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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. Determination of the abundance and carbon isotope composition of elemental carbon in sediments

    NASA Astrophysics Data System (ADS)

    Bird, Michael I.; Gröcke, Darren R.

    1997-08-01

    We report measurements of the susceptibility of a variety of elemental and organic carbon samples to oxidative degradation using both acid dichromate and basic peroxide reagents. Organic carbon is rapidly oxidized using either reagent, or both reagents sequentially. Elemental carbon exhibits a wide range of susceptibilities to oxidation related both to the degree to which the precursor plant material was carbonized during pyrolysis and to the surface area available for oxidation. Despite a range of susceptibilities, a component of oxidation-resistant elemental carbon has been identified which can be reproducibly separated from organic contaminants. The carbon isotope composition (δ 13C value) of the precursor plant materials underwent a 0-1.6‰ decrease during the production of the elemental carbon by pyrolysis, while the subsequent oxidative degradation of the samples resulted in only small (generally < 0.5%o) changes in the δ 13C value of the remaining elemental carbon. The results suggest that the technique can be used to obtain records of elemental carbon abundance in marine sediment cores, and thus a record of the intensity of biomass burning on adjacent continental land masses in the geologic past. In addition, the δ 13C value of the elemental carbon can provide an indication of the type of vegetation being burnt.

  3. 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.

  4. 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.

  5. Abundance, distribution, and isotopic composition of particulate black carbon in the northern Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Yang, Weifeng; Guo, Laodong

    2014-11-01

    There exists increasing evidence supporting the important role of black carbon in global carbon cycles. Particulate black carbon (PBC) is allochthonous and has distinct reactivities compared to the bulk particulate organic carbon (tot-POC) in marine environments. However, the abundance, geochemical behavior of PBC and its importance in oceanic carbon budget remain poorly understood. Here we report the abundance, distribution, and stable isotopic signatures of BC derived from the chemo-thermal oxidation (CTO-375) method (BCCTO) in the Gulf of Mexico. Our results show that BCCTO abundance decreased from shelf to basin, and more than a half of riverine BCCTO could be removed over the shelf. Moreover, BCCTO is much more refractory compared to the tot-POC and has δ13C values lower than those of BC-excluded POC. These results highlight the significance of PBC in marine carbon cycles and potentially suggest the need for a new end-member term in quantifying POC sources in the ocean.

  6. 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.

  7. Carbon, hydrogen and nitrogen in carbonaceous chondrites Abundances and isotopic compositions in bulk samples

    NASA Technical Reports Server (NTRS)

    Kerridge, J. F.

    1985-01-01

    Whole-rock samples of 25 carbonaceous chondrites were analyzed for contents of C, H and N and delta C-13, delta D and delta N-15. Inhomogeneous distribution of these isotopes within individual meteorites is pronounced in several cases. Few systematic intermeteorite trends were observed; N data are suggestive of isotopic inhomogeneity in the early solar system. Several chondrites revealed unusual compositions which would repay further, more detailed study. The data are also useful for classification of carbonaceous chondrites; N abundance and isotopic compositions can differentiate existing taxonomic groups with close to 100 percent reliability; Al Rais and Renazzo clearly constitute a discrete 'grouplet', and there are hints that both CI and CM groups may each be divisible into two subgroups.

  8. 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

  9. CNO abundances and carbon isotope ratios in evolved stars of the open clusters NGC 2324, NGC 2477, and NGC 3960

    NASA Astrophysics Data System (ADS)

    Tautvaišienė, Gražina; Drazdauskas, Arnas; Bragaglia, Angela; Randich, Sofia; Ženovienė, Renata

