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Sample records for abundance carbon isotope

  1. Abundances in red giant stars - Carbon and oxygen isotopes in carbon-rich molecular envelopes

    NASA Technical Reports Server (NTRS)

    Wannier, P. G.; Sahai, R.

    1987-01-01

    Millimeter-wave observations have been made of isotopically substituted CO toward the envelopes of 11 carbon-rich stars. In every case, C-13O was detected and model calculations were used to estimate the C-12/C-13 abundance ratio. C-17O was detected toward three, and possibly four, envelopes, with sensitive upper limits for two others. The CO-18 variant was detected in two envelopes. New results include determinations of oxygen isotopic ratios in the two carbon-rich protoplanetary nebulae CRL 26688 and CRL 618. As with other classes of red giant stars, the carbon-rich giants seem to be significantly, though variably, enriched in O-17. These results, in combination with observations in interstellar molecular clouds, indicate that current knowledge of stellar production of the CNO nuclides is far from satisfactory.

  2. Natural abundances of carbon isotopes in acetate from a coastal marine sediment

    NASA Technical Reports Server (NTRS)

    Blair, N. E.; Martens, C. S.; Des Marais, D. J.

    1987-01-01

    Measurements of the natural abundances of carbon isotopes were made in acetate samples isolated from the anoxic marine sediment of Cape Lookout Bight, North Carolina. The typical value of the total acetate carbon isotope ratio (delta 13C) was -16.1 +/- 0.2 per mil. The methyl and carboxyl groups were determined to be -26.4 +/- 0.3 and -6.0 +/- 0.3 per mil, respectively, for one sample. The isotopic composition of the acetate is thought to have resulted from isotopic discriminations that occurred during the cycling of that molecule. Measurements of this type, which have not been made previously in the natural environment, may provide information about the dominant microbial pathways in anoxic sediments as well as the processes that influence the carbon isotopic composition of biogenic methane from many sources.

  3. Carbon and nitrogen biogeochemistry in the ocean: A study using stable isotope natural abundance

    NASA Technical Reports Server (NTRS)

    Rau, G. H.; Desmarais, David J.

    1985-01-01

    Determining the biogeochemical pathways traveled by carbon and nitrogen in the ocean is fundamental to the understanding of how the ocean participates in the cycling of these elements within the biosphere. Because biological production, metabolism, and respiration can significantly alter the natural abundance of C-13 and N-15, these abundances can provide important information about the nature of these biological processes and their variability in the marine environment. The research initially seeks to characterize the spatial and temporal patterns of stable isotope abundances in organic matter, and to relate these abundances to C and N biogeochemical processes within selected areas of the northeastern Pacific Ocean.

  4. Abundances in red giant stars - Nitrogen isotopes in carbon-rich molecular envelopes

    NASA Technical Reports Server (NTRS)

    Wannier, P. G.; Andersson, B.-G.; Olofsson, H.; Ukita, N.; Young, K.

    1991-01-01

    Results are presented of millimeter- and submillimeter-wave observations of HCN and HCCCN that were made of the circmustellar envelopes of eight carbon stars, including the two protoplanetary nebulae CRL 618 and CRL 2688. The observations yield a measure of the double ratio (N-14)(C-13)/(N-15)(C-12). Measured C-12/C-13 ratios are used to estimate the N-14/N-15 abundance ratio, with the resulting lower limits in all eight envelopes and possible direct determinations in two envelopes. The two determinations and four of the remaining six lower limits are found to be in excess of the terrestrial value of N-14/N-15 = 272, indicating an evolution of the nitrogen isotope ratio, which is consistent with stellar CNO processing. Observations of thermal SiO (v = 0, J = 2-1) emission show that the Si-29/Si-28 ratio can be determined in carbon stars, and further observations are indicated.

  5. [Humus composition and stable carbon isotope natural abundance in paddy soil under long-term fertilization].

    PubMed

    Ma, Li; Yang, Lin-Zhang; Ci, En; Wang, Yan; Yin, Shi-Xue; Shen, Ming-Xing

    2008-09-01

    Soil samples were collected from an experimental paddy field with long-term (26 years) fertilization in Taihu Lake region of Jiangsu Province to study the effects of different fertilization on the organic carbon distribution and stable carbon isotope natural abundance (delta 13C) in the soil profile, and on the humus composition. The results showed that long-term fertilization increased the organic carbon content in top soil significantly, and there was a significantly negative exponential correlation between soil organic carbon content and soil depth (P < 0.01). The organic carbon content in 10-30 cm soil layer under chemical fertilizations and in 20-40 cm soil layer under organic fertilizations was relatively stable. Soil delta 13C increased gradually with soil depth, its variation range being from -24% per thousand to -28 per thousand, and had a significantly negative linear correlation with soil organic carbon content (P < 0.05). In 0-20 cm soil layer, the delta 13C in treatments organic manure (M), M + NP, M + NPK, M + straw (R) + N, and R + N decreased significantly; while in 30-50 cm soil layer, the delta 13C in all organic fertilization treatments except R + N increased significantly. Tightly combined humus (humin) was the main humus composition in the soil, occupying 50% or more, and the rest were loosely and stably combined humus. Long-term fertilization increased the content of loosely combined humus and the ratio of humic acid (HA) to fulvic acid (FA).

  6. Natural-abundance stable carbon isotopes of small-subunit ribosomal RNA (SSU rRNA) from Guaymas Basin (Mexico)

    NASA Astrophysics Data System (ADS)

    MacGregor, B. J.; Mendlovitz, H.; Albert, D.; Teske, A. P.

    2012-12-01

    Small-subunit ribosomal RNA (SSU rRNA) is a phylogenetically informative molecule found in all species. Because it is poorly preserved in most environments, it is a useful marker for active microbial populations. We are using the natural-abundance stable carbon isotopic composition of specific microbial groups to help identify the carbon substrates contributing to microbial biomass in a variety of marine environments. At Guaymas Basin, hydrothermal fluids interact with abundant sedimentary organic carbon to produce natural gas and petroleum. Where this reaches the sediment surface, it can support dense patches of seafloor life, including Beggiatoa mats. We report here on the stable carbon isotopic composition of SSU rRNA from a Beggiatoa mat transect, a cold background site, a warm site with high oil concentration, and a second Beggiatoa mat. The central part of the transect mat overlay the steepest temperature gradient, and was visually dominated by orange Beggiatoa. This was fringed by white Beggiatoa mat and bare, but still warm, sediment. Methane concentrations were saturating beneath the orange and white mats and at the oily site, lower beneath bare sediment, and below detection at the background site. Our initial hypotheses were that rRNA isotopic composition would be strongly influenced by methane supply, and that archaeal rRNA might be lighter than bacterial due to contributions from methanogens and anaerobic methane oxidizers. We used biotin-labeled oligonucleotides to capture Bacterial and Archaeal SSU rRNA for isotopic determination. Background-site rRNA was isotopically heaviest, and bacterial RNA from below 2 cm at the oily site was lightest, consistent with control by methane. Within the transect mat, however, the pattern was more complicated; at some sediment depths, rRNA from the mat periphery was isotopically lightest. Part of this may be due to the spatially and temporally variable paths followed by hydrothermal fluid, which can include horizontal

  7. Millimeter-scale variations of stable isotope abundances in carbonates from banded iron-formations in the Hamersley Group of Western Australia

    NASA Technical Reports Server (NTRS)

    Baur, M. E.; Hayes, J. M.; Studley, S. A.; Walter, M. R.

    1985-01-01

    Several diamond drill cores from formations within the Hamersley Group of Western Australia have been studied for evidence of short-range variations in the isotopic compositions of the carbonates. For a set of 32 adjacent microbands analyzed in a specimen from the Marra Mamba Iron Formation, carbon isotope compositions of individual microbands ranged from -2.8 to -19.8 per mil compared to PDB and oxygen isotope compositions ranged from 10.2 to 20.8 per mil compared to SMOW. A pattern of alternating abundances was present, with the average isotopic contrasts between adjacent microbands being 3.0 per mil for carbon and 3.1 per mil for oxygen. Similar results were obtained for a suite of 34 microbands (in four groups) from the Bruno's Band unit of the Mount Sylvia Formation. Difficulties were experienced in preparing samples of single microbands from the Dales Gorge Member of the Brockman Iron Formation, but overall isotopic compositions were in good agreement with values reported by previous authors. Chemical analyses showed that isotopically light carbon and oxygen were correlated with increased concentrations of iron. The preservation of these millimeter-scale variations in isotopic abundances is interpreted as inconsistent with a metamorphic origin for the isotopically light carbon in the BIF carbonates. A biological origin is favored for the correlated variations in 13C and Fe, and it is suggested that the 13C-depleted carbonates may derive either from fermentative metabolism or from anaerobic respiration. A model is presented in which these processes occur near the sediment-water interface and are coupled with an initial oxidative precipitation of the iron.

  8. Evaluating microbial carbon sources in Athabasca oil sands tailings ponds using natural abundance stable and radiocarbon isotopes

    NASA Astrophysics Data System (ADS)

    Ahad, J. M.; Pakdel, H.

    2013-12-01

    Natural abundance stable (δ13C) and radiocarbon (Δ14C) isotopes of phospholipid fatty acids (PLFAs) were used to evaluate the carbon sources utilized by the active microbial populations in surface sediments from Athabasca oil sands tailings ponds. The absence of algal-specific PLFAs at three of the four sites investigated, in conjunction with δ13C signatures for PLFAs that were generally within ~3‰ of that reported for oil sands bitumen (~ -30‰), indicated that the microbial communities growing on petroleum constituents were dominated by aerobic heterotrophs. The Δ14C values of PLFAs ranged from -906 to -586‰ and pointed to a significant uptake of fossil carbon (up to ~90% of microbial carbon derived from petroleum), particularly in PLFAs (e.g., cy17:0 and cy19:0) often associated with petroleum hydrocarbon degrading bacteria. The comparatively higher levels of 14C in other, less specific PLFAs (e.g., 16:0) indicated the preferential uptake of younger organic matter by the general microbial population (~50-80% of microbial carbon derived from petroleum). Since the main carbon pools in tailings sediment were essentially 'radiocarbon dead' (i.e., no detectable 14C), the principal source for this modern carbon is considered to be the Athabasca River, which provides the bulk of the water used in the bitumen extraction process. The preferential uptake of the minor amount of young and presumably more biodegradable material present in systems otherwise dominated by recalcitrant petroleum constituents has important implications for remediation strategies. On the one hand, it implies that mining-related organic contaminants could persist in the environment long after tailings pond reclamation has begun. Alternatively, it may be that the young, labile organic matter provided by the Athabasca River plays an important role in stimulating or supporting the microbial utilization of petroleum carbon in oil sands tailings ponds via co-metabolism or priming processes

  9. Changes in carbon sources fueling benthic secondary production over depth and time: coupling Chironomidae stable carbon isotopes to larval abundance.

    PubMed

    Frossard, Victor; Verneaux, Valérie; Millet, Laurent; Magny, Michel; Perga, Marie-Elodie

    2015-06-01

    Stable C isotope ratio (δ(13)C) values of chironomid remains (head capsules; HC) were used to infer changes in benthic C sources over the last 150 years for two French sub-Alpine lakes. The HCs were retrieved from a series of sediment cores from different depths. The HC δ(13)C values started to decrease with the onset of eutrophication. The HC δ(13)C temporal patterns varied among depths, which revealed spatial differences in the contribution of methanotrophic bacteria to the benthic secondary production. The estimates of the methane (CH4)-derived C contribution to chironomid biomass ranged from a few percent prior to the 1930s to up to 30 % in recent times. The chironomid fluxes increased concomitantly with changes in HC δ(13)C values before a drastic decrease due to the development of hypoxic conditions. The hypoxia reinforced the implication for CH4-derived C transfer to chironomid production. In Lake Annecy, the HC δ(13)C values were negatively correlated to total organic C (TOC) content in the sediment (Corg), whereas no relationship was found in Lake Bourget. In Lake Bourget, chironomid abundances reached their maximum with TOC contents between 1 and 1.5 % Corg, which could constitute a threshold for change in chironomid abundance and consequently for the integration of CH4-derived C into the lake food webs. Our results indicated that the CH4-derived C contribution to the benthic food webs occurred at different depths in these two large, deep lakes (deep waters and sublittoral zone), and that the trophic transfer of this C was promoted in sublittoral zones where O2 gradients were dynamic.

  10. Abundance and isotope systematics of carbon in subglacial basalts, geothermal gases and fluids from Iceland's rift zones

    NASA Astrophysics Data System (ADS)

    Barry, P. H.; Hilton, D. R.; Fueri, E.; Halldorsson, S. A.; Fischer, T. P.; Gronvold, K.

    2010-12-01

    P. H. BARRY1*, D. R. HILTON1, E. FÜRI1, S.A. HALLDÓRSON1, T.P. FISCHER2, K. GRONVOLD3 1 Scripps Institution of Oceanography, UCSD, La Jolla, California 92093, USA (*Correspondence: pbarry@ucsd.edu). 2University of New Mexico, Albuquerque, NM 87131, USA. 3University of Iceland, Askja, Sturlugata 7, IS-101, Reykjavik, Iceland Carbon dioxide (CO2) is the dominant non-aqueous volatile species found in oceanic basalts and geothermal fluids and serves as the carrier gas for trace volatiles such as He and other noble gases. The aim of this study is to identify the superimposed effects of degassing and crustal contamination on the CO2 systematics of the Icelandic hotspot in order to reveal and characterize the carbon abundance and isotopic features of the underlying mantle source. Our approach involves coupling CO2 with He, utilizing the sensitivity of 3He/4He ratios to reveal mantle and crustal inputs. We report new C-isotope (δ13C) and abundance characteristics for a suite of 47 subglacial basalts and 50 geothermal gases and fluids from Iceland. CO2 contents in hyaloclastite glasses are extremely low (10-100 ppm) and likely residual following extensive degassing whereas geothermal fluids are dominated by CO2 (>90 %). C-isotopes range from -27.2 to -3.6 ‰ (vs. PDB) for basalts and from -18.8 to 2.86 ‰ (vs. PDB) for geothermal samples (mean = -4.2 ± 3.6 ‰). CO2/3He ratios range from 108 to 1012 for basalts and from 105 to 1012 for geothermal samples: In both cases, our results extend He-CO2 relationships over a much broader range than reported previously [1]. Taken together, these data suggest that several processes including mixing, degassing, and/or syn- or post-eruptive crustal contamination may act to modify CO2 source characteristics. Equilibrium degassing models are compatible with ~75 % of the basalt data, and preliminary results indicate that initial Icelandic source characteristics are ~500 ppm CO2 and δ13C ~ -5 ‰ (vs. PDB). These values are high

  11. Carbon isotope geochemistry and geobiology

    NASA Technical Reports Server (NTRS)

    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. High Relative Abundance of Biofuel Sourced Ethanol in Precipitation in the US and Brazil Determined Using Compound Specific Stable Carbon Isotopes

    NASA Astrophysics Data System (ADS)

    Shimizu, M. S.; Felix, J. D. D.; Casas, M.; Avery, G. B., Jr.; Kieber, R. J.; Mead, R. N.; Willey, J. D.; Lane, C.

    2017-12-01

    Ethanol biofuel production and consumption have increased exponentially over the last two decades to help reduce greenhouse gas emissions. Currently, 85% of global ethanol production and consumption occurs in the US and Brazil. Increasing biofuel ethanol usage in these two countries enhances emissions of uncombusted ethanol to the atmosphere contributing to poor air quality. Although measurements of ethanol in the air and the precipitation reveal elevated ethanol concentrations in densely populated cities, other sources such as natural vegetation can contribute to emission to the atmosphere. Previous modeling studies indicated up to 12% of atmospheric ethanol is from anthropogenic emissions. Only one gas phase study in southern Florida attempted to constrain the two sources through direct isotopic measurements. The current study used a stable carbon isotope method to constrain sources of ethanol in rainwater from the US and Brazil. A method was developed using solid phase microextraction (SPME) with subsequent analysis by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). Stable carbon isotope signatures (δ13C) of vehicle ethanol emission sources for both the US (-9.8‰) and Brazil (-12.7‰) represented C4 plants as feedstock (corn and sugarcane) for biofuel production. An isotope mixing model using biofuel from vehicles (C4 plants) and biogenic (C3 plants) end-members was implemented to estimate ethanol source apportionment in the rain. We found that stable carbon isotope ratio of ethanol in the rain ranged between -22.6‰ and -12.7‰. Our results suggest that the contribution of biofuel to atmospheric ethanol can be higher than previously estimated. As biofuel usage increasing globally, it is essential to determine the relative abundance of anthropogenic ethanol in other areas of the world.

  13. Plant family identity distinguishes patterns of carbon and nitrogen stable isotope abundance and nitrogen concentration in mycoheterotrophic plants associated with ectomycorrhizal fungi.

    PubMed

    Hynson, Nicole A; Schiebold, Julienne M-I; Gebauer, Gerhard

    2016-09-01

    Mycoheterotrophy entails plants meeting all or a portion of their carbon (C) demands via symbiotic interactions with root-inhabiting mycorrhizal fungi. Ecophysiological traits of mycoheterotrophs, such as their C stable isotope abundances, strongly correlate with the degree of species' dependency on fungal C gains relative to C gains via photosynthesis. Less explored is the relationship between plant evolutionary history and mycoheterotrophic plant ecophysiology. We hypothesized that the C and nitrogen (N) stable isotope compositions, and N concentrations of fully and partially mycoheterotrophic species differentiate them from autotrophs, and that plant family identity would be an additional and significant explanatory factor for differences in these traits among species. We focused on mycoheterotrophic species that associate with ectomycorrhizal fungi from plant families Ericaceae and Orchidaceae. Published and unpublished data were compiled on the N concentrations, C and N stable isotope abundances (δ(13)C and δ(15)N) of fully (n = 18) and partially (n = 22) mycoheterotrophic species from each plant family as well as corresponding autotrophic reference species (n = 156). These data were used to calculate site-independent C and N stable isotope enrichment factors (ε). Then we tested for differences in N concentration, (13)C and (15)N enrichment among plant families and trophic strategies. We found that in addition to differentiating partially and fully mycoheterotrophic species from each other and from autotrophs, C and N stable isotope enrichment also differentiates plant species based on familial identity. Differences in N concentrations clustered at the plant family level rather than the degree of dependency on mycoheterotrophy. We posit that differences in stable isotope composition and N concentrations are related to plant family-specific physiological interactions with fungi and their environments. © The Author 2016. Published by Oxford University Press

  14. Plant family identity distinguishes patterns of carbon and nitrogen stable isotope abundance and nitrogen concentration in mycoheterotrophic plants associated with ectomycorrhizal fungi

    PubMed Central

    Hynson, Nicole A.; Schiebold, Julienne M.-I.; Gebauer, Gerhard

    2016-01-01

    Background and Aims Mycoheterotrophy entails plants meeting all or a portion of their carbon (C) demands via symbiotic interactions with root-inhabiting mycorrhizal fungi. Ecophysiological traits of mycoheterotrophs, such as their C stable isotope abundances, strongly correlate with the degree of species’ dependency on fungal C gains relative to C gains via photosynthesis. Less explored is the relationship between plant evolutionary history and mycoheterotrophic plant ecophysiology. We hypothesized that the C and nitrogen (N) stable isotope compositions, and N concentrations of fully and partially mycoheterotrophic species differentiate them from autotrophs, and that plant family identity would be an additional and significant explanatory factor for differences in these traits among species. We focused on mycoheterotrophic species that associate with ectomycorrhizal fungi from plant families Ericaceae and Orchidaceae. Methods Published and unpublished data were compiled on the N concentrations, C and N stable isotope abundances (δ13C and δ15N) of fully (n = 18) and partially (n = 22) mycoheterotrophic species from each plant family as well as corresponding autotrophic reference species (n = 156). These data were used to calculate site-independent C and N stable isotope enrichment factors (ε). Then we tested for differences in N concentration, 13C and 15N enrichment among plant families and trophic strategies. Key Results We found that in addition to differentiating partially and fully mycoheterotrophic species from each other and from autotrophs, C and N stable isotope enrichment also differentiates plant species based on familial identity. Differences in N concentrations clustered at the plant family level rather than the degree of dependency on mycoheterotrophy. Conclusions We posit that differences in stable isotope composition and N concentrations are related to plant family-specific physiological interactions with fungi and their environments. PMID

  15. Stable Carbon Isotope Ratios of Individual Pollen Grains as a Proxy for C3- Versus C4-Grass Abundance in Paleorecords: A Validation Study

    NASA Astrophysics Data System (ADS)

    Nelson, D. M.; Hu, F.; Pearson, A.

    2007-12-01

    C3 and C4 grasses have distinct influences on major biogeochemical processes and unique responses to important environmental controls. Difficulties in distinguishing between these two functional groups of grasses have hindered paleoecological studies of grass-dominated ecosystems. We recently developed a technique to analyze the stable carbon isotope composition of individual grass-pollen grains using a spooling- wire microcombustion device interfaced with an isotope-ratio mass spectrometer (Nelson et al. 2007). This technique holds promise for improving C3 and C4 grass reconstructions. It requires ~90% fewer grains than typical methods and avoids assumptions associated with mixing models. However, our previous work was based on known C3 and C4 grasses from herbarium specimens and field collections and the technique had not been test using geological samples. To test the ability of this technique to reproduce the abundance of C3 and C4 grasses on the landscape, we measured δ13C values of >1500 individual grains of grass pollen isolated from the surface sediments of 10 North American lakes that span a large gradient of C3 and C4 grass abundance. Results indicate a strong positive correlation (r=0.94) between % C4-grass pollen (derived from classifying δ13C values from single grains as C3 and C4) and the literature-reported abundance of C4 grasses on the landscape. However, the measured % C4-grass pollen shows some deviation from the actual abundance at sites with high proportions of C4 grasses. This is likely caused by uncertainty in the magnitude, composition, and variability of the analytical blank associated with these measurements. Correcting for this deviation using regression analysis improves the estimation of the abundance of C4 grasses on the landscape. Comparison of the % C4-grass pollen with C/N and δ13C measurements of total organic matter in the same lake-sediment samples illustrates the distinct advantage of grass-pollen δ13C as a proxy for

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

    PubMed

    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.

  17. Helium and Carbon Isotope and Relative Abundance Relationships in Lau Basin Basalts: Resolving Mantle Source Composition from Degassing and Contamination Effects

    NASA Astrophysics Data System (ADS)

    Vukajlovich, D. J.; Hilton, D. R.; Castillo, P. R.; Hawkins, J. W.

    2005-12-01

    The Lau Basin has multiple mantle source components including contributions from the Indian and Pacific MORB sources, Tonga-Kermadec Arc and Samoan plume. In order to characterize the volatile systematics of these various sources and to map their spatial distribution, we have sampled basaltic glasses from over 50 dredge sites covering all known spreading centers in the basin as well as many off-axis seamounts. Here, we report He abundance and isotope results obtained by crushing, in addition to CO2 released through stepped heating, from sites at the Mangatolu Triple Junction (MTJ), Rochambeau Bank (RB), Peggy Ridge, and the Northern, Eastern and Central Lau Spreading Centers. High 3He/4He ratios from RB (up to 23 RA, where RA = air 3He/4He) confirm the presence of a plume component in the northwestern Lau Basin (Poreda, EPSL, 1985). Central and Eastern Lau Spreading Center basalts have 3He/4He ratios between 8.3 and 9.4 RA, consistent with a depleted, MORB-like mantle source with little influence from slab or crustal helium. In contrast, the large range in helium isotope ratios of MTJ samples (0.85 to 7.9 RA) and the correlation between low He abundances (~2 - 3 × 10-9 cm3/g) and low helium isotope ratios suggests the volatiles in this region have been severely affected by degassing and additions of radiogenic (crustal) He. CO2 abundances and carbon isotopes for samples from RB vary from 70 to 119 ppm ([CO2]total) with δ13Cvesicle falling between -12.3 to -14.8 ‰ and δ13Cdissolved lying between -9.3 to -10.7 ‰. In the MTJ, low helium concentration samples have δ13C as low as -27.4 ‰ and [CO2]total as low as 7.6ppm; interestingly, this region also has samples with the highest measured values (up to -6.3 ‰ and 132ppm total C). Combining the carbon and helium data, CO2/3He ratios in the MTJ range from arc-like values (~1010) to sediment or crustal values (~1013) showing the superimposition of degassing and/or contamination effects on a predominant slab

  18. NITROGEN AND CARBON STABLE ISOTOPE ABUNDANCES SUPPORT THE MYCO-HETEROTROPHIC NATURE AND HOST-SPECIFICITY OF CERTAIN ACHLOROPHYLLOUS PLANTS

    EPA Science Inventory


    ? Over 400 species of achlorophyllous vascular plants are thought to obtain all carbon from symbiotic fungi. Consequently, they are termed ?myco-heterotrophic.' However, direct evidence of myco-heterotrophy in these plants is limited.
    ? During an investigation of the pat...

  19. Distribution, abundance and carbon isotopic composition of gaseous hydrocarbons in Big Soda Lake, Nevada - An alkaline, meromictic lake

    NASA Technical Reports Server (NTRS)

    Oremland, R. S.; Des Marais, D. J.

    1983-01-01

    The study of the distribution and isotopic composition of low molecular weight hydrocarbon gases at the Big Soda Lake, Nevada, has shown that while neither ethylene nor propylene were found in the lake, ethane, propane, isobutane and n-butane concentrations all increased with water column depth. It is concluded that methane has a biogenic origin in both the sediments and the anoxic water column, and that C2-C4 alkanes have biogenic origins in the monimolimnion water and shallow sediments. The changes observed in delta C-13/CH4/ and CH4/(C2H6 + C3H8) with depth in the water column and sedimeents are probably due to bacterial processes, which may include anaerobic methane oxidation and different rates of methanogenesis, and C2-to-C4 alkane production by microorganisms.

  20. Isotope-abundance variations of selected elements (IUPAC technical report)

    USGS Publications Warehouse

    Coplen, T.B.; Böhlke, J.K.; De Bievre, P.; Ding, T.; Holden, N.E.; Hopple, J.A.; Krouse, H.R.; Lamberty, A.; Peiser, H.S.; Revesz, K.; Rieder, S.E.; Rosman, K.J.R.; Roth, E.; Taylor, P.D.P.; Vocke, R.D.; Xiao, Y.K.

    2002-01-01

    Documented variations in the isotopic compositions of some chemical elements are responsible for expanded uncertainties in the standard atomic weights published by the Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry. This report summarizes reported variations in the isotopic compositions of 20 elements that are due to physical and chemical fractionation processes (not due to radioactive decay) and their effects on the standard atomic-weight uncertainties. For 11 of those elements (hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine, copper, and selenium), standard atomic-weight uncertainties have been assigned values that are substantially larger than analytical uncertainties because of common isotope-abundance variations in materials of natural terrestrial origin. For 2 elements (chromium and thallium), recently reported isotope-abundance variations potentially are large enough to result in future expansion of their atomic-weight uncertainties. For 7 elements (magnesium, calcium, iron, zinc, molybdenum, palladium, and tellurium), documented isotope variations in materials of natural terrestrial origin are too small to have a significant effect on their standard atomic-weight uncertainties. This compilation indicates the extent to which the atomic weight of an element in a given material may differ from the standard atomic weight of the element. For most elements given above, data are graphically illustrated by a diagram in which the materials are specified in the ordinate and the compositional ranges are plotted along the abscissa in scales of (1) atomic weight, (2) mole fraction of a selected isotope, and (3) delta value of a selected isotope ratio.

  1. Distribution, abundance and carbon isotopic composition of gaseous hydrocarbons in Big Soda Lake, Nevada: An alkaline, meromictic lake

    USGS Publications Warehouse

    Oremland, R.S.; Des Marais, D.J.

    1983-01-01

    Distribution and isotopic composition (??13C) of low molecular weight hydrocarbon gases were studied in Big Soda Lake (depth = 64 m), an alkaline, meromictic lake with permanently anoxic bottom waters. Methane increased with depth in the anoxic mixolimnion (depth = 20-35 m), reached uniform concentrations (55 ??M/l) in the monimolimnion (35-64 m) and again increased with depth in monimolimnion bottom sediments (>400 ??M/kg below 1 m sub-bottom depth). The ??13C[CH4] values in bottom sediment below 1 m sub-bottom depth (<-70 per mil) increased with vertical distance up the core (??13C[CH4] = -55 per mil at sediment surface). Monimolimnion ??13C[CH4] values (-55 to -61 per mil) were greater than most ??13C[CH4] values found in the anoxic mixolimnion (92% of samples had ??13C[CH4] values between -20 and -48 per mil). No significant concentrations of ethylene or propylene were found in the lake. However ethane, propane, isobutane and n-butane concentrations all increased with water column depth, with respective maximum concentrations of 260, 80, 23 and 22 nM/l encountered between 50-60 m depth. Concentrations of ethane, propane and butanes decreased with depth in the bottom sediments. Ratios of CH4 [C2H6 + C3H8] were high (250-620) in the anoxic mixolimnion, decreased to ~161 in the monimolimnion and increased with depth in the sediment to values as high as 1736. We concluded that methane has a biogenic origin in both the sediments and the anoxic water column and that C2-C4 alkanes have biogenic origins in the monimolimnion water and shallow sediments. The changes observed in ??13C[CH4] and CH4 (C2H6 + C3H8) with depth in the water column and sediments are probably caused by bacteria] processes. These might include anaerobic methane oxidation and different rates of methanogenesis and C2 to C4 alkane production by microorganisms. ?? 1983.

  2. Carbon-13 Isotopic Abundance and Concentration of Atmospheric Methane for Background Air in the Southern and Northern Hemispheres from 1978 to 1989 (NDP-049)

    DOE Data Explorer

    Stevens, C. M. [Chemical Technology Division, Argonne National Laboratory, Argonne, Illinois (USA)

    2012-01-01

    This data package presents atmospheric CH4 concentration and 13C isotopic abundance data derived from air samples collected over the period 1978-1989 at globally distributed clean-air sites. The data set comprises 201 records, 166 from the Northern Hemisphere and 35 from the Southern Hemisphere. The air samples were collected mostly in rural or marine locations remote from large sources of CH4 and are considered representative of tropospheric background conditions. The air samples were processed by isolation of CH4 from air and conversion to CO2 for isotopic analysis by isotope ratio mass spectrometry. These data represent one of the earliest records of 13C isotopic yy!measurements for atmospheric methane and have been used to refine estimates of CH4 emissions, calculate annual growth rates of emissions from changing sources, and provide evidence for changes in the rate of atmospheric removal of CH4. The data records consist of sample collection date; number of samples combined for analysis; sampling location; analysis date; CH4 concentration; 13C isotopic abundance; and flag codes to indicate outliers, repeated analyses, and other information.

  3. Raman scattering method and apparatus for measuring isotope ratios and isotopic abundances

    DOEpatents

    Harney, Robert C.; Bloom, Stewart D.

    1978-01-01

    Raman scattering is used to measure isotope ratios and/or isotopic abundances. A beam of quasi-monochromatic photons is directed onto the sample to be analyzed, and the resulting Raman-scattered photons are detected and counted for each isotopic species of interest. These photon counts are treated mathematically to yield the desired isotope ratios or isotopic abundances.

  4. Carbon isotope and abundance systematics of Icelandic geothermal gases, fluids and subglacial basalts with implications for mantle plume-related CO2 fluxes

    NASA Astrophysics Data System (ADS)

    Barry, P. H.; Hilton, D. R.; Füri, E.; Halldórsson, S. A.; Grönvold, K.

    2014-06-01

    We report new carbon dioxide (CO2) abundance and isotope data for 71 geothermal gases and fluids from both high-temperature (HT > 150 °C at 1 km depth) and low-temperature (LT < 150 °C at 1 km depth) geothermal systems located within neovolcanic zones and older segments of the Icelandic crust, respectively. These data are supplemented by CO2 data obtained by stepped heating of 47 subglacial basaltic glasses collected from the neovolcanic zones. The sample suite has been characterized previously for He-Ne (geothermal) and He-Ne-Ar (basalt) systematics (Füri et al., 2010), allowing elemental ratios to be calculated for individual samples. Geothermal fluids are characterized by a wide range in carbon isotope ratios (δ13C), from -18.8‰ to +4.6‰ (vs. VPDB), and CO2/3He values that span eight orders of magnitude, from 1 × 104 to 2 × 1012. Extreme geothermal values suggest that original source compositions have been extensively modified by hydrothermal processes such as degassing and/or calcite precipitation. Basaltic glasses are also characterized by a wide range in δ13C values, from -27.2‰ to -3.6‰, whereas CO2/3He values span a narrower range, from 1 × 108 to 1 × 1012. The combination of both low δ13C values and low CO2 contents in basalts indicates that magmas are extensively and variably degassed. Using an equilibrium degassing model, we estimate that pre-eruptive basaltic melts beneath Iceland contain ∼531 ± 64 ppm CO2 with δ13C values of -2.5 ± 1.1‰, in good agreement with estimates from olivine-hosted melt inclusions (Metrich et al., 1991) and depleted MORB mantle (DMM) CO2 source estimates (Marty, 2012). In addition, pre-eruptive CO2 compositions are estimated for individual segments of the Icelandic axial rift zones, and show a marked decrease from north to south (Northern Rift Zone = 550 ± 66 ppm; Eastern Rift Zone = 371 ± 45 ppm; Western Rift Zone = 206 ± 24 ppm). Notably, these results are model dependent, and selection of a lower

  5. Carbon isotopic fractionation in heterotrophic microbial metabolism

    NASA Technical Reports Server (NTRS)

    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.

  6. Assessment of marine-derived nutrients in the Copper River Delta, Alaska, using natural abundance of the stable isotopes of nitrogen, sulfur, and carbon

    USGS Publications Warehouse

    Kline, Thomas C.; Woody, Carol Ann; Bishop, Mary Anne; Powers, Sean P.; Knudsen, E. Eric

    2007-01-01

    We performed nitrogen, sulfur, and carbon stable isotope analysis (SIA) on maturing and juvenile anadromous sockeye and coho salmon, and periphyton in two Copper River delta watersheds of Alaska to trace salmonderived nutrients during 2003–2004. Maturing salmon were isotopically enriched relative to alternate freshwater N, S, and C sources as expected, with differences consistent with species trophic level differences, and minor system, sex, and year-to-year differences, enabling use of SIA to trace these salmon-derived nutrients. Periphyton naturally colonized, incubated, and collected using Wildco Periphtyon Samplers in and near spawning sites was 34S- and 15N-enriched, as expected, and at all freshwater sites was 13C-depleted. At nonspawning and coho-only sites, periphyton 34S and 15N was generally low. However, 34S was low enough at some sites to be suggestive of sulfate reduction, complicating the use of S isotopes. Juvenile salmon SIA ranged in values consistent with using production derived from re-mineralization as well as direct utilization, but only by a minority fraction of coho salmon. Dependency on salmon-derived nutrients ranged from relatively high to relatively low, suggesting a space-limited system. No one particular isotope was found to be superior for determining the relative importance of salmon-derived nutrients.

  7. Following Carbon Isotopes from Methane to Molecules

    NASA Astrophysics Data System (ADS)

    Freeman, K. H.

    2017-12-01

    Continuous-flow methods introduced by Hayes (Matthews and Hayes, 1978; Freeman et al., 1990; Hayes et al., 1990) for compound-specific isotope analyses (CSIA) transformed how we study the origins and fates of organic compounds. This analytical revolution launched several decades of research in which researchers connect individual molecular structures to diverse environmental and climate processes affecting their isotopic profiles. Among the first applications, and one of the more dramatic isotopically, was tracing the flow of natural methane into cellular carbon and cellular biochemical constituents. Microbial oxidation of methane can be tracked by strongly 13C-depleted organic carbon in early Earth sedimentary environments, in marine and lake-derived biomarkers in oils, and in modern organisms and their environments. These signatures constrain microbial carbon cycling and inform our understanding of ocean redox. The measurement of molecular isotopes has jumped forward once again, and it is now possible to determine isotope abundances at specific positions within increasingly complex organic structures. In addition, recent analytical developments have lowered sample sensitivity limits of CSIA to picomole levels. These new tools have opened new ways to measure methane carbon in the natural environment and within biochemical pathways. This talk will highlight how molecular isotope methods enable us to follow the fate of methane carbon in complex environments and along diverse metabolic pathways, from trace fluids to specific carbon positions within microbial biomarkers.

  8. Carbon Isotope Chemistry in Molecular Clouds

    NASA Technical Reports Server (NTRS)

    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.

  9. Organic chemistry of Murchison meteorite: Carbon isotopic fractionation

    NASA Technical Reports Server (NTRS)

    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.

  10. Reporting of nitrogen-isotope abundances (Technical Report)

    USGS Publications Warehouse

    Coplen, Tyler B.; Krouse, H.R.; Böhlke, John Karl

    1992-01-01

    To eliminate possible confusion in the reporting of nitrogen-isotope analyses, the Commission on Atomic Weights and Isotopic Abundances recommends that the value 272 be employed for the 14N/15N value of N2 in air for calculating atom percent 15N from measured δ15N values.

  11. Isotopic abundance in atom trap trace analysis

    DOEpatents

    Lu, Zheng-Tian; Hu, Shiu-Ming; Jiang, Wei; Mueller, Peter

    2014-03-18

    A method and system for detecting ratios and amounts of isotopes of noble gases. The method and system is constructed to be able to measure noble gas isotopes in water and ice, which helps reveal the geological age of the samples and understand their movements. The method and system uses a combination of a cooled discharge source, a beam collimator, a beam slower and magneto-optic trap with a laser to apply resonance frequency energy to the noble gas to be quenched and detected.

  12. Synthetic isotope mixtures for the calibration of isotope amount ratio measurements of carbon

    NASA Astrophysics Data System (ADS)

    Russe, K.; Valkiers, S.; Taylor, P. D. P.

    2004-07-01

    Synthetic isotope mixtures for the calibration of carbon isotope amount ratio measurements have been prepared by mixing carbon tetrafluoride highly enriched in 13C with carbon tetrafluoride depleted in 13C. Mixing procedures based on volumetry and gravimetry are described. The mixtures served as primary measurement standards for the calibration of isotope amount ratio measurements of the Isotopic Reference Materials PEF1, NBS22 and USGS24. Thus SI-traceable measurements of absolute carbon isotope amount ratios have been performed for the first time without any hypothesis needed for a correction of oxygen isotope abundances, such as is the case for measurements on carbon dioxide. As a result, "absolute" carbon isotope amount ratios determined via carbon tetrafluoride have smaller uncertainties than those published for carbon dioxide. From the measurements of the Reference Materials concerned, the absolute carbon isotope amount ratio of Vienna Pee Dee Belemnite (VPDB)--the hypothetical material upon which the scale for relative carbon isotope ratio measurements is based--was calculated to be R13(VPDB) = (11 101 +/- 16) × 10-6.

  13. Carbon isotopes in mollusk shell carbonates

    NASA Astrophysics Data System (ADS)

    McConnaughey, Ted A.; Gillikin, David Paul

    2008-10-01

    Mollusk shells contain many isotopic clues about calcification physiology and environmental conditions at the time of shell formation. In this review, we use both published and unpublished data to discuss carbon isotopes in both bivalve and gastropod shell carbonates. Land snails construct their shells mainly from respired CO2, and shell δ13C reflects the local mix of C3 and C4 plants consumed. Shell δ13C is typically >10‰ heavier than diet, probably because respiratory gas exchange discards CO2, and retains the isotopically heavier HCO3 -. Respired CO2 contributes less to the shells of aquatic mollusks, because CO2/O2 ratios are usually higher in water than in air, leading to more replacement of respired CO2 by environmental CO2. Fluid exchange with the environment also brings additional dissolved inorganic carbon (DIC) into the calcification site. Shell δ13C is typically a few ‰ lower than ambient DIC, and often decreases with age. Shell δ13C retains clues about processes such as ecosystem metabolism and estuarine mixing. Ca2+ ATPase-based models of calcification physiology developed for corals and algae likely apply to mollusks, too, but lower pH and carbonic anhydrase at the calcification site probably suppress kinetic isotope effects. Carbon isotopes in biogenic carbonates are clearly complex, but cautious interpretation can provide a wealth of information, especially after vital effects are better understood.

  14. Elemental, isotopic and molecular abundances in comets

    NASA Technical Reports Server (NTRS)

    Delsemme, A. H.

    1986-01-01

    The chemical composition of comet nuclei and the factors affecting it are discussed, summarizing the results of recent theoretical, experimental, and observational investigations. Consideration is given to the evidence supporting the view that the nucleus is radially differentiation (except for a thin outer layer), surface differentiation by heat processing and outgassing, and mantle buildup on an undifferentiated core. The nature of the refractory and volatile components is examined, and the elemental and isotopic compositions are given in tables and characterized. The uncertain (except for H2O) molecular composition of the volatile fraction is considered, and it is suggested that some oxides or aldehydes (such as CO, CO2, and H2CO), but no large amounts of fully hydrogenated compounds (such as CH4 and NH3) are included.

  15. Isotope-abundance variations and atomic weights of selected elements: 2016 (IUPAC Technical Report)

    USGS Publications Warehouse

    Coplen, Tyler B.; Shrestha, Yesha

    2016-01-01

    There are 63 chemical elements that have two or more isotopes that are used to determine their standard atomic weights. The isotopic abundances and atomic weights of these elements can vary in normal materials due to physical and chemical fractionation processes (not due to radioactive decay). These variations are well known for 12 elements (hydrogen, lithium, boron, carbon, nitrogen, oxygen, magnesium, silicon, sulfur, chlorine, bromine, and thallium), and the standard atomic weight of each of these elements is given by IUPAC as an interval with lower and upper bounds. Graphical plots of selected materials and compounds of each of these elements have been published previously. Herein and at the URL http://dx.doi.org/10.5066/F7GF0RN2, we provide isotopic abundances, isotope-delta values, and atomic weights for each of the upper and lower bounds of these materials and compounds.

  16. Aerosol carbon isotope composition over Baltic Sea

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

    Particulate carbonaceous matter is significant contributor to ambient particulate matter originating from intervening sources which contribution is difficult to quantify due to source diversity, chemical complexity and processes during atmospheric transport. Carbon isotope analysis can be extremely useful in source apportionment of organic matter due to the unique isotopic signatures associated with anthropocentric (fossil fuel), continental (terrestrial plants) and marine sources, and is particularly effective when these sources are mixed (Ceburnis et al., 2011;Ceburnis et al., 2016). We will present the isotope ratio measurement results of aerosol collected during the cruise in the Baltic Sea. Sampling campaign of PM10 and size segregated aerosol particles was performed on the R/V "Oceania" in October 2015. Air mass back trajectories were prevailing both from the continental and marine areas during the sampling period. The total carbon concentration varied from 1 µg/m3 to 8 µg/m3. Two end members (δ13C = -25‰ and δ13C = -28 ‰ ) were established from the total stable carbon isotope analysis in PM10 fraction. δ13C analysis in size segregated aerosol particles revealed δ13C values being highest in the 1 - 2.5 µm range (δ13C = -24.9 ‰ ) during continental transport, while lowest TC δ13C values (δ13C ≈ -27 ‰ ) were detected in the size range D50 <1 µm during stormy weather when air mass trajectory prevailed from the western direction. These measurements revealed that simplified isotope mixing model can not be applied for the aerosol source apportionment (Masalaite et al., 2015) in the perturbed marine environment. Additionally, concentration of bacteria and fungi were measured in size segregated and PM10 aerosol fraction. We were able to relate aerosol source δ13C end members with the abundance of bacteria and fungi over Baltic Sea combining air mass trajectories, stable isotope data, fungi and bacteria concentrations. Ceburnis, D., Garbaras, A

  17. Isotopic Abundances as Tracers of the Processes of Lunar Formation

    NASA Astrophysics Data System (ADS)

    Pahlevan, K.

    2011-12-01

    Ever since Apollo, isotopic abundances have been used as tracers to study lunar formation, in particular, to study the sources of the lunar material. In the last decade, however, a number of isotopic similarities have been observed between the lunar samples and the Earth's mantle such that these two reservoirs are now known to be indistinguishable from one another to high precision for a variety of isotopic tracers. This occurs against the backdrop of a Solar System that exhibits widespread heterogeneity with respect to these tracers, a situation that strongly argues that the source of the lunar material is the silicate Earth. To reconcile this observation with the fact that the Moon is thought to result from the collision of two isotopically distinct planetary bodies, a scenario has emerged in which the material from the Moon-forming impactor and the proto-Earth are homogenized in the aftermath of the giant impact. This takes place via turbulent mixing in the time after the giant impact but before lunar accretion while the Earth-Moon system exists in the form of a continuous, high-temperature fluid. Importantly, this high-temperature phase of the evolution occurs in the presence of at least two phases (liquid + vapor) making possible chemical and isotopic fractionation. While equilibrium isotopic fractionation tends to zero at high temperatures, and the post giant impact environment experiences some of the highest temperatures encountered in the Earth sciences, there are several factors that nevertheless make equilibrium isotope effects important probes of this early evolution. (1) Because the vaporization of silicates involves decomposition reactions, the bonding environment for elements in the liquid is often very different from that in the vapor. This difference makes the magnitude of isotopic fractionation intrinsically large, even at the relevant temperatures. (2) Since the isotopic composition of a silicate liquid and co-existing vapor are distinctly

  18. Report on carbon and nitrogen abundance studies

    NASA Technical Reports Server (NTRS)

    Boehm-Vitense, Erika

    1991-01-01

    The aim of the proposal was to determine the nitrogen to carbon abundance ratios from transition layer lines in stars with different T(sub eff) and luminosities. The equations which give the surface emission line fluxes and the measured ratio of the NV to CIV emission line fluxes are presented and explained. The abundance results are compared with those of photospheric abundance studies for stars in common with the photospheric investigations. The results show that the analyses are at least as accurate as the photospheric determinations. These studies can be extended to F and early G stars for which photospheric abundance determinations for giants are hard to do because molecular bands become too weak. The abundance determination in the context of stellar evolution is addressed. The N/C abundance ratio increases steeply at the point of evolution for which the convection zone reaches deepest. Looking at the evolution of the rotation velocities v sin i, a steep decrease in v sin i is related to the increasing depth of the convection zone. It is concluded that the decrease in v sin i for T(sub eff) less than or approximately = 5800 K is most probably due to the rearrangement of the angular momentum in the stars due to deep convective mixing. It appears that the convection zone is rotating with nearly depth independent angular momentum. Other research results and ongoing projects are discussed.

  19. The Abundance and Isotopic Composition of Hg in Extraterrestrial Materials

    NASA Technical Reports Server (NTRS)

    Lauretta, D. S.

    2004-01-01

    During the past three year grant period we made excellent progress in our study of the abundances and isotopic compositions of Hg and other volatile trace elements in extraterrestrial materials. As part of my startup package I received funds to construct a state-of-the-art experimental facility to study gas-solid reaction kinetics. Much of our effort was spent developing the methodology to measure the abundance and isotopic composition of Hg at ultratrace levels in solid materials. In our first study, the abundance and isotopic composition of Hg was determined in bulk samples of the Murchison (CM) and Allende (CV) carbonaceous chondrites. We have continued our study of mercury in primitive meteorites and expanded the suite of meteorites to include other members of the CM and CV chondrite group as well as CI and CO chondrites. Samples of the CI chondrite Orgueil, the CM chondrites Murray, Nogoya, and Cold Bokkeveld, the CO chondrites Kainsaz, Omans, and Isna, and the CV chondrites Vigarano, Mokoia, and Grosnaja were tested. We have developed a thermal analysis ICP-MS technique and applied it to the study of a suite of thermally labile elements (Zn, As, Se, Cd, In, Sn, Sb, Te, Hg, Au, Tl, Pb, and Bi) in geologic materials as well.

  20. Measurement of isotope abundance variations in nature by gravimetric spiking isotope dilution analysis (GS-IDA).

    PubMed

    Chew, Gina; Walczyk, Thomas

    2013-04-02

    Subtle variations in the isotopic composition of elements carry unique information about physical and chemical processes in nature and are now exploited widely in diverse areas of research. Reliable measurement of natural isotope abundance variations is among the biggest challenges in inorganic mass spectrometry as they are highly sensitive to methodological bias. For decades, double spiking of the sample with a mix of two stable isotopes has been considered the reference technique for measuring such variations both by multicollector-inductively coupled plasma mass spectrometry (MC-ICPMS) and multicollector-thermal ionization mass spectrometry (MC-TIMS). However, this technique can only be applied to elements having at least four stable isotopes. Here we present a novel approach that requires measurement of three isotope signals only and which is more robust than the conventional double spiking technique. This became possible by gravimetric mixing of the sample with an isotopic spike in different proportions and by applying principles of isotope dilution for data analysis (GS-IDA). The potential and principle use of the technique is demonstrated for Mg in human urine using MC-TIMS for isotopic analysis. Mg is an element inaccessible to double spiking methods as it consists of three stable isotopes only and shows great potential for metabolically induced isotope effects waiting to be explored.

  1. Seasonal variability in the abundance and stable carbon-isotopic composition of lipid biomarkers in suspended particulate matter from a stratified equatorial lake (Lake Chala, Kenya/Tanzania): Implications for the sedimentary record

    NASA Astrophysics Data System (ADS)

    van Bree, L. G. J.; Peterse, F.; van der Meer, M. T. J.; Middelburg, J. J.; Negash, A. M. D.; De Crop, W.; Cocquyt, C.; Wieringa, J. J.; Verschuren, D.; Sinninghe Damsté, J. S.

    2018-07-01

    We studied the distribution and stable carbon-isotopic (δ13C) composition of various lipid biomarkers in suspended particulate matter (SPM) from the water column of Lake Chala, a permanently stratified crater lake in equatorial East Africa, to evaluate their capacity to reflect seasonality in water-column processes and associated changes in the lake's phytoplankton community. This lake has large seasonal variation in water-column dynamics (stratified during wet seasons and mixing during dry seasons) with associated phytoplankton succession. We analyzed lipid biomarkers in SPM collected monthly at 5 depths (0-80 m) from September 2013 to January 2015. Seasonal variation in total phytoplankton biovolume is strongly reflected in the concentration of phytadienes, a derivative of the general photosynthetic pigment chlorophyll. The wax and wane of several specific biomarker lipids between June and December 2014 reflect pronounced phytoplankton succession after deep mixing, starting with a long and sustained chlorophyte bloom (reflected by C23:1, C25:1 and C27:1n-alkenes, and C21 and C23n-alkanes), followed by a peak in diatoms between July and October (loliolide and isololiolide), and then eustigmatophytes (C30 and C32 1,15 diols) once stratification resumes in October. Peak abundance of the C19:1n-alkene during shallow mixing of the water column in January-February 2014 can be tentatively linked to the seasonal distribution of cyanobacteria. The concentration, seasonal variability, and low δ13C values of the C28 fatty acid in the SPM suggest that this biomarker is produced in the water column of Lake Chala instead of having the typically assumed vascular plant origin. The δ13C signature of particulate carbon and all aquatic biomarkers become increasingly more negative (by up to 16‰) during mixing-induced episodes of high productivity, whereas enrichment would be expected during such blooms. This reversed fractionation may be attributed to chemically enhanced

  2. Abundant carbon in the mantle beneath Hawai`i

    NASA Astrophysics Data System (ADS)

    Anderson, Kyle R.; Poland, Michael P.

    2017-09-01

    Estimates of carbon concentrations in Earth’s mantle vary over more than an order of magnitude, hindering our ability to understand mantle structure and mineralogy, partial melting, and the carbon cycle. CO2 concentrations in mantle-derived magmas supplying hotspot ocean island volcanoes yield our most direct constraints on mantle carbon, but are extensively modified by degassing during ascent. Here we show that undegassed magmatic and mantle carbon concentrations may be estimated in a Bayesian framework using diverse geologic information at an ocean island volcano. Our CO2 concentration estimates do not rely upon complex degassing models, geochemical tracer elements, assumed magma supply rates, or rare undegassed rock samples. Rather, we couple volcanic CO2 emission rates with probabilistic magma supply rates, which are obtained indirectly from magma storage and eruption rates. We estimate that the CO2 content of mantle-derived magma supplying Hawai`i’s active volcanoes is 0.97-0.19+0.25 wt%--roughly 40% higher than previously believed--and is supplied from a mantle source region with a carbon concentration of 263-62+81 ppm. Our results suggest that mantle plumes and ocean island basalts are carbon-rich. Our data also shed light on helium isotope abundances, CO2/Nb ratios, and may imply higher CO2 emission rates from ocean island volcanoes.

  3. Abundant carbon in the mantle beneath Hawai`i

    USGS Publications Warehouse

    Anderson, Kyle R.; Poland, Michael

    2017-01-01

    Estimates of carbon concentrations in Earth’s mantle vary over more than an order of magnitude, hindering our ability to understand mantle structure and mineralogy, partial melting, and the carbon cycle. CO2 concentrations in mantle-derived magmas supplying hotspot ocean island volcanoes yield our most direct constraints on mantle carbon, but are extensively modified by degassing during ascent. Here we show that undegassed magmatic and mantle carbon concentrations may be estimated in a Bayesian framework using diverse geologic information at an ocean island volcano. Our CO2 concentration estimates do not rely upon complex degassing models, geochemical tracer elements, assumed magma supply rates, or rare undegassed rock samples. Rather, we couple volcanic CO2 emission rates with probabilistic magma supply rates, which are obtained indirectly from magma storage and eruption rates. We estimate that the CO2content of mantle-derived magma supplying Hawai‘i’s active volcanoes is 0.97−0.19+0.25 wt%—roughly 40% higher than previously believed—and is supplied from a mantle source region with a carbon concentration of 263−62+81 ppm. Our results suggest that mantle plumes and ocean island basalts are carbon-rich. Our data also shed light on helium isotope abundances, CO2/Nb ratios, and may imply higher CO2 emission rates from ocean island volcanoes.

  4. The Abundance and Isotopic Composition of Hg in Extraterrestrial Materials

    NASA Technical Reports Server (NTRS)

    Blum, J. D.; Klaue, Bjorn

    2005-01-01

    During the three year grant period we made excellent progress in our study of the abundances and isotopic compositions of Hg and other volatile trace elements in extraterrestrial materials. At the time the grant started, our collaborating PI, Dante Lauretts, was a postdoctoral research associate working with Peter Buseck at Arizona State University. The work on chondritic Hg was done in collaboration with Dante Lauretta and Peter Buseck and this study was published in Lauretta et a1 (2001a). In July, 2001 Dante Lauretta accepted a position as an Assistant Professor in the Lunar and Planetary Laboratory at the University of Arizona. His funding was transferred and this grant has supported much of his research activities during his first two years at the U of A. Several other papers are in preparation and will be published soon. We presented papers on this topic at Goldschmidt Conferences, the Lunar and Planetary Science Conferences, and the Annual Meetings of the Meteoritical Society. The work done under this grant has spurred several new directions of inquiry, which we are still pursuing. Included in this paper are the studies of bulk abundances and isotopic compositions of metreoritic Mercury, and the development of a thermal analysis ICP-MS technique applied to thermally liable elements.

  5. Elemental and isotopic abundances in the solar wind

    NASA Technical Reports Server (NTRS)

    Geiss, J.

    1972-01-01

    The use of collecting foils and lunar material to assay the isotopic composition of the solar wind is reviewed. Arguments are given to show that lunar surface correlated gases are likely to be most useful in studying the history of the solar wind, though the isotopic abundances are thought to give a good approximation to the solar wind composition. The results of the analysis of Surveyor material are also given. The conditions leading to a significant component of the interstellar gas entering the inner solar system are reviewed and suggestions made for experimental searches for this fraction. A critical discussion is given of the different ways in which the basic solar composition could be modified by fractionation taking place between the sun's surface and points of observation such as on the Moon or in interplanetary space. An extended review is made of the relation of isotopic and elemental composition of the interplanetary gas to the dynamic behavior of the solar corona, especially processes leading to fractionation. Lastly, connection is made between the subject of composition, nucleosynthesis and the convective zone of the sun, and processes leading to modification of initial accretion of certain gases on the Earth and Moon.

  6. Carbon isotope effects associated with autotrophic acetogenesis

    NASA Technical Reports Server (NTRS)

    Gelwicks, J. T.; Risatti, J. B.; Hayes, J. M.

    1989-01-01

    The carbon kinetic isotope effects associated with synthesis of acetate from CO2 and H2 during autotrophic growth of Acetobacterium woodii at 30 degrees C have been measured by isotopic analyses of CO2, methyl-carbon, and total acetate. Closed systems allowing construction of complete mass balances at varying stages of growth were utilized, and the effects of the partitioning of carbon between CO2 and HCO3- were taken account. For the overall reaction, total carbonate --> total acetate, isotope effects measured in replicate experiments ranged from -59.0 +/- 0.9% to -57.2 +/- 2.3%. Taking into account all measurements, the weighted mean and standard deviation are -58.6 +/- 0.7%. There is no evidence for intramolecular ordering in the acetate. The carbon isotopic composition of sedimentary acetate, otherwise expected to be near that of sedimentary organic carbon, is likely to be depleted in environments in which autotrophic acetogenesis is occurring.

  7. The carbon isotopic composition of ecosystem breath

    NASA Astrophysics Data System (ADS)

    Ehleringer, J.

    2008-05-01

    At the global scale, there are repeatable annual fluctuations in the concentration and isotopic composition of atmospheric carbon dioxide, sometimes referred to as the "breathing of the planet". Vegetation components within ecosystems fix carbon dioxide through photosynthesis into stable organic compounds; simultaneously both vegetation and heterotrophic components of the ecosystem release previously fixed carbon as respiration. These two-way fluxes influencing carbon dioxide exchange between the biosphere and the atmosphere impact both the concentration and isotopic composition of carbon dioxide within the convective boundary layer. Over space, the compounding effects of gas exchange activities from ecosystems become reflected in both regional and global changes in the concentration and isotopic composition of atmospheric carbon dioxide. When these two parameters are plotted against each other, there are significant linear relationships between the carbon isotopic composition and inverse concentration of atmospheric carbon dioxide. At the ecosystem scale, these "Keeling plots" intercepts of C3-dominated ecosystems describe the carbon isotope ratio of biospheric gas exchange. Using Farquhar's model, these carbon isotope values can be translated into quantitative measures of the drought-dependent control of photosynthesis by stomata as water availability changes through time. This approach is useful in aggregating the influences of drought across regional landscapes as it provides a quantitative measure of stomatal influence on photosynthetic gas exchange at the ecosystem-to-region scales. Multi-year analyses of the drought-dependent trends across terrestrial ecosystems show a repeated pattern with water stress in all but one C3-ecosystem type. Ecosystems that are dominated by ring-porous trees appear not to exhibit a dynamic stomatal response to water stress and therefore, there is little dependence of the carbon isotope ratio of gas exchange on site water balance

  8. Potassium isotope abundances in Australasian tektites and microtektites.

    NASA Astrophysics Data System (ADS)

    Herzog, G. F.; O'D. Alexander, C. M.; Berger, E. L.; Delaney, J. S.; Glass, B. P.

    2008-10-01

    We report electron microprobe determinations of the elemental compositions of 11 Australasian layered tektites and 28 Australasian microtektites; and ion microprobe determinations of the 41K/39K ratios of all 11 tektites and 13 of the microtektites. The elemental compositions agree well with literature values, although the average potassium concentrations measured here for microtektites, 1.1 1.6 wt%, are lower than published average values, 1.9 2.9 wt%. The potassium isotope abundances of the Australasian layered tektites vary little. The average value of δ41K, 0.02 ± 0.12‰ (1σ mean), is indistinguishable from the terrestrial value (= 0 by definition) as represented by our standard, thereby confirming four earlier tektite analyses of Humayun and Koeberl (2004). In agreement with those authors, we conclude that evaporation has significantly altered neither the isotopic nor the elemental composition of Australasian layered tektites for elements less volatile than potassium. Although the average 41K/39K ratio of the microtektites, 1.1 ± 1.7‰ (1σ mean), is also statistically indistinguishable from the value for the standard, the individual ratios vary over a very large range, from -10.6 ± 1.4‰ to +13.8 ± 1.5‰ and at least three of them are significantly different from zero. We interpret these larger variations in terms of the evaporation of isotopically light potassium; condensation of potassium in the vapor plume; partial or complete stirring and quenching of the melts; and the possible uptake of potassium from seawater. That the average 41K/39K ratio of the microtektites equals the terrestrial value suggests that the microtektite-forming system was compositionally closed with respect to potassium and less volatile elements. The possibility remains open that 41K/39K ratios of microtektites vary systematically with location in the strewn field.

  9. Carbon and its isotopes in mid-oceanic basaltic glasses

    USGS Publications Warehouse

    Des Marais, D.J.; Moore, J.G.

    1984-01-01

    Three carbon components are evident in eleven analyzed mid-oceanic basalts: carbon on sample surfaces (resembling adsorbed gases, organic matter, or other non-magmatic carbon species acquired by the glasses subsequent to their eruption), mantle carbon dioxide in vesicles, and mantle carbon dissolved in the glasses. The combustion technique employed recovered only reduced sulfur, all of which appears to be indigenous to the glasses. The dissolved carbon concentration (measured in vesicle-free glass) increases with the eruption depth of the spreading ridge, and is consistent with earlier data which show that magma carbon solubility increases with pressure. The total glass carbon content (dissolved plus vesicular carbon) may be controlled by the depth of the shallowest ridge magma chamber. Carbon isotopic fractionation accompanies magma degassing; vesicle CO2 is about 3.8??? enriched in 13C, relative to dissolved carbon. Despite this fractionation, ??13CPDB values for all spreading ridge glasses lie within the range -5.6 and -7.5, and the ??13CPDB of mantle carbon likely lies between -5 and -7. The carbon abundances and ??13CPDB values of Kilauea East Rift glasses apparently are influenced by the differentiation and movement of magma within that Hawaiian volcano. Using 3He and carbon data for submarine hydrothermal fluids, the present-day mid-oceanic ridge mantle carbon flux is estimated very roughly to be about 1.0 ?? 1013 g C/yr. Such a flux requires 8 Gyr to accumulate the earth's present crustal carbon inventory. ?? 1984.

  10. Martian carbon dioxide: Clues from isotopes in SNC meteorites

    NASA Technical Reports Server (NTRS)

    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.

  11. Exotic Structure of Carbon Isotopes

    NASA Astrophysics Data System (ADS)

    Suzuki, Toshio; Sagawa, Hiroyuki; Hagino, Kouichi

    2003-12-01

    Ground state properties of C isotopes, deformation and elecromagnetic moments, as well as electric dipole transition strength are investigated. We first study the ground state properties of C isotopes using a deformed Hartree-Fock (HF) + BCS model with Skyrme interactions. Isotope dependence of the deformation properties is investigated. Shallow deformation minima are found in several neutron-rich C isotopes. It is also shown that the deformation minima appear in both the oblate and the prolate sides in 17C and 19C having almost the same binding energies. Next, we carry out shell model calculations to study electromagnetic moments and electric dipole transitions of 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 deformation and spin-parities of the ground states of these nuclei. Electric dipole states of C isotopes are studied focusing on the interplay between low energy Pigmy strength and giant dipole resonances. Low peak energies, two-peak structure and large widths of the giant resonances show deformation effects. Calculated transition strength below dipole giant resonance in heavier C isotopes than 15C is found to exhaust 12 ~ 15% of the Thomas-Reiche-Kuhn sum rule value and 50 ~ 80% of the cluster sum rule value.

  12. Evidence from carbon isotope measurements for diverse origins of sedimentary hydrocarbons

    NASA Technical Reports Server (NTRS)

    Freeman, K. H.; Hayes, J. M.; Trendel, J. M.; Albrecht, P.

    1990-01-01

    The organic matter found in sedimentary rocks must derive from many sources; not only from ancient primary producers but also from consumers and secondary producers. In all of these organisms, isotope effects can affect the abundance and distribution of 13C in metabolites. Here, by using an improved form of a previously described technique in which the effluent of a gas chromatograph is continuously analysed isotopically, we report evidence of the diverse origins of sedimentary organic matter. The record of 13C abundances in sedimentary carbonate and total organic carbon can be interpreted in terms of variations in the global carbon cycle. Our results demonstrate, however, that isotope variations within sedimentary organic mixtures substantially exceed those observed between samples of total organic carbon. Resolution of isotope variations at the molecular level offers a new and convenient means of refining views both of localized palaeoenvironments and of control mechanisms within the global carbon cycle.

  13. Gluconeogenesis from labeled carbon: estimating isotope dilution

    SciTech Connect

    Kelleher, J.K.

    1986-03-01

    To estimate the rate of gluconeogenesis from steady-state incorporation of labeled 3-carbon precursors into glucose, isotope dilution must be considered so that the rate of labeling of glucose can be quantitatively converted to the rate of gluconeogenesis. An expression for the value of this isotope dilution can be derived using mathematical techniques and a model of the tricarboxylic acid (TCA) cycle. The present investigation employs a more complex model than that used in previous studies. This model includes the following pathways that may affect the correction for isotope dilution: 1) flux of 3-carbon precursor to the oxaloacetate pool via acetyl-CoAmore » and the TCA cycle; 2) flux of 4- or 5-carbon compounds into the TCA cycle; 3) reversible flux between oxaloacetate (OAA) and pyruvate and between OAA and fumarate; 4) incomplete equilibrium between OAA pools; and 5) isotope dilution of 3-carbon tracers between the experimentally measured pool and the precursor for the TCA-cycle OAA pool. Experimental tests are outlined which investigators can use to determine whether these pathways are significant in a specific steady-state system. The study indicated that flux through these five pathways can significantly affect the correction for isotope dilution. To correct for the effects of these pathways an alternative method for calculating isotope dilution is proposed using citrate to relate the specific activities of acetyl-CoA and OAA.« less

  14. Stable isotope analysis of Dacryoconarid carbonate microfossils: a new tool for Devonian oxygen and carbon isotope stratigraphy.

    PubMed

    Frappier, Amy Benoit; Lindemann, Richard H; Frappier, Brian R

    2015-04-30

    Dacryoconarids are extinct marine zooplankton known from abundant, globally distributed calcite microfossils in the Devonian, but their shell stable isotope composition has not been previously explored. Devonian stable isotope stratigraphy is currently limited to less common invertebrates or bulk rock analyses of uncertain provenance. As with Cenozoic planktonic foraminifera, isotopic analysis of dacryoconarid shells could facilitate higher-resolution, geographically widespread stable isotope records of paleoenvironmental change, including marine hypoxia events, climate changes, and biocrises. We explored the use of Dacryoconarid isotope stratigraphy as a viable method in interpreting paleoenvironments. We applied an established method for determining stable isotope ratios (δ(13) C, δ(18) O values) of small carbonate microfossils to very well-preserved dacryoconarid shells. We analyzed individual calcite shells representing five common genera using a Kiel carbonate device coupled to a MAT 253 isotope ratio mass spectrometer. Calcite shell δ(13) C and δ(18) O values were compared by taxonomic group, rock unit, and locality. Single dacryoconarid calcite shells are suitable for stable isotope analysis using a Kiel-IRMS setup. The dacryoconarid shell δ(13) C values (-4.7 to 2.3‰) and δ(18) O values (-10.3 to -4.8‰) were consistent across taxa, independent of shell size or part, but varied systematically through time. Lower fossil δ(18) O values were associated with warmer water temperature and more variable δ(13) C values were associated with major bioevents. Dacryoconarid δ(13) C and δ(18) O values differed from bulk rock carbonate values. Dacryoconarid individual microfossil δ(13) C and δ(18) O values are highly sensitive to paleoenvironmental changes, thus providing a promising avenue for stable isotope chemostratigraphy to better resolve regional to global paleoceanographic changes throughout the upper Silurian to the upper Devonian. Our results

  15. New Carbonate Standard Reference Materials for Boron Isotope Geochemistry

    NASA Astrophysics Data System (ADS)

    Stewart, J.; Christopher, S. J.; Day, R. D.

    2015-12-01

    The isotopic composition of boron (δ11B) in marine carbonates is well established as a proxy for past ocean pH. Yet, before palaeoceanographic interpretation can be made, rigorous assessment of analytical uncertainty of δ11B data is required; particularly in light of recent interlaboratory comparison studies that reported significant measurement disagreement between laboratories [1]. Well characterised boron standard reference materials (SRMs) in a carbonate matrix are needed to assess the accuracy and precision of carbonate δ11B measurements throughout the entire procedural chemistry; from sample cleaning, to ionic separation of boron from the carbonate matrix, and final δ11B measurement by multi-collector inductively coupled plasma mass spectrometry. To date only two carbonate reference materials exist that have been value-assigned by the boron isotope measurement community [2]; JCp-1 (porites coral) and JCt-1 (Giant Clam) [3]. The National Institute of Standards and Technology (NIST) will supplement these existing standards with new solution based inorganic carbonate boron SRMs that replicate typical foraminiferal and coral B/Ca ratios and δ11B values. These new SRMs will not only ensure quality control of full procedural chemistry between laboratories, but have the added benefits of being both in abundant supply and free from any restrictions associated with shipment of biogenic samples derived from protected species. Here we present in-house δ11B measurements of these new boron carbonate SRM solutions. These preliminary data will feed into an interlaboratory comparison study to establish certified values for these new NIST SRMs. 1. Foster, G.L., et al., Chemical Geology, 2013. 358(0): p. 1-14. 2. Gutjahr, M., et al., Boron Isotope Intercomparison Project (BIIP): Development of a new carbonate standard for stable isotopic analyses. Geophysical Research Abstracts, EGU General Assembly 2014, 2014. 16(EGU2014-5028-1). 3. Inoue, M., et al., Geostandards and

  16. Site-Specific Carbon Isotopes in Organics

    NASA Astrophysics Data System (ADS)

    Piasecki, A.; Eiler, J. M.

