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Sample records for carbon isotopic fractionation

  1. Carbon isotopic fractionation in heterotrophic microbial metabolism

    Science.gov (United States)

    Blair, N.; Leu, A.; Munoz, E.; Olsen, J.; Kwong, E.; Des Marais, D.

    1985-01-01

    Differences in the natural-abundance carbon stable isotopic compositions between products from aerobic cultures of Escherichia coli K-12 were measured. Respired CO2 was 3.4 percent depleted in C-13 relative to the glucose used as the carbon source, whereas the acetate was 12.3 percent enriched in C-13. The acetate C-13 enrichment was solely in the carboxyl group. Even though the total cellular carbon was only 0.6 percent depleted in C-13, intracellular components exhibited a significant isotopic heterogeneity. The protein and lipid fractions were -1.1 and -2.7 percent, respectively. Aspartic and glutamic acids were -1.6 and +2.7 percent, respectively, yet citrate was isotopically identical to the glucose. Probable sites of carbon isotopic fractionation include the enzyme, phosphotransacetylase, and the Krebs cycle.

  2. Carbon isotope fractionation in protoplanetary disks

    CERN Document Server

    Woods, Paul M

    2008-01-01

    We investigate the gas-phase and grain-surface chemistry in the inner 30 AU of a typical protoplanetary disk using a new model which calculates the gas temperature by solving the gas heating and cooling balance and which has an improved treatment of the UV radiation field. We discuss inner-disk chemistry in general, obtaining excellent agreement with recent observations which have probed the material in the inner regions of protoplanetary disks. We also apply our model to study the isotopic fractionation of carbon. Results show that the fractionation ratio, 12C/13C, of the system varies with radius and height in the disk. Different behaviour is seen in the fractionation of different species. We compare our results with 12C/13C ratios in the Solar System comets, and find a stark contrast, indicative of reprocessing.

  3. Organic chemistry of Murchison meteorite: Carbon isotopic fractionation

    Science.gov (United States)

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

    1986-01-01

    The carbon isotopic composition of individual organic compounds of meteoritic origin remains unknown, as most reported carbon isotopic ratios are for bulk carbon or solvent extractable fractions. The researchers managed to determine the carbon isotopic ratios for individual hydrocarbons and monocarboxylic acids isolated from a Murchison sample by a freeze-thaw-ultrasonication technique. The abundances of monocarboxylic acids and saturated hydrocarbons decreased with increasing carbon number and the acids are more abundant than the hydrocarbon with the same carbon number. For both classes of compounds, the C-13 to C-12 ratios decreased with increasing carbon number in a roughly parallel manner, and each carboxylic acid exhibits a higher isotopic number than the hydrocarbon containing the same number of carbon atoms. These trends are consistent with a kinetically controlled synthesis of higher homologues for lower ones.

  4. Magnesium isotope fractionation in bacterial mediated carbonate precipitation experiments

    Science.gov (United States)

    Parkinson, I. J.; Pearce, C. R.; Polacskek, T.; Cockell, C.; Hammond, S. J.

    2012-12-01

    Magnesium is an essential component of life, with pivotal roles in the generation of cellular energy as well as in plant chlorophyll [1]. The bio-geochemical cycling of Mg is associated with mass dependant fractionation (MDF) of the three stable Mg isotopes [1]. The largest MDF of Mg isotopes has been recorded in carbonates, with foraminiferal tests having δ26Mg compositions up to 5 ‰ lighter than modern seawater [2]. Magnesium isotopes may also be fractionated during bacterially mediated carbonate precipitation and such carbonates are known to have formed in both modern and ancient Earth surface environments [3, 4], with cyanobacteria having a dominant role in carbonate formation during the Archean. In this study, we aim to better constrain the extent to which Mg isotope fractionation occurs during cellular processes, and to identify when, and how, this signal is transferred to carbonates. To this end we have undertaken biologically-mediated carbonate precipitation experiments that were performed in artificial seawater, but with the molar Mg/Ca ratio set to 0.6 and with the solution spiked with 0.4% yeast extract. The bacterial strain used was marine isolate Halomonas sp. (gram-negative). Experiments were run in the dark at 21 degree C for two to three months and produced carbonate spheres of various sizes up to 300 μm in diameter, but with the majority have diameters of ~100 μm. Control experiments run in sterile controls (`empty` medium without bacteria) yielded no precipitates, indicating a bacterial control on the precipitation. The carbonate spheres are produced are amenable to SEM, EMP and Mg isotopic analysis by MC-ICP-MS. Our new data will shed light on tracing bacterial signals in carbonates from the geological record. [1] Young & Galy (2004). Rev. Min. Geochem. 55, p197-230. [2] Pogge von Strandmann (2008). Geochem. Geophys. Geosys. 9 DOI:10.1029/2008GC002209. [3] Castanier, et al. (1999). Sed. Geol. 126, 9-23. [4] Cacchio, et al. (2003

  5. Fractionation behavior of chromium isotopes during coprecipitation with calcium carbonate

    DEFF Research Database (Denmark)

    Rodler, Alexandra; Sánchez-Pastor, Nuria; Fernández-Díaz, Lurdes;

    2015-01-01

    Interest in chromium (Cr) isotope incorporation into carbonates arises from the observation that Cr isotopic composition of carbonates could be used as a paleoclimate proxy to elucidate past fluctuations of oxygen contents in atmosphere and hydrosphere. The use of Cr isotopes to track paleoenviro......Interest in chromium (Cr) isotope incorporation into carbonates arises from the observation that Cr isotopic composition of carbonates could be used as a paleoclimate proxy to elucidate past fluctuations of oxygen contents in atmosphere and hydrosphere. The use of Cr isotopes to track...

  6. Boron isotope fractionation in magma via crustal carbonate dissolution.

    Science.gov (United States)

    Deegan, Frances M; Troll, Valentin R; Whitehouse, Martin J; Jolis, Ester M; Freda, Carmela

    2016-08-04

    Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ(11)B values down to -41.5‰, reflecting preferential partitioning of (10)B into the assimilating melt. Loss of (11)B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports (11)B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ(11)B melt values in arc magmas could flag shallow-level additions to the subduction cycle.

  7. C isotope fractionation during heterotrophic activity driven carbonate precipitation

    Science.gov (United States)

    Balci, Nurgul; Demirel, Cansu

    2016-04-01

    Stable carbon isotopic fractionation during carbonate precipitation induced by environmentally enriched heterotrophic halophilic microorganims was experimentally investigated under various salinity (% 4.5, %8, %15) conditions at 30 °C. Halophilic heterotrophic microorganims were enriched from a hypersaline Lake Acigöl located in SW Turkey (Balci et al.,2015) and later used for the precipitation experiments (solid and liquid medium). The carbonate precipitates had relatively high δ13C values (-4.3 to -16.9 ‰) compared to the δ13C values of the organic compounds that ranged from -27.5 to -25.4 ‰. At salinity of 4.5 % δ13C values of carbonate ranged from -4.9 ‰ to -10.9 ‰ with a 13C-enrichment factor of +20 to +16 ‰ higher than the δ13C values of the associated DOC (-27.5) . At salinity 8 % δ13C values of carbonate ranged from -16.3 ‰ to -11.7 ‰ with a 13C-enrichment factor of+11.3 to+15.9 ‰ higher than the δ13C values of the associated DOC. The respected values for 15 % salinity ranged from -12.3 ‰ to -9.7 ‰ with a 13C-enrichment factor of +15.2 to+16.8 ‰ higher than the δ13C values of the associated DOC. The carbonate precipitates produced in the solid medium are more enriched in 13C relative to liquid culture experiments. These results suggest that the carbon in the solid was derived from both the bacterial oxidation of organic compounds in the medium and from the atmospheric CO2. A solid medium used in the experiments may have suppressed convective and advective mass transport favouring diffusion-controlled system. This determination suggests that the rate and equilibration of CO2 exchange with the atmosphere is the major control on C isotope composition of carbonate minerals precipitated in the experiments. Key words: Lake Acıgöl, halophilic bacteria, carbonate biomineralization, C isotopes References Nurgul Balci, Meryem Menekşe, Nevin Gül Karagüler, M. Şeref Sönmez,Patrick Meister 2015.Reproducing authigenic carbonate

  8. CO2-dependent carbon isotope fractionation in dinoflagellates relates to their inorganic carbon fluxes

    NARCIS (Netherlands)

    Hoins, M.; Eberlein, T.; Van de Waal, D.B.; Sluijs, A.|info:eu-repo/dai/nl/311474748; Reichart, G.-J.|info:eu-repo/dai/nl/165599081; Rost, B.

    2016-01-01

    Carbon isotope fractionation (εp) between the inorganic carbon source and organic matter has been proposed to be a function of pCO2. To understand the CO2-dependency of εp and species-specific differences therein, inorganic carbon fluxes in the four dinoflagellate species Alexandrium fundyense, Scri

  9. Carbon and nitrogen isotope systematics in diamond: Different sensitivities to isotopic fractionation or a decoupled origin?

    Science.gov (United States)

    Hogberg, K.; Stachel, T.; Stern, R. A.

    2016-11-01

    Using stable isotope data obtained on multiple aliquots of diamonds from worldwide sources, it has been argued that carbon and nitrogen in diamond are decoupled. Here we re-investigate the carbon-nitrogen relationship based on the most comprehensive microbeam data set to date of stable isotopes and nitrogen concentrations in diamonds (n = 94) from a single locality. Our diamond samples, derived from two kimberlites in the Chidliak Field (NE Canada), show large variability in δ13C (- 28.4 ‰ to - 1.1‰, mode at - 5.8‰), δ15N (- 5.8 to + 18.8‰, mode at - 3.0‰) and nitrogen contents ([N]; 3800 to less than 1 at.ppm). In combination, cathodoluminescence imaging and microbeam analyses reveal that the diamonds grew from multiple fluid pulses, with at least one major hiatus documented in some samples that was associated with a resorption event and an abrupt change from low δ13C and [N] to mantle-like δ13C and high [N]. Overall, δ13C appears to be uncorrelated to δ15N and [N] on both the inter- and intra-diamond levels. Co-variations of δ15N-log[N], however, result in at least two parallel, negatively correlated linear arrays, which are also present on the level of the individual diamonds falling on these two trends. These arrays emerge from the two principal data clusters, are characterized by slightly negative and slightly positive δ15N (about - 3 and + 2‰, respectively) and variable but overall high [N]. Using published values for the diamond-fluid nitrogen isotope fractionation factor and nitrogen partition coefficient, these trends are perfectly reproduced by a Rayleigh fractionation model. Overall, three key elements are identified in the formation of the diamond suite studied: (1.) a low δ13C and low [N] component that possibly is directly associated with an eclogitic diamond substrate or introduced during an early stage fluid event. (2.) Repeated influx of a variably nitrogen-rich mantle fluid (mildly negative δ13C and δ15N). (3.) In waning

  10. Chromium isotope fractionation during coprecipitation with calcium carbonate

    DEFF Research Database (Denmark)

    Rodler, Alexandra; Sánchez-Pastor, Nuria; Fernández-Díaz, Lurdes

    the Archaean and Protoerozoic, needs careful assessment of the signal robustness and necessitates a thorough understanding of the Cr cycle in Earth system processes. We conducted experiments testing the incorporation and isotopic fractionation of chromate into the calcite lattice. Our experiments indicate...... et al., 2007, Water Air Soil Poll. 179, 381-390. [2] Sánchez-Pastor et al., 2011, Cryst. Growth Des. 11, 3081-3089....

  11. Stable carbon isotope fractionation of six strongly fractionating microorganisms is not affected by growth temperature under laboratory conditions

    Science.gov (United States)

    Penger, Jörn; Conrad, Ralf; Blaser, Martin

    2014-09-01

    Temperature is the major driving force for many biological as well as chemical reactions and may impact the fractionation of stable carbon isotopes. Thus, a good correlation between temperature and fractionation is observed in many chemical systems that are controlled by an equilibrium isotope effect. In contrast, biological systems that are usually controlled by a kinetic isotope effect are less well studied with respect to temperature effects and have shown contrasting results. We studied three different biological pathways (methylotrophic methanogenesis, hydrogenotrophic methanogenesis, acetogenesis by the acetyl-CoA pathway) which are characterized by very strong carbon isotope enrichment factors (-50‰ to -83‰). The microorganisms (Methanosarcina barkeri, Methanosarcina acetivorans, Methanolobus zinderi, Methanothermobacter marburgensis, Methanothermobacter thermoautotrophicus, Thermoanaerobacter kivui) exhibiting these pathways were grown at different temperatures ranging between 25 and 68 °C, and the fractionation factors were determined from 13C/12C isotope discrimination during substrate depletion and product formation. Our experiments showed that the fractionation factors were different for the different metabolic pathways but were not much affected by the different growth temperatures. Slight variations were well within the standard errors of replication and regression analysis. Our results showed that temperature had no significant effect on the fractionation of stable carbon isotopes during anaerobic microbial metabolism with relatively strong isotope fractionation.

  12. Photosynthetic fractionation of the stable isotopes of oxygen and carbon

    Energy Technology Data Exchange (ETDEWEB)

    Guy, R.D. (Carnegie Institution of Washington, Stanford, CA (United States)); Fogel, M.L.; Berry, J.A. (Carnegie Inst. of Washington, Washington, DC (United States))

    1993-01-01

    Isotope discrimination during photosynthetic exchange of O[sub 2] and CO[sub 2] was measured using enzyme, thylakoid, and whole cell preparations. Evolved oxygen from isolated spinach thylakoids was isotopically identical (within analytical error) to its source water. Similar results were obtained with Anacystis nidulans Richter and Phaeodactylum tricornutum Bohlin cultures purged with helium. For consumptive reactions, discrimination ([triangle], where 1 + [triangle]/1000 equals the isotope effect, k[sup 16]/k[sup 18] or k[sup 12]/k[sup 13]) was determined by analysis of residual substrate (O[sub 2] or CO[sub 2]). The [triangle] for the Mehler reaction, mediated by ferredoxin or methylviologen, was 15.3[per thousand]. Oxygen isotope discrimination during oxygenation of ribulose-1,5-bisphosphate (RuBP) catalyzed by RuBP carboxylase/oxygenase (Rubisco) was 21.3[per thousand] and independent of enzyme source, unlike carbon isotope dicrimination: 30.3[per thousand] for spinach enzyme and 19.6 to 23[per thousand] for Rhodospirillum rubrum and A. nidulans enzymes, depending on reaction conditions. The [triangle] for O[sub 2] consumption catalyzed by glycolate oxidase was 22.7[per thousand]. Consistent with this, when Asparagus sprengeri Regel mesopyll cells approached the compensation point within a sealed vessel, the [delta][sup 18]O of dissolved O[sub 2] came to a steady-state value of about 21.5[per thousand] relative to the source water. The results provide improved estimates of discrimination factors in several reactions prominent in the global oxygen cycle and indicate that photorespiration plays a significant part in determining the isotopic composition of atmospheric oxygen. 47 refs., 8 figs., 2 tabs.

  13. CO2-dependent carbon isotope fractionation in dinoflagellates relates to their inorganic carbon fluxes.

    Science.gov (United States)

    Hoins, Mirja; Eberlein, Tim; Van de Waal, Dedmer B; Sluijs, Appy; Reichart, Gert-Jan; Rost, Björn

    2016-08-01

    Carbon isotope fractionation (εp) between the inorganic carbon source and organic matter has been proposed to be a function of pCO2. To understand the CO2-dependency of εp and species-specific differences therein, inorganic carbon fluxes in the four dinoflagellate species Alexandrium fundyense, Scrippsiella trochoidea, Gonyaulax spinifera and Protoceratium reticulatum have been measured by means of membrane-inlet mass spectrometry. In-vivo assays were carried out at different CO2 concentrations, representing a range of pCO2 from 180 to 1200 μatm. The relative bicarbonate contribution (i.e. the ratio of bicarbonate uptake to total inorganic carbon uptake) and leakage (i.e. the ratio of CO2 efflux to total inorganic carbon uptake) varied from 0.2 to 0.5 and 0.4 to 0.7, respectively, and differed significantly between species. These ratios were fed into a single-compartment model, and εp values were calculated and compared to carbon isotope fractionation measured under the same conditions. For all investigated species, modeled and measured εp values were comparable (A. fundyense, S. trochoidea, P. reticulatum) and/or showed similar trends with pCO2 (A. fundyense, G. spinifera, P. reticulatum). Offsets are attributed to biases in inorganic flux measurements, an overestimated fractionation factor for the CO2-fixing enzyme RubisCO, or the fact that intracellular inorganic carbon fluxes were not taken into account in the model. This study demonstrates that CO2-dependency in εp can largely be explained by the inorganic carbon fluxes of the individual dinoflagellates.

  14. Intracellular Cadmium Isotope Fractionation

    Science.gov (United States)

    Horner, T. J.; Lee, R. B.; Henderson, G. M.; Rickaby, R. E.

    2011-12-01

    Recent stable isotope studies into the biological utilization of transition metals (e.g. Cu, Fe, Zn, Cd) suggest several stepwise cellular processes can fractionate isotopes in both culture and nature. However, the determination of fractionation factors is often unsatisfactory, as significant variability can exist - even between different organisms with the same cellular functions. Thus, it has not been possible to adequately understand the source and mechanisms of metal isotopic fractionation. In order to address this problem, we investigated the biological fractionation of Cd isotopes within genetically-modified bacteria (E. coli). There is currently only one known biological use or requirement of Cd, a Cd/Zn carbonic anhydrase (CdCA, from the marine diatom T. weissfloggii), which we introduce into the E. coli genome. We have also developed a cleaning procedure that allows for the treating of bacteria so as to study the isotopic composition of different cellular components. We find that whole cells always exhibit a preference for uptake of the lighter isotopes of Cd. Notably, whole cells appear to have a similar Cd isotopic composition regardless of the expression of CdCA within the E. coli. However, isotopic fractionation can occur within the genetically modified E. coli during Cd use, such that Cd bound in CdCA can display a distinct isotopic composition compared to the cell as a whole. Thus, the externally observed fractionation is independent of the internal uses of Cd, with the largest Cd isotope fractionation occurring during cross-membrane transport. A general implication of these experiments is that trace metal isotopic fractionation most likely reflects metal transport into biological cells (either actively or passively), rather than relating to expression of specific physiological function and genetic expression of different metalloenzymes.

  15. Stable carbon isotope fractionation of organic cyst-forming dinoflagellates: Evaluating the potential for a CO

    NARCIS (Netherlands)

    Hoins, M.; Van de Waal, D.B.; Eberlein, T.; Reichart, G.-J.; Rost, B.; Sluijs, A.

    2015-01-01

    Over the past decades, significant progress has been made regarding the quantification and mechanistic understanding of stable carbon isotope fractionation (13C fractionation) in photosynthetic unicellular organisms in response to changes in the partial pressure of atmospheric CO2 (pCO2). However, h

  16. Carbon isotope fractionation reveals distinct process of CH4 emission from different compartments of paddy ecosystem

    Science.gov (United States)

    Zhang, Guangbin; Yu, Haiyang; Fan, Xianfang; Ma, Jing; Xu, Hua

    2016-06-01

    Carbon isotopic fractionations in the processes of CH4 emission from paddy field remain poorly understood. The δ13C-values of CH4 in association with production, oxidation and transport of CH4 in different pools of a paddy field were determined, and the stable carbon isotope fractionations were calibrated to assess relative contribution of acetate to CH4 production (fac) and fraction of CH4 oxidized (fox) by different pathways. The apparent isotope fractionation for CO2 conversion to CH4 (αapp) was 1.041-1.056 in the soil and 1.046-1.080 on the roots, indicating that fac was 10-60% and 0-50%, respectively. Isotope fractionation associated with CH4 oxidation (αox) was 1.021 ± 0.007 in the soil and 1.013 ± 0.005 on the roots, and the transport fractionation (ɛtransport) by rice plants was estimated to be -16.7‰ ~ -11.1‰. Rhizospheric fox was about 30-100%, and it was more important at the beginning but decreased fast towards the end of season. Large value of fox was also observed at the soil-water interface and soil and roots surfaces, respectively. The results demonstrate that carbon isotopic fractionations which might be different in different conditions were sensitive to the estimations of fac and fox in paddy field.

  17. Distribution and fractionation mechanism of stable carbon isotope of coalbed methane

    Institute of Scientific and Technical Information of China (English)

    QIN Shengfei; TANG Xiuyi; SONG Yan; WANG Hongyan

    2006-01-01

    The stable carbon isotope values of coalbed methane range widely,and also are generally lighter than that of gases in normal coal-formed gas fields with similar coal rank.There exists strong carbon isotope fractionation in coalbed methane and it makes the carbon isotope value lighter.The correlation between the carbon isotope value and Ro in coalbed methane is less obvious.The coaly source rock maturity cannot be judged by coalbed methane carbon isotope value.The carbon isotopes of coalbed methane become lighter in much different degree due to the hydrodynamics.The stronger the hydrodynamics is,the lighter the CBM carbon isotopic value becomes.Many previous investigations indicated that the desorption-diffusion effects make the carbon isotope value of coalbed methane lighter.However,the explanation has encountered many problems.The authors of this article suggest that the flowing groundwater dissolution to free methane in coal seams and the free methane exchange with absorbed one is the carbon isotope fractionation mechanism in coalbed methane.The flowing groundwater in coal can easily take more 13CH4 away from free gas and comparatively leave more 12CH4.This will make 12CH4 density in free gas comparatively higher than that in absorbed gas.The remaining 12CH4 in free gas then exchanges with the adsorbed methane in coal matrix.Some absorbed 13CH4 can be replaced and become free gas.Some free 12CH4 can be absorbed again into coal matrix and become absorbed gas.Part of the newly replaced 13CH4 in free gas will also be taken away by water,leaving preferentially more 12CH4.The remaining 12CH4 in free gas will exchange again with adsorbed methane in the coal matrix.These processes occur all the time.Through accumulative effect,the 12CH4 will be greatly concentrated in coal.Thus,the stable carbon isotope of coalbed methane becomes dramatically lighter.Through simulation experiment on water-dissolved methane,it had been proved that the flowing water could fractionate the

  18. Variability in carbon and nitrogen isotope fractionation associated with bacterial hydrolysis of atrazine

    Science.gov (United States)

    Meyer, A.; Penning, H.; Elsner, M.

    2009-04-01

    Even after legislative prohibition in 1991 by the European Union, the pesticide atrazine and its metabolites are still detected in surface and ground water frequently exceeding the permitted drinking water concentration limit of 0,1 g/L. Despite much recent research on atrazine, its risk assessment in the environment is still a major challenge because of the difficulty of establishing mass balances in the subsurface. To obtain a better insight into the fate of atrazine, we developed compound-specific stable isotope analysis (CSIA) for atrazine. CSIA has proven valuable for assessing organic contaminants in subsurface environments, on the one hand for source identification and on the other hand to trace (bio)chemical degradation reactions through isotope fractionation in the compounds. Such assessment is based on the Rayleigh equation and therein on the isotope enrichment factor ɛ, which must be determined experimentally beforehand. In ongoing work, we therefore measured carbon and nitrogen isotope fractionation associated with biotic hydrolsis of atrazine. C and N isotope enrichment factors were determined in resting cell experiments for Pseudomonas sp. ADP, Chelatobacter heintzii and Arthrobacter aurescens TC1, strains that hydrolyse atrazine in the initial transformation reaction. Carbon and nitrogen isotope enrichment factors were distinctly different between the bacterial strains. However, when plotting shifts in carbon isotope ratios versus shifts in nitrogen isotope ratios the slopes of the different degradation experiments coincided well. These results give evidence that all bacterial strains were carrying out the same initial biochemical degradation reaction, but that the associated isotope fractionation, as represented by the enrichment factors, was masked to a different extent owing to different rate determining steps prior to the isotopically sensitive bond cleavage (commitment to catalysis). Our study therefore illustrates the benefit of multi

  19. Combined carbon and hydrogen isotope fractionation investigations for elucidating benzene biodegradation pathways

    NARCIS (Netherlands)

    Fischer, A.; Herklotz, I.; Herrmann, S.; Thullner, M.; Weelink, S.A.B.; Stams, A.J.M.; Richnow, H.H.; Vogt, C.

    2008-01-01

    Recently, combined carbon and hydrogen isotope fractionation investigations have emerged as a powerful tool for the characterization of reaction mechanisms relevant for the removal of organic pollutants. Here, we applied this approach in order to differentiate benzene biodegradation pathways under o

  20. Insights to PETM Terrestrial Records from Global Patterns in Carbon Isotope Fractionation by Modern Plants

    Science.gov (United States)

    Freeman, K. H.; Diefendorf, A. F.; Mueller, K. E.; Wing, S. L.; Koch, P. L.

    2009-12-01

    Global patterns in plant fractionation and δ13C values of leaves are potentially important for understanding and predicting ecologic impacts of climate change, yet clear, global patterns have not emerged from the copious, highly variable leaf δ13C values published to date. Understanding drivers in modern plant fractionation at large spatial scales has potential to strengthen understanding of isotopic variability in ancient terrestrial organic matter and how it encodes climate and ecological signals. We converted published leaf δ13C-leaf data into mean fractionation values for 334 woody C3 plant species at 105 globally distributed locations to evaluate the influence of environmental properties and plant functional type. Biome designation reflects both community composition and climate properties, so it is not unexpected that in our study it exerts the greatest predictive power on leaf fractionation values. Pulling apart the influences of different environmental factors, precipitation has the next strongest correlation with fractionation, consistent with limitations on photosynthesis and global patterns of ecosystem productivity due to water availability. Individual plant functional types exhibit similar relationships between fractionation and both biome designation and precipitation amount. However, mean fractionation values for evergreen gymnosperms are 1-2.7‰ lower than other woody plant types when environmental factors are constrained. Our results illustrate that both plant type and precipitation can independently result in differences in isotope fractionation of up to several permil. The predictive relationships from our study provide a framework for assessing models of plant fractionation at large spatial scales, and potentially enable predictive spatial mapping of carbon isotopic patterns, both for plants and soil organic carbon. We use these relationships to re-evaluate the 5 ‰ carbon isotope excursion of the PETM in the Bighorn Basin recorded in plant

  1. Stable carbon and radiocarbon isotope compositions of particle size fractions to determine origins of sedimentary organic matter in an estuary

    NARCIS (Netherlands)

    Megens, L; van der Plicht, J; de Leeuw, JW; Smedes, F; Altabet, M.

    2002-01-01

    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 (

  2. Carbon isotope fractionation by the marine ammonia-oxidizing archaeon Nitrosopumilus maritimus

    OpenAIRE

    Könneke, Martin; Lipp, Julius Sebastian; Hinrichs, Kai-Uwe

    2012-01-01

    Abstract Ammonia-oxidizing archaea (AOA) are abundant and widely distributed microorganisms in aquatic and terrestrial habitats. By catalyzing the first and rate limiting step in nitrification, these chemolithoautotrophs play a significant role in the global nitrogen cycle and contribute to primary production. Here, the carbon isotopic fractionation relative to inorganic carbon source was determined for bulk biomass, biphytanes and polar lipid bound sugars of a marine AOA pure culture. Bu...

  3. Carbon isotope fractionation of chlorinated ethenes during oxidation by Fe{sup 2+} activated persulfate

    Energy Technology Data Exchange (ETDEWEB)

    Marchesi, Massimo, E-mail: m2marche@uwaterloo.ca [Departament de Cristallografia, Mineralogia i Diposits Minerals, Universitat de Barcelona, Barcelona, Catalunya 08028 (Spain); Earth and Environmental Department, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); Aravena, Ramon [Earth and Environmental Department, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); Sra, Kanwartej S. [Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); Golder Associates Inc, Toronto, Ontario, Canada L5N 5Z7 (Canada); Thomson, Neil R. [Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); Otero, Neus; Soler, Albert [Departament de Cristallografia, Mineralogia i Diposits Minerals, Universitat de Barcelona, Barcelona, Catalunya 08028 (Spain); Mancini, Silvia [Golder Associates Inc, Toronto, Ontario, Canada L5N 5Z7 (Canada)

    2012-09-01

    The increased use of persulfate (S{sub 2}O{sub 8}{sup 2-}) for in situ chemical oxidation to treat groundwater and soils contaminated by chlorinated hydrocarbon compounds (CHCs) requires unbiased methods to assess treatment performance. Stable carbon isotope analysis offers a potential tool for assessing the in situ treatment performance of persulfate at sites contaminated with CHCs. This study investigated the extent of C isotope fractionation during oxidation of tetrachloroethene (PCE), trichloroethene (TCE) and cis-dichloroethene (cis-DCE) by persulfate activated by ferrous ion (Fe{sup 2+}). An average carbon isotope enrichment factor {epsilon}{sub bulk} of - 4.9 Per-Mille-Sign for PCE, - 3.6 Per-Mille-Sign for TCE and - 7.6 Per-Mille-Sign for cis-DCE were obtained in batch experiments. Variations in the initial S{sub 2}O{sub 8}{sup 2-}/Fe{sup 2+}/CHC molar ratios did not result in any significant differences in carbon isotope fractionation. The occurrence of carbon isotope fractionation during oxidation and the lack of dependence of enrichment factors upon the S{sub 2}O{sub 8}{sup 2-}/Fe{sup 2+}/CHC molar ratio demonstrate that carbon isotope analysis can potentially be used at contaminated sites as an additional technique to estimate treatment efficacy during oxidation of CHCs by Fe{sup 2+} activated persulfate. Highlights: Black-Right-Pointing-Pointer The performance of in situ chemical oxidation (ISCO) is still difficult to assess. Black-Right-Pointing-Pointer We investigated the potential of carbon isotope analysis as a new assessing tool. Black-Right-Pointing-Pointer C isotope of PCE, TCE and DCE oxidized by persulfate activated by Fe{sup 2+} was measured. Black-Right-Pointing-Pointer Enrichment factors of - 4.9 Per-Mille-Sign for PCE, - 3.6 Per-Mille-Sign for TCE and - 7.6 Per-Mille-Sign for cisDCE were obtained. Black-Right-Pointing-Pointer Carbon isotope can potentially be used to estimate the ISCO treatment efficacy.

  4. Carbon isotope fractionation during photorespiration and carboxylation in Senecio.

    Science.gov (United States)

    Lanigan, Gary J; Betson, Nicholas; Griffiths, Howard; Seibt, Ulli

    2008-12-01

    The magnitude of fractionation during photorespiration and the effect on net photosynthetic (13)C discrimination (Delta) were investigated for three Senecio species, S. squalidus, S. cineraria, and S. greyii. We determined the contributions of different processes during photosynthesis to Delta by comparing observations (Delta(obs)) with discrimination predicted from gas-exchange measurements (Delta(pred)). Photorespiration rates were manipulated by altering the O(2) partial pressure (pO(2)) in the air surrounding the leaves. Contributions from (13)C-depleted photorespiratory CO(2) were largest at high pO(2). The parameters for photorespiratory fractionation (f), net fractionation during carboxylation by Rubisco and phosphoenolpyruvate carboxylase (b), and mesophyll conductance (g(i)) were determined simultaneously for all measurements. Instead of using Delta(obs) data to obtain g(i) and f successively, which requires that b is known, we treated b, f, and g(i) as unknowns. We propose this as an alternative approach to analyze measurements under field conditions when b and g(i) are not known or cannot be determined in separate experiments. Good agreement between modeled and observed Delta was achieved with f = 11.6 per thousand +/- 1.5 per thousand, b = 26.0 per thousand +/- 0.3 per thousand, and g(i) of 0.27 +/- 0.01, 0.25 +/- 0.01, and 0.22 +/- 0.01 mol m(-2) s(-1) for S. squalidus, S. cineraria, and S. greyii, respectively. We estimate that photorespiratory fractionation decreases Delta by about 1.2 per thousand on average under field conditions. In addition, diurnal changes in Delta are likely to reflect variations in photorespiration even at the canopy level. Our results emphasize that the effects of photorespiration must be taken into account when partitioning net CO(2) exchange of ecosystems into gross fluxes of photosynthesis and respiration.

  5. An unusual isotopic fractionation of boron in synthetic calcium carbonate precipitated from seawater and saline water

    Institute of Scientific and Technical Information of China (English)

    XIAO Yingkai; LI Shizhen; WEI Haizhen; SUN Aide; ZHOU Weijian; LIU Weiguo

    2006-01-01

    Inorganic calcium carbonate precipitation from natural seawater and saline water at various pH values was carried out experimentally. The results show the clear positive relationships between boron concentration and δ11B of inorganic calcium carbonate with the pH of natural seawater and saline water. However, the variations of boron isotopic fractionation between inorganic calcite and seawater/saline water with pH are inconsistent with the hypothesis that B(OH)4- is the dominant species incorporated into the biogenic calcite structure. The isotopic fractionation factors α Between synthetic calcium carbonate precipitate and parent solutions increase systematically as pH increases, from 0.9884 at pH 7.60 to 1.0072 at pH 8.60 for seawater and from 0.9826 at pH 7.60 to 1.0178 at pH 8.75 for saline water. An unusual boron isotopic fractionation factor of larger than 1 in synthetic calcium carbonate precipitated from seawater/saline water at higher pH is observed, which implies that a substantial amount of the isotopically heavier B(OH)3 species must be incorporated preferentially into synthetic inorganic carbonate. The results propose that the incorporation of B(OH)3 is attributed to the formation of Mg(OH)2 at higher pH of calcifying microenvironment during the synthetic calcium carbonate precipitation. The preliminary experiment of Mg(OH)2 precipitated from artificial seawater shows that heavier 11B is enriched in Mg(OH)2 precipitation, which suggests that isotopically heavier B(OH)3 species incorporated preferentially into Mg(OH)2 precipitation.This result cannot be applied to explain the boron isotopic fractionation of marine bio-carbonate because of the possibility that the unusual environment in this study appears in formation of marine bio-carbonate is infinitesimal. We, however, must pay more attention to this phenomenon observed in this study, which accidentally appears in especially natural environment.

  6. Fractionation between inorganic and organic carbon during the Lomagundi (2.22 2.1 Ga) carbon isotope excursion

    Science.gov (United States)

    Bekker, A.; Holmden, C.; Beukes, N. J.; Kenig, F.; Eglinton, B.; Patterson, W. P.

    2008-07-01

    The Lomagundi (2.22-2.1 Ga) positive carbon isotope excursion in shallow-marine sedimentary carbonates has been associated with the rise in atmospheric oxygen, but subsequent studies have demonstrated that the carbon isotope excursion was preceded by the rise in atmospheric oxygen. The amount of oxygen released to the exosphere during the Lomagundi excursion is constrained by the average global fractionation between inorganic and organic carbon, which is poorly characterized. Because dissolved inorganic and organic carbon reservoirs were arguably larger in the Paleoproterozoic ocean, at a time of lower solar luminosity and lower ocean redox state, decoupling between these two variables might be expected. We determined carbon isotope values of carbonate and organic matter in carbonates and shales of the Silverton Formation, South Africa and in the correlative Sengoma Argillite Formation, near the border in Botswana. These units were deposited between 2.22 and 2.06 Ga along the margin of the Kaapvaal Craton in an open-marine deltaic setting and experienced lower greenschist facies metamorphism. The prodelta to offshore marine shales are overlain by a subtidal carbonate sequence. Carbonates exhibit elevated 13C values ranging from 8.3 to 11.2‰ vs. VPDB consistent with deposition during the Lomagundi positive excursion. The total organic carbon (TOC) contents range from 0.01 to 0.6% and δ13C values range from - 24.8 to - 13.9‰. Thus, the isotopic fractionation between organic and carbonate carbon was on average 30.3 ± 2.8‰ ( n = 32) in the shallow-marine environment. The underlying Sengoma shales have highly variable TOC contents (0.14 to 21.94%) and δ13C values (- 33.7 to - 20.8‰) with an average of - 27.0 ± 3.0‰ ( n = 50). Considering that the shales were also deposited during the Lomagundi excursion, and taking δ13C values of the overlying carbonates as representative of the δ13C value of dissolved inorganic carbon during shale deposition, a carbon

  7. Stable carbon isotope fractionation during the biodegradation of lambda-cyhalothrin

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Xiaoli [MOE Key Laboratory of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058 (China); Department of Environmental Engineering, Quzhou University, Quzhou 324000 (China); Xu, Zemin [MOE Key Laboratory of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058 (China); Zhang, Xichang [Laboratory for Teaching in Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058 (China); Yang, Fangxing, E-mail: fxyang@zju.edu.cn [MOE Key Laboratory of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058 (China); Department of Effect-Directed Analysis, Helmholtz Centre for Environmental Research — UFZ, Leipzig 04318 (Germany)

    2015-11-01

    In this study, the microbial degradation of lambda-cyhalothrin in soil was investigated using compound-specific stable isotope analysis. The results revealed that lambda-cyhalothrin was biodegraded in soil under laboratory conditions. The half-lives of lambda-cyhalothrin were determined to be 49 and 161 days in non-sterile and sterile soils spiked with 2 mg/kg lambda-cyhalothrin and 84 and 154 days in non-sterile and sterile soils spiked with 10 mg/kg lambda-cyhalothrin, respectively. The biodegradation of lambda-cyhalothrin resulted in carbon isotope fractionation, which shifted from − 29.0‰ to − 26.5‰ in soil spiked with 2 mg/kg lambda-cyhalothrin, and to − 27.5‰ with 10 mg/kg lambda-cyhalothrin. A relationship was established between the stable carbon isotope fraction and the residual concentrations of lambda-cyhalothrin by the Rayleigh equation in which the carbon isotope enrichment factor ε of the microbial degradation of lambda-cyhalothrin in the soil was calculated as − 2.53‰. This study provides an approach to quantitatively evaluate the biodegradation of lambda-cyhalothrin in soil in field studies. - Highlights: • Abiotic and biotic degradation of lambda-cyhalothrin were observed in soil. • Biodegradation of lambda-cyhalothrin was evaluated by CSIA. • Biodegradation of lambda-cyhalothrin leads to carbon isotope fractionation. • An enrichment factor ε of lambda-cyhalothrin was determined as − 2.53‰.

  8. Improved quantification of microbial CH4 oxidation efficiency in Arctic wetland soils using carbon isotope fractionation

    Directory of Open Access Journals (Sweden)

    E.-M. Pfeiffer

    2012-12-01

    Full Text Available Permafrost-affected tundra soils are significant sources of the climate-relevant trace gas methane (CH4. The observed accelerated warming of the Arctic will cause a deeper permafrost thawing followed by increased carbon mineralization and CH4 formation in water saturated tundra soils which might cause a positive feedback to climate change. Aerobic CH4 oxidation is regarded as the key process reducing CH4 emissions from wetlands, but quantification of turnover rates has remained difficult so far. The application of carbon stable isotope fractionation enables the in situ quantification of CH4 oxidation efficiency in arctic wetland soils. The aim of the current study is to quantify CH4 oxidation efficiency in permafrost-affected tundra soils in Russia's Lena River Delta based on stable isotope signatures of CH4. Therefore, depth profiles of CH4 concentrations and δ13CH4-signatures were measured and the fractionation factors for the processes of oxidation (αox and diffusion (αdiff were determined. Most previous studies employing stable isotope fractionation for the quantification of CH4 oxidation in soils of other habitats (e.g. landfill cover soils have assumed a gas transport dominated by advection (αtrans = 1. In tundra soils, however, diffusion is the main gas transport mechanism, aside from ebullition. Hence, diffusive stable isotope fractionation has to be considered. For the first time, the stable isotope fractionation of CH4 diffusion through water-saturated soils was determined with an αdiff = 1.001 ± 0.000 (n = 3. CH4 stable isotope fractionation during diffusion through air-filled pores of the investigated polygonal tundra soils was αdiff = 1.013 ± 0.003 (n = 18. Furthermore, it was found that αox differs widely between sites and horizons (mean αox, = 1.017 ± 0.009 and needs to be determined individually. The impact of both fractionation factors on the quantification of CH4 oxidation was analyzed by considering both the

  9. Carbon Isotopic Fractionation During Formation of Macromolecular Organic Grain Coatings via FTT Reactions

    Science.gov (United States)

    Nuth, J. A.; Johnson, N. M.; Elsila-Cook, J.; Kopstein, M.

    2011-01-01

    Observations of carbon isotopic fractionation of various organic compounds found in meteorites may provide useful diagnostic information concerning the environments and mechanisms that were responsible for their formation. Unfortunately, carbon has only two stable isotopes, making interpretation of such observations quite problematic. Chemical reactions can increase or decrease the C-13/C-12 ratio by various amounts, but the final ratio will depend on the total reaction pathway followed from the source carbon to the final product, a path not readily discernable after 4.5 billion years. In 1970 Libby showed that the C-13/C-12 ratios of terrestrial and meteoritic carbon were similar by comparing carbon from the Murchison meteorite to that of terrestrial sediments. More recent studies have shown that the C-13/C-12 ratio of the Earth and meteorites may be considerably enriched in C-13 compared to the ratio observed in the solar wind [2], possibly suggesting that carbon produced via ion-molecule reactions in cold dark clouds could be an important source of terrestrial and meteoritic carbon. However, meteoritic carbon has been subjected to parent body processing that could have resulted in significant changes to the C-13/C-12 ratio originally present while significant variation has been observed in the C-13/C-12 ratio of the same molecule extracted from different terrestrial sources. Again we must conclude that understanding the ratio found in meteorites may be difficult.

  10. Carbon isotope fractionation of 1,1,1-trichloroethane during base-catalyzed persulfate treatment

    Energy Technology Data Exchange (ETDEWEB)

    Marchesi, Massimo, E-mail: m2marche@uwaterloo.ca [Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); Thomson, Neil R. [Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); Aravena, Ramon [Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); Sra, Kanwartej S. [Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 (Canada); Golder Associates Inc, Toronto, Ontario, Canada L5N 5Z7 (Canada); Otero, Neus; Soler, Albert [Departament de Cristal.lographia, Mineralogia i Diposits Minerals, Facultat de Geologia, Universitat de Barcelona, Barcelona, Spain 08028 (Spain)

    2013-09-15

    Highlights: • Treatability and C fractionation of 1,1,1-TCA by base-catalyzed S{sub 2}O{sub 8}{sup 2−} was studied. • The rate of degradation of 1,1,1-TCA increased with a higher OH{sup −}:S{sub 2}O{sub 8}{sup 2−} ratio. •Base-catalyzed S{sub 2}O{sub 8}{sup 2−} can potentially treat recalcitrant compound like 1,1,1-TCA. • An enrichment factor of −7.0‰ independent of the OH{sup −}:S{sub 2}O{sub 8}{sup 2−} ratio was obtained. • Carbon isotope can potentially be used to estimate the ISCO treatment efficacy. -- Abstract: The extent of carbon isotope fractionation during degradation of 1,1,1-trichloroethane (1,1,1-TCA) by a base-catalyzed persulfate (S{sub 2}O{sub 8}{sup 2−}) treatment system was investigated. Significant destruction of 1,1,1-TCA was observed at a pH of ∼12. An increase in the NaOH:S{sub 2}O{sub 8}{sup 2−} molar ratio from 0.2:1 to 8:1 enhanced the reaction rate of 1,1,1-TCA by a factor of ∼5 to yield complete (>99.9%) destruction. An average carbon isotope enrichment fractionation factor which was independent of the NaOH:S{sub 2}O{sub 8}{sup 2−} molar ratio of −7.0 ± 0.2‰ was obtained. This significant carbon isotope fractionation and the lack of dependence on changes in the NaOH:S{sub 2}O{sub 8}{sup 2−} molar ratio demonstrates that carbon isotope analysis can potentially be used in situ as a performance assessment tool to estimate the degradation effectiveness of 1,1,1-TCA by a base-catalyzed persulfate system.

  11. Stable carbon isotope fractionation in the UV photolysis of CFC-11 and CFC-12

    Directory of Open Access Journals (Sweden)

    A. Zuiderweg

    2011-12-01

    Full Text Available The chlorofluorocarbons CFC-11 (CCl3F and CFC-12 (CCl2F2 are stable atmospheric compounds that are produced at the earth's surface, but removed only at high altitudes in the stratosphere, where their removal liberates atomic chlorine that then catalytically destroys stratospheric ozone. For such long-lived compounds, isotope effects in the stratospheric removal reactions have a large effect on their global isotope budgets. We have determined the photolytic isotope fractionation for stable carbon isotopes of CFC-11 and CFC-12 in laboratory experiments. 13C/12C isotope fractionations (ϵ range from (−23.7 ± 0.9 to (−17.5 ± 0.4‰ for CFC-11 and (−69.2 ± 3.4 to (−49.4 ± 2.3‰ for CFC-12 between 203 and 288 K, a temperature range relevant to conditions in the troposphere and stratosphere. These results suggest that CFCs should become strongly enriched in 13C with decreasing mixing ratio in the stratosphere, similar to what has been recently observed for CFC chlorine isotopes. In conjunction with the strong variations in CFC emissions before and after the Montréal Protocol, the stratospheric enrichments should also lead to a significant temporal increase in the 13C content of the CFCs at the surface over the past decades, which should be recorded in atmospheric air archives such as firn air.

  12. Experimental fractionation of stable carbon isotopes during degassing of carbon dioxide and precipitation of calcite from aqueous solutions

    Science.gov (United States)

    Müller, K.; Winde, V.; Escher, P.; von Geldern, R.; Böttcher, M. E.

    2012-04-01

    Processes in the carbonate system of surface waters are in particular sensitive to variations of boundary conditions as, for instance, the partial pressure of carbon dioxide in the atmosphere and the aqueous solution. Examples range from streams, rivers, to coastal marine waters. The flux of carbon dioxide from continental flowing waters was recently included into calculations of the global carbon budget (Butman & Raymond, 2011, Nature Geo.). These solutions, are often supersaturated in carbon dioxide with respect to the atmosphere. The degassing of carbon dioxide is associated with a kinetically controlled fractionation of the stable carbon isotopes, which has to be considered in balancing water-air carbon dioxide fluxes. The degassing process additionally leads to the super-saturation of the aqueous solution with respect to calcium carbonate. Stable isotope fractionation is of particular value to identify and quantify processes at the water-gas phase interface and link these non-equilibrium processes to the formation mechanisms of calcite and the hydrodynamics of surface waters. Experiments were carried out with or without inert N2 gas flow to degas carbon dioxide from initially supersaturated solutions. Natural solutions used are from different stations of the Elbe estuary, the Jade Bay, the backbarrier tidal area of Spiekeroog Island, carbonate springs of Rügen Island, and the Baltic Sea coastline. Results are compared experiments using bottled mineral waters. By following the (physico) chemical changes in the solutions (pH, TA, Ca PHREEQC modeling) it was found, that two evolutionary stages can be differentiated. Reaction progress led to the preferential liberation of carbon dioxide containing the light carbon isotope, following a Rayleigh-type process. After an induction period, where only degassing of carbon dioxide took place, a second stage was observed where calcite began to form from the highly supersaturated solutions. In this stage the carbonate

  13. Variation of carbon isotope fractionation in hydrogenotrophic methanogenic microbial cultures and environmental samples at different energy status

    NARCIS (Netherlands)

    Penning, H.; Plugge, C.M.; Galand, P.E.; Conrad, R.

    2005-01-01

    Methane is a major product of anaerobic degradation of organic matter and an important greenhouse gas. Its stable carbon isotope composition can be used to reveal active methanogenic pathways, if associated isotope fractionation factors are known. To clarify the causes that lead to the wide variatio

  14. Stable Carbon Isotopic Fractionation in Smoke and Char Produced During Biomass Burning

    Science.gov (United States)

    Wang, Y.; Hsieh, Y.

    2006-12-01

    Stable isotopic ratio of carbon has been used extensively as a tracer of carbon sources in the environment. It has been documented that burning of C4 grasses resulted in significant depletion of C13 in the charcoal while burning of wood and C3 grass did not. This study was initiated to investigate the stable carbon isotopic fractionation of the smoke and char produced during biomass burnings. Samples of Juncus romerianus (C3 salt marsh grass) and Spartina alterniflora (C4 salt marsh grass), Eremochloa ophiuroides (centipede, a C4 lawn grass) and woody debris of a pine forest were colleted and burned in open air fire place. The particulate matter with diameters less than 2.5 micron (PM2.5) emitted from the burning was collected using a PM sampler. The original biomass, PM2.5, black C in PM2.5 and char (ash) were analyzed for their C, N and S thermograms using a multi-elemental scanning thermal analyzer and their stable C isotopic ratios were measured using an EA-IRMS. The results indicate that burning of wood and C3 grass did not produce significant C isotopic fractionation in PM2.5, black C in PM2.5 and char with respect to the original material. However, there was a significant C13-depletion in PM2.5 (-6.2 per mil), black C in PM2.5 (-4.6 per mil) and chars (-4.6 per mil) produced by burning of the C4 centipede grass; whereas the C4 Spartina salt marsh grass produced a C13-depletion in PM2.5 (-2.3 per mil) and black C in PM2.5 (-3.6 per mil), and a slight C13-enrichment in char (0.5 per mil). The isotope fractionation associated with burning of C4 vegetation is probably dependent on species and burning conditions and warrant further study.

  15. Stable carbon isotope fractionation of organic cyst-forming dinoflagellates : Evaluating the potential for a CO2 proxy

    NARCIS (Netherlands)

    Hoins, Mirja; Van de Waal, Dedmer B.; Eberlein, Tim; Reichart, Gert Jan; Rost, Björn; Sluijs, Appy

    2015-01-01

    Over the past decades, significant progress has been made regarding the quantification and mechanistic understanding of stable carbon isotope fractionation (13C fractionation) in photosynthetic unicellular organisms in response to changes in the partial pressure of atmospheric CO2 (pCO2). However, h

  16. Stable carbon isotope fractionation of organic cyst-forming dinoflagellates: evaluating the potential for a CO2 proxy

    NARCIS (Netherlands)

    Hoins, Mirja; Van de Waal, Dedmer B.; Eberlein, Tim; Reichart, Gert-Jan; Rost, Björn; Sluijs, Appy

    2015-01-01

    Over the past decades, significant progress has been made regarding the quantification and mechanistic understanding of stable carbon isotope fractionation (13C fractionation) in photosynthetic unicellular organisms in response to changes in the partial pressure of atmospheric CO2 (pCO2). However, h

  17. Compound specific isotopic fractionation patterns suggest different carbon metabolisms among Chloroflexus-like bacteria in hot spring microbial mats

    NARCIS (Netherlands)

    Sinninghe Damsté, J.S.; Meer, M.T.J. van der; Schouten, S.; Leeuw, J.W. de; Ward, D.M.

    2003-01-01

    Stable carbon isotope fractionations between dissolved inorganic carbon and lipid biomarkers suggest photoautotrophy by Chloroflexus-like organisms in sulfidic and nonsulfidic Yellowstone hot springs. Where co-occurring, cyanobacteria appear to cross-feed Chloroflexus-like organisms supporting photo

  18. Carbon isotope fractionation of dissolved inorganic carbon (DIC) due to outgassing of carbon dioxide from a headwater stream

    Science.gov (United States)

    Doctor, D.H.; Kendall, C.; Sebestyen, S.D.; Shanley, J.B.; Ohte, N.; Boyer, E.W.

    2008-01-01

    The stable isotopic composition of dissolved inorganic carbon (??13C-DIC) was investigated as a potential tracer of streamflow generation processes at the Sleepers River Research Watershed, Vermont, USA. Downstream sampling showed ?? 13C-DIC increased between 3-5??? from the stream source to the outlet weir approximately 0??5 km downstream, concomitant with increasing pH and decreasing PCO2. An increase in ??13C-DIC of 2.4 ?? 0??1??? per log unit decrease of excess PCO2 (stream PCO2 normalized to atmospheric PCO2) was observed from downstream transect data collected during snowmelt. Isotopic fractionation of DIC due to CO2 outgassing rather than exchange with atmospheric CO2 may be the primary cause of increased ?? 13C-DIC values downstream when PCO2 of surface freshwater exceeds twice the atmospheric CO2 concentration. Although CO2 outgassing caused a general increase in stream ??13C-DIC values, points of localized groundwater seepage into the stream were identified by decreases in ??13C-DIC and increases in DIC concentration of the stream water superimposed upon the general downstream trend. In addition, comparison between snowmelt, early spring and summer seasons showed that DIC is flushed from shallow groundwater flowpaths during snowmelt and is replaced by a greater proportion of DIC derived from soil CO2 during the early spring growing season. Thus, in spite of effects from CO2 outgassing, ??13C of DIC can be a useful indicator of groundwater additions to headwater streams and a tracer of carbon dynamics in catchments. Copyright ?? 2007 John Wiley & Sons, Ltd.

  19. Stable carbon and hydrogen isotopic fractionations of alkane compounds and crude oil during aerobically microbial degradation

    Institute of Scientific and Technical Information of China (English)

    PENG Xianzhi; ZHANG Gan; CHEN Fanzhong; LIU Guoqing

    2004-01-01

    Normal alkane compounds dodecane, pentadecane, hexadecane, octadecane, tetracosane, isoprenoid alkane pristane and a crude oil sample were aerobically biodegraded with a pure bacterial strain GIM2.5 and white rot fungus Phanerochaete Chrysosporium-1767 to monitor the kinetic fractionation of the molecular stable carbon (δ13C) and hydrogen (δD) isotopes in the course of biodegradation. Both δ13C (V-PDB) and δ D (V-SMOW) remained stable for the standard alkane compounds and n-alkane components (from n-C13 to n-C25) of the crude oil, generally varying in the range of ±0.5‰ and ±5‰ respectively, within the range of the instrumental precisions, especially for those molecularly heavier than n-C16 during microbial degradation. These results indicate that molecular stable carbon and hydrogen isotopic fingerprints can be promising indicators for tracing the sources of petroleum-related contaminants in the environment, especially in the case of severe weathering when they are difficult to be unambiguously identified by the chemical fingerprints alone.

  20. The effects of atmospheric [CO2] on carbon isotope fractionation and magnesium incorporation into biogenic marine calcite

    Science.gov (United States)

    Vieira, Veronica

    1997-01-01

    The influences of atmospheric carbon dioxide on the fractionation of carbon isotopes and the magnesium incorporation into biogenic marine calcite were investigated using samples of the calcareous alga Amphiroa and benthic foraminifer Sorites grown in the Biosphere 2 Ocean system under variable atmospheric CO2 concentrations (approximately 500 to 1200 ppm). Carbon isotope fractionation was studied in both the organic matter and the skeletal carbonate. Magnesium analysis was to be performed on the carbonate removed during decalcification. These data have not been collected due to technical problems. Carbon isotope data from Amphiroa yields a linear relation between [CO2] and Delta(sup 13)C(sub Corg)values suggesting that the fractionation of carbon isotopes during photosynthesis is positively correlated with atmospheric [CO2]. [CO2] and Delta(sup 13)C(sub Corg) values for Sorites produce a relation that is best described by a hyperbolic function where Delta(sup 13)C(sub Corg) values increase between 300 and 700 ppm and decrease from 700 to 1200 ppm. Further investigation of this relation and Sorites physiology is needed.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-11-15

    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.

  2. Carbon dioxide-water oxygen isotope fractionation factor using chlorine trifluoride and guanidine hydrochloride techniques

    Energy Technology Data Exchange (ETDEWEB)

    Dugan, J.P. Jr.; Borthwick, J.

    1986-12-01

    A new value for the CO/sub 2/-H/sub 2/O oxygen isotope fractionation factor of 1.04145 +/- 0.000 15 (2sigma) has been determined. The data have been normalized to the V-SMOW/V-SLAP scale and were obtained by measuring isotopic compositions with the guanidine hydrochloride and chlorine trifluoride techniques.

  3. The effect of atmospheric CO2 concentration on carbon isotope fractionation in C3 land plants

    Science.gov (United States)

    Schubert, Brian A.; Jahren, A. Hope

    2012-11-01

    Because atmospheric carbon dioxide is the ultimate source of all land-plant carbon, workers have suggested that pCO2 level may exert control over the amount of 13C incorporated into plant tissues. However, experiments growing plants under elevated pCO2 in both chamber and field settings, as well as meta-analyses of ecological and agricultural data, have yielded a wide range of estimates for the effect of pCO2 on the net isotopic discrimination (Δδ13Cp) between plant tissue (δ13Cp) and atmospheric CO2 (δ13CCO2). Because plant stomata respond sensitively to plant water status and simultaneously alter the concentration of pCO2 inside the plant (ci) relative to outside the plant (ca), any experiment that lacks environmental control over water availability across treatments could result in additional isotopic variation sufficient to mask or cancel the direct influence of pCO2 on Δδ13Cp. We present new data from plant growth chambers featuring enhanced dynamic stabilization of moisture availability and relative humidity, in addition to providing constant light, nutrient, δ13CCO2, and pCO2 level for up to four weeks of plant growth. Within these chambers, we grew a total of 191 C3 plants (128 Raphanus sativus plants and 63 Arabidopsis thaliana) across fifteen levels of pCO2 ranging from 370 to 4200 ppm. Three types of plant tissue were harvested and analyzed for carbon isotope value: above-ground tissues, below-ground tissues, and leaf-extracted nC31-alkanes. We observed strong hyperbolic correlations (R ⩾ 0.94) between the pCO2 level and Δδ13Cp for each type of plant tissue analyzed; furthermore the linear relationships previously suggested by experiments across small (10-350 ppm) changes in pCO2 (e.g., 300-310 ppm or 350-700 ppm) closely agree with the amount of fractionation per ppm increase in pCO2 calculated from our hyperbolic relationship. In this way, our work is consistent with, and provides a unifying relationship for, previous work on carbon isotopes

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

    Science.gov (United States)

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

    2010-11-01

    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.

  5. Boron isotopic fractionation in laboratory inorganic carbonate precipitation: Evidence for the incorpora-tion of B(OH)3 into carbonate

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    A laboratory inorganic carbonate precipitation experiment at high pH of 8.96 to 9.34 was conducted, and the boron isotopic fractionations of the precipitated carbonate were measured. The data show that boron isotopic fractionation factors (αcarb-3) between carbonate and B(OH)3 in seawater range 0.937 and 0.965, with an average value of 0.953. Our results together with those reported by Sanyal and collabo-rators show that the αcarb-3 values between carbonate and B(OH)3 in solution are not constant but are negatively correlated with the pH of seawater. The measured boron isotopic compositions of carbonate precipitation (δ11Bcarb) do not exactly lie on the best-fit theoretical δ 11B4-pH curves and neither do they exactly parallel any theoretical δ 11B4-pH curves. Therefore, it is reasonable to argue that a changeable proportion of B(OH)3 with pH of seawater should also be incorporated into carbonate except for the dominant incorporation of B(OH)4- in carbonate . Hence, in the reconstruction of the paleo-pH of sea-water from boron isotopes in marine biogenic carbonates, the use of theoretical boron isotopic frac-tionation factor (α4-3) between B(OH)4- and B(OH)3 is not suitable. Instead, an empirical equation should be established.

  6. Simulation Experiments on the Reaction of CH4-CaSO4 and Its Carbon Kinetic Isotope Fractionation

    Institute of Scientific and Technical Information of China (English)

    YueChangtao; LiShuyuan; DingKangle; ZhongNingning

    2005-01-01

    Thermochemical sulfate reduction (TSR) in geological deposits can account for the accumulation of H,S in deep sour gas reservoirs. In this paper, thermal simulation experiments on the reaction of CH4-CaSO4 were carried out using an autoclave at high temperatures and high pressures. The products were characterized with analytical methods including carbon isotope analysis. It is found that the reaction can proceed to produce H2S, H2O and CaCO3 as the main products. Based on the experimental results, the carbon kinetic isotope fractionation was investigated, and the value of Ki(kinetic isotope effect) was calculated. The results obtained in this paper can provide useful information to explain the occurrence of H2S in deep carbonate gas reservoirs.

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

    Science.gov (United States)

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

    1991-01-01

    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. Isotopic fractionation of carbon, deuterium and nitrogen : a full chemical study

    CERN Document Server

    Roueff, E; Hickson, K M

    2015-01-01

    Context. The increased sensitivity and high spectral resolution of millimeter telescopes allow the detection of an increasing number of isotopically substituted molecules in the interstellar medium. The 14N/ 15N ratio is difficult to measure directly for carbon containing molecules. Aims. We want to check the underlying hypothesis that the 13C/ 12C ratio of nitriles and isonitriles is equal to the elemental value via a chemical time dependent gas phase chemical model. Methods. We have built a chemical network containing D, 13C and 15N molecular species after a careful check of the possible fractionation reactions at work in the gas phase. Results. Model results obtained for 2 different physical conditions corresponding respectively to a moderately dense cloud in an early evolutionary stage and a dense depleted pre-stellar core tend to show that ammonia and its singly deuterated form are somewhat enriched in 15N, in agreement with observations. The 14N/ 15N ratio in N2H+ is found to be close to the elemental v...

  9. Stable carbon isotope fractionation in pollen of Atlas cedar: first steps towards a new palaeoecological proxy for Northwest Africa

    Science.gov (United States)

    Bell, Benjamin; Fletcher, William; Ryan, Peter; Grant, Helen; Ilmen, Rachid

    2016-04-01

    Analysis of stable carbon isotopes can provide information on climate and the environmental conditions at different growth stages of the plant, both past and present. Carbon isotope discrimination in plant tissue is already well understood, and can be used as a drought stress indicator for semi-arid regions. Stable carbon isotope ratios measured directly on pollen provides the potential for the development of long-term environmental proxies (spanning thousands of years), as pollen is well preserved in the environment. Atlas Cedar (Cedrus atlantica Endl. Manetti ex Carrière), is an ideal test case to develop a pollen stable carbon isotope proxy. The tree grows across a wide altitudinal and climatic range and is extremely sensitive to moisture availability. The pollen is abundant, and easily identifiable to the species level in pollen analysis because different cedar species are geographically confined to different regions of the world. In 2015 we sampled 76 individual cedar trees across latitudinal, altitudinal and environmental gradients, highly focused on the Middle Atlas region of Morocco, with 25 additional samples from botanical gardens across Europe and the US to extend these gradients. Here, we report new stable carbon isotope data from pollen, leaf and stem wood from these samples with a view to assessing and quantifying species-specific fractionation effects associated with pollen production. The isotopic response of individual trees at local and wider geographical scales to altitude and climatic conditions is presented. This research forms part of an ongoing PhD project working to develop and calibrate a modern carbon isotope proxy in Atlas cedar pollen, which can ultimately be applied to fossil sequences and complement existing multi-proxy records (e.g. pollen analysis in lake sediments, tree-rings).

  10. Pressurized laboratory experiments show no stable carbon isotope fractionation of methane during gas hydrate dissolution and dissociation.

    Science.gov (United States)

    Lapham, Laura L; Wilson, Rachel M; Chanton, Jeffrey P

    2012-01-15

    The stable carbon isotopic ratio of methane (δ(13)C-CH(4)) recovered from marine sediments containing gas hydrate is often used to infer the gas source and associated microbial processes. This is a powerful approach because of distinct isotopic fractionation patterns associated with methane production by biogenic and thermogenic pathways and microbial oxidation. However, isotope fractionations due to physical processes, such as hydrate dissolution, have not been fully evaluated. We have conducted experiments to determine if hydrate dissolution or dissociation (two distinct physical processes) results in isotopic fractionation. In a pressure chamber, hydrate was formed from a methane gas source at 2.5 MPa and 4 °C, well within the hydrate stability field. Following formation, the methane source was removed while maintaining the hydrate at the same pressure and temperature which stimulated hydrate dissolution. Over the duration of two dissolution experiments (each ~20-30 days), water and headspace samples were periodically collected and measured for methane concentrations and δ(13)C-CH(4) while the hydrate dissolved. For both experiments, the methane concentrations in the pressure chamber water and headspace increased over time, indicating that the hydrate was dissolving, but the δ(13)C-CH(4) values showed no significant trend and remained constant, within 0.5‰. This lack of isotope change over time indicates that there is no fractionation during hydrate dissolution. We also investigated previous findings that little isotopic fractionation occurs when the gas hydrate dissociates into gas bubbles and water due to the release of pressure. Over a 2.5 MPa pressure drop, the difference in the δ(13)C-CH(4) was dissociates and demonstrated that there is no fractionation when the hydrate dissolves. Therefore, measured δ(13)C-CH(4) values near gas hydrates are not affected by physical processes, and can thus be interpreted to result from either the gas source or

  11. Stable isotope measurements of carbon fractions (OC/EC) in airborne particulate: A new dimension for source characterization and apportionment

    Science.gov (United States)

    Huang, L.; Brook, J. R.; Zhang, W.; Li, S. M.; Graham, L.; Ernst, D.; Chivulescu, A.; Lu, G.

    A method to measure 13C/ 12C ratios of individual carbon fractions of airborne particular matter (PM) from filter samples using a stepwise thermal desorption/combustion OC/EC analyzer (via thermal optical transmission, (TOT) coupled with gas chromatography separation, followed by isotopic ratio mass spectrometer (GC-IRMS) analysis has been developed. In the TOT instrument, carbon fractions are released at different temperature ranges and different redox conditions. Organic carbon fraction (OC) was released at a relatively low temperature ( T=550 °C), whereas, elemental carbon or black carbon fraction (EC or BC) was released at a high temperature ( T>800 °C) via combustion. A temperature step of 870 °C without oxygen was chosen to remove the impact of carbonate carbon (CC) and possible cross-impact from OC and EC. All the fractions were collected cryogenically and subject to carbon isotope measurements via GC-IRMS. To evaluate the precision, accuracy and linearity range of the measurements, the different types of blanks and standards were investigated, including OC (i.e. glucose, sucrose, n-Alkanes and polycyclic aromatic hydrocarbons (PAHs), CC (i.e. carbonates) and EC (i.e. carbon black and graphite). The overall precision and the accuracy of the method is ˜0.3‰. The method was applied to Pacific2001 aerosol samples from the Greater Vancouver area in Canada. The results show that good baseline separations in thermographs can be achieved for individual carbon fractions (i.e. OC and EC) using optimized temperature plateau and retention times; relative small difference in carbon isotopic composition between OC and EC ( ΔC=δ13C-δ13C) were found in tunnel samples, whereas, the largest Δ 13C OC-EC were obtained in forest air samples; the Δ 13C OC-EC in ambient PM is likely dependant upon the dominant sources present in the vicinity of the sampling sites; the distribution of 13C/ 12C ratios of OC/EC can provide useful information for source characterization

  12. Studies of carbon--isotope fractionation. Annual progress report, December 1, 1974--November 30, 1975

    Energy Technology Data Exchange (ETDEWEB)

    Ishida, T.

    1975-12-01

    The vapor pressure isotope effect of /sup 13/C//sup 12/C-substitution in CClF/sub 3/ was measured at temperatures between 169/sup 0/ and 206/sup 0/K by means of cryogenic distillation. The /sup 13/C//sup 12/C-vapor pressure isotope effect in CHF/sub 3/ was also studied at temperatures between 161/sup 0/ and 205/sup 0/K by a similar method. The construction of a cryostat has progressed as scheduled. The investigation of carbon isotope exchange equilibria between carbon dioxide and various carbamates dissolved in various organic solvents has continued. The five-stage system of Taylor-Ghate design was improved to shorten the transient time. A single stage apparatus was designed, built, and tested. These systems are used to measure the equilibrium constants and various phase equilibria involved in the carbon dioxide--carbamate system. The investigation of the explicit method of total isotope effect has made progress. A satisfactory approximation was found for the classical partition function of a Morse oscillator. The method gives a reasonable result at rho identical with /sup 1///sub 2/..sqrt..(u/sub e//x/sub e/) greater than 1.5. The medium cluster approach was applied to isotopic methanes to investigate the effects of intermolecular distance and mutual orientations of molecules in the liquid upon vapor pressure isotope effect. It was found that all geometrical effects studied tend to vanish as the size of clusters is increased. Isotope effect in the zero-point energy shifts on condensation was calculated on the basis of London dispersion forces in liquid and a semi-empirical molecular orbital theory, and was favorably compared with experimental results. (auth)

  13. Stable carbon isotope fractionation of organic cyst-forming dinoflagellates: Evaluating the potential for a CO2 proxy

    Science.gov (United States)

    Hoins, Mirja; Van de Waal, Dedmer B.; Eberlein, Tim; Reichart, Gert-Jan; Rost, Björn; Sluijs, Appy

    2015-07-01

    Over the past decades, significant progress has been made regarding the quantification and mechanistic understanding of stable carbon isotope fractionation (13C fractionation) in photosynthetic unicellular organisms in response to changes in the partial pressure of atmospheric CO2 (pCO2). However, hardly any data is available for organic cyst-forming dinoflagellates while this is an ecologically important group with a unique fossil record. We performed dilute batch experiments with four harmful dinoflagellate species known for their ability to form organic cysts: Alexandrium tamarense, Scrippsiella trochoidea, Gonyaulax spinifera and Protoceratium reticulatum. Cells were grown at a range of dissolved CO2 concentrations characterizing past, modern and projected future values (∼5-50 μmol L-1), representing atmospheric pCO2 of 180, 380, 800 and 1200 μatm. In all tested species, 13C fractionation depends on CO2 with a slope of up to 0.17‰ (μmol L)-1. Even more consistent correlations were found between 13C fractionation and the combined effects of particulate organic carbon quota (POC quota; pg C cell-1) and CO2. Carbon isotope fractionation as well as its response to CO2 is species-specific. These results may be interpreted as a first step towards a proxy for past pCO2 based on carbon isotope ratios of fossil organic dinoflagellate cysts. However, additional culture experiments focusing on environmental variables other than pCO2, physiological underpinning of the recorded response, testing for possible offsets in 13C values between cells and cysts, as well as field calibration studies are required to establish a reliable proxy.

  14. Effect of Different Carbon Substrates on Nitrate Stable Isotope Fractionation During Microbial Denitrification

    DEFF Research Database (Denmark)

    Wunderlich, Anja; Meckenstock, Rainer; Einsiedl, Florian

    2012-01-01

    .1 ± 0.8‰; ε18O, −23.7 ± 1.8‰ to −19.9 ± 0.8‰). The observed isotope effects did not depend on the growth kinetics which were similar for the three types of electron donors. We suggest that different carbon sources change the observed isotope enrichment factors by changing the relative kinetics...... of nitrate transport across the cell wall compared to the kinetics of the intracellular nitrate reduction step of microbial denitrification....

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

    Science.gov (United States)

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

    2015-08-01

    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.

  16. Stable carbon isotope fractionation in chlorinated ethene degradation by bacteria expressing three toluene oxygenases

    Directory of Open Access Journals (Sweden)

    Scott eClingenpeel

    2012-02-01

    Full Text Available One difficulty in using bioremediation at a contaminated site is demonstrating that biodegradation is actually occurring in situ. The stable isotope composition of contaminants may help with this, since they can serve as an indicator of biological activity. To use this approach it is necessary to establish how a particular biodegradation pathway affects the isotopic composition of a contaminant. This study examined bacterial strains expressing three aerobic enzymes for their effect on the 13C/12C ratio when degrading both trichloroethene (TCE and cis-1,2-dichloroethene (c-DCE: toluene 3-monoxygenase, toluene 4-monooxygenase, and toluene 2,3-dioxygenase. We found no significant differences in fractionation among the three enzymes for either compound. Aerobic degradation of c-DCE occurred with low fractionation producing δ13C enrichment factors of -0.9±0.5 to -1.2±0.5, in contrast to reported anaerobic degradation δ13C enrichment factors of -14.1‰ to -20.4‰. Aerobic degradation of TCE resulted in δ13C enrichment factors of -11.6±4.1‰ to -14.7±3.0‰ which overlap reported δ13C enrichment factors for anaerobic TCE degradation of -2.5‰ to -13.8‰. The data from this study suggest that stable isotopes could serve as a diagnostic for detecting aerobic biodegradation of TCE by toluene oxygenases at contaminated sites.

