for the composite. Electrochemical impedance results showed the importance of adsorption/diffusion phenomena in both materials.

  10. Variation in the terrestrial isotopic composition and atomic weight of argon

    Böhlke, John Karl


    The isotopic composition and atomic weight of argon (Ar) are variable in terrestrial materials. Those variations are a source of uncertainty in the assignment of standard properties for Ar, but they provide useful information in many areas of science. Variations in the stable isotopic composition and atomic weight of Ar are caused by several different processes, including (1) isotope production from other elements by radioactive decay (radiogenic isotopes) or other nuclear transformations (e.g., nucleogenic isotopes), and (2) isotopic fractionation by physical-chemical processes such as diffusion or phase equilibria. Physical-chemical processes cause correlated mass-dependent variations in the Ar isotope-amount ratios (40Ar/36Ar, 38Ar/36Ar), whereas nuclear transformation processes cause non-mass-dependent variations. While atmospheric Ar can serve as an abundant and homogeneous isotopic reference, deviations from the atmospheric isotopic ratios in other Ar occurrences limit the precision with which a standard atomic weight can be given for Ar. Published data indicate variation of Ar atomic weights in normal terrestrial materials between about 39.7931 and 39.9624. The upper bound of this interval is given by the atomic mass of 40Ar, as some samples contain almost pure radiogenic 40Ar. The lower bound is derived from analyses of pitchblende (uranium mineral) containing large amounts of nucleogenic 36Ar and 38Ar. Within this interval, measurements of different isotope ratios (40Ar/36Ar or 38Ar/36Ar) at various levels of precision are widely used for studies in geochronology, water–rock interaction, atmospheric evolution, and other fields.

  11. Molybdenum isotopic composition of single silicon carbides from supernovae.

    Amari, S.; Clayton, R. N.; Davis, A. M.; Lewis, R. S.; Pellin, M. J.


    Presolar silicon carbide grains form in a variety of types of stars, including asymptotic giant branch red giant stars and supernovae. The dominant mechanisms of heavy element nucleosynthesis, the s-process and r-process, are thought to occur in AGB stars and supernovae, respectively. We have previously reported that mainstream SiC grains have strong enrichments in the s-process isotopes of Sr, Zr and Mo. We report here the first measurements of Mo isotopes in X-type SiC grains, which have previously been identified as having formed from supernova ejecta.

  12. Potassium Isotopic Compositions of NIST Potassium Standards and 40Ar/39Ar Mineral Standards

    Morgan, Leah; Tappa, Mike; Ellam, Rob; Mark, Darren; Higgins, John; Simon, Justin I.


    Knowledge of the isotopic ratios of standards, spikes, and reference materials is fundamental to the accuracy of many geochronological methods. For example, the 238U/235U ratio relevant to U-Pb geochronology was recently re-determined [1] and shown to differ significantly from the previously accepted value employed during age determinations. These underlying values are fundamental to accurate age calculations in many isotopic systems, and uncertainty in these values can represent a significant (and often unrecognized) portion of the uncertainty budget for determined ages. The potassium isotopic composition of mineral standards, or neutron flux monitors, is a critical, but often overlooked component in the calculation of K-Ar and 40Ar/39Ar ages. It is currently assumed that all terrestrial materials have abundances indistinguishable from that of NIST SRM 985 [2]; this is apparently a reasonable assumption at the 0.25per mille level (1s) [3]. The 40Ar/39Ar method further relies on the assumption that standards and samples (including primary and secondary standards) have indistinguishable 40K/39K values. We will present data establishing the potassium isotopic compositions of NIST isotopic K SRM 985, elemental K SRM 999b, and 40Ar/39Ar biotite mineral standard GA1550 (sample MD-2). Stable isotopic compositions (41K/39K) were measured by the peak shoulder method with high resolution MC-ICP-MS (Thermo Scientific NEPTUNE Plus), using the accepted value of NIST isotopic SRM 985 [2] for fractionation [4] corrections [5]. 40K abundances were measured by TIMS (Thermo Scientific TRITON), using 41K/39K values from ICP-MS measurements (or, for SRM 985, values from [2]) for internal fractionation corrections. Collectively these data represent an important step towards a metrologically traceable calibration of 40K concentrations in primary 40Ar/39Ar mineral standards and improve uncertainties by ca. an order of magnitude in the potassium isotopic compositions of standards.

  13. About the possibility of creating a continuous range of standards with different isotopic composition of carbon

    S. A. Sadykov


    Full Text Available It is established that the carbon isotopic composition in the formation of calcium carbonate is changed depending on the magnetic field strength. The formation of calcium carbonate occurred due to the interaction of calcium hydroxide with atmospheric carbon dioxide. The profile of isotopic relations13C/12C of the newly formed calcium carbonate is approximated by the equation of the parabola for certain values of tension solenoidal magnetic field. The possibility of creating standards with a continuous series of values of the content of carbon stable isotopes based on the data suggested.

  14. The isotopic composition of dissolved inorganic nitrogen in hydrothermal vent fluids

    Lehmann, M. F.; Bourbonnais, A.; Butterfield, D. A.


    Hydrothermal vent systems at mid-ocean ridges are sites with rapid rates of biomass production, sustained by chemolithoautotrophic bacteria at the base of the vent community food chains. The exact metabolic pathways, in particular those that involve nitrogen (N), and the rates at which the metabolic reactions take place are poorly constrained. In previous studies, very low 15N/14N ratios have been attributed to strong N isotope fractionation during chemosynthetic assimilation of ammonium. However, actual data on the N isotopic composition of dissolved inorganic N in vent systems, which could provide coherent information on the sources of N during chemolithoautotrophic biosynthesis, do not exist. Furthermore, the fate of hydrothermally discharged ammonium as well as that of nitrate that is mixed in from the ocean water column have not been the focus of much attention. As a consequence, little is known about N-cycle reactions within hydrothermal vent systems. We will present nitrate isotope (15N/14N and 18O/16O) data from various sites at Axial Volcano on the Juan de Fuca ridge. Their integration with nitrate concentration data suggests non-conservative behavior of nitrate along temperature gradients. Highest N and O isotope ratios (7.6 permil and 21.0 permil, respectively) are found in average diffuse fluids (17°C). Elevated N and O isotope ratios were associated with decreased nitrate concentrations and indicate a nitrate consuming process that fractionates both N and O isotopes. The ratio of 15N versus 18O enrichment in residual nitrate is, however, not consistent with previous reports on nitrate N versus O isotope fractionation during denitrification in the suboxic ocean water column, implying anomalous N and O isotope fractionation during denitrification in hydrothermal vent fluids and/or the presence of additional microbially mediated N transformations that affect the N and O isotope composition of the nitrate pool in the Axial hydrothermal vent system in a

  15. Zirconium isotope constraints on the composition of Theia and current Moon-forming theories

    Akram, W.; Schönbächler, M.


    The giant impact theory is the most widely recognized formation scenario of the Earth's Moon. Giant impact models based on dynamical simulations predict that the Moon acquired a significant amount of impactor (Theia) material, which is challenging to reconcile with geochemical data for O, Si, Cr, Ti and W isotopes in the Earth and Moon. Three new giant impact scenarios have been proposed to account for this discrepancy - hit-and-run impact, impact with a fast-spinning protoEarth and massive impactors - each one reducing the proportion of the impactor in the Moon compared to the original canonical giant impact model. The validity of each theory and their different dynamical varieties are evaluated here using an integrated approach that considers new high-precision Zr isotope measurements of lunar rocks, and quantitative geochemical modelling of the isotopic composition of the impactor Theia. All analysed lunar samples (whole-rock, ilmenite and pyroxene separates) display identical Zr isotope compositions to that of the Earth within the uncertainty of 13 ppm for 96Zr/90Zr (2σ weighted average). This 13 ppm upper limit is used to infer the most extreme isotopic composition that Theia could have possessed, relative to the Earth, for each of the proposed giant impact theories. The calculated Theian composition is compared with the Zr isotope compositions of different solar system materials in order to constrain the source region of the impactor. As a first order approximation, we show that all considered models (including the canonical) are plausible, alleviating the initial requirement for the new giant impact models. Albeit, the canonical and hit-and-run models are the most restrictive, suggesting that the impactor originated from a region close to the Earth. The fast-spinning protoEarth and massive impactor models are more relaxed and increase the allowed impactor distance from the Earth. Similar calculations carried out for O, Cr, Ti and Si isotope data support

  16. Water transport in protoplanetary disks and the hydrogen isotopic composition of chondrites

    Jacquet, Emmanuel


    The D/H ratios of carbonaceous chondrites, believed to reflect that of water in the inner early solar system, are intermediate between the protosolar value and that of most comets. The isotopic composition of cometary water has been accounted for by several models where the isotopic composition of water vapor evolved by isotopic exchange with hydrogen gas in the protoplanetary disk. However, the position and the wide variations of the distribution of D/H ratios in carbonaceous chondrites have yet to be explained. In this paper, we assume that the D/H composition of cometary ice was achieved in the disk building phase and model the further isotopic evolution of water in the inner disk in the classical T Tauri stage. Reaction kinetics compel isotopic exchange between water and hydrogen gas to stop at $\\sim$500 K, but equilibrated water can be transported to the snow line (and beyond) via turbulent diffusion and consequently mix with isotopically comet-like water. Under certain simplifying assumptions, we calcul...

  17. Preparation and corrosion resistance of MAO/Ni-P composite coat on Mg alloy

    Fan, Xizhi; Wang, Ying; Zou, Binglin; Gu, Lijian; Huang, Wenzhi; Cao, Xueqiang


    Microarc oxidation (MAO) coat was designed as an intermediate layer for the electroless plated Ni-P top coat, providing inert surface and necessary hardness for Mg alloy substrate. The composite coat was successfully prepared to improve the corrosion resistance of Mg alloy. The preparation and the characterization of the composite coat were investigated. The results show that the pre-treatment of MAO before electroless plating plays an important role in the deposition of compact composite coat. The activation (by HF solution) makes the MAO coat dense with uniform cracks which supply excellent bonding interface for Ni-P coat. Compared with monolithic MAO or Ni-P coat, the composite coat has excellent corrosion resistance and stable bonding interface. There is main pit corrosion at substrate after the corrosive medium penetrating through the whole coat. With the inert MAO interlayer, the electrochemical corrosion between the Ni-P and substrate is effectively inhibited.

  18. Pressure die cast graphite dispersed Al-Si-Mg alloy matrix composites

    Pillai, U.T.S. (Regional Research Lab. (CSIR), Trivandrum (India)); Pai, B.C. (Regional Research Lab. (CSIR), Trivandrum (India)); Kelukutty, V.S. (Regional Research Lab. (CSIR), Trivandrum (India)); Satyanarayana, K.G. (Regional Research Lab. (CSIR), Trivandrum (India))


    An improvement in casting of aluminium alloy graphite particulate composite synthesized by stir casting is discussed. About 15 wt.% graphite particles were dispersed in Al-Si-Mg (LM 25) alloy by the rheocasting technique. The composite ingots were used as a master alloy and diluted further with LM 25 alloy to obtain a 5 wt.% dispersion of graphite in the matrix. The composite ingots thus processed were subsequently remelted and pressure die cast into plates. Macroscopic and microscopic examination of the plates revealed fewer defects and a fine distribution of particles. The ultimate tensile strength evaluated in this composite was superior (132-136 MPa) to that of gravity die cast (85-95 MPa) composites. The fracture toughness of the composites was in the range 8-10 MPa m[sup 1/2]. (orig.)

  19. Thallium-isotopic compositions of euxinic sediments as a proxy for global manganese-oxide burial

    Owens, Jeremy D.; Nielsen, Sune G.; Horner, Tristan J.; Ostrander, Chadlin M.; Peterson, Larry C.


    Thallium (Tl) isotopes are a new and potentially powerful paleoredox proxy that may track bottom water oxygen conditions based on the global burial flux of manganese oxides. Thallium has a residence time of ∼20 thousand years, which is longer than the ocean mixing time, and it has been inferred that modern oxic seawater is conservative with respect to both concentration and isotopes. Marine sources of Tl have nearly identical isotopic values. Therefore, the Tl sinks, adsorption onto manganese oxides and low temperature oceanic crust alteration (the dominant seawater output), are the primary controls of the seawater isotopic composition. For relatively short-term, ∼million years, redox events it is reasonable to assume that the dominant mechanism that alters the Tl isotopic composition of seawater is associated with manganese oxide burial because large variability in low temperature ocean crust alteration is controlled by long-term, multi-million years, average ocean crust production rates. This study presents new Tl isotope data for an open ocean transect in the South Atlantic, and depth transects for two euxinic basins (anoxic and free sulfide in the water column), the Cariaco Basin and Black Sea. The Tl isotopic signature of open ocean seawater in the South Atlantic was found to be homogeneous with ε205Tl = -6.0 ± 0.3 (±2 SD, n = 41) while oxic waters from Cariaco and the Black Sea are -5.6 and -2.2, respectively. Combined with existing data from the Pacific and Arctic Oceans, our Atlantic data establish the conservatism of Tl isotopes in the global ocean. In contrast, partially- and predominantly-restricted basins reveal Tl isotope differences that vary between open-ocean (-6) and continental material (-2) ε205Tl, scaling with the degree of restriction. Regardless of the differences between basins, Tl is quantitatively removed from their euxinic waters below the chemocline. The burial of Tl in euxinic sediments is estimated to be an order of magnitude

  20. The oxygen isotopic composition of the Sun inferred from captured solar wind.

    McKeegan, K D; Kallio, A P A; Heber, V S; Jarzebinski, G; Mao, P H; Coath, C D; Kunihiro, T; Wiens, R C; Nordholt, J E; Moses, R W; Reisenfeld, D B; Jurewicz, A J G; Burnett, D S


    All planetary materials sampled thus far vary in their relative abundance of the major isotope of oxygen, (16)O, such that it has not been possible to define a primordial solar system composition. We measured the oxygen isotopic composition of solar wind captured and returned to Earth by NASA's Genesis mission. Our results demonstrate that the Sun is highly enriched in (16)O relative to the Earth, Moon, Mars, and bulk meteorites. Because the solar photosphere preserves the average isotopic composition of the solar system for elements heavier than lithium, we conclude that essentially all rocky materials in the inner solar system were enriched in (17)O and (18)O, relative to (16)O, by ~7%, probably via non-mass-dependent chemistry before accretion of the first planetesimals.

  1. Chronological study of oxygen isotope composition for the solar protoplanetary disk recorded in a fluffy Type A CAI from Vigarano

    Kawasaki, Noriyuki; Itoh, Shoichi; Sakamoto, Naoya; Yurimoto, Hisayoshi


    Fluffy Type A Ca-Al-rich inclusions (CAIs) containing reversely zoned melilite crystals are suggested to be aggregates of direct condensates from solar nebular gas. We conducted an investigation of 26Al-26Mg systematics of a fluffy Type A CAI from Vigarano, named V2-01, with known oxygen isotopic distributions of reversely zoned melilite crystals; we also conducted oxygen isotope measurements of coexisting minerals. Two of six reversely zoned melilite crystals show continuous variations in magnesium isotopic composition, with δ25Mg decreasing along the inferred direction of crystal growth, which supports the idea that they originated through condensation. Petrography suggests that the constituent minerals of V2-01 formed in the following order: first spinel and fassaite enclosed by melilite, then reversely zoned melilite crystals, and spinel and diopside in the Wark-Lovering rim. The spinel enclosed by melilite has 16O-rich compositions (Δ17O ∼ -24‰) and on an Al-Mg evolutionary diagram plots along model isochron with an initial value of (26Al/27Al)0 = (5.6 ± 0.2) × 10-5. The fassaite enclosed by melilite crystals shows variable oxygen isotopic compositions (Δ17O ∼ -12‰ and -17‰) and plots on an isochron with (26Al/27Al)0 = (5.6 ± 0.2) × 10-5. The oxygen isotopic compositions of reversely zoned melilite showed continuous variations in Δ17O along the inferred direction of crystal growth, suggesting that surrounding nebular gas, during the formation of the reversely zoned melilite, changed from 16O-poor (Δ17O values larger than -10‰) to 16O-rich (Δ17O ∼ -25‰). The six reversely zoned melilite crystals show indistinguishable initial 26Al/27Al values with an average (26Al/27Al)0 of (4.7 ± 0.3) × 10-5, which is clearly distinguishable from the value of enclosed spinel and fassaite, indicating a younger formation age than the enclosed spinel and fassaite. The spinel and diopside from the Wark-Lovering rim show 16O-rich compositions (Δ17O

  2. Zinc isotope fractionation during mantle melting and constraints on the Zn isotope composition of Earth's upper mantle

    Wang, Ze-Zhou; Liu, Sheng-Ao; Liu, Jingao; Huang, Jian; Xiao, Yan; Chu, Zhu-Yin; Zhao, Xin-Miao; Tang, Limei


    compositions of MORB. Therefore, preferential melting of spinel in the peridotites may account for the Zn isotopic difference between spinel peridotites and basalts. By contrast, the absence of Zn isotope fractionation between silicate minerals suggests that Zn isotopes are not significantly fractionated during partial melting of spinel-free garnet-facies mantle. If the studied non-metasomatized peridotites represent the refractory upper mantle, mass balance calculation shows that the depleted MORB mantle (DMM) has a δ66Zn value of +0.20 ± 0.05‰ (2SD), which is lighter than the primitive upper mantle (PUM) estimated in previous studies (+0.28 ± 0.05‰, 2SD, Chen et al., 2013b; +0.30 ± 0.07‰, 2SD, Doucet et al., 2016). This indicates that the Earth's upper mantle has a heterogeneous Zn isotopic composition vertically, which is probably due to shallow mantle melting processes.

  3. Variation in the Carbon Isotope Compositions of Phytoliths Across a Climate Gradient

    Webb, E. A.; Longstaffe, F. J.


    The carbon isotope composition of plant organic matter within a single species may vary in response to changes in temperature, relative humidity, precipitation amount, altitude, nutrient availability, light levels and amount of canopy. All of these factors affect the rate of carbon assimilation during photosynthesis. Silica phytoliths, which form in the cells and intercellular spaces of terrestrial plants, occlude some of the plant's organic matrix. Carbon sequestered in phytoliths is protected from decay and may therefore be preserved in soils after most other plant material has decomposed. The carbon isotope composition of phytoliths may therefore have potential as an archive of climatic conditions during soil accumulation. In this study, the carbon isotope compositions of modern plant tissues and their phytoliths are compared for the C4 grass species Calamovilfa longifolia across the climate gradient of the North American prairies. The carbon isotope compositions of C. longifolia tissues ranged from -15 to -10 permil, with lower values being most typical of leaf tissues and with greater variability occurring in samples from lower latitudes. Carbonaceous compounds occluded in the phytoliths, by comparison, were depleted of carbon-13 by 5 to 15 permil relative to the tissues from the same plant. Understanding the causes of this offset, which is significantly larger and more variable than reported in previous studies, is necessary before the full potential of the carbon-isotope phytolith proxy can be realized.

  4. SIMSISH technique does not alter the apparent isotopic composition of bacterial cells.

    Olivier Chapleur

    Full Text Available In order to identify the function of uncultured microorganisms in their environment, the SIMSISH method, combining in situ hybridization (ISH and nanoscale secondary ion mass spectrometry (nanoSIMS imaging, has been proposed to determine the quantitative uptake of specific labelled substrates by uncultured microbes at the single cell level. This technique requires the hybridization of rRNA targeted halogenated DNA probes on fixed and permeabilized microorganisms. Exogenous atoms are introduced into cells and endogenous atoms removed during the experimental procedures. Consequently differences between the original and the apparent isotopic composition of cells may occur. In the present study, the influence of the experimental procedures of SIMSISH on the isotopic composition of carbon in E. coli cells was evaluated with nanoSIMS and compared to elemental analyser-isotopic ratio mass spectrometer (EA-IRMS measurements. Our results show that fixation and hybridization have a very limited, reproducible and homogeneous influence on the isotopic composition of cells. Thereby, the SIMSISH procedure minimizes the contamination of the sample by exogenous atoms, thus providing a means to detect the phylogenetic identity and to measure precisely the carbon isotopic composition at the single cell level. This technique was successfully applied to a complex sample with double bromine - iodine labelling targeting a large group of bacteria and a specific archaea to evaluate their specific (13C uptake during labelled methanol anaerobic degradation.

  5. SIMSISH technique does not alter the apparent isotopic composition of bacterial cells.

    Chapleur, Olivier; Wu, Ting-Di; Guerquin-Kern, Jean-Luc; Mazéas, Laurent; Bouchez, Théodore


    In order to identify the function of uncultured microorganisms in their environment, the SIMSISH method, combining in situ hybridization (ISH) and nanoscale secondary ion mass spectrometry (nanoSIMS) imaging, has been proposed to determine the quantitative uptake of specific labelled substrates by uncultured microbes at the single cell level. This technique requires the hybridization of rRNA targeted halogenated DNA probes on fixed and permeabilized microorganisms. Exogenous atoms are introduced into cells and endogenous atoms removed during the experimental procedures. Consequently differences between the original and the apparent isotopic composition of cells may occur. In the present study, the influence of the experimental procedures of SIMSISH on the isotopic composition of carbon in E. coli cells was evaluated with nanoSIMS and compared to elemental analyser-isotopic ratio mass spectrometer (EA-IRMS) measurements. Our results show that fixation and hybridization have a very limited, reproducible and homogeneous influence on the isotopic composition of cells. Thereby, the SIMSISH procedure minimizes the contamination of the sample by exogenous atoms, thus providing a means to detect the phylogenetic identity and to measure precisely the carbon isotopic composition at the single cell level. This technique was successfully applied to a complex sample with double bromine - iodine labelling targeting a large group of bacteria and a specific archaea to evaluate their specific (13)C uptake during labelled methanol anaerobic degradation.

  6. Mg-Doped Hydroxyapatite/Chitosan Composite Coated 316L Stainless Steel Implants for Biomedical Applications.

    Sutha, S; Dhineshbabu, N R; Prabhu, M; Rajendran, V


    In this investigation, ultrasonication process was used for the synthesis of magnesium doped nano-hydroxyapatite (MH) (0, 1, 2, and 3 mol% of Mg concentration) particles with controlled size and surface morphology. The size of the prepared MH particles was in the range of 20-100 nm with narrow distribution. Increase in the concentration of Mg reduced the particle size distribution from 60 to 40 nm. On incorporation of Mg in HAp lattice, an increase of 20-66 nm in specific surface area was observed in microporous HAp particles. XRF and XRD patterns reveal that the particles possess stoichiometric composition with reduced crystallinity with respect to the Mg concentration. Surface morphology of MH/chitosan (CTS) coated implant was found to be uniform without any defects. The corrosion rate of the implant decreased with increase in Mg concentration. The in vitro formation of bonelike apatite layer on the surface of the MH/CTS coated implant was observed from simulated body fluid studies. The antimicrobial activity of the MH/CTS composites against gram-positive and gram-negative bacterial strains indicated that increasing Mg concentration enhanced antimicrobial properties. Nanoindentation analysis of apatite coated implant surface reveals that the mechanical property depends on the concentration of magnesium in HAp. From the cytotoxicity analysis against NIH 3T3 fibroblast, it was observed that the Mg incorporated HAp/CTS composite was less toxic than the MHO/CTS composite. From this result, it was concluded that the MH/CTS nanocomposites coated implant is the excellent material for implants.

  7. Investigation of the Mg isotopes using the shell-model-like approach in relativistic mean field theory

    Bai, Hong-Bo; Zhang, Zhen-Hua; Li, Xiao-Wei


    Ground state properties for Mg isotopes, including binding energies, one- and two-neutron separation energies, pairing energies, nuclear matter radii and quadrupole deformation parameters, are obtained from the self-consistent relativistic mean field (RMF) model with the pairing correlations treated by a shell-mode-like approach (SLAP), in which the particle-number is conserved and the blocking effects are treated exactly. The experimental data, including the binding energies and the one- and two-neutron separation energies, which are sensitive to the treatment of pairing correlations and block effects, are well reproduced by the RMF+SLAP calculations. Supported by NSFC (11465001,11275098, 11275248, 11505058,11165001) and Natural Science Foundation of Inner Mongolia of China (2016BS0102)

  8. Isotope shifts of the (3s3p) 3P0,1,2-(3s4s) 3S1 Mg I transitions

    He, Ming; Therkildsen, Kasper T.; Jensen, Brian B.;


    We report measurements of the isotope shifts of the (3s3p)P30,1,2-(3s4s)S31 Mg I transitions for the stable isotopes M24g (I=0) , M25g (I=5/2) , and M26g (I=0) . Furthermore, the M25g S31 hyperfine coefficient A(S31)=(-321.6±1.5)MHz is extracted and found to be in excellent agreement with state...

  9. Spurious and functional correlates of the isotopic composition of a generalist across a tropical rainforest landscape

    Poirson Evan K


    Full Text Available Abstract Background The isotopic composition of generalist consumers may be expected to vary in space as a consequence of spatial heterogeneity in isotope ratios, the abundance of resources, and competition. We aim to account for the spatial variation in the carbon and nitrogen isotopic composition of a generalized predatory species across a 500 ha. tropical rain forest landscape. We test competing models to account for relative influence of resources and competitors to the carbon and nitrogen isotopic enrichment of gypsy ants (Aphaenogaster araneoides, taking into account site-specific differences in baseline isotope ratios. Results We found that 75% of the variance in the fraction of 15N in the tissue of A. araneoides was accounted by one environmental parameter, the concentration of soil phosphorus. After taking into account landscape-scale variation in baseline resources, the most parsimonious model indicated that colony growth and leaf litter biomass accounted for nearly all of the variance in the δ15N discrimination factor, whereas the δ13C discrimination factor was most parsimoniously associated with colony size and the rate of leaf litter decomposition. There was no indication that competitor density or diversity accounted for spatial differences in the isotopic composition of gypsy ants. Conclusion Across a 500 ha. landscape, soil phosphorus accounted for spatial variation in baseline nitrogen isotope ratios. The δ15N discrimination factor of a higher order consumer in this food web was structured by bottom-up influences - the quantity and decomposition rate of leaf litter. Stable isotope studies on the trophic biology of consumers may benefit from explicit spatial design to account for edaphic properties that alter the baseline at fine spatial grains.

  10. The isotopic composition of methane in the stratosphere: high-altitude balloon sample measurements

    T. Röckmann


    Full Text Available The isotopic composition of stratospheric methane has been determined on a large suite of air samples from stratospheric balloon flights covering subtropical to polar latitudes and a time period of 16 yr. 154 samples were analyzed for δ13C and 119 samples for δD, increasing the previously published dataset for balloon borne samples by an order of magnitude, and more than doubling the total available stratospheric data (including aircraft samples published to date. The samples also cover a large range in mixing ratio from tropospheric values near 1800 ppb down to only 250 ppb, and the strong isotope fractionation processes accordingly increase the isotopic composition up to δ13C = −14‰ and δD = +190‰, the largest enrichments observed for atmospheric CH4 so far. When analyzing and comparing kinetic isotope effects (KIEs derived from single balloon profiles, it is necessary to take into account the residence time in the stratosphere in combination with the observed mixing ratio and isotope trends in the troposphere, and the range of isotope values covered by the individual profile. The isotopic composition of CH4 in the stratosphere is affected by both chemical and dynamical processes. This severely hampers interpretation of the data in terms of the relative fractions of the three important sink mechanisms (reaction with OH, O(1D and Cl. It is shown that a formal sink partitioning using the measured data severely underestimates the fraction removed by OH, which is likely due to the insensitivity of the measurements to the kinetic fractionation in the lower stratosphere. Full quantitative interpretation of the CH4 isotope data in terms of the three sink reactions requires a global model.

  11. Influence of Si on Interfacial Combination of SiCp/Al-Mg-Si Composite

    Han Jianmin; Li Ronghua; Li Mingwei; Cui Shihai; Li Weijing; Wang Jinhua


    The scanning electron microscopy (SEM) analysis results of Si distribution in the interface between SiC reinforcements and aluminum matrix of a stir casting SiCp/Al-Mg-Si composite were presented. Results show that there is Si precipitation deposit on the interface of the composite and Si connects with SiC reinforcements in one side and connects with aluminum matrix in the other side. Si phase plays as a connecting bridge, which contributes to the interfacial combination of SiCp/Al composite.

  12. Hydrogen isotope composition of mantle-derived mica megacryst from ion micro probe analysis

    夏群科; 陈道公; 支霞臣


    The hydrogen isotope composition of a mantle-derived mica megacryst from Cenozoic basanite from NUshan, Anhui Province has been determined by ion micro probe. The results demonstrate that δD and water content of the megacryst were heterogeneous on the micro scale, which resulted from reaction with meteoric water after being brought to the surface. The primary δD of mica megacrysts was about-23‰, suggesting the recycled crustal materials in its source. By combining these values with those of other researchers, it is believed that the hydrogen isotope composition of the mantle is heterogeneous at least on the large scale.

  13. Sulfur isotopic composition of modern seafloor hydrothermal sediment and its geological significance

    曾志刚; 李军; 蒋富清; 秦蕴珊; 翟世奎


    A total of 1 264 sulfur isotopic values for modem seafloor hydrothermel sediments from different hydrothermal fidds have been collected. On this basis, combining our sulfur isotpic data for surface hydrothermal sediments from the Jade hydrohtermal field in the Okinawa Trough and the TAG hydrothermal field in the Mid-Atlantic Ridge, respectively, and comparing the sulfur isotopic compositions and analyzing their sources of sulfur in seafloor hydrothermal sediments from different geologic-tectonic setting, the results show that: ( 1 ) sulfur isotopic values of sulfides and sulfates in modern seafloor hydrothermal sediments are concentrated in a narrow range, δ34S values of sulfides vary from l × 10-3 to 9 × 10- 3, with a mean of 4.5 × 10- 3 ( n = 1 042), δ34S values of sulfates vary from 19 × 10- 3 to 24× 10-3, with a mean of 21.3× 10-3 (n =217); (2) comparing the sulfur isotopic compositions of hydrothermal sediments from the sediment-hosted hydrothermal fields, the range of sulfur isotopic values for hydrothermal sediments from the sediment-free hydrothermal fields is narrow relatively; (3) the differences of sulfur isotopic compositions in sulfides from different hydrothermal fields show the differences in the sources of sulfur. The sulfur of hydrothermal sulfides in the sediment-free mid-ocean ridges is mainly from mid-ocean ridge basalt, and partially from the reduced seawater sulfate, and it is the result of partially reduced seawater sulfate mixed with basaltic sulfur. In the sediment-hosted nid-ocean ridges and the back-arc basins, the volcanics, the sediments and the organic matters also can offer their sulfur for forming hydrothermal sulfides; (4) the variations of sulfur isotopic compositions and the different sources of sulfur for hydrothermal sediments may be attributed to the various physical-chemical characteristics of hydrothermal fluids, the magmatic evolution and the different geologic-tectonic settings of seafloor hydrothermal systems.

  14. Mg/Casea surface temperatures during the Marine Isotope Stage 31 collapse of the Ross Ice Shelf

    Dunbar, G. B.


    The recovery of the AND-1b and CRP-1 drill cores from the Southwest Ross Sea highlighted the potential instability in of the Ross Ice Shelf and the West Antarctic Ice Sheet it buttresses. Both cores recovered a few individuals of the planktonic foraminifera Neogloboquadrina pachyderma from marine isotope stage (MIS) 31. This interval is significant because it marks the youngest occurrence of open ocean diatom sediment at AND-1b, which is now situated under the McMurdo Ice Shelf, indicating a substantial retreat of the Ross Ice Shelf occurred during this interglacial. However, sediment deposited after MIS 31 at both sites is represented only by glacial-dominated sediment, suggesting a critical environmental threshold had been crossed enabling the Ross Ice Shelf to form and persist. Numerical modeling by Pollard and DeConto (Nature, 2009) suggested that sub-ice oceanic melting is a critical element in the stability of ice shelves and that "WAIS will begin to collapse when nearby ocean temperatures warm by roughly 5°C." Laser ablation ICPMS measurement of the Mg/Ca content of N. pachyderma shows that although there is considerable heterogeneity in the distribution of Mg in their tests the mean Mg/Ca of a sample population appears proportional to calcification temperature. By empirically calibrating Mg/Ca in CRP-1 N. pachyderma against values measured in modern populations collected from Ross Sea and Southern Ocean sites with SSTs ranging from 1.2°C to 14°C it is concluded that SST during MIS 31 was warmer than today by 5-9°C, consistent with model projections.