    2012-12-01

    Natural organic molecules exhibit a wide range of internal site-specific isotope variation (i.e., molecules with same isotopic substitution type but different site). Such variations are generally unconstrained by bulk isotopic measurements. If known, site-specific variations might constrain temperatures of equilibrium, mechanisms of formation or consumption reactions, and possibly other details. For example, lipids can exhibit carbon isotope differences of up to 30‰ between adjacent carbon sites as a result of fractionations arising during decarboxylation of pyruvate and other steps in lipid biosynthesis(1). We present a method for site-specific carbon isotope analysis of propane, based on high-resolution, multi-collector gas source mass spectrometry, using a novel prototype instrument - the Thermo MAT 253 Ultra. This machine has an inlet system and electron bombardment ion source resembling those in conventional stable isotope gas source mass spectrometers, and the energy filter, magnet, and detector array resembling those in multi-collector ICPMS and TIMS. The detector array has 7 detector positions, 6 of which are movable, and each of which can collect ions with either a faraday cup (read through amplifiers ranging from 107-1012 ohms) or an SEM. High mass resolving power (up to 27,000, MRP = M/dM definition) is achieved through a narrow entrance slit, adjustable from 250 to 5 μm. Such resolution can cleanly separate isobaric interferences between isotopologues of organic molecules having the same cardinal mass (e.g., 13CH3 and 12CH2D). We use this technology to analyze the isotopologues and fragments of propane, and use such data to solve for the site-specific carbon isotope fractionation. By measuring isotopologues of both the one-carbon (13CH3) and the two-carbon (13C12CH4) fragment ion, we can solve for both bulk δ13C and the difference in δ13C between the terminal and central carbon position. We tested this method by analyzing mixtures between natural

  17. Carbon and sulfur distributions and abundances in lunar fines

    NASA Technical Reports Server (NTRS)

    Gibson, E. K., Jr.; Moore, G. W.

    1973-01-01

    Total sulfur abundances have been determined for 20 Apollo 14, 15, and 16 soil samples and one Apollo 14 breccia. Sulfur concentrations range from 474 to 844 microg S/g. Volatilization experiments on selected samples have been carried out using step-wise heating. Sample residues have been analyzed for their total carbon and sulfur abundances to establish the material balance in lunar fines for these two elements. Volatilization experiments have established that between 31 to 54 microg C/g remains in soils which have been heated at 1100 C for 24 hours under vacuum. The residual carbon is believed to be indigenous lunar carbon whereas all forms of carbon lost from samples below 1100 C is extralunar carbon. Total carbon and sulfur abundances taken from the literature have been used to show the depletion of volatile elements with increasing grade for the Apollo 14 breccias.

  18. Carbon and nitrogen abundances determined from transition layer lines

    NASA Technical Reports Server (NTRS)

    Boehm-Vitense, Erika; Mena-Werth, Jose

    1992-01-01

    The possibility of determining relative carbon, nitrogen, and silicon abundances from the emission-line fluxes in the lower transition layers between stellar chromospheres and coronae is explored. Observations for main-sequence and luminosity class IV stars with presumably solar element abundances show that for the lower transition layers Em = BT sup -gamma. For a given carbon abundance the constants gamma and B in this relation can be determined from the C II and C IV emission-line fluxes. From the N V and S IV lines, the abundances of these elements relative to carbon can be determined from their surface emission-line fluxes. Ratios of N/C abundances determined in this way for some giants and supergiants agree within the limits of errors with those determined from molecular bands. For giants, an increase in the ratio of N/C at B-V of about 0.8 is found, as expected theoretically.

  19. Isotopic inferences of ancient biochemistries - Carbon, sulfur, hydrogen, and nitrogen

    NASA Technical Reports Server (NTRS)

    Schidlowski, M.; Hayes, J. M.; Kaplan, I. R.

    1983-01-01

    In processes of biological incorporation and subsequent biochemical processing sizable isotope effects occur as a result of both thermodynamic and kinetic fractionations which take place during metabolic and biosynthetic reactions. In this chapter a review is provided of earlier work and recent studies on isotope fractionations in the biogeochemical cycles of carbon, sulfur, hydrogen, and nitrogen. Attention is given to the biochemistry of carbon isotope fractionation, carbon isotope fractionation in extant plants and microorganisms, isotope fractionation in the terrestrial carbon cycle, the effects of diagenesis and metamorphism on the isotopic composition of sedimentary carbon, the isotopic composition of sedimentary carbon through time, implications of the sedimentary carbon isotope record, the biochemistry of sulfur isotope fractionation, pathways of the biogeochemical cycle of nitrogen, and the D/H ratio in naturally occurring materials.

  20. Atmospheric Trace Gas Abundances and Stable Isotope Ratios via IR-LIF

    NASA Technical Reports Server (NTRS)

    Blake, Geoffrey A.

    2004-01-01

    We propose to develop new technologies with support provided by PIDDP that will enable the in situ measurements of abundances and stable isotope ratios in important radiatively and biogenically active gases such as carbon dioxide, carbon monoxide, water, methane, nitrous oxide, and hydrogen sulfide to very high precision (0.1 per mil or better for the isotopic ratios, for example). Such measurements, impossible at present, could provide pivotal new constraints on the global (bio)geochemical budgets of these critical species, and could also be used to examine the dynamics of atmospheric transport on Mars, Titan, and other solar system bodies. We believe the combination of solid state light sources with imaging of the IR laser induced fluorescence (IR-LIF) via newly available detector arrays will make such in situ measurements possible for the first time. Even under ambient terrestrial conditions, the LIF yield from vibrational excitation of species such as water and carbon dioxide should produce emission measures well in excess of ten billion photons/sec from samples volumes of order 1 c.c. These count rates can, in principle, yield detection limits into the sub-ppt range that are required for the in situ isotopic study of atmospheric trace gases. While promising, such technologies are relatively immature, but developing rapidly, and there are a great many uncertainties regarding their applicability to in situ IR-LIF planetary studies. We therefore feel PIDDP support will be critical to developing these new tools, and propose a three-year program to combine microchip near-IR lasers with low background detection axes and state-of-the-art HgCdTe detectors developed for astronomical spectroscopy to investigate the sensitivity of IR-LIF under realistic planetary conditions, to optimize the optical pumping and filtering schemes for important species, and to apply the spectrometer to the non-destructive measurement of stable isotopes in a variety of test samples. These

  1. Fluorine Abundances in AGB Carbon Stars: New Results?

    NASA Astrophysics Data System (ADS)

    Abia, C.; de Laverny, P.; Recio-Blanco, A.; Domínguez, I.; Cristallo, S.; Straniero, O.

    2009-09-01

    A recent reanalysis of the fluorine abundance in three Galactic Asymptotic Giant Branch (AGB) carbon stars (TX Psc, AQ Sgr and R Scl) by Abia et al. (2009) results in estimates of fluorine abundances systematically lower by ~0.8 dex on average, with respect to the sole previous estimates by Jorissen, Smith & Lambert (1992). The new F abundances are in better agreement with the predictions of full-network stellar models of low-mass (<3 Msolar) AGB stars.

  2. Coprecipitation and isotopic fractionation of boron in modern biogenic carbonates

    SciTech Connect

    Vengosh, A.; Chivas, A.R.; McCulloch, M.T.

    1991-10-01

    The abundances and isotopic composition of boron in modern, biogenic calcareous skeletons from the Gulf of Elat, Israel, the Great Barrier Reef, Australia, and in deep-sea sediments have been examined by negative thermal-ionization mass spectrometry. The selected species (Foraminifera, Pteropoda, corals, Gastropoda, and Pelecypoda) yield large variations in boron concentration that range from 1 ppm in gastropod shells to 80 ppm in corals. The variations of {delta}{sup 11}B may be controlled by isotopic exchange of boron species in which {sup 10}B is preferentially partitioned into the tetrahedral species, and coprecipitation of different proportions of trigonal and tetrahedral species in themore » calcium carbonates. The B content and {delta}{sup 11}B values of deep-sea sediments, Foraminifera tests, and corals are used to estimate the global oceanic sink of elemental boron by calcium carbonate deposition. As a result of enrichment of B in corals, a substantially higher biogenic sink of 6.4 {plus minus} 0.9 {times} 10{sup 10} g/yr is calculated for carbonates. This is only slightly lower than the sink for desorbable B in marine sediments (10 {times} 10{sup 10} g/yr) and approximately half that of altered oceanic crust (14 {times} 10{sup 10} g/yr). Thus, carbonates are an important sink for B in the oceans being {approximately}20% of the total sinks. The preferential incorporation of {sup 10}B into calcium carbonate results in oceanic {sup 11}B-enrichment, estimated as 1.2 {plus minus} 0.3 {times} 10{sup 12} per mil {center dot} g/yr. The boron-isotope composition of authigenic, well-preserved carbonate skeletons may provide a useful tool to record secular boron-isotope variations in seawater at various times in the geological record.« less

  3. Carbon isotope fractionation during microbial methane oxidation

    NASA Astrophysics Data System (ADS)

    Barker, James F.; Fritz, Peter

    1981-09-01

    Methane, a common trace constituent of groundwaters, occasionally makes up more than 20% of the total carbon in groundwaters1,2. In aerobic environments CH4-rich waters can enable microbial food chain supporting a mixed culture of bacteria with methane oxidation as the primary energy source to develop3. Such processes may influence the isotopic composition of the residual methane and because 13C/12C analyses have been used to characterize the genesis of methanes found in different environments, an understanding of the magnitude of such effects is necessary. In addition, carbon dioxide produced by the methane-utilizing bacteria can be added to the inorganic carbon pool of affected groundwaters. We found carbon dioxide experimentally produced by methane-utilizing bacteria to be enriched in 12C by 5.0-29.6‰, relative to the residual methane. Where methane-bearing groundwaters discharged into aerobic environments microbial methane oxidation occurred, with the residual methane becoming progressively enriched in 13C. Various models have been proposed to explain the 13C/12C and 14C content of the dissolved inorganic carbon (DIC) of groundwaters in terms of additions or losses during flow in the subsurface4,5. The knowledge of both stable carbon isotope ratios in various pools and the magnitude of carbon isotope fractionation during various processes allows geochemists to use the 13C/12C ratio of the DIC along with water chemistry to estimate corrected 14C groundwater ages4,5. We show here that a knowledge of the carbon isotope fractionation between CH4 and CO2 during microbial methane-utilization could modify such models for application to groundwaters affected by microbial methane oxidation.

  4. Anatomy of a cluster IDP. Part 2: Noble gas abundances, trace element geochemistry, isotopic abundances, and trace organic chemistry of several fragments from L2008#5

    NASA Technical Reports Server (NTRS)

    Thomas, K. L.; Clemett, S. J.; Flynn, G. J.; Keller, L. P.; Mckay, David S.; Messenger, S.; Nier, A. O.; Schlutter, D. J.; Sutton, S. R.; Walker, R. M.

    1994-01-01

    The topics discussed include the following: noble gas content and release temperatures; trace element abundances; heating summary of cluster fragments; isotopic measurements; and trace organic chemistry.

  5. Determination of lithium isotopes at natural abundance levels by atomic absorption spectrometry

    USGS Publications Warehouse

    Meier, A.L.

    1982-01-01

    The relationships of the absorption of 6Li and 7Li hollow cathode lamp emissions are used to determine lithium isotopic composition in the natural abundance range of geologic materials. Absorption was found to have a nonlinear dependence upon total lithium concentration and isotopic composition. A method using nonlinear equations to describe the relationship of the absorption of 6Li and 7Li lamp radiation is proposed as a means of calculating isotopic composition that is independent of total lithium concentration.

  6. Laser ablation molecular isotopic spectrometry of carbon isotopes

    NASA Astrophysics Data System (ADS)

    Bol‧shakov, Alexander A.; Mao, Xianglei; Jain, Jinesh; McIntyre, Dustin L.; Russo, Richard E.

    2015-11-01

    Quantitative determination of carbon isotopes using Laser Ablation Molecular Isotopic Spectrometry (LAMIS) is described. Optical emission of diatomic molecules CN and C2 is used in these measurements. Two quantification approaches are presented: empirical calibration of spectra using a set of reference standards and numerical fitting of a simulated spectrum to the experimental one. Formation mechanisms of C2 and CN in laser ablation plasma are briefly reviewed to provide insights for implementation of LAMIS measurements. A simulated spectrum of the 12C2 Swan system was synthesized using four constituents within 473.5-476.5 nm. Simulation included three branches of 12C2 (1-0), branches R(0-0) and R(1-1), and branch P(9-8) of 12C2. Spectral positions of the tail lines in R(0-0) and R(1-1) were experimentally measured, since they were not accurately known before. The Swan band (1-0) of the isotopologue 13C12C was also simulated. Fitting to the experimental spectrum yielded the ratio 13C/12C = 1.08% in a good agreement with measurements by isotope ratio mass spectrometry. LAMIS promises to be useful in coal, oil and shale exploration, carbon sequestration monitoring, and agronomy studies.

  7. Early changes in tissue amino acid metabolism and nutrient routing in rats fed a high-fat diet: evidence from natural isotope abundances of nitrogen and carbon in tissue proteins.

    PubMed

    Mantha, Olivier L; Polakof, Sergio; Huneau, Jean-François; Mariotti, François; Poupin, Nathalie; Zalko, Daniel; Fouillet, Helene

    2018-05-01

    Little is known about how diet-induced obesity and insulin resistance affect protein and amino acid (AA) metabolism in tissues. The natural relative abundances of the heavy stable isotopes of C (δ 13C) and N (δ 15N) in tissue proteins offer novel and promising biomarkers of AA metabolism. They, respectively, reflect the use of dietary macronutrients for tissue AA synthesis and the relative metabolic use of tissue AA for oxidation v. protein synthesis. In this study, δ 13C and δ 15N were measured in the proteins of various tissues in young adult rats exposed perinatally and/or fed after weaning with a normal- or a high-fat (HF) diet, the aim being to characterise HF-induced tissue-specific changes in AA metabolism. HF feeding was shown to increase the routing of dietary fat to all tissue proteins via non-indispensable AA synthesis, but did not affect AA allocation between catabolic and anabolic processes in most tissues. However, the proportion of AA directed towards oxidation rather than protein synthesis was increased in the small intestine and decreased in the tibialis anterior muscle and adipose tissue. In adipose tissue, the AA reallocation was observed in the case of perinatal or post-weaning exposure to HF, whereas in the small intestine and tibialis anterior muscle the AA reallocation was only observed after HF exposure that covered both the perinatal and post-weaning periods. In conclusion, HF exposure induced an early reorganisation of AA metabolism involving tissue-specific effects, and in particular a decrease in the relative allocation of AA to oxidation in several peripheral tissues.

  8. Carbon isotopes in biological carbonates: Respiration and photosynthesis

    USGS Publications Warehouse

    McConnaughey, T.A.; Burdett, J.; Whelan, J.F.; Paull, C.K.

    1997-01-01

    Respired carbon dioxide is an important constituent in the carbonates of most air breathing animals but is much less important in the carbonates of most aquatic animals. This difference is illustrated using carbon isotope data from freshwater and terrestrial snails, ahermatypic corals, and chemoautotrophic and methanotrophic pelecypods. Literature data from fish otoliths and bird and mammal shell and bone carbonates are also considered. Environmental CO2/O2 ratios appear to be the major controlling variable. Atmospheric CO2/O2 ratios are about thirty times lower than in most natural waters, hence air breathing animals absorb less environmental CO2 in the course of obtaining O2. Tissue CO2 therefore, does not isotopically equilibrate with environmental CO2 as thoroughly in air breathers as in aquatic animals, and this is reflected in skeletal carbonates. Animals having efficient oxygen transport systems, such as vertebrates, also accumulate more respired CO2 in their tissues. Photosynthetic corals calcify mainly during the daytime when photosynthetic CO2 uptake is several times faster than respiratory CO2 release. Photosynthesis, therefore, affects skeletal ??13C more strongly than does respiration. Corals also illustrate how "metabolic" effects on skeletal isotopic composition can be estimated, despite the presence of much larger "kinetic" isotope effects. Copyright ?? 1997 Elsevier Science Ltd.

  9. Carbon isotopes in biological carbonates: Respiration and photosynthesis

    NASA Astrophysics Data System (ADS)

    McConnaughey, Ted A.; Burdett, Jim; Whelan, Joseph F.; Paull, Charles K.

    1997-02-01

    Respired carbon dioxide is an important constituent in the carbonates of most air breathing animals but is much less important in the carbonates of most aquatic animals. This difference is illustrated using carbon isotope data from freshwater and terrestrial snails, ahermatypic corals, and chemoautotrophic and methanotrophic pelecypods. Literature data from fish otoliths and bird and mammal shell and bone carbonates are also considered. Environmental CO 2/O 2 ratios appear to be the major controlling variable. Atmospheric CO 2/O 2 ratios are about thirty times lower than in most natural waters, hence air breathing animals absorb less environmental CO 2 in the course of obtaining 0 2. Tissue CO 2 therefore, does not isotopically equilibrate with environmental CO 2 as thoroughly in air breathers as in aquatic animals, and this is reflected in skeletal carbonates. Animals having efficient oxygen transport systems, such as vertebrates, also accumulate more respired CO 2 in their tissues. Photosynthetic corals calcify mainly during the daytime when photosynthetic CO 2 uptake is several times faster than respiratory CO 2 release. Photosynthesis, therefore, affects skeletal δ13C more strongly than does respiration. Corals also illustrate how "metabolic" effects on skeletal isotopic composition can be estimated, despite the presence of much larger "kinetic" isotope effects.

  10. What Drives Carbon Isotope Fractionation by the Terrestrial Biosphere?

    NASA Astrophysics Data System (ADS)

    Still, Christopher; Rastogi, Bharat

    2017-11-01

    During photosynthesis, terrestrial plants preferentially assimilate the lighter and much more abundant form of carbon, 12C, which accounts for roughly 99% of naturally occurring forms of this element. This photosynthetic preference for lighter carbon is driven principally by differences in molecular diffusion of carbon dioxide with differing 13C/12C across stomatal pores on leaves, followed by differences in carboxylation rates by the Rubisco enzyme that is central to the process of photosynthesis. As a result of these slight preferences, which work out to about a 2% difference in the fixation rates of 12CO2 versus 13CO2 by C3 vegetation, plant tissues are depleted in the heavier form of carbon (13C) relative to atmospheric CO2. This difference has been exploited in a wide range of scientific applications, as the photosynthetic isotope signature is passed to ecosystem carbon pools and through ecological food webs. What is less appreciated is the signature that terrestrial carbon exchanges leave on atmospheric CO2, as the net uptake of carbon by land plants during their growing season not only draws down the local CO2 concentration, it also leaves behind relatively more CO2 molecules containing 13C. The converse happens outside the growing season, when autotrophic and heterotrophic respiration predominate. During these periods, atmospheric CO2 concentration increases and its corresponding carbon isotope composition becomes relatively depleted in 13C as the products of photosynthesis are respired, along with some small isotope fractionation that happen downstream of the initial photosynthetic assimilation. Similar phenomena were first observed at shorter time scales by the eminent carbon cycle scientist, Charles (Dave) Keeling. Keeling collected samples of air in glass flasks from sites along the Big Sur coast that he later measured for CO2 concentration and carbon isotope composition (δ13C) in his lab (Keeling, 1998). From these samples, Keeling observed increasing

  11. Daily Variation of Isotope Ratios in Mars Atmospheric Carbon Dioxide

    NASA Astrophysics Data System (ADS)

    Livengood, Timothy A.; Kostiuk, Theodor; Kolasinski, John R.; Hewagama, Tilak; Henning, Wade G.; Sornig, Manuela; Stangier, Tobias; Krause, Pia; Sonnabend, Guido; Mahaffy, Paul R.

    2014-11-01

    The atmosphere of Mars has been shown by ground based high-resolution infrared spectroscopy and in situ measurements with the Phoenix lander and Mars Science Laboratory Curiosity rover to be enriched in C and O heavy isotopes, consistent with preferential loss of light isotopes in eroding Mars’ primordial atmosphere. The relative abundance of heavy isotopes, combined with contemporary measurements of loss rates to be obtained with MAVEN, will enable estimating the primordial atmospheric inventory on Mars. IR spectroscopy of Mars collected in May 2012 as well as in March and May of 2014 from the NASA IRTF has resolved transitions of all three singly-substituted minor isotopologues of carbon dioxide in addition to the normal isotope, enabling remote measurements of all the carbon and oxygen isotope ratios as a function of latitude, longitude, and time of day. Earlier measurements obtained in October 2007 demonstrated that the relative abundance of O-18 increased linearly with increasing surface temperature over a relatively warm early-afternoon temperature range, but did not extend far enough to inspect the effect of late-afternoon cooling. These results imply that isotopically enriched gas is sequestered overnight when surface temperature is minimum and desorbs through the course of the day as temperature increases. Current spectroscopic constants indicate that the peak isotopic enrichment could be significantly greater than what has been measured in situ, apparently due to sampling the atmosphere at different time of day and surface temperature. The observing runs in 2012 and 2014 measured O-18 enrichment at several local times in both morning and afternoon sectors as well as at the subsolar, equatorial, and anti-subsolar latitudes. The two runs in 2014 have additionally observed O-17 and C-13 transitions in the morning sector, from local dawn to noon. These observations include a limited sampling of measurements over Gale Crater, which can be compared with

  12. Bringing organic carbon isotopes and phytoliths to the table as additional constraints on paleoelevation

    NASA Astrophysics Data System (ADS)

    Sheldon, N. D.; Cotton, J. M.; Hren, M. T.; Hyland, E. G.; Smith, S. Y.; Strömberg, C. A. E.

    2015-12-01

    A commonly used tool in paleotectonic and paleoaltimetry studies is the oxygen isotopic composition of authigenic carbonates formed that formed in lakes or soils, with both spatial (e.g., shoreline to mountain top) or temporally resolved records potentially providing constraints. However, in many cases there is a substantial spread in the oxygen isotope data for a given time period, often to the point of allowing for essentially any interpretation of the data depending upon how they have been used by the investigator. One potential way of distinguishing between different potential paleotectonic or paleoaltimetric interpretations is to use carbon isotope and plant microfossil (phytolith) analyses from the same paleosols to screen the oxygen isotope data by looking for evidence of evaporative enrichment. For example, if both inorganic (carbonate) and organic carbon isotopes are measured from the same paleosol, then in it possible to determine if the two isotope record equilibrium conditions or if they record disequilibrium driven by kinetic effects. In the former case, the oxygen isotope results can be considered reliable whereas in the latter case, the oxygen isotope results can be considered unreliable and could be culled from the interpretation. Similarly, because the distribution of C4 plants varies as a function of temperature and elevation, the presence/absence or abundance of C4 plant phytoliths, or of carbon isotope compositions that require a component of C4 vegetation can also be used to constrain paleoelevation by providing a maximum elevation constraint. Worked examples will include the late Miocene-Pliocene of Catamarca, Argentina, where phytoliths and organic carbon isotopes provide a maximum elevation constraint and can be used to demonstrate that oxygen isotopes do not provide a locally useful constraint on paleoelevation, and Eocene-Miocene of southwestern Montana where organic matter and phytoliths can be used to select between different potential

  13. Carbon isotopic composition of individual Precambrian microfossils

    NASA Technical Reports Server (NTRS)

    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.

  14. A Modern Analogue for Proterozoic Inverse Carbon Isotope Signatures

    NASA Astrophysics Data System (ADS)

    Close, H. G.; Diefendorf, A. F.; Freeman, K. H.; Pearson, A.

    2008-12-01

    The carbon isotope distribution preserved in sedimentary lipids changes near the Neoproterozoic-Cambrian boundary. In older samples, n-alkyl lipids contain more 13C than both isoprenoid lipids and kerogen [1]. In younger samples, the opposite prevails. Although extreme heterotrophy has been invoked as a mechanism to explain the enrichment in 13C [2], here we suggest another explanation. The switch may reflect a fundamental transition from an oligotrophic ocean dominated by prokaryotic biomass, to an ocean in which carbon fixation is more intensive and burial is dominated by eukaryotic biomass. An analogue for Proterozoic ordering is found in the modern, oligotrophic Pacific Ocean, where n-alkyl lipids of picoplankton (0.2-0.5 μm particulate matter) contain excess 13C relative to the same lipids found in larger size classes (> 0.5 μm). Picoplanktonic lipids are heavier isotopically (-18 ‰) than both the sterols of eukaryotes (-23 ‰ to -26 ‰) and the total organic matter (-20 ‰; TOM). The 0.2-0.5 μm size class also has a distinct chain-length abundance profile. Although large particles must be the vehicle for total carbon export, paradoxically the lipid component of export production appears to be dominated by the 0.2-0.5 μm source. The picoplanktonic chain lengths and isotopic composition dominate lipids of TOM at 670 meters. When the ratio of prokaryotic to eukaryotic production is high, as in the modern central Pacific Ocean, it appears that exported material has an inverse carbon isotope signature similar to that preserved in Precambrian samples. [1] Logan, G. A. et al., Nature 376:53-56 (1995). [2] Rothman, D. H. et al., PNAS 100:8124-8129 (2003).

  15. Isotope Variations in Terrestrial Carbonates and Thermal Springs as Biomarkers: Analogs for Martian Processes

    NASA Technical Reports Server (NTRS)

    Socki, Richard A.; Gibson, Everett K., Jr.; Bissada, K. K.

    2006-01-01

    Stable isotope measurements of carbonate minerals contained within ALH84001 [1] suggest that fluids were present at 3.9 Gy on Mars [2, 3, 4, 5]. Both oxygen and carbon isotopes provide independent means of deciphering paleoenvironmental conditions at the time of carbonate mineral precipitation. In terrestrial carbonate rocks oxygen isotopes not only indicate the paleotemperature of the precipitating fluid, but also provide clues to environmental conditions that affected the fluid chemistry. Carbon isotopes, on the other hand, can indicate the presence or absence of organic compounds during precipitation (i.e. biogenically vs. thermogenically-generated methane), thus serving as a potential biomarker. We have undertaken a study of micro scale stable isotope variations measured in some terrestrial carbonates and the influence of organic compounds associated with the formation of these carbonates. Preliminary results indicate that isotope variations occur within narrow and discrete intervals, providing clues to paleoenvironmental conditions that include both biological and non-biological activity. These results carry implications for deciphering Martian isotope data and therefore potential biological prospecting on the planet Mars. Recently, Fourier Transform Spectrometer observations have detected methane occurring in the Martian atmosphere [6] that could be attributed to a possible biogenic source. Indeed, Mars Express has detected the presence of methane in the Martian atmosphere [7], with evidence indicating that methane abundances are greatest above those basins with high water concentrations.

  16. BOREAS TE-5 Leaf Carbon Isotope Data

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

    The BOREAS TE-5 team collected measurements in the NSA and SSA on gas exchange, gas composition, and tree growth. This documentation describes leaf carbon isotope data that were collected in 1993 and 1994 at the NSA and SSA OJP sites, the SSA OBS site, and the NSA UBS site. In addition, leaf carbon isotope data were collected in 1994 only at the NSA and SSA OA sites. These data was collected to provide seasonal integrated physiological information for 10 to 15 common species at these 6 BOREAS sites. The data are stored 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).

  17. Single Species Dinoflagellate Cyst Carbon Isotope Ecology across the Paleocene-Eocene Thermal Maximum

    NASA Astrophysics Data System (ADS)

    Sluijs, A.; Roij, L. V.; Frieling, J.; Laks, J.; Reichart, G. J.

    2017-12-01

    We present the first ever species-specific records of fossil dinoflagellate cyst stable carbon isotope ratios (δ13C). These records across a Paleocene-Eocene Thermal Maximum section in New Jersey were established using a novel coupled laser ablation - isotope ratio mass spectrometer setup. The overall good correspondence with carbonate δ13C records across the characteristic PETM carbon isotope excursion indicates that the δ13C of dissolved inorganic carbon exerts a major control on dinocysts δ13C. Pronounced and consistent differences between species, however, reflect the differential physiological response to changing seawater carbonate chemistry following PETM carbon injection. Moreover, they reflect different habitats or life cycle processes, notably related to bloom intensity. Intriguingly, decreased inter-specimen variability during the PETM in a species that also drops in abundance suggests a more limited niche, either in time (seasonal) or space. This opens a new approach for ecological and evolutionary reconstructions based on organic microfossils.

  18. The Carbon Isotope Ratio in Local Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Goto, Miwa; Usuda, Tomonori; Takato, Naruhisa; Masahiko, Hayashi; Sakamoto, Seiichi; Mitchell, George

    We report the carbon isotope ratio in nearby molecular clouds LkHα 101, AFGL 490, and Mon R2 IRS 3. The vibrational transition bands of 12CO ν = 2 ← 0 and 13CO ν = 1 ← 0 were observed with high resolution near-infrared spectroscopy (R = 23,000) to measure the relative abundance of 13CO to 12CO. The isotopic ratios are 12CO/13CO = 1379 (LkHα 101), 8649 (AFGL 490), and 158 (Mon R2 IRS 3), which is twice higher than in the solar neighborhood. The molecular clouds are with high visible extinction (AV = 10 70 mag), well shielded from destructive FUV field. It is questionable that the selective photo-destruction of 13CO plays a major role in biasing isotope ratio. Uncertainty in the Doppler parameters of the unresolved absorption lines, and possible emission filling of fundamental transitions are suspected to account for the high 12CO/13CO ratio. Higher resolution spectroscopy (R ~ 100,000) is the key to go for the accurate measurement of isotope ratio.

  19. Natural Isotope Abundance in Metabolites: Techniques and Kinetic Isotope Effect Measurement in Plant, Animal, and Human Tissues.

    PubMed

    Tea, Illa; Tcherkez, Guillaume

    2017-01-01

    The natural isotope abundance in bulk organic matter or tissues is not a sufficient base to investigate physiological properties, biosynthetic mechanisms, and nutrition sources of biological systems. In fact, isotope effects in metabolism lead to a heterogeneous distribution of 2 H, 18 O, 13 C, and 15 N isotopes in metabolites. Therefore, compound-specific isotopic analysis (CSIA) is crucial to biological and medical applications of stable isotopes. Here, we review methods to implement CSIA for 15 N and 13 C from plant, animal, and human samples and discuss technical solutions that have been used for the conversion to CO 2 and N 2 for IRMS analysis, derivatization and isotope effect measurements. It appears that despite the flexibility of instruments used for CSIA, there is no universal method simply because the chemical nature of metabolites of interest varies considerably. Also, CSIA methods are often limited by isotope effects in sample preparation or the addition of atoms from the derivatizing reagents, and this implies that corrections must be made to calculate a proper δ-value. Therefore, CSIA has an enormous potential for biomedical applications, but its utilization requires precautions for its successful application. © 2017 Elsevier Inc. All rights reserved.

  20. Carbon chain abundance in the diffuse interstellar medium

    NASA Technical Reports Server (NTRS)

    Allamandola, L. J.; Hudgins, D. M.; Bauschlicher, C. W. Jr; Langhoff, S. R.

    1999-01-01

    Thanks to the mid-IR sensitivities of the ISO and IRTS orbiting spectrometers it is now possible to search the diffuse interstellar medium for heretofore inaccessible molecular emission. In view of the recent strong case for the presence of C(7-) (Kirkwood et al. 1998, Tulej et al. 1998),and the fact that carbon chains possess prominent infrared active modes in a very clean portion of the interstellar spectrum, we have analyzed the IRTS spectrum of the diffuse interstellar medium for the infrared signatures of these species. Theoretical and experimental infrared band frequencies and absolute intensities of many different carbon chain species are presented. These include cyanopolyynes, neutral and anionic linear carbon molecules, and neutral and ionized, even-numbered, hydrogenated carbon chains. We show that--as a family--these species have abundances in the diffuse ISM on the order of 10(-10) with respect to hydrogen, values consistent with their abundances in dense molecular clouds. Assuming an average length of 10 C atoms per C-chain implies that roughly a millionth of the cosmically available carbon is in the form of carbon chains and that carbon chains can account for a few percent of the visible to near-IR diffuse interstellar band (DIB) total equivalent width (not DIB number).

  1. Oxygen isotope fractionation in divalent metal carbonates

    USGS Publications Warehouse

    O'Neil, J.R.; Clayton, R.N.; Mayeda, T.K.

    1969-01-01

    Equilibrium fractionation factors for the distribution of 18O between alkaline-earth carbonates and water have been measured over the temperature range 0-500??C. The fractionation factors ?? can be represented by the equations CaCO3-H2O, 1000 ln??=2.78(106 T-2)-3.39, SrCO3-H 2O, 1000 ln??=2.69(106 T-2)-3.74, BaCO3-H2O, 1000 ln??=2.57(106 T -2)-4.73. Measurements on MnCO3, CdCO3, and PbCO3 were made at isolated temperatures. A statistical-mechanical calculation of the isotopic partition function ratios gives reasonably good agreement with experiment. Both cationic size and mass are important in isotopic fractionation, the former predominantly in its effect on the internal vibrations of the anion, the latter in its effect on the lattice vibrations.

  2. Breath carbon stable isotope ratios identify changes in energy balance and substrate utilization in humans

    USDA-ARS?s Scientific Manuscript database

    Rapid detection of shifts in substrate utilization and energy balance would provide a compelling biofeedback tool to enable individuals to lose weight. In a pilot study, we tested whether the natural abundance of exhaled carbon stable isotope ratios (breath d13C values) reflects shifts between negat...

  3. Carbon Abundances in Starburst Galaxies of the Local Universe

    SciTech Connect

    Peña-Guerrero, María A.; Leitherer, Claus; Mink, Selma de

    The cosmological origin of carbon, the fourth most abundant element in the universe, is not well known and a matter of heavy debate. We investigate the behavior of C/O to O/H in order to constrain the production mechanism of carbon. We measured emission-line intensities in the spectral range from 1600 to 10000 Å on Space Telescope Imaging Spectrograph (STIS) long-slit spectra of 18 starburst galaxies in the local universe. We determined chemical abundances through traditional nebular analysis, and we used a Markov Chain Monte Carlo method to determine where our carbon and oxygen abundances lie in the parameter space. Wemore » conclude that our C and O abundance measurements are sensible. We analyzed the behavior of our sample in the [C/O] versus [O/H] diagram with respect to other objects such as DLAs, neutral ISM measurements, and disk and halo stars, finding that each type of object seems to be located in a specific region of the diagram. Our sample shows a steeper C/O versus O/H slope with respect to other samples, suggesting that massive stars contribute more to the production of C than N at higher metallicities, only for objects where massive stars are numerous; otherwise, intermediate-mass stars dominate the C and N production.« less

  4. Carbon Abundances in Starburst Galaxies of the Local Universe

    NASA Astrophysics Data System (ADS)

    Peña-Guerrero, María A.; Leitherer, Claus; de Mink, Selma; Wofford, Aida; Kewley, Lisa

    2017-10-01

    The cosmological origin of carbon, the fourth most abundant element in the universe, is not well known and a matter of heavy debate. We investigate the behavior of C/O to O/H in order to constrain the production mechanism of carbon. We measured emission-line intensities in the spectral range from 1600 to 10000 Å on Space Telescope Imaging Spectrograph (STIS) long-slit spectra of 18 starburst galaxies in the local universe. We determined chemical abundances through traditional nebular analysis, and we used a Markov Chain Monte Carlo method to determine where our carbon and oxygen abundances lie in the parameter space. We conclude that our C and O abundance measurements are sensible. We analyzed the behavior of our sample in the [C/O] versus [O/H] diagram with respect to other objects such as DLAs, neutral ISM measurements, and disk and halo stars, finding that each type of object seems to be located in a specific region of the diagram. Our sample shows a steeper C/O versus O/H slope with respect to other samples, suggesting that massive stars contribute more to the production of C than N at higher metallicities, only for objects where massive stars are numerous; otherwise, intermediate-mass stars dominate the C and N production.

  5. Calcium isotope evidence for suppression of carbonate dissolution in carbonate-bearing organic-rich sediments

    NASA Astrophysics Data System (ADS)

    Turchyn, Alexandra V.; DePaolo, Donald J.

    2011-11-01

    Pore fluid calcium isotope, calcium concentration and strontium concentration data are used to measure the rates of diagenetic dissolution and precipitation of calcite in deep-sea sediments containing abundant clay and organic material. This type of study of deep-sea sediment diagenesis provides unique information about the ultra-slow chemical reactions that occur in natural marine sediments that affect global geochemical cycles and the preservation of paleo-environmental information in carbonate fossils. For this study, calcium isotope ratios (δ 44/40Ca) of pore fluid calcium from Ocean Drilling Program (ODP) Sites 984 (North Atlantic) and 1082 (off the coast of West Africa) were measured to augment available pore fluid measurements of calcium and strontium concentration. Both study sites have high sedimentation rates and support quantitative sulfate reduction, methanogenesis and anaerobic methane oxidation. The pattern of change of δ 44/40Ca of pore fluid calcium versus depth at Sites 984 and 1082 differs markedly from that of previously studied deep-sea Sites like 590B and 807, which are composed of nearly pure carbonate sediment. In the 984 and 1082 pore fluids, δ 44/40Ca remains elevated near seawater values deep in the sediments, rather than shifting rapidly toward the δ 44/40Ca of carbonate solids. This observation indicates that the rate of calcite dissolution is far lower than at previously studied carbonate-rich sites. The data are fit using a numerical model, as well as more approximate analytical models, to estimate the rates of carbonate dissolution and precipitation and the relationship of these rates to the abundance of clay and organic material. Our models give mutually consistent results and indicate that calcite dissolution rates at Sites 984 and 1082 are roughly two orders of magnitude lower than at previously studied carbonate-rich sites, and the rate correlates with the abundance of clay. Our calculated rates are conservative for these

  6. Coprecipitation and isotopic fractionation of boron in modern biogenic carbonates

    NASA Astrophysics Data System (ADS)

    Vengosh, Avner; Kolodny, Yehoshua; Starinsky, Abraham; Chivas, Allan R.; McCulloch, Malcolm T.

    1991-10-01

    The abundances and isotopic composition of boron in modern, biogenic calcareous skeletons from the Gulf of Elat, Israel, the Great Barrier Reef, Australia, and in deep-sea sediments have been examined by negative thermal-ionization mass spectrometry. The selected species (Foraminifera, Pteropoda, corals, Gastropoda, and Pelecypoda) yield large variations in boron concentration that range from 1 ppm in gastropod shells to 80 ppm in corals. The boron content of the biogenic skeletons is independent of mineralogical composition and is probably related to biological (vital) effects. The δ11B values of the carbonates range from 14.2 to 32.2%. (relative to NBS SRM 951) and overlap with the δ11B values of modern deep-sea carbonate sediments ( δ11B = 8.9 to 26.2%.). The variations of δ11B may be controlled by isotopic exchange of boron species in which 10B is preferentially partitioned into the tetrahedral species, and coprecipitation of different proportions of trigonal and tetrahedral species in the calcium carbonates. Carbonates with low δ11B values (~ 15%.) may indicate preferential incorporation of tetrahedral species, whereas the higher δ11B values (~30%.) may indicate (1) uptake of both boron species assuming equilibrium with seawater (2) preferential incorporation of B(OH) 4- from in situ high-pH internal fluids of organisms that are isolated from seawater. The B content and δ11B values of deep-sea sediments, Foraminifera tests, and corals are used to estimate the global oceanic sink of elemental boron by calcium carbonate deposition. As a result of enrichment of B in corals, a substantially higher biogenic sink of 6.4 ± 0.9 × 10 10 g/yr is calculated for carbonates. This is only slightly lower than the sink for desorbable B in marine sediments (10 × 10 10 g/yr) and approximately half that of altered oceanic crust (14 × 10 10 g/yr). Thus, carbonates are an important sink for B in the oceans being ~20% of the total sinks. The preferential incorporation of

  7. Oxygen and carbon isotope disequilibria in Galapagos corals: isotopic thermometry and calcification physiology

    SciTech Connect

    McConnaughey, T.A.

    1986-01-01

    Biological carbonate skeletons are built largely from carbon dioxide, which reacts to form carbonate ion within thin extracellular solutions. The light isotopes of carbon and oxygen react faster than the heavy isotopes, depleting the resulting carbonate ions in /sup 13/C and /sup 18/O. Calcium carbonate precipitation occurs sufficiently fast that the skeleton remains out of isotopic equilibrium with surrounding fluids. This explanation for isotopic disequilibrium in biological carbonates was partially simulated in vitro, producing results similar to those seen in non-photosynthetic corals. Photosynthetic corals have higher /sup 13/C//sup 12/C ratios due to the preferential removal of /sup 12/C (as organicmore » carbon) from the reservoir of dissolved inorganic carbon. The oxygen isotopic variations in corals can be used to reconstruct past sea surface temperatures to an accuracy of about 0.5/sup 0/C. The carbon isotopic content of photosynthetic corals provides an indication of cloudiness. Using isotopic data from Galapagos corals, it was possible to construct proxy histories of the El Nino phenomenon. The physiology of skeletogenesis appears to be surprisingly similar in calcium carbonate, calcium phosphate, and silica precipitating systems.« less

  8. A carbon isotope mass balance for an anoxic marine sediment: Isotopic signatures of diagenesis

    NASA Technical Reports Server (NTRS)

    Boehme, Susan E.

    1993-01-01

    A carbon isotope mass balance was determined for the sediments of Cape Lookout Bight, NC to constrain the carbon budgets published previously. The diffusive, ebullitive and burial fluxes of sigma CO2 and CH4, as well as the carbon isotope signatures of these fluxes, were measured. The flux-weighted isotopic signature of the remineralized carbon (-18.9 plus or minus 2.7 per mil) agreed with the isotopic composition of the remineralized organic carbon determined from the particulate organic carbon (POC) delta(C-13) profiles (-19.2 plus or minus 0.2), verifying the flux and isotopic signature estimates. The measured delta(C-13) values of the sigma CO2 and CH4 diffusive fluxes were significantly different from those calculated from porewater gradients. The differences appear to be influenced by methane oxidation at the sediment-water interface, although other potential processes cannot be excluded. The isotope mass balance provides important information concerning the locations of potential diagenetic isotope effects. Specifically, the absence of downcore change in the delta(C-13) value of the POC fraction and the identical isotopic composition of the POC and the products of remineralization indicate that no isotopic fractionation is expressed during the initial breakdown of the POC, despite its isotopically heterogeneous composition.

  9. Isotopic abundances of Hg in mercury stars inferred from the Hg II line at 3984 A

    NASA Technical Reports Server (NTRS)

    White, R. E.; Vaughan, A. H., Jr.; Preston, G. W.; Swings, J. P.

    1976-01-01

    Wavelengths of the Hg II absorption feature at 3984 A in 30 Hg stars are distributed uniformly from the value for the terrestrial mix to a value that corresponds to nearly pure Hg-204. The wavelengths are correlated loosely with effective temperatures inferred from Q(UBV). Relative isotopic abundances derived from partially resolved profiles of the 3984-A line in iota CrB, chi Lup, and HR 4072 suggest that mass-dependent fractionation has occurred in all three stars. It is supposed that such fractionation occurs in all Hg stars, and a scheme whereby isotopic compositions can be inferred from a comparison of stellar wavelengths and equivalent widths with those calculated for a family of fractionated isotopic mixes. Theoretical profiles calculated for the derived isotopic composition agree well with high-resolution interferometric profiles obtained for three of the stars.

  10. Analysis of the site-specific carbon isotope composition of propane by gas source isotope ratio mass spectrometer

    NASA Astrophysics Data System (ADS)

    Piasecki, Alison; Sessions, Alex; Lawson, Michael; Ferreira, A. A.; Neto, E. V. Santos; Eiler, John M.

    2016-09-01

    Site-specific isotope ratio measurements potentially provide valuable information about the formation and degradation of complex molecules-information that is lost in conventional bulk isotopic measurements. Here we discuss the background and possible applications of such measurements, and present a technique for studying the site-specific carbon isotope composition of propane at natural abundance based on mass spectrometric analysis of the intact propane molecule and its fragment ions. We demonstrate the feasibility of this approach through measurements of mixtures of natural propane and propane synthesized with site-specific 13C enrichment, and we document the limits of precision of our technique. We show that mass balance calculations of the bulk δ13C of propane based on our site-specific measurements is generally consistent with independent constraints on bulk δ13C. We further demonstrate the accuracy of the technique, and illustrate one of its simpler applications by documenting the site-specific carbon isotope signature associated with gas phase diffusion of propane, confirming that our measurements conform to the predictions of the kinetic theory of gases. This method can be applied to propane samples of moderate size (tens of micromoles) isolated from natural gases. Thus, it provides a means of studying the site-specific stable isotope systematics of propane at natural isotope abundances on sample sizes that are readily recovered from many natural environments. This method may also serve as a model for future techniques that apply high-resolution mass spectrometry to study the site-specific isotopic distributions of larger organic molecules, with potential applications to biosynthesis, forensics and other geochemical subjects.

  11. Measurement of natural carbon isotopic composition of acetone in human urine.

    PubMed

    Yamada, Keita; Ohishi, Kazuki; Gilbert, Alexis; Akasaka, Mai; Yoshida, Naohiro; Yoshimura, Ryoko

    2016-02-01

    The natural carbon isotopic composition of acetone in urine was measured in healthy subjects using gas chromatography-combustion-isotope ratio mass spectrometry combined with headspace solid-phase microextraction (HS-SPME-GC-C-IRMS). Before applying the technique to a urine sample, we optimized the measurement conditions of HS-SPME-GC-C-IRMS using aqueous solutions of commercial acetone reagents. The optimization enabled us to determine the carbon isotopic compositions within ±0.2 ‰ of precision and ±0.3‰ of error using 0.05 or 0.2 mL of aqueous solutions with acetone concentrations of 0.3-121 mg/L. For several days, we monitored the carbon isotopic compositions and concentrations of acetone in urine from three subjects who lived a daily life with no restrictions. We also monitored one subject for 3 days including a fasting period of 24 h. These results suggest that changes in the availability of glucose in the liver are reflected in changes in the carbon isotopic compositions of urine acetone. Results demonstrate that carbon isotopic measurement of metabolites in human biological samples at natural abundance levels has great potential as a tool for detecting metabolic changes caused by changes in physiological states and disease.

  12. Preservation of carbonate clumped isotopes in sedimentary paleoclimate archives

    NASA Astrophysics Data System (ADS)

    Henkes, G. A.; Passey, B. H.; Grossman, E. L.; Shenton, B.; Perez-Huerta, A.

    2014-12-01

    Carbonate clumped isotope thermometry is increasingly used to reconstruct paleotemperatures of ancient terrestrial environments. One promising application is elucidating paleoelevation from carbonate archives such as paleosols, lacustrine marls, and fossil freshwater shells. Unlike conventional stable isotope approaches (e.g., mineral δ18O or δD), clumped isotope thermometry is independent of the isotopic composition of the precipitating waters and can therefore be used to reconstruct elevation by both the temperature-altitude relationship and the rainfall δ18O-altitude relationship. However, interpretation of clumped isotope data is not without its own complications. Like conventional stable isotopes, clumped isotope paleotemperatures can be effectively reset to warmer values by dissolution/reprecipitation-type diagenesis during sedimentary burial. It is also known that carbonate clumped isotope bonds (i.e., 13C-18O) are susceptible to 'reordering' in the solid mineral lattice at warmer burial temperatures, with laboratory studies of natural carbonates indicating activation of this phenomenon at temperatures as low as 100 °C over geologic timescales. A challenge in applying carbonate clumped isotope thermometry to natural samples is now evaluating terrestrial archives with respect to both types of alteration: 'open-system' alteration and 'closed-system' bond reordering. In this talk we will review our experimental efforts to constrain the kinetics of clumped isotope reordering, with relevance to low-temperature carbonates like fossil shells and early diagenetic minerals, and present new laboratory data that further inform our theoretical framework for the mechanism(s) of 13C-18O bond reordering. Together with traditional analytical and petrographic screening for recrystallization, empirical and laboratory studies of carbonate clumped isotope reordering represent the next steps in evaluating isotopic records of paleoclimate, paleobiology, and paleoelevation

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

    NASA Astrophysics Data System (ADS)

    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. Absolute Isotopic Abundance Ratios and the Accuracy of Δ47 Measurements

    NASA Astrophysics Data System (ADS)

    Daeron, M.; Blamart, D.; Peral, M.; Affek, H. P.

    2016-12-01

    Conversion from raw IRMS data to clumped isotope anomalies in CO2 (Δ47) relies on four external parameters: the (13C/12C) ratio of VPDB, the (17O/16O) and (18O/16O) ratios of VSMOW (or VPDB-CO2), and the slope of the triple oxygen isotope line (λ). Here we investigate the influence that these isotopic parameters exert on measured Δ47 values, using real-world data corresponding to 7 months of measurements; simulations based on randomly generated data; precise comparisons between water-equilibrated CO2 samples and between carbonate standards believed to share quasi-identical Δ47 values; reprocessing of two carbonate calibration data sets with different slopes of Δ47 versus T. Using different sets of isotopic parameters generally produces systematic offsets as large as 0.04 ‰ in final Δ47 values. What's more, even using a single set of isotopic parameters can produce intra- and inter-laboratory discrepancies in final Δ47 values, if some of these parameters are inaccurate. Depending on the isotopic compositions of the standards used for conversion to "absolute" values, these errors should correlate strongly with either δ13C or δ18O, or more weakly with both. Based on measurements of samples expected to display identical Δ47 values, such as 25°C water-equilibrated CO2 with different carbon and oxygen isotope compositions, or high-temperature standards ETH-1 and ETH-2, we conclude that the isotopic parameters used so far in most clumped isotope studies produces large, systematic errors controlled by the relative bulk isotopic compositions of samples and standards, which should be one of the key factors responsible for current inter-laboratory discrepancies. By contrast, the isotopic parameters of Brand et al. [2010] appear to yield accurate Δ47 values regardless of bulk isotopic composition. References:Brand, Assonov and Coplen [2010] http://dx.doi.org/10.1351/PAC-REP-09-01-05

  15. Ar39 Detection at the 10-16 Isotopic Abundance Level with Atom Trap Trace Analysis

    NASA Astrophysics Data System (ADS)

    Jiang, W.; Williams, W.; Bailey, K.; Davis, A. M.; Hu, S.-M.; Lu, Z.-T.; O'Connor, T. P.; Purtschert, R.; Sturchio, N. C.; Sun, Y. R.; Mueller, P.

    2011-03-01

    Atom trap trace analysis, a laser-based atom counting method, has been applied to analyze atmospheric Ar39 (half-life=269yr), a cosmogenic isotope with an isotopic abundance of 8×10-16. In addition to the superior selectivity demonstrated in this work, the counting rate and efficiency of atom trap trace analysis have been improved by 2 orders of magnitude over prior results. The significant applications of this new analytical capability lie in radioisotope dating of ice and water samples and in the development of dark matter detectors.

  16. The Oxygen Isotopic Composition of MIL 090001: A CR2 Chondrite with Abundant Refractory Inclusions

    NASA Technical Reports Server (NTRS)

    Keller, Lindsay P.; McKeegan, K. D.; Sharp, Z. D.

    2012-01-01

    MIL 090001 is a large (>6 kg) carbonaceous chondrite that was classified as a member of the CV reduced subgroup (CVred) that was recovered during the 2009-2010 ANSMET field season [1]. Based on the abundance of refractory inclusions and the extent of aqueous alteration, Keller [2] suggested a CV2 classification. Here we report additional mineralogical and petrographic data for MIL 090001, its whole-rock oxygen isotopic composition and ion microprobe analyses of individual phases. The whole rock oxygen isotopic analyses show that MIL 090001 should be classified as a CR chondrite.

  17. Oxygen and carbon isotopic growth record in a reef coral from the florida keys and a deep-sea coral from blake plateau

    USGS Publications Warehouse

    Emiliani, C.; Harold, Hudson J.; Shinn, E.A.; George, R.Y.

    1978-01-01

    Carbon and oxygen isotope analysis through a 30-year (1944 to 1974) growth of Montastrea annularis from Hen and Chickens Reef (Florida Keys) shows a strong yearly variation in the abundances of both carbon-13 and oxygen-18 and a broad inverse relationship between the two isotopes. Normal annual dense bands are formed during the summer and are characterized by heavy carbon and light oxygen. "Stress bands" are formed during particularly severe winters and are characterized by heavy carbon and heavy oxygen. The isotopic effect of Zooxanthellae metabolism dominates the temperature effect on the oxygen-18/oxygen-16 ratio. The isotopic results on the deep-sea solitary coral Bathypsammia tintinnabulum, where Zooxanthellae are nonexistent, indicates that the abundance of the heavy isotopes carbon-13 and oxygen-18 is inversely related to the growth rate, with both carbon and oxygen approaching equilibrium values with increasing skeletal age.

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

    NASA Astrophysics Data System (ADS)

    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

  19. A new solar carbon abundance based on non-LTE CN molecular spectra

    NASA Technical Reports Server (NTRS)

    Mount, G. H.; Linsky, J. L.

    1975-01-01

    A detailed non-LTE analysis of solar CN spectra strongly suggest a revised carbon abundance for the sun. We recommend a value of log carbon abundance = 8.35 plus or minus 0.15 which is significantly lower than the presently accepted value of log carbon abundance = 8.55. This revision may have important consequences in astrophysics.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    USGS Publications Warehouse

    Wigley, T.M.L.; Plummer, Niel; 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.

  2. Stable carbon and sulfur isotopes as records of the early biosphere

    NASA Technical Reports Server (NTRS)

    Desmarais, David J.

    1989-01-01

    The abundance ratios of the stable isotopes of light elements such as carbon and sulfur can differ between various naturally-occurring chemical compounds. If coexisting compounds have achieved mutual chemical and isotopic equilibrium, then the relative isotopic composition can record the conditions at which equilibrium was last maintained. If coexisting chemical compounds indeed formed simultaneously but had not achieved mutual equilibrium, then their relative isotopic compositions often reflect the conditions and mechanisms associated with the kinetically controlled reactions responsible for their production. In the context of Mars, the stable isotopic compositions of various minerals might record not only the earlier environmental conditions of the planet, but also whether or not the chemistry of life ever occurred there. Two major geochemical reservoirs occur in Earth's crust, both for carbon and sulfur. In rocks formed in low temperature sedimentary environments, the oxidized forms of these elements tend to be enriched in the isotope having the larger mass, relative to the reduced forms. In sediments where the organics and sulfides were formed by biological processes, these isotopic contrasts were caused by the processes of biological CO2 fixation and dissimilatory sulfate reduction. Such isotopic contrasts between oxidized and reduced forms of carbon and sulfur are permitted by thermodynamics at ambient temperatures. However, nonbiological chemical reactions associated with the production of organic matter and the reduction of organics and sulfides are extremely slow at ambient temperatures. Thus the synthesis of organics and sulfides under ambient conditions illustrates life's profound role as a chemical catalyst that has altered the chemistry of Earth's crust. Because the stable isotopes of carbon and sulfur can reflect their chemistry, they are useful probes of the Martian surface.

  3. Isotopic disequilibrium in Globigerina bulloides and carbon isotope response to productivity increase in Southern Ocean.

    PubMed

    Prasanna, K; Ghosh, Prosenjit; Bhattacharya, S K; Mohan, K; Anilkumar, N

    2016-02-23

    Oxygen and carbon isotope ratios in planktonic foraminifera Globigerina bulloides collected from tow samples along a transect from the equatorial Indian ocean to the Southern Ocean (45°E and 80°E and 10°N to 53°S) were analysed and compared with the equilibrium δ(18)O and δ(13)C values of calcite calculated using the temperature and isotopic composition of the water column. The results agree within ~0.25‰ for the region between 10°N and 40°S and 75-200 m water depth which is considered to be the habitat of Globigerina bulloides. Further south (from 40°S to 55°S), however, the measured δ(18)O and δ(13)C values are higher than the expected values by ~2‰ and ~1‰ respectively. These enrichments can be attributed to either a 'vital effect' or a higher calcification rate. An interesting pattern of increase in the δ(13)C(DIC) value of the surface water with latitude is observed between 35°S and~ 60°S, with a peak at~ 42°S. This can be caused by increased organic matter production and associated removal. A simple model accounting for the increase in the δ(13)C(DIC) values is proposed which fits well with the observed chlorophyll abundance as a function of latitude.

  4. Isotopic disequilibrium in Globigerina bulloides and carbon isotope response to productivity increase in Southern Ocean

    PubMed Central

    Prasanna, K.; Ghosh, Prosenjit; Bhattacharya, S. K.; Mohan, K.; Anilkumar, N.

    2016-01-01

    Oxygen and carbon isotope ratios in planktonic foraminifera Globigerina bulloides collected from tow samples along a transect from the equatorial Indian ocean to the Southern Ocean (45°E and 80°E and 10°N to 53°S) were analysed and compared with the equilibrium δ18O and δ13C values of calcite calculated using the temperature and isotopic composition of the water column. The results agree within ~0.25‰ for the region between 10°N and 40°S and 75–200 m water depth which is considered to be the habitat of Globigerina bulloides. Further south (from 40°S to 55°S), however, the measured δ18O and δ13C values are higher than the expected values by ~2‰ and ~1‰ respectively. These enrichments can be attributed to either a ‘vital effect’ or a higher calcification rate. An interesting pattern of increase in the δ13C(DIC) value of the surface water with latitude is observed between 35°S and~ 60°S, with a peak at~ 42°S. This can be caused by increased organic matter production and associated removal. A simple model accounting for the increase in the δ13C(DIC) values is proposed which fits well with the observed chlorophyll abundance as a function of latitude. PMID:26903274

  5. An isotopic study of biogeochemical relationships between carbonates and organic carbon in the Greenhorn Formation

    NASA Technical Reports Server (NTRS)

    Hayes, J. M.; Popp, Brian N.; Takigiku, Ray; Johnson, Marcus W.

    1989-01-01

    Carbon-isotopic compositions of total carbonate, inoceramid carbonate, micritic carbonate, secondary cements, total organic carbon, and geoporphyrins have been measured in 76 different beds within a 17-m interval of a core through the Greenhorn Formation, an interbedded limestone and calcareous shale unit of Cretaceous age from the Western Interior Seaway of North America. Results are considered in terms of variations in the processes of primary production and in secondary processes. It is shown that the porphyrin isotopic record reflects primary isotopic variations more closely than the TOC isotopic record and that, in these sediments, TOC is enriched in C-13 relative to its primary precursor by 0.6 to 2.8 percent. This enrichment is attributed to isotope effects within the consumer foodweb and is associated with respiratory heterotrophy. Variation in this secondary enrichment are correlated with variations in the isotopic composition of marine carbonate.

  6. Mercury Abundances and Isotopic Compositions in the Murchison (CM) and Allende (CV)Carbonaceous Chondrites

    NASA Technical Reports Server (NTRS)

    Lauretta, D. S.; Klaue, B.; Blum, J. D.; Buseck, P. R.

    2001-01-01

    The abundance and isotopic composition of Hg was determined in bulk samples of both the Murchison (CM) and Allende (CV) carbonaceous chondrites using single- and multi-collector inductively coupled plasma mass spectrometry (ICP-MS). The bulk abundances of Hg are 294 6 15 ng/g in Murchison and 30.0 6 1.5 ng/g in Allende. These values are within the range of previous measurements of bulk Hg abundances by neutron activation analysis (NAA). Prior studies suggested that both meteorites contain isotopically anomalous Hg, with d l 96/202Hg values for the anomalous, thermal-release components from bulk samples ranging from 2260 %o to 1440 9/00 in Murchison and from 2620 9/00 to 1540 9/00 in Allende (Jovanovic and Reed, 1976a; 1976b; Kumar and Goel, 1992). Our multi-collector ICP-MS measurements suggest that the relative abundances of all seven stable Hg isotopes in both meteorites are identical to terrestrial values within 0.2 to 0.5 9/00m. On-line thermal-release experiments were performed by coupling a programmable oven with the singlecollector ICP-MS. Powdered aliquots of each meteorite were linearly heated from room temperature to 900 C over twenty-five minutes under an Ar atmosphere to measure the isotopic composition of Hg released fiom the meteorites as a h c t i o n of temperature. In separate experiments, the release profiles of S and Se were determined simultaneously with Hg to constrain the Hg distribution within the meteorites and to evaluate the possibility of Se interferences in previous NAA studies. The Hg-release patterns differ between Allende and Murchison. The Hg-release profile for Allende contains two distinct peaks, at 225" and 343"C, whereas the profile for Murchison has only one peak, at 344 C. No isotopically anomalous Hg was detected in the thermal-release experiments at a precision level of 5 to 30 9/00, depending on the isotope ratio. In both meteorites the Hg peak at ;340"C correlates with a peak in the S-release profile. This correlation

  7. Isotopic exchange of carbon-bound hydrogen over geologic timescales

    NASA Astrophysics Data System (ADS)

    Sessions, Alex L.; Sylva, Sean P.; Summons, Roger E.; Hayes, John M.

    2004-04-01

    The increasing popularity of compound-specific hydrogen isotope (D/H) analyses for investigating sedimentary organic matter raises numerous questions about the exchange of carbon-bound hydrogen over geologic timescales. Important questions include the rates of isotopic exchange, methods for diagnosing exchange in ancient samples, and the isotopic consequences of that exchange. This article provides a review of relevant literature data along with new data from several pilot studies to investigate such issues. Published experimental estimates of exchange rates between organic hydrogen and water indicate that at warm temperatures (50-100°C) exchange likely occurs on timescales of 104 to 108 yr. Incubation experiments using organic compounds and D-enriched water, combined with compound-specific D/H analyses, provide a new and highly sensitive method for measuring exchange at low temperatures. Comparison of δD values for isoprenoid and n-alkyl carbon skeletons in sedimentary organic matter provides no evidence for exchange in young (<1 Ma), cool sediments, but strong evidence for exchange in ancient (>350 Ma) rocks. Specific rates of exchange are probably influenced by the nature and abundance of organic matter, pore-water chemistry, the presence of catalytic mineral surfaces, and perhaps even enzymatic activity. Estimates of equilibrium fractionation factors between organic H and water indicate that typical lipids will be depleted in D relative to water by ∼75 to 140‰ at equilibrium (30°C). Thus large differences in δD between organic molecules and water cannot be unambiguously interpreted as evidence against hydrogen exchange. A better approach may be to use changes in stereochemistry as a proxy for hydrogen exchange. For example, estimated rates of H exchange in pristane are similar to predicted rates for stereochemical inversion in steranes and hopanes. The isotopic consequences of this exchange remain in question. Incubations of cholestene with D2O indicate

  8. Stable carbon isotope depth profiles and soil organic carbon dynamics in the lower Mississippi Basin

    USGS Publications Warehouse

    Wynn, J.G.; Harden, J.W.; Fries, T.L.

    2006-01-01

    Analysis of depth trends of 13C abundance in soil organic matter and of 13C abundance from soil-respired CO2 provides useful indications of the dynamics of the terrestrial carbon cycle and of paleoecological change. We measured depth trends of 13C abundance from cropland and control pairs of soils in the lower Mississippi Basin, as well as the 13C abundance of soil-respired CO2 produced during approximately 1-year soil incubation, to determine the role of several candidate processes on the 13C depth profile of soil organic matter. Depth profiles of 13C from uncultivated control soils show a strong relationship between the natural logarithm of soil organic carbon concentration and its isotopic composition, consistent with a model Rayleigh distillation of 13C in decomposing soil due to kinetic fractionation during decomposition. Laboratory incubations showed that initially respired CO 2 had a relatively constant 13C content, despite large differences in the 13C content of bulk soil organic matter. Initially respired CO2 was consistently 13C-depleted with respect to bulk soil and became increasingly 13C-depleted during 1-year, consistent with the hypothesis of accumulation of 13C in the products of microbial decomposition, but showing increasing decomposition of 13C-depleted stable organic components during decomposition without input of fresh biomass. We use the difference between 13C / 12C ratios (calculated as ??-values) between respired CO 2 and bulk soil organic carbon as an index of the degree of decomposition of soil, showing trends which are consistent with trends of 14C activity, and with results of a two-pooled kinetic decomposition rate model describing CO2 production data recorded during 1 year of incubation. We also observed inconsistencies with the Rayleigh distillation model in paired cropland soils and reasons for these inconsistencies are discussed. ?? 2005 Elsevier B.V. All rights reserved.

  9. Relative and accurate measurement of protein abundance using 15N stable isotope labeling in Arabidopsis (SILIA).

    PubMed

    Guo, Guangyu; Li, Ning

    2011-07-01

    In the quantitative proteomic studies, numerous in vitro and in vivo peptide labeling strategies have been successfully applied to measure differentially regulated protein and peptide abundance. These approaches have been proven to be versatile and repeatable in biological discoveries. (15)N metabolic labeling is one of these widely adopted and economical methods. However, due to the differential incorporation rates of (15)N or (14)N, the labeling results produce imperfectly matched isotopic envelopes between the heavy and light nitrogen-labeled peptides. In the present study, we have modified the solid Arabidopsis growth medium to standardize the (15)N supply, which led to a uniform incorporation of (15)N into the whole plant protein complement. The incorporation rate (97.43±0.11%) of (15)N into (15)N-coded peptides was determined by correlating the intensities of peptide ions with the labeling efficiencies according to Gaussian distribution. The resulting actual incorporation rate (97.44%) and natural abundance of (15)N/(14)N-coded peptides are used to re-calculate the intensities of isotopic envelopes of differentially labeled peptides, respectively. A modified (15)N/(14)N stable isotope labeling strategy, SILIA, is assessed and the results demonstrate that this approach is able to differentiate the fold change in protein abundance down to 10%. The machine dynamic range limitation and purification step will make the precursor ion ratio deriving from the actual ratio fold change. It is suggested that the differentially mixed (15)N-coded and (14)N-coded plant protein samples that are used to establish the protein abundance standard curve should be prepared following a similar protein isolation protocol used to isolate the proteins to be quantitated. Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.

  10. Carbon Monoxide Isotopes: On the Trail of Galactic Chemical Evolution

    NASA Technical Reports Server (NTRS)

    Langer, W.

    1995-01-01

    From the early days of the discovery of radio emission from carbon monoxide it was realized that it offered unusual potential for under- standing the chemical evolution of the Galaxy and external galaxies through measurements of molecular isotopes. These results bear on stellar nucleosynthesis, star formation, and gases in the interstellar medium. Progress in isotopic radio measurements will be reviewed.

  11. Origin of petroporphyrins. 2. Evidence from stable carbon isotopes

    NASA Technical Reports Server (NTRS)

    Boreham, C. J.; Fookes, C. J.; Popp, B. N.; Hayes, J. M.

    1990-01-01

    Compared with the carbon-13 isotopic composition of the ubiquitous C32DPEP (DPEP, deoxophylloerythroetioporphyrin) the heavy but equivalent carbon-13 isotopic composition for the porphyrin structures 15(2)-methyl-15,17-ethano-17-nor-H-C30DPEP and 15,17-butano-, 13,15-ethano-13(2),17-propano-, and 13(1)-methyl-13,15-ethano-13(2),17-propanoporphyrin suggests a common precursor, presumably chlorophyll c, for these petroporphyrins isolated from the marine Julia Creek oil shale and the lacustrine Condor oil shale. Similarly, the heavy but variable carbon-13 isotopic composition of 7-nor-H-C31DPEP compared with C32DPEP is consistent with an origin from both chlorophyll b and chlorophyll c3. The equivalent carbon-13 isotopic composition for 13(2)-methyl-C33DPEP compared with C32DPEP suggests a common origin resulting from a weighted average of chlorophyll inputs.

  12. BIODEGRADATION OF FLUORANTHENE AS MONITORED USING STABLE CARBON ISOTOPES

    EPA Science Inventory

    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,...

  13. The carbon isotope biogeochemistry of methane production in anoxic sediments. 1: Field observations

    NASA Technical Reports Server (NTRS)

    Blair, Neal E.; Boehme, Susan E.; Carter, W. Dale, Jr.