  17. The Paleocene Eocene carbon isotope excursion in higher plant organic matter: Differential fractionation of angiosperms and conifers in the Arctic

    Science.gov (United States)

    Schouten, Stefan; Woltering, Martijn; Rijpstra, W. Irene C.; Sluijs, Appy; Brinkhuis, Henk; Sinninghe Damsté, Jaap S.

    2007-06-01

    A study of upper Paleocene-lower Eocene (P-E) sediments deposited on the Lomonosov Ridge in the central Arctic Ocean reveals relatively high abundances of terrestrial biomarkers. These include dehydroabietane and simonellite derived from conifers (gymnosperms) and a tetra-aromatic triterpenoid derived from angiosperms. The relative percentage of the angiosperm biomarker of the summed angiosperm + conifer biomarkers was increased at the end of the Paleocene-Eocene thermal maximum (PETM), different when observed with pollen counts which showed a relative decrease in angiosperm pollen. Stable carbon isotopic analysis of these biomarkers shows that the negative carbon isotope excursion (CIE) during the PETM amounts to 3‰ for both conifer biomarkers, dehydroabietane and simonellite, comparable to the magnitude of the CIE inferred from marine carbonates, but significantly lower than the 4.5‰ of the terrestrial C 29n-alkane [M. Pagani, N. Pedentchouk, M. Huber, A. Sluijs, S. Schouten, H. Brinkhuis, J.S. Sinninghe Damsté, G.R. Dickens, and the IODP Expedition 302 Expedition Scientists (2006), Arctic's hydrology during global warming at the Paleocene-Eocene thermal maximum. Nature, 442, 671-675.], which is a compound sourced by both conifers and angiosperms. Conspicuously, the angiosperm-sourced aromatic triterpane shows a much larger CIE of 6‰ and suggests that angiosperms increased in their carbon isotopic fractionation during the PETM. Our results thus indicate that the 4.5‰ C 29n-alkane CIE reported previously represents the average CIE of conifers and angiosperms at this site and suggest that the large and variable CIE observed in terrestrial records may be partly explained by the variable contributions of conifers and angiosperms. The differential response in isotopic fractionation of angiosperms and conifers points to different physiological responses of these vegetation types to the rise in temperature, humidity, and greenhouse gases during the PETM.

  18. Ca isotope stratigraphy across the Cenomanian-Turonian OAE 2: Links between volcanism, seawater geochemistry, and the carbonate fractionation factor

    Science.gov (United States)

    Du Vivier, Alice D. C.; Jacobson, Andrew D.; Lehn, Gregory O.; Selby, David; Hurtgen, Matthew T.; Sageman, Bradley B.

    2015-04-01

    The Ca isotope composition of marine carbonate rocks offers potential to reconstruct drivers of environmental change in the geologic past. This study reports new, high-precision Ca isotope records (δ44/40Ca; 2σSD = ± 0.04 ‰) for three sections spanning a major perturbation to the Cretaceous ocean-climate system known as Ocean Anoxic Event 2 (OAE 2): central Colorado, USA (Portland #1 core), southeastern France (Pont d'Issole), and Hokkaido, Japan (Oyubari, Yezo Group). In addition, we generated new data for selected samples from Eastbourne, England (English Chalk), where a previous Ca isotope study was completed using different methodology (Blättler et al., 2011). Strata of the Yezo Group contain little carbonate (∼1 wt.% on average) and accordingly did not yield a clear δ44/40Ca signal. The Portland core and the Pont d'Issole section display comparable δ44/40Ca values, which increase by ∼ 0.10- 0.15 ‰ at the onset of OAE 2 and then decrease to near-initial values across the event. The Eastbourne δ44/40Ca values are higher than previously reported. They are also higher than the δ44/40Ca values for the Portland core and the Pont d'Issole section but define a similar pattern. According to a numerical model of the marine Ca cycle, elevated hydrothermal inputs have little impact on seawater δ44/40Ca values. Elevated riverine (chemical weathering) inputs produce a transient negative isotope excursion, which significantly differs from the positive isotope excursions observed in the Portland, Pont d'Issole, and Eastbourne records. A decrease in the magnitude of the carbonate fractionation factor provides the best explanation for a positive shift in δ44/40Ca values, especially given the rapid nature of the excursion. Because a decrease in the fractionation factor corresponds to an increase in the Ca/CO3 ratio of seawater, we tentatively attribute the positive Ca isotope excursion to transient ocean acidification, i.e., a reduction in the concentration of

  19. Natural fractionation of uranium isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Noordmann, Janine

    2015-01-24

    The topic of this thesis was the investigation of U (n({sup 238}U) / n({sup 235}U)) isotope variations in nature with a focus on samples (1) that represent the continental crust and its weathering products (i.e. granites, shales and river water) (2) that represent products of hydrothermal alteration on mid-ocean ridges (i.e. altered basalts, carbonate veins and hydrothermal water) and (3) from restricted euxinic basins (i.e. from the water column and respective sediments). The overall goal was to explore the environmental conditions and unravel the mechanisms that fractionate the two most abundant U isotopes, n({sup 238}U) and n({sup 235}U), on Earth.

  20. 3D-CSIA: carbon, chlorine, and hydrogen isotope fractionation in transformation of TCE to ethene by a Dehalococcoides culture.

    Science.gov (United States)

    Kuder, Tomasz; van Breukelen, Boris M; Vanderford, Mindy; Philp, Paul

    2013-09-03

    Carbon (C), chlorine (Cl), and hydrogen (H) isotope effects were determined during dechlorination of TCE to ethene by a mixed Dehalococcoides (Dhc) culture. The C isotope effects for the dechlorination steps were consistent with data published in the past for reductive dechlorination (RD) by Dhc. The Cl effects (combined with an inverse H effect in TCE) suggested that dechlorination proceeded through nucleophilic reactions with cobalamin rather than by an electron transfer mechanism. Depletions of (37)Cl in daughter compounds, resulting from fractionation at positions away from the dechlorination center (secondary isotope effects), further support the nucleophilic dechlorination mechanism. Determination of C and Cl isotope ratios of the reactants and products in the reductive dechlorination chain offers a potential tool for differentiation of Dhc activity from alternative transformation mechanisms (e.g., aerobic degradation and reductive dechlorination proceeding via outer sphere mechanisms), in studies of in situ attenuation of chlorinated ethenes. Hydrogenation of the reaction products (DCE, VC, and ethene) showed a major preference for the (1)H isotope. Detection of depleted dechlorination products could provide a line of evidence in discrimination between alternative sources of TCE (e.g., evolution from DNAPL sources or from conversion of PCE).

  1. Evaluation of gas chromatographic isotope fractionation and process contamination by carbon in compound-specific radiocarbon analysis.

    Science.gov (United States)

    Zencak, Zdenek; Reddy, Christopher M; Teuten, Emma L; Xu, Li; McNichol, Ann P; Gustafsson, Orjan

    2007-03-01

    The relevance of both modern and fossil carbon contamination as well as isotope fractionation during preparative gas chromatography for compound-specific radiocarbon analysis (CSRA) was evaluated. Two independent laboratories investigated the influence of modern carbon contamination in the sample cleanup procedure and preparative capillary gas chromatography (pcGC) of a radiocarbon-dead 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169) reference. The isolated samples were analyzed for their 14C/12C ratio by accelerator mass spectrometry. Sample Delta14C values of -996 +/- 20 and -985 +/- 20 per thousand agreed with a Delta14C of -995 +/- 20 per thousand for the unprocessed PCB 169, suggesting that no significant contamination by nonfossil carbon was introduced during the sample preparation process at either laboratory. A reference compound containing a modern 14C/12C ratio (vanillin) was employed to evaluate process contamination from fossil C. No negative bias due to fossil C was observed (sample Delta14C value of 165 +/- 20 per thousand agreed with Delta14C of 155 +/- 12 per thousand for the unprocessed vanillin). The extent of isotopic fractionation that can be induced during pcGC was evaluated by partially collecting the vanillin model compound of modern 14C/12C abundance. A significant change in the delta13C and delta14C values was observed when only parts of the eluting peak were collected (delta13C values ranged from -15.75 to -49.91 per thousand and delta14C values from -82.4 to +4.71 per thousand). Delta14C values, which are normalized to a delta13C of -25 per thousand, did not deviate significantly (-58.9 to -5.8 per thousand, considering the uncertainty of approximately +/-20 per thousand). This means that normalization of radiocarbon results to a delta13C of -25 per thousand, normally performed to remove effects of environmental isotope fractionation on 14C-based age determinations, also cor-rects sufficiently for putative isotopic fractionation that may

  2. Variability in carbon isotope fractionation of trichloroethene during degradation by persulfate activated with zero-valent iron: Effects of inorganic anions

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yunde [State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074 (China); School of Environmental Studies, China University of Geosciences, Wuhan 430074 (China); Zhou, Aiguo, E-mail: aiguozhou@cug.edu.cn [State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074 (China); School of Environmental Studies, China University of Geosciences, Wuhan 430074 (China); Gan, Yiqun; Li, Xiaoqian [State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074 (China); School of Environmental Studies, China University of Geosciences, Wuhan 430074 (China)

    2016-04-01

    Stable carbon isotope analysis has the potential to be used for assessing the performance of in situ remediation of organic contaminants. Successful application of this isotope technique requires understanding the magnitude and variability in carbon isotope fractionation associated with the reactions under consideration. This study investigated the influence of inorganic anions (sulfate, bicarbonate, and chloride) on carbon isotope fractionation of trichloroethene (TCE) during its degradation by persulfate activated with zero-valent iron. The results demonstrated that the significant carbon isotope fractionation (enrichment factors ε ranging from − 3.4 ± 0.3 to − 4.3 ± 0.3 ‰) was independent on the zero-iron dosage, sulfate concentration, and bicarbonate concentration. However, the ε values (ranging from − 7.0 ± 0.4 to − 13.6 ± 1.2 ‰) were dependent on the chloride concentration, indicating that chloride could significantly affect carbon isotope fractionation during TCE degradation by persulfate activated with zero-valent iron. The dependence of ε values on chloride concentration, indicated that TCE degradation mechanisms may be different from the degradation mechanism caused by sulfate radical (SO{sub 4}·{sup −}). Ignoring the effect of chloride on ε value may cause numerous uncertainties in quantitative assessment of the performance of the in situ chemical oxidation (ISCO). - Highlights: • Significant C isotope fractionation for TCE degradation by Fe{sup 0} activated persulfate. • The enrichment factors was independent of Fe{sup 0}, SO{sub 4}{sup 2−}, or HCO{sub 3}{sup −} concentration. • Cl{sup −} significantly influenced the carbon isotope fractionation.

  3. Variability in carbon isotope fractionation of trichloroethene during degradation by persulfate activated with zero-valent iron: Effects of inorganic anions.

    Science.gov (United States)

    Liu, Yunde; Zhou, Aiguo; Gan, Yiqun; Li, Xiaoqian

    2016-04-01

    Stable carbon isotope analysis has the potential to be used for assessing the performance of in situ remediation of organic contaminants. Successful application of this isotope technique requires understanding the magnitude and variability in carbon isotope fractionation associated with the reactions under consideration. This study investigated the influence of inorganic anions (sulfate, bicarbonate, and chloride) on carbon isotope fractionation of trichloroethene (TCE) during its degradation by persulfate activated with zero-valent iron. The results demonstrated that the significant carbon isotope fractionation (enrichment factors ε ranging from -3.4±0.3 to -4.3±0.3‰) was independent on the zero-iron dosage, sulfate concentration, and bicarbonate concentration. However, the ε values (ranging from -7.0±0.4 to -13.6±1.2‰) were dependent on the chloride concentration, indicating that chloride could significantly affect carbon isotope fractionation during TCE degradation by persulfate activated with zero-valent iron. The dependence of ε values on chloride concentration, indicated that TCE degradation mechanisms may be different from the degradation mechanism caused by sulfate radical (SO4(-)). Ignoring the effect of chloride on ε value may cause numerous uncertainties in quantitative assessment of the performance of the in situ chemical oxidation (ISCO).

  4. Dynamic changes of carbon isotope apparent fractionation factor to describe transition to syntrophic acetate oxidation during cellulose and acetate methanization.

    Science.gov (United States)

    Vavilin, Vasily A; Rytov, Sergey V

    2017-05-01

    To identify predominant metabolic pathway for cellulose methanization new equations that take into account dynamics of 13C are added to the basic model of cellulose methanization. The correct stoichiometry of hydrolysis, acidogenesis, acetogenesis and methanogenesis steps including biomass is considered. Using experimental data by Laukenmann et al. [Identification of methanogenic pathway in anaerobic digesters using stable carbon isotopes. Eng. Life Sci. 2010;10:1-6], who reported about the importance of ace`tate oxidation during mesophilic cellulose methanization, the model confirmed that, at high biomass concentration of acetate oxidizers, the carbon isotope fractionation factor amounts to about 1.085. The same model, suggested firstly for cellulose degradation, was used to describe, secondly, changes in, and in methane and carbon dioxide during mesophylic acetate methanization measured by Grossin-Debattista [Fractionnements isotopiques (13C/12C) engendres par la methanogenese: apports pour la comprehension des processus de biodegradation lors de la digestion anaerobie [doctoral thesis]. 2011. Bordeaux: Universite Bordeaux-1;2011. Available from: http://ori-oai.u-bordeaux1.fr/pdf/2011/GROSSIN-DEBATTISTA_JULIEN_2011.pdf . French].The model showed that under various ammonium concentrations, at dominating acetoclastic methanogenesis, the value decreases over time to a low level (1.016), while at dominating syntrophic acetate oxidation, coupled with hydrogenotrophic methanogenesis, slightly increases, reaching 1.060 at the end of incubation.

  5. Distribution of lipid biomarkers and carbon isotope fractionation in contrasting trophic environments of the South East Pacific

    Directory of Open Access Journals (Sweden)

    I. Tolosa

    2008-06-01

    Full Text Available The distribution of lipid biomarkers and their stable carbon isotope composition was investigated on suspended particles from different contrasting trophic environments at six sites in the South East Pacific. High algal biomass with diatom-related lipids (24-methylcholesta-5,24(28-dien-3β-ol, C25 HBI alkenes, C16:4 FA, C20:5 FA was characteristic in the upwelling zone, whereas haptophyte lipids (long-chain (C37-C39 unsaturated ketones were proportionally most abundant in the nutrient-poor settings of the centre of the South Pacific Gyre and on its easter edge. The dinoflagellate–sterol, 4α-23,24-trimethylcholest-22(E-en-3β-ol, was a minor contributor in all of the studied area and the cyanobacteria-hydrocarbon, C17n-alkane, was at maximum in the high nutrient low chlorophyll regime of the subequatorial waters near the Marquesas archipelago.

    The taxonomic and spatial variability of the relationships between carbon photosynthetic fractionation and environmental conditions for four specific algal taxa (diatoms, haptophytes, dinoflagellates and cyanobacteria was also investigated. The carbon isotope fractionation factor (εp of the 24-methylcholesta-5,24(28-dien-3β-ol diatom marker, varied over a range of 16% along the different trophic systems. In contrast, εp of dinoflagellate, cyanobacteria and alkenone markers varied only by 7–10‰. The low fractionation factors and small variations between the different phytoplankton markers measured in the upwelling area likely reveals uniformly high specific growth rates within the four phytoplankton taxa, and/or that transport of inorganic carbon into phytoplankton cells may not only occur by diffusion but also by other carbon concentrating mechanisms (CCM. In contrast, in the oligotrophic zone, i.e. gyre and eastgyre, relatively high εp values, especially for the diatom marker

  6. Diet induced differences in carbon isotope fractionation between sirenians and terrestrial ungulates

    Science.gov (United States)

    Clementz, M.T.; Koch, P.L.; Beck, C.A.

    2007-01-01

    Carbon isotope differences (??13C) between bioapatite and diet, collagen and diet, and bioapatite and collagen were calculated for four species of sirenians, Dugong dugon (Mu??ller), Trichechus manatus (Linnaeus), Trichechus inunguis (Natterer), and the extinct Hydrodamalis gigas (Zimmerman). Bone and tooth samples were taken from archived materials collected from populations during the mid eighteenth century (H. gigas), between 1978 and 1984 (T. manatus, T. inunguis), and between 1997 and 1999 (D. dugon). Mean ??13C values were compared with those for terrestrial ungulates, carnivores, and six species of carnivorous marine mammals (cetaceans = 1; pinnipeds = 4; mustelids = 1). Significant differences in mean ??13C values among species for all tissue types were detected that separated species or populations foraging on freshwater plants or attached marine macroalgae (??13C values -4???; ??13Cbioapatite-diet ???11???). Likewise, ??13Cbioapatite-collagen values for freshwater and algal-foraging species (???7???) were greater than those for seagrass-foraging species (???5???). Variation in ??13C values calculated between tissues and between tissues and diet among species may relate to the nutritional composition of a species' diet and the extent and type of microbial fermentation that occurs during digestion of different types of plants. These results highlight the complications that can arise when making dietary interpretations without having first determined species-specific ??13Ctissue-diet values. ?? 2007 Springer-Verlag.

  7. Different carbon isotope fractionation patterns during the development of phototrophic freshwater and marine biofilms

    Directory of Open Access Journals (Sweden)

    M. Staal

    2007-08-01

    Full Text Available Natural phototrophic biofilms are influenced by a broad array of abiotic and biotic factors and vary over temporal and spatial scales. Different developmental stages can be distinguished and growth rates will vary due to the thickening of the biofilm, which is expected to lead to a limitation of light or mass transport. This study shows that variation in CO2(aq availability leads to a fractionation shift and thereby affects δ13C signatures during biofilm development. For phototrophic freshwater biofilms it was found that the δ13C value became less negative with the thickening of the biofilm, while the opposite trend was found in marine biofilms. Modeling and pH profiling indicated that the trend in the freshwater system was caused by an increase in CO2(aq limitation resulting in an increase of HCO3 as C-source. The opposite trend in the marine system could be explained by a higher heterotrophic biomass and activity causing a higher carbon recycling and thereby lower δ13C values. We conclude that δ13C was more related to the net areal photosynthesis rate and carbon recycling, rather than to the growth rate of the biofilms.

  8. Organic fraction of the total carbon burial flux deduced from carbon isotopes across the Permo-Triassic boundary at Meishan,Zhejiang Province,China

    Institute of Scientific and Technical Information of China (English)

    HUANG Junhua; LUO Genming; BAI Xiao; TANG Xinyan

    2007-01-01

    By combining the carbon cycle model with the records of carbonate and organic (kerogen) carbon isotope,this paper presents the calculation of the fraction of organic carbon burial (forg) of beds 23-40 at the global boundary stratotype section and point (GSSP) of the Permian-Triassic boundary at Meishan,Zhejiang Province.The resulting calculation produces two episodes of forg maxima observed to occur at beds 23-24 and 27-29,which respectively corresponds to the two episodic anoxic events indicated by the flourish of green sulfur bacteria.Two episodic forg minima occurred at beds 25-26 and 32-34,generally coincident with the flourish of cyanobacteria (bed 26 and upper part of beds 29 to 34) as shown by the high value of 2-melthyhopnoanes.It appears that the forg is related to the redox conditions,with greater forg values observed under the reductive condition.The relationship between forg and the total organic carbon (TOC) content was complex.The forg value was low at some beds with a high TOC content (such as bed 26),while high observed at some beds with a low TOC content (e.g.bed 27).This association infers the important contribution of primary productivity to the TOC content.The original organic burial could be thus calculated through the configuration of the function of the primary productivity and forg,which can be used to correct the residual TOC measured today.This investigation indicates that compiling the organic-inorganic carbon isotopes with the carbon cycle model favors to understand the fraction of organic carbon burial,providing information for the reconstruction of the coupling among biota,environments and organic burial.

  9. Fractional Absorption of Active Absorbable Algal Calcium (AAACa and Calcium Carbonate Measured by a Dual Stable-Isotope Method

    Directory of Open Access Journals (Sweden)

    Steven A. Abrams

    2010-07-01

    Full Text Available With the use of stable isotopes, this study aimed to compare the bioavailability of active absorbable algal calcium (AAACa, obtained from oyster shell powder heated to a high temperature, with an additional heated seaweed component (Heated Algal Ingredient, HAI, with that of calcium carbonate. In 10 postmenopausal women volunteers aged 59 to 77 years (mean ± S.D., 67 ± 5.3, the fractional calcium absorption of AAACa and CaCO3 was measured by a dual stable isotope method. 44Ca-enriched CaCO3 and AAACa were administered in all subjects one month apart. After a fixed-menu breakfast and pre-test urine collection (Urine 0, 42Ca-enriched CaCl2 was intravenously injected, followed by oral administration of 44Ca-enriched CaCO3 without carrier 15 minutes later, and complete urine collection for the next 24 hours (Urine 24. The fractional calcium absorption was calculated as the ratio of Augmentation of 44Ca from Urine 0 to Urine 24/ augmentation of 42Ca from Urine 0 to Urine 24. Differences and changes of 44Ca and 42Ca were corrected by comparing each with 43Ca. Fractional absorption of AAACa (mean ± S.D., 23.1 ± 6.4, was distinctly and significantly higher than that of CaCO3 (14.7 ± 6.4; p = 0.0060 by paired t-test. The mean fractional absorption was approximately 1.57-times higher for AAACa than for CaCO3. The serum 25(OH vitamin D level was low (mean ± S.D., 14.2 ± 4.95 ng/ml, as is common in this age group in Japan. Among the parameters of the bone and mineral metabolism measured, none displayed a significant correlation with the fractional absorption of CaCO3 and AAACa. Higher fractional absorption of AAACa compared with CaCO3 supports previous reports on the more beneficial effect of AAACa than CaCO3 for osteoporosis.

  10. Growth rate and size effect on carbon isotopic fractionation in diatom-bound organic matter in recent Southern Ocean sediments

    Science.gov (United States)

    Stoll, Heather M.; Mendez-Vicente, Ana; Abrevaya, Lorena; Anderson, Robert F.; Rigual-Hernández, Andrés S.; Gonzalez-Lemos, Saul

    2017-01-01

    Carbon isotopic fractionation during photosynthesis (εp) is used to reconstruct past CO2 and phytoplankton growth rates, typically by measuring the δ13C of biomarkers produced by coccolithophorids. However, organic molecules bound within diatom frustules represent another phase for measurement of δ13C and offer the opportunity to obtain εp for specific diatom sizes and geometries. Here, from core top sediments covering a strong productivity gradient in the Southern Ocean, we present determinations of δ13C and εp from frustule-bound organic matter from a fine opal fraction dominated by pennate diatoms and a coarse opal fraction dominated by larger centric diatoms. The δ13C of the pennate diatom fraction is typically 2.8‰ more positive than that of the centric fraction. Both fractions show a comparable range of 9-10‰ over the core top transect. εp is lowest (6.3‰ in pennate fraction) between the Polar Front (PF) and Southern Antarctic Circumpolar Current Front (SACCF) and increases both to the north and south, with maximum values at greatest distance from the PF (18‰ in the pennate fraction). These spatial changes in εp are too large to arise from the rather modest variation in dissolved CO2 in surface waters across the core top transect. We suggest instead that the maximum εp reflects higher diatom growth rates, and in the case of pennate diatom F. kerguelensis also an increase in the frustule width and volume to surface area ratio. Both processes may result from enhanced Fe supply due to upwelling of circumpolar deep water between the PF and SACCF. Farther south, diatom growth is strongly Fe-limited and farther north it is Fe and Si co-limited. The optima of growth rates between the PF and SACCF appears to be a general feature in all sectors of the Southern Ocean. Such growth rate-induced changes in diatom εp allow us to resolve a 5° northward displacement of the PF during glacial times compared to interglacial times. By estimating CO2 aq in

  11. Carbon isotope geochemistry and geobiology

    Science.gov (United States)

    Desmarais, D.

    1985-01-01

    Carbon isotope fractionation values were used to understand the history of the biosphere. For example, plankton analyses confirmed that marine extinctions at the end of the Cretaceous period were indeed severe (see Hsu's article in Sundquist and Broeker, 1984). Variations in the isotopic compositions of carbonates and evaporitic sulfates during the Paleozoic reflect the relative abundances of euxinic (anoxic) marine environments and organic deposits from terrestrial flora. The carbon isotopic composition of Precambrian sediments suggest that the enzyme ribulose bisphosphate carboxylase has existed for perhaps 3.5 billion years.

  12. The separation of stable isotopes of carbon

    Science.gov (United States)

    Oziashvili, E. D.; Egiazarov, A. S.

    1989-04-01

    The present state of work on the separation of carbon isotopes by diffusion, fractional distillation, chemical isotopic exchange, and the selective excitation and dissociation of molecules in electrical discharges or in the field of laser radiation has been examined. The characteristics of new laboratory and industrial assemblies for separating carbon isotopes have been described. Promising directions of study aimed at developing effective technological processes for separating carbon isotopes have been noted. The bibliography contains 148 references.

  13. Application of δ13C and δ15N isotopic signatures of organic matter fractions sequentially separated from adjacent arable and forest soils to identify carbon stabilization mechanisms

    Directory of Open Access Journals (Sweden)

    M. Sommer

    2011-03-01

    Full Text Available Identifying the chemical mechanisms behind soil carbon bound in organo-mineral complexes is necessary to determine the degree to which soil organic carbon is stabilized belowground. We used the δ13C and δ15N isotopic signatures from two organic matter (OM fractions from soil to identify the likely binding mechanisms involved. We used OM fractions hypothesized to contain carbon stabilized through organo-mineral complexes: (1 OM separated chemically with sodium pyrophosphate (OM(PY and (2 OM stabilized in microstructures found in the chemical extraction residue (OM(ER. Furthermore, because the OM fractions were separated from five different soils with paired forest and arable land use histories, we could address the impact of land use change on carbon binding and processing mechanisms within these soils. We used partial least squares regression to analyze patterns in the isotopic signature of OM with established proxies of different binding mechanisms. Parsing soil OM into different fractions is a systematic method of dissection, however, we are primarily interested in how OM is bound in soil as a whole, requiring a means of re-assembly. Thus, we implemented the recent zonal framework described by Kleber et al. (2007 to relate our findings to undisturbed soil. The δ15N signature of OM fractions served as a reliable indicator for microbial processed carbon in both arable and forest land use types. The δ13C signature of OM fractions in arable sites did not correlate well with proxies of soil mineral properties while a consistent pattern of enrichment was seen in the δ13C of OM fractions in the forest sites. We found a significant difference in δ13C of pooled OM fractions between the forest and arable land use type although it was relatively small (<1‰. We found different binding mechanisms predominate in each land use type. The isotopic signatures of OM fractions from arable soils were highly related to the clay and silt size particles

  14. Application of δ13C and δ15N isotopic signatures of organic matter fractions sequentially separated from adjacent arable and forest soils to identify carbon stabilization mechanisms

    Directory of Open Access Journals (Sweden)

    M. Sommer

    2011-10-01

    Full Text Available Identifying the chemical mechanisms behind soil carbon bound in organo-mineral complexes is necessary to determine the degree to which soil organic carbon is stabilized belowground. Analysis of δ13C and δ15N isotopic signatures of stabilized OM fractions along with soil mineral characteristics may yield important information about OM-mineral associations and their processing history. We anlayzed the δ13C and δ15N isotopic signatures from two organic matter (OM fractions along with soil mineral proxies to identify the likely binding mechanisms involved. We analyzed OM fractions hypothesized to contain carbon stabilized through organo-mineral complexes: (1 OM separated chemically with sodium pyrophosphate (OM(PY and (2 OM occluded in micro-structures found in the chemical extraction residue (OM(ER. Because the OM fractions were separated from five different soils with paired forest and arable land use histories, we could address the impact of land use change on carbon binding and processing mechanisms. We used partial least squares regression to analyze patterns in the isotopic signature of OM with established mineral and chemical proxies indicative for certain binding mechanisms. We found different mechanisms predominate in each land use type. For arable soils, the formation of OM(PY-Ca-mineral associations was identified as an important OM binding mechanism. Therefore, we hypothesize an increased stabilization of microbial processed OM(PY through Ca2+ interactions. In general, we found the forest soils to contain on average 10% more stabilized carbon relative to total carbon stocks, than the agricultural counter part. In forest soils, we found a positive relationship between isotopic signatures of OM(PY and the ratio of soil organic carbon content to soil surface area (SOC/SSA. This indicates that the OM(PY fractions of forest soils represent layers of slower exchange not directly attached to mineral surfaces. From the isotopic composition

  15. Estimating evolution of δ13CH4 during methanization of cellulosic waste based on stoichiometric chemical reactions, microbial dynamics and stable carbon isotope fractionation.

    Science.gov (United States)

    Vavilin, V A

    2012-04-01

    A change in δ(13)CH(4) during mesophilic methanization of cellulosic waste (paper and cardboard) was described using a mathematical model based on stoichiometric chemical reactions, microbial dynamics and the equation for the (13)C isotope accumulation in products including isotope fractionation. In this study, experimental data, previously obtained by Qu et al. (2009), was used to model metabolic pathways of cellulose transformation. A significant change in δ(13)CH(4) occurred in time during cellulosic waste methanization which was in accordance with the model. It was explained by the change in input of acetoclastic and hydrogenotrophic methanogenesis as well as by fractionation of stable carbon isotopes (13)C and (12)C which was much higher for hydrogenotrophic methanogenesis when compared to acetoclastic methanogenesis.

  16. An experimental investigation of multiple sulfur isotope fractionations during heterogenous reactions between SO2 and activated carbon

    Science.gov (United States)

    Hamasaki, H.; Watanabe, Y.; Ohmoto, H.

    2010-12-01

    Watanabe et al. (2009) reported that the reduced-S species produced from reactions between solid organic compounds and aqueous sulfate at 150-200 °C possessed anomalous isotopic fractionation (AIF) of S: Δ33S = 0.1 to 2.1 ‰. Based partly on these data, they suggested that the AIF-S signatures in some sedimentary rocks were produced during thermochemical sulfate reduction by solid organic compounds during the early stage of sediment diagenesis, rather than by atmospheric UV photolysis of volcanic SO2. Theoretical study by Lasaga et al. (2008) also suggested that variable AIF-S signatures could be generated during chemisorption of aqueous (or gaseous) S species on a solid surface (e.g., kerogen) under certain conditions. The main objective of this study was, therefore, to evaluate S isotope effects during different stages of reactions (e.g., adsorption, redox reactions) between a solid organic compound and SO2. We have conducted several series of experiments in a closed pyrex-glass system. About 1.8 gm (0.15 moles) of activated C (0.25-1.0 mm in diameter) was first evacuated at 300 °C for 5 days. Then 2.5 mmoles of pure SO2 gas was introduced in the system to react with activated carbon at 200 or 250 °C. Once the pSO2 became stabilized (typically after ~1 day), an aliquot of the SO2 gas (0.1 to 1.5 mmoles) was withdrawn into a pyrex-glass tube containing 20 % H2O2 solution to collect the SO2 as sulfate. After the pSO2 reached to a new steady value, another aliquot of SO2 was withdrawn from the system; sampling was continued until the amount of SO2 gas in the system decreased to 5 % of the initial value. The collected sulfate was converted to Ag2S for isotope analysis. After a series of experiment at 200 °C and another at 250 °C, the activated carbon was removed from the reaction system, treated sequentially by different chemical solutions to extract different forms of S compounds; the extracted S compounds were analyzed for their contents and isotopic ratios

  17. Interannual Variability in Carbon and Nitrogen Stable Isotopic Signatures of Size-Fractionated POM from the South Florida Coastal Zone

    Science.gov (United States)

    Evans, S. L.; Anderson, W. T.; Jochem, F. J.; Fourqurean, J. W.

    2004-12-01

    Environmental conditions in South Florida coastal waters have been of local and national concern over the past 15 years. Attention has focused on the ecosystem impacts of salinity increases, seagrass die-off, increased algal bloom frequency, waste water influence, groundwater discharge, and exchange between Florida Bay, the Gulf of Mexico, and the Atlantic Ocean. Changes in water quality and productivity levels may be reflected in the isotopic signatures of coastal zone primary producers. Recent work with seagrasses in South Florida has demonstrated high seasonal and spatial variability in C and N isotopic signatures and decoupling between the two isotopic systems as they vary. To better understand the sources of seasonal and spatial fluctuation, size fractionated POM (particulate organic matter) samples have been collected on a quarterly basis since Sept. 2002. Fractions collected include >150μ m, 50-150μ m, and 0.1-50μ m using Nitex mesh sieves and a portable pump system deployed from a small boat at 10 sites around the Florida Keys and Florida Bay. It was hypothesized that planktonic groups respond more quickly to changes in water quality then seagrasses, and thus variations may be more clearly attributed to environmental parameters. Significant spatial and temporal variability is evident both within site between size fractions and between sites. Seasonal oscillations of up to 4‰ were observed in N isotopic values and 6‰ in C isotopic values of the 50-150μ m size fraction, which is dominated by diatoms and dinoflagellates. δ 13C values are depleted in the late winter/early spring sampling period possibly reflecting decreased productivity stress on available C pools. 13C depletion is generally coincident with δ 15N enrichment in the late winter/early spring, possibly demonstrating changes in DIN pools (NO3- and NH4+ concentrations) or changes in decomposition or denitrification rates. Broad groupings appear to separate Atlantic coral reef sites

  18. Argon isotope fractionation induced by stepwise heating

    Science.gov (United States)

    Trieloff, Mario; Falter, Martina; Buikin, Alexei I.; Korochantseva, Ekaterina V.; Jessberger, Elmar K.; Altherr, Rainer

    2005-03-01

    Noble gas isotopes are widely used to elucidate the history of the rocks in which they have been trapped, either from distinct reservoirs or by accumulation following radioactive decay. To extract noble gases from their host rocks, stepwise heating is the most commonly used technique to deconvolve isotopically different components, e.g., atmospheric, in situ radiogenic, or excess radiogenic from mantle or crustal reservoirs. The accurate determination of the isotopic composition of these different components is of crucial importance, e.g., for ages obtained by 40Ar- 39Ar stepheating plateaus. However, diffusion theory-based model calculations predict that the stepwise thermal extraction process from mineral phases induces isotope fractionation and, hence, adulterates the original composition. Such effects are largely unconsidered, as they are small and a compelling experimental observation is lacking. We report the first unequivocal evidence for significant mass fractionation of argon isotopes during thermal extraction, observed on shungite, a carbon-rich Precambrian sedimentary rock. The degree of fractionation, as monitored by 38Ar/ 36Ar and 40Ar/ 36Ar ratios, very well agrees with theoretical predictions assuming an inverse square root dependence of diffusion coefficient and atomic mass, resulting in easier extraction of lighter isotopes. Hence, subatmospheric 40Ar/ 36Ar ratios obtained for argon extracted at low temperatures may not represent paleoatmospheric argon. Shungite argon resembles modern atmospheric composition, but constraints on the timing of trapping appear difficult to obtain, as shungites are multicomponent systems. In 40Ar- 39Ar stepwise heating, the isotope fractionation effect could cause systematic underestimations of plateau ages, between 0.15 and 0.4% depending on age, or considerably higher if samples contain appreciable atmospheric Ar. The magnitude of this effect is similar to the presently achieved uncertainties of this increasingly

  19. Carbon isotopic fractionations during the Fischer-Tropsch synthesis%费托合成反应中的碳同位素分馏

    Institute of Scientific and Technical Information of China (English)

    倪云燕; 靳永斌

    2011-01-01

    To understand the carbon isotope fractionation during the mineral-catalized Fischer-Traopsch synthesis of hydrocarbons under hydrothermal conditions, experiments on formic acid were carried out under 300 ℃ and 35 MPa using gold tubes in the presence of Fe as a catalyst.The experiments were composed of two groups: with and without water.Due to the limited volume of gold tubes, only methane was available for isotopic analyses among all produced hydrocarbons.The results demonstrate that CO2 is the gas most enriched in 13C whereas methane is the gas most depleted in 13C.Moreover,methane became more and more depleted in 13C with the increase of reaction time.The carbon isotopic fractionation between CO2 and CH4 (α(CO2-CH4)) reached 1.052-1.059 at 144 h, which is similar to those of microbial reduction of CO2 to CH4 by methanogenic bacteria (1.048-1.079).This implies that the carbon isotopic fractionation during the Fischer-Tropsch synthesis is controlled by kinetic isotopic effects.%为了深入研究费托合成反应中的碳同位素分馏,在300℃和35 MPa条件下,以Fe粉为催化剂,利用密闭黄金管对甲酸进行了费托合成实验.实验分为加水和不加水两组.由于金管客积有限,实验中烷烃类产物的碳同位素只测试到甲烷.两组实验都显示,CO2是最富集13C的气体,而甲烷则最贫13C,并且随着反应的进行变得越来越贫13C.在第144 h时CO2与甲烷之间的碳同位素分馏α(CO2-CH4)达到1.052~1.059,与产甲烷菌将CO2还原为CH4过程中所发生的碳同位素分馏(1.048~1.079)相似.实验表明费托合成实验过程受到碳同位素动力学的控制.图4表3参70

  20. Fractionation of Boron Isotopes in Icelandic Hydrothermal Systems

    Energy Technology Data Exchange (ETDEWEB)

    Aggarwal, J.K.; Palmer, M.R.

    1995-01-01

    Boron isotope ratios have been determined in a variety of different geothermal waters from hydrothermal systems across Iceland. Isotope ratios from the high temperature meteoric water recharged systems reflect the isotope ratio of the host rocks without any apparent fractionation. Seawater recharged geothermal systems exhibit more positive {delta}{sup 11}B values than the meteoric water recharged geothermal systems. Water/rock ratios can be assessed from boron isotope ratios in the saline hydrothermal systems. Low temperature hydrothermal systems also exhibit more positive {delta}{sup 11}B than the high temperature systems, indicating fractionation of boron due to adsorption of the lighter isotope onto secondary minerals. Fractionation of boron in carbonate deposits may indicate the level of equilibrium attained within the systems.

  1. Diversity of sulfur isotope fractionations by sulfate-reducing prokaryotes

    DEFF Research Database (Denmark)

    Detmers, Jan; Brüchert, Volker; Habicht, K S;

    2001-01-01

    Batch culture experiments were performed with 32 different sulfate-reducing prokaryotes to explore the diversity in sulfur isotope fractionation during dissimilatory sulfate reduction by pure cultures. The selected strains reflect the phylogenetic and physiologic diversity of presently known....... Sulfate reducers that oxidized the carbon source completely to CO2 showed greater fractionations than sulfate reducers that released acetate as the final product of carbon oxidation. Different metabolic pathways and variable regulation of sulfate transport across the cell membrane all potentially affect...

  2. Experimentally-determined carbon isotope fractionation in and between methane-bearing melt and fluid to upper mantle temperatures and pressures

    Science.gov (United States)

    Mysen, Bjorn

    2016-07-01

    The behavior of melts and fluids is at the core of understanding formation and evolution of the Earth. To advance our understanding of their role, high-pressure/-temperature experiments were employed to determine melt and fluid structure together with carbon isotope partitioning within and between (CH4 +H2O +H2)-saturated aluminosilicate melts and (CH4 +H2O +H2)-fluids. The samples were characterized with vibrational spectroscopy while at temperatures and pressures from 475° to 850 °C and 92 to 1158 MPa, respectively. The solution equilibrium is 2CH4 +Qn = 2 CH3- +H2O +Q n + 1 where the superscript, n, in the Qn-notation describes silicate species where n denotes the number of bridging oxygen. The solution equilibrium affects the carbon isotope fractionation factor between melt and fluid, αmelt/fluid. Moreover, it is significantly temperature-dependent. The αmelt/fluid < 1 with temperatures less than about 1050 °C, and is greater than 1 at higher temperature. Methane-bearing melts can exist in the upper mantle at fO2 ≤fO2 (MW) (Mysen et al., 2011). Reduced (Csbnd H)-species in present-day upper mantle magma, therefore, are likely. During melting and crystallization in this environment, the δ13C of melts increases with temperature at a rate of ∼ 0.6 ‰ /°C. From the simple-system data presented here, at T ≤ 1050°C, melt in equilibrium with a peridotite-(CH4 +H2O +H2)-bearing mantle source will be isotopically lighter than fluid. At higher temperatures, melts will be isotopically heavier. Degassing at T ≤ 1050°C will shift δ13C of degassed magma to more positive values, whereas degassing at T ≥ 1050°C, will reduce the δ13C of the degassed magma.

  3. Copper isotope fractionation by desert shrubs

    Energy Technology Data Exchange (ETDEWEB)

    Navarrete, Jesica U., E-mail: jnavarrete2@miners.utep.edu [University of Texas at El Paso, Department of Geological Sciences, 500 W. University Ave, El Paso, TX 79968 (United States); Viveros, Marian; Ellzey, Joanne T. [University of Texas at El Paso, Department of Biological Sciences, El Paso, TX 79968 (United States); Borrok, David M. [University of Texas at El Paso, Department of Geological Sciences, 500 W. University Ave, El Paso, TX 79968 (United States)

    2011-06-15

    Copper has two naturally occurring stable isotopes of masses 63 and 65 which can undergo mass dependent fractionation during various biotic and abiotic chemical reactions. These interactions and their resulting Cu isotope fractionations can be used to determine the mechanisms involved in the cycling of Cu in natural systems. In this study, Cu isotope changes were investigated at the organismal level in the metal-accumulating desert plant, Prosopis pubescens. Initial results suggest that the lighter Cu isotope was preferentially incorporated into the leaves of the plant, which may suggest that Cu was actively transported via intracellular proteins. The roots and stems show a smaller degree of Cu isotope fractionation and the direction and magnitude of the fractionations was dependent upon the levels of Cu exposure. Based on this and previous work with bacteria and yeast, a trend is emerging that suggests the lighter Cu isotope is preferentially incorporated into biological components, while the heavier Cu isotope tends to become enriched in aqueous solutions. In bacteria, plants and animals, intracellular Cu concentrations are strictly regulated via dozens of enzymes that can bind, transport, and store Cu. Many of these enzymes reduce Cu(II) to Cu(I). These initial results seem to fit into a broader picture of Cu isotope cycling in natural systems where oxidation/reduction reactions are fundamental in controlling the distributions of Cu isotopes.

  4. Stable carbon isotope fractionation during bacterial acetylene fermentation: Potential for life detection in hydrocarbon-rich volatiles of icy planet(oid)s

    Science.gov (United States)

    Miller, Laurence; Baesman, Shaun; Oremland, Ron

    2015-01-01

    We report the first study of stable carbon isotope fractionation during microbial fermentation of acetylene (C2H2) in sediments, sediment enrichments, and bacterial cultures. Kinetic isotope effects (KIEs) averaged 3.7 ± 0.5‰ for slurries prepared with sediment collected at an intertidal mudflat in San Francisco Bay and 2.7 ± 0.2‰ for a pure culture of Pelobacter sp. isolated from these sediments. A similar KIE of 1.8 ± 0.7‰ was obtained for methanogenic enrichments derived from sediment collected at freshwater Searsville Lake, California. However, C2H2 uptake by a highly enriched mixed culture (strain SV7) obtained from Searsville Lake sediments resulted in a larger KIE of 9.0 ± 0.7‰. These are modest KIEs when compared with fractionation observed during oxidation of C1 compounds such as methane and methyl halides but are comparable to results obtained with other C2compounds. These observations may be useful in distinguishing biologically active processes operating at distant locales in the Solar System where C2H2 is present. These locales include the surface of Saturn's largest moon Titan and the vaporous water- and hydrocarbon-rich jets emanating from Enceladus.

  5. Silicon isotope fractionation during magmatic differentiation

    Science.gov (United States)

    Savage, Paul S.; Georg, R. Bastian; Williams, Helen M.; Burton, Kevin W.; Halliday, Alex N.

    2011-10-01

    The Si isotopic composition of Earth's mantle is thought to be homogeneous (δ 30Si = -0.29 ± 0.08‰, 2 s.d.) and not greatly affected by partial melting and recycling. Previous analyses of evolved igneous material indicate that such rocks are isotopically heavy relative to the mantle. To understand this variation, it is necessary to investigate the degree of Si isotopic fractionation that takes place during magmatic differentiation. Here we report Si isotopic compositions of lavas from Hekla volcano, Iceland, which has formed in a region devoid of old, geochemically diverse crust. We show that Si isotopic composition varies linearly as a function of silica content, with more differentiated rocks possessing heavier isotopic compositions. Data for samples from the Afar Rift Zone, as well as various igneous USGS standards are collinear with the Hekla trend, providing evidence of a fundamental relationship between magmatic differentiation and Si isotopes. The effect of fractionation has been tested by studying cumulates from the Skaergaard Complex, which show that olivine and pyroxene are isotopically light, and plagioclase heavy, relative to the Si isotopic composition of the Earth's mantle. Therefore, Si isotopes can be utilised to model the competing effects of mafic and felsic mineral fractionation in evolving silicate liquids and cumulates. At an average SiO 2 content of ˜60 wt.%, the predicted δ 30Si value of the continental crust that should result from magmatic fractionation alone is -0.23 ± 0.05‰ (2 s.e.), barely heavier than the mantle. This is, at most, a maximum estimate, as this does not take into account weathered material whose formation drives the products toward lighter δ 30Si values. Mass balance calculations suggest that removal of continental crust of this composition from the upper mantle will not affect the Si isotopic composition of the mantle.

  6. Uranium isotope fractionation during coprecipitation with aragonite and calcite

    Science.gov (United States)

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

    2016-09-01

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

  7. The use of alkaline hydrolysis as a novel strategy for chloroform remediation: the feasibility of using construction wastes and evaluation of carbon isotopic fractionation.

    Science.gov (United States)

    Torrentó, Clara; Audí-Miró, Carme; Bordeleau, Geneviève; Marchesi, Massimo; Rosell, Mònica; Otero, Neus; Soler, Albert

    2014-01-01

    Laboratory and field-scale pilot experiments were performed to evaluate the feasibility of chloroform degradation by alkaline hydrolysis and the potential of δ(13)C values to assess this induced reaction process at contaminated sites. In batch experiments, alkaline conditions were induced by adding crushed concrete (pH 12.33 ± 0.07), a filtered concrete solution (pH 12.27 ± 0.04), a filtered cement solution (pH 12.66 ± 0.02) and a pH 12 buffer solution (pH 11.92 ± 0.11). The resulting chloroform degradation after 28 days was 94, 96, 99, and 72%, respectively. The experimental data were described using a pseudo-first-order kinetic model, resulting in pseudo-first-order rate constant values of 0.10, 0.12, 0.20, and 0.05 d(-1), respectively. Furthermore, the significant chloroform carbon isotopic fractionation associated with alkaline hydrolysis of chloroform (-53 ± 3‰) and its independence from pH in the admittedly limited tested pH range imply a great potential for the use of δ(13)C values for in situ monitoring of the efficacy of remediation approaches based on alkaline hydrolysis. The carbon isotopic fractionation obtained at the lab scale allowed the calculation of the percentage of chloroform degradation in field-scale pilot experiments where alkaline conditions were induced in two recharge water interception trenches filled with concrete-based construction wastes. A maximum of approximately 30-40% of chloroform degradation was achieved during the two studied recharge periods. Although further research is required, the treatment of chloroform in groundwater through the use of concrete-based construction wastes is proposed. This strategy would also imply the recycling of construction and demolition wastes for use in value-added applications to increase economic and environmental benefits.

  8. [Distribution characteristics of soil humus fractions stable carbon isotope natural abundance (delta 13C) in paddy field under long-term ridge culture].

    Science.gov (United States)

    Tang, Xiao-hong; Luo, You-jin; Ren, Zhen-jiang; Lü, Jia-ke; Wei, Chao-fu

    2011-04-01

    A 16-year field experiment was conducted in a ridge culture paddy field in the hilly region of Sichuan Basin, aimed to investigate the distribution characteristics of stable carbon isotope natural abundance (delta 13C) in soil humus fractions. The soil organic carbon (SOC) content in the paddy field under different cultivation modes ranked in the order of wide ridge culture > ridge culture > paddy and upland rotation. In soil humus substances (HS), humin (HU) was the main composition, occupying 21% - 30% of the total SOC. In the extracted soil carbon, humic acid (HA) dominated, occupying 17% - 21% of SOC and 38% - 65% of HS. The delta 13C value of SOC ranged from -27.9 per thousand to -25.6 per thousand, and the difference of the delta 13C value between 0-5 cm and 20-40 cm soil layers was about 1.9 per thousand. The delta 13C value of HA under different cultivation modes was 1 per thousand - 2 per thousand lower than that of SOC, and more approached to the delta 13C value of rapeseed and rice residues. As for fulvic acid (FA), its delta 13C value was about 2 per thousand and 4 per thousand higher than that of SOC and HA, respectively. The delta 13C value of HU in plough layer (0-20 cm) and plow layer (20-40 cm) ranged from -23.7 per thousand - -24.9 per thousand and -22.6 per thousand - -24.2 per thousand, respectively, reflecting the admixture of young and old HS. The delta 13C value in various organic carbon fractions was HU>FA>SOC>rapeseed and rice residues>HA. Long-term rice planting benefited the increase of SOC content, and cultivation mode played an important role in affecting the distribution patterns of soil humus delta 13C in plough layer and plow layer.

  9. Microscale reservoir effects on microbial sulfur isotope fractionation

    Science.gov (United States)

    Louca, Stilianos; Crowe, Sean A.

    2017-04-01

    Microbial sulfate reduction can impart strong sulfur isotope fractionation by preferentially using the lighter 32SO42- over the heavier 34SO42-. The magnitude of fractionation depends on a number of factors, including ambient concentrations of sulfate and electron donors. Sulfur isotope compositions in sedimentary rocks thus facilitate reconstruction of past environmental conditions, such as seawater sulfate concentrations, primary productivity, organic carbon burial, and sulfur fluxes into or out of the ocean. Knowing the processes that regulate the magnitude of sulfur isotope fractionation is necessary for the correct interpretation of the geological record, but so far theoretical work has focused mostly on internal cellular processes. In sulfate-limited environments, like low sulfate lakes and the Archean ocean, microbial sulfate reduction can lead to sulfate depletion in the water column and an enrichment in isotopically heavy sulfate. This reservoir effect in turn mutes the fractionation expressed in the water column and ultimately preserved in sediments relative to the biologically induced fractionation. Here we use mathematical modeling to show that similar reservoir effects can also appear at the microscale in close proximity to sulfate-reducing cells. These microscale reservoir effects have the potential to modulate sulfur isotope fractionation to a considerable degree, especially at low (micromolar) sulfate concentrations. As a result, background sulfate concentrations, sulfate reduction rates, and extracellular ion diffusion rates can influence the fractionation expressed even if the physiologically induced fractionation is constant. This has implications for the interpretation of biogenic sulfur isotope fractionations expressed in the geological record, because the correct estimation of the environmental conditions that would promote these fractionations requires consideration of microscale reservoir effects. We discuss these implications, and

  10. A kinetic analysis of leaf uptake of COS and its relation to transpiration, photosynthesis and carbon isotope fractionation

    Directory of Open Access Journals (Sweden)

    U. Seibt

    2009-09-01

    Full Text Available Carbonyl sulfide (COS is an atmospheric trace gas that holds great promise for studies of terrestrial carbon and water exchange. In leaves, COS follows the same pathway as CO2 during photosynthesis. Both gases are taken up in enzyme reactions, making COS and CO2 uptake closely coupled at the leaf scale. The biological background of leaf COS uptake is a hydrolysis reaction catalyzed by the enzyme carbonic anhydrase. Based on this, we derive and test a simple kinetic model of leaf COS uptake, and relate COS to CO2 and water fluxes at the leaf scale. The equation was found to predict realistic COS fluxes compared to observations from field and laboratory chambers. We confirm that COS uptake at the leaf level is directly linked to stomatal conductance. As a consequence, the ratio of deposition velocities (uptake rate divided by ambient mole fraction for leaf COS and CO2 fluxes can provide an estimate of Ci/Ca the ratio of intercellular to atmospheric CO2, an important plant gas exchange parameter that cannot be measured directly. The majority of published deposition velocity ratios for leaf studies on a variety of species fall in the range of 1.5 to 4, corresponding to Ci/Ca ratios of 0.5 to 0.8. In addition, we utilize the coupling of Ci/Ca and photosynthetic ˆ13C discrimination to derive an estimate of 2.8±0.3 for the global mean ratio of deposition velocities. This corresponds to a global vegetation sink of COS in the order of 900±100 Gg S yr−1. COS can now be implemented in the same model framework as CO2 and water vapour. Atmospheric COS measurements can then provide independent constraints on CO2 and water cycles at ecosystem, regional and global scales.

  11. Chromium stable isotope fractionation in modern biogeochemical cycling

    DEFF Research Database (Denmark)

    Paulukat, Cora Stefanie

    oxygen in the Earth’s atmosphere. Oxidative rock weathering on land induces oxidation of immobile Cr(III) to mobile Cr(VI). Isotopically relatively heavy Cr(VI) is released to runoff, and transported by rivers to the oceans, where it is incorporated into chemical sediments and carbonate shells...... laterite soils from India, formed on ultramafic rocks, indicates extensive leaching of isotopically heavy Cr(VI). Transferring this knowledge to ancient weathering profiles, negatively fractionated Cr is clear evidence for the presence of free oxygen in the atmosphere. The second part demonstrates...... that the positively fractionated Cr from the catchment area is preserved during its riverine transport to the sea. A global compilation of surface seawater Cr-isotope compositions shows a heterogeneous Cr-isotope distribution in the oceans, indicating that the signal is influenced by local factors as reduction...

  12. The non-mass-dependent oxygen isotope effect in the electrodissociation of carbon dioxide - A step toward understanding NoMaD chemistry. [fractionations in meteorites

    Science.gov (United States)

    Heidenreich, J. E., III; Thiemens, M. H.

    1985-01-01

    A non-mass dependent (NoMaD) oxygen isotope effect is demonstrated in the dissociation of CO2 similar to that observed in the electrosynthesis of ozone. The molecular oxygen produced carries the signature of two separate isotopic fractionation processes; a mass-dependent fractionation probably due to CO2 + O isotopic exchange, and a secondary NoMaD fractionation (delta O-17 = 0.97 + or - 0.09 delta O-18, with the O2 depleted in O-17 and O-18). It is suggested that the effect is due to either the formation or relaxation of ozone in an excited electronic state. This represents the latest advance in the understanding of chemical NoMaD effects which may be essential to the explanation of non-mass-dependent fractionations observed in meteorites.

  13. Carbon Isotope Fractionation in Reactions of 1,2-Dibromoethane with FeS and Hydrogen Sulfide

    Science.gov (United States)

    EDB (1,2-dibromoethane) is frequently detected at sites impacted by leaded gasoline. In reducing environments, EDB is highly susceptible to abiotic degradation. A study was conducted to evaluate the potential of compound-specific isotope analysis (CSIA) in assessing abiotic degr...

  14. Iron isotopic fractionation during continental weathering

    Energy Technology Data Exchange (ETDEWEB)

    Fantle, Matthew S.; DePaolo, Donald J.

    2003-10-01

    The biological activity on continents and the oxygen content of the atmosphere determine the chemical pathways through which Fe is processed at the Earth's surface. Experiments have shown that the relevant chemical pathways fractionate Fe isotopes. Measurements of soils, streams, and deep-sea clay indicate that the {sup 56}Fe/{sup 54}Fe ratio ({delta}{sup 56}Fe relative to igneous rocks) varies from +1{per_thousand} for weathering residues like soils and clays, to -3{per_thousand} for dissolved Fe in streams. These measurements confirm that weathering processes produce substantial fractionation of Fe isotopes in the modern oxidizing Earth surface environment. The results imply that biologically-mediated processes, which preferentially mobilize light Fe isotopes, are critical to Fe chemistry in weathering environments, and that the {delta}{sup 56}Fe of marine dissolved Fe should be variable and negative. Diagenetic reduction of Fe in marine sediments may also be a significant component of the global Fe isotope cycle. Iron isotopes provide a tracer for the influence of biological activity and oxygen in weathering processes through Earth history. Iron isotopic fractionation during weathering may have been smaller or absent in an oxygen-poor environment such as that of the early Precambrian Earth.

  15. Isotopic Fractionation of Selenium Oxyanions in Wetlands

    Science.gov (United States)

    Clark, S. K.; Johnson, T. M.

    2004-05-01

    As oxic surface waters pass through aquatic macrophytes and over anoxic sediments in wetlands and lakes, the dissolved Se load often decreases; and, Se isotope ratio measurements can provide information about the mechanisms involved. Previous work on microbially induced isotopic fractionation of Se oxyanions under nearly natural conditions using wetland sediments shows consistent Se isotopic shifts during reduction of Se(VI) and Se(IV) to insoluble Se(0). However, previous isotopic studies of total dissolved selenium in wetlands found little to no isotopic shift as dissolved selenium concentrations decreased. This suggests that plant/algal uptake, followed by deposition and degradation, is the primary route of Se transfer into sediments. However, it is possible that the effective isotopic fractionation between Se in the surface water and Se deposited into sediments is somehow much less than the fractionation induced by the reduction reaction, or that cycling of organically bound Se is involved. In this study, we report Se isotope data for Se(VI), Se(IV) and total dissolved Se, Se(T), in surface waters from three wetland/lake sites: Sweitzer Lake, CO; 33-Mile Reservoir, WY; and, a small pond adjacent to Benton Lake, MT. We isolated Se(IV) via hydride generation, and Se(VI) via ion exchange. Se(T), including any organic components, was also analyzed. Isotope analysis was performed on an Isoprobe MC-ICPMS, using a method modified from that of Rouxel et al. (2002). We used the 82Se + 74Se double spike approach, and spiked samples before species separation. Our results for all three locations indicate similar trends in concentration changes and isotopic shifts between the inflow and outflow waters. Se(T) concentrations decrease by 45-70%, and Se(VI) concentrations decrease by 60-90%, whereas Se(IV) concentrations increase by 60-150%. Concomitant 80Se/76Se shifts are +0.5-0.8‰ for Se(T); -0.1-0.5‰ for Se(VI); and +0.4-6.5‰ for Se(IV). These data provide greater

  16. Chromium isotope uptake in carbonates

    DEFF Research Database (Denmark)

    Rodler, Alexandra

    composition of contemporaneous seawater. Marine carbonates are ubiquitous throughout Earth’s rock record rendering them a particularly interesting archive for constraining past changes in ocean chemistry. This thesis includes an investigation of the fractionation behavior of Cr isotopesduring coprecipitation......Chromium (Cr) is a redox sensitive element potentially capable of tracing fine-scale fluctuations of the oxygenation of Earth’s early surface environments and seawater. The Cr isotope composition of carbonates could perhaps be used as paleo-redox proxy to elucidate changes in the geological past...... related to the rise of oxygen and the evolution of the biosphere. However, before the Cr isotopesystem can be applied to faithfully delineate paleo-environmental changes, careful assessment of the signal robustness and a thorough understanding of the Cr cycle in Earth system processes is necessary...

  17. Carbon-Isotope Composition of Biochemical Fractions and the Regulation of Carbon Balance in Leaves of the C3-Crassulacean Acid Metabolism Intermediate Clusia minor L. Growing in Trinidad.

    Science.gov (United States)

    Borland, A. M.; Griffiths, H.; Broadmeadow, MSJ.; Fordham, M. C.; Maxwell, C.

    1994-10-01

    Carbon-isotope ratios ([delta]13Cs) were measured for various bio-chemical fractions quantitatively extracted from naturally exposed and shaded leaves of the C3-Crassulacean acid metabolism (CAM) intermediate Clusia minor, sampled at dawn and dusk on days during the wet and dry seasons in Trinidad. As the activity of CAM increased in response to decreased availability of water and higher photon flux density, organic acids and soluble sugars were enriched in 13C by approximately 3.5 to 4%[per mille (thousand) sign] compared to plants sampled during the wet season. The induction of CAM was accompanied by a doubling in size of the reserve carbohydrate pools. Moreover, stoichiometric measurements indicated that degradation of both chloroplastic reserves and soluble sugars were necessary to supply phosphoenolpyruvate for the synthesis of organic acids at night. Results also suggest that two pools of soluble sugars exist in leaves of C. minor that perform CAM, one a vacuolar pool enriched in 13C and the second a transport pool depleted in 13C. Estimates of carbon-isotope discrimination expressed during CAM, derived from the trafficking among inorganic carbon, organic acids, and carbohydrate pools overnight, ranged from 0.9 to 3.1%[per mille (thousand) sign]. The [delta]13C of structural material did not change significantly between wet and dry seasons, indicating that most of the carbon used in growth was derived from C3 carboxylation.

  18. OXYGEN ISOTOPE FRACTION ATION IN URANIUM OXIDES

    Institute of Scientific and Technical Information of China (English)

    郑永飞

    1995-01-01

    Thermodynamic oxygen isotope factors for uranium oxides have been calculated by means of the modified increment method.The sequence of 18O-enrichment in the uranium oxides with respect to the common rock-forming minerals is predicted as follows:spinelfractionation factors between the uranium oxides and water and between the uranium oxides and the other minerals have been obtained for 0-1200℃.The theoretical results are applicable to the isotopic geothermometry of uranium ores when pairing with other gangue minerals in hydrothermal uranium deposits.

  19. Insights Into the Recent Rise in Atmospheric Methane Inferred from Observed Mole Fractions and Stable Carbon Isotopes

    Science.gov (United States)

    White, J. W. C.; Michel, S. E.; Tans, P. P.; Vaughn, B. H.; Dlugokencky, E. J.; Sherwood, O.; Miller, J. B.; Masarie, K. A.

    2015-12-01

    Methane is a troublesome greenhouse gas. It has multiple natural and anthropogenic sources, including microbial production in low oxygen environments, fossil sources related to coal and natural gas production, and biomass burning, making source attribution difficult. Atmospheric methane concentration rose rapidly in the industrial period, increasing by 250%, only to stall out in the first decade this century, and then rising again after 2007. Its emission is strongly related to variables that are hard to predict, such as precipitation rates, biomass burning, and natural gas use, so future projections remain murky. And unlike CO2, which is strongly tied to energy use, anthropogenic impacts on methane are strongly tied to food production. Finally, methane is expected to be released from a thawing Arctic in large, but largely unknown quantities. Understanding methane as a greenhouse gas is imperative if anthropogenic impacts on the climate system are to be managed in the future. This talk addresses what we can say about the recent rise in methane using mole fractions and 13C data from the existing NOAA Cooperative Global Air Sampling Network. The approach is strongly data based, and while we will present model results, the data itself are clear on several points. While attention is increasingly focused on the Arctic, the north-south gradient of CH4 concentration does not support significant changes to Boreal and Arctic emissions. This finding raises the question of how methane will behave in a warmer, wetter world. We use a simple, three end-member model, run in both forward and inverse modes, to look more deeply into the sources of the recent increase. Evidence exists for recent increases in fossil sources, in line with methane production as a fuel source, although the contribution is small. Better data are needed to constrain the 13C of sources, including the fossil sources, a problem we are working on. Importantly, while the current monitoring network is adequate

  20. Copper isotope fractionation between aqueous compounds relevant to low temperature geochemistry and biology

    Science.gov (United States)

    Fujii, Toshiyuki; Moynier, Frédéric; Abe, Minori; Nemoto, Keisuke; Albarède, Francis

    2013-06-01

    Isotope fractionation between the common Cu species present in solution (Cu+, Cu2+, hydroxide, chloride, sulfide, carbonate, oxalate, and ascorbate) has been investigated using both ab initio methods and experimental solvent extraction techniques. In order to establish unambiguously the existence of equilibrium isotope fractionation (as opposed to kinetic isotope fractionation), we first performed laboratory-scale liquid-liquid distribution experiments. Upon exchange between HCl medium and a macrocyclic complex, the 65Cu/63Cu ratio fractionated by -1.06‰ to -0.39‰. The acidity dependence of the fractionation was appropriately explained by ligand exchange reactions between hydrated H2O and Cl- via intramolecular vibrations. The magnitude of the Cu isotope fractionation among important Cu ligands was also estimated by ab initio methods. The magnitude of the nuclear field shift effect to the Cu isotope fractionation represents only ˜3% of the mass-dependent fractionation. The theoretical estimation was expanded to chlorides, hydroxides, sulfides, sulfates, and carbonates under different conditions of pH. Copper isotope fractionation of up to 2‰ is expected for different forms of Cu present in seawater and for different sediments (carbonates, hydroxides, and sulfides). We found that Cu in dissolved carbonates and sulfates is isotopically much heavier (+0.6‰) than free Cu. Isotope fractionation of Cu in hydroxide is minimal. The relevance of these new results to the understanding of metabolic processes was also discussed. Copper is an essential element used by a large number of proteins for electron transfer. Further theoretical estimates of δ65Cu in hydrated Cu(I) and Cu(II) ions, Cu(II) ascorbates, and Cu(II) oxalate predict Cu isotope fractionation during the breakdown of ascorbate into oxalate and account for the isotopically heavy Cu found in animal kidneys.

  1. The Precise Radio Observation of the 13C Isotopic Fractionation for Carbon Chain Molecule HC3N in the Low-Mass Star Forming Region L1527

    Science.gov (United States)

    Araki, Mitsunori; Takano, Shuro; Sakai, Nami; Yamamoto, Satoshi; Oyama, Takahiro; Kuze, Nobuhiko; Tsukiyama, Koichi

    2016-06-01

    We observed the three 13C isotopic species of HC3N with the high signal-to-noise ratios in L1527 using Green Bank 100 m telescope and Nobeyama 45 m telescope to explore the production scheme of HC3N, where L1527 is the low-mass star forming region in the phase of a warm carbon chain chemistry region. The spectral lines of the J = 5--4, 9--8, 10--9, and 12--11 transitions in the 44-109 GHz region were used to measure isotopic ratios. The abundance of HCCCN was determined from the line intensities of the two weak hyperfine components of the J = 5-4 transition. The isotopic ratios were precisely determined to be 1.00 : 1.01 : 1.35 : 86.4 for [H13CCCN] : [HC13CCN] : [HCC13CN] : [HCCCN]. It was found that the abundance of H13CCCN is equal to that of HC13CCN, and it was implied that HC3N is mainly formed by the reaction schemes via C2H2 and C2H2+ in L1527. This would suggest a universality of dicarbide chemistry producing HC3N irrespective of evolutional phases from a starless dark cloud to a warm carbon chain chemistry region. Sakai, N., Sakai, T., Hirota, T., & Yamamoto, S. 2008, ApJ, 672, 371 Takano, S., Masuda, A., Hirahara, Y., et al. 1998, A&A, 329, 1156

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

    Science.gov (United States)

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

    2008-12-01

    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

  3. Isotopic Fractionation in Comets: Quantifying the Contribution of Interstellar Chemistry

    Science.gov (United States)

    Charnley, Steven

    2010-01-01

    Anomalously fractionated isotopic material is found in many primitive Solar System objects, such as meteorites and comets. It is thought, in some cases, to trace interstellar matter that was incorporated into the Solar Nebula without undergoing significant processing. We will present the results of models of the nitrogen, oxygen, and carbon fractionation chemistry in dense molecular clouds, particularly in cares where substantial freeze-taut of molecules on to dust has occurred. The range of fractionation ratios expected in different interstellar molecules will be discussed and compared to the ratios measured in molecular clouds, comets and meteoritic material. These models make several predictions that can be tested in the near future by molecular line observations, particularly with the GBT.

  4. Fundamental studies on kinetic isotope effect (KIE) of hydrogen isotope fractionation in natural gas systems

    Science.gov (United States)

    Ni, Yunyan; Ma, Qisheng; Ellis, Geoffrey S.; Dai, Jinxing; Katz, Barry; Zhang, Shuichang; Tang, Yongchun

    2011-05-01

    Based on quantum chemistry calculations for normal octane homolytic cracking, a kinetic hydrogen isotope fractionation model for methane, ethane, and propane formation is proposed. The activation energy differences between D-substitute and non-substituted methane, ethane, and propane are 318.6, 281.7, and 280.2 cal/mol, respectively. In order to determine the effect of the entropy contribution for hydrogen isotopic substitution, a transition state for ethane bond rupture was determined based on density function theory (DFT) calculations. The kinetic isotope effect (KIE) associated with bond rupture in D and H substituted ethane results in a frequency factor ratio of 1.07. Based on the proposed mathematical model of hydrogen isotope fractionation, one can potentially quantify natural gas thermal maturity from measured hydrogen isotope values. Calculated gas maturity values determined by the proposed mathematical model using δD values in ethane from several basins in the world are in close agreement with similar predictions based on the δ 13C composition of ethane. However, gas maturity values calculated from field data of methane and propane using both hydrogen and carbon kinetic isotopic models do not agree as closely. It is possible that δD values in methane may be affected by microbial mixing and that propane values might be more susceptible to hydrogen exchange with water or to analytical errors. Although the model used in this study is quite preliminary, the results demonstrate that kinetic isotope fractionation effects in hydrogen may be useful in quantitative models of natural gas generation, and that δD values in ethane might be more suitable for modeling than comparable values in methane and propane.

  5. Fundamental studies on kinetic isotope effect (KIE) of hydrogen isotope fractionation in natural gas systems

    Science.gov (United States)

    Ni, Y.; Ma, Q.; Ellis, G.S.; Dai, J.; Katz, B.; Zhang, S.; Tang, Y.

    2011-01-01

    Based on quantum chemistry calculations for normal octane homolytic cracking, a kinetic hydrogen isotope fractionation model for methane, ethane, and propane formation is proposed. The activation energy differences between D-substitute and non-substituted methane, ethane, and propane are 318.6, 281.7, and 280.2cal/mol, respectively. In order to determine the effect of the entropy contribution for hydrogen isotopic substitution, a transition state for ethane bond rupture was determined based on density function theory (DFT) calculations. The kinetic isotope effect (KIE) associated with bond rupture in D and H substituted ethane results in a frequency factor ratio of 1.07. Based on the proposed mathematical model of hydrogen isotope fractionation, one can potentially quantify natural gas thermal maturity from measured hydrogen isotope values. Calculated gas maturity values determined by the proposed mathematical model using ??D values in ethane from several basins in the world are in close agreement with similar predictions based on the ??13C composition of ethane. However, gas maturity values calculated from field data of methane and propane using both hydrogen and carbon kinetic isotopic models do not agree as closely. It is possible that ??D values in methane may be affected by microbial mixing and that propane values might be more susceptible to hydrogen exchange with water or to analytical errors. Although the model used in this study is quite preliminary, the results demonstrate that kinetic isotope fractionation effects in hydrogen may be useful in quantitative models of natural gas generation, and that ??D values in ethane might be more suitable for modeling than comparable values in methane and propane. ?? 2011 Elsevier Ltd.

  6. Variation in oxygen isotope fractionation during cellulose synthesis: intramolecular and biosynthetic effects.

    Science.gov (United States)

    Sternberg, Leonel; Pinzon, Maria Camila; Anderson, William T; Jahren, A Hope

    2006-10-01

    The oxygen isotopic composition of plant cellulose is commonly used for the interpretations of climate, ecophysiology and dendrochronology in both modern and palaeoenvironments. Further applications of this analytical tool depends on our in-depth knowledge of the isotopic fractionations associated with the biochemical pathways leading to cellulose. Here, we test two important assumptions regarding isotopic effects resulting from the location of oxygen in the carbohydrate moiety and the biosynthetic pathway towards cellulose synthesis. We show that the oxygen isotopic fractionation of the oxygen attached to carbon 2 of the glucose moieties differs from the average fractionation of the oxygens attached to carbons 3-6 from cellulose by at least 9%, for cellulose synthesized within seedlings of two different species (Triticum aestivum L. and Ricinus communis L.). The fractionation for a given oxygen in cellulose synthesized by the Triticum seedlings, which have starch as their primary carbon source, is different than the corresponding fractionation in Ricinus seedlings, within which lipids are the primary carbon source. This observation shows that the biosynthetic pathway towards cellulose affects oxygen isotope partitioning, a fact heretofore undemonstrated. Our findings may explain the species-dependent variability in the overall oxygen isotope fractionation during cellulose synthesis, and may provide much-needed insight for palaeoclimate reconstruction using fossil cellulose.