  15. Plutonium isotopes in the atmosphere of Central Europe: Isotopic composition and time evolution vs. circulation factors.

    Kierepko, Renata; Mietelski, Jerzy W; Ustrnul, Zbigniew; Anczkiewicz, Robert; Wershofen, Herbert; Holgye, Zoltan; Kapała, Jacek; Isajenko, Krzysztof


    This paper reports evidence of Pu isotopes in the lower part of the troposphere of Central Europe. The data were obtained based on atmospheric aerosol fraction samples collected from four places in three countries (participating in the informal European network known as the Ring of Five (Ro5)) forming a cell with a surface area of about 200,000km(2). We compared our original data sets from Krakow (Poland, 1990-2007) and Bialystok (Poland, 1991-2007) with the results from two other locations, Prague (Czech Republic; 1997-2004) and Braunschweig (Germany; 1990-2003) to find time evolution of the Pu isotopes. The levels of the activity concentration for (238)Pu and for ((239+240))Pu were estimated to be a few and some tens of nBqm(-3), respectively. However, we also noted some results were much higher (even about 70 times higher) than the average concentration of (238)Pu in the atmosphere. The achieved complex data sets were used to test a new approach to the problem of solving mixing isotopic traces from various sources (here up to three) in one sample. Results of our model, supported by mesoscale atmospheric circulation parameters, suggest that Pu from nuclear weapon accidents or tests and nuclear burnt-up fuel are present in the air.

  16. Nonlinear temperature characteristic of thermal expansion of Grf/Mg composites

    SONG Mei-hui; XIU Zi-yang; WU Gao-hui; CHEN Guo-qin


    Graphite fiber reinforced magnesium matrix(Grf/Mg) composites were fabricated by squeeze casting technology. M40 graphite fibers were reinforced to AZ91D and ZM6, their thermal expansion behaviors of M40/AZ91D and M40/ZM6 composites in the temperature range from 20 to 490 ℃ were investigated. The results show that the interfacial species and thermal stress have significant influence on the thermal expansion behavior of the composites. Simultaneously, the longitudinal coefficient of thermal expansion of Grf/Mg composites are affected by the thermal stress, interfacial species and yield strength of matrix alloy, it also decreases with increasing temperature and descending rate of longitudinal coefficient of thermal expansion(CTEs) of Grf/Mg composites changed in different temperature ranges. In terms of different descending rates, the curve of coefficient of thermal expansion vs temperature can be divided into three stages. The matrix alloys M40/AZ91D and M40/ZM6 yield at 170 and 155℃ in the thermal expansion, respectively.

  17. The effect of phosphomonoesterases on the oxygen isotope composition of phosphate

    von Sperber, Christian; Kries, Hajo; Tamburini, Federica; Bernasconi, Stefano M.; Frossard, Emmanuel


    Plants and microorganisms under phosphorus (P) stress release extracellular phosphatases as a strategy to acquire inorganic phosphate (Pi). These enzymes catalyze the hydrolysis of phosphoesters leading to a release of Pi. During the enzymatic hydrolysis an isotopic fractionation (ε) occurs leaving an imprint on the oxygen isotope composition of the released Pi which might be used to trace phosphorus in the environment. Therefore, enzymatic assays with acid phosphatases from wheat germ and potato tuber and alkaline phosphatase from Escherichia coli were prepared in order to determine the oxygen isotope fractionation caused by these enzymes. Adenosine 5‧ monophosphate and glycerol phosphate were used as substrates. The oxygen isotope fractionation caused by acid phosphatases is 20-30‰ smaller than for alkaline phosphatases, resulting in a difference of 5-7.5‰ in δ18O of Pi depending on the enzyme. We attribute the enzyme dependence of the isotopic fractionation to distinct reaction mechanisms of the two types of phosphatases. The observed difference is large enough to distinguish between the two enzymatic processes in environmental samples. These findings show that the oxygen isotope composition of Pi can be used to trace different enzymatic processes, offering an analytical tool that might contribute to a better understanding of the P-cycle in the environment.

  18. Chemical and Isotopic Composition of Waters and Dissolved Gases in Some Thermal Springs of Sicily and Adjacent Volcanic Islands, Italy

    Grassa, Fausto; Capasso, Giorgio; Favara, Rocco; Inguaggiato, Salvatore


    Hydrochemical (major and some minor constituents), stable isotope ([InlineMediaObject not available: see fulltext.] and [InlineMediaObject not available: see fulltext.], δ13CTDIC total dissolved inorganic carbon) and dissolved gas composition have been determined on 33 thermal discharges located throughout Sicily (Italy) and its adjacent islands. On the basis of major ion contents, four main water types have been distinguished: (1) a Na-Cl type; (2) a Ca-Mg > Na-SO4-Cl type; (3) a Ca-Mg-HCO3 type and (4) a Na-HCO3 type water. Most waters are meteoric in origin or resulting from mixing between meteoric water and heavy-isotope end members. In some samples, δ 18O values reflect the effects of equilibrium processes between thermal waters and rocks (positive 18O-shift) or thermal waters and CO2 (negative 18O-shift). Dissolved gas composition indicates the occurrence of gas/water interaction processes in thermal aquifers. N2/O2 ratios higher than air-saturated water (ASW), suggest the presence of geochemical processes responsible for dissolved oxygen consumption. High CO2 contents (more than 3000 cc/litre STP) dissolved in the thermal waters indicate the presence of an external source of carbon dioxide-rich gas. TDIC content and δ 13C TDIC show very large ranges from 4.6 to 145.3 mmol/Kg and from 10.0‰ and 2.8‰, respectively. Calculated values indicate the significant contribution from a deep source of carbon dioxide inorganic in origin. Interaction with Mediterranean magmatic CO2 characterized by heavier carbon isotope ratios ([InlineMediaObject not available: see fulltext.] value from -3 to 0‰ vs V-PDB (CAPASSO et al., 1997, GIAMMANCO et al., 1998; INGUAGGIATO et al., 2000) with respect to MORB value and/or input of CO2-derived from thermal decomposition of marine carbonates have been inferred.

  19. Characterizing the Effect of Shock on Isotopic Ages. 2; Mg-Suite Troctolite Major Elements

    Edmunson, Jennifer; Cohen, Barbara


    Two troctolites from the lunar magnesium suite (Mg-suite), 76335 and 76535, have Sm-147-ND-143 and Rb-87- Sr-87 ages that do not indicate the same age for their respective sample. In the case of 76335, the Sm-147-ND-143 age is 4278 +/- 60 Ma, but the Rb-87-Sr-87 data does not reveal an isochron]. For 76535, the Sm-147-ND-143 age is significantly younger (4260 +/- 60 Ma) than the Rb-87- Sr-87 age (4570 +/- 70 Ma, Lambda = 1.402x10(exp -11)). This study was designed to discover why the Sm-147-ND-143 and Rb-87-Sr-87 ages did not match for each individual sample.

  20. Carbon isotope composition of latex does not reflect temporal variations of photosynthetic carbon isotope discrimination in rubber trees (Hevea brasiliensis).

    Kanpanon, Nicha; Kasemsap, Poonpipope; Thaler, Philippe; Kositsup, Boonthida; Gay, Frédéric; Lacote, Régis; Epron, Daniel


    Latex, the cytoplasm of laticiferous cells localized in the inner bark of rubber trees (Hevea brasiliensis Müll. Arg.), is collected by tapping the bark. Following tapping, latex flows out of the trunk and is regenerated, whereas in untapped trees, there is no natural exudation. It is still unknown whether the carbohydrates used for latex regeneration in tapped trees is coming from recent photosynthates or from stored carbohydrates, and in the former case, it is expected that latex carbon isotope composition of tapped trees will vary seasonally, whereas latex isotope composition of untapped trees will be more stable. Temporal variations of carbon isotope composition of trunk latex (δ(13)C-L), leaf soluble compounds (δ(13)C-S) and bulk leaf material (δ(13)C-B) collected from tapped and untapped 20-year-old trees were compared. A marked difference in δ(13)C-L was observed between tapped and untapped trees whatever the season. Trunk latex from tapped trees was more depleted (1.6‰ on average) with more variable δ(13)C values than those of untapped trees. δ(13)C-L was higher and more stable across seasons than δ(13)C-S and δ(13)C-B, with a maximum seasonal difference of 0.7‰ for tapped trees and 0.3‰ for untapped trees. δ(13)C-B was lower in tapped than in untapped trees, increasing from August (middle of the rainy season) to April (end of the dry season). Differences in δ(13)C-L and δ(13)C-B between tapped and untapped trees indicated that tapping affects the metabolism of both laticiferous cells and leaves. The lack of correlation between δ(13)C-L and δ(13)C-S suggests that recent photosynthates are mixed in the large pool of stored carbohydrates that are involved in latex regeneration after tapping.

  1. Coupled isotopes of plant wax and hemicellulose markers record information on relative humidity and isotopic composition of precipitation

    M. Tuthorn


    Full Text Available The δ2H isotopic composition of leaf waxes is used increasingly for paleohydrological and -climate reconstructions. However, it is challenging to disentangle past changes in the isotopic composition of precipitation and changes in evapotranspirative enrichment of leaf water. We analyzed δ2H on n-alkanes and fatty acids in topsoils along a climate transect in Argentina, for which we had previously measured δ18O on plant-derived sugars. Our results indicate that leaf wax biomarker δ2H values (δ2Hlipids primarily reflect δ2Hsource water (precipitation, but are modulated by evapotranspirative enrichment. A mechanistic model is able to produce the main trends in δ2Hlipids along the transect, but seems to slightly underestimate evapotranspirative enrichment in arid regions and overestimate it in grass-dominated ecosystems. Furthermore, the (i coupling of the δ2Hlipid and δ18Osugar biomarker results and (ii application of biosynthetic fractionation factors allows calculating the δ2H-δ18O isotopic composition of leaf water along the transect. This also yields the deuterium excess (d excess of leaf water, which mainly reflects evapotranspirative enrichment, and can be used to model relative air humidity (RH. The high correlation of modeled (reconstructed based on biomarker results and measured RH, as well as the good agreement between modeled and actual δ2H and δ18O of precipitation along the transect lends support to the coupled δ2Hlipid and δ18Osugar biomarker approach for future paleoclimate research.

  2. Molybdenum Isotopic Composition of the Archean Mantle As Inferred from Studies of Komatiites

    Greber, N. D.; Puchtel, I. S.; Nagler, T. F.; Mezger, K.


    Molybdenum isotopic composition has been shown to be a powerful tool in studies of planetary processes, e.g. estimating core formation temperatures [1,2]. However, Mo isotope compositions of terrestrial reservoirs are not well constrained. In order to better constrain the Mo isotopic composition of the early Earth's mantle, komatiites from four locations were analyzed for their Mo concentrations and isotopic compositions. Komatiites are particularly appropriate for this type of study because they formed by high degrees of partial melting of the mantle leading to a complete base metal sulfide removal from the residual mantle and the production of sulfur-undersaturated melts and thus a quantitative removal of Mo from the source into the melt. All samples, except for two strongly altered specimens specifically chosen to study the effects of secondary alteration, are very fresh having preserved most of their primary mineralogy. The Mo concentrations in komatiites range from 10 to 120 ng/g. Fresh komatiites have lighter δ98Mo (NIST SRM 3134 = 0.25‰, [3]) than altered samples. The estimated primary Mo isotope compositions of the studied komatiite melts range from 0.02 ± 0.16‰ to 0.19 ± 0.14‰ and are therefore indistinguishable within analytical uncertainty (2SD) from published values for chondritic meteorites (0.09 ± 0.04 ‰; 2SD; [2]) and lighter than the proposed average for Earth's continental crust (0.3 to 0.4‰ [4]). All data combined, although overlapping in errors, show a consistent trend of lighter δ98Mo and lower Mo concentrations in more melt-depleted mantle sources, indicating incompatible behaviour of Mo and preferential mobilization of heavy Mo isotopes during mantle melting. [1] Hin et al. (2013) EPSL, 379 [2] Burkhardt et al. (2014) EPSL, 391 [3] Nägler, et al. (2014) GGR, 38. [4] Voegelin et al. (2014) Lithos, 190-191.

  3. Lead isotope studies of the Guerrero composite terrane, west-central Mexico: implications for ore genesis

    Potra, Adriana; Macfarlane, Andrew W.


    New thermal ionization mass spectrometry and multi-collector inductively coupled plasma mass spectrometry Pb isotope analyses of three Cenozoic ores from the La Verde porphyry copper deposit located in the Zihuatanejo-Huetamo subterrane of the Guerrero composite terrane are presented and the metal sources are evaluated. Lead isotope ratios of 3 Cenozoic ores from the El Malacate and La Esmeralda porphyry copper deposits located in the Zihuatanejo-Huetamo subterrane and of 14 ores from the Zimapan and La Negra skarn deposits from the adjoining Sierra Madre terrane are also presented to look for systematic differences in the lead isotope trends and ore metal sources among the proposed exotic tectonostratigraphic terranes of southern Mexico. Comparison among the isotopic signatures of ores from the Sierra Madre terrane and distinct subterranes of the Guerrero terrane supports the idea that there is no direct correlation between the distinct suspect terranes of Mexico and the isotopic signatures of the associated Cenozoic ores. Rather, these Pb isotope patterns are interpreted to reflect increasing crustal contribution to mantle-derived magmas as the arc advanced eastward onto a progressively thicker continental crust. The lead isotope trend observed in Cenozoic ores is not recognized in the ores from Mesozoic volcanogenic massive sulfide and sedimentary exhalative deposits. The Mesozoic ores formed prior to the amalgamation of the Guerrero composite terrane to the continental margin, which took place during the Late Cretaceous, in intraoceanic island arc and intracontinental marginal basin settings, while the Tertiary deposits formed after this event in a continental arc setting. Lead isotope ratios of the Mesozoic and Cenozoic ores appear to reflect these differences in tectonic setting of ore formation. Most Pb isotope values of ores from the La Verde deposit (206Pb/204Pb = 18.674-18.719) are less radiogenic than those of the host igneous rocks, but plot within the

  4. Unexpected variations in the triple oxygen isotope composition of stratospheric carbon dioxide.

    Wiegel, Aaron A; Cole, Amanda S; Hoag, Katherine J; Atlas, Elliot L; Schauffler, Sue M; Boering, Kristie A


    We report observations of stratospheric CO2 that reveal surprisingly large anomalous enrichments in (17)O that vary systematically with latitude, altitude, and season. The triple isotope slopes reached 1.95 ± 0.05(1σ) in the middle stratosphere and 2.22 ± 0.07 in the Arctic vortex versus 1.71 ± 0.03 from previous observations and a remarkable factor of 4 larger than the mass-dependent value of 0.52. Kinetics modeling of laboratory measurements of photochemical ozone-CO2 isotope exchange demonstrates that non-mass-dependent isotope effects in ozone formation alone quantitatively account for the (17)O anomaly in CO2 in the laboratory, resolving long-standing discrepancies between models and laboratory measurements. Model sensitivities to hypothetical mass-dependent isotope effects in reactions involving O3, O((1)D), or CO2 and to an empirically derived temperature dependence of the anomalous kinetic isotope effects in ozone formation then provide a conceptual framework for understanding the differences in the isotopic composition and the triple isotope slopes between the laboratory and the stratosphere and between different regions of the stratosphere. This understanding in turn provides a firmer foundation for the diverse biogeochemical and paleoclimate applications of (17)O anomalies in tropospheric CO2, O2, mineral sulfates, and fossil bones and teeth, which all derive from stratospheric CO2.

  5. Computation assisted design of favored composition for ternary Mg-Cu-Y metallic glass formation.

    Wang, Q; Li, J H; Liu, B X


    With the aid of ab initio calculations, a realistic interatomic potential was constructed for the Mg-Cu-Y ternary system under the proposed formalism of smoothed and long-range second-moment approximation of tight-binding. Taking the potential as the starting base, an atomistic computation/simulation route was developed for designing favored and optimized compositions for Mg-Cu-Y metallic glass formation. Simulations revealed that the physical origin of metallic glass formation is the collapse of crystalline lattice when solute concentration exceeds a critical value, thus leading to predict a hexagonal region in the Mg-Cu-Y composition triangle, within which metallic glass formation is energetically favored. It is proposed that the hexagonal region can be defined as the intrinsic glass formation region, or quantitative glass formation ability of the system. Inside the hexagonal region, the driving force for formation of each specific glassy alloy was further calculated and correlated with its forming ability in practice. Calculations pinpointed the optimized stoichiometry in the Mg-Cu-Y system to be Mg64Cu16Y20, at which the formation driving force reaches its maximum, suggesting that metallic glasses designed to have compositions around Mg64Cu16Y20 are most stable or easiest to obtain. The predictions derived directly from the atomistic simulations are supported by experimental observations reported so far in the literature. Furthermore, Honeycutt-Anderson analysis indicated that pentagonal bipyramids (although not aggregating to form icosahedra) dominate in the local structure of the Mg-Cu-Y metallic glasses. A microscopic picture of the medium-range packing can then be described as an extended network of the pentagonal bipyramids, entangled with the fourfold and sixfold disclination lines, jointly fulfilling the space of the metallic glasses.

  6. Numerical modeling of radioactive neutron capture influence of Hf isotopic composition dynamics rate in the RBMK-1500 reactor

    Jurkevicius, A; Auzelyte, V; Remeikis, V


    The nuclide composition of the nuclear fuel and isotopic composition of the hafnium in the radial neutron flux detectors of the RBMK-1500 reactor were numerically modelled. The sequence SAS2 from package SCALE 4.3 was used for calculations. The nuclear fuel nuclide concentrations, the concentration of Hf isotopes, the neutron absorption rate on Hf isotopes and summary absorption rate dependences on the fuel assembly burn up are presented. (author)

  7. Isotopic composition of Murchison organic compounds: Intramolecular carbon isotope fractionation of acetic acid. Simulation studies of cosmochemical organic syntheses

    Yuen, G. U.; Cronin, J. R.; Blair, N. E.; Desmarais, D. J.; Chang, S.


    Recently, in our laboratories, samples of Murchison acetic acid were decarboxylated successfully and the carbon isotopic composition was measured for the methane released by this procedure. These analyses showed significant differences in C-13/C-12 ratios for the methyl and carboxyl carbons of the acetic acid molecule, strongly suggesting that more than one carbon source may be involved in the synthesis of the Murchison organic compounds. On the basis of this finding, laboratory model systems simulating cosmochemical synthesis are being studied, especially those processes capable of involving two or more starting carbon sources.

  8. Exploring the impact of temperature and fluid chemistry on Ca and Sr isotope composition of Arctica islandica shells via experimental alteration

    Goos, Manuela; Eisenhauer, Anton; Liebetrau, Volker; Böhm, Florian; Fietzke, Jan; Nehrke, Gernot; Buhl, Dieter; Mavromatis, Vasileios; Dietzel, Martin


    Carbonate shells of marine organisms record by their chemical and isotopic composition environmental conditions like temperature, salinity and pH during their formation. However, primary signals can be overprinted by diagenesis, which has to be considered for the interpretation of environmental proxy data and on the other side may provide additional information about distinct reaction pathways throughout diagenesis (e.g. Allison et al, 2007). Aragonitic Arctica islandica shells widely used as proxy archives (e.g. Schöne et al, 2005) were chosen for hydrothermal alteration experiments in order to get a more detailed insight into diagenetic effects. Here we present results of experiments in which Arctica islandica shell fragments were exposed to North Sea seawater at temperatures of 100r{ }C and 175r{ }C at distinct reaction times. Strontium isotope composition of the experimental medium was adjusted from an original composition of δ 88/86SrSRM987= 0.391(1)‰ and 87Sr/86Sr= 0.70921(1) to δ 88/86SrSRM987= 0.179(1)‰ and 87Sr/86Sr= 0.70789(1) by sulfate extraction and Sr replacement procedures. The artificially altered shell material (six sub-samples of six shell fragments) and the corresponding solutions were prepared and analyzed. Results show that at 100r{ }C aragonite is still the predominant phase, but show lower peak intensities with Raman and XRD near the surface of the shell fragments. At 175r{ }C the aragonitic shell material recrystallized almost completely to calcite. In addition a rim of weakly ordered dolomite (10μ m) was found around these samples. Analysis of element concentrations of initial and final solutions show that at 175r{ }C Sr and Ca concentrations increase (Sr: 79 to 183 μ mol/l; Ca: 8 to 30 mmol/l), while Mg concentration decreases (Mg: 42 to 22 mmol/l). A corresponding Sr and Ca depletion along with an increase of Mg occurred in the samples, especially in the dolomite rim. At 100r{ }C only minor increase of Sr, Ca and Mg

  9. In situ observations of the isotopic composition of methane at the Cabauw tall tower site

    Röckmann, Thomas; Eyer, Simon; van der Veen, Carina; Popa, Maria E.; Tuzson, Béla; Monteil, Guillaume; Houweling, Sander; Harris, Eliza; Brunner, Dominik; Fischer, Hubertus; Zazzeri, Giulia; Lowry, David; Nisbet, Euan G.; Brand, Willi A.; Necki, Jaroslav M.; Emmenegger, Lukas; Mohn, Joachim


    High-precision analyses of the isotopic composition of methane in ambient air can potentially be used to discriminate between different source categories. Due to the complexity of isotope ratio measurements, such analyses have generally been performed in the laboratory on air samples collected in the field. This poses a limitation on the temporal resolution at which the isotopic composition can be monitored with reasonable logistical effort. Here we present the performance of a dual isotope ratio mass spectrometric system (IRMS) and a quantum cascade laser absorption spectroscopy (QCLAS)-based technique for in situ analysis of the isotopic composition of methane under field conditions. Both systems were deployed at the Cabauw Experimental Site for Atmospheric Research (CESAR) in the Netherlands and performed in situ, high-frequency (approx. hourly) measurements for a period of more than 5 months. The IRMS and QCLAS instruments were in excellent agreement with a slight systematic offset of (+0.25 ± 0.04) ‰ for δ13C and (-4.3 ± 0.4) ‰ for δD. This was corrected for, yielding a combined dataset with more than 2500 measurements of both δ13C and δD. The high-precision and high-temporal-resolution dataset not only reveals the overwhelming contribution of isotopically depleted agricultural CH4 emissions from ruminants at the Cabauw site but also allows the identification of specific events with elevated contributions from more enriched sources such as natural gas and landfills. The final dataset was compared to model calculations using the global model TM5 and the mesoscale model FLEXPART-COSMO. The results of both models agree better with the measurements when the TNO-MACC emission inventory is used in the models than when the EDGAR inventory is used. This suggests that high-resolution isotope measurements have the potential to further constrain the methane budget when they are performed at multiple sites that are representative for the entire European domain.

  10. Higher peroxidase activity, leaf nutrient contents and carbon isotope composition changes in Arabidopsis thaliana are related to rutin stress.

    Hussain, M Iftikhar; Reigosa, Manuel J


    Rutin, a plant secondary metabolite that is used in cosmetics and food additive and has known medicinal properties, protects plants from UV-B radiation and diseases. Rutin has been suggested to have potential in weed management, but its mode of action at physiological level is unknown. Here, we report the biochemical, physiological and oxidative response of Arabidopsis thaliana to rutin at micromolar concentrations. It was found that fresh weight; leaf mineral contents (nitrogen, sodium, potassium, copper and aluminum) were decreased following 1 week exposure to rutin. Arabidopsis roots generate significant amounts of reactive oxygen species after rutin treatment, consequently increasing membrane lipid peroxidation, decreasing leaf Ca(2+), Mg(2+), Zn(2+), Fe(2+) contents and losing root viability. Carbon isotope composition in A. thaliana leaves was less negative after rutin application than the control. Carbon isotope discrimination values were decreased following rutin treatment, with the highest reduction compared to the control at 750μM rutin. Rutin also inhibited the ratio of CO2 from leaf to air (ci/ca) at all concentrations. Total protein contents in A. thaliana leaves were decreased following rutin treatment. It was concluded carbon isotope discrimination coincided with protein degradation, increase lipid peroxidation and a decrease in ci/ca values may be the primary action site of rutin. The present results suggest that rutin possesses allelopathic potential and could be used as a candidate to develop environment friendly natural herbicide.

  11. Multiple sulfur isotope composition of oxidized Samoan melts and the implications of a sulfur isotope 'mantle array' in chemical geodynamics

    Labidi, J.; Cartigny, P.; Jackson, M. G.


    To better address how subducted protoliths drive the Earth's mantle sulfur isotope heterogeneity, we report new data for sulfur (S) and copper (Cu) abundances, S speciation and multiple S isotopic compositions (32S, 33S, 34S, 36S) in 15 fresh submarine basaltic glasses from the Samoan archipelago, which defines the enriched-mantle-2 (EM2) endmember. Bulk S abundances vary between 835 and 2279 ppm. About 17 ± 11% of sulfur is oxidized (S6+) but displays no consistent trend with bulk S abundance or any other geochemical tracer. The S isotope composition of both dissolved sulfide and sulfate yield homogeneous Δ33S and Δ36S values, within error of Canyon Diablo Troilite (CDT). In contrast, δ34S values are variable, ranging between +0.11 and +2.79‰ (±0.12‰ 1σ) for reduced sulfur, whereas oxidized sulfur values vary between +4.19 and +9.71‰ (±0.80‰, 1σ). Importantly, δ34S of the reduced S pool correlates with the 87Sr/86Sr ratios of the glasses, in a manner similar to that previously reported for South-Atlantic MORB, extending the trend to δ34S values up to + 2.79 ± 0.04 ‰, the highest value reported for undegassed oceanic basalts. As for EM-1 basalts from the South Atlantic ridge, the linear δ34S-87Sr/86Sr trend requires the EM-2 endmember to be relatively S-rich, and only sediments can account for these isotopic characteristics. While many authors argue that both the EM-1 and EM-2 mantle components record subduction of various protoliths (e.g. upper or lower continental crust, lithospheric mantle versus intra-metasomatized mantle, or others), it is proposed here that they primarily reflect sediment recycling. Their distinct Pb isotope variation can be accounted for by varying the proportion of S-poor recycled oceanic crust in the source of mantle plumes.

  12. Isotopic composition analysis and age dating of uranium samples by high resolution gamma ray spectrometry

    Apostol, A. I.; Pantelica, A.; Sima, O.; Fugaru, V.


    Non-destructive methods were applied to determine the isotopic composition and the time elapsed since last chemical purification of nine uranium samples. The applied methods are based on measuring gamma and X radiations of uranium samples by high resolution low energy gamma spectrometric system with planar high purity germanium detector and low background gamma spectrometric system with coaxial high purity germanium detector. The "Multigroup γ-ray Analysis Method for Uranium" (MGAU) code was used for the precise determination of samples' isotopic composition. The age of the samples was determined from the isotopic ratio 214Bi/234U. This ratio was calculated from the analyzed spectra of each uranium sample, using relative detection efficiency. Special attention is paid to the coincidence summing corrections that have to be taken into account when performing this type of analysis. In addition, an alternative approach for the age determination using full energy peak efficiencies obtained by Monte Carlo simulations with the GESPECOR code is described.

  13. Isotopic Composition of Xenon in Petroleum from the Shell Bullwinkle Field

    J Nuzzo*; M Hyman; M W Rowe; Mnraoz; R L Palma; J Westrich


    We have measured the abundance and isotopic composition of xenon in petroleum samples from the Shell Bullwinkle Field off the coast of Louisiana. We used an oxidation and purification procedure designed to insure complete extraction and clean up of xenon from the petroleum. The xenon isotopic composition was found to be similar to the atmospheric value for one petroleum sample. While the results of the second sample suggest possible enrichment of the heavier isotopes, the errors associated with these excesses preclude a definitive statement to that effect. No monoisotopic enrichment in 129Xe was detected in either sample, the presence of which might have allowed us to deduce the petroleum age. Our results represent only the second xenon measurement from petroleum, and the concentrations are within the range of values published in the earlier report.

  14. Isotope composition and volume of Earth´s early oceans

    Pope, Emily Catherine; Bird, Dennis K.; Rosing, Minik Thorleif


    Oxygen and hydrogen isotope compositions of Earth´s seawater are controlled by volatile fluxes among mantle, lithospheric (oceanic and continental crust), and atmospheric reservoirs. Throughout geologic time the oxygen mass budget was likely conserved within these Earth system reservoirs......, but hydrogen´s was not, as it can escape to space. Isotopic properties of serpentine from the approximately 3.8 Ga Isua Supracrustal Belt in West Greenland are used to characterize hydrogen and oxygen isotope compositions of ancient seawater. Archaean oceans were depleted in deuterium [expressed as Î...... in Earth´s oceans. Our calculations predict that the oceans of early Earth were up to 26% more voluminous, and atmospheric CH4 and CO2 concentrations determined from limits on hydrogen escape to space are consistent with clement conditions on Archaean Earth....

  15. Abnormal composition of carbon isotopes in underground alkaline waters of Kuzbass

    Shvartsev, S. L.; Lepokurova, O. E.; Ponomarchuk, V. A.; Domrocheva, E. V.; Sizikov, D. A.


    The first data on abnormally high δ13C values in hydrocarbonates (HCO 3 - ) dissolved in underground waters of coal deposits of Kuzbass (up to +30.9‰) are reported. It is shown that such an unusual isotope composition of waters results from the long, strictly directed interaction in the water-rock-gas-organic material system occurring under the conditions of hindered water exchange. Extensive fractionation of C isotopes is the result of the evolution of the water-rock-gas-coal system after penetration of infiltration waters into the coal deposits and their long interaction with all these components, rather than metamorphism of organic material upon its transformation into coal. With respect to such an approach, the isotope composition of dissolved C may indicate the duration of the evolution in the water-rock-gas-organic material system.

  16. Isotopic composition of carbon and oxygen of carbonates of oil and gas-bearing deposits of Western Siberia

    Golyshev, S.I.; Cherepnin, A.V.; Rozhnev, A.N.


    There is measured the isotopic composition of carbon and oxygen in 129 samples of carbonates and carbonate cements of oil and gas-bearing Paleozoic and Mezozoic deposits of Western Siberia. The isotopic composition of samples of marine deposits varies from -1.2 to +6.1% for carbon and from 19.8 to 29.1% for oxygen and has a mean isotopic composition of 1.9 to 24.8%. Catagenetic processes lead to lightening of the isotopic composition of secondary carbonate on the average by 5% for carbon and 9% for oxygen. The most intense lightening of isotopic composition is observed in samples disposed near oil and gas deposits.

  17. Improved critical current density of MgB2--carbon nanotubes composite.

    Shekhar, Chandra; Giri, Rajiv; Malik, S K; Srivastav, O N


    In the present study, we report a systematic study of doping/admixing of carbon nanotubes (CNTs) in different concentrations in MgB2. The composite material corresponding to MgB2-x at.% CNTs (35 at.% > or = x > or = 0 at.%) have been prepared by solid-state reaction at ambient pressure. All the samples in the present investigation have been subjected to structural/microstructural characterization employing XRD, Scanning electron microscopic (SEM), and Transmission electron microscopic (TEM) techniques. The magnetization measurements were performed by Physical property measurement system (PPMS) and electrical transport measurements have been done by the four-probe technique. The microstructural investigations reveal the formation of MgB2-carbon nanotube composites. A CNT connecting the MgB2 grains may enhance critical current density due to its size (approximately 5-20 nm diameter) compatible with coherence length of MgB2 (approximately 5-6 nm) and ballistic transport current carrying capability along the tube axis. The transport critical current density (Jct) of MgB2 samples with varying CNTs concentration have been found to vary significantly e.g., Jct of the MgB2 sample with 10 at.% CNT addition is approximately 2.3 x 10(3) A/cm2 and its value for MgB2 sample without CNT addition is approximately 7.2 x 102 A/cm2 at 20 K. In order to study the flux pinning effect of CNTs doping/ admixing in MgB2, the evaluation of intragrain critical current density (JJ) has been carried out through magnetic measurements on the fine powdered version of the as synthesized samples. The optimum result on Jc is obtained for 10 at.% CNTs admixed MgB2 sample at 5 K, the Jc reaches approximately 5.2 x 10(6) A/cm2 in self field, -1.6 x 10(6) A/cm2 at 1 T, approximately 2.9 x 10(5) A/cm2 at 2.6 T, and approximately 3.9 x 10(4) A/cm2 at 4 T. The high value of intragrain Jc in 10 at.% CNTs admixed MgB2 superconductor has been attributed to the incorporation of CNTs into the crystal matrix of

  18. In situ oxygen isotope compositions in olivines of different types of cosmic spherules: An assessment of relationships to chondritic particles

    Rudraswami, N. G.; Shyam Prasad, M.; Jones, R. H.; Nagashima, K.