    1993-01-01

    The natural abundance C-13/C-12 ratio of methane from anoxic marine and freshwater sediments in temperate climates varies seasonally. Carbon isotopic measurements of the methanogenic precursors, acetate and dissolved inorganic carbon, from the marine sediments of Cape Lookout Bight, North Carolina were used to determine the sources of the seasonal variations at that site. Movement of the methanogenic zone over an isotopic gradient within the dissolved CO2 pool appears to be the dominant control of the methane C-13/C-12 ratio from February to June. The onset of acetoclastic methane-production is a second important controlling process during mid-summer. An apparent temperature dependence on the fractionation factor for CO2-reduction may have a significant influence on the isotopic composition of methane throughout the year.

  14. Carbon Isotopic Ratios of Amino Acids in Stardust-Returned Samples

    NASA Technical Reports Server (NTRS)

    Elsila, Jamie E.; Glavin, Daniel P.; Dworkin, Jason P.

    2009-01-01

    NASA's Stardust spacecraft returned to Earth samples from comet 81P/Wild 2 in January 2006. Preliminary examinations revealed the presence of a suite of organic compounds including several amines and amino acids, but the origin of these compounds could not be identified. Here. we present the carbon isotopic ratios of glycine and E-aminocaproic acid (EACH), the two most abundant amino acids observed, in Stardust-returned foil samples measured by gas chromatography-combustion-isotope ratio crass spectrometry coupled with quadrupole mass spectrometry (GC-QMS/IRMS).

  15. Carbon Isotopic Measurements of Amino Acids in Stardust-Returned Samples

    NASA Technical Reports Server (NTRS)

    Elsila, Jamie

    2009-01-01

    NASA's Stardust spacecraft returned to Earth samples from comet 81P/Wild 2 in January 2006. Preliminary examinations revealed the presence of a suite of organic compounds including several amines and amino acids, but the origin of these compounds could not be identified. Here, we present the carbon isotopic ratios of glycine and e-aminocaproic acid (EACA), the two most abundant amino acids, in Stardust-returned foil samples measured by gas chromatography-combustion-isotope ratio mass spectrometry coupled with quadrupole mass spectrometry (GC-CAMS/IRMS).

  16. An investigation of techniques for the measurement and interpretation of cosmic ray isotopic abundances. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Wiedenbeck, M. E.

    1977-01-01

    An instrument, the Caltech High Energy Isotope Spectrometer Telescope was developed to measure isotopic abundances of cosmic ray nuclei by employing an energy loss - residual energy technique. A detailed analysis was made of the mass resolution capabilities of this instrument. A formalism, based on the leaky box model of cosmic ray propagation, was developed for obtaining isotopic abundance ratios at the cosmic ray sources from abundances measured in local interstellar space for elements having three or more stable isotopes, one of which is believed to be absent at the cosmic ray sources. It was shown that the dominant sources of uncertainty in the derived source ratios are uncorrelated errors in the fragmentation cross sections and statistical uncertainties in measuring local interstellar abundances. These results were applied to estimate the extent to which uncertainties must be reduced in order to distinguish between cosmic ray production in a solar-like environment and in various environments with greater neutron enrichments.

  17. Linking Carbonic Anhydrase Abundance and Diversity in Soils to Ecological Function

    NASA Astrophysics Data System (ADS)

    Pang, E.; Meredith, L. K.; Welander, P. V.

    2015-12-01

    Carbonic anhydrase (CA) is an ancient enzyme widespread among bacteria, archaea, and eukarya that catalyzes the following reaction: CO2 + H2O ⇌ HCO3- + H+. Its functions are critical for key cellular processes such as concentrating CO2 for autotrophic growth, pH regulation, and pathogen survival in hosts. Currently, there are six known CA classes (α, β, γ, δ, η, ζ) arising from several distinct evolutionary lineages. CA are widespread in sequenced genomes, with many organisms containing multiple classes of CA or multiple CA of the same class. Soils host rich microbial communities with diverse and important ecological functions, but the diversity and abundance of CA in soils has not been explored. CA appears to play an important, but poorly understood, role in some biogeochemical cycles such as those of CO2 and its oxygen isotope composition and also carbonyl sulfide (COS), which are potential tracers in predictive carbon cycle models. Recognizing the prevalence and functional significance of CA in soils, we used a combined bioinformatics and molecular biology approach to address fundamental questions regarding the abundance, diversity, and function of CA in soils. To characterize the abundance and diversity of the different CA classes in soils, we analyzed existing soil metagenomic and metatranscriptomic data from the DOE Joint Genome Institute databases. Out of the six classes of CA, we only found the α, β, and γ classes to be present in soils, with the β class being the most abundant. We also looked at genomes of sequenced soil microorganisms to learn what combination of CA classes they contain, from which we can begin to predict the physiological role of CA. To characterize the functional roles of the different CA classes in soils, we collected soil samples from a variety of biomes with diverse chemical and physical properties and quantified the rate of two CA-mediated processes: soil uptake of COS and acceleration of the oxygen isotope exchange

  18. Observations of Carbon Isotopic Fractionation in Interstellar Formaldehyde

    NASA Technical Reports Server (NTRS)

    Wirstrom, E. S.; Charnley, S. B.; Geppert, W. D.; Persson, C. M.

    2012-01-01

    Primitive Solar System materials (e.g. chondrites. IDPs, the Stardust sample) show large variations in isotopic composition of the major volatiles (H, C, N, and O ) even within samples, witnessing to various degrees of processing in the protosolar nebula. For ex ample. the very pronounced D enhancements observed in IDPs [I] . are only generated in the cold. dense component of the interstellar medium (ISM), or protoplanetary disks, through ion-molecule reactions in the presence of interstellar dust. If this isotopic anomaly has an interstellar origin, this leaves open the possibility for preservation of other isotopic signatures throughout the form ation of the Solar System. The most common form of carbon in the ISM is CO molecules, and there are two potential sources of C-13 fractionation in this reservoir: low temperature chemistry and selective photodissociation. While gas-phase chemistry in cold interstellar clouds preferentially incorporates C-13 into CO [2], the effect of self-shielding in the presence of UV radiation instead leads to a relative enhancement of the more abundant isotopologue, 12CO. Solar System organic material exhibit rather small fluctuations in delta C-13 as compared to delta N-15 and delta D [3][1], the reason for which is still unclear. However, the fact that both C-13 depleted and enhanced material exists could indicate an interstellar origin where the two fractionation processes have both played a part. Formaldehyde (H2CO) is observed in the gas-phase in a wide range of interstellar environments, as well as in cometary comae. It is proposed as an important reactant in the formation of more complex organic molecules in the heated environments around young stars, and formaldehyde polymers have been suggested as the common origin of chondritic insoluable organic matter (IOM) and cometary refractory organic solids [4]. The relatively high gas-phase abundance of H2CO observed in molecular clouds (10(exp- 9) - 10(exp- 8) relative to H2) makes

  19. 13C and 15N natural isotope abundance reflects breast cancer cell metabolism

    NASA Astrophysics Data System (ADS)

    Tea, Illa; Martineau, Estelle; Antheaume, Ingrid; Lalande, Julie; Mauve, Caroline; Gilard, Francoise; Barillé-Nion, Sophie; Blackburn, Anneke C.; Tcherkez, Guillaume

    2016-09-01

    Breast cancer is the most common cancer in women worldwide. Despite the information provided by anatomopathological assessment and molecular markers (such as receptor expression ER, PR, HER2), breast cancer therapies and prognostics depend on the metabolic properties of tumor cells. However, metabolomics have not provided a robust and congruent biomarker yet, likely because individual metabolite contents are insufficient to encapsulate all of the alterations in metabolic fluxes. Here, we took advantage of natural 13C and 15N isotope abundance to show there are isotopic differences between healthy and cancer biopsy tissues or between healthy and malignant cultured cell lines. Isotope mass balance further suggests that these differences are mostly related to lipid metabolism, anaplerosis and urea cycle, three pathways known to be impacted in malignant cells. Our results demonstrate that the isotope signature is a good descriptor of metabolism since it integrates modifications in C partitioning and N excretion altogether. Our present study is thus a starting point to possible clinical applications such as patient screening and biopsy characterization in every cancer that is associated with metabolic changes.

  20. Abundance and isotopic composition of gases in the martian atmosphere from the Curiosity rover.

    PubMed

    Mahaffy, Paul R; Webster, Christopher R; Atreya, Sushil K; Franz, Heather; Wong, Michael; Conrad, Pamela G; Harpold, Dan; Jones, John J; Leshin, Laurie A; Manning, Heidi; Owen, Tobias; Pepin, Robert O; Squyres, Steven; Trainer, Melissa

    2013-07-19

    Volume mixing and isotope ratios secured with repeated atmospheric measurements taken with the Sample Analysis at Mars instrument suite on the Curiosity rover are: carbon dioxide (CO2), 0.960(±0.007); argon-40 ((40)Ar), 0.0193(±0.0001); nitrogen (N2), 0.0189(±0.0003); oxygen, 1.45(±0.09) × 10(-3); carbon monoxide, < 1.0 × 10(-3); and (40)Ar/(36)Ar, 1.9(±0.3) × 10(3). The (40)Ar/N2 ratio is 1.7 times greater and the (40)Ar/(36)Ar ratio 1.6 times lower than values reported by the Viking Lander mass spectrometer in 1976, whereas other values are generally consistent with Viking and remote sensing observations. The (40)Ar/(36)Ar ratio is consistent with martian meteoritic values, which provides additional strong support for a martian origin of these rocks. The isotopic signature δ(13)C from CO2 of ~45 per mil is independently measured with two instruments. This heavy isotope enrichment in carbon supports the hypothesis of substantial atmospheric loss.

  1. Carbon isotopic patterns of amino acids associated with various microbial metabolic pathways and physiological conditions

    NASA Astrophysics Data System (ADS)

    Wang, P. L.; Hsiao, K. T.; Lin, L. H.

    2017-12-01

    Amino acids represent one of the most important categories of biomolecule. Their abundance and isotopic patterns have been broadly used to address issues related to biochemical processes and elemental cycling in natural environments. Previous studies have shown that various carbon assimilative pathways of microorganisms (e.g. autotrophy, heterotrophy and acetotrophy) could be distinguished by carbon isotopic patterns of amino acids. However, the taxonomic and catabolic coverage are limited in previous examination. This study aims to uncover the carbon isotopic patterns of amino acids for microorganisms remaining uncharacterized but bearing biogeochemical and ecological significance in anoxic environments. To fulfill the purpose, two anaerobic strains were isolated from riverine wetland and mud volcano in Taiwan. One strain is a sulfate reducing bacterium (related to Desulfovibrio marrakechensis), which is capable of utilizing either H2 or lactate, and the other is a methanogen (related to Methanolobus profundi), which grows solely with methyl-group compounds. Carbon isotope analyses of amino acids were performed on cells grown in exponential and stationary phase. The isotopic patterns were similar for all examined cultures, showing successive 13C depletion along synthetic pathways. No significant difference was observed for the methanogen and lactate-utilizing sulfate reducer harvested in exponential and stationary phases. In contrast, the H2-utilizing sulfate reducer harvested in stationary phase depleted and enriched 13C in aspartic acid and glycine, respectively when compared with that harvested in exponential phase. Such variations might infer the change of carbon flux during synthesis of these two amino acids in the reverse TCA cycle. In addition, the discriminant function analysis for all available data from culture studies further attests the capability of using carbon isotope patterns of amino acids in identifying microbial metabolisms.

  2. Experimental Assessment of Carbon Isotopes of Light Hydrocarbons under Different Redox Conditions

    NASA Astrophysics Data System (ADS)

    Fu, Q.; Chen, X.

    2017-12-01

    Hydrocarbons can be derived from a variety of carbon sources, by different processes, and under a wide range of physicochemical conditions. Other than bacterial activities facilitating biogenic hydrocarbon formation at low temperatures, decomposition of complex organic matter in sedimentary rocks at elevated temperatures produce thermogenic hydrocarbons, whereas abiogenic hydrocarbons are mainly generated through Fischer-Tropsch type synthesis with mineral catalysts. The carbon isotope has been used extensively to distinguish hydrocarbons of different origins and their formation conditions. For each type of hydrocarbons, however, environmental conditions may change reaction pathways and corresponding isotope fractionations. To better understand the variation of carbon isotopes caused by environmental variables, mineral constraints in particular, a series of laboratory experiments are conducted. In experiments where thermogenic hydrocarbons are formed, oil shale is the source material with different gypsum contents (0, 0.3, 0.5, and 1 wt.%). The abundance of generated light straight chain hydrocarbons decreases with increasing gypsum content, but their carbon isotopes become heavier. For example, the δ13C value of methane increases from -55.1‰ to -41.4‰ with gypsum varying between 0 and 1 wt.%. In similar experiments with the presence of MnO2, carbon isotope values of light alkanes are also higher, but with limited magnitudes (e.g., 3 to 4‰ for methane). In another experiment with dissolved H2 gas of 100 mmol/kg, light alkanes become depleted in 13C than experiments without H2. For example, there is a depletion of 2.7‰ for methane. The variation of carbon isotope values of light alkanes suggests the redox condition, constrained by mineral assemblage, fluid composition, and physical environment, play an important role in isotope fractionation. The pathway of hydrocarbon generation may be different under oxidized or reducing conditions. A set of experiments

  3. Abundances of carbon-enhanced metal-poor stars as constraints on their formation

    NASA Astrophysics Data System (ADS)

    Hansen, C. J.; Nordström, B.; Hansen, T. T.; Kennedy, C. R.; Placco, V. M.; Beers, T. C.; Andersen, J.; Cescutti, G.; Chiappini, C.

    2016-04-01

    Context. An increasing fraction of carbon-enhanced metal-poor (CEMP) stars is found as their iron abundance, [Fe/H], decreases below [Fe/H] =-2.0. The CEMP-s stars have the highest absolute carbon abundances, [C/H], and are thought to owe their enrichment in carbon and the slow neutron-capture (s-process) elements to mass transfer from a former asymptotic giant branch (AGB) binary companion. The most Fe-poor CEMP stars are normally single, exhibit somewhat lower [C/H] than CEMP-s stars, but show no s-process element enhancement (CEMP-no stars). Abundance determinations of CNO offer clues to their formation sites. Aims: Our aim is to use the medium-resolution spectrograph X-Shooter/VLT to determine stellar parameters and abundances for C, N, Sr, and Ba in several classes of CEMP stars in order to further classify and constrain the astrophysical formation sites of these stars. Methods: Atmospheric parameters for our programme stars were estimated from a combination of V-K photometry, model isochrone fits, and estimates from a modified version of the SDSS/SEGUE spectroscopic pipeline. We then used X-Shooter spectra in conjunction with the 1D local thermodynamic equilibrium spectrum synthesis code MOOG, 1D ATLAS9 atmosphere models to derive stellar abundances, and, where possible, isotopic 12C/13C ratios. Results: Abundances (or limits) of C, N, Sr, and Ba are derived for a sample of 27 faint metal-poor stars for which the X-Shooter spectra have sufficient signal-to-noise ratios (S/N). These moderate resolution, low S/N (~10-40) spectra prove sufficient to perform limited chemical tagging and enable assignment of these stars into the CEMP subclasses (CEMP-s and CEMP-no). According to the derived abundances, 17 of our sample stars are CEMP-s and 3 are CEMP-no, while the remaining 7 are carbon-normal. For four CEMP stars, the subclassification remains uncertain, and two of them may be pulsating AGB stars. Conclusions: The derived stellar abundances trace the formation

  4. Methylhopane Biomarker and Carbon Isotopic Evidence for Late Archean Aerobic Ecosystems

    NASA Technical Reports Server (NTRS)

    Eigenbrode, Jennifer L.; Freeman, Katherine H.; Summons, Roger E.

    2007-01-01

    Molecular fossils are particularly valuable in early Earth studies because they provide information about microbial sources and ecology. Here we report on the distribution of 2- methyl and 3-methylhopanes preserved in a 2.72-2.56 billion-year-old section of shallow and deepwater sediments of the Hamersley Province [Eigenbrode et aI., submitted]. These biomarkers are mostly from cyanobacteria and oxygen-respiring methanotrophs, respectively. The relative abundance of 2-methylhopanes increases with carbonate abundance in shallow-water facies indicating cyanobacteria were key microbes in shallow ecosystems and suggesting they supplied both molecular oxygen and fixed carbon. The relative abundance of 3-methylhopane strongly correlates with kerogen-carbon isotopic values, and is more abundant in the samples with 13C-enriched signatures. Thus, molecular data provides evidence for cycling of methane in shallow settings, even though the anoxic deeper environments bear stronger 13C-depletion, which together suggests a more complex methane cycle than previously envisioned. Detailed facies analysis of the Hamersley carbon-isotope record reveals temporal changes suggesting continued oxidation of shallow settings favoring the expansion of aerobic ecosystems and respiring organisms [Eigenbrode et aI., 2006, PNAS, 103: 15759]. Similar analysis of published carbon-isotopic records suggests similar, but diachronous, expansion of oxygenated habitats in shallow then deep waters as anaerobic microbial communities gave way to respiring communities fueled by oxygenic photosynthesis before the post 2.45-Ga atmospheric oxygenation event [Eigenbrode et aI., 2006]. The robust relationships observed provide geochemical support for methanogenesis, aerobic methanotrophy, and oxygenic photosynthesis in the late Archean, as well as major ecological shifts linked to biogeochemical reorganization.

  5. Sims Analysis of Water Abundance and Hydrogen Isotope in Lunar Highland Plagioclase

    NASA Technical Reports Server (NTRS)

    Hui, Hejiu; Guan, Yunbin; Chen, Yang; Peslier, Anne H.; Zhang, Youxue; Liu, Yang; Rossman, George R.; Eiler, John M.; Neal, Clive R.

    2015-01-01

    The detection of indigenous water in mare basaltic glass beads has challenged the view established since the Apollo era of a "dry" Moon. Since this discovery, measurements of water in lunar apatite, olivine-hosted melt inclusions, agglutinates, and nominally anhydrous minerals have confirmed that lunar igneous materials contain water, implying that some parts of lunar mantle may have as much water as Earth's upper mantle. The interpretation of hydrogen (H) isotopes in lunar samples, however, is controversial. The large variation of H isotope ratios in lunar apatite (delta Deuterium = -202 to +1010 per mille) has been taken as evidence that water in the lunar interior comes from the lunar mantle, solar wind protons, and/or comets. The very low deuterium/H ratios in lunar agglutinates indicate that solar wind protons have contributed to their hydrogen content. Conversely, H isotopes in lunar volcanic glass beads and olivine-hosted melt inclusions being similar to those of common terrestrial igneous rocks, suggest a common origin for water in both Earth and Moon. Lunar water could be inherited from carbonaceous chondrites, consistent with the model of late accretion of chondrite-type materials to the Moon as proposed by. One complication about the sources of lunar water, is that geologic processes (e.g., late accretion and magmatic degassing) may have modified the H isotope signatures of lunar materials. Recent FTIR analyses have shown that plagioclases in lunar ferroan anorthosite contain approximately 6 ppm H2O. So far, ferroan anorthosite is the only available lithology that is believed to be a primary product of the lunar magma ocean (LMO). A possible consequence is that the LMO could have contained up to approximately 320 ppm H2O. Here we examine the possible sources of water in the LMO through measurements of water abundances and H isotopes in plagioclase of two ferroan anorthosites and one troctolite from lunar highlands.

  6. Relationships between tree height and carbon isotope discrimination

    Treesearch

    Nate G. McDowell; Barbara J. Bond; Lee T. Dickman; Michael G. Ryan; David Whitehead

    2011-01-01

    Understanding how tree size impacts leaf- and crown-level gas exchange is essential to predicting forest yields and carbon and water budgets. The stable carbon isotope ratio of organic matter has been used to examine the relationship of gas exchange to tree size for a host of species because it carries a temporally integrated signature of foliar photosynthesis and...

  7. Abundance of SiC2 in carbon star envelopes

    NASA Astrophysics Data System (ADS)

    Massalkhi, S.; Agúndez, M.; Cernicharo, J.; Velilla Prieto, L.; Goicoechea, J. R.; Quintana-Lacaci, G.; Fonfría, J. P.; Alcolea, J.; Bujarrabal, V.

    2018-03-01

    Context. Silicon carbide dust is ubiquitous in circumstellar envelopes around C-rich asymptotic giant branch (AGB) stars. However, the main gas-phase precursors leading to the formation of SiC dust have not yet been identified. The most obvious candidates among the molecules containing an Si-C bond detected in C-rich AGB stars are SiC2, SiC, and Si2C. To date, the ring molecule SiC2 has been observed in a handful of evolved stars, while SiC and Si2C have only been detected in the C-star envelope IRC +10216. Aim. We aim to study how widespread and abundant SiC2, SiC, and Si2C are in envelopes around C-rich AGB stars, and whether or not these species play an active role as gas-phase precursors of silicon carbide dust in the ejecta of carbon stars. Methods: We carried out sensitive observations with the IRAM 30 m telescope of a sample of 25 C-rich AGB stars to search for emission lines of SiC2, SiC, and Si2C in the λ 2 mm band. We performed non-LTE excitation and radiative transfer calculations based on the LVG method to model the observed lines of SiC2 and to derive SiC2 fractional abundances in the observed envelopes. Results: We detect SiC2 in most of the sources, SiC in about half of them, and do not detect Si2C in any source except IRC +10216. Most of these detections are reported for the first time in this work. We find a positive correlation between the SiC and SiC2 line emission, which suggests that both species are chemically linked; the SiC radical is probably the photodissociation product of SiC2 in the external layer of the envelope. We find a clear trend where the denser the envelope, the less abundant SiC2 is. The observed trend is interpreted as evidence of efficient incorporation of SiC2 onto dust grains, a process that is favored at high densities owing to the higher rate at which collisions between particles take place. Conclusions: The observed behavior of a decline in the SiC2 abundance with increasing density strongly suggests that SiC2 is an

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

    NASA Technical Reports Server (NTRS)

    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.

  9. Rhenium-osmium isotope and highly-siderophile-element abundance systematics of angrite meteorites

    NASA Astrophysics Data System (ADS)

    Riches, Amy J. V.; Day, James M. D.; Walker, Richard J.; Simonetti, Antonio; Liu, Yang; Neal, Clive R.; Taylor, Lawrence A.

    2012-11-01

    Coupled 187Os/188Os compositions and highly-siderophile-element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundance data are reported for eight angrite achondrite meteorites that include quenched- and slowly-cooled textural types. These data are combined with new major- and trace-element concentrations determined for bulk-rock powder fractions and constituent mineral phases, to assess angrite petrogenesis. Angrite meteorites span a wide-range of HSE abundances from <0.005 ppb Os (e.g., Northwest Africa [NWA] 1296; Angra dos Reis) to >100 ppb Os (NWA 4931). Chondritic to supra-chondritic 187Os/188Os (0.1201-0.2127) measured for Angra dos Reis and quenched-angrites correspond to inter- and intra-sample heterogeneities in Re/Os and HSE abundances. Quenched-angrites have chondritic-relative rare-earth-element (REE) abundances at 10-15×CI-chondrite, and their Os-isotope and HSE abundance variations represent mixtures of pristine uncontaminated crustal materials that experienced addition (<0.8%) of exogenous chondritic materials during or after crystallization. Slowly-cooled angrites (NWA 4590 and NWA 4801) have fractionated REE-patterns, chondritic to sub-chondritic 187Os/188Os (0.1056-0.1195), as well as low-Re/Os (0.03-0.13), Pd/Os (0.071-0.946), and relatively low-Pt/Os (0.792-2.640). Sub-chondritic 187Os/188Os compositions in NWA 4590 and NWA 4801 are unusual amongst planetary basalts, and their HSE and REE characteristics may be linked to melting of mantle sources that witnessed prior basaltic melt depletion. Angrite HSE-Yb systematics suggest that the HSE behaved moderately-incompatibly during angrite magma crystallization, implying the presence of metal in the crystallizing assemblage. The new HSE abundance and 187Os/188Os compositions indicate that the silicate mantle of the angrite parent body(ies) (APB) had HSE abundances in chondritic-relative proportions but at variable abundances at the time of angrite crystallization. The HSE systematics of angrites are

  10. The Antarctic environment and its effect upon the total carbon and sulfur abundances in recovered meteorites

    NASA Technical Reports Server (NTRS)

    Gibson, E. K., Jr.; Andrawes, F. F.

    1980-01-01

    Total carbon and sulfur abundances have been measured for 25 meteorites recovered from the Allan Hills area of Antarctica. The majority (greater than 67%) of the meteorites analyzed do not contain enriched carbon abundances resulting from weathering processes. The presence of secondary carbonates in samples which give no apparent evidence of weathering was noted during pyrolysis experiments, despite the 'normal' total carbon abundances. In selected cases, the surfaces of weathered samples may contain up to a factor of two greater carbon content than the interior. Variations in carbon abundances may reflect the degree of weathering and the amount of secondary minerals present. One of the surprises of this study is that the majority of the Antarctic meteorites studied do not exhibit total carbon and sulfur abundances outside the ranges previously observed for falls.

  11. The evolution of the global selenium cycle: Secular trends in Se isotopes and abundances

    NASA Astrophysics Data System (ADS)

    Stüeken, E. E.; Buick, R.; Bekker, A.; Catling, D.; Foriel, J.; Guy, B. M.; Kah, L. C.; Machel, H. G.; Montañez, I. P.; Poulton, S. W.

    2015-08-01

    The Earth's surface has undergone major transitions in its redox state over the past three billion years, which have affected the mobility and distribution of many elements. Here we use Se isotopic and abundance measurements of marine and non-marine mudrocks to reconstruct the evolution of the biogeochemical Se cycle from ∼3.2 Gyr onwards. The six stable isotopes of Se are predominantly fractionated during redox reactions under suboxic conditions, which makes Se a potentially valuable new tool for identifying intermediate stages from an anoxic to a fully oxygenated world. δ82/78Se shows small fractionations of mostly less than 2‰ throughout Earth's history and all are mass-dependent within error. In the Archean, especially after 2.7 Gyr, we find an isotopic enrichment in marine (+0.37 ± 0.27‰) relative to non-marine samples (-0.28 ± 0.67‰), paired with increasing Se abundances. Student t-tests show that these trends are statistically significant. Although we cannot completely rule out the possibility of volcanic Se addition, these trends may indicate the onset of oxidative weathering on land, followed by non-quantitative reduction of Se oxyanions during fluvial transport. The Paleoproterozoic Great Oxidation Event (GOE) is not reflected in the marine δ82/78Se record. However, we find a major inflection in the secular δ82/78Se trend during the Neoproterozoic, from a Precambrian mean of +0.42 ± 0.45‰ to a Phanerozoic mean of -0.19 ± 0.59‰. This drop probably reflects the oxygenation of the deep ocean at this time, stabilizing Se oxyanions throughout the water column. Since then, reduction of Se oxyanions has likely been restricted to anoxic basins and diagenetic environments in sediments. In light of recent Cr isotope data, it is likely that oxidative weathering before the Neoproterozoic produced Se oxyanions in the intermediate redox state SeIV, whereas the fully oxidized species SeVI became more abundant after the Neoproterozoic rise of

  12. Uranium isotope fractionation in biogenic carbonates: biological effects

    NASA Astrophysics Data System (ADS)

    Chen, X.; Romaniello, S. J.; Herrmann, A. D.; Anbar, A. D.

    2017-12-01

    Recent laboratory experiments have demonstrated small but potentially significant isotope fractionation ( 0.10 ‰ for 238U/235U) during uranium (U) incorporation into abiotic calcite and aragonite, with heavier U isotopes preferentially enriched in the precipitates [1]. In contrast, measurements of natural biogenic carbonates to date have not been able to resolve significant U isotopic fractionation from seawater although this might be expected given a typical measurement precision of ± 0.10 ‰. Determining whether or not biogenic carbonates display U isotope fractionation similar to abiotic carbonates could have important implications for understanding the mechanisms of U incorporation into various biogenic carbonates. Furthermore, because most marine carbonates are biogenic, the extent of isotopic fractionation, if any, could have important implications for the interpretation of sedimentary carbonates record similar to effects observed for Cr and B isotopes [2, 3]. To resolve this discrepancy, we utilized a higher precision 238U/235U method which uses larger sample sizes to improve measurement precision of natural samples to ± 0.02 ‰ (2 se, N = 6) [4]. Using this method, we have surveyed 238U/235U in primary biogenic skeletal carbonates including scleractinian corals, green and red algae, and mollusks, as well as non-skeletal carbonates such as stromatolites, ooids, and carbonate sands from the Bahamas, Gulf of California, and French Polynesia. New high-precision U isotopes measurements reveal that biogenic skeletal carbonates are typically 0.02 - 0.08 ‰ heavier than modern seawater. Scleractinian corals display values closest to seawater (- 0.37 ‰), while green algae, red algae, mollusks, and echinoderms display variable but larger extents of fractionation up to 0.08 ‰. The direction and magnitude of U isotope fractionation in these biogenic precipitates are generally consistent with results from abiotic coprecipitation experiments, but may be

  13. A Novel Airborne Carbon Isotope Analyzer for Methane and Carbon Dioxide Source Fingerprinting

    NASA Astrophysics Data System (ADS)

    Berman, E. S.; Huang, Y. W.; Owano, T. G.; Leifer, I.

    2014-12-01

    Recent field studies on major sources of the important greenhouse gas methane (CH4) indicate significant underestimation of methane release from fossil fuel industrial (FFI) and animal husbandry sources, among others. In addition, uncertainties still exist with respect to carbon dioxide (CO2) measurements, especially source fingerprinting. CO2 isotopic analysis provides a valuable in situ measurement approach to fingerprint CH4 and CO2as associated with combustion sources, leakage from geologic reservoirs, or biogenic sources. As a result, these measurements can characterize strong combustion source plumes, such as power plant emissions, and discriminate these emissions from other sources. As part of the COMEX (CO2 and MEthane eXperiment) campaign, a novel CO2 isotopic analyzer was installed and collected data aboard the CIRPAS Twin Otter aircraft. Developing methods to derive CH4 and CO2 budgets from remote sensing data is the goal of the summer 2014 COMEX campaign, which combines hyperspectral imaging (HSI) and non-imaging spectroscopy (NIS) with in situ airborne and surface data. COMEX leverages the synergy between high spatial resolution HSI and moderate spatial resolution NIS. The carbon dioxide isotope analyzer developed by Los Gatos Research (LGR) uses LGR's patented Off-Axis ICOS (Integrated Cavity Output Spectroscopy) technology and incorporates proprietary internal thermal control for high sensitivity and optimal instrument stability. This analyzer measures CO2 concentration as well as δ13C, δ18O, and δ17O from CO2 at natural abundance (100-3000 ppm). The laboratory accuracy is ±1.2 ppm (1σ) in CO2 from 370-1000 ppm, with a long-term (1000 s) precision of ±0.012 ppm. The long-term precision for both δ13C and δ18O is 0.04 ‰, and for δ17O is 0.06 ‰. The analyzer was field-tested as part of the COWGAS campaign, a pre-cursor campaign to COMEX in March 2014, where it successfully discriminated plumes related to combustion processes associated with

  14. Abundance, stable isotopic composition, and export fluxes of DOC, POC, and DIC from the Lower Mississippi River during 2006–2008

    USGS Publications Warehouse

    Cai, Yihua; Guo, Laodong; Wang, Xuri; Aiken, George R.

    2015-01-01

    Sources, abundance, isotopic compositions, and export fluxes of dissolved inorganic carbon (DIC), dissolved and colloidal organic carbon (DOC and COC), and particulate organic carbon (POC), and their response to hydrologic regimes were examined through monthly sampling from the Lower Mississippi River during 2006–2008. DIC was the most abundant carbon species, followed by POC and DOC. Concentration and δ13C of DIC decreased with increasing river discharge, while those of DOC remained fairly stable. COC comprised 61 ± 3% of the bulk DOC with similar δ13C abundances but higher percentages of hydrophobic organic acids than DOC, suggesting its aromatic and diagenetically younger status. POC showed peak concentrations during medium flooding events and at the rising limb of large flooding events. While δ13C-POC increased, δ15N of particulate nitrogen decreased with increasing discharge. Overall, the differences in δ13C between DOC or DIC and POC show an inverse correlation with river discharge. The higher input of soil organic matter and respired CO2 during wet seasons was likely the main driver for the convergence of δ13C between DIC and DOC or POC, whereas enhanced in situ primary production and respiration during dry seasons might be responsible for their isotopic divergence. Carbon export fluxes from the Mississippi River were estimated to be 13.6 Tg C yr−1 for DIC, 1.88 Tg C yr−1 for DOC, and 2.30 Tg C yr−1 for POC during 2006–2008. The discharge-normalized DIC yield decreased during wet seasons, while those of POC and DOC increased and remained constant, respectively, implying variable responses in carbon export to the increasing discharge.

  15. Does burial diagenesis reset pristine isotopic compositions in paleosol carbonates?

    NASA Astrophysics Data System (ADS)

    Bera, M. K.; Sarkar, A.; Tandon, S. K.; Samanta, A.; Sanyal, P.

    2010-11-01

    Sedimentological study of early Oligocene continental carbonates from the fluvial Dagshai Formation of the Himalayan foreland basin, India resulted in the recognition of four different types namely, soil, palustrine, pedogenically modified palustrine and groundwater carbonates. Stable oxygen and carbon isotopic ( δ18O and δ13C) analyses of fabric selective carbonate microsamples show that although the pristine isotopic compositions are largely altered during deep-burial diagenesis, complete isotopic homogenization does not occur. δ18O and δ13C analyses of ~ 200 calcrete and palustrine carbonates from different stratigraphic horizons and comparison with δ18O of more robust bioapatite (fossil vertebrate tooth) phase show that dense micrites (~ > 70% carbonate) invariably preserve the pristine δ18O value (mean) of ~ - 9.8‰, while altered carbonates show much lower δ18O value ~ - 13.8‰. Such inhomogeneity causes large intra-sample and intra-soil profile variability as high as > 5‰, suggesting that soils behave like a closed system where diagenetic overprinting occurs in local domains. A simple fluid-rock interaction model suggests active participation of clay minerals to enhance the effect of fluid-rock ratio in local domains during diagenesis. This places an upper limit of 70% micrite concentration above which the effect of diagenetic alteration is minimal. Careful sampling of dense micritic part of the soil carbonate nodules, therefore, does provide pristine isotopic composition and it is inappropriate, as proposed recently, to reject the paleoclimatic potential of all paleosol carbonates affected by burial diagenesis. Based on pristine δ13C value of - 8.8 ± 0.2‰ in soil carbonates an atmospheric CO 2 concentration between ~ 764 and ~ 306 ppmv is estimated for the early Oligocene (~ 31 Ma) Dagshai time. These data show excellent agreement between two independent proxy records (viz. soil carbonate and marine alkenone) and support early Oligocene

  16. Carbon and nitrogen isotopic compositions of alkyl porphyrins from the Triassic Serpiano oil shale

    NASA Technical Reports Server (NTRS)

    Chicarelli, M. I.; Hayes, J. M.; Popp, B. N.; Eckardt, C. B.; Maxwell, J. R.

    1993-01-01

    The carbon and nitrogen isotopic compositions of seven of the most abundant alkylporphyrins from the Serpiano oil shale (marine, Triassic) were determined. For the C31 and C32 butanoporphyrins, values of delta 13CPDB and delta 15NAIR averaged -24.0% and -3.1%. In contrast, the C31 and C32 methylpropanoporphyrins, DPEP, and a C30 13-nor etioporphyrin had delta 13C and delta 15N values averaging -27.5 and -3.3%, respectively. Carbon and nitrogen isotopic values for kerogen averaged -30.8 and -0.9, whereas those for total extract averaged -31.6, and -4.0%. The butanoporphyrins apparently derive from a biological source different from that giving rise to the other porphyrins, their 13C enrichment not being related to carbon isotopic fractionation accompanying diagenetic reactions. The delta 15N values for all the porphyrins indicate that the depletion of 15N observed in the kerogen is of primary origin. Consistent with the very high abundance of hopanoids and methyl hopanoids in the aliphatic hydrocarbon fraction, it is suggested that cyanobacterial fixation of N2 may have been the main cause of 15N depletion.

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

    NASA Astrophysics Data System (ADS)

    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

  18. Isotopic anomalies from neutron reactions during explosive carbon burning

    NASA Technical Reports Server (NTRS)

    Lee, T.; Schramm, D. N.; Wefel, J. P.; Blake, J. B.

    1978-01-01

    The possibility that the newly discovered correlated isotopic anomalies for heavy elements in the Allende meteorite were synthesized in the secondary neutron capture episode during the explosive carbon burning, the possible source of the O-16 and Al-26 anomalies, is examined. Explosive carbon burning calculations under typical conditions were first performed to generate time profiles of temperature, density, and free particle concentrations. These quantities were inputted into a general neutron capture code which calculates the resulting isotopic pattern from exposing the preexisting heavy seed nuclei to these free particles during the explosive carbon burning conditions. The interpretation avoids the problem of the Sr isotopic data and may resolve the conflict between the time scales inferred from 1-129, Pu-244, and Al-26.

  19. Hyperfine Induced Transitions as Diagnostics of Low Density Plasmas and Isotopic Abundance ratios.

    NASA Astrophysics Data System (ADS)

    Brage, T.; Judge, P. G.; Aboussaid, A.; Godefroid, M. R.; Jonsson, P.; Leckrone, D. S.

    1996-05-01

    We propose a new diagnostics of isotope abundance ratios and electron densities for low density plasmas, in the form of J = 0 -> J(') = 0 radiative transitions. These are usually viewed as being allowed only through two-photon decay, but they may also be induced by the hyperfine (HPF) interaction in atomic ions. This predicts a companion line to the E1] and M2 lines in the UV0.01 multiplet of ions isoelectronic to beryllium (e.g. C III, N IV, O V and Fe XXII) or magnesium (e.g. Si II, Ca IX, Fe XV and Ni XVII). As an example the companion line to the well known lambda lambda 1906.7,1908.7 lines in C III will be at 1909.597 Angstroms, but only present in the (13) C isotope (which has nuclear spin different from zero). We present new and accurate decay rates for the nsnp (3P^oJ) -> ns(2) (1S_{J('}=0)) transitions in ions of the Be (n=2) and Mg (n=3) isoelectronic sequences. We show that the HPF induced decay rates for the J = 0 -> J(') = 0 transitions are many orders of magnitude larger than those for the competing two-photon processes and, when present, are typically one or two orders of magnitude smaller than the decay rates of the magnetic quadrupole ( J = 2-> J(') = 0) transitions for these ions. We show that several of these HPF-induced transitions are of potential astrophysical interest, in ions of C, N, Na, Mg, Al, Si, K, Cr, Fe and Ni. We highlight those cases that may be of particular diagnostic value for determining isotopic abundance ratios and/or electron densities from UV or EUV emission line data. We present our atomic data in the form of scaling laws so that, given the isotopic nuclear spin and magnetic moment, a simple expression yields estimates for HPF induced decay rates. We examine some UV solar and nebular data in the light of these new results and suggest possible cases for future study. We could not find evidence for the existence of HPF induced lines in the spectra we examined, but we demonstrate that existing data have come close to providing

  20. Late Glacial Tropical Savannas in Sundaland Inferred From Stable Carbon Isotope Records of Cave Guano

    NASA Astrophysics Data System (ADS)

    Wurster, C. M.; Bird, M. I.; Bull, I.; Dungait, J.; Bryant, C. L.; Ertunç, T.; Hunt, C.; Lewis, H. A.; Paz, V.

    2008-12-01

    During the Last Glacial Period (LGP), reduced global sea level exposed the continental shelf south of Thailand to Sumatra, Java, and Borneo to form the contiguous continent of Sundaland. However, the type and extent of vegetation that existed on much of this exposed landmass during the LGP remains speculative. Extensive bird and bat guano deposits in caves throughout this region span beyond 40,000 yr BP, and contain a wealth of untapped stratigraphic palaeoenvironmental information. Stable carbon isotope ratios of insectivorous bird and bat guano contain a reliable record of the animal's diet and, through non-specific insect predation, reflect the relative abundance of major physiological pathways in plants. Various physiological pathways of carbon fixation in plants yield differing stable carbon isotope ratios. Stable carbon isotope values of C3 plants are lower than C4 vegetation due to different enzymatic discriminations of the heavy isotope through the carbon fixing pathways. In tropical locales, grasses nearly always follow the C4 photosynthetic pathway, whereas tropical rainforest uses C3 photosynthesis, providing a proxy for vegetation and therefore climate change in the past. Here we discuss four guano stable-isotope records, based on insect cuticle and n-alkane analysis, supplemented by pollen analysis. All sites suggest a C3 dominated ecosystem for the Holocene, consistent with the wet tropical forest vegetation present at all locations. Two sites from Palawan Island, Philippines, record stable carbon isotope values of guano that document a drastic change from C3 (forest) to C4 (savanna) dominated ecosystems during the Last Glacial Maximum (LGM). A third location, at Niah Great Cave, Malaysia, indicates C3-dominant vegetation throughout the record, but does display variation in stable carbon isotope values likely linked to humidity changes. A fourth location, Batu Caves in Peninsular Malaysia, also indicates open vegetation during the LGM. Vegetation

  1. Isotopic compositions of carbonates and organic carbon from upper Proterozoic successions in Namibia: stratigraphic variation and the effects of diagenesis and metamorphism

    NASA Technical Reports Server (NTRS)

    Kaufman, A. J.; Hayes, J. M.; Knoll, A. H.; Germs, G. J.

    1991-01-01

    The carbon isotope geochemistry of carbonates and organic carbon in the late Proterozoic Damara Supergroup of Namibia, including the Nama, Witvlei, and Gariep groups on the Kalahari Craton and the Mulden and Otavi groups on the Congo Craton, has been investigated as an extension of previous studies of secular variations in the isotopic composition of late Proterozoic seawater. Subsamples of microspar and dolomicrospar were determined, through petrographic and cathodoluminescence examination, to represent the "least-altered" portions of the rock. Carbon-isotopic abundances in these phases are nearly equal to those in total carbonate, suggesting that 13C abundances of late Proterozoic fine-grained carbonates have not been significantly altered by meteoric diagenesis, although 18O abundances often differ significantly. Reduced and variable carbon-isotopic differences between carbonates and organic carbon in these sediments indicate that isotopic compositions of organic carbon have been altered significantly by thermal and deformational processes, likely associated with the Pan-African Orogeny. Distinctive stratigraphic patterns of secular variation, similar to those noted in other, widely separated late Proterozoic basins, are found in carbon-isotopic compositions of carbonates from the Nama and Otavi groups. For example, in Nama Group carbonates delta 13C values rise dramatically from -4 to +5% within a short stratigraphic interval. This excursion suggests correlation with similar excursions noted in Ediacaran-aged successions of Siberia, India, and China. Enrichment of 13C (delta 13C> +5%) in Otavi Group carbonates reflects those in Upper Riphean successions of the Akademikerbreen Group, Svalbard, its correlatives in East Greenland, and the Shaler Group, northwest Canada. The widespread distribution of successions with comparable isotopic signatures supports hypotheses that variations in delta 13C reflect global changes in the isotopic composition of late

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

    NASA Technical Reports Server (NTRS)

    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).

  3. Specific activity and isotope abundances of strontium in purified strontium-82

    SciTech Connect

    Fitzsimmons, J. M.; Medvedev, D. G.; Mausner, L. F.

    2015-11-12

    A linear accelerator was used to irradiate a rubidium chloride target with protons to produce strontium-82 (Sr-82), and the Sr-82 was purified by ion exchange chromatography. The amount of strontium associated with the purified Sr-82 was determined by either: ICP-OES or method B which consisted of a summation of strontium quantified by gamma spectroscopy and ICP-MS. The summation method agreed within 10% to the ICP-OES for the total mass of strontium and the subsequent specific activities were determined to be 0.25–0.52 TBq mg -1. Method B was used to determine the isotope abundances by weight% of the purified Sr-82, andmore » the abundances were: Sr-82 (10–20.7%), Sr-83 (0–0.05%), Sr-84 (35–48.5%), Sr-85 (16–25%), Sr-86 (12.5–23%), Sr-87 (0%), and Sr-88 (0–10%). The purified strontium contained mass amounts of Sr-82, Sr-84, Sr-85, Sr-86, and Sr-88 in abundances not associated with natural abundance, and 90% of the strontium was produced by the proton irradiation. A comparison of ICP-OES and method B for the analysis of Sr-82 indicated analysis by ICP-OES would be easier to determine total mass of strontium and comply with regulatory requirements. An ICP-OES analytical method for Sr-82 analysis was established and validated according to regulatory guidelines.« less

  4. Characteristics of Martian Crustal Materials and Implications for Magmatic Assimilation: Preliminary Re-Os Isotope and Highly Siderophile Element Abundance Data for Nakhlites and Tissint

    NASA Astrophysics Data System (ADS)

    Mari, N.; Riches, A. J. V.; Hallis, L. J.; Lee, M. R.

    2017-07-01

    This project, for the first time, aims to integrate nakhlite Os-isotope compositions and HSE abundance data with S-isotope compositions for sample fractions for which textural information is constrained prior to destructive analyses.

  5. Development of a Field-Deployable Methane Carbon Isotope Analyzer

    NASA Astrophysics Data System (ADS)

    Dong, Feng; Baer, Douglas

    2010-05-01

    Methane is a potent greenhouse gas, whose atmospheric surface mixing ratio has almost doubled compared with preindustrial values. Methane can be produced by biogenic processes, thermogenic processes or biomass, with different isotopic signatures. As a key molecule involved in the radiative forcing in the atmosphere, methane is thus one of the most important molecules linking the biosphere and atmosphere. Therefore precise measurements of mixing ratios and isotopic compositions will help scientists to better understand methane sources and sinks. To date, high precision isotope measurements have been exclusively performed with conventional isotope ratio mass spectrometry, which involves intensive labor and is not readily field deployable. Optical studies using infrared laser spectroscopy have also been reported to measure the isotopic ratios. However, the precision of optical-based analyses, to date, is typically unsatisfactory without pre-concentration procedures. We present characterization of the performance of a portable Methane Carbon Isotope Analyzer (MCIA), based on cavity enhanced laser absorption spectroscopy technique, that provides in-situ measurements of the carbon isotope ratio (13C/12C or del_13C) and methane mixing ratio (CH4). The sample is introduced to the analyzer directly without any requirement for pretreatment or preconcentration. A typical precision of less than 1 per mill (< 0.1%) with a 10-ppm methane sample can be achieved in a measurement time of less than 100 seconds. The MCIA can report carbon isotope ratio and concentration measurements over a very wide range of methane concentrations. Results of laboratory tests and field measurements will be presented.

  6. Aptian Carbon Isotope Stratigraphy in Sierra del Rosario, Northeastern Mexico

    NASA Astrophysics Data System (ADS)

    Barragan-Manzo, R.; Moreno-Bedmar, J.; Nuñez, F.; Company, M.

    2013-05-01

    In most recent years Aptian carbon isotope stratigraphy has been widely studied in Europe where isotopic stages have been developed to correlate global events. Two negative excursions have been recorded in the Lower Aptian, the older is OAE 1a in the middle part, and a younger negative excursion labeled "Aparein level", which occurs in the uppermost part of the Lower Aptian. In Mexico previous works reported a carbon isotope negative excursion in the lowermost part of the La Peña Formation that was assigned to the onset of Oceanic Anoxic Event 1a (=OAE 1a). In this work we study the isotopic record of the δ13Ccarb of 32 bulk rock samples of limestone from the uppermost part of the Cupido Formation and the lower part of the La Peña Formation at the Francisco Zarco Dam Section (=FZD), Durango State, northeastern Mexico. The isotopic data are calibrated using the latest ammonite biostratigraphic biozonation of the Aptian. This age calibration allows us to make a precise correlation between the carbon isotopic record of Mexico and several European sections (e.g. Spain and France). In the studied Francisco Zarco Dam section we recognize a negative carbon isotopic excursion in the Dufrenoyia justinae ammonite Zone that corresponds to the "Aparein level", which we correlate using the ammonite zonation of others European sections (Figure 1). This correlation allows us to see how the negative excursion that characterizes the "Aparein level" is consistent with the C7 segment. Thus, our recent stratigraphic study allows us to conclude that the ammonite record in the lowermost part of the La Peña Formation is regionally isochronous, and correlates with the Dufrenoyia justinae Zone and Lower Aptian isotope interval C7. In agreement to these biostratigraphic data, the supposed record of the OAE 1a in the lowermost part of the La Peña Formation is not correct, and the carbon isotope negative excursion must be assigned to the younger event "Aparein level". Taking this into

  7. Combining stable isotope isotope geochemistry and carbonic anhydrase activity to trace vital effect in carbonate precipitation experiments

    NASA Astrophysics Data System (ADS)

    Thaler, C.; Ader, M.; Menez, B.; Guyot, F. J.

    2013-12-01

    Carbonates precipitated by skeleton-forming eukaryotic organisms are often characterized by non-equilibrium isotopic signatures. This specificity is referred to as the "vital effect" and can be used as an isotopic evidence to trace life. Combining stable isotope geochemistry and enzymology (using the enzyme carbonic anhydrase) we aim to demonstrate that prokaryotes are also able to precipitate carbonate with a non-equilibrium d18OCaCO3. Indeed, if in an biomineralization experiment carbonates are precipitated with a vital effect, the addition of carbonic anhydrase should drive the system to isotope equilibrium, And provide a comparison point to estimate the vital effect range. This protocol allowed us to identify a -20‰ vital effect for the d18O of carbonates precipitated by Sporosarcina pasteurii, a bacterial model of carbonatogen metabolisms. This approach is thus a powerfull tool for the understanding of microbe carbonatogen activity and will probably bring new insights into the understanding of bacterial activity in subsurface and during diagenesis.

  8. Testing Urey's carbonate-silicate cycle using the calcium isotopic composition of sedimentary carbonates

    NASA Astrophysics Data System (ADS)

    Blättler, Clara L.; Higgins, John A.

    2017-12-01

    Carbonate minerals constitute a major component of the sedimentary geological record and an archive of a fraction of the carbon and calcium cycled through the Earth's surface reservoirs for over three billion years. For calcium, carbonate minerals constitute the ultimate sink for almost all calcium liberated during continental and submarine weathering of silicate minerals. This study presents >500 stable isotope ratios of calcium in Precambrian carbonate sediments, both limestones and dolomites, in an attempt to characterize the isotope mass balance of the sedimentary carbonate reservoir through time. The mean of the dataset is indistinguishable from estimates of the calcium isotope ratio of bulk silicate Earth, consistent with the Urey cycle being the dominant mechanism exchanging calcium among surface reservoirs. The variability in bulk sediment calcium isotope ratios within each geological unit does not reflect changes in the global calcium cycle, but rather highlights the importance of local mineralogical and/or diagenetic effects in the carbonate record. This dataset demonstrates the potential for calcium isotope ratios to help assess these local effects, such as the former presence of aragonite, even in rocks with a history of neomorphism and recrystallization. Additionally, 29 calcium isotope measurements are presented from ODP (Ocean Drilling Program) Site 801 that contribute to the characterization of altered oceanic crust as an additional sink for calcium, and whose distinct isotopic signature places a limit on the importance of this subduction flux over Earth history.

  9. Beyond temperature: Clumped isotope signatures in dissolved inorganic carbon species and the influence of solution chemistry on carbonate mineral composition

    NASA Astrophysics Data System (ADS)

    Tripati, Aradhna K.; Hill, Pamela S.; Eagle, Robert A.; Mosenfelder, Jed L.; Tang, Jianwu; Schauble, Edwin A.; Eiler, John M.; Zeebe, Richard E.; Uchikawa, Joji; Coplen, Tyler B.; Ries, Justin B.; Henry, Drew

    2015-10-01

    ;Clumped-isotope; thermometry is an emerging tool to probe the temperature history of surface and subsurface environments based on measurements of the proportion of 13C and 18O isotopes bound to each other within carbonate minerals in 13C18O16O22- groups (heavy isotope ;clumps;). Although most clumped isotope geothermometry implicitly presumes carbonate crystals have attained lattice equilibrium (i.e., thermodynamic equilibrium for a mineral, which is independent of solution chemistry), several factors other than temperature, including dissolved inorganic carbon (DIC) speciation may influence mineral isotopic signatures. Therefore we used a combination of approaches to understand the potential influence of different variables on the clumped isotope (and oxygen isotope) composition of minerals. We conducted witherite precipitation experiments at a single temperature and at varied pH to empirically determine 13C-18O bond ordering (Δ47) and δ18O of CO32- and HCO3- molecules at a 25 °C equilibrium. Ab initio cluster models based on density functional theory were used to predict equilibrium 13C-18O bond abundances and δ18O of different DIC species and minerals as a function of temperature. Experiments and theory indicate Δ47 and δ18O compositions of CO32- and HCO3- ions are significantly different from each other. Experiments constrain the Δ47-δ18O slope for a pH effect (0.011 ± 0.001; 12 ⩾ pH ⩾ 7). Rapidly-growing temperate corals exhibit disequilibrium mineral isotopic signatures with a Δ47-δ18O slope of 0.011 ± 0.003, consistent with a pH effect. Our theoretical calculations for carbonate minerals indicate equilibrium lattice calcite values for Δ47 and δ18O are intermediate between HCO3- and CO32-. We analyzed synthetic calcites grown at temperatures ranging from 0.5 to 50 °C with and without the enzyme carbonic anhydrase present. This enzyme catalyzes oxygen isotopic exchange between DIC species and is present in many natural systems. The two

  10. The influence of authigenic clay formation on the mineralogy and stable isotopic record of lacustrine carbonates

    NASA Astrophysics Data System (ADS)

    Bristow, Thomas F.; Kennedy, Martin J.; Morrison, Keith D.; Mrofka, David D.

    2012-08-01

    The mineralogical, compositional and stable isotopic variability of lacustrine carbonates are frequently used as proxies for ancient paleoenvironmental change in continental settings, under the assumption that precipitated carbonates reflect conditions and chemistry of ancient lake waters. In some saline and alkaline lake systems, however, authigenic clay minerals, forming at or near the sediment water interface, are a major sedimentary component. Often these clays are rich in Mg, influencing the geochemical budget of lake waters, and are therefore expected to influence the properties of contemporaneous authigenic carbonate precipitates (which may also contain Mg). This paper documents evidence for a systematic feedback between clay mineral and carbonate authigenesis through multiple precessionally driven, m-scale sedimentary cycles in lacustrine oil-shale deposits of the Eocene Green River Formation from the Uinta Basin (NE Utah). In the studied section, authigenic, Mg-rich, trioctahedral smectite content varies cyclically between 9 and 39 wt.%. The highest concentrations occur in oil-shales and calcareous mudstones deposited during high lake level intervals that favored sedimentary condensation, lengthening the time available for clay diagenesis and reducing dilution by other siliciclastic phases. An inverse relation between dolomite percentage of carbonate and trioctahedral smectite abundance suggests the Mg uptake during clay authigenesis provides a first order control on carbonate mineralogy that better explains carbonate mineralogical trends than the possible alternative controls of (1) variable Mg/Ca ratios in lake water and (2) degree of microbial activity in sediments. We also observe that cyclical change in carbonate mineralogy, believed to be induced by clay authigenesis, also causes isotopic covariation between δ13CPDB and δ18OPDB of bulk sediments because of differences in the equilibrium fractionation factors of dolomite and calcite (˜2‰ and ˜2

  11. The puzzle of the CNO isotope ratios in asymptotic giant branch carbon stars

    NASA Astrophysics Data System (ADS)

    Abia, C.; Hedrosa, R. P.; Domínguez, I.; Straniero, O.

    2017-03-01

    Context. The abundance ratios of the main isotopes of carbon, nitrogen and oxygen are modified by the CNO-cycle in the stellar interiors. When the different dredge-up events mix the burning material with the envelope, valuable information on the nucleosynthesis and mixing processes can be extracted by measuring these isotope ratios. Aims: Previous determinations of the oxygen isotopic ratios in asymptotic giant branch (AGB) carbon stars were at odds with the existing theoretical predictions. We aim to redetermine the oxygen ratios in these stars using new spectral analysis tools and further develop discussions on the carbon and nitrogen isotopic ratios in order to elucidate this problem. Methods: Oxygen isotopic ratios were derived from spectra in the K-band in a sample of galactic AGB carbon stars of different spectral types and near solar metallicity. Synthetic spectra calculated in local thermodynamic equillibrium (LTE) with spherical carbon-rich atmosphere models and updated molecular line lists were used. The CNO isotope ratios derived in a homogeneous way, were compared with theoretical predictions for low-mass (1.5-3 M⊙) AGB stars computed with the FUNS code assuming extra mixing both during the RGB and AGB phases. Results: For most of the stars the 16O/17O/18O ratios derived are in good agreement with theoretical predictions confirming that, for AGB stars, are established using the values reached after the first dredge-up (FDU) according to the initial stellar mass. This fact, as far as the oxygen isotopic ratios are concerned, leaves little space for the operation of any extra mixing mechanism during the AGB phase. Nevertheless, for a few stars with large 16O/17O/18O, the operation of such a mechanism might be required, although their observed 12C/13C and 14N/15N ratios would be difficult to reconcile within this scenario. Furthermore, J-type stars tend to have lower 16O/17O ratios than the normal carbon stars, as already indicated in previous studies

  12. ISO/GUM UNCERTAINTIES AND CIAAW (UNCERTAINTY TREATMENT FOR RECOMMENDED ATOMIC WEIGHTS AND ISOTOPIC ABUNDANCES)

    SciTech Connect

    HOLDEN,N.E.

    2007-07-23

    The International Organization for Standardization (ISO) has published a Guide to the expression of Uncertainty in Measurement (GUM). The IUPAC Commission on Isotopic Abundance and Atomic Weight (CIAAW) began attaching uncertainty limits to their recommended values about forty years ago. CIAAW's method for determining and assigning uncertainties has evolved over time. We trace this evolution to their present method and their effort to incorporate the basic ISO/GUM procedures into evaluations of these uncertainties. We discuss some dilemma the CIAAW faces in their present method and whether it is consistent with the application of the ISO/GUM rules. We discuss the attemptmore » to incorporate variations in measured isotope ratios, due to natural fractionation, into the ISO/GUM system. We make some observations about the inconsistent treatment in the incorporation of natural variations into recommended data and uncertainties. A recommendation for expressing atomic weight values using a tabulated range of values for various chemical elements is discussed.« less

  13. CARBON ISOTOPE DISCRIMINATION AND GROWTH RESPONSE TO STAND DENSITY REDUCTIONS IN OLD PINUS PONDEROSA TREES

    EPA Science Inventory

    Carbon isotope ratios ( 13C) of tree rings are commonly used for paleoclimatic reconstruction and for inferring canopy water-use efficiency (WUE). However, the responsiveness of carbon isotope discrimination ( ) to site disturbance and resource availability has only rarely been ...

  14. Behaviour of Structural Carbonate Stable Carbon and Oxygen Isotope Compositions in Bioapatite During Burning of Bone

    NASA Astrophysics Data System (ADS)

    Munro, L. E.; Longstaffe, F. J.; White, C. D.

    2003-12-01

    Bioapatite, the principal inorganic phase comprising bone, commonly contains a small fraction of carbonate, which has been substituted into the phosphate structure during bone formation. The isotopic compositions of both the phosphate oxygen and the structural carbonate oxygen are now commonly used in palaeoclimatological and bioarchaeological investigations. The potential for post-mortem alteration of these isotopic compositions, therefore, is of interest, with the behaviour of structural carbonate being of most concern. In bioarchaeological studies, alteration of bone isotopic compositions has the potential to occur not only during low-temperature processes associated with burial but also during food preparation involving heating (burning, boiling). Here, we examine the stable isotopic behaviour of structural carbonate oxygen and carbon, and coexisting phosphate oxygen during the burning of bone. Freshly deceased (6<8 months) white-tailed deer leg bones (Odocoileus virginianus) were collected from Pinery Provincial Park, Ontario, Canada. Each long bone was sectioned and incrementally heated from 25 to 900° C, in 25° intervals. The samples were then ground to a standardized grain-size (45<63μ m), and changes in bioapatite crystallinity (CI) were determined using powder X-ray diffraction (pXRD), and Fourier transform infra-red spectroscopy (FTIR). Combined differential thermal and thermogravimetric analyses (DTA/TG) were used to evaluate weight loss and associated reactions during heating. Stable carbon isotope compositions of the bioapatite remain relatively constant (+/-1‰ ) during heating to 650° C. A 4‰ increase in stable carbon isotopic composition then occurs between 650-750° C, accompanied by an increase in CI, followed by a 10‰ decline at temperatures above 800° C, as carbonate carbon is lost. Carbonate and phosphate oxygen isotopic compositions are correlated over the entire heating range, with carbonate being enriched relative to phosphate by

  15. ANALYSIS OF RICIN TOXIN PREPARATIONS FOR CARBOHYDRATE AND FATTY ACID ABUNDANCE AND ISOTOPE RATIO INFORMATION

    SciTech Connect

    Wunschel, David S.; Kreuzer-Martin, Helen W.; Antolick, Kathryn C.

    2009-12-01

    , one employing a quadrupole MS system for compound identification and an isotope ratio MS for measuring the stable isotope ratios of deuterium and hydrogen (D/H) in fatty acids. Finally, the method for analyzing the compound abundance data is included. This study indicates that removal of ricinoleic acid is a conserved consequence of each processing step we tested. Furthermore, the stable isotope D/H ratio of ricinoleic acid distinguished between two of the three castor seed sources. Concentrations of arabinose, xylose, mannose, glucosamine and myo-inositol differentiated between crude or acetone extracted samples and samples produced by protein precipitation. Taken together these data illustrate the ability to distinguish between processes used to purify a ricin sample as well as potentially the source seeds.« less

  16. Stable isotopes of carbon and nitrogen in the study of avian and mammalian trophic ecology

    Treesearch

    Jeffrey F. Kelly

    2000-01-01

    Differential fractionation of stable isotopes of carbon during photosynthesis causes C4 plants and C3 plants to have distinct carbon-isotope signatures. In addition, marine C3 plants have stable-isotope ratios of carbon that are intermediate between C4 and terrestrial C3 plants. The direct incorporation of the carbon-isotope ratio (13C/12C) of plants into consumers...

  17. How the oxygen isotope ratio of rain water influences the isotope ratio of chicken eggshell carbonate

    NASA Astrophysics Data System (ADS)

    Price, Gregory; Grimes, Stephen

    2015-04-01

    The stable oxygen isotope ratio of chicken eggshell carbonate was analysed from chicken eggs laid under free range, and organic farming regimes from across the UK. The eggshell carbonate oxygen isotope data shows a clear depletion in delta18O distribution from the southwest to the northeast. Although consistently offset by around 1 permil, the same isotopic distribution as that seen in eggshell carbonate is observed in the delta18O ratio of rainfall and groundwater from across the UK. This distribution is related to the Rayleigh distillation of rainfall driven by westerly winds across the UK landmass. The clear relationship observed between eggshell delta18O values and that of rainwater presumably reflects the nature of free range chickens which must be drinking locally derived rainwater and supplementing their diet and water intake with locally derived food. These results suggest that the oxygen isotope value of chicken eggshells can be used as a forensic tool to identify the locality that free range and organic eggs were laid within the UK. Furthermore, if suitable material is preserved in the archaeological and geological record then such a relationship can potentially be used to establish the oxygen isotope value of rainwater from which ancient and / or ancestral birds lived.

  18. Carbon isotope effect during abiogenic oxidation of methane

    NASA Astrophysics Data System (ADS)

    Kiyosu, Yasuhiro; Roy Krouse, H.

    1989-11-01

    The oxidation of methane during flow over CuO and Fe 2O 3 has been examined in the temperature range of 400-650°C. The reaction rate and carbon isotope fractionation are dependent upon the choice of oxide and temperature. The activation energy is lower for hematite (8.0 kcal mole -1) than for cupric oxide (16.6 kcal mole -1). The measured ratios of the isotopic rate constants α =k 12/k 13 were found to have temperature dependences given by: 10 3(α - 1) =2.93 × 10 6/T 2 + 8.11 (cupric oxide) 10 3(α - 1) =7.44 × 10 6/T 2 + 6.56 (hematite) Abiogenic oxidation of methane is probably a significant mechanism for fractionating carbon isotopes in nature.

  19. Carbon and hydrogen isotope fractionation by moderately thermophilic methanogens

    NASA Astrophysics Data System (ADS)

    Valentine, David L.; Chidthaisong, Amnat; Rice, Andrew; Reeburgh, William S.; Tyler, Stanley C.

    2004-04-01

    A series of laboratory studies were conducted to increase understanding of stable carbon (13C/12C) and hydrogen (D/H) isotope fractionation arising from methanogenesis by moderately thermophilic acetate- and hydrogen-consuming methanogens. Studies of the aceticlastic reaction were conducted with two closely related strains of Methanosaeta thermophila. Results demonstrate a carbon isotope fractionation of only 7‰ (α = 1.007) between the methyl position of acetate and the resulting methane. Methane formed by this process is enriched in 13C when compared with other natural sources of methane; the magnitude of this isotope effect raises the possibility that methane produced at elevated temperature by the aceticlastic reaction could be mistaken for thermogenic methane based on carbon isotopic content. Studies of H2/CO2 methanogenesis were conducted with Methanothermobacter marburgensis. The fractionation of carbon isotopes between CO2 and CH4 was found to range from 22 to 58‰ (1.023 ≤ α ≤ 1.064). Greater fractionation was associated with low levels of molecular hydrogen and steady-state metabolism. The fractionation of hydrogen isotopes between source H2O and CH4 was found to range from 127 to 275‰ (1.16 ≤ α ≤ 1.43). Fractionation was dependent on growth phase with greater fractionation associated with later growth stages. The maximum observed fractionation factor was 1.43, independent of the δD-H2 supplied to the culture. Fractionation was positively correlated with temperature and/or metabolic rate. Results demonstrate significant variability in both hydrogen and carbon isotope fractionation during methanogenesis from H2/CO2. The relatively small fractionation associated with deuterium during H2/CO2 methanogenesis provides an explanation for the relatively enriched deuterium content of biogenic natural gas originating from a variety of thermal environments. Results from these experiments are used to develop a hypothesis that differential

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

    NASA Astrophysics Data System (ADS)

    Romanek, C.

    2010-12-01

    The stable carbon isotope composition of bivalve shells is a valuable archive of paleobiological and paleoenvironmental information. Previous work has shown that the carbon isotope composition of the shell is related to the carbon isotope composition of dissolved inorganic carbon (DIC) in the ambient water in which a bivalve lives, as well as metabolic carbon derived from bivalve respiration. The contribution of metabolic carbon varies among organisms, but it is generally thought to be relatively low (e.g., <10%) in shells from aquatic organism and high (>90%) in the shells from terrestrial organisms. Because metabolic carbon contains significantly more C-12 than DIC, negative excursions from the expected environmental (DIC) signal are interpreted to reflect an increased contribution of metabolic carbon in the shell. This observation contrasts sharply with modeled carbon isotope compositions for shell layers deposited from the inner extrapallial fluid (EPF). Previous studies have shown that growth lines within the inner shell layer of bivalves are produced during periods of anaerobiosis when acidic metabolic byproducts (e.g., succinic acid) are neutralized (or buffered) by shell dissolution. This requires the pH of EPF to decrease below ambient levels (~7.5) until a state of undersaturation is achieved that promotes shell dissolution. This condition may occur when aquatic bivalves are subjected to external stressors originating from ecological (predation) or environmental (exposure to atm; low dissolved oxygen; contaminant release) pressures; normal physiological processes will restore the pH of EPF when the pressure is removed. As a consequence of this process, a temporal window should also exist in EPF at relatively low pH where shell carbonate is deposited at a reduced saturation state and precipitation rate. For example, EPF chemistry should remain slightly supersaturated with respect to aragonite given a drop of one pH unit (6.5), but under closed conditions

  1. Sediment Tracking Using Carbon and Nitrogen Stable Isotopes

    NASA Astrophysics Data System (ADS)

    Fox, J. F.; Papanicolaou, A.