  7. Experimental, in-situ carbon solution mechanisms and isotope fractionation in and between (C-O-H)-saturated silicate melt and silicate-saturated (C-O-H) fluid to upper mantle temperatures and pressures

    Science.gov (United States)

    Mysen, Bjorn

    2017-02-01

    Our understanding of materials transport processes in the Earth relies on characterizing the behavior of fluid and melt in silicate-(C-O-H) systems at high temperature and pressure. Here, Raman spectroscopy was employed to determine structure of and carbon isotope partitioning between melts and fluids in alkali aluminosilicate-C-O-H systems. The experimental data were recorded in-situ while the samples were at equilibrium in a hydrothermal diamond anvil cell at temperatures and pressures to 825 °C and >1300 MPa, respectively. The carbon solution equilibrium in both (C-O-H)-saturated melt and coexisting, silicate-saturated (C-O-H) fluid is 2CO3 + H2O + 2Qn + 1 = 2HCO3 + 2Qn. In the Qn-notation, the superscript, n, is the number of bridging oxygen in silicate structural units. At least one oxygen in CO3 and HCO3 groups likely is shared with silicate tetrahedra. The structural behavior of volatile components described with this equilibrium governs carbon isotope fractionation factors between melt and fluid. For example, the ΔH equals 3.2 ± 0.7 kJ/mol for the bulk 13C/12C exchange equilibrium between fluid and melt. From these experimental data, it is suggested that at deep crustal and upper mantle temperatures and pressures, the δ13C-differences between coexisting silicate-saturated (C-O-H) fluid and (C-O-H)-saturated silicate melts may change by more than 100‰ as a function of temperature in the range of magmatic processes. Absent information on temperature and pressure, the use of carbon isotopes of mantle-derived magma to derive isotopic composition of magma source regions in the Earth's interior, therefore, should be exercised with care.

  8. Carbon isotopic composition of individual Precambrian microfossils.

    Science.gov (United States)

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

    2000-08-01

    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.

  9. Carbon isotopic composition of individual Precambrian microfossils

    Science.gov (United States)

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

    2000-01-01

    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.

  10. Molybdenum isotope fractionation in the mantle

    Science.gov (United States)

    Liang, Yu-Hsuan; Halliday, Alex N.; Siebert, Chris; Fitton, J. Godfrey; Burton, Kevin W.; Wang, Kuo-Lung; Harvey, Jason

    2017-02-01

    We report double-spike molybdenum (Mo) isotope data for forty-two mafic and fifteen ultramafic rocks from diverse locations and compare these with results for five chondrites. The δ98/95Mo values (normalized to NIST SRM 3134) range from -0.59 ± 0.04 to +0.10 ± 0.08‰. The compositions of one carbonaceous (CI) and four ordinary chondrites are relatively uniform (-0.14 ± 0.01‰, 95% ci (confidence interval)) in excellent agreement with previous data. These values are just resolvable from the mean of 10 mid-ocean ridge basalts (MORBs) (0.00 ± 0.02‰, 95% ci). The compositions of 13 mantle-derived ultramafic xenoliths from Kilbourne Hole, Tariat and Vitim are more diverse (-0.39 to -0.07‰) with a mean of -0.22 ± 0.06‰ (95% ci). On this basis, the isotopic composition of the bulk silicate Earth (BSE or Primitive Mantle) is within error identical to chondrites. The mean Mo concentration of the ultramafic xenoliths (0.19 ± 0.07 ppm, 95% ci) is similar in magnitude to that of MORB (0.48 ± 0.13 ppm, 95% ci), providing evidence, either for a more compatible behaviour than previously thought or for selective Mo enrichment of the subcontinental lithospheric mantle. Intraplate and ocean island basalts (OIBs) display significant isotopic variability within a single locality from MORB-like to strongly negative (-0.59 ± 0.04‰). The most extreme values measured are for nephelinites from the Cameroon Line and Trinidade, which also have anomalously high Ce/Pb and low Mo/Ce relative to normal oceanic basalts. δ98/95Mo correlates negatively with Ce/Pb and U/Pb, and positively with Mo/Ce, explicable if a phase such as an oxide or a sulphide liquid selectively retains isotopically heavy Mo in the mantle and fractionates its isotopic composition in low degree partial melts. If residual phases retain Mo during partial melting, it is possible that the [Mo] for the BSE may be misrepresented by values estimated from basalts. This would be consistent with the high Mo

  11. Clumped-isotope thermometry of magnesium carbonates in ultramafic rocks

    Science.gov (United States)

    García del Real, Pablo; Maher, Kate; Kluge, Tobias; Bird, Dennis K.; Brown, Gordon E.; John, Cédric M.

    2016-11-01

    Magnesium carbonate minerals produced by reaction of H2O-CO2 with ultramafic rocks occur in a wide range of paragenetic and tectonic settings and can thus provide insights into a variety of geologic processes, including (1) deposition of ore-grade, massive-vein cryptocrystalline magnesite; (2) formation of hydrous magnesium carbonates in weathering environments; and (3) metamorphic carbonate alteration of ultramafic rocks. However, the application of traditional geochemical and isotopic methods to infer temperatures of mineralization, the nature of mineralizing fluids, and the mechanisms controlling the transformation of dissolved CO2 into magnesium carbonates in these settings is difficult because the fluids are usually not preserved. Clumped-isotope compositions of magnesium carbonates provide a means to determine primary mineralization or (re)equilibration temperature, which permits the reconstruction of geologic processes that govern magnesium carbonate formation. We first provide an evaluation of the acid fractionation correction for magnesium carbonates using synthetic magnesite and hydromagnesite, along with natural metamorphic magnesite and low-temperature hydromagnesite precipitated within a mine adit. We show that the acid fractionation correction for magnesium carbonates is virtually indistinguishable from other carbonate acid fractionation corrections given current mass spectrometer resolution and error. In addition, we employ carbonate clumped-isotope thermometry on natural magnesium carbonates from various geologic environments and tectonic settings. Cryptocrystalline magnesite vein deposits from California (Red Mountain magnesite mine), Austria (Kraubath locality), Turkey (Tutluca mine, Eskişehir district) and Iran (Derakht-Senjed deposit) exhibit broadly uniform Δ47 compositions that yield apparent clumped-isotope temperatures that average 23.7 ± 5.0 °C. Based on oxygen isotope thermometry, these clumped-isotope temperatures suggest

  12. Uranium Isotope Fractionation during Adsorption, (Co)precipitation, and Biotic Reduction.

    Science.gov (United States)

    Dang, Duc Huy; Novotnik, Breda; Wang, Wei; Georg, R Bastian; Evans, R Douglas

    2016-12-06

    Uranium contamination of surface environments is a problem associated with both U-ore extraction/processing and situations in which groundwater comes into contact with geological formations high in uranium. Apart from the environmental concerns about U contamination, its accumulation and isotope composition have been used in marine sediments as a paleoproxy of the Earth's oxygenation history. Understanding U isotope geochemistry is then essential either to develop sustainable remediation procedures as well as for use in paleotracer applications. We report on parameters controlling U immobilization and U isotope fractionation by adsorption onto Mn/Fe oxides, precipitation with phosphate, and biotic reduction. The light U isotope ((235)U) is preferentially adsorbed on Mn/Fe oxides in an oxic system. When adsorbed onto Mn/Fe oxides, dissolved organic carbon and carbonate are the most efficient ligands limiting U binding resulting in slight differences in U isotope composition (δ(238)U = 0.22 ± 0.06‰) compared to the DOC/DIC-free configuration (δ(238)U = 0.39 ± 0.04‰). Uranium precipitation with phosphate does not induce isotope fractionation. In contrast, during U biotic reduction, the heavy U isotope ((238)U) is accumulated in reduced species (δ(238)U up to -1‰). The different trends of U isotope fractionation in oxic and anoxic environments makes its isotope composition a useful tracer for both environmental and paleogeochemical applications.

  13. Mass-dependent fractionation of nickel isotopes in meteoritic metal

    Science.gov (United States)

    Cook, David L.; Wadhwa, Meenakshi; Clayton, Robert N.; Dauphas, Nicolas; Janney, Philip E.; Davis, Andrew M.

    We measured nickel isotopes via multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) in the bulk metal from 36 meteorites, including chondrites, pallasites, and irons (magmatic and non-magmatic). The Ni isotopes in these meteorites are mass fractionated; the fractionation spans an overall range of ≈0.4‰ amu-1. The ranges of Ni isotopic compositions (relative to the SRM 986 Ni isotopic standard) in metal from iron meteorites (≈0.0 to ≈0.3‰ amu-1) and chondrites (≈0.0 to ≈0.2‰ amu-1) are similar, whereas the range in pallasite metal (≈-0.1 to 0.0‰ amu-1) appears distinct. The fractionation of Ni isotopes within a suite of fourteen IIIAB irons (≈0.0 to ≈0.3‰ amu-1) spans the entire range measured in all magmatic irons. However, the degree of Ni isotopic fractionation in these samples does not correlate with their Ni content, suggesting that core crystallization did not fractionate Ni isotopes in a systematic way. We also measured the Ni and Fe isotopes in adjacent kamacite and taenite from the Toluca IAB iron meteorite. Nickel isotopes show clearly resolvable fractionation between these two phases; kamacite is heavier relative to taenite by ≈0.4‰ amu-1. In contrast, the Fe isotopes do not show a resolvable fractionation between kamacite and taenite. The observed isotopic compositions of kamacite and taenite can be understood in terms of kinetic fractionation due to diffusion of Ni during cooling of the Fe-Ni alloy and the development of the Widmanstätten pattern.

  14. Microbially Mediated Kinetic Sulfur Isotope Fractionation: Reactive Transport Modeling Benchmark

    Science.gov (United States)

    Wanner, C.; Druhan, J. L.; Cheng, Y.; Amos, R. T.; Steefel, C. I.; Ajo Franklin, J. B.

    2014-12-01

    Microbially mediated sulfate reduction is a ubiquitous process in many subsurface systems. Isotopic fractionation is characteristic of this anaerobic process, since sulfate reducing bacteria (SRB) favor the reduction of the lighter sulfate isotopologue (S32O42-) over the heavier isotopologue (S34O42-). Detection of isotopic shifts have been utilized as a proxy for the onset of sulfate reduction in subsurface systems such as oil reservoirs and aquifers undergoing uranium bioremediation. Reactive transport modeling (RTM) of kinetic sulfur isotope fractionation has been applied to field and laboratory studies. These RTM approaches employ different mathematical formulations in the representation of kinetic sulfur isotope fractionation. In order to test the various formulations, we propose a benchmark problem set for the simulation of kinetic sulfur isotope fractionation during microbially mediated sulfate reduction. The benchmark problem set is comprised of four problem levels and is based on a recent laboratory column experimental study of sulfur isotope fractionation. Pertinent processes impacting sulfur isotopic composition such as microbial sulfate reduction and dispersion are included in the problem set. To date, participating RTM codes are: CRUNCHTOPE, TOUGHREACT, MIN3P and THE GEOCHEMIST'S WORKBENCH. Preliminary results from various codes show reasonable agreement for the problem levels simulating sulfur isotope fractionation in 1D.

  15. Mass transfer and carbon isotope evolution in natural water systems

    Science.gov (United States)

    Wigley, T.M.L.; Plummer, L.N.; Pearson, F.J.

    1978-01-01

    This paper presents a theoretical treatment of the evolution of the carbon isotopes C13 and C14 in natural waters and in precipitates which derive from such waters. The effects of an arbitrary number of sources (such as dissolution of carbonate minerals and oxidation of organic material) and sinks (such as mineral precipitation, CO2 degassing and production of methane), and of equilibrium fractionation between solid, gas and aqueous phases are considered. The results are expressed as equations relating changes in isotopic composition to changes in conventional carbonate chemistry. One implication of the equations is that the isotopic composition of an aqueous phase may approach a limiting value whenever there are simultaneous inputs and outputs of carbonate. In order to unambiguously interpret isotopic data from carbonate precipitates and identify reactants and products in reacting natural waters, it is essential that isotopic changes are determined chiefly by reactant and product stoichiometry, independent of reaction path. We demonstrate that this is so by means of quantitative examples. The evolution equations are applied to: 1. (1) carbon-14 dating of groundwaters; 2. (2) interpretation of the isotopic composition of carbonate precipitates, carbonate cements and diagenetically altered carbonates; and 3. (3) the identification of chemical reaction stoichiometry. These applications are illustrated by examples which show the variation of ??C13 in solutions and in precipitates formed under a variety of conditions involving incongruent dissolution, CO2 degassing, methane production and mineral precipitation. ?? 1978.

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

    OpenAIRE

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

    2007-01-01

    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...

  17. Carbon isotopic studies of organic matter in Precambrian rocks.

    Science.gov (United States)

    Oehler, D. Z.; Schopf, J. W.; Kvenvolden, K. A.

    1972-01-01

    A survey has been undertaken of the carbon composition of the total organic fraction of a suite of Precambrian sediments to detect isotopic trends possibly correlative with early evolutionary events. Early Precambrian cherts of the Fig Tree and upper and middle Onverwacht groups of South Africa were examined for this purpose. Reduced carbon in these cherts was found to be isotopically similar to photosynthetically produced organic matter of younger geological age. Reduced carbon in lower Onverwacht cherts was found to be anomalously heavy; it is suggested that this discontinuity may reflect a major event in biological evolution.

  18. Robust optical carbon dioxide isotope analyzer Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Isotopic analysis of carbon dioxide is an important tool for characterization of the exchange and transformation of carbon between the biosphere and the atmosphere....

  19. Direct path integral estimators for isotope fractionation ratios

    CERN Document Server

    Cheng, Bingqing

    2014-01-01

    Fractionation of isotopes among distinct molecules or phases is a quantum effect which is often exploited to obtain insights on reaction mechanisms, biochemical, geochemical and atmospheric phenomena. Accurate evaluation of isotope ratios in atomistic simulations is challenging, because one needs to perform a thermodynamic integration with respect to the isotope mass, along with time-consuming path integral calculations. By re-formulating the problem as a particle exchange in the ring polymer partition function, we derive new estimators giving direct access to the differential partitioning of isotopes, which can simplify the calculations by avoiding thermodynamic integration. We demonstrate the efficiency of these estimators by applying them to investigate the isotope fractionation ratios in the gas-phase Zundel cation, and in a few simple hydrocarbons.

  20. Iron isotope fractionation in marine invertebrates in near shore environments

    Science.gov (United States)

    Emmanuel, S.; Schuessler, J. A.; Vinther, J.; Matthews, A.; von Blanckenburg, F.

    2014-04-01

    Chitons (Mollusca) are marine invertebrates that produce radula (teeth or rasping tongue) containing high concentrations of biomineralized magnetite and other iron bearing minerals. As Fe isotope signatures are influenced by redox processes and biological fractionation, Fe isotopes in chiton radula might be expected to provide an effective tracer of ambient oceanic conditions and biogeochemical cycling. Here, in a pilot study to measure Fe isotopes in marine invertebrates, we examine Fe isotopes in modern marine chiton radula collected from different locations in the Atlantic and Pacific oceans to assess the range of isotopic values, and to test whether or not the isotopic signatures reflect seawater values. Furthermore, by comparing two species that have very different feeding habits but collected from the same location, we infer a possible link between diet and Fe isotopic signatures. Values of δ56Fe (relative to IRMM-014) in chiton teeth range from -1.90 to 0.00‰ (±0.05‰ (2σ) uncertainty in δ56Fe), probably reflecting a combination of geographical control and biological fractionation processes. Comparison with published local surface seawater Fe isotope data shows a consistent negative offset of chiton teeth Fe isotope compositions relative to seawater. Strikingly, two different species from the same locality in the North Pacific (Puget Sound, Washington, USA) have distinct isotopic signatures. Tonicella lineata, which feeds on red algae, has a mean δ56Fe of -0.65 ± 0.26‰ (2σ, 3 specimens), while Mopalia muscosa, which feeds primarily on green algae, shows lighter isotopic values with a mean δ56Fe of -1.47 ± 0.98‰ (2σ, 5 specimens). Although chitons are not simple recorders of the ambient seawater Fe isotopic signature, these preliminary results suggest that Fe isotopes provide information concerning Fe biogeochemical cycling in near shore environments, and might be used to probe sources of Fe in the diets of different organisms.

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

    Science.gov (United States)

    Romanek, C.

    2010-12-01

    fractionation relations dictate that shell carbonate should be preferentially enriched in C-13 by 3 to 5 per mill (from 30° to 0°C) compared to EPF at a pH of 7.5. Anomalous positive excursions are rarely, if ever, observed in shell carbonate and they have yet to be associated with growth cessation markers in bivalves. The most likely explanation for the lack of anomalous positive values is that the percentage of metabolic carbon increases in EPF when bivalves experience stressful condition. This influx of metabolic carbon is balanced to a measureable extent by the enhanced fractionation of carbon isotopes during shell deposition from EPF at relatively low pH. These two processes may be combined in a quantitative model to extract a historical record of metabolic activity from the carbon isotope profiles of bivalve shells.

  2. Isotope fractionation during the anaerobic consumption of acetate by methanogenic and sulfate-reducing microorganisms

    Science.gov (United States)

    Gövert, D.; Conrad, R.

    2009-04-01

    During the anaerobic degradation of organic matter in anoxic sediments and soils acetate is the most important substrate for the final step in production of CO2 and/or CH4. Sulfate-reducing bacteria (SRB) and methane-producing archaea both compete for the available acetate. Knowledge about the fractionation of 13C/12C of acetate carbon by these microbial groups is still limited. Therefore, we determined carbon isotope fractionation in different cultures of acetate-utilizing SRB (Desulfobacter postgatei, D. hydrogenophilus, Desulfobacca acetoxidans) and methanogens (Methanosarcina barkeri, M. acetivorans). Including literature values (e.g., Methanosaeta concilii), isotopic enrichment factors (epsilon) ranged between -35 and +2 permil, possibly involving equilibrium isotope effects besides kinetic isotope effects. The values of epsilon were dependent on the acetate-catabolic pathway of the particular microorganism, the methyl or carboxyl position of acetate, and the relative availability or limitation of the substrate acetate. Patterns of isotope fractionation in anoxic lake sediments and rice field soil seem to reflect the characteristics of the microorganisms actively involved in acetate catabolism. Hence, it might be possible using environmental isotopic information to determine the type of microbial metabolism converting acetate to CO2 and/or CH4.

  3. Cr stable isotope fractionation and reaction kinetics in aqueous milieu

    Science.gov (United States)

    Zink, S.; Schoenberg, R.; Staubwasser, M.

    2009-12-01

    Mass-dependent stable Cr isotope variations show great potential to monitor the natural attenuation of anthropogenic chromate pollution as well as to investigate changes in environmental conditions in the present and the past. However, accurate interpretation of mass-dependent Cr isotope variations requires profound knowledge of the Cr isotope fractionation behaviour during redox transitions and the isotope exchange kinetics of the reactions involved. Here, we present a comprehensive dataset of stable Cr isotope fractionation and reaction kinetics during Cr(III) oxidation, Cr(VI) reduction and isotopic exchange between soluble Cr(III) and Cr(VI) in aqueous milieu. All experiments were carried out with both oxidation states (i.e. Cr(III) and Cr(VI)) in solution, using H2O2 as oxidising as well as reducing agent. The pH conditions were varied to investigate the influence of the different Cr(III) and Cr(VI) species on the Cr isotope fractionation and on the reaction mechanisms during the enforced redox transitions. All Cr stable isotope measurements were performed by high-resolution MC-ICP-MS [1]. The reduction of Cr(VI) to Cr(III) with H2O2 under strongly acidic conditions shows an equilibrium isotope fractionation of Δ(53,52Cr)Cr(III)-Cr(VI) of -3.54 ± 0.35 ‰. This value is within uncertainty equal to that of -3.4 ± 0.1 ‰ reported by Ellis et al. [2], who used natural sediment and magnetite as reducing agents at pH 6 to 7. At pH = 7 our reduction experiments show a unidirectional, kinetic isotope fractionation Δ(53,52Cr)Cr(III)-Cr(VI) of approximately -5 ‰ for reduction rates of up to 80 %, but a strong deviation from this Rayleigh-type process for higher reduction rates. However, at a pH value of 7 H2O2 supports the temporary formation and decomposition of Cr(V)-peroxo complexes that might explain this fractionation behaviour and deviation from a single Rayleigh type trend. The oxidation experiments of Cr(III) to Cr(VI) were carried out in alkaline media

  4. Hydrogen isotope fractionation in methane plasma

    Science.gov (United States)

    Robert, François; Derenne, Sylvie; Lombardi, Guillaume; Hassouni, Khaled; Michau, Armelle; Reinhardt, Peter; Duhamel, Rémi; Gonzalez, Adriana; Biron, Kasia

    2017-01-01

    The hydrogen isotope ratio (D/H) is commonly used to reconstruct the chemical processes at the origin of water and organic compounds in the early solar system. On the one hand, the large enrichments in deuterium of the insoluble organic matter (IOM) isolated from the carbonaceous meteorites are interpreted as a heritage of the interstellar medium or resulting from ion‑molecule reactions taking place in the diffuse part of the protosolar nebula. On the other hand, the molecular structure of this IOM suggests that organic radicals have played a central role in a gas-phase organosynthesis. So as to reproduce this type of chemistry between organic radicals, experiments based on a microwave plasma of CH4 have been performed. They yielded a black organic residue in which ion microprobe analyses revealed hydrogen isotopic anomalies at a submicrometric spatial resolution. They likely reflect differences in the D/H ratios between the various CHx radicals whose polymerization is at the origin of the IOM. These isotopic heterogeneities, usually referred to as hot and cold spots, are commensurable with those observed in meteorite IOM. As a consequence, the appearance of organic radicals in the ionized regions of the disk surrounding the Sun during its formation may have triggered the formation of organic compounds.

  5. A Clumped Isotope Calibration for Lacustrine Carbonates

    Science.gov (United States)

    Mitsunaga, B. A.; Mering, J. A.; Petryshyn, V. A.; Dunbar, R. B.; Cohen, A. S.; Liu, X.; Kaufman, D. S.; Eagle, R.; Tripati, A.

    2014-12-01

    Our capacity to understand Earth's environmental history is highly dependent on the accuracy of past climate reconstructions. Unfortunately, many terrestrial proxies—tree rings, speleothems, leaf margin analyses, etc.—are influenced by the effects of both temperature and precipitation. Methods that can isolate the effects of temperature alone are needed, and clumped isotope thermometry has the potential to be a useful tool for determining terrestrial climates. Multiple studies have shown that the fraction of 13C—18O bonds in carbonates is inversely related to the temperature at which the rocks formed and may be a useful proxy for reconstructing temperatures on land. An in-depth survey of lacustrine carbonates, however, has not yet been published. Therefore we have been measuring the abundance of 13C18O16O in the CO2 produced by the dissolution of modern lake samples' carbonate minerals in phosphoric acid and comparing results to independently known estimates of lake water temperature and air temperature. Some of the sample types we have investigated include endogenic carbonates, freshwater gastropods, bivalves, microbialites, and ooids.

  6. Kinetic Isotopic Fractionation During Diffusion of Ionic Speciesin Water

    Energy Technology Data Exchange (ETDEWEB)

    Richter, Frank M.; Mendybaev, Ruslan A.; Christensen, John; Hutcheon, Ian D.; Williams, Ross W.; Sturchio, Neil C.; Beloso Jr.,Abelardo D.

    2005-06-09

    Experiments specifically designed to measure the ratio of the diffusivities of ions dissolved in water were used to determine D{sub Li}/D{sub K}, D{sub 7{sub Li}}/D{sub 6{sub Li}}, D{sub 25{sub Mg}}/D{sub 24{sub Mg}}, D{sub 26{sub Mg}}/D{sub 25{sub Mg}}, and D{sub 37{sub Cl}}/D{sub 35{sub Cl}}. The measured ratio of the diffusion coefficients for Li and K in water (D{sub Li}/D{sub K} = 0.6) is in good agreement with published data, providing evidence that the experimental design being used resolves the relative mobility of ions with adequate precision to also be used for determining the fractionation of isotopes by diffusion in water. In the case of Li we found measurable isotopic fractionation associated with the diffusion of dissolved LiCl (D{sub 7{sub Li}}/D{sub 6{sub Li}} = 0.99772 {+-} 0.00026). This difference in the diffusion coefficient of {sup 7}Li compared to {sup 6}Li is significantly less than reported in an earlier study, a difference we attribute to the fact that in the earlier study Li diffused through a membrane separating the water reservoirs. Our experiments involving Mg diffusing in water found no measurable isotopic fractionation (D{sub 25{sub Mg}}/D{sub 24{sub Mg}} = 1.00003 {+-} 0.00006). Cl isotopes were fractionated during diffusion in water (D{sub 37{sub Cl}}/D{sub 35{sub Cl}} = 0.99857 {+-} 0.00080) whether or not the co-diffuser (Li or Mg) was isotopically fractionated. The isotopic fractionation associated with the diffusion of ions in water is much smaller than values we found previously for the isotopic fractionation of Li and Ca isotopes by diffusion in molten silicate liquids. A major distinction between water and silicate liquids is that water, being a polar liquid, surrounds dissolved ions with hydration shells, which very likely play an important but still poorly understood role in reducing isotopic fractionation associated with diffusion.

  7. Stable isotopes in tree rings: towards a mechanistic understanding of isotope fractionation and mixing processes from the leaves to the wood.

    Science.gov (United States)

    Gessler, Arthur; Ferrio, Juan Pedro; Hommel, Robert; Treydte, Kerstin; Werner, Roland A; Monson, Russell K

    2014-08-01

    The mechanistic understanding of isotope fractionation processes is increasing but we still lack detailed knowledge of the processes that determine the isotopic composition of the tree-ring archive over the long term. Especially with regard to the path from leaf photosynthate production to wood formation, post-assimilation fractionations/processes might cause at least a partial decoupling between the leaf isotope signals that record processes such as stomatal conductance, transpiration and photosynthesis, and the wood or cellulose signals that are stored in the paleophysiological record. In this review, we start from the rather well understood processes at the leaf level such as photosynthetic carbon isotope fractionation, leaf water evaporative isotope enrichment and the issue of the isotopic composition of inorganic sources (CO2 and H2O), though we focus on the less explored 'downstream' processes related to metabolism and transport. We further summarize the roles of cellulose and lignin as important chemical constituents of wood, and the processes that determine the transfer of photosynthate (sucrose) and associated isotopic signals to wood production. We cover the broad topics of post-carboxylation carbon isotope fractionation and of the exchange of organic oxygen with water within the tree. In two case studies, we assess the transfer of carbon and oxygen isotopic signals from leaves to tree rings. Finally we address the issue of different temporal scales and link isotope fractionation at the shorter time scale for processes in the leaf to the isotopic ratio as recorded across longer time scales of the tree-ring archive.

  8. Cd isotope fractionation during simulated and natural weathering.

    Science.gov (United States)

    Zhang, Yuxu; Wen, Hanjie; Zhu, Chuanwei; Fan, Haifeng; Luo, Chongguang; Liu, Jie; Cloquet, Christophe

    2016-09-01

    In practice, stable Cd isotope ratios are being applied to trace pollution sources in the natural environment. However, Cd isotope fractionation during weathering processes is not yet fully understood. We investigated Cd isotope fractionation of PbZn ore in leaching experiments and in the environment under natural weathering processes. Our leaching experiments demonstrated that the leachate was enriched with heavy Cd isotopes, relative to initial and residual samples (Δ(114/110)Cdleachate - initial state = 0.40-0.50‰, Δ(114/110)Cdleachate -residual state = 0.36-0.53‰). For natural samples, δ(114/110)Cd values of stream sediments were higher than those of the corresponding soil samples collected from the riverbank, Δ(114/110)Cdstream sediment -soil can be up to 0.50‰. This observation is consistent with our leaching experiments, which indicate significant Cd isotope fractionation during natural weathering processes. Therefore, natural contributions should be considered when using Cd isotopes to trace anthropogenic pollution in water and sediment systems.

  9. Silicon Isotopic Fractionation of CAI-like Vacuum Evaporation Residues

    Energy Technology Data Exchange (ETDEWEB)

    Knight, K; Kita, N; Mendybaev, R; Richter, F; Davis, A; Valley, J

    2009-06-18

    Calcium-, aluminum-rich inclusions (CAIs) are often enriched in the heavy isotopes of magnesium and silicon relative to bulk solar system materials. It is likely that these isotopic enrichments resulted from evaporative mass loss of magnesium and silicon from early solar system condensates while they were molten during one or more high-temperature reheating events. Quantitative interpretation of these enrichments requires laboratory determinations of the evaporation kinetics and associated isotopic fractionation effects for these elements. The experimental data for the kinetics of evaporation of magnesium and silicon and the evaporative isotopic fractionation of magnesium is reasonably complete for Type B CAI liquids (Richter et al., 2002, 2007a). However, the isotopic fractionation factor for silicon evaporating from such liquids has not been as extensively studied. Here we report new ion microprobe silicon isotopic measurements of residual glass from partial evaporation of Type B CAI liquids into vacuum. The silicon isotopic fractionation is reported as a kinetic fractionation factor, {alpha}{sub Si}, corresponding to the ratio of the silicon isotopic composition of the evaporation flux to that of the residual silicate liquid. For CAI-like melts, we find that {alpha}{sub Si} = 0.98985 {+-} 0.00044 (2{sigma}) for {sup 29}Si/{sup 28}Si with no resolvable variation with temperature over the temperature range of the experiments, 1600-1900 C. This value is different from what has been reported for evaporation of liquid Mg{sub 2}SiO{sub 4} (Davis et al., 1990) and of a melt with CI chondritic proportions of the major elements (Wang et al., 2001). There appears to be some compositional control on {alpha}{sub Si}, whereas no compositional effects have been reported for {alpha}{sub Mg}. We use the values of {alpha}Si and {alpha}Mg, to calculate the chemical compositions of the unevaporated precursors of a number of isotopically fractionated CAIs from CV chondrites whose

  10. Modes of planetary-scale Fe isotope fractionation

    Science.gov (United States)

    Schoenberg, Ronny; Blanckenburg, Friedhelm von

    2006-12-01

    A comprehensive set of high-precision Fe isotope data for the principle meteorite types and silicate reservoirs of the Earth is used to investigate iron isotope fractionation at inter- and intra-planetary scales. 14 chondrite analyses yield a homogeneous Fe isotope composition with an average δ56Fe/ 54Fe value of - 0.015 ± 0.020‰ (2 SE) relative to the international iron standard IRMM-014. Eight non-cumulate and polymict eucrite meteorites that sample the silicate portion of the HED (howardite-eucrite-diogenite) parent body yield an average δ56Fe/ 54Fe value of - 0.001 ± 0.017‰, indistinguishable to the chondritic Fe isotope composition. Fe isotope ratios that are indistinguishable to the chondritic value have also been published for SNC meteorites. This inner-solar system homogeneity in Fe isotopes suggests that planetary accretion itself did not significantly fractionate iron. Nine mantle xenoliths yield a 2 σ envelope of - 0.13‰ to + 0.09‰ in δ56Fe/ 54Fe. Using this range as proxy for the bulk silicate Earth in a mass balance model places the Fe isotope composition of the outer liquid core that contains ca. 83% of Earth's total iron to within ± 0.020‰ of the chondritic δ56Fe/ 54Fe value. These calculations allow to interprete magmatic iron meteorites ( δ56Fe/ 54Fe = + 0.047 ± 0.016‰; N = 8) to be representative for the Earth's inner metallic core. Eight terrestrial basalt samples yield a homogeneous Fe isotope composition with an average δ56Fe/ 54Fe value of + 0.072 ± 0.016‰. The observation that terrestrial basalts appear to be slightly heavier than mantle xenoliths and that thus partial mantle melting preferentially transfers heavy iron into the melt [S. Weyer, A.D. Anbar, G.P. Brey, C. Munker, K. Mezger and A.B. Woodland, Iron isotope fractionation during planetary differentiation, Earth and Planetary Science Letters 240(2), 251-264, 2005.] is intriguing, but also raises some important questions: first it is questionable whether the

  11. Theoretical prediction for several important equilibrium Ge isotope fractionation factors

    Science.gov (United States)

    Tang, M.; Li, X.; Liu, Y.

    2008-12-01

    As a newly emerging field, the stable isotope geochemistry of germanium (Ge) needs basic equilibrium fractionation factors to explore its unknown world. In this study, the Ge isotope fractionations between systems including the aqueous Ge(OH)4 and GeO(OH)3- which are the dominant Ge species in seawater, the Ge-bearing organic complexes (e.g. Ge-catechol, Ge-oxalic acid and Ge-citric acid), the quartz- (or opal- ), albite-, K-feldspar- and olivine- like mineral structures are studied. It is the first time that some geologically important equilibrium Ge isotope fractionation factors are reported. Surprisingly, up to 5 per mil large isotopic fractionations between these Ge isotope systems are found at 25 degree. These results suggest a potentially broad application for the Ge isotope geochemistry. Our theoretical calculations are based on the Urey model (or Bigeleisen-Mayer equation) and high level quantum chemistry calculations. The B3LYP/6-311+G(d,p) level quantum chemistry method and the explicit solvent model ("water droplet" method) are used. Many different conformers are also used for the aqueous complexes in order to reduce the possible errors coming from the differences of configurations in solution. The accuracy of our calculation of the Ge isotopic fractionations is estimated about 0.2 per mil. Our results show quartz-like or opal-like structure can enrich most heavy Ge isotopes. Relative to quartz (or opal), some Ge isotopic fractionations are (at 25 C): quartz-organic Ge = 4-5,quartz-Ge(OH)4 =0.9,quartz-GeO(OH)3- =1.5,quartz-albite=0.6,quartz-K-feldspar=0.4 and quartz-olivine=3.9 per mil. The large fractionations between inorganic Ge complexes and organic Ge ones could be used to distinguish the possible bio-involving processes. Our results suggest a good explanation to the experimental observations of Siebert et al. (2006) and Rouxel et al. (2006) and provide important constraints to the study of Ge cycle in ocean.

  12. Stable carbon and nitrogen isotopic fractionation between diet and swine tissues Fracionamento isotópico de carbono e nitrogênio entre a dieta e tecidos de porcos

    Directory of Open Access Journals (Sweden)

    Gabriela Bielefeld Nardoto

    2006-12-01

    Full Text Available Naturally occurring stable isotope ratios can be a powerful tool in studies of animal nutrition, provided that the assumptions required for dietary reconstruction are validated by studies such as the one presented here. The objective of this study was to document the magnitude of isotopic fractionation between swine diet and their different tissues. For this, the isotopic ratios of carbon and nitrogen of the diet and selected tissues (hair, nail, liver, muscle, fat and cartilage were determined. The delta13C and delta15N of the diet were -15.9‰ and 1.3‰, respectively, and all delta15N of swine tissues were 2.2 to 3.0‰ enriched in 15N in relation to the diet. Little variation in delta15N occurred among tissues, with exception to liver that was less enriched in 15N than the nail. Nail and hair presented no 13C enrichment relative to diet. Cartilage was ~1.0‰ enriched in 13C as compared to diet. Liver and muscle were on average 2.1‰ more depleted in 13C in relation to diet as well as fat tissues. Some of the C and N isotope ratios of swine tissues differed in organs, but the isotopic fractionation trends among tissues appears to be similar to other mammals. Therefore our data provide a good baseline to interpret stable isotope patterns in domestic mammals (such as swine in controlled or semi-controlled experiments.O uso da abundância natural de isótopos estáveis pode ser uma ferramenta útil em estudos de nutrição animal, de forma que a base necessária para a reconstrução da dieta alimentar pode ser validada a partir de estudos como o apresentado aqui. O objetivo deste estudo foi documentar a magnitude do fracionamento isotópico entre a dieta e os tecidos de porcos domésticos. Para tanto, foram determinadas as razões isotópicas de carbono e nitrogênio de alguns tecidos selecionados (pêlo, unha, fígado, músculo, gordura e cartilagem. Os valores de delta13C e delta15N da ração fornecida foram -15,9‰ e 1,3

  13. Iron isotope fractionation between aqueous ferrous iron and goethite

    Science.gov (United States)

    Beard, Brian L.; Handler, Robert M.; Scherer, Michelle M.; Wu, Lingling; Czaja, Andrew D.; Heimann, Adriana; Johnson, Clark M.

    2010-06-01

    The equilibrium Fe isotope fractionation factor between aqueous Fe(II) and goethite has been experimentally measured to be - 1.05 ± 0.08‰ in 56Fe/54Fe (2σ) at 22 °C, using the three-isotope method. Experiments were done using two sizes of goethite (81 × 11 nm and 590 × 42 nm), and the experimental products were subjected to serial extraction using acid partial dissolution techniques to determine if surface Fe(III) atoms have different isotopic properties than the bulk goethite. These experiments indicate that the interaction of Fe(II)aq and goethite is dynamic and results in complete or near-complete Fe isotope exchange over 30 days, involving at least four components: Fe(II)aq, goethite, sorbed Fe(II), and Fe(III)surface. The equilibrium fractionation factor between Fe(II)aq and Fe(II)sorb is the same for both sizes of goethite, at Δ56FeFe(II)aq-Fe(II)sorb = - 1.24 ± 0.14‰; this fractionation factor is significantly different than the results of previous studies on Fe(II) sorption to goethite. The proportion of the Fe(III)surface component is greatest in the experiments that used the smallest goethite, and the Fe(III)surface-Fe(II)aq fractionation is estimated to be at least + 2.1‰. The high Fe(III)surface-Fe(II)aq fractionation may exert a significant influence on the Fe isotope compositions of aqueous Fe(II) in natural systems that contain nanoparticulate goethite, including those involving bacterial iron reduction. These results demonstrate that the isotopic properties of nano-scale minerals may be distinct from micron-scale or larger minerals, as is the case for other thermodynamic properties of nanoparticles.

  14. Mass Independent Fractionation of Hg Isotopes Preserved in the Precambrian

    Science.gov (United States)

    Thibodeau, A. M.; Bergquist, B. A.; Kah, L. C.; Ono, S.; Ghosh, S.; Hazen, R. M.

    2013-12-01

    Mercury (Hg) is a photochemically active, redox-sensitive, chalcophilic metal with complex biogeochemistry that displays a wide range of mass-dependent (MDF) and mass-independent (MIF) stable isotopic fractionation. In the past decade, Hg isotopes have emerged as important tracers of both the sources and cycling of Hg in the modern environment. However, their utility as environmental proxies in ancient rocks remains largely unexplored. The potential of Hg isotopes to inform Precambrian environments derives from the observation that Hg isotopes with odd atomic mass numbers (199Hg and 201Hg) undergo large MIF by the magnetic isotope effect (MIE) and smaller MIF through the nuclear volume effect (NVE). Small MIF produced via NVE has been observed for numerous transformations and is characterized by MIF ratios (Δ199Hg/Δ201Hg) of about 1.6. Large Hg-MIF driven by MIE has been observed during photochemical transformations and is characterized by Δ199Hg/Δ201Hg ratios between 1 and 1.3. This MIF signal is sensitive to a range of environmental conditions, including the amount and type of solar radiation, the presence and type of complexing organic ligands, and the Hg/dissolved organic carbon (DOC) ratio. Thus, it is hoped that Hg-MIF signals may indirectly record changes in atmospheric composition or seawater chemistry if preserved in marine sedimentary records. Previous work has clearly demonstrated that Hg-MIF signals are preserved in Archean and Paleoproterozoic marine shales and massive sulfide deposits. Here, we present evidence that such signals are also preserved in marine shales of mid-Proterozoic age, including the ~1.3 Ga Sulky formation (Dismal Lakes Group, NW Arctic), the ~1.45 Ga Greyson Shale (Belt Basin, Montana), and the ~1.5 Ga Katalsy formation (Kypry Group, Eastern European Platform). We observe that the Greyson shale and shales within the Sulky formation yield negative Hg-MIF with Δ199Hg/Δ201Hg ratios close to 1 and that Kaltasy group sediments

  15. Chromium Isotopes in Marine Carbonates - an Indicator for Climatic Change?

    Science.gov (United States)

    Frei, R.; Gaucher, C.

    2010-12-01

    Chromium (Cr) stable isotopes experience an increased interest as a tracer of Cr (VI) reduction in groundwater and thus showed their potential as a monitor of remediation of anthropogenic and natural contamination in water (Berna et al., 2009; Izbicki et al., 2008). Chromium stable isotopes in Fe-rich chemical sediments (BIFs and Fe-cherts) have recently also been used as a tracer for Earth's atmospheric oxygenation through time (Frei et al., 2009). We have applied the Cr isotope system to organic-rich carbonates from a late Ediacaran succession in Uruguay (Polanco Formation), from which we have previously analyzed BIFs with extremely fractionated (δ53Cr up to 5.0 ‰) Cr isotope signatures that are part of an underlying deep water clastic sediment (shale-dominated) sequence (Yerbal Formation) deposited in a glacio-marine environment (Gaucher et al.,2004). δ53Cr values of organic rich carbonates correlate with positive and negative carbon isotope excursions (δ13C PDB between -3 and +3 ‰) and with systematic changes in strontium isotope compositions, commonly interpreted as to reflect fluctuations in organic (photosynthetic algae) production related to fluctuations in atmospheric oxygen and weathering intensities, respectively. Slightly positively fractioned δ53Cr values (up to +0.25‰), paralleling positive (δ13C PDB and 87Sr/86Sr ratio excursions would thereby trace elevated atmospheric oxygen levels/pulses possibly related to glacier retreat/melting stages that caused bioproductivity to increase. While the causal link between these multiple isotopic tracers and the mechanisms of Cr stripping into carbonates has to be further investigated in detail, the first indications from this study point to a potentially promising use of stable Cr isotopes in organic-rich carbonates to monitor fluctuations of atmospheric oxygen, particularly over the Neoproterozoic and Phanerozoic ice age periods. E.C. Berna et al. (2010) Cr stable isotopes as indicators of Cr

  16. Oxygen and Chlorine Isotopic Fractionation During Microbial Reduction of Perchlorate

    Science.gov (United States)

    Beloso, A. D.; Sturchio, N. C.; Böhlke, J. K.; Streger, S. H.; Heraty, L. J.; Hatzinger, P. B.

    2006-12-01

    Perchlorate is a widespread environmental contaminant that has both anthropogenic and natural sources. Stable isotope ratios of O and Cl in perchlorate have been used recently to distinguish perchlorate of different origins. Isotopic ratios may also be useful for identifying the occurrence and extent of biodegradation of perchlorate in natural environments, information that is critical for assessing natural attenuation of this contaminant. For this approach to be useful, however, the extent of isotopic fractionation of both Cl and O by bacteria must be determined, and the influence of environmental variables on this process must be defined. During this laboratory study, the O and Cl isotope ratios of perchlorate were monitored as a function of degradation by two separate bacterial species (Azospira suillum JPLRND and Dechlorospirillum sp. FBR2) at both 10 °C and 22 °C with acetate as the electron donor. Perchlorate was completely degraded by both strains within 280 hr at 22 °C and 615 hr at 10 °C. Measured values of isotopic fractionation factors were ɛ18O = -36.6 to -29.0 ‰ and ɛ37Cl = -14.5 to - 11.5 ‰, and these showed no apparent systematic variation with either temperature or bacterial strain. One experiment using 18O-enriched water (δ18O = 200‰) gave results indistinguishable from those observed in isotopically normal water, indicating little or no isotopic exchange between perchlorate and water during biodegradation. The fractionation factor ratio ɛ18O/ɛ37Cl was nearly invariant in all experiments at 2.50 ± 0.04. These data indicate that isotopic analysis will be useful for documenting perchlorate biodegradation in soils and groundwater. The establishment of a microbial fractionation factor ratio (ɛ18O/ɛ37Cl) also has significance for forensic studies, as these data indicate that fractionation via biodegradation will not cause the reported mass-dependent Cl and O isotopic signatures of synthetic and natural perchlorate to overlap.

  17. Mo isotope fractionation during hydrothermal evolution of porphyry Cu systems

    Science.gov (United States)

    Shafiei, Behnam; Shamanian, GholamHossein; Mathur, Ryan; Mirnejad, Hassan

    2015-03-01

    We present Mo isotope compositions of molybdenite types from three successive stages of ore deposition in several porphyry copper deposits of the Kerman region, Iran. The data provide new insights into controlling processes on Mo isotope fractionation during the hydrothermal evolution of porphyry systems. The Mo isotope compositions of 27 molybdenite samples show wide variations in δ97Mo ranging from -0.37 to +0.92 ‰. The data reveal that molybdenites in the early and transitional stages of mineralization (preferentially 2H polytypes; δ97Mo mean = 0.35 ‰) have higher δ97Mo values than late stage (mainly 3R polytypes; δ97Mo mean = 0.02 ‰) molybdenites. This trend suggests that fractionation of Mo isotopes occurred in high-temperature stages of mineralization and that hydrothermal systems generally evolve towards precipitation of molybdenite with lower δ97Mo values. Taking into account the genetic models proposed for porphyry Cu deposits along with the temperature-dependent fractionation of Mo isotope ratios, it is proposed that large variations of Mo isotopes in the early and the transitional stages of ore deposition could be controlled by the separation of the immiscible ore-forming fluid phases with different density, pH, and ƒO2 properties (i.e., brine and vapor). The fractionation of Mo isotopes during fluid boiling and Rayleigh distillation processes likely dominates the Mo isotope budget of the remaining ore-forming fluids for the late stage of mineralization. The lower δ97Mo values in the late stage of mineralization can be explained by depletion of the late ore-forming hydrothermal solutions in 97Mo, as these fluids have moved to considerable distance from the source. Finally, the relationship observed between MoS2 polytypes (2H and 3R) and their Mo isotopic compositions can be explained by the molecular vibration theory, in which heavier isotopes are preferentially partitioned into denser primary 2H MoS2 crystals.

  18. Isotopic fractionation between seawater and the shell of

    NARCIS (Netherlands)

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

    2012-01-01

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

  19. Hydrogen isotope fractionation in the photolysis of formaldehyde

    NARCIS (Netherlands)

    Rhee, T.S.; Brenninkmeijer, C.A.M.; Röckmann, T.

    2007-01-01

    Experiments investigating the isotopic fractionation in the formation of H2 by the photolysis of CH2O under tropospheric conditions are reported and discussed. The deuterium (D) depletion in H2 produced is 500(±20)‰ with respect to the parent CH2O. We also observed that complete photolysis of CH2O u

  20. Light effects on the isotopic fractionation of skeletal oxygen and carbon in the cultured zooxanthellate coral, Acropora: implications for coral-growth rates

    Directory of Open Access Journals (Sweden)

    S. Reynaud

    2010-03-01

    Full Text Available Skeletal isotopic and metabolic measurements of the branching coral Acropora cultured in constant conditions and subjected to two light intensities were revisited. We individually compared the data recorded at low light (LL and high light (HL for 24 colonies, all derived from the same parent colony. Metabolic and isotopic responses to the different light levels were highly variable. High light led to productivity enhancement, reduction of surface extension, doubling of aragonite deposited weight and increased δ18O levels in all nubbins; responses in respiration and δ13C were not clear. The partitioning of the colonies cultured at HL into two groups, one showing a δ13C enrichment and the other a δ13C decrease revealed common behaviors. Samples showing an increase in δ13C were associated with the co-variation of low surface extension and high productivity while samples showing a decrease in δ13C were associated with the co-variation of higher surface extension and limited productivity. This experiment, which allowed for the separation of temperature and light effects on the coral, highlighted the significant light influences on both skeletal δ18O and δ13C. The high scattering of inter-colony δ18O observed at one site could be due to the differing photosynthetic responses of symbiotic algal assemblages. We compared our results with observations by Gladfelter on Acropora cervicornis (1982. Both set of results highlight the relationships between coral-growth rates, micro-structures and photosynthetic activity. It appears that extension growth and skeleton thickening are two separate growth modes, and thickening is light-enhanced while extension is light-suppressed. There are multiple consequences of these findings for paleoclimatic reconstructions involving corals.

  1. Light effects on the isotopic fractionation of skeletal oxygen and carbon in the cultured zooxanthellate coral, Acropora: implications for coral-growth rates

    Science.gov (United States)

    Juillet-Leclerc, A.; Reynaud, S.

    2010-03-01

    Skeletal isotopic and metabolic measurements of the branching coral Acropora cultured in constant conditions and subjected to two light intensities were revisited. We individually compared the data recorded at low light (LL) and high light (HL) for 24 colonies, all derived from the same parent colony. Metabolic and isotopic responses to the different light levels were highly variable. High light led to productivity enhancement, reduction of surface extension, doubling of aragonite deposited weight and increased δ18O levels in all nubbins; responses in respiration and δ13C were not clear. The partitioning of the colonies cultured at HL into two groups, one showing a δ13C enrichment and the other a δ13C decrease revealed common behaviors. Samples showing an increase in δ13C were associated with the co-variation of low surface extension and high productivity while samples showing a decrease in δ13C were associated with the co-variation of higher surface extension and limited productivity. This experiment, which allowed for the separation of temperature and light effects on the coral, highlighted the significant light influences on both skeletal δ18O and δ13C. The high scattering of inter-colony δ18O observed at one site could be due to the differing photosynthetic responses of symbiotic algal assemblages. We compared our results with observations by Gladfelter on Acropora cervicornis (1982). Both set of results highlight the relationships between coral-growth rates, micro-structures and photosynthetic activity. It appears that extension growth and skeleton thickening are two separate growth modes, and thickening is light-enhanced while extension is light-suppressed. There are multiple consequences of these findings for paleoclimatic reconstructions involving corals.

  2. Light effects on the isotopic fractionation of skeletal oxygen and carbon in the cultured zooxanthellate coral, Acropora: implications for coral-growth rates

    Directory of Open Access Journals (Sweden)

    S. Reynaud

    2009-11-01

    Full Text Available Skeletal isotopic and metabolic measurements of the branching coral Acropora cultured in constant conditions and subjected to two light intensities were revisited. We individually compared the data recorded at low light (LL and high light (HL for 24 colonies, all derived from the same parent colony. Metabolic and isotopic responses to the different light levels were highly variable. High light led to productivity enhancement, reduction of surface extension, doubling of aragonite deposited weight and increased δ18O levels in all nubbins; responses in respiration and δ13C were not clear. The partitioning of the colonies into two groups, one showing a δ13C increase and the other a δ13C decrease with increased light, revealed common behaviors. Samples showing an increase in δ13C were associated with the co-variation of low surface extension and high productivity while samples showing a decrease in δ13C were associated with the co-variation of higher surface extension and limited productivity. This experiment, which allowed for the separation of temperature and light effects on the coral, highlighted the significant light influences on both skeletal δ18O and δ13C. The high scattering of inter-colony δ18O observed at one site could be due to the differing photosynthetic responses of symbiotic algal assemblages. The δ13C responses could also be related to differing algal distributions in different skeletal portions. Our results were compared to observations by Gladfelter on Acropora cervicornis (1982. Both set of results highlight the relationships between coral-growth rates, micro-structures and photosynthetic activity. It appears that extension growth and accretion are two separate growth modes, and accretion is light-enhanced while extension is light-repressed. There are multiple consequences of these findings for paleoclimatic reconstructions involving corals.

  3. Cadmium isotope fractionation during adsorption to Mn-oxyhydroxide

    Science.gov (United States)

    Wasylenki, L. E.; Swihart, J. W.

    2013-12-01

    The heavy metal cadmium is of interest both as a toxic contaminant in groundwater and as a critical nutrient for some marine diatoms [1], yet little is known about the biogeochemistry of this element. Horner et al. [2] suggested that Cd stable isotopes could potentially enable reconstruction of biological use of Cd in the marine realm: since cultured diatoms fractionate Cd isotopes [3], and ferromanganese crusts appear to incorporate a faithful record of deepwater Cd isotopes [2], depth profiles in such crusts may yield information about the extent of Cd assimilation of isotopically light Cd by diatoms over time. Although no work has yet been published regarding the use of stable isotopes to track reactive transport of Cd in contaminated aquifers, others have recently demonstrated the potential of isotopes to track reactions affecting the mobility of other toxic metals (e.g., [4]). With both of these potential applications in mind, we conducted two sets of experiments, at low and high ionic strength, in which Cd partially adsorbed to potassium birnessite. Our goals are to quantify the fractionations and to constrain the mechanisms governing Cd isotope behavior during adsorption to an environmentally abundant scavenger of Cd. Suspensions of synthetic birnessite were doped with various amounts of dissolved Cd2+ at pH ~8.3. Following reaction, the dissolved and adsorbed pools of Cd were separated by filtration, purified by anion exchange chromatography, and analyzed by multicollector ICP-MS using a double-spike routine. In all cases, lighter isotopes preferentially adsorbed to the birnessite particles. At low ionic strength (ILacan et al. (2006) Geochim. Cosmochim. Acta. 70, 5104. [4] Berna et al. (2010) Env. Sci. & Tech. 44, 1043.

  4. The origin of carbon isotope vital effects in coccolith calcite

    Science.gov (United States)

    McClelland, H. L. O.; Bruggeman, J.; Hermoso, M.; Rickaby, R. E. M.

    2017-01-01

    Calcite microfossils are widely used to study climate and oceanography in Earth's geological past. Coccoliths, readily preserved calcite plates produced by a group of single-celled surface-ocean dwelling algae called coccolithophores, have formed a significant fraction of marine sediments since the Late Triassic. However, unlike the shells of foraminifera, their zooplankton counterparts, coccoliths remain underused in palaeo-reconstructions. Precipitated in an intracellular chemical and isotopic microenvironment, coccolith calcite exhibits large and enigmatic departures from the isotopic composition of abiogenic calcite, known as vital effects. Here we show that the calcification to carbon fixation ratio determines whether coccolith calcite is isotopically heavier or lighter than abiogenic calcite, and that the size of the deviation is determined by the degree of carbon utilization. We discuss the theoretical potential for, and current limitations of, coccolith-based CO2 paleobarometry, that may eventually facilitate use of the ubiquitous and geologically extensive sedimentary archive. PMID:28262764

  5. Isotope Fractionation of Toluene: A Perspective to Characterise Microbial In Situ Degradation

    Directory of Open Access Journals (Sweden)

    H.H. Richnow

    2002-01-01

    Full Text Available A concept to assess in situ biodegradation of organic contaminants in aquifers is presented. The alteration of the carbon isotope composition of contaminants along the groundwater flow path indicates microbial degradation processes and can be used as an indicator for in situ biodegradation. The Rayleigh equation was applied to calculate the percentage of the in situ biodegradation (B[%] using the change in the isotopic composition of contaminants (Rt/R0 along the ground water flow path and a kinetic carbon isotope fractionation factor (αC derived from defined biodegradation experiments in the laboratory. When the groundwater hydrology is known and a representative source concentration (C0 for a groundwater flow path can be determined, the extent of in situ biodegradation can be quantified.

  6. Nitrogen isotopic fractionation during abiotic synthesis of organic solid particles

    Science.gov (United States)

    Kuga, Maïa; Carrasco, Nathalie; Marty, Bernard; Marrocchi, Yves; Bernard, Sylvain; Rigaudier, Thomas; Fleury, Benjamin; Tissandier, Laurent

    2014-05-01

    The formation of organic compounds is generally assumed to result from abiotic processes in the Solar System, with the exception of biogenic organics on Earth. Nitrogen-bearing organics are of particular interest, notably for prebiotic perspectives but also for overall comprehension of organic formation in the young Solar System and in planetary atmospheres. We have investigated abiotic synthesis of organics upon plasma discharge, with special attention to N isotope fractionation. Organic aerosols were synthesized from N2-CH4 and N2-CO gaseous mixtures using low-pressure plasma discharge experiments, aimed at simulating chemistry occurring in Titan's atmosphere and in the protosolar nebula, respectively. The nitrogen content, the N speciation and the N isotopic composition were analyzed in the resulting organic aerosols. Nitrogen is efficiently incorporated into the synthesized solids, independently of the oxidation degree, of the N2 content of the starting gas mixture, and of the nitrogen speciation in the aerosols. The aerosols are depleted in 15N by 15-25‰ relative to the initial N2 gas, whatever the experimental setup is. Such an isotopic fractionation is attributed to mass-dependent kinetic effect(s). Nitrogen isotope fractionation upon electric discharge cannot account for the large N isotope variations observed among Solar System objects and reservoirs. Extreme N isotope signatures in the Solar System are more likely the result of self-shielding during N2 photodissociation, exotic effect during photodissociation of N2 and/or low temperature ion-molecule isotope exchange. Kinetic N isotope fractionation may play a significant role in the Titan's atmosphere. On the Titan's night side, 15N-depletion resulting from electron driven reactions may counterbalance photo-induced 15N enrichments occurring on the day's side. We also suggest that the low δ15N values of Archaean organic matter (Beaumont and Robert, 1999) are partly the result of abiotic synthesis of

  7. Iron isotope fractionation during microbial dissimilatory iron oxide reduction in simulated Archaean seawater.

    Science.gov (United States)

    Percak-Dennett, E M; Beard, B L; Xu, H; Konishi, H; Johnson, C M; Roden, E E

    2011-05-01

    The largest Fe isotope excursion yet measured in marine sedimentary rocks occurs in shales, carbonates, and banded iron formations of Neoarchaean and Paleoproterozoic age. The results of field and laboratory studies suggest a potential role for microbial dissimilatory iron reduction (DIR) in producing this excursion. However, most experimental studies of Fe isotope fractionation during DIR have been conducted in simple geochemical systems, using pure Fe(III) oxide substrates that are not direct analogues to phases likely to have been present in Precambrian marine environments. In this study, Fe isotope fractionation was investigated during microbial reduction of an amorphous Fe(III) oxide-silica coprecipitate in anoxic, high-silica, low-sulphate artificial Archaean seawater at 30 °C to determine if such conditions alter the extent of reduction or isotopic fractionations relative to those observed in simple systems. The Fe(III)-Si coprecipitate was highly reducible (c. 80% reduction) in the presence of excess acetate. The coprecipitate did not undergo phase conversion (e.g. to green rust, magnetite or siderite) during reduction. Iron isotope fractionations suggest that rapid and near-complete isotope exchange took place among all Fe(II) and Fe(III) components, in contrast to previous work on goethite and hematite, where exchange was limited to the outer few atom layers of the substrate. Large quantities of low-δ(56)Fe Fe(II) (aqueous and solid phase) were produced during reduction of the Fe(III)-Si coprecipitate. These findings shed new light on DIR as a mechanism for producing Fe isotope variations observed in Neoarchaean and Paleoproterozoic marine sedimentary rocks.

  8. Magnesium isotope fractionation during differentiation of Harney Peak granite

    Science.gov (United States)

    Ke, S.; Teng, F.; Walker, R. J.

    2009-12-01

    Although numerous studies have sought to constrain the Mg isotopic composition of mantle rocks, few studies have focused on the Mg isotopic compositions of crustal rocks, particularly evolved igneous rocks, such as granites. Granites are a major component of the upper continental crust and can be produced by partial melting of the deep continental crust. Studies of granites, therefore, can potentially provide important constraints on Mg isotopic composition variations in the continental crust as related to sources and petrogenetic processes. In order to explore the behavior of Mg isotopes during partial melting of continental crust, as well as granite differentiation, we have begun a study of a set of well-characterized samples from S-type Harney Peak granite, its potential source rocks and associated Tin Mountain pegmatite from Black Hills, South Dakota, USA. δ26Mg values of Harney Peak granites and Tin Mountain pegmatite vary significantly (from -0.69 to +0.11), well beyond the range of their potential source rocks (from -0.40 to +0.15) — early Proterozoic schists and late Archean metagranites. The large Mg isotopic variations within the granite suite likely, in part, reflect heterogeneities in source rocks, as previously shown for oxygen and Nd isotopes. A greater cause of the variations may be fractionations that occur during partial melting and subsequent differentiation of granitic melts, as suggested by the correlations between δ26Mg with SiO2, Al2O3, Na2O and Sr.

  9. Photosynthetic carbon isotope discrimination and its relationship to the carbon isotope signals of stem, soil and ecosystem respiration.

    Science.gov (United States)

    Wingate, Lisa; Ogée, Jérôme; Burlett, Régis; Bosc, Alexandre; Devaux, Marion; Grace, John; Loustau, Denis; Gessler, Arthur

    2010-10-01

    • Photosynthetic carbon (C) isotope discrimination (Δ(Α)) labels photosynthates (δ(A) ) and atmospheric CO(2) (δ(a)) with variable C isotope compositions during fluctuating environmental conditions. In this context, the C isotope composition of respired CO(2) within ecosystems is often hypothesized to vary temporally with Δ(Α). • We investigated the relationship between Δ(Α) and the C isotope signals from stem (δ(W)), soil (δ(S)) and ecosystem (δ(E)) respired CO(2) to environmental fluctuations, using novel tuneable diode laser absorption spectrometer instrumentation in a mature maritime pine forest. • Broad seasonal changes in Δ(Α) were reflected in δ(W,) δ(S) and δ(E). However, respired CO(2) signals had smaller short-term variations than Δ(A) and were offset and delayed by 2-10 d, indicating fractionation and isotopic mixing in a large C pool. Variations in δ(S) did not follow Δ(A) at all times, especially during rainy periods and when there is a strong demand for C allocation above ground. • It is likely that future isotope-enabled vegetation models will need to develop transfer functions that can account for these phenomena in order to interpret and predict the isotopic impact of biosphere gas exchange on the C isotope composition of atmospheric CO(2).

  10. Cadmium Isotope Fractionation in Seawater - A Signature of Nutrient Utilization

    Science.gov (United States)

    Wichtlhuber, S.; Rehkaemper, M.; Halliday, A. N.

    2005-12-01

    Cadmium displays a nutrient-like distribution akin to phosphorous in the oceans. This has been attributed to the assimilation of Cd by phytoplankton in surface waters and re-mineralization at depth. If biological uptake is associated with kinetic isotopic fractionation, as recently suggested by Lacan et al. (2005), then the Cd-depleted surface waters of the oceans (with Cd contents of Lacan et al., 2005). In this study, we have extended the search for Cd isotope variations in the oceans with analyses of two depth profiles and various additional seawater samples from the North Pacific, the Arctic, and the Southern Ocean. The Cd isotope measurements utilized a double spike technique in conjunction with multiple-collector inductively coupled plasma mass spectrometry (MC-ICPMS), to achieve a precision and accuracy of about ± 0.8 to 1.5 ɛ114/110Cd. This precision is about a factor of 3 to 4 better than that of previous studies, which did not utilize a double spike. The data collected for the samples display a clear co-variation of Cd isotope compositions with Cd concentrations. The most Cd-rich water samples (with ~1 nmol/kg Cd) display the "lightest" Cd isotope compositions with ɛ114/110Cd ~ +3, akin to results previously obtained for crustal and mantle rocks (Wombacher et. al, 2003). In contrast, samples from the upper water column of the North Pacific (with Lacan et al. (2005), because inorganic geological processes (other than evaporation/condensation) do not appear to generate isotope effects as large as those observed in the present study (Wombacher et. al, 2003). These preliminary results suggest that Cd isotopes have the potential to become a useful proxy of nutrient utilization, which could supplement the Cd/Ca and δ13C records of previous studies, if suitable sedimentary archives can be identified that preserve the Cd isotope signatures of past seawater. References: Lacan F., Francois R., Ji Y. and Sherrell R., 2005. Does oceanic productivity production

  11. Dissolved Organic Carbon Cycling in Forested Watersheds: A Carbon Isotope Approach

    Science.gov (United States)

    Schiff, S. L.; Aravena, R.; Trumbore, S. E.; Dillon, P. J.

    1990-12-01

    Dissolved organic carbon (DOC) is important in the acid-base chemistry of acid-sensitive freshwater systems; in the complexation, mobility, persistence, and toxicity of metals and other pollutants; and in lake carbon metabolism. Carbon isotopes (13C and 14C) are used to study the origin, transport, and fate of DOC in a softwater catchment in central Ontario. Precipitation, soil percolates, groundwaters, stream, beaver pond, and lake waters, and lake sediment pore water were characterized chemically and isotopically. In addition to total DOC, isotopic measurements were made on the humic and fulvic DOC fractions. The lake is a net sink for DOC. Δ14C results indicate that the turnover time of most of the DOC in streams, lakes, and wetlands is fast, less than 40 years, and on the same time scale as changes in acidic deposition. DOC in groundwaters is composed of older carbon than surface waters, indicating extensive cycling of DOC in the upper soil zone or aquifer.

  12. Species-dependent silicon isotope fractionation in unialgal cultures of marine diatoms

    Science.gov (United States)

    Sutton, J. N.; Varela, D. E.; Brzezinski, M. A.; Beucher, C.

    2011-12-01

    Variations in the natural abundance of stable isotopes of silicon (expressed as δ30Si in %) are a key tool for studying the marine silicon (Si) cycle in modern and ancient oceans. In particular, this tool can be used to track relative differences in silicic acid drawdown in surface waters by siliceous microplankton. Diatoms are siliceous phytoplankton that dominate the cycling of Si in the oceans. They represent a major source of primary production and are important in the transfer of Si, nitrogen, phosphorus, and atmospheric carbon to the deep sea. Previous investigations of Si isotope fractionation in diatom cultures have ruled out the influence of temperature (12-22°C) and shown that Si fractionation was invariant in different species of temperate diatoms (De La Rocha et al. 1997). However, the application of this proxy for marine paleo-silicon reconstructions has typically only been used in polar regions, such as the Southern Ocean, where high primary production rates give rise to diatom-rich sediments. Here, we present results on the fractionation of Si isotopes by four species of polar diatoms grown in semi-continuous cultures (Chaetoceros brevis, Fragilariopsis kerguelensis, Porosira glacialis, and Thalassiosira antarctica). To compare with previous studies (De La Rocha et al, 1997), we also tested Si isotope fractionation by two species of temperate diatoms (Thalassiosira pseudonana and Thalassiosira weissflogii). The temperate species yielded Si isotope fractionation (Δ30Si) values of -0.81 % (±0.12, SD, n=11) for T. pseudonana and -1.03% (±0.09, SD, n=3) for T. weissflogii, that are identical to the previously reported fractionation of -1.1 % (±0.4, SD, n=6) (De La Rocha et al. 1997). Similarly, our data for polar species F. kerguelensis, P. glacialis and T. antarctica suggest a fractionation of -0.7 to -1.1 %. Interestingly, our preliminary results from Chaetoceros brevis cultures show a Si isotope fractionation value of about -2.61 % (±0.05, SD

  13. Carbon isotope geochemistry in the Yalujiang estuary

    Institute of Scientific and Technical Information of China (English)

    吴莹; 张经

    2001-01-01

    The distribution of particulate organic carbon (POC) along the lower reaches is similar between the dry season and the flood season in the Yalujiang Estuary, North China. However, the values of particulate organic carbon of the upperstream in the dry season are one magnitude lower than the concentrations in the flood season. Stable carbon isotope ratios have been used to study the sources of particulate organic carbon in the Yalujiang Estuary. The isotopic composition of POC shows a range from -23.1‰ to -29.4‰ with a little seasonal variation. The isotopic evidence indicates that the POC in the Yalujiang Estuary is predominantly of terrestrial origin rather than a result of in situ plankton. The study of the ratio of POC: Chla shows that the turbidity maximum plays an important role in POC cycle in the Yalujiang Estuary. Organic detritus and soil erosion are the main contributions to POC in the turbidity maximum, especially in the flood season.

  14. Cd Isotope Fractionation During Adsorption Varies with Salinity

    Science.gov (United States)

    Wasylenki, L. E.; Montanez, G.; Anbar, A. D.

    2009-12-01

    Because its marine concentration profile is very similar to that of phosphate [1], Cd is considered to have potential as a paleophosphate or paleonutrient proxy in the geologic record. Previous work [2,3] has established that lighter isotopes of Cd are preferentially assimilated by phytoplankton, leaving surface waters isotopically heavy. Another recent study [4] suggests that analysis of Cd isotope variations in transects of ferromanganese crusts could reveal past variations in the extent to which Cd, and thus phosphate, has been depleted over time. This idea presumes that the extent of consumption of Cd by phytoplankton is reflected in the isotopic composition of seawater and that the Cd isotopic composition of seawater is in turn faithfully recorded in ferromanganese crusts. To test the latter assumption, Rehkämper et al. [4] measured the Cd isotopic composition of 15 Fe-Mn crusts from various ocean basins and found that 13 of those samples were within analytical error of the Cd isotopic composition of deep seawater from [3], indicating that Cd often does not fractionate appreciably during incorporation into ferromanganese crusts. Other studies [5,6] have likewise revealed little or no variation in Cd isotopic compositions among various terrestrial rocks and carbonaceous chondrites, suggesting that few earth processes significantly fractionate Cd isotopes. To test this conclusion experimentally, we performed adsorption experiments in which aqueous Cd was allowed to adsorb to synthetic birnessite (Mn oxyhydroxide). Stock solutions of dissolved Cd and birnessite suspension were mixed and agitated from 1 to 48 hours at room temperature. Some experiments had 0.1m KNO3 as background electrolyte, while others had 0.3m NaCl + 0.1m KNO3. After filtration, both the fluid with remaining dissolved Cd and solids with adsorbed Cd were purified with anion exchange chemistry. Column yields and proportions of dissolved and adsorbed Cd were determined by ICP-MS, and isotope

  15. Chromium isotope fractionation during oxidative weathering of a modern basaltic weathering profile

    DEFF Research Database (Denmark)

    D'Arcy, Joan Mary; Døssing, Lasse Nørbye; Frei, Robert

    to fractionate under both reducing and oxidizing conditions [1, 2]. Recent studies on d53Cr isotopes in laterite soils show that oxidative weathering of Cr-bearing rocks is accompanied by an isotopic fractionation, where by the lighter isotopes are retained in the residual soil and the heavier isotope...

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

    Science.gov (United States)

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

    2013-01-01

    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.).

  17. Calcium isotopic fractionation in microbially mediated gypsum precipitates

    Science.gov (United States)

    Harouaka, Khadouja; Mansor, Muammar; Macalady, Jennifer L.; Fantle, Matthew S.

    2016-07-01

    Gypsum (CaSO4·2H2O) precipitation experiments were carried out at low pH in the presence of the sulfur oxidizing bacterium Acidithiobacillus thiooxidans. The observed Ca isotopic fractionation (expressed as Δ44/40Cas-f = δ44/40Casolid-δ44/40Cafluid) at the end of each experimental time period (∼50 to 60 days) was -1.41‰ to -1.09‰ in the biotic experiments, -1.09‰ in the killed control, and -1.01‰ to -0.88‰ in the abiotic controls. As there were no strong differences in the solution chemistry and the rate at which gypsum precipitated in the biotic and abiotic controls, we deduce a biological Ca isotope effect on the order of -0.3‰. The isotope effect correlates with a difference in crystal aspect ratios between the biotic experiments (8.05 ± 3.99) and abiotic controls (31.9 ± 8.40). We hypothesize that soluble and/or insoluble organic compounds selectively inhibit crystal growth at specific crystal faces, and that the growth inhibition affects the fractionation factor associated with gypsum precipitation. The experimental results help explain Ca isotopic variability in gypsum sampled from a sulfidic cave system, in which gypsum crystals exhibiting a diversity of morphologies (microcrystalline to cm-scale needles) have a broad range of δ44/40Ca values (∼1.2-0.4‰) relative to the limestone wall (δ44/40Ca = 1.3‰). In light of the laboratory experiments, the variation in Ca isotope values in the caves can be interpreted as a consequence of gypsum precipitation in the presence of microbial organic matter and subsequent isotopic re-equilibration with the Ca source.