    Cosmic spherules collected from deep sea sediments of the Indian Ocean having different textures such as scoriaceous (4), relict-bearing (16), porphyritic (35) and barred olivine (2) were investigated for petrography, as well as high precision oxygen isotopic studies on olivine grains using secondary ion mass spectrometry (SIMS). The oxide FeO/MgO ratios of large olivines (>20 μm) in cosmic spherules have low values similar to those seen in the olivines of carbonaceous chondrite chondrules, rather than matching the compositions of matrix. The oxygen isotope compositions of olivines in cosmic spherules have a wide range of δ18O, δ17O and Δ17O values as follows: -9 to 40‰, -13 to 22‰ and -11 to 6‰. Our results suggest that the oxygen isotope compositions of the scoriaceous, relict-bearing, porphyritic and barred spherules show provenance related to the carbonaceous (CM, CV, CO and CR) chondrites. The different types of spherules that has experienced varied atmospheric heating during entry has not significantly altered the Δ17O values. However, one of the relict-bearing spherules with a large relict grain has Δ17O = 5.7‰, suggesting that it is derived from 16O-poor material that is not recognized in the meteorite record. A majority of the spherules have Δ17O ranging from -4 to -2‰, similar to values in chondrules from carbonaceous chondrites, signifying that chondrules of carbonaceous chondrites are the major contributors to the flux of micrometeorites, with an insignificant fraction derived from ordinary chondrites. Furthermore, barred spherule data shows that during atmospheric entry an increase in ∼10‰ of δ18O value surges Δ17O value by ∼1‰.

  19. Crystal Structure and Hydrogen Storage Behaviors of Mg/MoS2 Composites from Ball Milling

    HAN Zongying; ZHOU Shixue; WANG Naifei; ZHANG Qianqian; ZHANG Tonghuan; RAN Weixian


    The Mg/MoS2 composites were prepared by ball milling under argon atmosphere, and the effect of MoS2 on the crystal structure and hydrogen storage properties of Mg was investigated. It is found that 10 wt% of MoS2 is sufifcient to prevent particle aggregation and cold welding during the milling process. The crystallite size of Mg will remain constant at slightly less than 38.8 nm with the milling process due to the size conifnement effect of MoS2. The dehydrogenation temperature of MgH2 is reduced to 390.4-429.4℃ due to the crystallite size reduction. Through iftting by Johnson-Mehl-Avrami model, it is found that Mg crystal grows by three dimension controlled by interface transformation during the process of MgH2 decomposition. MoS2 has a weak catalyst effect on the decomposition of MgH2 and activation energy of 148.9 kJ/mol is needed for the dehydrogenation process calculated by the Arrhenius equation.

  20. Isotope variations of dissolved Zn in the Rio Grande watershed, USA: The role of adsorption on Zn isotope composition

    Szynkiewicz, Anna; Borrok, David M.


    In order to better understand the factors influencing zinc (Zn) isotope composition in hydrological systems, we analyzed the δ66Zn of dissolved Zn in the streams and groundwater of the Upper and Middle Rio Grande watershed in Colorado and New Mexico, United States. The stream water samples have a wider variation of δ66Zn (-0.57 to + 0.41 ‰ relative to the JMC 3-0749-Lyon standard) than groundwater samples (-0.13 to + 0.12 ‰) and than samples from streams that are in close proximity to abandoned mining sites (+0.24 to + 0.40 ‰). Regional changes of bedrock geology, from primarily igneous rocks to primarily sedimentary rocks, have no resolvable effect on the δ66Zn of aqueous samples. Instead, an increase in water pH from 7.5 to 8.5 corresponds to a considerable decrease in the δ66Zn of dissolved Zn (R2 = - 0.37, p = 0.003, n = 22). Consequently, we link the observed Zn isotope variations to the process of adsorption of Zn onto suspended sediment and bedrock minerals (average Δ66Znadsorbed-dissolved = + 0.31 ‰). Our results are in good agreement with previous experimental and empirical studies suggesting that Zn adsorption leads to a residual dissolved pool enriched in light Zn isotopes. Given that anthropogenic Zn sources can also be responsible for lowering of δ66Zn, and may overlap with the pH/adsorption effect on δ66Zn, the latter needs to be carefully considered in future studies to differentiate between natural and anthropogenic factors influencing Zn isotopes in this and other aquatic systems.

  1. Wear Behavior of Al-Mg2Si Cast In-situ Composite: Effect of Mg2Si Different Volume Fractions

    Ghiasinejad, J.; Emamy, M.; Ghorbani, M. R.; Malekan, A.


    Al-Mg2Si in situ composites are great candidates for automobile brake discs due to their low density, reasonably high young's modulus and low thermal expansion coefficient. Thus, understanding wear properties of this composite is of a great importance. In this study wear behavior of an in-situ Al-Mg2Si composite, prepared from a simple casting route, has been investigated using a pin-on-disc configuration concerning the effect of Mg2Si volume fractions, 15, 20 and 25% respectively. It was found that the weight loss increases with increase in reinforce volume fraction which can be due to a coarse morphology of primary Mg2Si particles. It was found that the variations of weight loss with sliding distance comprise different regimes of which the mechanisms are discussed.

  2. Corrosion characteristics of Al-Si-Mg/SiC{sub p} composites with varying Si/Mg molar ratio in neutral chloride solutions

    Escalera-Lozano, R.; Pech-Canul, M.I. [Cinvestav Saltillo (Mexico); Pech-Canul, M.A.; Quintana, P. [Departamento de Fisica Aplicada, Merida, Yuc. (Mexico)


    The corrosion resistance of Al-Mg-Si/SiC{sub p} composites produced by the pressureless infiltration method [using SiC{sub p} preforms with 50% porosity containing rice hull ash (RHA) and four custom-made alloys with varying Si/Mg molar ratio] was evaluated in neutral 0.1 M NaCl solutions. The deleterious phase Al{sub 4}C{sub 3} was successfully suppressed in composites with Si/Mg molar ratios of 0.89 and 1.05, but not in those with lower Si/Mg molar ratios (0.12 and 0.49). Results of cyclic polarizations in deareated 0.1 M NaCl solutions showed that with increasing Si/Mg molar ratio, passive current density increased but pitting susceptibility decreased both for reinforced and unreinforced alloys. Immersion tests in aerated 0.1 M NaCl showed that for composites with Si/Mg molar ratios of 0.12 and 0.49 chemical degradation by hydrolysis of Al{sub 4}C{sub 3} was followed by intense anodic dissolution at the matrix-reinforcement interface, while composites corresponding to Si/Mg molar ratios of 0.89 and 1.05 did not exhibit intense localized attack. Possible reasons for the improvement in resistance to localized corrosion are discussed. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

  3. Antibacterial characteristics of CaCO{sub 3}-MgO composites

    Yamamoto, Osamu, E-mail: [Center for Geo-Environmental Science, Faculty of Engineering and Resource Science, Akita University, 1-1 Tegata Gakuen-machi, Akita 010-8502 (Japan); Ohira, Toshiaki; Alvarez, Kelly [Center for Geo-Environmental Science, Faculty of Engineering and Resource Science, Akita University, 1-1 Tegata Gakuen-machi, Akita 010-8502 (Japan); Fukuda, Masayuki [Division of Dentistry and Oral Surgery, Akita University Hospital, 1-1-1 Hondo, Akita 010-8543 (Japan)


    Dentifrices, such as tooth-paste, are pastes containing insoluble abrasives that aid in the removal of plaque from the teeth and help to polish them. Composite powders contributing to oral hygiene application, i.e., nano-scale MgO crystallite dispersed in CaCO{sub 3} grain, were fabricated by the thermal decomposition of dolomite. The composite obtained by heating at 800 deg. C consisted of CaCO{sub 3} grains including 20 nm MgO fine crystallite, being the purpose powder in this study. The antibacterial activity of these powders related to gram-positive and gram-negative bacteria was evaluated in vitro. The thermal decomposition above 800 deg. C resulted in the mixture of CaO and MgO. Antibacterial activity of the composite enhanced with increasing powder concentration. Though antibacterial action toward Staphylococcus aureus was greater than towards Escherichia coli, the death rate constant was identical in both bacteria. It can be concluded that the obtained composite possesses two functions able to improve the oral hygiene: as a tooth abrasive and as an antibacterial agent.

  4. Calcium isotopic compositions as tracers of vegetation activity in boreal permafrost ecosystems (Kulingdakan watershed, Central Siberia)

    Bagard, M.; Schmitt, A.; Chabaux, F. J.; Viers, J.; Pokrovsky, O. S.; Prokushkin, A. S.; Stille, P.; Dupré, B.


    In this work, we propose to investigate the geochemical potential of calcium isotopic fractionations in a forested boreal watershed to trace the impact of vegetation activity. This is the first study carried out in a geographical area characterized by deep and continuous permafrost. For this survey, we measured Ca and Sr isotopic compositions in the different compartments (stream waters, soil solutions, precipitations, rock, soils and soil leachates, vegetation) of a 4,100 ha Siberian watershed, the Kulingdakan watershed (Putorana Plateau, Central Siberia). Our results show that the activity of the vegetation is the only process that fractionates significantly calcium isotopes within the watershed. Indeed, Ca uptake by plants and its subsequent storage in larch tree organs favours 40Ca relatively to 44Ca. Vegetation decomposition releases light δ44/40Ca that affects calcium isotopic compositions of soil solution and soil exchangeable fractions. However, this biological impact is significant only for the South-facing slope of the watershed. Indeed, soil pools from the North-facing slope present no imprint of organic matter degradation in their δ44/40Ca signatures. Furthermore, the major difference between South- and North- facing slopes lies in the importance of the vegetation and its decomposition rate. Thus, we propose that in boreal permafrost areas with limited runoff, the available stock of biomass is critical to induce or not a significant vegetation impact on the calcium isotopic compositions in the soil-water system. As a consequence, the study of preserved calcium isotopic compositions in paleosoil exchangeable phases might bring relevant information on the evolution of biological activity at the watershed scale.

  5. Stable water isotopic composition of the Antarctic subglacial Lake Vostok: implications for understanding the lake's hydrology.

    Ekaykin, Alexey A; Lipenkov, Vladimir Y; Kozachek, Anna V; Vladimirova, Diana O


    We estimated the stable isotopic composition of water from the subglacial Lake Vostok using two different sets of samples: (1) water frozen on the drill bit immediately after the first lake unsealing and (2) water frozen in the borehole after the unsealing and re-drilled one year later. The most reliable values of the water isotopic composition are: -59.0 ± 0.3 ‰ for oxygen-18, -455 ± 1 ‰ for deuterium and 17 ± 1 ‰ for d-excess. This result is also confirmed by the modelling of isotopic transformations in the water which froze in the borehole, and by a laboratory experiment simulating this process. A comparison of the newly obtained water isotopic composition with that of the lake ice (-56.2 ‰ for oxygen-18, -442.4 ‰ for deuterium and 7.2 ‰ for d-excess) leads to the conclusion that the lake ice is very likely formed in isotopic equilibrium with water. In turn, this means that ice is formed by a slow freezing without formation of frazil ice crystals and/or water pockets. This conclusion agrees well with the observed physical and chemical properties of the lake's accreted ice. However, our estimate of the water's isotopic composition is only valid for the upper water layer and may not be representative for the deeper layers of the lake, so further investigations are required.

  6. The carbon isotope composition of atmospheric CO 2 in Paris

    Widory, David; Javoy, Marc


    One characteristic of air pollution in the urban environment is high CO 2 concentrations resulting from human activities. Determining the relative contributions of the different CO 2 sources can be addressed simply and elegantly by combining isotope and concentration measurements. Using this approach on atmospheric CO 2 samples collected in Paris, its suburbs and the open country provides fairly accurate conclusions. Our results show that air pollution within the first few metres above ground results basically from binary mixtures among which road traffic is the main contributor and, in particular, vehicles using unleaded gasoline (˜90% of the total). Heating sources, which account for 50% of the CO 2 input below the atmospheric inversion level, and vehicles using diesel contribute very little. Human respiration has a recognisable signature at street level under certain circumstances. The combined isotope and concentration analysis provides a sensitive tracer of local variations, even detecting the occasional prevalence of human respiration and the onset of actions in which natural gas is burnt. It also detects surprising inlets of 'clean air' (CO 2-wise) in the very centre of the city.

  7. The isotopic composition of methane in polar ice cores

    Craig, H.; Chou, C. C.; Welhan, J. A.; Stevens, C. M.; Engelkemeir, A.


    Air bubbles in polar ice cores indicate that about 300 years ago the atmospheric mixing ratio of methane began to increase rapidly. Today the mixing ratio is about 1.7 parts per million by volume, and, having doubled once in the past several hundred years, it will double again in the next 60 years if current rates continue. Carbon isotope ratios in methane up to 350 years in age have been measured with as little as 25 kilograms of polar ice recovered in 4-meter-long ice-core segments. The data show that: (1) in situ microbiology or chemistry has not altered the ice-core methane concentrations, and (2) that the carbon-13 to carbon-12 ratio of atmospheric CH4 in ice from 100 years and 300 years ago was about 2 per mil lower than at present. Atmospheric methane has a rich spectrum of isotopic sources: the ice-core data indicate that anthropogenic burning of the earth's biomass is the principal cause of the recent C-13H4 enrichment, although other factors may also contribute.

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

    LIU ZongXiu; GU ZhaoYan; WU NaiQin; XU Bing


    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.

  9. The atomic weight and isotopic composition of boron and their variation in nature

    Holden, N.E.


    The boron isotopic composition and atomic weight value and their variation in nature are reviewed. Questions are raised about the previously recommended value and the uncertainty for the atomic weight. The problem of what constitutes an acceptable range for normal material and what should then be considered geologically exceptional is discussed. Recent measurements make some previous decisions in need of re-evaluation.

  10. Impact of metabolism and growth phase on the hydrogen isotopic composition of microbial fatty acids

    Heinzelmann, S.M.; Villanueva, L.; Sinke-Schoen, D.; Sinninghe Damsté, J.S.; Schouten, S.; Van der Meer, M.T.J.


    Microorganisms are involved in all elemental cycles and therefore it is important to study their metabolism in the natural environment. A recent technique to investigate this is the hydrogen isotopic composition of microbial fatty acids, i.e., heterotrophic microorganisms produce fatty acids enriche

  11. Interpretation of groundwater origin in the Velenje coal mine on the basis of isotope composition

    Janko Urbanc


    Full Text Available The aim of the investigation was to determine the isotopic properties of cave waters from the Velenje coal mine and define the recharge areas of individual aquifers. With regard to the oxygen isotope composition, groundwater in the Velenje coal mine can beclassified into three types. Typical d18O values of the first type are around -9 ‰ and are found in surface waters in the vicinity of the mine, therefore it is supposed that these waters are recharged locally. The second type is represented mainly by waters from thelower part of the pliocene aquifer. The average oxygen composition of these waters is about -11 ‰. This isotope composition is considerably different from the isotope composition of recent waters from the mine’s vicinity, which leads to the conclusion that these are older, fossile waters. These waters also have a very high degree of mineralization and consequently conductivity. Waters of the third type have average δ18O values around -10 ‰ and originate mainly from triassic dolomites. These waters could be a mixture of recentand old waters, but it is also possible that they flow into the coal mine from the higher areas of Paški Kozjak.

  12. Soil moisture effects on the carbon isotope composition of soil respiration

    Claire L. Phillips; Nick Nickerson; David Risk; Zachary E. Kayler; Chris Andersen; Alan Mix; Barbara J. Bond


    The carbon isotopic composition (δ13C) of recently assimilated plant carbon is known to depend on water-stress, caused either by low soil moisture or by low atmospheric humidity. Air humidity has also been shown to correlate with the δ13C of soil respiration, which suggests indirectly that recently fixed photosynthates...

  13. Single-molecule fluorescence autocorrelation experiments on pentacene : The dependence of intersystem crossing on isotopic composition

    Brouwer, A.C.J.; Köhler, J.; Oijen, A.M. van; Groenen, E.J.J.; Schmidt, J.


    Single pentacene molecules containing 13C or 1H in a pentacene-d14 doped p-terphenyl crystal have been studied by fluorescence autocorrelation. The triplet dynamics has been analyzed and a systematic dependence of the S1→T1 intersystem crossing rate on isotopic composition was found. This variation

  14. The Cl Isotope Composition of the Moon as evidence for an Anhydrous Mantle (Invited)

    Sharp, Z. D.; Shearer, C., Jr.; McKeegan, K. D.; Barnes, J.; Wang, Y.


    The chlorine isotope composition of primitive terrestrial basalts and carbonaceous chondrites cover a narrow range centered around 0‰ with a total variation of ± 0.5‰. In contrast, the chlorine isotope composition of bulk samples and in situ ion microprobe analyses of lunar basalts and glasses cover a range of 25‰. Three possibilities were considered to explain the large spread: 1) initial isotopic heterogeneities, 2) devolatilization from solar wind/micrometeorite bombardment, 3) degassing under anhydrous conditions. The first of these possibilities is rejected because the Moon went through an magma ocean stage which would have homogenized any isotopic heterogeneities. To examine surface effects, we chose samples that have extremely different degrees of surface exposure. We find no correlation between the Cl isotope composition and surface exposure. We also conducted a laboratory experiment in which a thin film of NaCl was bombarded with a proton source for 24 hours with no change in Cl isotope composition. The third possibility is that the fractionation is explained by the anhydrous character of the Moon. On Earth, the volatiling Cl species is HCl. HCl is known to preferentially incorporate 37Cl relative to 35Cl due to the high bond strength of the molecule. This is offset by the higher translational velocity of H35Cl, so that overall, there is very little Cl isotope fractionation during degassing. We propose that lunar basalts were anhydrous and the volatile Cl species were metal chlorides, such as ZnCl2, NaCl, FeCl2, etc. The bond strength of metal chlorides and Cl dissolved in a basalt are similar, so that fractionation is caused mainly by volatilization, with the light isotopologue preferentially lost to the vapor phase. This idea is supported by the consistent lower Cl isotope ratios of water soluble salt fraction (~10 ‰ lower) and the lowest lunar Cl isotope values close to those of bulk Earth. The H content of lunar magmas must have been lower

  15. Mg-composition induced effects on the physical behavior of sprayed Zn{sub 1-x}Mg{sub x}O films

    Reddy, K.T. Ramakrishna, E-mail: [Thin Film Laboratory, Department of Physics, Sri Venkateswara University, Tirupati - 517 502 (India); Prathap, P.; Revathi, N.; Reddy, A.S.N. [Thin Film Laboratory, Department of Physics, Sri Venkateswara University, Tirupati - 517 502 (India); Miles, R.W. [School of Engineering and Computing, Northumbria University, Newcastle NE1 8ST (United Kingdom)


    Thin films of Zn{sub 1-x}Mg{sub x}O, with Mg compositions in the range, 0 < x < 0.4, have been deposited onto soda-lime glass substrates using chemical spray pyrolysis. The effects of altering the alloy composition on the chemical and physical properties of the layers were investigated using X-ray photoelectron spectroscopy, atomic force microscopy, Raman, optical and electrical measurements. The data shows systematic shifts in the properties of the layers with Mg-content. In particular, the optical absorption data showed that the influence of Mg-content on the energy gap of Zn{sub 1-x}Mg{sub x}O films is significant. Layers with x = 0.24 had an optical energy band gap, E{sub g} = 3.87 eV. The best layers produced had properties appropriate for application as Cd-free buffer layers in copper indium gallium selenide (CIGS) solar cells.

  16. Magnetic properties of soft layer/FePt-MgO exchange coupled composite Perpendicular recording media

    Yin Jin-Hua; Takao Suzuki; Pan Li-Qing


    The magnetic properties of exchange coupled composite(ECC)media that are composed of perpendicular magnetic recording media FePt-MgO and two kinds of soft layers have been studied by using an x-ray diffractometer,a polar Kerr magneto-optical system(PMOKE)and a vibrating sample magnetometer(VSM).The results show that ECC media can reduce the coercivities of perpendicular magnetic recording media FePt-MgO.The ECC media with granular-type soft layers have weaker exchange couplings between magnetic grains and the magnetization process,for ECC media of this kind mainly follow the Stoner-Wohlfarth model.

  17. Search for halo nucleus in Mg isotopes through the measurements of reaction cross sections towards the vicinity of neutron drip line

    Takechi M.


    Full Text Available Reaction cross sections (σR for 24–38Mg on C targets at the energies of around 240 MeV/nucleon have been measured precisely at RIBF, RIKEN for the purpose of obtaining the crucial information on the changes of nuclear structure in unstable nuclei, especially around the so-called “island of inversion” region. In the island of inversion region, which includes neutron-rich Ne, Na, and Mg isotopes, the vanishing of the N = 20 magic number for neutrons have been discussed along with nuclear deformation. The present result suggest deformation features of Mg isotopes and shows a large cross section of weakly-bound nucleus 37Mg, which could be caused by a neutron halo formation.

  18. Isotopic composition and neutronics of the Okelobondo natural reactor

    Palenik, Christopher Samuel

    The Oklo-Okelobondo and Bangombe uranium deposits, in Gabon, Africa host Earth's only known natural nuclear fission reactors. These 2 billion year old reactors represent a unique opportunity to study used nuclear fuel over geologic periods of time. The reactors in these deposits have been studied as a means by which to constrain the source term of fission product concentrations produced during reactor operation. The source term depends on the neutronic parameters, which include reactor operation duration, neutron flux and the neutron energy spectrum. Reactor operation has been modeled using a point-source computer simulation (Oak Ridge Isotope Generation and Depletion, ORIGEN, code) for a light water reactor. Model results have been constrained using secondary ionization mass spectroscopy (SIMS) isotopic measurements of the fission products Nd and Te, as well as U in uraninite from samples collected in the Okelobondo reactor zone. Based upon the constraints on the operating conditions, the pre-reactor concentrations of Nd (150 ppm +/- 75 ppm) and Te (<1 ppm) in uraninite were estimated. Related to the burnup measured in Okelobondo samples (0.7 to 13.8 GWd/MTU), the final fission product inventories of Nd (90 to 1200 ppm) and Te (10 to 110 ppm) were calculated. By the same means, the ranges of all other fission products and actinides produced during reactor operation were calculated as a function of burnup. These results provide a source term against which the present elemental and decay abundances at the fission reactor can be compared. Furthermore, they provide new insights into the extent to which a "fossil" nuclear reactor can be characterized on the basis of its isotopic signatures. In addition, results from the study of two other natural systems related to the radionuclide and fission product transport are included. A detailed mineralogical characterization of the uranyl mineralogy at the Bangombe uranium deposit in Gabon, Africa was completed to improve

  19. Magnesium isotope fractionation during carbonatite magmatism at Oldoinyo Lengai, Tanzania

    Li, Wang-Ye; Teng, Fang-Zhen; Halama, Ralf; Keller, Jörg; Klaudius, Jurgis


    To investigate the behaviour of Mg isotopes during carbonatite magmatism, we analyzed Mg isotopic compositions of natrocarbonatites and peralkaline silicate rocks from Oldoinyo Lengai, Tanzania. The olivine melilitites from the vicinity of Oldoinyo Lengai have homogeneous and mantle-like Mg isotopic compositions (δ26Mg of -0.30 to -0.26‰), indicating limited Mg isotope fractionation during mantle melting. The highly evolved peralkaline silicate rocks not related to silicate-carbonatite liquid immiscibility, including phonolites from the unit Lengai I, combeite-wollastonite nephelinites (CWNs) from the unit Lengai II A and carbonated combeite-wollastonite-melilite nephelinites (carbCWMNs), have δ26Mg values (from -0.25 to -0.10‰) clustered around the mantle value. By contrast, the CWNs from the unit Lengai II B, which evolved from the silicate melts that were presumably generated by silicate-carbonatite liquid immiscibility, have heavier Mg isotopes (δ26Mg of -0.06 to +0.09‰). Such a difference suggests Mg isotope fractionation during liquid immiscibility and implies, based on mass-balance calculations, that the original carbonatite melts at Lengai were isotopically light. The variable and positive δ26Mg values of natrocarbonatites (from +0.13 to +0.37‰) hence require a change of their Mg isotopic compositions subsequent to liquid immiscibility. The negative correlations between δ26Mg values and contents of alkali and alkaline earth metals of natrocarbonatites suggest Mg isotope fractionation during fractional crystallization of carbonatite melts, with heavy Mg isotopes enriched in the residual melts relative to fractionated carbonate minerals. Collectively, significant Mg isotope fractionation may occur during both silicate-carbonatite liquid immiscibility and fractional crystallization of carbonatite melts, making Mg isotopes a potentially useful tracer of these processes relevant to carbonatite petrogenesis.

  20. Oxygen and nitrogen isotopic composition of nitrate in commercial fertilizers, nitric acid, and reagent salts.

    Michalski, Greg; Kolanowski, Michelle; Riha, Krystin M


    Nitrate is a key component of synthetic fertilizers that can be beneficial to crop production in agro-ecosystems, but can also cause damage to natural ecosystems if it is exported in large amounts. Stable isotopes, both oxygen and nitrogen, have been used to trace the sources and fate of nitrate in various ecosystems. However, the oxygen isotope composition of synthetic and organic nitrates is poorly constrained. Here, we present a study on the N and O isotope composition of nitrate-based fertilizers. The δ(15)N values of synthetic and natural nitrates were 0 ± 2 ‰ similar to the air N2 from which they are derived. The δ(18)O values of synthetic nitrates were 23 ± 3 ‰, similar to air O2, and natural nitrate fertilizer δ(18)O values (55 ± 5 ‰) were similar to those observed in atmospheric nitrate. The Δ(17)O values of synthetic fertilizer nitrate were approximately zero following a mass-dependent isotope relationship, while natural nitrate fertilizers had Δ(17)O values of 18 ± 2 ‰ similar to nitrate produced photochemically in the atmosphere. These narrow ranges of values can be used to assess the amount of nitrate arising from fertilizers in mixed systems where more than one nitrate source exists (soil, rivers, and lakes) using simple isotope mixing models.

  1. Structure, mechanical property and corrosion behaviors of (HA+β-TCP)/Mg-5Sn composite with interpenetrating networks.

    Wang, X; Li, J T; Xie, M Y; Qu, L J; Zhang, P; Li, X L


    In this paper, a novel (Hydroxyapatite+β-tricalcium phosphate)/Mg-5Sn ((HA+β-TCP)/Mg-5Sn) composite with interpenetrating networks was fabricated by infiltrating Mg-5Sn alloy into porous HA+β-TCP using suction casting technique. The structure, mechanical property and corrosion behaviors of the composite have been evaluated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), mechanical testing, electrochemical and immersion test. It is shown that the molten Mg-5Sn alloy has infiltrated not only into the pores but also into the struts of the HA+β-TCP scaffold to forming a compact composite. The microstructure observation also shows that the Mg alloy contacts to the HA+β-TCP closely, and no reaction layer can be found between Mg-5Sn alloy and scaffold. The ultimate compressive strength of the composite is as high as 176MPa, which is about four fifths of the strength of the Mg-5Sn bulk alloy. The electrochemical and immersion tests indicate that the corrosion resistance of the composite is better than that of the Mg-5Sn bulk alloy. The corrosion products on the composite surface are mainly Mg(OH)2, Ca3(PO4)2 and HA. Appropriate mechanical and corrosion properties of the (HA+β-TCP)/Mg-5Sn composite indicate its possibility for new bone tissue implant materials.

  2. Impacts of microbial community composition on isotope fractionation during reductive dechlorination of tetrachloroethylene.

    Dong, Yiran; Butler, Elizabeth C; Philp, R Paul; Krumholz, Lee R


    Isotope fractionation has been used with increasing frequency as a tool to quantify degradation of chlorinated aliphatic pollutants in the environment. The objective of this research was to determine if the electron donor present in enrichment cultures prepared from uncontaminated sediments influenced the extent of isotope fractionation of tetrachloroethylene (PCE), either directly, or through its influence on microbial community composition. Two PCE-degrading enrichment cultures were prepared from Duck Pond (DP) sediment and were incubated with formate (DPF) or H(2) (DPH) as electron donor. DPF and DPH were significantly different in both product distribution and extent of isotope fractionation. Chemical and isotope analyses indicated that electron donors did not directly affect the product distribution or the extent of isotope fractionation for PCE reductive dechlorination. Instead, restriction fragment length polymorphism (RFLP) and sequence analysis of the 16S rRNA clone libraries of DPF and DPH identified distinct microbial communities in each enrichment culture, suggesting that differences in microbial communities were responsible for distinct product distributions and isotope fractionation between the two cultures. A dominant species identified only in DPH was closely related to known dehalogenating species (Sulfurospirillum multivorans and Sulfurospirillum halorespirans) and may be responsible for PCE degradation in DPH. Our study suggests that different dechlorinators exist at the same site and can be preferentially stimulated by different electron donors, especially over the long-term (i.e., years), typical of in-situ ground water remediation.

  3. Hydrogen storage in Mg-LiBH4 composites catalyzed by FeF3

    Puszkiel, Julián; Gennari, Fabiana C.; Arneodo Larochette, Pierre; Troiani, Horacio E.; Karimi, Fahim; Pistidda, Claudio; Gosalawit-Utke, Rapee; Jepsen, Julian; Jensen, Torben R.; Gundlach, Carsten; Tolkiehn, Martin; Bellosta von Colbe, José; Klassen, Thomas; Dornheim, Martin


    Mg-10 mol% LiBH4 composite plus small amounts of FeF3 is investigated in the present work. The presence of LiBH4 during the milling process noticeably modifies the size and morphology of the Mg agglomerates, leading to faster hydrogenation and reaching almost the theoretical hydrogen capacity owing to enhanced hydrogen diffusion mechanism. However, the dehydrogenation of the system at low temperatures (≤300 °C) is still slow. Thus, FeF3 addition is proposed to improve the dehydrogenation kinetic behavior. From experimental results, it is found that the presence of FeF3 results in an additional size reduction of the Mg agglomerates between ∼10 and ∼100 μm and the formation of stable phases such as MgF2, LiF and FeB. The FeB species might have a catalytic effect upon the MgH2 decomposition. As a further result of the FeF3 addition, the Mg-10 mol%LiBH4-5 mol% FeF3 material shows improved dehydrogenation properties: reduced dehydrogenation activation energy, faster hydrogen desorption rate and reversible hydrogen capacities of about 5 wt% at 275 °C.

  4. Western Indian Ocean circulation and climate variability on different time scales. A study based on stable oxygen and carbon isotopes, benthic foraminiferal assemblages and Mg/Ca paleothermometry

    Romahn, Sarah


    In order to understand the Earth's climate evolution it is crucial to evaluate the role of low-latitude oceans in the global climate system, as they are connected to both hemispheres via atmospheric and oceanic circulation and thus hold the potential to disentangle the asynchronicity of short-term Pleistocene climate variability. However, the potential of low latitude oceans to respond to and force large-scale changes of the climate system is still debated. The aim of this thesis is to examine and to understand the causal relationship of both atmospheric and oceanic changes in the tropical western Indian Ocean on centennial-, millennial and glacial-interglacial timescales. For this purpose I investigated stable oxygen and carbon isotope compositions of both planktic and benthic foraminiferal tests, Mg/Ca ratios of planktic foraminiferal tests as well as benthic foraminiferal assemblages and sedimentary geochemical parameters on two sediment cores (GeoB12615-4, 446 m and GeoB12616-4, 1449 m) from the continental slope off Tanzania, East Africa.