    2002-12-01

    As landscapes are stripped of valuable, nutrient rich topsoils and streams are clouded with habitat degrading fine sediment, it becomes increasingly important to identify and mitigate erosive surfaces. Particle tracking using vegetative derived carbon (C) and nitrogen (N) isotopic signatures and carbon/nitrogen (C/N) atomic ratios offer a promising technique to identify such problematic sources. Consultants and researchers successfully use C, N, and other stable isotopes of water for hydrologic purposes, such as quantifying groundwater vs. surface water contribution to a hydrograph. Recently, C and N isotopes and C/N atomic ratios of sediment were used to determine sediment mass balance within estuarine environments. The current research investigates C and N isotopes and C/N atomic ratios of source sediment for two primary purposes: (1) to establish a blueprint methodology for estimating sediment source and erosion rates within a watershed using this isotopic technology coupled with mineralogy fingerprinting techniques, radionuclide transport monitoring, and erosion-transport models, and (2) to complete field studies of upland erosion processes, such as, solifluction, mass wasting, creep, fluvial erosion, and vegetative induced erosion. Upland and floodplain sediment profiles and riverine suspended sediment were sampled on two occasions, May 2002 and August 2002, in the upper Palouse River watershed of northern Idaho. Over 300 samples were obtained from deep intermountain valley (i.e. forest) and rolling crop field (i.e. agriculture) locations. Preliminary sample treatment was completed at the Washington State University Water Quality Laboratory where samples were dried, removed of organic constituents, and prepared for isotopic analysis. C and N isotope and C/N atomic ratio analyses was performed at the University of Idaho Natural Resources Stable Isotope Laboratory using a Costech 4010 Elemental Combustion System connected with a continuous flow inlet system to

  2. Beyond temperature: Clumped isotope signatures in dissolved inorganic carbon species and the influence of solution chemistry on carbonate mineral composition

    USGS Publications Warehouse

    Tripati, Aradhna K.; Hill, Pamela S.; Eagle, Robert A.; Mosenfelder, Jed L.; Tang, Jianwu; Schauble, Edwin A.; Eiler, John M.; Zeebe, Richard E.; Uchikawa, Joji; Coplen, Tyler B.; Ries, Justin B.; Henry, Drew

    2015-01-01

    “Clumped-isotope” thermometry is an emerging tool to probe the temperature history of surface and subsurface environments based on measurements of the proportion of 13C and 18O isotopes bound to each other within carbonate minerals in 13C18O16O22- groups (heavy isotope “clumps”). Although most clumped isotope geothermometry implicitly presumes carbonate crystals have attained lattice equilibrium (i.e., thermodynamic equilibrium for a mineral, which is independent of solution chemistry), several factors other than temperature, including dissolved inorganic carbon (DIC) speciation may influence mineral isotopic signatures. Therefore we used a combination of approaches to understand the potential influence of different variables on the clumped isotope (and oxygen isotope) composition of minerals.We conducted witherite precipitation experiments at a single temperature and at varied pH to empirically determine 13C-18O bond ordering (Δ47) and δ18O of CO32- and HCO3- molecules at a 25 °C equilibrium. Ab initio cluster models based on density functional theory were used to predict equilibrium 13C-18O bond abundances and δ18O of different DIC species and minerals as a function of temperature. Experiments and theory indicate Δ47 and δ18O compositions of CO32- and HCO3- ions are significantly different from each other. Experiments constrain the Δ47-δ18O slope for a pH effect (0.011 ± 0.001; 12 ⩾ pH ⩾ 7). Rapidly-growing temperate corals exhibit disequilibrium mineral isotopic signatures with a Δ47-δ18O slope of 0.011 ± 0.003, consistent with a pH effect.Our theoretical calculations for carbonate minerals indicate equilibrium lattice calcite values for Δ47 and δ18O are intermediate between HCO3− and CO32−. We analyzed synthetic calcites grown at temperatures ranging from 0.5 to 50 °C with and without the enzyme carbonic anhydrase present. This enzyme catalyzes oxygen isotopic exchange between DIC species and is present in many

  3. Stable carbon isotope fractionation by sulfate-reducing bacteria

    NASA Technical Reports Server (NTRS)

    Londry, Kathleen L.; Des Marais, David J.

    2003-01-01

    Biogeochemical transformations occurring in the anoxic zones of stratified sedimentary microbial communities can profoundly influence the isotopic and organic signatures preserved in the fossil record. Accordingly, we have determined carbon isotope discrimination that is associated with both heterotrophic and lithotrophic growth of pure cultures of sulfate-reducing bacteria (SRB). For heterotrophic-growth experiments, substrate consumption was monitored to completion. Sealed vessels containing SRB cultures were harvested at different time intervals, and delta(13)C values were determined for gaseous CO(2), organic substrates, and products such as biomass. For three of the four SRB, carbon isotope effects between the substrates, acetate or lactate and CO(2), and the cell biomass were small, ranging from 0 to 2 per thousand. However, for Desulfotomaculum acetoxidans, the carbon incorporated into biomass was isotopically heavier than the available substrates by 8 to 9 per thousand. SRB grown lithoautotrophically consumed less than 3% of the available CO(2) and exhibited substantial discrimination (calculated as isotope fractionation factors [alpha]), as follows: for Desulfobacterium autotrophicum, alpha values ranged from 1.0100 to 1.0123; for Desulfobacter hydrogenophilus, the alpha value was 0.0138, and for Desulfotomaculum acetoxidans, the alpha value was 1.0310. Mixotrophic growth of Desulfovibrio desulfuricans on acetate and CO(2) resulted in biomass with a delta(13)C composition intermediate to that of the substrates. The extent of fractionation depended on which enzymatic pathways were used, the direction in which the pathways operated, and the growth rate, but fractionation was not dependent on the growth phase. To the extent that environmental conditions affect the availability of organic substrates (e.g., acetate) and reducing power (e.g., H(2)), ecological forces can also influence carbon isotope discrimination by SRB.

  4. Optimizing sample pretreatment for compound-specific stable carbon isotopic analysis of amino sugars in marine sediment

    NASA Astrophysics Data System (ADS)

    Zhu, R.; Lin, Y.-S.; Lipp, J. S.; Meador, T. B.; Hinrichs, K.-U.

    2014-01-01

    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.

  5. Optimizing sample pretreatment for compound-specific stable carbon isotopic analysis of amino sugars in marine sediment

    NASA Astrophysics Data System (ADS)

    Zhu, R.; Lin, Y.-S.; Lipp, J. S.; Meador, T. B.; Hinrichs, K.-U.

    2014-09-01

    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. Compound-specific stable carbon isotopic analysis of amino sugars obtained from marine sediment extracts indicated that glucosamine and galactosamine were mainly derived from organic detritus, whereas muramic acid showed isotopic imprints from indigenous bacterial activities. The δ13C analysis of amino sugars provides a valuable addition to the biomarker-based characterization of microbial metabolism in the deep marine biosphere, which so far has been lipid oriented and biased towards the detection of archaeal signals.

  6. Yucca Mountain Area Saturated Zone Dissolved Organic Carbon Isotopic Data

    SciTech Connect

    Thomas, James; Decker, David; Patterson, Gary

    2007-06-25

    Groundwater samples in the Yucca Mountain area were collected for chemical and isotopic analyses and measurements of water temperature, pH, specific conductivity, and alkalinity were obtained at the well or spring at the time of sampling. For this project, groundwater samples were analyzed for major-ion chemistry, deuterium, oxygen-18, and carbon isotopes of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC). The U.S. Geological Survey (USGS) performed all the fieldwork on this project including measurement of water chemistry field parameters and sample collection. The major ions dissolved in the groundwater, deuterium, oxygen-18, and carbon isotopes of dissolved inorganic carbon (DIC)more » were analyzed by the USGS. All preparation and processing of samples for DOC carbon isotopic analyses and geochemical modeling were performed by the Desert Research Institute (DRI). Analysis of the DOC carbon dioxide gas produced at DRI to obtain carbon-13 and carbon-14 values was conducted at the University of Arizona Accelerator Facility (a NSHE Yucca Mountain project QA qualified contract facility). The major-ion chemistry, deuterium, oxygen-18, and carbon isotopes of DIC were used in geochemical modeling (NETPATH) to determine groundwater sources, flow paths, mixing, and ages. The carbon isotopes of DOC were used to calculate groundwater ages that are independent of DIC model corrected carbon-14 ages. The DIC model corrected carbon-14 calculated ages were used to evaluate groundwater travel times for mixtures of water including water beneath Yucca Mountain. When possible, groundwater travel times were calculated for groundwater flow from beneath Yucca Mountain to down gradient sample sites. DOC carbon-14 groundwater ages were also calculated for groundwaters in the Yucca Mountain area. When possible, groundwater travel times were estimated for groundwater flow from beneath Yucca Mountain to down gradient groundwater sample sites using the DOC calculated

  7. Changing carbon isotope ratio of atmospheric carbon dioxide: implications for food authentication.

    PubMed

    Peck, William H; Tubman, Stephanie C

    2010-02-24

    Carbon isotopes are often used to detect the addition of foreign sugars to foods. This technique takes advantage of the natural difference in carbon isotope ratio between C(3) and C(4) plants. Many foods are derived from C(3) plants, but the low-cost sweeteners corn and sugar cane are C(4) plants. Most adulteration studies do not take into account the secular shift of the carbon isotope ratio of atmospheric carbon dioxide caused by fossil fuel burning, a shift also seen in plant tissues. As a result statistical tests and threshold values that evaluate authenticity of foods based on carbon isotope ratios may need to be corrected for changing atmospheric isotope values. Literature and new data show that the atmospheric trend in carbon isotopes is seen in a 36-year data set of maple syrup analyses (n = 246), demonstrating that published thresholds for cane or corn sugar adulteration in maple syrup (and other foods) have become progressively more lenient over time.

  8. Carbon-Isotopic Dynamics of Streams, Taylor Valley, Antarctica: Biological Effects

    NASA Technical Reports Server (NTRS)

    Neumann, K.; DesMarais, D. J.

    1998-01-01

    We have investigated the role of biological processes in the C-isotopic dynamics of the aquatic ecosystems in Taylor Valley, Antarctica. This cold desert ecosystem is characterized by the complete lack of vascular plants, and the presence of algal mats in ephemeral streams and perennially ice covered lakes. Streams having abundant algal mats and mosses have very low sigma CO2 concentrations, as well as the most depleted delta C-13 values (-4%). Previous work has shown that algal mats in these streams have delta C-13 values averaging -7.01%. These values are similar to those observed in the algal mats in shallow areas of the lakes in Taylor Valley, where CO2 is thought to be colimiting to growth. These low Sigma CO2 concentrations, and delta C(13) signatures heavier than the algal mats, suggest that CO2 may be colimiting in the streams, as well. Streams with little algal growth, especially the longer ones in Fryxell Basin, have higher Sigma CO2 concentrations and much more enriched isotopic signatures (as high as +8%). In these streams, the dissolution of isotopically enriched, cryogenic CaCO3 is probably the major source of dissolved carbonate. The delta C(13) geochemistry of Antarctic streams is radically different from the geochemistry of more temperate streams, as it is not affected by terrestrially produced, isotopically depleted Sigma CO2. These results have important implications for the understanding of "biogenic" carbonate that might have been produced from aquatic ecosystems in the past on Mars.

  9. Carbonate “clumped” isotope signatures in aragonitic scleractinian and calcitic gorgonian deep-sea corals

    SciTech Connect

    Kimball, Justine; Eagle, Robert; Dunbar, Robert

    Here, deep-sea corals are a potentially valuable archive of the temperature and ocean chemistry of intermediate and deep waters. Living in near-constant temperature, salinity, and pH and having amongst the slowest calcification rates observed in carbonate-precipitating biological organisms, deep-sea corals can provide valuable constraints on processes driving mineral equilibrium and disequilibrium isotope signatures. Here we report new data to further develop “clumped” isotopes as a paleothermometer in deep-sea corals as well as to investigate mineral-specific, taxon-specific, and growth-rate-related effects. Carbonate clumped isotope thermometry is based on measurements of the abundance of the doubly substituted isotopologue 13C 18O 16O 2 inmore » carbonate minerals, analyzed in CO 2 gas liberated on phosphoric acid digestion of carbonates and reported as Δ 47 values. We analyzed Δ 47 in live-collected aragonitic scleractinian ( Enallopsammia sp.) and high-Mg calcitic gorgonian (Isididae and Coralliidae) deep-sea corals and compared results to published data for other aragonitic scleractinian taxa. Measured Δ 47 values were compared to in situ temperatures, and the relationship between Δ 47 and temperature was determined for each group to investigate taxon-specific effects. We find that aragonitic scleractinian deep-sea corals exhibit higher values than high-Mg calcitic gorgonian corals and the two groups of coral produce statistically different relationships between Δ 47–temperature calibrations. These data are significant in the interpretation of all carbonate clumped isotope calibration data as they show that distinct Δ 47–temperature calibrations can be observed in different materials recovered from the same environment and analyzed using the same instrumentation, phosphoric acid composition, digestion temperature and technique, CO 2 gas purification apparatus, and data handling. There are three possible explanations for the origin of these

  10. Carbonate “clumped” isotope signatures in aragonitic scleractinian and calcitic gorgonian deep-sea corals

    DOE PAGES

    Kimball, Justine; Eagle, Robert; Dunbar, Robert

    2016-12-12

    Here, deep-sea corals are a potentially valuable archive of the temperature and ocean chemistry of intermediate and deep waters. Living in near-constant temperature, salinity, and pH and having amongst the slowest calcification rates observed in carbonate-precipitating biological organisms, deep-sea corals can provide valuable constraints on processes driving mineral equilibrium and disequilibrium isotope signatures. Here we report new data to further develop “clumped” isotopes as a paleothermometer in deep-sea corals as well as to investigate mineral-specific, taxon-specific, and growth-rate-related effects. Carbonate clumped isotope thermometry is based on measurements of the abundance of the doubly substituted isotopologue 13C 18O 16O 2 inmore » carbonate minerals, analyzed in CO 2 gas liberated on phosphoric acid digestion of carbonates and reported as Δ 47 values. We analyzed Δ 47 in live-collected aragonitic scleractinian ( Enallopsammia sp.) and high-Mg calcitic gorgonian (Isididae and Coralliidae) deep-sea corals and compared results to published data for other aragonitic scleractinian taxa. Measured Δ 47 values were compared to in situ temperatures, and the relationship between Δ 47 and temperature was determined for each group to investigate taxon-specific effects. We find that aragonitic scleractinian deep-sea corals exhibit higher values than high-Mg calcitic gorgonian corals and the two groups of coral produce statistically different relationships between Δ 47–temperature calibrations. These data are significant in the interpretation of all carbonate clumped isotope calibration data as they show that distinct Δ 47–temperature calibrations can be observed in different materials recovered from the same environment and analyzed using the same instrumentation, phosphoric acid composition, digestion temperature and technique, CO 2 gas purification apparatus, and data handling. There are three possible explanations for the origin of these

  11. A carbon isotope challenge to the snowball Earth.

    PubMed

    Sansjofre, P; Ader, M; Trindade, R I F; Elie, M; Lyons, J; Cartigny, P; Nogueira, A C R

    2011-10-05

    The snowball Earth hypothesis postulates that the planet was entirely covered by ice for millions of years in the Neoproterozoic era, in a self-enhanced glaciation caused by the high albedo of the ice-covered planet. In a hard-snowball picture, the subsequent rapid unfreezing resulted from an ultra-greenhouse event attributed to the buildup of volcanic carbon dioxide (CO(2)) during glaciation. High partial pressures of atmospheric CO(2) (pCO2; from 20,000 to 90,000 p.p.m.v.) in the aftermath of the Marinoan glaciation (∼635 Myr ago) have been inferred from both boron and triple oxygen isotopes. These pCO2 values are 50 to 225 times higher than present-day levels. Here, we re-evaluate these estimates using paired carbon isotopic data for carbonate layers that cap Neoproterozoic glacial deposits and are considered to record post-glacial sea level rise. The new data reported here for Brazilian cap carbonates, together with previous ones for time-equivalent units, provide estimates lower than 3,200 p.p.m.v.--and possibly as low as the current value of ∼400 p.p.m.v. Our new constraint, and our re-interpretation of the boron and triple oxygen isotope data, provide a completely different picture of the late Neoproterozoic environment, with low atmospheric concentrations of carbon dioxide and oxygen that are inconsistent with a hard-snowball Earth.

  12. Comparison of gas chromatography/isotope ratio mass spectrometry and liquid chromatography/isotope ratio mass spectrometry for carbon stable-isotope analysis of carbohydrates.

    PubMed

    Moerdijk-Poortvliet, Tanja C W; Schierbeek, Henk; Houtekamer, Marco; van Engeland, Tom; Derrien, Delphine; Stal, Lucas J; Boschker, Henricus T S

    2015-07-15

    We compared gas chromatography/isotope ratio mass spectrometry (GC/IRMS) and liquid chromatography/isotope ratio mass spectrometry (LC/IRMS) for the measurement of δ(13)C values in carbohydrates. Contrary to GC/IRMS, no derivatisation is needed for LC/IRMS analysis of carbohydrates. Hence, although LC/IRMS is expected to be more accurate and precise, no direct comparison has been reported. GC/IRMS with the aldonitrile penta-acetate (ANPA) derivatisation method was compared with LC/IRMS without derivatisation. A large number of glucose standards and a variety of natural samples were analysed for five neutral carbohydrates at natural abundance as well as at (13)C-enriched levels. Gas chromatography/chemical ionisation mass spectrometry (GC/CIMS) was applied to check for incomplete derivatisation of the carbohydrate, which would impair the accuracy of the GC/IRMS method. The LC/IRMS technique provided excellent precision (±0.08‰ and ±3.1‰ at natural abundance and enrichment levels, respectively) for the glucose standards and this technique proved to be superior to GC/IRMS (±0.62‰ and ±19.8‰ at natural abundance and enrichment levels, respectively). For GC/IRMS measurements the derivatisation correction and the conversion of carbohydrates into CO2 had a considerable effect on the measured δ(13)C values. However, we did not find any significant differences in the accuracy of the two techniques over the full range of natural δ(13)C abundances and (13)C-labelled glucose. The difference in the performance of GC/IRMS and LC/IRMS diminished when the δ(13)C values were measured in natural samples, because the chromatographic performance and background correction became critical factors, particularly for LC/IRMS. The derivatisation of carbohydrates for the GC/IRMS method was complete. Although both LC/IRMS and GC/IRMS are reliable techniques for compound-specific stable carbon isotope analysis of carbohydrates (provided that derivatisation is complete and the

  13. The Determination of the Natural Abundance of the Isotopes of Chlorine: An Introductory Experiment in Mass Spectrometry.

    ERIC Educational Resources Information Center

    O'Malley, Rebecca M.

    1982-01-01

    Describes a laboratory experiment which introduces basic principles and experimental techniques of mass spectrometry for fourth year undergraduate (B.Sc.) students. Laboratory procedures, background information, and discussion of results are provided for the experiment in which the natural isotopic abundance of chlorine is determined. (Author/JN)

  14. A Carbonate Li Isotope Record Through Earth's History

    NASA Astrophysics Data System (ADS)

    Asael, D.; Kalderon-Asael, B.; Planavsky, N.

    2016-12-01

    Lithium (Li) isotopes emerge as a powerful geochemical proxy for tracking continental weathering through time. Extensive work on Li fractionation in modern systems has brought to a profound understanding of the modern Li budget as well as to a consensus that marine carbonates faithfully record seawater Li isotope signature. As such record is essential in order to track global-scale changes in weathering processes and intensity through Earth's history, we have generated Li isotope data from marine carbonates from over 40 units, ranging in age from 3.0 Ga to modern. Preliminary results provide evidence for strongly inhibited weathering-mediated clay formation prior to the Paleozoic, which we attribute to the pre-Paleozoic lack of land plants. The initial rise in the Li isotope values is observed during the Ordovician, which is followed by a subsequent drop to background values and then begins the generally increasing trend that is already well reported. These findings are open for interpretation but they still support the view that the emergence of land plants dramatically changed the process of weathering and it seems that biomass has a potentially significant role in mineral breakdown in soils. Li isotopes provide a novel perspective on weathering and the impact on the Earth system of the rise of land plants - one of the most significant transitions in Earth's history.

  15. Siderophile and chalcophile element abundances in oceanic basalts, Pb isotope evolution and growth of the earth's core

    NASA Technical Reports Server (NTRS)

    Newsom, H. E.; White, W. M.; Jochum, K. P.; Hofmann, A. W.

    1986-01-01

    The hypothesis that the mantle Pb isotope ratios reflect continued extraction of Pb into the earth's core over geologic time is evaluated by studying the depeletion of chalcophile and siderophile elements in the mantle. Oceanic basalt samples are analyzed in order to determine the Pb, Sr, and Nd isotropic compositions and the abundances of siderophile and chalcophile elements and incompatible lithophile elements. The data reveal that there is no systematic variation of siderophile or chalcophile element abundances relative to abundances of lithophile elements and the Pb/Ce ratio of the mantle is constant. It is suggested that the crust formation involves nonmagmatic and magmatic processes.

  16. Magnesium isotope fractionation in bacterial mediated carbonate precipitation experiments

    NASA Astrophysics Data System (ADS)

    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

  17. Experimental high temperature carbon isotope fractionation involving graphite

    NASA Astrophysics Data System (ADS)

    Kueter, N.; Schmidt, M. W.; Lilley, M. D.; Bernasconi, S. M.

    2016-12-01

    Graphite/carbonate carbon isotope fractionation was mainly investigated at 400- 800°C and is based on empirical calibrations, theoretical calculations and few experiments [1,2]. Own work on COH-fluid/graphite isotope fractionation shows that in experiments up to 1000oC a fluid phase is always enriched in 13C compared to coexisting graphitic carbon. The eventual kinetic isotope effect in these experiments is best displayed by the graphitic carbon being at least 3 ‰ lighter than methane. Only few experiments done in the graphite/carbonate pair dealt with higher temperatures reaching 1400°C, indicating a fractionation of up to 2 ‰ at temperatures of the Earth's mantle [2-4]. To better understand carbon isotope fractionation in crustal systems and still overcome kinetic effects, we study the graphite/carbonatite pair with piston cylinder experiments in the Na2CO3-CaCO3-CaO-COH system. Tartaric acid (C4H6O6) supplies reduced carbon, time series are performed at 10 kbar, 1300-1800°C. Initial experiments at 1300°C produce well-ordered, micron-sized graphite flakes growing attached to the capsule walls while the Na-Ca-carbonatite-melt quenches to dendritic textures. No gaseous phase was observed. Conditions well above the liquidus of the Na2CO3-CaCO3-binary lead to dissolution of the H2O from tartaric acid decomposition in the melt, any CO2-component is bound by the excess CaO to CaCO3melt while in the relatively oxidizing capsule environment any CH4-component reacts with CO2 to carbon and H2O. The graphite and the carbonatite quench are measured for their δ13C composition using a GasBench II (carbonate-dissolution in phosphoric acid) and TC/EA (residual graphite combusted in oxygen atmosphere) system coupled to a Thermo Fischer IRMS. Our results expand from the graphite-carbonate system to graphite-fluid system when adding available fluid-carbonate fractionation factors, but are also directly applicable to diamond synthesis as graphite is often found as a

  18. Stable Isotope Values of Nitrogen and Carbon in Particulate ...

    EPA Pesticide Factsheets

    Data set from “Patterns in stable isotope values of nitrogen and carbon in particulate matter from the Northwest Atlantic Continental Shelf, from the Gulf of Maine to Cape Hatteras” by Oczkowski et al. These are the data upon which all results and conclusion are made. Publishing the data allow for use by wider audience. Stable isotope dynamics on the shelf can inform both nearshore and open ocean research efforts, providing an important link along the marine continuum. To our knowledge, this data set is unique in its spatial coverage and variables measured.

  19. The Importance of CO2 Utilizing Chemolithoautotrophic Microorganisms for Carbon Sequestration and Isotope Signatures of SOM in Tropical Rainforest Soils

    NASA Astrophysics Data System (ADS)

    Nowak, M. E.; Behrendt, T.; Quesada, B.; Yanez Serrano, A. M.; Trumbore, S.

    2015-12-01

    Soil organic matter (SOM) is a major compartment of the tropical carbon cycle with up to 26 % of global carbon stocks stored in tropical soils. Understanding factors and processes driving SOM dynamics under changing climate conditions is crucial for predicting the role of tropical forest ecosystems to act as a carbon sink or source. Soil microorganisms are major drivers of the belowground carbon cycle by releasing CO2 by soil respiration but also by stabilizing and storing SOM, as indicated by recent research. Our investigations focus on chemolithoautotrophic microorganisms, a group that relies on CO2 as their carbon source. Chemolithoautotrophic microorganisms have been shown to be highly abundant in soils, whereas their role in SOM sequestration is still poorly understood. In tropical soils, the activity of chemolithoautotropic microbes might be important for generating and stabilizing carbon, especially in the deeper soil, which is rich in CO2 and reduced energy sources like Fe2+. They further might impact carbon isotope signatures (13C and 14C) of SOM, because of enzymatic fractionation during carboxylation and the use of carbon, which has a distinct isotopic composition than other carbon sources at the same depth. In order to study the activity of chemolithoautotropic microbes and their importance for SOM, we conducted isotope and isotope-labelling studies, gas measurements as well as molecular analyses at soils from the Atto site from 0 to 1 meter depth. These soils are classified as Ferralsols and Alisols and represent the most abundant soil types in the Amazon. With this we will be able to gain knowledge about the function and identity of an important group of microorganisms and their contribution to crucial biogeochemical cycles in the world`s most important ecosystem.

  20. USE OF FATTY ACID STABLE CARBON ISOTOPE RATIO TO INDICATE MICROBIAL CARBON SOURCE IN TROPICAL SOILS

    EPA Science Inventory


    We use measurements of the concentration and stable carbon isotope ratio of individual microbial phospholipid fatty acids (PLFAs) in soils as indicators of live microbial biomass levels, broad microbial community structure, and microbial carbon source. For studies of soil o...

  1. Triple oxygen isotopes in biogenic and sedimentary carbonates

    NASA Astrophysics Data System (ADS)

    Passey, Benjamin H.; Hu, Huanting; Ji, Haoyuan; Montanari, Shaena; Li, Shuning; Henkes, Gregory A.; Levin, Naomi E.

    2014-09-01

    The 17O anomaly (Δ17O) of natural waters has been shown to be sensitive to evaporation in a way analogous to deuterium excess, with evaporated bodies of water (e.g., leaf waters, lake waters, animal body waters) tending to have lower Δ17O than primary meteoric waters. In animal body water, Δ17O relates to the intake of evaporated waters, evaporative effluxes of water, and the Δ17O value of atmospheric O2, which itself carries signatures of global carbon cycling and photochemical reactions in the stratosphere. Carbonates have the potential to record the triple oxygen isotope compositions of parent waters, allowing reconstruction of past water compositions, but such investigations have awaited development of methods for high-precision measurement of Δ17O of carbonate. We describe optimized methods based on a sequential acid digestion/reduction/fluorination approach that yield Δ17O data with the high precision (∼0.010‰, 1σ) needed to resolve subtle environmental signals. We report the first high-precision Δ17O dataset for terrestrial carbonates, focusing on vertebrate biogenic carbonates and soil carbonates, but also including marine invertebrates and high-temperature carbonates. We determine apparent three-isotope fractionation factors between the O2 analyte derived from carbonate and the parent waters of the carbonate. These in combination with appropriate temperature estimates (from clumped isotope thermometry, or known or estimated body temperatures) are used to calculate the δ18O and Δ17O of parent waters. The clearest pattern to emerge is the strong 17O-depletion in avian, dinosaurian, and mammalian body water (from analyses of eggshell and tooth enamel) relative to meteoric waters, following expected influences of evaporated water (e.g., leaf water) and atmospheric O2 on vertebrate body water. Parent waters of the soil carbonates studied here have Δ17O values that are similar to or slightly lower than global precipitation. Our results suggest

  2. In situ analysis of carbon isotopes in North American diamonds

    NASA Astrophysics Data System (ADS)

    van Rythoven, A. D.; Hauri, E. H.; Wang, J.; McCandless, T.; Shirey, S. B.; Schulze, D. J.

    2010-12-01

    Diamonds from three North American kimberlite occurrences were investigated with cathodoluminescence (CL) and secondary ion mass spectrometry (SIMS) to determine their growth history and carbon isotope composition. Diamonds analyzed include fourteen from Lynx (Quebec), twelve from Kelsey Lake (Colorado) and eleven from A154 South (Diavik mine, Northwest Territories). Growth histories for the diamonds vary from simple to highly complex based on their CL images and depending on the individual stone. Deformation laminae are evident in CL images of the Lynx diamonds that typically are brownish in color. Two to five points per diamond were analyzed by SIMS for carbon isotope composition. Sample heterogeneity is minimal in terms of δ13C (vs. PDB) values. Points within single diamond had a maximum range of approximately 1 ‰. The results for the A154 South (-6.4 to -3 ‰) and Kelsey Lake (-11.2 to -2.6 ‰) stones were in accordance with earlier reported values. The Lynx kimberlite stones have anomalously high ratios and range from -3.5 to +0.2 ‰ (average: -1.4 ‰). No previous carbon isotope analyses on diamonds from Lynx or any other eastern Superior craton occurrence have been published. The diamonds possess carbon isotope ratios higher than those for the only other reported analyses of Superior craton diamonds at Wawa, Ontario (-5.5 to -1.1 ‰). In global terms, the only published analyses of diamonds that consistently contain even higher values are those from New South Wales (Australia). However, these diamonds are alluvial and contain eclogitic and/or exotic mineral inclusions. The Lynx diamonds are entirely peridotitic and from a primary deposit. The unusually low (i.e. >-5‰) δ13C values of the Lynx (and Wawa) diamonds may indicate a different carbon reservoir for the Superior craton mantle as compared to other cratons.

  3. ICL-based TDLAS sensor for real-time breath gas analysis of carbon monoxide isotopes.

    PubMed

    Ghorbani, Ramin; Schmidt, Florian M

    2017-05-29

    We present a compact sensor for carbon monoxide (CO) in air and exhaled breath based on a room temperature interband cascade laser (ICL) operating at 4.69 µm, a low-volume circular multipass cell and wavelength modulation absorption spectroscopy. A fringe-limited (1σ) sensitivity of 6.5 × 10 -8 cm -1 Hz -1/2 and a detection limit of 9 ± 5 ppbv at 0.07 s acquisition time are achieved, which constitutes a 25-fold improvement compared to direct absorption spectroscopy. Integration over 10 s increases the precision to 0.6 ppbv. The setup also allows measuring the stable isotope 13 CO in breath. We demonstrate quantification of indoor air CO and real-time detection of CO expirograms from healthy non-smokers and a healthy smoker before and after smoking. Isotope ratio analysis indicates depletion of 13 CO in breath compared to natural abundance.

  4. Boron isotope fractionation in magma via crustal carbonate dissolution

    PubMed Central

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

    2016-01-01

    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 δ11B values down to −41.5‰, reflecting preferential partitioning of 10B into the assimilating melt. Loss of 11B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports 11B 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 δ11B melt values in arc magmas could flag shallow-level additions to the subduction cycle. PMID:27488228

  5. Boron isotope fractionation in magma via crustal carbonate dissolution

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    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 δ11B values down to -41.5‰, reflecting preferential partitioning of 10B into the assimilating melt. Loss of 11B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports 11B 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 δ11B melt values in arc magmas could flag shallow-level additions to the subduction cycle.

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

    PubMed

    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. Patterns in Stable Isotope Values of Nitrogen and Carbon in ...

    EPA Pesticide Factsheets

    Stable isotope measurements of nitrogen and carbon (15N, 13ddC) are often used to characterize estuarine, nearshore, and open ocean ecosystems. Reliable information about the spatial distribution of base-level stable isotope values, often represented by primary producers, is critical to interpreting values in these ecosystems. While base-level isotope data are generally readily available for estuaries, nearshore coastal waters, and the open ocean, the continental shelf is less studied. To address this, and as a first step toward developing a surrogate for base-level isotopic signature in this region, we collected surface and deep water samples from the United States’ eastern continental shelf in the Western Atlantic Ocean, from the Gulf of Maine to Cape Hatteras, periodically between 2000 and 2013. During the study, particulate matter 15dN values ranged from 0.8 to 17.4‰, and 13dC values from −26.4 to −15.6‰over the region. We used spatial autocorrelation analysis and random forest modeling to examine the spatial trends and potential environmental drivers of the stable isotope values. We observed general trends toward lower values for both nitrogen and carbon isotopes at the seaward edge of the shelf. Conversely, higher 15dN and 13dC values were observed on the landward edge of the shelf, in particular in the southern portion of the sampling area. Across all sites, the magnitude of the difference between the 15dN of subsurface and surface particulate m

  8. Carbon and nitrogen abundances in red giant stars in the globular cluster 47 Tucanae

    NASA Technical Reports Server (NTRS)

    Dickens, R. J.; Bell, R. A.; Gustafsson, B.

    1979-01-01

    The effects of changes in temperature, gravity, overall metal abundance, and carbon and nitrogen abundances have been investigated for model stellar spectra and colors representing globular-cluster giants of moderate metal deficiency. The results are presented in the form of spectral atlases and theoretical color-color diagrams. Using these results, approximate abundances of carbon and nitrogen have been derived for some red giant stars in 47 Tuc, from intermediate- and low-dispersion spectra and from intermediate- and narrow-band photometry. In all the normal giants studied, nitrogen is overabundant by up to about a factor of 5 (the precise value depends on the adopted carbon abundance), with different enhancements for different giants. The observational material is not sufficient to distinguish between a normal carbon abundance and a slight carbon depletion for the giant-branch stars, but carbon appears to be somewhat depleted in stars on the asymptotic giant branch. A most probable value of M/H = -0.8 for the overall cluster metal abundance is suggested from analysis of Stromgren photometry of red horizontal-branch stars.

  9. Calcium and Oxygen Isotopic Composition of Calcium Carbonates

    NASA Astrophysics Data System (ADS)

    Niedermayr, Andrea; Eisenhauer, Anton; Böhm, Florian; Kisakürek, Basak; Balzer, Isabelle; Immenhauser, Adrian; Jürgen Köhler, Stephan; Dietzel, Martin

    2016-04-01

    Different isotopic systems are influenced in multiple ways corresponding to the crystal structure, dehydration, deprotonation, adsorption, desorption, isotope exchange and diffusion processes. In this study we investigated the structural and kinetic effects on fractionation of stable Ca- and O-isotopes during CaCO3 precipitation. Calcite, aragonite and vaterite were precipitated using the CO2 diffusion technique[1]at a constant pH of 8.3, but various temperatures (6, 10, 25 and 40° C) and precipitation rates R (101.5 to 105 μmol h-1 m-2). The calcium isotopic fractionation between solution and vaterite is lower (Δ44/40Ca= -0.10 to -0.55 ‰) compared to calcite (-0.69 to -2.04 ‰) and aragonite (-0.91 to -1.55 ‰). In contrast the fractionation of oxygen isotopes is highest for vaterite (32.1 ‰), followed by aragonite (29.2 ‰) and calcite (27.6 ‰) at 25° C and equilibrium. The enrichment of 18O vs. 16O in all polymorphs decreases with increasing precipitation rate by around -0.7 ‰ per log(R). The calcium isotopic fractionation between calcite/ vaterite and aqueous Ca2+ increases with increasing precipitation rate by ˜0.45 ‰ per log(R) and ˜0.1 ‰ per log(R) at 25° C and 40° C, respectively. In contrast the fractionation of Ca-isotopes between aragonite and aqueous Ca2+ decreases with increasing precipitation rates. The large enrichment of 18O vs. 16O isotopes in carbonates is related to the strong bond of oxygen to the small and highly charged C4+-ion. In contrast equilibrium isotopic fractionation between solution and calcite or vaterite is nearly zero as the Ca-O bond length is similar for calcite, vaterite and the hydrated Ca. Aragonite incorporates preferentially the lighter 40Ca isotope as it has very large Ca-O bonds in comparison to the hydrated Ca. At the crystal surface the lighter 40Ca isotopes are preferentially incorporated as dehydration and diffusion of lighter isotopes are faster. Consequently, the surface becomes enriched in 40

  10. Carbon isotopic evidence for photosynthesis in Early Cambrian oceans

    NASA Astrophysics Data System (ADS)

    Surge, Donna M.; Savarese, Michael; Dodd, J. Robert; Lohmann, Kyger C.

    1997-06-01

    Were the first metazoan reefs ecologically similar to modern tropical reefs, enabling them to persist under oligotrophic conditions? We tested the hypothesis of ecological similarity by employing a geochemical approach. Petrography, cathodoluminescence, trace elements, and stable isotope analyses of primary precipitates of the Lower Cambrian Ajax Limestone, South Australia, indicate preservation of original C isotopic composition. All primary carbonate components exhibit C isotopic values similar to the composition of inorganically precipitated fibrous marine cements, suggesting that archaeocyaths and the calcimicrobe Epiphyton precipitated skeletal carbonate in equilibrium with ambient seawater in the absence of vital effects. Such data do not support the contention that archaeocyaths possessed photosymbionts. However, a +0.55‰ shift in δ13C occurs in reefs developed under shallower-water conditions relative to deeper reefs. This shift suggests the stratification of primary production in Early Cambrian oceans. The pattern is similar to that seen in the modern ocean, whereby significant photosynthesis modulates the C isotopic composition of the photic zone.

  11. Molecular carbon isotopic evidence for the origin of geothermal hydrocarbons

    USGS Publications Warehouse

    Des Marais, D.J.; Donchin, J.H.; Nehring, N.L.; Truesdell, A.H.

    1981-01-01

    Previous interest in light hydrocarbons from geothermal systems has focused principally on the origin of the methane1 and the estimation of subsurface temperatures from the carbon isotopic content of coexisting methane and carbon dioxide1-3. Higher molecular weight hydrocarbons were first reported in gases from Yellowstone National Park4, and have since been found to occur commonly in geothermal emanations in the western United States5. Isotopic measurements of individual geothermal hydrocarbons are now reported which help to explain the origin of these hydrocarbons. The thermal decomposition of sedimentary or groundwater organic matter is a principal source of hydrocarbons in four geothermal areas in western North America. ?? 1981 Nature Publishing Group.

  12. Descriptions of carbon isotopes within the energy density functional theory

    SciTech Connect

    Ismail, Atef; Cheong, Lee Yen; Yahya, Noorhana

    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 themore » blocking effect plays a significant role in the shell model configurations.« less

  13. Molecular carbon isotope variations in core samples taken at the Permian-Triassic boundary layers in southern China

    NASA Astrophysics Data System (ADS)

    Wang, Ruiliang; Zhang, Shuichang; Brassell, Simon; Wang, Jiaxue; Lu, Zhengyuan; Ming, Qingzhong; Wang, Xiaomei; Bian, Lizeng

    2012-07-01

    Stable carbon isotope composition (δ13C) of carbonate sediments and the molecular (biomarker) characteristics of a continuous Permian-Triassic (PT) layer in southern China were studied to obtain geochemical signals of global change at the Permian-Triassic boundary (PTB). Carbonate carbon isotope values shifted toward positive before the end of the Permian period and then shifted negative above the PTB into the Triassic period. Molecular carbon isotope values of biomarkers followed the same trend at and below the PTB and remained negative in the Triassic layer. These biomarkers were acyclic isoprenoids, ranging from C15 to C40, steranes (C27 dominates) and terpenoids that were all significantly more abundant in samples from the Permian layer than those from the Triassic layer. The Triassic layer was distinguished by the dominance of higher molecular weight (waxy) n-alkanes. Stable carbon isotope values of individual components, including n-alkanes and acyclic isoprenoids such as phytane, isop-C25, and squalane, are depleted in δ13C by up to 8-10‰ in the Triassic samples as compared to the Permian. Measured molecular and isotopic variations of organic matter in the PT layers support the generally accepted view of Permian oceanic stagnation followed by a massive upwelling of toxic deep waters at the PTB. A series of large-scale (global) outgassing events may be associated with the carbon isotope shift we measured. This is also consistent with the lithological evidence we observed of white thin-clay layers in this region. Our findings, in context with a generally accepted stagnant Permian ocean, followed by massive upwelling of toxic deep waters might be the major causes of the largest global mass extinction event that occurred at the Permian-Triassic boundary.

  14. Investigating controls on boron isotope ratios in shallow marine carbonates

    NASA Astrophysics Data System (ADS)

    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

  15. Stable carbon and nitrogen isotope analysis of avian uric acid.

    PubMed

    Bird, Michael I; Tait, Elaine; Wurster, Christopher M; Furness, Robert W

    2008-11-01

    We report results obtained using a new technique developed to measure the stable-isotope composition of uric acid isolated from bird excreta (guano). Results from a diet-switch feeding trial using zebra finches suggest that the delta(13)C of uric acid in the guano equilibrates with the diet of the bird within 3 days of a change in diet, while the equilibration time for delta(15)N may be longer. The average carbon isotope discrimination between uric acid and food before the diet switch was +0.34 +/- 1 per thousand (1sigma) while after the diet switch this increased slightly to +0.83 +/- 0.7 per thousand (1sigma). Nitrogen isotope discrimination was +1.3 +/- 0.3 per thousand (1sigma) and +0.3 +/- 0.3 per thousand (1sigma) before and after the diet switch; however, it is possible that the nitrogen isotope values did not fully equilibrate with diet switch over the course of the experiment. Analyses of other chemical fractions of the guano (organic residue after uric acid extraction and non-uric acid organics solubilised during extraction) suggest a total range of up to 3 per thousand for both delta(13)C and delta(15)N values in individual components of a single bulk guano sample. The analysis of natural samples from a range of terrestrial and marine species demonstrates that the technique yields isotopic compositions consistent with the known diets of the birds. The results from natural samples further demonstrate that multiple samples from the same species collected from the same location yield similar results, while different species from the same location exhibit a range of isotopic compositions indicative of different dietary preferences. Given that many samples of guano can be rapidly collected without any requirement to capture specimens for invasive sampling, the stable-isotope analysis of uric acid offers a new, simple and potentially powerful tool for studying avian ecology and metabolism.

  16. The use of carbon stable isotope ratios in drugs characterization

    SciTech Connect

    Magdas, D. A., E-mail: gabriela.cristea@itim-cj.ro; Cristea, G., E-mail: gabriela.cristea@itim-cj.ro; Bot, A., E-mail: gabriela.cristea@itim-cj.ro

    Isotopic Ratio Mass Spectrometry (IRMS) is an effective toll to be used for drug product authentication. The isotopic composition could be used to assist in the differentiation between batches of drugs and assist in the identification of counterfeit materials on the market. Only two factors affect the isotopic ratios in pharmaceutical components: the isotopic composition of the raw materials and the synthetic processes performed upon them. Counterfeiting of pharmaceutical drugs threatens consumer confidence in drug products companies' economical well-being. In this preliminary study, the analyzed samples consist in two types of commercially available analgesics, which were purchases from Romanian pharmacies.more » Differences in δ{sup 13}C between batches from −29.7 to −31.6% were observed, demonstrating that this method can be used to differentiate among individual drug batches and subsequently identify counterfeits on the market. On the other hand, carbon isotopic ratios differences among producers were recorded, the variations being between −31.3 to −34.9% for the same type of analgesic, but from different manufactures.« less

  17. The use of carbon stable isotope ratios in drugs characterization

    NASA Astrophysics Data System (ADS)

    Magdas, D. A.; Cristea, G.; Bot, A.; Mirel, V.

    2013-11-01

    Isotopic Ratio Mass Spectrometry (IRMS) is an effective toll to be used for drug product authentication. The isotopic composition could be used to assist in the differentiation between batches of drugs and assist in the identification of counterfeit materials on the market. Only two factors affect the isotopic ratios in pharmaceutical components: the isotopic composition of the raw materials and the synthetic processes performed upon them. Counterfeiting of pharmaceutical drugs threatens consumer confidence in drug products companies' economical well-being. In this preliminary study, the analyzed samples consist in two types of commercially available analgesics, which were purchases from Romanian pharmacies. Differences in δ13C between batches from -29.7 to -31.6% were observed, demonstrating that this method can be used to differentiate among individual drug batches and subsequently identify counterfeits on the market. On the other hand, carbon isotopic ratios differences among producers were recorded, the variations being between -31.3 to -34.9% for the same type of analgesic, but from different manufactures.

  18. Stable carbon, nitrogen and sulfur isotopes in non-carbonate fractions of cold-seep carbonates

    NASA Astrophysics Data System (ADS)

    Feng, Dong; Peng, Yongbo; Peckmann, Jörn; Roberts, Harry; Chen, Duofu

    2017-04-01

    Sulfate-driven anaerobic oxidation of methane (AOM) supports chemosynthesis-based communities and limits the release of methane from marine sediments. This process promotes the formation of carbonates close to the seafloor along continental margins. The geochemical characteristics of the carbonate minerals of these rocks are increasingly understood, questions remain about the geochemical characteristics of the non-carbonate fractions. Here, we report stable carbon, nitrogen and sulfur isotope patterns in non-carbonate fractions of seep carbonates. The authigenic carbonates were collected from three modern seep provinces (Black Sea, Gulf of Mexico, and South China Sea) and three ancient seep deposits (Marmorito, northern Italy, Miocene; SR4 deposit of the Lincoln Creek Formation and Whiskey Creek, western Washington, USA, Eocene to Oligocene). The δ13C values of non-carbonate fractions range from ˜-25‰ to -80‰ VPDB. These values indicate that fossil methane mixed with varying amounts of pelagic organic matter is the dominant source of carbon in these fractions. The relatively small offset between the δ34S signatures of the non-carbonate fractions and the respective sulfide minerals suggests that locally produced hydrogen sulfide is the main source of sulfur in seep environments. The δ15N values of the non-carbonate fractions are generally lower than the corresponding values of deep-sea sediments, suggesting that organic nitrogen is mostly of a local origin. This study reveals the potential of using δ13C, δ15N, δ34S values to discern seep and non-seep deposits. In cases where δ13Ccarbonate values are only moderately low due to mixing processes and lipid biomarkers have been erased in the course of burial, it is difficult to trace back AOM owing to the lack of other records. This problem is even more pronounced when authigenic carbonate is not available in ancient seep environments. Acknowledgments: The authors thank BOEM and NOAA for their years' support

  19. Constraining the global bromomethane budget from carbon stable isotopes

    NASA Astrophysics Data System (ADS)

    Bahlmann, Enno; Wittmer, Julian; Greule, Markus; Zetzsch, Cornelius; Seifert, Richard; Keppler, Frank

    2016-04-01

    Despite intense research in the last two decades, the global bromomethane (CH3Br) budget remains unbalanced with the known sinks exceeding the known sources by about 25%. The reaction with OH is the largest sink for CH3Br. We have determined the kinetic isotope effects for the reactions of CH3Br with the OH and Cl radical in order to better constrain the global CH3Br budget from an isotopic perspective. The isotope fractionation experiments were performed at 20±1°C in a 3500 L Teflon smog-chamber with initial CH3Br mixing ratios of about 2 and 10 ppm and perflourohexane (25 ppb) as internal standard. Atomic chlorine (Cl) was generated via photolysis of molecular chlorine (Cl2) using a solar simulator with an actinic flux comparable to that of the sun in mid-summer in Germany. OH radicals were generated via the photolysis of ozone (O3) at 253.7 nm in the presence of water vapor (RH = 70%).The mixing ratios of CH3Br, and perflourohexane were monitored by GC-MS with a time resolution of 15 minutes throughout the experiments. From each experiment 10 to 15 sub samples were taken in regular time intervals for subsequent carbon isotope ratio determinations by GC-IRMS performed at two independent laboratories in parallel. We found a kinetic isotope effect (KIE) of 17.6±3.3‰ for the reaction of CH3Br with OH and a KIE of 9.8±1.4 ‰ for the reaction with Cl*. We used these fractionation factors along with new data on the isotopic composition of CH3Br in the troposphere (-34±7‰) and the surface ocean (-26±7‰) along with reported source signatures, to constrain the unknown source from an isotopic perspective. The largest uncertainty in estimating the isotopic composition of the unknown source arises from the soil sink. Microbial degradation in soils is the second largest sink and assigned with a large fractionation factors of about 50‰. However, field experiments revealed substantially smaller apparent fractionation factors ranging from 11 to 22‰. In addition

  20. Forward Modeling of Carbonate Proxy Data from Planktonic Foraminifera using Oxygen Isotope Tracers in a Global Ocean Model

    NASA Technical Reports Server (NTRS)

    Schmidt, Gavin A.

    1999-01-01

    The distribution and variation of oxygen isotopes in seawater are calculated using the Goddard Institute for Space Studies global ocean model. Simple ecological models are used to estimate the planktonic foraminiferal abundance as a function of depth, column temperature, season, light intensity, and density stratification. These models are combined to forward model isotopic signals recorded in calcareous ocean sediment. The sensitivity of the results to the changes in foraminiferal ecology, secondary calcification, and dissolution are also examined. Simulated present-day isotopic values for ecology relevant for multiple species compare well with core-top data. Hindcasts of sea surface temperature and salinity are made from time series of the modeled carbonate isotope values as the model climate changes. Paleoclimatic inferences from these carbonate isotope records are strongly affected by erroneous assumptions concerning the covariations of temperature, salinity, and delta (sup 18)O(sub w). Habitat-imposed biases are less important, although errors due to temperature-dependent abundances can be significant.

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

    DOE PAGES

    Garcia del Real, Pablo; Maher, Kate; Kluge, Tobias; ...

    2016-08-19

    Here, magnesium carbonate minerals produced by reaction of H 2O–CO 2 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 deposition of ore-grade, massive-vein cryptocrystalline magnesite; formation of hydrous magnesium carbonates in weathering environments; and 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 CO 2 into magnesium carbonates in these settings is difficult because the fluids are usually notmore » preserved.« less

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

    SciTech Connect

    Garcia del Real, Pablo; Maher, Kate; Kluge, Tobias

    Here, magnesium carbonate minerals produced by reaction of H 2O–CO 2 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 deposition of ore-grade, massive-vein cryptocrystalline magnesite; formation of hydrous magnesium carbonates in weathering environments; and 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 CO 2 into magnesium carbonates in these settings is difficult because the fluids are usually notmore » preserved.« less

  3. Basal area growth, carbon isotope discrimination, and intrinsic ...

    EPA Pesticide Factsheets

    Many hectares of intensively managed Douglas-fir (Pseudotsuga menziesii Mirb. Franco) stands in western North America are fertilized with nitrogen to increase growth rates. Understanding the mechanisms of response facilitates prioritization of stands for treatment. The objective of this study was to test the hypothesis that the short-term basal area growth response to a single application of 224 kg N ha-1 as urea was associated with reduced stable carbon isotope discrimination (∆13C) and increased intrinsic water use efficiency (iWUE) in a 20-yr-old plantation of Douglas-fir in the Oregon Coast Range, USA. Increment cores were measured to estimate earlywood, latewood, and total basal area increment over a time series from 1997 to 2015. Stable carbon isotope discrimination and iWUE were estimated using earlywood and latewood stable carbon isotope concentrations in tree-ring holocellulose starting seven years before fertilization in early 2009 and ending seven years after treatment. A highly significant interaction effect between fertilization treatment and year was found for total basal area growth and earlywood basal area increment. Fertilized trees showed significant total basal area growth and earlywood basal area increment in the first (2009) and second (2010) growing seasons after fertilization in 2009. A marginally significant fertilization effect was found for latewood basal area increment only in the first growing season after treatment. A significant i

  4. Stable carbon and nitrogen isotope enrichment in primate tissues

    PubMed Central

    Carter, Melinda L.; Karpanty, Sarah M.; Zihlman, Adrienne L.; Koch, Paul L.; Dominy, Nathaniel J.

    2010-01-01

    Isotopic studies of wild primates have used a wide range of tissues to infer diet and model the foraging ecologies of extinct species. The use of mismatched tissues for such comparisons can be problematic because differences in amino acid compositions can lead to small isotopic differences between tissues. Additionally, physiological and dietary differences among primate species could lead to variable offsets between apatite carbonate and collagen. To improve our understanding of the isotopic chemistry of primates, we explored the apparent enrichment (ε*) between bone collagen and muscle, collagen and fur or hair keratin, muscle and keratin, and collagen and bone carbonate across the primate order. We found that the mean ε* values of proteinaceous tissues were small (≤1‰), and uncorrelated with body size or phylogenetic relatedness. Additionally, ε* values did not vary by habitat, sex, age, or manner of death. The mean ε* value between bone carbonate and collagen (5.6 ± 1.2‰) was consistent with values reported for omnivorous mammals consuming monoisotopic diets. These primate-specific apparent enrichment values will be a valuable tool for cross-species comparisons. Additionally, they will facilitate dietary comparisons between living and fossil primates. Electronic supplementary material The online version of this article (doi:10.1007/s00442-010-1701-6) contains supplementary material, which is available to authorized users. PMID:20628886

  5. Stable carbon isotopes: possible clues to early life on Mars.

    PubMed

    Schidlowski, M

    1992-01-01

    Organic and inorganic carbon in terrestrial near-surface environments are characterized by a marked difference in their 13C/12C ratios which can be traced back in the Earth's sedimentary record over almost 4 billion years. There is no doubt that the bias in favour of 12C displayed by biogenic matter derives, for the most part, from the isotope-selecting properties of the carbon-fixing enzyme (ribulose-1,5-bisphosphate carboxylase) that is operative in the principal photosynthetic pathway and promotes most of the carbon transfer from the non-living to the living realm. Postulating a universality of biological principles in analogy to the proven universality of the laws of physics and chemistry, we may expect enzymatic reactions in exobiological systems to be beset with B similar kinetic fractionation effects. Hence, the retrieval from the oldest Martian sediments of isotopic fractionations between reduced and oxidized (carbonate) carbon may substantially constrain current conjectures on the possible existence of former life on Mars.

  6. Testing the ``Wildfire Hypothesis:'' Terrestrial Organic Carbon Burning as the Cause of the Paleocene-Eocene Boundary Carbon Isotope Excursion

    NASA Astrophysics Data System (ADS)

    Moore, E. A.; Kurtz, A. C.

    2005-12-01

    The 3‰ negative carbon isotope excursion (CIE) at the Paleocene-Eocene boundary has generally been attributed to dissociation of seafloor methane hydrates. We are testing the alternative hypothesis that the carbon cycle perturbation resulted from wildfires affecting the extensive peatlands and coal swamps formed in the Paleocene. Accounting for the CIE with terrestrial organic carbon rather than methane requires a significantly larger net release of fossil carbon to the ocean-atmosphere, which may be more consistent with the extreme global warming and ocean acidification characteristic of the Paleocene-Eocene Thermal Maximum (PETM). While other researchers have noted evidence of fires at the Paleocene-Eocene boundary in individual locations, the research presented here is designed to test the "wildfire hypothesis" for the Paleocene-Eocene boundary by examining marine sediments for evidence of a global increase in wildfire activity. Such fires would produce massive amounts of soot, widely distributed by wind and well preserved in marine sediments as refractory black carbon. We expect that global wildfires occurring at the Paleocene-Eocene boundary would produce a peak in black carbon abundance at the PETM horizon. We are using the method of Gelinas et al. (2001) to produce high-resolution concentration profiles of black carbon across the Paleocene-Eocene boundary using seafloor sediments from ODP cores, beginning with the Bass River core from ODP leg 174AX and site 1209 from ODP leg 198. This method involves the chemical and thermal extraction of non-refractory carbon followed by combustion of the residual black carbon and measurement as CO2. Measurement of the δ 13C of the black carbon will put additional constraints on the source of the organic material combusted, and will allow us to determine if this organic material was formed prior to or during the CIE.

  7. Calibrated sulfur isotope abundance ratios of three IAEA sulfur isotope reference materials and V-CDT with a reassessment of the atomic weight of sulfur

    NASA Astrophysics Data System (ADS)

    Ding, T.; Valkiers, S.; Kipphardt, H.; De Bièvre, P.; Taylor, P. D. P.; Gonfiantini, R.; Krouse, R.

    2001-08-01

    Calibrated values have been obtained for sulfur isotope abundance ratios of sulfur isotope reference materials distributed by the IAEA (Vienna). For the calibration of the measurements, a set of synthetic isotope mixtures were prepared gravimetrically from high purity Ag2S materials enriched in32S, 33S, and 34S. All materials were converted into SF6 gas and subsequently, their sulfur isotope ratios were measured on the SF5+ species using a special gas source mass spectrometer equipped with a molecular flow inlet system (IRMM's Avogadro II amount comparator). Values for the 32S/34S abundance ratios are 22.650 4(20), 22.142 4(20), and 23.393 3(17) for IAEA-S-1, IAEA-S-2, and IAEA-S-3, respectively. The calculated 32S/34S abundance ratio for V-CDT is 22.643 6(20), which is very close to the calibrated ratio obtained by Ding et al. (1999). In this way, the zero point of the VCDT scale is anchored firmly to the international system of units SI. The 32S/33S abundance ratios are 126.942(47), 125.473(55), 129.072(32), and 126.948(47) for IAEA-S-1, IAEA-S-2, IAEA-S-3, and V-CDT, respectively. In this way, the linearity of the V-CDT scale is improved over this range. The values of the sulfur molar mass for IAEA-S-1 and V-CDT were calculated to be 32.063 877(56) and 32.063 911(56), respectively, the values with the smallest combined uncertainty ever reported for the sulfur molar masses (atomic weights).

  8. Widespread kelp-derived carbon in pelagic and benthic nearshore fishes suggested by stable isotope analysis

    NASA Astrophysics Data System (ADS)

    von Biela, Vanessa R.; Newsome, Seth D.; Bodkin, James L.; Kruse, Gordon H.; Zimmerman, Christian E.

    2016-11-01

    Kelp forests provide habitat for diverse and abundant fish assemblages, but the extent to which kelp provides a source of energy to fish and other predators is unclear. To examine the use of kelp-derived energy by fishes we estimated the contribution of kelp- and phytoplankton-derived carbon using carbon (δ13C) and nitrogen (δ15N) isotopes measured in muscle tissue. Benthic-foraging kelp greenling (Hexagrammos decagrammus) and pelagic-foraging black rockfish (Sebastes melanops) were collected at eight sites spanning ∼35 to 60°N from the California Current (upwelling) to Alaska Coastal Current (downwelling) in the northeast Pacific Ocean. Muscle δ13C values were expected to be higher for fish tissue primarily derived from kelp, a benthic macroalgae, and lower for tissue primarily derived from phytoplankton, pelagic microalgae. Muscle δ13C values were higher in benthic-feeding kelp greenling than in pelagic-feeding black rockfish at seven of eight sites, indicating more kelp-derived carbon in greenling as expected. Estimates of kelp carbon contributions ranged from 36 to 89% in kelp greenling and 32 to 65% in black rockfish using carbon isotope mixing models. Isotopic evidence suggests that these two nearshore fishes routinely derive energy from kelp and phytoplankton, across coastal upwelling and downwelling systems. Thus, the foraging mode of nearshore predators has a small influence on their ultimate energy source as energy produced by benthic macroalgae and pelagic microalgae were incorporated in fish tissue regardless of feeding mode and suggest strong and widespread benthic-pelagic coupling. Widespread kelp contributions to benthic- and pelagic-feeding fishes suggests that kelp energy provides a benefit to nearshore fishes and highlights the potential for kelp and fish production to be linked.

  9. The abundances of solar accelerated nuclei from carbon to iron.

    NASA Technical Reports Server (NTRS)

    Mogro-Campero, A.; Simpson, J. A.

    1972-01-01

    Revised observation periods and new data are found to confirm previous evidence that the overabundance of solar-flare nuclei with respect to solar photospheric and coronal abundances increases with increasing atomic number. It is also verified that enhancements can vary from flare to flare and that this variability is large enough to explain the differences observed by various investigators regarding the magnitude of solar-flare high-Z particle enhancements. Additional evidence for a two-stage solar acceleration mechanism is obtained. It is shown that the galactic cosmic-ray source composition displays a similar overabundance as a function of atomic number.

  10. C isotope fractionation during heterotrophic activity driven carbonate precipitation

    NASA Astrophysics Data System (ADS)

    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

  11. Refined Estimates of Carbon Abundances for Carbon-Enhanced Metal-Poor Stars

    NASA Astrophysics Data System (ADS)

    Rossi, S.; Placco, V. M.; Beers, T. C.; Marsteller, B.; Kennedy, C. R.; Sivarani, T.; Masseron, T.; Plez, B.

    2008-03-01

    We present results from a refined set of procedures for estimation of the metallicities ([Fe/H]) and carbon abundance ratios ([C/Fe]) based on a much larger sample of calibration objects (on the order of 500 stars) then were available to Rossi et al. (2005), due to a dramatic increase in the number of stars with measurements obtained from high-resolution analyses in the past few years. We compare results obtained from a new calibration of the KP and GP indices with that obtained from a custom set of spectral synthesis based on MOOG. In cases where the GP index approaches saturation, it is clear that only spectral synthesis achieve reliable results.

  12. The clumped isotope geothermometer in soil and paleosol carbonate

    NASA Astrophysics Data System (ADS)

    Quade, J.; Eiler, J.; Daëron, M.; Achyuthan, H.

    2013-03-01

    We studied both modern soils and buried paleosols in order to understand the relationship of temperature (T°C(47)) estimated from clumped isotope compositions (Δ47) of soil carbonates to actual surface and burial temperatures. Carbonates from modern soils with differing rainfall seasonality were sampled from Arizona, Nevada, Tibet, Pakistan, and India. T°C(47) obtained from these soils shows that soil carbonate forms in the warmest months of the year, in the late morning to afternoon, and probably in response to intense soil dewatering. T°C(47) obtained from modern soil carbonate ranges from 10.8 to 39.5 °C. On average, T°C(47) exceeds mean annual temperature by 10-15 °C due to summertime bias in soil carbonate formation, and to summertime ground heating by incident solar radiation. Secondary controls on T°C(47) are soil depth and shading. Site mean annual air temperature (MAAT) across a broad range (0-30 °C) of site temperatures is highly correlated with T°C(47) from soils, following the equation: MAAT(°C)=1.20(T°C(47)0)-21.72(r2=0.92) where T°C(47)0 is the effective air temperature at the site estimated from T°C(47). The effective air temperature represents the air temperature required to account for the T°C(47) at each site, after consideration of variations in T°C(47) with soil depth and ground heating. The highly correlated relationship in this equation should now permit mean annual temperature in the past to be reconstructed from T°C(47) in paleosol carbonate, assuming one is studying paleosols that formed in environments generally similar in seasonality and ground cover to our calibration sites. T°C(47)0 decreases systematically with elevation gain in the Himalaya, following the equation: elevation(m)=-229(T°C(47)0)+9300(r2=0.95) Assuming that temperature varied similarly with elevation in the past, this equation can be used to reconstruct paleoelevation from clumped isotope analysis of ancient soil carbonates. We also measured T°C(47

  13. Ratios of Carbon Isotopes in Microbial Lipids as an Indicator of Substrate Usage

    PubMed Central

    Abraham, Wolf-Rainer; Hesse, Christian; Pelz, Oliver

    1998-01-01

    The occurrence and abundance of microbial fatty acids have been used for the identification of microorganisms in microbial communities. However, these fatty acids can also be used as indicators of substrate usage. For this, a systematic investigation of the discrimination of the stable carbon isotopes by different microorganisms is necessary. We grew 11 strains representing major bacterial and fungal species with four different isotopically defined carbon sources and determined the isotope ratios of fatty acids of different lipid fractions. A comparison of the differences of δ13C values of palmitic acid (C16:0) with the δ13C values of the substrates revealed that the isotope ratio is independent of the growth stage and that most microorganisms showed enrichment of C16:0 with 13C when growing on glycerol. With the exception of Burkholderia gladioli, all microorganism showed depletion of 13C in C16:0 while incorporating the carbons of glucose, and most of them were enriched with 13C from mannose, with the exception of Pseudomonas fluorescens and the Zygomycotina. Usually, the glycolipid fractions are depleted in 13C compared to the phospholipid fractions. The δ13C pattern was not uniform within the different fatty acids of a given microbial species. Generally, tetradecanoic acid (C14:0) was depleted of 13C compared to palmitic acid (C16:0) while octadecanoic acid (C18:0) was enriched. These results are important for the calibration of a new method in which δ13C values of fatty acids from the environment delineate the use of bacterial substrates in an ecosystem. PMID:9797266

  14. Trace sulfate in mid-Proterozoic carbonates and the sulfur isotope record of biospheric evolution

    NASA Astrophysics Data System (ADS)

    Gellatly, Anne M.; Lyons, Timothy W.

    2005-08-01

    Concentrations of oceanic and atmospheric oxygen have varied over geologic time as a function of sulfur and carbon cycling at or near the Earth's surface. This balance is expressed in the sulfur isotope composition of seawater sulfate. Given the near absence of gypsum in pre-Phanerozoic sediments, trace amounts of carbonate-associated sulfate (CAS) within limestones or dolostones provide the best available constraints on the isotopic composition of sulfate in Precambrian seawater. Although absolute CAS concentrations, which range from those below detection to ˜120 ppm sulfate in this study, may be compromised by diagenesis, the sulfur isotope compositions can be buffered sufficiently to retain primary values. Stratigraphically controlled δ 34S measurements for CAS from three mid-Proterozoic carbonate successions (˜1.2 Ga Mescal Limestone, Apache Group, Arizona, USA; ˜1.45-1.47 Ga Helena and Newland formations, Belt Supergroup, Montana, USA; and ˜1.65 Ga Paradise Creek Formation, McNamara Group, NW Queensland, Australia) show large isotopic variability (+9.1‰ to +18.9‰, -1.1‰ to +27.3‰, and +14.1‰ to +37.3‰, respectively) over stratigraphic intervals of ˜50 to 450 m. This rapid variability, ranging from scattered to highly systematic, and overall low CAS abundances can be linked to sulfate concentrations in the mid-Proterozoic ocean that were substantially lower than those of the Phanerozoic but higher than values inferred for the Archean. Results from the Belt Supergroup specifically corroborate previous arguments for seawater contributions to the basin. Limited sulfate availability that tracks the oxygenation history of the early atmosphere is also consistent with the possibility of extensive deep-ocean sulfate reduction, the scarcity of bedded gypsum, and the stratigraphic δ 34S trends and 34S enrichments commonly observed for iron sulfides of mid-Proterozoic age.

  15. Ratios of carbon isotopes in microbial lipids as an indicator of substrate usage.

    PubMed

    Abraham, W R; Hesse, C; Pelz, O

    1998-11-01

    The occurrence and abundance of microbial fatty acids have been used for the identification of microorganisms in microbial communities. However, these fatty acids can also be used as indicators of substrate usage. For this, a systematic investigation of the discrimination of the stable carbon isotopes by different microorganisms is necessary. We grew 11 strains representing major bacterial and fungal species with four different isotopically defined carbon sources and determined the isotope ratios of fatty acids of different lipid fractions. A comparison of the differences of delta13C values of palmitic acid (C16:0) with the delta13C values of the substrates revealed that the isotope ratio is independent of the growth stage and that most microorganisms showed enrichment of C16:0 with 13C when growing on glycerol. With the exception of Burkholderia gladioli, all microorganism showed depletion of 13C in C16:0 while incorporating the carbons of glucose, and most of them were enriched with 13C from mannose, with the exception of Pseudomonas fluorescens and the Zygomycotina. Usually, the glycolipid fractions are depleted in 13C compared to the phospholipid fractions. The delta13C pattern was not uniform within the different fatty acids of a given microbial species. Generally, tetradecanoic acid (C14:0) was depleted of 13C compared to palmitic acid (C16:0) while octadecanoic acid (C18:0) was enriched. These results are important for the calibration of a new method in which delta13C values of fatty acids from the environment delineate the use of bacterial substrates in an ecosystem.

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

    NASA Astrophysics Data System (ADS)

    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

  17. STABLE ISOTOPIC EVIDENCE OF CARBON AND NITROGEN USE IN CULTURED ECTOMYCORRHIZAL AND SAPROTROPHIC FUNGI

    EPA Science Inventory

    Stable isotopes in sporocarps have proven useful for inferring ectomycorrhizal or saprotrophic status and understanding carbon (C) and nitrogen (N) utilization. However, greater understanding of processes producing isotopic concentrations is needed. We measured natural abundanc...

  18. Photosynthetic Fractionation of the Stable Isotopes of Oxygen and Carbon.

    PubMed Central

    Guy, R. D.; Fogel, M. L.; Berry, J. A.

    1993-01-01

    Isotope discrimination during photosynthetic exchange of O2 and CO2 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 ([delta], where 1 + [delta]/1000 equals the isotope effect, k16/k18 or k12/k13) was determined by analysis of residual substrate (O2 or CO2). The [delta] for the Mehler reaction, mediated by ferredoxin or methylviologen, was 15.3[per mille (thousand) sign]. Oxygen isotope discrimination during oxygenation of ribulose-1,5-bisphosphate (RuBP) catalyzed by RuBP carboxylase/oxygenase (Rubisco) was 21.3[per mille (thousand) sign] and independent of enzyme source, unlike carbon isotope discrimination: 30.3[per mille (thousand) sign] for spinach enzyme and 19.6 to 23[per mille (thousand) sign] for Rhodospirillum rubrum and A. nidulans enzymes, depending on reaction conditions. The [delta] for O2 consumption catalyzed by glycolate oxidase was 22.7[per mille (thousand) sign]. The expected overall [delta] for photorespiration is about 21.7[per mille (thousand) sign]. Consistent with this, when Asparagus sprengeri Regel mesophyll cells approached the compensation point within a sealed vessel, the [delta]18O of dissolved O2 came to a steady-state value of about 21.5[per mille (thousand) sign] relative to the source water. The results provide improved estimates of discrimination factors in several reactions prominent in the global O cycle and indicate that photorespiration plays a significant part in determining the isotopic composition of atmospheric oxygen. PMID:12231663

  19. Radiocarbon and stable-isotope geochemistry of organic and inorganic carbon in Lake Superior

    NASA Astrophysics Data System (ADS)

    Zigah, Prosper K.; Minor, Elizabeth C.; Werne, Josef P.