  18. Cryogenic Calcite: A Morphologic and Isotopic Analog to the ALH84001 Carbonates

    Science.gov (United States)

    Niles, P. B.; Leshin, L. A.; Socki, R. A.; Guan, Y.; Ming, D. W.; Gibson, E. K.

    2004-01-01

    Martian meteorite ALH84001 carbonates preserve large and variable microscale isotopic compositions, which in some way reflect their formation environment. These measurements show large variations (>20%) in the carbon and oxygen isotopic compositions of the carbonates on a 10-20 micron scale that are correlated with chemical composition. However, the utilization of these data sets for interpreting the formation conditions of the carbonates is complex due to lack of suitable terrestrial analogs and the difficulty of modeling under non-equilibrium conditions. Thus, the mechanisms and processes are largely unknown that create and preserve large microscale isotopic variations in carbonate minerals. Experimental tests of the possible environments and mechanisms that lead to large microscale isotopic variations can help address these concerns. One possible mechanism for creating large carbon isotopic variations in carbonates involves the freezing of water. Carbonates precipitate during extensive CO2 degassing that occurs during the freezing process as the fluid s decreasing volume drives CO2 out. This rapid CO2 degassing results in a kinetic isotopic fractionation where the CO2 gas has a much lighter isotopic composition causing an enrichment of 13C in the remaining dissolved bicarbonate. This study seeks to determine the suitability of cryogenically formed carbonates as analogs to ALH84001 carbonates. Specifically, our objective is to determine how accurately models using equilibrium fractionation factors approximate the isotopic compositions of cryogenically precipitated carbonates. This includes determining the accuracy of applying equilibrium fractionation factors during a kinetic process, and determining how isotopic variations in the fluid are preserved in microscale variations in the precipitated carbonates.

  19. Hydrogen isotope fractionation by Methanothermobacter thermoautotrophicus in coculture and pure culture conditions

    Science.gov (United States)

    Yoshioka, Hideyoshi; Sakata, Susumu; Kamagata, Yoichi

    2008-06-01

    We grew a hydrogen-utilizing methanogen, Methanothermobacter thermoautotrophicus strain ΔH, in coculture and pure culture conditions to evaluate the hydrogen isotope fractionation associated with carbonate reduction under low (6 mM; pure culture) concentrations of H 2 in the headspace. In the cocultures, which were grown at 55 °C with a thermophilic butyrate-oxidizing syntroph, the hydrogen isotopic relationship between methane and water was well represented by the following equation: δD=0.725(±0.003)·δDO-275(±3), in which the hydrogen isotope fractionation factor ( αH) was 0.725 ± 0.003. The relationship was consistent with the isotopic data on methane and water from terrestrial fields (a peat bog in Washington State, USA, and a sandy aquifer in Denmark), where carbonate reduction was reported to be the dominant pathway of methanogenesis. In the pure cultures, grown at 55 and 65 °C, the αH values were 0.755 ± 0.014 and 0.749 ± 0.014, respectively. Dependence of αH on growth temperature was not observed. The αH value at 55 °C in the pure culture was slightly higher than that in the coculture, a finding that disagrees with a hypothesis proposed by Burke [Burke, Jr. R. A. (1993) Possible influence of hydrogen concentration on microbial methane stable hydrogen isotopic composition. Chemosphere26, 55-67] that hydrogen isotope fractionation between methane and water increases (and αH decreases) with increasing H 2 concentration.

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

    Institute of Scientific and Technical Information of China (English)

    LIU ZongXiu; GU ZhaoYan; WU NaiQin; XU Bing

    2007-01-01

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

  1. Evaluation of Speleothem Oxygen Isotope Fractionation from a Tropical Cave on the Island of Guam

    Science.gov (United States)

    Moore, M. W.; Hardt, B. F.; Banner, J. L.; Jenson, J. W.

    2013-12-01

    Recent studies in the tropics apply oxygen isotope variations in speleothems as proxies for changes in past hydroclimate, yet little work has been done to study the modern tropical cave environment. Oxygen isotope time series in speleothems are commonly used to interpret past climate based on the assumption of equilibrium fractionation. When re-constructing paleoclimate, there are limited tools available to assess potential non-equilibrium isotope effects. One approach is to test for agreement of oxygen isotope values between parallel-milled tracks from a stalagmite. A stalagmite collected from Jinapsan Cave on the island of Guam supports the argument for equilibrium as multiple overlapping transects along the growth axis show consistent replication. However, to fully evaluate the fractionation processes relating to calcite growth, we have also studied the relationship between modern drip water and modern speleothem calcite. To accomplish this, we collected monthly dripwater samples and deployed artificial substrates under active drips to measure calcite growth rates and to assess the state of isotopic equilibrium between speleothem calcite and drip water. We evaluate the processes controlling the δ18O values of calcite formed on substrates relative to values for the dripwater feeding the site of the speleothem in Jinapsan Cave. The studied drip site shows seasonal variability in dripwater δ18O of ~1‰, with more negative composition occurring during the wet season. The δ18O of the substrate calcite sampled at the point of first growth (analogous to the growth axis in a speleothem) also shows a seasonal cycle of about 1‰, yet the values are more positive than predicted by the equilibrium equation of Kim & O'Neil 1997. In addition, carbon and oxygen isotopic composition between substrates strongly covary. Correlation of carbon and oxygen isotopes between substrates at the point of first growth may be explained by prior calcite precipitation. Carbon isotope

  2. Carbon isotope anomalies in carbonates of the Karelian series

    Science.gov (United States)

    Iudovich, Ia. E.; Makarikhin, V. V.; Medvedev, P. V.; Sukhanov, N. V.

    1990-07-01

    Results are presented on carbon isotope distributions in carbonates of the Karelian complex. A highly anomalous isotopic composition was found in carbonate rocks aged from 2.6 to 1.9 b.y. In the stromatolitic carbonates of the Onega water table, delta-(C-13) reaches a value of +18 percent, while the shungite layer of the Zaonega horizon is characterized by a wide dispersion (from +7.9 to -11.8 percent). These data are in good agreement with the known geochemical boundary (about 2.2 b.y. ago) in the history of the earth.

  3. Hydrogen isotope fractionation in the photolysis of formaldehyde

    Directory of Open Access Journals (Sweden)

    T. S. Rhee

    2007-08-01

    Full Text Available Experiments investigating the isotopic fractionation in the formation of H2 by the photolysis of CH2O under tropospheric conditions are reported and discussed. The deuterium (D depletion in H2 produced is 500(±20‰ with respect to the parent CH2O. We also observed that complete photolysis of CH2O under atmospheric conditions produces H2 that has virtually the same isotopic ratio as that of the parent CH2O. These findings imply that there must be a very strong concomitant isotopic enrichment in the radical channel (CH2O + → CHO + H as compared to the molecular channel (CH2O + → H2 + CO of the photolysis of CH2O in order to balance the relatively small isotopic fractionation in the competing reaction of CH2O with OH. Using a 1-box photochemistry model we calculated the isotopic fractionation factor for the radical channel to be 0.22(±0.08, which is equivalent to a 780(±80‰ enrichment in D of the remaining CH2O. When CH2O is in photochemical steady state, the isotopic ratio of the H2 produced is determined not only by the isotopic fractionation occurring during the photolytical production of H2m but also by overall fractionation for the removal processes of CH2O (αf, and is represented by the ratio of αmf. Applying the isotopic fractionation factors relevant to CH2O photolysis obtained in the present study to the troposphere, the ratio of αmf varies from ~0.8 to ~1.2 depending on the fraction of CH2O that reacts with OH and that produces H2. This range of αmf can render the H2 produced from the photochemical oxidation of CH4 to be enriched in D (with respect to the original CH

  4. Hydrogen isotope fractionation in the photolysis of formaldehyde

    Directory of Open Access Journals (Sweden)

    T. S. Rhee

    2008-03-01

    Full Text Available Experiments investigating the isotopic fractionation in the formation of H2 by the photolysis of CH2O under tropospheric conditions are reported and discussed. The deuterium (D depletion in the H2 produced is 500(±20‰ with respect to the parent CH2O. We also observed that complete photolysis of CH2O under atmospheric conditions produces H2 that has virtually the same isotope ratio as that of the parent CH2O. These findings imply that there must be a very strong concomitant isotopic enrichment in the radical channel (CH2O+hν → CHO+H as compared to the molecular channel (CH2O+hν → H2+CO of the photolysis of CH2O in order to balance the relatively small isotopic fractionation in the competing reaction of CH2O with OH. Using a 1-box photochemistry model we calculated the isotopic fractionation factor for the radical channel to be 0.22(±0.08, which is equivalent to a 780(±80‰ enrichment in D of the remaining CH2O. When CH2O is in photochemical steady state, the isotope ratio of the H2 produced is determined not only by the isotopic fractionation occurring during the photolytical production of H2m but also by overall fractionation for the removal processes of CH2O (αf, and is represented by the ratio of αmf. Applying the isotopic fractionation factors relevant to CH2O photolysis obtained in the present study to the troposphere, the ratio of αmf varies from ~0.8 to ~1.2 depending on the fraction of CH2O that reacts with OH and that produces H2. This range of αmf can render the H2 produced from the photochemical oxidation of CH4 to

  5. Silicon Isotopic Fractionation in a Tropical Soil-Plant System

    Science.gov (United States)

    Opfergelt, S.; Delstanche, S.; Cardinal, D.; Andre, L.; Delvaux, B.

    2006-12-01

    Silica fluxes to soil solutions and water streams are controlled by both abiotic and biotic processes occurring in a Si soil-plant cycle that can be significant in comparison with Si weathering input and hydrological output. The quantification of Si-isotopic fractionation by these processes is highly promising to study the Si soil-plant cycle. Therein, the fate of aqueous monosilicic acid H4SiO4, as produced by silicate weathering, may take four paths: (1) uptake by plants and recycling through falling litter, (2) formation of clay minerals, (3) specific adsorption onto Al and Fe oxides, (4) leaching in drainage waters and export from watersheds. Here we report on detailed Si-isotopic compositions of various Si pools in a tropical soil-plant system involving old stands of banana (Musa acuminata Colla, cv Grande Naine) cropped on a weathering sequence of soils derived from andesitic volcanic ash and pumice deposits in Cameroon, West Africa. Si-isotopic compositions were measured by MC-ICP-MS in dry plasma mode with external Mg doping with a reproducibility of 0.08 permil (2stdev). Results were expressed as delta29Si vs NBS28. The compositions were determined in plant parts, bulk soils, clay fractions (less than 2um) and stream waters used for crop irrigation. Of the weathering sequence, we selected young (Y) and old (O) volcanic soils (vs). Yvs are rich in weatherable minerals, and contain large amounts of pumice gravels; their clay fraction (10-35 percent) contains allophane, halloysite and ferrihydrite. Oppositely, Ovs are strongly weathered and fine clayey soils (75-96 percent clay) rich in halloysite, kaolinite, gibbsite and goethite. Intra-plant fractionation between roots and shoots and within shoots confirmed our previous data measured on banana plants grown in hydroponics. The bulk plant isotopic composition was heavier at Ovs than at Yvs giving a fractionation factor per atomic mass unit between plants and their irrigation water Si source (+0.61 permil) of

  6. Exotic Structure of Carbon Isotopes

    CERN Document Server

    Suzuki, T; Hagino, K; Suzuki, Toshio; Sagawa, Hiroyuki; Hagino, Kouichi

    2002-01-01

    We studied firstly the ground state properties of C-isotopes using a deformed Hartree-Fock (HF)+ BCS model with Skyrme interactions. Shallow deformation minima are found in several neutron$-$rich C-isotopes. It is shown also that the deformation minima appear in both the oblate and the prolate sides in $^{17}$C and $^{19}$C having almost the same binding energies. Secondly, we carried out shell model calculations to study electromagnetic moments and electric dipole transitions of the C-isotopes. We point out the clear configuration dependence of the quadrupole and magnetic moments in the odd C-isotopes, which will be useful to find out the deformations and the spin-parities of the ground states of these nuclei. We studied electric dipole states of C-isotopes focusing on the interplay between low energy Pigmy strength and giant dipole resonances. Reasonable agreement is obtained with available experimental data for the photoreaction cross sections both in the low energy region below $\\hbar \\omega $=14 MeV and ...

  7. S-Isotope Fractionation between Fluid and Silicate Melts

    Science.gov (United States)

    Fiege, A.; Holtz, F.; Shimizu, N.; Behrens, H.; Mandeville, C. W.; Simon, A. C.

    2013-12-01

    Large amounts of sulfur (S) can be released from silicate melts during volcanic eruption. Degassing of magma can lead to S-isotope fractionation between fluid and melt. However, experimental data on fluid-melt S-isotope fractionation are scarce and no data exist for silicate melts at temperatures (T) > 1000°C. Recent advances in in situ S-isotope analyses using secondary ion mass spectroscopy (SIMS) enable determinations of the isotopic composition in silicate glasses with low S content [1] and allow us to investigate experimentally fluid-melt S-isotope fractionation effects in magmatic systems. Isothermal decompression experiments were conducted in internally heated pressure vessels (IHPV). Volatile-bearing (~3 to ~8 wt% H2O, 140 to 2700 ppm S, 0 to 1000 ppm Cl) andesitic and basaltic glasses were synthesized at ~1040°C, ~500 MPa and log(fO2) = QFM to QFM+4 (QFM: quartz-magnetite-fayalite buffer). The decompression experiments were carried out at T = 1030 to 1200°C and similar fO2. Pressure (P) was released continuously from ~400 MPa to 150, 100 or 70 MPa with rates (r) ranging from 0.001 to 0.2 MPa/s. The samples were either rapidly quenched after decompression or annealed for various times (tA) at final conditions (1 to 72 h) before quenching. The volatile-bearing starting glasses and the partially degassed experimental glasses were analyzed by electron microprobe (e.g. Cl-, S-content), IR-spectroscopy (H2O content) and SIMS (δ34S). The gas-melt isotope fractionation factors (αg-m) were estimated following Holloway and Blank [2] and utilizing mass balance calculations. The results show that αg-m remains constant within error over the investigated range of r and tA, reflecting fluid-melt equilibrium fractionation of S isotopes for given T and fO2. Data obtained for oxidizing conditions (~QFM+4) are in agreement with observations in arc magmas [3] and close to what is predicted by previous theoretical and experimental data [4; 5; 6]; e.g. a α(SO2 gas - SO42

  8. Microbial mass-dependent fractionation of chromium isotopes

    Science.gov (United States)

    Sikora, Eric R.; Johnson, Thomas M.; Bullen, Thomas D.

    2008-08-01

    Mass-dependent fractionation of Cr isotopes occurs during dissimilatory Cr(VI) reduction by Shewanella oneidensis strain MR-1. Cells suspended in a simple buffer solution, with various concentrations of lactate or formate added as electron donor, reduced 5 or 10 μM Cr(VI) to Cr(III) over days to weeks. In all nine batch experiments, 53Cr/ 52Cr ratios of the unreacted Cr(VI) increased as reduction proceeded. In eight experiments covering a range of added donor concentrations up to 100 μM, isotopic fractionation factors were nearly invariant, ranging from 1.0040 to 1.0045, with a mean value somewhat larger than that previously reported for abiotic Cr(VI) reduction (1.0034). One experiment containing much greater donor concentration (10 mM lactate) reduced Cr(VI) much faster and exhibited a lesser fractionation factor (1.0018). These results indicate that 53Cr/ 52Cr measurements should be effective as indicators of Cr(VI) reduction, either bacterial or abiotic. However, variability in the fractionation factor is poorly constrained and should be studied for a variety of microbial and abiotic reduction pathways.

  9. Microbial mass-dependent fractionation of chromium isotopes

    Science.gov (United States)

    Sikora, E.R.; Johnson, T.M.; Bullen, T.D.

    2008-01-01

    Mass-dependent fractionation of Cr isotopes occurs during dissimilatory Cr(VI) reduction by Shewanella oneidensis strain MR-1. Cells suspended in a simple buffer solution, with various concentrations of lactate or formate added as electron donor, reduced 5 or 10 ??M Cr(VI) to Cr(III) over days to weeks. In all nine batch experiments, 53Cr/52Cr ratios of the unreacted Cr(VI) increased as reduction proceeded. In eight experiments covering a range of added donor concentrations up to 100 ??M, isotopic fractionation factors were nearly invariant, ranging from 1.0040 to 1.0045, with a mean value somewhat larger than that previously reported for abiotic Cr(VI) reduction (1.0034). One experiment containing much greater donor concentration (10 mM lactate) reduced Cr(VI) much faster and exhibited a lesser fractionation factor (1.0018). These results indicate that 53Cr/52Cr measurements should be effective as indicators of Cr(VI) reduction, either bacterial or abiotic. However, variability in the fractionation factor is poorly constrained and should be studied for a variety of microbial and abiotic reduction pathways. ?? 2008 Elsevier Ltd.

  10. Wavelength dependence of isotope fractionation in N2O photolysis

    Directory of Open Access Journals (Sweden)

    P. J. Crutzen

    2002-10-01

    Full Text Available In previous reports on isotopic fractionation in the ultraviolet photolysis of nitrous oxide (N2O only enrichments of heavy isotopes in the remaining N2O fraction have been found. However, most direct photolysis experiments have been performed at wavelengths far from the absorption maximum at 182 nm. Here we present high-precision measurements of the 15N and 18O fractionation constants (e in photolysis at 185 nm. Small, but statistically robust depletions of heavy isotopes for the terminal atoms in the linear N2O molecule are found. This means that the absorption cross sections s(15N14N16O and s(14N218O are larger than s(14N216O at this specific wavelength. In contrast, the central N atom becomes enriched in 15N. The corresponding fractionation constants (±1 standard deviation are 15e1 = s(15N14N16O/s(14N216O - 1 = (3.7 ± 0.2%o 18e = s(14N218O/s(14N216O - 1 = (4.5 ± 0.2%o  and   15e2 = s(chem{14N15N16O/s(14N216O - 1 = (-18.6 ± 0.5 %o To our knowledge, this is the first documented case of such a heavy isotope depletion in the photolysis of N2O which supports theoretical models and pioneering vacuum ultraviolet spectroscopic measurements of 15N substituted N2O species that predict fluctuations of e around zero in this spectral region (Selwyn and Johnston, 1981. Such a variability in isotopic fractionation could have consequences for atmospheric models of N2O isotopes since actinic flux varies also strongly over narrow wavelength regions between 175 and 200 nm due to the Schumann-Runge bands of oxygen. However, the spacing between maxima and minima of the fractionation constants and of the actinic flux differ by two orders of magnitude in the wavelength  domain. The wavelength dependence of fractionation constants in N2O photolysis can thus be approximated by a linear fit with negligible consequences on the actual value of the spectrally averaged fractionation constant. In order to establish this linear fit, additional measurements at

  11. The ecophysiology of sulfur isotope fractionation by sulfate reducing bacteria in response to variable environmental conditions

    Science.gov (United States)

    Leavitt, W.; Bradley, A. S.; Johnston, D. T.; Pereira, I. A. C.; Venceslau, S.; Wallace, C.

    2014-12-01

    Microbial sulfate reducers (MSR) drive the Earth's biogeochemical sulfur cycle. At the heart of this energy metabolism is a cascade of redox transformations coupling organic carbon and/or hydrogen oxidation to the dissimilatory reduction of sulfate to sulfide. The sulfide produced is depleted in the heavier isotopes of sulfur relative to sulfate. The magnitude of discrimination (fractionation) depends on: i) the cell-specific sulfate reduction rate (csSRR, Kaplan & Rittenberg (1964) Can. J. Microbio.; Chambers et al. (1975) Can. J. Microbio; Sim et al. (2011) GCA; Leavitt et al. (2013) PNAS), ii) the ambient sulfate concentration (Harrison & Thode (1958) Research; Habicht et al. (2002) Science; Bradley et al. in review), iii) both sulfate and electron donor availability, or iv) an intrinsic physiological limitation (e.g. cellular division rate). When neither sulfate nor electron donor limits csSRR a more complex function relates the magnitude of isotope fractionation to cell physiology and environmental conditions. In recent and on-going work we have examined the importance of enzyme-specific fractionation factors, as well as the influence of electron donor or electron acceptor availability under carefully controlled culture conditions (e.g. Leavitt et al. (2013) PNAS). In light of recent advances in MSR genetics and biochemistry we utilize well-characterized mutant strains, along with a continuous-culture methodology (Leavitt et al. (2013) PNAS) to further probe the fractionation capacity of this metabolism under controlled physiological conditions. We present our latest findings on the magnitude of S and D/H isotope fractionation in both wild type and mutant strains. We will discuss these in light of recent theoretical advances (Wing & Halevy (2014) PNAS), examining the mode and relevance of MSR isotope fractionation in the laboratory to modern and ancient environmental settings, particularly anoxic marine sediments.

  12. First-principles models of equilibrium tellurium isotope fractionation

    Science.gov (United States)

    Haghnegahdar, M. A.; Schauble, E. A.; Fornadel, A. P.; Spry, P. G.

    2013-12-01

    In this study, equilibrium mass-dependent isotopic fractionation among representative Te-bearing species is estimated with first-principles thermodynamic calculations. Tellurium is a group 16 element (along with O, S, and Se) with eight stable isotopes ranging in mass from 120Te to 130Te, and six commonly-occurring oxidation states: -II, -I, 0, +II, +IV, and +VI. In its reduced form, Te(-II), tellurium has a unique crystal-chemical role as a bond partner for gold and silver in epithermal and orogenic gold deposits, which likely form when oxidized Te species (e.g., H2TeO3, TeO32-) or perhaps polytellurides (e.g., Te22-) interact with precious metals in hydrothermal solution. Te(IV) is the most common oxidation state at the Earth's surface, including surface outcrops of telluride ore deposits, where tellurite and tellurate minerals form by oxidation. In the ocean, dissolved tellurium tends to be scavenged by particulate matter. Te(VI) is more abundant than Te(IV) in the ocean water (1), even though it is thought to be less stable thermodynamically. This variety of valence states in natural systems and range of isotopic masses suggest that tellurium could exhibit geochemically useful isotope abundance variations. Tellurium isotope fractionations were determined for representative molecules and crystals of varying complexity and chemistry. Gas-phase calculations are combined with supermolecular cluster models of aqueous and solid species. These in turn are compared with plane-wave density functional theory calculations with periodic boundary conditions. In general, heavyTe/lightTe is predicted to be higher for more oxidized species, and lower for reduced species, with 130Te/125Te fractionations as large as 4‰ at 100οC between coexisting Te(IV) and Te(-II) or Te(0) compounds. This is a much larger fractionation than has been observed in naturally occurring redox pairs (i.e., Te (0) vs. Te(IV) species) so far, suggesting that disequilibrium processes may control

  13. Predicting equilibrium uranium isotope fractionation in crystals and solution

    Science.gov (United States)

    Schauble, E. A.

    2015-12-01

    Despite the rapidly growing interest in using 238U/235U measurements as a proxy for changes in oxygen abundance in surface and near-surface environments, the present theoretical understanding of uranium isotope fractionation is limited to a few simple gas-phase molecules and analogues of dissolved species (e.g., 1,2,3). Understanding uranium isotope fractionation behavior in more complicated species, such as crystals and adsorption complexes, will help in the design and interpretation of experiments and field studies, and may suggest other uses for 38U/235U measurements. In this study, a recently developed first-principles method for estimating the nuclear volume component of field shift fractionation in crystals and complex molecular species (4) is combined with mass-dependent fractionation theory to predict equilibrium 38U/235U fractionations in aqueous and crystalline uranium compounds, including uraninite (UO2). The nuclear field shift effect, caused by the interaction of electrons with the finite volume of the positive charge distribution in uranium nuclei, is estimated using Density Functional Theory and the Projector Augmented Wave method (DFT-PAW). Tests against relativistic electronic structure calculations and Mössbauer isomer shift data indicate that the DFT-PAW method is reasonably accurate, while being much better suited to models of complex and crystalline species. Initial results confirm previous predictions that the nuclear volume effect overwhelms mass depdendent fractionation in U(VI)-U(IV) exchange reactions, leading to higher 238U/235U in U(IV) species (i.e., for UO2 xtal vs. UO22+aq, ln αNV ≈ +1.8‰ , ln αMD ≈ -0.8‰, ln αTotal ≈ +1.0‰ at 25ºC). UO2 and U(H2O)94+, are within ~0.4‰ of each other, while U(VI) species appear to be more variable. This suggests that speciation is likely to significantly affect natural uranium isotope fractionations, in addition to oxidation state. Tentatively, it appears that uranyl-type (UO22

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

    Institute of Scientific and Technical Information of China (English)

    沈平

    1995-01-01

    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

  15. Barium isotope fractionation during witherite (BaCO3) dissolution, precipitation and at equilibrium

    Science.gov (United States)

    Mavromatis, Vasileios; van Zuilen, Kirsten; Purgstaller, Bettina; Baldermann, Andre; Nägler, Thomas F.; Dietzel, Martin

    2016-10-01

    This study examines the behavior of Ba isotope fractionation between witherite and fluid during mineral dissolution, precipitation and at chemical equilibrium. Experiments were performed in batch reactors at 25 °C in 10-2 M NaCl solution where the pH was adjusted by continuous bubbling of a water saturated gas phase of CO2 or atmospheric air. During witherite dissolution no Ba isotope fractionation was observed between solid and fluid. In contrast, during witherite precipitation, caused by a pH increase, a preferential uptake of the lighter 134Ba isotopomer in the solid phase was observed. In this case, the isotope fractionation factor αwitherite-fluid is calculated to be 0.99993 ± 0.00004 (or Δ137/134Bawitherite-fluid ≈ -0.07 ± 0.04‰, 2 sd). The most interesting feature of this study, however, is that after the attainment of chemical equilibrium, the Ba isotope composition of the aqueous phase is progressively becoming lighter, indicating a continuous exchange of Ba2+ ions between witherite and fluid. Mass balance calculations indicate that the detachment of Ba from the solid is not only restricted to the outer surface layer of the solid, but affects several (∼7 unit cells) subsurface layers of the crystal. This observation comes in excellent agreement with the concept of a dynamic system at chemical equilibrium in a mineral-fluid system, denoting that the time required for the achievement of isotopic equilibrium in the witherite-fluid system is longer compared to that observed for chemical equilibrium. Overall, these results indicate that the isotopic composition of Ba bearing carbonates in natural environments may be altered due to changes in fluid composition without a net dissolution/precipitation to be observed.

  16. Large Sulfur Isotope Fractionation Does Not Require Disproportionation

    Science.gov (United States)

    Sim, Min Sub; Bosak, Tanja; Ono, Shuhei

    2011-07-01

    The composition of sulfur isotopes in sedimentary sulfides and sulfates traces the sulfur cycle throughout Earth’s history. In particular, depletions of sulfur-34 (34S) in sulfide relative to sulfate exceeding 47 per mil (‰) often serve as a proxy for the disproportionation of intermediate sulfur species in addition to sulfate reduction. Here, we demonstrate that a pure, actively growing culture of a marine sulfate-reducing bacterium can deplete 34S by up to 66‰ during sulfate reduction alone and in the absence of an extracellular oxidative sulfur cycle. Therefore, similar magnitudes of sulfur isotope fractionation in sedimentary rocks do not unambiguously record the presence of other sulfur-based metabolisms or the stepwise oxygenation of Earth’s surface environment during the Proterozoic.

  17. Large sulfur isotope fractionation does not require disproportionation.

    Science.gov (United States)

    Sim, Min Sub; Bosak, Tanja; Ono, Shuhei

    2011-07-01

    The composition of sulfur isotopes in sedimentary sulfides and sulfates traces the sulfur cycle throughout Earth's history. In particular, depletions of sulfur-34 ((34)S) in sulfide relative to sulfate exceeding 47 per mil (‰) often serve as a proxy for the disproportionation of intermediate sulfur species in addition to sulfate reduction. Here, we demonstrate that a pure, actively growing culture of a marine sulfate-reducing bacterium can deplete (34)S by up to 66‰ during sulfate reduction alone and in the absence of an extracellular oxidative sulfur cycle. Therefore, similar magnitudes of sulfur isotope fractionation in sedimentary rocks do not unambiguously record the presence of other sulfur-based metabolisms or the stepwise oxygenation of Earth's surface environment during the Proterozoic.

  18. Fractionation of Stable Isotopes in Atmospheric Aerosol Reactions

    DEFF Research Database (Denmark)

    Meusinger, Carl

    -pinene - an abundant precursor to biogenic aerosol 3. Oxidation of SO2 to sulfuric acid - one of the key species in aerosol formation Laboratory experiments were designed and conducted as part of this thesis to investigate these processes. In addition, advanced data treatment and chemical modeling were performed...... reactions and undergo complex chemical and physical changes during their lifetimes. In order to assess processes that form and alter aerosols, information provided by stable isotopes can be used to help constrain estimates on the strength of aerosol sources and sinks. This thesis studies (mass......-independent) fractionation processes of stable isotopes of C, N, O and S in order to investigate three different systems related to aerosols: 1. Post-depositional processes of nitrate in snow that obscure nitrate ice core records 2. Formation and aging of secondary organic aerosol generated by ozonolysis of X...

  19. Isotope Fractionation by Diffusion in Liquids (Final Technical Report)

    Energy Technology Data Exchange (ETDEWEB)

    Richter, Frank [Univ. of Chicago, IL (United States)

    2016-11-09

    The overall objective of the DOE-funded research by grant DE-FG02-01ER15254 was document and quantify kinetic isotope fractionations during chemical and thermal (i.e., Soret) diffusion in liquids (silicate melts and water) and in the later years to include alloys and major minerals such as olivine and pyroxene. The research involved both laboratory experiments and applications to natural settings. The key idea is that major element zoning on natural geologic materials is common and can arise for either changes in melt composition during cooling and crystallization or from diffusion. The isotope effects associated with diffusion that we have documented are the key for determining whether or not the zoning observed in a natural system was the result of diffusion. Only in those cases were the zoning is demonstrably due to diffusion can use independently measured rates of diffusion to constrain the thermal evolution of the system.

  20. Experimental determination of magnesium isotope fractionation during higher plant growth

    Science.gov (United States)

    Bolou-Bi, Emile B.; Poszwa, Anne; Leyval, Corinne; Vigier, Nathalie

    2010-05-01

    Two higher plant species (rye grass and clover) were cultivated under laboratory conditions on two substrates (solution, phlogopite) in order to constrain the corresponding Mg isotope fractionations during plant growth and Mg uptake. We show that bulk plants are systematically enriched in heavy isotopes relative to their nutrient source. The Δ 26Mg plant-source range from 0.72‰ to 0.26‰ for rye grass and from 1.05‰ to 0.41‰ for clover. Plants grown on phlogopite display Mg isotope signatures (relative to the Mg source) ˜0.3‰ lower than hydroponic plants. For a given substrate, rye grass display lower δ 26Mg (by ˜0.3‰) relative to clover. Magnesium desorbed from rye grass roots display a δ 26Mg greater than the nutrient solution. Adsorption experiments on dead and living rye grass roots also indicate a significant enrichment in heavy isotopes of the Mg adsorbed on the root surface. Our results indicate that the key processes responsible for heavy isotope enrichment in plants are located at the root level. Both species also exhibit an enrichment in light isotopes from roots to shoots (Δ 26Mg leaf-root = -0.65‰ and -0.34‰ for rye grass and clover grown on phlogopite respectively, and Δ 26Mg leaf-root of -0.06‰ and -0.22‰ for the same species grown hydroponically). This heavy isotope depletion in leaves can be explained by biological processes that affect leaves and roots differently: (1) organo-Mg complex (including chlorophyll) formation, and (2) Mg transport within plant. For both species, a positive correlation between δ 26Mg and K/Mg was observed among the various organs. This correlation is consistent with the link between K and Mg internal cycles, as well as with formation of organo-magnesium compounds associated with enrichment in heavy isotopes. Considering our results together with the published range for δ 26Mg of natural plants and rivers, we estimate that a significant change in continental vegetation would induce a change of

  1. Soil Carbon: Compositional and Isotopic Analysis

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-11-01

    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.

  2. Isotope Fractionation Studies in Prestellar Cores: The Case of Nitrogen

    Science.gov (United States)

    Milam, Stefanie N.; Charnley, Steven B.

    2011-01-01

    Isotopically fractionated material is found in many solar system objects, including meteorites and comets. It is considered, in some cases, to trace interstellar material that was incorporated into the solar system without undergoing significant processing, thus preserving the fractionation. In interstellar molecular clouds, ion-molecule chemistry continually cycles nitrogen between the two main reservoirs - N and N2 - leading to only minor N-15 enrichments. Charnley and Rodgers showed that depletion of CO removes oxygen from the gas and weakens this cycle such that significant N-15 fractionation can occur for N2 and other N-bearing species in such cores. Observations are being conducted at millimeter and submillimeter wavelengths employing various facilities in order to both spatially and spectrally, resolve emission from these cores. A preliminary study to obtain the N-14/N-15 ratio in nitriles (HCN and HNC) was conducted at the Arizona Radio Observatory's 12m telescope on Kitt Peak, AZ. Spectra were obtained at high resolution (0.08 km/s) in order to resolve dynamic properties of each source as well as to resolve hyperfine structure present in certain isotopologues. This study included four dark cloud cores, observed to have varying levels of molecular depletion: L1521E, L1498, L1544, and L1521F. Previous studies of the N-14/N-15 ratio towards LI544 were obtained with N2H+ and NIH3, yielding ratios of 446 and >700, respectively. The discrepancy observed in these two measurements suggests a strong chemical dependence on the fractionation of nitrogen. Ratios (C,N, and D) obtained from isotopologues for a particular molecule are likely tracing the same chemical heritage and are directly comparable within a given source. Results and comparisons between the protostellar evolutionary state and isomer isotope fractionation as well as between other N-bearing species will be presented.

  3. Carbon isotopes as indicators of peatland growth?

    Science.gov (United States)

    Alewell, Christine; Krüger, Jan Paul; von Sengbusch, Pascal; Szidat, Sönke; Leifeld, Jens

    2016-04-01

    As undisturbed and/or growing peatlands store considerable amounts of carbon and are unique in their biodiversity and species assemblage, the knowledge of the current status of peatlands (growing with carbon sequestration, stagnating or degrading with carbon emissions) is crucial for landscape management and nature conservation. However, monitoring of peatland status requires long term measurements and is only feasible with expert knowledge. The latter determination is increasingly impeded in a scientific world, where taxonomic expert knowledge and funding of long term monitoring is rare. Stable carbon and nitrogen isotopes depth profiles in peatland soils have been shown to be a useful tool to monitor the degradation of peatlands due to permafrost thawing in Northern Sweden (Alewell et al., 2011; Krüger et al., 2014), drainage in Southern Finland (Krüger et al., 2016) as well as land use intensification in Northern Germany (Krüger et al., 2015). Here, we tackle the questions if we are able to differentiate between growing and degrading peats with the use of a combination of carbon stable (δ13C) and radiogenic isotope data (14C) with peat stratification information (degree of humification and macroscopic plant remains). Results indicate that isotope data are a useful tool to approximate peatland status, but that expert taxonomic knowledge will be needed for the final conclusion on peatland growth. Thus, isotope tools might be used for landscape screening to pin point sites for detailed taxonomic monitoring. As the method remains qualitative future research at these sites will need to integrate quantitative approaches to determine carbon loss or gain (soil C balances by ash content or C accumulation methods by radiocarbon data; Krüger et al., 2016). Alewell, C., R. Giesler, J. Klaminder, J. Leifeld, and M. Rollog. 2011. Stable carbon isotopes as indicators for micro-geomorphic changes in palsa peats. Biogeosciences, 8, 1769-1778. Krüger, J. P., Leifeld, J

  4. Cr isotope fractionation in metal-mineral-microbe interactions

    Science.gov (United States)

    Zhang, Qiong; Porcelli, Don; Thompson, Ian; Amor, Ken; Galer, Stephen

    2016-04-01

    Microbes interact with metals and minerals in the environments, altering their physical and chemical state whilst in turn the metals and minerals affect microbial growth, activity and survival. The interactions between Cr, Fe minerals and bacteria were investigated in this study. Cr(VI) reduction experiments by two iron-reducing bacteria, Pseudomonas fluorescens LB 300 and Shewanella oneidensis MR 1, in the presence of two iron oxide minerals, goethite and hematite, were conducted. Both minerals were found to inhibit the Cr(VI) reduction rate by Pseudomonas fluorescens LB 300 but accelerated Shewanella oneidensis MR 1. The Cr isotopic fractionation factor generated by both bacteria was mostly independent of the presence of the minerals, except for hematite with Pseudomonas fluorescens LB 300, where the ɛ was much higher. Aqueous Fe(III) in the solution did not have any detectable impact on either bacterial Cr reduction rates or the isotopic fractionation factors, indicating that the reduction of Cr(VI) occurred prior to that of Fe(III). The presence of aqueous Fe(II) induced a very fast abiotic reduction of Cr, but had little impact on the bacterial Cr reduction rates or its isotope fractionations. The evidence suggests that the different impact that Fe minerals had on the bacteria were related to the way they attached to the minerals and the difference in the reduction mechanism. SEM images confirmed that the attachment of Pseudomonas fluorescens LB 300 on the mineral surfaces were much more tightly packed than that of Shewanella oneidensis MR 1, so reducing mineral-metal interactions.

  5. Deciphering Carbon Isotope Excursions in Separated Biogenic and Diagenetic Carbonates

    Science.gov (United States)

    Hermoso, M.; Minoletti, F.; Hesselbo, S.; Jenkyns, H.; Rickaby, R.; Diester-Haass, L.; Delsate, D.

    2008-12-01

    The long-term evolution of the carbon-isotope ratio in the sedimentary archive is classically linked with changes in primary productivity and organic matter burial. There have been sudden and pronounced shifts, so-called Carbon Isotope Excursions (CIEs) in the long-term trends as evidenced by synchronous shifts from various basins. These geochemical perturbations may have various explanations such as changes of the efficiency of the carbon sink; sudden infusion of isotopically-light carbon into the Ocean-Atmosphere system; or advection of 12C-rich source from bottom water in a stratified water column. Beside the record of primary changes in seawater chemistry, a possible diagenetic overprint may also mime such CIEs in the sedimentary record. The aim of this contribution is to illustrate through three critical intervals (the Early Toarcian, the K-P boundary and the Mid-Miocene Montery Event) how the various micron-sized sedimentary particles specifically record these CIEs, which are respectively associated with major paleoceanographical events. New techniques for getting monotaxic calcareous nannofossil assemblages from the sediment (Minoletti et al., accepted) enable the isotopic measurement at various depths within the surface water and from bottom water by analyzing early diagenetic precipitations (rhombs and micarbs). The integration of these high-resolution isotopic signals in terms of amplitudes affords to recognize diagenetic artifacts in some sections displaying coeval decrease in the carbonate content. For both Early Toarcian and K-P events, corroborative records of CIE records in both primary calcite and bottom water carbonate indicate a global C-isotope perturbation of the water column. For the Monterey event, the evolution of calcareous nannoplankton and the foraminifera isotopic records are in overall agreement, but in detail, the coccolith-discoaster and foraminifer ratio in the sediment, related to environmental changes, is likely to produce isotopic

  6. The three-isotope method for equilibrium isotope fractionation factor determination: Unfounded optimism

    Science.gov (United States)

    Cao, X.; Hayles, J. A.; Bao, H.

    2015-12-01

    The equilibrium isotope fractionation factor α is a fundamental parameter in stable isotope geochemistry. Although equilibrium α can be determined by theoretical calculation or by measurement of natural samples, direct laboratory experiments are ultimately required to verify those results. The attainment of a true exchange equilibrium in experiments is often difficult, but three methods have been devised and used to ensure that an equilibrium α has been obtained in an isotope exchange experiment. These are the two-directional method, partial-exchange method, and three-isotope method. Of these, the three-isotope method is thought to be the most rigorous. Using water-water exchange as a basic unit, we have developed a set of complex exchange models to study when and why the three-isotope method may work well or not. We found that the method cannot promise to lead to an equilibrium α before the kinetic complexity of the specific exchange experiment is known. An equilibrium point in δ17O-δ18O space can be reached only when all of the isotope exchange pathways are fully reversible, i.e. there is no mass loss at any instant, and the forward and backward reactions share the same pathway. If the exchange pathways are not fully reversible, steady state may be reached, but a steady state α can be very different from the equilibrium α. Our results validated the earlier warning that the trajectory for three-isotope evolution in δ17O-δ18O space may be a distinctly curved line or contain more than one straight line due to the non-fully reversible isotope exchange reactions. The three-isotope method for equilibrium α determination is not as rigorous or as promising as it may seem. Instead, the trajectory of three-isotope evolution provides detailed insights into the kinetics of isotope exchange between compounds. If multiple components exist in the exchange system, the δ17O-δ18O evolving trajectory would be more complex.

  7. Constraints on neon and argon isotopic fractionation in solar wind.

    Science.gov (United States)

    Meshik, Alex; Mabry, Jennifer; Hohenberg, Charles; Marrocchi, Yves; Pravdivtseva, Olga; Burnett, Donald; Olinger, Chad; Wiens, Roger; Reisenfeld, Dan; Allton, Judith; McNamara, Karen; Stansbery, Eileen; Jurewicz, Amy J G

    2007-10-19

    To evaluate the isotopic composition of the solar nebula from which the planets formed, the relation between isotopes measured in the solar wind and on the Sun's surface needs to be known. The Genesis Discovery mission returned independent samples of three types of solar wind produced by different solar processes that provide a check on possible isotopic variations, or fractionation, between the solar-wind and solar-surface material. At a high level of precision, we observed no significant inter-regime differences in 20Ne/22Ne or 36Ar/38Ar values. For 20Ne/22Ne, the difference between low- and high-speed wind components is 0.24 +/- 0.37%; for 36Ar/38Ar, it is 0.11 +/- 0.26%. Our measured 36Ar/38Ar ratio in the solar wind of 5.501 +/- 0.005 is 3.42 +/- 0.09% higher than that of the terrestrial atmosphere, which may reflect atmospheric losses early in Earth's history.

  8. Cadmium isotope fractionation of materials derived from various industrial processes.

    Science.gov (United States)

    Martinková, Eva; Chrastný, Vladislav; Francová, Michaela; Šípková, Adéla; Čuřík, Jan; Myška, Oldřich; Mižič, Lukáš

    2016-01-25

    Our study represents ϵ(114/110) Cd NIST3108 values of materials resulting from anthropogenic activities such as coal burning, smelting, refining, metal coating, and the glass industry. Additionally, primary sources (ore samples, pigment, coal) processed in the industrial premises were studied. Two sphalerites, galena, coal and pigment samples exhibited ϵ(114/110) CdNIST3108 values of 1.0±0.2, 0.2±0.2, 1.3±0.1, -2.3±0.2 and -0.1±0.3, respectively. In general, all studied industrial processes were accompanied by Cd isotope fractionation. Most of the industrial materials studied were clearly distinguishable from the samples used as a primary source based on ϵ(114/110) Cd NIST3108 values. The heaviest ϵ(114/110) CdNIST3108 value of 58.6±0.9 was found for slag resulting from coal combustion, and the lightest ϵ(114/110) CdNIST3108 value of -23±2.5 was observed for waste material after Pb refinement. It is evident that ϵ(114/110) Cd NIST3108 values depend on technological processes, and in case of incomplete Cd transfer from source to final waste material, every industrial activity creates differences in Cd isotope composition. Our results show that Cd isotope analysis is a promising tool to track the origins of industrial waste products.

  9. Retrievals of boundary layer methane and isotope fractionation on Titan

    Science.gov (United States)

    Adamkovics, Mate; Lora, Juan M.; Mitchell, Jonathan L.

    2016-10-01

    The amount of methane in the boundary layer on Titan is an interesting diagnostic of whether or not it might be seeping out of the regolith. We know that kinetic fractionation of methane isotopes can be diagnostic of evaporation at the surface and condensation in the atmosphere. If a parcel is constrained to follow a moist adiabat while condensation occurs, we can predict the amount of fractionation that is expected (Ádámkovics & Mitchell, 2016). We will present our most recent efforts to measure boundary layer methane abundance and isotopic composition, which include our recently published Keck NIRSPAO observations from 17 July 2014 (Ádámkovics et al., 2016), as well as preliminary results from follow-up measurements made on 15 May 2016. Our measurements are tantalizingly close to being able to distinguish between different hydrological parameterizations of the polar regions in the Titan Atmospheric Model (Lora & Ádámkovics, 2016). We will discuss the systematic uncertainties that can be evaluated with the combination of these two datasets and the prospects for exceptionally high S/N observations via particularly deep integrations over multiple nights.

  10. Fractionation of Nitrogen and Oxygen Isotopes During Microbial Nitrate Reduction

    Science.gov (United States)

    Lehmann, M. F.; Bernasconi, S. M.; Reichert, P.; Barbieri, A.; McKenzie, J. A.

    2001-12-01

    Lakes represent an important continental sink of fixed nitrogen. Besides the burial of particulate nitrogen, fixed nitrogen is eliminated from lakes by emission of N2 and N2O to the atmosphere during dissimilative nitrate reduction within suboxic and anoxic waters or sediments. The understanding and quantification of this efficient nitrogen removal process in eutrophic lakes is crucial for nitrogen budget modelling and the application and evaluation of lake restoration measures. In order to use natural abundance N and O isotope ratios as tracers for microbial nitrate reduction and to obtain quantitative estimates on its intensity, it is crucial to constrain the associated isotope fractionation. This is the first report of nitrogen and oxygen isotope effects associated with microbial nitrate reduction in lacustrine environments. Nitrate reduction in suboxic and anoxic waters of the southern basin of Lake Lugano (Switzerland) is demonstrated by a progressive nitrate depletion coupled to increasing δ 15N and δ 18O values for residual nitrate. 15N and 18O enrichment factors (ɛ ) were estimated using a closed-system (Rayleigh-distillation) model and a dynamic reaction-diffusion model. Calculated enrichment factors ɛ ranged between -11.2 and -22‰ for 15N and between -6.6 and -11.3‰ for 18O with both nitrogen and oxygen isotope fractionation being greatest during times with the highest nitrate reduction rates. The closed-system model neglects vertical diffusive mixing and does not distinguish between sedimentary and water-column nitrate reduction. Therefore, it tends to underestimate the intrinsic isotope effect of microbial nitrate reduction. Based upon results from earlier studies that indicate that nitrate reduction in sediments displays a highly reduced N-isotope effect (Brandes and Devol, 1997), model-derived enrichment factors could be used to discern the relative importance of nitrate reduction in the water column and in the sediment. Sedimentary nitrate

  11. Isotopic Fractionation in Primitive Material: Quantifying the Contribution of Interstellar Chemistry

    Science.gov (United States)

    Charnley, Steven

    2010-01-01

    Anomalously fractionated isotopic material is found in many primitive Solar System objects, such as meteorites and comets. It is thought, in some cases, to trace interstellar matter that was incorporated into the Solar Nebula without undergoing significant processing. We will present the results of models of the nitrogen, oxygen, and carbon fractionation chemistry in dense molecular clouds, particularly in cores where substantial freeze-out of molecules on to dust has occurred. The range of fractionation ratios expected in different interstellar molecules will be discussed and compared to the ratios measured in molecular clouds, comets and meteoritic material. These models make several predictions that can be tested in the near future by molecular line observations, particularly with ALMA.

  12. Experimental study on stable isotopic fractionation of evaporating water under varying temperature

    Institute of Scientific and Technical Information of China (English)

    Hai-ying HU; Wei-min BAO; Tao WANG; Si-min QU

    2009-01-01

    The variation of stable isotope ratios in natural waters provides valuable information that can be used to trace water movement. Evaporation plays a crucial role in determining the variation of stable isotopes. In this paper, several evaporation experiments were conducted in order to study the stable isotopic fractionation mechanism of water and analyze the influence of different temperatures on evaporation fractionation. Three group experiments of water evaporation under different temperatures and initial isotopic values were carried out. The results show that fractionation factors of hydrogen and oxygen may increase with temperature, and the average enrichment degree of hydrogen isotope D is 3.432 times that of oxygen isotope 18O. The results also show that the isotopic composition of the initial water has little influence on water evaporation fractionation, which is mainly affected by the state variables in the evaporation process, such as temperature. This research provides experimental data for further understanding the evaporation fractionation mechanism.

  13. Carbon Isotope Chemistry in Molecular Clouds

    Science.gov (United States)

    Robertson, Amy N.; Willacy, Karen

    2012-01-01

    Few details of carbon isotope chemistry are known, especially the chemical processes that occur in astronomical environments like molecular clouds. Observational evidence shows that the C-12/C-13 abundance ratios vary due to the location of the C-13 atom within the molecular structure. The different abundances are a result of the diverse formation pathways that can occur. Modeling can be used to explore the production pathways of carbon molecules in an effort to understand and explain the chemical evolution of molecular clouds.

  14. Carbon isotope excursions in paleosol carbonate marking five early Eocene hyperthermals in the Bighorn Basin, Wyoming

    Directory of Open Access Journals (Sweden)

    H. A. Abels

    2015-05-01

    Full Text Available Transient greenhouse warming events in the Paleocene and Eocene were associated with the addition of isotopically-light carbon to the exogenic atmosphere–ocean carbon pool, leading to substantial environmental and biotic change. The magnitude of an accompanying carbon isotope excursion (CIE can be used to constrain both the sources and amounts of carbon released during an event, as well as to correlate marine and terrestrial records with high precision. The Paleocene Eocene Thermal Maximum (PETM is well documented, but CIE records for the subsequent warming events are still rare especially from the terrestrial realm. Here, we provide new CIE records for two of the smaller hyperthermal events, I1 and I2, in paleosol carbonate, as well as two additional records of ETM2 and H2 in the Bighorn Basin. Stratigraphic comparison of this expanded, high-resolution terrestrial carbon isotope record to the deep-sea benthic foraminifera records from ODP Sites 1262 and 1263, Walvis Ridge, in the southern Atlantic Ocean corroborates that the Bighorn Basin fluvial sediments record global atmospheric change. The stratigraphic thicknesses of the eccentricity-driven hyperthermals in these archives are in line with precession-forcing of the 7 m thick fluvial overbank-avulsion sedimentary cycles. Using the CALMAG bulk oxide mean annual precipitation proxy, we reconstruct similar or slightly wetter than background soil moisture contents during the four younger hyperthermals, in contrast to drying observed during the PETM. Soil carbonate CIEs vary in magnitude proportionally with the marine CIEs for the four smaller early Eocene hyperthermals. This relationship breaks down for the PETM, with the soil carbonate CIE ~ 2–4‰ less than expected if all five linearly relate to marine CIEs. If the PETM CO2 forcing was similar but scaled to the younger hyperthermals, photosynthetic isotope fractionation or soil environmental factors are needed to explain this anomaly. We

  15. Nitrogen isotopic fractionation during abiotic synthesis of organic solid particles

    CERN Document Server

    Kuga, Maïa; Marty, Bernard; Marrocchi, Yves; Bernard, Sylvain; Rigaudier, Thomas; Fleury, Benjamin; Tissandier, Laurent

    2014-01-01

    The formation of organic compounds is generally assumed to result from abiotic processes in the Solar System, with the exception of biogenic organics on Earth. Nitrogen-bearing organics are of particular interest, notably for prebiotic perspectives but also for overall comprehension of organic formation in the young solar system and in planetary atmospheres. We have investigated abiotic synthesis of organics upon plasma discharge, with special attention to N isotope fractionation. Organic aerosols were synthesized from N2-CH4 and N2-CO gaseous mixtures using low-pressure plasma discharge experiments, aimed at simulating chemistry occurring in Titan s atmosphere and in the protosolar nebula, respectively. Nitrogen is efficiently incorporated into the synthesized solids, independently of the oxidation degree, of the N2 content of the starting gas mixture, and of the nitrogen speciation in the aerosols. The aerosols are depleted in 15N by 15-25 permil relative to the initial N2 gas, whatever the experimental set...

  16. Chlorine and carbon isotope measurements can help assessing the effectivenes of a zero valent iron barrier

    Science.gov (United States)

    Cretnik, S.; Audi, C.; Bernstein, A.; Palau, J.; Soler, A.; Elsner, M.

    2012-04-01

    Chlorinated aliphatic hydrocarbons (CAH's) such as trichloroethene (TCE), cis-dichloroethene (cis-DCE) and vinylchloride (VC) are extensively used in industrial applications. One of the most promising remediation techniques for CAH's in groundwater is their removal via abiotic reductive dechlorination using Zero Valent Iron (ZVI). This is applied for the treatment of contaminated sites by installing permeable reactive barriers (PRB). In this study, isotope fractionation of chlorinated ethylenes in transformation by cast iron has been investigated, because such types of iron are commonly used in PRBs. Batch experiments have been carried out in closed flasks, containing cast iron with aqueous solutions of TCE, cDCE and VC. These substrates and their respective products have been monitored by headspace samplings for their concentration (by GC-FID) and isotope fractionation of carbon and chlorine (by GC-IRMS). A decreasing reactivity trend was observed when compounds contain less chlorine atoms, with differences in rate constants of about one order of magnitude between each of the substances TCE > cDCE > VC. This resulted in the accumulation of products with fewer chlorine atoms. Therefore a similar observation can be expected if degradation in the field is incomplete, for example in the case of aged or improperly designed PRB. Pronounced carbon and chlorine isotope fractionation was measured for each of the compounds, and characteristic dual isotope plots (C, Cl) were obtained for TCE and cDCE. These results may serve as an important reference for the interpretation of isotope data from field sites, since stable isotope fractionation is widely recognized as robust indicator for such pollutant transformations. However, carbon isotope fractionation in a given parent compound may be caused by either abiotic or biotic degradation. In the field, it can therefore be difficult to delineate the contribution of abiotic transformation by PRB in the presence of ongoing

  17. Calcium isotope fractionation between aqueous compounds relevant to low-temperature geochemistry, biology and medicine

    Science.gov (United States)

    Moynier, Frédéric; Fujii, Toshiyuki

    2017-01-01

    Stable Ca isotopes are fractionated between bones, urine and blood of animals and between soils, roots and leaves of plants by >1000 ppm for the 44Ca/40Ca ratio. These isotopic variations have important implications to understand Ca transport and fluxes in living organisms; however, the mechanisms of isotopic fractionation are unclear. Here we present ab initio calculations for the isotopic fractionation between various aqueous species of Ca and show that this fractionation can be up to 3000 ppm. We show that the Ca isotopic fractionation between soil solutions and plant roots can be explained by the difference of isotopic fractionation between the different first shell hydration degree of Ca2+ and that the isotopic fractionation between roots and leaves is controlled by the precipitation of Ca-oxalates. The isotopic fractionation between blood and urine is due to the complexation of heavy Ca with citrate and oxalates in urine. Calculations are presented for additional Ca species that may be useful to interpret future Ca isotopic measurements. PMID:28276502

  18. Calcium isotope fractionation between aqueous compounds relevant to low-temperature geochemistry, biology and medicine.

    Science.gov (United States)

    Moynier, Frédéric; Fujii, Toshiyuki

    2017-03-09

    Stable Ca isotopes are fractionated between bones, urine and blood of animals and between soils, roots and leaves of plants by >1000 ppm for the (44)Ca/(40)Ca ratio. These isotopic variations have important implications to understand Ca transport and fluxes in living organisms; however, the mechanisms of isotopic fractionation are unclear. Here we present ab initio calculations for the isotopic fractionation between various aqueous species of Ca and show that this fractionation can be up to 3000 ppm. We show that the Ca isotopic fractionation between soil solutions and plant roots can be explained by the difference of isotopic fractionation between the different first shell hydration degree of Ca(2+) and that the isotopic fractionation between roots and leaves is controlled by the precipitation of Ca-oxalates. The isotopic fractionation between blood and urine is due to the complexation of heavy Ca with citrate and oxalates in urine. Calculations are presented for additional Ca species that may be useful to interpret future Ca isotopic measurements.

  19. Carbon and hydrogen isotopic effects of stomatal density in Arabidopsis thaliana

    Science.gov (United States)

    Lee, Hyejung; Feakins, Sarah J.; Sternberg, Leonel da S. L.

    2016-04-01

    Stomata are key gateways mediating carbon uptake and water loss from plants. Varied stomatal densities in fossil leaves raise the possibility that isotope effects associated with the openness of exchange may have mediated plant wax biomarker isotopic proxies for paleovegetation and paleoclimate in the geological record. Here we use Arabidopsis thaliana, a widely used model organism, to provide the first controlled tests of stomatal density on carbon and hydrogen isotopic compositions of cuticular waxes. Laboratory grown wildtype and mutants with suppressed and overexpressed stomatal densities allow us to directly test the isotope effects of stomatal densities independent of most other environmental or biological variables. Hydrogen isotope (D/H) measurements of both plant waters and plant wax n-alkanes allow us to directly constrain the isotopic effects of leaf water isotopic enrichment via transpiration and biosynthetic fractionations, which together determine the net fractionation between irrigation water and n-alkane hydrogen isotopic composition. We also measure carbon isotopic fractionations of n-alkanes and bulk leaf tissue associated with different stomatal densities. We find offsets of +15‰ for δD and -3‰ for δ13C for the overexpressed mutant compared to the suppressed mutant. Since the range of stomatal densities expressed is comparable to that found in extant plants and the Cenozoic fossil record, the results allow us to consider the magnitude of isotope effects that may be incurred by these plant adaptive responses. This study highlights the potential of genetic mutants to isolate individual isotope effects and add to our fundamental understanding of how genetics and physiology influence plant biochemicals including plant wax biomarkers.

  20. Observations of nitrogen isotope fractionation in deeply embedded protostars

    CERN Document Server

    Wampfler, S F; Bizzarro, M; Bisschop, S E

    2014-01-01

    (Abridged) The terrestrial planets, comets, and meteorites are significantly enriched in 15N compared to the Sun and Jupiter. While the solar and jovian nitrogen isotope ratio is believed to represent the composition of the protosolar nebula, a still unidentified process has caused 15N-enrichment in the solids. Several mechanisms have been proposed to explain the variations, including chemical fractionation. However, observational results that constrain the fractionation models are scarce. While there is evidence of 15N-enrichment in prestellar cores, it is unclear how the signature evolves into the protostellar phases. Our aim is to measure the 14N/15N ratio around three nearby, embedded low-to-intermediate-mass protostars. Isotopologues of HCN and HNC were used to probe the 14N/15N ratio. A selection of H13CN, HC15N, HN13C, and H15NC transitions was observed with the APEX telescope. The 14N/15N ratios were derived from the integrated intensities assuming a standard 12C/13C ratio. The assumption of optically...

  1. Two-Dimensional Stable Isotope Fractionation During Aerobic and Anaerobic Alkane Biodegradation and Implications for the Field

    Science.gov (United States)

    El Morris, Brandon; Suflita, Joseph M.; Richnow, Hans-Hermann

    2010-05-01

    Quantitatively, n-alkanes comprise a major portion of most crude oils. In petroliferous formations, it may be possible to relate the loss of these compounds to the levels of biodegradation occurring in situ [1]. Moreover, it is important to develop indicators of alkane degradation that may be used to monitor bioremediation of hydrocarbon-impacted environments. Desulfoglaeba alkanexedens and Pseudomonas putida GPo1 were used to determine if carbon and hydrogen stable isotope fractionation could differentiate between n-alkane degradation under anaerobic and aerobic conditions, respectively in the context of the Rayleigh equation model [2]. Bacterial cultures were sacrificed by acidification and headspace samples were analyzed for stable isotope composition using gas chromatography-isotope ratio mass spectrometry. Carbon enrichment factors (bulk) for anaerobic and aerobic biodegradation of hexane were -5.52 ± 0.2‰ and -4.34 ± 0.3‰, respectively. Hydrogen enrichment during hexane degradation was -43.14 ± 6.32‰ under sulfate-reducing conditions, and was too low for quantification during aerobiosis. Collectively, this indicates that the correlation between carbon and hydrogen stable isotope fractionation (may be used to help elucidate in situ microbial processes in oil reservoirs, and during intrinsic as well as engineered remediation efforts. References 1. Asif, M.; Grice, K.; Fazeelat, T., Assessment of petroleum biodegradation using stable hydrogen isotopes of individual saturated hydrocarbon and polycyclic aromatic hydrocarbon distributions in oils from the Upper Indus Basin, Pakistan. Organic Geochemistry 2009, 40, (3), 301-311. 2. Fischer, A.; Herklotz, I.; Herrmann, S.; Thullner, M.; Weelink, S. A. B.; Stams, A., J. M.; Schloemann, M.; Richnow, H.-H.; Vogt, C., Combined carbon and hydrogen isotope fractionation investigations for elucidating benzene biodegradation pathways. Environ. Sci. Technol. 2008, 42, 4356-4363.

  2. The relationship between carbon and oxygen isotopic composition characteristics of carbonates in loess sediments and paleoclimate

    Institute of Scientific and Technical Information of China (English)

    李春园; 王先彬; 文启彬; 邵波

    1995-01-01

    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.

  3. Determination of mass-dependent isotopic fractionation of cerium and neodymium in geochemical samples by MC-ICPMS.

    Science.gov (United States)

    Ohno, Takeshi; Hirata, Takafumi

    2013-01-01

    We have developed a new analytical method to determine the mass-dependent isotopic fractionations on Ce and Nd in geochemical samples. Mass discrimination effects on Ce and Nd were externally corrected by normalizing (149)Sm/(147)Sm and (153)Eu/(151)Eu, being 0.92124 and 1.0916, respectively based on an exponential law. The reproducibility of the isotopic ratio measurements on (142)Ce/(140)Ce, (146)Nd/(144)Nd and (148)Nd/(144)Nd were 0.08‰ (2SD, n = 25), 0.06‰ (2SD, n = 39) and 0.12‰ (2SD, n = 39), respectively. The present technique was applied to determine the variations of the Ce and Nd isotopic ratios for five geochemical reference materials (igneous rocks, JB-1a and JA-2; sedimentary rocks, JMn-1, JCh-1 and JDo-1). The resulting ratios for two igneous rocks (JB-1a and JA-2) and two sedimentary rocks (JMn-1 and JCh-1) did not vary significantly among the samples, whereas the Ce and Nd isotope ratios for the carbonate samples (JDo-1) were significantly higher than those for igneous and sedimentary rock samples. The 1:1 simple correlation between δ(142)Ce and δ(146)Nd indicates that there were no significant difference in the degree of isotopic fractionation between the Ce and Nd. This suggests that the isotopic fractionation for Ce found in the JDo-1 could be induced by geochemical or physicochemical processes without changing the oxidation status of Ce, since the redox-reaction can produce larger isotopic fractionation than the reactions without changing the oxidation state. The variations in the Ce and Nd isotope ratios for geochemical samples could provide new information concerning the physico-chemical processes of the sample formation.

  4. Helium and carbon isotopes in Indian diamonds

    Science.gov (United States)

    Wiens, R.; Lal, D.; Craig, H.

    1990-09-01

    Helium and carbon isotope measurements in Indian diamonds (from Andhra Pradesh) were carried out using samples that included mined diamonds from primary kimberlite source rocks and alluvial diamonds from river gravel. The He and C isotope concentrations in diamonds from these two sources were compared, and the Indian diamonds were compared to those from other regions. Results indicate that most of the He-3 in the alluvial diamonds is of cosmogenic origin and that the alluvial diamonds may also have a significant He-4 component due to alpha particles implanted during storage in a secondary matrix. One diamond, a mined kimberlite specimen, was found to have the lowest He-4 content (0.018 microcc/g) so far recorded in diamonds.

  5. The Precambrian marine carbonate isotope database: version 1.1.

    OpenAIRE

    G. A. Shields; Veizer, J.

    2002-01-01

    We present a compilation of strontium, carbon, and oxygen isotope compositions of roughly 10,000 marine carbonate rocks of Archean - Ordovician age (3800 Ma – 450 Ma). The Precambrian Marine Carbonate Isotope Database (PMCID) has been compiled from 152 published and 3 unpublished articles and books of the past 40 years. Also included are 30 categories of relevant “metadata” that allow detailed comparisons and quality assessments of the isotope data to be made. The PMCID will be updated period...

  6. Diffusion related isotopic fractionation effects with one-dimensional advective–dispersive transport

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Bruce S. [Civil Engineering Department, University of Toronto, 35 St George Street, Toronto, ON M5S 1A4 (Canada); Lollar, Barbara Sherwood [Earth Sciences Department, University of Toronto, 22 Russell Street, Toronto, ON M5S 3B1 (Canada); Passeport, Elodie [Civil Engineering Department, University of Toronto, 35 St George Street, Toronto, ON M5S 1A4 (Canada); Chemical Engineering and Applied Chemistry Department, University of Toronto, 200 College Street, Toronto, ON M5S 3E5 (Canada); Sleep, Brent E., E-mail: sleep@ecf.utoronto.ca [Civil Engineering Department, University of Toronto, 35 St George Street, Toronto, ON M5S 1A4 (Canada)

    2016-04-15

    Aqueous phase diffusion-related isotope fractionation (DRIF) for carbon isotopes was investigated for common groundwater contaminants in systems in which transport could be considered to be one-dimensional. This paper focuses not only on theoretically observable DRIF effects in these systems but introduces the important concept of constraining “observable” DRIF based on constraints imposed by the scale of measurements in the field, and on standard limits of detection and analytical uncertainty. Specifically, constraints for the detection of DRIF were determined in terms of the diffusive fractionation factor, the initial concentration of contaminants (C{sub 0}), the method detection limit (MDL) for isotopic analysis, the transport time, and the ratio of the longitudinal mechanical dispersion coefficient to effective molecular diffusion coefficient (D{sub mech}/D{sub eff}). The results allow a determination of field conditions under which DRIF may be an important factor in the use of stable carbon isotope measurements for evaluation of contaminant transport and transformation for one-dimensional advective–dispersive transport. This study demonstrates that for diffusion-dominated transport of BTEX, MTBE, and chlorinated ethenes, DRIF effects are only detectable for the smaller molar mass compounds such as vinyl chloride for C{sub 0}/MDL ratios of 50 or higher. Much larger C{sub 0}/MDL ratios, corresponding to higher source concentrations or lower detection limits, are necessary for DRIF to be detectable for the higher molar mass compounds. The distance over which DRIF is observable for VC is small (less than 1 m) for a relatively young diffusive plume (< 100 years), and DRIF will not easily be detected by using the conventional sampling approach with “typical” well spacing (at least several meters). With contaminant transport by advection, mechanical dispersion, and molecular diffusion this study suggests that in field sites where D{sub mech}/D{sub eff} is

  7. Comment on "Abiotic pyrite formation produces a large Fe isotope fractionation".

    Science.gov (United States)

    Czaja, Andrew D; Johnson, Clark M; Yamaguchi, Kosei E; Beard, Brian L

    2012-02-01

    Guilbaud et al. (Reports, 24 June 2011, p. 1548) suggest that the geologic record of Fe isotope fractionation can be explained by abiological precipitation of pyrite. We argue that a detailed understanding of the depositional setting, mineralogy, and geologic history of Precambrian sedimentary rocks indicates that the Fe isotope record dominantly reflects biological fractionations and Fe redox processes.

  8. The molecular mechanism of Mo isotope fractionation during adsorption to birnessite

    Science.gov (United States)

    Wasylenki, L.E.; Weeks, C.L.; Bargar, J.R.; Spiro, T.G.; Hein, J.R.; Anbar, A.D.

    2011-01-01

    Fractionation of Mo isotopes during adsorption to manganese oxides is a primary control on the global ocean Mo isotope budget. Previous attempts to explain what drives the surprisingly large isotope effect ??97/95Modissolved-??97/95Moadsorbed=1.8??? have not successfully resolved the fractionation mechanism. New evidence from extended X-ray absorption fine structure analysis and density functional theory suggests that Mo forms a polymolybdate complex on the surfaces of experimental and natural samples. Mo in this polynuclear structure is in distorted octahedral coordination, while Mo remaining in solution is predominantly in tetrahedral coordination as MoO42- Our results indicate that the difference in coordination environment between dissolved Mo and adsorbed Mo is the cause of isotope fractionation. The molecular mechanism of metal isotope fractionation in this system should enable us to explain and possibly predict metal isotope effects in other systems where transition metals adsorb to mineral surfaces. ?? 2011 Elsevier Ltd.

  9. Mantle Degassing and Diamond Genesis:A Carbon Isotope Perspective

    Institute of Scientific and Technical Information of China (English)

    郑永飞

    1994-01-01

    The effect of Co2 and CH4 degassing from the mantle on the carbon isotopic composition of diamond has been quantitatively modeled in terms of the principles of Rayleigh distillation.Assuming the δ13 C value of -5‰ for the mantle,the outgassing of CO2 can result in the large negative δ13 C values of diamond,whereas the outgassing of CH4 can drive the δ13C values of diamond in the positive direction.The theoretical expectations can be used to explain the full range of δ13 C values from-34.4‰5 to+5‰ observed for natural diamonds.It is possible that diamond formation was triggered by the degassing of Co2 and/or CH4 from the mantle and the associated fractional crystallization of carbonate-bearing melt.

  10. Carbon isotopes and water use efficiency in C4 plants.

    Science.gov (United States)

    Ellsworth, Patrick Z; Cousins, Asaph B

    2016-06-01

    Drought is a major agricultural problem worldwide. Therefore, selection for increased water use efficiency (WUE) in food and biofuel crop species will be an important trait in plant breeding programs. The leaf carbon isotopic composition (δ(13)Cleaf) has been suggested to serve as a rapid and effective high throughput phenotyping method for WUE in both C3 and C4 species. This is because WUE, leaf carbon discrimination (Δ(13)Cleaf), and δ(13)Cleaf are correlated through their relationships with intercellular to ambient CO2 partial pressures (Ci/Ca). However, in C4 plants, changing environmental conditions may influence photosynthetic efficiency (bundle-sheath leakiness) and post-photosynthetic fractionation that will potentially alter the relationship between δ(13)Cleaf and Ci/Ca. Here we discuss how these factors influence the relationship between δ(13)Cleaf and WUE, and the potential of using δ(13)Cleaf as a meaningful proxy for WUE.

  11. Evaluating reaction pathways of hydrothermal abiotic organic synthesis at elevated temperatures and pressures using carbon isotopes

    Science.gov (United States)

    Fu, Qi; Socki, Richard A.; Niles, Paul B.