  5. Fracture toughness of Al-4%Mg/Al{sub 2}O{sub 3}p composites

    Pestes, R.H. [Hewlett-Packard, Camus, WA 98607 (United States); Kamat, S.V. [Mechanical and Materials Engineering Department, Washington State University, Pullman, WA 99164-2920 (United States); Hirth, J.P. [Mechanical and Materials Engineering Department, Washington State University, Pullman, WA 99164-2920 (United States)


    Fracture toughness tests were carried out on Al-4%Mg/Al{sub 2}O{sub 3}p composites containing different sizes and volume fractions of alumina particulates. The results indicated that the fracture toughness was dependent on the interparticle spacing provided the particulate size was below a critical size. The critical particle size corresponds to the situation wherein the energy release rate on particulate cracking is sufficient to trigger dynamic unstable crack extension. ((orig.))

  6. Sedimentary nitrate reduction and its effect on the N-isotopic composition of oceanic nitrate

    Lehmann, M. F.; Sigman, D. M.; McCorkle, D. C.


    A prerequisite for assessing denitrification fluxes in a specific environment using water column nitrate N isotope ratios is the knowledge of the expressed N isotope effects of water column and/or benthic denitrification in this environment. Here, we aim at assessing the effects of benthic nitrogen cycling on the N isotopic composition of the oceanic nitrate pool in deep-sea sediments, which are believed to harbour a large portion of the global benthic denitrification. We report 15N/14N ratios of pore water nitrate in pelagic sediments from the deep Bering Sea, where benthic nitrate reduction has previously been identified as a significant sink of fixed nitrogen. Porewater profiles from multicores indicate strong 15N enrichment in porewater nitrate at all stations, as one goes deeper in the sediments and nitrate concentrations decrease (δ15N generally reached 25-35‰). Our data are consistent with variable biological isotope effect (ɛ) for dissimilatory nitrate reduction ranging between 13 to 30 ‰. A one-dimensional diffusion-reaction model including organic matter degradation, nitrification, and denitrification indicates that, although denitrification leads to a pore water nitrate pool that is enriched in 15N, N isotope fractionation is poorly expressed at the scale of sediment-water nitrate exchange, independent of whether sediments are a net sink or a net source of nitrate. The apparent nitrate isotope effect of sedimentary denitrification on nitrate in overlying waters is generally below 2‰, as a result of diffusive transport limitation into, and within, the sediments and/or the production of light nitrate during nitrification. Thus, our data suggest that the low expressed isotope effect of benthic denitrification observed previously in reactive shelf sediments also applies to deep-sea sediments. However, where ammonium fluxes out of the sediments, it is enriched in 15-N, and may ultimately lead to an N-isotopic enrichment of the water-column nitrate

  7. Influence of sea ice cover on evaporation and water vapour isotopic composition in the Arctic

    Bonne, Jean-Louis; Werner, Martin; Meyer, Hanno; Kipfstuhl, Sepp; Rabe, Benjamin; Behrens, Melanie; Schönicke, Lutz; Steen-Larsen, Hans Christian


    Since July 2015, water stable isotopes (HDO and H218O) have been measured at two Arctic facilities: during the summer on board of the research vessel Polarstern, and year-round at the Siberian coastal site of Samoylov, situated in the Lena delta (N 72°22', E 126°29'), close to the Laptev Sea. In both places, the isotopic composition of water vapour is analysed continuously in surface air. Additional isotopic measurements are performed on a daily basis in ocean surface water samples taken on Polarstern and on an event basis from precipitation sampled in Samoylov. The two Polarstern summer campaigns cover a large region of the western Artic Ocean, including a one-month campaign in the central and eastern Arctic crossing the North Pole in September 2015, with very cold conditions (up to -20°C). Combining ocean and atmospheric observations from Polarstern allows an evaluation of local surface water evaporation and its isotopic fingerprint relative to the oceanic and meteorological conditions as well as the partial sea ice cover. In the central and eastern Arctic, a large area of complete sea ice cover also revealed a strong impact on the advected moisture above the ice cap under very cold conditions. A first year of Siberian observations at Samoylov depicted a large seasonal variability, with extremely dry and isotopically depleted winter values. Contrasted seasonal isotopic regimes might be utilized for identifying moisture sources changes in the region, such as ocean surface closure by sea ice, or freezing of the Lena River. Besides documenting the present meteorology and changes in the Arctic, our measurements will contribute to a better interpretation of regional paleoclimate records based on water isotopes and to the evaluation of climate models in the Arctic. A first model-data comparison of our measurements with simulation results by the isotope-enabled atmospheric general circulation model ECHAM5-wiso have revealed relevant model biases in the Arctic realm.

  8. Regulation of Isotopic Composition of Water - way of Improvement of Cosmonauts Drinking Water Functional Properties

    Kulikova, Ekaterina; Utina, Dina; Vorozhtsova, Svetlana; Severyuhin, Yuri; Abrosimova, Anna; Sinyak, Yuri; Ivanov, Alexander

    The problem in providing drinking water to cosmonauts is solved - at this moment there is a task to improve the functional properties of the water. One of the perspectives of this trend is the use of light isotopic water. The animal studies have shown that long-term consumption of water with a depletion of deuterium and oxygen heavy isotopes accelerates the rise of mass non-irradiated mice, the phase fluctuations reducing or increasing hematological parameters were having adaptive nature. These fluctuations didn’t overcome values beyond the physiological norm of this type of animal. It is established that the therapeutic use of light isotopic water with 35 - 90 ppm in deuterium increases the survival of irradiated mice by an average of 30%, contributes to the preservation of irradiated animals body weight. Treatment of acute radiation sickness with light isotopic water stimulates hematopoietic recovery. At the same time, keeping mice drinking light isotopic water for 7 - 8 days before the irradiation (from 4 to 8.5 Gr) has no effect on the level of radio resistance. Longer keeping mice on light isotopic water, for 14 -21 days - reduction in life expectancy, animal mass, bone marrow cellularity and the level of white blood cells in irradiated animals is noted. It was established that keeping mice on light isotopic water for 14 days before exposure in experimental animals causes an increase in the mitotic index and the frequency of formation of aberrant mitosis after 24 hours of Co(60) gamma radiation in doses of 1 , 2, and 4 Gr. Thus, it is clear that the regulation of the isotopic composition of drinking water - way to improve its functional properties.

  9. Optical constants and their dispersion of Ag-MgF2 nanoparticle composite films

    Zhaoqi Sun(孙兆奇); Daming Sun(孙大明)


    Ag-MgF2 composite films with different Ag fractions were prepared through a co-evaporation method.Microstructure analysis shows that the films are composed of amorphous MgF2 matrix and embedded fcc-Ag nanoparticles. The optical constants and their dispersion of the films, within the wavelength range of 250 - 650 nm, were measured by reflecting spectroscopic ellipsometry. The maximum of the imaginary part ε" of the complex dielectric permittivity attributing to the surface plasmon resonance polarization of the Ag nanoparticles in an Ag-MgF2 film, and the tangent of the phase-shift angle δ resulting from the dielectric loss of the film, occur at λ = 435 nm and λ = 420 nm, respectively. Based on Maxwell-Garnett effective medium theory, the experimentally observed dispersion spectra were reasonably described.

  10. The influence of traffic and wood combustion on the stable isotopic composition of carbon monoxide

    M. Saurer


    Full Text Available Carbon monoxide in the atmosphere is originating from various combustion and oxidation processes. Recently, the proportion of CO resulting from the combustion of wood for domestic heating may have increased due to political measures promoting this renewable energy source. Here, we used the stable isotope composition of CO (δ13C and δ18O for the characterization of different CO sources in Switzerland, along with other indicators for traffic and wood combustion (NOx-concentration, aerosol light absorption at different wavelengths. We assessed diurnal variations of the isotopic composition of CO at 3 sites during winter: a village site dominated by domestic heating, a site close to a motorway and a rural site. The isotope ratios of wood combustion emissions were studied at a test facility, indicating significantly lower δ18O of CO from wood combustion compared to traffic emissions. At the village and the motorway site, we observed very pronounced diurnal δ18O-variations of CO with an amplitude of up to 8‰. Solving the isotope mass balance equation for three distinct sources (wood combustion, traffic, clean background air resulted in diurnal patterns consistent with other indicators for wood burning and traffic. The average night-time contribution of wood-burning to total CO was 70% at the village site, 49% at the motorway site and 29% at the rural site based on the isotope mass balance. The results, however, depend strongly on the pure source isotope values, which are not very well known. We therefore additionally applied a combined CO/NOx-isotope model for verification. Here, we separated the CO emissions into different sources based on distinct CO/NOx emissions ratios for wood combustion and traffic, and inserted this information in the isotope mass balance equation. Accordingly, a highly significant agreement between measured and calculated δ18

  11. Isotopic Composition of Gaseous Elemental Mercury (Hg0) at Various Sites in Japan

    Yamakawa, A.; Moriya, K.; Yoshinaga, J.


    Mercury (Hg) is a toxic heavy metal, which exists in various chemical forms in the environmental system. In the atmosphere, Hg exists in three forms (Hg0(g), Hg+2(g), and Hg(p)). Hg0(g) is the dominant species of atmospheric Hg, accounting for >95% of the total Hg in the atmosphere. Because Hg0(g) is highly volatile and has limited solubility in water, it cannot be easily removed by wet or dry deposition processes. Therefore, the residence time of Hg0(g) in the atmosphere is relatively long (1 to 2 years), allowing long-range transport from mercury emission source(s). Conversely, Hg+2(g) and Hg(p) are effectively removed from the atmosphere through wet and dry depositions. The determination of mercury source attribution using quantitative data is challenging because Hg0(g) may be deposited on an area upon oxidation to Hg+2(g) and associated with aerosols and particulates to form Hg(p) while the global cycling of Hg0(g). Over the last decade, the development of analytical methods of highly precise Hg isotopic measurements demonstrated mass-dependent fractionation (MDF) and mass-independent fractionation (MIF) of Hg isotopes in environmental samples. For instance, MDF of Hg isotopes is thought to occur during various natural and industrial Hg transformations. MIF of Hg isotopes is observed during abiotic reduction, photochemical and non-photochemical, and physical and chemical processes. Such processes lead to differences in the Hg isotopic composition of different emission sources, both natural and anthropogenic, and atmospheric processes (i.e., transportation, oxidation/reduction, deposition, and reemission). Therefore, Hg isotopic compositions could be used to trace the sources and processes of atmospheric Hg. For securing the reliability and accuracy of atmospheric Hg isotope data, the methods of collection, pretreatment, and isotopic measurement for Hg0(g) were developed to obtain high recovery yield of samples with no Hg isotopic fractionation during each

  12. Perpendicular magnetic anisotropy in composite MgO/CoFeB/Ta/[Co/Pd]n structures

    Garcia-Vazquez, Valentin; Chang, Yao-Jen; Canizo-Cabrera, A.; Garzon-Roman, Abel; Wu, Te-ho


    The impact of a non-magnetic Ta spacer layer on the perpendicular magnetic anisotropy (PMA) of composite magnetic structures constituted by ultra-thin Co/Pd multilayers (MLs) and MgO/CoFeB was studied. Composite structures lacking a Ta layer present in-plane magnetic anisotropy. The strong perpendicular anisotropy observed in sole Co/Pd MLs is not sufficient to pull the magnetic moment out of the film plane, not even after annealing at 300 or 350 °C. PMA with squareness values close to unity and annealing stability up to 350 °C is observed after the insertion of an ultra-thin Ta layer. Our study demonstrates that Ta layer is essential for obtaining perpendicular magnetic axis in MgO/CoFeB/Ta/[Co/Pd]6. The exchange coupling between the MgO/CoFeB bilayer and the Co/Pd MLs is ferromagnetic with sharp switching characteristics. Perpendicular composite structures with sharp magnetization reversal and annealing stability are relevant in perpendicular CoFeB-based magnetic tunnel junctions for the development of gigabit-scale nonvolatile memory.

  13. Fabrication and Characterization of Electrospun PCL-MgO-Keratin-Based Composite Nanofibers for Biomedical Applications

    Maame A. D. Boakye


    Full Text Available Polymeric nanofibers are of great interest in biomedical applications, such as tissue engineering, drug delivery and wound healing, due to their ability to mimic and restore the function of natural extracellular matrix (ECM found in tissues. Electrospinning has been heavily used to fabricate nanofibers because of its reliability and effectiveness. In our research, we fabricated poly(ε-caprolactone-(PCL, magnesium oxide-(MgO and keratin (K-based composite nanofibers by electrospinning a blend solution of PCL, MgO and/or K. The electrospun nanofibers were analyzed by scanning electron microscopy (SEM, Fourier transform infrared spectroscopy (FTIR, mechanical tensile testing and inductively-coupled plasma optical emission spectroscopy (ICP-OES. Nanofibers with diameters in the range of 0.2–2.2 µm were produced by using different ratios of PCL/MgO and PCL-K/MgO. These fibers showed a uniform morphology with suitable mechanical properties; ultimate tensile strength up to 3 MPa and Young’s modulus 10 MPa. The structural integrity of nanofiber mats was retained in aqueous and phosphate buffer saline (PBS medium. This study provides a new composite material with structural and material properties suitable for potential application in tissue engineering.

  14. The influence of chemical composition on the properties and structure Al-Si-Cu(Mg alloys

    M. Kaczorowski


    Full Text Available The mechanical properties of different chemical composition AlSiCuMg type cast alloys after precipitation hardening are presented. The aim of the study was to find out how much the changes in chemistry of aluminum cast alloys permissible by EN-PN standards may influence the mechanical properties of these alloys. Eight AlSi5Cu3(Mg type cast alloys of different content alloying elements were selected for the study. The specimens cut form test castings were subjected to precipitation hardening heat treatment. The age hardened specimens were evaluated using tensile test, hardness measurements and impact test. Moreover, the structure investigation were carried out using either conventional light Metallography and scanning (SEM and transmission (TEM electron microscopy. The two last methods were used for fractography observations and precipitation process observations respectively. It was concluded that the changes in chemical composition which can reach even 2,5wt.% cause essential differences of the structure and mechanical properties of the alloys. As followed from quantitative evaluation and as could be predicted theoretically, copper and silicon mostly influenced the mechanical properties of AlSi5Cu3(Mg type cast alloys. Moreover it was showed that the total concentration of alloying elements accelerated and intensifies the process of decomposition of supersaturated solid solution. The increase of Cu and Mg concentration increased the density of precipitates. It increases of strength properties of the alloys which are accompanied with decreasing in ductility.

  15. Hydriding and Dehydriding Characteristics of Mechanically Alloyed LaMg17Ni Composite Material

    李谦; 蒋利军; 林勤; 周国治; 詹峰; 郑强; 魏秀英


    A composite material with the nominal composition LaMg17Ni was synthesized by mechanical alloying and the hydriding/dehydriding (H/D) behaviors of this material were studied at several temperatures. This material has a hydrogen storage capacity (5.76% H2, mass fraction) lower than conventionally alloyed La2Mg17 (6.63% H2, mass fraction) without activation but shows a superior hydriding/dehydriding kinetic property. At 523 K it absorbed 4.97% (mass fraction) in less than 1 min, approximately 100 times faster than La2Mg17 alloy under the same conditions. This attractive kinetic property of the alloy can be ascribed to the catalytic action of Mg2Ni, LaH2 and La as well as the multiphase structure formed in the preparation processes. The relationships between the equilibrium plateau pressure and the temperature can be expressed as lgpeq=-2797/T+4.267 (553 K≤T≤623 K) for hydriding and lgpeq=-3957/T+6.063(553 K≤T≤623 K) for dehydriding.

  16. Chemical and Oxygen Isotopic Composition of Roman and Late Antique Glass from Northern Greece

    Alberta Silvestri


    Full Text Available The present paper emphasizes the importance of measuring the oxygen isotopic and chemical compositions of ancient glass, in order to constrain some features such as age, raw materials, and production technologies and to identify the “fingerprint” of local productions. In this context, thirty-nine Roman and late Antique glass samples and eight chert samples from northern Greece were selected and analysed for their oxygen isotopic and chemical compositions. Results show that the majority of glass samples are produced using natron as flux and have δ18O values of about 15.5‰, plus or minus a few tenths of one per mil, suggesting that raw materials probably come from Levantine area. Four samples are heavily enriched in 18O, and their chemical composition clearly shows that they were made with soda plant ash as flux. Isotopic and chemical data of Greek chert samples support the hypothesis of local production of the above samples. About half of the glass samples have chemical compositions, which allow their age to be constrained to the late Antique period. For the remaining glass, similarities with literature compositional groups are reported and discussed.

  17. A non-terrestrial 16O-rich isotopic composition for the protosolar nebula.

    Hashizume, Ko; Chaussidon, Marc


    The discovery in primitive components of meteorites of large oxygen isotopic variations that could not be attributed to mass-dependent fractionation effects has raised a fundamental question: what is the composition of the protosolar gas from which the host grains formed? This composition is probably preserved in the outer layers of the Sun, but the resolution of astronomical spectroscopic measurements is still too poor to be useful for comparison with planetary material. Here we report a precise determination of the oxygen isotopic composition of the solar wind from particles implanted in the outer hundreds of nanometres of metallic grains in the lunar regolith. These layers of the grains are enriched in 16O by >20 +/- 4 per thousand relative to the Earth, Mars and bulk meteorites, which implies the existence in the solar accretion disk of reactions--as yet unknown--that were able to change the 17O/16O and 18O/16O ratios in a way that was not dependent strictly on the mass of the isotope. Photochemical self-shielding of the CO gas irradiated by ultraviolet light may be one of these key processes, because it depends on the abundance of the isotopes, rather than their masses.

  18. The specific carbon isotopic compositions of branched and cyclic hydrocarbons from Fushun oil shale

    DUAN Yi; WU Baoxiang; ZHENG Guodong; ZHANG Hui; ZHENG Chaoyang


    Various branched and cyclic hydrocarbons are isolated from the Fushun oil shale and their carbon isotopes are determined. The analytical results show that the branched and cyclic hydrocarbons are fully separated from n-alkanes by 5 A Molecular-sieve adduction using long time and cold solvent. The branched and cyclic hydrocarbon fraction obtained by this method is able to satisfy the analytic requests of GC-IRMS. The carbon isotopic compositions of these branched and cyclic hydrocarbons obtained from the sample indicate that they are derived from photoautotrophic algae, chemoautotrophic bacteria (-3.4‰ --39.0‰) and methanotrophic bacteria (-38.4‰--46.3‰). However the long-chain 2-methyl-branched alkanes indicate that their carbon isotopic compositions reflect biological origin from higher plants. The carbon isotopic composition of C30 4-methyl sterane (-22.1‰) is the heaviest in all studied ste- ranes, showing that the carbon source or growth condition for its precursor, dinoflagellate, may be different from that of regular steranes. The variation trend of δ13C values between isomers of hopanes shows that 13C-enriched precursors take precedence in process of their epimerization. Methanotrophic hopanes presented reveal the processes of strong transformation of organic matter and cycling of organic carbon in the water column and early diagenesis of oil shale.

  19. Stable carbon isotope composition of monoterpanes in essential oils and crude oils


    Twenty-five monoterpanes from six types of essential oils and hydrogenated turpentine oil have been identified and their stable carbon isotope composition determined.Monoterpanes in essential oils sourced from terrestrial higher plants display a δ13C value in the range of-34‰-26‰,and mostly between-29‰ and-27‰.The δ13C value of any single monoterpane is very consistent in different essential oils.Acyclic monoterpanes show closer isotope composition between-28.6‰ and-26.2‰,with an average value of-27.7‰.In contrast,the isotope composition of cyclic monoterpanes is more scattered with an average value of-28.6‰.Isotopic fractionation with 13C enrichment has been observed during both artificial and geological hydrogenation of monoterpenoids to monoterpanes,and this is more obvious for the acyclic monoterpenoids.In addition to higher plants,acyclic monoterpane 2,6-dimethylheptane in crude oil can also be originated from other organic inputs.

  20. Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts

    Rizo, Hanika; Walker, Richard J.; Carlson, Richard W.; Horan, Mary F.; Mukhopadhyay, Sujoy; Manthos, Vicky; Francis, Don; Jackson, Matthew G.


    How much of Earth's compositional variation dates to processes that occurred during planet formation remains an unanswered question. High-precision tungsten isotopic data from rocks from two large igneous provinces, the North Atlantic Igneous Province and the Ontong Java Plateau, reveal preservation to the Phanerozoic of tungsten isotopic heterogeneities in the mantle. These heterogeneities, caused by the decay of hafnium-182 in mantle domains with high hafnium/tungsten ratios, were created during the first ~50 million years of solar system history, indicating that portions of the mantle that formed during Earth’s primary accretionary period have survived to the present.

  1. The Oxygen Isotopic Composition of MIL 090001: A CR2 Chondrite with Abundant Refractory Inclusions

    Keller, Lindsay P.; McKeegan, K. D.; Sharp, Z. D.


    MIL 090001 is a large (>6 kg) carbonaceous chondrite that was classified as a member of the CV reduced subgroup (CVred) that was recovered during the 2009-2010 ANSMET field season [1]. Based on the abundance of refractory inclusions and the extent of aqueous alteration, Keller [2] suggested a CV2 classification. Here we report additional mineralogical and petrographic data for MIL 090001, its whole-rock oxygen isotopic composition and ion microprobe analyses of individual phases. The whole rock oxygen isotopic analyses show that MIL 090001 should be classified as a CR chondrite.

  2. Electrochemical performance of Si-CeMg{sub 12} composites as anode materials for Li-ion batteries

    Lu, Z.W. [Institute of New Energy Material Chemistry, Nankai University, Tianjin 300071 (China); Tianjin Institute of Power Sources, Tianjin 300381 (China); Wang, G.; Gao, X.P. [Institute of New Energy Material Chemistry, Nankai University, Tianjin 300071 (China); Liu, X.J.; Wang, J.Q. [Tianjin Institute of Power Sources, Tianjin 300381 (China)


    The Si-CeMg{sub 12} composites with 30 wt.%, 40 wt.% and 50 wt.% Si, were synthesized by directly ball milling Si and CeMg{sub 12} alloy. The microstructure of the Si-CeMg{sub 12} composites is confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. It is demonstrated from TEM images that active Si nanoparticles are distributed in the inactive CeMg{sub 12} matrix. The electrochemical performance of the Si-CeMg{sub 12} composites as a function of Si content is investigated. The maximum reversible (charge) capacities of the ball-milled Si-CeMg{sub 12} composites with 30 wt.%, 40 wt.% and 50 wt.% Si reach 470, 690 and 1080 mAh g{sup -1}, respectively, after full activations. It is found that the Si-CeMg{sub 12} composite with 40 wt.% Si delivers a larger reversible capacity and better cycle ability because the uniform distribution of active Si nanoparticles embedded in the CeMg{sub 12} matrix, which can accommodate the volume expansion of the composite during Li-alloying/dealloying processes. After subsequent cycles, the recrystallization of Si with lattice shrinkage is observed, which is unfavorable to the Li-alloying/dealloying reaction. The degeneration of CeMg{sub 12}-Si composites during repeated cycling is attributed not only to the Si pulverization led by the volume change, but partially also to the irreversible phase transformation of Si. (author)

  3. Temperature and Oxygen Isotope Composition of The Ediacaran Ocean: Constraints From Clumped Isotope Carbonate Thermometry

    Bonifacie, M.; Eiler, J. M.; Fike, D. A.


    The temperature and chemical variations of the early oceans on Earth are highly debated, particularly for periods associated with significant evolutionary change and/or extinction. The temperature of past oceans has been estimated based on conventional carbonate-water and/or silicate-water stable oxygen isotope thermometry. Precambrian carbonates and silicates both exhibit a long-term secular trend of increasing δ18O values with decreasing age. This trend has been used to support two opposite - though related - interpretations: the Earth's oceans gradually cooled over the course of the Proterozoic eon, from a maximum of ~ 60-90°C at ~ 2.5Ga (and were, on average, relatively warm during much of the Paleozoic era) [1]. This interpretation has been supported by Si-isotope proxies and the thermal tolerances of proteins in various classes of microbial organisms [2-3]. Alternatively, the δ18O value of the oceans has gradually increased through time [4-5], and mean Earth surface temperatures varied over a narrow range similar to modern conditions. In other terms, one either assumes an ocean of constant δ18O and infers that climate varied dramatically, or vise versa. Finally, it is possible that post- depositional processes (e.g., diagenesis, burial metamorphism, weathering) has modified the δ18O values of all or most Precambrian sedimentary carbonates and silicates, overprinting any paleoclimatic variations. Carbonate 'clumped isotope' thermometry provides a new way to independently test these hypotheses because it allows one to determine the apparent growth temperatures of carbonate minerals based on their abundances of 13C-18O bonds, as reflected by the 'Δ47' value of CO2 extracted by phosphoric acid digestion [6]. This method is thermodynamically based and independent of the δ18O of water from which the carbonate grew. We will report the initial results of measurements of 'Δ47 for a suite of carbonates from the Sultanate of Oman. This Ediacaran age (~ 635 to

  4. Change of Sm-Nd isotope composition during weathering of till

    Öhlander, Björn; Ingri, Johan; Land, Magnus; Schöberg, Hans


    Weathering of till in northern Sweden results in the formation of well-developed spodosols. The till is dominated by 1.9-1.8 Ga granitic material. The REE are among the elements most strongly depleted during weathering, and the loss of REE from the E-horizon decreases as the atomic number increases. To study if weathering leads to a change of the Nd isotope composition, we have analysed the Nd isotopic composition of the various horizons including living plants and humus of two profiles of weathered till (typic haplocryods) in northern Sweden. As much as between 65.6 and 75.3% of the Sm and Nd in the fraction has been lost from the E-horizon, and between 32.5 and 54.7% from the B-horizon. Nd has been lost to a slightly greater extent than Sm. The two C-horizon samples have ɛ Nd(0) values of -22.1 and -23.2. Corresponding E-horizon values are -18.1 and -20.2. The B-horizon values are intermediate between the values of the E and C horizons. It is concluded that the weathering leads to a change in the Sm/Nd ratio resulting in a change of the Sm-Nd isotope composition. The plant and humus samples deviate even more from the unweathered till. For one station the results could be interpreted as if the Sm and Nd taken up by the plants had similar isotope characteristics as the amounts of these elements released by weathering in the E-horizon. For the other station it is probable that the Nd isotope composition of the organic samples is dominated by Nd released by till weathering which, however, is mixed with another Nd-source, possibly an airborne component. The explanation to the change of isotope compostion in the till is that a larger proportion of the Nd released by weathering is released from minerals with a lower Sm/Nd ratio than the bulk soil, compared with the amount released from minerals with a higher Sm/Nd ratio. Although the various REE-carrying minerals had the same initial Nd isotopic composition, 1.8-1.9 Ga of decay of 147Sm to 143Nd has resulted in a

  5. Precipitation Sequence of a SiC Particle Reinforced Al-Mg-Si Alloy Composite

    Shen, Rujuan; Wang, Yihan; Guo, Baisong; Song, Min


    In this study, the precipitation sequence of a 5 vol.% SiC particles reinforced Al-1.12 wt.%Mg-0.77 wt.%Si alloy composite fabricated by traditional powder metallurgy method was investigated by transmission electron microscopy and hardness measurements. The results indicated that the addition of SiC reinforcements not only suppresses the initial aging stage but also influences the subsequent precipitates. The precipitation sequence of the composite aged at 175 °C can be described as: Guinier-Preston (G.P.) zone → β″ → β' → B', which was confirmed by high-resolution transmission electron microscopy. This work might provide the guidance for the design and fabrication of hardenable automobile body sheet by Al-based composites with enhanced mechanical properties.

  6. Precipitation Sequence of a SiC Particle Reinforced Al-Mg-Si Alloy Composite

    Shen, Rujuan; Wang, Yihan; Guo, Baisong; Song, Min


    In this study, the precipitation sequence of a 5 vol.% SiC particles reinforced Al-1.12 wt.%Mg-0.77 wt.%Si alloy composite fabricated by traditional powder metallurgy method was investigated by transmission electron microscopy and hardness measurements. The results indicated that the addition of SiC reinforcements not only suppresses the initial aging stage but also influences the subsequent precipitates. The precipitation sequence of the composite aged at 175 °C can be described as: Guinier-Preston (G.P.) zone → β″ → β' → B', which was confirmed by high-resolution transmission electron microscopy. This work might provide the guidance for the design and fabrication of hardenable automobile body sheet by Al-based composites with enhanced mechanical properties.

  7. Neutron absorption of Al-Si-Mg-B{sub 4}C composite

    Abdullah, Yusof, E-mail:; Yusof, Mohd Reusmaazran [Malaysian Nuclear Agency, 43000, Bangi Selangor (Malaysia); Ibrahim, Anis Syukriah; Daud, Abdul Razak [Department of Applied Physics, Faculty of Science & Technology, National University of Malaysia, 43600, Bangi Selangor (Malaysia)


    Al-Si-Mg-B{sub 4}C composites containing 2-8 wt% of B{sub 4}C were prepared by stir casting technique. Homogenization treatment was carried out at temperatures of 540°C for 4 houra and followed by ageing at 180°C for 2 houra. Microstructure and phase identification were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. Neutron absorption study was investigated using neutron source Am/Be{sup 241}. The result indicated that higher B{sub 4}C content improved the neutron absorption property. Meanwhile homogeneity of the composite was increased by ageing processes. This composite is potential to be used as neutron shielding material especially for nuclear reactor application.

  8. Dehydrogenation properties and mechanisms of MgH2-NiCl2 and MgH2-NiCl2-graphene hydrogen storage composites

    Zhang, J.; Qu, H.; Yan, S.; Yin, L. R.; Zhou, D. W.


    The four hydrogen storage systems including pure MgH2, MgH2-5 wt%NiCl2, MgH2-10 wt%NiCl2 and MgH2-10 wt%NiCl2-10 wt%graphene were prepared by ball-milling in this work. Using experimental X-ray diffraction, scanning electron microscopy and differential scanning calorimetry testing methods in combination with first-principle calculations, the dehydrogenation properties and mechanisms of NiCl2 single-doped and NiCl2-graphene co-doped MgH2 composites were systematically investigated. Experimental results show that the NiCl2 single-doping is conductive to decreasing the size of MgH2 grains and particles. The co-doping of NiCl2 and graphene not only reduces the size of MgH2 grains and particles, but also contributes to the uniformity of MgH2 particles. As compared with milled pure MgH2, the dehydrogenation peak temperatures are decreased by 24 °C and 47 °C for the 10 wt%NiCl2 single-doped and 10 wt%NiCl2-10 wt%graphene co-doped MgH2 systems, respectively. It is demonstrated that the co-doping of NiCl2 and graphene exhibits the synergistic effects of confinement and catalysis on improving the dehydrogenation properties of MgH2. The first-principle calculations indicate that the co-doping of NiCl2 and graphene leads to the distortion of MgH2 atomic-configuration and results in the charge transfer between the dopants and MgH2, which induce the weakened structural stability and decreased dehydrogenation enthalpy of MgH2.

  9. Predicting the Isotopic Composition of Subduction-Filtered Subducted Oceanic Crust and Sediment

    White, W. M.


    The chemical and isotopic character of mantle plumes, which produce oceanic island volcanoes, are widely thought to reflect the presence of recycled oceanic crust and sediment. Isotopic systematics suggest the “cycle time” for this process is 1 Ga or longer, but it should be possible to use a simple mass balance approach to discern how the presently operating subduction zone filter affects the ratios of radioactive parent to radiogenic daughter isotopes. Simple uniformitarian assumptions can then be used to predict the present isotopic composition of anciently subducted lithosphere. Our underlying assumption in deciphering the subduction zone filter is that the flux of an element into the deep mantle is simply equal to the flux of element into the subduction zone less the flux of that element into subduction zone magmas. The former is readily calculated from published data. The latter can be calculated by estimating parental magma compositions, arc accretion rates, and the assumption that arc magma compositions differ from MORB only because of material derived from subducting crust and sediment. Using this approach for 8 intra-oceanic subduction zones, we find 73% of Th and Pb, 79% of U, 80% of Rb and Sr, 93% of Nd and 98% of Sm survive the subduction zone filter. The subduction zone filter systematically increases Sm/Nd ratios in all subduction zones, but the effect is small, with a weighted mean increase of 1.5%. The effect of subduction is to decrease the Sm/Nd of the mantle, but only slightly. The effect of subduction is to increase the Rb/Sr of the mantle, but the subduction zone filter does not have a systematic effect on Rb/Sr ratios: it significantly increases in Rb/Sr in 3 subduction zones and significantly decreases it in one; the weighted mean shows no significant change. The effect of the subduction zone filter on U/Pb is also not systematic. U/Pb ratios in the mantle fluxes are bimodal, with values equal to or lower than the bulk Earth value in 4

  10. Mg-Zn based composites reinforced with bioactive glass (45S5) fabricated via powder metallurgy

    Ab llah, N.; Jamaludin, S. B.; Daud, Z. C.; Zaludin, M. A. F.