    2012-03-01

    We present a lake-wide investigation of Lake Superior carbon and organic matter biogeochemistry using radiocarbon, stable isotope, and carbon concentrations. Dissolved inorganic carbon (DIC) abundance in the lake was 121-122 Tg C, with offshore concentration andδ13C values being laterally homogenous and tightly coupled to the physical and thermal regime and biochemical processes. Offshore Δ14C of DIC (50-65‰) exhibited lateral homogeneity and was more 14C enriched than co-occurring atmospheric CO2 (˜38‰); nearshore Δ14C of DIC (36-38‰) was similar to atmospheric CO2. Dissolved organic carbon (DOC) abundance was 14.2-16.4 Tg C. DOC's concentration and δ13C were homogenous in June (mixed lake), but varied laterally during August (stratification) possibly due to spatial differences in lake productivity. Throughout sampling, DOC had modern radiocarbon values (14-58‰) indicating a semilabile nature with a turnover time of ≤60 years. Lake particulate organic carbon (POC, 0.9-1.3 Tg C) was consistently 13C depleted relative to DOC. The δ15N of epilimnetic particulate organic nitrogen shifted to more negative values during stratification possibly indicating greater use of nitrate (rather than ammonium) by phytoplankton in August. POC's radiocarbon was spatially heterogeneous (Δ14C range: 58‰ to -303‰), and generally 14C depleted relative to DOC and DIC. POC 14C depletion could not be accounted for by black carbon in the lake but, because of its spatial and temporal distribution, is attributed to sediment resuspension. The presence of old POC within the epilimnion of the open lake indicates possible benthic-pelagic coupling in the lake's organic carbon cycle; the ultimate fate of this old POC bears further investigation.

  20. Altitude effect on leaf wax carbon isotopic composition in humid tropical forests

    NASA Astrophysics Data System (ADS)

    Wu, Mong Sin; Feakins, Sarah J.; Martin, Roberta E.; Shenkin, Alexander; Bentley, Lisa Patrick; Blonder, Benjamin; Salinas, Norma; Asner, Gregory P.; Malhi, Yadvinder

    2017-06-01

    The carbon isotopic composition of plant leaf wax biomarkers is commonly used to reconstruct paleoenvironmental conditions. Adding to the limited calibration information available for modern tropical forests, we analyzed plant leaf and leaf wax carbon isotopic compositions in forest canopy trees across a highly biodiverse, 3.3 km elevation gradient on the eastern flank of the Andes Mountains. We sampled the dominant tree species and assessed their relative abundance in each tree community. In total, 405 sunlit canopy leaves were sampled across 129 species and nine forest plots along the elevation profile for bulk leaf and leaf wax n-alkane (C27-C33) concentration and carbon isotopic analyses (δ13C); a subset (76 individuals, 29 species, five forest plots) were additionally analyzed for n-alkanoic acid (C22-C32) concentrations and δ13C. δ13C values display trends of +0.87 ± 0.16‰ km-1 (95% CI, r2 = 0.96, p < 0.01) for bulk leaves and +1.45 ± 0.33‰ km-1 (95% CI, r2 = 0.94, p < 0.01) for C29n-alkane, the dominant chain length. These carbon isotopic gradients are defined in multi-species sample sets and corroborated in a widespread genus and several families, suggesting the biochemical response to environment is robust to taxonomic turnover. We calculate fractionations and compare to adiabatic gradients, environmental variables, leaf wax n-alkane concentrations, and sun/shade position to assess factors influencing foliar chemical response. For the 4 km forested elevation range of the Andes, 4-6‰ higher δ13C values are expected for upland versus lowland C3 plant bulk leaves and their n-alkyl lipids, and we expect this pattern to be a systematic feature of very wet tropical montane environments. This elevation dependency of δ13C values should inform interpretations of sedimentary archives, as 13C-enriched values may derive from C4 grasses, petrogenic inputs or upland C3 plants. Finally, we outline the potential for leaf wax carbon isotopes to trace biomarker

  1. Carbonate concretions as a significant component of ancient marine carbon cycles: Insights from paired organic and inorganic carbon isotope analyses of a Cretaceous shale

    NASA Astrophysics Data System (ADS)

    Loyd, S. J.

    2014-12-01

    Carbonate concretions often occur within fine-grained, organic-rich sedimentary rocks. This association reflects the common production of diagenetic minerals through biologic cycling of organic matter. Chemical analysis of carbonate concretions provides the rare opportunity to explore ancient shallow diagenetic environments, which are inherently transient due to progressive burial but are an integral component of the marine carbon cycle. The late Cretaceous Holz Shale (~80 Ma) contains abundant calcite concretions that exhibit textural and geochemical characteristics indicative of relatively shallow formation (i.e., near the sediment-water interface). Sampled concretions contain between 5.4 and 9.8 wt.% total inorganic carbon (TIC), or ~45 and 82 wt.% CaCO3, compared to host shale values which average ~1.5 wt.% TIC. Organic carbon isotope compositions (δ13Corg) are relatively constant in host and concretion samples ranging from ­-26.3 to -24.0‰ (VPDB). Carbonate carbon isotope compositions (δ13Ccarb) range from -22.5 to -3.4‰, indicating a significant but not entirely organic source of carbon. Concretions of the lower Holz Shale exhibit considerably elevated δ13Ccarb values averaging -4.8‰, whereas upper Holz Shale concretions express an average δ13Ccarb value of -17.0‰. If the remaining carbonate for lower Holz Shale concretions is sourced from marine fluids and/or dissolved marine carbonate minerals (e.g., shells), a simple mass balance indicates that ~28% of concretion carbon was sourced from organic matter and ~72% from late Cretaceous marine inorganic carbon (with δ13C ~ +2.5‰). Upper Holz Shale calculations indicate a ~73% contribution from organic matter and a ~27% contribution from inorganic carbon. When normalized for carbonate, organic contents within the concretions are ~2-13 wt.% enriched compared to host contents. This potentially reflects the protective nature of cementation that acts to limit permeability and chemical destruction of

  2. PHOTOCHEMICALLY-INDUCED ALTERATION OF STABLE CARBON ISOTOPE RATIOS (DELTA C-13) IN TERRIGENOUS DISSOLVED ORGANIC CARBON

    EPA Science Inventory

    Exposure of riverine waters to natural sunlight initiated alterations in stable carbon isotope ratios (delta C-13) of the associated dissolved organic carbon (DOC). Water samples were collected from two compositionally distinct coastal river systems in the southeastern United Sta...

  3. A continuous 250,000 yr record of oxygen and carbon isotopes in ostracode and bulk-sediment carbonate from Bear Lake, Utah-Idaho

    USGS Publications Warehouse

    Bright, Jordon; Kaufman, D.S.; Forester, R.M.; Dean, W.E.

    2006-01-01

    Oxygen and carbon isotopes from a continuous, 120-m-long, carbonate-rich core from Bear Lake, Utah-Idaho, document dramatic fluctuations in the hydrologic budget of the lake over the last 250,000 yr. Isotopic analyses of bulk sediment samples capture millennial-scale variability. Ostracode calcite was analyzed from 78 levels, mainly from the upper half of the core where valves are better preserved, to compare the isotopic value of purely endogenic carbonate with the bulk sediment, which comprises both endogenic and detrital components. The long core exhibits three relatively brief intervals with abundant endogenic aragonite (50??10%) and enriched ??18O and ??13C. These intervals are interpreted as warm/dry periods when the lake retracted into a topographically closed basin. We correlate these intervals with the interglacial periods of marine oxygen-isotope stages 1, 5e, and 7a, consistent with the presently available geochronological control. During most of the time represented by the core, the lake was fresher than the modern lake, as evidenced by depleted ??18O and ??13C in bulk-sediment carbonate. ?? 2006 Elsevier Ltd. All rights reserved.

  4. Textural and isotopic evidence for Ca-Mg carbonate pedogenesis

    NASA Astrophysics Data System (ADS)

    Diaz-Hernandez, J. L.; Sánchez-Navas, A.; Delgado, A.; Yepes, J.; Garcia-Casco, A.

    2018-02-01

    Models for evaluating the terrestrial carbon cycle must take into account not only soil organic carbon, represented by a mixture of plant and animal remains, but also soil inorganic carbon, contained in minerals, mainly in calcite and dolomite. Thick soil caliches derived from weathering of mafic and ultramafic rocks must be considered as sinks for carbon storage in soils. The formation of calcite and dolomite from pedogenic alteration of volcanic tephras under an aridic moisture regime is studied in an unusually thick 3-m soil profile on Gran Canaria island (Canary Islands, Spain). The biological activity of the pedogenic environment (soil respiration) releases CO2 incorporated as dissolved inorganic carbon (DIC) in waters. It drives the formation of low-magnesian calcite and calcian dolomite over basaltic substrates, with a δ13C negative signature (-8 to -6‰ vs. V-PDB). Precipitation of authigenic carbonates in the soil is accompanied by the formation of Mg-rich clay minerals and quartz after the weathering of basalts. Mineralogical, textural, compositional, and isotopic variations throughout the soil profile studied indicate that dolomite formed at greater depths and earlier than the calcite. The isotopic signatures of the surficial calcite and deeper dolomite crusts are primary and resulted from the dissolution-precipitation cycles that led to the formation of both types of caliches under different physicochemical conditions. Dolomite formed within a clay-rich matrix through diffusive transport of reactants. It is precipitated from water with more negative δ18O values (-1.5 to -3.5‰ vs. V-SMOW) in the subsoil compared to those of water in equilibrium with surficial calcite. Thus, calcite precipitated after dolomite, and directly from percolating solutions in equilibrium with vadose water enriched in δ18O (-0.5 to +1.5‰) due to the evaporation processes. The accumulation of inorganic carbon reaches 586.1 kg m-2 in the soil studied, which means that the

  5. RAPID AND PRECISE METHOD FOR MEASURING STABLE CARBON ISOTOPE RATIOS OF DISSOLVED INORGANIC CARBON

    EPA Science Inventory

    We describe a method for rapid preparation, concentration and stable isotopic analysis of dissolved inorganic carbon (d13C-DIC). Liberation of CO2 was accomplished by placing 100 ?l phosphoric acid and 0.9 ml water in an evacuated 1.7-ml gas chromatography (GC) injection vial. Fo...

  6. Coupled Mo-U abundances and isotopes in a small marine euxinic basin: Constraints on processes in euxinic basins

    NASA Astrophysics Data System (ADS)

    Bura-Nakić, Elvira; Andersen, Morten B.; Archer, Corey; de Souza, Gregory F.; Marguš, Marija; Vance, Derek

    2018-02-01

    Sedimentary molybdenum (Mo) and uranium (U) abundances, as well as their isotope systematics, are used to reconstruct the evolution of the oxygenation state of the surface Earth from the geological record. Their utility in this endeavour must be underpinned by a thorough understanding of their behaviour in modern settings. In this study, Mo-U concentrations and their isotope compositions were measured in the water column, sinking particles, sediments and pore waters of the marine euxinic Lake Rogoznica (Adriatic Sea, Croatia) over a two year period, with the aim of shedding light on the specific processes that control Mo-U accumulation and isotope fractionations in anoxic sediment. Lake Rogoznica is a 15 m deep stratified sea-lake that is anoxic and euxinic at depth. The deep euxinic part of the lake generally shows Mo depletions consistent with near-quantitative Mo removal and uptake into sediments, with Mo isotope compositions close to the oceanic composition. The data also, however, show evidence for periodic additions of isotopically light Mo to the lake waters, possibly released from authigenic precipitates formed in the upper oxic layer and subsequently processed through the euxinic layer. The data also show evidence for a small isotopic offset (∼0.3‰ on 98Mo/95Mo) between particulate and dissolved Mo, even at highest sulfide concentrations, suggesting minor Mo isotope fractionation during uptake into euxinic sediments. Uranium concentrations decrease towards the bottom of the lake, where it also becomes isotopically lighter. The U systematics in the lake show clear evidence for a dominant U removal mechanism via diffusion into, and precipitation in, euxinic sediments, though the diffusion profile is mixed away under conditions of increased density stratification between an upper oxic and lower anoxic layer. The U diffusion-driven precipitation is best described with an effective 238U/235U fractionation of +0.6‰, in line with other studied euxinic

  7. Stable Carbon Isotopes in Treerings; Revisiting the Paleocloud Proxy.

    NASA Astrophysics Data System (ADS)

    Gagen, M.; Zorita, E.; Dorado Liñán, I.; Loader, N.; McCarroll, D.; Robertson, I.; Young, G.

    2017-12-01

    The long term relationship between cloud cover and temperature is one of the most important climate feedbacks contributing to determining the value of climate sensitivity. Climate models still reveal a large spread in the simulation of changes in cloud cover under future warming scenarios and clarity might be aided by a picture of the past variability of cloudiness. Stable carbon isotope ratios from tree ring records have been successfully piloted as a palaeocloud proxy in geographical areas traditionally producing strong dendroclimatological reconstructions (high northern latitudes in the Northern Hemisphere) and with some notable successes elsewhere too. An expansion of tree-ring based palaeocloud reconstructions might help to estimate past variations of cloud cover in periods colder or warmer than the 20th century, providing a way to test model test this specific aspect. Calibration with measured instrumental sunshine and cloud data reveals stable carbon isotope ratios from tree rings as an indicator of incoming short wave solar radiation (SWR) in non-moisture stressed sites, but the statistical identification of the SWR signal is hampered by its interannual co-variability with air temperature during the growing season. Here we present a spatio-temporal statistical analysis of a multivariate stable carbon isotope tree ring data set over Europe to assess its usefulness to reconstruct past solar radiation changes. The interannual co-variability of the tree ring records stronger covariation with SWR than with air temperature. The resulting spatial patterns of interannual co-variability are strongly linked to atmospheric circulation in a physically consistent manner. However, the multidecadal variations in the proxy records show a less physically coherent picture. We explore whether atmospheric corrections applied to the proxy series are contributing to differences in the multi decadal signal and investigate whether multidecadal variations in soil moisture perturb

  8. Abundant Pre-Industrial Carbon Emitted by Arctic Inland Waters

    NASA Astrophysics Data System (ADS)

    Dean, J.; Van der Velde, Y.; Billett, M. F.; Dinsmore, K. J.; Garnett, M.; Meisel, O.; Dolman, A. J.

    2017-12-01

    Mobilization of carbon (C) derived from soil/sediment organic matter into inland freshwaters constitutes a substantial, but poorly-constrained, component of the global C cycle. Radiocarbon (14C) analysis has proven a valuable tool in tracing the sources and fate of mobilized C, but aquatic 14C studies in permafrost regions rarely detect 'old' C (assimilated from the atmosphere into plants and soil prior to AD1950). This is partly due to a focus on dissolved organic C (DOC) in many Arctic inland water 14C studies to date, now known to be an insensitive method for detecting old C. Crucially, the emission of greenhouse gases (GHGs) derived from old permafrost C by aquatic systems contributes to a positive climate feedback loop: the 'Permafrost Climate Feedback' (PCF). Here, we measure directly the 14C content and quantify fluxes of aquatic CO2 and CH4, alongside DOC and particulate-OC, in freshwater systems of the Canadian and Siberian Arctic tundra - the first such concurrent 14C measurements from freshwater systems. Aquatic C increased in age significantly over the snow-free season as the active layer deepened (Figure 1). However, 'modern' C (assimilated since AD1950) still dominated aquatic CO2 and CH4 emissions, except where deep ancient (6,000 to 50,000 yBP) C was exposed. Age distribution modeling of these bulk 14C samples indicated that 'pre-industrial' C (assimilated prior to AD1750) comprised 15-30% of aquatic GHGs (Figure 1). Further, we estimate that 15-20% of total CO2 and CH4 emissions were derived from old C previously locked up in permafrost soils and thus contributed to the PCF. These results demonstrate the previously unknown presence of aged C within Arctic headwater GHG emissions that could be equivalent to 7.5-28.2 Tg C yr-1 across the pan-Arctic.

  9. Modeling Chemical and Isotopic Variations in Lab Formed Hydrothermal Carbonates

    NASA Technical Reports Server (NTRS)

    Niles, P. B.; Leshin, L. A.; Golden, D. C.; Socki, R. A.; Guan, Y.; Ming, D. W.

    2005-01-01

    Chemical and mineralogical data (e.g. [1]) from Mars suggest that the history of liquid water on the planet was more sporadic in nature than long-lived. The non-equilibrium chemical and isotopic compositions of the carbonates preserved in the martian meteorite ALH84001 are direct evidence of ancient secondary minerals that have not undergone significant diagenesis or stabilization processes typical of long-lived aqueous systems on Earth. Thus secondary minerals and sediments on Mars may primarily record the characteristics of the aqueous environment in which they formed without being significantly overprinted by subsequent diagenetic processes during burial.

  10. Monsoon Variability In The Western Arabian Sea During Last 10,000 Years BP: A Planktic Foraminiferal Abundances And It's Stable Isotope Records

    NASA Astrophysics Data System (ADS)

    Singh, A. K.; Tiwari, M.; Sinha, D. K.; Ramesh, R.

    2007-12-01

    : The western Arabian Sea responds to the southwest monsoon winds by upwelling colder and nutrient rich waters from the deeper layers, causing a reduction in the sea surface temperature and enhanced biological productivity. A number of paleoclimatic studies have been carried out in this region to elucidate past monsoon variability (Sirocco et al., 1993; Gupta et al, 2003; Tiwari, 2005; Saher et.al.; 2007). Globigerina bulloides, a planktic foraminiferal species normally inhabiting surface ocean waters in temperate latitudes ( Be and Tolderlund , 1977) also becomes abundant at tropical latitudes upwelling occurs, and in these cases its abundance can exceed considerably. The conspicuous fluctuation in the abundance of Gg.bulloides during upwelling and non upwelling intervals is established through several studies ( Thiede and Junger, 1980, Gupta et al, 2003) This robust relation has been used as a proxy for wind velocity at several different times in the past in the Arabian Sea (Anderson et.al., 2002). A significant result from some of these centennially resolved Holocene records is declining abundance of Globigerina bulloides which is paralleled by reduced insolation record and this has been inferred as declining strength of Asian Monsoon. We are presenting here the data from the core SS4018 from near the Gulf of Aden, Western Arabian Sea taken at a water depth of 2830 m, precisely dated by the radiocarbon method using Accelerator Mass Spectrometry on planktonic foraminiferal separates. We have carried out the planktic foraminiferal census counts for each sample to know the relative abundance of key species. In addition to this, we have also employed multi- proxy approach such as oxygen and carbon isotopes of planktic foraminiferal tests, TOC, CaCO3 (%) to strengthen our interpretation and also to understand the relationships amongst the proxies themselves. Abundance of the key planktic foraminiferal species and other proxy records reveal at least 3 major climatic

  11. Methodologies for extraction of dissolved inorganic carbon for stable carbon isotope studies : evaluation and alternatives

    USGS Publications Warehouse

    Hassan, Afifa Afifi

    1982-01-01

    The gas evolution and the strontium carbonate precipitation techniques to extract dissolved inorganic carbon (DIC) for stable carbon isotope analysis were investigated. Theoretical considerations, involving thermodynamic calculations and computer simulation pointed out several possible sources of error in delta carbon-13 measurements of the DIC and demonstrated the need for experimental evaluation of the magnitude of the error. An alternative analytical technique, equilibration with out-gassed vapor phase, is proposed. The experimental studies revealed that delta carbon-13 of the DIC extracted from a 0.01 molar NaHC03 solution by both techniques agreed within 0.1 per mil with the delta carbon-13 of the DIC extracted by the precipitation technique, and an increase of only 0.27 per mil in that extracted by the gas evolution technique. The efficiency of extraction of DIC decreased with sulfate concentration in the precipitation technique but was independent of sulfate concentration in the gas evolution technique. Both the precipitation and gas evolution technique were found to be satisfactory for extraction of DIC from different kinds of natural water for stable carbon isotope analysis, provided appropriate precautions are observed in handling the samples. For example, it was found that diffusion of atmospheric carbon dioxide does alter the delta carbon-13 of the samples contained in polyethylene bottles; filtration and drying in the air change the delta carbon-13 of the samples contained in polyethylene bottles; filtration and drying in the air change the delta carbon-13 of the precipitation technique; hot manganese dioxide purification changes the delta carbon-13 of carbon dioxide. (USGS)

  12. Helium-carbon isotopic composition of thermal waters from Tunisia

    NASA Astrophysics Data System (ADS)

    Fourré, E.; Aiuppa, A.; di Napoli, R.; Parello, F.; Gaubi, E.; Jean-Baptiste, P.; Allard, P.; Calabrese, S.; Ben Mammou, A.

    2010-12-01

    Tunisia has numerous thermo-mineral springs. Previous studies have shown that their chemical composition and occurrence are strongly influenced by the regional geology, however little work has been conducted to date to investigate the isotopic composition of volatiles associated with these geothermal manifestations. Here, we report the results of an extensive survey of both natural hot springs and production wells across Tunisia aimed at investigating the spatial distribution of the 3He/4He ratio and associated carbon isotopic compositions. With respect to helium isotopes, not unexpectedly, the lowest 3He/4He values (0.01-0.02 Ra) are associated with the old groundwaters of the “Continental Intercalaire” aquifer of the stable Saharan Platform. The 3He/4He values are equal to the crustal production ratio, with no detectable amount of mantle-derived 3He, in agreement with previous studies of helium isotopes in sedimentary basin, which conclude that tectonically-stable regions are essentially impermeable to mantle volatiles. The low 3He/4He domain extends to the entire Atlasic domain of central Tunisia. This Atlasic domain also displays the highest helium concentrations : along the Gafsa Fault, helium concentrations of 1777 and 4723 x 10-8 cm3STP/g (the highest value of our data set) are observed in the production wells of Sidi Ahmed Zarrouk. This emphasizes the role of deep tectonic features in channelling and transporting deep crustal volatiles to shallow levels. The eastern margin of Tunisia displays higher 3He/4He values indicative of a substantial mantle volatile input. The highest value is recorded in the carbo-gaseous mineral water of Ain Garci (2.4 Ra). This northeastern part of the African plate commonly referred to as the Pelagian block extends from Tunisia to Sicily and is characterized by strong extensional tectonics (Pantelleria rift zone) and present-day magmatic activity. This lithospheric stretching and decompressional mantle melts production in

  13. Isotopic Ratios of Carbon and Oxygen in Titan’s CO using ALMA

    NASA Astrophysics Data System (ADS)

    Serigano, Joseph; Nixon, C. A.; Cordiner, M. A.; Irwin, P. G. J.; Teanby, N. A.; Charnley, S. B.; Lindberg, J. E.

    2016-04-01

    We report interferometric observations of carbon monoxide (CO) and its isotopologues in Titan’s atmosphere using the Atacama Large Millimeter/submillimeter Array (ALMA). The following transitions were detected: CO (J = 1-0, 2-1, 3-2, 6-5), 13CO (J = 2-1, 3-2, 6-5), C18O (J = 2-1, 3-2), and C17O (J = 3-2). Molecular abundances and the vertical atmospheric temperature profile were derived by modeling the observed emission line profiles using NEMESIS, a line-by-line radiative transfer code. We present the first spectroscopic detection of 17O in the outer solar system with C17O detected at >8σ confidence. The abundance of CO was determined to be 49.6 +/- 1.8 ppm, assumed to be constant with altitude, with isotopic ratios 12C/13C = 89.9 +/- 3.4, 16O/18O = 486 +/- 22, and 16O/17O = 2917 +/- 359. The measurements of 12C/13C and 16O/18O ratios are the most precise values obtained in Titan’s atmospheric CO to date. Our results are in good agreement with previous studies and suggest no significant deviations from standard terrestrial isotopic ratios.

  14. Isotopic Ratios of Carbon and Oxygen in Titan's CO Using Alma

    NASA Technical Reports Server (NTRS)

    Serigano, Joseph; Nixon, C. A.; Cordiner, M. A.; Irwin, P. G. J.; Teanby, N. A.; Charnley, S. B.; Lindberg, J. E.

    2016-01-01

    We report interferometric observations of carbon monoxide (CO) and its isotopologues in Titan's atmosphere using the Atacama Large Millimeter/submillimeter Array (ALMA). The following transitions were detected: CO (J = 1-0, 2-1, 3-2, 6-5), C-13 O (J = 2-1, 3-2, 6-5), C-18 O (J = 2-1, 3-2), and C-17 O (J = 3-2). Molecular abundances and the vertical atmospheric temperature profile were derived by modeling the observed emission line profiles using NEMESIS, a line-by-line radiative transfer code. We present the first spectroscopic detection of O-17 in the outer solar system with C-17 O detected at greater than 8 sigma confidence. The abundance of CO was determined to be 49.6 +/- 1.8 ppm, assumed to be constant with altitude, with isotopic ratios C-12/C-13 = 89.9 +/- 3.4, O-16/O-18 = 486 +/- 22, and O-16/O-17 = 2917 +/- 359. The measurements of C-12/C-13 and O-16/O-18 ratios are the most precise values obtained in Titan's atmospheric CO to date. Our results are in good agreement with previous studies and suggest no significant deviations from standard terrestrial isotopic ratios.

  15. Tracking Movement of Plant Carbon Through Soil to Water by Lignin Phenol Stable Carbon Isotope Composition in a Small Agricultural Watershed

    NASA Astrophysics Data System (ADS)

    Crooker, K.; Filley, T.; Six, J.; Frey, J.

    2005-12-01

    Few studies integrate land cover, soil physical structure, and aquatic physical fractions when investigating the fate of agricultural carbon in watersheds. In crop systems that involve rotations of soy (a C3 plant) and corn (a C4 plant) the large intrinsic differences in stable carbon isotope values and lignin plus cutin chemistry enable tracking of plant carbon movement from soil fractions to DOM and overland flow during precipitation events. In a small (~3Km2) agricultural basin in central Indiana, we studied plant carbon dynamics in a soy/corn agricultural rotation (2004-2005) to determine the relative inputs of these two plants to soil fractions and the resultant contributions to dissolved, colloidal, and particulate organic matter when mobilized. Using bulk isotope values the fraction of carbon derived from corn in macroaggregates (>250 micron), microaggregates (53-250 mm), and silts plus clays (<53 mm) ranged from 39, 49, to 42%, respectively. Unlike bulk analyses, compound specific isotope analysis of lignin in the soil fractions revealed a wide range of relative inputs among the monomers with cinnamyl phenols being almost exclusively (~ 93%) derived from corn. Syringyl phenols ranged from 75-56% corn and vanillyl phenols ranged from 37-40% corn carbon. The relative input among the fractions mirrors closely the comparative plant chemistry abundances between soy and corn. During export of DOM from the land to the stream the relative abundance of plant source varied with discharge (0.05-1.8 m3/sec) as increases in flow increased the relative export of corn-derived C from the fields. Over the full range of flows lignin phenols varied from 0.05 to 82% corn-derived with the greatest relative corn input for cinnamyl and syringyl carbon. The trend with stream discharge indicates a progressive movement of particulate corn residues with overland flow. Ongoing studies look to resolve contributions of algae, bacteria and terrestrial plants to soil fractions and their

  16. Variability in the carbon isotope composition of individual amino acids in plant proteins from different sources: 1 Leaves.

    PubMed

    Lynch, Anthony H; Kruger, Nicholas J; Hedges, Robert E M; McCullagh, James S O

    2016-05-01

    The natural carbon isotope composition of individual amino acids from plant leaf proteins has been measured to establish potential sources of variability. The plant leaves studied, taken from a range of plant groups (forbs, trees, grasses, and freshwater aquatic plants), showed no significant influence of either season or environment (water and light availability) on their Δδ(13)C values. Plant groups did, however, differ in carbon isotope composition, although no consistent differences were identified at the species level. A discriminant analysis model was constructed which allowed leaves from (1) nettles, (2) Pooideae, (3) other Poales, (4) trees and (5) freshwater higher plants to be distinguished from each other on the basis of their natural abundance (13)C/(12)C ratios of individual amino acids. Differences in carbon isotope composition are known to be retained, to some extent, in the tissues of their consumers, and hence an understanding of compound-specific variation in (13)C/(12)C fractional abundance in plants has the potential to provide dietary insights of value in archaeological and ecological studies. Copyright © 2016 Elsevier Ltd. All rights reserved.

  17. Light Nuclei and Isotope Abundances in Cosmic Rays. Results from AMS-01

    NASA Astrophysics Data System (ADS)

    Tomassetti, N.

    2011-06-01

    Observations of the chemical and isotopic composition of light cosmic-ray nuclei can be used to constrain the propagation models. Nearly 200,000 light nuclei (Z > 2) have been observed by AMS-01 during the 10-day flight STS-91 in June 1998. Using these data, we have measured Li, Be, B and C in the kinetic energy range 0.35 - 45 GeV/nucleon. In this proceeding, our charge and isotopic composition results are presented and discussed.

  18. Carbon isotope fractionation of sapropelic organic matter during early diagenesis

    USGS Publications Warehouse

    Spiker, E. C.; Hatcher, P.G.

    1984-01-01

    Study of an algal, sapropelic sediment from Mangrove Lake, Bermuda shows that the mass balance of carbon and stable carbon isotopes in the major organic constituents is accounted for by a relatively straightforward model of selective preservation during diagenesis. The loss of 13C-enriched carbohydrates is the principal factor controlling the intermolecular mass balance of 13C in the sapropel. Results indicate that labile components are decomposed leaving as a residual concentrate in the sediment an insoluble humic substance that may be an original biochemical component of algae and associated bacteria. An overall decrease of up to about 4??? in the ?? 13C values of the organic matter is observed as a result of early diagenesis. ?? 1984.

  19. Micropowder collecting technique for stable isotope analysis of carbonates.

    PubMed

    Sakai, Saburo; Kodan, Tsuyoshi

    2011-05-15

    Micromilling is a conventional technique used in the analysis of the isotopic composition of geological materials, which improves the spatial resolution of sample collection for analysis. However, a problem still remains concerning the recovery ratio of the milled sample. We constructed a simple apparatus consisting of a vacuum pump, a sintered metal filter, electrically conductive rubber stopper and a stainless steel tube for transferring the milled powder into a reaction vial. In our preliminary experiments on carbonate powder, we achieved a rapid recovery of 5 to 100 µg of carbonate with a high recovery ratio (>90%). This technique shortens the sample preparation time, improves the recovery ratio, and homogenizes the sample quantity, which, in turn, improves the analytical reproducibility. Copyright © 2011 John Wiley & Sons, Ltd.

  20. Study on strontium isotope abundance-ratio measurements by using a 13-MeV proton beam

    NASA Astrophysics Data System (ADS)

    Jeong, Cheol-Ki; Jang, Han; Lee, Goung-Jin

    2016-09-01

    The Rb-Sr dating method is used in dating Paleozoic and Precambrian rocks. This method measures the 87Rb and the 87Sr concentrations by using thermal ionization mass spectrometry (TIMS) [J. Hefne et al., Inter. J. Phys. Sci. 3(1), 28 (2008)]. In addition, it calculates the initial 87Sr/86Sr ratio to increase the reliability of Rb-Sr dating. In this study, the 87Sr/86Sr ratio was measured by using a 13-MeV proton accelerator. Proton kinetic energies are in the range of tens of megaelectronvolts, and protons have large absorption cross-sections for ( p, n) reactions with most substances. After absorbing a proton with such a high kinetic energy, an element is converted into a nuclide with its atomic number increased by one via nuclear transmutation. These nuclides usually have short half-lives and return to the original state through radioactive decay. When a strontium sample is irradiated with protons, nuclear transmutation occurs; thus, the strontium isotope present in the sample changes to a yttrium isotope, which is an activated radioisotope. Based on this, the 87Sr/86Sr ratio was calculated by analyzing the gamma-rays emitted by each yttrium isotope. The KIRAMS-13 cyclotron at the Cyclotron Center of Chosun University, where 13-MeV protons can be extracted, was utilized in our experiment. The 87Sr/86Sr isotope ratio was computed for samples irradiated with these protons, and the result was similar to the isotope ratio for the Standard Reference Material, i.e., 98.2 ± 3.4%. As part of the analysis, proton activation analyses were performed using 13-MeV protons, and the experimental results of this research suggest a possible approach for measuring the strontium-isotope abundance ratio of samples.

  1. Chemical and carbon isotopic composition of dissolved organic carbon in a regional confined methanogenic aquifer

    USGS Publications Warehouse

    Aravena, R.; Wassenaar, L.I.; Spiker, E. C.

    2004-01-01

    This study demonstrates the advantage of a combined use of chemical and isotopic tools to understand the dissolved organic carbon (DOC) cycle in a regional confined methanogenic aquifer. DOC concentration and carbon isotopic data demonstrate that the soil zone is a primary carbon source of groundwater DOC in areas close to recharge zones. An in-situ DOC source linked to organic rich sediments present in the aquifer matrix is controlling the DOC pool in the central part of the groundwater flow system. DOC fractions, 13C-NMR on fulvic acids and 14C data on DOC and CH4 support the hypothesis that the in-situ DOC source is a terrestrial organic matter and discard the Ordovician bedrock as a source of DOC. ?? 2004 Taylor and Francis Ltd.

  2. Seasonality of Leaf Carbon Isotopic Composition and Leaf Water Isotopic Enrichment in a Mixed Evergreen Forest in Southern California

    NASA Astrophysics Data System (ADS)

    Santiago, L. S.; Sickman, J. O.; Goulden, M.; DeVan, C.; Pasquini, S. C.; Pivovaroff, A. L.

    2011-12-01

    Leaf carbon isotopic composition and leaf water isotopic enrichment reflect physiological processes and are important for linking local and regional scale processes to global patterns. We investigated how seasonality affects the isotopic composition of bulk leaf carbon, leaf sugar carbon, and leaf water hydrogen under a Mediterranean climate. Leaf and stem samples were collected monthly from four tree species (Calocedrus decurrens, Pinus lambertiana, Pinus ponderosa, and Quercus chrysolepis) at the James San Jacinto Mountain Reserve in southern California. Mean monthly bulk leaf carbon isotopic composition varied from -34.5 % in P. ponderosa to -24.7 % in P. lambertiana and became more depleted in 13C from the spring to the summer. Mean monthly leaf sugar varied from -29.3 % in P. ponderosa to -21.8 % in P. lambertiana and was enriched in 13C during the winter, spring and autumn, but depleted during the mid-summer. Leaf water hydrogen isotopic composition was 28.4 to 68.8 % more enriched in deuterium than source water and this enrichment was greater as seasonal drought progressed. These data indicate that leaf carbon and leaf water hydrogen isotopic composition provide sensitive measures that connect plant physiological processes to short-term climatic variability.

  3. Barium isotope abundances in meteorites and their implications for early Solar System evolution

    NASA Astrophysics Data System (ADS)

    Bermingham, K. R.; Mezger, K.; Scherer, E. E.; Horan, M. F.; Carlson, R. W.; Upadhyay, D.; Magna, T.; Pack, A.

    2016-02-01

    Several nucleosynthetic processes contributed material to the Solar System, but the relative contributions of each process, the timing of their input into the solar nebula, and how well these components were homogenized in the solar nebula remain only partially constrained. The Ba isotope system is particularly useful in addressing these issues because Ba isotopes are synthesized via three nucleosynthetic processes (s-, r-, p-process). In this study, high precision Ba isotope analyses of 22 different whole rock chondrites and achondrites (carbonaceous chondrites, ordinary chondrites, enstatite chondrites, Martian meteorites, and eucrites) were performed to constrain the distribution of Ba isotopes on the regional scale in the Solar System. A melting method using aerodynamic levitation and CO2-laser heating was used to oxidize SiC, a primary carrier of Ba among presolar grains in carbonaceous chondrites. Destruction of these grains during the fusion process enabled the complete digestion of these samples. The Ba isotope data presented here are thus the first for which complete dissolution of the bulk meteorite samples was certain. Enstatite chondrites, ordinary chondrites, and all achondrites measured here possess Ba isotope compositions that are not resolved from the terrestrial composition. Barium isotope anomalies are evident in most of the carbonaceous chondrites analyzed, but the 135Ba anomalies are generally smaller than previously reported for similarly sized splits of CM2 meteorites. Variation in the size of the 135Ba anomaly is also apparent in fused samples from the same parent body (e.g., CM2 meteorites) and in different pieces from the same meteorite (e.g., Orgueil, CI). Here, we investigate the potential causes of variability in 135Ba, including the contribution of radiogenic 135Ba from the decay of 135Cs and incomplete homogenization of the presolar components on the <0.8 g sample scale.

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

    NASA Astrophysics Data System (ADS)

    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

  5. Follow the Carbon: Isotopic Labeling Studies of Early Earth Aerosol.

    PubMed

    Hicks, Raea K; Day, Douglas A; Jimenez, Jose L; Tolbert, Margaret A

    2016-11-01

    Despite the faint young Sun, early Earth might have been kept warm by an atmosphere containing the greenhouse gases CH 4 and CO 2 in mixing ratios higher than those found on Earth today. Laboratory and modeling studies suggest that an atmosphere containing these trace gases could lead to the formation of organic aerosol haze due to UV photochemistry. Chemical mechanisms proposed to explain haze formation rely on CH 4 as the source of carbon and treat CO 2 as a source of oxygen only, but this has not previously been verified experimentally. In the present work, we use isotopically labeled precursor gases and unit-mass resolution (UMR) and high-resolution (HR) aerosol mass spectrometry to examine the sources of carbon and oxygen to photochemical aerosol formed in a CH 4 /CO 2 /N 2 atmosphere. UMR results suggest that CH 4 contributes 70-100% of carbon in the aerosol, while HR results constrain the value from 94% to 100%. We also confirm that CO 2 contributes approximately 10% of the total mass to the aerosol as oxygen. These results have implications for the geochemical interpretations of inclusions found in Archean rocks on Earth and for the astrobiological potential of other planetary atmospheres. Key Words: Atmosphere-Early Earth-Planetary atmospheres-Carbon dioxide-Methane. Astrobiology 16, 822-830.

  6. Temperature evolution and the oxygen isotope composition of Phanerozoic oceans from carbonate clumped isotope thermometry

    NASA Astrophysics Data System (ADS)

    Henkes, Gregory A.; Passey, Benjamin H.; Grossman, Ethan L.; Shenton, Brock J.; Yancey, Thomas E.; Pérez-Huerta, Alberto

    2018-05-01

    Surface temperature is among the most important parameters describing planetary climate and habitability, and yet there remains considerable debate about the temperature evolution of the Earth's oceans during the Phanerozoic Eon (541 million years ago to present), the time during which complex metazoan life radiated on Earth. Here we critically assess the emerging record of Phanerozoic ocean temperatures based on carbonate clumped isotope thermometry of fossil brachiopod and mollusk shells, and we present new data that fill important gaps in the Late Paleozoic record. We evaluate and reject the hypothesis that solid-state reordering of 13C-18O bonds has destroyed the primary clumped isotope temperature signal of most fossils during sedimentary burial at elevated temperatures. The resulting Phanerozoic record, which shows a general coupling between tropical seawater temperatures and atmospheric carbon dioxide (CO2) levels since the Paleozoic, indicates that tropical temperatures during the icehouse climate of the Carboniferous period were broadly similar to present (∼25-30 °C), and suggests that benthic metazoans were able to thrive at temperatures of 35-40 °C during intervals of the early and possibly the latest Paleozoic when CO2 levels were likely 5-10× higher than present-day values. Equally important, there is no resolvable trend in seawater oxygen isotope ratios (δ18 O) over the past ∼500 million years, indicating that the average temperature of oxygen exchange between seawater and the oceanic crust has been high (∼270 °C) since at least the early Paleozoic, which points to mid-ocean ridges as the dominant locus of water-rock interaction over the past half-billion years.

  7. Simulation of carbon isotope discrimination of the terrestrial biosphere

    NASA Astrophysics Data System (ADS)

    Suits, N. S.; Denning, A. S.; Berry, J. A.; Still, C. J.; Kaduk, J.; Miller, J. B.; Baker, I. T.

    2005-03-01

    We introduce a multistage model of carbon isotope discrimination during C3 photosynthesis and global maps of C3/C4 plant ratios to an ecophysiological model of the terrestrial biosphere (SiB2) in order to predict the carbon isotope ratios of terrestrial plant carbon globally at a 1° resolution. The model is driven by observed meteorology from the European Centre for Medium-Range Weather Forecasts (ECMWF), constrained by satellite-derived Normalized Difference Vegetation Index (NDVI) and run for the years 1983-1993. Modeled mean annual C3 discrimination during this period is 19.2‰; total mean annual discrimination by the terrestrial biosphere (C3 and C4 plants) is 15.9‰. We test simulation results in three ways. First, we compare the modeled response of C3 discrimination to changes in physiological stress, including daily variations in vapor pressure deficit (vpd) and monthly variations in precipitation, to observed changes in discrimination inferred from Keeling plot intercepts. Second, we compare mean δ13C ratios from selected biomes (Broadleaf, Temperate Broadleaf, Temperate Conifer, and Boreal) to the observed values from Keeling plots at these biomes. Third, we compare simulated zonal δ13C ratios in the Northern Hemisphere (20°N to 60°N) to values predicted from high-frequency variations in measured atmospheric CO2 and δ13C from terrestrially dominated sites within the NOAA-Globalview flask network. The modeled response to changes in vapor pressure deficit compares favorably to observations. Simulated discrimination in tropical forests of the Amazon basin is less sensitive to changes in monthly precipitation than is suggested by some observations. Mean model δ13C ratios for Broadleaf, Temperate Broadleaf, Temperate Conifer, and Boreal biomes compare well with the few measurements available; however, there is more variability in observations than in the simulation, and modeled δ13C values for tropical forests are heavy relative to observations

  8. Carbon, Hydrogen, and Oxygen Isotope Ratios of Cellulose from Plants Having Intermediary Photosynthetic Modes 1

    PubMed Central

    Sternberg, Leonel O'Reilly; Deniro, Michael J.; Ting, Irwin P.

    1984-01-01

    Carbon and hydrogen isotope ratios of cellulose nitrate and oxygen isotope ratios of cellulose from species of greenhouse plants having different photosynthetic modes were determined. When hydrogen isotope ratios are plotted against carbon isotope ratios, four clusters of points are discernible, each representing different photosynthetic modes: C3 plants, C4 plants, CAM plants, and C3 plants that can shift to CAM or show the phenomenon referred to as CAM-cycling. The combination of oxygen and carbon isotope ratios does not distinguish among the different photosynthetic modes. Analysis of the carbon and hydrogen isotope ratios of cellulose nitrate should prove useful for screening different photosynthetic modes in field specimens that grew near one another. This method will be particularly useful for detection of plants which show CAM-cycling. PMID:16663360

  9. Abundances and isotopic compositions of rhenium and osmium in pyrite samples from the Huaibei coalfield, Anhui, China

    USGS Publications Warehouse

    Liu, Gaisheng; Chou, C.-L.; Peng, Z.; Yang, G.

    2008-01-01

    Two pyrite samples from the Shihezi Formation (Lower Permian), Huaibei coalfield, Anhui, China, have been analyzed for abundances and isotopic compositions of rhenium and osmium using negative thermal ion mass spectrometry. The Re-Os ages of the pyrites are 64.4 and 226 Ma, which are younger than the formation age of the coal seam. The pyrite samples may consist of pyrite formed at various stages during the history of coal formation. The ??Osvalues of the two pyrite samples are +17 and +18, respectively. Such high ??Osvalues are reported for the first time for recycles crustal materials from a sedimentary basin. ?? Springer-Verlag 2007.

  10. Modeling whole-tree carbon assimilation rate using observed transpiration rates and needle sugar carbon isotope ratios.

    PubMed

    Hu, Jia; Moore, David J P; Riveros-Iregui, Diego A; Burns, Sean P; Monson, Russell K

    2010-03-01

    *Understanding controls over plant-atmosphere CO(2) exchange is important for quantifying carbon budgets across a range of spatial and temporal scales. In this study, we used a simple approach to estimate whole-tree CO(2) assimilation rate (A(Tree)) in a subalpine forest ecosystem. *We analysed the carbon isotope ratio (delta(13)C) of extracted needle sugars and combined it with the daytime leaf-to-air vapor pressure deficit to estimate tree water-use efficiency (WUE). The estimated WUE was then combined with observations of tree transpiration rate (E) using sap flow techniques to estimate A(Tree). Estimates of A(Tree) for the three dominant tree species in the forest were combined with species distribution and tree size to estimate and gross primary productivity (GPP) using an ecosystem process model. *A sensitivity analysis showed that estimates of A(Tree) were more sensitive to dynamics in E than delta(13)C. At the ecosystem scale, the abundance of lodgepole pine trees influenced seasonal dynamics in GPP considerably more than Engelmann spruce and subalpine fir because of its greater sensitivity of E to seasonal climate variation. *The results provide the framework for a nondestructive method for estimating whole-tree carbon assimilation rate and ecosystem GPP over daily-to weekly time scales.

  11. Regional prediction of carbon isotopes in soil carbonates for Asian dust source tracer

    NASA Astrophysics Data System (ADS)

    Chen, Bing; Cui, Xinjuan; Wang, Yaqiang

    2016-10-01

    Dust particles emitted from deserts and semi-arid lands in northern China cause particulate pollution that increases the burden of disease particularly for urban population in East Asia. The stable carbon isotopes (δ13C) of carbonates in soils and dust aerosols in northern China were investigated. We found that the δ13C of carbonates in surface soils in northern China showed clearly the negative correlation (R2 = 0.73) with Normalized Difference Vegetation Index (NDVI). Using Moderate Resolution Imaging Spectroradiometer (MODIS) satellite-derived NDVI, we predicted the regional distribution of δ13C of soil carbonates in deserts, sandy lands, and steppe areas. The predictions show the mean δ13C of -0.4 ± 0.7‰ in soil carbonates in Taklimakan Desert and Gobi Deserts, and the isotope values decrease to -3.3 ± 1.1‰ in sandy lands. The increase in vegetation coverage depletes 13C in soil carbonates, thus the steppe areas are predicted by the lowest δ13C levels (-8.1 ± 1.7‰). The measurements of atmospheric dust samples at eight sites showed that the Asian dust sources were well assigned by the 13C mapping in surface soils. Predicting 13C in large geographical areas with fine resolution offers a cost-effective tracer to monitor dust emissions from sandy lands and steppe areas which show an increasing role in Asian dust loading driven by climate change and human activities.

  12. Variability in magnesium, carbon and oxygen isotope compositions, and trace element contents of brachiopod shells: implications for paleoceanographic studies

    NASA Astrophysics Data System (ADS)

    Rollion-Bard, Claire; Saulnier, Ségolène; Vigier, Nathalie; Schumacher, Aimryc; Chaussidon, Marc; Lécuyer, Christophe

    2016-04-01

    Magnesium content in the ocean is ≈ 1290 ppm and is one of the most abundant elements. It is involved in the carbon cycle via the dissolution and precipitation of carbonates, especially Mg-rich carbonates as dolomites. The Mg/Ca ratio of the ocean is believed to have changed through time. The causes of these variations, i.e. hydrothermal activity change or enhanced precipitation of dolomite, could be constrained using the magnesium isotope composition (δ26Mg) of carbonates. Brachiopods, as marine environmental proxies, have the advantage to occur worldwide in a depth range from intertidal to abyssal, and have been found in the geological record since the Cambrian. Moreover, as their shell is in low-Mg calcite, they are quite resistant to diagenetic processes. Here we report δ26Mg, δ18O, δ13C values along with trace element contents of one modern brachiopod specimen (Terebratalia transversa) and one fossil specimen (Terebratula scillae, 2.3 Ma). We combined δ26Mg values with oxygen and carbon isotope compositions and trace element contents to look for possible shell geochemical heterogeneities in order to investigate the processes that control the Mg isotope composition of brachiopod shells. We also evaluate the potential of brachiopods as a proxy of past seawater δ26Mg values. The two investigated brachiopod shells present the same range of δ26Mg variation (up to 2 ‰)). This variation cannot be ascribed to changes in environmental parameters, i.e. temperature or pH. As previously observed, the primary layer of calcite shows the largest degree of oxygen and carbon isotope disequilibrium relative to seawater. In contrast, the δ26Mg value of this layer is comparable to that of the secondary calcite layer value. In both T. scillae and T. transversa, negative trends are observable between magnesium isotopic compositions and oxygen and carbon isotopic compositions. These trends, combined to linear relationships between δ26Mg values and REE contents, are best

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

    Treesearch

    Daniel H. Doctor; Carol Kendall; Stephen D. Sebestyen; James B. Shanley; Nobuhito Ohte; Elizabeth W. Boyer

    2008-01-01

    The stable isotopic composition of dissolved inorganic carbon (δ13C-DIC) was investigated as a potential tracer of streamflow generation processes at the Sleepers River Research Watershed, Vermont, USA. Downstream sampling showed δ13C-DIC increased between 3-5% from the stream source to the outlet weir...

  14. Reactive transport modeling of stable carbon isotope fractionation in a multi-phase multi-component system during carbon sequestration

    DOE PAGES

    Zhang, Shuo; DePaolo, Donald J.; Zheng, Liange; ...

    2014-12-31

    Carbon stable isotopes can be used in characterization and monitoring of CO 2 sequestration sites to track the migration of the CO 2 plume and identify leakage sources, and to evaluate the chemical reactions that take place in the CO 2-water-rock system. However, there are few tools available to incorporate stable isotope information into flow and transport codes used for CO 2 sequestration problems. We present a numerical tool for modeling the transport of stable carbon isotopes in multiphase reactive systems relevant to geologic carbon sequestration. The code is an extension of the reactive transport code TOUGHREACT. The transport modulemore » of TOUGHREACT was modified to include separate isotopic species of CO 2 gas and dissolved inorganic carbon (CO 2, CO 3 2-, HCO 3 -,…). Any process of transport or reaction influencing a given carbon species also influences its isotopic ratio. Isotopic fractionation is thus fully integrated within the dynamic system. The chemical module and database have been expanded to include isotopic exchange and fractionation between the carbon species in both gas and aqueous phases. The performance of the code is verified by modeling ideal systems and comparing with theoretical results. Efforts are also made to fit field data from the Pembina CO 2 injection project in Canada. We show that the exchange of carbon isotopes between dissolved and gaseous carbon species combined with fluid flow and transport, produce isotopic effects that are significantly different from simple two-component mixing. These effects are important for understanding the isotopic variations observed in field demonstrations.« less

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

    NASA Technical Reports Server (NTRS)

    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.

  16. Marine Carbonate Component in the Mantle Beneath the Southeastern Tibetan Plateau: Evidence From Magnesium and Calcium Isotopes

    NASA Astrophysics Data System (ADS)

    Liu, Fang; Li, Xin; Wang, Guiqin; Liu, Yufei; Zhu, Hongli; Kang, Jinting; Huang, Fang; Sun, Weidong; Xia, Xiaoping; Zhang, Zhaofeng

    2017-12-01

    Tracing and identifying recycled carbonates is a key issue to reconstruct the deep carbon cycle. To better understand carbonate subduction and recycling beneath the southeastern Tibetan Plateau, high-K cal-alkaline volcanic rocks including trachy-basalts and trachy-andesites from Tengchong were studied using Mg and Ca isotopes. The low δ26Mg (-0.31 ± 0.03‰ to -0.38 ± 0.03‰) and δ44/40Ca (0.67 ± 0.07‰ to 0.80 ± 0.04‰) values of these volcanic rocks compared to those of the mantle (-0.25 ± 0.07‰ and 0.94 ± 0.05‰, respectively) indicate the incorporation of isotopically light materials into the mantle source, which may be carbonate-bearing sediments with low δ26Mg and δ44/40Ca values. In addition, no correlations of δ26Mg and δ44/40Ca with either SiO2 contents or trace element abundance ratios (e.g., Sm/Yb and Ba/Y) were observed, suggesting that limited Mg and Ca isotopic fractionation occurred during cal-alkaline magmatic differentiation. A binary mixing model using Mg-Ca isotopes shows that 5-8% carbonates dominated primarily by dolostone were recycled back into the mantle. Since Tengchong volcanism is still active and probably related to ongoing plate tectonic movement, we propose that the recycled carbonates are derived from oceanic crust related to the ongoing subduction of the Indian plate.

  17. Equilibrium carbon and hydrogen isotope fractionation in iron

    NASA Astrophysics Data System (ADS)

    Schauble, E. A.

    2009-12-01

    Recent theoretical and experimental studies (e.g., [1-3]) have suggested that Si- and Fe-isotopic signatures can be used to characterize the compositions and conditions of segregation of metallic cores in planetary interiors. This study expands the theoretical framework to include carbon and hydrogen, which may also be alloying elements. Hydrogen (D/H) and carbon (13C/12C) fractionations in iron-rich metallic melts are estimated by modeling analogous iron-rich crystals, i.e., dhcp-FeH and η-Fe2C. C- and H-atoms in these crystals are completely coordinated by iron. The driving energy for equilibrium fractionation is assumed to come from the reduction of vibrational frequencies when heavy isotopes are substituted for light ones; vibrations are assumed to be harmonic. This treatment is crude at high temperature, and for the relatively anharmonic vibrations typical of hydrogen-bearing substances, but may provide a reasonably accurate, semi-quantitative approximation of real fractionation behavior. Vibrational frequencies of all crystals are modeled with density functional theory, using gradient-corrected functionals and ultrasoft pseudopotentials. For both carbon and hydrogen, the models suggest that the metal phase will be strongly depleted in heavy isotopes. At 2000 K, 1 atm, η-Fe2C will have 3‰ lower 13C/12C than coexisting diamond. Combining this result with previous high-temperature theoretical and experimental studies (e.g., [4]), metal-graphite fractionation is expected to be very similar, while metal-CO2 fractionation will be almost twice as large, ca. -5‰. Deuterium/hydrogen fractionations are expected to be an order of magnitude larger, with 50-70‰ lower D/H in dhcp-FeH than in coexisting H2 gas at 2000 K, and approximately 100‰ lower D/H than water vapor. These fractionations are much larger than those inferred for silicon and iron, as expected given the differences in atomic mass. References: 1. Georg et al. (2007) Nature 447:1102; 2. Rustad & Yin

  18. Contribution of deep sourced carbon from hydrocarbon seeps to sedimentary organic carbon: Evidence from Δ14C and δ13C isotopes

    NASA Astrophysics Data System (ADS)

    Feng, D.; Peckmann, J.; Peng, Y.; Liang, Q.; Roberts, H. H.; Chen, D.

    2017-12-01

    Sulfate-driven anaerobic oxidation of methane (AOM) limits the release of methane from marine sediments and promotes the formation of carbonates close to the seafloor along continental margins. It has been established that hydrocarbon seeps are a source of dissolved inorganic and organic carbon to marine environments. However, questions remain about the contribution of deep sourced carbon from hydrocarbon seeps to the sedimentary organic carbon pool. For a number of hydrocarbon seeps from the South China Sea and the Gulf of Mexico, the portion of modern carbon was determined based on natural radiocarbon abundances (Δ14C) and stable carbon isotope (δ13Corganic carbon) compositions of the non-carbonate fractions extracted from authigenic carbonates. Samples from both areas show a mixing trend between ideal planktonic organic carbon (δ13C = -22‰ VPDB and 90% modern carbon) and the ambient methane. The δ13Corganic carbon values of non-carbonate fractions from three ancient seep deposits (northern Italy, Miocene; western Washington State, USA, Eocene to Oligocene) confirm that the proxy can be used to constrain the record of sulfate-driven AOM through most of Earth history by measuring the δ13C values of organic carbon. This study reveals the potential of using δ13C values of organic carbon to discern seep and non-seep environments. This new approach is particularly promising when authigenic carbonate is not present in ancient sedimentary environments. Acknowledgments: The authors thank BOEM and NOAA for their years' support of the deep-sea dives. Funding was provided by the NSF of China (Grants: 41422602 and 41373085).

  19. Stable isotopic constraints on global soil organic carbon turnover

    NASA Astrophysics Data System (ADS)

    Wang, Chao; Houlton, Benjamin Z.; Liu, Dongwei; Hou, Jianfeng; Cheng, Weixin; Bai, Edith

    2018-02-01

    Carbon dioxide release during soil organic carbon (SOC) turnover is a pivotal component of atmospheric CO2 concentrations and global climate change. However, reliably measuring SOC turnover rates on large spatial and temporal scales remains challenging. Here we use a natural carbon isotope approach, defined as beta (β), which was quantified from the δ13C of vegetation and soil reported in the literature (176 separate soil profiles), to examine large-scale controls of climate, soil physical properties and nutrients over patterns of SOC turnover across terrestrial biomes worldwide. We report a significant relationship between β and calculated soil C turnover rates (k), which were estimated by dividing soil heterotrophic respiration rates by SOC pools. ln( - β) exhibits a significant linear relationship with mean annual temperature, but a more complex polynomial relationship with mean annual precipitation, implying strong-feedbacks of SOC turnover to climate changes. Soil nitrogen (N) and clay content correlate strongly and positively with ln( - β), revealing the additional influence of nutrients and physical soil properties on SOC decomposition rates. Furthermore, a strong (R2 = 0.76; p < 0.001) linear relationship between ln( - β) and estimates of litter and root decomposition rates suggests similar controls over rates of organic matter decay among the generalized soil C stocks. Overall, these findings demonstrate the utility of soil δ13C for independently benchmarking global models of soil C turnover and thereby improving predictions of multiple global change influences over terrestrial C-climate feedback.

  20. The magnesium isotope record of cave carbonate archives

    NASA Astrophysics Data System (ADS)

    Riechelmann, S.; Buhl, D.; Schröder-Ritzrau, A.; Riechelmann, D. F. C.; Richter, D. K.; Vonhof, H. B.; Wassenburg, J. A.; Geske, A.; Spötl, C.; Immenhauser, A.

    2012-05-01

    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 and weathering balance. Several data points in the Austrian and two data points in the

  1. The magnesium isotope record of cave carbonate archives

    NASA Astrophysics Data System (ADS)

    Riechelmann, S.; Buhl, D.; Schröder-Ritzrau, A.; Riechelmann, D. F. C.; Richter, D. K.; Vonhof, H. B.; Wassenburg, J. A.; Geske, A.; Spötl, C.; Immenhauser, A.

    2012-11-01

    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 affecting soil zone activity and weathering balance. Several δ26Mg values of the Austrian and two

  2. Carbon isotopes of dissolved inorganic carbon reflect utilization of different carbon sources by microbial communities in two limestone aquifer assemblages

    NASA Astrophysics Data System (ADS)

    Nowak, Martin E.; Schwab, Valérie F.; Lazar, Cassandre S.; Behrendt, Thomas; Kohlhepp, Bernd; Totsche, Kai Uwe; Küsel, Kirsten; Trumbore, Susan E.

    2017-08-01

    Isotopes of dissolved inorganic carbon (DIC) are used to indicate both transit times and biogeochemical evolution of groundwaters. These signals can be complicated in carbonate aquifers, as both abiotic (i.e., carbonate equilibria) and biotic factors influence the δ13C and 14C of DIC. We applied a novel graphical method for tracking changes in the δ13C and 14C of DIC in two distinct aquifer complexes identified in the Hainich Critical Zone Exploratory (CZE), a platform to study how water transport links surface and shallow groundwaters in limestone and marlstone rocks in central Germany. For more quantitative estimates of contributions of different biotic and abiotic carbon sources to the DIC pool, we used the NETPATH geochemical modeling program, which accounts for changes in dissolved ions in addition to C isotopes. Although water residence times in the Hainich CZE aquifers based on hydrogeology are relatively short (years or less), DIC isotopes in the shallow, mostly anoxic, aquifer assemblage (HTU) were depleted in 14C compared to a deeper, oxic, aquifer complex (HTL). Carbon isotopes and chemical changes in the deeper HTL wells could be explained by interaction of recharge waters equilibrated with post-bomb 14C sources with carbonates. However, oxygen depletion and δ13C and 14C values of DIC below those expected from the processes of carbonate equilibrium alone indicate considerably different biogeochemical evolution of waters in the upper aquifer assemblage (HTU wells). Changes in 14C and 13C in the upper aquifer complexes result from a number of biotic and abiotic processes, including oxidation of 14C-depleted OM derived from recycled microbial carbon and sedimentary organic matter as well as water-rock interactions. The microbial pathways inferred from DIC isotope shifts and changes in water chemistry in the HTU wells were supported by comparison with in situ microbial community structure based on 16S rRNA analyses. Our findings demonstrate the large

  3. The reduction and oxidation of ceria: A natural abundance triple oxygen isotope perspective

    NASA Astrophysics Data System (ADS)

    Hayles, Justin; Bao, Huiming

    2015-06-01

    Ceria (CeO2) is a heavily studied material in catalytic chemistry for use as an oxygen storage medium, oxygen partial pressure regulator, fuel additive, and for the production of syngas, among other applications. Ceria powders are readily reduced and lose structural oxygen when subjected to low pO2 and/or high temperature conditions. Such dis-stoichiometric ceria can then re-oxidize under higher pO2 and/or lower temperature by incorporating new oxygen into the previously formed oxygen site vacancies. Despite extensive studies on ceria, the mechanisms for oxygen adsorption-desorption, dissociation-association, and diffusion of oxygen species on ceria surface and within the crystal structure are not well known. We predict that a large kinetic oxygen isotope effect should accompany the release and incorporation of ceria oxygen. As the first attempt to determine the existence and the degree of the isotope effect, this study focuses on a set of simple room-temperature re-oxidation experiments that are also relevant to a laboratory procedure using ceria to measure the triple oxygen isotope composition of CO2. Triple-oxygen-isotope labeled ceria powders are heated at 700 °C and cooled under vacuum prior to exposure to air. By combining results from independent experimental sets with different initial oxygen isotope labels and using a combined mass-balance and triangulation approach, we have determined the isotope fractionation factors for both high temperature reduction in vacuum (⩽10-4 mbar) and room temperature re-oxidation in air. Results indicate that there is a 1.5‰ ± 0.8‰ increase in the δ18O value of ceria after being heated in vacuum at 700 °C for 1 h. When the vacuum is broken at room temperature, the previously heated ceria incorporates 3-19% of its final structural oxygen from air, with a δ18O value of 2.1-4.1+7.7 ‰ for the incorporated oxygen. The substantial incorporation of oxygen from air supports that oxygen mobility is high in vacancy

  4. Carbon and nitrogen isotope ratios of juvenile winter flounder ...

    EPA Pesticide Factsheets

    Stable carbon and nitrogen isotope ratios were measured in the muscle tissues of young-of-the-year (YOY) winter flounder, Pseudopleuronectes americanus, collected from several estuarine systems along the coast of Rhode Island, USA. These systems included three coastal lagoons (Ninigret Pond, Green Hill Pond and Point Judith Pond), an estuarine river (Narrow River) and Narragansett Bay. Results from sampling over a three-year period showed some year-to-year variability for 13C within waterbodies; however, 15N values were not significantly different (P > 0.05) within systems among the three years studied. he 13C trends observed along transects in Narrow River and Narragansett Bay showed isotopically depleted terrestrial signals in the upper reaches of the estuaries and more positive values indicative of marine organic material in the lower regions of these systems. Significant differences (P < 0.05) in 15N were observed among estuarine systems. Fish from the coastal lagoons had the lowest 15N values followed by those from Narrow River and then Narragansett Bay. Some unexpected trends in 15N were observed within Narragansett Bay. The Bay has a strong north-south gradient in nutrient concentrations due to large sewage inputs in the upper Bay which was not reflected in flounder 15N values. As expected, YOY flounder from stations in the lower-Bay had depleted 15N values compared to those from the other locations. However, the 15N ratios o

  5. Stable-carbon isotopic composition of maple sap and foliage.

    PubMed

    Leavitt, S W; Long, A

    1985-06-01

    The (13)C/(12)C ratios of Acer grandidentatum sap sugar collected during the dormant period are compared to those of buds, leaves, and wood developed over the following growing season. As the primary carbon source for cellulose manufacture at initiation of annual growth in deciduous trees, sap sucrose would be expected to have an isotopic composition similar to first-formed cellulose. Although constancy in concentration and (13)C/(12)C ratios of the maple sap sugar suggests any gains or losses (e.g. to maintenance metabolism) do not appreciably alter composition, the (13)C/(12)C ratios of cellulose of the enlarging buds in the spring are quite distinct from those of the sap sugar, seemingly precluding a simple direct biochemical pathway of sap sucrose-->glucose-->cellulose in favor of a more complex pathway with greater likelihood of isotopic fractionation. The (13)C/(12)C ratios of the leaves and in the growth ring were initially similar to the sap sugar but decreased steadily over the growing season.

  6. Partitioning Ecosystem Respiration Using Stable Carbon Isotopes in a Mixed C3 Annual Grassland

    NASA Astrophysics Data System (ADS)

    Tu, K. P.

    2001-12-01

    -third being heterotrophic. Belowground respiration, comprised of both autotrophic (root) and heterotrophic (microbial) components, accounted for nearly two-thirds of total ecosystem respiration. Root and microbial respiration each contributed to nearly half of total belowground respiration (53% and 47%, respectively). Similarly, plant respiration was divided nearly equally between that from roots (52%) and leaves (48%). Partitioning using natural abundance stable carbon isotope ratios was made possible because of the relatively large differences in δ 13C values among the various sources in this entirely C3 system. To our knowledge, such large isotopic differences in respired CO2 among different plant tissues and belowground components have not been documented before. Further research is needed to determine how such differences may arise and to establish if similar differences exist in other ecosystems or at different times of the growing season. Our results also imply that interpretation of above-canopy Keeling plot intercepts may be complicated by both multiple (and isotopically distinct) sources and by isotopic fractionation that occurs either during the respiration process itself or during the transfer of carbon compounds prior to respiration.

  7. Characterization of Northern California petroleum by stable carbon isotopes

    USGS Publications Warehouse

    Lillis, Paul G.; Magoon, Leslie B.; Stanley, Richard G.; McLaughlin, Robert J.; Warden, Augusta

    2001-01-01

    The purpose of this study is to characterize natural occurrences of petroleum at the surface and in the subsurface within northern California in order to define and map petroleum systems for U.S. Geological Survey energy resource assessments. Furthermore, the chemical characterization and mapping of natural petroleum occurrences could also be used to discriminate natural occurrences from accidental oil spills during the activities of extraction or transportation of petroleum. Samples include petroleum from exploratory well tests, producing fields, natural seeps, and oil-stained rocks, and condensates from gas wells. Most of the sample localities are in northern California but a few samples from central and southern California are included for comparison (table 1). Even though other analyses were performed, only stable carbon isotope (δ13C) data are presented here for brevity and because δ13C values are one of the most discriminating characteristics of California petroleum.

  8. Nature of POC transport in a mangrove ecosystem: A carbon stable isotopic study

    NASA Astrophysics Data System (ADS)

    Rezende, C. E.; Lacerda, L. D.; Ovall, A. R. C.; Silva, C. A. R.; Martinelli, L. A.

    1990-06-01

    The isotopic composition of particulate organic carbon (POC) was studied during five tidal cycles in a mangrove creek of Sepetiba Bay, Rio de Janeiro, Brazil. The results show that a mixture of organic carbon from mangrove and marine origins is always present in the creek. Mean mangrove contribution to the POC varied from 16% to 100% and was dependent on tidal amplitude. The results suggest that oceanic carbon can be an important component of carbon balance in mangrove ecosystems. Therefore, earlier carbon balance studies from mangroves which did not include measurements of carbon isotopic composition should be interpreted with care.

  9. On-site isotopic analysis of dissolved inorganic carbon using an isotope ratio infrared spectrometer

    NASA Astrophysics Data System (ADS)

    Stoltmann, Tim; Mandic, Magda; Stöbener, Nils; Wapelhorst, Eric; Aepfler, Rebecca; Hinrichs, Kai-Uwe; Taubner, Heidi; Jost, Hj; Elvert, Marcus

    2016-04-01

    An Isotope Ratio Infrared Spectrometer (IRIS) has been adapted to perform measurements of δ13C of dissolved inorganic carbon (DIC) in marine pore waters. The resulting prototype allowed highly automated analysis of δ13C isotopic ratios and CO2 concentration. We achieved a throughput of up to 70 samples per day with DIC contents as low as 1.7 μmol C. We achieved an internal precision of 0.066 ‰ and an external precision of 0.16 ‰, which is comparable to values given for Isotope Ratio Mass Spectrometers (IRMS). The prototype instrument is field deployable, suitable for shipboard analysis of deep sea core pore waters. However, the validation of the prototype was centered around a field campaign in Eckernförde Bay, NW- Baltic Sea. As a proof of concept, a shallow site within an area of submarine groundwater discharge (SGD) and a site outside this area was investigated. We present profiles of δ13C of DIC over 50 cm exhibiting well understood methane turnover processes (anaerobic oxidation of methane). At the lowest point below the seafloor, microbial reduction of CO2 to CH4 dominates. 12CO2 is reduced preferentially over 13CO2, leading to more positive δ13C values in the remaining DIC pool; in layers closer to the surface, the oxidation of CH4 to CO2 becomes more prominent. Since the CH4 pool is enriched in 12C a shift to more negative δ13C can be observed in the DIC pool. In the upper 15 cm, the pore water DIC mixes with the sea water DIC, increasing δ13C again. Finally, we will present recent developments to further improve performance and future plans for deployments on research cruises.