    2015-04-01

    Experiments were performed to better understand the role of environmental factors on reaction pathways and corresponding carbon isotope fractionations during abiotic hydrothermal synthesis of organic compounds using piston cylinder apparatus at 750 °C and 5.5 kbars. Chemical compositions of experimental products and corresponding carbon isotopic values were obtained by a Pyrolysis-GC-MS-IRMS system. Alkanes (methane and ethane), straight-chain saturated alcohols (ethanol and n-butanol) and monocarboxylic acids (formic and acetic acids) were generated with ethanol being the only organic compound with higher δ13C than CO2. CO was not detected in experimental products owing to the favorable water-gas shift reaction under high water pressure conditions. The pattern of δ13C values of CO2, carboxylic acids and alkanes are consistent with their equilibrium isotope relationships: CO2 > carboxylic acids > alkanes, but the magnitude of the fractionation among them is higher than predicted isotope equilibrium values. In particular, the isotopic fractionation between CO2 and CH4 remained constant at ∼31‰, indicating a kinetic effect during CO2 reduction processes. No "isotope reversal" of δ13C values for alkanes or carboxylic acids was observed, which indicates a different reaction pathway than what is typically observed during Fischer-Tropsch synthesis under gas phase conditions. Under constraints imposed in experiments, the anomalous 13C isotope enrichment in ethanol suggests that hydroxymethylene is the organic intermediate, and that the generation of other organic compounds enriched in 12C were facilitated by subsequent Rayleigh fractionation of hydroxymethylene reacting with H2 and/or H2O. Carbon isotope fractionation data obtained in this study are instrumental in assessing the controlling factors on abiotic formation of organic compounds in hydrothermal systems. Knowledge on how environmental conditions affect reaction pathways of abiotic synthesis of organic

  12. Mass-dependent and -independent fractionation of isotopes in Ni and Pb chelate complex formation reactions

    Science.gov (United States)

    Nomura, Masao; Kudo, Takashi; Adachi, Atsuhiko; Aida, Masao; Fujii, Yasuhiko

    2013-11-01

    Mass independent fractionation (MIF) has been a very interesting topic in the field of inorganic isotope chemistry, in particular, geo- and cosmo- chemistry. In the present work, we studied the isotope fractionation of Ni(II) and Pb(II) ions in complex formation with chelating reagent EDTA. To obtain clear results on the mass dependence of the isotope fractionation, we have conducted long-distance ion exchange chromatography of Ni(II) and Pb(II), using chelate complex reagent EDTA. The results apparently show that the isotope fractionation in Ni complex formation system is governed by the mass dependent rule. On the other hand the isotope fractionation in the Pb complex system is governed by the mass independent rule or the nuclear volume effect.

  13. Mass-dependent and -independent fractionation of isotopes in Ni and Pb chelate complex formation reactions

    Energy Technology Data Exchange (ETDEWEB)

    Nomura, Masao; Kudo, Takashi; Adachi, Atsuhiko; Aida, Masao; Fujii, Yasuhiko [Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, O-okayama Meguroku, Tokyo, 152-8550 (Japan)

    2013-11-13

    Mass independent fractionation (MIF) has been a very interesting topic in the field of inorganic isotope chemistry, in particular, geo- and cosmo- chemistry. In the present work, we studied the isotope fractionation of Ni(II) and Pb(II) ions in complex formation with chelating reagent EDTA. To obtain clear results on the mass dependence of the isotope fractionation, we have conducted long-distance ion exchange chromatography of Ni(II) and Pb(II), using chelate complex reagent EDTA. The results apparently show that the isotope fractionation in Ni complex formation system is governed by the mass dependent rule. On the other hand the isotope fractionation in the Pb complex system is governed by the mass independent rule or the nuclear volume effect.

  14. Stability of Soil Carbon Fractions - from molecules to aggregates

    Science.gov (United States)

    Mueller, C. W.; Mueller, K. E.; Freeman, K. H.; Eissenstat, D.; Kögel-Knabner, I.

    2009-12-01

    The turnover of soil organic matter (SOM) is controlled both by its chemical composition, its spatial bioavailability and the association with the mineral phase. Separation by physical fractionation of bulk soils and subsequent chemical analysis of these fractions should give insights to how compositional differences in SOM drive turnover rates of different size-defined carbon pools. The main objective of the study was to elucidate the relative abundance and recalcitrance of lignin and plant lipids (e.g. cutin and suberin) in the course of SOM decomposition within aggregated bulk soils and SOM fractions. By the parallel incubation of physically-separated size fractions and bulk soils of the Ah horizon from a forested soil (Picea abies L.Karst) over a period of 400 days, a unique set of samples was created to study SOM dynamics. We used solid-state 13C-CPMAS NMR spectroscopy and GC-MS (after copper oxide oxidation and solvent extraction) to analyze the composition of the incubated samples. The abundance and isotopic composition (including 13C and 14C) of respired CO2 further enabled us to monitor the dynamics of SOM mineralization. This approach allowed for differentiating between C stabilization of soil fractions due to accessibility/aggregation and to recalcitrance at different scales of resolution (GC-MS, NMR). A relative enrichment of alkyl C and decreasing lignin contents in the order of sand cutin, and suberin monomers measured by GC-MS before and after the incubation indicate selective degradation and preservation patterns at the molecular scale that are rarely observed and are unresolved by NMR analyses. We suggest that the monomer-specific patterns of lignin, cutin, and suberin decomposition facilitate better understanding and modelling of SOM dynamics by providing a tool to potentially separate the influence of input rates from selective preservation on the abundance of these bipolymers in soil.

  15. Stable isotopes in caves over altitudinal gradients: fractionation behaviour and inferences for speleothem sensitivity to climate change

    Directory of Open Access Journals (Sweden)

    V. E. Johnston

    2013-01-01

    Full Text Available The interpretation of stable isotope ratios in speleothem calcite is complex, and only in a few cases, unequivocal relationships with palaeoclimate parameters have been attained. A major issue is temperature, which has an effect on both the isotope incorporation into calcite and on environmental processes. Here, a field approach is taken, by studying the isotopic composition of calcites from monitored caves located in steep altitudinal topography in the northern Italian Alps. These create a thermal gradient (3–12 °C apt to study the effects of temperature on the speleothem isotope record. Our data indicate that the magnitude of oxygen isotope disequilibrium effects, calculated as an offset from the experimentally determined equilibrium, decreases with increased elevation (cooler temperatures and faster drip rate. Carbon isotope values exhibit 13C enrichment at high altitudes (colder temperatures and slow drip rates. The results obtained support modelling and laboratory cave analogue experiments that indicate temperature, drip rate, pCO2 and supersaturation are important factors controlling stable isotope fractionation, but also stress the significance of ventilation and evaporation in the cave environment. It is proposed that the effects on stable isotope ratios observed along the altitudinal gradient can be analogues for glacial to interglacial temperature changes in regions which were extensively glaciated in the past.

  16. Microbial Enzyme Activity and Carbon Cycling in Grassland Soil Fractions

    Science.gov (United States)

    Allison, S. D.; Jastrow, J. D.

    2004-12-01

    Extracellular enzymes are necessary to degrade complex organic compounds present in soils. Using physical fractionation procedures, we tested whether old soil carbon is spatially isolated from degradative enzymes across a prairie restoration chronosequence in Illinois, USA. We found that carbon-degrading enzymes were abundant in all soil fractions, including macroaggregates, microaggregates, and the clay fraction, which contains carbon with a mean residence time of ~200 years. The activities of two cellulose-degrading enzymes and a chitin-degrading enzyme were 2-10 times greater in organic matter fractions than in bulk soil, consistent with the rapid turnover of these fractions. Polyphenol oxidase activity was 3 times greater in the clay fraction than in the bulk soil, despite very slow carbon turnover in this fraction. Changes in enzyme activity across the restoration chronosequence were small once adjusted for increases in soil carbon concentration, although polyphenol oxidase activity per unit carbon declined by 50% in native prairie versus cultivated soil. These results are consistent with a `two-pool' model of enzyme and carbon turnover in grassland soils. In light organic matter fractions, enzyme production and carbon turnover both occur rapidly. However, in mineral-dominated fractions, both enzymes and their carbon substrates are immobilized on mineral surfaces, leading to slow turnover. Soil carbon accumulation in the clay fraction and across the prairie restoration chronosequence probably reflects increasing physical isolation of enzymes and substrates on the molecular scale, rather than the micron to millimeter scale.

  17. A Test of Carbon and Oxygen Stable Isotope Ratio Process Models in Tree Rings.

    Science.gov (United States)

    Roden, J. S.; Farquhar, G. D.

    2008-12-01

    Stable isotopes ratios of carbon and oxygen in tree ring cellulose have been used to infer environmental change. Process-based models have been developed to clarify the potential of historic tree ring records for meaningful paleoclimatic reconstructions. However, isotopic variation can be influenced by multiple environmental factors making simplistic interpretations problematic. Recently, the dual isotope approach, where the variation in one stable isotope ratio (e.g. oxygen) is used to constrain the interpretation of variation in another (e.g. carbon), has been shown to have the potential to de-convolute isotopic analysis. However, this approach requires further testing to determine its applicability for paleo-reconstructions using tree-ring time series. We present a study where the information needed to parameterize mechanistic models for both carbon and oxygen stable isotope ratios were collected in controlled environment chambers for two species (Pinus radiata and Eucalyptus globulus). The seedlings were exposed to treatments designed to modify leaf temperature, transpiration rates, stomatal conductance and photosynthetic capacity. Both species were grown for over 100 days under two humidity regimes that differed by 20%. Stomatal conductance was significantly different between species and for seedlings under drought conditions but not between other treatments or humidity regimes. The treatments produced large differences in transpiration rate and photosynthesis. Treatments that effected photosynthetic rates but not stomatal conductance influenced carbon isotope discrimination more than those that influenced primarily conductance. The various treatments produced a range in oxygen isotope ratios of 7 ‰. Process models predicted greater oxygen isotope enrichment in tree ring cellulose than observed. The oxygen isotope ratios of bulk leaf water were reasonably well predicted by current steady-state models. However, the fractional difference between models that

  18. Carbon-isotopic analysis of dissolved acetate.

    Science.gov (United States)

    Gelwicks, J T; Hayes, J M

    1990-01-01

    Heating of dried, acetate-containing solids together with oxalic acid dihydrate conveniently releases acetic acid for purification by gas chromatography. For determination of the carbon-isotopic composition of total acetate, the acetate-containing zone of the chromatographic effluent can be routed directly to a combustion furnace coupled to a vacuum system allowing recovery, purification, and packaging of CO2 for mass-spectrometric analysis. For analysis of methyl carbon, acetic acid can be cryogenically trapped from the chromatographic effluent, then transferred to a tube containing excess NaOH. The tube is evacuated, sealed, and heated to 500 degrees C to produce methane by pyrolysis of sodium acetate. Subsequent combustion of the methane allows determination of the 13C content at the methyl position in the parent acetate. With typical blanks, the standard deviation of single analyses is less than 0.4% for acetate samples larger than 5 micromoles. A full treatment of uncertainties is outlined.

  19. The Oxidant Budget of Dissolved Organic Carbon Driven Isotope Excursions

    Science.gov (United States)

    Bristow, T. F.; Kennedy, M. J.

    2008-12-01

    Negative carbon isotope values, falling below the mantle average of about -5 per mil, in carbonate phases of Ediacaran age sedimentary rocks are widely regarded as reflecting negative excursions in the carbon isotopic composition of seawater lasting millions of years. These isotopic signals form the basis of chemostratigraphic correlations between Ediacaran aged sections in different parts of the world, and have been used to track the oxidation of the biosphere. However, these isotopic values are difficult to accommodate within limits prescribed by the current understanding of the carbon cycle, and a hypothetical Precambrian ocean dissolved organic carbon (DOC) pool 100 to 1000 times the size of the modern provides a potential source of depleted carbon not considered in Phanerozoic carbon cycle budgets. We present box model results that show the remineralization of such a DOC pool to drive an isotope excursion of the magnitude observed in the geological record exhausts global budgets of free oxygen and sulfate in 800 k.y. These results are incompatible with the estimated duration of late Ediacaran isotope excursions of more than 10 m.y., as well as geochemical and biological indicators that oceanic sulfate and oxygen levels were maintained or even increased at the same time. Therefore the carbon isotope record is probably not a useful tool for monitoring oxygen levels in the atmosphere and ocean. Covariation between the carbon and oxygen isotope records is often observed during negative excursions and is indicative of local processes or diagenetic overprinting.

  20. The Stable and Radio- Carbon Isotopic Content of Labile and Refractory Carbon in Atmospheric Particulate Matter

    Science.gov (United States)

    McNichol, A. P.; Rosenheim, B. E.; Gerlach, D. S.; Hayes, J. M.

    2006-12-01

    Studies of the isotopic content of atmospheric particulate matter are hampered by difficulties in chemically defining the pools of carbon and analytically isolating the different pools. We are conducting studies on reference materials and atmospheric aerosol samples to develop a method to measure stable and radio- carbon isotopes on the labile and refractory carbon. We are using a flow-through combustion system that allows us to combust, collect and measure the isotopic content of the gases produced at all stages of heating/oxidizing. We compare our results to those measured using a chemothermal oxidation method (CTO) (Gustafsson et al., 2001). In this method, refractory carbon is defined as the material remaining after pre- combusting a sample at 375°C in the presence of oxygen for 24 hours. The reference materials are diesel soot, apple leaves and a hybrid of the two (DiesApple), all from NIST. These provide carbon with two well-defined fractions -- the soot provides refractory carbon that is radiocarbon dead and the apple leaves provide organic carbon that is radiocarbon modern. Radiocarbon results from DiesApple indicate that the "refractory" carbon defined by the CTO method is actually a mixture of old and modern carbon that contains over 25% modern carbon. This suggests that charred material formed from the apples leaves during the pre-combustion step is contributing to the fraction we identify as refractory carbon. We are studying this by analyzing the individual materials and the mixture using our flow-through system. First results with this system indicate that the refractory fraction trapped from the DiesApple contains much less modern carbon than the CTO method, less than 7%. We will present detailed concentration and isotopic results of the generation of carbon dioxide during programmed combustion of each of the reference materials. We studied the radiocarbon content of both the total carbon (TC) and refractory carbon in the fine particulate matter (PM

  1. The modeling of carbon isotope kinetics and its application to the evaluation of natural gas

    Institute of Scientific and Technical Information of China (English)

    Xianqing LI; Xianming XIAO; Yongchun TANG; Hui TIAN; Qiang ZHOU; Yunfeng YANG; Peng DONG; Yan WANG; Zhihong SONG

    2008-01-01

    The modeling of carbon isotope kinetics of natural gas is an issue driving pioneering research in the oil and gas geochemistry in China and internationally.Combined with the sedimentary burial history and basin geothermal history,the modeling of carbon isotope kinetics provides a new and effective means for the determination of the origin and accumulation history of natural gas pools.In this paper,we introduce the modeling of carbon isotope kinetics of natural gas formation and its applications to the assessment of natural gas maturity,the determination of the gas source,the history of gas accumulation,and the oil-gas ratio.It is shown that this approach is of great value for these applications.The carbon isotopic characteristics of natural gas are not only affected by the gas source and maturity of the source rock,but also are related to the accumulation condition and geothermal gradient in a basin.There are obvious differences in the characteristics of carbon isotope ratios between instantaneous gas and cumulative gas.Different basins have different kinetic models of carbon isotope fractionation,which depends on the gas source condition,the accumulation history and the sedimentary-tectonic history.Since the origin of natural gas in the superimposed basin in China is very complicated,and the natural gas pool is characterized by multiphase and variable gas-sources,this paper may provide a new perspective on the study and evaluation of natural gas.

  2. Fractionation of Fe isotopes during Fe(II) oxidation by a marine photoferrotroph is controlled by the formation of organic Fe-complexes and colloidal Fe fractions

    Science.gov (United States)

    Swanner, Elizabeth D.; Wu, Wenfang; Schoenberg, Ronny; Byrne, James; Michel, F. Marc; Pan, Yongxin; Kappler, Andreas

    2015-09-01

    Much interest exists in finding mineralogical, organic, morphological, or isotopic biosignatures for Fe(II)-oxidizing bacteria (FeOB) that are retained in Fe-rich sediments, which could indicate the activity of these organisms in Fe-rich seawater, more common in the Precambrian Era. To date, the effort to establish a clear Fe isotopic signature in Fe minerals produced by Fe(II)-oxidizing metabolisms has been thwarted by the large kinetic fractionation incurred as freshly oxidized aqueous Fe(III) rapidly precipitates as Fe(III) (oxyhydr)oxide minerals at near neutral pH. The Fe(III) (oxyhydr)oxide minerals resulting from abiotic Fe(II) oxidation are isotopically heavy compared to the Fe(II) precursor and are not clearly distinguishable from minerals formed by FeOB isotopically. However, in marine hydrothermal systems and Fe(II)-rich springs the minerals formed are often isotopically lighter than expected considering the fraction of Fe(II) that has been oxidized and experimentally-determined fractionation factors. We measured the Fe isotopic composition of aqueous Fe (Feaq) and the final Fe mineral (Feppt) produced in batch experiment using the marine Fe(II)-oxidizing phototroph Rhodovulum iodosum. The δ56Feaq data are best described by a kinetic fractionation model, while the evolution of δ56Feppt appears to be controlled by a separate fractionation process. We propose that soluble Fe(III), and Fe(II) and Fe(III) extracted from the Feppt may act as intermediates between Fe(II) oxidation and Fe(III) precipitation. Based on 57Fe Mössbauer spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy, and X-ray total scattering, we suggests these Fe phases, collectively Fe(II/III)interm, may consist of organic-ligand bound, sorbed, and/or colloidal Fe(II) and Fe(III) mineral phases that are isotopically lighter than the final Fe(III) mineral product. Similar intermediate phases, formed in response to organic carbon produced by FeOB and inorganic

  3. A global deglacial negative carbon isotope excursion in speleothem calcite

    Science.gov (United States)

    Breecker, D.

    2015-12-01

    δ13C values of speleothem calcite decreased globally during the last deglaciation defining a carbon isotope excursion (CIE) despite relatively constant δ13C values of carbon in the ocean-atmosphere system. The magnitude of the CIE varied with latitude, increasing poleward from ~2‰ in the tropics to as much as 7‰ at high latitudes. This recent CIE provides an interesting comparison with CIEs observed in deep time. A substantial portion of this CIE can be explained by the increase in atmospheric pCO2 that accompanied deglaciation. The dependence of C3 plant δ13C values on atmospheric pCO2 predicts a 2‰ δ13C decrease driven by the deglacial pCO2 increase. I propose that this signal was transferred to caves and thus explains nearly 100% of the CIE magnitude observed in the tropics and no less than 30% at the highest latitudes in the compilation. An atmospheric pCO2 control on speleothem δ13C values, if real, will need to be corrected for using ice core data before δ13C records can be interpreted in a paleoclimate context. The decrease in the magnitude of the equilibrium calcite-CO2 carbon isotope fractionation factor explains a maximum of 1‰ of the CIE at the highest northern latitude in the compilation, which experienced the largest deglacial warming. Much of the residual extratropical CIE was likely driven by increasing belowground respiration rates, which were presumably pronounced at high latitudes as glacial retreat exposed fresh surfaces and/or vegetation density increased. The largest increases in belowground respiration would have therefore occurred at the highest latitudes, explaining the meridional trend. This work supports the notion that increases in atmospheric pCO2 and belowground respiration rates can result in large CIEs recorded in terrestrial carbonates, which, as previously suggested, may explain the magnitude of the PETM CIE as recorded by paleosol carbonates.

  4. The evolution of Carbon isotopes in calcite in the presence of cyanobacteria

    Science.gov (United States)

    Grimm, Christian; Mavromatis, Vasileios; Pokrovsky, Oleg S.; Oelkers, Eric H.

    2016-04-01

    Stable isotopic compositions in carbonates are widely used as indicators of environmental conditions prevailing during mineral formation. This reconstruction is substantially based on the assumption that there is no change in the mineral composition over geological time. However, recent experimental studies have shown that carbon and magnesium isotopes in hydrous Mg-carbonates undergo continuous re-equilibration with the ambient solution even after mineral precipitation stopped ([1] and [2], respectively). To verify whether this holds true for anhydrous Ca-bearing carbonates which readily form at earth's surface environments, a series of batch system calcite precipitation experiments were performed in the presence of actively growing cyanobacteria Synechococcus sp. The bacteria were grown at ambient temperature in a BG11 culture medium (SIGMA C3061) and continuous stirring, air-bubbling and illumination. Calcite precipitation was initiated by the addition of 8.5mM CaCl2 and 0-50 mM NaHCO3 or NaHCO3-Na2CO3 mixtures. The presence of cyanobacteria is on one hand promoting CaCO3 formation due to increasing pH resulting from photosynthesis. On the other hand, actively growing cyanobacteria drastically change carbon isotope signature of the aqueous fluid phase by preferably incorporating the lighter 12C isotope into biomass [1]. This study explores the effect of continuously changing carbon isotope compositions in dissolved inorganic carbon (DIC) on precipitated calcite which is in chemical equilibrium with the ambient fluid phase. [1] Mavromatis et al. (2015). The continuous re-equilibration of carbon isotope compositions of hydrous Mg-carbonates in the presence of cyanobacteria. Chem. Geol. 404, 41-51 [2] Mavromatis et al. (2012). Magnesium isotope fractionation during hydrous magnesium carbonate precipitation with and without cyanobacteria. Geochim. Cosmochim. Acta 76, 161-174

  5. Zinc Isotope Variability in Three Coal-Fired Power Plants: A Predictive Model for Determining Isotopic Fractionation during Combustion.

    Science.gov (United States)

    Ochoa Gonzalez, R; Weiss, D

    2015-10-20

    The zinc (Zn) isotope compositions of feed materials and combustion byproducts were investigated in three different coal-fired power plants, and the results were used to develop a generalized model that can account for Zn isotopic fractionation during coal combustion. The isotope signatures in the coal (δ(66)ZnIRMM) ranged between +0.73 and +1.18‰, values that fall well within those previously determined for peat (+0.6 ±2.0‰). We therefore propose that the speciation of Zn in peat determines the isotope fingerprint in coal. All of the bottom ashes collected in these power plants were isotopically depleted in the heavy isotopes relative to the coals, with δ(66)ZnIRMM values ranging between +0.26‰ and +0.64‰. This suggests that the heavy isotopes, possibly associated with the organic matter of the coal, may be preferentially released into the vapor phase. The fly ash in all of these power plants was, in contrast, enriched in the heavy isotopes relative to coal. The signatures in the fly ash can be accounted for using a simple unidirectional fractionation model with isotope fractionation factors (αsolid-vapor) ranging between 1.0003 and 1.0007, and we suggest that condensation is the controlling process. The model proposed allows, once the isotope composition of the feed coal is known, the constraining of the Zn signatures in the byproducts. This will now enable the integration of Zn isotopes as a quantitative tool for the source apportionment of this metal from coal combustion in the atmosphere.

  6. Carbon allocation and carbon isotope fluxes in the plant-soil-atmosphere continuum: a review

    Science.gov (United States)

    Brüggemann, N.; Gessler, A.; Kayler, Z.; Keel, S. G.; Badeck, F.; Barthel, M.; Boeckx, P.; Buchmann, N.; Brugnoli, E.; Esperschütz, J.; Gavrichkova, O.; Ghashghaie, J.; Gomez-Casanovas, N.; Keitel, C.; Knohl, A.; Kuptz, D.; Palacio, S.; Salmon, Y.; Uchida, Y.; Bahn, M.

    2011-11-01

    The terrestrial carbon (C) cycle has received increasing interest over the past few decades, however, there is still a lack of understanding of the fate of newly assimilated C allocated within plants and to the soil, stored within ecosystems and lost to the atmosphere. Stable carbon isotope studies can give novel insights into these issues. In this review we provide an overview of an emerging picture of plant-soil-atmosphere C fluxes, as based on C isotope studies, and identify processes determining related C isotope signatures. The first part of the review focuses on isotopic fractionation processes within plants during and after photosynthesis. The second major part elaborates on plant-internal and plant-rhizosphere C allocation patterns at different time scales (diel, seasonal, interannual), including the speed of C transfer and time lags in the coupling of assimilation and respiration, as well as the magnitude and controls of plant-soil C allocation and respiratory fluxes. Plant responses to changing environmental conditions, the functional relationship between the physiological and phenological status of plants and C transfer, and interactions between C, water and nutrient dynamics are discussed. The role of the C counterflow from the rhizosphere to the aboveground parts of the plants, e.g. via CO2 dissolved in the xylem water or as xylem-transported sugars, is highlighted. The third part is centered around belowground C turnover, focusing especially on above- and belowground litter inputs, soil organic matter formation and turnover, production and loss of dissolved organic C, soil respiration and CO2 fixation by soil microbes. Furthermore, plant controls on microbial communities and activity via exudates and litter production as well as microbial community effects on C mineralization are reviewed. A further part of the paper is dedicated to physical interactions between soil CO2 and the soil matrix, such as CO2 diffusion and dissolution processes within the

  7. Degradation changes stable carbon isotope depth profiles in palsa peatlands

    Directory of Open Access Journals (Sweden)

    J. P. Krüger

    2014-01-01

    Full Text Available Palsa peatlands are a significant carbon pool in the global carbon cycle and are projected to change by global warming due to accelerated permafrost thaw. Our aim was to use stable carbon isotopes as indicators of palsa degradation. Depth profiles of stable carbon isotopes generally reflect organic matter dynamics in soils with an increase of δ13C values during aerobic decomposition and stable or decreasing δ13C values with depth during anaerobic decomposition. Stable carbon isotope depth profiles of undisturbed and degraded sites of hummocks as well as hollows at three palsa peatlands in northern Sweden were used to investigate the degradation processes. The depth patterns of stable isotopes clearly differ between intact and degraded hummocks at all sites. Erosion and cryoturbation at the degraded sites significantly changes the stable carbon isotope depth profiles. At the intact hummocks the uplifting of peat material by permafrost is indicated by a turning in the δ13C depth trend and this assessment is supported by a change in the C / N ratios. For hollows isotope patterns were less clear, but some hollows and degraded hollows in the palsa peatlands show differences in their stable carbon isotope depth profiles indicating enhanced degradation rates. We conclude that the degradation of palsa peatlands by accelerated permafrost thawing could be identified with stable carbon isotope depth profiles. At intact hummocks δ13C depth patterns display the uplifting of peat material by a change in peat decomposition processes.

  8. Phanerozoic and Neoproterozoic Negative Carbon Isotope Excursions, Diagenesis and Terrestrialization

    Science.gov (United States)

    Paul, K.; Kennedy, M. J.

    2008-12-01

    Comprehensive data sets of Phanerozoic and late Precambrian carbon isotope data derived from carbonate rocks show a similar positive relation when cross-plotted with oxygen isotope values. The range and slope between the time periods is identical and the processes responsible for the relation have been well documented in Quaternary sediments. These processes include the stabilization of isotope values to ambient meteoric water values during shallow burial and flushing of carbonate sediments. Both data sets show strongly depleted carbon (-9 per mil PDB) and oxygen isotope values that retain seemingly systematic stratigraphic patterns with the Quaternary and Phanerozoic examples that demonstrably record meteroric water values. Similar values and patterns in the Precambrian are interpreted as primary marine in origin with significant implications for an ocean carbon mass balance not possible in the Phanerozoic carbon cycle. A similar compilation of carbonates older than one billion years do not show a relation between carbon and oxygen isotopes, lacking the negative carbon values evident in the younger record. We hypothesize that this difference records the onset of significant organic carbon on the land surface and the alteration of meteoric waters toward Phanerozoic values. We demonstrate the meteoric affinities of Neoproterozoic carbonates containing prominent negative isotope excursions recorded in the Shuram and Wonoka Formations of Oman and South Australia commonly attributed to whole ocean isotope variation. The conspicuous absence of negative carbon isotope values with normal marine oxygenisotope values in the Phanerozoic and Neoproterozic identifies a consistent relation between these time intervals and suggests that, as well accepted in the Phanerozoic, negative carbon isotope excursions less than -3 per mil are not a record of marine processes, but rather the later terrestrial biotic influence on meteoric water values.

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

    Science.gov (United States)

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

    2005-12-01

    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.

  10. Decoupling of carbon isotope records between organic matter and carbonate prior to the Toarcian Oceanic Anoxic Event (Early Jurassic)

    Science.gov (United States)

    Bodin, Stephane; Kothe, Tim; Krencker, Francois-Nicolas; Suan, Guillaume; Heimhofer, Ulrich; Immenhauser, Adrian

    2014-05-01

    Across the Pliensbachian-Toarcian boundary (P-To, Early Jurassic), ca. 1 Myr before the Toarcian Oceanic Anoxic Event (T-OAE), an initial negative carbon isotope excursion has been documented in western Tethys sedimentary rocks. In carbonate, its amplitude (2-3 permil) is similar to the subsequent excursion recorded at the onset of the T-OAE. Being also associated with a rapid warming event, the significance of this first carbon isotope shift, in terms of paleoenvironmental interpretation and triggering mechanism, remains however elusive. Taking advantage of expanded and rather continuous sections in the High Atlas of Morocco, several high-resolution, paired organic-inorganic carbon isotope records have been obtained across the Upper Pliensbachian - Lower Toarcian interval. At the onset of the T-OAE, an abrupt 1-2 permil negative shift is recorded in both organic and inorganic phases, succeeded by a relatively longer term 1-2 permil negative trend and a final slow return to pre-excursion conditions. In accordance with previous interpretations, this pattern indicates a perturbation of the entire exogenic carbon isotope reservoir at the onset of the T-OAE by the sudden release of isotopically light carbon into the atmosphere. By contrast, there is no negative shift in carbon isotopes for the P-To event recorded in bulk organic matter of Morocco. Given the strong dominance of terrestrial particles in the bulk organic matter fraction, this absence indicates that massive input of 12C-rich carbon into the atmosphere is not likely to have happened during the P-To event. A pronounced (2 permil) and abrupt negative shift in carbon isotope is however recorded in the bulk carbonate phase. We suggest that this decoupling between organic and inorganic phase is due to changes in the nature of the bulk carbonate phase. Indeed, the negative shift occurs at the lithological transition between Pliensbachian-lowermost Toarcian limestone-marl alternations and the Lower Toarcian marl

  11. Experimental determination of barium isotope fractionation during diffusion and adsorption processes at low temperatures

    Science.gov (United States)

    van Zuilen, Kirsten; Müller, Thomas; Nägler, Thomas F.; Dietzel, Martin; Küsters, Tim

    2016-08-01

    Variations in barium (Ba) stable isotope abundances measured in low and high temperature environments have recently received increasing attention. The actual processes controlling Ba isotope fractionation, however, remain mostly elusive. In this study, we present the first experimental approach to quantify the contribution of diffusion and adsorption on mass-dependent Ba isotope fractionation during transport of aqueous Ba2+ ions through a porous medium. Experiments have been carried out in which a BaCl2 solution of known isotopic composition diffused through u-shaped glass tubes filled with silica hydrogel at 10 °C and 25 °C for up to 201 days. The diffused Ba was highly fractionated by up to -2.15‰ in δ137/134Ba, despite the low relative difference in atomic mass. The time-dependent isotope fractionation can be successfully reproduced by a diffusive transport model accounting for mass-dependent differences in the effective diffusivities of the Ba isotope species (D137Ba /D134Ba =(m134 /m137) β). Values of β extracted from the transport model were in the range of 0.010-0.011. Independently conducted batch experiments revealed that adsorption of Ba onto the surface of silica hydrogel favoured the heavier Ba isotopes (α = 1.00015 ± 0.00008). The contribution of adsorption on the overall isotope fractionation in the diffusion experiments, however, was found to be small. Our results contribute to the understanding of Ba isotope fractionation processes, which is crucial for interpreting natural isotope variations and the assessment of Ba isotope ratios as geochemical proxies.

  12. Zinc isotope evidence for a large-scale carbonated mantle beneath eastern China

    Science.gov (United States)

    Liu, Sheng-Ao; Wang, Ze-Zhou; Li, Shu-Guang; Huang, Jian; Yang, Wei

    2016-06-01

    A large set of zinc (Zn) stable isotope data for continental basalts from eastern China were reported to investigate the application of Zn isotopes as a new tracer of deep carbonate cycling. All of the basalts with ages of 120 Ma basalts from eastern China (0.27 ± 0.06‰; 2sd). Given that Zn isotope fractionation during magmatic differentiation is limited (≤0.1‰), the elevated δ66Zn values reflect the involvement of isotopically heavy crustal materials (e.g., carbonates with an average δ66Zn of ∼0.91‰) in the mantle sources. SiO2 contents of the recycled Mg (Zn)-rich carbonates in the mantle beneath eastern China since the Late Mesozoic. Since Zn is a trace element in the mantle and Zn isotopic compositions of marine carbonates and the mantle differ markedly, we highlight Zn isotopes as a new and useful tool of tracing deep carbonate cycling in the Earth's mantle.

  13. Conformational effect of dicyclo-hexano-18-crown-6 on isotopic fractionation of zinc: DFT approach

    Energy Technology Data Exchange (ETDEWEB)

    Boda, A.; Singha Deb, A. K.; Ali, Sk. M.; Shenoy, K. T.; Ghosh, S. K. [Chemical Engineering Division, Chemical Engineering Group, Bhabha Atomic Research Centre, Mumbai-400085 (India)

    2014-04-24

    Generalized gradient approximated BP86 density functional employing triple zeta valence plus polarization (TZVP) basis set has been used to compute the reduced partition function ratio and isotopic separation factor for zinc isotopes. The isotopic separation factor was found to be in good agreement with the experimental results. The isotopic separation factor was found to depend on the conformation of the crown ether ligand. The trans-trans conformation shows the highest fractionation compared to cis-cis conformer. The present theoretical results can thus be used to plan the isotope separation experiments.

  14. Mass Dependent Fractionation of Hg Isotopes in Source Rocks, Mineral Deposits and Spring Waters of the California Coast Ranges, USA

    Science.gov (United States)

    Smith, C. N.; Kesler, S. E.; Blum, J. D.; Rytuba, J. J.

    2007-12-01

    We present here the first study of the isotopic composition of Hg in rocks, ore deposits, and active hydrothermal systems from the California Coast Ranges, one of Earth's largest Hg-depositing systems. The Franciscan Complex and Great Valley Sequence, which form the bedrock in the California Coast Ranges, are intruded and overlain by Tertiary volcanic rocks including the Clear Lake Volcanic Sequence. These rocks contain two types of Hg deposits, hot-spring deposits that form at shallow depths (geothermal systems that release Hg to the present surface. The Franciscan Complex and Great Valley Sequence contain clastic sedimentary rocks with higher concentrations of Hg than volcanic rocks of the Clear Lake Volcanic Field. Mean Hg isotope compositions for all three rock units are similar, although the range of values in Franciscan Complex rocks is greater than in either Great Valley or Clear Lake rocks. Hot spring and silica-carbonate Hg deposits have similar average isotopic compositions that are indistinguishable from averages for the three rock units, although δ202Hg values for the Hg deposits have a greater variance than the country rocks. Precipitates from dilute spring and saline thermal waters in the area have similarly large variance and a mean δ202Hg value that is significantly lower than the ore deposits and rocks. These observations indicate there is little or no isotopic fractionation during release of Hg from its source rocks into hydrothermal solutions. Isotopic fractionation does appear to take place during transport and concentration of Hg in deposits, especially in their uppermost parts. Boiling of hydrothermal fluids is likely the most important process causing of the observed Hg isotope fractionation. This should result in the release of Hg with low δ202Hg values into the atmosphere from the top of these hydrothermal systems and a consequent enrichment in heavy Hg isotopes in the upper crust through time.

  15. [Carbon isotope (13C/12C) effect of photorespiration in photosynthetic organisms. Evidence for existence, probable mechanism].

    Science.gov (United States)

    Ivlev, A A

    2002-01-01

    Experimental evidence in favor of the new phenomenon predicted for photosynthesizing organisms, the fractionation of carbon isotopes in photorespiration is presented. A possible mechanism of this process is discussed. The fractionation of carbon in isotopes photorespiration occurs in the oxygenase phase of the functioning of ribulosebisphosphate carboxylase/oxygenase (rubisco), the key enzyme of photosynthesis, which is capable to act as carboxylase and oxygenase. Which function of the enzyme is active depends on CO2/O2 concentration ratio, which periodically changes in a cell. The key reaction in the mechanism of carbon isotope fractionation in photorespiration is glycine decarboxylation, which results in the splitting and removal from the cell of CO2 enriched with 12C and the accumulation of 13C photorespiratory carbon flow. The coupling of photorespiration and CO2 photoassimilation gives rise to two isotopically different carbon flows, which fill up separate carbohydrate pools, which are the sources of carbon in the following syntheses in the dark phase of photosynthesis. This enables one to identify, from the carbon isotope ratio of metabolites, their involvement in the photorespiratory and assimilatory carbon flows, to investigate the pathways of carbon metabolism, and to estimate more thoroughly the biosynthetic role of photorespiration.

  16. Simulation of cloud microphysical effects on water isotope fractionation in a frontal system

    Science.gov (United States)

    Chen, J. P.; Tsai, I. C.; Chen, W. Y.; Liang, M. C.

    2014-12-01

    The stable water isotopic composition changes due to fractionation during phase changes. This information is useful for understanding the water cycle, such as the water vapor source, transport and cloud microphysical processes. In conventional atmospheric models, the isotope exchange between liquid and gas phase is usually assumed to be in an equilibrium state, which is not sufficient to describe the highly kinetic phase transformation processes in clouds. In this study, a two-moment microphysical scheme incorporated into the NCAR Weather Research and Forecasting (WRF) model is modified to simulate the isotope fractionations. Experimentally determined stable water isotope thermal equilibrium data are converted into isotope saturation vapor pressure, which is then put into the two-stream Maxwellian kinetic equation to calculate the fractionation during vapor condensation/evaporation or deposition/sublimation. Isotope mass transfer between liquid- and ice-phase hydrometeors during freezing/melting are also considered explicitly. The simulation results were compared with rainwater isotope measurements and showed fairly good agreement. Sensitivity tests were also conducted to quantify the contribution of rainwater isotopic due to water vapor source and transport, condensation environment conditions, and cloud microphysical processes. The results show that isotopic water vapor source dominates the stable isotope concentration in rainwater but the cloud microphysical processes including the ice-phase processes are also quite important. The results also showed that the two-stream Maxwellian kinetic method would cause significantly more deuterium to be transported into higher altitudes during convection than the thermal equilibrium method.

  17. Magnesium isotope fractionation by chemical diffusion in natural settings and in laboratory analogues

    Science.gov (United States)

    Chopra, Rahul; Richter, Frank M.; Bruce Watson, E.; Scullard, Christian R.

    2012-07-01

    Laboratory experiments are used to document isotopic fractionation of magnesium by chemical diffusion in a silicate melt and the results compared to the magnesium isotopic composition across contacts between igneous rocks of different composition in natural settings. The natural samples are from transects from felsic to mafic rocks at Vinal Cove in the Vinalhaven Intrusive Complex, Maine and from the Aztec Wash pluton in Nevada. Two laboratory diffusion couples made by juxtaposing melts made from powders of the felsic and mafic compositions sampled at Vinal Cove were annealed at about 1500 °C for 22.5 and 10 h, respectively. The transport of magnesium in the diffusion couples resulted in easily measured magnesium isotopic fractionations at the interface (δ26Mg∼1.5‰). These isotopic fractionations provide a distinctive isotopic “fingerprint” that we use to determine whether chemical gradients in natural settings where melts of different composition were juxtaposed were due to chemical diffusion. The magnesium isotopic fractionation along one profile at Vinal Cove is exactly what one would expect based on the fractionations found in the laboratory experiments. This is an important result in that it shows that the isotope fractionation by chemical diffusion found in highly controlled laboratory experiments can be found in a natural setting. This correspondence implies that chemical diffusion was the dominant process responsible for the transport of magnesium across this particular contact at Vinal Cove. A second Vinal Cove profile has a very similar gradient in magnesium concentration but with significantly less magnesium isotopic fractionation than expected. This suggests that mass transport at this location was only partly by diffusion and that some other mass transport mechanism such as mechanical mixing must have also played a role. The magnesium isotopic composition of samples from Aztec Wash shows no resolvable isotopic fractionation across the contact

  18. Normalization of stable isotope data for carbonate minerals: implementation of IUPAC guideline

    Science.gov (United States)

    Kim, Sang-Tae; Coplen, Tyler B.; Horita, Juske

    2015-01-01

    Carbonate minerals provide a rich source of geochemical information because their δ13C and δ18O values provide information about surface and subsurface Earth processes. However, a significant problem is that the same δ18O value is not reported for the identical carbonate sample when analyzed in different isotope laboratories in spite of the fact that the International Union of Pure and Applied Chemistry (IUPAC) has provided reporting guidelines for two decades. This issue arises because (1) the δ18O measurements are performed on CO2 evolved by reaction of carbonates with phosphoric acid, (2) the acid-liberated CO2 is isotopically fractionated (enriched in 18O) because it contains only two-thirds of the oxygen from the solid carbonate, (3) this oxygen isotopic fractionation factor is a function of mineralogy, temperature, concentration of the phosphoric acid, and δ18O value of water in the phosphoric acid, (4) researchers may use any one of an assortment of oxygen isotopic fractionation factors that have been published for various minerals at various reaction temperatures, and (5) it sometimes is not clear how one should calculate δ18OVPDB values on a scale normalized such that the δ18O value of SLAP reference water is −55.5 ‰ relative to VSMOW reference water.

  19. A synthetic standard for the analysis of carbon isotopes of carbon in silicates, and the observation of a significant water-associated matrix effect

    OpenAIRE

    House, Christopher H.

    2015-01-01

    Background Due to the biogeochemical fractionation of isotopes, organic material can be heterogeneous at the microscale. Because this heterogentiy preserves in the rock record, the microscale measurement of carbon isotopes is an important frontier of geobiology. Such analyses via secondary ion mass spectrometry (SIMS) have been, however, held back by the lack of an appropriate homogeneous synthetic standard that can be shared between laboratories. Such a standard would need to yield a carbon ...

  20. Carbon isotopic characterization of formaldehyde emitted by vehicles in Guangzhou, China

    Science.gov (United States)

    Hu, Ping; Wen, Sheng; Liu, Yonglin; Bi, Xinhui; Chan, Lo Yin; Feng, Jialiang; Wang, Xinming; Sheng, Guoying; Fu, Jiamo

    2014-04-01

    Formaldehyde (HCHO) is the most abundant carbonyl compound in the atmosphere, and vehicle exhaust emission is one of its important anthropogenic sources. However, there is still uncertainty regarding HCHO flux from vehicle emission as well as from other sources. Herein, automobile source was characterized using HCHO carbon isotopic ratio to assess its contributions to atmospheric flux and demonstrate the complex production/consumption processes during combustion in engine cylinder and subsequent catalytic treatment of exhaust. Vehicle exhausts were sampled under different idling states and HCHO carbon isotopic ratios were measured by gas chromatograph-combustion-isotopic ratio mass spectrometry (GC-C-IRMS). The HCHO directly emitted from stand-alone engines (gasoline and diesel) running at different load was also sampled and measured. The HCHO carbon isotopic ratios were from -30.8 to -25.7‰ for gasoline engine, and from -26.2 to -20.7‰ for diesel engine, respectively. For diesel vehicle without catalytic converter, the HCHO carbon isotopic ratios were -22.1 ± 2.1‰, and for gasoline vehicle with catalytic converter, the ratios were -21.4 ± 0.7‰. Most of the HCHO carbon isotopic ratios were heavier than the fuel isotopic ratios (from -29 to -27‰). For gasoline vehicle, the isotopic fractionation (Δ13C) between HCHO and fuel isotopic ratios was 7.4 ± 0.7‰, which was higher than that of HCHO from stand-alone gasoline engine (Δ13Cmax = 2.7‰), suggesting additional consumption by the catalytic converter. For diesel vehicle without catalytic converter, Δ13C was 5.7 ± 2.0‰, similar to that of stand-alone diesel engine. In general, the carbon isotopic signatures of HCHO emitted from automobiles were not sensitive to idling states or to other vehicle parameters in our study condition. On comparing these HCHO carbon isotopic data with those of past studies, the atmospheric HCHO in a bus station in Guangzhou might mainly come from vehicle emission for

  1. Intramolecular carbon isotope distribution of acetic acid in vinegar.

    Science.gov (United States)

    Hattori, Ryota; Yamada, Keita; Kikuchi, Makiko; Hirano, Satoshi; Yoshida, Naohiro

    2011-09-14

    Compound-specific carbon isotope analysis of acetic acid is useful for origin discrimination and quality control of vinegar. Intramolecular carbon isotope distributions, which are each carbon isotope ratios of the methyl and carboxyl carbons in the acetic acid molecule, may be required to obtain more detailed information to discriminate such origin. In this study, improved gas chromatography-pyrolysis-gas chromatography-combustion-isotope ratio mass spectrometry (GC-Py-GC-C-IRMS) combined with headspace solid-phase microextraction (HS-SPME) was used to measure the intramolecular carbon isotope distributions of acetic acid in 14 Japanese vinegars. The results demonstrated that the methyl carbons of acetic acid molecules in vinegars produced from plants were mostly isotopically depleted in (13)C relative to the carboxyl carbon. Moreover, isotopic differences (δ(13)C(carboxyl) - δ(13)C(methyl)) had a wide range from -0.3 to 18.2‰, and these values differed among botanical origins, C3, C4, and CAM plants.

  2. Carbon Stable Isotopes as Indicators of Coastal Eutrophication

    Science.gov (United States)

    Coastal ecologists and managers have frequently used nitrogen stable isotopes (δ15N) to trace and monitor anthropogenic nitrogen (N) in coastal ecosystems. However, the interpretation of δ15N data can often be challenging, if not confounding, as the isotope values fractionate su...

  3. Simulating speleothem growth in the laboratory: Determination of stable isotope fractionation factors during precipitation of speleothem calcite

    Science.gov (United States)

    Hansen, Maximilian; Schöne, Bernd R.; Spötl, Christoph; Scholz, Denis

    2016-04-01

    We present laboratory experiments aiming to understand the processes affecting the δ13C and δ18O values of speleothems during precipitation of calcite from a thin layer of solution. In particular, we determined the precipitation rates and the isotope fractionation factors in dependence of several parameters, such as temperature, cave pCO2 and supersaturation with respect to calcite. The experiments were performed in a climate box in order to simulate cave conditions and to control them during the experiments[1]. In the experiments, a thin film of a CaCO3-CO2-H2O-solution supersaturated with respect to calcite flew down an inclined marble surface or a sand-blasted borosilicate glass plate, and the drip water was sampled at different distances and, thus, residence times on the plate. Subsequently, pH, electrical conductivity and the δ13C and δ18O values of the dissolved inorganic carbon (DIC) as well as the precipitated CaCO3 were determined. In addition, we determined the stable isotope values of the drip water and the atmosphere inside the box during the experiments. This enabled the identification of carbon and oxygen isotope fractionation factors between all carbonate species. The experiments were conducted at 10, 20 and 30 ° C, a pCO2 of 1000 and 3000 ppmV and with a Ca2+ concentration of 2 and 5 mmol/l. We observed an exponential decay of conductivity with increasing distance of flow documenting progressive precipitation of calcite confirming previous observations[2]. The corresponding time constants of precipitation range from 180 to 660 s. Both the δ13C and δ18O values show a progressive increase along the flow path. The enrichment of the δ13C values seems to be strongly influenced by kinetic isotope fractionation, whereas the δ18O values are in the range of isotopic equilibrium. The fractionation between the precipitated CaCO3 and DIC is between -1 and - 6.5 ‰ for carbon isotopes (13ɛ) and between -1.5 and -3 ‰ for oxygen isotopes (18ɛ). The

  4. Mother-embryo isotope (δ 15 N, δ 13 C) fractionation and mercury (Hg) transfer in aplacental deep-sea sharks : aplacental shark isotope fractionation and hg

    OpenAIRE

    Le Bourg, B.; Kiszka, J.; Bustamante, P.

    2014-01-01

    Stable carbon (δ13C) and nitrogen (δ15N) isotopic values and total mercury (Hg) concentrations were analysed in muscle and liver of mothers and embryos of two aplacental shark species, Squalus megalops and Centrophorus moluccensis. Embryos of the two species had similar or lower isotopic values than their respective mothers, the only exception being for δ13C, which was higher in the liver of C. moluccensis embryos than in their mothers. Hg concentrations were systematically lower in embryos c...

  5. Fractionation of Stable Cadmium Isotopes in the Cadmium Tolerant Ricinus communis and Hyperaccumulator Solanum nigrum

    Science.gov (United States)

    Wei, Rongfei; Guo, Qingjun; Wen, Hanjie; Liu, Congqiang; Yang, Junxing; Peters, Marc; Hu, Jian; Zhu, Guangxu; Zhang, Hanzhi; Tian, Liyan; Han, Xiaokun; Ma, Jie; Zhu, Chuanwei; Wan, Yingxin

    2016-04-01

    Cadmium (Cd) isotopes provide new insights into Cd uptake, transport and storage mechanisms in plants. Therefore, the present study adopted the Cd-tolerant Ricinus communis and Cd-hyperaccumulator Solanum nigrum, which were cultured under controlled conditions in a nutrient solution with variable Cd supply, to test the isotopic fractionation of Cd during plant uptake. The Cd isotope compositions of nutrient solutions and organs of the plants were measured by multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS). The mass balance of Cd isotope yields isotope fractionations between plant and Cd source (δ114/110Cdorgans-solution) of ‑0.70‰ to ‑0.22‰ in Ricinus communis and ‑0.51‰ to ‑0.33‰ in Solanum nigrum. Moreover, Cd isotope fractionation during Cd transport from stem to leaf differs between the Cd-tolerant and -hyperaccumulator species. Based on these results, the processes (diffusion, adsorption, uptake or complexation), which may induce Cd isotope fractionation in plants, have been discussed. Overall, the present study indicates potential applications of Cd isotopes for investigating plant physiology.

  6. Fractionation of Stable Cadmium Isotopes in the Cadmium Tolerant Ricinus communis and Hyperaccumulator Solanum nigrum

    Science.gov (United States)

    Wei, Rongfei; Guo, Qingjun; Wen, Hanjie; Liu, Congqiang; Yang, Junxing; Peters, Marc; Hu, Jian; Zhu, Guangxu; Zhang, Hanzhi; Tian, Liyan; Han, Xiaokun; Ma, Jie; Zhu, Chuanwei; Wan, Yingxin

    2016-01-01

    Cadmium (Cd) isotopes provide new insights into Cd uptake, transport and storage mechanisms in plants. Therefore, the present study adopted the Cd-tolerant Ricinus communis and Cd-hyperaccumulator Solanum nigrum, which were cultured under controlled conditions in a nutrient solution with variable Cd supply, to test the isotopic fractionation of Cd during plant uptake. The Cd isotope compositions of nutrient solutions and organs of the plants were measured by multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS). The mass balance of Cd isotope yields isotope fractionations between plant and Cd source (δ114/110Cdorgans-solution) of −0.70‰ to −0.22‰ in Ricinus communis and −0.51‰ to −0.33‰ in Solanum nigrum. Moreover, Cd isotope fractionation during Cd transport from stem to leaf differs between the Cd-tolerant and -hyperaccumulator species. Based on these results, the processes (diffusion, adsorption, uptake or complexation), which may induce Cd isotope fractionation in plants, have been discussed. Overall, the present study indicates potential applications of Cd isotopes for investigating plant physiology. PMID:27076359

  7. Copper speciation and isotopic fractionation in plants: uptake and translocation mechanisms.

    Science.gov (United States)

    Ryan, Brooke M; Kirby, Jason K; Degryse, Fien; Harris, Hugh; McLaughlin, Mike J; Scheiderich, Kathleen

    2013-07-01

    The fractionation of stable copper (Cu) isotopes during uptake into plant roots and translocation to shoots can provide information on Cu acquisition mechanisms. Isotope fractionation ((65) Cu/(63) Cu) and intact tissue speciation techniques (X-ray absorption spectroscopy, XAS) were used to examine the uptake, translocation and speciation of Cu in strategy I (tomato-Solanum lycopersicum) and strategy II (oat-Avena sativa) plant species. Plants were grown in controlled solution cultures, under varied iron (Fe) conditions, to test whether the stimulation of Fe-acquiring mechanisms can affect Cu uptake in plants. Isotopically light Cu was preferentially incorporated into tomatoes (Δ(65) Cu(whole plant-solution ) = c. -1‰), whereas oats showed minimal isotopic fractionation, with no effect of Fe supply in either species. The heavier isotope was preferentially translocated to shoots in tomato, whereas oat plants showed no significant fractionation during translocation. The majority of Cu in the roots and leaves of both species existed as sulfur-coordinated Cu(I) species resembling glutathione/cysteine-rich proteins. The presence of isotopically light Cu in tomatoes is attributed to a reductive uptake mechanism, and the isotopic shifts within various tissues are attributed to redox cycling during translocation. The lack of isotopic discrimination in oat plants suggests that Cu uptake and translocation are not redox selective.

  8. Tracking the weathering of basalts on Mars using lithium isotope fractionation models

    Science.gov (United States)

    Fairén, Alberto G.; Losa-Adams, Elisabeth; Gil-Lozano, Carolina; Gago-Duport, Luis; Uceda, Esther R.; Squyres, Steven W.; Rodríguez, J. Alexis P.; Davila, Alfonso F.; McKay, Christopher P.

    2015-04-01

    Lithium (Li), the lightest of the alkali elements, has geochemical properties that include high aqueous solubility (Li is the most fluid mobile element) and high relative abundance in basalt-forming minerals (values ranking between 0.2 and 12 ppm). Li isotopes are particularly subject to fractionation because the two stable isotopes of lithium—7Li and 6Li—have a large relative mass difference (˜15%) that results in significant fractionation between water and solid phases. The extent of Li isotope fractionation during aqueous alteration of basalt depends on the dissolution rate of primary minerals—the source of Li—and on the precipitation kinetics, leading to formation of secondary phases. Consequently, a detailed analysis of Li isotopic ratios in both solution and secondary mineral lattices could provide clues about past Martian weathering conditions, including weathering extent, temperature, pH, supersaturation, and evaporation rate of the initial solutions in contact with basalt rocks. In this paper, we discuss ways in which Martian aqueous processes could have lead to Li isotope fractionation. We show that Li isotopic data obtained by future exploration of Mars could be relevant to highlighting different processes of Li isotopic fractionation in the past, and therefore to understanding basalt weathering and environmental conditions early in the planet's history.

  9. Iron isotope fractionation during Fe uptake and translocation in alpine plants.

    Science.gov (United States)

    Kiczka, Mirjam; Wiederhold, Jan G; Kraemer, Stephan M; Bourdon, Bernard; Kretzschmar, Ruben

    2010-08-15

    The potential of stable Fe isotopes as a tracer for the biogeochemical Fe cycle depends on the understanding and quantification of the fractionation processes involved. Iron uptake and cycling by plants may influence Fe speciation in soils. Here, we determined the Fe isotopic composition of different plant parts including the complete root system of three alpine plant species (Oxyria digyna, Rumex scutatus, Agrostis gigantea) in a granitic glacier forefield, which allowed us, for the first time, to distinguish between uptake and in-plant fractionation processes. The overall range of fractionation was 4.5 per thousand in delta(56)Fe. Mass balance calculations demonstrated that fractionation toward lighter Fe isotopic composition occurred in two steps during uptake: (1) before active uptake, probably during mineral dissolution and (2) during selective uptake of Fe at the plasma membrane with an enrichment factor of -1.0 to -1.7 per thousand for all three species. Iron isotopes were further fractionated during remobilization from old into new plant tissue, which changed the isotopic composition of leaves and flowers over the season. This study demonstrates the potential of Fe isotopes as a new tool in plant nutrition studies but also reveals challenges for the future application of Fe isotope signatures in soil-plant environments.

  10. Molecular and carbon isotopic compositions of gas inclusions of deep carbonate rocks in the Tarim Basin

    Institute of Scientific and Technical Information of China (English)

    ZHOU Shixin; WANG Xianbin; MENG Zifang; LI Yuan; Paul Farrimond; LI Liwu; DUAN Yi

    2004-01-01

    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 isotopic compositions of gases released by vacuum electromagnetism crushing were also measured. Although the molecular compositions of gas inclusions show differences between the two methods, the overall characteristics are that gas inclusions mainly contain CO2, whilst hydrocarbon gases, such as CH4, C2H6 and C3H8, are less abundant. The content of CO is higher in the stepwise heating experiment than that in the method of vacuum electromagnetism crushing, and there are only minor amounts of N2, H2 and O2 in gas inclusions. Methane δ13C values of gas inclusions in Lower Ordovician and Upper Cambrian rocks (from 5713.7 to 6422 m; -52‰-63‰) are similar to those of bacterial methane, but their chemical compositions do not exhibit the dry character in comparison with biogenic gases. These characteristics of deep gas inclusions may be related to the migration fractionation. Some deep natural gases with light carbon isotopic characteristics in the Tazhong Uplift may have a similar origin. The δ13C1 values of gas inclusions in Lower Cambrian rocks (7117-7124 m) are heavier (-39‰), consistent with highly mature natural gases. Carbon isotopic compositions of CO2 in the gas inclusions of deep carbonate rocks are similar (from -4‰ to -13‰) to those of deep natural gases, indicating predominantly an inorganic origin.

  11. Clumped isotope calibration data for lacustrine carbonates: A progress report

    Science.gov (United States)

    Tripati, A.

    2015-12-01

    Our capacity to understand Earth's environmental history is highly dependent on the accuracy of reconstructions of past climates. Lake sediments provide important archives of terrestrial climate change, and represent an important tool for reconstructing paleohydrology, paleoclimate, paleoenvironment, and paleoaltimetry. Unfortunately, while multiple methods for constraining marine temperature exist, quantitative terrestrial proxies are scarcer - tree rings, speleothems, and leaf margin analyses have all been used with varying degrees of accuracy. Clumped isotope thermometry has the potential to be a useful instrument for determining terrestrial climates: multiple studies have shown the fraction of 13C—18O bonds in carbonates is inversely related to the temperature at which the rocks formed. We have been measuring the abundance of 13C18O16O in the CO2 produced by the dissolution of carbonate minerals in phosphoric acid in modern lake samples and comparing results to independently known estimates of lake water temperature. Here we discuss an extensive calibration dataset comprised of 132 analyses of 97 samples from 44 localities, including microbialites, tufas, and micrites endogenic carbonates, freshwater gastropods, bivalves, microbialites, and ooids.

  12. Tracing paleo-ocean redox using Cr isotopes in carbonates spanning the Great Oxidation Event

    Science.gov (United States)

    Holmden, C. E.; Bekker, A.

    2013-12-01

    Cr is an element whose isotopes are fractionated by redox reactions in the Earth's exogenic system, such as those occuring during oxidative weathering on the continents and scavenging into reduced marine sediments. Frei et al. (2009) proposed that the range of Cr isotope fractionation in exogenic materials in the absence of molecular oxygen would likely not extend beyond the range in igneous rocks, which is quite small (δ53Cr = -0.1 ×0.1‰). They tested their hypothesis on iron formations spanning the Great Oxidation Event (GOE) and found small fractionations that predated the GOE, but no permil level fractionation until the Neoproterozoic. We tested whether δ53Cr values in shallow-water carbonates spanning the GOE might record steps in the rise of atmospheric oxygen between 2.45 and 2.06 Ga. Carbonates representing 15 formations were chosen with depositonal ages ranging between 2.5 Ga and 1.9 Ga. We find very little Cr isotope fractionation recorded in carbonates deposited during this time with the exception of those corresponding to the peak of the Lomagundi Event at ca. 2.15 Ga. A defining characterisitic of the Lomagundi Event is the widespread prevalance of shallow-water carbonate platforms with abundant stromatolites, making their deposits an ideal lithology to record the state of the seawater Cr cycle. Five formations deposited during this time yield δ53Cr values with permil level fractionation recorded in some examples, in both positive and negative directions with respect to the igenous rock baseline. The data suggests that although the oxidative part of the Cr cycle started at least during the peak of the Lomagundi Event, the Cr(VI) reservoir and its residence time remained small, making it susceptible to local processes. 1. Frei et al. (2009) Fluctuations in Precambrian atmospheric oxygen recorded by Cr isotopes, Nature, v. 461, 250-253.

  13. Mercury (Hg) in meteorites: Variations in abundance, thermal release profile, mass-dependent and mass-independent isotopic fractionation

    Science.gov (United States)

    Meier, Matthias M. M.; Cloquet, Christophe; Marty, Bernard

    2016-06-01

    We have measured the concentration, isotopic composition and thermal release profiles of Mercury (Hg) in a suite of meteorites, including both chondrites and achondrites. We find large variations in Hg concentration between different meteorites (ca. 10 ppb to 14,000 ppb), with the highest concentration orders of magnitude above the expected bulk solar system silicates value. From the presence of several different Hg carrier phases in thermal release profiles (150-650 °C), we argue that these variations are unlikely to be mainly due to terrestrial contamination. The Hg abundance of meteorites shows no correlation with petrographic type, or mass-dependent fractionation of Hg isotopes. Most carbonaceous chondrites show mass-independent enrichments in the odd-numbered isotopes 199Hg and 201Hg. We show that the enrichments are not nucleosynthetic, as we do not find corresponding nucleosynthetic deficits of 196Hg. Instead, they can partially be explained by Hg evaporation and redeposition during heating of asteroids from primordial radionuclides and late-stage impact heating. Non-carbonaceous chondrites, most achondrites and the Earth do not show these enrichments in vapor-phase Hg. All meteorites studied here have however isotopically light Hg (δ202Hg = ∼-7 to -1) relative to the Earth's average crustal values, which could suggest that the Earth has lost a significant fraction of its primordial Hg. However, the late accretion of carbonaceous chondritic material on the order of ∼2%, which has been suggested to account for the water, carbon, nitrogen and noble gas inventories of the Earth, can also contribute most or all of the Earth's current Hg budget. In this case, the isotopically heavy Hg of the Earth's crust would have to be the result of isotopic fractionation between surface and deep-Earth reservoirs.

  14. Towards a better understanding of magnesium-isotope ratios from marine skeletal carbonates

    Science.gov (United States)

    Hippler, Dorothee; Buhl, Dieter; Witbaard, Rob; Richter, Detlev K.; Immenhauser, Adrian

    2009-10-01

    This study presents magnesium stable-isotope compositions of various biogenic carbonates of several marine calcifying organisms and an algae species, seawater samples collected from the western Dutch Wadden Sea, and reference materials. The aim of this study is to explore the influence of mineralogy, taxonomy and environmental factors (e.g., seawater isotopic composition, temperature, salinity) on magnesium-isotopic (δ 26Mg) ratios of skeletal carbonates. Using high-precision multi-collector inductively coupled plasma mass spectrometry, we observed that the magnesium-isotopic composition of seawater from the semi-enclosed Dutch Wadden Sea is identical to that of open marine seawater. We further found that a considerable component of the observed variability in δ 26Mg values of marine skeletal carbonates can be attributed to differences in mineralogy. Furthermore, magnesium-isotope fractionation is species-dependent, with all skeletal carbonates being isotopically lighter than seawater. While δ 26Mg values of skeletal aragonite and high-magnesium calcite of coralline red algae indicate the absence or negligibility of metabolic influences, the δ 26Mg values of echinoids, brachiopods and bivalves likely result from a taxon-specific level of control on Mg-isotope incorporation during biocalcification. Moreover, no resolvable salinity and temperature effect were observed for coralline red algae and echinoids. In contrast, Mg-isotope data of bivalves yield ambiguous results, which require further validation. The data presented here, point to a limited use of Mg isotopes as temperature proxy, but highlight the method's potential as tracer of seawater chemistry through Earth's history.

  15. Hydrogen and carbon isotope systematics in hydrogenotrophic methanogenesis under H2-limited and H2-enriched conditions: implications for the origin of methane and its isotopic diagnosis

    Science.gov (United States)

    Okumura, Tomoyo; Kawagucci, Shinsuke; Saito, Yayoi; Matsui, Yohei; Takai, Ken; Imachi, Hiroyuki

    2016-12-01

    Hydrogen and carbon isotope systematics of H2O-H2-CO2-CH4 in hydrogenotrophic methanogenesis and their relation to H2 availability were investigated. Two H2-syntrophic cocultures of fermentatively hydrogenogenic bacteria and hydrogenotrophic methanogens under conditions of cultures of hydrogenotrophic methanogens under conditions of 105 Pa-H2 were tested. Carbon isotope fractionation between CH4 and CO2 during hydrogenotrophic methanogenesis was correlated with pH2, as indicated in previous studies. The hydrogen isotope ratio of CH4 produced during rapid growth of the thermophilic methanogen Methanothermococcus okinawensis under high pH2 conditions ( 105 Pa) was affected by the isotopic composition of H2, as concluded in a previous study of Methanothermobacter thermautotrophicus. This " {δ D}_{{H}_2} effect" is a possible cause of the diversity of previously reported values for hydrogen isotope fractionation between CH4 and H2O examined in H2-enriched culture experiments. Hydrogen isotope fractionation between CH4 and H2O, defined by (1000 + {δ D}_{{CH}_4} )/(1000 + {δ D}_{{H}_2O} ), during hydrogenotrophic methanogenesis of the H2-syntrophic cocultures was in the range 0.67-0.69. The hydrogen isotope fractionation of our H2-syntrophic dataset overlaps with those obtained not only from low- pH2 experiments reported so far but also from natural samples of "young" methane reservoirs (0.66-0.74). Conversely, such hydrogen isotope fractionation is not consistent with that of "aged" methane in geological samples (≥0.79), which has been regarded as methane produced via hydrogenotrophic methanogenesis from the carbon isotope fractionation. As a possible process inducing the inconsistency in hydrogen isotope signatures between experiments and geological samples, we hypothesize that the hydrogen isotope signature of CH4 imprinted at the time of methanogenesis, as in the experiments and natural young methane, may be altered by diagenetic hydrogen isotope exchange

  16. Analytical modelling of stable isotope fractionation of volatile organic compounds in the unsaturated zone

    CERN Document Server

    Bouchard, D; Höhener, P; Hunkeler, D; 10.1016/j.jconhyd.2010.09.006

    2011-01-01

    Analytical models were developed that simulate stable isotope ratios of volatile organic compounds (VOCs) near a point source contamination in the unsaturated zone. The models describe diffusive transport of VOCs, biodegradation and source ageing. The mass transport is governed by Fick's law for diffusion, and the equation for reactive transport of VOCs in the soil gas phase was solved for different source geometries and for different boundary conditions. Model results were compared to experimental data from a one-dimensional laboratory column and a radial-symmetric field experiment, and the comparison yielded a satisfying agreement. The model results clearly illustrate the significant isotope fractionation by gas-phase diffusion under transient state conditions. This leads to an initial depletion of heavy isotopes with increasing distance from the source. The isotope evolution of the source is governed by the combined effects of isotope fractionation due to vaporization, diffusion and biodegradation. The net...

  17. Impacts of microbial community composition on isotope fractionation during reductive dechlorination of tetrachloroethylene.

    Science.gov (United States)

    Dong, Yiran; Butler, Elizabeth C; Philp, R Paul; Krumholz, Lee R

    2011-04-01

    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.

  18. Iron isotope fractionation during magmatic differentiation in Kilauea Iki lava lake.

    Science.gov (United States)

    Teng, Fang-Zhen; Dauphas, Nicolas; Helz, Rosalind T

    2008-06-20

    Magmatic differentiation helps produce the chemical and petrographic diversity of terrestrial rocks. The extent to which magmatic differentiation fractionates nonradiogenic isotopes is uncertain for some elements. We report analyses of iron isotopes in basalts from Kilauea Iki lava lake, Hawaii. The iron isotopic compositions (56Fe/54Fe) of late-stagemeltveins are 0.2 permil (per thousand) greater than values for olivine cumulates. Olivine phenocrysts are up to 1.2 per thousand lighter than those of whole rocks. These results demonstrate that iron isotopes fractionate during magmatic differentiation at both whole-rock and crystal scales. This characteristic of iron relative to the characteristics of magnesium and lithium, for which no fractionation has been found, may be related to its complex redox chemistry in magmatic systems and makes iron a potential tool for studying planetary differentiation.

  19. Carbon mass-balance modeling and carbon isotope exchange processes in the Curonian Lagoon

    Science.gov (United States)

    Barisevičiūtė, Rūta; Žilius, Mindaugas; Ertürk, Ali; Petkuvienė, Jolita

    2016-04-01

    The Curonian lagoon one of the largest coastal lagoons in Europe is located in the southeastern part of the Baltic Sea and lies along the Baltic coast of Lithuania and the Kaliningrad region of Russia. It is influenced by a discharge of the Nemunas and other smaller rivers and saline water of the Baltic Sea. The narrow (width 0.4 km, deep 8-14 m) Klaipėda Strait is the only way for fresh water run-off and brackish water intrusions. This research is focused on carbon isotope fractionations related with air - water exchange, primary production and organic carbon sedimentation, mineralization and uptake from both marine and terrestrial sources.

  20. BIODEGRADATION OF FLUORANTHENE AS MONITORED USING STABLE CARBON ISOTOPES

    Science.gov (United States)

    The measurement of stable isotope ratios of carbon (d13C values) was investigated as a viable technique to monitor the intrinsic bioremediation of polycyclic aromatic hydrocarbons (PAHs). Biometer-flask experiments were conducted in which the bacterium, Sphingomonas paucimobilis,...

  1. Impact of bioavailability restrictions on microbially induced stable isotope fractionation. 1. Theoretical calculation.

    Science.gov (United States)

    Thullner, Martin; Kampara, Makeba; Richnow, Hans H; Harms, Hauke; Wick, Lukas Y

    2008-09-01

    The microbial degradation of organic substrates often exhibits a fractionation of stable isotopes which leads to an enrichment of the heavier isotope in the remaining substrate. The use of this effect to quantify the amount of biodegraded substrate in contaminated aquifers requires that the isotope fractionation factor is constant in time and space. In many natural and engineered systems the bioavailable concentration at the location of the enzymes differs from the average bulk concentration of the substrate. When enzymatically driven substrate degradation is coupled to a preceding transport step controlling the bioavailability of the substrate, the observed isotope fractionation becomes a function of the bulk substrate concentration. The sensitivity of the observed isotope fractionation factor toward such substrate concentration changes depends on the ratio of bulk substrate concentration and Michaelis-Menten constant and on the ratio between the specific affinity of the microorganisms toward the substrate and the first order rate constant of the bioavailability limiting transport process. Highest sensitivities toward substrate concentration were found for combinations of high substrate concentration with low substrate bioavailability (i.e., high ratios of substrate concentration and Michaelis-Menten constant, and high ratios of specific affinity and transport rate constant). As a consequence, changes in concentration and isotopic composition of a bioavailability limited substrate in batch experiments should not exhibit a linear relation in a Rayleigh plot, and the slope of the Rayleigh plot should show a decreasing trend with concentration decrease. When using isotope fractionation to quantify biodegradation along groundwater flow paths, changes in observed isotope fractionation might occur while contaminant concentration decreases along a flow path.

  2. Temperature effects on the fractionation of multiple sulfur isotopes by Thermodesulfobacterium and Desulfovibrio strains

    Science.gov (United States)

    Wang, P.; Sun, C.; Ono, S.; Lin, L.