    Metallic implants are shifting from bio-inert to bioactive and biodegradable materials. These changes are made in order to improve the stress shielding effect and bio-compatibility and also avoid the second surgery procedure. Second surgery procedure is required if the patient experienced infection and implant loosening. An implant is predicted to be well for 15 to 20 years inside patient body. Currently, magnesium alloys are found to be the new biomaterials because of their properties close to the human bones and also able to degrade in the human body. In this work, magnesium-zinc based composites reinforced with different content (5, 15, 20 wt. %) of bioactive glass (45S5) were fabricated through powder metallurgy technique. The composites were sintered at 450˚C. Density and porosity of the composites were determined using the gas pycnometer. Microstructure of the composites was observed using an optical microscope. In-vitro bioactivity behavior was evaluated in the simulated body fluid (SBF) for 7 days. Fourier Transform Infrared (FTIR) was used to characterize the apatite forming on the samples surface. The microstructure of the composite showed that the pore segregated near the grain boundaries and bioglass clustering was observed with increasing content of bioglass. The true density of the composites increased with the increasing content of bioglass and the highest value of porosity was indicated by the Mg-Zn reinforced with 20 wt.% of bioglass. The addition of bio-glass to the Mg-Zn has also induced the formation of apatite layer after soaking in SBF solution.

  11. Microstructure Evolution and Mechanical and Corrosion Behavior of Accumulative Roll Bonded Mg-2%Zn/Al-7075 Multilayered Composite

    Anne, Gajanan; Ramesh, M. R.; Shivananda Nayaka, H.; Arya, Shashi Bhushan; Sahu, Sandeep


    Multilayered composite of Mg-2%Zn/Al-7075 was developed by accumulative roll bonding (ARB) of wrought Mg-2%Zn and aluminum 7075 alloy. The Mg-2%Zn/Al-7075 multilayered composite exhibited density of 2295 kg/m3 and an average grain size of 1 and 1.3 μm in Mg-2%Zn and Al-7075 layers, respectively. A thorough microstructural characterization was performed on the composites by scanning electron microscope, electron backscatter diffraction (EBSD), transmission electron microscope and phase analysis by x-ray diffraction. In addition, mechanical properties were evaluated by microhardness and tensile tests. Corrosion behavior of the multilayered composite was examined using electrochemical polarization test. EBSD analysis showed the presence of ultrafine grains with high-angle grain boundaries. The composite exhibited a significant improvement in ultimate tensile strength ( 1.82 times) and elongation ( 1.5 times) as compared with Mg-2%Zn alloy, after four-pass ARB process.

  12. Mechanical properties of particulate composites based on a body-centered-cubic Mg-Li alloy containing boron

    Whalen, R. T.; Gonzalez-Doncel, G.; Robinson, S. L.; Sherby, O. D.


    The effect of substituting the Mg metal in Mg-B composites by a Mg-14 wt pct Li solid solution on the ductility of the resulting composite was investigated using elastic modulus measurements on the P/M composite material prepared with a dispersion of B particles (in a vol pct range of 0-30) in a matrix of Mg-14 wt pct Li-1.5 wt pct Al. It was found that the elastic modulus of the composites increased rapidly with increasing boron, with specific stiffness values reaching about two times that of most structural materials. The values of the compression and tensile strengths increased significantly with boron additions. Good tensile ductility was achieved at the level of 10 vol pct B. However, at 20 vol pct B, the Mg-Li composite exhibited only limited tensile ductility (about 2 percent total elongation).

  13. Stable isotope and chemical compositions of European and Australasian ciders as a guide to authenticity.

    Carter, James F; Yates, Hans S A; Tinggi, Ujang


    This paper presents a data set derived from the analysis of bottled and canned ciders that may be used for comparison with suspected counterfeit or substitute products. Isotopic analysis of the solid residues from ciders (predominantly sugar) provided a means to determine the addition of C4 plant sugars. The added sugars were found to comprise cane sugar, high-fructose corn syrup, glucose, or combinations. The majority of ciders from Australia and New Zealand were found to contain significant amounts of added sugar, which provided a limited means to distinguish these ciders from European ciders. The hydrogen and oxygen isotopic compositions of the whole ciders (predominantly water) were shown to be controlled by two factors, the water available to the parent plant and evaporation. Analysis of data derived from both isotopic and chemical analysis of ciders provided a means to discriminate between regions and countries of manufacture.

  14. Modelling the regional climate and isotopic composition of Svalbard precipitation using REMOiso

    Divine..[], D.V.; Sjolte, Jesper; Isaksson, E.;


    Simulations of a regional (approx. 50 km resolution) circulation model REMOiso with embedded stable water isotope module covering the period 1958-2001 are compared with the two instrumental climate and four isotope series (d18O) from western Svalbard. We examine the data from ice cores drilled...... on Svalbard ice caps in 1997 (Lomonosovfonna, 1250 m asl) and 2005 (Holtedahlfonna, 1150 m asl) and the GNIP series from Ny-angstrom lesund and Isfjord Radio. The surface air temperature (SAT) and precipitation data from Longyearbyen and Ny-angstrom lesund are used to assess the skill of the model...... in reproducing the local climate. The model successfully captures the climate variations on the daily to multidecadal times scales although it tends to systematically underestimate the winter SAT. Analysis suggests that REMOiso performs better at simulating isotope compositions of precipitation in the winter...

  15. Carbon isotope composition of low molecular weight hydrocarbons and monocarboxylic acids from Murchison meteorite

    Yuen, G.; Blair, N.; Des Marais, D. J.; Chang, S.


    Carbon isotopic compositions have been measured for individual hydrocarbons and monocarboxylic acids from the Murchison meteorite, a C2 carbonaceous chondrite which fell in Australia in 1969. With few exceptions, notably benzene, the volatile products are substantially isotopically heavier than their terrestrial counterparts, signifying their extraterrestrial origin. For both classes of compounds, the ratio of C-13 to C-12 decreases with increasing carbon number in a roughly parallel manner, and each carboxylic acid exhibits a higher isotopic ratio than the hydrocarbon containing the same number of carbon atoms. These trends are consistent with the kinetically controlled synthesis of higher homologues from lower ones. The results suggest the possibility that the production mechanisms for hydrocarbons and carboxylic acids may be similar, and impose constraints on the identity of the reactant species.

  16. Absolute isotopic composition and atomic weight of neodymium using thermal ionization mass spectrometry.

    Zhao, Motian; Zhou, Tao; Wang, Jun; Lu, Hai; Fang, Xiang; Guo, Chunhua; Li, Qiuli; Li, Chaofeng


    Synthetic mixtures prepared gravimetrically from highly enriched isotopes of neodymium in the form of oxides of well-defined purity were used to calibrate a thermal ionization mass spectrometer. A new error analysis was applied to calculate the final uncertainty of the atomic weight value. Measurements on natural neodymium samples yielded an absolute isotopic composition of 27.153(19) atomic percent (at.%) 142Nd, 12.173(18) at.% 143Nd, 23.798(12) at.% 144Nd, 8.293(7) at.% 145Nd, 17.189(17) at.% 146Nd, 5.756(8) at.% 148Nd, and 5.638(9) at.% 150Nd, and the atomic weight of neodymium as 144.2415(13), with uncertainties given on the basis of 95% confidence limits. No isotopic fractionation was found in terrestrial neodymium materials.

  17. A variety of microstructures in Mg/Cu super-laminate composites caused by competitive reactions during hydrogenation

    Tanaka, K.; Shibata, K.; Nishida, Y.; Kurumatani, K.; Kondo, R.; Kikuchi, S.; Takeshita, H. T.


    A variety of microstructures in Mg/Cu super-laminate composites (SLCs) caused by competitive reactions during hydrogenation has been shown experimentally. Two types of MgCu2 structures, three-dimensional (3-D) network and layer, were observed after initial hydrogenation of Mg/Cu SLCs under the conditions of 573K, 86.4ks in H2 of 3-3MPa. It was proposed that Mg/Cu SLCs could be hydrogenated by two kinds of processes. The one is alloying Mg with Cu to form Mg2Cu followed by hydrogenation of Mg2Cu, leading to the formation of 3-D network of MgCu2. The other is hydrogenation of Mg followed by the reaction of MgH2 to Cu, leading to the formation of layer MgCu2. SEM observations revealed that there existed Mg2Cu nano-crystals at the interface between Mg and Cu in as-rolled Mg/Cu SLCs, and layer MgCu2 at the interface between MgH2 and Cu in pellets of MgH2 powder and Cu powder heated under the conditions of 673K, 86.4ks in H2 of 8.0 MPa. The existence of Mg2Cu nano-crystals enables alloying Mg with Cu at low temperatures (<473K).

  18. Stable isotope study of a new chondrichthyan fauna (Kimmeridgian, Porrentruy, Swiss Jura): an unusual freshwater-influenced isotopic composition for the hybodont shark Asteracanthus

    Leuzinger, L.; Kocsis, L.; Billon-Bruyat, J.-P.; Spezzaferri, S.; Vennemann, T.


    Chondrichthyan teeth (sharks, rays, and chimaeras) are mineralized in isotopic equilibrium with the surrounding water, and parameters such as water temperature and salinity can be inferred from the oxygen isotopic composition (δ18Op) of their bioapatite. We analysed a new chondrichthyan assemblage, as well as teeth from bony fish (Pycnodontiformes). All specimens are from Kimmeridgian coastal marine deposits of the Swiss Jura (vicinity of Porrentruy, Ajoie district, NW Switzerland). While the overall faunal composition and the isotopic composition of bony fish are generally consistent with marine conditions, unusually low δ18Op values were measured for the hybodont shark Asteracanthus. These values are also lower compared to previously published data from older European Jurassic localities. Additional analyses on material from Solothurn (Kimmeridgian, NW Switzerland) also have comparable, low-18O isotopic compositions for Asteracanthus. The data are hence interpreted to represent a so far unique, freshwater-influenced isotopic composition for this shark that is classically considered a marine genus. While reproduction in freshwater or brackish realms is established for other hybodonts, a similar behaviour for Asteracanthus is proposed here. Regular excursions into lower salinity waters can be linked to the age of the deposits and correspond to an ecological adaptation, most likely driven by the Kimmeridgian transgression and by the competition of the hybodont shark Asteracanthus with the rapidly diversifying neoselachians (modern sharks).

  19. Stable isotope study of a new chondrichthyan fauna (Kimmeridgian, Porrentruy, Swiss Jura: an unusual freshwater-influenced isotopic composition for the hybodont shark Asteracanthus

    L. Leuzinger


    Full Text Available Chondrichthyan teeth (sharks, rays and chimaeras are mineralised in isotopic equilibrium with the surrounding water, and parameters such as water temperature and salinity can be inferred from the oxygen isotopic composition (δ18Op of their bioapatite. We analysed a new chondrichthyan assemblage, as well as teeth from bony fish (Pycnodontiformes. All specimens are from Kimmeridgian coastal marine deposits of the Swiss Jura (vicinity of Porrentruy, Ajoie district, NW Switzerland. While the overall faunal composition and the isotopic composition of bony fish are consistent with marine conditions, unusually low δ18Op values were measured for the hybodont shark Asteracanthus. These values are also lower compared to previously published data from older European Jurassic localities. Additional analyses on material from Solothurn (Kimmeridgian, NW Switzerland also have comparable, low-18O isotopic compositions for Asteracanthus. The data are hence interpreted to represent a so far unique, freshwater-influenced isotopic composition for this shark that is classically considered as a marine genus. While reproduction in freshwater or brackish realms is established for other hybodonts, a similar behaviour for Asteracanthus is proposed here. Regular excursions into lower salinity waters can be linked to the age of the deposits and correspond to an ecological adaptation, most likely driven by the Kimmeridgian transgression and by the competition of the primitive shark Asteracanthus with the rapidly diversifying neoselachians (modern sharks.

  20. Experimental assessment of environmental influences on the stable isotopic composition of Daphnia pulicaria and their ephippia

    Schilder, J.; Tellenbach, C.; Möst, M.; Spaak, P.; van Hardenbroek, M.; Wooller, M. J.; Heiri, O.


    The stable isotopic composition of fossil resting eggs (ephippia) of Daphnia spp. is being used to reconstruct past environmental conditions in lake ecosystems. However, the underlying assumption that the stable isotopic composition of the ephippia reflects the stable isotopic composition of the parent Daphnia, of their diet and of the environmental water have yet to be confirmed in a controlled experimental setting. We performed experiments with Daphnia pulicaria cultures, which included a control treatment conducted at 12 °C in filtered lake water and with a diet of fresh algae, and three treatments in which we manipulated the stable carbon isotopic composition (δ13C value) of the algae, stable oxygen isotopic composition (δ18O value) of the water, and the water temperature, respectively. The stable nitrogen isotopic composition (δ15N value) of the algae was similar for all treatments. At 12 °C, differences in algal δ13C values and in δ18O values of water are reflected in those of Daphnia. The differences between ephippia and Daphnia stable isotope ratios were similar in the different treatments (δ13C: + 0.2 ± 0.4‰ (SD); δ15N: -1.6 ± 0.4‰; δ18O: -0.9 ± 0.4‰) indicating that changes in dietary δ13C and δ18O values of water are passed on to these fossilizing structures. A higher water temperature (20 °C) resulted in lower δ13C values in Daphnia and ephippia than in the other treatments with the same food source and in a minor change in the difference between δ13C values of ephippia and Daphnia (to -1.3 ± 0.3‰). This may have been due to microbial processes or increased algal respiration rates in the experimental containers, which may not affect Daphnia in natural environments. There was no significant difference in the offset between δ18O and δ15N values of ephippia and Daphnia between the 12 °C and 20 °C treatments, but the δ18O values of Daphnia and ephippia were on average 1.2‰ lower at 20 °C compared with 12 °C. We conclude

  1. Lead isotopic compositions of common arsenical pesticides used in New England

    Ayuso, Robert; Foley, Nora; Robinson, Gilpin; Wandless, Gregory; Dillingham, Jeremy


    The three most important arsenical pesticides and herbicides that were extensively used on apple, blueberry, and potato crops in New England from mid-1800s to recent times are lead arsenate, calcium arsenate, and sodium arsenate. Lead arsenate was probably the most heavily used of the arsenical pesticides until it was banned in 1988. Other metal-arsenic pesticides were also used but in lesser amounts. A recent report identified areas in New England where arsenical pesticides were used extensively (Robinson and Ayuso, 2004). On the basis of factor analysis of metal concentrations in stream sediment samples, a positive correlation with pesticide use was shown in regions having stream sediment sample populations that contained concentrations of high arsenic and lead. Lead isotope compositions of stream sediments from areas with heavy use of the pesticides could not be entirely explained by lead originating from rock sulfides and their weathering products. An industrial lead contribution (mostly from atmospheric deposition of lead) was suggested in general to explain the lead isotopic distributions of the stream sediments that could not be accounted for by the natural lead in the environment. We concluded that when agricultural land previously contaminated with arsenical pesticides is urbanized, pesticide residues in the soils and stream sediments could be released into the groundwater. No lead isotopic data characterizing the compositions of pesticides were available for comparison. We have determined the lead isotopic compositions of commonly used pesticides in New England, such as lead arsenate, sodium metaarsenite, and calcium arsenate, in order to assist in future isotopic comparisons and to better establish anthropogenic sources of Pb and As. New data are also presented for copper acetoarsenite (or Paris green), methyl arsonic acid and methane arsonic acid, as well as for arsanilic acid, all of which are used as feed additives to promote swine and poultry growth

  2. Soil Drying Effects on the Carbon Isotope Composition of Soil Respiration

    Phillips, C. L.; Nickerson, N.; Risk, D.; Kayler, Z. E.; Rugh, W.; Mix, A. C.; Bond, B. J.


    Stable isotopes are used widely as a tool for determining sources of carbon (C) fluxes in ecosystem C studies. Environmental factors that change over time, such as moisture, can create dynamic changes in the isotopic composition of C assimilated by plants, and offers a unique opportunity to distinguish fast- responding plant C from slower-responding soil C pools, which under steady-state conditions may be too similar isotopically to partition. Monitoring the isotopic composition of soil respiration over a period of changing moisture conditions is potentially a useful approach for characterizing plant contributions to soil respiration. But this partitioning hinges on the assumption that any change in the isotopic signature of soil respiration is solely due to recent photosynthetic discrimination, and that post-photosynthetic processes, such as microbial respiration, do not discriminate as moisture decreases. The purpose of the present study is to test the assumption that δ13CO2 from microbial respiration remains static as soil dries. We conducted a series of greenhouse experiments employing different techniques to isolate microbial respiration from root respiration. The first involves removing roots from soil, and showed that when roots are present, respiration from dry soil is enriched in 13C relative to moist soil, but when roots are absent, respiration is isotopically similar from moist and dry soils. This indicates that rhizospheric respiration changes isotopically with moisture whereas soil microbial respiration does not. In contrast, a second experiment in which soil columns without plants were monitored as they dried, showed respiration from very dry soil to be enriched by 8‰ relative to moist soil. However, simulations with an isotopologue-based soil gas diffusion model demonstrate that at least a portion of the apparent enrichment is due to non-steady state gas transport processes. Careful sampling methodologies which prevent or account for non

  3. Nanoporous composites prepared by a combination of SBA-15 with Mg-Al mixed oxides. Water vapor sorption properties.

    Pérez-Verdejo, Amaury; Sampieri, Alvaro; Pfeiffer, Heriberto; Ruiz-Reyes, Mayra; Santamaría, Juana-Deisy; Fetter, Geolar


    This work presents two easy ways for preparing nanostructured mesoporous composites by interconnecting and combining SBA-15 with mixed oxides derived from a calcined Mg-Al hydrotalcite. Two different Mg-Al hydrotalcite addition procedures were implemented, either after or during the SBA-15 synthesis (in situ method). The first procedure, i.e., the post-synthesis method, produces a composite material with Mg-Al mixed oxides homogeneously dispersed on the SBA-15 nanoporous surface. The resulting composites present textural properties similar to the SBA-15. On the other hand, with the second procedure (in situ method), Mg and Al mixed oxides occur on the porous composite, which displays a cauliflower morphology. This is an important microporosity contribution and micro and mesoporous surfaces coexist in almost the same proportion. Furthermore, the nanostructured mesoporous composites present an extraordinary water vapor sorption capacity. Such composites might be utilized as as acid-base catalysts, adsorbents, sensors or storage nanomaterials.

  4. REE characteristics and Pb, Sr and Nd isotopic compositions of steel plant emissions.

    Geagea, M Lahd; Stille, P; Millet, M; Perrone, Th


    A comprehensive Pb-Sr-Nd isotope and REE tracer study of atmospheric trace metal pollution by a steel plant situated to the north of the urban communities of Strasbourg (France) and Kehl (Germany) has been performed using tree barks as biomonitors. The 206Pb/207Pb and 208Pb/207Pb isotopic ratios of the steel plant's filter dust are similar to values found in dust of waste incinerators. The 87Sr/86Sr ratio is similar to present-day ratios of Phanerozoic or Precambrian granitic rocks. The 143Nd/144Nd isotopic composition is very low and corresponds to an (Nd) value of -17.5. Such a low value is characteristic of old Precambrian granitic rocks and banded iron formations. Thus, this low (Nd) value might point to the origin of the iron necessary for the steel production. The fact, that this isotopic composition does not occur in crustal rocks of Western Central Europe makes the Nd isotope ratio a powerful tool to trace steel plants atmospheric emissions. The rare earth element (REE) distribution pattern of the steel plant's filter dust shows very specific fractionations like La and Nd enrichments which are traceable in tree barks over a distance of 4 km. The Pb, Sr and Nd isotope ratios not only enable the steel plant's emissions to be traced in a north-easterly direction, along the principal wind pathway but also enables the interference of this emission at 4 km NE from the steel plant with another atmospheric component originating from the Strasbourg Rhine harbour to be identified.

  5. Detection of phosphohydrolytic enzyme activity through the oxygen isotope composition of dissolved phosphate

    Colman, A. S.


    Phosphohydrolytic enzymes play an important role in phosphorus remineralization. As they release phosphate (Pi) from various organophosphorus compounds, these enzymes facilitate the transfer of oxygen atoms from water to the phosphoryl moieties. Most such enzymatic reactions impart a significant isotopic fractionation to the oxygen transferred. If this reaction occurs within a cell, then the resultant oxygen isotope signal is overprinted by continued recycling of the Pi. However, if this reaction occurs extracellularly, then the isotopic signal will be preserved until the Pi is transported back into a cell. Thus, the oxygen isotope composition of Pi (δ18Op) in an aquatic ecosystem can serve as a useful indicator of the mechanisms by which P is remineralized. We develop a time-dependent model illustrating the sensitivity of the δ18O of dissolved phosphate to various modes of P remineralization. The model is informed by cell lysis experiments that reveal the relative proportions of P­i that are directly liberated from cytosol vs. regenerated from co-liberated dissolved organic phosphorus compounds via extracellular hydrolysis. By incorporating both cellular uptake and release fluxes of P, we show that the degree of isotopic disequilibrium in an aquatic ecosystem can be a strong indicator of P remineralization mode. Apparent oxygen isotope equilibrium between Pi and water arises in this model as a steady-state scenario in which fractionation upon cellular uptake of Pi counterbalances the hydrolytic source flux of disequilibrated Pi. Low and high rates of extracellular phosphohydrolase activity are shown to produce steady-state δ18Op values that are respectively above or below thermodynamic equilibrium compositions.

  6. Ground state properties of neutron-rich Mg isotopes the "island of inversion" studied with laser and $\\beta$-NMR spectroscopy

    Kowalska, M


    Studies in regions of the nuclear chart in which the model predictions of properties of nuclei fail can bring a better understanding of the strong interaction in the nuclear medium. To such regions belongs the so called "island of inversion" centered around Ne, Na and Mg isotopes with 20 neutrons in which unexpected ground-state spins, large deformations and dense low-energy spectra appear. This is a strong argument that the magic N=20 is not a closed shell in this area. In this thesis investigations of isotope shifts of stable $^{24-26}$Mg, as well as spins and magnetic moments of short-lived $^{29,31}$Mg are presented. The successful studies were performed at the ISOLDE facility at CERN using collinear laser and $\\beta$-NMR spectroscopy techniques. The isotopes were investigated as single-charged ions in the 280 nm transition from the atomic ground state $^2\\!$S$_{1/2}$ to one of the two lowest excited states $^2\\!$P$_{1/2 ,\\,3/2}$ using continuous wave laser beams. The isotope-shift measurements with fluor...

  7. Diamond growth history from in situ measurement of Pb and S isotopic compositions of sulfide inclusions

    Rudnick, Roberta L.; Eldridge, C. Stewart; Bulanova, Galina P.


    In a continuing effort to understand crust-mantle dynamics, we have determined the S and Pb isotopic compositions of mantle sulfides encapsulated within diamonds from under the Siberian craton and compared these results to those of previously investigated African counterparts. Because diamond inclusions are isolated from exchange with surrounding mantle, they may preserve the history of diamond growth and act as direct tracers of the origins of mantle materials. Study of these inclusions may thus offer the best chance of recognizing global-scale interaction between Earth's crust and mantle. Although δ34S values of the Siberian sulfides do not deviate significantly from the mantle value of 0‰ ± 3‰, Pb isotopic compositions are highly variable. Pb isotopic compositions of sulfides from peridotitic suite diamonds generally plot near the terrestrial Pb growth curve, with model ages ranging between 0 and 2 Ga, whereas sulfides from eclogitic suite diamonds have radiogenic compositions, plotting beyond the growth curve. These results, which are similar to those for sulfides in African diamonds, suggest that the sulfides from eclogitic suite diamonds were derived from a source with an unusually high U/Pb ratio and may indicate a common process (such as subduction of crystal materials into the mantle) operating beneath Africa and Siberia. The absence of extremely radiogenic Pb in sulfides from eclogite xenoliths suggests that the radiogenic material from which eclogitic suite diamonds grew was a transient feature of the mantle, associated with diamond growth. The ultimate origin of this high U/Pb signature, however, remains enigmatic. Large variations in Pb isotopic composition of sulfides from different zones in a single peridotitic suite diamond document (1) crystallization of the diamond's core near 2.0 Ga, (2) growth of its outer zone in an environment with a high U/Pb ratio similar to the growth environment of eclogitic suite diamonds, and (3) growth of the

  8. Chemistry and isotopic composition of precipitation and surface waters in Khumbu valley (Nepal Himalaya): N dynamics of high elevation basins.

    Balestrini, Raffaella; Polesello, Stefano; Sacchi, Elisa


    We monitored the chemical and isotopic compositions of wet depositions, at the Pyramid International Laboratory (5050 ma.s.l.), and surrounding surface waters, in the Khumbu basin, to understand precipitation chemistry and to obtain insights regarding ecosystem responses to atmospheric inputs. The major cations in the precipitation were NH4(+) and Ca(2+), whereas the main anion was HCO3(-), which constituted approximately 69% of the anions, followed by NO3(-), SO4(2-) and Cl(-). Data analysis suggested that Na(+), Cl(-) and K(+) were derived from the long-range transport of marine aerosols. Ca(2+), Mg(2+) and HCO3(-) were related to rock and soil dust contributions and the NO3(-) and SO4(2-) concentrations were derived from anthropogenic sources. Furthermore, NH4(+) was derived from gaseous NH3 scavenging. The isotopic composition of weekly precipitation ranged from -1.9 to -23.2‰ in δ(18)O, and from -0.8 to -174‰ in δ(2)H, with depleted values characterizing the central part of the monsoon period. The chemical composition of the stream water was dominated by calcite and/or gypsum dissolution. However, the isotopic composition of the stream water did not fully reflect the composition of the monsoon precipitation, which suggested that other water sources contributed to the stream flow. Precipitation contents for all ions were the lowest ones among those measured in high elevation sites around the world. During the monsoon periods the depositions were not substantially influenced by anthropogenic inputs, while in pre- and post-monsoon seasons the Himalayas could not represent an effective barrier for airborne pollution. In the late monsoon phase, the increase of ionic contents in precipitation could also be due to a change in the moisture source. The calculated atmospheric N load (0.30 kg ha(-1) y(-1)) was considerably lower than the levels that were measured in other high-altitude environments. Nevertheless, the NO3(-) concentrations in the surface waters

  9. Isotope composition of winter precipitation and snow cover in the foothills of the Altai

    N. S. Malygina


    Full Text Available Over the past three decades, several general circulation models of the atmosphere and ocean (atmospheric and oceanic general circulation models  – GCMs have been improved by modeling the hydrological cycle with the use of isotopologues (isotopes of water HDO and H2 18O. Input parameters for the GCM models taking into account changes in the isotope composition of atmospheric precipitation were, above all, the results obtained by the network GNIP – Global Network of Isotopes in Precipitation. At different times, on the vast territory of Russia there were only about 40 simultaneously functioning stations where the sampling of atmospheric precipitation was performed. In this study we present the results of the isotope composition of samples taken on the foothills of the Altai during two winter seasons of 2014/15 and 2015/16. Values of the isotope composition of precipitation changed in a wide range and their maximum fluctuations were 25, 202 and 18‰ for δ18О, dexc and δD, respectively. The weighted-mean values of δ18О and δD of the precipitation analyzed for the above two seasons were close to each other (−21.1 and −158.1‰ for the first season and −21.1 and −161.9‰ for the second one, while dexc values differed significantly. The comparison of the results of isotope analysis of the snow cover integral samples with the corresponding in the time interval the weighted-mean values of precipitation showed high consistency. However, despite the similarity of values of δ18О and δD, calculated for precipitation and snow cover, and the results, interpolated in IsoMAP (from data of the GNIP stations for 1960–2010, the dexc values were close to mean annual values of IsoMAP for only the second winter season. According to the trajectory analysis (the HYSPLIT model, the revealed differences between both, the seasons, and the long-term average values of IsoMAP, were associated with a change of main regions where the air masses

  10. Hf isotopic compositions of the standard zircons for U-Pb dating

    XU Ping; WU Fuyuan; XIE Liewen; YANG Yueheng


    Using the newly published Yb isotopic abundances and the mass bias relationship between Yb and Hf, we carried out an analysis of Hf isotopes in the standard zircon 91500 by means of 193 nm laser attached to Neptune multi-collector ICP-MS (LA-MC-ICPMS). The obtained Hf isotopic data, in either in situ or line scan modes, are not only identical for different spot sizes, but also are consistent with previously published results obtained on TIMS or other MC-ICPMS machines within errors. This indicates that it is possible to obtain reliable 176Hf/177Hf isotopic ratios for zircon in either in situ or line scan conditions on LA-MC-ICPMS machine, and the applied procedures in our study for elemental interfering correction are appropriate for the purpose of acquiring satisfactory accuracy for Hf isotope analyses. The Hf isotopic compositions of four zircon standards in high spatial resolution U-Pb dating, 91500, CZ3,CN92-1 and TEMORA, are measured, respectively. The obtained 176Hf/177Hf ratios are 0.282316+4 (n = 34, 2σ) for 91500, 0.281704±6 (n = 16, 2σ) for CZ3, 0.282200±6 (n = 20,2σ-) for CN92-1 and 0.282684±14 (n = 24, 2σ) for TEMORA,respectively, with 176Lu/177Hf ratios of ~0.00031, 0.000036,0.00083 and 0.00127. Zircons 91500 and CZ3 show narrower variations in 176Hf/177Hf and 176Lu/177Hf ratios than those of zircons CN92-1 and TEMORA, and thus are appropriate standards for the Hf isotope analysis.

  11. Effects of Mg content on aging behavior of sub-micron Al2O3p/Al-Cu-Mg composites

    JIANG Long-tao; ZHU De-zhi; CHEN Guo-qin; XIU Zi-yang; WU Gao-hui


    30%Al2O3p/Al-Cu-2.0Mg composite and Al2O3p/Al-Cu-2.5Mg composite with 0.3 μm-Al2O3 particles were fabricated.Age-hardening behaviors of two composites and the related matrix alloys were studied by means of Brinell-hardness measurement,DSC and TEM. The results show that the hardness of the composite is improved obviously because of the addition of sub-micron Al2O3 particles. But the hardness increment of Al2O3p/Al composite after aging is lower than that of the related matrix alloy.Moreover, the formation of GP region is suppressed by the addition of sub-micron Al2O3 particles, which broadens the exothermic peak of S' phase. The increment of Mg content has a different influence on accelerating the aging processes of aluminum alloys and the composites, and the hardness also increases.

  12. Refinement of Mg{sub 2}Si reinforcement in a commercial Al–20%Mg{sub 2}Si in-situ composite with bismuth, antimony and strontium

    Nordin, Nur Azmah; Farahany, Saeed, E-mail:; Ourdjini, Ali; Abu Bakar, Tuty Asma; Hamzah, Esah


    Refinement by addition elements of Al–Mg{sub 2}Si alloys is known to result in a change of primary Mg{sub 2}Si morphology. In this paper, the effects of Bi, Sb and Sr on the characteristic parameters of Al–20%Mg{sub 2}Si in-situ composite have been investigated by computer aided cooling curve thermal analysis and microstructural inspection. Size, density and aspect ratio measurements showed that additions of 0.4 wt.% Bi, 0.8 wt.% Sb and 0.01 wt.% Sr refined the Mg{sub 2}Si reinforcement. Exceeding these concentrations, however, resulted in coarsening of Mg{sub 2}Si particles with no change in the morphology. The results also showed that addition elements caused a decrease in the nucleation and growth temperatures of Mg{sub 2}Si particles. The refining effect of Bi, Sb and Sr is likely to be related to the effect of oxide bifilms suspended in the composite melt as favored nucleation substrates for Mg{sub 2}Si particles. - Highlight: • 0.4 wt.%, 0.8 wt.% and 0.01 wt.% is the optimum content for Bi, Sb and Sr addition. • Exceeding optimum concentration resulted in the coarsening of reinforcements. • Nucleation and growth temperatures decrease with addition of Bi, Sb and Sr. • The refining effect of Bi, Sb and Sr is likely to be related to the oxide bifilms.