  10. Stable isotope analysis of dissolved carbon species of Hot Lake, WA

    NASA Astrophysics Data System (ADS)

    Courtney, S.; Moran, J.; Cory, A. B.; Lindemann, S. R.; Fredrickson, J.

    2013-12-01

    shore of the lake immediately after removal from the lake) under various conditions (with labeled and unlabeled substrate, in the presence and absence of daylight, with and without undermat sediment) performed as both constant labeling and pulse-chase experiments. We incubated mat sections in lake water (from equivalent depth to the collected mat) spiked either with 13C-labeled or natural abundance organic (acetate or glucose) or inorganic (bicarbonate) substrates. For those conditions in which inorganic carbon was added, we measured the DOC of the water in each condition to measure conversion from DIC to DOC and vice versa for consumption/conversion of DOC to DIC. By comparing the GasBench DIC/DOC results of these various conditions over the course of the experiments, we assessed carbon flow into and out of the mat around a daily cycle. The assessments were made using the δ13C values and data of the lake water samples from the IRMS in conjunction with bulk mat isotope values. Our data show significant interactions between DIC and DOC pools and allow us to estimate the daily balance between carbon fixation and remineralization mediated by the microbial mat.

  11. Models of earth structure inferred from neodymium and strontium isotopic abundances

    PubMed Central

    Wasserburg, G. J.; DePaolo, D. J.

    1979-01-01

    A simplified model of earth structure based on the Nd and Sr isotopic characteristics of oceanic and continental tholeiitic flood basalts is presented, taking into account the motion of crustal plates and a chemical balance for trace elements. The resulting structure that is inferred consists of a lower mantle that is still essentially undifferentiated, overlain by an upper mantle that is the residue of the original source from which the continents were derived. PMID:16592688

  12. Helium Isotopes and Noble Gas Abundances of Cave Dripping Water in Three Caves in East Asia

    NASA Astrophysics Data System (ADS)

    Chen, A. T.; Shen, C. C.; Tan, M.; Li, T.; Uemura, R.; Asami, R.

    2015-12-01

    Paleo-temperature recorded in nature archives is a critical parameter to understand climate change in the past. With advantages of unique inert chemical characteristics and sensitive solubilities with temperature, dissolved noble gases in speleothem inclusion water were recently proposed to retrieve terrestrial temperature history. In order to accurately apply this newly-developed speleothem noble gas temperature (NGT) as a reliable proxy, a fundamental issue about behaviors of noble gases in the karst should be first clarified. In this study, we measured noble gas contents in air and dripping water to evaluate any ratio deviation between noble gases. Cave dripping water samples was collected from three selected caves, Shihua Cave in northern China, Furong Cave in southwestern, and Gyukusen Cave in an island located in the western Pacific. For these caves are characterized by a thorough mixing and long-term storage of waters in a karst aquifer by the absence of seasonal oxygen isotope shifts. Ratios of dripping water noble gases are statistically insignificant from air data. Helium isotopic ratios in the dripping water samples match air value. The results indicate that elemental and isotopic signatures of noble gases from air can be frankly preserved in the epikarst and support the fidelity of NGT techniques.

  13. A New and Improved Carbon Dioxide Isotope Analyzer for Understanding Soil-Plant-Atmosphere Interactions

    NASA Astrophysics Data System (ADS)

    Huang, Y. W.; Berman, E. S.; Owano, T. G.; Verfaillie, J. G.; Oikawa, P. Y.; Baldocchi, D. D.; Still, C. J.; Gardner, A.; Baer, D. S.; Rastogi, B.

    2015-12-01

    Stable CO2 isotopes provide information on biogeochemical processes that occur at the soil-plant-atmosphere interface. While δ13C measurement can provide information on the sources of the CO2, be it photosynthesis, natural gas combustion, other fossil fuel sources, landfills or other sources, δ18O, and δ17O are thought to be determined by the hydrological cycling of the CO2. Though researchers have called for analytical tools for CO2 isotope measurements that are reliable and field-deployable, developing such instrument remains a challenge. The carbon dioxide isotope analyzer developed by Los Gatos Research (LGR) uses LGR's patented Off-Axis ICOS (Integrated Cavity Output Spectroscopy) technology and incorporates proprietary internal thermal control for high sensitivity and optimal instrument stability. This new and improved analyzer measures CO2 concentration as well as δ13C, δ18O, and δ17O from CO2 at natural abundance (150-2500 ppm). The laboratory precision is ±200 ppb (1σ) in CO2 at 1 s, with a long-term (2 min) precision of ±20 ppb. The 1-second precision for both δ13C and δ18O is 0.7 ‰, and for δ17O is 1.8 ‰. The long-term (2 min) precision for both δ13C and δ18O is 0.08 ‰, and for δ17O is 0.18 ‰. The instrument has improved precision, stability and user interface over previous LGR CO2 isotope instruments and can be easily programmed for periodic referencing and sampling from different sources when coupled with LGR's multiport inlet unit (MIU). We have deployed two of these instruments at two different field sites, one at Twitchell Island in Sacramento County, CA to monitor the CO2 isotopic fluxes from an alfalfa field from 6/29/2015-7/13/2015, and the other at the Wind River Experimental Forest in Washington to monitor primarily the oxygen isotopes of CO2 within the canopy from 8/4/2015 through mid-November 2015. Methodology, laboratory development and testing and field performance are presented.

  14. Combined simulation of carbon and water isotopes in a global ocean model

    NASA Astrophysics Data System (ADS)

    Paul, André; Krandick, Annegret; Gebbie, Jake; Marchal, Olivier; Dutkiewicz, Stephanie; Losch, Martin; Kurahashi-Nakamura, Takasumi; Tharammal, Thejna

    2013-04-01

    Carbon and water isotopes are included as passive tracers in the MIT general circulation model (MITgcm). The implementation of the carbon isotopes is based on the existing MITgcm carbon cycle component and involves the fractionation processes during photosynthesis and air-sea gas exchange. Special care is given to the use of a real freshwater flux boundary condition in conjunction with the nonlinear free surface of the ocean model. The isotopic content of precipitation and water vapor is obtained from an atmospheric GCM (the NCAR CAM3) and mapped onto the MITgcm grid system, but the kinetic fractionation during evaporation is treated explicitly in the ocean model. In a number of simulations, we test the sensitivity of the carbon isotope distributions to the formulation of fractionation during photosynthesis and compare the results to modern observations of δ13C and Δ14C from GEOSECS, WOCE and CLIVAR. Similarly, we compare the resulting distribution of oxygen isotopes to modern δ18O data from the NASA GISS Global Seawater Oxygen-18 Database. The overall agreement is good, but there are discrepancies in the carbon isotope composition of the surface water and the oxygen isotope composition of the intermediate and deep waters. The combined simulation of carbon and water isotopes in a global ocean model will provide a framework for studying present and past states of ocean circulation such as postulated from deep-sea sediment records.

  15. Improvement of 2,4-dinitrophenylhydrazine derivatization method for carbon isotope analysis of atmospheric acetone.

    PubMed

    Wen, Sheng; Yu, Yingxin; Guo, Songjun; Feng, Yanli; Sheng, Guoying; Wang, Xinming; Bi, Xinhui; Fu, Jiamo; Jia, Wanglu

    2006-01-01

    Through simulation experiments of atmospheric sampling, a method via 2,4-dinitrophenylhydrazine (DNPH) derivatization was developed to measure the carbon isotopic composition of atmospheric acetone. Using acetone and a DNPH reagent of known carbon isotopic compositions, the simulation experiments were performed to show that no carbon isotope fractionation occurred during the processes: the differences between the predicted and measured data of acetone-DNPH derivatives were all less than 0.5 per thousand. The results permitted the calculation of the carbon isotopic compositions of atmospheric acetone using a mass balance equation. In this method, the atmospheric acetone was collected by a DNPH-coated silica cartridge, washed out as acetone-DNPH derivatives, and then analyzed by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Using this method, the first available delta13C data of atmospheric acetone are presented. Copyright 2006 John Wiley & Sons, Ltd.

  16. Temporal variability in arctic fox diet as reflected in stable-carbon isotopes; the importance of sea ice.

    PubMed

    Roth, James D

    2002-09-01

    Consumption of marine foods by terrestrial predators can lead to increased predator densities, potentially impacting their terrestrial resources. For arctic foxes (Alopex lagopus), access to such marine foods in winter depends on sea ice, which is threatened by global climate change. To quantify the importance of marine foods (seal carrion and seal pups) and document temporal variation in arctic fox diet I measured the ratios of the stable isotopes of carbon ((13)C/(12)C) in hair of arctic foxes near Cape Churchill, Manitoba, from 1994 to 1997. These hair samples were compared to the stable carbon isotope ratios of several prey species. Isotopic differences between seasonally dimorphic pelage types indicated a diet with a greater marine content in winter when sea ice provided access to seal carrion. Annual variation in arctic fox diet in both summer and winter was correlated with lemming abundance. Marine food sources became much more important in winters with low lemming populations, accounting for nearly half of the winter protein intake following a lemming decline. Potential alternative summer foods with isotopic signatures differing from lemmings included goose eggs and caribou, but these were unavailable in winter. Reliance on marine food sources in winter during periods of low lemming density demonstrates the importance of the sea ice as a potential habitat for this arctic fox population and suggests that a continued decline in sea ice extent will disrupt an important link between the marine and terrestrial ecosystems.

  17. The Abundance and Isotopic Composition of Water in Howardite-Eucrite-Diogenite Meteorites

    NASA Astrophysics Data System (ADS)

    Barrett, T. J.; Tartèse, R.; Anand, M.; Franchi, I. A.; Grady, M. M.; Greenwood, R. C.; Charlier, B. L. A.

    2014-09-01

    Using SIMs techniques we measure OH abundances and D/H ratios in apatite grains from two Eucrites (DaG 945, DaG 844).The average δD values of these two samples are also similar to carbonaceous chondrites, the Earth and the Moon.

  18. Radiocarbon and stable carbon isotope compositions of chemically fractionated soil organic matter in a temperate-zone forest.

    PubMed

    Koarashi, Jun; Iida, Takao; Asano, Tomohiro

    2005-01-01

    To better understand the role of soil organic matter in terrestrial carbon cycle, carbon isotope compositions in soil samples from a temperate-zone forest were measured for bulk, acid-insoluble and base-insoluble organic matter fractions separated by a chemical fractionation method. The measurements also made it possible to estimate indirectly radiocarbon ((14)C) abundances of acid- and base-soluble organic matter fractions, through a mass balance of carbon among the fractions. The depth profiles of (14)C abundances showed that (1) bomb-derived (14)C has penetrated the first 16cm mineral soil at least; (2) Delta(14)C values of acid-soluble organic matter fraction are considerably higher than those of other fractions; and (3) a significant amount of the bomb-derived (14)C has been preserved as the base-soluble organic matter around litter-mineral soil boundary. In contrast, no or little bomb-derived (14)C was observed for the base-insoluble fraction in all sampling depths, indicating that this recalcitrant fraction, accounting for approximately 15% of total carbon in this temperate-zone forest soil, plays a role as a long-term sink in the carbon cycle. These results suggest that bulk soil organic matter cannot provide a representative indicator as a source or a sink of carbon in soil, particularly on annual to decadal timescales.

  19. Abundant pre-industrial carbon detected in Canadian Arctic headwaters: implications for the permafrost carbon feedback

    NASA Astrophysics Data System (ADS)

    Dean, J. F.; van der Velde, Y.; Garnett, M. H.; Dinsmore, K. J.; Baxter, R.; Lessels, J. S.; Smith, P.; Street, L. E.; Subke, J.-A.; Tetzlaff, D.; Washbourne, I.; Wookey, P. A.; Billett, M. F.

    2018-03-01

    Mobilization of soil/sediment organic carbon into inland waters constitutes a substantial, but poorly-constrained, component of the global carbon cycle. Radiocarbon (14C) analysis has proven a valuable tool in tracing the sources and fate of mobilized carbon, but aquatic 14C studies in permafrost regions rarely detect ‘old’ carbon (assimilated from the atmosphere into plants and soil prior to AD1950). The emission of greenhouse gases derived from old carbon by aquatic systems may indicate that carbon sequestered prior to AD1950 is being destabilized, thus contributing to the ‘permafrost carbon feedback’ (PCF). Here, we measure directly the 14C content of aquatic CO2, alongside dissolved organic carbon, in headwater systems of the western Canadian Arctic—the first such concurrent measurements in the Arctic. Age distribution analysis indicates that the age of mobilized aquatic carbon increased significantly during the 2014 snow-free season as the active layer deepened. This increase in age was more pronounced in DOC, rising from 101-228 years before sampling date (a 120%-125% increase) compared to CO2, which rose from 92-151 years before sampling date (a 59%-63% increase). ‘Pre-industrial’ aged carbon (assimilated prior to ~AD1750) comprised 15%-40% of the total aquatic carbon fluxes, demonstrating the prevalence of old carbon to Arctic headwaters. Although the presence of this old carbon is not necessarily indicative of a net positive PCF, we provide an approach and baseline data which can be used for future assessment of the PCF.

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

    NASA Astrophysics Data System (ADS)

    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

  1. Precise and traceable carbon isotope ratio measurements by multicollector ICP-MS: what next?

    PubMed

    Santamaria-Fernandez, Rebeca

    2010-06-01

    This article reviews recent developments in the use of multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) to provide high-precision carbon isotope ratio measurements. MC-ICP-MS could become an alternative method to isotope ratio mass spectrometry (IRMS) for rapid carbon isotope ratio determinations in organic compounds and characterisation and certification of isotopic reference materials. In this overview, the advantages, drawbacks and potential of the method for future applications are critically discussed. Furthermore, suggestions for future improvements in terms of precision and sensitivity are made. No doubt, this is an exciting analytical challenge and, as such, hurdles will need to be cleared.

  2. Breath carbon stable isotope ratios identify changes in energy balance and substrate utilization in humans.

    PubMed

    Whigham, L D; Butz, D E; Johnson, L K; Schoeller, D A; Abbott, D H; Porter, W P; Cook, M E

    2014-09-01

    Rapid detection of shifts in substrate utilization and energy balance would provide a compelling biofeedback tool for individuals attempting weight loss. As a proof of concept, we tested whether the natural abundance of exhaled carbon stable isotope ratios (breath δ(13)C) reflects shifts between negative and positive energy balance. Volunteers (n=5) consumed a 40% energy-restricted diet for 6 days followed by 50% excess on day 7. Breath was sampled immediately before and 1 h and 2 h after breakfast, lunch and dinner. Exhaled breath δ(13)C values were measured by cavity ring-down spectroscopy. Using repeated measures analysis of variance (ANOVA) followed by Dunnett's contrasts, pre-breakfast breath values on days 2-6 were compared with day 1, and postprandial day 7 time points were compared with pre-breakfast day 7. Energy restriction diminished pre-breakfast breath δ(13)C by day 3 (P<0.05). On day 7, increased energy intake was first detected immediately before dinner (-23.8±0.6 vs -21.9±0.7‰, P=0.002 (means±s.d.)), and breath δ(13)C remained elevated at least 2 h post dinner. In conclusion, when shifting between negative and positive energy balance, breath δ(13)C showed anticipated isotopic changes. Although additional research is needed to determine specificity and repeatability, this method may provide a biomarker for marked increases in caloric intake.

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

    NASA Astrophysics Data System (ADS)

    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.

    2011-04-01

    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. The last 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

  4. [Seasonality and contribution to acid rain of the carbon abundance in rainwater].

    PubMed

    Xu, Tao; Song, Zhi-guang; Liu, Jun-feng; Wang, Cui-ping

    2008-02-01

    This paper reports the results from a study of the carbon abundance in rainwater of Guangzhou city, China. The determination of TOC, DOC, POC and PEC helps to study the seasonality of carbon abundance and its contribution to the acid rain. The results display the fact that the average contents of TOC, DOC, POC and PEC are 7.10 mg/L, 3.58 mg/L, 3.60 mg/L and 0.72 mg/L, respectively. These results confirm the deep effect of the organic pollutant to the rain. The seasonality exists in the carbon abundance of rainwater. The contents of TOC and DOC are up to the maximum in spring and the minimum in summer; the contribution of POC to TOC in summer is obviously higher than that in other seasons; and the relative content of POC is clearly higher in dry season than that in wet season. The seasonality reflects the more emission of the total pollutant in spring and the solid particle pollutant in summer than those in other seasons. Moreover, the emission of the organic pollutant from the mobile vehicles is more obvious in dry season than that in wet season. The contents of TOC and DOC have the negative correlation to the pH values, which confirms the contribution effect of the organic pollutant, such as vehicle emission, to the acid rain.

  5. The influence of kinetics on the oxygen isotope composition of calcium carbonate

    NASA Astrophysics Data System (ADS)

    Watkins, James M.; Nielsen, Laura C.; Ryerson, Frederick J.; DePaolo, Donald J.

    2013-08-01

    Paleotemperature reconstructions rely on knowledge of the equilibrium separation of oxygen isotopes between aqueous solution and calcium carbonate. Although oxygen isotope separation is expected on theoretical grounds, the temperature-dependence remains uncertain because other factors, such as slow exchange of isotopes between dissolved CO2-species and water, can obscure the temperature signal. This is problematic for crystal growth experiments on laboratory timescales and for interpreting the oxygen isotope composition of crystals formed in natural settings. We present results from experiments in which inorganic calcite is precipitated in the presence of 0.25 μM dissolved bovine carbonic anhydrase (CA). The presence of dissolved CA accelerates oxygen isotope equilibration between the dissolved carbon species CO2, H2CO3, HCO3-, CO32- and water, thereby eliminating this source of isotopic disequilibrium during calcite growth. The experimental results allow us to isolate, for the first time, kinetic oxygen isotope effects occurring at the calcite-water interface. We present a framework of ion-by-ion growth of calcite that reconciles our new measurements with measurements of natural cave calcites that are the best candidate for having precipitated under near-equilibrium conditions. Our findings suggest that isotopic equilibrium between calcite and water is unlikely to have been established in laboratory experiments or in many natural settings. The use of CA in carbonate precipitation experiments offers new opportunities to refine oxygen isotope-based geothermometers and to interrogate environmental variables other than temperature that influence calcite growth rates.

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

    NASA Technical Reports Server (NTRS)

    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.

  7. Wildfire Activity Across the Triassic-Jurassic Boundary in the Polish Basin: Evidence from New Fossil Charcoal & Carbon-isotope Data

    NASA Astrophysics Data System (ADS)

    Pointer, R.; Belcher, C.; Hesselbo, S. P.; Hodbod, M.; Pieńkowski, G.

    2017-12-01

    New fossil charcoal abundance and carbon-isotope data from two sedimentary cores provide new evidence of extreme environmental conditions in the Polish Basin during the Latest Triassic to Earliest Jurassic. Sedimentary cores from the Polish Basin provide an excellent record of terrestrial environmental conditions across the Triassic-Jurassic Boundary, a time of climatic extremes. Previous work has shown that the marine realm was affected by a large perturbation to the carbon cycle across the Triassic-Jurassic Boundary (manifested by large negative and positive carbon-isotope excursions) and limited records of charcoal abundance and organic geochemistry have indicated important changes in fire regime in the coeval ecosystems. Here we present two new carbon-isotope records generated from fossil plant matter across the Triassic-Jurassic boundary, and present new charcoal records. The charcoal abundance data confirm that there was variation in wildfire activity during the Late Triassic-Early Jurassic in the Polish Basin. Peaks in the number of fossil charcoal fragments present occur in both sedimentary cores, and increases in fossil charcoal abundance are linked to wildfires, signalling a short-lived rise in wildfire activity. Fossil charcoal abundance does not appear to be fully controlled by total organic matter content, depositional environment or bioturbation. We argue that increased wildfire activity is likely caused by an increase in ignition of plant material as a result of an elevated number of lightning strikes. Global warming (caused by a massive input of carbon into the atmosphere, as indicated by carbon-isotope data) can increase storm activity, leading to increased numbers of lightning strikes. Previous Triassic-Jurassic Boundary wildfire studies have found fossil charcoal abundance peaks at other northern hemisphere sites (Denmark & Greenland), and concluded that they represent increases in wildfire activity in the earliest Jurassic. Our new charcoal and

  8. Insights into Paleogene biogeochemistry from coupled carbon and sulfur isotopes in foraminiferal calcite.

    NASA Astrophysics Data System (ADS)

    Rennie, V.; Paris, G.; Abramovitch, S.; Sessions, A. L.; Adkins, J. F.; Turchyn, A. V.

    2014-12-01

    The Paleogene witnessed large-scale environmental changes, including the beginning of long-term Cenozoic cooling. The carbon isotope composition of foraminiferal calcite suggests a major reorganization of the carbon cycle over the Paleogene, with enhanced organic carbon burial in the Paleocene, and subsequent oxidation of this organic carbon or increased volcanism throughout the Eocene. The sulfur cycle is linked to the carbon cycle via the breakdown of organic carbon during bacterial sulfate reduction. Over geological time, carbon and sulfur isotopic shifts are often coupled due to enhanced pyrite burial being coupled to enhanced organic carbon burial, and enhanced pyrite weathering being coupled to enhanced organic carbon weathering. However, over the Paleogene, carbon and sulfur isotopes are fully decoupled, with the sulfur isotope record showing only one major shift in the early Eocene, after most of the carbon isotope variability is complete. One complication of interpreting the evolution of the sulfur cycle over the Cenozoic, is the fact that the mineral proxies used (typically barite) may not be temporally coincident with those used to reconstruct the carbon cycle (typically carbonate). Furthermore, these minerals are preserved in different locations, and therefore often must be extracted from different sediment cores in different ocean basins, leading to age-model uncertainty when the records are merged. To properly ascertain the phasing between early Cenozoic changes in the carbon cycle and the sulfur cycle, we would ideally measure all isotope records on the same mineral. A new sulfur isotope analytical technique [1] has been optimised for foraminiferal calcite as a proxy for seawater δ34SSO4. The δ34SSO4 in foraminiferal calcite can then be tied to records of carbon isotopes from stratigraphically identical samples, resolving previous age model uncertainties. We present coupled carbon and sulfur isotope records from the same core over the early

  9. Carbon isotopic composition of assimilated and respired CO2 in Southeastern US pine forests

    NASA Astrophysics Data System (ADS)

    Mortazavi, B.; Conte, M. H.; Chanton, J.; Martin, T.; Teklemerian, T.; Cropper, W.; Weber, J.

    2010-12-01

    We measured the 13C of assimilated carbon [foliage organic matter (δCOM), leaf soluble carbohydrates ((δCSC), and leaf waxes ((δCW)] and respiratory carbon [foliage (δCF), soil (δCS) and ecosystem respired CO2 (δCR)] over a two-year period at two sites in central Florida that are typical of Southeastern US coastal plain pine ecosystems. Our objective was to determine how climatic variables, operating by affecting plant physiology and photosynthetic discrimination (Δ), influence the isotopic composition of assimilated carbon pools and of ecosystem respired CO2. The first site was a naturally regenerated 32 m tall stand of mature longleaf pine (Pinus palustris Mill.) with mature slash pine (Pinus elliottii) subdominants, while the second was a planted, mid-rotation 13 m tall stand of slash pine (Pinus elliottii var. elliottii Engelm.). δCOM, δCSC, δCW, and δCF of P. palustris were 13C enriched by about 2‰ relative to that of P. elliottii in the mid-rotation plantation. Despite this enrichment, mean δCR of the P. palustris stand was similar to that at the P. elliottii plantation, reflecting additional respiratory inputs from the more isotopically depleted P. elliottii subdominant and understory. In both P. palustris and P. elliottii, a small decrease was observed in δCOM over the two year study, but not in δCSC, δCF, δCS or δCR. Intriguingly, a significant 2‰ decrease was also observed in the very long chain needlewaxes (C32-36 n-alkanoic acids), but not the more abundant C24-28 waxes. As the carbon in waxes is supplied by internal storage reserves, our data suggest there may be distinct carbon source pathways for waxes of differing chain lengths. The long-term decrease in the 13C of foliar carbon and waxes also suggests recovery from severe drought conditions prior to our study. δCF and δCR were consistently 13C enriched relative to assimilated C and were insensitive to variations in vapor pressure deficit (D). The small variability in δCA and

  10. Mesozoic black shales, source mixing and carbon isotopes

    NASA Astrophysics Data System (ADS)

    Suan, Guillaume

    2016-04-01

    Over the last decades, considerable attention has been devoted to the paleoenvironmental and biogeochemical significance of Mesozoic black shales. Black shale-bearing successions indeed often display marked changes in the organic carbon isotope composition (δ13Corg), which have been commonly interpreted as evidence for dramatic perturbations of global carbon budgets and CO2 levels. Arguably the majority of these studies have discarded some more "local" explanations when interpreting δ13Corg profiles, most often because comparable profiles occur on geographically large and distant areas. Based on newly acquired data and selected examples from the literature, I will show that the changing contribution of organic components with distinct δ13C signatures exerts a major but overlooked influence of Mesozoic δ13Corg profiles. Such a bias occurs across a wide spectrum of sedimentological settings and ages, as shown by the good correlation between δ13Corg values and proxies of kerogen proportions (such as rock-eval, biomarker, palynofacies and palynological data) recorded in Mesozoic marginal to deep marine successions of Triassic, Jurassic and Cretaceous age. In most of these successions, labile, 12C-enriched amorphous organic matter of marine origin dominates strata deposited under anoxic conditions, while oxidation-resistant, 13C-rich terrestrial particles dominate strata deposited under well-oxygenated conditions. This influence is further illustrated by weathering profiles of Toarcian (Lower Jurassic) black shales from France, where weathered areas dominated by refractory organic matter show dramatic 13C-enrichment (and decreased total organic carbon and pyrite contents) compared to non-weathered portions of the same horizon. The implications of these results for chemostratigraphic correlations and pCO2 reconstructions of Mesozoic will be discussed, as well as strategies to overcome this major bias.

  11. Carbonic Anhydrase, Calcification Dynamics and Stable Isotope Vital Effects: Deep Sea Corals and Beyond

    NASA Astrophysics Data System (ADS)

    Chen, S.; Gagnon, A. C.; Adkins, J. F.

    2017-12-01

    The stable isotope compositions of biogenic carbonates have been used for paleoceanographic and paleoclimatic reconstructions for decades, and produced some of the most iconic records in the field. However, we still lack a fully mechanistic understanding of the stable isotope proxies, especially the biological overprint on the environmental signals termed "vital effects". A ubiquitous feature of stable isotope vital effects in marine calcifying organisms is a strong correlation between δ18O and δ13C in a range of values that are depleted from equilibrium. Two mechanisms have been proposed to explain this correlation, one based on kinetic isotope effects during CO2(aq)-HCO3- inter-conversion, the other based on equilibrium isotope exchange during pH dependent speciation of the dissolved inorganic carbon pool. Neither mechanism explains all the stable isotope features observed in biogenic carbonates. Here we present a fully kinetic model of biomineralization and its isotope effects using deep sea corals as a test organism. A key component of our model is the consideration of the enzyme carbonic anhydrase in catalyzing the CO2(aq)-HCO3- inter-conversion reactions in the extracellular calcifying fluid (ECF). We find that the amount of carbonic anhydrase not only modulates the carbonate chemistry of the calcifying fluid, but also helps explain the slope of the δ18O-δ13C correlation. With this model, we are not only able to fit deep sea coral data, but also explain the stable isotope vital effects of other calcifying organisms. This fully kinetic model of stable isotope vital effects and the underlying calcification dynamics may also help us better understand mechanisms of other paleoceanographic tracers in biogenic carbonates, including boron isotopes and trace metal proxies.

  12. Environmental forcing of terrestrial carbon isotope excursion amplification across five Eocene hyperthermals

    NASA Astrophysics Data System (ADS)

    Bowen, G. J.; Abels, H.

    2015-12-01

    Abrupt changes in the isotope composition of exogenic carbon pools accompany many major episodes of global change in the geologic record. The global expression of this change in substrates that reflect multiple carbon pools provides important evidence that many events reflect persistent, global redistribution of carbon between reduced and oxidized stocks. As the diversity of records documenting any event grows, however, discrepancies in the expression of carbon isotope change among substrates are almost always revealed. These differences in magnitude, pace, and pattern of change can complicate interpretations of global carbon redistribution, but under ideal circumstances can also provide additional information on changes in specific environmental and biogeochemical systems that accompanied the global events. Here we evaluate possible environmental influences on new terrestrial records of the negative carbon isotope excursions (CIEs) associated with multiple hyperthermals of the Early Eocene, which show a common pattern of amplified carbon isotope change in terrestrial paleosol carbonate records relative to that recorded in marine substrates. Scaling relationships between climate and carbon-cycle proxies suggest that that the climatic (temperature) impact of each event scaled proportionally with the magnitude of its marine CIE, likely implying that all events involved release of reduced carbon with a similar isotopic composition. Amplification of the terrestrial CIEs, however, does not scale with event magnitude, being proportionally less for the first, largest event (the PETM). We conduct a sensitivity test of a coupled plant-soil carbon isotope model to identify conditions that could account for the observed CIE scaling. At least two possibilities consistent with independent lines of evidence emerge: first, varying effects of pCO2 change on photosynthetic carbon isotope discrimination under changing background pCO2, and second, contrasting changes in regional

  13. Soil Carbon-Fixation Rates and Associated Bacterial Diversity and Abundance in Three Natural Ecosystems.

    PubMed

    Lynn, Tin Mar; Ge, Tida; Yuan, Hongzhao; Wei, Xiaomeng; Wu, Xiaohong; Xiao, Keqing; Kumaresan, Deepak; Yu, San San; Wu, Jinshui; Whiteley, Andrew S

    2017-04-01

    CO 2 assimilation by autotrophic microbes is an important process in soil carbon cycling, and our understanding of the community composition of autotrophs in natural soils and their role in carbon sequestration of these soils is still limited. Here, we investigated the autotrophic C incorporation in soils from three natural ecosystems, i.e., wetland (WL), grassland (GR), and forest (FO) based on the incorporation of labeled C into the microbial biomass. Microbial assimilation of 14 C ( 14 C-MBC) differed among the soils from three ecosystems, accounting for 14.2-20.2% of 14 C-labeled soil organic carbon ( 14 C-SOC). We observed a positive correlation between the cbbL (ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) large-subunit gene) abundance, 14 C-SOC level, and 14 C-MBC concentration confirming the role of autotrophic bacteria in soil carbon sequestration. Distinct cbbL-bearing bacterial communities were present in each soil type; form IA and form IC RubisCO-bearing bacteria were most abundant in WL, followed by GR soils, with sequences from FO soils exclusively derived from the form IC clade. Phylogenetically, the diversity of CO 2 -fixing autotrophs and CO oxidizers differed significantly with soil type, whereas cbbL-bearing bacterial communities were similar when assessed using coxL. We demonstrate that local edaphic factors such as pH and salinity affect the C-fixation rate as well as cbbL and coxL gene abundance and diversity. Such insights into the effect of soil type on the autotrophic bacterial capacity and subsequent carbon cycling of natural ecosystems will provide information to enhance the sustainable management of these important natural ecosystems.

  14. In Situ Carbon Isotope Analysis by Laser Ablation MC-ICP-MS.

    PubMed

    Chen, Wei; Lu, Jue; Jiang, Shao-Yong; Zhao, Kui-Dong; Duan, Deng-Fei

    2017-12-19

    Carbon isotopes have been widely used in tracing a wide variety of geological and environmental processes. The carbon isotope composition of bulk rocks and minerals was conventionally analyzed by isotope ratio mass spectrometry (IRMS), and, more recently, secondary ionization mass spectrometry (SIMS) has been widely used to determine carbon isotope composition of carbon-bearing solid materials with good spatial resolution. Here, we present a new method that couples a RESOlution S155 193 nm laser ablation system with a Nu Plasma II MC-ICP-MS, with the aim of measuring carbon isotopes in situ in carbonate minerals (i.e., calcite and aragonite). Under routine operating conditions for δ 13 C analysis, instrumental bias generally drifts by 0.8‰-2.0‰ in a typical analytical session of 2-3 h. Using a magmatic calcite as the standard, the carbon isotopic composition was determined for a suite of calcite samples with δ 13 C values in the range of -6.94‰ to 1.48‰. The obtained δ 13 C data are comparable to IRMS values. The combined standard uncertainty for magmatic calcite is <0.3‰ (1s). No significant matrix effects have been identified in calcite with the amplitude of chemical composition variation (i.e., MnO, SrO, MgO, or FeO) up to 2.5 wt %. Two modern corals were investigated using magmatic calcite as the calibration standard, and the average δ 13 C values for both corals are similar to the bulk IRMS values. Moreover, coral exhibits significant heterogeneity in carbon isotope compositions, with differences up to 4.85‰ within an individual coral. This study indicates that LA-MC-ICP-MS can serve as an appropriate method to analyze carbon isotopes of carbonate minerals in situ.

  15. Analysis of dissolved organic carbon concentration and 13C isotopic signature by TOC-IRMS - assessment of analytical performance

    NASA Astrophysics Data System (ADS)

    Kirkels, Frédérique; Cerli, Chiara; Federherr, Eugen; Kalbitz, Karsten

    2013-04-01

    samples did not affect the precision of the analysis of natural abundance and labeled samples. Natural DOM, derived from different soils and assessed at various concentrations, was measured with similar good analytical performance, and also tested for the effect of freezing and re-dissolving. We found good performance of TOC-IRMS in comparison with other systems capable of determining C concentration and isotopic signatures. We recognize the advantages of this system providing: - High sample throughput, short measurement time (15 minutes), flexible sample volume - Easy maintenance, handling, rapid sample preparation (no pretreatment) This preliminary assessment highlights wide-ranging opportunities for further research on concentrations and isotopic signatures by TOC-IRMS to elucidate the role of dissolved carbon in terrestrial and aquatic systems.

  16. Peatland Microbial Carbon Use Under Warming using Isotopic Fractionation

    NASA Astrophysics Data System (ADS)

    Gutknecht, J.

    2016-12-01

    Peatlands are a critical natural resource, especially in their role as carbon sinks. Most of the world's peatlands are located in Northern ecosystems where the climate is changing at a rapid pace, and there is great interest and concern with how climate change will influence them. Although studies regarding the response of peatlands to climate change have emerged, the microbial mediation of C cycling in these systems is still less well understood. In this study, 13CPLFA analysis was used to characterize the microbial community and it's carbon use at the Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE) Project. The SPRUCE project is an extensive study of the response of peatlands to climatic manipulation in the Marcell Experimental Forest in northern Minnesota. Heating rods were installed in peatland plots where peat is being warmed at several levels including ambient, +2.5, +4.5, +6.75, and +9 degrees Celsius, at a depth of 3 meters, beginning July of 2014. Samples were taken June 2014, September 2014, and June 2015, throughout the depth profile. We found very high microbial, and especially fungal growth at shallow depths, owing in part to the influence of fungal-like lipids present in Sphagnum stems, and in part to dense mycorrhizal colonization in shrub and tree species. Isotopic data shows that microbial biomass has an enriched δ13C lower in the peat profile, indicating as expected that microbes at depth utilize older carbon or carbon more enriched in 13C. The increase over depth in the δ13C signature may also reflect the increased dominance of pre-industrial carbon that is more enriched in 13C. In this early period of warming we did not see clear effects of warming, either due to the highly heterogeneous microbial growth across the bog, or to the short term deep warming only. We expect that with the initiation of aboveground warming in July 2016, warming will begin to show stronger effects on microbial C cycling.

  17. Carbonate "Clumped" Isotope Determination of Seawater Temperature During the End-Triassic Extinction Event

    NASA Astrophysics Data System (ADS)

    Gammariello, R. T., Jr.; Petryshyn, V. A.; Ibarra, Y.; Greene, S. E.; Corsetti, F. A.; Bottjer, D. J.; Tripati, A.

    2014-12-01

    Stromatolites are laminated sedimentary structures that are commonly thought to be created by cyanobacteria, either through the trapping and binding of sediment, or through metabolically-induced precipitation. However, stromatolite formation is poorly understood. In general, stromatolite abundance was higher in the Proterozoic than the Phanerozoic, but notable increases in stromatolite abundance occur in association with Phanerozoic mass extinction events. Here, we focus on stromatolites from the latest Triassic Cotham Marble (United Kingdom) that are associated with the extinction interval. The end-Triassic mass extinction is coincident with large-scale volcanism in the Central Atlantic Magmatic Province (CAMP) and the associated breakup of Pangea. Some hypothesize that CAMP-associated increases in atmospheric CO2 led to a rise in global temperatures and ocean acidification that caused or enhanced the extinction. In order to quantify the role of climate change with respect to the end-Triassic mass extinction, we applied the carbonate "clumped" isotope paleothermometer to the well-preserved Cotham Marble stromatolites. The stromatolites were deposited in the shallow Tethys Sea, and today occur in several localities across the southwestern UK. The stromatolites alternate on the cm scale between laminated and dendrolitic microstructures and each was microdrilled for clumped isotope analysis. The two microstructures display different temperatures of formation, where the dendrolitic portions apparently grew under cooler conditions than laminated layers, and younger layers grew in cooler conditions than older layers. Our results suggest that temperature fluctuated and potentially trended towards amelioration of the warm temperatures during the deposition of the Cotham Marble.

  18. Carbon isotope ratios of selected volatiles in Citrus sinensis and in orange-flavoured food.

    PubMed

    Schipilliti, Luisa; Bonaccorsi, Ivana; Cotroneo, Antonella; Dugo, Paola; Mondello, Luigi

    2015-11-01

    Twenty genuine samples of industrially cold-pressed sweet orange essential oils, were analysed by gas chromatography-combustion-isotope ratio mass spectrometry to determine the values of the carbon isotope ratios (δ(13)C(VPDB)) of selected volatiles and assess the corresponding range of authenticity. Successively, four commercial orange-flavoured products were analysed under identical conditions to evaluate the authenticity of the orange flavour. The samples were extracted by solid-phase microextraction under optimised conditions. The evaluation was performed by using an internal standard procedure to neglect the contribution due to the original environment to the isotopic abundance of (13)C. The composition of the volatile fraction of the essential oils and of the flavoured products was determined by gas chromatography coupled to mass spectrometry with linear retention indices, and by gas chromatography with a flame ionisation detector. The δ(13)C(VPDB) values of seven secondary metabolites determined here were successfully used to characterise genuine orange essential oil. These values were used to evaluate the quality of orange-flavoured products, revealing the presence of compounds of different origin, not compatible with the values of genuine orange secondary metabolites. This study provides the range of authenticity of δ(13)C(VPDB) of seven different secondary metabolites in sweet orange genuine essential oil, useful for evaluating the genuineness of orange flavour. In accord with a previous study on different essential oils, the values determined here can be successfully applied for the evaluation of a large number of flavoured food stuffs and correlated with their origins. © 2014 Society of Chemical Industry.

  19. Accurate experimental determination of the isotope effects on the triple point temperature of water. I. Dependence on the 2H abundance

    NASA Astrophysics Data System (ADS)

    Faghihi, V.; Peruzzi, A.; Aerts-Bijma, A. T.; Jansen, H. G.; Spriensma, J. J.; van Geel, J.; Meijer, H. A. J.

    2015-12-01

    Variation in the isotopic composition of water is one of the major contributors to uncertainty in the realization of the triple point of water (TPW). Although the dependence of the TPW on the isotopic composition of the water has been known for years, there is still a lack of a detailed and accurate experimental determination of the values for the correction constants. This paper is the first of two articles (Part I and Part II) that address quantification of isotope abundance effects on the triple point temperature of water. In this paper, we describe our experimental assessment of the 2H isotope effect. We manufactured five triple point cells with prepared water mixtures with a range of 2H isotopic abundances encompassing widely the natural abundance range, while the 18O and 17O isotopic abundance were kept approximately constant and the 18O  -  17O ratio was close to the Meijer-Li relationship for natural waters. The selected range of 2H isotopic abundances led to cells that realised TPW temperatures between approximately  -140 μK to  +2500 μK with respect to the TPW temperature as realized by VSMOW (Vienna Standard Mean Ocean Water). Our experiment led to determination of the value for the δ2H correction parameter of A2H  =  673 μK / (‰ deviation of δ2H from VSMOW) with a combined uncertainty of 4 μK (k  =  1, or 1σ).

  20. Light Isotope Abundances in Solar Energetic Particles Measured by the NINA-2 Instrument

    NASA Astrophysics Data System (ADS)

    Mikhailov, V. V.; Bakaldin, A.; Galper, A.; Koldashov, S.; Korotkov, M.; Leonov, A.; Mikhaylova, J.; Voronov, S.; Bidoli, V.; Casolino, M.; De Pascale, M.; Furano, G.; Iannucci, A.; Morselli, A.; Picozza, P.; Sparvoli, R.; Boezio, M.; Bonvicini, V.; Vacchi, A.; Zampa, N.; Ambriola, M.; Bellotti, R.; Cafagna, F.; Circella, M.; De Marzo, C.; Adriani, O.; Papini, P.; Spillantini, P.; Straulino, S.; Vannuccini, E.; Ricci, M.; Castellini, G.

    2003-07-01

    The instrument NINA-2 flew on board the satellite MITA between July 2000 and August 2001, in circular polar orbit. This paper reports about a set of Solar Energetic Particle events measured by the NINA-2 instrument. The detector has mass resolution of about 0.15 amu for light nuclei and gives the possibility to observe hydrogen and helium isotop es in the energy range 10-50 MeV/n. Data of 3 He and 4 He were used to determine the 3 He/4 He ratio. For each event the deuterium-to-proton ratio was also estimated. This ratio, averaged over all events, is less than 3×10-5 .

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Laboratory calibration of the calcium carbonate clumped isotope thermometer in the 25-250 °C temperature range

    NASA Astrophysics Data System (ADS)

    Kluge, Tobias; John, Cédric M.; Jourdan, Anne-Lise; Davis, Simon; Crawshaw, John

    2015-05-01

    Many fields of Earth sciences benefit from the knowledge of mineral formation temperatures. For example, carbonates are extensively used for reconstruction of the Earth's past climatic variations by determining ocean, lake, and soil paleotemperatures. Furthermore, diagenetic minerals and their formation or alteration temperature may provide information about the burial history of important geological units and can have practical applications, for instance, for reconstructing the geochemical and thermal histories of hydrocarbon reservoirs. Carbonate clumped isotope thermometry is a relatively new technique that can provide the formation temperature of carbonate minerals without requiring a priori knowledge of the isotopic composition of the initial solution. It is based on the temperature-dependent abundance of the rare 13C-18O bonds in carbonate minerals, specified as a Δ47 value. The clumped isotope thermometer has been calibrated experimentally from 1 °C to 70 °C. However, higher temperatures that are relevant to geological processes have so far not been directly calibrated in the laboratory. In order to close this calibration gap and to provide a robust basis for the application of clumped isotopes to high-temperature geological processes we precipitated CaCO3 (mainly calcite) in the laboratory between 23 and 250 °C. We used two different precipitation techniques: first, minerals were precipitated from a CaCO3 supersaturated solution at atmospheric pressure (23-91 °C), and, second, from a solution resulting from the mixing of CaCl2 and NaHCO3 in a pressurized reaction vessel at a pressure of up to 80 bar (25-250 °C).

  3. Triple oxygen isotope composition of tropospheric carbon dioxide and terrestrial carbonates

    NASA Astrophysics Data System (ADS)

    Hofmann, M. E.; Horváth, B.; Pack, A.

    2011-12-01

    The triple oxygen isotope composition of tropospheric CO2 is a potential new tracer in urban air studies and for biosphere-atmosphere interactions [1]. In this study, we are analyzing CO2 from different provenances in order to trace the influx of anthropogenic CO2 to urban air and to test predictions on the stratosphere-troposphere exchange flux. Since July 2010, we are monitoring the triple oxygen isotope composition of CO2 in urban air in a two-week interval. For this purpose, carbon dioxide was extracted from ~450L of ambient air on the campus of the University of Göttingen using a Russian Doll type cryogenic trap [2]. The CO2 was analyzed by CO2-CeO2 equilibration at 685°C and subsequent IR laser fluorination of CeO2 and CF-irmMS [3]. All triple oxygen isotope data are reported as Δ17OTFL values relative to the terrestrial fractionation line (TFL) with a slope βTFL=0.5251 and an intercept γTFL=-0.014%. On average, the Δ17OTFL value of ambient CO2 was -0.11±0.05% (SD) with a seasonal cycle of 0.04±0.01%. Lower Δ17O values were observed during wintertime. In order to test the potential of Δ17O as a tracer for anthropogenic CO2, we analyzed CO2 from different combustion processes. Our results showed that the Δ17O anomaly of tropospheric O2 [4] is passed on fully, or partially to the combustion CO2 [5]. We estimate that elevated anthropogenic emission during wintertime could be responsible for a decrease in Δ17O of urban air CO2 of -0.02±0.01%. In order to predict the triple oxygen isotope composition of tropospheric CO2 on a global scale, we revised the box model calculation from Hoag et al. [1]. For the exponent β for CO2-water equilibrium, we assume that βCO2-water=0.522±0.001 [6]. Furthermore, we took into account that the Δ17OTFL value of CO2 released from soils is affected by kinetic fractionation. Thus, we obtained a Δ17OTFL value for global tropospheric CO2 of -0.13%. The model calculation agrees well with the Δ17OTFL value determined for

  4. Carbon Stable Isotope Values in Plankton and Mussels Reflect Changes in Carbonate Chemistry Associated with Nutrient Enhanced Net Production.

    PubMed

    Oczkowski, Autumn; Taplin, Bryan; Pruell, Richard; Pimenta, Adam; Johnson, Roxanne; Grear, Jason

    2018-02-14

    Coastal ecosystems are inherently complex and potentially adaptive as they respond to changes in nutrient loads and climate. We documented the role that carbon stable isotope (δ 13 C) measurements could play in understanding that adaptation with a series of three Ecostat (i.e., continuous culture) experiments. We quantified linkages among δ 13 C, nutrients, carbonate chemistry, primary, and secondary production in temperate estuarine waters. Experimental culture vessels (9.1 L) containing 33% whole and 67% filtered (0.2 μm) seawater were amended with dissolved inorganic nitrogen (N) and phosphorous (P) in low (3 vessels; 5 μM N, 0.3 μM P), moderate (3 vessels; 25 μM N, 1.6 μM P), and high amounts (3 vessels; 50 μM N, 3.1 μM P). The parameters necessary to calculate carbonate chemistry, chlorophyll- a concentrations, and particulate δ 13 C values were measured throughout the 14 day experiments. Outflow lines from the experimental vessels fed 250 ml containers seeded with juvenile blue mussels (Mytilus edulis). Mussel subsamples were harvested on days 0, 7, and 14 and their tissues were analyzed for δ 13 C values. We consistently observed that particulate δ 13 C values were positively correlated with chlorophyll-a, carbonate chemistry, and to changes in the ratio of bicarbonate to dissolved carbon dioxide ( [Formula: see text] :CO 2 ). While the relative proportion of [Formula: see text] to CO 2 increased over the 14 days, concentrations of each declined, reflecting the drawdown of carbon associated with enhanced production. Plankton δ 13 C values, like chlorophyll- a concentrations, increased over the course of each experiment, with the greatest increases in the moderate and high treatments. Trends in δ 13 C over time were also observed in the mussel tissues. Despite ecological variability and different plankton abundances the experiments consistently demonstrated how δ 13 C values in primary producers and consumers reflected nutrient availability

  5. Dissolution of barite for the analysis of strontium isotopes and other chemical and isotopic variations using aqueous sodium carbonate

    USGS Publications Warehouse

    Breit, G.N.; Simmons, E.C.; Goldhaber, M.B.

    1985-01-01

    A simple procedure for preparing barite samples for chemical and isotopic analysis is described. Sulfate ion, in barite, in the presence of high concentrations of aqueous sodium carbonate, is replaced by carbonate. This replacement forms insoluble carbonates with the cations commonly in barite: Ba, Sr, Ca and Pb. Sulfate is released into the solution by the carbonate replacement and is separated by filtration. The aqueous sulfate can then be reprecipitated for analysis of the sulfur and oxygen isotopes. The cations in the carbonate phase can be dissolved by acidifying the solid residue. Sr can be separated from the solution for Sr isotope analysis by ion-exchange chromatography. The sodium carbonate used contains amounts of Sr which will affect almost all barite 87Sr 86Sr ratios by less than 0.00001 at 1.95?? of the mean. The procedure is preferred over other techniques used for preparing barite samples for the determination of 87Sr 86Sr ratios because it is simple, rapid and enables simultaneous determination of many compositional parameters on the same material. ?? 1985.

  6. A sorghum (Sorghum bicolor) mutant with altered carbon isotope ratio.

    PubMed

    Rizal, Govinda; Karki, Shanta; Thakur, Vivek; Wanchana, Samart; Alonso-Cantabrana, Hugo; Dionora, Jacque; Sheehy, John E; Furbank, Robert; von Caemmerer, Susanne; Quick, William Paul

    2017-01-01

    Recent efforts to engineer C4 photosynthetic traits into C3 plants such as rice demand an understanding of the genetic elements that enable C4 plants to outperform C3 plants. As a part of the C4 Rice Consortium's efforts to identify genes needed to support C4 photosynthesis, EMS mutagenized sorghum populations were generated and screened to identify genes that cause a loss of C4 function. Stable carbon isotope ratio (δ13C) of leaf dry matter has been used to distinguishspecies with C3 and C4 photosynthetic pathways. Here, we report the identification of a sorghum (Sorghum bicolor) mutant with a low δ13C characteristic. A mutant (named Mut33) with a pale phenotype and stunted growth was identified from an EMS treated sorghum M2 population. The stable carbon isotope analysis of the mutants showed a decrease of 13C uptake capacity. The noise of random mutation was reduced by crossing the mutant and its wildtype (WT). The back-cross (BC1F1) progenies were like the WT parent in terms of 13C values and plant phenotypes. All the BC1F2 plants with low δ13C died before they produced their 6th leaf. Gas exchange measurements of the low δ13C sorghum mutants showed a higher CO2 compensation point (25.24 μmol CO2.mol-1air) and the maximum rate of photosynthesis was less than 5μmol.m-2.s-1. To identify the genetic determinant of this trait, four DNA pools were isolated; two each from normal and low δ13C BC1F2 mutant plants. These were sequenced using an Illumina platform. Comparison of allele frequency of the single nucleotide polymorphisms (SNPs) between the pools with contrasting phenotype showed that a locus in Chromosome 10 between 57,941,104 and 59,985,708 bps had an allele frequency of 1. There were 211 mutations and 37 genes in the locus, out of which mutations in 9 genes showed non-synonymous changes. This finding is expected to contribute to future research on the identification of the causal factor differentiating C4 from C3 species that can be used in the

  7. A sorghum (Sorghum bicolor) mutant with altered carbon isotope ratio

    PubMed Central

    Karki, Shanta; Thakur, Vivek; Wanchana, Samart; Alonso-Cantabrana, Hugo; Dionora, Jacque; Sheehy, John E.; Furbank, Robert; von Caemmerer, Susanne; Quick, William Paul

    2017-01-01

    Recent efforts to engineer C4 photosynthetic traits into C3 plants such as rice demand an understanding of the genetic elements that enable C4 plants to outperform C3 plants. As a part of the C4 Rice Consortium’s efforts to identify genes needed to support C4 photosynthesis, EMS mutagenized sorghum populations were generated and screened to identify genes that cause a loss of C4 function. Stable carbon isotope ratio (δ13C) of leaf dry matter has been used to distinguishspecies with C3 and C4 photosynthetic pathways. Here, we report the identification of a sorghum (Sorghum bicolor) mutant with a low δ13C characteristic. A mutant (named Mut33) with a pale phenotype and stunted growth was identified from an EMS treated sorghum M2 population. The stable carbon isotope analysis of the mutants showed a decrease of 13C uptake capacity. The noise of random mutation was reduced by crossing the mutant and its wildtype (WT). The back-cross (BC1F1) progenies were like the WT parent in terms of 13C values and plant phenotypes. All the BC1F2 plants with low δ13C died before they produced their 6th leaf. Gas exchange measurements of the low δ13C sorghum mutants showed a higher CO2 compensation point (25.24 μmol CO2.mol-1air) and the maximum rate of photosynthesis was less than 5μmol.m-2.s-1. To identify the genetic determinant of this trait, four DNA pools were isolated; two each from normal and low δ13C BC1F2 mutant plants. These were sequenced using an Illumina platform. Comparison of allele frequency of the single nucleotide polymorphisms (SNPs) between the pools with contrasting phenotype showed that a locus in Chromosome 10 between 57,941,104 and 59,985,708 bps had an allele frequency of 1. There were 211 mutations and 37 genes in the locus, out of which mutations in 9 genes showed non-synonymous changes. This finding is expected to contribute to future research on the identification of the causal factor differentiating C4 from C3 species that can be used in the

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

    NASA Astrophysics Data System (ADS)

    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

  9. Determining the Local Abundance of Martian Methane and its 13-C/l2-C and D/H Isotopic Ratios for Comparison with Related Gas and Soil Analysis on the 2011 Mars Science Laboratory (MSL) Mission

    NASA Technical Reports Server (NTRS)

    Webster, Christopher R.; Mahaffy, Paul R.

    2011-01-01

    Understanding the origin of Martian methane will require numerous complementary measurements from both in situ and remote sensing investigations and laboratory work to correlate planetary surface geophysics with atmospheric dynamics and chemistry. Three instruments (Quadrupole Mass Spectrometer (QMS), Gas Chromatograph (GC) and Tunable Laser Spectrometer (TLS)) with sophisticated sample handling and processing capability make up the Sample Analysis at Mars (SAM) analytical chemistry suite on NASA s 2011 Mars Science Laboratory (MSL) Mission. Leveraging off the SAM sample and gas processing capability that includes methane enrichment, TLS has unprecedented sensitivity for measuring absolute methane (parts-per-trillion), water, and carbon dioxide abundances in both the Martian atmosphere and evolved from heated soil samples. In concert with a wide variety of associated trace gases (e.g. SO2, H2S, NH3, higher hydrocarbons, organics, etc.) and other isotope ratios measured by SAM, TLS will focus on determining the absolute abundances of methane, water and carbon dioxide, and their isotope ratios: 13C/12C and D/H in methane; 13C/12C and 18O/17O/16O in carbon dioxide; and 18O/17O/16O and D/H in water. Measurements near the MSL landing site will be correlated with satellite (Mars Express, Mars 2016) and ground-based observations.

  10. Rate-dependent carbon and nitrogen kinetic isotope fractionation in hydrolysis of isoproturon.

    PubMed

    Penning, Holger; Cramer, Christopher J; Elsner, Martin

    2008-11-01

    Stable isotope fractionation permits quantifying contaminant degradation in the field when the transformation reaction is associated with a consistent isotope enrichment factor epsilon. When interpreted in conjunction with dual isotope plots, isotope fractionation is also particularly useful for elucidating reaction mechanisms. To assess the consistency of epsilon and dual isotope slopes in a two-step reaction, we investigated the abiotic hydrolysis of the herbicide isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea) using a fragmentation method that allows measuring isotope ratios in different parts of the molecule. Carbon and nitrogen position-specific isotope fractionation, as well as slopes in dual isotope plots, varied linearly with rate constants k(obs) depending on the presence of buffers that mediate the initial zwitterion formation. The correlation can be explained by two consecutive reaction steps (zwitterion formation followed by dimethylamine elimination) each of which has a different kinetic isotope effect and may be rate-limiting. Intrinsic isotope effects for both steps, extracted from our kinetic data using a novel theoretical treatment, agree well with values computed from density functional calculations. Our study therefore demonstrates that more variable isotope fractionation may be observed in simple chemical reactions than commonly thought, but that consistent epsilon or dual isotope slopes may nonetheless be encountered in certain molecular fragments.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  12. Lipid Correction for Carbon Stable Isotope Analysis of Deep-sea Fishes

    EPA Science Inventory

    Lipid extraction is used prior to stable isotope analysis of fish tissues to remove variability in the carbon stable isotope ratio (d13C) caused by varying lipid content among samples. Our objective was to evaluate an application of a mass balance correction for the effect of lip...

  13. Spatial and Temporal Trends in Stable Carbon and Oxygen Isotope Ratios of Juvenile Winter Flounder

    EPA Science Inventory

    Isotopic ratios of fish otoliths have been used in numerous studies as natural tags or markers to aid the study of connectivity among fish populations. We investigated the use of spatial and temporal changes in the stable carbon and oxygen isotope ratios of otoliths to different...

  14. Soil drying effects on the carbon isotope composition of soil respiration

    EPA Science Inventory

    Stable isotopes are used widely as a tool for determining sources of carbon (C) fluxes in ecosystem C studies. Environmental factors that change over time, such as moisture, can create dynamic changes in the isotopic composition of C assimilated by plants, and offers a unique opp...

  15. Speleothems as proxy for the carbon isotope composition of atmospheric CO2

    NASA Astrophysics Data System (ADS)

    Baskaran, M.; Krishnamurthy, R. V.

    1993-12-01

    We have measured the stable isotope ratios of carbon in a suite of recent cave deposits (less than 200 years) from the San Saba County, Texas, USA. The methodology for dating these deposits using excess Pb-210 was recently established (Baskaran and Iliffe, 1993). The carbon isotope ratios of these samples, spanning the time period approximately 1800-1990 AD, reflect the carbon isotope ratio of atmospheric CO2 for the same period. The pathways by which the delta C-13 of atmospheric CO2 is imprinted on these speleothems can be explained using a model developed by Cerling (1984). The results suggest that the carbon isotope ratios of speleothems can be used to develop long-term, high-resolution chronologies of the delta C-13 of atmospheric CO2 and, by implication, the concentration of the atmospheric CO2.

  16. Late Triassic tropical climate of Pangea: Carbon isotopic and other insights into the rise of dinosaurs

    NASA Astrophysics Data System (ADS)

    Whiteside, J. H.; Lindström, S.; Irmis, R. B.; Glasspool, I.; Schaller, M. F.; Dunlavey, M.; Nesbitt, S. J.; Smith, N. D.; Turner, A. H.

    2015-12-01

    The rarity and species-poor nature of early dinosaurs and their relatives at low paleolatitudes persisted for 30 million years after their origin and 10-15 million years after they became abundant and speciose at higher latitudes. New environmental reconstructions from stable carbon isotope ratios of preserved organic matter (δ13Corg), atmospheric pCO2 data based on the δ13C of soil carbonate, palynological, and wildfire data from charcoal from early dinosaur-bearing strata at low paleolatitudes in western North America show that variations in δ13Corg and palynomorph ecotypes are tightly correlated, displaying large and high-frequency excursions. These variations occurred within an environment characterized by elevated and increasing atmospheric pCO2, pervasive wildfires, and rapidly fluctuating extreme climatic conditions. Whereas pseudosuchian archosaur-dominated communities were able to persist in these same regions until the end-Triassic, the large-bodied, fast-growing tachymetabolic dinosaurian herbivores were not. We hypothesize that the greater resources required by the herbivores made it difficult from them to adapt to the unstable conditions at low paleolatitudes in the Late Triassic.

  17. CARBON ABUNDANCES FOR RED GIANTS IN THE DRACO DWARF SPHEROIDAL GALAXY

    SciTech Connect

    Shetrone, Matthew D.; Stanford, Laura M.; Smith, Graeme H.

    2013-05-15

    Measurements of [C/Fe], [Ca/H], and [Fe/H] have been derived from Keck I LRISb spectra of 35 giants in the Draco dwarf spheroidal galaxy. The iron abundances are derived by a spectrum synthesis modeling of the wavelength region from 4850 to 5375 A, while calcium and carbon abundances are obtained by fitting the Ca II H and K lines and the CH G band, respectively. A range in metallicity of -2.9 {<=} [Fe/H] {<=} -1.6 is found within the giants sampled, with a good correlation between [Fe/H] and [Ca/H]. The great majority of stars in the sample would be classified asmore » having weak absorption in the {lambda}3883 CN band, with only a small scatter in band strengths at a given luminosity on the red giant branch. In this sense the behavior of CN among the Draco giants is consistent with the predominantly weak CN bands found among red giants in globular clusters of metallicity [Fe/H] < -1.8. Over half of the giants in the Draco sample have [Fe/H] > -2.25, and among these there is a trend for the [C/Fe] abundance to decrease with increasing luminosity on the red giant branch. This is a phenomenon that is also seen among both field and globular cluster giants of the Galactic halo, where it has been interpreted as a consequence of deep mixing of material between the base of the convective envelope and the outer limits of the hydrogen-burning shell. However, among the six Draco giants observed that turn out to have metallicities -2.65 < [Fe/H] < -2.25 there is no such trend seen in the carbon abundance. This may be due to small sample statistics or primordial inhomogeneities in carbon abundance among the most metal-poor Draco stars. We identify a potential carbon-rich extremely metal-poor star in our sample. This candidate will require follow-up observations for confirmation.« less

  18. Natural abundance N stable isotopes in plants and soils as an indicator of N deposition hotspots in urban environments

    NASA Astrophysics Data System (ADS)

    Trammell, T. L.

    2017-12-01

    The natural abundance of stable isotopes in plants and soils has been utilized to understand ecological phenomenon. Foliar δ15N is an integrator of soil δ15N, atmospheric N sources, and fractionation processes that occur during plant N uptake, plant N assimilation, and mycorrhizal associations. The amount of reactive N in the environment has greatly increased due to human activities, and urban ecosystems experience excess N deposition that can have cascading effects on plants and soils. Foliar δ15N has been shown to increase with increasing N deposition and nitrification rates suggesting increased foliar δ15N occurs with greater N inputs as a result of accelerated soil N cycling. Thus, foliar δ15N can be an indication of soil N availability for plant uptake and soil N cycling rates, since high N availability results in increased soil N cycling and subsequent loss of 14N. Limited research has utilized foliar and soil δ15N in urban forests to assess the importance of plant uptake of atmospheric N deposition and to gain insight about ecosystem processes. Previous investigations found foliar δ15N of mature trees in urban forests is not only related to elevated pollutant-derived N deposition, but also to soil N availability and soil N cycling rates. Similarly, enriched foliar δ15N of urban saplings was attributed to soil characteristics that indicated higher nitrification, thus, greater nitrate leaching and low N retention in the urban soils. These studies demonstrate the need for measuring the δ15N of various plant and soil N sources while simultaneously measuring soil N processes (e.g., net nitrification rates) in order to use natural abundance δ15N of plants and soils to assess N sources and cycling in urban forests. A conceptual framework that illustrates biogenic and anthropogenic controls on nitrogen isotope composition in urban plants and soils will be presented along with foliar and soil δ15N from urban forests across several cities as a proof of

  19. Freezing and fractionation: effects of preservation on carbon and nitrogen stable isotope ratios of some limnetic organisms.

    PubMed

    Wolf, J Marshall; Johnson, Brett; Silver, Douglas; Pate, William; Christianson, Kyle

    2016-03-15

    Stable isotopes of carbon and nitrogen have become important natural tracers for studying food-web structure and function. Considerable research has demonstrated that chemical preservatives and fixatives shift the isotopic ratios of aquatic organisms. Much less is known about the effects of freezing as a preservation method although this technique is commonly used. We conducted a controlled experiment to test the effects of freezing (-10 °C) and flash freezing (–79 °C) on the carbon and nitrogen isotope ratios of zooplankton (Cladocera), Mysis diluviana and Rainbow Trout (Oncorhynchus mykiss). Subsamples (~0.5 mg) of dried material were analyzed for percentage carbon, percentage nitrogen, and the relative abundance of stable carbon and nitrogen isotopes (δ13C and δ15N values) using a Carlo Erba NC2500 elemental analyzer interfaced to a ThermoFinnigan MAT Delta Plus isotope ratio mass spectrometer. The effects of freezing were taxon-dependent. Freezing had no effect on the isotopic or elemental values of Rainbow Trout muscle. Effects on the δ13C and δ15N values of zooplankton and Mysis were statistically significant but small relative to typical values of trophic fractionation. The treatment-control offsets had larger absolute values for Mysis (δ13C: ≤0.76 ± 0.41‰, δ15N: ≤0.37 ± 0.16‰) than for zooplankton (δ13C: ≤0.12 ± 0.06‰, δ15N: ≤0.30 ± 0.27‰). The effects of freezing were more variable for the δ13C values of Mysis, and more variable for the δ15N values of zooplankton. Generally, both freezing methods reduced the carbon content of zooplankton and Mysis, but freezing had a negative effect on the %N of zooplankton and a positive effect on the %N of Mysis. The species-dependencies and variability of freezing effects on aquatic organisms suggest that more research is needed to understand the mechanisms responsible for freezing-related fractionation before standardized protocols for freezing as a preservation method can be adopted.

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

    NASA Astrophysics Data System (ADS)

    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

  1. Fractionation of carbon (13C/12C) isotopes in glycine decarboxylase reaction.

    PubMed

    Ivlev, A A; Bykova, N V; Igamberdiev, A U

    1996-05-20

    Fractionation of carbon isotopes (13C/12C) by glycine decarboxylase (GDC) was investigated in mitochondrial preparations isolated from photosynthetic tissues of different plants (Pisum, Medicago, Triticum, Hordeum, Spinacia, Brassica, Wolffia). 20 mM glycine was supplied to mitochondria, and the CO2 formed was absorbed and analyzed for isotopic content. CO2 evolved by mitochondria of Pisum was enriched up to 8% in 12C compared to the carboxylic atom of glycine. CO2 evolved by mitochondria of the other plants investigated was enriched by 5-16% in 13C. Carbon isotope effects were sensitive to reaction conditions (pH and the presence of GDC cofactors). Theoretical treatment of the reaction mechanism enabled us to conclude that the value and even the sign of the carbon isotope effect in glycine decarboxylation depend on the contribution of the enzyme-substrate binding step and of the decarboxylation step itself to the overall reaction rate. Therefore, the fractionation of carbon isotopes in GDC reaction was revealed which provides essential isotopic effects in plants in addition to the well-known effect of carbon isotope fractionation by the central photosynthetic enzyme, ribulose-1,5-biphosphate carboxylase.

  2. Sulfur and carbon isotope biogeochemistry of a rewetted brackish fen

    NASA Astrophysics Data System (ADS)

    Koebsch, Franziska; Gehre, Matthias; Winkel, Matthias; Koehler, Stefan; Koch, Marian; Jurasinski, Gerald; Spitzy, Alejandro; Liebner, Susanne; Sachs, Torsten; Schmiedinger, Iris; Kretzschmann, Lisett; Saborowski, Anke; Böttcher, Michael E.

    2015-04-01

    Coastal wetlands are at the interface between terrestrial freshwater and marine and exhibit very specific biogeochemical conditions. Intermittent sea water intrusion affects metabolic pathways, i. e. anaerobic carbon metabolism is progressively dominated by sulfate reduction with lower contribution of methanogenesis whilst methane production is increasingly shifted from acetoclastic to hydrogenotrophic. Due to expanding anthropogenic impact a large proportion of coastal ecosystems is degraded with severe implications for the biogeochemical processes. We use concentration patterns and stable isotope signatures of water, sulfate, dissolved carbonate, and methane (δ2H, δ13C, δ18O, δ34S) to investigate the S and C metabolic cycle in a rewetted fen close to the southern Baltic Sea border. Such studies are crucial to better predict dynamic ecosystem feedback to global change like organic matter (OM) decomposition or greenhouse gas emissions. Yet, little is known about the metabolic pathways in such environments. The study site is part of the TERENO Observatory "Northeastern German Lowlands' and measurements of methane emissions have run since 2009. High methane fluxes up to 800 mg m-2 hr-1 indicate that methanogenesis is the dominant C metabolism pathway despite of high sulfate concentrations (up to 37 mM). The presented data are part of a comprehensive biogeochemical investigation that we conducted in autumn 2014 and that comprises 4 pore water profiles and sediment samples within a transect of 300-1500 m distance to the Baltic Sea. Depth of organic layers ranged from 25 to 140 cm with high OM contents (up to 90 dwt.%). Sulfate/chloride ratios in the pore waters were lower than in the Baltic Sea for most sites and sediment depths indicated a substantial net sulfate loss. Sulfide concentrations were negligible at the top and increased parallel to the sulfate concentrations with depth to values of up to 0.3 mM. One pore water profiles situated 1150 m from the Baltic

  3. Autotrophic and heterotrophic acquisition of carbon and nitrogen by a mixotrophic chrysophyte established through stable isotope analysis

    PubMed Central

    Terrado, Ramon; Pasulka, Alexis L; Lie, Alle A-Y; Orphan, Victoria J; Heidelberg, Karla B; Caron, David A

    2017-01-01

    Collectively, phagotrophic algae (mixotrophs) form a functional continuum of nutritional modes between autotrophy and heterotrophy, but the specific physiological benefits of mixotrophic nutrition differ among taxa. Ochromonas spp. are ubiquitous chrysophytes that exhibit high nutritional flexibility, although most species generally fall towards the heterotrophic end of the mixotrophy spectrum. We assessed the sources of carbon and nitrogen in Ochromonas sp. strain BG-1 growing mixotrophically via short-term stable isotope probing. An axenic culture was grown in the presence of either heat-killed bacteria enriched with 15N and 13C, or unlabeled heat-killed bacteria and labeled inorganic substrates (13C-bicarbonate and 15N-ammonium). The alga exhibited high growth rates (up to 2 divisions per day) only until heat-killed bacteria were depleted. NanoSIMS and bulk IRMS isotope analyses revealed that Ochromonas obtained 84–99% of its carbon and 88–95% of its nitrogen from consumed bacteria. The chrysophyte assimilated inorganic 13C-carbon and 15N-nitrogen when bacterial abundances were very low, but autotrophic (photosynthetic) activity was insufficient to support net population growth of the alga. Our use of nanoSIMS represents its first application towards the study of a mixotrophic alga, enabling a better understanding and quantitative assessment of carbon and nutrient acquisition by this species. PMID:28524870

  4. Autotrophic and heterotrophic acquisition of carbon and nitrogen by a mixotrophic chrysophyte established through stable isotope analysis.