    2012-12-01

    Microbial dissimilatory sulfate reduction is one of the major mechanisms driving anaerobic mineralization of organic matter in global ocean. While sulfate-reducing prokaryotes are well known to fractionate sulfur isotopes during dissimilatory sulfate reduction, unraveling the isotopic compositions of sulfur-bearing minerals preserved in sedimentary records could provide invaluable constraints on the evolution of seawater chemistry and metabolic pathways. Variations in the sulfur isotope fractionations are partly due to inherent differences among species and also affected by environmental conditions. The isotope fractionations caused by microbial sulfate reduction have been interpreted to be a sequence of enzyme-catalyzed isotope fractionation steps. Therefore, the fractionation factor depends on (1) the sulfate flux into and out of the cell, and (2) the flux of sulfur transformation between the internal pools. Whether the multiple sulfur isotope effect could be quantitatively predicted using such a metabolic flux model would provide insights into the cellular machinery catalyzing with sulfate reduction. This study examined the multiple sulfur isotope fractionation patterns associated with a thermophilic Thermodesulfobacterium-related strain and a mesophilic Desulfovibrio gigas over a wide temperature range. The Thermodesulfobacterium-related strain grew between 34 and 79°C with an optimal temperature at 72°C and the highest cell-specific sulfate reduction rate at 77°C. The 34ɛ values ranged between 8.2 and 31.6‰ with a maximum at 68°C. The D. gigas grew between 10 and 45 °C with an optimal temperature at 30°C and the highest cell-specific sulfate reduction rate at 41°C. The 34ɛ values ranged between 10.3 and 29.7‰ with higher magnitude at both lower and higher temperatures. The results of multiple sulfur isotope measurements expand the previously reported range and cannot be described by a solution field of the metabolic flux model, which calculates

  3. Stable carbon isotopes in tree rings: the failure of uniformitarianism

    Science.gov (United States)

    McCarroll, Danny

    2010-05-01

    When tree rings are used to reconstruct past climate we rely on the uniformitarian principle that ‘the present is the key to the past'. Relationships between measured parameters and climate that can be calibrated and verified over the instrumental period are assumed to be applicable at longer timescales. In the case of δ13C, however, the uniformitarian principle fails for two reasons. (1) The instrumental calibration period is also the period of anthropogenic increase in atmospheric CO2. δ13C is a function of the ratio of internal to ambient CO2, so maintaining constant δ13C over the industrial period requires an active plastic response, either restricting stomatal conductance or increasing assimilation rate. In some areas trees may have reached the limits of their plasticity so that over the last few decades δ13C values have been declining, independent of any changes in climate. If no correction is made, the recent response to climate will be a poor indicator of behaviour in the past. (2) Tree ring δ13C is often used to reconstruct past temperatures even though temperature rarely has a strong direct control over fractionation. The link is therefore via either sunshine or humidity, which over the calibration period may be very strongly correlated with temperature. Long isotope chronologies, when compared with independent evidence of past temperatures, however, can show periods of marked divergence. The strong covariance of temperature, sunshine and humidity over the last century may not have persisted over longer timescales with larger climatic perturbations. In the case of carbon isotopes the key to the past is not statistical inference based on recent behaviour, but a clear mechanistic understanding of the influence of climate and other factors on fractionation.

  4. Cr isotope fractionation factors for Cr(VI) reduction by a metabolically diverse group of bacteria

    Science.gov (United States)

    Basu, Anirban; Johnson, Thomas M.; Sanford, Robert A.

    2014-10-01

    Reduction of Cr(VI) is an important process that determines the geochemical behavior, mobility and bioavailability of Cr in both terrestrial and marine environments. Many metabolically diverse microorganisms possess Cr(VI) reduction capacity. Cr(VI) reduction fractionates Cr isotopes and thus 53Cr/52Cr ratios can be used to monitor Cr(VI) reduction and redox conditions. The magnitude of isotopic fractionation (ε) for a variety of microbial reduction mechanisms must be known for accurate interpretation of observed shifts in 53Cr/52Cr ratios. We determined isotopic fractionation factors for Cr(VI) reduction by metal reducers Geobacter sulfurreducens and Shewanella sp. strain NR, a denitrifying soil bacterium Pseudomonas stutzeri DCP-Ps1, and a sulfate reducer Desulfovibrio vulgaris. All bacteria investigated in this study produced significant Cr isotope fractionation. The fractionation (ε) for G. sulfurreducens, Shewanella sp. (NR), P. stutzeri DCP-Ps1, and D. vulgaris were -3.03‰ ± 0.12‰, -2.17‰ ± 0.22‰, -3.14‰ ± 0.13‰, and -3.01‰ ± 0.11‰, respectively. Despite differences in microbial strains in this study, the ε did not vary significantly except for Shewanella sp. (NR). Our results suggest that strong isotopic fractionation is induced during Cr(VI) reduction under electron donor poor (∼300 μM) conditions.

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

    Energy Technology Data Exchange (ETDEWEB)

    Gromov, Sergey S.

    2014-11-01

    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

  6. Oxygen isotope fractionation between human phosphate and water revisited

    DEFF Research Database (Denmark)

    Daux, Valérie; Lécuyer, Christophe; Héran, Marie-Anne;

    2008-01-01

    The oxygen isotope composition of human phosphatic tissues (delta18OP) has great potential for reconstructing climate and population migration, but this technique has not been applied to early human evolution. To facilitate this application we analyzed delta18OP values of modern human teeth...

  7. Carbon allocation and carbon isotope fluxes in the plant-soil-atmosphere continuum: a review

    Directory of Open Access Journals (Sweden)

    N. Brüggemann

    2011-04-01

    Full Text Available The terrestrial carbon (C cycle has received increasing interest over the past few decades, however, there is still a lack of understanding of the fate of newly assimilated C allocated within plants and to the soil, stored within ecosystems and lost to the atmosphere. Stable carbon isotope studies can give novel insights into these issues. In this review we provide an overview of an emerging picture of plant-soil-atmosphere C fluxes, as based on C isotope studies, and identify processes determining related C isotope signatures. The first part of the review focuses on isotopic fractionation processes within plants during and after photosynthesis. The second major part elaborates on plant-internal and plant-rhizosphere C allocation patterns at different time scales (diel, seasonal, interannual, including the speed of C transfer and time lags in the coupling of assimilation and respiration, as well as the magnitude and controls of plant-soil C allocation and respiratory fluxes. Plant responses to changing environmental conditions, the functional relationship between the physiological and phenological status of plants and C transfer, and interactions between C, water and nutrient dynamics are discussed. The role of the C counterflow from the rhizosphere to the aboveground parts of the plants, e.g. via CO2 dissolved in the xylem water or as xylem-transported sugars, is highlighted. The third part is centered around belowground C turnover, focusing especially on above- and belowground litter inputs, soil organic matter formation and turnover, production and loss of dissolved organic C, soil respiration and CO2 fixation by soil microbes. Furthermore, plant controls on microbial communities and activity via exudates and litter production as well as microbial community effects on C mineralization are reviewed. The last part of the paper is dedicated to physical interactions between soil CO2 and the soil matrix, such as CO

  8. Sulfur isotope fractionation during bacterial sulfate reduction in organic-rich sediments

    DEFF Research Database (Denmark)

    Habicht, K S; Canfield, D E

    1997-01-01

    Isotope fractionation during sulfate reduction by natural populations of sulfate-reducing bacteria was investigated in the cyanobacterial microbial mats of Solar Lake, Sinai and the sediments of Logten Lagoon sulfuretum, Denmark. Fractionation was measured at different sediment depths, sulfate...... concentrations, and incubation temperatures. Rates of sulfate reduction varied between 0.1 and 37 micromoles cm-3 d-1, with the highest rates among the highest ever reported from natural sediments. The depletion of 34S during dissimilatory sulfate reduction ranged from 16% to 42%, with the largest 34S...... sulfate reduction. Therefore, additional processes contributing to the fractionation of sulfur isotopes in the sediments are indicated. From both Solar Lake and Logten Lagoon we were able to enrich cultures of elemental sulfur-disproportionating bacteria. We suggest that isotope fractionation accompanying...

  9. The specific carbon isotopic compositions of branched and cyclic hydrocarbons from Fushun oil shale

    Institute of Scientific and Technical Information of China (English)

    DUAN Yi; WU Baoxiang; ZHENG Guodong; ZHANG Hui; ZHENG Chaoyang

    2004-01-01

    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.

  10. Carbon and Nitrogen Isotope Systematics in a Sector-Zoned Diamond from the Mir Kimberlite, Yakutia

    Science.gov (United States)

    Hauri, E.; Bulanova, G.; Pearson, G.; Griffin, B.

    2002-05-01

    A single Yakutian octahedral diamond, displaying striking cubic and octahedral growth sectors surrounded by an octahedral rim, has been analysed for carbon and nitrogen isotopic compositions by SIMS and for nitrogen concentration (by SIMS and FTIR) and nitrogen aggregation state (FTIR). A graphite "seed" inclusion identified within the diamond, enriched in K, Ca, Ti, Rb and Sr, provides evidence that the diamond may have grown from a carbonate melt/fluid interacting with upper mantle rocks. Carbon and nitrogen isotope compositions become progressively heavier from the core region (d13C = -7 to -5 and d15N= -3) towards the inner rim zones (d13C = -3 and d15N = +8.9 to +5) of the diamond. Nitrogen concentration and aggregation measurements show corresponding decreases that generally correlate with the isotopic variations. These systematic variations within the core and intermediate regions of the diamond are consistent with their formation during diamond growth from CO2-rich fluids as a continuous event, accompanied by slight progressive isotopic fractionation of carbon and nitrogen. However, the observed isotope and nitrogen abundance trends are not those predicted from thermodynamic modelling of fluid-solid equilibria in a C-N-O-H-bearing system due to changes in parameters such as fO2 (Deines, 1980; Deines et al 1989). Within the finely-zoned octahedral rim region, non-systematic variations in nitrogen abundance, nitrogen aggregation, and nitrogen and carbon isotope ratios were observed. Several interpretations are given for this phenomenon, including kinetic effects during growth of the diamond rim under different conditions from those of the core-intermediate regions, or rapidly changing fluid sources during the growth. No fractionation of nitrogen isotopes between cubic and octahedral growth zones was identified within the studied diamond, in contrast with the fractionation phenomena found in synthetic diamonds of mixed growth. Our results illustrate the

  11. Utility of 5A molecular sieves to measure carbon isotope ratios in lipid biomarkers.

    Science.gov (United States)

    Tolosa, Imma; Ogrinc, Nives

    2007-09-21

    A procedure using 5A zeolite sorption to separate cyclic/branched organic compounds from the linear ones was developed and carbon isotopic fractionation effects were investigated in different families of compounds, e.g. within the hydrocarbon and alcohol compounds. The 5A sieve has a pore size such that only linear components can be incorporated into the pores whereas the cyclic/branched compounds are remaining free in the organic solution. The sorbed compounds were released from the molecular sieve with HF and solvent extracted with hexane. The method enables the isolation of linear saturated classes, such as n-alkanes and n-fatty alcohols from branched/cyclic compounds without isotopic fractionation for compound-specific isotope analysis (CSIA) of delta(13)C. However, alkene hydrocarbons, sterols and some aromatics were completely or partly degraded with the molecular sieve.

  12. Evidence from carbon isotope measurements for biological origins of individual longchain n-alkanes in sediments from the Nansha Sea, China

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Carbon isotopes are measured for individual long-chain n-alkanes in sediments from the Nansha Sea. The features of carbon isotopic compositions of individual n-alkanes and their origins are studied. The results show that the long-chain n-aikanes have a light carbon isotopic composition and a genetic feature of mixing sources, and low-latitude higher plants and microbes are considered to be their main end member sources. Based on the abundances and carbon isotopic compositions of individual n-alkanes, the fractional contributions of the two end member sources to individual n-aikanes are quantitatively calculated by using a mixing model. The obtained data indicate that the fractional contributions of the two biological sources are different in the three samples. A trend is that the contribution of microbes increases with the depth. These results provide the theory basis and quantitatively studied method for carbon isotopic applied research of individual n-alkanes.

  13. Experimental oxygen isotope fractionation between siderite-water and phosphoric acid liberated CO2-siderite

    Science.gov (United States)

    Carothers, W.W.; Adami, L.H.; Rosenbauer, R.J.

    1988-01-01

    The equilibrium fractionation of O isotopes between synthetic siderite and water has been measured at temperatures ranging from 33?? to 197??C. The fractionation between siderite and water over this temperature range can be represented by the equation: 103 ln ?? = 3.13 ?? 106T-2 - 3.50. Comparison between the experimental and theoretical fractionations is favorable only at approximately 200??C; at lower temperatures, they generally differ by up to 2 permil. Siderite was prepared by the slow addition of ferrous chloride solutions to sodium bicarbonate solutions at the experimental temperatures. It was also used to determine the O isotope fractionation factors between phosphoric acid liberated CO2 and siderite. The fractionation factors for this pair at 25?? and 50??C are 1.01175 and 1.01075, respectively. Preliminary results of the measured C isotope fractionation between siderite and Co2 also indicate C isotopic equilibrium during precipitation of siderite. The measured distribution of 13C between siderite and CO2 coincides with the theoretical values only at about 120??C. Experimental and theoretical C fractionations differ up to 3 permil at higher and lower temperatures. ?? 1988.

  14. Simulations of an isotopic fractionation by freezing in an open system

    Institute of Scientific and Technical Information of China (English)

    Yoshinori Iizuka

    2003-01-01

    This paper presents a model of isotopic fractionation by freezing under near-equilibrium conditions in an open system and uses the model to predict the fractionation curve and slope gradient of δ18O versus δD.The simulation results show that 1) the fractionation curve and slope gradient are determined by the ratio of freezing rate to input rate, 2) the isotopic value in the initial stage of freezing is determined by the isotopic value of initial water; 3) in the latter half of freezing in an open system, the isotopic value converges to a certain value determined by that of input water.These results suggest that the shape of the fractionation curve is the method to distinguish whether freezing occurred in a closed or open system.This analysis is applied to an isotopic curve observed in basal ice of Hamna Glacier, Sya drainage, East Antarctica.The isotopic curve indicates formation by regelation in an open system with a ratio of freezing/input rates of about 10/4.

  15. Mercury isotope fractionation during ore retorting in the Almadén mining district, Spain

    Science.gov (United States)

    Gray, John E.; Pribil, Michael J.; Higueras, Pablo L.

    2013-01-01

    Almadén, Spain, is the world's largest mercury (Hg) mining district, which has produced over 250,000 metric tons of Hg representing about 30% of the historical Hg produced worldwide. The objective of this study was to measure Hg isotopic compositions of cinnabar ore, mine waste calcine (retorted ore), elemental Hg (Hg0(L)), and elemental Hg gas (Hg0(g)), to evaluate potential Hg isotopic fractionation. Almadén cinnabar ore δ202Hg varied from − 0.92 to 0.15‰ (mean of − 0.56‰, σ = 0.35‰, n = 7), whereas calcine was isotopically heavier and δ202Hg ranged from − 0.03‰ to 1.01‰ (mean of 0.43‰, σ = 0.44‰, n = 8). The average δ202Hg enrichment of 0.99‰ between cinnabar ore and calcines generated during ore retorting indicated Hg isotopic mass dependent fractionation (MDF). Mass independent fractionation (MIF) was not observed in any of the samples in this study. Laboratory retorting experiments of cinnabar also were carried out to evaluate Hg isotopic fractionation of products generated during retorting such as calcine, Hg0(L), and Hg0(g). Calcine and Hg0(L) generated during these retorting experiments showed an enrichment in δ202Hg of as much as 1.90‰ and 0.67‰, respectively, compared to the original cinnabar ore. The δ202Hg for Hg0(g) generated during the retorting experiments was as much as 1.16‰ isotopically lighter compared to cinnabar, thus, when cinnabar ore was roasted, the resultant calcines formed were isotopically heavier, whereas the Hg0(g) generated was isotopically lighter in Hg isotopes.

  16. Temperature effect on leaf water deuterium enrichment and isotopic fractionation during leaf lipid biosynthesis: results from controlled growth of C3 and C4 land plants.

    Science.gov (United States)

    Zhou, Youping; Grice, Kliti; Chikaraishi, Yoshito; Stuart-Williams, Hilary; Farquhar, Graham D; Ohkouchi, Naohiko

    2011-02-01

    The hydrogen isotopic ratios ((2)H/(1)H) of land plant leaf water and the carbon-bound hydrogen of leaf wax lipids are valuable indicators for climatic, physiological, metabolic and geochemical studies. Temperature will exert a profound effect on the stable isotopic composition of leaf water and leaf lipids as it directly influences the isotopic equilibrium (IE) during leaf water evaporation and cellular water dissociation. It is also expected to affect the kinetics of enzymes involved in lipid biosynthesis, and therefore the balance of hydrogen inputs along different biochemical routes. We conducted a controlled growth experiment to examine the effect of temperature on the stable hydrogen isotopic composition of leaf water and the biological and biochemical isotopic fractionations during lipid biosynthesis. We find that leaf water (2)H enrichment at 20°C is lower than that at 30°C. This is contrary to the expectation that at lower temperatures leaf water should be more enriched in (2)H due to a larger equilibrium isotope effect associated with evapotranspiration from the leaf if all other variables are held constant. A hypothesis is presented to explain the apparent discrepancy whereby lower temperature-induced down-regulation of available aquaporin water channels and/or partial closure of transmembrane water channel forces water flow to "detour" to a more convoluted apoplastic pathway, effectively increasing the length over which diffusion acts against advection as described by the Péclet effect (Farquhar and Lloyd, 1993) and decreasing the average leaf water enrichment. The impact of temperature on leaf water enrichment is not reflected in the biological isotopic fractionation or the biochemical isotopic fractionation during lipid biosynthesis. Neither the biological nor biochemical fractionations at 20°C are significantly different from that at 30°C, implying that temperature has a negligible effect on the isotopic fractionation during lipid biosynthesis.

  17. Stable carbon isotope ratios of ambient secondary organic aerosols in Toronto

    Science.gov (United States)

    Saccon, M.; Kornilova, A.; Huang, L.; Moukhtar, S.; Rudolph, J.

    2015-09-01

    A method to quantify concentrations and stable carbon isotope ratios of secondary organic aerosols has been applied to study atmospheric nitrophenols in Toronto, Canada. The sampling of five nitrophenols, all with substantial secondary formation from the photooxidation of aromatic volatile organic compounds (VOCs), was conducted in the gas phase and particulate matter (PM) together and in PM alone. Their concentrations in the atmosphere are in the low ng m-3 range and, consequently, a large volume of air (> 1000 m3) is needed to analyze samples for stable carbon isotope ratios, resulting in sampling periods of typically 24 h. While this extended sampling period increases the representativeness of average values, it at the same time reduces possibilities to identify meteorological conditions or atmospheric pollution levels determining nitrophenol concentrations and isotope ratios. Average measured carbon isotope ratios of the different nitrophenols are between -34 and -33 ‰, which is well within the range predicted by mass balance. However, the observed carbon isotope ratios cover a range of nearly 9 ‰ and approximately 20 % of the isotope ratios of the products have isotope ratios lower than predicted from the kinetic isotope effect of the first step of the reaction mechanism and the isotope ratio of the precursor. This can be explained by isotope fractionation during reaction steps following the initial reaction of the precursor VOCs with the OH radical. Limited evidence for local production of nitrophenols is observed since sampling was done in the Toronto area, an urban center with significant anthropogenic emission sources. Strong evidence for significant local formation of nitrophenols is only found for samples collected in summer. On average, the difference in carbon isotope ratios between nitrophenols in the particle phase and in the gas phase is insignificant, but for a limited number of observations in summer, a substantial difference is observed. This

  18. Biometrics from the carbon isotope ratio analysis of amino acids in human hair.

    Science.gov (United States)

    Jackson, Glen P; An, Yan; Konstantynova, Kateryna I; Rashaid, Ayat H B

    2015-01-01

    This study compares and contrasts the ability to classify individuals into different grouping factors through either bulk isotope ratio analysis or amino-acid-specific isotope ratio analysis of human hair. Using LC-IRMS, we measured the isotope ratios of 14 amino acids in hair proteins independently, and leucine/isoleucine as a co-eluting pair, to provide 15 variables for classification. Multivariate analysis confirmed that the essential amino acids and non-essential amino acids were mostly independent variables in the classification rules, thereby enabling the separation of dietary factors of isotope intake from intrinsic or phenotypic factors of isotope fractionation. Multivariate analysis revealed at least two potential sources of non-dietary factors influencing the carbon isotope ratio values of the amino acids in human hair: body mass index (BMI) and age. These results provide evidence that compound-specific isotope ratio analysis has the potential to go beyond region-of-origin or geospatial movements of individuals-obtainable through bulk isotope measurements-to the provision of physical and characteristic traits about the individuals, such as age and BMI. Further development and refinement, for example to genetic, metabolic, disease and hormonal factors could ultimately be of great assistance in forensic and clinical casework.

  19. Soil organic carbon assessments in cropping systems using isotopic techniques

    Science.gov (United States)

    Martín De Dios Herrero, Juan; Cruz Colazo, Juan; Guzman, María Laura; Saenz, Claudio; Sager, Ricardo; Sakadevan, Karuppan

    2016-04-01

    Introduction of improved farming practices are important to address the challenges of agricultural production, food security, climate change and resource use efficiency. The integration of livestock with crops provides many benefits including: (1) resource conservation, (2) ecosystem services, (3) soil quality improvements, and (4) risk reduction through diversification of enterprises. Integrated crop livestock systems (ICLS) with the combination of no-tillage and pastures are useful practices to enhance soil organic carbon (SOC) compared with continuous cropping systems (CCS). In this study, the SOC and its fractions in two cropping systems namely (1) ICLS, and (2) CCS were evaluated in Southern Santa Fe Province in Argentina, and the use of delta carbon-13 technique and soil physical fractionation were evaluated to identify sources of SOC in these systems. Two farms inside the same soil cartographic unit and landscape position in the region were compared. The ICLS farm produces lucerne (Medicago sativa Merrill) and oat (Avena sativa L.) grazed by cattle alternatively with grain summer crops sequence of soybean (Glicine max L.) and corn (Zea mays L.), and the farm under continuous cropping system (CCS) produces soybean and corn in a continuous sequence. The soil in the area is predominantly a Typic Hapludoll. Soil samples from 0-5 and 0-20 cm depths (n=4) after the harvest of grain crops were collected in each system and analyzed for total organic carbon (SOC, 0-2000 μm), particulate organic carbon (POC, 50-100 μm) and mineral organic carbon (MOC, <50 μm). Delta carbon-13 was determined by isotopic ratio mass spectrometry. In addition, a site with natural vegetation (reference site, REF) was also sampled for delta carbon-13 determination. ANOVA and Tukey statistical analysis were carried out for all data. The SOC was higher in ICLS than in CCS at both depths (20.8 vs 17.7 g kg-1 for 0-5 cm and 16.1 vs 12.7 g kg-1 at 0-20 cm, respectively, P<0.05). MOC was

  20. The magnesium isotope record of cave carbonate archives

    Directory of Open Access Journals (Sweden)

    S. Riechelmann

    2012-11-01

    Full Text Available Here we explore the potential of magnesium (δ26Mg isotope time-series data as continental climate proxies in speleothem calcite archives. For this purpose, a total of six Pleistocene and Holocene stalagmites from caves in Germany, Morocco and Peru and two flowstones from a cave in Austria were investigated. These caves represent the semi-arid to arid (Morocco, the warm-temperate (Germany, the equatorial-humid (Peru and the cold-humid (Austria climate zones. Changes in the calcite magnesium isotope signature with time are compared against carbon and oxygen isotope records from these speleothems. Similar to other proxies, the non-trivial interaction of a number of environmental, equilibrium and disequilibrium processes governs the δ26Mg fractionation in continental settings. These include the different sources of magnesium isotopes such as rainwater or snow as well as soil and host rock, soil zone biogenic activity, shifts in silicate versus carbonate weathering ratios and residence time of water in the soil and karst zone. Pleistocene stalagmites from Morocco show the lowest mean δ26Mg values (GDA: −4.26 ± 0.07‰ and HK3: −4.17 ± 0.15‰, and the data are well explained in terms of changes in aridity over time. The Pleistocene to Holocene stalagmites from Peru show the highest mean value of all stalagmites (NC-A and NC-B δ26Mg: −3.96 ± 0.04‰ but only minor variations in Mg-isotope composition, which is consistent with the rather stable equatorial climate at this site. Holocene stalagmites from Germany (AH-1 mean δ26Mg: −4.01 ± 0.07‰; BU 4 mean δ26Mg: −4.20 ± 0.10‰ suggest changes in outside air temperature was the principal driver rather than rainfall amount. The alpine Pleistocene flowstones from Austria (SPA 52: −3.00 ± 0.73‰; SPA 59: −3.70 ± 0.43‰ are affected by glacial versus interglacial climate change with outside air temperature

  1. The magnesium isotope record of cave carbonate archives

    Directory of Open Access Journals (Sweden)

    S. Riechelmann

    2012-05-01

    Full Text Available Here we explore the potential of time-series magnesium (δ26Mg isotope data as continental climate proxies in speleothem calcite archives. For this purpose, a total of six Pleistocene and Holocene stalagmites from caves in Germany, Morocco and Peru and two flowstones from a cave in Austria were investigated. These caves represent the semi-arid to arid (Morocco, the warm-temperate (Germany, the equatorial-humid (Peru and the cold-humid (Austria climate zones. Changes in the calcite magnesium isotope signature with time are placed against carbon and oxygen isotope records from these speleothems. Similar to other proxies, the non-trivial interaction of a number of environmental, equilibrium and non-equilibrium processes governs the δ26Mg fractionation in continental settings. These include the different sources of magnesium isotopes such as rain water or snow as well as soil and hostrock, soil zone biogenic activity, shifts in silicate versus carbonate weathering ratios and residence time of water in the soil and karst zone. Pleistocene stalagmites from Morocco show the lowest mean δ26Mg values (GDA: −4.26 ± 0.07 ‰ and HK3: −4.17 ± 0.15 ‰ and the data are well explained in terms of changes in aridity over time. The Pleistocene to Holocene stalagmites from Peru show the highest mean value (NC-A and NC-B δ26Mg: −3.96 ± 0.04 ‰ but only minor variations in Mg-isotope composition, which is in concert with the rather stable equatorial climate at this site. Holocene stalagmites from Germany (AH-1 mean δ26Mg: −4.01 ± 0.07 ‰; BU 4 mean δ26Mg: −4.20 ± 0.10 ‰ record changes in outside air temperature as driving factor rather than rainfall amount. The alpine Pleistocene flowstones from Austria (SPA 52: −3.00 ± 0.73 ‰; SPA 59: −3.70 ± 0.43 ‰ are affected by glacial versus interglacial climate change with outside air temperature affecting soil zone activity

  2. Electron-bifurcating transhydrogenase is central to hydrogen isotope fractionation during lipid biosynthesis in sulfate reducing bacteria

    Science.gov (United States)

    Leavitt, W.; Flynn, T. M.; Suess, M.; Bradley, A. S.

    2015-12-01

    A significant range in microbial lipid 2H/1H ratios is observed in modern marine sediments [Li et al. 2009. GCA]. The magnitude of hydrogen isotope fractionation between microbial lipids and growth water (2ɛlipid-H2O) is hypothesized to relate to the central carbon and energy metabolism [Zhang et al. 2009. PNAS]. These observations have raised the intriguing possibility for culture independent identification of the dominant metabolic pathways operating in environments critical to the geological record. One such metabolism we would like to track for its global significance in sedimentary carbon cycling is bacterial sulfate reduction [Jørgensen. 1982. Nature]. To-date, heterotrophic sulfate reducing bacteria (SRB) have been observed to produce lipids that are depleted in fatty acid H-isotope composition, relative to growth water (2ɛlipid-H2O ~ -125 to -175 ‰), with experiments on different substrates yielding little variability [Campbell et al. 2009. GCA; Osburn. 2013; Dawson et al. 2015. Geobiology]. In stark contrast, aerobic heterotrophs show a wide range in fractionations (2ɛlipid-H2O ~ +300 to -125‰) which seems to scale with the route cellular carbon metabolism [Zhang et al. 2009. PNAS; Heinzelmann et al. 2015. Front Microbio]. Recent work in aerobic methylotrophs [Bradley et al. 2014. AGU] implicates transhydrogenase (TH) activity as a critical control on 2ɛlipid-H2O. This work suggests a specific driving mechanism for this range in fractionation is the ratio of intracellular NADPH/NADH, and more fundamentally, the intracellular redox state. In SRB a key component of energy metabolism is the activity of electron-bifurcating TH [Price et al. 2014. Front Microbio], for which a recent transposon mutant library has generated a number of knockouts in the target gene [Kuehl et al. 2014. mBio] in the model organism Desulfovibrio alaskensis strain G20. In this study we compare growth rates, fatty acid concentrations and 2ɛlipid-H2O from wild type and TH

  3. Carbonate Mineral Formation on Mars: Clues from Stable Isotope Variation Seen in Cryogenic Laboratory Studies of Carbonate Salts

    Science.gov (United States)

    Socki, Richard; Niles, Paul B.; Sun, Tao; Fu, Qi; Romanek, Christopher S.; Gibson, Everett K.

    2013-01-01

    The geologic history of water on the planet Mars is intimately connected to the formation of carbonate minerals through atmospheric CO2 and its control of the climate history of Mars. Carbonate mineral formation under modern martian atmospheric conditions could be a critical factor in controlling the martian climate in a means similar to the rock weathering cycle on Earth. The combination of evidence for liquid water on the martian surface and cold surface conditions suggest fluid freezing could be very common on the surface of Mars. Cryogenic calcite forms readily when a rise in pH occurs as a result of carbon dioxide degassing quickly from freezing Ca-bicarbonate-rich water solutions. This is a process that has been observed in some terrestrial settings such as arctic permafrost cave deposits, lakebeds of the Dry Valleys of Antarctica, and in aufeis (river icings) from rivers of N.E. Alaska. We report here the results of a series of laboratory experiments that were conducted to simulate potential cryogenic carbonate formation on the planet Mars. These results indicate that carbonates grown under martian conditions (controlled atmospheric pressure and temperature) show enrichments from starting bicarbonate fluids in both carbon and oxygen isotopes beyond equilibrium values with average delta13C(DIC-CARB) values of 20.5%0 which exceed the expected equilibrium fractionation factor of [10(sup 3) ln alpha = 13%0] at 0 degC. Oxygen isotopes showed a smaller enrichment with delta18O(H2O-CARB) values of 35.5%0, slightly exceeding the equilibrium fractionation factor of [10(sup 3) ln alpha = 34%0 ] at 0degC. Large kinetic carbon isotope effects during carbonate precipitation could substantially affect the carbon isotope evolution of CO2 on Mars allowing for more efficient removal of 13C from the Noachian atmosphere enriched by atmospheric loss. This mechanism would be consistent with the observations of large carbon isotope variations in martian materials despite the

  4. Fractionation of iron species and iron isotopes in the Baltic Sea euphotic zone

    Directory of Open Access Journals (Sweden)

    J. Gelting

    2009-07-01

    Full Text Available Measurements of the physiochemical speciation of Fe in the euphotic zone were performed at three different locations, over a well defined salinity gradient, during spring and summer in the Baltic Sea. The average of total Fe changed from 114 nM in the Bothnian Sea, 44 nM at Landsort Deep and 15 nM at Gotland Deep. Particulate Fe (PFe was the dominating phase at all stations and on average accounted for 75–85% of the total Fe pool. At all three locations, a decrease in total Fe of 80–90% from initial measurements compared to the summer was found. A strong positive correlation between PFe and chl-a was observed. Hence, primary production strongly regulates cycling of suspended Fe. However, this relation is not dominated by active uptake of Fe in phytoplankton; instead this reflects cycling of phosphorus, growth of diatoms, and removal of PFe during phytoplankton sedimentation. The average colloidal iron fraction, CFe, showed decreasing concentrations along the salinity gradient; Bothnian Sea 15 nM; Landsort Deep 1 nM and Gotland Deep 0.5 nM. Field Flow Fractionation data indicate that the main colloidal carrier phase for Fe in the Baltic Sea is a carbon-rich fulvic acid associated compound, likely of riverine origin. The Fe isotope composition (δ56Fe of the PFe showed constant positive values in the Bothnian Sea surface waters (+0.08 to +0.20‰. Enrichment of heavy Fe in the Bothnian Sea PFe is most likely associated to input of aggregated land derived Fe-oxyhydroxides and a rapid overturn of Fe(II. At the Landsort deep, the fractionation of PFe changed between −0.08‰ to +0.28‰. The negative values, in early spring, probably indicate exchange over the oxic-anoxic boundary at ~80 m depth.

  5. Mouse skin damages caused by fractionated irradiation with carbon ions

    Energy Technology Data Exchange (ETDEWEB)

    Ando, K.; Chen, Y.J.; Ohira, C.; Nojima, K.; Ando, S.; Kobayashi, N.; Ohbuchi, T.; Shimizu, W. [Space and Particle Radiation Science Research Group, Chiba (Japan); Koike, S.; Kanai, T. [National Inst. of Radiological Sciences, Chiba (Japan). Div. of Accelerator Physics

    1997-09-01

    We have investigated carbon-dose responses of early and late skin damages after daily fractionations to the mouse leg. Depilated legs were irradiated with 7 different positions within 290 MeV/u carbon beams. Fractionation schedules were 1, 2, 4 and 8 daily fractions. Skin reaction was scored every other day for 32 days. Five highest scores in individual mice were averaged, and used as averaged peak reaction. The isoeffect doses to produce an averaged peak skin reaction of 3.0 (moist desquamation) on dose-response curves were calculated with 95% confidence limit. The isoeffect dose for control gamma rays constantly increased with an increase in the number of fraction. The isoeffect doses in low LET carbon ions of 14- and 20 keV/{mu}m also increased up to 4 fractions, but did not increase when 4 fractions increased to 8 fractions. The saturation of isoeffect dose was more prominently observed for 40 keV/{mu}m in such that the isoeffect doses did not change among 2, 4 and 8 fractions. The isoeffect doses for LET higher than 50 keV/{mu}m were smaller than those for lower LET. However, the isoeffect doses for 50-, 60-, 80- and 100 keV/{mu} steadily increased with an increase in the number of fraction and did not show any saturation up to 8 fractions. Relation between LET and RBE was linear for all fractionation schedules. The slope of regression line in 4 fractions was steepest, and significantly (P<0.05) different from that in 1 fraction. (orig.)

  6. Calcium and calcium isotope changes during carbon cycle perturbations at the end-Permian

    Science.gov (United States)

    Komar, Nemanja; Zeebe, Richard

    2016-04-01

    Negative carbon and calcium isotope excursions, as well as climate shifts, took place during the most severe mass extinction event in Earth's history, the end-Permian (˜252 Ma). Investigating the connection between carbon and calcium cycles during transient carbon cycle perturbation events, such as the end-Permian, may help resolve the intricacies between the coupled calcium-carbon cycles, as well as provide a tool for constraining the causes of mass extinction. Here, we identify the deficiencies of a simplified calcium model employed in several previous studies and we demonstrate the importance of a fully coupled carbon-cycle model when investigating the dynamics of carbon and calcium cycling. Simulations with a modified version of the LOSCAR model, which includes a fully coupled carbon-calcium cycle, indicate that increased weathering rates and ocean acidification (potentially caused by Siberian Trap volcanism) are not capable of producing trends observed in the record, as previously claimed. Our model results suggest that combined effects of carbon input via Siberian Trap volcanism (12,000 Pg C), the cessation of biological carbon export, and variable calcium isotope fractionation (due to a change in the seawater carbonate ion concentration) represents a more plausible scenario. This scenario successfully reconciles δ13C and δ44Ca trends observed in the sediment record, as well as the proposed warming of >6oC.

  7. A theoretical model of isotopic fractionation by thermal diffusion and its implementation on silicate melts

    Science.gov (United States)

    Xuefang, L.; Liu, Y.

    2015-12-01

    Huang et al (2010) found that Fe, Ca and Mg isotope fractionations of high-temperature silicate melts are only associated with the temperature gradients in thermal diffusion processes and are independent of compositions and mean temperatures [1]. Richter et al (2010) doubted that the existing data are sufficient to obtain such conclusion [2]. A few theoretical models have been proposed for explaining isotopic fractionations in these processes under high temperatures [3, 4]. However, molecular-level mechanisms and theoretical treatments of these processes are still under debating. Here we provide a unified theory based on the local thermodynamic equilibrium treatment (LTE) of statistical mechanics for evaluating thermal isotopic fractionations under a wide range of temperatures. Under high temperatures, our theory however can be reasonably approximated to this equation: where A and B are constants which are related to specific isotope systems and chemical compositions of silicate melts. If the thermal gradient is not very large and the mean temperature is high, the second part of the above equation can be safely neglected and obtain an extremely simple equation which is linearly depended on temperatures, agreeing with what Huang et al (2010) concluded. Based on this terse equation, we can not only easily provide isotope fractionation data for almost all kinds of isotope systems, but also can provide the mechanisms of isotope fractionation in thermal diffusion processes. [1] Huang et al (2010) Nature 464, 396-400. [2] Richter et al (2010) Nature 472, E1-E1. [3] Dominguez et al (2011) Nature 473, 70-73.

  8. Metal isotopes and carbonate proxy archives: Model-based perspectives on diagenesis

    Science.gov (United States)

    Fantle, M. S.; Higgins, J. A.; Griffith, E. M.

    2014-12-01

    Metal isotopes are novel tools, and have expanded the geochemical toolbox for elucidating the functioning of the Earth over various time scales. Carbonate-based stable isotope proxies now extend well beyond the traditional major elements (C and O) to include Ca, as well as trace elements such as Sr, S, Mg, B, Li, Cd, and U. Such trace isotopic proxies may contain invaluable information about the Earth system in the past, but can be susceptible to diagenetic alteration over long time scales. It is therefore critical that diagenetic effects are understood and can be recognized in ancient rocks. The extent of alteration depends on reaction rate and advection velocity in the sedimentary section, and elemental partitioning and isotopic effects associated with diagenesis. Numerical approaches, such as reactive transport models, are extremely useful tools for constraining such variables, and for testing hypotheses related to alteration of proxy records. Reactive transport models allow for constraints on calcite recrystallization rates in natural systems; data from ODP Sites 807A, 1170A, 1171A, and 806B suggest rapid recrystallization in relatively young sediments, as well as a Ca isotopic fractionation factor (α) associated with calcite recrystallization close to 1 (Δ=0). While the former is critical for addressing the fidelity and accuracy of a variety of geochemical proxies, the latter is distinctly different from that associated with the formation of carbonates in the surface ocean (Δ~ -1.35‰), suggesting considerable isotopic leverage to alter Ca isotopes during diagenesis. While Ca isotopes are generally well buffered in carbonate-rich sediments, this leverage to alter may be expressed as a reduction in the amplitude of geochemical variability in the solid or as a result of reactions near the sediment-seawater interface (as seen at ODP Site 1221 associated with chemical burndown during the PETM). Further, the Ca and Mg isotopic compositions of shallow water

  9. Isotopic fractionation during the uptake and elimination of inorganic mercury by a marine fish.

    Science.gov (United States)

    Xu, Xiaoyu; Wang, Wen-Xiong

    2015-11-01

    This study investigated the mass dependent (MDF) and independent fractionation (MIF) of stable mercury isotopes in fish during the uptake and elimination of inorganic species. Mercury accumulation during the exposure led to re-equilibration of organ isotopic compositions with the external sources, and elimination terminated the equilibrating with isotope ratios moving back to the original values. Generally, the isotopic behaviors corresponded to the changes of Hg accumulation in the muscle and liver, causing by the internal transportation, organ redistribution, and mixing of different sources. A small degree of MDF caused by biotransformation of Hg in the liver was documented during the elimination, whereas MIF was not observed. The absence of MIF during geochemical and metabolic processes suggested that mercury isotopes can be used as source tracers. Additionally, fish liver is a more responsive organ than muscle to track Hg source when it is mainly composed of inorganic species.

  10. Carbon isotopic study of individual alcohol compounds in modern sediments from Nansha Islands sea area, China

    Institute of Scientific and Technical Information of China (English)

    段毅; 文启彬; 郑国东; 罗斌杰

    1997-01-01

    Carbon isotopic compositions of individual n-alkanols and sterols in modern sediments from the Nan-sha Islands sea area are measured after derivatization to trimethylsilyl ethers by the new isotopic analytical technique of GC/C/IRMS. The effects of the three added silyl carbon atoms in every alcohol molecule on these compound isotopic compositions and the characteristics of their carbon isotopic compositions are studied. Then their biological sources are discussed using their carbon isotopic compositions.

  11. Carbon allocation and carbon isotope fluxes in the plant-soil-atmosphere continuum: a review

    Directory of Open Access Journals (Sweden)

    N. Brüggemann

    2011-11-01

    Full Text Available The terrestrial carbon (C cycle has received increasing interest over the past few decades, however, there is still a lack of understanding of the fate of newly assimilated C allocated within plants and to the soil, stored within ecosystems and lost to the atmosphere. Stable carbon isotope studies can give novel insights into these issues. In this review we provide an overview of an emerging picture of plant-soil-atmosphere C fluxes, as based on C isotope studies, and identify processes determining related C isotope signatures. The first part of the review focuses on isotopic fractionation processes within plants during and after photosynthesis. The second major part elaborates on plant-internal and plant-rhizosphere C allocation patterns at different time scales (diel, seasonal, interannual, including the speed of C transfer and time lags in the coupling of assimilation and respiration, as well as the magnitude and controls of plant-soil C allocation and respiratory fluxes. Plant responses to changing environmental conditions, the functional relationship between the physiological and phenological status of plants and C transfer, and interactions between C, water and nutrient dynamics are discussed. The role of the C counterflow from the rhizosphere to the aboveground parts of the plants, e.g. via CO2 dissolved in the xylem water or as xylem-transported sugars, is highlighted. The third part is centered around belowground C turnover, focusing especially on above- and belowground litter inputs, soil organic matter formation and turnover, production and loss of dissolved organic C, soil respiration and CO2 fixation by soil microbes. Furthermore, plant controls on microbial communities and activity via exudates and litter production as well as microbial community effects on C mineralization are reviewed. A further part of the paper is dedicated to physical interactions between soil CO2 and the soil matrix, such as

  12. Fractionation of iron species and iron isotopes in the Baltic Sea euphotic zone

    Directory of Open Access Journals (Sweden)

    J. Gelting

    2010-08-01

    Full Text Available To indentify sources and transport mechanisms of iron in a coastal marine environment, we conducted measurements of the physiochemical speciation of Fe in the euphotic zone at three different locations in the Baltic Sea. In addition to sampling across a salinity gradient, we conducted this study over the spring and summer season. Moving from the riverine input characterized low salinity Bothnian Sea, via the Landsort Deep near Stockholm, towards the Gotland Deep in the Baltic Proper, total Fe concentrations averaged 114, 44, and 15 nM, respectively. At all three locations, a decrease in total Fe of 80–90% from early spring to summer was observed. Particulate Fe (PFe was the dominating phase at all stations and accounted for 75–85% of the total Fe pool on average. The Fe isotope composition (δ 56Fe of the PFe showed constant positive values in the Bothnian Sea surface waters (+0.08 to +0.20‰. Enrichment of heavy Fe in the Bothnian Sea PFe is possibly associated to input of aggregated land derived Fe-oxyhydroxides and oxidation of dissolved Fe(II. At the Landsort Deep the isotopic fractionation of PFe changed between −0.08‰ to +0.28‰ over the sampling period. The negative values in early spring indicate transport of PFe from the oxic-anoxic boundary at ∼80 m depth. The average colloidal iron fraction (CFe showed decreasing concentrations along the salinity gradient; Bothnian Sea 15 nM; Landsort Deep 1 nM, and Gotland Deep 0.5 nM. Field Flow Fractionation data indicate that the main colloidal carrier phase for Fe in the Baltic Sea is a carbon-rich fulvic acid associated compound, likely of riverine origin. A strong positive correlation between PFe and chl-a indicates that cycling of suspended Fe is at least partially controlled by primary production. However, this relationship may not be dominated by active uptake of Fe into phytoplankton, but instead may reflect scavenging and removal of PFe during phytoplankton

  13. Separation of polybrominated diphenyl ethers in fish for compound-specific stable carbon isotope analysis

    Energy Technology Data Exchange (ETDEWEB)

    Zeng, Yan-Hong [State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China); Graduate University of Chinese Academy of Sciences, Beijing, 100049 (China); Luo, Xiao-Jun, E-mail: luoxiaoj@gig.ac.cn [State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China); Chen, Hua-Shan; Wu, Jiang-Ping; Chen, She-Jun; Mai, Bi-Xian [State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China)

    2012-05-15

    A separation and isotopic analysis method was developed to accurately measure the stable carbon isotope ratios of polybrominated diphenyl ethers (PBDEs) with three to six substituted bromine atoms in fish samples. Sample extracts were treated with concentrated sulfuric acid to remove lipids, purified using complex silica gel column chromatography, and finally processed using alumina/silica (Al/Si) gel column chromatography. The purities of extracts were verified by gas chromatography and mass spectrometry (GC-MS) in the full-scan mode. The average recoveries of all compounds across the purification method were between 60% and 110%, with the exception of BDE-154. The stable carbon isotopic compositions of PBDEs can be measured with a standard deviation of less than 0.5 Per-Mille-Sign . No significant isotopic fraction was found during the purification of the main PBDE congeners. A significant change in the stable carbon isotope ratio of BDE-47 was observed in fish carcasses compared to the original isotopic signatures, implying that PBDE stable carbon isotopic compositions can be used to trace the biotransformation of PBDEs in biota. - Highlights: Black-Right-Pointing-Pointer A method for the purification of PBDEs for CSIA was developed. Black-Right-Pointing-Pointer The {delta}{sup 13}C of PBDE congeners can be measured with a standard deviation of less than 0.5 Per-Mille-Sign . Black-Right-Pointing-Pointer Common carp were exposed to a PBDE mixture to investigate debromination. Black-Right-Pointing-Pointer Ratios of the {delta}{sup 13}C values can be used to trace the debromination of PBDE in fish.

  14. Stable isotope fractionation at a glacial hydrothermal field: implications for biogeochemistry and biosignatures on Mars

    Science.gov (United States)

    Cousins, C.; Bowden, R.; Fogel, M.; Cockell, C.; Crawford, I.; Gunn, M.; Karlsson, M. T.; Thorsteinsson, T.

    2012-12-01

    Hydrothermal environments that arise through the interaction between volcanogenic heat and glacial ice are ideal sites for understanding microbial biogeochemical processes on Earth, and also potentially on Mars where similar volcano-cryosphere interactions are thought to have occurred in the past. The Kverkfjöll subglacial basaltic volcano in central Iceland is geographically isolated, with little influence from flora, fauna, and human activity. Major environmental inputs include geothermal heat, meltwater from ice and snow, and outgassing of CO2, H2S, and SO2. Large physiochemical gradients exist, from steaming fumaroles and boiling hydrothermal pools, to frozen geothermal ground and glacial ice. Stable isotope measurements of total organic carbon, total sulphur, and total nitrogen were coupled with metagenomic analysis of the residing microbial communities, with the aim to identify biogeochemical relationships and processes operating within the Kverkfjöll geothermal environment, and also to identify any isotopic biosignatures that could be preserved within geothermal sediments. This study focused on a variety of samples taken along a hot spring stream that fed into a large ice-confined geothermal lake. Samples analysed range from unconsolidated hot spring sediments, well-developed microbial mats, and dissolved sulphate from hot spring fluids. From the anoxic spring source, the stream water increases in dissolved oxygen, decreases in temperature, yet maintains a pH of ~4. The spring environment is dominated by dissolved sulphate (~2.3 mM), with lower levels of nitrate (~50 μM), phosphorus (~5μM), and ammonium (~1.5 μM). Stable S isotope analysis reveals a fractionation of ~3.2 ‰ between sediment sulphide (as pyrite; δ34S ~0‰), and dissolved water sulphate (δ34S ~3.2 ‰) consistently along the hot spring stream, indicating the presence of an active sulphur cycle, although not one dominated by sulphate reduction (e.g. very negative sulphide δ34S). This

  15. Oxygen isotope fractionation between bird eggshell calcite and body water: application to fossil eggs from Lanzarote (Canary Islands).

    Science.gov (United States)

    Lazzerini, Nicolas; Lécuyer, Christophe; Amiot, Romain; Angst, Delphine; Buffetaut, Eric; Fourel, François; Daux, Valérie; Betancort, Juan Francisco; Flandrois, Jean-Pierre; Marco, Antonio Sánchez; Lomoschitz, Alejandro

    2016-10-01

    Oxygen and carbon isotope compositions of fossil bird eggshell calcite (δ(18)Ocalc and δ(13)Ccalc) are regularly used to reconstruct paleoenvironmental conditions. However, the interpretation of δ(18)Ocalc values of fossil eggshells has been limited to qualitative variations in local climatic conditions as oxygen isotope fractionations between calcite, body fluids, and drinking water have not been determined yet. For this purpose, eggshell, albumen water, and drinking water of extant birds have been analyzed for their oxygen and carbon isotope compositions. Relative enrichments in (18)O relative to (16)O between body fluids and drinking water of +1.6 ± 0.9 ‰ for semi-aquatic birds and of +4.4 ± 1.9 ‰ for terrestrial birds are observed. Surprisingly, no significant dependence to body temperature on the oxygen isotope fractionation between eggshell calcite and body fluids is observed, suggesting that bird eggshells precipitate out of equilibrium. Two empirical equations relating the δ(18)Ocalc value of eggshell calcite to the δ(18)Ow value of ingested water have been established for terrestrial and semi-aquatic birds. These equations have been applied to fossil eggshells from Lanzarote in order to infer the ecologies of the Pleistocene marine bird Puffinus sp. and of the enigmatic giant birds from the Pliocene. Both δ(13)Ccalc and δ(18)Ocalc values of Puffinus eggshells point to a semi-aquatic marine bird ingesting mostly seawater, whereas low δ(13)Ccalc and high δ(18)Ocalc values of eggshells from the Pliocene giant bird suggest a terrestrial lifestyle. This set of equations can help to quantitatively estimate the origin of waters ingested by extinct birds as well as to infer either local environmental or climatic conditions.

  16. Oxygen isotope fractionation between bird eggshell calcite and body water: application to fossil eggs from Lanzarote (Canary Islands)

    Science.gov (United States)

    Lazzerini, Nicolas; Lécuyer, Christophe; Amiot, Romain; Angst, Delphine; Buffetaut, Eric; Fourel, François; Daux, Valérie; Betancort, Juan Francisco; Flandrois, Jean-Pierre; Marco, Antonio Sánchez; Lomoschitz, Alejandro

    2016-10-01

    Oxygen and carbon isotope compositions of fossil bird eggshell calcite (δ18Ocalc and δ13Ccalc) are regularly used to reconstruct paleoenvironmental conditions. However, the interpretation of δ18Ocalc values of fossil eggshells has been limited to qualitative variations in local climatic conditions as oxygen isotope fractionations between calcite, body fluids, and drinking water have not been determined yet. For this purpose, eggshell, albumen water, and drinking water of extant birds have been analyzed for their oxygen and carbon isotope compositions. Relative enrichments in 18O relative to 16O between body fluids and drinking water of +1.6 ± 0.9 ‰ for semi-aquatic birds and of +4.4 ± 1.9 ‰ for terrestrial birds are observed. Surprisingly, no significant dependence to body temperature on the oxygen isotope fractionation between eggshell calcite and body fluids is observed, suggesting that bird eggshells precipitate out of equilibrium. Two empirical equations relating the δ18Ocalc value of eggshell calcite to the δ18Ow value of ingested water have been established for terrestrial and semi-aquatic birds. These equations have been applied to fossil eggshells from Lanzarote in order to infer the ecologies of the Pleistocene marine bird Puffinus sp. and of the enigmatic giant birds from the Pliocene. Both δ13Ccalc and δ18Ocalc values of Puffinus eggshells point to a semi-aquatic marine bird ingesting mostly seawater, whereas low δ13Ccalc and high δ18Ocalc values of eggshells from the Pliocene giant bird suggest a terrestrial lifestyle. This set of equations can help to quantitatively estimate the origin of waters ingested by extinct birds as well as to infer either local environmental or climatic conditions.

  17. Fractionated Mercury Isotopes in Fish: The Effects of Nuclear Mass, Spin, and Volume

    Science.gov (United States)

    Das, R.; Odom, A. L.

    2007-12-01

    Mercury is long known as a common environmental contaminant. In methylated form it is even more toxic and the methylation process is facilitated by microbial activities. Methyl mercury easily crosses cell membrane and accumulates in soft tissues of fishes and finally biomagnifies with increasing trophic levels. Natural variations in the isotopic composition of mercury have been reported and such variations have emphasized mass dependent fractionations, while theory and laboratory experiments indicate that mass-independent isotopic fractionation (MIF) effects are likely to be found as well. This study focuses on the MIF of mercury isotopes in the soft tissues of fishes. Samples include both fresh water and marine fish, from different continents and oceans. Approximately 1 gm of fish soft tissue was dissolved in 5 ml of conc. aqua regia for 24 hrs and filtered through a ¬¬¬100 μm filter paper and diluted with DI water. Hg is measured as a gaseous phase generated by reduction of the sample with SnCl2 in a continuous- flow cold-vapor generator connected to a Thermo-Finnigan Neptune MC-ICPMS. To minimize instrumental fractionation isotope ratios were measured by sample standard bracketing and reported as δ‰ relative to NIST SRM 3133 Hg standard where δAHg = [(A Hg/202Hg)sample/(A Hg/202Hg)NIST313] -1 ×1000‰. In this study we have measured the isotope ratios 198Hg/202Hg, 199Hg/202Hg, 200Hg/202Hg, 201Hg/202Hg and 204Hg/202Hg. In all the fish samples δ198Hg, δ200Hg, δ202Hg, δ204Hg define a mass- dependent fractionation sequence, where as the δ199Hg and δ201Hg depart from the mass- dependent fractionation line and indicate an excess of the odd-N isotopes. The magnitude of the deviation (ΔAHg where A=199 or 201) as obtained by difference between the measured δ199Hg and δ201Hg of the samples and the value obtained by linear scaling defined by the even-N isotopes ranges from approximately 0.2 ‰ to 3‰. The ratios of Δ199Hg /Δ201Hg range from 0.8 to 1

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

    Indian Academy of Sciences (India)

    S Banerjee; S K Bhattacharya; S Sarkar

    2006-02-01

    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.

  19. Stable isotope fractionation analysis as a tool to monitor biodegradation in contaminated acquifers

    Science.gov (United States)

    Meckenstock, Rainer U.; Morasch, Barbara; Griebler, Christian; Richnow, Hans H.

    2004-12-01

    The assessment of biodegradation in contaminated aquifers has become an issue of increasing importance in the recent years. To some extent, this can be related to the acceptance of intrinsic bioremediation or monitored natural attenuation as a means to manage contaminated sites. Among the few existing methods to detect biodegradation in the subsurface, stable isotope fractionation analysis (SIFA) is one of the most promising approaches which is pronounced by the drastically increasing number of applications. This review covers the recent laboratory and field studies assessing biodegradation of contaminants via stable isotope analysis. Stable isotope enrichment factors have been found that vary from no fractionation for dioxygenase reactions converting aromatic hydrocarbons over moderate fractionation by monooxygenase reactions ( ɛ=-3‰) and some anaerobic studies on microbial degradation of aromatic hydrocarbons ( ɛ=-1.7‰) to larger fractionations by anaerobic dehalogenation reactions of chlorinated solvents ( ɛ=between -5‰ and -30‰). The different isotope enrichment factors can be related to the respective biochemical reactions. Based on that knowledge, we discuss under what circumstances SIFA can be used for a qualitative or even a quantitative assessment of biodegradation in the environment. In a steadily increasing number of cases, it was possible to explain biodegradation processes in the field based on isotope enrichment factors obtained from laboratory experiments with pure cultures and measured isotope values from the field. The review will focus on the aerobic and anaerobic degradation of aromatic hydrocarbons and chlorinated solvents as the major contaminants of groundwater. Advances in the instrumental development for stable isotope analysis are only mentioned if it is important for the understanding of the application.

  20. Carbon and Oxygen Isotope Ratios in Rona Limestone, Romania

    Directory of Open Access Journals (Sweden)

    Stela Cuna

    2001-04-01

    Full Text Available The carbon and oxygen isotopic compositions of limestones provide criteria for the evaluation of the depositional environment. For Jurassic and younger samples, the best discrimination between marine and fresh-water limestones is given by Z parameter, calculated as a linear correlation between δ13C and δ18O (‰ PDB. Rona Limestone (Upper Paleocene - Lower Eocene, outcropping on a small area in NW Transylvania (Meseş area is a local lacustrine facies. There, it divides Jibou Formation into the Lower Red Member and the Upper Variegated Member, respectively. Recently, a sequence containing a marine nannoplankton assemblage was identified in the base of Rona deposits. The main goal of our study was to characterize, based on the isotopic record, the primary environment of formation of the deposit, as well as that in which some diagenetic processes (the formation of dolomite and of green clay around the siliceous chert nodules took place. Ten samples representing limestones, dolomitic limestone, marls and the green carbonate-rich clay were studied from petrographical and mineralogical points of view, and the carbon and oxygen isotopic ratios from the carbonate (calcite component were measured. In conclusion, it was found that the procedure of extraction of CO2 we used enabled the discrimination between the isotopic prints of calcite vs. dolomite. This pleads for considering our results as a primary isotopic pattern in the bulk rock. The oxygen and carbon isotope data indicate a fresh-water depositional environment with Z<120. The δ13C mean value (-4.96 ‰ PDB is, generally, representative for fresh-water carbonates of the Tertiary period. The same environment characterized also the formation of carbonates within the green clay.

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

    Science.gov (United States)

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

    2017-02-01

    The zinc (Zn) stable isotope system has great potential for tracing planetary formation and differentiation processes due to its chalcophile, lithophile and moderately volatile character. As an initial approach, the terrestrial mantle, and by inference, the bulk silicate Earth (BSE), have previously been suggested to have an average δ66Zn value of ∼+0.28‰ (relative to JMC 3-0749L) primarily based on oceanic basalts. Nevertheless, data for mantle peridotites are relatively scarce and it remains unclear whether Zn isotopes are fractionated during mantle melting. To address this issue, we report high-precision (±0.04‰; 2SD) Zn isotope data for well-characterized peridotites (n = 47) from cratonic and orogenic settings, as well as their mineral separates. Basalts including mid-ocean ridge basalts (MORB) and ocean island basalts (OIB) were also measured to avoid inter-laboratory bias. The MORB analyzed have homogeneous δ66Zn values of +0.28 ± 0.03‰ (here and throughout the text, errors are given as 2SD), similar to those of OIB obtained in this study and in the literature (+0.31 ± 0.09‰). Excluding the metasomatized peridotites that exhibit a wide δ66Zn range of -0.44‰ to +0.42‰, the non-metasomatized peridotites have relatively uniform δ66Zn value of +0.18 ± 0.06‰, which is lighter than both MORB and OIB. This difference suggests a small but detectable Zn isotope fractionation (∼0.1‰) during mantle partial melting. The magnitude of inter-mineral fractionation between olivine and pyroxene is, on average, close to zero, but spinels are always isotopically heavier than coexisting olivines (Δ66ZnSpl-Ol = +0.12 ± 0.07‰) due to the stiffer Zn-O bonds in spinel than silicate minerals (Ol, Opx and Cpx). Zinc concentrations in spinels are 11-88 times higher than those in silicate minerals, and our modelling suggests that spinel consumption during mantle melting plays a key role in generating high Zn concentrations and heavy Zn isotopic

  2. Iron and nickel isotope fractionation by diffusion, with applications to iron meteorites

    Science.gov (United States)

    Watson, Heather C.; Richter, Frank; Liu, Ankun; Huss, Gary R.

    2016-10-01

    Mass-dependent, kinetic fractionation of isotopes through processes such as diffusion can result in measurable isotopic signatures. When these signatures are retained in geologic materials, they can be used to help interpret their thermal histories. The mass dependence of the diffusion coefficient of isotopes 1 and 2 can be written as (D1 /D2) =(m2 /m1) β, where D1 and D2 are the diffusion coefficients of m1 and m2 respectively, and β is an empirical coefficient that relates the two ratios. Experiments have been performed to measure β in the Fe-Ni alloy system. Diffusion couple experiments between pure Fe and Ni metals were run in a piston cylinder at 1300-1400 °C and 1 GPa. Concentration and isotopic profiles were measured by electron microprobe and ion microprobe respectively. We find that a single β coefficient of β = 0.32 ± 0.04 can describe the isotopic effect in all experiments. This result is comparable to the isotope effect determined in many other similar alloy systems. The new β coefficient is used in a model of the isotopic profiles to be expected during the Widmanstätten pattern formation in iron meteorites. The results are consistent with previous estimates of the cooling rate of the iron meteorite Toluca. The application of isotopic constraints based on these results in addition to conventional cooling rate models could provide a more robust picture of the thermal history of these early planetary bodies.

  3. Stable isotope fractionations during reactive transport of phosphate in packed-bed sediment columns

    Science.gov (United States)

    Jaisi, Deb P.

    2013-11-01

    Characterizing reactivity and fate of contaminants in subsurface environments that are isolated from direct visualization is a major challenge. Stable isotopes coupled with concentration could be used as a potential tool to quantitatively analyze the chemical variability of the contaminant during reactive transport processes in the subsurface environment. This study was aimed at determining whether abiotic reactions of phosphate during its transport involve fractionation of oxygen isotopes in phosphate (δ18Op). It included the effects of solution chemistry and hydrodynamics on δ18Op values during phosphate transport through a packed-bed column prepared by using natural sediment collected from the Cape Cod aquifer in Massachusetts. Results show that the isotopic fractionation between effluent and influent phosphate at early stage of transport could be ~ 1.3‰ at higher flow rates with isotopically-light phosphate (P16O4) preferentially retained in the sediment column. This fractionation, however, decreased and became insignificant as more phosphate passed through the column. Mobilization of phosphate initially sorbed onto sediments caused a large kinetic isotopic fractionation with isotopically-light phosphate preferentially remobilized from the sediment column, but over longer time periods, this fractionation decreased and became insignificant as well. These results collectively suggest that abiotic reactive transport processes exert minimal influence on the δ18Op composition of subsurface systems. Alternatively, fluctuation in flow rate and subsequent remobilization of phosphate could be detectable through transient changes in δ18Op values. These findings extend the burgeoning application of δ18Op to identify the different sources and geochemical processes of phosphate in the subsurface environments.

  4. Stable isotope fractionations during reactive transport of phosphate in packed-bed sediment columns.

    Science.gov (United States)

    Jaisi, Deb P

    2013-11-01

    Characterizing reactivity and fate of contaminants in subsurface environments that are isolated from direct visualization is a major challenge. Stable isotopes coupled with concentration could be used as a potential tool to quantitatively analyze the chemical variability of the contaminant during reactive transport processes in the subsurface environment. This study was aimed at determining whether abiotic reactions of phosphate during its transport involve fractionation of oxygen isotopes in phosphate (δ(18)Op). It included the effects of solution chemistry and hydrodynamics on δ(18)Op values during phosphate transport through a packed-bed column prepared by using natural sediment collected from the Cape Cod aquifer in Massachusetts. Results show that the isotopic fractionation between effluent and influent phosphate at early stage of transport could be ~1.3‰ at higher flow rates with isotopically-light phosphate (P(16)O4) preferentially retained in the sediment column. This fractionation, however, decreased and became insignificant as more phosphate passed through the column. Mobilization of phosphate initially sorbed onto sediments caused a large kinetic isotopic fractionation with isotopically-light phosphate preferentially remobilized from the sediment column, but over longer time periods, this fractionation decreased and became insignificant as well. These results collectively suggest that abiotic reactive transport processes exert minimal influence on the δ(18)Op composition of subsurface systems. Alternatively, fluctuation in flow rate and subsequent remobilization of phosphate could be detectable through transient changes in δ(18)Op values. These findings extend the burgeoning application of δ(18)Op to identify the different sources and geochemical processes of phosphate in the subsurface environments.

  5. Equilibrium fractionation of H and O isotopes in water from path integral molecular dynamics

    Science.gov (United States)

    Pinilla, Carlos; Blanchard, Marc; Balan, Etienne; Ferlat, Guillaume; Vuilleumier, Rodolphe; Mauri, Francesco

    2014-06-01

    The equilibrium fractionation factor between two phases is of importance for the understanding of many planetary and environmental processes. Although thermodynamic equilibrium can be achieved between minerals at high temperature, many natural processes involve reactions between liquids or aqueous solutions and solids. For crystals, the fractionation factor α can be theoretically determined using a statistical thermodynamic approach based on the vibrational properties of the phases. These calculations are mostly performed in the harmonic approximation, using empirical or ab-initio force fields. In the case of aperiodic and dynamic systems such as liquids or solutions, similar calculations can be done using finite-size molecular clusters or snapshots obtained from molecular dynamics (MD) runs. It is however difficult to assess the effect of these approximate models on the isotopic fractionation properties. In this work we present a systematic study of the calculation of the D/H and 18O/16O equilibrium fractionation factors in water for the liquid/vapour and ice/vapour phases using several levels of theory within the simulations. Namely, we use a thermodynamic integration approach based on Path Integral MD calculations (PIMD) and an empirical potential model of water. Compared with standard MD, PIMD takes into account quantum effects in the thermodynamic modeling of systems and the exact fractionation factor for a given potential can be obtained. We compare these exact results with those of modeling strategies usually used, which involve the mapping of the quantum system on its harmonic counterpart. The results show the importance of including configurational disorder for the estimation of isotope fractionation in liquid phases. In addition, the convergence of the fractionation factor as a function of parameters such as the size of the simulated system and multiple isotope substitution is analyzed, showing that isotope fractionation is essentially a local effect in

  6. Stable carbon isotope ratios of ambient aromatic volatile organic compounds

    Science.gov (United States)

    Kornilova, Anna; Huang, Lin; Saccon, Marina; Rudolph, Jochen

    2016-09-01

    Measurements of mixing ratios and stable carbon isotope ratios of aromatic volatile organic compounds (VOC) in the atmosphere were made in Toronto (Canada) in 2009 and 2010. Consistent with the kinetic isotope effect for reactions of aromatic VOC with the OH radical the observed stable carbon isotope ratios are on average significantly heavier than the isotope ratios of their emissions. The change of carbon isotope ratio between emission and observation is used to determine the extent of photochemical processing (photochemical age, ∫ [OH]dt) of the different VOC. It is found that ∫ [OH]dt of different VOC depends strongly on the VOC reactivity. This demonstrates that for this set of observations the assumption of a uniform ∫ [OH]dt for VOC with different reactivity is not justified and that the observed values for ∫ [OH]dt are the result of mixing of VOC from air masses with different values for ∫ [OH]dt. Based on comparison between carbon isotope ratios and VOC concentration ratios it is also found that the varying influence of sources with different VOC emission ratios has a larger impact on VOC concentration ratios than photochemical processing. It is concluded that for this data set the use of VOC concentration ratios to determine ∫ [OH]dt would result in values for ∫ [OH]dt inconsistent with carbon isotope ratios and that the concept of a uniform ∫ [OH]dt for an air mass has to be replaced by the concept of individual values of an average ∫ [OH]dt for VOC with different reactivity.

  7. Carbon isotope biogeochemistry of plant resins and derived hydrocarbons

    Energy Technology Data Exchange (ETDEWEB)

    Murray, A.P.; Edwards, D.; Hope, J.M.; Boreham, C.J. [Australian Geological Survey Organisation, Canberra (Australia)] [and others

    1998-12-31

    Hydrocarbons derived from plant resins are major components of some terrigenous oils and bitumens. These compounds are structurally distinct and this makes then useful biomarkers applicable in petroleum exploration as well as sources of biogeochemical information about palaeoenvironment and palaeobotany. Although recent studies have elucidated the molecular structure of resinites, very little information has been available for the carbon isotope composition of resinites and no studies of resin-derived compounds in oils had been performed prior to the present study. Hence, carbon stable isotope analyses were carried out on a suite of modern and fossil resins of diverse origins, including compound specific isotope analysis of individual hydrocarbons produced during resin pyrolysis. Oils derived from resinite source organic matter were also analysed. The results showed that ``Class I`` resinites derived from gymnosperms were enriched in the heavy carbon isotope compared with those from angiosperms (``Class I`` resinites). Furthermore, both fossil resinites themselves and individual hydrocarbons derived from them were isotopically heavy compared with modern plant resins. The isotopic signatures of diterpanes and triterpanes in various early Tertiary oils from Australasia and Southeast Asia reflect their origins from gymnosperms and angiosperms, respectively. (author)

  8. Linking mercury, carbon, and nitrogen stable isotopes in Tibetan biota: Implications for using mercury stable isotopes as source tracers.

    Science.gov (United States)

    Xu, Xiaoyu; Zhang, Qianggong; Wang, Wen-Xiong

    2016-05-06

    Tibetan Plateau is located at a mountain region isolated from direct anthropogenic sources. Mercury concentrations and stable isotopes of carbon, nitrogen, and mercury were analyzed in sediment and biota for Nam Co and Yamdrok Lake. Biotic mercury concentrations and high food web magnification factors suggested that Tibetan Plateau is no longer a pristine site. The primary source of methylmercury was microbial production in local sediment despite the lack of direct methylmercury input. Strong ultraviolet intensity led to extensive photochemical reactions and up to 65% of methylmercury in water was photo-demethylated before entering the food webs. Biota displayed very high Δ(199)Hg signatures, with some highest value (8.6%) ever in living organisms. The δ(202)Hg and Δ(199)Hg in sediment and biotic samples increased with trophic positions (δ(15)N) and %methylmercury. Fish total length closely correlated to δ(13)C and Δ(199)Hg values due to dissimilar carbon sources and methylmercury pools in different living waters. This is the first mercury isotope study on high altitude lake ecosystems that demonstrated specific isotope fractionations of mercury under extreme environmental conditions.

  9. Absence of fractionation of mercury isotopes during trophic transfer of methylmercury to freshwater fish in captivity

    Science.gov (United States)

    Kwon, Sae Yun; Blum, Joel D.; Carvan, Michael J.; Basu, Niladri; Head, Jessica A.; Madenjian, Charles P.; David, Solomon R.

    2012-01-01

    We performed two controlled experiments to determine the amount of mass-dependent and mass-independent fractionation (MDF and MIF) of methylmercury (MeHg) during trophic transfer into fish. In experiment 1, juvenile yellow perch (Perca flavescens) were raised in captivity on commercial food pellets and then their diet was either maintained on unamended food pellets (0.1 μg/g MeHg) or was switched to food pellets with 1.0 μg/g or 4.0 μg/g of added MeHg, for a period of 2 months. The difference in δ202Hg (MDF) and Δ199Hg (MIF) between fish tissues and food pellets with added MeHg was within the analytical uncertainty (δ202Hg, 0.07 ‰; Δ199Hg, 0.06 ‰), indicating no isotope fractionation. In experiment 2, lake trout (Salvelinus namaycush) were raised in captivity on food pellets and then shifted to a diet of bloater (Coregonus hoyi) for 6 months. The δ202Hg and Δ199Hg of the lake trout equaled the isotopic composition of the bloater after 6 months, reflecting reequilibration of the Hg isotopic composition of the fish to new food sources and a lack of isotope fractionation during trophic transfer. We suggest that the stable Hg isotope ratios in fish can be used to trace environmental sources of Hg in aquatic ecosystems.

  10. Sulfur Isotopic Characteristics of Coal in China and Sulfur Isotopic Fractionation during Coal—burning Process

    Institute of Scientific and Technical Information of China (English)

    洪业汤; 张鸿斌; 等

    1993-01-01

    The determined results of the sulfur contents and isotopic composition of coal samples from major coal mines in 15 provinces and regions of China show that the coal mined in the north of China is characterized by higher 34S and lower sulfur content, but that in the south of China has lower 34S and higher sulfur content.During the coal-burning process in both indrstrial and daily use of coal as fuel the released sulfur dioxide is always enriched in lighter sulfur isotope relative to the corresponding coal;the particles are always enriched in heavier sulfur isotope.The discussion on the environmental geochemical significance of the above-mentioned results also has been made.