  13. Controlling Factors of the Stable Isotope Composition in the Precipitation of Islamabad, Pakistan

    Shakir Hussain


    Full Text Available Significant temporal variations in δ18O and deuterium isotopes were found in the rainfall water of Islamabad, Pakistan, over a 15-year period (1992–2006. The data were obtained from the International Atomic Energy Agency/Global Network of Isotopes in Precipitation (IAEA/GNIP database, and statistical correlations were investigated. In particular, this study provides the first detailed analysis of GNIP data for Islamabad. Both dry (1999-2000 and wet years (1994, 1997, and 2000 were chosen to investigate the correlations between precipitation amount, vapor flux, and temperature. We observed obvious differences between the dry and wet years and among seasons as well. Long-term features in the isotope composition agreed with the global meteorological water line, whereas short-term values followed rainfall amounts; that is, a total of 72% of the precipitation’s isotopic signature was dependent on the rainfall amount, and temperature controlled 73% of the isotopic features during October to May. The lower d-excess values were attributed to conditions during the spring season and a secondary evaporation boost during dry years; precipitation originating from the Mediterranean Sea showed high d-excess values. Overall, the results of this study contribute to the understanding of precipitation variations and their association with water vapor transport over Islamabad, Pakistan.

  14. Neoproterozoic variations in the C-isotopic composition of seawater: stratigraphic and biogeochemical implications.

    Kaufman, A J; Knoll, A H


    The recent proliferation of stratigraphic studies of delta 13C variation in carbonates and organic C in later Neoproterozoic and basal Cambrian successions (approximately 850-530 Ma) indicates a strong oscillating trend in the C-isotopic composition of surface seawater. Alone, this trend does not adequately characterize discrete intervals in Neoproterozoic time. However, integrated with the vectorial signals provided by fossils and Sr-isotopic variations, C isotope chemostratigraphy facilitates the interbasinal correlation of later Neoproterozoic successions. Results of these studies are evaluated in terms of four stratigraphic intervals: (1) the Precambrian/Cambrian boundary, (2) the post-Varanger terminal Proterozoic, (3) the late Cryogenian, and (4) the early Cryogenian. Where biostratigraphic or radiometric data constrain the age of Neoproterozoic sedimentary sequences, secular variations in C and Sr isotopes can provide a level of stratigraphic resolution exceeding that provided by fossils alone. Isotopic data place strong constraints on the chemical evolution of seawater, linking it to major tectonic and paleoclimatic events. They also provide a biogeochemical framework for the understanding of the initial radiation of macroscopic metazoans, which is associated stratigraphically, and perhaps causally, with a global increase in the burial of organic C and a concomitant rise of atmospheric O2.

  15. From interstellar abundances to grain composition: the major dust constituents Mg, Si and Fe

    Voshchinnikov, N V


    We analyse observational correlations for three elements entering into the composition of interstellar silicate and oxide grains. Using current solar abundances (Asplund et al. 2009), we convert the gas-phase abundances into dust-phase abundances for 196 sightlines. We deduce a sharp difference in abundances for sightlines located at low ($|b|30\\degr$) galactic latitudes. For high-latitude stars the ratios Mg/Si and Fe/Si in dust are close to 1.5. For disk stars they are reduced to ${\\rm Mg/Si} \\sim 1.2$ and ${\\rm Fe/Si} \\sim 1.05$. The derived numbers indicate that 1) the dust grains cannot be the mixture of silicates with olivine and pyroxene composition only and some amount of magnesium or iron (or both) should be in another population and 2) the destruction of Mg-rich grains in the warm medium is more effective than of Fe-rich grains. We reveal a decrease of dust-phase abundances and correspondingly an increase of gas-phase abundances with distance $D$ for stars with $D\\ga 400$\\,pc. We attribute this fact...

  16. Anthropogenic Pb input into Bohai Bay, China: Evidence from stable Pb isotopic compositions in sediments

    Hu, Ningjing; Huang, Peng


    Anthropogenic Pb input into Bohai Bay, China: Evidence from stable Pb isotopic compositions in sediments Hu Ning-jinga, Huang Pengb,, Liu Ji-huaa, a First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China b Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China To investigate the source of Pb within Bohai Bay, Pb concentrations and Pb isotopic compositions (204Pb, 206Pb, 207Pb, and 208Pb) of surface sediments in this area were determined. The Pb concentration in this bay varied widely from 6.9 to 39.2 μg/g (average: 21.8 ± 7.8 μg/g), and the Pb isotopic compositions ranged from 0.8338 to 0.8864 (average: 2.0997 ± 0.0180) for 208Pb/206Pb and from 2.0797 to 2.1531 (average: 0.8477 ± 0.0135) for 207Pb/206Pb, presenting in three distinct clusters. The Pb isotopic ratios of sediments from the northeastern (NE zone) and northwestern (NW zone) coastal areas were significantly influenced by anthropogenic sources such as coal combustion and automobile emission. In sediments from the central and southern Bohai Bay (C-S zone); however, Pb mainly originated from the Yellow River catchment, as a result of lithogenic sediment (from rock weathering) accumulation. The Pb isotopic ratios further indicate that, apart from riverine inputs, the neighboring large-scale ports and aerosols significantly contributed to the anthropogenic Pb contained in these sediments. Pb contamination in the Haihe and Luanhe river mouths as well as in the regions near ports is also suggested from anthropogenic enrichment factors. As cities and ports continue to develop around Bohai Bay, a long-term extensive sewage monitoring program is highly recommended.

  17. Stable chromium isotopic composition of meteorites and metal-silicate experiments: Implications for fractionation during core formation

    Bonnand, P.; Williams, H. M.; Parkinson, I. J.; Wood, B. J.; Halliday, A. N.


    We present new mass independent and mass dependent Cr isotope compositions for meteorites measured by double spike thermal ionisation mass spectrometry. Small differences in both mass independent 53Cr and 54Cr relative to the Bulk Silicate Earth are reported and are very similar to previously published values. Carbonaceous chondrites are characterised by an excess in 54Cr compared to ordinary and enstatite chondrites which make mass independent Cr isotopes a useful tool for distinguishing between meteoritic groups. Mass dependent stable Cr isotope compositions for the same samples are also reported. Carbonaceous and ordinary chondrites are identical within uncertainty with average δ53 Cr values of - 0.118 ± 0.040 ‰ and - 0.143 ± 0.074 ‰ respectively. The heaviest isotope compositions are recorded by an enstatite chondrite and a CO carbonaceous chondrite, both of which have relatively reduced chemical compositions implying some stable Cr isotope fractionation related to redox processes in the circumstellar disk. The average δ53 Cr values for chondrites are within error of the estimate for the Bulk Silicate Earth (BSE) also determined by double spiking. The lack of isotopic difference between chondritic material and the BSE provides evidence that Cr isotopes were not fractionated during core formation on Earth. A series of high-pressure experiments was also carried out to investigate stable Cr isotope fractionation between metal and silicate and no demonstrable fractionation was observed, consistent with our meteorites data. Mass dependent Cr isotope data for achondrites suggest that Cr isotopes are fractionated during magmatic differentiation and therefore further work is required to constrain the Cr isotopic compositions of the mantles of Vesta and Mars.

  18. Tribological Analysis of Mg2Si Particulates Reinforced Powder Metallurgy Magnesium Alloy Composites under Oil Lubrication Condition

    Katsuyoshi Kondoh


    Full Text Available For the evaluation of wear behavior of Mg composites under oil lubrication conditions, powder metallurgy Mg97Y2Zn1 alloy reinforced with additive Mg2Si particles were fabricated by the repeated plastic working (RPW and hot extrusion. The RPW process was effective in refining both Mg2Si reinforcements and α-Mg grains causing the matrix hardening. When increasing the repetition number of RPW process from 200 to 600 cycles, the particle size of Mg2Si additives changed from 8 μm to 1~2 μm, and α-Mg grain size was 1 μm or less. With regard to the defensive and offensive properties of Mg alloys reinforced with Mg2Si dispersoids, the composite had superior adhesive wear resistance compared with the conventional Mg alloys because of its extremely high microhardness of 95~180 Hv by RPW process. The uniform distribution of refined Mg2Si particles was useful for improving both defensive and offensive properties against AZ31B counter disk specimens. The Mg2Si prominent dispersoids in the matrix were also effective in forming the oil grooves around them, and caused the low and stable friction coefficient. On the other hand, in the case of the composite containing coarse Mg2Si particles, severely deep scratches were given on the counter face of the AZ31B disk, and resulted in an unstable and high friction coefficient.

  19. Reconstructing Cambro-Ordovician Seawater Composition using Clumped Isotope Paleothermometry on Calcitic and Phosphatic Brachiopods

    Bergmann, K.; Robles, M.; Finnegan, S.; Hughes, N. C.; Eiler, J. M.; Fischer, W. W.


    A secular increase in δ18O values of marine fossils through early Phanerozoic time raises questions about the evolution of climate and the water cycle. This pattern suggests two end-member hypotheses 1) surface temperatures during early Paleozoic time were very warm, in excess of 40°C (tropical MAT), or 2) the isotopic composition of seawater increased by up to 7-8‰. It has been difficult to evaluate these hypotheses because the δ18O composition of fossils depends on both temperature and the δ18O of water. Furthermore, primary isotopic signatures can be overprinted by diagenetic processes that modify geological materials. This too could explain the decrease in δ18O values of marine fossils with age. Carbonate clumped isotope thermometry can constrain this problem by providing an independent measure of crystallization temperature and, when paired with classical δ18O paleothermometry, can determine the isotopic composition of the fluid the mineral last equilibrated with. Combined with traditional tools, this method has the potential to untangle primary isotopic signatures from diagenetic signals. We measured the isotopic ordering of CO3 groups (Δ47) substituted into the phosphate lattice of phosphatic brachiopods in Cambrian strata. Phosphatic fossils are generally less soluble than carbonates in surface and diagenetic environments, and so are hypothesized to provide a more robust record of primary growth conditions. They also provide an archive prior to the rise of thick shelled calcitic fossils during the Ordovician Radiation. Additionally, measurements of the δ18O of the CO3 groups can be compared with the δ18O of PO4 groups to test whether their mutual fractionation is consistent with primary growth and the apparent temperature recorded by carbonate clumped isotope measurements. We are constructing a phosphatic brachiopod calibration for carbonate clumped isotope thermometry, and Δ47 values of CO2 extracted from modern phosphatic brachiopods suggest

  20. Pb Isotope Compositions of Shibaqinghao Gold Deposit in Central Inner Mongolia, China

    ZHANG Hongying; LIANG Yibo


    There are two types of gold ore in Shibaqinghao gold deposit, a mylonite ore and a quartz - vein ore. Pb isotope compositions for mylonite ore are characterized by lower Pb isotope ratios ranging from 16.63 to 17.45 (206Pb/204Pb), 15.31 to15.48 (207Pb/204pb), 36.52 to 38.85 (208Pb/204Pb). They are scattered very close to a model curve of the mantle evolution. These ratios suggest that gold in the mylonite ore might be derived from the country rocks, which originated directly in the upper mantle. Pb isotope compositions for quartz - vein ore are characterized by higher Pb isotope ratios ranging from 18.23 to 19.74 (206Pb/204Pb), 15.69 to 15.89 (207Pb/204Pb), 38.64 to 40. 13 (208Pb/204Pb). They are scattered very close to a model curve of the upper crustal evolution. These facts indicate that the gold in the quartz - vein ore might be related to some granitic magma generated in the crust.

  1. Elemental and isotopic fingerprint of Argentinean wheat. Matching soil, water, and crop composition to differentiate provenance.

    Podio, Natalia S; Baroni, María V; Badini, Raúl G; Inga, Marcela; Ostera, Héctor A; Cagnoni, Mariana; Gautier, Eduardo A; García, Pilar Peral; Hoogewerff, Jurian; Wunderlin, Daniel A


    The aim of this study was to investigate if elemental and isotopic signatures of Argentinean wheat can be used to develop a reliable fingerprint to assess its geographical provenance. For this pilot study we used wheat cultivated at three different regions (Buenos Aires, Córdoba, and Entre Ríos), together with matching soil and water. Elemental composition was determined by ICP-MS. δ(13)C and δ(15)N were measured by isotopic ratio mass spectrometry, while (87)Sr/(86)Sr ratio was determined using thermal ionization mass spectrometry. Wheat samples from three sampling sites were differentiated by the combination of 11 key variables (K/Rb, Ca/Sr, Ba, (87)Sr/(86)Sr, Co, Mo, Zn, Mn, Eu, δ(13)C, and Na), demonstrating differences among the three studied regions. The application of generalized Procrustes analysis showed 99.2% consensus between cultivation soil, irrigation water, and wheat samples, in addition to clear differences between studied areas. Furthermore, canonical correlation analysis showed significant correlation between the elemental and isotopic profiles of wheat and those corresponding to both soil and water (r(2) = 0.97, p wheat samples using different statistical methods, showing that wheat elemental and isotopic compositions are mainly related to soil and irrigation water characteristics of the site of growth.

  2. Spacial and temporal variation of H and O isotopic compositions of the Xijiang Rivers System

    Han, G.


    Pin Lv1, Fushan Li2, Yang Tang2 School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 10083, China The State Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China The H and O isotope compositions in the Xijiang River water was investigated on the sample collected from the mainstream and main tributaries in Aug. 2014 and in Jan. 2015. Large variation ranges were observed for δD with (-35.3‰ to -77.1‰ in summer, -31.3‰ to -76.6‰ in winter) andδ18O (-4.8‰ to -10.3‰ in summer, -4.5‰ to -10.3‰ in winter). From the river head to the river mouth, the H and O isotope compositions of the river water collected in the high-discharge and low-discharge period display always a similar variation pattern. On the basis of isotopic composition of river water, the Xijiang River may be separated by three subbasins including the upper basin, the middle basin and the lower basin. The upper reached river water contains relatively low values of δD and δ18O. The values of δD and δ18O in the middle reaches are quite variable because of the middle basin severely disturbed through water impoundments. The lower reaches river water contains high values of δD and δ18O. The differences of δD and δ18O compositions between various tributaries and its effect to the δD and δ18O of the mainstream reflects also the constraint of the meteoric water to the Xijiang River. Evaporation has also important effect to the H and O isotope compositions of the Xijiang River, and it is found that evaporation can also raise the δD and δ18O values of the water during the dry season. Our investigation indicates that the H and O isotope tracing method can play a key role in studying the interaction between river water and other waters, such as the meteoric water, underground water, and lake water. The combination of proper H and O isotope study with conventional meteoric and

  3. Hydrogen isotope composition of leaf wax n-alkanes in Arabidopsis lines with different transpiration rates

    Pedentchouk, N.; Lawson, T.; Eley, Y.; McAusland, L.


    Stable isotopic compositions of oxygen and hydrogen are used widely to investigate modern and ancient water cycles. The D/H composition of organic compounds derived from terrestrial plants has recently attracted significant attention as a proxy for palaeohydrology. However, the role of various plant physiological and biochemical factors in controlling the D/H signature of leaf wax lipids in extant plants remains unclear. The focus of this study is to investigate the effect of plant transpiration on the D/H composition of n-alkanes in terrestrial plants. This experiment includes 4 varieties of Arabidopsis thaliana that differ with respect to stomatal density and stomatal geometry. All 4 varieties were grown indoors under identical temperature, relative humidity, light and watering regimes and then sampled for leaf wax and leaf water stable isotopic measurements. During growth, stomatal conductance to carbon dioxide and water vapour were also determined. We found that the plants varied significantly in terms of their transpiration rates. Transpiration rates were significantly higher in Arabidopsis ost1 and ost1-1 varieties (2.4 and 3.2 mmol m-2 s-1, respectively) than in Arabidopsis RbohD and Col-0 (1.5 and 1.4). However, hydrogen isotope measurements of n-alkanes extracted from leaf waxes revealed a very different pattern. Varieties ost1, ost1-1, and RbohD have very similar deltaD values of n-C29 alkane (-125, -128, and -127 per mil), whereas the deltaD value of Col-0 is more negative (-137 per mil). The initial results of this work suggest that plant transpiration is decoupled from the D/H composition of n-alkanes. In other words, physical processes that affect water vapour movement between the plant and its environment apparently cannot account for the stable hydrogen isotope composition of organic compounds that comprise leaf waxes. Additional, perhaps biochemical, processes that affect hydrogen isotope fractionation during photosynthesis might need to be invoked

  4. Atmospheric control on isotopic composition and d-excess in water vapor over ocean surface

    Fan, Naixin

    For decades, stable isotopes of water have been used as proxies to infer the variation of the hydrological cycle. However, it is still not clear how various atmospheric processes quantitatively control kinetic fractionation during evaporation over the ocean. Understanding kinetic fractionation is important in that the interpretation of the isotopic composition record preserved in ice cores and precipitation relies in part on the isotopic information at the moisture source. In addition, the isotopic composition of vapor contains information about variation of atmospheric processes such as turbulence and change in moisture source region which is useful for studying meteorological processes and climate change. In this study the isotopic composition of water vapor in the marine boundary layer (MBL) over the ocean was investigated using a combination of a newly developed marine boundary layer (MBL) model and observational data. The new model has a more realistic MBL structure than previous models and includes new features such as vertical advection of air and diffusion coefficients that vary continuously in the vertical direction. A robust linear relationship between deltaD and delta18O was found in observational oceanic water vapor data and the model can well capture the characteristics of this relationship. The individual role of atmospheric processes or variables on deltaD, delta18O and d-excess was quantitatively investigated and an overview of the combined effect of all the meteorological processes is provided. In particular, we emphasize that the properties of subsiding air (such as its mixing ratio and isotopic values) are crucial to the isotopic composition of surface water vapor. Relative humidity has been used to represent the moisture deficit that drives evaporative isotopic fluxes, however, we argue that it has serious limitations in explaining d-excess variation as latitude varies. We introduce a new quantity Gd=SST-Td, the difference between the sea

  5. Modelling the isotopic composition of snow using backward trajectories : a particular precipitation event in Dronning Maud Land, Antarctica

    Helsen, MM; Van de Wal, RSW; Van den Broeke, MR; Kerstel, ERT; Masson-Delmotte, [No Value; Meijer, HAJ; Reijmer, CH; Scheele, MP; Jacka, J


    We consider a specific accumulation event that occurred in January 2002 in western Dronning Maud Land, Antarctica. Snow samples were obtained a few days after accumulation. We combine meteorological analyses and isotopic modelling to describe the isotopic composition of moisture during transport. Ba

  6. The effects of growth phase and salinity on the hydrogen isotopic composition of alkenones produced by coastal haptophyte algae

    Chivall, D.; M'Boule, D.; Sinke-Schoen, D.; Sinninghe Damsté, J.S.; Schouten, S.; van der Meer, M.T.J.


    The isotopic fractionation of hydrogen during the biosynthesis of alkenones produced by marine haptophyte algae has been shown to depend on salinity and, as such, the hydrogen isotopic composition of alkenones is emerging as a palaeosalinity proxy. The relationship between fractionation and salinity

  7. Situation of sewage input reflected by nitrogen isotopic composition in a sediment core of Hongfeng Lake


    Nitrogen in Hongfeng South Lake water mainly comes from sewage with high N concentrations from Pingba Chemical Fertilizer Plant (PCFP). Studies on the sediment core HF010427 sampled in the lake showed that the upward increase of nitrogen isotopic composition of sedimentary organic nitrogen (δ15Norg) accorded with the trend of industrial total production (TP) of PCFC. On the contrary, diagenesis will theoretically cause an upward decrease of δ15Norg. Because no treatment of sewage water was carried out, TP corresponds with sewage emission, indicating that sedimentary δ15Norg can reflect well the total trend of sewage input. The very similar profile shape between nitrogen isotopic composition of sedimentary absorbed ammonium (δ15NH4+absorbed) and TP of PCFP suggests that δ15NH4+absorbed can be used to reconstruct more detailed situation of sewage input. The study has a reference to history investigation of sewage input.

  8. A rapid method for determination of the isotopic composition of uranium samples by alpha spectrometry

    Martin Sanchez, A.; Tome, F.V.; Diaz Bejarano, J.; Jurado Vargas, M. (Dept. de Fisica, Univ. Extremadura, Badajoz (Spain))


    A simple method of analyzing alpha spectra from natural and enriched or depleted uranium samples is developed. The procedure is non-iterative, and takes into consideration low-energy tail and branching-ratio corrections to accurately calculate the area corresponding to each uranium isotope ({sup 234}U, {sup 235}U, {sup 236}U, {sup 238}U) in the spectrum, and then the isotopic composition of the sample. A BASIC computer program, called ENURA, has been developed to perform all the necessary calculations to give the results together with their uncertainties. Several samples were prepared with different uranium concentrations made from standard solutions with known compositions, and the method was checked against the experimental measurements from these samples. Other series of uranium spectra were theoretically constructed using a given line shape in order to cover the required range of enriched or depleted uranium. (orig.).

  9. Isotopic compositions and probable origins of organic molecules in the Eocene Messel shale

    Hayes, J. M.; Takigiku, Ray; Ocampo, Ruben; Callot, Enry J.; Albrecht, Pierre


    It is shown here that the carbon isotopic compositions of biomarkers from the Eocene Messel shale, accumulated 47 + or - 2 million years ago in anaerobic waters at the bottom of a lake, allow identification of specific sources for some materials and reconstruction of carbon flows within the lake and its sediments. The C-13 content of organic matter synthesized by lacustrine primary producers can be estimated from the observed C-13 content of the geoporphyrins derived from their chlorophylls. Total organic material in the shale is depleted in C-13 by six parts per thousand relative to that input. This difference cannot be explained by selective loss of components enriched in C-13, nor, as shown by isotopic compositions of other biomarkers, by inputs from land plants surrounding the lake or from methanogenic bacteria.

  10. Accurate measurement of neodymium isotopic composition using Neptune MC-ICP-MS

    Yueheng YANG; Hongfu ZHANG; Liewen XIE; Fuyuan WU


    This paper reports the measurement of the Neodymium isotopic composition by Neptune Multiple Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS) over the last two years. Although there is concomitant Cerium in the chemical separation process, this has no significant influence on the Neodymium analysis. As for the sample containing small amounts of Samarium (Sm/Nd<0.04), direct calibration for isobaric interference and mass discrimina-tion by the exponential law can be obtained by assuming that Samarium mass discrimination is the same as that of Neodymium. Geological samples after traditional chemi-cal separation were measured by Neptune MC-ICP-MS and Thermal Ionization Mass Spectrometry (TIMS) respectively. The results show that Neptune MC-ICP-MS can measure Neodymium isotopic composition as precisely the TIMS does and is even more effective and less time-consuming than the TIMS Method.

  11. Experimental assessment of environmental influences on the stable isotopic composition of Daphnia pulicaria and their ephippia

    J. Schilder


    δ15N values of ephippia and Daphnia between the 12 °C and 20 °C treatments, but the δ18O values of Daphnia and ephippia were on average 1.2‰ lower at 20 °C compared with 12 °C. We conclude that the stable isotopic composition of Daphnia ephippia provides information on that of the parent Daphnia and of the food and water they were exposed to, with small offsets between Daphnia and ephippia relative to variations in Daphnia stable isotopic composition reported from downcore studies. However, our experiments also indicate that temperature may have a minor influence on the δ13C, δ15N and δ18O values of Daphnia body tissue and ephippia. This aspect deserves attention in further controlled experiments.

  12. Effects of MgO modified β-TCP nanoparticles on the microstructure and properties of β-TCP/Mg-Zn-Zr composites

    H.R. Zheng


    Full Text Available The mechanical properties and corrosion resistance of magnesium alloy composites were improved by the addition of MgO surface modified tricalcium phosphate ceramic nanoparticles (m-β-TCP. Mg-3Zn-0.8Zr composites with unmodified (MZZT and modified (MZZMT nanoparticles were produced by high shear mixing technology. Effects of MgO m-β-TCP nanoparticles on the microstructure, mechanical properties, electrochemical corrosion properties and cytocompatibility of Mg-Zn-Zr/β-TCP composites were investigated. After hot extrusion deformation and dynamic recrystallization, the grain size of MZZMT was the half size of MZZT and the distribution of m-β-TCP particles in the matrix was more uniform than β-TCP particles. The yield tensile strength (YTS, ultimate tensile strength (UTS, and corrosion potential (Ecorr of MZZMT were higher than MZZT; the corrosion current density (Icorr of MZZMT was lower than MZZT. Cell proliferation of co-cultured MZZMT and MZZT composite samples were roughly the same and the cell number at each time point is higher for MZZMT than for MZZT samples.

  13. Electrochemical Properties of CeMg12+x%Ni Composites (x=0~200) Prepared by Ball-Milling

    Wang Li; Wang Xinhua; Chen Changpin; Xiao Xuezhang


    The electrochemical properties of the as-cast and ball-milled CeMg12+x%(mass fraction) Ni (vs. CeMg12) (x=0, 50, 100 and 200) composites were investigated. The microstructure and discharge capacity of the ball-milled CeMg12+x%Ni composites differ greatly depending on the amount of Ni introduced during ball-milling. The more nickel powder added, the more advantageous for the formation of the amorphous structure. And the discharge capacities of the ball-milled composites increase with increasing amount of nickel added. After 90 h ball-milling, the CeMg12+200% Ni composite exhibits a high discharge capacity of 1170 mAh·g-1(CeMg12)-1 at 303 K. The improvement of electrochemical capacity is attributed to the formation of a homogeneous amorphous structure as well as the modification of the surface state after Ni addition.

  14. Mineralogy and Oxygen Isotope Compositions of an Unusual Hibonite-Perovskite Refractory Inclusion from Allende

    Keller, L. P.; Snead, C.; Rahman, Z.; McKeegan, K. D.


    Hibonite-rich Ca- and Al-rich inclusions (CAIs) are among the earliest formed solids that condensed in the early nebula. We discovered an unusual refractory inclusion from the Allende CV3 chondrite (SHAL) containing an approx 500 micron long single crystal of hibonite and co-existing coarse-grained perovskite. The mineralogy and petrography of SHAL show strong similarities to some FUN inclusions, especially HAL. Here we report on the mineralogy, petrography, mineral chemistry and oxygen isotopic compositions in SHAL.

  15. An assessment of upper mantle heterogeneity based on abyssal peridotite isotopic compositions

    Warren, J. M.; Shimizu, N.; Sakaguchi, C.; Dick, H. J. B.; Nakamura, E.


    Abyssal peridotites, the depleted solid residues of ocean ridge melting, are the most direct samples available to assess upper oceanic mantle composition. We present detailed isotope and trace element analyses of pyroxene mineral separates from Southwest Indian Ridge abyssal peridotites and pyroxenites in order to constrain the size and length scale of mantle heterogeneity. Our results demonstrate that the mantle can be highly heterogeneous to account adequately for the complexities of ancient and recent melting processes.

  16. Spatial variability in the isotopic composition of rainfall in a small headwater catchment and its effect on hydrograph separation

    Fischer, Benjamin M. C.; van Meerveld, H. J. (Ilja); Seibert, Jan


    Isotope hydrograph separation (IHS) is a valuable tool to study runoff generation processes. To perform an IHS, samples of baseflow (pre-event water) and streamflow are taken at the catchment outlet. For rainfall (event water) either a bulk sample is collected or it is sampled sequentially during the event. For small headwater catchment studies, event water samples are usually taken at only one sampling location in or near the catchment because the spatial variability in the isotopic composition of rainfall is assumed to be small. However, few studies have tested this assumption. In this study, we investigated the spatiotemporal variability in the isotopic composition of rainfall and its effects on IHS results using detailed measurements from a small pre-alpine headwater catchment in Switzerland. Rainfall was sampled sequentially at eight locations across the 4.3 km2 Zwäckentobel catchment and stream water was collected in three subcatchments (0.15, 0.23, and 0.70 km2) during ten events. The spatial variability in rainfall amount, average and maximum rainfall intensity and the isotopic composition of rainfall was different for each event. There was no significant relation between the isotopic composition of rainfall and total rainfall amount, rainfall intensity or elevation. For eight of the ten studied events the temporal variability in the isotopic composition of rainfall was larger than the spatial variability in the rainfall isotopic composition. The isotope hydrograph separation results, using only one rain sampler, varied considerably depending on which rain sampler was used to represent the isotopic composition of event water. The calculated minimum pre-event water contributions differed up to 60%. The differences were particularly large for events with a large spatial variability in the isotopic composition of rainfall and a small difference between the event and pre-event water isotopic composition. Our results demonstrate that even in small catchments

  17. Investigating the source, transport, and isotope composition of water vapor in the planetary boundary layer

    Griffis, Timothy J.; Wood, Jeffrey D.; Baker, John M.; Lee, Xuhui; Xiao, Ke; Chen, Zichong; Welp, Lisa R.; Schultz, Natalie M.; Gorski, Galen; Chen, Ming; Nieber, John


    Increasing atmospheric humidity and convective precipitation over land provide evidence of intensification of the hydrologic cycle - an expected response to surface warming. The extent to which terrestrial ecosystems modulate these hydrologic factors is important to understand feedbacks in the climate system. We measured the oxygen and hydrogen isotope composition of water vapor at a very tall tower (185 m) in the upper Midwest, United States, to diagnose the sources, transport, and fractionation of water vapor in the planetary boundary layer (PBL) over a 3-year period (2010 to 2012). These measurements represent the first set of annual water vapor isotope observations for this region. Several simple isotope models and cross-wavelet analyses were used to assess the importance of the Rayleigh distillation process, evaporation, and PBL entrainment processes on the isotope composition of water vapor. The vapor isotope composition at this tall tower site showed a large seasonal amplitude (mean monthly δ18Ov ranged from -40.2 to -15.9 ‰ and δ2Hv ranged from -278.7 to -113.0 ‰) and followed the familiar Rayleigh distillation relation with water vapor mixing ratio when considering the entire hourly data set. However, this relation was strongly modulated by evaporation and PBL entrainment processes at timescales ranging from hours to several days. The wavelet coherence spectra indicate that the oxygen isotope ratio and the deuterium excess (dv) of water vapor are sensitive to synoptic and PBL processes. According to the phase of the coherence analyses, we show that evaporation often leads changes in dv, confirming that it is a potential tracer of regional evaporation. Isotope mixing models indicate that on average about 31 % of the growing season PBL water vapor is derived from regional evaporation. However, isoforcing calculations and mixing model analyses for high PBL water vapor mixing ratio events ( > 25 mmol mol-1) indicate that regional evaporation can account

  18. Segmentation of the Cascade Arc Based on Compositional and Sr and Nd Isotopic Variations in Primitive Volcanic Rocks

    Schmidt, M. E.; Grunder, A. L.