    PubMed

    Terrado, Ramon; Pasulka, Alexis L; Lie, Alle A-Y; Orphan, Victoria J; Heidelberg, Karla B; Caron, David A

    2017-09-01

    Collectively, phagotrophic algae (mixotrophs) form a functional continuum of nutritional modes between autotrophy and heterotrophy, but the specific physiological benefits of mixotrophic nutrition differ among taxa. Ochromonas spp. are ubiquitous chrysophytes that exhibit high nutritional flexibility, although most species generally fall towards the heterotrophic end of the mixotrophy spectrum. We assessed the sources of carbon and nitrogen in Ochromonas sp. strain BG-1 growing mixotrophically via short-term stable isotope probing. An axenic culture was grown in the presence of either heat-killed bacteria enriched with 15 N and 13 C, or unlabeled heat-killed bacteria and labeled inorganic substrates ( 13 C-bicarbonate and 15 N-ammonium). The alga exhibited high growth rates (up to 2 divisions per day) only until heat-killed bacteria were depleted. NanoSIMS and bulk IRMS isotope analyses revealed that Ochromonas obtained 84-99% of its carbon and 88-95% of its nitrogen from consumed bacteria. The chrysophyte assimilated inorganic 13 C-carbon and 15 N-nitrogen when bacterial abundances were very low, but autotrophic (photosynthetic) activity was insufficient to support net population growth of the alga. Our use of nanoSIMS represents its first application towards the study of a mixotrophic alga, enabling a better understanding and quantitative assessment of carbon and nutrient acquisition by this species.

  5. A New Method for Evaluating the Carbon Isotope Characteristics of Carbonate Formed Under Cryogenic Conditions Analogous to Mars

    NASA Technical Reports Server (NTRS)

    Niles, P. B.; Socki, R. A.; Hredzak, P. L.

    2007-01-01

    The two upcoming robotic missions to Mars, Phoenix and MSL, will both have the capability of measuring the carbon isotopic composition of CO2 in the martian atmosphere, as well as possible CO2 trapped in carbonate minerals in the Martian soil. Results from orbital and landed missions now clearly indicate that no large scale deposits of carbonate materials exist at the surface. However, some results from orbital remote sensing have been interpreted to indicate that carbonate minerals are present as fine particles interspersed at low concentrations (approx. 2%) in the martian dust. One likely mechanism for the production of these carbonates is during the freezing of transient water near the surface. Large deposits of near surface ice and photographic evidence for flowing water on the surface suggest that transient melting and refreezing of H2O is an active process on Mars. Any exposure of these fluids to the CO2 rich atmosphere should al-low the production of HCO3- solutions. Carbonates are likely precipitates from these solutions during freezing as extensive CO2 degassing, driven by the fluid s decreasing volume, drives CO2 out. This rapid CO2 degassing increases the pH of the solution and drives carbonate precipitation. It has been shown in previous studies that this rapid CO2 degassing also results in a kinetic isotopic fractionation where the CO2 gas has a much lighter isotopic composition causing a large isotope enrichment of C-13 in the precipitated carbonate. This kinetic isotope enrichment may be very common in the current martian environment, and may be a very important factor in understanding the very high deltaC-13 values of carbonates found in the martian meteorites. However, while previous studies have succeeded in generally quantifying the magnitude of this effect, detailed studies of the consistency of this effect, and the freezing rates needed to produce it are needed to understand any carbon isotope analyses from carbonate minerals in the martian

  6. The linkage between nutrient supply, intracellular enzyme abundances and bacterial growth: New evidences from the central carbon metabolism of Corynebacterium glutamicum.

    PubMed

    Noack, Stephan; Voges, Raphael; Gätgens, Jochem; Wiechert, Wolfgang

    2017-09-20

    Corynebacterium glutamicum serves as important production host for small molecular compounds that are derived from precursor molecules of the central carbon metabolism. It is therefore a well-studied model organism of industrial biotechnology. However, a deeper understanding of the regulatory principles underlying the synthesis of central metabolic enzymes under different environmental conditions as well as its impact on cell growth is still missing. We studied enzyme abundances in C. glutamicum in response to growth on: (i) one limiting carbon source by sampling chemostat and fed-batch cultivations and (ii) changing carbon sources provided in excess by sampling batch cultivations. The targeted quantification of 20 central metabolic enzymes by isotope dilution mass spectrometry revealed that cells maintain stable enzyme concentrations when grown on d-glucose as single carbon and energy source and, most importantly, independent of its availability. By contrast, switching from d-glucose to d-fructose, d-mannose, d-arabitol, acetate, l-lactate or l-glutamate results in highly specific enzyme regulation patterns that can partly be explained by the activity of known transcriptional regulators. Based on these experimental results we propose a simple framework for modeling cell population growth as a nested function of nutrient supply and intracellular enzyme abundances. In summary, our study extends the basis for the formulation of predictive mechanistic models of bacterial growth, applicable in industrial bioprocess development. Copyright © 2017 Elsevier B.V. All rights reserved.

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

    NASA Astrophysics Data System (ADS)

    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

  8. Carbon allocation belowground in Pinus pinaster using stable carbon isotope pulse labeling technique

    NASA Astrophysics Data System (ADS)

    Dannoura, M.; Bosc, A.; Chipeaux, C.; Sartore, M.; Lambrot, C.; Trichet, P.; Bakker, M.; Loustau, D.; Epron, D.

    2010-12-01

    Carbon allocation belowground competes with aboveground growth and biomass production. In the other hand, it contributes to resource acquisition such as nutrient, water and carbon sequestration in soil. Thus, a better characterization of carbon flow from plant to soil and its residence time within each compartment is an important issue for understanding and modeling forest ecosystem carbon budget. 13C pulse labeling of whole crown was conducted at 4 seasons to study the fate of assimilated carbon by photosynthesis into the root on 12 year old Pinus pinaster planted in the INRA domain of Pierroton. Maritime pine is the most widely planted species in South-West Europe. Stem, root and soil CO2 effluxes and their isotope composition were measured continuously by tunable diode laser absorption spectroscopy with a trace gas analyzer (TGA 100A; Campbell Scientific) coupled to flow-through chambers. 13CO2 recovery and peak were observed in respiration of each compartment after labeling. It appeared sequentially from top of stem to bottom, and to coarse root. The maximum velocity of carbon transfer was calculated as the difference in time lag of recovery between two positions on the trunk or on the root. It ranged between 0.08-0.2 m h-1 in stem and between 0.04-0.12 m h-1 in coarse root. This velocity was higher in warmer season, and the difference between time lag of recovery and peak increased after first frost. Photosynthates arrived underground 1.5 to 5 days after labeling, at similar time in soil CO2 effluxes and coarse root respiration. 0.08-1.4 g of carbon was respired per tree during first 20 days following labeling. It presented 0.6 -10% of 13C used for labeling and it is strongly related to seasons. The isotope signal was detected in fine root organs and microbial biomass by periodical core sampling. The peak was observed 6 days after labeling in early summer while it was delayed more than 10 days in autumn and winter with less amount of carbon allocated

  9. USE OF THE COMPOSITION AND STABLE CARBON ISOTOPE RATIO OF MICROBIAL FATTY ACIDS TO STUDY CARBON CYCLING

    EPA Science Inventory

    We use measurements of the concentration and stable carbon isotopic ratio (Gamma 13C) of individual microbial phospholipid fatty acids (PLFAS) in soils and sediments as indicators of live microbial biomass levels and microbial carbon source. For studies of soil organic matter (SO...

  10. USE OF STABLE CARBON ISOTOPE RATIOS OF FATTY ACIDS TO EVALUATE MICROBIAL CARBON SOURCES IN TERRESTRIAL ENVIRONMENTS

    EPA Science Inventory

    We use measurements of the concentration and stable carbon isotopic ratio (D 13C) of individual microbial phospholipid fatty acids (PLFAs) in soils as indicators of live microbial biomass levels and microbial carbon source. We found that intensive sugar cane cultivation leads to ...

  11. PRODUCTION AND TRANSPORT OF CARBON DIOXIDE IN A CONTAMINATED VADOSE ZONE: A STABLE AND RADIOACTIVE CARBON ISOTOPE STUDY

    EPA Science Inventory

    Analyses of soil gas compositions and stable and radioactive carbon isotopes in the vadose zone above an alluvial aquifer were conducted at an organic solvent disposal site in southeast Phoenix, AZ. The study investigated the source and movement of carbon dioxide above a plume of...

  12. Dual-Carbon sources fuel the OCS deep-reef Community, a stable isotope investigation

    USGS Publications Warehouse

    Sulak, Kenneth J.; Berg, J.; Randall, Michael T.; Dennis, George D.; Brooks, R.A.

    2008-01-01

    The hypothesis that phytoplankton is the sole carbon source for the OCS deep-reef community (>60 m) was tested. Trophic structure for NE Gulf of Mexico deep reefs was analyzed via carbon and nitrogen stable isotopes. Carbon signatures for 114 entities (carbon sources, sediment, fishes, and invertebrates) supported surface phytoplankton as the primary fuel for the deep reef. However, a second carbon source, the macroalga Sargassum, with its epiphytic macroalgal associate, Cladophora liniformis, was also identified. Macroalgal carbon signatures were detected among 23 consumer entities. Most notably, macroalgae contributed 45 % of total carbon to the 13C isotopic spectrum of the particulate-feeding reef-crest gorgonian Nicella. The discontinuous spatial distribution of some sessile deep-reef invertebrates utilizing pelagic macroalgal carbon may be trophically tied to the contagious distribution of Sargassum biomass along major ocean surface features.

  13. GasBench/isotope ratio mass spectrometry: a carbon isotope approach to detect exogenous CO(2) in sparkling drinks.

    PubMed

    Cabañero, Ana I; San-Hipólito, Tamar; Rupérez, Mercedes

    2007-01-01

    A new procedure for the determination of carbon dioxide (CO(2)) (13)C/(12)C isotope ratios, using direct injection into a GasBench/isotope ratio mass spectrometry (GasBench/IRMS) system, has been developed to improve isotopic methods devoted to the study of the authenticity of sparkling drinks. Thirty-nine commercial sparkling drink samples from various origins were analyzed. Values of delta(13)C(cava) ranged from -20.30 per thousand to -23.63 per thousand, when C3 sugar addition was performed for a second alcoholic fermentation. Values of delta(13)C(water) ranged from -5.59 per thousand to -6.87 per thousand in the case of naturally carbonated water or water fortified with gas from the spring, and delta(13)C(water) ranged from -29.36 per thousand to -42.09 per thousand when industrial CO(2) was added. It has been demonstrated that the addition of C4 sugar to semi-sparkling wine (aguja) and industrial CO(2) addition to sparkling wine (cava) or water can be detected. The new procedure has advantages over existing methods in terms of analysis time and sample treatment. In addition, it is the first isotopic method developed that allows (13)C/(12)C determination directly from a liquid sample without previous CO(2) extraction. No significant isotopic fractionation was observed nor any influence by secondary compounds present in the liquid phase. Copyright (c) 2007 John Wiley & Sons, Ltd.

  14. [A review of water and carbon flux partitioning and coupling in SPAC using stable isotope techniques].

    PubMed

    Xu, Xiao Wu; Yu, Xin Xiao; Jia, Guo Dong; Li, Han Zhi; Lu, Wei Wei; Liu, Zi Qiang

    2017-07-18

    Soil-vegetation-atmosphere continuum (SPAC) is one of the important research objects in the field of terrestrial hydrology, ecology and global change. The process of water and carbon cycling, and their coupling mechanism are frontier issues. With characteristics of tracing, integration and indication, stable isotope techniques contribute to the estimation of the relationship between carbon sequestration and water consumption in ecosystems. In this review, based on a brief introduction of stable isotope principles and techniques, the applications of stable isotope techniques to water and carbon exchange in SPAC using optical stable isotope techniques were mainly explained, including: partitioning of net carbon exchange into photosynthesis and respiration; partitioning of evapotranspiration into transpiration and evaporation; coupling of water and carbon cycle at the ecosystem scale. Advanced techniques and methods provided long-term and high frequency measurements for isotope signals at the ecosystem scale, but the issues about the precision and accuracy for measurements, partitioning of ecosystem respiration, adaptability for models under non-steady state, scaling up, coupling mechanism of water and carbon cycles, were challenging. The main existing research findings, limitations and future research prospects were discussed, which might help new research and technology development in the field of stable isotope ecology.

  15. Tectonic controls on the long-term carbon isotope mass balance.

    PubMed

    Shields, Graham A; Mills, Benjamin J W

    2017-04-25

    The long-term, steady-state marine carbon isotope record reflects changes to the proportional burial rate of organic carbon relative to total carbon on a global scale. For this reason, times of high δ 13 C are conventionally interpreted to be oxygenation events caused by excess organic burial. Here we show that the carbon isotope mass balance is also significantly affected by tectonic uplift and erosion via changes to the inorganic carbon cycle that are independent of changes to the isotopic composition of carbon input. This view is supported by inverse covariance between δ 13 C and a range of uplift proxies, including seawater 87 Sr/ 86 Sr, which demonstrates how erosional forcing of carbonate weathering outweighs that of organic burial on geological timescales. A model of the long-term carbon cycle shows that increases in δ 13 C need not be associated with increased organic burial and that alternative tectonic drivers (erosion, outgassing) provide testable and plausible explanations for sustained deviations from the long-term δ 13 C mean. Our approach emphasizes the commonly overlooked difference between how net and gross carbon fluxes affect the long-term carbon isotope mass balance, and may lead to reassessment of the role that the δ 13 C record plays in reconstructing the oxygenation of earth's surface environment.

  16. Tectonic controls on the long-term carbon isotope mass balance

    PubMed Central

    Mills, Benjamin J. W.

    2017-01-01

    The long-term, steady-state marine carbon isotope record reflects changes to the proportional burial rate of organic carbon relative to total carbon on a global scale. For this reason, times of high δ13C are conventionally interpreted to be oxygenation events caused by excess organic burial. Here we show that the carbon isotope mass balance is also significantly affected by tectonic uplift and erosion via changes to the inorganic carbon cycle that are independent of changes to the isotopic composition of carbon input. This view is supported by inverse covariance between δ13C and a range of uplift proxies, including seawater 87Sr/86Sr, which demonstrates how erosional forcing of carbonate weathering outweighs that of organic burial on geological timescales. A model of the long-term carbon cycle shows that increases in δ13C need not be associated with increased organic burial and that alternative tectonic drivers (erosion, outgassing) provide testable and plausible explanations for sustained deviations from the long-term δ13C mean. Our approach emphasizes the commonly overlooked difference between how net and gross carbon fluxes affect the long-term carbon isotope mass balance, and may lead to reassessment of the role that the δ13C record plays in reconstructing the oxygenation of earth’s surface environment. PMID:28396434

  17. Petro-structural, geochemical and carbon and oxygen isotopic study on carbonates crosscuting the Oman Ophiolite peridotites: evidence of polygenic CO2 trapping

    NASA Astrophysics Data System (ADS)

    Noël, J.; Godard, M.; Martinez, I.; Oliot, E.; Williams, M. J.; Rodriguez, O.; Chaduteau, C.; Gouze, P.

    2017-12-01

    Carbon trapping in ophiolitic peridotites contributes to the global carbon cycle between solid Earth and its outer envelopes (through subduction and/or modern alteration). To investigate this process, we performed petro-structural (microtomography, EBSD, EPMA) and geochemical studies (LA-ICP-MS, carbon and oxygen isotopes on bulk and minerals using SHRIMP) of harzburgites cored in the Oman Ophiolite. Studied harzburgites are highly serpentinized (> 90 %) and crosscut by 3 generations of carbonates (> 20 Vol%) with compositions from calcite to dolomite (Mg/Ca = 0-0.85). Type 1 carbonates are fine penetrative veinlets and mesh core after olivine. They have low REE (e.g., Yb = 0.08-0.23 x CI-chondrite) and negative Ce anomalies. They have δ13CPDB = -15.2 to 1.10‰ and δ18OSMOW = 17.5 to 33.7‰, suggesting precipitation temperatures up to 110°C. Type 2 carbonates are pluri-mm veins bounded by cm-thick serpentinized vein selvages, oriented dominantly parallel to mantle foliation. Dynamic recrystallization is observed, indicating polygenetic formation: well crystallized calcite with REE abundances similar to Type 1 carbonates are locally replaced by small dolomite and calcite grains with higher REE (e.g., Yb = 0.35-1.0 x CI-chondrite) and positive Gd anomaly. Type 2 carbonates have δ13CPDB = -12.6 to -4.1‰ and δ18OSMOW = 25.0 to 32.7‰, suggesting precipitation temperatures from 10 to 60°C. Type 3 carbonates are late pluri-mm to cm veins reactivating Type 2 veins. They consist of small grains of dolomite and calcite with REE abundances similar to recrystallized Type 2 carbonates. Type 3 carbonates have δ13CPDB = -8.3 to -5.8‰ and δ18OSMOW = 28.8 to 32.7‰, suggesting precipitation temperatures <35°C. δ13C data indicate an evolution of fluid composition precipitating carbonates from seawater- and sediment-derived fluids to meteoric water. Carbonate formation starts during oceanic lithospheric cooling and occurs as a penetrative process at the expense of

  18. Carbonate clumped isotopes and in situ temperature monitoring for Holocene soils in the San Luis Valley, USA indicate springtime carbonate formation

    NASA Astrophysics Data System (ADS)

    Hudson, A. M.; Paces, J. B.; Ruleman, C.

    2017-12-01

    Pedogenic carbonate horizons are abundant in semi-arid and arid regions worldwide and within the geologic record. They present a widely distributed archive of past environmental conditions, driven by global climate or tectonically-controlled elevation changes. Oxygen and carbon isotopes in calcite-rich nodules and clast rinds are widely-applied indicators of past soil water and CO2 composition linked to changing precipitation and plant communities. The temperature of carbonate formation, however, provides key constraint on past water/CO2 values and elucidate why they may have changed in the past. Clumped isotope thermometry can provide this constraint and additional climate information, given the carbonate forming system is well understood. We present preliminary clumped isotope (Δ47) temperatures for Holocene soil carbonates, constrained by 14C and U-Th disequilibrium dating, compared with two years of in situ soil temperature data to better understand the mechanism and seasonality of carbonate formation in the San Luis Valley region of the southern Rocky Mountains. Five temperature-monitoring sites ranging in elevation (1940-2450 m) and latitude (36.2-37.9°N) were installed in a variety of settings (range front, valley center, and canyon). The resulting records show indistinguishable seasonal temperature variations at >60 cm depth. This suggests Δ47 temperatures should be comparable at sites across the region. Temperatures based on Δ47 measurements of Holocene (>1.8 to 11.0 ka BP) carbonates at these sites yield consistent inter-site temperatures of 10±4°C, which are similar to modern springtime soil temperatures at depth. This seasonality matches previous results of isotopic modeling at sites further south along the Rio Grande corridor. Temperatures during March to May show multiple, abrupt warming and cooling cycles on weekly timescales caused by wetting and drying of the soil during spring precipitation events. This may drive carbonate precipitation

  19. Methane flux and carbon isotope composition correlate to shifting plant and microbial communities along a permafrost thaw gradient

    NASA Astrophysics Data System (ADS)

    McCalley, C. K.; Mondav, R.; Chanton, J.; Crill, P. M.; Hodgkins, S. B.; Kim, E.; Rich, V. I.; Wehr, R.; Woodcroft, B. J.; Tyson, G. W.; Saleska, S. R.

    2012-12-01

    Methane flux from high latitude wetlands is a critical component of the global carbon budget and is highly sensitive to climate change, with observed and predicted increases as permafrost thaws. Microorganisms mediate wetland methane cycling, but connections between ecosystem-scale flux and underlying microbial dynamics are poorly understood. To address this gap we used isotopic (laser absorption spectrometry) and molecular (16S rRNA gene amplicon sequencing) techniques in a high latitude (68° N) wetland to investigate the relationship between microbial community composition and methane emissions across a permafrost thaw gradient. The transition from permafrost dominated, well drained palsas, through intermediate thaw sites dominated by Sphagnum spp., to wet sites with no underlying permafrost dominated by Eriophorum angustifolium is associated with substantial increases in methane emission. Across this thaw progression the carbon isotopic composition of emitted methane increased from -79.5 ‰ in the intermediate-thawing site to -66.4 ‰ in the thawed site, indicating a relative shift from CO2-reductive towards acetoclastic methanogenesis. Increases in methane flux under thaw were correlated with increasing abundance of methane-producing archaeal clades and increases in methane isotopic composition were associated with shifts in the archaeal community. While CO2 reducing methanogens were found throughout thawing and thawed sites, methanogens of the Methanosarcina (the order of Archaea that contains all known acetoclastic methanogens) were most associated with the fully thawed site. These results directly link microbial community composition to ecosystem scale changes in the magnitude and isotopic composition of methane emissions under permafrost thaw. If isotopic shifts of this magnitude are characteristic of methane dynamics under permafrost loss they should also become detectable in global atmospheric methane observations, providing a global scale tracer of

  20. Geochemically distinct carbon isotope distributions in Allochromatium vinosum DSM 180T grown photoautotrophically and photoheterotrophically.

    PubMed

    Tang, T; Mohr, W; Sattin, S R; Rogers, D R; Girguis, P R; Pearson, A

    2017-03-01

    Anoxygenic, photosynthetic bacteria are common at redox boundaries. They are of interest in microbial ecology and geosciences through their role in linking the carbon, sulfur, and iron cycles, yet much remains unknown about how their flexible carbon metabolism-permitting either autotrophic or heterotrophic growth-is recorded in the bulk sedimentary and lipid biomarker records. Here, we investigated patterns of carbon isotope fractionation in a model photosynthetic sulfur-oxidizing bacterium, Allochromatium vinosum DSM180 T . In one treatment, A. vinosum was grown with CO 2 as the sole carbon source, while in a second treatment, it was grown on acetate. Different intracellular isotope patterns were observed for fatty acids, phytol, individual amino acids, intact proteins, and total RNA between the two experiments. Photoautotrophic CO 2 fixation yielded typical isotopic ordering for the lipid biomarkers: δ 13 C values of phytol > n-alkyl lipids. In contrast, growth on acetate greatly suppressed intracellular isotopic heterogeneity across all molecular classes, except for a marked 13 C-depletion in phytol. This caused isotopic "inversion" in the lipids (δ 13 C values of phytol < n-alkyl lipids). The finding suggests that inverse δ 13 C patterns of n-alkanes and pristane/phytane in the geologic record may be at least in part a signal for photoheterotrophy. In both experimental scenarios, the relative isotope distributions could be predicted from an isotope flux-balance model, demonstrating that microbial carbon metabolisms can be interrogated by combining compound-specific stable isotope analysis with metabolic modeling. Isotopic differences among molecular classes may be a means of fingerprinting microbial carbon metabolism, both in the modern environment and the geologic record. © 2017 John Wiley & Sons Ltd.

  1. Using stable isotopes of carbon to investigate the seasonal variation of carbon transfer in a northwestern Arkansas cave

    USGS Publications Warehouse

    Knierim, Katherine J.; Pollock, Erik; Hays, Phillip D.; Khojasteh, Jam

    2015-01-01

    Stable-isotope analyses are valuable in karst settings, where characterizing biogeochemical cycling of carbon along groundwater flow paths is critical for understanding and protecting sensitive cave and karst water resources. This study quantified the seasonal changes in concentration and isotopic composition (δ13C) of aqueous and gaseous carbon species—dissolved inorganic carbon (DIC) and gaseous carbon dioxide (CO2)—to characterize sources and transfer of these species along a karst flow path, with emphasis on a cave environment. Gas and water samples were collected from the soil and a cave in northwestern Arkansas approximately once a month for one year to characterize carbon cycling along a conceptual groundwater flow path. In the soil, as the DIC concentration increased, the isotopic composition of the DIC became relatively lighter, indicating an organic carbon source for a component of the DIC and corroborating soil DIC as a proxy for soil respiration. In the cave, a positive correlation between DIC and surface temperature was due to increased soil respiration as the organic carbon signal from the soil was transferred to the cave environment via the aqueous phase. CO2 concentration was lowest in the cave during colder months and increased exponentially with increasing surface temperature, presumably due to higher rates of soil respiration during warmer periods and changing ventilation patterns between the surface and cave atmosphere. Isotopic disequilibrium between CO2 and DIC in the cave was greatest when CO2 concentration was changing during November/ December and March/April, presumably due to the rapid addition or removal of gaseous CO2. The isotopic disequilibrium between DIC and CO2 provided evidence that cave CO2 was a mixture of carbon from several sources, which was mostly constrained by mixture between atmospheric CO2 and soil CO2. The concentration and isotopic composition of gaseous and aqueous carbon species were controlled by month

  2. Photospheric carbon and oxygen abundances of F-G type stars in the Pleiades cluster*

    NASA Astrophysics Data System (ADS)

    Takeda, Yoichi; Hashimoto, Osamu; Honda, Satoshi

    2017-02-01

    In order to investigate the carbon-to-oxygen ratio of the young open cluster M 45 (Pleiades), the C and O abundances of 32 selected F-G type dwarfs (in the effective temperature range of Teff ˜ 5800-7600 K and projected rotational velocity range of vesin i ˜ 10-110 km s-1) belonging to this cluster were determined by applying the synthetic spectrum-fitting technique to C i 5380 and O i 6156-8 lines. The non-local thermodynamical equilibrium corrections for these C i and O i lines were found to be practically negligible (less than a few hundredths dex).The resulting C and O abundances (along with the Fe abundance) turned out nearly uniform without any systematic dependence upon Teff or vesin i. We found, however, in spite of almost solar Fe abundance ([Fe/H] ˜ 0), carbon turned out to be slightly subsolar ([C/H] ˜ -0.1) while that of oxygen was slightly supersolar ([O/H] ˜ +0.1). This leads to a conclusion that the [C/O] ratio was moderately subsolar (˜ -0.2) in the primordial gas from which these Pleiades stars were formed ˜ 120-130 Myr ago. Interestingly, similarly young B-type stars are reported to show just the same result ([C/O] ˜ -0.2), while rather aged (˜ 1-10 Gyr) field F-G stars of near-solar metallicity yield almost the solar value ([C/O] ˜ 0) on average. Such a difference in the C/O ratio between two star groups of distinctly different ages may be explained as a consequence of the orbit migration mechanism which Galactic stars may undergo over a long time.

  3. Organic carbon isotope constraints on the dissolved organic carbon (DOC) reservoir at the Cryogenian-Ediacaran transition

    NASA Astrophysics Data System (ADS)

    Jiang, Ganqing; Wang, Xinqiang; Shi, Xiaoying; Zhang, Shihong; Xiao, Shuhai; Dong, Jin

    2010-10-01

    Prominent negative carbonate carbon isotope (δ 13C carb) anomalies from some Ediacaran successions are accompanied by invariant or decoupled organic carbon isotope (δ 13C org) values and have been interpreted as resulting from the remineralization of a large dissolved organic carbon (DOC) reservoir capable of buffering carbon isotopes of organic matter. This inferred oceanic DOC reservoir was thought to have initiated with the onset of Cryogenian glaciations (ca. 720 Ma) and lasted for millions of years until the late Ediacaran Period (< 560 Ma). Carbon isotope analyses of the basal Doushantuo Formation (ca. 635 Ma) in south China reveal that (1) the cap carbonate has δ 13C org around -26‰ (VPDB) and relatively low Δδ 13C (22 ± 2‰) and (2) the overlying organic-rich black shale and shaly dolostone have more negative δ 13C org (-28‰ to -35‰) and higher Δδ 13C (28‰-30‰). Both δ 13C carb and δ 13C org show a + 6‰ shift within a 4-m-thick interval overlying the Doushantuo cap carbonate. The δ 13C org values of the cap carbonate are associated with low TOC (mostly < 0.1%); their paleoceanographic significance requires further tests in other Ediacaran basins. The co-varying positive shift in δ 13C carb and δ 13C org following cap carbonate deposition is best interpreted as resulting from a rapid increase in organic carbon burial, which may have resulted in the rise of oxygen and heralded the first appearance of animals a few meters above the Doushantuo cap carbonate. The data suggest that a large oceanic DOC reservoir did not exist in the early Ediacaran ocean. Excess oceanic DOC required to explain the Ediacaran Shuram and upper Doushantuo δ 13C excursions, if it existed, had to be developed during the Ediacaran Period after cap carbonate deposition.

  4. CARBON AND OXYGEN ISOTOPIC RATIOS FOR NEARBY MIRAS

    SciTech Connect

    Hinkle, Kenneth H.; Lebzelter, Thomas; Straniero, Oscar, E-mail: khinkle@noao.edu, E-mail: thomas.lebzelter@univie.ac.at, E-mail: straniero@oa-teramo.inaf.it

    2016-07-01

    Carbon and oxygen isotopic ratios are reported for a sample of 46 Mira and SRa-type variable asymptotic giant branch (AGB) stars. Vibration–rotation first and second-overtone CO lines in 1.5–2.5 μ m spectra were measured to derive isotopic ratios for {sup 12}C/{sup 13}C, {sup 16}O/{sup 17}O, and {sup 16}O/{sup 18}O. Comparisons with previous measurements for individual stars and with various samples of evolved stars, as available in the extant literature, are discussed. Models for solar composition AGB stars of different initial masses are used to interpret our results. We find that the majority of M-stars have main sequence masses ≤2 Mmore » {sub ⊙} and have not experienced sizable third dredge-up (TDU) episodes. The progenitors of the four S-type stars in our sample are slightly more massive. Of the six C-stars in the sample three have clear evidence relating their origin to the occurrence of TDU. Comparisons with O-rich presolar grains from AGB stars that lived before the formation of the solar system reveal variations in the interstellar medium chemical composition. The present generation of low-mass AGB stars, as represented by our sample of long period variables (LPVs), shows a large spread of {sup 16}O/{sup 17}O ratios, similar to that of group 1 presolar grains and in agreement with theoretical expectations for the composition of mass 1.2–2 M {sub ⊙} stars after the first dredge-up. In contrast, the {sup 16}O/{sup 18}O ratios of present-day LPVs are definitely smaller than those of group 1 grains. This is most probably a consequence of the the decrease with time of the {sup 16}O/{sup 18}O ratio in the interstellar medium due to the chemical evolution of the Milky Way. One star in our sample has an O composition similar to that of group 2 presolar grains originating in an AGB star undergoing extra-mixing. This may indicate that the extra-mixing process is hampered at high metallicity, or, equivalently, favored at low metallicity. Similarly to

  5. The synthesis of a tritium, carbon-14, and stable isotope-labeled cathepsin C inhibitors.

    PubMed

    Allen, Paul; Bragg, Ryan A; Caffrey, Moya; Ericsson, Cecilia; Hickey, Michael J; Kingston, Lee P; Elmore, Charles S

    2017-02-01

    As part of a medicinal chemistry program aimed at developing a highly potent and selective cathepsin C inhibitor, tritium, carbon-14, and stable isotope-labeled materials were required. The synthesis of tritium-labeled methanesulfonate 5 was achieved via catalytic tritiolysis of a chloro precursor, albeit at a low radiochemical purity of 67%. Tritium-labeled AZD5248 was prepared via a 3-stage synthesis, utilizing amide-directed hydrogen isotope exchange. Carbon-14 and stable isotope-labeled AZD5248 were successfully prepared through modifications of the medicinal chemistry synthetic route, enabling the use of available labeled intermediates. Copyright © 2016 John Wiley & Sons, Ltd.

  6. Petrography and stable isotope geochemistry of Oligocene-Miocene continental carbonates in south Texas: Implications for paleoclimate and paleoenvironment near sea-level

    NASA Astrophysics Data System (ADS)

    Godfrey, Conan; Fan, Majie; Jesmok, Greg; Upadhyay, Deepshikha; Tripati, Aradhna

    2018-05-01

    Cenozoic sedimentary rocks in the southern Texas Gulf Coastal Plains contain abundant continental carbonates that are useful for reconstructing terrestrial paleoclimate and paleoenvironment in a region near sea-level. Our field observations and thin section characterizations of the Oligocene and Miocene continental carbonates in south Texas identified three types of pedogenic carbonates, including rhizoliths, carbonate nodules, and platy horizons, and two types of groundwater carbonates, including carbonate-cemented beds and carbonate concretions, with distinctive macromorphologic and micromorphologic features. Based on preservations of authigenic microfabrics and variations of carbon and oxygen isotopic compositions, we suggest these carbonates experienced minimal diagenesis, and their stable isotopic compositions reflect paleoclimate and paleoenvironment in south Texas. Our Oligocene and Miocene carbonate clumped isotope temperatures (T(Δ47)) are 23-28 °C, slightly less than or comparable to the range of modern mean annual and mean warm season air temperature (21-27 °C) in the study area. These T(Δ47) values do not show any dependency on carbonate-type, or trends through time suggesting that groundwater carbonates were formed at shallow depths. These data could indicate that air temperature in south Texas was relatively stable since the early Oligocene. The reconstructed paleo-surface water δ18O values are similar to modern surface water which could indicate that meteoric water δ18O values also remained stable since the early Oligocene. Mean pedogenic carbonate δ13C values increased - 4.6‰ during the late Miocene, most likely reflecting an expansion of C4 grassland in south Texas. This study provides the first mid- and late Cenozoic continental records of paleoclimate and paleoecology in a low-latitude, near sea-level region.

  7. Carbon isotope signature of dissolved inorganic carbon (DIC) in precipitation and atmospheric CO2.

    PubMed

    Górka, Maciej; Sauer, Peter E; Lewicka-Szczebak, Dominika; Jędrysek, Mariusz-Orion

    2011-01-01

    This paper describes results of chemical and isotopic analysis of inorganic carbon species in the atmosphere and precipitation for the calendar year 2008 in Wrocław (SW Poland). Atmospheric air samples (collected weekly) and rainwater samples (collected after rain episodes) were analysed for CO2 and dissolved inorganic carbon (DIC) concentrations and for δ13C composition. The values obtained varied in the ranges: atmospheric CO2: 337-448 ppm; δ13CCO2 from -14.4 to -8.4‰; DIC in precipitation: 0.6-5.5 mg dm(-3); δ13CDIC from -22.2 to +0.2‰. No statistical correlation was observed between the concentration and δ13C value of atmospheric CO2 and DIC in precipitation. These observations contradict the commonly held assumption that atmospheric CO2 controls the DIC in precipitation. We infer that DIC is generated in ambient air temperatures, but from other sources than the measured atmospheric CO2. The calculated isotopic composition of a hypothetical CO2 source for DIC forming ranges from -31.4 to -11.0‰, showing significant seasonal variations accordingly to changing anthropogenic impact and atmospheric mixing processes. Copyright © 2010 Elsevier Ltd. All rights reserved.

  8. Carbon and nitrogen abundance determinations from transition layer lines. [giant stars

    NASA Technical Reports Server (NTRS)

    Boehm-Vitense, Erika; Mena-Werth, Jose

    1988-01-01

    For red giants a smooth increase in the nitrogen to carbon abundance ratio for increasing B-V as is expected for the first dredge up phase when the outer convection zone deepens is found. An average increase in the nitrogen to silicon ratio for B-V = 0.6 which goes back to almost solar values for cool giants with B - V approximately 1.0 is reported. It looks as if Si would be enriched for deeper mixing contrary to expectations from standard evolution theory.

  9. Stable Isotope Measurements of Carbon Dioxide, Methane, and Hydrogen Sulfide Gas Using Frequency Modulation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Nowak-Lovato, K.

    2014-12-01

    Seepage from enhanced oil recovery, carbon storage, and natural gas sites can emit trace gases such as carbon dioxide, methane, and hydrogen sulfide. Trace gas emission at these locations demonstrate unique light stable isotope signatures that provide information to enable source identification of the material. Light stable isotope detection through surface monitoring, offers the ability to distinguish between trace gases emitted from sources such as, biological (fertilizers and wastes), mineral (coal or seams), or liquid organic systems (oil and gas reservoirs). To make light stable isotope measurements, we employ the ultra-sensitive technique, frequency modulation spectroscopy (FMS). FMS is an absorption technique with sensitivity enhancements approximately 100-1000x more than standard absorption spectroscopy with the advantage of providing stable isotope signature information. We have developed an integrated in situ (point source) system that measures carbon dioxide, methane and hydrogen sulfide with isotopic resolution and enhanced sensitivity. The in situ instrument involves the continuous collection of air and records the stable isotope ratio for the gas being detected. We have included in-line flask collection points to obtain gas samples for validation of isotopic concentrations using our in-house isotope ratio mass spectroscopy (IRMS). We present calibration curves for each species addressed above to demonstrate the sensitivity and accuracy of the system. We also show field deployment data demonstrating the capabilities of the system in making live dynamic measurements from an active source.

  10. Early Triassic fluctuations of the global carbon cycle: New evidence from paired carbon isotopes in the western USA basin

    NASA Astrophysics Data System (ADS)

    Caravaca, Gwénaël; Thomazo, Christophe; Vennin, Emmanuelle; Olivier, Nicolas; Cocquerez, Théophile; Escarguel, Gilles; Fara, Emmanuel; Jenks, James F.; Bylund, Kevin G.; Stephen, Daniel A.; Brayard, Arnaud

    2017-07-01

    In the aftermath of the catastrophic end-Permian mass extinction, the Early Triassic records recurrent perturbations in the carbon isotope signal, most notably during the Smithian and through the Smithian/Spathian Boundary (SSB; 1.5 myr after the Permian/Triassic boundary), which show some of the largest excursions of the Phanerozoic. The late Smithian also corresponds to major biotic turnovers and environmental changes, such as temperature fluctuations, that deeply impacted the recovery after the end-Permian mass extinction. Here we document the paired carbon isotope signal along with an analysis of the trace and major elements at the long-known Hot Springs section (southeastern Idaho, USA). This section records Early Triassic sediments from the Griesbachian-Dienerian up to the lower Spathian. We show that the organic and carbonate δ13C variations mirror the signals identified at a global scale. Particularly, the middle Smithian-SSB event represented by a negative-positive isotopic couplet is well identified and is not of diagenetic origin. We also document a positive excursion potentially corresponding to the Dienerian/Smithian Boundary. Observed Smithian-Spathian excursions are recorded similarly in both the organic and carbonate reservoirs, but the organic matter signal systematically shows unexpectedly dampened variations compared to its carbonate counterpart. Additionally, we show that variations in the net isotopic effect (i.e., Δ13C) probably resulted from a complex set of forcing parameters including either a mixing between terrestrial and marine organic matter depending on the evolution of the depositional setting, or variations in the biological fractionation. We establish that the Δ13C signal cannot be directly related to CO2-driven temperature variations at Hot Springs. Even though the carbon isotope signal mirrors the Early Triassic variations known at the global scale, the Hot Springs signal probably also reflects local influences on the carbon

  11. Pico and nanoplankton abundance and carbon stocks along the Brazilian Bight

    PubMed Central

    Lopes dos Santos, Adriana; Marie, Dominique; Helena Pellizari, Vivian; Pereira Brandini, Frederico; Vaulot, Daniel

    2016-01-01

    Pico and nanoplankton communities from the Southwest Atlantic Ocean along the Brazilian Bight are poorly described. The hydrography in this region is dominated by a complex system of layered water masses, which includes the warm and oligotrophic Tropical Water (TW), the cold and nutrient rich South Atlantic Central Water (SACW) and the Coastal Water (CW), which have highly variable properties. In order to assess how pico- and nanoplankton communities are distributed in these different water masses, we determined by flow cytometry the abundance of heterotrophic bacteria, Prochlorococcus, Synechococcus and autotrophic pico and nanoeukaryotes along three transects, extending from 23°S to 31°S and 39°W to 49°W. Heterotrophic bacteria (including archaea, maximum of 1.5 × 106 cells mL−1) were most abundant in Coastal and Tropical Water whereas Prochlorococcus was most abundant in open-ocean oligotrophic waters (maximum of 300 × 103 cells mL−1). Synechococcus(up to 81 × 103 cells mL−1), as well as autotrophic pico and nanoeukaryotes seemed to benefit from the influx of nutrient-rich waters near the continental slope. Autotrophic pico and nanoeukaryotes were also abundant in deep chlorophyll maximum (DCM) layers from offshore waters, and their highest abundances were 20 × 103 cells mL−1 and 5 × 103 cells mL−1, respectively. These data are consistent with previous observations in other marine areas where Synechococcus and autotrophic eukaryotes dominate mesotrophic waters, whereas Prochlorococcus dominate in more oligotrophic areas. Regardless of the microbial community structure near the surface, the carbon stock dominance by autotrophic picoeukaryotes near the DCM is possibly linked to vertical mixing of oligotrophic surface waters with the nutrient-rich SACW and their tolerance to lower light levels. PMID:27867760

  12. Integrated carbon and chlorine isotope modeling: applications to chlorinated aliphatic hydrocarbons dechlorination.

    PubMed

    Jin, Biao; Haderlein, Stefan B; Rolle, Massimo

    2013-02-05

    We propose a self-consistent method to predict the evolution of carbon and chlorine isotope ratios during degradation of chlorinated hydrocarbons. The method treats explicitly the cleavage of isotopically different C-Cl bonds and thus considers, simultaneously, combined carbon-chlorine isotopologues. To illustrate the proposed modeling approach we focus on the reductive dehalogenation of chlorinated ethenes. We compare our method with the currently available approach, in which carbon and chlorine isotopologues are treated separately. The new approach provides an accurate description of dual-isotope effects regardless of the extent of the isotope fractionation and physical characteristics of the experimental system. We successfully applied the new approach to published experimental results on dehalogenation of chlorinated ethenes both in well-mixed systems and in situations where mass-transfer limitations control the overall rate of biodegradation. The advantages of our self-consistent dual isotope modeling approach proved to be most evident when isotope fractionation factors of carbon and chlorine differed significantly and for systems with mass-transfer limitations, where both physical and (bio)chemical transformation processes affect the observed isotopic values.

  13. QUANTIFYING THE CARBON ABUNDANCES IN THE SECONDARY STARS OF SS CYGNI, RU PEGASI, AND GK PERSEI

    SciTech Connect

    Harrison, Thomas E.; Hamilton, Ryan T., E-mail: tharriso@nmsu.edu, E-mail: rthamilton@sofia.usra.edu

    We use a modified version of MOOG to generate large grids of synthetic spectra in an attempt to derive quantitative abundances for three CVs (GK Per, RU Peg, and SS Cyg) by comparing the models to moderate resolution (R ∼ 25,000) K-band spectra obtained with NIRSPEC on Keck. For each of the three systems we find solar, or slightly sub-solar values for [Fe/H], but significant deficits of carbon: for SS Cyg we find [C/Fe] = −0.50, for RU Peg [C/Fe] = −0.75, and for GK Per [C/Fe] = −1.00. We show that it is possible to use lower resolution (Rmore » ∼ 2000) spectra to quantify carbon deficits. We examine realistic veiling scenarios and find that emission from H i or CO cannot reproduce the observations.« less

  14. Carbon isotopic evidence for microbial control of carbon supply to Orca Basin at the seawater-brine interface

    NASA Astrophysics Data System (ADS)

    Shah, S. R.; Joye, S. B.; Brandes, J. A.; McNichol, A. P.

    2013-05-01

    Orca Basin, an intraslope basin on the Texas-Louisiana continental slope, hosts a hypersaline, anoxic brine in its lowermost 200 m in which limited microbial activity has been reported. This brine contains a large reservoir of reduced and aged carbon, and appears to be stable at decadal time scales: concentrations and isotopic composition of dissolved inorganic (DIC) and organic carbon (DOC) are similar to measurements made in the 1970s. Both DIC and DOC are more "aged" within the brine pool than in overlying water, and the isotopic contrast between brine carbon and seawater carbon is much greater for DIC than DOC. While the stable carbon isotopic composition of brine DIC points towards a combination of methane and organic carbon remineralization as its source, radiocarbon and box model results point to the brine interface as the major source region for DIC, allowing for only limited oxidation of methane diffusing upwards from sediments. This conclusion is consistent with previous studies that identify the seawater-brine interface as the focus of microbial activity associated with Orca Basin brine. Isotopic similarities between DIC and DOC suggest a different relationship between these two carbon reservoirs than is typically observed in deep ocean basins. Radiocarbon values implicate the seawater-brine interface region as the likely source region for DOC to the brine as well as DIC.

  15. Water Table Depth Reconstruction in Ombrotrophic Peatlands Using Biomarker Abundance Ratios and Compound-Specific Hydrogen Isotope Composition

    NASA Astrophysics Data System (ADS)

    Nichols, J. E.; Jackson, S. T.; Booth, R. K.; Pendall, E. G.; Huang, Y.

    2005-12-01

    Sediment cores from ombrotrophic peat bogs provide sensitive records of changes in precipitation/evaporation (P/E) balance. Various proxies have been developed to reconstruct surface moisture conditions in peat bogs, including testate amoebae, plant macrofossils, and peat humification. Studying species composition of testate amoeba assemblages is time consuming and requires specialized training. Humification index can be influenced by environmental factors other than moisture balance. The plant macrofossil proxy is less quantitative and cannot be performed on highly decomposed samples. We demonstrate that the ratio of C23 alkane to C29 alkane abundance may provide a simple alternative or complementary means of tracking peatland water-table depth. Data for this proxy can be collected quickly using a small sample (100 mg dry). Water-table depth decreases during drought, and abundance of Sphagnum, the dominant peat-forming genus, decreases as vascular plants increase. Sphagnum moss produces mainly medium chain-length alkanes (C21-C25) while vascular plants (grasses and shrubs) produce primarily longer chain-length alkanes (C27-C31). Therefore, C23:C29 n-alkane ratios quantitatively track the water table depth fluctuations in peat bogs. We compared C23:C29 n-alkane ratios in a core from Minden Bog (southeastern Michigan) with water table depth reconstructions based on testate-amoeba assemblages and humification. The 184-cm core spans the past ~3kyr of continuous peat deposition in the bog. Our results indicate that the alkane ratios closely track the water table depth variations, with C29 most abundant during droughts. We also explored the use of D/H ratios in Sphagnum biomarkers as a water-table depth proxy. Compound-specific hydrogen isotope ratio analyses were performed on Sphagnum biomarkers: C23 and C25 alkane and C24 acid. Dry periods are represented in these records by an enrichment of deuterium in these Sphagnum-specific compounds. These events also correlate

  16. Oxygen and Carbon Isotope Variations in a Modern Rodent Community – Implications for Palaeoenvironmental Reconstructions

    PubMed Central

    Gehler, Alexander; Tütken, Thomas; Pack, Andreas

    2012-01-01

    Background The oxygen (δ18O) and carbon (δ13C) isotope compositions of bioapatite from skeletal remains of fossil mammals are well-established proxies for the reconstruction of palaeoenvironmental and palaeoclimatic conditions. Stable isotope studies of modern analogues are an important prerequisite for such reconstructions from fossil mammal remains. While numerous studies have investigated modern large- and medium-sized mammals, comparable studies are rare for small mammals. Due to their high abundance in terrestrial ecosystems, short life spans and small habitat size, small mammals are good recorders of local environments. Methodology/Findings The δ18O and δ13C values of teeth and bones of seven sympatric modern rodent species collected from owl pellets at a single locality were measured, and the inter-specific, intra-specific and intra-individual variations were evaluated. Minimum sample sizes to obtain reproducible population δ18O means within one standard deviation were determined. These parameters are comparable to existing data from large mammals. Additionally, the fractionation between coexisting carbonate (δ18OCO3) and phosphate (δ18OPO4) in rodent bioapatite was determined, and δ18O values were compared to existing calibration equations between the δ18O of rodent bioapatite and local surface water (δ18OLW). Specific calibration equations between δ18OPO4 and δ18OLW may be applicable on a taxonomic level higher than the species. However, a significant bias can occur when bone-based equations are applied to tooth-data and vice versa, which is due to differences in skeletal tissue formation times. δ13C values reflect the rodents’ diet and agree well with field observations of their nutritional behaviour. Conclusions/Significance Rodents have a high potential for the reconstruction of palaeoenvironmental conditions by means of bioapatite δ18O and δ13C analysis. No significant disadvantages compared to larger mammals were observed. However

  17. Growth versus metabolic tissue replacement in mouse tissues determined by stable carbon and nitrogen isotope analysis

    NASA Astrophysics Data System (ADS)

    Macavoy, S. E.; Jamil, T.; Macko, S. A.; Arneson, L. S.

    2003-12-01

    Stable isotope analysis is becoming an extensively used tool in animal ecology. The isotopes most commonly used for analysis in terrestrial systems are those of carbon and nitrogen, due to differential carbon fractionation in C3 and C4 plants, and the approximately 3‰ enrichment in 15N per trophic level. Although isotope signatures in animal tissues presumably reflect the local food web, analysis is often complicated by differential nutrient routing and fractionation by tissues, and by the possibility that large organisms are not in isotopic equilibrium with the foods available in their immediate environment. Additionally, the rate at which organisms incorporate the isotope signature of a food through both growth and metabolic tissue replacement is largely unknown. In this study we have assessed the rate of carbon and nitrogen isotopic turnover in liver, muscle and blood in mice following a diet change. By determining growth rates, we were able to determine the proportion of tissue turnover caused by growth versus that caused by metabolic tissue replacement. Growth was found to account for approximately 10% of observed tissue turnover in sexually mature mice (Mus musculus). Blood carbon was found to have the shortest half-life (16.9 days), followed by muscle (24.7 days). Liver carbon turnover was not as well described by the exponential decay equations as other tissues. However, substantial liver carbon turnover was observed by the 28th day after diet switch. Surprisingly, these tissues primarily reflect the carbon signature of the protein, rather than carbohydrate, source in their diet. The nitrogen signature in all tissues was enriched by 3 - 5‰ over their dietary protein source, depending on tissue type, and the isotopic turnover rates were comparable to those observed in carbon.

  18. Grasland Stable Isotope Flux Measurements: Three Isotopomers of Carbon Dioxide Measured by QCL Spectroscopy

    NASA Astrophysics Data System (ADS)

    Zeeman, M. J.; Tuzson, B.; Eugster, W.; Werner, R. A.; Buchmann, N.; Emmenegger, L.

    2007-12-01

    To improve our understanding of greenhouse gas dynamics of managed ecosystems such as grasslands, we not only need to investigate the effects of management (e.g., grass cuts) and weather events (e.g., rainy days) on carbon dioxide fluxes, but also need to increase the time resolution of our measurements. Thus, for the first time, we assessed respiration and assimilation fluxes with high time resolution (5Hz) stable isotope measurements at an intensively managed farmland in Switzerland (Chamau, 400m ASL). Two different methods were used to quantify fluxes of carbon dioxide and associated fluxes of stable carbon isotopes: (1) the flux gradient method, and (2) the eddy covariance method. During a week long intensive measurement campaign, we (1) measured mixing ratios of carbon dioxide isotopomers (12C16O2, 12C16O18O, 13C16O2) with a Quantum Cascade Laser (QCL, Aerodyne Inc.) spectroscope and (2) collected air samples for isotope analyses (13C/12C) and (18O/16O) of carbon dioxide by Isotope Ratio Mass Spectrometry (IRMS, Finnigan) every two hours, concurrently along a height profile (z = 0.05; 0.10; 0.31; 2.15m). In the following week, the QCL setup was used for closed-path eddy covariance flux measurement of the carbon dioxide isotopomers, with the air inlet located next to an open-path Infra Red Gas Analyzers (IRGA, LiCor 7500) used simultaneously for carbon dioxide measurements. During this second week, an area of grass inside the footprint was cut and harvested after several days. The first results of in-field continuous QCL measurements of carbon dioxide mixing ratios and their stable isotopic ratios show good agreement with IRGA measurements and isotope analysis of flask samples by IRMS. Thus, QCL spectroscopy is a very promising tool for stable isotope flux investigations.

  19. Fractionation of carbon isotopes by phytoplankton and estimates of ancient CO2 levels

    NASA Technical Reports Server (NTRS)

    Freeman, K. H.; Hayes, J. M.

    1992-01-01

    Reports of the 13C content of marine particulate organic carbon are compiled and on the basis of GEOSECS data and temperatures, concentrations, and isotopic compositions of dissolved CO2 in the waters in which the related phytoplankton grew are estimated. In this way, the fractionation of carbon isotopes during photosynthetic fixation of CO2 is found to be significantly correlated with concentrations of dissolved CO2. Because ancient carbon isotopic fractionations have been determined from analyses of sedimentary porphyrins [Popp et al., 1989], the relationship between isotopic fractionation and concentrations of dissolved CO2 developed here can be employed to estimate concentrations of CO2 dissolved in ancient oceans and, in turn, partial pressures of CO2 in ancient atmospheres. The calculations take into account the temperature dependence of chemical and isotopic equilibria in the dissolved-inorganic-carbon system and of air-sea equilibria. Paleoenvironmental temperatures for each sample are estimated from reconstructions of paleogeography, latitudinal temperature gradients, and secular changes in low-latitude sea surface temperature. It is estimated that atmospheric partial pressures of CO2 were over 1000 micro atm 160 - 100 Ma ago, then declined to values near 300 micro atm during the next 100 Ma. Analysis of a high-resolution record of carbon isotopic fractionation at the Cenomanian-Turonian boundary suggests that the partial pressure of CO2 in the atmosphere was drawn down from values near 840 micro atm to values near 700 micro atm during the anoxic event.

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

    NASA Astrophysics Data System (ADS)

    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.

  1. Determination of nitrogen to carbon abundance ratios from transition layer emission lines

    NASA Technical Reports Server (NTRS)

    Boehm-Vitense, Erika

    1992-01-01

    We have finished studying the nitrogen to carbon abundance ratios for stars with different effective temperatures T(sub eff) and luminosities using transition layer emission lines and using spectra available in the IUE archives. The N/C abundance ratio determinations using transition layer emission lines are as accurate as the photospheric abundance determinations as found by comparison of results obtained by both methods for the same stars. Our measurements confirm photospheric abundance determinations in regions of the HR diagram where they can be obtained. Our studies have extended the temperature range to higher temperatures. They have shown the exact positions in the HR diagram where the mixing due to the outer convection zones reaches deep enough to bring nuclear processed material to the surface. This occurs at effective temperatures which are higher by delta log T(sub eff) approximately 0.04 or roughly 400 K than expected theoretically. Since the depth of the convection zone increases rapidly with decreasing T(sub eff) this may indicate considerable overshoot beyond the lower boundary of the convection zone. Our N/C abundance ratio determinations from transition layer emission lines have confirmed that the actual enrichment observed for some cool giants is larger than expected theoretically, again indicating a larger degree of mixing in several stars either from below or from above. For the supergiants it probably indicates overshoot above the convective core in the progenitor main sequence stars. For the more massive giants this may also be the case, though we did not find a correlation between delta log N/C and the absolute magnitudes, but these are rather uncertain. As byproducts of these studies we also found anomalies in Si/C and N/C abundance ratios for F giants which can be understood as the relict of surface abundance changes for their main sequence progenitors due to diffusion. This anomaly disappears for G giants, for which the depths of the

  2. Partitioning nitrogen losses by natural abundance nitrogen isotope composition in a process-based statistical modelling framework

    NASA Astrophysics Data System (ADS)

    Dong, Ning; Wright, Ian; Prentice, Iain Colin

    2017-04-01

    Natural abundance of the stable isotope 15N is an under-utilized resource for research on the global terrestrial nitrogen cycle. Mass balance considerations suggest that if reactive N inputs have a roughly constant isotopic signature, soil δ15N should be mainly determined by the fraction of N losses by leaching - which barely discriminates against 15N - versus gaseous N losses, which discriminate strongly against 15N. We defined simple process-oriented functions of runoff (frunoff) and soil temperature (ftemp) and investigated the dependencies of soil and foliage δ15N (from global compilations of both types of measurement) on their ratio. Both plant and soil δ15N were found to systematically increase with ftemp/frunoff. Consistent with previous analyses, foliage δ15N was offset (more negative) with respect to soil δ15N, with significant differences in this offset between (from largest to smallest offset) ericoid, ectomycorrhizal, arbuscular mycorrhizal and non-mycorrhizal associated plants. δ15N values tend to be large and positive in the driest environments and to decline as frunoff increases, while also being lower in cold environments and increasing as ftemp increases. The fitted statistical model was used to estimate the gaseous fraction of total N losses from ecosystems (fgas) on a global grid basis. In common with earlier results, the largest values of fgas are predicted in the tropics and semi-arid subtropics. This analysis provides an indirectly estimated global mapping of fgas, which could be used as an improved benchmark for terrestrial nitrogen cycle models.

  3. Stable carbon isotopic compositions of intact polar lipids reveal complex carbon flow patterns among hydrocarbon degrading microbial communities at the Chapopote asphalt volcano

    NASA Astrophysics Data System (ADS)

    Schubotz, Florence; Lipp, Julius S.; Elvert, Marcus; Hinrichs, Kai-Uwe

    2011-08-01

    Seepage of asphalt forms the basis of a cold seep system at 3000 m water depth at the Chapopote Knoll in the southern Gulf of Mexico. Anaerobic microbial communities are stimulated in the oil-impregnated sediments as evidenced by the presence of intact polar membrane lipids (IPLs) derived from archaea and Bacteria at depths up to 7 m below the seafloor. Detailed investigation of stable carbon isotope composition (δ 13C) of alkyl and acyl moieties derived from a range of IPL precursors with distinct polar head groups resolved the complexity of carbon metabolisms and utilization of diverse carbon sources by uncultured microbial communities. In surface sediments most of the polar lipid-derived fatty acids with phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and diphosphatidylglycerol (DPG) head groups could be tentatively assigned to autotrophic sulfate-reducing bacteria, with a relatively small proportion involved in the anaerobic oxidation of methane. Derivatives of phosphatidyl-( N)-methylethanolamine (PME) were abundant and could be predominantly assigned to heterotrophic oil-degrading bacteria. Archaeal IPLs with phosphate-based hydroxyarchaeols and diglycosidic glyceroldibiphytanylglyceroltetraethers (GDGTs) were assigned to methanotrophic archaea of the ANME-2 and ANME-1 cluster, respectively, whereas δ 13C values of phosphate-based archaeols and mixed phosphate-based and diglycosidic GDGTs point to methanogenic archaea. At a 7 m deep sulfate-methane transition zone that is linked to the upward movement of gas-laden petroleum, a distinct increase in abundance of archaeal IPLs such as phosphate-based hydroxyarchaeols and diglycosidic archaeol and GDGTs is observed; their δ 13C values are consistent with their origin from both methanotrophic and methanogenic archaea. This study reveals previously hidden, highly complex patterns in the carbon-flow of versatile microbial communities involved in the degradation of heavy oil including hydrocarbon gases

  4. Carbon isotope fractionation between Fe-carbide and diamond; a light C isotope reservoir in the deep Earth and Core?

    NASA Astrophysics Data System (ADS)

    Mikhail, S.; Jones, A. P.; Hunt, S. A.; Guillermier, C.; Dobson, D. P.; Tomlinson, E.; Dan, H.; Milledge, H.; Franchi, I.; Wood, I.; Beard, A.; Verchovsky, S.

    2010-12-01

    The largest accessible reservoir for terrestrial carbon is the mantle; however the core may yield even more. Carbon is commonly proposed as the light element (or one of) to make up the observed density deficit in the earth’s metallic core (NAKAJIMA et al., 2009). The potential isotopic effects of carbon incorporation into the core have not yet been investigated. In-situ ion probe (nanoSIMS) mapping and imaging of carbon isotope variations across rare sub-mm-scale Fe-rich carbide inclusions in mantle diamond (from Jagersfontein, South Africa) show the carbide to be significantly depleted in 13C relative to their diamond host. Distinctive textures suggest metallic liquid precipitates similar in geometry to (giant) nitrogen platelets, controlled by the octahedral symmetry of diamond, which we interpret as syngenic formation. The difference in δ13C values between the two natural phases for diamond-Fe carbide, gives an isotopic fractionation factor (ΔC) which agrees well with HPHT multi-anvil experiments (5-9 GPa and >1400°C). Our measured ΔC between Fe-carbide and diamond may only have local significance, but the measured isotopic values represent characterization of the highest PT carbide known (i.e. > minimum depth of the diamond stability field ≈ 150 km). The direction and magnitude of ΔC agrees with observations of the ΔC between cohenite-graphite in iron meteorites (DEINES and WICKMAN, 1975) and both agree with HPHT experiments, thus suggesting that carbon in the deep Earth, and particularly in the core, may be similarly fractionated (i.e. depleted in the 13C). Since metallic liquid drained from the silicate mantle to form the core during the early Earth, we can use our values as a proxy to constrain evolution of deep carbon reservoirs such as the core and bulk silicate Earth. For example, we can test the suggestion of Grady et al (2004) that the upper mantle value of δ13C ≈ -5 ‰ may not be representative of the bulk Earth, since solar system

  5. Site-specific equilibrium isotopic fractionation of oxygen, carbon and calcium in apatite

    NASA Astrophysics Data System (ADS)

    Aufort, Julie; Ségalen, Loïc; Gervais, Christel; Paulatto, Lorenzo; Blanchard, Marc; Balan, Etienne

    2017-12-01

    The stable isotope composition of biogenic apatite is an important geochemical marker that can record environmental parameters and is widely used to infer past climates, biomineralization processes, dietary preferences and habitat of vertebrates. In this study, theoretical equilibrium isotopic fractionation of oxygen, carbon and calcium in hydroxyapatite and carbonate-bearing hydroxyapatite is investigated using first-principles methods based on density-functional theory and compared to the theoretical isotopic fractionation properties of calcite, CO2 and H2O. Considering the variability of apatite crystal-chemistry, special attention is given to specific contributions of crystal sites to isotopic fractionation. Significant internal fractionation is calculated for oxygen and carbon isotopes in CO3 between the different structural sites occupied by carbonate groups in apatite (typically 7‰ for both 18O/16O and 13C/12C fractionation at 37 °C). Compared with calcite-water oxygen isotope fractionation, occurrence of A-type substitution in apatite structure, in addition to the main B-type substitution, could explain the larger temperature dependence of oxygen isotope fractionation measured at low temperature between carbonate in apatite and water. Theoretical internal fractionation of oxygen isotopes between carbonate and phosphate in B-type carbonated apatite (∼8‰ at 37 °C) is consistent with experimental values obtained from modern and well-preserved fossil bio-apatites. Concerning calcium, theoretical results suggest a small fractionation between apatite and calcite (-0.17‰ at 37 °C). Internal fractionation reaching 0.8‰ at 37 °C occurs between the two Ca sites in hydroxyapatite. Furthermore, the Ca isotopic fractionation properties of apatite are affected by the occurrence of carbonate groups, which could contribute to the variability observed on natural samples. Owing to the complexity of apatite crystal-chemistry and in light of the theoretical

  6. Carbonate petrography, kerogen distribution, and carbon and oxygen isotope variations in an early Proterozoic transition from limestone to iron-formation deposition, Transvaal Supergroup, South Africa

    NASA Technical Reports Server (NTRS)

    Beukes, N. J.; Klein, C.; Kaufman, A. J.; Hayes, J. M.

    1990-01-01

    sparites are most depleted in 13C. Carbonates in oxide-rich iron-formations are more depleted in 13C than those in siderite-rich iron-formation whereas the kerogens in oxide banded iron-formations (BIF) are more enriched. This implies that the siderite-rich iron-formations were not derived from oxide-rich iron-formation through reduction of ferric iron by organic matter. Organic matter oxidation by ferric iron did, however, decrease the abundance of kerogen in oxide-rich iron-formation and led to the formation of isotopically very light sparry carbonates. Siderite and calcmicrosparite both represent recrystallized primary micritic precipitates but differ in their 13C composition, with the siderites depleted in 13C by 4.6 per mil on average relative to calcmicrosparite. This means that the siderites were precipitated from water with dissolved inorganic carbon depleted in 13C by about 9 per mil relative to that from which the limestones precipitated. This implies an ocean system stratified with regard to total carbonate, with the deeper water, from which siderite-rich iron-formation formed, depleted in 13C. Iron-formations were deposited in areas of very low organic matter supply. Depletion of 13C may, therefore, derive not from degradation of organic matter but from hydrothermal activity, a conclusion which is supported by 18O composition of the carbonate minerals and trace element and rare earth element (REE) compositions of the iron-formations.

  7. Carbon Stable Isotopes as Indicators of Coastal Eutrophication

    EPA Science Inventory

    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...

  8. Light Isotope Abundances in Solar Energetic Particles Measured by the Space Instrument NINA

    NASA Astrophysics Data System (ADS)

    Bakaldin, A.; Galper, A.; Koldashov, S.; Korotkov, M.; Mikhailov, A.; Leonov, V.; Murashov, A.; Voronov, S.; Bidoli, V.; Casolino, M.; De Pascale, M.; Furano, G.; Iannucci, A.; Morselli, A.; Picozza, P.; Sparvoli, R.; Bonvicini, M.; Boezio, V.; Cirami, R.; Vacchi, A.; Zampa, N.; Ambriola, M.; Bellotti, R.; Cafagna, F.; Ciacio, F.; Circella, M.; De Marzo, C.; Adriani, O.; Papini, P.; Piccardi, S.; Spillantini, P.; Straulino, S.; Vannuccini, E.; Bartalucci, S.; Ricci, M.; Castellini, G.

    2002-09-01

    This article reports nine solar energetic particle (SEP) events detected by the New Instrument for Nuclear Analysis (NINA) between 1998 October and 1999 April. NINA is a silicon-based particle detector mounted on board the Russian satellite Resurs-01-4, which has flown at an altitude of about 800 km in polar inclination since 1998 July. For every solar event, the power-law 4He spectrum across the energy interval 10-50 MeV nucleon-1 was reconstructed and spectral indexes, γ, from 1.8 to 6.8 extracted. Data of 3He and 4He were used to determine the 3He/4He ratio, which for some SEP events indicated an enrichment in 3He. For the 1998 November 7 event, the ratio reached a maximum value of 0.33+/-0.06, with spectral indexes of γ=2.5+/-0.6 and γ=3.7+/-0.3 for 3He and 4He, respectively. The 3He/4He ratio averaged over the remaining events was 0.011+/-0.004. For all events, a deuterium-to-proton ratio was estimated. An upper limit on the average value over all events was 2H/1H<4×10-5 across the energy interval 9-12 MeV nucleon-1. Upper limits on the 3H/1H counting ratio for all events were determined. For the 1998 November 14 SEP event, the high flux of heavy particles detected made it possible to reconstruct the carbon, nitrogen, and oxygen flux.

  9. Carbon and nitrogen abundances in F- and G-type stars

    NASA Technical Reports Server (NTRS)

    Clegg, R. E. S.

    1977-01-01

    Carbon and nitrogen abundances have been obtained for a sample of 11-F- and G-type dwarfs covering a range in Fe/H abundance ratio from -0.8 to +0.3. Model atmospheres, which included the effects of convection and line blanketing, were used to calculate synthetic spectra of the CH, CN, and NH molecular bands. Effective oscillator strengths for the bands studied were found by matching synthetic spectra calculated from a model solar atmosphere with the observed solar bands. Many of the metal-poor stars, and particularly the high-velocity stars, were found to have substantial nitrogen over-deficiencies, suggesting that N is manufactured mostly in a secondary manner. The carbon-to-iron ratios were similar to the solar ratio, although there may be slight C over-deficiencies in metal-poor stars. However, the variation in C/Fe is not as marked as that found recently by Hearnshaw (1974). A comprehensive discussion of the theoretical errors is given, and some applications to Galactic evolution are noted.