  11. Combination of carbon isotope ratio with hydrogen isotope ratio determinations in sports drug testing.

    Science.gov (United States)

    Piper, Thomas; Emery, Caroline; Thomas, Andreas; Saugy, Martial; Thevis, Mario

    2013-06-01

    Carbon isotope ratio (CIR) analysis has been routinely and successfully applied to doping control analysis for many years to uncover the misuse of endogenous steroids such as testosterone. Over the years, several challenges and limitations of this approach became apparent, e.g., the influence of inadequate chromatographic separation on CIR values or the emergence of steroid preparations comprising identical CIRs as endogenous steroids. While the latter has been addressed recently by the implementation of hydrogen isotope ratios (HIR), an improved sample preparation for CIR avoiding co-eluting compounds is presented herein together with newly established reference values of those endogenous steroids being relevant for doping controls. From the fraction of glucuronidated steroids 5β-pregnane-3α,20α-diol, 5α-androst-16-en-3α-ol, 3α-Hydroxy-5β-androstane-11,17-dione, 3α-hydroxy-5α-androstan-17-one (ANDRO), 3α-hydroxy-5β-androstan-17-one (ETIO), 3β-hydroxy-androst-5-en-17-one (DHEA), 5α- and 5β-androstane-3α,17β-diol (5aDIOL and 5bDIOL), 17β-hydroxy-androst-4-en-3-one and 17α-hydroxy-androst-4-en-3-one were included. In addition, sulfate conjugates of ANDRO, ETIO, DHEA, 3β-hydroxy-5α-androstan-17-one plus 17α- and androst-5-ene-3β,17β-diol were considered and analyzed after acidic solvolysis. The results obtained for the reference population encompassing n = 67 males and females confirmed earlier findings regarding factors influencing endogenous CIR. Variations in sample preparation influenced CIR measurements especially for 5aDIOL and 5bDIOL, the most valuable steroidal analytes for the detection of testosterone misuse. Earlier investigations on the HIR of the same reference population enabled the evaluation of combined measurements of CIR and HIR and its usefulness regarding both steroid metabolism studies and doping control analysis. The combination of both stable isotopes would allow for lower reference limits providing the same statistical

  12. Stable carbon isotope ratios of intact GDGTs indicate heterogeneous sources to marine sediments

    Science.gov (United States)

    Pearson, Ann; Hurley, Sarah J.; Walter, Sunita R. Shah; Kusch, Stephanie; Lichtin, Samantha; Zhang, Yi Ge

    2016-05-01

    Thaumarchaeota, the major sources of marine glycerol dibiphytanyl glycerol tetraether lipids (GDGTs), are believed to fix the majority of their carbon directly from dissolved inorganic carbon (DIC). The δ13C values of GDGTs (δ13CGDGT) may be powerful tools for reconstructing variations in the ocean carbon cycle, including paleoproductivity and water mass circulation, if they can be related to values of δ13CDIC. To date, isotope measurements primarily are made on the C40 biphytane skeletons of GDGTs, rather than on complete tetraether structures. This approach erases information revealed by the isotopic heterogeneity of GDGTs within a sample and may impart an isotopic fractionation associated with the ether cleavage. To circumvent these issues, we present δ13C values for GDGTs from twelve recent sediments representing ten continental margin locations. Samples are purified by orthogonal dimensions of HPLC, followed by measurement of δ13C values by Spooling Wire Microcombustion (SWiM)-isotope ratio mass spectrometry (IRMS) with 1σ precision and accuracy of ±0.25‰. Using this approach, we confirm that GDGTs, generally around -19‰, are isotopically "heavy" compared to other marine lipids. However, measured δ13CGDGT values are inconsistent with predicted values based on the 13C content of DIC in the overlying water column and the previously-published biosynthetic isotope fractionation for a pure culture of an autotrophic marine thaumarchaeon. In some sediments, the isotopic composition of individual GDGTs differs, indicating multiple source inputs. The data appear to confirm that crenarchaeol primarily is a biomarker for Thaumarchaeota, but its δ13C values still cannot be explained solely by autotrophic carbon fixation. Overall the complexity of the results suggests that both organic carbon assimilation (ca. 25% of total carbon) and multiple source(s) of exogenous GDGTs (contributing generally <30% of input to sediments) are necessary to explain the observed

  13. Salinity dependent hydrogen isotope fractionation in alkenones produced by coastal and open ocean haptophyte algae

    NARCIS (Netherlands)

    M'boule, D.; Chivall, D.; Sinke-Schoen, D.; Sinninghe Damsté, J.S.; Schouten, S.; van der Meer, M.T.J.

    2014-01-01

    The hydrogen isotope fractionation in alkenones produced by haptophyte algae is a promising new proxy for paleosalinity reconstructions. To constrain and further develop this proxy the coastal haptophyte Isochrysis galbana and the open ocean haptophyte alga Emiliania huxleyi were cultured at differe

  14. Isotopic fractionation of boron in growing corals and its palaeoenvironmental implication

    Digital Repository Service at National Institute of Oceanography (India)

    Xiao, Y.K.; Shirodkar, P.V; Zhang, C.G.; Wei, H.Z.; Liu, W.G.; Zhou, W.J.

    to be incorporated into corals. Based on the measured δ11B values of growing corals and coexisting sea water as well as the pH of co-existing sea water, a new isotopic fractionation factor α43 between two boron species, B(OH)4 – and B(OH)3, has been measured to be 0...

  15. Selenium sorption and isotope fractionation: Iron(III) oxides versus iron(II) sulfides

    NARCIS (Netherlands)

    Mitchell, K.; Couture, R.-M.; Johnson, T.M.; Mason, P.R.D.; Van Cappellen, P.

    2013-01-01

    Sorption and reduction are important processes influencing the environmental mobility and cycling of Se. In this study, we determined the rates of reaction and isotopic fractionations of Se(IV) and Se(VI) during sorption to iron oxides (2-line ferrihydrite, hematite and goethite) and iron sulfides (

  16. Ice-vapor equilibrium fractionation factor of hydrogen and oxygen isotopes

    DEFF Research Database (Denmark)

    Ellehøj, Mads Dam; Steen-Larsen, Hans Christian; Johnsen, Sigfus Johann;

    2013-01-01

    RATIONALE: The equilibrium fractionation factors govern the relative change in the isotopic composition during phase transitions of water. The commonly used results, which were published more than 40 years ago, are limited to a minimum temperature of -33 degrees C. This limits the reliability...

  17. 不同蛋白源对军曹鱼幼鱼碳、氮稳定同位素分馏的影响%The effects of different diet protein sources on carbon and nitrogen isotope fractionation of juvenile cobiaRachycentron canadumL

    Institute of Scientific and Technical Information of China (English)

    周晖; 陈刚; 施钢; 张健东; 董晓慧

    2014-01-01

    为研究饲料中不同蛋白源对军曹鱼幼鱼碳、氮稳定同位素分馏的影响,配制3种等氮等能饲料。D1以鱼粉为蛋白源, D2和D3饲料中分别以啤酒酵母和玉米蛋白替代10%的鱼粉蛋白,投喂幼鱼24d。结果表明,啤酒酵母和玉米蛋白替代10%的鱼粉蛋白后,幼鱼的体质量增加率显著下降。随养殖时间的延长,所有处理组幼鱼的碳稳定同位素比率δ13C逐渐上升而氮稳定同位素比率δ15N逐渐下降;虽然全鱼和肌肉δ15N的变化速度存在差异,但各饲料组全鱼和肌肉的δ13C和δ15N都在24d后与饲料达到平衡。当饲料中10%的鱼粉蛋白被啤酒酵母和玉米蛋白替代之后,幼鱼肌肉和全鱼样品与饲料相比的碳同位素富集Δ13C值下降,而氮同位素富集Δ15N值则上升。其中全鱼Δ13C从4.19‰分别下降到3.94‰和3.63‰,肌肉Δ13C从4.46‰分别下降到3.98‰和3.67‰;全鱼Δ15N从0.18‰分别增加到0.88‰和0.94‰,肌肉Δ15N从0.18‰分别增加到0.74‰和0.87‰。军曹鱼在摄食3种不同蛋白源饲料时,其全鱼和肌肉的Δ13C和Δ15N的变化趋势相似,但全鱼δ15N的变化速度慢于肌肉。据此可推断,肌肉可在生态学营养级研究(长时间尺度)中代表军曹鱼的碳、氮同位素特征;但在代谢生理学研究中(短时间尺度),肌肉就无法准确反映军曹鱼全鱼的δ15N变化过程。%In order to investigate the effects of different diet protein sources on carbon and nitrogen isotope fractionation of juvenile cobiaRachycentron canadumL., three isonitrogenous and isocaloric diets were formulated. The protein source in D1 was fish meal; beer yeast meal and corn gluten meal protein replaced 10% fish meal in D2 and D3, respectively. The diets were fed to juvenile cobia for 24 days. The results showed that, when 10% fish meal was replaced, the weight gain rate (WGR) of cobia decreased significantly. The carbon isotope ratioδ13

  18. Carbon isotope analysis of n-alkanes in dust from the lower atmosphere over the eastern Atlantic

    NARCIS (Netherlands)

    Sinninghe Damsté, J.S.; Schefuß, E.; Ratmeyer, V.; Stuut, J-B.W.; Jansen, J.H.F.

    2003-01-01

    Atmospheric dust samples collected along a transect off the West African coast have been investigated for their lipid content and compound-specific stable carbon isotope compositions. The saturated hydrocarbon fractions of the organic solvent extracts consist mainly of long-chain n-alkanes derived f

  19. BOREAS TE-5 Tree Ring and Carbon Isotope Ratio Data

    Science.gov (United States)

    Hall, Forrest G. (Editor); Curd, Shelaine (Editor); Ehleriinger, Jim; Brooks, J. Renee; Flanagan, Larry

    2000-01-01

    The BOREAS TE-5 team collected several data sets to investigate the vegetation-atmosphere CO2 and H2O exchange processes. These data include tree ring widths and cellulose carbon isotope data from coniferous trees collected at the BOREAS NSA and SSA in 1993 and 1994 by the BOREAS TE-5 team. Ring width data are provided for both Picea mariana and Pinus banksiana. The carbon isotope data are provided only for Pinus banksiana. The data are provided in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

  20. In Vivo Mass-independent Fractionation of Mercury Isotopes in Fish

    Science.gov (United States)

    Das, R.; Odom, L. A.

    2008-12-01

    Recent experimental work and analyses of natural samples have revealed both mass-dependent and mass- independent isotope fractionation effects in mercury. These findings portend new avenues toward understanding the global mercury cycle. It has been shown experimentally that photo reduction of Hg+2 and methylmercury in water with concomitant release of the reduced, gaseous species Hg° results in the residual methylmercury possessing a mass-independent isotope effect. This effect is a relative enrichment of isotopes 199Hg and 201Hg over the even mass number isotopes when compared to the mercury standard NIST SRM3133. Large mass independent fractionation (MIF) effects (Δ199Hg values of a few ‰) have been found in mercury in fish and interpreted as isotope effects inherited from the water. To evaluate the possibility that MIF might be produced within the fish, we have analyzed 38 samples that include zooplankton and twelve different species of fish from a single lake collected over a 2-month time period for mercury isotopic compositions. Trophic levels of the same fish specimens had previously been determined from stomach contents and nitrogen isotopes. Zooplankton in the lake contain mercury with Δ199Hg and Δ201Hg values of +0.43 (±0.07) and +0.44 (±0.07) respectively. Among the fish species there is a striking correspondence between trophic level and Δ199Hg and Δ201Hg values for primary, secondary, and tertiary consumers. The Δ199Hg values ranges over ~1‰ from ~+0.4 in zooplankton, juvenile bluegill and several other small fishes to Δ199Hg = + 1.36 for the Florida gar that is the top predator fish in the lake. These observations indicate that the MIF effect, rather than being an artifact of the water column is produced in vivo. Partial separation of 199Hg and 201Hg from isotopes of even neutron number can be achieved by the magnetic isotope effect in reactions involving sufficiently long-lived intermediate free radicals, where nuclear - electron

  1. Ultrahigh-Temperature Metamorphism in Madurai Granulites, Southern India: Evidence from Carbon Isotope Thermometry.

    Science.gov (United States)

    Satish-Kumar

    2000-07-01

    Ultrahigh-temperature (UHT) metamorphism in the Madurai Block of the southern Indian granulite terrain has been verified using the calcite-graphite isotope exchange thermometer. Carbon isotope thermometry has been applied to marbles from a locality near the reported occurrence of sapphirine granulites that have yielded temperature estimates of around 1000 degrees C. The delta(13)C and delta(18)O values of calcite are homogenous, implying equilibration of the isotopes during metamorphism. However, the delta(13)C values of single graphite crystals show variations in the order of 1 per thousand within a hand specimen. Detailed isotopic zonation studies indicate that graphite preserves either the time-integrated crystal growth history or reequilibrium fractionation during its cooling history. The graphite cores preserve higher delta(13)C values than the rims. The fractionation between calcite and graphite cores gives the highest metamorphic temperature of about 1060 degrees C, which matches the petrologically inferred temperature estimates in the high-magnesian pelites. The fractionation between graphite rims and calcite suggests a temperature of around 750 degrees C, which is interpreted to reflect retrograde cooling. This event is also observed in the sapphirine granulites. Calcite-graphite thermometry thus provides a useful tool to define UHT metamorphism in granulite terrains.

  2. Fractionation of hydrogen isotopes by sulfate- and nitrate-reducing bacteria

    Directory of Open Access Journals (Sweden)

    Magdalena Rose Osburn

    2016-08-01

    Full Text Available Hydrogen atoms from water and food are incorporated into biomass during cellular metabolism and biosynthesis, fractionating the isotopes of hydrogen –protium and deuterium –that are recorded in biomolecules. While these fractionations are often relatively constant in plants, large variations in the magnitude of fractionation are observed for many heterotrophic microbes utilizing different central metabolic pathways. The correlation between metabolism and lipid δ2H provides a potential basis for reconstructing environmental and ecological parameters, but the calibration dataset has thus far been limited mainly to aerobes. Here we report on the hydrogen isotopic fractionations of lipids produced by nitrate-respiring and sulfate-reducing bacteria. We observe only small differences in fractionation between oxygen- and nitrate-respiring growth conditions, with a typical pattern of variation between substrates that is broadly consistent with previously described trends. In contrast, fractionation by sulfate-reducing bacteria does not vary significantly between different substrates, even when autotrophic and heterotrophic growth conditions are compared. This result is in marked contrast to previously published observations and has significant implications for the interpretation of environmental hydrogen isotope data. We evaluate these trends in light of metabolic gene content of each strain, growth rate, and potential flux and reservoir-size effects of cellular hydrogen, but find no single variable that can account for the differences between nitrate- and sulfate-respiring bacteria. The emerging picture of bacterial hydrogen isotope fractionation is therefore more complex than the simple correspondence between δ2H and metabolic pathway previously understood from aerobes. Despite the complexity, the large signals and rich variability of observed lipid δ2H suggest much potential as an environmental recorder of metabolism.

  3. Fractionation of Hydrogen Isotopes by Sulfate- and Nitrate-Reducing Bacteria.

    Science.gov (United States)

    Osburn, Magdalena R; Dawson, Katherine S; Fogel, Marilyn L; Sessions, Alex L

    2016-01-01

    Hydrogen atoms from water and food are incorporated into biomass during cellular metabolism and biosynthesis, fractionating the isotopes of hydrogen-protium and deuterium-that are recorded in biomolecules. While these fractionations are often relatively constant in plants, large variations in the magnitude of fractionation are observed for many heterotrophic microbes utilizing different central metabolic pathways. The correlation between metabolism and lipid δ(2)H provides a potential basis for reconstructing environmental and ecological parameters, but the calibration dataset has thus far been limited mainly to aerobes. Here we report on the hydrogen isotopic fractionations of lipids produced by nitrate-respiring and sulfate-reducing bacteria. We observe only small differences in fractionation between oxygen- and nitrate-respiring growth conditions, with a typical pattern of variation between substrates that is broadly consistent with previously described trends. In contrast, fractionation by sulfate-reducing bacteria does not vary significantly between different substrates, even when autotrophic and heterotrophic growth conditions are compared. This result is in marked contrast to previously published observations and has significant implications for the interpretation of environmental hydrogen isotope data. We evaluate these trends in light of metabolic gene content of each strain, growth rate, and potential flux and reservoir-size effects of cellular hydrogen, but find no single variable that can account for the differences between nitrate- and sulfate-respiring bacteria. The emerging picture of bacterial hydrogen isotope fractionation is therefore more complex than the simple correspondence between δ(2)H and metabolic pathway previously understood from aerobes. Despite the complexity, the large signals and rich variability of observed lipid δ(2)H suggest much potential as an environmental recorder of metabolism.

  4. Iron and zinc isotope fractionation during uptake and translocation in rice (Oryza sativa) grown in oxic and anoxic soils

    Science.gov (United States)

    Arnold, Tim; Markovic, Tamara; Kirk, Guy J. D.; Schönbächler, Maria; Rehkämper, Mark; Zhao, Fangjie J.; Weiss, Dominik J.

    2015-11-01

    Stable isotope fractionation is emerging quickly as a powerful novel technique to study metal uptake and translocation in plants. Fundamental to this development is a thorough understanding of the processes that lead to isotope fractionation under differing environmental conditions. In this study, we investigated Zn and Fe isotope fractionation in rice grown to maturity in anaerobic and aerobic soils under greenhouse conditions. The overall Zn isotope fractionation between the soil and above ground plant material was negligible in aerobic soil but significant in anaerobic soil with isotopically lighter Zn in the rice plant. The observed range of fractionation is in line with previously determined fractionations of Zn in rice grown in hydroponic solutions and submerged soils and emphasizes the effect of taking up different chemical forms of Zn, most likely free and organically complexed Zn. The Zn in the grain was isotopically lighter than in the rest of the above ground plant in rice grown in aerobic and anaerobic soils alike. This suggests that in the course of the grain loading and during the translocation within the plant important biochemical and/or biophysical processes occur. The isotope fractionation observed in the grains would be consistent with an unidirectional controlled transport from shoot to grain with a fractionation factor of α ≈ 0.9994. Iron isotopes showed an isotopic lighter signature in shoot and grain compared to the bulk soil or the leachate in aerobic and anaerobic soils alike. The negative direction of isotopic fractionation is consistent with possible changes in the redox state of Fe occurring during the uptake and translocation processes. The isotope fractionation pattern between shoots and grain material are different for Zn and Fe which finally suggests that different mechanisms operate during translocation and grain-loading in rice for these two key micronutrients.

  5. Diffusion-driven magnesium and iron isotope fractionation in Hawaiian olivine

    Science.gov (United States)

    Teng, F.-Z.; Dauphas, N.; Helz, R.T.; Gao, S.; Huang, S.

    2011-01-01

    Diffusion plays an important role in Earth sciences to estimate the timescales of geological processes such as erosion, sediment burial, and magma cooling. In igneous systems, these diffusive processes are recorded in the form of crystal zoning. However, meaningful interpretation of these signatures is often hampered by the fact that they cannot be unambiguously ascribed to a single process (e.g., magmatic fractionation, diffusion limited transport in the crystal or in the liquid). Here we show that Mg and Fe isotope fractionations in olivine crystals can be used to trace diffusive processes in magmatic systems. Over sixty olivine fragments from Hawaiian basalts show isotopically fractionated Mg and Fe relative to basalts worldwide, with up to 0.4??? variation in 26Mg/24Mg ratios and 1.6??? variation in 56Fe/54Fe ratios. The linearly and negatively correlated Mg and Fe isotopic compositions [i.e., ??56Fe=(??3.3??0.3)????26Mg], co-variations of Mg and Fe isotopic compositions with Fe/Mg ratios of olivine fragments, and modeling results based on Mg and Fe elemental profiles demonstrate the coupled Mg and Fe isotope fractionation to be a manifestation of Mg-Fe inter-diffusion in zoned olivines during magmatic differentiation. This characteristic can be used to constrain the nature of mineral zoning in igneous and metamorphic rocks, and hence determine the residence times of crystals in magmas, the composition of primary melts, and the duration of metamorphic events. With improvements in methodology, in situ isotope mapping will become an essential tool of petrology to identify diffusion in crystals. ?? 2011 Elsevier B.V.

  6. Tracking transformation processes of organic micropollutants in aquatic environments using multi-element isotope fractionation analysis

    Energy Technology Data Exchange (ETDEWEB)

    Hofstetter, Thomas B., E-mail: thomas.hofstetter@eawag.ch [Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Duebendorf (Switzerland)] [Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zurich, CH-8092 Zurich (Switzerland); Bolotin, Jakov [Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Duebendorf (Switzerland); Skarpeli-Liati, Marita; Wijker, Reto [Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Duebendorf (Switzerland)] [Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zurich, CH-8092 Zurich (Switzerland); Kurt, Zohre; Nishino, Shirley F.; Spain, Jim C. [School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332 (United States)

    2011-06-15

    The quantitative description of enzymatic or abiotic transformations of man-made organic micropollutants in rivers, lakes, and groundwaters is one of the major challenges associated with the risk assessment of water resource contamination. Compound-specific isotope analysis enables one to identify (bio)degradation pathways based on changes in the contaminants' stable isotope ratios even if multiple reactive and non-reactive processes cause concentrations to decrease. Here, we investigated how the magnitude and variability of isotope fractionation in some priority pollutants is determined by the kinetics and mechanisms of important enzymatic and abiotic redox reactions. For nitroaromatic compounds and substituted anilines, we illustrate that competing transformation pathways can be assessed via trends of N and C isotope signatures.

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

    Science.gov (United States)

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

    2011-07-01

    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.

  8. Oxygen Isotope Fractionation in TiO2 Polymorphs and Application to Geothermometry of Eclogites

    Institute of Scientific and Technical Information of China (English)

    郑永飞

    1995-01-01

    Oxygen isotope fractionation in TiO2 polymorphs has been calculated by the modi-fied increment method .The results that rutile is enriched in 18O relative to brookite but depleted in 18O relative to anatase.Due to the same crystal structure ,oxygen isotope partitioning in the TiO2 polymorphs is determined by the cation-oxygen inter-atomic distances.The theoretical calibrations involving rutile are in fair agreement with known experimental measurements and empirical estimates.Application of the theoretic-cal quartz-rutile calibration to geothermometry of natural eclogite assemblages indicates the preservation of isotopic equilibrium at high temperatures.The isotopic temperatures calculated are only slightly lower than the non-isotopic temperatures,indicating the slow rates of exchange for oxygen diffusion in rutile.The kinetics of exchange for oxygen diffu-sion in rutile is accordingly estimated by reconciling the differences between the isotopic and the non-isotopic temperatures.The rates of exchange for oxygen diffusion in rutile should be smaller than those for hornblende,but may be equal to or greater than those for diopside.

  9. Fractionation of stable isotopes in perchlorate and nitrate during in situ biodegradation in a sandy aquifer

    Science.gov (United States)

    Bohlke, Johnkarl F.; Hatzinger, P.B.; Sturchio, N.C.; Gu, B.; Heraty, L.J.; Borden, R.C.

    2009-01-01

    An in situ experiment was performed in a shallow alluvial aquifer in Maryland to quantify the fractionation of stable isotopes in perchlorate (Cl and O) and nitrate (N and O) during biodegradation. An emulsified soybean oil substrate that was previously injected into this aquifer provided the electron donor necessary for biological perchlorate reduction and denitrification. During the field experiment, groundwater extracted from an upgradient well was pumped into an injection well located within the in situ oil barrier, and then groundwater samples were withdrawn for the next 30 h. After correction for dilution (using Br– as a conservative tracer of the injectate), perchlorate concentrations decreased by 78% and nitrate concentrations decreased by 82% during the initial 8.6 h after the injection. The observed ratio of fractionation effects of O and Cl isotopes in perchlorate (e18O/e37Cl) was 2.6, which is similar to that observed in the laboratory using pure cultures (2.5). Denitrification by indigenous bacteria fractionated O and N isotopes in nitrate at a ratio of ~0.8 (e18O/e15N), which is within the range of values reported previously for denitrification. However, the magnitudes of the individual apparent in situ isotope fractionation effects for perchlorate and nitrate were appreciably smaller than those reported in homogeneous closed systems (0.2 to 0.6 times), even after adjustment for dilution. These results indicate that (1) isotope fractionation factor ratios (e18O/e37Cl, e18O/e15N) derived from homogeneous laboratory systems (e.g. pure culture studies) can be used qualitatively to confirm the occurrence of in situ biodegradation of both perchlorate and nitrate, but (2) the magnitudes of the individual apparent e values cannot be used quantitatively to estimate the in situ extent of biodegradation of either anion.

  10. Thorium isotopes in colloidal fraction of water from San Marcos Dam, Chihuahua, Mexico

    Science.gov (United States)

    Cabral-Lares, M.; Melgoza, A.; Montero-Cabrera, M. E.; Renteria-Villalobos, M.

    2013-07-01

    The main interest of this stiidy is to assess the contents and distribution of Th-series isotopes in colloidal fraction of surface water from San Marcos dam, because the suspended particulate matter serves as transport medium for several pollutants. The aim of this work was to assess the distribution of thorium isotopes (232Th and 230Th) contained in suspended matter. Samples were taken from three surface points along the San Marcos dam: water input, midpoint, and near to dam wall. In this last point, a depth sampling was also carried out. Here, three depth points were taken at 0.4, 8 and 15 meters. To evaluate the thorium behavior in surface water, from every water sample the colloidal fraction was separated, between 1 and 0.1 μm. Thorium isotopes concentraron in samples were obtained by alpha spectrometry. Activity concentrations obtained of 232Th and 230Th in surface points ranged from 0.3 to 0.5 Bq ṡ L-1, whereas in depth points ranged from 0.4 to 3.2 Bq ṡ L-1, respectively. The results show that 230Th is in higher concentration than 232Th in colloidal fraction. This can be attributed to a preference of these colloids to adsorb uranium. Thus, the activity ratio 230Th/232Th in colloidal fraction showed values from 2.3 to 10.2. In surface points along the dam, 230Th activity concentration decreases while 232Th concentration remains constant. On the other hand, activity concentrations of both isotopes showed a pointed out enhancement with depth. The results have shown a possible lixiviation of uranium from geological substrate into the surface water and an important fractionation of thorium isotopes, which suggest that thorium is non-homogeneously distributed along San Marcos dam.

  11. The clumped isotopic record of Neoproterozoic carbonates, Sultanate of Oman

    Science.gov (United States)

    Bergmann, K. D.; Eiler, J. M.; Fischer, W. W.; Osburn, M. R.; Grotzinger, J. P.

    2011-12-01

    The Huqf Supergroup of the Sultanate of Oman records several important events in latest Precambrian time, including two glaciations in the Abu Mahara Group (ca. 725 - isotope excursion in the Nafun Group (ca. isotopic excursions, hypothesized to record perturbations of the surficial Earth carbon cycle or post-depositional diagenetic processes. Rigorous interpretation of these records requires a more thorough assessment of diagenetic processes. To better understand the significance and cause of these large amplitude isotopic excursions, we employed carbonate clumped isotope thermometry. This method allows us to estimate the absolute temperature of carbonate precipitation, including recrystallization, based on the temperature dependent abundance of carbonate ions containing both 13C and 18O. These estimates are accompanied by a measurement of carbonate δ18O, which in conjunction with temperature, can be used to calculate the oxygen isotopic composition of the fluid from which the carbonate precipitated. We analyzed stratigraphically constrained samples from a range of paleoenvironments with differing burial histories (1 - >10km maximum burial depth) to constrain the temperature and fluid composition of recrystallization. Clumped isotope temperatures from Huqf Supergroup samples range from 35-175°C. The isotopic composition of the fluid these rocks equilibrated with ranges from -3.7 to 15.7% VSMOW. This large range in temperature and fluid composition separates into distinct populations that differ systematically with independent constraints on petrography, stratigraphy and burial history. The data indicate the Abu Mahara, Nafun and Ara groups have unique diagenetic histories. In central Oman, the post-glacial Abu Mahara cap dolostone shows high temperature, rock buffered diagenesis (Tavg = 176°C; δ18Ofluid = 15% VSMOW), the Nafun Group generally experienced lower temperature, fluid buffered diagenesis (Tavg = 69°C; δ18Ofluid = 1% VSMOW) and the Ara Group

  12. Isotopic fractionation of argon during stepwise release from shungite

    Science.gov (United States)

    Rison, W.

    1980-05-01

    It is noted that in previous attempts to determine the Ar-40/Ar-36 ratio in the ancient atmosphere, the only direct measurement yielding a value below the atmospheric value of today is for argon released at low temperatures from a pre-Cambrian shungite. In the present work, a low value for Ar-40/Ar-36 in gas released from a type I shungite at low temperatures is confirmed. Attention is given to a study of the accompanying Ar-38/Ar-36 ratios and the enhanced ratio of Ar-40/Ar-36 for the fractions released at high temperatures which shows that the effect observed is a result of the stepwise heating and the argon diffusion mobilized thereby. It is suggested that the low Ar-40/Ar-36 obtained in the past is from the same source rather than reflecting the isotropic composition of the pre-Cambrian atmosphere, and that the type I shungite may exhibit simple volume diffusion over macroscopic dimensions as glasses do. It is concluded that if this is so, the diffusion parameters obtained from the data would imply rapid exchange with the atmosphere for any argon initially trapped in the veins of the material.

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

    Directory of Open Access Journals (Sweden)

    J. Kimball

    2015-12-01

    between the corals of different mineralogy is in the same direction as published theoretical predictions for the offset between calcite and aragonite, although the magnitude of the offset is different. One possibility is that the deep-sea coral results reflect that crystals may attain nominal mineral equilibrium clumped isotope signatures only under conditions of extremely slow growth. In that case, a possible explanation for the attainment of disequilibrium bulk isotope signatures and equilibrium clumped isotope signatures by deep-sea corals is that extraordinarily slow growth rates can promote the occurrence of isotopic reordering in the interfacial region of growing crystals. We also cannot rule out a component of a biological "vital-effect" influencing clumped isotope signatures in one or both orders of coral. Based on published experimental data and theoretical calculations, these biological "vital" effects could arise from kinetic isotope effects due to the source of carbon used for calcification, temperature- and pH-dependent rates of CO2 hydration and/or hydroxylation, calcifying fluid pH, the activity of carbonic anhydrase, the residence time of dissolved inorganic carbon in the calcifying fluid, and calcification rate. A third possible explanation is the occurrence of variable acid digestion fractionation factors. Although a recent study has suggested that dolomite, calcite, and aragonite may have similar clumped isotope acid digestion fractionation factors, the influence of acid digestion kinetics on Δ47 is a subject that warrants further investigation.

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

    Science.gov (United States)

    Kimball, Justine; Eagle, Robert; Dunbar, Robert

    2016-12-01

    between the corals of different mineralogy is in the same direction as published theoretical predictions for the offset between calcite and aragonite although the magnitude of the offset is different. One possibility is that the deep-sea coral results reflect high-Mg and aragonite crystals attaining nominal mineral equilibrium clumped isotope signatures due to conditions of extremely slow growth. In that case, a possible explanation for the attainment of disequilibrium bulk isotope signatures and equilibrium clumped isotope signatures by deep-sea corals is that extraordinarily slow growth rates can promote the occurrence of isotopic reordering in the interfacial region of growing crystals. We also cannot rule out a component of a biological "vital effect" influencing clumped isotope signatures in one or both orders of coral. Based on published experimental data and theoretical calculations, these biological vital effects could arise from kinetic isotope effects due to the source of carbon used for calcification, temperature- and pH-dependent rates of CO2 hydration and/or hydroxylation, calcifying fluid pH, the activity of carbonic anhydrase, the residence time of dissolved inorganic carbon in the calcifying fluid, and calcification rate. A third possible explanation is the occurrence of variable acid digestion fractionation factors. Although a recent study has suggested that dolomite, calcite, and aragonite may have similar clumped isotope acid digestion fractionation factors, the influence of acid digestion kinetics on Δ47 is a subject that warrants further investigation.

  15. Isotopic evolution of the terminal Neoproterozoic and early Cambrian carbon cycle on the northern Yangtze Platform, South China

    Institute of Scientific and Technical Information of China (English)

    GUO Qingjun; LIU Congqiang; Harald STRAUSS; Tatiana GOLDBERG

    2003-01-01

    Profound geotectonic, climatic and biological changes occur during the terminal Neoproterozoic and its transition into the early Cambrian. These are reflected in temporal variations of the chemical and isotopic composition of seawater. We are studying a sequence of sedimentary rocks at the Shatan section, northern Yangtze Platform, Sichuan Province of China. This succession comprises, in ascending stratigraphic order, predominantly calcareous sediments of the Sinian upper Dengying Formation and black shales of the lower Cambrian Guojiaba Formation (time equivalent of Niutitang Fm.). Paleoenvironmental setting represents shallow-water shelf deposits. The objective of our study is to provide temporal records for the isotopic compositions of organic and carbonate carbon throughout this time interval. Organic carbon isotope values display a range between -35.8‰ and -30.1‰ with clear stratigraphic variations. Carbonate carbon isotope data vary between -3.5‰ and +0.5‰. These secular variations are interpreted to reflect perturbations of the global carbon cycle, specifically changes in the fractional burial of organic carbon. However, local conditions have further affected the isotopic signals.

  16. Theoretical calculation of equilibrium copper (I) isotope fractionations in ore-forming fluid

    Science.gov (United States)

    Seo, J.; Lee, I.; Lee, S.

    2006-05-01

    Equilibrium isotope fractionation of Cu (I) complexes in hydrothermal ore-forming fluid is calculated. Ab-initio quantum calculation of molecular structures and vibrational frequencies is conducted by Density Functional Theory (DFT) and Hartree-Fock Self Consistent Field (HF-SCF) method. Cu isotope (65Cu, 63Cu) exchange is expressed as reduced partition function ratios, 103·ln(β65-63), for liquid phase complexes (copper chlorides, copper hydrosulfides), and vapor phase complexes (hydrated copper chloride). Isodensity Polarizable Continuum Model (IPCM) is applied to the liquid complexes, whereas the vapor complexes are calculated in vacuo. Large fractionation (more than 2‰ at 25°C) is predicted between coexisting phases without changing oxidation state. CuCl(H2O)2 (vapor phase) is enriched in 65Cu better than any other studied complexes, whereas [CuCl3]2- (liquid phase) is mostly depleted. Heavy copper isotope is favor to partition into vapor phase complexes than coexisting liquid phase complexes. In the sea-floor hydrothermal system, after separation of phases into vapor and brine, vapor phase (CuCl(H2O)2) and chlorine-rich brine ([CuCl3]2-) will show +0.418‰ and -0.688‰ deviation from [CuCl2]1- at 150°C, respectively. However, most of the dominant copper-bearing species in hydrothermal condition, [CuCl2]1- and [Cu(HS)2]1-, fractionate at almost the same degree. Possible ranges of copper isotope ratio, δ65Cu, can be constrained from the calculated equilibrium isotope fractionation. Changes of oxidation state in low-temperature (e.g. supergene formation) have been thought to trigger most copper isotope fractionations, so far. However, measurable Cu isotope fractionation (1.106‰ at 150°C and 0.615‰ at 300°C) in hydrothermal ore-forming fluid is predicted within +1 valence state by theoretical study. Molecular structures and vibrational frequencies are compared with measured data. However, there is no experimental or theoretical work of some molecules

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

    Science.gov (United States)

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

    2014-10-01

    due to intensive impact-induced shearing stress, or the ultimate destruction of the Shallowater parent body. Analysis of separated enstatite meteorite mineral phases show that the magnetic phase (Fe metal) is systematically enriched in the heavier Fe isotopes when compared to non-magnetic phases (Fe hosted in troilite), which agrees with previous experimental observations and theoretical calculations. The difference between magnetic and non-magnetic phases from enstatite achondrites provides an equilibrium metal-sulfide Fe isotopic fractionation factor of Δ56Femetal-troilite = δ56Femetal - δ56Fetroilite of 0.129 ± 0.060‰ (2 SE) at 1060 ± 80 K, which confirms the predictions of previous theoretical calculations.

  18. Stable Te isotope fractionation in tellurium-bearing minerals from precious metal hydrothermal ore deposits

    Science.gov (United States)

    Fornadel, Andrew P.; Spry, Paul G.; Haghnegahdar, Mojhgan A.; Schauble, Edwin A.; Jackson, Simon E.; Mills, Stuart J.

    2017-04-01

    The tellurium isotope compositions of naturally-occurring tellurides, native tellurium, and tellurites were measured by multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS) and compared to theoretical values for equilibrium mass-dependent isotopic fractionation of representative Te-bearing species estimated with first-principles thermodynamic calculations. Calculated fractionation models suggest that 130/125Te fractionations as large as 4‰ occur at 100 °C between coexisting tellurates (Te VI) and tellurides (Te -II) or or native tellurium Te(0), and smaller, typically secondary emmonsite, δ130/125Te compositions were identical. The coincidence of δ130/125Te between all oxidized and reduced species in this study and the apparent lack of isotopic fractionation between native tellurium and emmonsite in one sample suggest that oxidation processes cause little to no fractionation. Because Te is predominantly transported as an oxidized aqueous phase or as a reduced vapor phase under hydrothermal conditions, either a reduction of oxidized Te in hydrothermal liquids or deposition of Te from a reduced vapor to a solid is necessary to form the common tellurides and native tellurium in ore-forming systems. Our data suggest that these sorts of reactions during mineralization may account for a ∼3‰ range of δ130/125Te values. Based on the data ranges for Te minerals from various ore deposits, the underpinning geologic processes responsible for mineralization seem to have primary control on the magnitude of fractionation, with tellurides in epithermal gold deposits showing a narrower range of isotope values than those in orogenic gold and volcanogenic massive sulfide deposits.

  19. Martian carbon dioxide: Clues from isotopes in SNC meteorites

    Science.gov (United States)

    Karlsson, H. R.; Clayton, R. N.; Mayeda, T. K.; Jull, A. J. T.; Gibson, E. K., Jr.

    1993-01-01

    Attempts to unravel the origin and evolution of the atmosphere and hydrosphere on Mars from isotopic data have been hampered by the impreciseness of the measurements made by the Viking Lander and by Earth-based telescopes. The SNC meteorites which are possibly pieces of the Martian surface offer a unique opportunity to obtain more precise estimates of the planet's volatile inventory and isotopic composition. Recently, we reported results on oxygen isotopes of water extracted by pyrolysis from samples of Shergotty, Zagami, Nakhla, Chassigny, Lafayette, and EETA-79001. Now we describe complementary results on the stable isotopic composition of carbon dioxide extracted simultaneously from those same samples. We will also report on C-14 abundances obtained by accelerator mass spectrometry (AMS) for some of these CO2 samples.

  20. Spinel-olivine-pryoxene equilibrium iron isotopic fractionation and applications to natural peridotites

    Energy Technology Data Exchange (ETDEWEB)

    Roskosz, Mathieu; Sio, Corliss K. I.; Dauphas, Nicolas; Bi, Wenli; Tissot, Francois L. H.; Hu, Michael Y.; Zhao, Jiyong; Alp, Esen E.

    2015-11-15

    Eight spinel-group minerals were synthesized by a flux-growth method producing spinels with varying composition and Fe3+/Fe-tot ratios. The mean force constants of iron bonds in these minerals were determined by synchrotron nuclear resonant inelastic X-ray scattering (NRIXS) in order to determine the reduced isotopic partition function ratios (beta-factors) of these spinels. The mean force constants are strongly dependent on the Fe3+/Fe-tot of the spinel but are independent, or weakly dependent on other structural and compositional parameters. From our spectroscopic data, it is found that a single redox-dependent calibration line accounts for the effects of Fe3+/Fe-tot on the beta-factors of spinels. This calibration successfully describes the equilibrium Fe isotopes fractionation factors between spinels and silicates (olivine and pyroxenes). Our predictions are in excellent agreement with independent determinations for the equilibrium Fe isotopic fractionations for the magnetite- fayalite and the magnetite-hedenbergite couples. Our calibration applies to the entire range of Fe3+/Fe-tot ratios found in natural spinels and provides a basis for interpreting iron isotopic variations documented in mantle peridotites. Except for a few exceptions, most of the samples measured so far are in isotopic disequilibrium, reflecting metasomatism and partial melting processes.

  1. Uranium isotopic fractionation factors during U(VI) reduction by bacterial isolates

    Science.gov (United States)

    Basu, Anirban; Sanford, Robert A.; Johnson, Thomas M.; Lundstrom, Craig C.; Löffler, Frank E.

    2014-07-01

    We experimentally determined the magnitude of uranium isotopic fractionation induced by U(VI) reduction by metal reducing bacterial isolates. Our results indicate that microbial U(VI) reduction induces isotopic fractionation; heavier isotopes (i.e., 238U) partition into the solid U(IV) products. The magnitudes of isotopic fractionation (expressed as ε = 1000‰ * (α-1)) for 238U/235U were 0.68‰ ± 0.05‰ and 0.99‰ ± 0.12‰ for Geobacter sulfurreducens strain PCA and strain IFRC-N, respectively. The ε values for Anaeromyxobacter dehalogenans strain FRC-W, strain FRC-R5, a novel Shewanella isolate, and Desulfitobacterium sp. strain Viet1 were 0.72‰ ± 0.15‰, 0.99‰ ± 0.12‰, 0.96‰ ± 0.16‰ and 0.86‰ ± 0.06‰, respectively. Our results show that the maximum ε values of ∼1.0‰ were obtained with low biomass (∼107 cells/mL) and low electron donor concentrations (∼500 μM). These results provide an initial assessment of 238U/235U shifts induced by microbially-mediated U(VI) reduction, which is needed as 238U/235U data are increasingly applied as redox indicators in various geochemical settings.

  2. Evidence of isotopic fractionation of natural uranium in cultured human cells

    Science.gov (United States)

    Paredes, Eduardo; Avazeri, Emilie; Malard, Véronique; Vidaud, Claude; Reiller, Pascal E.; Ortega, Richard; Nonell, Anthony; Isnard, Hélène; Chartier, Frédéric; Bresson, Carole

    2016-12-01

    The study of the isotopic fractionation of endogen elements and toxic heavy metals in living organisms for biomedical applications, and for metabolic and toxicological studies, is a cutting-edge research topic. This paper shows that human neuroblastoma cells incorporated small amounts of uranium (U) after exposure to 10 µM natural U, with preferential uptake of the 235U isotope with regard to 238U. Efforts were made to develop and then validate a procedure for highly accurate n(238U)/n(235U) determinations in microsamples of cells. We found that intracellular U is enriched in 235U by 0.38 ± 0.13‰ (2σ, n = 7) relative to the exposure solutions. These in vitro experiments provide clues for the identification of biological processes responsible for uranium isotopic fractionation and link them to potential U incorporation pathways into neuronal cells. Suggested incorporation processes are a kinetically controlled process, such as facilitated transmembrane diffusion, and the uptake through a high-affinity uranium transport protein involving the modification of the uranyl (UO22+) coordination sphere. These findings open perspectives on the use of isotopic fractionation of metals in cellular models, offering a probe to track uptake/transport pathways and to help decipher associated cellular metabolic processes.

  3. Fractionation of Mercury Stable Isotopes during Microbial Methylmercury Production by Iron- and Sulfate-Reducing Bacteria.

    Science.gov (United States)

    Janssen, Sarah E; Schaefer, Jeffra K; Barkay, Tamar; Reinfelder, John R

    2016-08-01

    The biological production of monomethylmercury (MeHg) in soils and sediments is an important factor controlling mercury (Hg) accumulation in aquatic and terrestrial food webs. In this study we examined the fractionation of Hg stable isotopes during Hg methylation in nongrowing cultures of the anaerobic bacteria Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132. Both organisms showed mass-dependent, but no mass-independent fractionation of Hg stable isotopes during Hg methylation. Despite differences in methylation rates, the two bacteria had similar Hg fractionation factors (αr/p = 1.0009 and 1.0011, respectively). Unexpectedly, δ(202)Hg values of MeHg for both organisms were 0.4‰ higher than the value of initial inorganic Hg after about 35% of inorganic Hg had been methylated. These results indicate that a (202)Hg-enriched pool of inorganic Hg was preferentially utilized as a substrate for methylation by these organisms, but that multiple intra- and/or extracellular pools supplied inorganic Hg for biological methylation. Understanding the controls of the Hg stable isotopic composition of microbially produced MeHg is important to identifying bioavailable Hg in natural systems and the interpretation of Hg stable isotopes in aquatic food webs.

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

    Science.gov (United States)

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

    1992-01-01

    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. A study of oxygen isotopic fractionation during bio-induced calcite precipitation in eutrophic Baldeggersee, Switzerland

    NARCIS (Netherlands)

    Teranes, J.L.; McKenzie, J.A.; Bernasconi, S.M.; Lotter, A.F.; Sturm, M.

    1999-01-01

    Abstract—In order to better understand environmental factors controlling oxygen isotope shifts in autochthonous lacustrine carbonate sequences, we undertook an extensive one-year study (March, 1995 to February, 1996) of water-column chemistry and daily sediment trap material from a small lake in Cen

  6. Dissolved inorganic carbon and stable carbon isotopic evolution of neutral mine drainage interacting with atmospheric CO{sub 2(g)}

    Energy Technology Data Exchange (ETDEWEB)

    Abongwa, Pride Tamasang, E-mail: abongwa@okstate.edu; Atekwana, Eliot Anong; Puckette, James

    2016-03-01

    We investigated the spatial variations in the concentrations of dissolved inorganic carbon (DIC), the stable carbon isotopic composition (δ{sup 13}C) of DIC and the δ{sup 13}C of carbonate precipitated from neutral mine drainage interacting with the atmospheric CO{sub 2(g)}. We assessed the chemical, DIC and δ{sup 13}C{sub DIC} evolution of the mine drainage and the δ{sup 13}C evolution of carbonate precipitates for a distance of 562 m from the end of an 8 km tunnel that drains a mine. Our results show that as the mine drainage interacts with atmospheric CO{sub 2(g)} the outgassing of CO{sub 2} due to the high initial partial pressure of CO{sub 2} (pCO{sub 2}) causes the DIC to evolve under kinetic conditions followed by equilibration and then under equilibrium conditions. The carbonate evolution was characterized by spatial increases in pH, decreasing concentrations of Ca{sup 2+} and DIC and by the precipitation of carbonate. The δ{sup 13}C{sub DIC} showed a larger enrichment from the tunnel exit to 38 m, moderate continuous enrichment to 318 m and almost no enrichment to 562 m. On the other hand, the δ{sup 13}C of the carbonate precipitates also showed large enrichment from the tunnel exit to 38 m, moderate enrichment to 318 m after which the δ{sup 13}C remained nearly constant. The enrichment in the δ{sup 13}C of the DIC and the carbonate precipitates from 0 to 38 m from kinetic fractionation caused by CO{sub 2(g)} outgassing was followed by a mix of kinetic fractionation and equilibrium fractionation controlled by carbon exchange between DIC and atmospheric CO{sub 2(g)} to 318 m and then by equilibrium fractionation from 318 to 562 m. From the carbonate evolution in this neutral mine drainage, we estimated that 20% of the carbon was lost via CO{sub 2} outgassing, 12% was sequestered in sediments in the drainage ponds from calcite precipitation and the remainder 68% was exported to the local stream. - Highlights: • We assess the δ{sup 13}C in a

  7. Stable Ni Isotope Fractionation In Systems Relevant To Banded Iron-Formations

    Science.gov (United States)

    Howe, H.; Spivak-Birndorf, L.; Newkirk, D.; Wasylenki, L. E.

    2013-12-01

    An important event in the evolution of life was the rise of atmospheric oxygen during the Proterozoic. Preceding the rise in O2 was a decline in atmospheric methane concentrations, likely due to decreased productivity of methanogenic Archaea. Based on Ni concentrations in banded iron formations (BIF), Konhauser et al. (2009) hypothesized that mantle cooling during the Archaean reduced the amount of Ni present in igneous rocks and in oceans, causing a Ni shortage for methanogens. Methanogens use Ni for cofactor F430, a catalyst during methanogenesis. To confirm Konhauser's hypothesis, a proxy for methanogen productivity in the rock record is necessary, in order to determine whether a decline in methanogen populations correlated with the observed decrease in maximum Ni contents in rocks from the Archaean. Ni isotope ratios recorded in BIF (oceanic sediments consisting of layered iron oxides and cherts) may provide evidence of a decline in methane production. Cameron et al. (2009) have shown that methanogens preferentially assimilate light Ni isotopes. Thus Ni isotopes in BIF have potential use as biomarkers for methanogenesis. Ferrihydrite was almost certainly the dominant Fe-oxide phase precipitating during BIF deposition. Ferrihydrite nanoparticles have large surface areas and are able to remove aqueous metals from solution through multiple sorption mechanisms. Thus we investigated experimentally the relationship between Ni isotopes in solution and Ni associated with ferrihydrite. We experimented with two different sorption mechanisms: adsorption of aqueous Ni onto surfaces of synthetic ferrihydrite and coprecipitation of aqueous Ni with ferrihydrite. Preliminary results indicate that light isotopes are preferentially associated with ferrihydrite in both adsorption and coprecipitation experiments, with an average fractionation of 0.3‰ in terms of δ60/58 Ni. Future experiments will investigate whether the observed isotope fractionations reflect kinetics or

  8. Development of U isotope fractionation as an indictor or U(VI) reduction in uranium plumes

    Energy Technology Data Exchange (ETDEWEB)

    Lundstrom, Craig [Univ. of Illinois, Urbana-Champaign, IL (United States); Johnson, Thomas [Univ. of Illinois, Urbana-Champaign, IL (United States)

    2016-02-16

    This is the final report for a university research project that advanced development of a new technology for identifying chemical reduction of uranium contamination in groundwater at the Rifle Field Challenge site. Reduction changes mobile hexavalent uranium into immobile U(IV). The stable isotope ratio (238U/235U) measurements of U using multicollector ICP-mass spectrometry were performed to understand the chemical reduction and sorption processes during various field experiments. In addition laboratory experiments were performed to better understand the isotopic fractionations. The main objectives of this project were completed during the project period and two peer-reviewed articles were published to disseminate the information gained.

  9. Mass dependent stable isotope fractionation of mercury during mer mediated microbial degradation of monomethylmercury

    Science.gov (United States)

    Kritee, K.; Barkay, Tamar; Blum, Joel D.

    2009-03-01

    Controlling bioaccumulation of toxic monomethylmercury (MMHg) in aquatic food chains requires differentiation between biotic and abiotic pathways that lead to its production and degradation. Recent mercury (Hg) stable isotope measurements of natural samples suggest that Hg isotope ratios can be a powerful proxy for tracing dominant Hg transforming pathways in aquatic ecosystems. Specifically, it has been shown that photo-degradation of MMHg causes both mass dependent (MDF) and mass independent fractionation (MIF) of Hg isotopes. Because the extent of MDF and MIF observed in natural samples (e.g., fish, soil and sediments) can potentially be used to determine the relative importance of pathways leading to MMHg accumulation, it is important to determine the potential role of microbial pathways in contributing to the fractionation, especially MIF, observed in these samples. This study reports the extent of fractionation of Hg stable isotopes during degradation of MMHg to volatile elemental Hg and methane via the microbial Hg resistance ( mer) pathway in Escherichia coli carrying a mercury resistance ( mer) genetic system on a multi-copy plasmid. During experimental microbial degradation of MMHg, MMHg remaining in reactors became progressively heavier (increasing δ202Hg) with time and underwent mass dependent Rayleigh fractionation with a fractionation factor α202/198 = 1.0004 ± 0.0002 (2SD). However, MIF was not observed in any of the microbial MMHg degradation experiments indicating that the isotopic signature left by mer mediated MMHg degradation is significantly different from fractionation observed during DOC mediated photo-degradation of MMHg. Additionally, a clear suppression of Hg isotope fractionation, both during reduction of Hg(II) and degradation of MMHg, was observed when the cell densities increased, possibly due to a reduction in substrate bioavailability. We propose a multi-step framework for understanding the extent of fractionation seen in our MMHg

  10. To "b" or not to "b": evaluating the effect of calcification on stable isotope fractionation in coccoliths and coccolithophore biomarkers (alkenones)

    Science.gov (United States)

    Stoll, Heather

    2013-04-01

    Coccolilthophore algae produce alkenone biomarkers, widely used for reconstruction of carbon isotopic fractionation during photosynthesis (epsilon p) and a proxy for past pCO2. The CaCO3 coccoliths produced by the algae are also the dominant carbonate contributor to marine sediments of Paleogene age and the carbon isotopic composition of this bulk carbonate is widely used to reconstruct variations in the exogenic carbon cycle. To date, the interaction between carbon uptake for calcification and photosynthesis has not been considered quantitatively. Given recent contraints on the permeability of cell membranes to CO2, I develop a new cellular model of carbon uptake and allocation within the coccolithophorid cell, including a separate compartment for the chloroplast and the coccolith vesicle(CV). The model can be applied to an inverse problem, to ascertain the active fluxes of HCO3- required to simulate the epsilon p and epsilon coccolith observed in coccolithophorids grown in culture. The inverse model shows that although HCO3- is supplied to both the chloroplast and CV, at low CO2 concentrations the cells preferentially allocate HCO3- to photosynthesis. This reduction in the HCO3- to CO2 uptake into the CV results in a negative shift in epsilon coccolith Consequently, the coccolith carbon isotopic composition is not a good proxy for the isotopic composition of marine DIC and would not be better than foraminifera for calculating epsilon p from in combination with the isotopic composition of sedimentary alkenones. The HCO3- uptake into the CV also affects epsilon p : higher uptake of HCO3- into the CV, at constant calcification and fixation rates, can result in shift to higher epsilonp.

  11. Extreme lithium isotopic fractionation in three zircon standards (Plešovice, Qinghu and Temora).

    Science.gov (United States)

    Gao, Yu-Ya; Li, Xian-Hua; Griffin, William L; Tang, Yan-Jie; Pearson, Norman J; Liu, Yu; Chu, Mei-Fei; Li, Qiu-Li; Tang, Guo-Qiang; O'Reilly, Suzanne Y

    2015-11-23

    To understand the behavior of Li in zircon, we have analyzed the abundance and isotopic composition of Li in three zircon standards (Plešovice, Qinghu and Temora) widely used for microbeam analysis of U-Pb ages and O-Hf isotopes. We have mapped Li concentration ([Li]) on large grains, using a Cameca 1280HR Secondary Ion Mass Spectrometer (SIMS). All zircons have a rim 5-20 μm wide in which [Li] is 5 to 20 times higher than in the core. Up to ~20‰ isotopic fractionation is observed on a small scale in the rims of a single zircon grain. The measured δ(7)Li values range from -14.3 to 3.7‰ for Plešovice, -22.8 to 1.4‰ for Qinghu and -4.7 to 16.1‰ for Temora zircon. The [Li] and δ(7)Li are highly variable at the rims, but relatively homogenous in the cores of the grains. From zircon rim to core, [Li] decreases rapidly, while δ(7)Li increases, suggesting that the large isotopic variation of Li in zircons could be caused by diffusion. Our data demonstrate that homogeneous δ(7)Li in the cores of zircon can retain the original isotopic signatures of the magmas, while the bulk analysis of Li isotopes in mineral separates and in bulk-rock samples may produce misleading data.

  12. Isotopic fractionation associated with [NiFe]- and [FeFe]-hydrogenases

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Hui; Gandhi, Hasand; Cornish, Adam J.; Moran, James J.; Kreuzer, Helen W.; Ostrom, Nathaniel; Hegg, Eric L.

    2016-01-30

    Hydrogenases catalyze the reversible formation of H2 from electrons and protons with high efficiency. Understanding the relationships between H2 production, H2 uptake, and H2-H2O exchange can provide insight into the metabolism of microbial communities in which H2 is an essential component in energy cycling. In this manuscript, we used stable H isotopes (1H and 2H) to probe the isotope effects associated with three [FeFe]-hydrogenases and three [NiFe]-hydrogenases. All six hydrogenases displayed fractionation factors for H2 formation that were significantly less than 1, producing H2 that was severely depleted in 2H relative to the substrate, water. Consistent with differences in their active site structure, the fractionation factors for each class appear to cluster, with the three [NiFe]-hydrogenases (α = 0.27-0.40) generally having smaller values than the three [FeFe]-hydrogenases (α = 0.41-0.55). We also obtained isotopic fractionation factors associated with H2 uptake and H2-H2O exchange under conditions similar to those utilized for H2 production, providing us with a more complete picture of the three reactions catalyzed by hydrogenases. The fractionation factors determined in our studies can be used as signatures for different hydrogenases to probe their activity under different growth conditions and to ascertain which hydrogenases are most responsible for H2 production and/or uptake in complex microbial communities.

  13. Modeling stable isotope and organic carbon in hillslope stormflow

    Science.gov (United States)

    Dusek, Jaromir; Vogel, Tomas; Dohnal, Michal; Marx, Anne; Jankovec, Jakub; Sanda, Martin; Votrubova, Jana; Barth, Johannes A. C.; Cislerova, Milena

    2016-04-01

    Reliable prediction of water movement and fluxes of dissolved substances (such as stable isotopes and organic carbon) at both the hillslope and the catchment scales remains a challenge due to complex boundary conditions and soil spatial heterogeneity. In addition, microbially mediated transformations of dissolved organic carbon (DOC) are known to affect balance of DOC in soils, hence the transformations need to be included in a conceptual model of a DOC transport. So far, only few studies utilized stable isotope information in modeling and even fewer linked dissolved carbon fluxes to mixing and/or transport models. In this study, stormflow dynamics of oxygen-18 isotope and dissolved organic carbon was analyzed using a physically based modeling approach. One-dimensional dual-continuum vertical flow and transport model, based on Richards and advection-dispersion equations, was used to simulate the subsurface transport processes in a forest soil during several observed rainfall-runoff episodes. The transport of heat in the soil profile was described by conduction-advection equation. Water flow and transport of solutes and heat were assumed to take place in two mutually communicating porous domains, the soil matrix and the network of preferential pathways. The rate of microbial transformations of DOC was assumed to depend on soil water content and soil temperature. Oxygen-18 and dissolved organic carbon concentrations were observed in soil pore water, hillslope stormflow (collected in the experimental hillslope trench), and stream discharge (at the catchment outlet). The modeling was used to analyze the transformation of input solute signals into output hillslope signals observed in the trench stormflow. Signatures of oxygen-18 isotope in hillslope stormflow as well as isotope concentration in soil pore water were predicted reasonably well. Due to complex nature of microbial transformations, prediction of DOC rate and transport was associated with a high uncertainty.

  14. Preliminary Nanosims Analysis of Carbon Isotope of Carbonates in Calcium-Aluminum-Rich Inclusions

    OpenAIRE

    Guan, Y.; Paque, J. M.; Burnett, D.S.; Eiler, J. M.

    2009-01-01

    Carbonate minerals observed in primitive meteorites are products of either terrestrial weathering or aqueous alteration in the early solar system. Most of the carbonate minerals in carbonaceous chondrites occur primarily as isolated grains in matrix, as crosscutting veins, or as replacement minerals in chondrules [e.g., 1, 2]. A few calcium-aluminum-rich inclusions (CAIs) have been reported containing carbonate minerals as well [2, 3]. The C and O isotopes of carbonates in c...

  15. Optimizing sample pretreatment for compound-specific stable carbon isotopic analysis of amino sugars in marine sediment

    Directory of Open Access Journals (Sweden)

    R. Zhu

    2014-01-01

    Full Text Available Amino sugars are quantitatively significant constituents of soil and marine sediment, but their sources and turnover in environmental samples remain poorly understood. The stable carbon isotopic composition of amino sugars can provide information on the lifestyles of their source organisms and can be monitored during incubations with labeled substrates to estimate the turnover rates of microbial populations. However, until now, such investigation has been carried out only with soil samples, partly because of the much lower abundance of amino sugars in marine environments. We therefore optimized a procedure for compound-specific isotopic analysis of amino sugars in marine sediment employing gas chromatography-isotope ratio mass spectrometry. The whole procedure consisted of hydrolysis, neutralization, enrichment, and derivatization of amino sugars. Except for the derivatization step, the protocol introduced negligible isotopic fractionation, and the minimum requirement of amino sugar for isotopic analysis was 20 ng, i.e. equivalent to ~ 8 ng of amino sugar carbon. Our results obtained from δ13C analysis of amino sugars in selected marine sediment samples showed that muramic acid had isotopic imprints from indigenous bacterial activities, whereas glucosamine and galactosamine were mainly derived from organic detritus. The analysis of stable carbon isotopic compositions of amino sugars opens a promising window for the investigation of microbial metabolisms in marine sediments and the deep marine biosphere.

  16. Carbon isotope fluctuations in Precambrian carbonate sequences of several localities in Brazil

    Directory of Open Access Journals (Sweden)

    SIAL ALCIDES N.

    2000-01-01

    Full Text Available Carbon isotope fluctuations in Precambrian sedimentary carbonates between 2.8 Ga and 0.60 Ga in Brazil are examined in this study. The carbonate facies of the BIF of the 2.8 Ga-old Carajás Formation, state of Pará in northern Brazil, has rather homogeneous delta13C (-5 o/ooPDB, compatible with carbonatization of a silicate protolith by a CO2-rich fluid from mantle degassing. The Paleoproterozoic Gandarela Formation, state of Minas Gerais, displays a narrow delta13C variation (-1.5 to +0.5 o/oo compatible with carbon isotope signatures of carbonates deposited around 2.4 Ga worldwide. The Fecho do Funil Formation has probably recorded the Lomagundi delta13C positive anomaly (+6.4 to +7.1 o/ooPDB. The magnesite-bearing carbonates of the Orós mobile belt, state of Ceará, exhibit carbon isotope fluctuation within the range for carbonates deposited at 1.8 Ga. The C-isotope record of the Frecheirinha Formation, northwestern state of Ceará, shows negative delta13C values in its lower portion (-2 o/oo and positive values up section (+1 to +3 o/oo, which suggests this sequence is a cap carbonate deposited after a glacial event around 0.95 Ga. The Jacoca and Acauã sedimentary carbonate Formations, state of Sergipe, NE Brazil, show carbon isotope fluctuations very similar to each other (average around -5 o/oo, compatible with a deposition around 0.76 Ga. The younger Olho D'Água carbonate Formation, however, also in the state of Sergipe, displays negative delta13C values at the lower portion of the Formation, changing dramatically up section to positive values as high as +10 o/oo, a characteristic compatible with a Sturtian cap carbonate deposited around 0.69 Ga. On the light of the C isotope data discussed in this study, it seems that delta13C fluctuations in Paleoproterozoic carbonates in Brazil are within the range found globally for metasedimentary carbonates of this age. Carbon isotope data proved to be very useful in establishing relative

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

    Energy Technology Data Exchange (ETDEWEB)

    Bernasconi, Stefano M., E-mail: Stefano.bernasconi@erdw.ethz.ch [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)

    2011-06-15

    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.

  18. Transient competitive complexation in biological kinetic isotope fractionation explains non-steady isotopic effects: Theory and application to denitrification in soils

    Energy Technology Data Exchange (ETDEWEB)

    Maggi, F.M.; Riley, W.J.

    2009-06-01

    The theoretical formulation of biological kinetic reactions in isotopic applications often assume first-order or Michaelis-Menten-Monod kinetics under the quasi-steady-state assumption to simplify the system kinetics. However, isotopic e ects have the same order of magnitude as the potential error introduced by these simpli cations. Both formulations lead to a constant fractionation factor which may yield incorrect estimations of the isotopic effect and a misleading interpretation of the isotopic signature of a reaction. We have analyzed the isotopic signature of denitri cation in biogeochemical soil systems by Menyailo and Hungate [2006], where high {sup 15}N{sub 2}O enrichment during N{sub 2}O production and inverse isotope fractionation during N{sub 2}O consumption could not be explained with first-order kinetics and the Rayleigh equation, or with the quasi-steady-state Michaelis-Menten-Monod kinetics. When the quasi-steady-state assumption was relaxed, transient Michaelis-Menten-Monod kinetics accurately reproduced the observations and aided in interpretation of experimental isotopic signatures. These results may imply a substantial revision in using the Rayleigh equation for interpretation of isotopic signatures and in modeling biological kinetic isotope fractionation with first-order kinetics or quasi-steady-state Michaelis-Menten-Monod kinetics.

  19. Iron and copper isotope fractionation during filtration and ultrafiltration of boreal organic-rich waters

    Science.gov (United States)

    Ilina, Svetlana M.; Viers, Jerome; Pokrovsky, Oleg S.; Poitrasson, Franck; Lapitsky, Sergey A.; Alekhin, Yuriy V.

    2010-05-01

    Typical feature of all boreal surface waters is high concentration of dissolved (complexes. Organic and organo-mineral colloids are the most likely carriers of trace metals such as Cu in rivers of the boreal zone. This work addresses colloidal speciation of Cu and Fe using conventional size separation technique, on-site frontal ultrafiltration. Specifically, we aimed to test the possibility of the presence of different pools of metal having specific isotopic signatures in different colloidal fractions using stable isotope measurements. We have chosen Cu for its high affinity to colloidal DOM and Fe for its tendency to form stable organo-mineral colloids of various size. Samples of natural waters were collected from small rivers, lakes, bogs, groundwater and soil environments in the Northern Karelia (NW Russia) during summer baseflow period. Large volumes (20-40 L) of water were filtered in the field through progressively decreasing pore size filters: 20, 10, 5, 0.8, 0.45, 0.22, 0.1 µm and 100, 10 and 1 kDa (1 kDa ~ 1 nm) using nylon and regenerated cellulose membranes and frontal ultrafiltration (Millipore, Amicon) devises. The homogeneity of the sample was verified by tracing radiogenic Sr isotopes in each fraction. In all filtrates and ultrafiltrates (permeates), and in selected retentates, stable isotopic composition of Cu and Fe was measured using double focusing high resolution MC-ICP MS (Neptune). We observe rather constant Cu isotopic ratio in all filtrate series and a systematic enrichment of heavy isotope of Fe with decreasing poresize. These preliminary results can be explained by strong complexation of Cu with small-size organic ligands of fulvic nature and its partial association with organo-mineral colloids. Both Fe(III) - OM complxeation and Fe(III) oxyhydroxides precipitation can be invoked to explain Fe isotope fractionation. This work allows, for the first, time, multi-isotopic approach to trace the origin of colloids in surficial waters and it

  20. Environmental and biosynthetic influences on carbon and hydrogen isotope ratios of leaf wax n-alkanes

    Science.gov (United States)

    McInerney, F. A.; Freeman, K. H.; Polissar, P. J.; Feakins, S. J.

    2013-12-01

    Both carbon and hydrogen isotope ratios of leaf-wax n-alkanes are influenced by the availability of water in a plant's growth environment. Carbon isotope ratios of bulk tissues in C3 plants demonstrate a strong inverse relationship with measures of available moisture (e.g. mean annual precipitation and precipitation/evaporation). Similarly, hydrogen isotope ratios of leaf wax n-alkanes (δDl) can be enriched relative to precipitation (δDw) by transpiration, which is related to relative humidity and the leaf-to-air vapor pressure deficit. Thus, D-enrichment of leaf-wax n-alkanes relative to precipitation, termed the apparent fractionation (2ɛl/w), becomes more positive with increasing aridity. In theory, more positive values of leaf-wax δ13C (δ13Cl) and 2ɛl/w of leaf-wax n-alkanes should both correspond to more arid conditions in C3 plants. Here we review published and unpublished data on over 100 plants to examine this relationship. Contrary to expectations, C3 dicots show no clear relationship between δ13Cl and 2ɛl/w. This global lack of correlation is surprising given our understanding of aridity related isotopic effects in C3 plants. One possibility is that the implicit assumption of constant fractionation between lipid and bulk tissue is flawed due to the effects of different biosynthetic carriers and reaction pathways. We explore this possibility by examining the offset of leaf-wax carbon isotopes from the bulk leaf tissue (13ɛl/bulk). Different offsets would indicate additional biosynthetic processes are affecting δ13Cl in addition to any direct effects from aridity. We find that 13ɛl/bulk is highly variable, ranging from -1 to -16‰, which could explain the lack of correlation between δ13Cl and 2ɛl/w. In addition, 13ɛl/bulk values for C3 and C4 monocots (averages of -10.6 and -11.4‰ respectively) represent significantly greater offset between leaf wax and bulk tissue than in C3 dicots (average of -4.3‰), which is consistent with previous

  1. Isotope dilution analysis for urinary fentanyl and its main metabolite, norfentanyl, in patients by isotopic fractionation using capillary gas chromatography

    Energy Technology Data Exchange (ETDEWEB)

    Sera, Shoji; Goromaru, Tsuyoshi [Fukuyama Univ., Hiroshima (Japan). Faculty of Pharmacy and Pharmaceutical Sciences; Sameshima, Teruko; Kawasaki, Koichi; Oda, Toshiyuki

    1998-07-01

    Isotope dilution analysis was applied to determine urinary excretion of fentanyl (FT) and its main metabolite, norfentanyl (Nor-FT), by isotopic fractionation using a capillary gas chromatograph equipped with a surface ionization detector (SID). Urinary FT was determined quantitatively in the range of 0.4-40 ng/ml using deuterium labeled FT (FT-{sup 2}H{sub 19}), as an internal standard. We also performed isotope dilution analysis of Nor-FT in urine. N-Alkylation was necessary to sensitively detect Nor-FT with SID. Methyl derivative was selected from 3 kinds of N-alkyl derivatives to increase sensitivity and peak resolution, and to prevent interference with urinary compound. Nor-FT concentration was quantitatively determined in the range of 10-400 ng/ml using deuterium labeled Nor-FT (Nor-FT-{sup 2}H{sub 10}). No endogenous compounds or concomitant drugs interfered with the detection of FT and Nor-FT in the urine of patients. The present method will be useful for pharmacokinetic studies and the evaluation of drug interactions in FT metabolism. (author)

  2. Application of stable carbon isotopes in long term mesocosm studies for carbon cycle investigation

    Science.gov (United States)

    Esposito, Mario

    2016-04-01

    Carbon dioxide (CO2) is an effective greenhouse gas. The Oceans absorb ca. 30% of the anthropogenic CO2 emissions and thereby partly attenuate deleterious climate effects. A consequence of the oceanic CO2 uptake is a decreased seawater pH and planktonic community shifts. The quantification of the anthropogenic perturbation was investigated through stable carbon isotope analysis in three "long term" mesocosm experiments (Sweden 2013, Gran Canaria 2014, Norway 2015) which reproduced near natural ecosystem conditions under both controlled and modified future CO2 level (up to 2000 ppm) scenarios. Parallel measurements of the stable isotope composition of dissolved inorganic carbon (δ13CDIC) dissolved organic carbon (δ13CDOC) and particulate carbon (δ13CTPC) both from the mesocosms water column and sediment traps showed similar trends in all the three experiments. A CO2 response was noticeable in the isotopic dataset, but increased CO2 levels had only a subtle effect on the concentrations of the dissolved and particulate organic carbon pool. Distinctive δ13C signatures of the particulate carbon pool both in the water column and the sediments were detectable for the different CO2 treatments and they were strongly correlated with the δ13CDIC signatures but not with the δ13CDOC pool. The validity of the isotopic data was verified by cross-analyses of multiple substances of known isotopic signatures on a GasBench, Elemental Analyser (EA) and on an in-house TOC-IRMS setup for the analysis of δ13CDIC, δ13CTPC and δ13CDOC, respectively. Results from these mesocosm experiments proved the stable carbon isotope approach to be an effective tool for quantifying the uptake and carbon transfer among the various compartments of the marine carbon system.