    We define four segments in the Cascade Volcanic Arc based on 87Sr/86Sr and 143Nd/144Nd of primitive volcanic rocks: 1) The North segment extends 450 km from Mt. Meager to Glacier Peak; 2) the 350-km Columbia segment includes volcanoes from Mt. Rainier to Mt. Jefferson; 3) the 250 km Central segment comprises the portion of the arc between the Three Sisters and Crater Lake; and 4) the 350-km South segment includes Mt. Shasta to Mt. Lassen. Isotopic data were compiled for primitive bulk composition (MgO concentrations >8 wt.% MgO) as a fingerprint mantle sources. The North segment has a range in 87Sr/86Sr of 0.7030-0.7037 and is distinguished by the predominance of calcalkaline basalts (CAB) and few low K tholeiites (LKT). The North segment lies on the North Cascade craton where convergence is near orthogonal. Oblique subduction occurs beneath the Columbia, Central, and South segments. The Columbia segment (87Sr/86Sr of 0.7028-0.7037) has both LKT and CABs as well as enriched ocean island-like basalts (OIB) that are found both on the arc axis and, especially at the Simcoe Volcanic Field, behind the arc. This segment lies primarily on the accreted Tertiary oceanic plateau terrane of the Columbia Embayment. The Central segment is dominated by LKT with lesser CAB and has the most restricted Sr isotopic range (0.7034- 0.7038). Like the South segment, the Central segment mainly overlies accreted terranes stitched by Mesozoic plutons and has Basin and Range (B&R) extension behind as well as locally within the arc. Medicine Lake Volcano, on the margin of the B&R behind Mt. Shasta is also dominated by LKT and has a narrow isotopic range like the Central segment. This suggests that the LKT's are related to extension in the arc. The South segment is distinguished by the widest Sr isotopic range (0.7028-0.7042) and the presence of high Mg basaltic andesite and andesite compositions in addition to LKT and CABs. These arc segments broadly correspond to physical segments that were

  19. Synthesis and Mechanical Characterisation of an Ultra-Fine Grained Ti-Mg Composite

    Markus Alfreider


    Full Text Available The importance of lightweight materials such as titanium and magnesium in various technical applications, for example aerospace, medical implants and lightweight construction is well appreciated. The present study is an attempt to combine and improve the mechanical properties of these two materials by forming an ultra-fine grained composite. The material, with a composition of 75 vol% (88.4 wt% Ti and 25 vol% (11.4 wt% Mg , was synthesized by powder compression and subsequently deformed by high-pressure torsion. Using focused ion beam machining, miniaturised compression samples were prepared and tested in-situ in a scanning electron microscope to gain insights into local deformation behaviour and mechanical properties of the nanocomposite. Results show outstanding yield strength of around 1250 MPa, which is roughly 200 to 500 MPa higher than literature reports of similar materials. The failure mode of the samples is accounted for by cracking along the phase boundaries.

  20. Determining and Controlling the Magnesium Composition in CdTe/CdMgTe Heterostructures

    LeBlanc, E. G.; Edirisooriya, M.; Ogedengbe, O. S.; Noriega, O. C.; Jayathilaka, P. A. R. D.; Rab, S.; Swartz, C. H.; Diercks, D. R.; Burton, G. L.; Gorman, B. P.; Wang, A.; Barnes, T. M.; Myers, T. H.


    The relationships between Mg composition, band gap, and lattice characteristics are investigated for Cd1-xMgxTe barrier layers using a combination of cathodoluminescence, energy dispersive x-ray spectroscopy, variable angle spectral ellipsometry, and atom probe tomography. The use of a simplified, yet accurate, variable angle spectral ellipsometry analysis is shown to be appropriate for fast determination of composition in thin Cd1-xMgxTe layers. The validity of using high-resolution x-ray diffraction for CdTe/Cd1-xMgxTe double heterostructures is discussed. The stability of CdTe/Cd1-xMgxTe heterostructures are investigated with respect to thermal processing.

  1. Isotropic negative permeability composite based on Mie resonance of the BST-MgO dielectric medium

    ZHAO Qian; KANG Lei; DU Bo; ZHAO HongJie; XIE Qin; LI Bo; ZHOU Ji; LI LongTu; MENG YongGang


    Isotropic negative permeability composite, composed of BST-MgO dielectric cubes with high permit-tivity dispersed in the Teflon substrate with low permittivity, was designed and fabricated based on Mie resonance and the effective medium theory. Measurements and simulations showed that the dielectric composite exhibited a strong sub-wavelength magnetic resonance at the first Mie resonance and possessed isotropic negative permeability, which resulted from the displacement current excited in the cubes. The dielectric particle was equivalent to a magnetic dipole at the magnetic resonance, which could be adjusted by the size and permitllvity of the particles. It may provide a convenient method to design isotropic metamaterials and invisible cloak at infrared and visible frequencies.

  2. Li Isotopic Composition and Concentration of the Upper Continental Crust: New Insights from Desert Loess

    Sauzeat, L.; Rudnick, R. L.; Chauvel, C.


    The isotopic composition of lithium (δ7Li) is recognized to be an excellent proxy of near-surface fluid-rock reactions during weathering. Using Li as a tracer of these processes however requires constraints on the average Li composition of terrestrial reservoirs, in particular that of the upper continental crust. To date, only one value for the average δ7Li value of the upper continental crust, derived from periglacial loess, shales, and granites is available in the literature (7δLi = 0 ± 4 (2σ), Teng et al., 2004). Several values exist for the average [Li] of the upper crust, but they differ by more than 30%. We measured the Li isotopic composition of about 30 desert and periglacial loess (unweathered windblown sediments) from several parts of the world (Europe, Argentina, China and Tajikistan). We demonstrate that desert loess, which is more homogeneous and representative of larger portions of the Earth's surface, provides a better proxy for the average composition of the upper continental crust compared to periglacial loess. The Li isotopic compositions and concentrations of desert loess are controlled by eolian sorting, which can be quantified as a binary isotopic mixing between a weathered fine-grained end-member and an unweathered coarse-grained end-member. Using correlations between Li isotopic compositions, Li concentrations and trace element concentrations in desert loess, we estimate new average values for the upper continental crust: 1 ± 2 (2σ); [Li] = 35.3 ± 4.6 (2σ) ppm. This δ7Li value is slightly higher than that previously published in Teng et al. (2004), but overlaps within uncertainty, whereas the [Li] is identical to that of Teng et al. (2004: 35 ± 11, 2σ); both new estimates have lower uncertainty. Our new estimate of [Li], along with that of Teng et al. (2004), are higher than all previous estimates for the upper continental crust, raising the question as to whether the average concentrations of other mobile alkali metals such as

  3. Temporal variations in lead concentrations and isotopic composition in the Southern California Bight

    Sanudo-Wilhelmy, S.A.; Flegal, A.R. (Univ. of California, Santa Cruz, CA (United States))


    Lead concentrations in surface waters of the Southern California Bight appear to have decreased threefold (from >170 to <60 pM) since they were initially measured by Clair Patterson and his associates in the 1970s. The decrease parallels a threefold decline in anthropogenic inputs of industrial lead to the bight over the past two decades. Moreover, mass balance calculations indicate that the primary source of lead to the bight now is upwelling. This is evidenced by the isotopic compositions of surface waters in the bight, which are most characteristic of Asian industrial lead aerosols (0.4793 [le] [sup 206]Pb/[sup 208]Pb [le] 0.4833) deposited in oceanic waters of the North Pacific. While the decrease in surface water lead concentrations in the bight reflects the reduction in industrial lead emissions from the United States, the isotopic compositions of surface waters in the southern reach of the bight reflect a concurrent increase in industrial lead emissions from Mexico (0.4852 [le] [sup 206]Pb/[sup 208]Pb [le] 0.4877). The isotopic composition ([sup 208]Pb/[sup 207]Pb [approximately] 2.427) of elevated lead concentrations of surface waters in San Diego Bay indicate that lead is being remobilized from contaminated sediments within that bay.

  4. Stable carbon and radiocarbon isotope compositions of particle size fractions to determine origins of sedimentary organic matter in an estuary

    Megens, L; van der Plicht, J; de Leeuw, JW; Smedes, F; Altabet, M.


    Stable and radioactive carbon isotopic compositions of particle size fractions of a surface sediment from the Ems-Dollard estuary vary considerably with particle size. The organic material in the fine fractions (

  5. Stable carbon and radiocarbon isotope compositions of particle size fractions to determine origins of sedimentary organic matter in an estuary

    Megens, L; van der Plicht, J; de Leeuw, JW; Smedes, F; Altabet, M.


    Stable and radioactive carbon isotopic compositions of particle size fractions of a surface sediment from the Ems-Dollard estuary vary considerably with particle size. The organic material in the fine fractions (

  6. Limitations of the isotopic composition of nitrates as a tracer of their origin

    Kloppmann, Wolfram; Mayer, Bernhard; Otero, Neus; Sebilo, Mathieu; Gooddy, Daren; Lapworth, Dan; Surridge, Ben; Petelet Giraud, Emmanuelle; Flehoc, Christine; Baran, Nicole


    Nitrogen and oxygen isotopes are traditionally considered and frequently used as tracers of nitrate sources in watersheds used for drinking water production. The enrichment of synthetic nitrate-containing fertilizers in 18O due to the contribution of atmospheric oxygen in the production process confers a specific isotopic fingerprint to mineral fertilizers. In spite of the still widespread use on nitrate-containing synthetic fertilizers, their characteristic N and O isotope signatures are rarely unambiguously observed in nitrate-contaminated groundwater. We postulate, in line with Mengis et al. (2001), that fertilizer-derived nitrate is not directly and rapidly transferred to groundwater but rather retained in the soil-plant system as organic N and then mineralized and re-oxidized (termed the mineralization-immobilization turnover, MIT) thereby re-setting the oxygen isotope composition of nitrate and also changing its N isotope ratios. We show examples from watersheds on diverse alluvial/clastic and carbonate aquifers in eastern and northern France where, in spite of the use of mineral fertilizers, evidenced also through other isotopic tracers (boron isotopes), both N and O-isotope ratios are very homogeneous and compatible with nitrification of ammonium where 2/3 of oxygen is derived from soil water and 1/3 from atmospheric O2. These field data are corroborated by lysimeter data from Canada. Even if in areas where ammonium is derived from chemical fertilizers, N values still tend to be lower than in areas where ammonium is derived from manure/sewage, this is clearly a limitation to the dual isotope method (N, O) for nitrate source identification, but has important implications for the nitrogen mobility and residence time in soils amended with synthetic fertilizers (Sebilo et al., 2013). Mengis M., Walther U., Bernasconi S. M., Wehrli B. (2001) Limitations of Using δ18O for the Source Identification of Nitrate in Agricultural Soils. Environmental Science

  7. Triple oxygen isotopic composition of the high-3He/4He mantle

    Starkey, N. A.; Jackson, C. R. M.; Greenwood, R. C.; Parman, S.; Franchi, I. A.; Jackson, M.; Fitton, J. G.; Stuart, F. M.; Kurz, M.; Larsen, L. M.


    Measurements of Xe isotope ratios in ocean island basalts (OIB) suggest that Earth's mantle accreted heterogeneously, and that compositional remnants of accretion are sampled by modern, high-3He/4He OIB associated with the Icelandic and Samoan plumes. If so, the high-3He/4He source may also have a distinct oxygen isotopic composition from the rest of the mantle. Here, we test if the major elements of the high-3He/4He source preserve any evidence of heterogeneous accretion using measurements of three oxygen isotopes on olivine from a variety of high-3He/4He OIB locations. To high precision, the Δ17O value of high-3He/4He olivines from Hawaii, Pitcairn, Baffin Island and Samoa, are indistinguishable from bulk mantle olivine (Δ17OBulk Mantle - Δ17OHigh 3He/4He olivine = -0.002 ± 0.004 (2 × SEM)‰). Thus, there is no resolvable oxygen isotope evidence for heterogeneous accretion in the high-3He/4He source. Modelling of mixing processes indicates that if an early-forming, oxygen-isotope distinct mantle did exist, either the anomaly was extremely small, or the anomaly was homogenised away by later mantle convection. The δ18O values of olivine with the highest 3He/4He ratios from a variety of OIB locations have a relatively uniform composition (∼5‰). This composition is intermediate to values associated with the depleted MORB mantle and the average mantle. Similarly, δ18O values of olivine from high-3He/4He OIB correlate with radiogenic isotope ratios of He, Sr, and Nd. Combined, this suggests that magmatic oxygen is sourced from the same mantle as other, more incompatible elements and that the intermediate δ18O value is a feature of the high-3He/4He mantle source. The processes responsible for the δ18O signature of high-3He/4He mantle are not certain, but δ18O-87Sr/86Sr correlations indicate that it may be connected to a predominance of a HIMU-like (high U/Pb) component or other moderate δ18O components recycled into the high-3He/4He source.

  8. Researches on the behaviour of cellular antiballistic composites based on AlMg-SiC alloys

    Bălţătescu, O.; Florea, R. M.; Rusu, I.; Carcea, I.


    The researches presented in this paper refers basically to the impact of a small/medium caliber bullet shot on a light armor built on the base of a AlMg-SiC metallic composite cellular/foam. Thus, we study the antiballistic behavior and protection properties of the armor, based on the effects that occur at the impact zone of the bullet with the composite surface. We performed an antiballistic behavior modeling by means of a finite element analysis, based on a "multi grid" Fast Finite Element (FFE) system. We used for this purpose the DYNA 2D software package. The obtained samples show after the impact the occurrence of concentration / deformation pores effect and intercellular cracks development to the interior of the composite. Those effects, depending on speed, mass and length of the projectile ballistic trajectory, reduce zonal tensions due to the effect of cell walls deformation. It was obtained a good correlation between modeling results and the electron microscope analyse of the impact area. It is worth mentioning that almost all values for impact energy absorbed by the composite armor are in the protection active zone provided by it.

  9. Tracking nitrous oxide emission processes at a suburban site with semicontinuous, in situ measurements of isotopic composition

    Harris, Eliza; Henne, Stephan; Hüglin, Christoph; Zellweger, Christoph; Tuzson, Béla; Ibraim, Erkan; Emmenegger, Lukas; Mohn, Joachim


    The isotopic composition of atmospheric nitrous oxide (N2O) was measured semicontinuously, at ˜35 min frequency in intermittent periods of 1-6 days over one and a half years, using preconcentration coupled to a quantum cascade laser spectrometer at the suburban site of Dübendorf, Switzerland. The achieved measurement repeatability was 0.08‰, 0.11‰, and 0.10‰ for δ18O, site preference, and δ15Nbulk respectively, which is better than or equal to standard flask sampling-based isotope ratio mass spectrometry performance. The observed mean diurnal cycle reflected the buildup of N2O from isotopically light sources on an isotopically heavy tropospheric background. The measurements were used to determine the source isotopic composition, which varied significantly compared to chemical and meteorological parameters monitored at the site. FLEXPART-COSMO transport modeling in combination with modified Emissions Database for Global Atmospheric Research inventory emissions was used to model N2O mole fractions at the site. Additionally, isotopic signatures were estimated for different source categories using literature data and used to simulate N2O isotopic composition over the measurement period. The model was able to capture variability in N2O mole fraction well, but simulations of isotopic composition showed little agreement with observations. In particular, measured source isotopic composition exhibited one magnitude larger variability than simulated, clearly indicating that the range of isotopic source signatures estimated from literature significantly underestimates true variability of source signatures. Source δ18O signature was found to be the most sensitive tracer for urban/industry versus agricultural N2O. δ15Nbulk and site preference may provide more insight into microbial and chemical emission processes than partitioning of anthropogenic source categories.

  10. Isotopic composition for source identification of mercury in atmospheric fine particles

    Huang, Qiang; Chen, Jiubin; Huang, Weilin; Fu, Pingqing; Guinot, Benjamin; Feng, Xinbin; Shang, Lihai; Wang, Zhuhong; Wang, Zhongwei; Yuan, Shengliu; Cai, Hongming; Wei, Lianfang; Yu, Ben


    The usefulness of mercury (Hg) isotopes for tracing the sources and pathways of Hg (and its vectors) in atmospheric fine particles (PM2.5) is uncertain. Here, we measured Hg isotopic compositions in 30 potential source materials and 23 PM2.5 samples collected in four seasons from the megacity Beijing (China) and combined the seasonal variation in both mass-dependent fractionation (represented by the ratio 202Hg / 198Hg, δ202Hg) and mass-independent fractionation of isotopes with odd and even mass numbers (represented by Δ199Hg and Δ200Hg, respectively) with geochemical parameters and meteorological data to identify the sources of PM2.5-Hg and possible atmospheric particulate Hg transformation. All PM2.5 samples were highly enriched in Hg and other heavy metals and displayed wide ranges of both δ202Hg (-2.18 to 0.51 ‰) and Δ199Hg (-0.53 to 0.57 ‰), as well as small positive Δ200Hg (0.02 to 0.17 ‰). The results indicated that the seasonal variation in Hg isotopic composition (and elemental concentrations) was likely derived from variable contributions from anthropogenic sources, with continuous input due to industrial activities (e.g., smelting, cement production and coal combustion) in all seasons, whereas coal combustion dominated in winter and biomass burning mainly found in autumn. The more positive Δ199Hg of PM2.5-Hg in spring and early summer was likely derived from long-range-transported Hg that had undergone extensive photochemical reduction. The study demonstrated that Hg isotopes may be potentially used for tracing the sources of particulate Hg and its vectors in the atmosphere.

  11. Probing the homogeneity of the isotopic composition and molar mass of the ‘Avogadro’-crystal

    Pramann, Axel; Lee, Kyoung-Seok; Noordmann, Janine; Rienitz, Olaf


    Improved measurements on silicon crystal samples highly enriched in the 28Si isotope (known as ‘Si28’ or AVO28 crystal material) have been carried out at PTB to investigate local isotopic variations in the original crystal. This material was used for the determination of the Avogadro constant NA and therefore plays an important role in the upcoming redefinition of the SI units kilogram and mole, using fundamental constants. Subsamples of the original crystal have been extensively studied over the past few years at the National Research Council (NRC, Canada), the National Metrology Institute of Japan (NMIJ, Japan), the National Institute of Standards and Technology (NIST, USA), the National Institute of Metrology (NIM, People’s Republic of China), and multiple times at PTB. In this study, four to five discrete, but adjacent samples were taken from three distinct axial positions of the crystal to obtain a more systematic and comprehensive understanding of the distribution of the isotopic composition and molar mass throughout the crystal. Moreover, improved state-of-the-art techniques in the experimental measurements as well as the evaluation approach and the determination of the calibration factors were utilized. The average molar mass of the measured samples is M  =  27.976 970 12(12) g mol-1 with a relative combined uncertainty uc,rel(M)  =  4.4 ×10-9. This value is in astounding agreement with the values of single samples measured and published by NIST, NMIJ, and PTB. With respect to the associated uncertainties, no significant variations in the molar mass and the isotopic composition as a function of the sample position in the boule were observed and thus could not be traced back to an inherent property of the crystal. This means that the crystal is not only ‘homogeneous’ with respect to molar mass but also has predominantly homogeneous distribution of the three stable Si isotopes.

  12. The bulk isotopic composition of hydrocarbons in subaerial volcanic-hydrothermal emissions from different tectonic settings

    Fiebig, J.; Tassi, F.; Vaselli, O.; Viveiros, M. F.; Silva, C.; Lopez, T. M.; D'Alessandro, W.; Stefansson, A.


    Assuming that methane and its higher chain homologues derive from a common source, carbon isotope patterns have been applied as a criterion to identify occurrences of abiogenic hydrocarbons. Based on these, it has been postulated that abiogenic hydrocarbon production occurs within several (ultra)mafic environments. More evolved volcanic-hydrothermal systems may also provide all the prerequisites necessary for abiogenic hydrocarbon production, such as availability of inorganic CO2, hydrogen and heat. We have investigated the chemical and isotopic composition of n-alkanes contained within subaerial hydrothermal discharges emitted from a range of hot spot, subduction and rift-related volcanoes to determine the origin of hydrocarbons in these systems. Amongst these are Nisyros (Greece), Vesuvio, Campi Flegrei, Ischia, Pantelleria and Vulcano (all Italy), Mt. Mageik and Trident (USA), Copahue (Argentina), Teide (Spain), Furnas and Fogo (Portugal). The carbon isotopic composition of methane emitted from these sites varies from -65 to -8‰ , whereas δ13C of ethane and propane exhibit a much narrower variation from -17‰ to -31‰. Methane that occurs most enriched in 13C is also characterized by relatively positive δD values ranging up to -80‰. Carbon isotope reversals between methane and ethane are only observed for locations exhibiting δ13C-CH4 values > -20‰, such as Teide, Pantelleria, Trident and Furnas. At Furnas, δ13C-CH4 varies by 50‰ within a relatively short distance of <50m between two vents, whereas δ13C-C2H6 varies by less than 2‰ only. For some of the investigated locations apparent carbon isotopic temperatures between methane and CO2 are in agreement with those derived from gas concentration geothermometers. At these locations methane, however seems to be in disequilibrium with ethane and propane. These findings imply that methane on the one hand and the C2+ hydrocarbons on the other hand often might derive from distinct sources.

  13. Sulfur isotopic composition and source identification of atmospheric environment in central Zhejiang,China


    Sulfur dioxide and sulfate aerosols in the atmosphere are significant factors leading to acidification of the atmospheric environment and worsening the pollution of acid deposition. Because of the "fingerprint" characteristics of the stable sulfur isotopic composition, sulfur isotope has been widely adopted in environmental researches concerning sulfur cycle and source identification. In this study, the atmospheric environment of Jinhua City, central Zhejiang Province, was continuously monitored, and the sulfur isotopic composition of SO2 and sulfate aerosols in the atmosphere was analyzed. The results indicate that the variation of δ34S values for SO2 ranges from 1.0‰ to 7.5‰, and annual average is 4.7‰±2.3‰, whereas that of sulfate aerosols ranges from 6.4‰ to 9.8‰,and annual average is 8.1‰±1.0‰. The δ 34S values for SO2 have significant seasonal variations, which are 7.0‰ in winter and 3.3‰ in summer. These variations cannot be attributed to a single factor, and we suggest a temperature-dependent isotope equilibrium fractionation and elevated biogenic sulfur emissions of isotopically light S in summer may be the main controlling mechanisms. Furthermore, we also discuss the δ 34S model of atmospheric SO2 oxidation to form sulfate, and suggest that heterogeneous oxidation dominates in the oxidation reactions of atmospheric SO2 in the central Zhejiang Province. We further suggest that the relative humidity in the atmosphere plays an important role in the oxidation mechanism of atmospheric SO2.

  14. Electron-Induced Secondary Electron Emission Properties of MgO/Au Composite Thin Film Prepared by Magnetron Sputtering

    Li, Jie; Hu, Wenbo; Wei, Qiang; Wu, Shengli; Hua, Xing; Zhang, Jintao


    As a type of electron-induced secondary electron emitter, MgO/Au composite thin film was prepared by reactive magnetron sputtering of individual Mg target and Au target, and the effects of key process parameters on its surface morphology and secondary electron emission (SEE) properties were investigated. It is found that to deposit a NiO buffer layer on the substrate is conducive to the subsequent growth of MgO grains owing to the lattice matching. The gold addition can raise the electrical conductivity of MgO film and further suppress the surface charging. However, the gold deposition would interfere with the MgO crystallization and increase the surface roughness of MgO/Au film. Therefore, MgO/Au composite thin film with a NiO buffer layer and proper deposition times of MgO and Au can achieve superior SEE properties due to good MgO crystallization, low surface roughness and reasonable electrical conductivity. The optimized MgO/Au composite thin film has a higher SEE coefficient and a lower 1-h SEE degradation rate under electron beam bombardment in comparison with MgO film.

  15. Hydrogen storage properties of Mg-Ni-Fe composites prepared by hydriding combustion synthesis and mechanical milling

    Zhu Yunfeng, E-mail: [College of Materials Science and Engineering, Nanjing University of Technology, Nanjing 210009 (China); Yang Yang; Wei Lingjun; Zhao Zelun; Li Liquan [College of Materials Science and Engineering, Nanjing University of Technology, Nanjing 210009 (China)


    Highlights: Black-Right-Pointing-Pointer Mg-Ni-Fe composite was prepared by the process of HCS + MM. Black-Right-Pointing-Pointer Fe is favorable to grain and particle refinement of the composite. Black-Right-Pointing-Pointer Mg-Ni-Fe composite exhibits superior hydrogen storage properties. Black-Right-Pointing-Pointer Mg{sub 2}Ni and Fe have synergistic catalysis on hydrogen storage properties. - Abstract: We reported the structures and superior hydrogen storage properties of the composites Mg{sub 90}Ni{sub 10-x}Fe{sub x} (x = 0, 2, 4, 6 and 8) prepared by the process of HCS + MM, i.e., the hydriding combustion synthesis followed by mechanical milling. By means of X-ray diffraction (XRD), scanning electron microscopy (SEM) with an energy dispersive X-ray spectrometer (EDX) and gas reaction controller (GRC), the crystal structures, surface morphologies and hydriding/dehydriding properties of the composites were studied in detail. The Mg{sub 90}Ni{sub 10-x}Fe{sub x} (x = 2, 4, 6 and 8) composites consist of MgH{sub 2}, Mg, Mg{sub 2}NiH{sub 4}, Mg{sub 2}NiH{sub 0.3} and Fe phases, while Mg{sub 90}Ni{sub 10} is composed of MgH{sub 2}, Mg, Mg{sub 2}NiH{sub 4} and Mg{sub 2}NiH{sub 0.3}. It is found that Mg{sub 90}Ni{sub 2}Fe{sub 8} has the best hydriding properties, requiring only 30 s to absorb 97% of its saturated hydrogen capacity of 4.80 wt.% at 373 K. The best dehydriding result is obtained with Mg{sub 90}Ni{sub 8}Fe{sub 2}, which desorbs 2.02 and 4.40 wt.% hydrogen at 493 and 523 K, respectively. The microstructures of the composites prepared by HCS + MM have remarkable influences on the enhanced hydriding/dehydriding properties. In addition, the catalytic effects of Mg{sub 2}Ni and Fe phases during hydriding/dehydriding were discussed in this study.

  16. Preparation, Characterization and Application of Mg(OH)2-PAM Inorganic-Organic Composite Polymer in Removing Reactive Dye

    Khai Ern Lee; Norhashimah Morad; Tjoon Tow Teng; Beng Teik Poh


    In this study, a series of inorganic-organic composite polymer was prepared. Magnesium hydroxide and polyacrylamide was composed in a composite matrix to prepare Mg(OH)2-PAM (MHPAM) inorganic-organic composite polymer. The characteristics of MHPAM inorganic-organic composite polymer was investigated in terms of chemical, physical, physical, thermal and morphological properties through FT-IR, conductivity, intrinsic viscosity, TGA and TEM, respectively. Results showed that the properties of MH...

  17. Synthesis of dittmarite/Mg(OH){sub 2} composite coating on AZ31 using hydrothermal treatment

    Zhao, Qing, E-mail:; Mahmood, Waqas; Zhu, Yanying


    Highlights: • Synthesis of dittmarite Mg(OH){sub 2} coating on AZ31 alloy by hydrothermal method. • The mechanism of composite coating growth and its characterizations. • The coating is corrosion resistant significantly. • Lack of hydroxyl deposition on the coating surface. • Strong adhesion between the coating and the substrate. • The synthesized coating meets the cytotoxicity standards. - Abstract: In this work, we have used hydrothermal method for the synthesis of dittmarite/Mg(OH){sub 2} composite (DMC) layer on AZ31 alloy of magnesium. The synthesized coating was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDS). In a test immersion into the Hank's mixture for 31 days, the synthesized coating inhibited corrosion of AZ31 significantly and the amorphous calcium apatite precursor deposited on the coating surface. In another tape test, we noticed strong adhesion between the coating and substrate that eventually concludes that the synthesized coating is hydrophilic and a promising candidate to be used in the absorbable implant materials. Besides, the cytotoxicity of the AZ31 alloy with DMC coating, grown under different conditions on L-929 cells in vitro was examined indirectly through the growth inhibition method (MTT assay). The cytotoxicity of the deposited coating lie between 0 ∼ 1 that indicates it as a promising biomaterial.

  18. Improving Corrosion Resistance of Cf/Mg Composites using Rare Earth Conversion Coatings

    Song Meihui; Wang Chunyu; Wu Gaohui


    The surface of carbon fiber reinforced Mg matrix (Cf/Mg) composites was modified by treatment of rare earth conversion coating, and nontoxic, non-pollution Ce conversion coatings were prepared. The effect of the coatings on corrosion behaviors of composites was investigated by electrochemical polarization technology and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. The higher Ecorr and lower icorr were obtained by Ce conversion coatings. EIS results showed that the higher values of R2 were obtained by treatment containing CeCl3, the high corrosion resistance occured in treatment containing CeCl3, the low corrosion resistance in uncoating sample, the coating of treatment containing Ce(NO3)3 was medium. The microstructure of Ce conversion coatings was observed by scanning electron microscopy (SEM), and the elements of corresponding for coatings was characterized by energy dispersive spectrometer (EDS). The micro-cracks and Ce-riched spherical particles were characteristics of these coatings.

  19. Assessing the ability of isotope-enabled General Circulation Models to simulate the variability of Iceland water vapor isotopic composition

    Erla Sveinbjornsdottir, Arny; Steen-Larsen, Hans Christian; Jonsson, Thorsteinn; Ritter, Francois; Riser, Camilla; Messon-Delmotte, Valerie; Bonne, Jean Louis; Dahl-Jensen, Dorthe


    During the fall of 2010 we installed an autonomous water vapor spectroscopy laser (Los Gatos Research analyzer) in a lighthouse on the Southwest coast of Iceland (63.83°N, 21.47°W). Despite initial significant problems with volcanic ash, high wind, and attack of sea gulls, the system has been continuously operational since the end of 2011 with limited down time. The system automatically performs calibration every 2 hours, which results in high accuracy and precision allowing for analysis of the second order parameter, d-excess, in the water vapor. We find a strong linear relationship between d-excess and local relative humidity (RH) when normalized to SST. The observed slope of approximately -45 o/oo/% is similar to theoretical predictions by Merlivat and Jouzel [1979] for smooth surface, but the calculated intercept is significant lower than predicted. Despite this good linear agreement with theoretical calculations, mismatches arise between the simulated seasonal cycle of water vapour isotopic composition using LMDZiso GCM nudged to large-scale winds from atmospheric analyses, and our data. The GCM is not able to capture seasonal variations in local RH, nor seasonal variations in d-excess. Based on daily data, the performance of LMDZiso to resolve day-to-day variability is measured based on the strength of the correlation coefficient between observations and model outputs. This correlation coefficient reaches ~0.8 for surface absolute humidity, but decreases to ~0.6 for δD and ~0.45 d-excess. Moreover, the magnitude of day-to-day humidity variations is also underestimated by LMDZiso, which can explain the underestimated magnitude of isotopic depletion. Finally, the simulated and observed d-excess vs. RH has similar slopes. We conclude that the under-estimation of d-excess variability may partly arise from the poor performance of the humidity simulations.

  20. Hydrogen sorption properties of Mg-20wt.%Fe 23 Y8 composite prepared by reactive mechanical alloying

    LI Zhinian; LIU Xiaopeng; HUANG Zuo; JIANG Lijun; WANG Shumao


    Mg-20wt.% Fe23Y8 composite was successfully prepared by reactive mechanical alloying (RMA). X-ray diffraction (XRD) measurement shows that the main phases of composite are MgH2 and Mg2FeH6. The composite exhibits excellent hydrogen abs/desorption properties and can absorb 4.36wt.% and 5.72wt.% hydrogen at 473 and 573 K in 10 min under 3.0 Mpa hydrogen pressure, respectively. The composite can desorb 5.27wt.% hydrogen at 573 K in 30 min under 0.02 Mpa hydrogen pressure. Compared with the pure MgH2, the hydrogen desorption temperature of Mg-20wt.% Fe23Y8 composite is decreased about 40 ℃. It is supposed that both the catalyst effect of Fe-Y distributed in Mg substrate and the crystal defects play the main role in improving hydrogen sorption properties of Mg-20wt.% Fe23Y8 composite.

  1. Magnesium isotope geochemistry in arc volcanism

    Teng, Fang-Zhen; Hu, Yan; Chauvel, Catherine


    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ26Mg of the Martinique Island lavas varies from -0.25 to -0.10, in contrast to the narrow range that characterizes the mantle (-0.25 ± 0.04, 2 SD). These high δ26Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid-mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration.

  2. Magnesium isotope geochemistry in arc volcanism.

    Teng, Fang-Zhen; Hu, Yan; Chauvel, Catherine


    Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ(26)Mg of the Martinique Island lavas varies from -0.25 to -0.10, in contrast to the narrow range that characterizes the mantle (-0.25 ± 0.04, 2 SD). These high δ(26)Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid-mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration.



    The variations in the isotopic compositions of chlorine in evaporation-controlled saline lake brines were determined by using an improved procedure for precise measurement of chlorine isotopes based on Cs2Cl+ ion by thermal ionization mass spectrometry. The results showed that variation in δ37Cl values in these evaporation-controlled brines are attributable to evaporation of brine accompanied by the deposition of saline minerals. The isotopic fractionation of chlorine between the deposited saline mineral and the co-existing brine caused the variation of δ37Cl values in the brine. In general the isotopic fractionation of chlorine in nature indicates enrichment of 37Cl in the solid phase relative to 35Cl. The reverse isotopic fractionation of chlorine in which 35Cl is enriched in the solid phase, was observed to some extent during quick deposition under laboratory conditions as well as in nature. The mechanism of isotopic fractionation of chlorine during evaporation deposition was studied.