  10. Oxygen isotope ratio measurements on carbon dioxide generated by reaction of microliter quantities of biological fluids with guanidine hydrochloride

    SciTech Connect

    Wong, W.W.; Lee, L.S.; Klein, P.D.

    1987-03-01

    Guanidine hydrochloride was used to convert water in biological fluids to carbon dioxide for oxygen isotope ratio measurements. Five 10-..mu..L aliquots each of five different saliva, urine, plasma, and human milk samples were allowed to react with 100 mg of guanidine hydrochloride at 260/sup 0/C to produce ammonia and carbon dioxide. Ammonia was removed with 100% phosphoric acid and carbon dioxide was cryogenically purified before isotope ratio measurement. At natural abundances, the delta/sup 18/O values of the biological fluids were reproducible to within 0.16% (standard deviation) and accurate to within 0.11 +/- 0.73% (x vector +/- SD) of the H/submore » 2/O-CO/sub 2/ equilibration values. At a 250% enrichment level of /sup 18/O, the delta/sup 18/O values of the biological fluids were reproducible to within 0.95% and accurate to -1.27 +/- 2.25%.« less

  11. Soil moisture effects on the carbon isotopic composition of soil respiration

    EPA Science Inventory

    The carbon isotopic composition ( 13C) of recently assimilated plant carbon is known to depend on water-stress, caused either by low soil moisture or by low atmospheric humidity. Air humidity has also been shown to correlate with the 13C of soil respiration, which suggests indir...

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

    Treesearch

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

    2010-01-01

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

  13. Evaluation of carbon isotope flux partitioning theory under simplified and controlled environmental conditions

    USDA-ARS?s Scientific Manuscript database

    Separation of the photosynthetic (Fp) and respiratory (Fr) fluxes of net CO2 exchange (Fn)remains a necessary step toward understanding the biological and physical controls on carbon cycling between the soil, biomass, and atmosphere. Despite recent advancements in stable carbon isotope partitioning ...

  14. Bryophyte Tissue-specific Carbon Isotope Record from Galindez Island, Argentine Islands, Western Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Beilman, D. W.; Yumol, L. M.; Yu, Z.; Parnikoza, I.

    2016-12-01

    Mossbank ecosystems of the western Antarctic Peninsula (AP) provide an under-utilized archive of past terrestrial environmental change. We measured the stable carbon isotope values (δ13C) of both modern and subfossil bryophytes to characterize differences between species and tissues and to identify changes over time. Living plants of common species including Polytrichum strictum and Chorisodontium aciphyllum were collected from several populations between 64° 09' and 67°35'S and had a wide range of δ13C values from -22 to -32‰ that were distinct between species and tissues. In particular, leaves were consistently more enriched in 13C than stems on average by 2‰. Radiocarbon-dated subfossil leaf tissue in a mossbank peat core raised from Galindez Island (65° 14' 51.4"S, 64° 15' 2.3" W) showed that peat formation began 2300 years ago, and provided evidence for very slow growth or a hiatus between about 1100 and 600 years ago during a period of colder air temperatures evident in depleted hydrogen and oxygen isotope values in James Ross Island ice on the eastern AP. Bryophyte macrofossil remains showed a relatively simple bryophyte community of mainly P. strictum throughout the core, but several periods when wet-adapted species became dominant. Subfossil leaf δ13C values of P. strictum varied from -24 to -30‰, and revealed source-independent discrimination that was higher in recent decades than any time during the last 2300 years. Changes in species' abundance between P. strictum and Pohlia nutans varied with discrimination, suggesting that mossbanks have been sensitive to hydroclimate variation during the Late Holocene, and that moss growth conditions at this western AP site have been anomalous in recent decades.

  15. The stable carbon isotope composition of methane produced and emitted from northern peatlands

    NASA Astrophysics Data System (ADS)

    Hornibrook, Edward R. C.

    Stable carbon isotope values, pore water concentration, and flux data for methane (CH4) were compiled for 26 peatlands situated in the northern hemisphere to explore relationships between trophic status and CH4 cycling. Methane produced in ombrotrophic bogs has δ13C values that are significantly more negative than CH4 formed in fens apparently because of poor dissociation of acetic acid or an absence of methanogenic archaea capable of metabolizing acetic acid under low pH conditions. The δ 13C values of CH4 in pore water of ombrotrophic and minerotrophic peatlands exhibit the opposite trend: δ13C(CH4) values become more positive with depth in rain-fed bogs and more negative with depth in fens. The key zone for methanogenesis occurs at shallow depths in both types of peatland and consequently, δ13C values of CH4 emitted from ombrotrophic bogs (-74.9 ± 9.8‰ n = 42) are more negative than from fens (-64.8 ± 4.0‰ n = 38). An abundance of graminoids in fens contributes to more positive δ13C(CH4) values in pore water through (1) release of root exudates which promotes aceticlastic methanogenesis, (2) rhizosphere oxidization of CH4 causing localized enrichment of 13CH4, and (3) preferential export of 12CH4 through aerenchyma, which also enriches pore water in 13CH4. Emissions from blanket bogs and raised bogs should be attributed more negative δ13C(CH4) values relative to fens in isotope-weighted mass balance budgets. Further study is needed of bogs that have an apparently low nutrient status but exhibit a pore water distribution of δ13C(CH4) values similar to fens.

  16. The Precambrian Biogeochemical Carbon Isotopic Record: Contributions of Thermal Versus Biological Processes

    NASA Technical Reports Server (NTRS)

    DesMarais, David J.; DeVincenzi, Donald L. (Technical Monitor)

    2000-01-01

    Superplumes offer a new approach for understanding global C cycles. Isotopes help to discern the impacts of geological, environmental and biological processes ujpun the evolution of these cycles. For example, C-13/C-12 values of coeval sedimentary organics and carbonates give global estimates of the fraction of C buried as organics (Forg), which today lies near 0.2. Before Oxygenic photosynthesis arose, our biosphere obtained reducing power for biosynthesis solely from thermal volatiles and rock alteration. Thus Forg was dominated by the mantle redox state, which has remained remarkably constant for greater than Gy. Recent data confirm that the long-term change in Forg had been small, indicating that the mantle redox buffer remains important even today. Oxygenic photosynthesis enabled life to obtain additional reducing power by splitting the water molecule. Accordingly, biological organic production rose above the level constrained by the mantle-derived flux of reduced species. For example, today, chemoautotrophs harvesting energy from hydrothermal emanations can synthesize at most between 0.2 x 10(exp 12) and 2x 10(exp 12) mol C yr-1 of organic C globally. In contrast, global photosynthetic productivity is estimated at 9000 x 10(exp 12) mol C yr-1. Occasionally photosynthetic productivity did contribute to dramatically -elevated Forg values (to 0.4 or more) as evidenced by very high carbonate C-13/C-12. The interplay between biological, tectonic and other environmental factors is illustrated by the mid-Archean to mid-Proterozoic isotopic record. The relatively constant C-13/C-12 values of Archean carbonates support the view that photosynthetically-driven Forg increases were not yet possible. In contrast, major excursions in C-13/C-12, and thus also in Forg, during the early Proterozoic confirmed the global importance of oxygenic photosynthesis by that time. Remarkably, the superplume event at 1.9 Ga did not trigger another major Forg increase, despite the

  17. Isotopic measurements (C,N,O) of detonation soot produced from labeled and unlabeled Composition B-3 indicate source of solid carbon residues

    NASA Astrophysics Data System (ADS)

    Podlesak, David; Manner, Virginia; Amato, Ronald; Dattelbaum, Dana; Gusavsen, Richard; Huber, Rachel

    2017-06-01

    Detonation of HE is an exothermic process whereby metastable complex molecules are converted to simple stable molecules such as H2 O, N2, CO, CO2, and solid carbon. The solid carbon contains various allotropes such as detonation nanodiamonds, graphite, and amorphous carbon. It is well known that certain HE formulations such as Composition B (60% RDX, 40% TNT) produce greater amounts of solid carbon than other more oxygen-balanced formulations. To develop a greater understanding of how formulation and environment influence solid carbon formation, we synthesized TNT and RDX with 13 C and 15 N at levels slightly above natural abundance levels. Synthesized RDX and TNT were mixed at a ratio of 60:40 to form Composition B and solid carbon residues were collected from detonations of isotopically-labeled as well as un-labelled Composition B. The raw HE and detonation residues were analyzed isotopically for C, N, O isotopic compositions. We will discuss differences between treatments groups as a function of formulation and environment. LA-UR - 17-21266.

  18. Seasonal variation in kangaroo tooth enamel oxygen and carbon isotopes in southern Australia

    NASA Astrophysics Data System (ADS)

    Brookman, Tom H.; Ambrose, Stanley H.

    2012-09-01

    Serial sampling of tooth enamel growth increments for carbon and oxygen isotopic analyses of Macropus (kangaroo) teeth was performed to assess the potential for reconstructing paleoseasonality. The carbon isotope composition of tooth enamel apatite carbonate reflects the proportional intake of C3 and C4 vegetation. The oxygen isotopic composition of enamel reflects that of ingested and metabolic water. Tooth enamel forms sequentially from the tip of the crown to the base, so dietary and environmental changes during the tooth's formation can be detected. δ13C and δ18O values were determined for a series of enamel samples drilled from the 3rd and 4th molars of kangaroos that were collected along a 900 km north-south transect in southern Australia. The serial sampling method did not yield pronounced seasonal isotopic variation patterns in Macropus enamel. The full extent of dietary isotopic variation may be obscured by attenuation of the isotopic signal during enamel mineralisation. Brachydont (low-crowned) Macropus teeth may be less sensitive to seasonal variation in isotopic composition due to time-averaging during mineralisation. However, geographic variations observed suggest that there may be potential for tracking latitudinal shifts in vegetation zones and seasonal environmental patterns in response to climate change.

  19. Biodegradation of Chlorofluorocarbons in a Groundwater Plume using Compound Specific Carbon Isotope Analysis

    NASA Astrophysics Data System (ADS)

    Phillips, E.; Manna, J.; Horst, A.; Gilevska, T.; Sherwood Lollar, B.; Mack, E. E.; Seger, E.; Lutz, E. J.; Norcoss, S.; Morgan, S. E.; West, K. A.; Dworatzek, S.; Webb, J.

    2017-12-01

    Compound specific isotope analysis (CSIA) measures isotope ratios of organic hydrocarbons to monitor intrinsic bioremediation processes that can transform contaminants in field settings. The fraction of original contaminant remaining can be determined using the measured isotope ratio of the contaminant by an experimentally determined fractionation factor. In this study, two separate biotransformation experiments were performed in the Stable Isotope Laboratory at the University of Toronto using CSIA. In these two experiments, a mixed culture derived from a contaminated site was amended with trichlorotrifluoroethane (CFC-113), or trichlorofluoromethane (CFC-11), respectively. The concentrations and carbon isotope ratios of CFC-113, or CFC-11 were analyzed to calculate the fractionation factor for the transformation of each compound. Subsequently, groundwater samples from 9 wells at a historically contaminated site were collected and analyzed. The experimentally determined fractionation factors were then used to evaluate the extent of transformation that had occurred at the field site. In the laboratory studies, significant carbon isotope fractionation was observed for both CFC-113 and CFC-11 as biotransformation proceeded. This significant fractionation is beneficial when evaluating biotransformation at field sites as it can be clearly differentiated from the effects of other physical processes such as transport, or volatilization. Although there was significant variation in the carbon isotope values of CFC-113 between different well locations at the field site, these variations may be due to differences in source carbon isotope signatures. For CFC-11, much more significant isotopic variation was observed within the same well and between wells, showing trends consistent with in situ biotransformation. Results from this study demonstrate that CSIA can be successfully applied to evaluate the extent of transformation of chlorofluorocarbons (CFCs) at contaminated field

  20. Highly Efficient Quantum Sieving in Porous Graphene-like Carbon Nitride for Light Isotopes Separation

    NASA Astrophysics Data System (ADS)

    Qu, Yuanyuan; Li, Feng; Zhou, Hongcai; Zhao, Mingwen

    2016-01-01

    Light isotopes separation, such as 3He/4He, H2/D2, H2/T2, etc., is crucial for various advanced technologies including isotope labeling, nuclear weapons, cryogenics and power generation. However, their nearly identical chemical properties made the separation challenging. The low productivity of the present isotopes separation approaches hinders the relevant applications. An efficient membrane with high performance for isotopes separation is quite appealing. Based on first-principles calculations, we theoretically demonstrated that highly efficient light isotopes separation, such as 3He/4He, can be reached in a porous graphene-like carbon nitride material via quantum sieving effect. Under moderate tensile strain, the quantum sieving of the carbon nitride membrane can be effectively tuned in a continuous way, leading to a temperature window with high 3He/4He selectivity and permeance acceptable for efficient isotopes harvest in industrial application. This mechanism also holds for separation of other light isotopes, such as H2/D2, H2/T2. Such tunable quantum sieving opens a promising avenue for light isotopes separation for industrial application.

  1. Abundant carbon substrates drive extremely high sulfate reduction rates and methane fluxes in Prairie Pothole Wetlands.

    PubMed

    Dalcin Martins, Paula; Hoyt, David W; Bansal, Sheel; Mills, Christopher T; Tfaily, Malak; Tangen, Brian A; Finocchiaro, Raymond G; Johnston, Michael D; McAdams, Brandon C; Solensky, Matthew J; Smith, Garrett J; Chin, Yu-Ping; Wilkins, Michael J

    2017-08-01

    Inland waters are increasingly recognized as critical sites of methane emissions to the atmosphere, but the biogeochemical reactions driving such fluxes are less well understood. The Prairie Pothole Region (PPR) of North America is one of the largest wetland complexes in the world, containing millions of small, shallow wetlands. The sediment pore waters of PPR wetlands contain some of the highest concentrations of dissolved organic carbon (DOC) and sulfur species ever recorded in terrestrial aquatic environments. Using a suite of geochemical and microbiological analyses, we measured the impact of sedimentary carbon and sulfur transformations in these wetlands on methane fluxes to the atmosphere. This research represents the first study of coupled geochemistry and microbiology within the PPR and demonstrates how the conversion of abundant labile DOC pools into methane results in some of the highest fluxes of this greenhouse gas to the atmosphere ever reported. Abundant DOC and sulfate additionally supported some of the highest sulfate reduction rates ever measured in terrestrial aquatic environments, which we infer to account for a large fraction of carbon mineralization in this system. Methane accumulations in zones of active sulfate reduction may be due to either the transport of free methane gas from deeper locations or the co-occurrence of methanogenesis and sulfate reduction. If both respiratory processes are concurrent, any competitive inhibition of methanogenesis by sulfate-reducing bacteria may be lessened by the presence of large labile DOC pools that yield noncompetitive substrates such as methanol. Our results reveal some of the underlying mechanisms that make PPR wetlands biogeochemical hotspots, which ultimately leads to their critical, but poorly recognized role in regional greenhouse gas emissions. © 2017 John Wiley & Sons Ltd.

  2. Abundant carbon substrates drive extremely high sulfate reduction rates and methane fluxes in Prairie Pothole Wetlands

    SciTech Connect

    Dalcin Martins, Paula; Hoyt, David W.; Bansal, Sheel

    Inland waters are increasingly recognized as critical sites of methane emissions to the atmosphere, but the biogeochemical reactions driving such fluxes are less well understood. The Prairie Pothole Region (PPR) of North America is one of the largest wetland complexes in the world, containing millions of small, shallow wetlands. The sediment pore waters of PPR wetlands contain some of the highest concentrations of dissolved organic carbon (DOC) and sulfur species ever recorded in terrestrial aquatic environments. Using a suite of geochemical and microbiological analyses we measured the impact of sedimentary carbon and sulfur transformations in these wetlands on methane fluxesmore » to the atmosphere. This research represents the first study of coupled geochemistry and microbiology within the PPR, and demonstrates how the conversion of abundant labile DOC pools into methane results in some of the highest fluxes of this greenhouse gas to the atmosphere ever reported. Abundant DOC and sulfate additionally supported some of the highest sulfate reduction rates ever measured in terrestrial aquatic environments, which we infer to account for a large fraction of carbon mineralization in this system. Methane accumulations in zones of active sulfate reduction may be due to either the transport of free methane gas from deeper locations, or the co-occurrence of methanogenesis and sulfate reduction. If both respiratory processes are concurrent, any competitive inhibition of methanogenesis by sulfate-reducing bacteria may be lessened by the presence of large labile DOC pools that yield non-competitive substrates such as methanol. Our results reveal some of the underlying mechanisms that make PPR wetlands biogeochemical hotspots, which ultimately leads to their critical, but poorly recognized role in regional greenhouse gas emissions.« less

  3. Abundant carbon substrates drive extremely high sulfate reduction rates and methane fluxes in Prairie Pothole Wetlands

    USGS Publications Warehouse

    Martins, Paula; Hoyt, David W.; Bansal, Sheel; Mills, Christopher T.; Tfaily, Malak; Tangen, Brian; Finocchiaro, Raymond; Johnston, Michael D.; McAdams, Brandon C.; Solensky, Matthew J.; Smith, Garrett J.; Chin, Yu-Ping; Wilkins, Michael J.

    2017-01-01

    Inland waters are increasingly recognized as critical sites of methane emissions to the atmosphere, but the biogeochemical reactions driving such fluxes are less well understood. The Prairie Pothole Region (PPR) of North America is one of the largest wetland complexes in the world, containing millions of small, shallow wetlands. The sediment pore waters of PPR wetlands contain some of the highest concentrations of dissolved organic carbon (DOC) and sulfur species ever recorded in terrestrial aquatic environments. Using a suite of geochemical and microbiological analyses, we measured the impact of sedimentary carbon and sulfur transformations in these wetlands on methane fluxes to the atmosphere. This research represents the first study of coupled geochemistry and microbiology within the PPR and demonstrates how the conversion of abundant labile DOC pools into methane results in some of the highest fluxes of this greenhouse gas to the atmosphere ever reported. Abundant DOC and sulfate additionally supported some of the highest sulfate reduction rates ever measured in terrestrial aquatic environments, which we infer to account for a large fraction of carbon mineralization in this system. Methane accumulations in zones of active sulfate reduction may be due to either the transport of free methane gas from deeper locations or the co-occurrence of methanogenesis and sulfate reduction. If both respiratory processes are concurrent, any competitive inhibition of methanogenesis by sulfate-reducing bacteria may be lessened by the presence of large labile DOC pools that yield noncompetitive substrates such as methanol. Our results reveal some of the underlying mechanisms that make PPR wetlands biogeochemical hotspots, which ultimately leads to their critical, but poorly recognized role in regional greenhouse gas emissions.

  4. s-Processing from MHD-induced mixing and isotopic abundances in presolar SiC grains

    NASA Astrophysics Data System (ADS)

    Palmerini, S.; Trippella, O.; Busso, M.; Vescovi, D.; Petrelli, M.; Zucchini, A.; Frondini, F.

    2018-01-01

    In the past years the observational evidence that s-process elements from Sr to Pb are produced by stars ascending the so-called Asymptotic Giant Branch (or "AGB") could not be explained by self-consistent models, forcing researchers to extensive parameterizations. The crucial point is to understand how protons can be injected from the envelope into the He-rich layers, yielding the formation of 13C and then the activation of the 13C (α,n)16O reaction. Only recently, attempts to solve this problem started to consider quantitatively physically-based mixing mechanisms. Among them, MHD processes in the plasma were suggested to yield mass transport through magnetic buoyancy. In this framework, we compare results of nucleosynthesis models for Low Mass AGB Stars (M≲ 3M⊙), developed from the MHD scenario, with the record of isotopic abundance ratios of s-elements in presolar SiC grains, which were shown to offer precise constraints on the 13C reservoir. We find that n-captures driven by magnetically-induced mixing can indeed account for the SiC data quite well and that this is due to the fact that our 13C distribution fulfils the above constraints rather accurately. We suggest that similar tests should be now performed using different physical models for mixing. Such comparisons would indeed improve decisively our understanding of the formation of the neutron source.

  5. Carbon isotope records reveal synchronicity between carbon cycle perturbation and the "Carnian Pluvial Event" in the Tethys realm (Late Triassic)

    NASA Astrophysics Data System (ADS)

    Dal Corso, Jacopo; Gianolla, Piero; Newton, Robert J.; Franceschi, Marco; Roghi, Guido; Caggiati, Marcello; Raucsik, Béla; Budai, Tamás; Haas, János; Preto, Nereo

    2015-04-01

    In the early Late Triassic a period of increased rainfall, named the Carnian Pluvial Event (CPE), is evidenced by major lithological changes in continental and marine successions worldwide. The environmental change seems to be closely associated with a negative carbon isotope excursion that was identified in a stratigraphic succession of the Dolomites (Italy) but the temporal relationship between these phenomena is still not well defined. Here we present organic-carbon isotope data from Carnian deep-water stratigraphic sections in Austria and Hungary, and carbonate petrography of samples from a marginal marine section in Italy. A negative 2-4‰ δ13C shift is recorded by bulk organic matter in the studied sections and is coincident with a similar feature highlighted in higher plant and marine algal biomarker carbon-isotope records from the Dolomites (Italy), thus testifying to a global change in the isotopic composition of the reservoirs of the exchangeable carbon. Our new observations verify that sedimentological changes related to the CPE coincide with the carbon cycle perturbation and therefore occurred synchronously within the western Tethys. Consistent with modern observations, our results show that the injection of 13C-depleted CO2 into the Carnian atmosphere-ocean system may have been directly responsible for the increase in rainfall by intensifying the Pangaean mega-monsoon activity. The consequent increased continental weathering and erosion led to the transfer of large amounts of siliciclastics into the basins that were rapidly filled up, while the increased nutrient flux triggered the local development of anoxia. The new carbonate petrography data show that these changes also coincided with the demise of platform microbial carbonate factories and their replacement with metazoan driven carbonate deposition. This had the effect of considerably decreasing carbonate deposition in shallow water environments.

  6. Stable oxygen and carbon isotope characteristics in speleothems from Southern Africa - how good are they?

    NASA Astrophysics Data System (ADS)

    Holmgren, K.

    2009-04-01

    Much remains to be understood about the interaction between the African climate system, its surrounding ocean-atmosphere climate variability and the global climate system. A better understanding of the regional climate evolution is crucial for understanding global climate dynamics and issues surrounding environmental change throughout Africa and a prerequisite for increasing climate forecasting capabilities for the region. As part of developing this understanding, a longer term perspective that reaches beyond the information available from instrumental records is required. Speleothems are frequently abundant in southern Africa. Quite a few records are now available, reporting significant changes in climate and environmental conditions over longer and shorter time scales. Conclusions are mainly based on the stable isotopic composition of the speleothems. The interpretation of the stable isotope data is, however, not always straight-forward, since many processes contribute to the observed signal in the speleothem and these processes may influence the signal differently at different spatial and temporal scales. For example was the Makapansgat speleothem oxygen isotope record, originally interpreted as being generally determined by shifts in atmospheric circulation pattern (Lee-Thorp et al. 2001, Holmgren et al. 2003), recently challenged and re-interpreted by Partin et al. (2008) to reflect annual rainfall amounts. Historically, less attention has been paid to the stable carbon isotope composition in speleothems. Today, an increasing number of studies demonstrate the potential of stable carbon variations as providing additional information on climate and environment. Measured variations can be a function of the amount of C3 versus C4 vegetation, vegetation cover and soil biological activity, bedrock proportion, rainfall amount and the drip rate. Clearly the multitudes of plausible processes behind the isotopic composition of speleothems in southern Africa (as well as

  7. Kinetic Fractionation of Stable Isotopes in Carbonates on Mars: Terrestrial Analogs

    NASA Technical Reports Server (NTRS)

    Socki, Richard A.; Gibson, Everett K., Jr.; Golden, D. C.; Ming, Douglas W.; McKay, Gordon A.

    2003-01-01

    An ancient Martian hydrosphere consisting of an alkali-rich ocean would likely produce solid carbonate minerals through the processes of evaporation and/or freezing. We postulate that both (or either) of these kinetically-driven processes would produce carbonate minerals whose stable isotopic compositions are highly fractionated (enriched) with respect to the source carbon. Various scenarios have been proposed for carbonate formation on Mars, including high temperature formation, hydrothermal alteration, precipitation from evaporating brines, and cryogenic formation. 13C and 18O -fractionated carbonates have previously been shown to form kinetically under some of these conditions, ie.: 1) alteration by hydrothermal processes, 2) low temperature precipitation (sedimentary) from evaporating bicarbonate (brine) solutions, and 3) precipitation during the process of cryogenic freezing of bicarbonate-rich fluids. Here we examine several terrestrial field settings within the context of kinetically controlled carbonate precipitation where stable isotope enrichments have been observed.

  8. Carbon isotopic fractionation in lipids from methanotrophic bacteria: relevance for interpretation of the geochemical record of biomarkers

    NASA Technical Reports Server (NTRS)

    Summons, R. E.; Jahnke, L. L.; Roksandic, Z.

    1994-01-01

    Experiments with cultured aerobic methane oxidising bacteria confirm that their biomarker lipids will be significantly depleted in 13C compared to the substrate. The methanotrophic bacteria Methylococcus capsulatus and Methylomonas methanica, grown on methane and using the RuMP cycle for carbon assimilation, show maximum 13C fractionation of approximately 30% in the resultant biomass. In M. capsulatus, the maximum fractionation is observed in the earliest part of the exponential growth stage and decreases to approximately 16% as cells approach stationary phase. This change may be associated with a shift from the particulate form to the soluble form of the methane monooxygenase enzyme. Less than maximum fractionation is observed when cells are grown with reduced methane availability. Biomass of M. capsulatus grown on methanol was depleted by 9% compared to the substrate. Additional strong 13C fractionation takes place during polyisoprenoid biosynthesis in methanotrophs. The delta 13C values of individual hopanoid and steroid biomarkers produced by these organisms were as much as l0% more negative than total biomass. In individual cultures, squalene was 13C-enriched by as much as 14% compared to the triterpane skeleton of bacteriohopaneaminopentol. Much of the isotopic dispersion in lipid metabolites could be attributed to shifts in their relative abundances, combined with an overall reduction in fractionation during the growth cycle. In cells grown on methanol, where there was no apparent effect of growth stage on overall fractionation there were still significant isotopic differences between closely related lipids including a 5.3% difference between the hopane and 3 beta-methylhopane skeletons. Hopane and sterane polyisoprenoids were also 13C-depleted compared to fatty acids. These observations have significant implications for the interpretation of specific compound isotopic signatures now being measured for hydrocarbons and other lipids present in sediments and

  9. Stable carbon isotopes and levoglucosan for PM2.5 elemental carbon source apportionments in the largest city of Northwest China

    NASA Astrophysics Data System (ADS)

    Zhao, Zhuzi; Cao, Junji; Zhang, Ting; Shen, Zhenxing; Ni, Haiyan; Tian, Jie; Wang, Qiyuan; Liu, Suixin; Zhou, Jiamao; Gu, Jian; Shen, Ganzhou

    2018-07-01

    Stable carbon isotopes provide information on aerosol sources, but no extensive long-term studies of these isotopes have been conducted in China, and they have mainly been used for qualitative rather than quantitative purposes. Here, 24 h PM2.5 samples (n = 58) were collected from July 2008 to June 2009 at Xi'an, China. The concentrations of organic and elemental carbon (OC and EC), water-soluble OC, and the stable carbon isotope abundances of OC and EC were determined. In spring, summer, autumn and winter, the mean stable carbon isotope in OC (δ13COC) were -26.4 ± 0.6, -25.8 ± 0.7, -25.0 ± 0.6 and -24.4 ± 0.8‰, respectively, and the corresponding δ13CEC values were -25.5 ± 0.4, -25.5 ± 0.8, -25.2 ± 0.7 and -23.7 ± 0.6‰. Large δ13CEC and δ13COC values in winter can be linked to the burning coal for residential heating. Less biomass is burned during spring and summer than winter or fall (manifested in the levels of levoglucosan, i.e., 178, 85, 370, 935 ng m-3 in spring, summer, autumn, and winter), and the more negative δ13COC in the warmer months can be explained by the formation of secondary organic aerosols. A levoglucosan tracer method combined with an isotope mass balance analysis indicated that biomass burning accounted for 1.6-29.0% of the EC, and the mean value in winter (14.9 ± 7.5%) was 7 times higher than summer (2.1 ± 0.4%), with intermediate values of 6.1 ± 5.6 and 4.5 ± 2.4% in autumn and spring. Coal combustion accounted for 45.9 ± 23.1% of the EC overall, and the percentages were 63.0, 37.2, 36.7, and 33.7% in winter, autumn, summer and spring respectively. Motor vehicles accounted for 46.6 ± 26.5% of the annual EC, and these contributed over half (56.7-61.8%) of the EC in all seasons except winter. Correlations between motor vehicle-EC and coal combustion-EC with established source indicators (B(ghi)P and As) support the source apportionment results. This paper describes a simple and accurate method for apportioning the

  10. Poster 9: Isotopic Ratios of Carbon and Oxygen in Titan's CO using ALMA

    NASA Astrophysics Data System (ADS)

    Serigano, Joseph; Nixion, Conor A.; Cordiner, Martin A.; Irwin, Patrick G. J.; Teanby, Nick A.; Charnley, Steven B.; Lindberg, Johan E.

    2016-06-01

    The advent of the Atacama Large Millimeter/Submillimeter Array (ALMA) has provided a new and powerful facility for probing the atmospheres of solar system targets at long wavelengths (84-720 GHz) where the rotational lines of small, polar molecules are prominent. In the complex atmosphere of Titan, photochemical processes dissociate and ionize molecular nitrogen and methane in the upper atmosphere, creating a complex inventory of trace hydrocarbons and nitriles. Additionally, the existence of oxygen on Titan facilitates the synthesis of molecules of potential astrobiological importance. Utilization of ground-based submillimeter observations of Titan has proven to be a powerful tool to complement results from spacecraft observations. ALMA provides the ability to probe this region in greater detail with unprecedented spectral and spatial resolution at high sensitivity, allowing for the derivation of vertical mixing profiles, molecular detections, and observations of latitudinal and seasonal variations. Recent ALMA studies of Titan have presented spectrally and spatially-resolved maps of HNC and HC3N emission (Cordiner et al. 2014), as well as the first spectroscopic detection of ethyl cyanide (C2H5CN) in Titan's atmosphere (Cordiner et al. 2015). This poster will focus on ALMA observations of carbon monoxide (CO) and its isotopologues 13CO, C18O, and C 17O in Titan's atmosphere. Molecular abundances and the vertical atmospheric temperature profile were derived by modeling the observed emission line profiles using NEMESIS, a line-by-line radiative transfer code (Irwin et al. 2008). This study reports the first spectroscopic detection of 17O in the outer solar system with C17O detected at >8σ confidence. The abundances of these molecules and isotopic ratios of 12C/13C, 16O/18O, and 16O/17O will be presented. General implications for the history of Titan from these measurements will be discussed.

  11. Detection of oxygen isotopic anomaly in terrestrial atmospheric carbonates and its implications to Mars

    PubMed Central

    Shaheen, R.; Abramian, A.; Horn, J.; Dominguez, G.; Sullivan, R.; Thiemens, Mark H.

    2010-01-01

    The debate of life on Mars centers around the source of the globular, micrometer-sized mineral carbonates in the ALH84001 meteorite; consequently, the identification of Martian processes that form carbonates is critical. This paper reports a previously undescribed carbonate formation process that occurs on Earth and, likely, on Mars. We identified micrometer-sized carbonates in terrestrial aerosols that possess excess 17O (0.4–3.9‰). The unique O-isotopic composition mechanistically describes the atmospheric heterogeneous chemical reaction on aerosol surfaces. Concomitant laboratory experiments define the transfer of ozone isotopic anomaly to carbonates via hydrogen peroxide formation when O3 reacts with surface adsorbed water. This previously unidentified chemical reaction scenario provides an explanation for production of the isotopically anomalous carbonates found in the SNC (shergottites, nakhlaites, chassignites) Martian meteorites and terrestrial atmospheric carbonates. The anomalous hydrogen peroxide formed on the aerosol surfaces may transfer its O-isotopic signature to the water reservoir, thus producing mass independently fractionated secondary mineral evaporites. The formation of peroxide via heterogeneous chemistry on aerosol surfaces also reveals a previously undescribed oxidative process of utility in understanding ozone and oxygen chemistry, both on Mars and Earth. PMID:21059939

  12. Detection of oxygen isotopic anomaly in terrestrial atmospheric carbonates and its implications to Mars.

    PubMed

    Shaheen, R; Abramian, A; Horn, J; Dominguez, G; Sullivan, R; Thiemens, Mark H

    2010-11-23

    The debate of life on Mars centers around the source of the globular, micrometer-sized mineral carbonates in the ALH84001 meteorite; consequently, the identification of Martian processes that form carbonates is critical. This paper reports a previously undescribed carbonate formation process that occurs on Earth and, likely, on Mars. We identified micrometer-sized carbonates in terrestrial aerosols that possess excess (17)O (0.4-3.9‰). The unique O-isotopic composition mechanistically describes the atmospheric heterogeneous chemical reaction on aerosol surfaces. Concomitant laboratory experiments define the transfer of ozone isotopic anomaly to carbonates via hydrogen peroxide formation when O(3) reacts with surface adsorbed water. This previously unidentified chemical reaction scenario provides an explanation for production of the isotopically anomalous carbonates found in the SNC (shergottites, nakhlaites, chassignites) Martian meteorites and terrestrial atmospheric carbonates. The anomalous hydrogen peroxide formed on the aerosol surfaces may transfer its O-isotopic signature to the water reservoir, thus producing mass independently fractionated secondary mineral evaporites. The formation of peroxide via heterogeneous chemistry on aerosol surfaces also reveals a previously undescribed oxidative process of utility in understanding ozone and oxygen chemistry, both on Mars and Earth.

  13. Coordinated In Situ Nanosims Analyses of H-C-O Isotopes in ALH 84001 Carbonates

    NASA Technical Reports Server (NTRS)

    Usui, T.; Alexander, C. M. O'D.; Wang, J.; Simon, J. I.; Jones, J. H.

    2016-01-01

    The surface geology and geomorphology of Mars indicate that it was once warm enough to maintain a large body of liquid water on its surface, though such a warm environment might have been transient. This study reports the hydrogen, carbon, and oxygen isotope compositions of the ancient atmosphere/hydrosphere of Mars based on in situ ion microprobe analyses of approximately 4 Ga-old carbonates in Allan Hills (ALH) 84001. The ALH 84001 carbonates are the most promising targets because they are thought to have formed from fluid that was closely associated with the Noachian atmosphere. While there are a number of carbon and oxygen isotope studies of the ALH 84001 carbonates, in situ hydrogen isotope analyses of these carbonates are limited and were reported more than a decade ago. Well-documented coordinated in situ analyses of carbon, oxygen and hydrogen isotopes provide an internally consistent dataset that can be used to constrain the nature of the Noachian atmosphere/hydrosphere and may eventually shed light on the hypothesis of ancient watery Mars.

  14. Carbon isotopes in the ocean model of the Community Earth System Model (CESM1)

    DOE PAGES

    Jahn, A.; Lindsay, K.; Giraud, X.; ...

    2015-08-05

    Carbon isotopes in the ocean are frequently used as paleoclimate proxies and as present-day geochemical ocean tracers. In order to allow a more direct comparison of climate model results with this large and currently underutilized data set, we added a carbon isotope module to the ocean model of the Community Earth System Model (CESM), containing the cycling of the stable isotope 13C and the radioactive isotope 14C. We implemented the 14C tracer in two ways: in the "abiotic" case, the 14C tracer is only subject to air–sea gas exchange, physical transport, and radioactive decay, while in the "biotic" version, themore » 14C additionally follows the 13C tracer through all biogeochemical and ecological processes. Thus, the abiotic 14C tracer can be run without the ecosystem module, requiring significantly fewer computational resources. The carbon isotope module calculates the carbon isotopic fractionation during gas exchange, photosynthesis, and calcium carbonate formation, while any subsequent biological process such as remineralization as well as any external inputs are assumed to occur without fractionation. Given the uncertainty associated with the biological fractionation during photosynthesis, we implemented and tested three parameterizations of different complexity. Compared to present-day observations, the model is able to simulate the oceanic 14C bomb uptake and the 13C Suess effect reasonably well compared to observations and other model studies. Lastly, at the same time, the carbon isotopes reveal biases in the physical model, for example, too sluggish ventilation of the deep Pacific Ocean.« less

  15. Toward estimation of origin of methane at ancient seeps — Carbon isotopes of seep carbonates, lipid biomarkers, and adsorbed gas

    NASA Astrophysics Data System (ADS)

    Miyajima, Yusuke; Watanabe, Yumiko; Ijiri, Akira; Goto, Akiko; Jenkins, Robert; Hasegawa, Takashi; Sakai, Saburo; Matsumoto, Ryo

    2017-04-01

    Methane is generated mainly by microbial or thermal degradation of organic matter, and the origin of methane can be estimated based on its stable carbon isotopic signature. Seafloor seepages of methane-charged fluids have been a major source of methane to the ocean, and knowing the origin of methane at the methane seeps can provide valuable insights into the subsurface fluid circulation and biogeochemical processes. Methane seeps in the geological past are archived as authigenic methane-derived carbonate rocks, which precipitate via an alkalinity increase facilitated by microbially mediated anaerobic oxidation of methane. Here we attempted to estimate origins of methane at ancient seeps, based on several proxies preserved within the seep carbonates. We examined methane-seep carbonate rocks in the Japan Sea region, collected from lower Miocene to middle Pleistocene sediments at 11 sites on land, and also carbonate nodules collected from the seafloor off Joetsu, where thermogenic methane is seeping. Carbon isotopic compositions of the carbonates and lipid biomarkers of methane-oxidizing archaea within them were analyzed. In order to directly know original isotopic signatures of methane, we also attempted to extract adsorbed methane through acid dissolution of the powdered carbonates. Early-diagenetic carbonate phases show various δ13C values between -64.7 and -4.7‰ vs. VPDB, suggesting either biogenic or thermogenic, or both origins of methane. A lipid biomarker pentamethylicosane (PMI) extracted from the ancient carbonates has δ13C values mostly lower than -100‰ , whereas that from the modern methane-derived carbonate nodule has a higher value (-80‰ ). The δ13C values of the seeping methane (-36‰ ) and PMI in the modern Joetsu seep carbonate shows an offset of -44‰ . If this carbon isotope offset was similar at the ancient seeps, the δ13C values of PMI indicate that methane at ancient seeps in the Japan Sea region was biogenic in origin, with δ13C

  16. Surface area dependence of calcium isotopic reequilibration in carbonates: Implications for isotopic signatures in the weathering zone

    NASA Astrophysics Data System (ADS)

    Fernandez, N. M.; Druhan, J. L.; Potrel, A.; Jacobson, A. D.

    2016-12-01

    The concept of dynamic equilibrium carries the implicit assumption of continued isotopic exchange between a mineral and the surrounding fluid. While this effect has received much attention in the marine paleoproxy literature, it has been relatively overlooked in application to the terrestrial environment. In weathering systems, a potential consequence is that rapid reequilibration may alter or erase isotopic signatures generated during secondary mineral formation. The extent and timescale over which isotopic signatures are reset in these hydrologic systems is unknown. Using reactive transport modeling, we show isotopic reequilibration under conditions reflecting terrestrial hydrologic settings to be significant and dependent on the reactive surface area of the solid. In particular, we suggest that the non-traditional stable isotopes commonly used in application to carbonates (e.g., Ca, Mg, Sr) are sensitive to these effects due to their rapid reaction rates. We aim to characterize the dependence of Ca isotopic reequilibration on surface area during calcite precipitation via batch experiments conducted at ambient temperature over 48-hour time periods. Calcite precipitation was performed in a closed batch reactor utilizing a controlled free-drift method. The batch reactors contained mixed supersaturated solutions of CaCl2 and NaHCO3 at an initial pH of 8.54. Precipitation was initiated by seed inoculation of calcite crystals with two distinct, pre-constrained surface areas. All experiments achieved the same final state of chemical equilibrium, but as expected, the fastest approach to equilibrium occurred for experiments employing calcite seeds with the highest surface area. This implies that differences in equilibrated Ca isotope ratios (δ44/40Ca) should reflect differences in surface area. This prediction is upheld by models of the experiments, indicating a measureable difference in δ44Ca during calcite precipitation where the higher surface area corresponds to

  17. Cretaceous shales from the western interior of North America: sulfur/carbon ratios and sulfur-isotope composition.

    USGS Publications Warehouse

    Gautier, D.L.

    1986-01-01

    Sulphur/carbon ratios in cores of selected Cretaceous marine shales average 0.67, a value greater than that observed in recent marine sediments and much higher than global values calculated for the Cretaceous. This may be ascribed to generally low levels of bioturbation and enhanced efficiency of sulphate reduction due to low oxygen levels in Cretaceous seaways. Isotopic compositions of pyrite sulphur vary systematically with level of oxygenation of the depositional environment and therefore with organic carbon abundance and type of organic matter. Samples with >4% organic carbon are extremely depleted in 34S (mean delta 34S -31per mille) and contain hydrogen-rich organic matter. Samples containing <1.5% organic carbon display relatively 'heavy' but wide-ranging delta 34S values (-34.6 to +16.8per mille) and contain hydrogen-poor organic matter. Samples with intermediate amounts of organic carbon have average delta 34S of -25.9per mille and contain both types of organic matter. Relations between the nature of these shales, and their sedimentation rate and depositional environment are discussed.-L.C.H.

  18. Accurate experimental determination of the isotope effects on the triple point temperature of water. II. Combined dependence on the 18O and 17O abundances

    NASA Astrophysics Data System (ADS)

    Faghihi, V.; Kozicki, M.; Aerts-Bijma, A. T.; Jansen, H. G.; Spriensma, J. J.; Peruzzi, A.; Meijer, H. A. J.

    2015-12-01

    This paper is the second of two articles on the quantification of isotope effects on the triple point temperature of water. In this second article, we address the combined effects of 18O and 17O isotopes. We manufactured five triple point cells with waters with 18O and 17O abundances exceeding widely the natural abundance range while maintaining their natural 18O/17O relationship. The 2H isotopic abundance was kept close to that of VSMOW (Vienna Standard Mean Ocean Water). These cells realized triple point temperatures ranging between  -220 μK to 1420 μK with respect to the temperature realized by a triple point cell filled with VSMOW. Our experiment allowed us to determine an accurate and reliable value for the newly defined combined 18, 17O correction parameter of AO  =  630 μK with a combined uncertainty of 10 μK. To apply this correction, only the 18O abundance of the TPW needs to be known (and the water needs to be of natural origin). Using the results of our two articles, we recommend a correction equation along with the coefficient values for isotopic compositions differing from that of VSMOW and compare the effect of this new equation on a number of triple point cells from the literature and from our own institute. Using our correction equation, the uncertainty in the isotope correction for triple point cell waters used around the world will be  <1 μK.

  19. METHOD FOR PRODUCING ISOTOPIC METHANES FROM LITHIUM CARBONATE AND LITHIUM HYDRIDE

    DOEpatents

    Frazer, J.W.

    1959-10-27

    A process is descrlbed for the production of methane and for the production of methane containing isotopes of hydrogen and/or carbon. Finely divided lithium hydrlde and litldum carbonate reactants are mixed in intimate contact and subsequently compacted under pressures of from 5000 to 60,000 psl. The compacted lithium hydride and lithium carbenate reactunts are dispised in a gas collecting apparatus. Subsequently, the compact is heated to a temperature in the range 350 to 400 deg C whereupon a solid-solid reaction takes place and gaseous methane is evolved. The evolved methane is contaminated with gaseous hydrogen and a very small amount of CO/sub 2/; however, the desired methane product is separated from sald impurities by well known chemical processes, e.g., condensation in a cold trap. The product methane contalns isotopes of carbon and hydrogen, the Isotopic composition being determined by the carbon isotopes originally present In the lithium carbonate and the hydrogen isotopes originally present in the lithium hydride.

  20. Carbon and oxygen isotope variations of the Middle-Late Triassic Al Aziziyah Formation, northwest Libya

    NASA Astrophysics Data System (ADS)

    Moustafa, Mohamed S. H.; Pope, Michael C.; Grossman, Ethan L.; Mriheel, Ibrahim Y.

    2016-06-01

    This study presents the δ13C and δ18O records from whole rock samples of the Middle-Late Triassic (Ladinian-Carnian) Al Aziziyah Formation that were deposited on a gently sloping carbonate ramp within the Jifarah Basin of Northwest Libya. The Al Aziziyah Formation consists of gray limestone, dolomite, and dolomitic limestone interbedded with shale. The Ghryan Dome and Kaf Bates sections were sampled and analyzed for carbon and oxygen isotope chemostratigraphy to integrate high-resolution carbon isotope data with an outcrop-based stratigraphy, to provide better age control of the Al Aziziyah Formation. This study also discusses the relation between the facies architecture of the Al Aziziyah Formation and the carbon isotope values. Seven stages of relative sea level rise and fall within the Ghryan Dome were identified based on facies stacking patterns, field observations and carbon stable isotopes. The Al Aziziyah Formation δ13C chemostratigraphic curve can be partially correlated with the Triassic global δ13C curve. This correlation indicates that the Al Aziziyah Formation was deposited during the Ladinian and early Carnian. No straight-forward relationship is seen between δ13C and relative sea level probably because local influences complicated systematic environmental and diagenetic isotopic effects associated with sea level change.

  1. Fractionation of carbon and hydrogen isotopes by methane-oxidizing bacteria

    USGS Publications Warehouse

    Coleman, D.D.; Risatti, J.B.; Schoell, M.

    1981-01-01

    Carbon isotopic analysis of methane has become a popular technique in the exploration for oil and gas because it can be used to differentiate between thermogenic and microbial gas and can sometimes be used for gas-source rock correlations. Methane-oxidizing bacteria, however, can significantly change the carbon isotopic composition of methane; the origin of gas that has been partially oxidized by these bacteria could therefore be misinterpreted. We cultured methane-oxidizing bacteria at two different temperatures and monitored the carbon and hydrogen isotopic compositions of the residual methane. The residual methane was enriched in both 13C and D. For both isotopic species, the enrichment at equivalent levels of conversion was greater at 26??C than at 11.5??C. The change in ??D relative to the change in ??13C was independent of temperature within the range studied. One culture exhibited a change in the fractionation pattern for carbon (but not for hydrogen) midway through the experiment, suggesting that bacterial oxidation of methane may occur via more than one pathway. The change in the ??D value for the residual methane was from 8 to 14 times greater than the change in the ??13C value, indicating that combined carbon and hydrogen isotopic analysis may be an effective way of identifying methane which has been subjected to partial oxidation by bacteria. ?? 1981.

  2. Large carbon isotope fractionation associated with oxidation of methyl halides by methylotrophic bacteria

    USGS Publications Warehouse

    Miller, L.G.; Kalin, Robert M.; McCauley, S.E.; Hamilton, John T.G.; Harper, D.B.; Millet, D.B.; Oremland, R.S.; Goldstein, Allen H.

    2001-01-01

    The largest biological fractionations of stable carbon isotopes observed in nature occur during production of methane by methanogenic archaea. These fractionations result in substantial (as much as ???70???) shifts in ??13C relative to the initial substrate. We now report that a stable carbon isotopic fractionation of comparable magnitude (up to 70???) occurs during oxidation of methyl halides by methylotrophic bacteria. We have demonstrated biological fractionation with whole Cells of three methylotrophs (strain IMB-1, strain CC495, and strain MB2) and, to a lesser extent, with the purified cobalamin-dependent methyltransferase enzyme obtained from strain CC495. Thus, the genetic similarities recently reported between methylotrophs, and methanogens with respect to their pathways for C1-unit metabolism are also reflected in the carbon isotopic fractionations achieved by these organisms. We found that only part of the observed fractionation of carbon isotopes could be accounted for by the activity of the corrinoid methyltransferase enzyme, suggesting fractionation by enzymes further along the degradation pathway. These observations are of potential biogeochemical significance in the application of stable carbon isotope ratios to constrain the tropospheric budgets for the ozone-depleting halocarbons, methyl bromide and methyl chloride.

  3. Carbon and hydrogen isotope fractionation during aerobic biodegradation of quinoline and 3-methylquinoline.

    PubMed

    Cui, Mingchao; Zhang, Wenbing; Fang, Jun; Liang, Qianqiong; Liu, Dongxuan

    2017-08-01

    Compound-specific isotope analysis has been used extensively to investigate the biodegradation of various organic pollutants. To date, little isotope fractionation information is available for the biodegradation of quinolinic compounds. In this study, we report on the carbon and hydrogen isotope fractionation during quinoline and 3-methylquinoline aerobic microbial degradation by a Comamonas sp. strain Q10. Degradation of quinoline and 3-methylquinoline was accompanied by isotope fractionation. Large hydrogen and small carbon isotope fractionation was observed for quinoline while minor carbon and hydrogen isotope fractionation effects occurred for 3-methylquinoline. Bulk carbon and hydrogen enrichment factors (ε bulk ) for quinoline biodegradation were -1.2 ± 0.1 and -38 ± 1‰, respectively, while -0.7 ± 0.1 and -5 ± 1‰ for 3-methylquinoline, respectively. This reveals a potential advantage for employing quinoline as the model compound and hydrogen isotope analysis for assessing aerobic biodegradation of quinolinic compounds. The apparent kinetic isotope effects (AKIE C ) values of carbon were 1.008 ± 0.0005 for quinoline and 1.0048 ± 0.0005 for 3-methylquinoline while AKIE H values of hydrogen of 1.264 ± 0.011 for quinoline and 1.0356 ± 0.0103 for 3-methylquinoline were obtained. The combined evaluation of carbon and hydrogen isotope fractionation yields Λ values (Λ = Δδ 2 H/Δδ 13 C ≈ εH bulk /εC bulk ) of 29 ± 2 for quinoline and 8 ± 2 for 3-methylquinoline. The results indicate that the substrate specificity may have a significant influence on the isotope fractionation for the biodegradation of quinolinic compounds. The substrate-specific isotope enrichment factors would be important for assessing the behavior and fate of quinolinic compounds in the environment.

  4. Bacterial and enchytraeid abundance accelerate soil carbon turnover along a lowland vegetation gradient in interior Alaska

    USGS Publications Warehouse

    Waldrop, M.P.; Harden, Jennifer W.; Turetsky, M.R.; Petersen, D.G.; McGuire, A.D.; Briones, M.J.I.; Churchill, A.C.; Doctor, D.H.; Pruett, L.E.

    2012-01-01

    Boreal wetlands are characterized by a mosaic of plant communities, including forests, shrublands, grasslands, and fens, which are structured largely by changes in topography and water table position. The soil associated with these plant communities contain quantitatively and qualitatively different forms of soil organic matter (SOM) and nutrient availability that drive changes in biogeochemical cycling rates. Therefore different boreal plant communities likely contain different soil biotic communities which in turn affect rates of organic matter decomposition. We examined relationships between plant communities, microbial communities, enchytraeids, and soil C turnover in near-surface soils along a shallow topographic soil moisture and vegetation gradient in interior Alaska. We tested the hypothesis that as soil moisture increases along the gradient, surface soils would become increasingly dominated by bacteria and mesofauna and have more rapid rates of C turnover. We utilized bomb radiocarbon techniques to infer rates of C turnover and the 13C isotopic composition of SOM and respired CO2 to infer the degree of soil humification. Soil phenol oxidase and peroxidase enzyme activities were generally higher in the rich fen compared with the forest and bog birch sites. Results indicated greater C fluxes and more rapid C turnover in the surface soils of the fen sites compared to the wetland forest and shrub sites. Quantitative PCR analyses of soil bacteria and archaea, combined with enchytraeid counts, indicated that surface soils from the lowland fen ecosystems had higher abundances of these microbial and mesofaunal groups. Fungal abundance was highly variable and not significantly different among sites. Microbial data was utilized in a food web model that confirmed that rapidly cycling systems are dominated by bacterial activity and enchytraeid grazing. However, our results also suggest that oxidative enzymes play an important role in the C mineralization process in

  5. Carbon Monoxide Stable Isotopes: Extraction Technique Development and Urban Atmospheric Analysis

    NASA Astrophysics Data System (ADS)

    Vimont, Isaac Josef

    We have developed an extraction system to analyze isotopes of carbon monoxide (CO). We then analyzed CO isotopes for two years at Indianapolis, IN, USA. These measurements were done at three towers, one of which measured incoming, background air into the city. We quantitatively removed the background signal and determined the urban CO mole fraction and isotopic enhancements. During the winter months, we constrained the isotopic signature and concluded that the majority of CO produced during the winter was produced by fossil fuel combustion. We found that the Indianapolis fossil fuel signature differed from that of studies done in Europe. Further, we performed a limited traffic study to look at CO isotopes from traffic. While this was not conclusive, it did support our hypothesis that a larger fraction of the Indianapolis vehicle fleet may have malfunctioning catalytic systems, which biases the isotopic results, particularly for delta18O. We used the wintertime fossil fuel isotopic signature to help constrain the summertime budget. It was hypothesized that a second source of CO was significant during the summer months. Oxidation of biogenically produced volatile organic compounds (BVOC's) was one possible source. Oxidized BVOC's were consistent with the changes between our winter and summer isotopic source signatures. We then used the isotopic signatures to determine that between zero and sixty percent of the summertime CO budget was produced from oxidized VOC's. This provided the first direct evidence of a larger percentage of urban CO being produced by oxidized VOC's.

  6. Stable carbon and nitrogen isotopes in vertical peat profiles of natural and drained boreal peatlands

    NASA Astrophysics Data System (ADS)

    Nykänen, Hannu; Mpamah, Promise; Rissanen, Antti; Pitkänen, Aki; Turunen, Jukka; Simola, Heikki

    2015-04-01

    Peatlands form a significant carbon pool in the global carbon cycle. Change in peat hydrology, due to global warming is projected to change microbiological processes and peat carbon pool. We tested if bulk stable carbon and nitrogen isotopes serve as indicators of severe long term drying in peatlands drained for forestry. Depth profile analysis of peat, for their carbon and nitrogen content as well as their carbon and nitrogen stable isotopic signatures, were conducted for peatlands in southern and eastern Finland, having ombrotrophic and minerotrophic natural and corresponding drained pairs or separate drained sites. The selection of sites allowed us to compare changes due to different fertility and changes due to long term artificial drying. Drainage lasting over 40 years has led to changes in hydrology, vegetation, nutrient mineralization and respiration. Furthermore, increased nutrient uptake and possible recycling of peat nitrogen and carbon trough vegetation back to the peat surface, also possibly has an effect on the stable isotopic composition of peat carbon and nitrogen. We think that drainage induced changes somehow correspond to those caused by changed hydrology due to climate change. We will present data from these measurements and discuss their implications for carbon and nitrogen flows in peatlands.

  7. Understanding the Marine Chromium Isotope Record from Modern and Ancient Carbonates

    NASA Astrophysics Data System (ADS)

    Parkinson, I. J.; Bonnand, P.; James, R. H.; Fairchild, I. J.; Dixon, S.

    2011-12-01

    Chromium isotopes may provide a powerful tool for reconstructing the redox state of ancient seawater because Cr isotope fractionation is large (up to 7% in δ53Cr) during the reduction of Cr(VI) to Cr(III) in natural waters [1]. Recent studies have demonstrated that although Cr(VI) is predicted to be the thermodynamically stable form in seawater (as CrO42-), significant amounts (5-20%) of Cr(III) may also be present in surface waters [2]. Therefore the δ53Cr of seawater could vary by up to 2%. Marine carbonates potentially provide a means to extracting information about the Cr isotopic composition of seawater in the geological past and we have developed a high-precision double-spike technique for analysing Cr isotopes in carbonates [3]. The δ53Cr of modern Bahamas Bank carbonates (+0.76%) is broadly consistent with these carbonates recording a seawater Cr signature. Moreover, these pure carbonates contain significant amounts of Cr (1-4 ppm), which indicates that Cr is strongly partitioned into calcium carbonate. Therefore carbonates are likely to provide a faithful record of the δ53Cr composition of seawater. Shallow marine carbonates from the Phanerozoic range in δ53Cr from +0.76 to +1.8%, and some Neoproterozoic carbonates also have heavy Cr isotopic compositions of +0.5 to +1.0 %. Such compositions may reflect changes in the inputs of Cr to the oceans and/or changes in the redox state of the oceans. However, to interpret Cr isotopic compositions in ancient carbonates additionally requires a careful assessment of their trace element contents. This study aims to demonstrate how a combination of redox sensitive trace elements, such as Ce, and Cr isotopes allow an assessment of the marine chromium isotope record. [1] Ellis et al., 2002, Science, 295, 2060-2062. [2] Connolly et al., 2006, Deep Sea Res. Part I, 2006 53, 1975-1988. [3] P. Bonnand, et al., 2011, J. Anal. At. Spectr., 26, 528-535.

  8. Contrasting Effects of Carbon and Sulfur on Fe-Isotope Fractionation between Metal and Silicate Melt during Planetary Core Formation

    NASA Astrophysics Data System (ADS)

    Elardo, S. M.; Shahar, A.

    2015-12-01

    There are numerous studies that show well-resolved Fe isotope fractionations in igneous materials from different planetary bodies. Potential explanations for these fractionations include a non-chondritic bulk planetary Fe isotopic composition, and equilibrium fractionation between Fe-alloys or minerals and silicate melts during planetary differentiation, mantle melting, or fractional crystallization. This is further complicated by the fact that these processes are not mutually exclusive, making the interpretation of Fe isotope data a complex task. Here we present new experimental results investigating the effect of C on Fe isotope fractionation between molten peridotite and an Fe-alloy. Experiments were conducted at 1 GPa and 1850° C for 0.5 - 3 hours on a mixture of an 54Fe-spiked peridotite and Fe-metal with and without Ni metal in an end-loaded piston cylinder at the Geophysical Laboratory. Carbon saturation was achieved with a graphite capsule, and resulted in C contents of the Fe-alloy in our experiments ranging from 3.8 - 4.9 wt. %. The metal and silicate phases from half of each experiment were separated manually and dissolved in concentrated acids. Iron was separated from matrix elements by anion exchange chromatagraphy. Iron-isotopic compositions were determined with the Nu Plasma II MC-ICP-MS at GL. The other half of each experiment was used for quantitative microbeam analysis. Equilibrium was assessed with a time series and the three-isotope exchange method. The Ni-free experiments resulted in no resolvable Fe isotope fractionation between the Fe-C-alloy and molten silicate. This is in contrast to the results of Shahar et al. (2015) which showed a fractionation for Δ57Fe of ~0.18 ‰ between a peridotite and an Fe-alloy with a similar S abundance to C in these experiments. The one experiment thus far that contained Ni (~4 wt. % in the alloy) showed a resolvable fractionation between the Fe-Ni-C alloy and silicate of ~0.10 ‰. Shahar et al. found a

  9. Simulation of dual carbon-bromine stable isotope fractionation during 1,2-dibromoethane degradation.

    PubMed

    Jin, Biao; Nijenhuis, Ivonne; Rolle, Massimo

    2018-06-01

    We performed a model-based investigation to simultaneously predict the evolution of concentration, as well as stable carbon and bromine isotope fractionation during 1,2-dibromoethane (EDB, ethylene dibromide) transformation in a closed system. The modelling approach considers bond-cleavage mechanisms during different reactions and allows evaluating dual carbon-bromine isotopic signals for chemical and biotic reactions, including aerobic and anaerobic biological transformation, dibromoelimination by Zn(0) and alkaline hydrolysis. The proposed model allowed us to accurately simulate the evolution of concentrations and isotope data observed in a previous laboratory study and to successfully identify different reaction pathways. Furthermore, we illustrated the model capabilities in degradation scenarios involving complex reaction systems. Specifically, we examined (i) the case of sequential multistep transformation of EDB and the isotopic evolution of the parent compound, the intermediate and the reaction product and (ii) the case of parallel competing abiotic pathways of EDB transformation in alkaline solution.

  10. A balloon measurement of the isotopic composition of galactic cosmic ray boron, carbon and nitrogen. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Zumberge, J. F.

    1981-01-01

    The isotopic compositions of galactic cosmic ray boron, carbon, and nitrogen were measured at energies near 300 MeV amu, using a balloon-borne instrument at an atmospheric depth of approximately 5 g/sq cm. The calibrations of the detectors comprising the instrument are described. The saturation properties of the cesium iodide scintillators used for measurement of particle energy are studied in the context of analyzing the data for mass. The achieved rms mass resolution varies from approximately 0.3 amu at boron to approximately 0.5 amu at nitrogen, consistent with a theoretical analysis of the contributing factors. Corrected for detector interactions and the effects of the residual atmosphere the results are B-10/B=0.33 (+0.17, -0.11), C-13/C=0.06 (+0.13, -0.11), and N-15/N=0.42 (+0.19, -0.17). A model of galactic propagation and solar modulation is described. Assuming a cosmic ray source composition of solar-like isotopic abundances, the model predicts abundances near Earth consistent with the measurements.

  11. Empirical High-Temperature Calibration for the Carbonate Clumped Isotopes Paleothermometer

    NASA Astrophysics Data System (ADS)

    Kluge, T.; John, C. M.; Jourdan, A.; Davis, S.; Crawshaw, J.

    2013-12-01

    The clumped isotope paleothermometer is being used in a wide range of applications related to carbonate mineral formation, focusing on temperature and fluid δ18O reconstruction. Whereas the range of typical Earth surface temperatures has been the focus of several studies based on laboratory experiments and biogenic carbonates of known growth temperatures, the clumped isotope-temperature relationship above 70 °C has not been assessed by direct precipitation of carbonates. We investigated the clumped isotope-temperature relationship by precipitating carbonates between 20 and 200°C in the laboratory. The setup consists of a pressurized vessel in which carbonate minerals are precipitated from the mixture of two solutions (CaCl2, NaHCO3). Both solutions are thermally and isotopically equilibrated before injection in the pressure vessel. Minerals precipitated in this setup generally consist of calcite. Samples were reacted with 105% orthophosphoric acid for 10 min at 90°C. The evolved CO2 was continuously collected and subsequently purified with a Porapak trap held at -35°C. Measurements were performed on a MAT 253 using the protocol of Huntington et al. (2009) and Dennis et al. (2011). Clumped isotope values from 20-90°C are consistent with carbonates that were precipitated from a CaCO3 super-saturated solution using the method of McCrea (1950). This demonstrates that the experimental setup does not induce any kinetic fractionation, and can be used for high-temperature carbonate precipitation. The new clumped isotope calibration at high temperature follows the theoretical calculations of Schauble et al. (2006) adjusted for phosphoric acid digestion at 90°C. We gratefully acknowledge funding from Qatar Petroleum, Shell and the Qatar Science and Technology Park.

  12. Determination of microbial carbon sources and cycling during remediation of petroleum hydrocarbon impacted soil using natural abundance (14)C analysis of PLFA.

    PubMed

    Cowie, Benjamin R; Greenberg, Bruce M; Slater, Gregory F

    2010-04-01

    In a petroleum impacted land-farm soil in Sarnia, Ontario, compound-specific natural abundance radiocarbon analysis identified biodegradation by the soil microbial community as a major pathway for hydrocarbon removal in a novel remediation system. During remediation of contaminated soils by a plant growth promoting rhizobacteria enhanced phytoremediation system (PEPS), the measured Delta(14)C of phospholipid fatty acid (PLFA) biomarkers ranged from -793 per thousand to -897 per thousand, directly demonstrating microbial uptake and utilization of petroleum hydrocarbons (Delta(14)C(PHC) = -1000 per thousand). Isotopic mass balance indicated that more than 80% of microbial PLFA carbon was derived from petroleum hydrocarbons (PHC) and a maximum of 20% was obtained from metabolism of more modern carbon sources. These PLFA from the contaminated soils were the most (14)C-depleted biomarkers ever measured for an in situ environmental system, and this study demonstrated that the microbial community in this soil was subsisting primarily on petroleum hydrocarbons. In contrast, the microbial community in a nearby uncontaminated control soil maintained a more modern Delta(14)C signature than total organic carbon (Delta(14)C(PLFA) = +36 per thousand to -147 per thousand, Delta(14)C(TOC) = -148 per thousand), indicating preferential consumption of the most modern plant-derived fraction of soil organic carbon. Measurements of delta(13)C and Delta(14)C of soil CO(2) additionally demonstrated that mineralization of PHC contributed to soil CO(2) at the contaminated site. The CO(2) in the uncontaminated control soil exhibited substantially more modern Delta(14)C values, and lower soil CO(2) concentrations than the contaminated soils, suggesting increased rates of soil respiration in the contaminated soils. In combination, these results demonstrated that biodegradation in the soil microbial community was a primary pathway of petroleum hydrocarbon removal in the PEPS system. This study

  13. Carbon isotope ratios and isotopic correlations between components in fruit juices

    NASA Astrophysics Data System (ADS)

    Wierzchnicki, Ryszard

    2013-04-01

    Nowadays food products are defined by geographical origin, method of production and by some regulations concerning terms of their authenticity. Important data for confirm the authenticity of product are providing by isotopic methods of food control. The method checks crucial criteria which characterize the authenticity of inspected product. The European Union Regulations clearly show the tendency for application of the isotopic methods for food authenticity control (wine, honey, juice). The aim of the legislation steps is the protection of European market from possibility of the commercial frauds. Method of isotope ratio mass spectrometry is very effective tool for the use distinguishably the food products of various geographical origin. The basic problem for identification of the sample origin is the lack of databases of isotopic composition of components and information about the correlations of the data. The subject of the work was study the isotopic correlations existing between components of fruits. The chemical and instrumental methods of separation: water, sugars, organic acids and pulp from fruit were implemented. IRMS technique was used to measure isotopic composition of samples. The final results for original samples of fruits (apple, strawberry etc.) will be presented and discussed. Acknowledgement: This work was supported by the Polish Ministry of Science and Higher Education under grant NR12-0043-10/2010.

  14. Stable Carbon and Nitrogen Isotope Ratios of Sodium and Potassium Cyanide as a Forensic Signature

    SciTech Connect

    Kruzer, Helen W; Horita, Juske; Moran, James J

    2012-01-01

    Sodium and potassium cyanide are highly toxic, produced in large amounts by the chemical industry, and linked to numerous high-profile crimes. The U.S. Centers for Disease Control and Prevention has identified cyanide as one of the most probable agents to be used in a future chemical terrorism event. We investigated whether stable C and N isotopic content of sodium and potassium cyanide could serve as a forensic signature for sample matching, using a collection of 65 cyanide samples. A few of these samples displayed non-homogeneous isotopic content associated with degradation to a carbonate salt and loss of hydrogen cyanide. Mostmore » samples had highly reproducible isotope content. Of these, >95% could be properly matched based on C and N isotope ratios, with a false match rate <3%. These results suggest that stable C and N isotope ratios are a useful forensic signature for matching cyanide samples.« less

  15. Stable carbon and nitrogen isotope ratios of sodium and potassium cyanide as a forensic signature.

    PubMed

    Kreuzer, Helen W; Horita, Juske; Moran, James J; Tomkins, Bruce A; Janszen, Derek B; Carman, April

    2012-01-01

    Sodium and potassium cyanide are highly toxic, produced in large amounts by the chemical industry, and linked to numerous high-profile crimes. The U.S. Centers for Disease Control and Prevention has identified cyanide as one of the most probable agents to be used in a chemical terrorism event. We investigated whether stable C and N isotopic content of sodium and potassium cyanide could serve as a forensic signature for sample matching, using a collection of 65 cyanide samples. Upon analysis, a few of the cyanide samples displayed nonhomogeneous isotopic content associated with degradation to a carbonate salt and loss of hydrogen cyanide. Most samples had highly reproducible isotope content. Of the 65 cyanide samples, >95% could be properly matched based on C and N isotope ratios, with a false match rate <3%. These results suggest that stable C and N isotope ratios are a useful forensic signature for matching cyanide samples. © 2011 American Academy of Forensic Sciences.

  16. Intraspecific carbon and nitrogen isotopic variability in foxtail millet (Setaria italica).

    PubMed

    Lightfoot, Emma; Przelomska, Natalia; Craven, Martha; O Connell, Tamsin C; He, Lu; Hunt, Harriet V; Jones, Martin K

    2016-07-15

    Isotopic palaeodietary studies generally focus on bone collagen from human and/or animal remains. While plant remains are rarely analysed, it is known that plant isotope values can vary as a result of numerous factors, including soil conditions, the environment and type of plant. The millets were important food crops in prehistoric Eurasia, yet little is known about the isotopic differences within millet species. Here we compare the stable isotope ratios within and between Setaria italica plants grown in a controlled environment chamber. Using homogenised samples, we compare carbon isotope ratios of leaves and grains, and nitrogen isotope ratios of grains, from 29 accessions of Setaria italica. We find significant isotopic variability within single leaves and panicles, and between leaves and panicles within the same plant, wh