  3. Carbon isotope composition of the Lower Triassic marine carbonates, Lower Yangtze Region, South China

    Institute of Scientific and Technical Information of China (English)

    ZUO; Jingxun; TONG; Jinnan; QIU; Haiou; ZHAO; Laishi

    2006-01-01

    Studies on three Lower Triassic sections located on the shallow water platform, the deep water slope and in the deep water basin in the Lower Yangtze Region, South China, show the similar trend of carbon isotope evolution. Biostratigraphic correlations among the Lower Triassic sections on the basis of standard conodont zones indicate that three negative shifts occurred in the Griesbachian, the Smithian and the late Spathian stages respectively, and one distinctly positive shift occurred in the early Spathian stage. Trend of carbon isotope evolution of the Lower Triassic reflects some significant changes in the global carbon cycle. Moreover, δ13C background values are intensively controlled by palaeogeographic environment. In general, δ13C values from deep-water slope carbonates are lighter than those from carbonate platform and heavier than those from deep-water basin carbonates. The positive carbon isotope excursion may be induced by a significant amount of organic carbon burial in marine sediments and increase in primary productivity. The large negative carbon isotope excursions during the Early Triassic in Lower Yangtze Region are interpreted to relate to volcano eruptions based on tuffaceous claystone interlayers observed near the Permian-Triassic boundary, the Induan- Olenekian boundary and the Lower Triassic-Middle Triassic boundary.

  4. Assessment of diffusive isotopic fractionation in polar firn, and application to ice core trace gas records

    DEFF Research Database (Denmark)

    Buizert, C.; Sowers, T.; Blunier, T.

    2013-01-01

    from ice cores; (5) arguably gives more accurate results than a combined firn densification-firn air transport modeling study would. We apply the method to records of CH, CO and NO mixing ratios, and we find that the correction is particularly important for C - . We apply the correction to C - records......During rapid variations of the atmospheric mixing ratio of a trace gas, diffusive transport in the porous firn layer atop ice sheets and glaciers alters the isotopic composition of that gas relative to the overlying atmosphere. Records of past atmospheric trace gas isotopic composition from ice...... cores and firn need to be corrected for this diffusive fractionation artifact. We present a novel, semi-empirical method to accurately estimate the magnitude of the diffusive fractionation in the ice core record. Our method (1) consists of a relatively simple analytical calculation; (2) requires only...

  5. Authenticity of carbon dioxide bubbles in French ciders through multiflow-isotope ratio mass spectrometry measurements.

    Science.gov (United States)

    Gaillard, Laetitia; Guyon, Francois; Salagoïty, Marie-Hélène; Médina, Bernard

    2013-12-01

    A procedure to detect whether carbon dioxide was added to French ciders has been developed. For this purpose, an optimised and simplified method is proposed to determine (13)C/(12)C isotope ratio of carbon dioxide (δ(13)C) in ciders. Three critical steps were checked: (1) influence of atmospheric CO2 remaining in the loaded vial, (2) impact of helium flush, (3) sampling speed. This study showed that atmospheric CO2 does not impact the measurement, that helium flush can lead to isotopic fractionation and finally, that a fractionation occurs only 5h after bottle opening. The method, without any other preparation, consists in sampling 0.2 mL of cold (4 °C) cider in a vial that is passed in an ultrasonic bath for 10 min at room temperature to enhance cider de-carbonation. The headspace CO2 is then analysed using the link Multiflow®-isotope ratio mass spectrometer. Each year, a data bank is developed by fermenting authentic apples juices in order to control cider authenticity. Over a four year span (2008-2011), the CO2 produced during the fermentation step was studied. This set of 61 authentic ciders, from various French production areas, was used to determine a δ(13)C value range of -22.59±0.92‰ for authentic ciders CO2 bubbles. 75 commercial ciders were analysed with this method. Most of the samples analysed present a gas δ(13)C value in the expected range. Nevertheless, some ciders have δ(13)C values outside the 3σ limit, revealing carbonation by technical CO2. This practice is not allowed for organic, "Controlled Appellation of Origin" ciders and ciders specifying natural carbonation on the label.

  6. Influences of calcium availability and tree species on Ca isotope fractionation in soil and vegetation

    Science.gov (United States)

    Page, B.D.; Bullen, T.D.; Mitchell, M.J.

    2008-01-01

    The calcium (Ca) isotope system is potentially of great use for understanding biogeochemical processes at multiple scales in forest ecosystems, yet remains largely unexplored for this purpose. In order to further our understanding of Ca behavior in forests, we examined two nearly adjacent hardwood-dominated catchments with differing soil Ca concentrations, developed from crystalline bedrock, to determine the variability of 44Ca/ 40Ca ratios (expressed as ??44Ca) within soil and vegetation pools. For both sugar maple and American beech, the Ca isotope compositions of the measured roots and calculated bulk trees were considerably lighter than those of soil pools at these sites, suggesting that the trees were able to preferentially take up light Ca at the root-soil interface. The Ca isotope compositions of three of four root samples were among the lightest values yet reported for terrestrial materials (??44Ca ???-3.95???). Our results further indicate that Ca isotopes were fractionated along the transpiration streams of both tree species with roots having the least ??44Ca values and leaf litter the greatest. An approximately 2??? difference in ??44Ca values between roots and leaf litter of both tree species suggests a persistent fractionation mechanism along the transpiration stream, likely related to Ca binding in wood tissue coupled with internal ion exchange. Finally, our data indicate that differing tree species demand for Ca and soil Ca concentrations together may influence Ca isotope distribution within the trees. Inter-catchment differences in Ca isotope distributions in soils and trees were minor, indicating that the results of our study may have broad transferability to studies of forest ecosystems in catchments developed on crystalline substrates elsewhere. ?? 2008 Springer Science+Business Media B.V.

  7. FAR-DEEP: organic carbon isotope chemostratigraphy of early Paleoproterozoic sediments from Fennoscandia

    Science.gov (United States)

    Illing, C. J.; Strauss, H.; Summons, R. E.; Kump, L.; Fallick, A. E.; Melezhik, V.; Far-Deep Scientists

    2010-12-01

    One major objective of the Fennoscandian Arctic Russia - Drilling Early Earth Project (FAR-DEEP) is to reconstruct ancient microbial ecosystems and the evolution of key metabolic pathways during the Archean-Proterozoic Transition (APT). Fifteen drill cores with a total length of 3650m were retrieved in three areas (Imandra/Varzuga and Pechenga Greenstone belts and Onega Basin) in northern Russia. Cores cover a time interval of some 700 my and have archived several important changes in Earth’s environment. Among them, the Great Oxygenation Event (GOE) at ca. 2350 million years ago resulted in large-scale environmental changes (e.g. Melezhik et al., 2005). Of similar importance, but specifically for global carbon cycling, are the Lomagundi-Jatuli Event (LJE; e.g. Melezhik et al., 2007) and the Shunga Event (SE; e.g. Melezhik et al., 2009). This work presents preliminary carbon isotope results for sedimentary organic matter (δ13Corg) contained in the major sedimentary formations cored by FAR-DEEP. The samples were processed via sealed tube combustion. The total variation in δ13Corg between -40 and -17 ‰ agrees well with previously published data (e.g. Eigenbrode and Freeman, 2006). But more informative than the organic carbon isotopic composition alone is the isotopic difference (Δ13C) between the organic (δ13Corg) and carbonate carbon (δ13Ccarb) isotopic composition: Δ13C = δ13Ccarb - δ13Corg This parameter provides information about the isotopic fractionation associated with biosynthesis and carbon cycling (e.g., Des Marais, 2001). Sediments from the lower Kuetsjärvi Formation (core 5A) and the upper part of the Tulomozero Formation (cores 10A, 10B, 11A), covering the LJE, display Δ13C values between 30 and 37‰. This isotopic difference continuous through the SE (cores 12A/B and 13). The broad parallel evolution of δ13Corg and δ13Ccarb indicates that respective perturbations affected the global carbon cycle. However, further refinement will be

  8. Salinity dependent hydrogen isotope fractionation in alkenones produced by coastal and open ocean haptophyte algae

    Science.gov (United States)

    M'boule, Daniela; Chivall, David; Sinke-Schoen, Danielle; Sinninghe Damsté, Jaap S.; Schouten, Stefan; van der Meer, Marcel T. J.

    2014-04-01

    The hydrogen isotope fractionation in alkenones produced by haptophyte algae is a promising new proxy for paleosalinity reconstructions. To constrain and further develop this proxy the coastal haptophyte Isochrysis galbana and the open ocean haptophyte alga Emiliania huxleyi were cultured at different salinities. The fractionation factor, αalkenones-water, ranged between 0.853 and 0.902 for I. galbana and 0.789 and 0.822 for E. huxleyi. The results show a strong linear correlation between the fractionation factor α and salinity for E. huxleyi, in agreement with earlier studies, but also for I. galbana. Both haptophytes show the same response to changes in salinity, represented by the slopes of the α-salinity relationship (˜0.002 per salinity unit). This suggests that the same process, in both coastal as well as open ocean haptophytes, is responsible for reducing fractionation with increasing salinity. However, there is a significant difference in absolute isotope fractionation between E. huxleyi and I. galbana, i.e. E. huxleyi produces alkenones which are 90‰ more depleted in D under the same culturing conditions than I. galbana. Our data suggest that the δD of alkenones can be used to reconstruct relative shifts in paleosalinity in coastal as well as open ocean environments with careful consideration of species composition and other complicating factors especially in coastal regions.

  9. Analysis of hydrogen isotope ratios by SIMS, and application to determining mineral-fluid isotope fractionation factors

    Energy Technology Data Exchange (ETDEWEB)

    Riciputi, L.R.; Chacko, T.; Cole, D.R.; Horita, J.

    1997-09-01

    Due to the large mass difference between the two isotopes, D/H ratios can be strongly affected by chemical processes. Thus, they can be sensitive monitors of fluid source, temperature, and fluid-rock interactions in geologic settings. The lack of confidence in fractionation factors has significantly hindered realization of the potential of D/H ratios in geochemical studies. The authors describe a new experimental method, relying on SIMS analysis, that allows the precise determination of mineral-water D/H fractionation factors, and the analytical considerations that are required to make both precise and accurate measurements. The development of this method is based on the fact that diffusion rates are markedly anisotropic in many hydrous minerals, varying by over five orders of magnitude depending on the crystallographic orientation. The diffusion rates can be determined by conducting controlled exchange experiments of fixed duration using isotopically labeled waters that are enriched (strongly) with D, and then measuring the depth profile by SIMS.

  10. Cr-isotope fractionation during oxidative weathering of ultramafic rocks and its impact on river waters

    DEFF Research Database (Denmark)

    Paulukat, Cora Stefanie; Døssing, Lasse Nørbye; Mondal, Sisir K.;

    We investigated Cr isotope fractionation during soil formation from Precambrian ultramafic rocks. A soil profile was logged in an active open-cast chromite mine (Sukinda Valley, India). In addition, mine and river waters, as well as seawater were collected to trace the Cr-isotope signal...... into the sea. The aim of the study is to recognize Cr isotope fractionation processes within the mining-area and the impact of the mine runoff on the δ53Cr of the nearby river. The weathering profile shows a distinct upward trend to more negative δ53Cr values. While the well preserved rocks at the base closely...... reflect mantle inventory (-0.124±0.101‰ 1), the δ53Cr from the more weathered upper part of the profile is as low as -1.28±0.022‰. These data are consistent with the findings of Crowe et al. (in press). They demonstrated that Cr(III) becomes oxidised during rock weathering, which leads to an isotopic...

  11. Separation of carbon nanotubes into chirally enriched fractions

    Science.gov (United States)

    Doorn, Stephen K [Los Alamos, NM; Niyogi, Sandip [Los Alamos, NM

    2012-04-10

    A mixture of single-walled carbon nanotubes ("SWNTs") is separated into fractions of enriched chirality by preparing an aqueous suspension of a mixture of SWNTs and a surfactant, injecting a portion of the suspension on a column of separation medium having a density gradient, and centrifuging the column. In some embodiments, salt is added prior to centrifugation. In other embodiments, the centrifugation is performed at a temperature below room temperature. Fractions separate as colored bands in the column. The diameter of the separated SWNTs decreases with increasing density along the gradient of the column. The colored bands can be withdrawn separately from the column.

  12. The Carbon Isotopic Content and Concentration of Ambient Formic and Acetic Acid

    Science.gov (United States)

    Johnson, Bryan Jay

    mass spectrometry. Carbon isotopic fractionation during exchange of HCOOH between the liquid and gas phases was investigated through a gas/liquid partitioning experiment. A first experimental measurement of the Henry's Law coefficient (K^{rm H}) averaged 7400 +/- 800 M/atm. Fractionation between HCOOH_{rm (g)} and HCOOH_{rm (aq)} was found to be negligible.

  13. Experimental and theoretical investigation of isotope fractionation of zinc between aqua, chloro, and macrocyclic complexes.

    Science.gov (United States)

    Fujii, Toshiyuki; Moynier, Frédéric; Telouk, Philippe; Abe, Minori

    2010-02-25

    This work reports on the chemical isotope fractionation of Zn(II) by a solvent extraction method with the crown ether dicyclohexano-18-crown-6. The (m)Zn/(64)Zn ratios (m = 66, 67, and 68) were analyzed by multiple-collector inductively coupled plasma mass spectrometry. The relative deviations of the (66)Zn/(64)Zn ratios relative to the unprocessed material (delta(66)Zn) was determined to be -0.51 to -0.32 in the acidity region 1.0-6.0 mol dm(-3) (M) HCl. The acidity dependence of delta(m)Zn was explained by the isotope exchange reactions between Zn(II) species (Zn(2+), ZnCl(+), ZnCl(2), ZnCl(3)(-), and ZnCl(4)(2-)) and the mole fractions of them. The magnitude of delta(m)Zn due to the related Zn(II) species estimated by quantum chemical calculations was in agreement with delta(m)Zn experimentally obtained. Contribution of nuclear field shift to the isotope fractionation was estimated to be less than 10% of delta(m)Zn by quantum chemical calculations.

  14. Simultaneous tracing of carbon and nitrogen isotopes in human cells.

    Science.gov (United States)

    Nilsson, Roland; Jain, Mohit

    2016-05-24

    Stable isotope tracing is a powerful method for interrogating metabolic enzyme activities across the metabolic network of living cells. However, most studies of mammalian cells have used (13)C-labeled tracers only and focused on reactions in central carbon metabolism. Cellular metabolism, however, involves other biologically important elements, including nitrogen, hydrogen, oxygen, phosphate and sulfur. Tracing stable isotopes of such elements may help shed light on poorly understood metabolic pathways. Here, we demonstrate the use of high-resolution mass spectrometry to simultaneously trace carbon and nitrogen metabolism in human cells cultured with (13)C- and (15)N-labeled glucose and glutamine. To facilitate interpretation of the complex isotopomer data generated, we extend current methods for metabolic flux analysis to handle multivariate mass isotopomer distributions (MMIDs). We find that observed MMIDs are broadly consistent with known biochemical pathways. Whereas measured (13)C MIDs were informative for central carbon metabolism, (15)N isotopes provided evidence for nitrogen-carrying reactions in amino acid and nucleotide metabolism. This computational and experimental methodology expands the scope of metabolic flux analysis beyond carbon metabolism, and may prove important to understanding metabolic phenotypes in health and disease.

  15. Carbon Isotopes of Alkanes in Hydrothermal Abiotic Organic Synthesis Processes at High Temperatures and Pressures: An Experimental Study

    Science.gov (United States)

    Fu, Qi; Socki, Richard A.; Niles, Paul B.

    2010-01-01

    Observation of methane in the Martian atmosphere has been reported by different detection techniques [1-4]. With more evidence showing extensive water-rock interaction in Martian history [5-7], abiotic formation by Fischer-Tropsch Type (FTT) synthesis during serpentization reactions may be one possible process responsible for methane generation on Mars [8, 9]. While the experimental studies performed to date leave little doubt that chemical reactions exist for the abiotic synthesis of organic compounds by mineral surface-catalyzed reactions [10-12], little is known about the reaction pathways by which CO2 and/or CO are reduced under hydrothermal conditions. Carbon and hydrogen isotope measurements of alkanes have been used as an effective tool to constrain the origin and reaction pathways of hydrocarbon formation. Alkanes generated by thermal breakdown of high molecular weight organic compounds have carbon and hydrogen isotopic signatures completely distinct from those formed abiotically [13-15]. Recent experimental studies, however, showed that different abiogenic hydrocarbon formation processes (e.g., polymerization vs. depolymerization) may have different carbon and hydrogen isotopic patterns [16]. Results from previous experiments studying decomposition of higher molecular weight organic compounds (lignite) also suggested that pressure could be a crucial factor affecting fractionation of carbon isotopes [17]. Under high pressure conditions, no experimental data are available describing fractionation of carbon isotope during mineral catalyzed FTT synthesis. Thus, hydrothermal experiments present an excellent opportunity to provide the requisite carbon isotope data. Such data can also be used to identify reaction pathways of abiotic organic synthesis under experimental conditions.

  16. Shear heating and clumped isotope reordering in carbonate faults

    Science.gov (United States)

    Siman-Tov, Shalev; Affek, Hagit P.; Matthews, Alan; Aharonov, Einat; Reches, Ze'ev

    2016-07-01

    Natural faults are expected to heat rapidly during seismic slip and to cool quite quickly after the slip event. Here we examine clumped isotope thermometry for its ability to identify such short duration elevated temperature events along frictionally heated carbonate faults. Our approach is based on measured Δ47 values that reflect the distribution of oxygen and carbon isotopes in the calcite lattice, measuring the abundance of 13Csbnd 18O bonds, which is affected by temperature. We examine three types of calcite rock samples: (1) crushed limestone grains that were rapidly heated and then cooled in static laboratory experiments, simulating the temperature cycle experienced by fault rock during an earthquake slip; (2) limestone samples that were experimentally sheared to simulate earthquake slip events; and (3) samples from Fault Mirrors (FMs) collected from principle slip surfaces of three natural carbonate faults. Extensive FM surfaces are believed to form during earthquake slip. Our experimental results show that Δ47 values decrease rapidly (in the course of seconds) with increasing temperature and shear velocity. On the other hand, carbonate shear zones from natural faults do not show such Δ47 decrease. We suggest that the Δ47 response may be controlled by nano-size grains, the high abundance of defects, and highly stressed/strained grain boundaries within the carbonate fault zone that can reduce the activation energy for diffusion, and thus lead to an increased rate of isotopic disordering during shear experiments. In our laboratory experiments the high stress and strain on grain contacts and the presence of nanograins thus allows for rapid disordering so that a change in Δ47 occurs in a very short and relatively low intensity heating events. In natural faults it may also lead to isotopic ordering after the cessation of frictional heating thus erasing the high temperature signature of Δ47.

  17. Stable silver isotope fractionation in the natural transformation process of silver nanoparticles.

    Science.gov (United States)

    Lu, Dawei; Liu, Qian; Zhang, Tuoya; Cai, Yong; Yin, Yongguang; Jiang, Guibin

    2016-08-01

    Nanoparticles in the environment can form by natural processes or be released due to human activities. Owing to limited analytical methods, the behaviour of nanoparticles in the natural environment is poorly understood and until now they have only been described by the variations in the nanoparticle size or the concentration of the element of interest. Here we show that by using inductively coupled plasma mass spectrometry to measure silver (Ag) isotope ratios it is possible to understand the transformation processes of silver nanoparticles (AgNPs) in the environment. We found that the formation and dissolution of AgNPs under natural conditions caused significant variations in the ratio of natural Ag isotopes ((107)Ag and (109)Ag) with an isotopic enrichment factor (ε) up to 0.86‰. Furthermore, we show that engineered AgNPs have distinctly different isotope fractionation effects to their naturally formed counterparts. Further studies will be needed to understand whether isotope analysis can be used to reveal the sources of AgNPs in the environment.

  18. Stable silver isotope fractionation in the natural transformation process of silver nanoparticles

    Science.gov (United States)

    Lu, Dawei; Liu, Qian; Zhang, Tuoya; Cai, Yong; Yin, Yongguang; Jiang, Guibin

    2016-08-01

    Nanoparticles in the environment can form by natural processes or be released due to human activities. Owing to limited analytical methods, the behaviour of nanoparticles in the natural environment is poorly understood and until now they have only been described by the variations in the nanoparticle size or the concentration of the element of interest. Here we show that by using inductively coupled plasma mass spectrometry to measure silver (Ag) isotope ratios it is possible to understand the transformation processes of silver nanoparticles (AgNPs) in the environment. We found that the formation and dissolution of AgNPs under natural conditions caused significant variations in the ratio of natural Ag isotopes (107Ag and 109Ag) with an isotopic enrichment factor (ε) up to 0.86‰. Furthermore, we show that engineered AgNPs have distinctly different isotope fractionation effects to their naturally formed counterparts. Further studies will be needed to understand whether isotope analysis can be used to reveal the sources of AgNPs in the environment.

  19. STABLE CARBON ISOTOPE ANALYSIS OF SUBFOSSIL WOOD FROM AUSTRIAN ALPS

    Science.gov (United States)

    KŁUSEK, MARZENA; PAWEŁCZYK, SŁAWOMIRA

    2015-01-01

    The presented studies were carried out in order to check the usefulness of subfossil wood for stable isotope analysis. The aim of research was also to define the optimal method of subfossil samples preparation. Subfossil samples used during the presented studies are a part of the multi-century dendrochronological scale. This chronology originates in an area situated around a small mountain lake — Schwarzersee, in Austria. The obtained results of stable carbon isotope measurements confirmed that the method of α-cellulose extraction by the application of acidic sodium chlorite and sodium hydroxide solutions removes resins and other mobile compounds from wood. Therefore, in the case of the analysed samples, the additional chemical process of extractives removing was found to be unnecessary. Studied wood samples contained an adequate proportion of α-cellulose similar to the values characteristic for the contemporary trees. This proved an adequate wood preservation which is essential for the conduction of isotopic research. PMID:26346297

  20. Carbon and Oxygen Isotope Stratigraphy of the Oxfordian Carbonate Rocks in Amu Darya Basin

    Institute of Scientific and Technical Information of China (English)

    Rongcai Zheng; Yanghui Pan; Can Zhao; Lei Wu; Renjin Chen; Rui Yang

    2013-01-01

    Based on the detailed research on petrologic and geochemical characteristics of deposition and diagenesis of Oxfordian carbonate rocks in Amu Darya Basin,Turkmenistan,carbon and oxygen isotopes were analyzed.The results show that the paleoenvironmental evolution reflected by the samples with well-preserved original carbon isotopes coincides with the carbon-isotope stratigraphic carve and is almost consistent with the global sea-level curve,the Mid-Oxfordian wide transgression,and the positive carbon-isotope excursion event.The Mid-Oxfordian continuing transgression not only laid the foundation for the development of the Oxfordian reef and shoal reservoirs in Amu Darya Basin but also provided an example for the Oxfordian global transgression and the resulting development of reefs and banks and high-speed organic carbon burial events.The response of oxygen isotopes in diagenetic environment showed that micrite limestones and granular limestones underwent weak diagenetic alteration,and the samples largely retained the original seawater features.Dolomitization and the precipitation of hydrothermal calcites tilling solution vugs and fractures before hydrocarbon accumulation occurred in a closed diagenetic environment where the main controlling factor is the temperature,and the diagenetic fluids were from the deep hot brine.The chalkification of the limestones after hydrocarbon accumulation occurred in the oiltield water systems.

  1. A supercritical oxidation system for the determination of carbon isotope ratios in marine dissolved organic carbon

    NARCIS (Netherlands)

    Le Clercq, Martijn; Van der Plicht, Johannes; Meijer, Harro A.J.

    1998-01-01

    An analytical oxidation system employing supercritical oxidation has been developed. It is designed to measure concentration and the natural carbon isotope ratios (C-13, C-14) Of dissolved organic carbon (DOC) and is especially suited for marine samples. The oxidation takes place in a ceramic tube a

  2. Precipitation of smithsonite under controlled pCO2 between 25 and 60° C - Fractionation of oxygen isotopes

    Science.gov (United States)

    Füger, Anja; Mavromatis, Vasileios; Leis, Albrecht; Dietzel, Martin

    2016-04-01

    Owing to the large fractionation (i.e. Δ18Osolid-diss. ˜30) between carbonate minerals and aqueous fluids with respect to their 18O/16O composition, the oxygen isotope composition of carbonates has been a fundamental tool for the estimation of mineral formation temperature by the geoscience community. Indeed the last 6 decades, a wide number of experimental studies investigated the temperature relation of Δ18Osolid-diss. between divalent metal carbonates and aqueous fluids. To date however no experimental data exist for the temperature dependence of Δ18Osolid-diss. between smithsonite (ZnCO3) and fluid. This lack of data likely stems from a kinetic barrier effect, that of the dehydration of aqueous Zn2+ and the formation of hydrozincite (Zn5(CO3)2(OH)6). Smithsonite is a secondary zinc mineral that is one of the components of zinc ore bodies. It is formed through oxidation of primary zinc ores by the reaction with a carbonate source or by precipitation of zinc salt solutions with a CO2-saturated and bicarbonate-rich solution. In this study we hydrothermally synthesized smithsonite at the temperature range between 25 and 60 ° C and report the temperature dependence of oxygen isotope distribution between smithsonite and aqueous fluid. In order to avoid the formation of hydrozincite our experiments were conducted in titanium batch reactors using Teflon-inlets where the CO2 pressure was adjusted to 10 bars. The low pH conditions provoked by the elevated pCO2 applied, lead to the dissolution of hydrozincite, which is initially formed by mixing of Na2HCO3 (0.1 M) and Zn(NO3)2.4 H2O (0.02 M) solutions, to yield - under the prevailing conditions - the thermodynamically stable mineral smithsonite.

  3. New triple oxygen isotope data of bulk and separated fractions from SNC meteorites: Evidence for mantle homogeneity of Mars

    Science.gov (United States)

    Ali, Arshad; Jabeen, Iffat; Gregory, David; Verish, Robert; Banerjee, Neil R.

    2016-05-01

    We report precise triple oxygen isotope data of bulk materials and separated fractions of several Shergotty-Nakhla-Chassigny (SNC) meteorites using enhanced laser-assisted fluorination technique. This study shows that SNCs have remarkably identical Δ17O and a narrow range in δ18O values suggesting that these meteorites have assimilated negligibly small surface materials (<5%), which is undetectable in the oxygen isotope compositions reported here. Also, fractionation factors in coexisting silicate mineral pairs (px-ol and mask-ol) further demonstrate isotopic equilibrium at magmatic temperatures. We present a mass-dependent fractionation line for bulk materials with a slope of 0.526 ± 0.016 (1SE) comparable to the slope obtained in an earlier study (0.526 ± 0.013; Franchi et al. 1999). We also present a new Martian fractionation line for SNCs constructed from separated fractions (i.e., pyroxene, olivine, and maskelynite) with a slope of 0.532 ± 0.009 (1SE). The identical fractionation lines run above and parallel to our terrestrial fractionation line with Δ17O = 0.318 ± 0.016‰ (SD) for bulk materials and 0.316 ± 0.009‰ (SD) for separated fractions. The conformity in slopes and Δ17O between bulk materials and separated fractions confirm oxygen isotope homogeneity in the Martian mantle though recent studies suggest that the Martian lithosphere may potentially have multiple oxygen isotope reservoirs.

  4. Aspect of human food ecology; Development of carbon and nitrogen isotope method

    Energy Technology Data Exchange (ETDEWEB)

    Minagawa, Masao (Hokkaido Univ., Sapporo (Japan))

    1994-01-01

    The isotopic dietary analysis was applied for some prehistoric human populations from East Asia, Latin America, and Oceania region. Most samples were from archeological sites from 1000 to 6000 year's bp. Some modern ethnological groups including Tibet, Kurud, Shelpa and Tlingit were also studied for evaluating prehistoric human food habit. Carbon and nitrogen isotope compositions of gelatin fractions have been analyzed for prehistoric bone samples. Analytical procedure for isotopes and data analyses for reconstructing dietary composition was developed and tested by a modern human food system. A stochastic method based on the Monte Carlo model was applied to estimate dependency of major food resources having unique isotope compositions in carbon and nitrogen, and has showed consistent results to the statistic food consumption record in Japan. Carbon and nitrogen isotope composition of human tissues showed distinct difference among human groups in both prehistoric and modern samples. These data were evaluated by difference of dietary patterns: contributions of marine food, terrestrial food, meat, C3 and C4 plant, which are characterized by the difference of [sup 13]C and [sup 15]N content. On the basis of the stochastic feeding simulation, dietary consumption patterns were estimated for Jomon fisher-hunter-gatherers, historic Ainu, prehistoric east Siberian, prehistoric Latin American farmers in Mexico and Peru, and prehistoric fisheres in Cook island. Results showed a remarkable relationship between animal protein dependence and marine food usage. This result will be discussed from following two possibilities; the human adaptation on marine resources would be one of the important direction to upgrade animal protein uptake, or marine food could be used as alternative protein source for terrestrial game animals. (author).

  5. Seasonal Variations in the Biochemical Fractionation of Hydrogen Isotopes by Spartina alterniflora.

    Science.gov (United States)

    Sessions, A. L.

    2005-12-01

    Hydrogen isotope ratios (D/H) of lipids are being intensively explored as a paleoenvironmental proxy, particularly for continental regimes where organic preservation in lakes is generally high. Several studies have already shown good correlations between δD values of lake water and sedimentary (core-top) lipids, but the fractionations indicated by those correlations do not agree well between studies. Moreover, the data cannot be adequately described by a single biochemical fractionation. These difficulties suggest that the relationship between environmental water and plant lipid δD is controlled by multiple environmental and biochemical factors. Understanding these factors will lead to a more robust interpretation of D/H as a paleoclimate proxy. Here we examine seasonal changes in biochemical H-isotopic fractionation by the salt marsh grass Spartina alterniflora. Because S. alterniflora grows partially submerged in a tidal estuary, it has an unlimited and isotopically unvarying source of water for growth. Thus environmental influences on fractionation should be negligible, allowing us to examine seasonal changes in biochemical fractionations. C27 and C29 n-alkanes, β-sitosterol, phytol, and C16 and C18 fatty acids were extracted and analyzed from 35 samples of S. alterniflora harvested from the same location over a period of 18 months. All lipids except β-sitosterol exhibit statistically significant depletions of D during summer months relative to the rest of the year. The magnitude of the isotopic shift is up to 36‰ in the fatty acids (δD values from -130 to -166‰), 31‰ in n-alkanes (-161 to -192‰), and 24‰ in phytol (-252 to -276‰). The shift in D/H ratio is in the opposite direction from that expected due to increased evapotranspiration during the summer months. The largest D-depletions coincide with periods of maximal growth. The observed pattern is interpreted as resulting from increased use of stored carbohydrates as substrates for lipid

  6. Enhanced biosynthetically directed fractional carbon-13 enrichment of proteins for backbone NMR assignments.

    Science.gov (United States)

    Wenrich, Broc R; Sonstrom, Reilly E; Gupta, Riju A; Rovnyak, David

    2015-11-01

    Routes to carbon-13 enrichment of bacterially expressed proteins include achieving uniform or positionally selective (e.g. ILV-Me, or (13)C', etc.) enrichment. We consider the potential for biosynthetically directed fractional enrichment (e.g. carbon-13 incorporation in the protein less than 100%) for performing routine n-(D)dimensional NMR spectroscopy of proteins. First, we demonstrate an approach to fractional isotope addition where the initial growth media containing natural abundance glucose is replenished at induction with a small amount (e.g. 10%(w/w)u-(13)C-glucose) of enriched nutrient. The approach considered here is to add 10% (e.g. 200mg for a 2g/L culture) u-(13)C-glucose at the induction time (OD600=0.8), resulting in a protein with enhanced (13)C incorporation that gives almost the same NMR signal levels as an exact 20% (13)C sample. Second, whereas fractional enrichment is used for obtaining stereospecific methyl assignments, we find that (13)C incorporation levels no greater than 20%(w/w) yield (13)C and (13)C-(13)C spin pair incorporation sufficient to conduct typical 3D-bioNMR backbone experiments on moderate instrumentation (600 MHz, RT probe). Typical 3D-bioNMR experiments of a fractionally enriched protein yield expected backbone connectivities, and did not show amino acid biases in this work, with one exception. When adding 10% u-(13)C glucose to expression media at induction, there is poor preservation of (13)Cα-(13)Cβ spin pairs in the amino acids ILV, leading to the absence of Cβ signals in HNCACB spectra for ILV, a potentially useful editing effect. Enhanced fractional carbon-13 enrichment provides lower-cost routes to high throughput protein NMR studies, and makes modern protein NMR more cost-accessible.

  7. Efficiency of Carbon Dioxide Fractional Laser in Skin Resurfacing

    Directory of Open Access Journals (Sweden)

    Andrej Petrov

    2016-05-01

    CONCLUSION: Multifunctional fractional carbon dioxide laser used in treatment of patients with acne and pigmentation from acne, as well as in the treatment of scars from different backgrounds, is an effective and safe method that causes statistically significant better effect of the treatment, greater patients’ satisfaction, minimal side effects and statistically better response to the therapy, according to assessments by the patient and the therapist.

  8. Silicon Isotope Fractionation by Banana Under Continuous Nutrient and Silica Flux

    Science.gov (United States)

    Opfergelt, S.; Cardinal, D.; Henriet, C.; Delvaux, B.; André, L.

    2004-12-01

    Silicon is absorbed by plants as aqueous H4SiO4 with other essential nutrients, and precipitates in aerial parts of the plant as phytolith, a biogenic opal. Phytoliths are restored to the soil by decomposition of organic debris from plant material. The role of higher plants in the biogeochemical cycle of silicon is therefore major although it is still poorly studied. Biomineralization processes are known to fractionate the three stable silicon isotopes with a preferential uptake of light isotopes. Therefore, following some preliminary results from Douthitt (1982), and studies presented in recent conferences (Ziegler et al., 2002; Ding et al., 2003), we suspect that phytolith production by plants could also fractionate the silicon isotopes. Inversely, intensity of phytolith-related isotopic fractionations might contribute to a better understanding of the soil-plant silicon cycle. Our study focused on banana, a silicon accumulating plant (>1% Si, dry weight).Musa acuminata cv Grande Naine has been grown in hydroponics under controlled conditions (light, temperature, humidity, nutrients) during six weeks. The nutrient supply was kept constant: three batches of five plants were grown with a continuous nutrient solution flow of 5, 50 and 100 ppm SiO2 respectively. Si isotopic compositions were measured in the source solution, and in silica extracted from the various parts of banana (roots, pseudostems, midribs and petioles, leaves), using a Nu Plasma multicollector mass spectrometer (MC-ICP-MS) operating in dry plasma mode. The results are expressed as δ 29Si relatively to the NBS28 standard, with an average precision of ± 0.03‰ . Silicon contents and morphological studies of phytoliths were also achieved. Banana δ 29Si varied between -0.18 and -0.76‰ with a source solution at -0.02‰ . Values of δ 29Si were less fractionated, relatively to the nutrient solution, in roots, where no phytoliths have been observed until now, than in upper parts of banana where

  9. Descriptions of carbon isotopes within the energy density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Ismail, Atef [Fundamental and Applied Sciences Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia and Department of Physics, Al-Azhar University, 71524 Assiut (Egypt); Cheong, Lee Yen; Yahya, Noorhana [Fundamental and Applied Sciences Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak (Malaysia); Tammam, M. [Department of Physics, Al-Azhar University, 71524 Assiut (Egypt)

    2014-10-24

    Within the energy density functional (EDF) theory, the structure properties of Carbon isotopes are systematically studied. The shell model calculations are done for both even-A and odd-A nuclei, to study the structure of rich-neutron Carbon isotopes. The EDF theory indicates the single-neutron halo structures in {sup 15}C, {sup 17}C and {sup 19}C, and the two-neutron halo structures in {sup 16}C and {sup 22}C nuclei. It is also found that close to the neutron drip-line, there exist amazing increase in the neutron radii and decrease on the binding energies BE, which are tightly related with the blocking effect and correspondingly the blocking effect plays a significant role in the shell model configurations.

  10. Surface Kinetic Model for the Fractionation of Trace Elements and Isotopes in Calcite Precipitated from Aqueous Solution

    Science.gov (United States)

    Depaolo, D. J.; Ryerson, F. J.; Watkins, J. M.; Bourg, I. C.; Yang, W.; Nielsen, L. C.; Druhan, J. L.

    2010-12-01

    The isotopic and trace element concentrations in calcite and other carbonate minerals form the basis for several paleoceanographic and paleoenvironmental indicators. The chemical and isotopic composition of natural calcites is determined by a combination of equilibrium partitioning and kinetic fractionations. Currently there is no general model that describes when equilibrium applies and how kinetic effects depend on the circumstances and rates of mineral growth. A useful approach is to separate the growth of calcite from aqueous solutions into forward (f) and backward (b) reactions, and to consider the mechanisms and fractionations that may be associated with each. We are evaluating a model where the net precipitation rate of calcite (Rp) is expressed as the difference between a forward rate (Rf) and a backward (dissolution) rate (Rb). Dissolution is approached only as Rp/Rb->0. Much natural calcite, including biogenic, forms under conditions where Rp ≫ Rb, hence the isotopic and trace element partitioning is strongly influenced by the kinetics of the forward reaction. Assuming that there are kinetic fractionations associated with the forward and backward reactions, a simple model can be developed for the dependence of calcite composition on precipitation rate. This model can explain most available experimental data on Ca and O isotopes, as well as Sr/Ca and Mn/Ca in calcite, and can be used to infer the behavior of other trace and minor elements. The critical parameter in applying the model is the value of Rb which to first order can be estimated from mineral dissolution rates, but apparently is not a constant, but instead varies with solution chemistry, especially at saturation conditions close to equilibrium. The surface kinetic model requires three parameters that are measureable experimentally and potentially also predictable from molecular dynamics simulation approaches. In this way it differs from the surface entrapment model of Watson (2004) which

  11. The effect of bonding environment on iron isotope fractionation between minerals at high temperature

    Science.gov (United States)

    Sossi, Paolo A.; O'Neill, Hugh St. C.

    2017-01-01

    Central to understanding the processes that drive stable isotope fractionation in nature is their quantification under controlled experimental conditions. The polyvalent element iron, given its abundance in terrestrial rocks, exerts controls on the structural and chemical properties of minerals and melts. The iron isotope compositions of typical high temperature minerals are, however, poorly constrained and their dependence on intensive (e.g. fO2) and extensive (e.g. compositional) variables is unknown. In this work, experiments involving a reference phase, 2 M FeCl2·4H2O(l), together with an oxide mix corresponding to the bulk composition of the chosen mineral were performed in a piston cylinder in Ag capsules. The oxide mix crystallised in situ at 1073 K and 1 GPa, in equilibrium with the iron chloride, and was held for 72 h. In order to characterise the effect of co-ordination and oxidation state on the isotope composition independently, exclusively Fe2+ minerals were substituted in: VIII-fold almandine, VI-fold ilmenite, fayalite and IV-fold chromite and hercynite. Δ57FeMin-FeCl2 increases in the order VIII ion. The composition of the VIFe2+-bearing minerals is similar to that of the aqueous FeCl2 fluid. To the degree that this represents the speciation of iron in fluids exsolving from magmas, the fractionation between them should be small, unless the iron is hosted in magnetite. By contrast, predominantly Fe2+-bearing mantle garnets should preserve a much lighter δ57Fe than their lower pressure spinel counterparts, a signature that may be reflected in partial melts from these lithologies. As the Fe-O bond lengths in fayalite and ilmenite are comparable, their isotope compositions overlap, suggesting that high Ti mare basalts acquired their heavy isotopic signature from ilmenite that crystallised late during lunar magma ocean solidification.

  12. Sulfur isotope fractionation during heterogeneous oxidation of SO2 on mineral dust

    Directory of Open Access Journals (Sweden)

    P. Hoppe

    2012-06-01

    Full Text Available Mineral dust is a major fraction of global atmospheric aerosol, and the oxidation of SO2 on mineral dust has implications for cloud formation, climate and the sulfur cycle. Stable sulfur isotopes can be used to understand the different oxidation processes occurring on mineral dust. This study presents measurements of the 34S/32S fractionation factor α34 for oxidation of SO2 on mineral dust surfaces and in the aqueous phase in mineral dust leachate. Sahara dust, which accounts for ~60% of global dust emissions and loading, was used for the experiments. The fractionation factor for aqueous oxidation in dust leachate is αleachate = 0.9917±0.0046, which is in agreement with previous measurements of aqueous SO2 oxidation by iron solutions. This fractionation factor is representative of a radical chain reaction oxidation pathway initiated by transition metal ions. Oxidation on the dust surface at subsaturated relative humidity (RH had an overall fractionation factor of αhet = 1.0096±0.0036 and was found to be almost an order of magnitude faster when the dust was simultaneously exposed to ozone, light and RH of ~40%. However, the presence of ozone, light and humidity did not influence isotope fractionation during oxidation on dust surfaces at subsaturated relative humidity. All the investigated reactions showed mass-dependent fractionation of 33S relative to 34S. A positive matrix factorization model was used to investigate surface oxidation on the different components of dust. Ilmenite, rutile and iron oxide were found to be the most reactive components, accounting for 85% of sulfate production with a fractionation factor of α34 = 1.012±0.010. This overlaps within the analytical uncertainty with the fractionation of other major atmospheric oxidation pathways such as the oxidation of SO2 by H2O2 and O3 in the aqueous phase and OH in the gas phase. Clay minerals accounted for roughly 12% of the sulfate production, and oxidation on clay minerals

  13. Investigating controls on boron isotope ratios in shallow marine carbonates

    Science.gov (United States)

    Zhang, Shuang; Henehan, Michael J.; Hull, Pincelli M.; Reid, R. Pamela; Hardisty, Dalton S.; Hood, Ashleigh v. S.; Planavsky, Noah J.

    2017-01-01

    The boron isotope-pH proxy has been widely used to reconstruct past ocean pH values. In both planktic foraminifera and corals, species-specific calibrations are required in order to reconstruct absolute values of pH, due to the prevalence of so-called vital effects - physiological modification of the primary environmental signals by the calcifying organisms. Shallow marine abiotic carbonate (e.g. ooids and cements) could conceivably avoid any such calibration requirement, and therefore provide a potentially useful archive for reconstructions in deep (pre-Cenozoic) time. However, shallow marine abiotic carbonates could also be affected by local shifts in pH caused by microbial photosynthesis and respiration, something that has up to now not been fully tested. In this study, we present boron isotope measurements from shallow modern marine carbonates, from the Bahama Bank and Belize to investigate the potential of using shallow water carbonates as pH archives, and to explore the role of microbial processes in driving nominally 'abiogenic' carbonate deposition. For Bahama bank samples, our boron-based pH estimates derived from a range of carbonate types (i.e. ooids, peloids, hardground cements, carbonate mud, stromatolitic micrite and calcified filament micrite) are higher than the estimated modern mean-annual seawater pH values for this region. Furthermore, the majority (73%) of our marine carbonate-based pH estimates fall out of the range of the estimated pre-industrial seawater pH values for this region. In shallow sediment cores, we did not observe a correlation between measured pore water pH and boron-derived pH estimates, suggesting boron isotope variability is a depositional rather than early diagenetic signal. For Belize reef cements, conversely, the pH estimates are lower than likely in situ seawater pH at the time of cement formation. This study indicates the potential for complications when using shallow marine non-skeletal carbonates as marine pH archives

  14. Adsorption as a cause for iron isotope fractionation in reduced groundwater

    Science.gov (United States)

    Teutsch, Nadya; von Gunten, Urs; Porcelli, Don; Cirpka, Olaf A.; Halliday, Alex N.

    2005-09-01

    Iron isotopes were used to investigate iron transformation processes during an in situ field experiment for removal of dissolved Fe from reduced groundwater. This experiment provided a unique setting for exploring Fe isotope fractionation in a natural system. Oxygen-containing water was injected at a test well into an aquifer containing Fe(II)-rich reduced water, leading to oxidation of Fe(II) and precipitation of Fe(III)(hydr)oxides. Subsequently, groundwater was extracted from the same well over a time period much longer than the injection time. Since the surrounding water is rich in Fe(II), the Fe(II) concentration in the extracted water increased over time. The increase was strongly retarded in comparison to a conservative tracer added to the injected solution, indicating that adsorption of Fe(II) onto the newly formed Fe(III)(hydr)oxides occurred. A series of injection-extraction (push-pull) cycles were performed at the same well. The δ 57Fe/ 54Fe of pre-experiment background groundwater (-0.57 ± 0.17 ‰) was lighter than the sediment leach of Fe(III) (-0.24 ± 0.08 ‰), probably due to slight fractionation (only ˜0.3 ‰) during microbial mediated reductive dissolution of Fe(III)(hydr)oxides present in the aquifer. During the experiment, Fe(II) was adsorbed from native groundwater drawn into the oxidized zone and onto Fe(III)(hydr)oxides producing a very light groundwater component with δ 57Fe/ 54Fe as low as -4 ‰, indicating that heavier Fe(II) is preferentially adsorbed to the newly formed Fe(III)(hydr)oxides surfaces. Iron concentrations increased with time of extraction, and δ 57Fe/ 54Fe linearly correlated with Fe concentrations (R 2 = 0.95). This pattern was reproducible over five individual cycles, indicating that the same process occurs during repeated injection/extraction cycles. We present a reactive transport model to explain the observed abiotic fractionation due to adsorption of Fe(II) on Fe(III)(hydr)oxides. The fractionation is

  15. A Martian Fractionation Line Constructed from Oxygen Isotope Analyses of Bulk Material and Minerals from SNC Meteorites

    Science.gov (United States)

    Banerjee, N. R.; Ali, A.; Jabeen, I.; Osinski, G.; Al-Rawas, A. D.; Nasir, S.; Flemming, R.; Shivak, J.; Gregory, D.

    2013-09-01

    Precise triple oxygen isotope data of SNC Martian meteorites are obtained by laser-assisted fluorination technique. Martian fractionation line is constructed using bulk material and mineral separates of SNC meteorites.

  16. Late Carboniferous to Late Permian carbon isotope stratigraphy

    DEFF Research Database (Denmark)

    Buggisch, Werner; Krainer, Karl; Schaffhauser, Maria;

    2015-01-01

    . Negative δ13C excursions are related to low-stand deposits and caused by diagenetic processes during subaerial exposure. The comparison with δ13C records from other parts of the world demonstrate that δ13C values are high in most unaltered samples, an overall negative trend during the Permian, as recently...... published, is not obvious and negative excursions related to changes in the carbon isotope composition of the global oceanic carbon pool cannot be confirmed, except for the Permian–Triassic boundary interval....

  17. Liquid-Vapor Argon Isotope Fractionation from the Triple Point to the Critical Point

    DEFF Research Database (Denmark)

    Phillips, J. T.; Linderstrøm-Lang, C. U.; Bigeleisen, J.

    1972-01-01

    are compared at the same molar volume. The isotope fractionation factor α for 36Ar∕40Ar between liquid and vapor has been measured from the triple point to the critical temperature. The results are compared with previous vapor pressure data, which cover the range 84–102°K. Although the agreement is within....... The fractionation factor approaches zero at the critical temperature with a nonclassical critical index equal to 0.42±0.02.〈∇2Uc〉/ρc in liquid argon is derived from the experimental fractionation data and calculations of 〈∇2Ug〉/ρg for a number of potential functions for gaseous argon....

  18. Molybdenum mobility and isotopic fractionation during subduction at the Mariana arc

    Science.gov (United States)

    Freymuth, Heye; Vils, Flurin; Willbold, Matthias; Taylor, Rex N.; Elliott, Tim

    2015-12-01

    -like mantle wedge. Thus we infer that the Pb and Mo budgets of the fluid component are dominated by contributions from the deeper, less altered (cooler) portion of the subducting Pacific crust. The high 98Mo/95Mo of this flux is likely caused by isotopic fractionation during dehydration and fluid flow in the slab. As a result, the residual mafic crust becomes isotopically lighter than the upper mantle from which it was derived. Our results suggest that the continental crust produced by arc magmatism should have an isotopically heavy Mo composition compared to the mantle, whilst a contribution of deep recycled oceanic crust to the sources of some ocean island basalts might be evident from an isotopically light Mo signature.

  19. Reduction of hexavalent chromium by ferrous iron: A process of chromium isotope fractionation and its relevance to natural environments

    DEFF Research Database (Denmark)

    Døssing, Lasse Nørbye; Dideriksen, Knud; Stipp, Susan Louise Svane;

    2011-01-01

    Stable chromium (Cr) isotopes can be used as a tracer for changing redox conditions in modern marine systems and in the geological record. We have investigated isotope fractionation during reduction of Cr(VI)aq by Fe(II)aq. Reduction of Cr(VI)aq by Fe(II)aq in batch experiments leads to significant...

  20. Extraction, separation, and intramolecular carbon isotope characterization of athabasca oil sands acids in environmental samples.

    Science.gov (United States)

    Ahad, Jason M E; Pakdel, Hooshang; Savard, Martine M; Simard, Marie-Christine; Smirnoff, Anna

    2012-12-04

    Here we report a novel approach to extract, isolate, and characterize high molecular weight organic acids found in the Athabasca oil sands region using preparative capillary gas chromatography (PCGC) followed by thermal conversion/elemental analysis-isotope ratio mass spectrometry (TC/EA-IRMS). A number of different "naphthenic acids" surrogate standards were analyzed as were samples from the bitumen-rich unprocessed McMurray Formation, oil sands process water, groundwater from monitoring wells, and surface water from the Athabasca River. The intramolecular carbon isotope signature generated by online pyrolysis (δ(13)C(pyr)) showed little variation (±0.6‰) within any given sample across a large range of mass fractions separated by PCGC. Oil sand, tailings ponds, and deep McMurray Formation groundwater were significantly heavier (up to ∼9‰) compared to surface water and shallow groundwater samples, demonstrating the potential use of this technique in source apportionment studies.

  1. Copper isotope fractionation during surface adsorption and intracellular incorporation by bacteria.

    Science.gov (United States)

    Navarrete, Jesica U; Borrok, David M; Viveros, Marian; Ellzey, Joanne T

    2011-02-01

    Copper isotopes may prove to be a useful tool for investigating bacteria-metal interactions recorded in natural waters, soils, and rocks. However, experimental data which attempt to constrain Cu isotope fractionation in biologic systems are limited and unclear. In this study, we utilized Cu isotopes (δ(65)Cu) to investigate Cu-bacteria interactions, including surface adsorption and intracellular incorporation. Experiments were conducted with individual representative species of Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria, as well as with wild-type consortia of microorganisms from several natural environments. Ph-dependent adsorption experiments were conducted with live and dead cells over the pH range 2.5-6. Surface adsorption experiments of Cu onto live bacterial cells resulted in apparent separation factors (Δ(65)Cu(solution-solid) = δ(65)Cu(solution) - δ(65)Cu(solid)) ranging from +0.3‰ to +1.4‰ for B. subtilis and +0.2‰ to +2.6‰ for E. coli. However, because heat-killed bacterial cells did not exhibit this behavior, the preference of the lighter Cu isotope by the cells is probably not related to reversible surface adsorption, but instead is a metabolically-driven phenomenon. Adsorption experiments with heat-killed cells yielded apparent separation factors ranging from +0.3‰ to -0.69‰ which likely reflects fractionation from complexation with organic acid surface functional group sites. For intracellular incorporation experiments the lab strains and natural consortia preferentially incorporated the lighter Cu isotope with an apparent Δ(65)Cu(solution-solid) ranging from ~+1.0‰ to +4.4‰. Our results indicate that live bacterial cells preferentially sequester the lighter Cu isotope regardless of the experimental conditions. The fractionation mechanisms involved are likely related to active cellular transport and regulation, including the reduction of Cu(II) to Cu(I). Because similar intracellular Cu

  2. Multiple sulfur isotopes fractionations associated with abiotic sulfur transformations in Yellowstone National Park geothermal springs

    Science.gov (United States)

    2014-01-01

    Background The paper presents a quantification of main (hydrogen sulfide and sulfate), as well as of intermediate sulfur species (zero-valent sulfur (ZVS), thiosulfate, sulfite, thiocyanate) in the Yellowstone National Park (YNP) hydrothermal springs and pools. We combined these measurements with the measurements of quadruple sulfur isotope composition of sulfate, hydrogen sulfide and zero-valent sulfur. The main goal of this research is to understand multiple sulfur isotope fractionation in the system, which is dominated by complex, mostly abiotic, sulfur cycling. Results Water samples from six springs and pools in the Yellowstone National Park were characterized by pH, chloride to sulfate ratios, sulfide and intermediate sulfur species concentrations. Concentrations of sulfate in pools indicate either oxidation of sulfide by mixing of deep parent water with shallow oxic water, or surface oxidation of sulfide with atmospheric oxygen. Thiosulfate concentrations are low (<6 μmol L-1) in the pools with low pH due to fast disproportionation of thiosulfate. In the pools with higher pH, the concentration of thiosulfate varies, depending on different geochemical pathways of thiosulfate formation. The δ34S values of sulfate in four systems were close to those calculated using a mixing line of the model based on dilution and boiling of a deep hot parent water body. In two pools δ34S values of sulfate varied significantly from the values calculated from this model. Sulfur isotope fractionation between ZVS and hydrogen sulfide was close to zero at pH < 4. At higher pH zero-valent sulfur is slightly heavier than hydrogen sulfide due to equilibration in the rhombic sulfur–polysulfide – hydrogen sulfide system. Triple sulfur isotope (32S, 33S, 34S) fractionation patterns in waters of hydrothermal pools are more consistent with redox processes involving intermediate sulfur species than with bacterial sulfate reduction. Small but resolved differences in ∆33S among

  3. Environmental impact and magnitude of paleosol carbonate carbon isotope excursions marking five early Eocene hyperthermals in the Bighorn Basin, Wyoming

    NARCIS (Netherlands)

    Abels, H.A.|info:eu-repo/dai/nl/304848018; Lauretano, V.; van Yperen, Anna E.; Hopman, Tarek; Zachos, J.C.; Lourens, L.J.|info:eu-repo/dai/nl/125023103; Gingerich, P.D.; Bowen, G.J.

    2016-01-01

    Transient greenhouse warming events in the Paleocene and Eocene were associated with the addition of isotopically light carbon to the exogenic atmosphere–ocean carbon system, leading to substantial environmental and biotic change. The magnitude of an accompanying carbon isotope excursion (CIE) can b

  4. Zinc and sulfur isotope variation in sphalerite from carbonate-hosted zinc deposits, Cantabria, Spain

    Science.gov (United States)

    Pašava, Jan; Tornos, Fernando; Chrastný, Vladislav

    2014-10-01

    We studied zinc and sulfur isotopes and the chemical composition of sphalerite samples from Picos de Europa (Aliva mine) and sphalerite and hydrozincite samples from La Florida mine, two carbonate-hosted Mississippi Valley-type (MVT) deposits located in northern Spain; despite being close, they are hosted in carbonatic rocks of different ages, Lower Carboniferous and Lower Cretaceous, respectively. The two generations of sphalerite at Picos de Europa show different δ66Zn values (stage 1 sphalerite +0.24 per mil and stage 2 sphalerite from -0.75 to +0.08 per mil). Both generations also differ in the sulfur isotope composition (stage 1 has δ34S = +6.6 and stage 2 has δ34S = -0.9 to +2.9 per mil) and the chemical composition (stage 1 sphalerite, compared to stage 2 sphalerite, is significantly enriched in Pb, As, Mn, Sb, slightly enriched in Ag, Ni, and Cu and depleted in Co, Ga, Tl, Te, Ge, and Sn). We suggest that Zn isotope fractionation was controlled predominantly by pH and T changes. High Zn isotope values reflect rapid precipitation of sphalerite from higher-temperature acidic fluids that carried Zn mostly as chloride species after interaction with carbonate rocks while lower Zn isotope values most likely resulted from a longer precipitation process from fluid at higher pH and decreasing T that carried dominantly Zn sulfide species. At La Florida, sphalerite samples show light 66Zn-depleted signatures with δ66Zn values from -0.80 to -0.01 per mil (mostly between -0.80 and -0.24 per mil) and δ34S values from +10.7 to +15.7 per mil without any relationship between the δ66Zn and δ34S values. Here, the variation in Zn isotope values is interpreted as related to mixing of fluids from two reservoirs. The Zn was carried by a single deep-seated and higher T (~250-320 °C) fluid, and precipitation took place after mixing with a connate S-rich fluid in a system with mH2S > mZn2+ as a result of change in pH, T, and Zn predominant species. The light δ66Zn

  5. Sulfur isotope fractionation during heterogeneous oxidation of SO2 on mineral dust

    Directory of Open Access Journals (Sweden)

    P. Hoppe

    2012-01-01

    Full Text Available Mineral dust is a major fraction of global atmospheric aerosol, and the oxidation of SO2 on mineral dust has implications for cloud formation, climate and the sulfur cycle. Stable sulfur isotopes can be used to understand the different oxidation processes occurring on mineral dust. This study presents measurements of the 34S/32S fractionation factor α34 for oxidation of SO2 on mineral dust surfaces and in the aqueous phase in mineral dust leachate. Sahara dust, which accounts for ~ 60% of global dust emissions and loading, was used for the experiments. The fractionation factor for aqueous oxidation in dust leachate is αleachate = 0.9917 ± 0.0046, which is in agreement with previous measurements of aqueous SO2 oxidation by iron solutions. This fractionation factor is representative of a radical chain reaction oxidation pathway initiated by transition metal ions. Oxidation on the dust surface at subsaturated relative humidity (RH had an overall fractionation factor of αhet = 1.0096 ± 0.0036 and was found to be almost an order of magnitude faster when the dust was simultaneously exposed to ozone, light and RH of ~ 40%. However, the presence of ozone, light and humidity did not influence isotope fractionation during oxidation on dust surfaces at subsaturated relative humidity. A positive matrix factorization model was used to investigate surface oxidation on the different components of dust. Ilmenite, rutile and iron oxide were found to be the most reactive components, accounting for 85% of sulfate production with a fractionation factor of α34 = 1.012 ± 0.010. This overlaps within the analytical uncertainty with the fractionation of other major atmospheric oxidation pathways such as the oxidation of SO2 by H2O2 and O3 in the aqueous phase and OH in the gas phase. Clay minerals accounted for roughly 12% of the sulfate production, and oxidation on clay minerals resulted in a very distinct fractionation factor of α34 = 1.085 ± 0.013. The

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

    Science.gov (United States)

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

    2017-02-01

    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

  7. Determination of the Fe(II)aq-magnetite equilibrium iron isotope fractionation factor using the three-isotope method and a multi-direction approach to equilibrium

    Science.gov (United States)

    Frierdich, Andrew J.; Beard, Brian L.; Scherer, Michelle M.; Johnson, Clark M.

    2014-04-01

    Magnetite is ubiquitous in the Earth's crust and its presence in modern marine sediments has been taken as an indicator of biogeochemical Fe cycling. Magnetite is also the most abundant Fe oxide in banded iron formations (BIFs) that have not been subjected to ore-forming alteration. Magnetite is therefore an important target of stable Fe isotope studies, and yet interpretations are currently difficult because of large uncertainties in the equilibrium stable Fe isotope fractionation factors for magnetite relative to fluids and other minerals. In this study, we utilized the three-isotope method (57Fe-56Fe-54Fe) to explore isotopic exchange via an enriched-57Fe tracer, and natural mass-dependent fractionation using 56Fe/54Fe variations, during reaction of aqueous Fe(II) (Fe(II)aq) with magnetite. Importantly, we employed a multi-direction approach to equilibrium by reacting four 57Fe-enriched Fe(II) solutions that had distinct 56Fe/54Fe ratios, which identifies changes in the instantaneous Fe isotope fractionation factor and hence identifies kinetic isotope effects. We find that isotopic exchange can be described by two 56Fe/54Fe fractionations, where an initial rapid exchange (∼66% isotopic mixing within 1 day) involved a relatively small Fe(II)aq-magnetite 56Fe/54Fe fractionation, followed by slower exchange (∼25% isotopic mixing over 50 days) that was associated with a larger Fe(II)aq-magnetite 56Fe/54Fe fractionation; this later fractionation is interpreted to approach isotopic equilibrium between Fe(II)aq and the total magnetite. All four Fe(II) solutions extrapolate to the same final equilibrium 56Fe/54Fe fractionation for Fe(II)aq-magnetite of -1.56±0.20‰ (2σ) at 22 °C. Additional experiments that synthesized magnetite via conversion of ferrihydrite by reaction with aqueous Fe(II) yield final 56Fe/54Fe fractionations that are identical to those of the exchange experiments. Our experimental results agree well with calculated fractionation factors using

  8. Extremely large fractionation of Li isotopes in a chromitite-bearing mantle sequence

    Science.gov (United States)

    Su, Ben-Xun; Zhou, Mei-Fu; Robinson, Paul T.

    2016-01-01

    We report Li isotopic compositions of olivine from the mantle sequence of the Luobusa ophiolite, southern Tibet. The olivine in the Luobusa ophiolite has Li concentrations from ~0.1 to 0.9 ppm and a broad range of δ7Li (+14 to −20‰). An inverse correlation of Li concentration and δ7Li in olivine from harzburgite suggests recent diffusive ingress of Li into the rock. Olivine from dunite enveloping podiform chromitites shows positive δ7Li values higher than those of MORB, whereas olivine from the chromitite has negative δ7Li values. Such variations are difficult to reconcile by diffusive fractionation and are thought to record the nature of the magma sources. Our results clearly indicate that the Luobusa chromitites formed from magmas with light Li isotopic compositions and that the dunites are products of melt-rock interaction. The isotopically light magmas originated by partial melting of a subducted slab after high degrees of dehydration and then penetrated the overlying mantle wedge. This study provides evidence for Li isotope heterogeneity in the mantle that resulted from subduction of a recycled oceanic component. PMID:26927333

  9. Geochemistry of brachiopods: Oxygen and carbon isotopic records of Paleozoic oceans

    Science.gov (United States)

    Veizer, Ján; Fritz, Peter; Jones, Brian

    1986-08-01

    Combined trace element and isotope studies of 319 brachiopods, covering the Ordovician to Permian time span, show that δ 13C and δ 18O in well preserved specimens varied during the Paleozoic. The overall δ 13C secular trend is in accord with the previously published observations, but its details are obscured by vital isotopic fractionation effects at generic level. Nonetheless, the results suggest that the negative correlation between marine δ 13C carbonate and δ 34S sulphate deteriorates at time scales of ⩽ 10 6 years, due to the long residence time, and thus slow response, of SO 42- in the ocean. For oxygen isotopes, all Devonian and older specimens have δ 18O of ⩽ -4%, while the well preserved Permian samples have near-present day δ 18O of about -1% (PDB). This isotopic dichotomy is probably not due to post-depositional phenomena, salinity, or biogenic fractionation effects. This leaves open the perennial arguments for a change in 18O /16O of sea water versus warmer ancient oceans. The present data are difficult to explain solely by the temperature alternative. The coincidence of the proposed shift in δ 18O with the large Late Paleozoic changes in marine 87Sr /86Sr , 13C /12C , 34S /32S , and "sea level stands" argues for a tectonic cause and for a change in 18O /16O of sea water, although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites. Whatever the precise cause, or combination of causes, the implications for tectonism and/or paleoclimatology are of first order significance.

  10. Copper in soil fractions and runoff in a vineyard catchment: Insights from copper stable isotopes.

    Science.gov (United States)

    Babcsányi, Izabella; Chabaux, François; Granet, Mathieu; Meite, Fatima; Payraudeau, Sylvain; Duplay, Joëlle; Imfeld, Gwenaël

    2016-07-01

    Understanding the fate of copper (Cu) fungicides in vineyard soils and catchments is a prerequisite to limit the off-site impact of Cu. Using Cu stable isotopes, Cu retention in soils and runoff transport was investigated in relation to the use of Cu fungicides and the hydrological conditions in a vineyard catchment (Rouffach, Haut-Rhin, France; mean slope: 15%). The δ(65)Cu values of the bulk vineyard soil varied moderately through the depth of the soil profiles (-0.12 to 0.24‰±0.08‰). The values were in the range of those of the fungicides (-0.21 to 0.11‰) and included the geogenic δ(65)Cu value of the untreated soil (0.08‰). However, δ(65)Cu values significantly differed between particle-size soil fractions (-0.37±0.10‰ in fine clays and 0.23±0.07‰ in silt). Together with the soil mineralogy, the results suggested Cu isotope fractionation primarily associated with the clay and fine clay fractions that include both SOM and mineral phases. The vegetation did not affect the Cu isotope patterns in the vineyard soils. Cu export by runoff from the catchment accounted for 1% of the applied Cu mass from 11th May to 20(th) July 2011, covering most of the Cu use period. 84% of the exported Cu mass was Cu bound to suspended particulate matter (SPM). The runoff displayed δ(65)Cu values from 0.52 to 1.35‰ in the dissolved phase (<0.45μm) compared to -0.34 to -0.02‰ in the SPM phase, indicating that clay and fine clay fractions were the main vectors of SPM-bound Cu in runoff. Overall, this study shows that Cu stable isotopes may allow identifying the Cu distribution in the soil fractions and their contribution to Cu export in runoff from Cu-contaminated catchments.

  11. First-principles investigation of equilibrium isotopic fractionation of Si and O isotopes among quartz, albite, anthorite, orthoenstatite, clinoenstatite, olivine, and zircon

    Science.gov (United States)

    Qin, T.; Wu, F.; Huang, F.; Wu, Z.

    2013-12-01

    Silicon is one of the most abundant elements in the crust and mantle. Because of advance of high precision analytical technique, Si isotope geochemistry has been widely applied into studies of a variety of important processes including planetary formation, core-mantle segregation, magmatism, and weathering of the crust. In order to better understanding Si isotope data in high temperature rock and mineral samples, it is critical to obtain equilibrium fractionation factors of Si isotopes among silicate minerals. However, experimental studies on calibrating Si isotope fractionation factors are still no available in literature. Here we used first-principles calculation based on density functional theory to investigate Si isotope fractionation factors among silicate minerals commonly occurring in magmatism in crustal level. These minerals include quartz, albite, anthorite, orthoenstatite, clinoenstatite, olivine, and zircon. We also calculated oxygen isotope fractionation factors among these minerals. Our results indicate the 18O-enrichment order among these minerals follows sequence of quartz > albite > anorthite > enstatite> zircon > olivine, showing good agreement with the data from previous experiments or natural sample measurement. For Si isotopes, our work shows that the 30Si-enrichment order in these minerals follows sequence of quartz > albite > anorthite > olivine ~ zircon > enstatite > diopside. These results are consistent with previous calculation [1] and observation from natural minerals. For example, Δ30Sianorthite-olivine = 0.2‰ at 1000oC based on our calculation, well consistent with value from the study of Skaergaard Intrusion (Δ30Siplagioclase-olivine = 0.24-27‰) [2] at same temperature. Our calculation indicates that Si isotopes can be significantly fractionated among silicate minerals during high temperature geochemical processes. References: [1] M. Méheut et al (2007), GCA 71:3170-3180. [2] P. S. Savage et al (2011), GCA 75:6124-6139.

  12. Organic carbon isotopes of the Sinian and Early Cambrian black shales on Yangtze Platform, China

    Institute of Scientific and Technical Information of China (English)

    李任伟; 卢家烂; 张淑坤; 雷加锦

    1999-01-01

    Organic matter of the Sinian and early Cambrian black shales on the Yangtze Platform belongs to the light carbon group of isotopes with the δ13C values from - 27 % to -35 % , which are lower than those of the contemporaneously deposited carbonates and phosphorites. A carbon isotope-stratified paleooceanographic model caused by upwelling is proposed, which can be used not only to interpret the characteristics of organic carbon isotopic compositions of the black shales, but also to interpret the paleogeographic difference in the organic carbon isotope compositions of various types of sedimentary rocks.

  13. Shock-Wave Heating Model for Chondrule Formation: Prevention of Isotopic Fractionation

    CERN Document Server

    Miura, H; Miura, Hitoshi; Nakamoto, Taishi

    2006-01-01

    Chondrules are considered to have much information on dust particles and processes in the solar nebula. It is naturally expected that protoplanetary disks observed in present star forming regions have similar dust particles and processes, so study of chondrule formation may provide us great information on the formation of the planetary systems. Evaporation during chondrule melting may have resulted in depletion of volatile elements in chondrules. However, no evidence for a large degree of heavy-isotope enrichment has been reported in chondrules. In order to meet this observed constraint, the rapid heating rate at temperatures below the silicate solidus is required to suppress the isotopic fractionation. We have developed a new shock-wave heating model taking into account the radiative transfer of the dust thermal continuum emission and the line emission of gas molecules and calculated the thermal history of chondrules. We have found that optically-thin shock waves for the thermal continuum emission from dust ...

  14. Allochthonous carbon hypothesis for bulk OM and n-alkane PETM carbon isotope discrepancies

    Science.gov (United States)

    Baczynski, A. A.; McInerney, F. A.; Wing, S. L.; Kraus, M. J.; Fricke, H. C.

    2011-12-01

    The Paleocene-Eocene Thermal Maximum (PETM), a period of abrupt, transient, and large-scale global warming fueled by a large release of isotopically light carbon, is a relevant analogue for episodes of rapid global warming and recovery. The PETM is recorded in pedogenic carbonate, bulk organic matter, and n-alkanes as a prominent negative carbon isotope excursion (CIE) in paleosols exposed in the Bighorn Basin, WY. Here we present a composite stable carbon isotope record from n-alkanes and dispersed soil organic δ13C records from five individual sections that span the PETM in the southeastern Bighorn Basin. Four sections are from a 10km transect in the Cabin Fork area and one section was collected at Sand Creek Divide. These five new dispersed organic carbon (DOC) isotope records are compared to the previously published Polecat Bench (Magioncalda et al. 2004) and Honeycombs (Yans et al. 2006) isotope records. The high-resolution n-alkane curve shows an abrupt, negative shift in δ13C values, an extended CIE body, and a rapid recovery to more positive δ13C values. Although the five DOC records show similarly abrupt negative shifts in δ13C values, the DOC CIEs are compressed, smaller in magnitude, and return to more positive δ13C values more gradually relative to the n-alkane record. Moreover, the stratigraphic thickness of the body of the excursion and the pattern of the recovery phase are not consistent among the five DOC records. We modeled predicted DOC δ13C values from the n-alkane record by applying enrichment factors based on modern plants to the n-alkane δ13C values. The anomaly, difference between the expected and observed DOC δ13C values, was calculated for the PETM records and compared to weight percent carbon and grain size. There is no correlation between pre- and post-PETM anomaly values and grain size or weight percent carbon. PETM anomaly values, however, do trend with both grain size and weight percent carbon. The largest PETM anomaly values

  15. Diel variations in the carbon isotope composition of respired CO2 and associated carbon sources: a review of dynamics and mechanisms

    Directory of Open Access Journals (Sweden)

    C. Werner

    2011-09-01

    Full Text Available Recent advances have improved our methodological approaches and theoretical understanding of post-photosynthetic carbon isotope fractionation processes. Nevertheless we still lack a clear picture of the origin of short-term variability in δ13C of respired CO2 (δ13Cres and organic carbon fractions on a diel basis. Closing this knowledge