  4. Biodegradation Resistance and Bioactivity of Hydroxyapatite Enhanced Mg-Zn Composites via Selective Laser Melting

    Cijun Shuai


    Full Text Available Mg-Zn alloys have attracted great attention as implant biomaterials due to their biodegradability and biomechanical compatibility. However, their clinical application was limited due to the too rapid degradation. In the study, hydroxyapatite (HA was incorporated into Mg-Zn alloy via selective laser melting. Results showed that the degradation rate slowed down due to the decrease of grain size and the formation of protective layer of bone-like apatite. Moreover, the grain size continually decreased with increasing HA content, which was attributed to the heterogeneous nucleation and increased number of nucleation particles in the process of solidification. At the same time, the amount of bone-like apatite increased because HA could provide favorable areas for apatite nucleation. Besides, HA also enhanced the hardness due to the fine grain strengthening and second phase strengthening. However, some pores occurred owing to the agglomerate of HA when its content was excessive, which decreased the biodegradation resistance. These results demonstrated that the Mg-Zn/HA composites were potential implant biomaterials.

  5. A thirty year record of the isotopic composition of atmospheric methane from North America

    Rice, A. L.; Teama, D. G.; Roeger, F. H.; Butenhoff, C. L.; Khalil, A. K.


    Methane (CH4) is one of the most important greenhouse gases after water vapor and carbon dioxide. Its atmospheric concentration increased from 650 ppb during the preindustrial era to nearly 1800 ppb in the present day due to human activities such as rice cultivation, animal husbandry, biomass burning, and fossil fuel production and use. Since the 1980s, the long-term growth rate of atmospheric CH4 slowed dramatically consistent with a leveling off of CH4 sources with significant interannual variability over this period. One powerful tool to constrain changes in sources and sinks is the use of stable isotopes of atmospheric CH4 because of the distinct values of carbon isotope (δ13C) and hydrogen isotope (δD) ratios in CH4 sources and characteristic isotopic fractionation effects in sinks. Measurements of the long-term trend of the isotopic composition of CH4 can improve the constraint of changes to the CH4 budget from microbial sources (e.g., wetlands, ruminants, and rice agriculture, δ13C ~-60 ‰, δD ~-300‰), fossil sources (e.g. natural gas and coal mining, δ13C ~-40‰, δD ~-200‰), and biomass burning (δ13C ~-25‰, δD ~-100‰). In this work, we present measurements of δ13C and δD of atmospheric CH4 from a unique archive of more than 200 air samples collected at Cape Meares, Oregon (45.5°N, 124°W) from 1978 to 1998. The measurements from this archive indicate enrichments in both isotope tracers over this period which average 0.017 (±0.002) ‰yr-1 for δ13C and 0.68 (±0.04) ‰yr-1 for δD. Seasonal cycles in δ13C and δD are also evident with amplitudes of ~ 0.3 ‰ and ~ 4 ‰, respectively; maximum values are found May-July and minimum values September-December, consistent with previous results from the mid-latitude northern hemisphere. Combining our results with more recent timeseries since 1988 from Olympic Peninsula (WA, 48°N), Montana de Oro (CA, 35°N), and Niwot Ridge (CO, 40°N) provides a composite record of the isotopic

  6. Hydrogen (H) Isotope Composition of Type II Kerogen Extracted by Pyrolysis-GC-MS-IRMS: Terrestrial Shale Deposits as Martian Analogs

    Socki, Richard A.; Pernia, Denet; Evans, Michael; Fu, Qi; Bissada, Kadry K.; Curiale, Joseph A.; Niles, Paul B.


    Described here is a technique for H isotope analysis of organic compounds pyrolyzed from kerogens isolated from gas- and liquids-rich shales. Application of this technique will progress the understanding of the use of H isotopes not only in potential kerogen occurrences on Mars, but also in terrestrial oil and gas resource plays. H isotope extraction and analyses were carried out utilizing a CDS 5000 Pyroprobe connected to a Thermo Trace GC interfaced with a Thermo MAT 253 IRMS. Also, a split of GC-separated products was sent to a DSQ II quadrupole MS to make qualitative and semi-quantitative compositional measurements of these products. Kerogen samples from five different basins (type II and II-S) were dehydrated (heated to 80 C overnight under vacuum) and analyzed for their H isotope compositions by Pyrolysis-GC-MS-TC-IRMS. This technique takes pyrolysis products separated via GC and reacts them in a high temperature conversion furnace (1450 C), which quantitatively forms H2. Samples ranging from 0.5 to 1.0mg in size, were pyrolyzed at 800 C for 30s. and separated on a Poraplot Q GC column. H isotope data from all kerogen samples typically show enrichment in D from low to high molecular weight. H2O average delta D = -215.2 per mille (V-SMOW), ranging from - 271.8 per mille for the Marcellus Shale to -51.9 per mille for a Polish shale. Higher molecular weight compounds like toluene (C7H8) have an average delta D of -89.7 per mille, ranging from -156.0 per mille for the Barnett Shale to -50.0 per mille for the Monterey Shale. We interpret these data as representative of potential H isotope exchange between hydrocarbons and sediment pore water during basin formation. Since hydrocarbon H isotopes readily exchange with water, these data may provide some useful information on gas-water or oil-water interaction in resource plays, and further as a possible indicator of paleoenvironmental conditions. Alternatively, our data may be an indication of H isotope exchange with

  7. Measurement of position-specific 13C isotopic composition of propane at the nanomole level

    Gilbert, Alexis; Yamada, Keita; Suda, Konomi; Ueno, Yuichiro; Yoshida, Naohiro


    We have developed a novel method for analyzing intramolecular carbon isotopic distribution of propane as a potential new tracer of its origin. The method is based on on-line pyrolysis of propane followed by analysis of carbon isotope ratios of the pyrolytic products methane, ethylene and ethane. Using propane samples spiked with 13C at the terminal methyl carbon, we characterize the origin of the pyrolytic fragments. We show that the exchange between C-atoms during the pyrolytic process is negligible, and thus that relative intramolecular isotope composition can be calculated. Preliminary data from 3 samples show that site-preference (SP) values, defined as the difference of δ13C values between terminal and sub-terminal C-atom positions of propane, range from -1.8‰ to -12.9‰. In addition, SP value obtained using our method for a thermogenic natural gas sample is consistent with that expected from theoretical models of thermal cracking, suggesting that the isotope fractionation associated with propane pyrolysis is negligible. The method will provide novel insights into the characterization of the origin of propane and will help better understand the biogeochemistry of natural gas deposits.

  8. Laboratory and Field Measurements of the Nitrogen Isotopic Composition of NOx

    Fibiger, D. L.; Miller, D. J.; Dahal, B. R.; Lew, A. F.; Peltier, R.; Hastings, M. G.


    The nitrogen isotopic composition of nitrogen oxides (NOx = NO + NO2) has been measured from several NOx emissions sources in prior studies. These measurements have utilized a variety of methods for collecting the NOx as nitrate or nitrite for isotopic analysis, but none of these methods have been verified for complete conversion of NOx. Less than 100% conversion can result in isotopic fractionations. We present a method for accurately measuring the nitrogen isotopic composition of NOx using a .25 M KMnO4 and 0.5 M NaOH solution. Based on laboratory tests, this technique has been found to collect all NOx passed through under a variety of conditions (e.g., air flow rate, NOx concentration, temperature, humidity), allowing for diagnosis of δ15N-NOx without correction for fractionation. The precision across the entire analytic technique is 1.5‰. This active collection method is advantageous for collecting NOx over short time scales in environments with highly variable NOx sources and concentrations. The major drawback of the NaOH/KMnO4 method is a significant nitrate background found in the KMnO4, but this background is consistent and can be easily accounted for. We aim to use this method to provide more robust constraints on the isotopic signatures of NOx emissions from different sources. Initial results will be presented from lab- and field-based collections of NOx emissions. Emissions from a diesel engine were measured in a laboratory smog chamber and yielded δ15N values with a mean of -18.0‰ (n = 5, 1σ = 0.97‰). Measurements of δ15N-NOx were also made on a rooftop between two highways in Providence, RI. The values ranged from -7.7 to -0.63‰ for different time periods sampled, with excellent reproducibility in side-by-side collections. Additionally, the NaOH/KMnO4 was deployed in a laboratory study of biomass burning (FLAME4) to analyze the nitrogen isotopic composition of NOx produced from the burning of variety of materials (e.g. trees, agricultural

  9. Uranium isotope composition of a laterite profile during extreme weathering of basalt in Guangdong, South China

    Huang, J.; Zhou, Z.; Gong, Y.; Lundstrom, C.; Huang, F.


    Rock weathering and soil formation in the critical zone are important for material cycle from the solid Earth to superficial system. Laterite is a major type of soil in South China forming at hot-humid climate, which has strong effect on the global uranium cycle. Uranium is closely related to the environmental redox condition because U is stable at U(Ⅳ) in anoxic condition and U(Ⅵ) as soluble uranyl ion (UO22+) under oxic circumstance. In order to understand the behavior of U isotopes during crust weathering, here we report uranium isotopic compositions of soil and base rock samples from a laterite profile originated from extreme weathering of basalt in Guangdong, South China. The uranium isotopic data were measured on a Nu Plasma MC-ICP-MS at the University of Illinois at Urbana-Champaign using the double spike method. The δ238U of BCR-1 is -0.29±0.03‰ (relative to the international standard CRM-112A), corresponding to a 238U/235U ratio of 137.911±0.004. Our result of BCR-1 agrees with previous analyses (e.g., -0.28‰ in Weyer et al. 2008) [1]. U contents of the laterite profile decrease from 1.9 ppm to 0.9 ppm with depth, and peak at 160 - 170 cm (2.3 ppm), much higher than the U content of base rocks (~0.5 ppm). In contrary, U/Th of laterites is lower than that of base rock (0.27) except the peak at the depth of 160-170 cm (0.38), indicating significant U loss during weathering. Notably, U isotope compositions of soils show a small variation from -0.38 to -0.28‰, consistent with the base rock within analytical error (0.05‰ to 0.08‰, 2sd). Such small variation can be explained by a "rind effect" (Wang et al., 2015) [2], by which U(Ⅳ) can be completely oxidized to U(VI) layer by layer during basalt weathering by dissolved oxygen. Therefore, our study indicates that U loss during basalt weathering at the hot-humid climate does not change U isotope composition of superficial water system. [1] Weyer S. et al. (2008) Natural fractionation of 238U/235

  10. Isotopic composition of dissolved boron and its geochemical behavior in a freshwater-seawater mixture at the estuary of the Changjiang (Yangtze) River


    The isotopic composition of dissolved boron, in combination with the elemental concentrations of B, Cl and salinities in freshwater-seawater mixed samples taken from the estuary of the Changjiang River, the largest one in China, was investigated in detail in this study. Brackish water and seawater samples from the estuary of the Changjiang River were collected during low water season in November, 1998. Boron isotopic compositions were determined by the Cs2BO2+-graphite technique with a analytical uncertainty of 0.2‰ for NIST SRM 951 and an average analytical uncertainty of 0.8‰ for the samples. The isotopic compositions of boron, expressed in δ11B, and boron concentrations in the Changjiang River at Nanjing and seawater from the open marine East Sea, China, are characterized by δ11B values of -5.4‰ and 40.0‰, as well as 0.0272 and 4.43 mg B/L, respectively. Well-defined correlations between δ11B values, B concentrations and Cl concentrations are interpreted in terms of binary mixing between river input water and East Sea seawater by a process of straightforward dilution. The offsets of δ11B values are not related to the contents of clastic sediment and to the addition of boron. These relationships favor a conservative behavior of boron at the estuarine of the Changjiang River.

  11. Stable isotope composition of land snail body water and its relation to environmental waters and shell carbonate

    Goodfriend, Glenn A.; Magaritz, Mordeckai; Gat, Joel R.


    Day-to-day and within-day (diel) variations in δD and δ18O of the body water of the land snail, Theba pisana, were studied at a site in the southern coastal plain of Israel. Three phases of variation, which relate to isotopic changes in atmospheric water vapor, were distinguished: 1) on rain days, snail water becomes isotopically depleted approximately in the direction of the rain isotope values, but always less depleted in D as is atmospheric water vapor; 2) during the 1-3 days following a rain, the snail water becomes isotopically enriched along a line with slope persists until the next rain event. The isotopic variations can be explained by isotopic equilibration with atmospheric water vapor and/or uptake of dew derived therefrom. During the winter, when the snails are active, there is only very minor enrichment in 18O relative to equilibrium with water vapor or dew, apparently as a result of metabolic activity. But this enrichment becomes pronounced after long periods of inactivity. Within-day variation in body water isotopic composition is minor on non-rain days. Shell carbonate is enriched in 18O by ca. 1-2%. relative to equilibrium with body water. In most regions, the isotopic composition of atmospheric water vapor (or dew) is a direct function of that of rain. Because the isotopic composition of snail body water is related to that of atmospheric water vapor and the isotopic composition of shell carbonate in turn is related to that of body water, land snail shell carbonate 18O should provide a reliable indication of rainfall 18O. However, local environmental conditions and the ecological properties of the snail species must be taken into account.

  12. Improvement in the transport critical current density and microstructure of isotopic Mg11B2 monofilament wires by optimizing the sintering temperature

    Qiu, Wenbin; Jie, Hyunseock; Patel, Dipak; Lu, Yao; Luzin, Vladimir; Devred, Arnaud; Somer, Mehmet; Shahabuddin, Mohammed; Kim, Jung Ho; Ma, Zongqing; Dou, Shi Xue; Hossain, Md. Shahriar Al


    Superconducting wires are widely used in fabricating magnetic coils in fusion reactors. In consideration of the stability of 11B against neutron irradiation and lower induced radio-activation properties, MgB2 superconductor with 11B serving as boron source is an alternative candidate to be used in fusion reactor with severe irradiation environment. In present work, a batch of monofilament isotopic Mg11B2 wires with amorphous 11B powder as precursor were fabricated using powder-in-tube (PIT) process at different sintering temperature, and the evolution of their microstructure and corresponding superconducting properties was systemically investigated. Accordingly, the best transport critical current density (Jc) = 2 × 104 A/cm2 was obtained at 4.2 K and 5 T, which is even comparable to multi-filament Mg11B2 isotope wires reported in other work. Surprisingly, transport Jc vanished in our wire which was heat-treated at excessively high temperature (800 °C). Combined with microstructure observation, it was found that lots of big interconnected microcracks and voids that can isolate the MgB2 grains formed in this whole sample, resulting in significant deterioration in inter-grain connectivity. The results can be a constructive guide in fabricating Mg11B2 wires to be used as magnet coils in fusion reactor systems such as ITER-type tokamak magnet.

  13. Microstructures in Centrifugal Casting of SiCp/AlSi9Mg Composites with Different Mould Rotation Speeds

    WANG Kai; SUN Wenju; LI Bo; XUIE Hansong; LIU Changming


    Two ingots were produced by centrifugal casting at mould rotational speeds of 600 rpm and 800 rpm using 20 vol% SiCp/AlSi9Mg composite melt, respectively. The microstructure along the radial direction of cross-sectional sample of ingots was presented. SiC particles migrated towards the external circumference of the tube, and the distribution of SiC particles became uniform under centrifugal force. Voids in 20 vol% SiCp/AlSi9Mg composite melt migrated towards the inner circumference of the tube. The quantitative analysis results indicated that not only SiC particles but also primary a phases segregated greatly in centrifugal casting resulting from the transportation behavior of constitutions with different densities in the SiCp/AlSi9Mg composite melt. In addition, the eutectic Si was broken owing to the motion of SiCp/AlSi9Mg composite melt during centrifugal casting.

  14. The isotope composition of inorganic germanium in seawater and deep sea sponges

    Guillermic, Maxence; Lalonde, Stefan V.; Hendry, Katharine R.; Rouxel, Olivier J.


    Although dissolved concentrations of germanium (Ge) and silicon (Si) in modern seawater are tightly correlated, uncertainties still exist in the modern marine Ge cycle. Germanium stable isotope systematics in marine systems should provide additional constraints on marine Ge sources and sinks, however the low concentration of Ge in seawater presents an analytical challenge for isotopic measurement. Here, we present a new method of pre-concentration of inorganic Ge from seawater which was applied to measure three Ge isotope profiles in the Southern Ocean and deep seawater from the Atlantic and Pacific Oceans. Germanium isotopic measurements were performed on Ge amounts as low as 2.6 ng using a double-spike approach and a hydride generation system coupled to a MC-ICP-MS. Germanium was co-precipitated with iron hydroxide and then purified through anion-exchange chromatography. Results for the deep (i.e. >1000 m depth) Pacific Ocean off Hawaii (nearby Loihi Seamount) and the deep Atlantic off Bermuda (BATS station) showed nearly identical δ74/70Ge values at 3.19 ± 0.31‰ (2SD, n = 9) and 2.93 ± 0.10‰ (2SD, n = 2), respectively. Vertical distributions of Ge concentration and isotope composition in the deep Southern Ocean for water depth > 1300 m yielded an average δ74/70Ge = 3.13 ± 0.25‰ (2SD, n = 14) and Ge/Si = 0.80 ± 0.09 μmol/mol (2SD, n = 12). Significant variations in δ74/70Ge, from 2.62 to 3.71‰, were measured in the first 1000 m in one station of the Southern Ocean near Sars Seamount in the Drake Passage, with the heaviest values measured in surface waters. Isotope fractionation by diatoms during opal biomineralization may explain the enrichment in heavy isotopes for both Ge and Si in surface seawater. However, examination of both oceanographic parameters and δ74/70Ge values suggest also that water mass mixing and potential contribution of shelf-derived Ge also could contribute to the variations. Combining these results with new Ge isotope data

  15. Noble gas abundances and isotopic compositions in mantle-derived xenoliths,NE China


    Following the researches of helium isotopic compositions in mantle-derived xenoliths in eastern China,this study reported noble gas abundances and isotopic compositions of mantle-derived xenoliths from Kuandian of Liaoning Province, Huinan of Jilin Province and Hannuoba of Hebei Province. Compared with the middle ocean ridge basalt (MORB) and other continental areas, mantle-derived xenoliths in NE China are characterized by slightly low noble gas abundances, 3He/4He equivalent to or lower than that of MORB, 40Ar/36Ar lower than that of MORB, 38Ar/36Ar and Ne-Kr-Xe isotopic ratios equivalent to those of atmosphere. These results indicate the heterogeneity of subcontinentai lithospheric mantle beneath northeastern China, that is, a MORB reservoir-like mantle beneath Kuandian and an enriched/metasomatized mantle beneath Huinan. Low 40Ar/36Ar ratios in the three studied areas may imply that a subducted atmospheric component has been preserved in the subcontinental lithospheric mantle.``

  16. The relationship between carbon and oxygen isotopic composition characteristics of carbonates in loess sediments and paleoclimate

    李春园; 王先彬; 文启彬; 邵波


    Based on the carbon and oxygen isotopic compositions of carbonates in loess sediments meas-ured by the methods of stepwise heating and phosphoric acid decomposition from five pieces of samples ofpaleosol,loess and eolian sand,respectively,the distributive characteristics in different temperature steps andthe fractionation mechanisms of carbon and oxygen isotope and their relation to the paleoclirnate are discussed.The preliminary results show that,by means of stepwise heating,different carbon and oxygen isotopiccompositions are obtained in different temperature steps and carbon and oxygen isotopic compositions ofpaleosol,loess and eolian sand are in a different distributive pattern in the range of studied temperaturesteps.The results also show that the δ13C ratios in 700-800℃ are more sensitive tracers of paleoclimatethan those measured by the method of phosphoric acid decomposition.The susceptibility to climatic changesof δ18O ratios analysed by the method of phosphoric acid decomposition is higher than those analysed by themethod of stepwise heating,but the δ18O ratios measured by these two methods do not effectively reflect cli-matic changes.

  17. Multiple oxygen and sulfur isotope compositions of secondary atmospheric sulfate in the city of Wuhan, central China

    Li, X.; Bao, H.; Zhou, A.; Wang, D.


    Secondary atmospheric sulfate (SAS) is the oxidation product and sink for sulfur gases of biological, volcanic, and anthropogenic origins on Earth. SAS can be produced from gas-phase OH-radical oxidation and five aqueous-phase chemical reactions including aqueous-phase S (IV) oxidation reactions by H2O2, O3, oxygen catalyzed by Fe3+ and Mn2+, and methyle hydrogen peroxide and peroxyacetic acid. The tropospheric sulfur oxidation pathway is therefore determined by cloud-water pH, dissolved [Fe2+] or [Mn2+] content, S emission rate, meteorological condition, and other factors. The S isotope composition is a good tracer for the source while the O isotopes, especially the triple O isotope compositions are a good tracer for S oxidation pathway. Jerkins and Bao (2006) provided the first set of multiple stable isotope compositions (δ34S, δ18O and Δ17O) for SAS collected from bulk atmosphere in Baton Rouge in the relatively rural southern USA. Their study revealed a long-tern average Δ17O value of ~+0.7‰ for SAS, and speculated that much of the Earth mid-latitudes may have a similar average SAS Δ17O value. Additional sampling campaign at different sites is necessarily for constructing and testing models on sulfur oxidation and transport in the troposphere. A total of 33 sulfate samples were collected from bulk atmospheric deposition over a 950-day period from May 2009 to December 2011 in the city of Wuhan, Hubei Province, China. Differing from Baton Rouge, Wuhan is an industrial metropolis with a population of 9.8 million and a high particulate matter content (115 μg/m3). It also has a subtropical monsoon climate, with rainwater pH at ~5.3 year-around. The rainwater ion concentrations have seasonal variations, typically low in summer and high in winter. The anions are dominated by SO42-, at an average concentration of 8.5 mg/L. There is little sulfate contribution from sea-salt (SS) sulfate or dusts in Wuhan. The isotopic compositions for bulk atmospheric sulfate

  18. Tracing the secular evolution of the UCC using the iron isotope composition of ancient glacial diamictites

    Liu, X. M.; Gaschnig, R. M.; Rudnick, R. L.; Hazen, R. M.; Shahar, A.


    Iron is the fourth most abundant element in the continental crust and influences global climate and biogeochemical cycles in the ocean1. Continental inputs, including river waters, sediments and atmospheric dust are dominant sources (>95%) of iron into the ocean2. Therefore, understanding how continental inputs may have changed through time is important in understanding the secular evolution of the marine Fe cycle. We analysed the Fe isotopic composition of twenty-four glacial diamictite composites, upper continental crust (UCC) proxies, with ages ranging from the Mesoarchean to the Paleozoic eras to characterize the secular evolution of the UCC. The diamictites all have elevated chemical index of alteration (CIA) and other characteristics of weathered regolith (e.g., strong depletion in soluble elements such as Sr), which they inherited from their upper crustal source region3. δ56Fe in the diamictite composites range from -0.59 to +0.23‰, however, most diamictites cluster with an average δ56Fe of 0.11± 0.20 (2s), overlapping juvenile continental material such as island arc basalts (IABs), which show a narrow range in δ56Fe from -0.04 to +0.14 ‰4. There is no obvious correlation between δ56Fe of the glacial diamictites and the CIA, except that the diamictite with the lowest δ56Fe at -0.59 ‰ also has the highest CIA = 89 (the Paleoproterozoic Makganyene Fm.). The data suggest that the Fe isotope compositions in the upper continental crust did not vary throughout Earth history. Interestingly, chemical weathering and sedimentary transport likely play only a minor role in producing Fe isotope variations in the upper continental crust. Anoxic weathering pre-GOE (Great Oxidation Event) does not seem to generate different Fe isotopic signatures from the post-GOE oxidative weathering environment in the upper continental crust. Therefore, large Fe isotopic fractionations observed in various marine sedimentary records are likely due to other processes occurring

  19. Hydrogen isotopic composition of the Martian mantle inferred from the newest Martian meteorite fall, Tissint

    Mane, P.; Hervig, R.; Wadhwa, M.; Garvie, L. A. J.; Balta, J. B.; McSween, H. Y.


    The hydrogen isotopic composition of planetary reservoirs can provide key constraints on the origin and history of water on planets. The sources of water and the hydrological evolution of Mars may be inferred from the hydrogen isotopic compositions of mineral phases in Martian meteorites, which are currently the only samples of Mars available for Earth-based laboratory investigations. Previous studies have shown that δD values in minerals in the Martian meteorites span a large range of -250 to +6000‰. The highest hydrogen isotope ratios likely represent a Martian atmospheric component: either interaction with a reservoir in equilibrium with the Martian atmosphere (such as crustal water), or direct incorporation of the Martian atmosphere due to shock processes. The lowest δD values may represent those of the Martian mantle, but it has also been suggested that these values may represent terrestrial contamination in Martian meteorites. Here we report the hydrogen isotopic compositions and water contents of a variety of phases (merrillites, maskelynites, olivines, and an olivine-hosted melt inclusion) in Tissint, the latest Martian meteorite fall that was minimally exposed to the terrestrial environment. We compared traditional sample preparation techniques with anhydrous sample preparation methods, to evaluate their effects on hydrogen isotopes, and find that for severely shocked meteorites like Tissint, the traditional sample preparation techniques increase water content and alter the D/H ratios toward more terrestrial-like values. In the anhydrously prepared Tissint sample, we see a large range of δD values, most likely resulting from a combination of processes including magmatic degassing, secondary alteration by crustal fluids, shock-related fractionation, and implantation of Martian atmosphere. Based on these data, our best estimate of the δD value for the Martian depleted mantle is -116 ± 94‰, which is the lowest value measured in a phase in the

  20. Gas Compositions and He-C Isotopic Ratios of Fumarolic Samples from Negros Island, Central Philippines

    Lee, Hsiao-Fen; Yang, Tsanyao Frank; Faith Lan, Tefang; Chen, Yue-Gau; Sincioco, Jaime S.; Solidum, Renato U., Jr.


    Four volcanoes that are distributed in the Negros Island, Central Philippines, include Kanlaon Volcano which is considered as one of the most active volcanoes in Philippines. All of these volcanoes are related to subduction system of Negros trench and form the Negros volcanic arc. Besides Kanlaon, from north to south, the volcanoes in Negros Island are Silay Volcano, Mandalagan Volcano and Cuernos de Negros Volcano. Although there is no eruption record of these three volcanoes in last 10,000 years, due to the ongoing solfataric/fumarolic activities, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) classifies these as 'potentially active' volcanoes. It means that there is still a considerable threat and risk of eruption. Fumarolic gas samples and bubbling gas samples of hot spring were collected in February 2007 and April 2008 to compare the compositions with others in the world. We analyzed the gas composition, carbon isotopes of CO2, and helium isotopes of these samples. The results of these samples show a similar composition as those of low-temperature fumaroles in other parts of the world, i.e., temperature 1. H2O is the major species of these gas samples, and CO2 is the dominant component after de-watering. Minor components include H2S, N2 and CH4. The gas composition of most of these samples falls in the range of affinity with convergent plate gases associated with groundwater based on the plot of N2-He-Ar diagram. The high 3He/4He ratios indicate a mantle-derived degassing source in origin, i.e., magma chambers could still exist beneath these volcanoes. Helium isotopes ratios show a decreasing trend from north to south, such distribution could be due to more crustal contamination caused by the collision event which happened in the northern part of the island. The carbon isotopic values of CO2 are far less negative than the values from a magma source. There are other carbon sources of CO2, most likely a thick sequence of limestone formation in

  1. Chemical and Isotope Compositions of Neogene Hippopotamidae Teeth From Lake Albert (Uganda): Implications for Environmental Change

    Brugmann, G. E.; Brachert, T. C.; Ssemmanda, I.; Mertz, D. F.


    The Neogene was a period of long-term global cooling and increasing climatic variability on astronomical time scales. Lake systems strongly depend on rainfall patterns and size or geographical distribution of river networks. To unravel environmental change and watershed dynamics in the western branch of the East African Rift (Lake Albert, Uganda) during the Late Neogene, we use proxy data (trace elements, O, C and Sr isotopes) from Hippopotamidae teeth. Laser ablation ICPMS profiles in enamel measured from the outside rim towards the dentin show an asymmetric trace element distribution in that the concentrations continuously decrease by up to 5 orders of magnitude within a distance of about 1 mm until a minimum is reached (migration pathways and palaeoenvironmental changes. On geological time scales δ13C compositions reflect a transition from pure C3 browsers (-11 per mil PDB) at 5 to 6 Ma towards C4 dominated grazers (0 per mil PDB) at 2.0 to 2.5 Ma. The oxygen stable isotope (δ18O) composition of enamel rises from 26 per mil at 5 to 6 Ma to a maximum of 32 per mil SMOW at 2.3 Ma. Increasing δ18O values suggest enhanced evaporation of the lake due to rising aridity. This is in agreement with a synchronous spread of C4 vegetation in the reach of Hippopotamid populations. The Sr isotopic composition of enamel displays a large variation and 87Sr/86Sr is 0.714 about 5 Ma ago, reaches a maximum of 0.717 at about 2.3 Ma and decreases from there on to about 0.708. Thus, Sr and O isotopic compositions correlate with each other on the geological time scale. This is plausible if the Sr isotopic composition of Hippopotamid enamel dominantly reflects the changes of the water chemistry of the lake, and is therefore a powerful tool for tracing ancient hydrological networks. The large variation of the Sr isotope composition can be explained if the lake is fed by different sources: water draining Cenozoic volcanic terrains have low 87Sr/86Sr (~ 0.704), whereas Proterozoic

  2. Effects of Composition and Structure of Mg/Al Oxides on Their Activity and Selectivity for the Condensation of Methyl Ketones

    Shylesh, Sankaranarayanapillai


    The effects of chemical composition and pretreatment on Mg–Al hydrotalcites and alumina-supported MgO were evaluated for the gas-phase, self-condensation reaction of C3–C5 biomass-derived methyl ketones. We show that the selectivity toward the acyclic dimer enone and the cyclic enone trimer can be tuned by controlling the temperature of hydrotalcite calcination. Methyl ketone cyclization is promoted by Lewis acidic sites present on the hydrotalcite catalysts. XRD and thermal decomposition analysis reveal that the formation of periclase MgO starts above 623 K accompanied by complete disappearance of the hydrotalcite structure and is accompanied by an increase in hydroxyl condensation as the formation of well-crystallized periclase. 27Al MQMAS and 25Mg MAS NMR show that at progressively higher temperatures, Al3+ cations diffuses out of the octahedral brucite layers and incorporate into the tetrahedral and octahedral sites of the MgO matrix thereby creating defects to compensate the excess positive charge generated. The oxygen anions adjacent to the Mg2+/Al3+ defects become coordinatively unsaturated, leading to the formation of new basic sites. A kinetic isotope effect, kH/kD = 0.96, is observed at 473 K for the reaction of (CH3)2CO versus (CD3)2CO, which suggests that carbon–carbon bond formation leading to the dimer aldol product is the rate-determining step in the condensation reaction of methyl ketones. We also show that acid–base catalysts having similar reactivity and higher hydrothermal stability to that of calcined hydrotalcites can be achieved by creating defects in MgO crystallites supported alumina as a consequence of the diffusion of Al3+ cations into MgO. The physical properties of these materials are shown to be very similar to those of hydrotalcite calcined at 823 K.

  3. Chlorine isotopic compositions of deep saline fluids in Ibusuki coastal geothermal region, Japan : using B–Cl isotopes to interpret fluid sources

    Musashi, Masaaki; Oi, Takao; Kreulen, Rob


    We report chlorine stable isotopic compositions (δ37Cl, expressed in ‰ relative to the standard mean ocean chloride) as well as δ2H and δ18O values of deep saline fluids taken at eight drill-holes reaching from 73 to 780 m below sea level in the Ibusuki coastal geothermal region, Japan. Analytical r

  4. Molecular and carbon isotopic compositions of gas inclusions of deep carbonate rocks in the Tarim Basin

    ZHOU Shixin; WANG Xianbin; MENG Zifang; LI Yuan; Paul Farrimond; LI Liwu; DUAN Yi


    Gaseous components of gas inclusions in deep carbonate rocks (>5700 m) from the Tacan 1 well were analyzed by online mass spectrometry by means of either the stepwise heating technique or vacuum electromagnetism crushing. The carbon