    2016-10-01

    Aims: Our main aim is to determine carbon-to-nitrogen and carbon isotope ratios for evolved giants in the open clusters NGC 2324, NGC 2477, and NGC 3960, which have turn-off masses of about 2 M⊙, and to compare them with predictions of theoretical models. Methods: High-resolution spectra were analysed using a differential synthetic spectrum method. Abundances of carbon were derived using the C2 Swan (0, 1) band heads at 5135 and 5635.5 Å. The wavelength interval 7940-8130 Å with strong CN features was analysed to determine nitrogen abundances and carbon isotope ratios. The oxygen abundances were determined from the [O i] line at 6300 Å. Results: The mean values of the CNO abundances are [C/Fe] = -0.35 ± 0.06 (s.d.), [N/Fe] = 0.28 ± 0.05, and [O/Fe] = -0.02 ± 0.10 in seven stars of NGC 2324; [C/Fe] = -0.26 ± 0.02, [N/Fe] = 0.39 ± 0.04, and [O/Fe] = -0.11 ± 0.06 in six stars of NGC 2477; and [C/Fe] = -0.39 ± 0.04, [N/Fe] = 0.32 ± 0.05, and [O/Fe] = -0.19 ± 0.06 in six stars of NGC 3960. The mean C/N ratio is equal to 0.92 ± 0.12, 0.91 ± 0.09, and 0.80 ± 0.13, respectively. The mean 12C /13C ratio is equal to 21 ± 1, 20 ± 1, and 16 ± 4, respectively. The 12C /13C and C/N ratios of stars in the investigated open clusters were compared with the ratios predicted by stellar evolution models. Conclusions: The mean values of the 12C /13C and C/N ratios in NGC 2324 and NGC 2477 agree well with the first dredge-up and thermohaline-induced extra-mixing models, which are similar for intermediate turn-off mass stars. The 12C /13C ratios in the investigated clump stars of NGC 3960 span from 10 to 20. The mean carbon isotope and C/N ratios in NGC 3960 are close to predictions of the model in which the thermohaline- and rotation-induced (if rotation velocity at the zero-age main sequence was 30% of the critical velocity) extra-mixing act together. Based on observations collected at ESO telescopes under programmes 072.D-0550 and 074.D-0571.

  10. Temporal variation in mycorrhizal diversity and carbon and nitrogen stable isotope abundance in the wintergreen meadow orchid Anacamptis morio.

    PubMed

    Ercole, Enrico; Adamo, Martino; Rodda, Michele; Gebauer, Gerhard; Girlanda, Mariangela; Perotto, Silvia

    2015-02-01

    Many adult orchids, especially photoautotrophic species, associate with a diverse range of mycorrhizal fungi, but little is known about the temporal changes that might occur in the diversity and functioning of orchid mycorrhiza during vegetative and reproductive plant growth. Temporal variations in the spectrum of mycorrhizal fungi and in stable isotope natural abundance were investigated in adult plants of Anacamptis morio, a wintergreen meadow orchid. Anacamptis morio associated with mycorrhizal fungi belonging to Tulasnella, Ceratobasidium and a clade of Pezizaceae (Ascomycetes). When a complete growing season was investigated, multivariate analyses indicated significant differences in the mycorrhizal fungal community. Among fungi identified from manually isolated pelotons, Tulasnella was more common in autumn and winter, the pezizacean clade was very frequent in spring, and Ceratobasidium was more frequent in summer. By contrast, relatively small variations were found in carbon (C) and nitrogen (N) stable isotope natural abundance, A. morio samples showing similar (15)N enrichment and (13)C depletion at the different sampling times. These observations suggest that, irrespective of differences in the seasonal environmental conditions, the plant phenological stages and the associated fungi, the isotopic content in mycorrhizal A. morio remains fairly constant over time.

  11. Tracing the source of cooking oils with an integrated approach of using stable carbon isotope and fatty acid abundance.

    PubMed

    Liu, Weiguo; Yang, Hong; Wang, Zheng; Liu, Jinzhao

    2012-08-15

    We report a new approach to identify swill-cooked oils that are recycled from tainted food and livestock waste from commercial vegetable and animal oils by means of carbon isotope values and relative abundance of fatty acids. We test this method using 40 cooking oil samples of different types with known sources. We found significant differences in both total organic carbon isotope as well as compound-specific isotope values and fatty acid C(14)/C(18) ratios between commercial vegetable oils refined from C(3) plants (from -35.7 to -27.0‰ and from 0 to 0.15) and animal oils (from -28.3 to -14.3‰ and from 0.1 to 0.6). Tested swill-cooked oils, which were generally refined by mixing with animal waste illegally, fall into a narrow δ(13)C/fatty acid ratio distribution: from -25.9 to -24.1‰ and from 0.1 to 0.2. Our data demonstrate that the index of a cross-plotting between fatty acid δ(13)C values and C(14)/C(18) ratios can be used to distinguish clean commercial cooking oils from illegal swill-cooked oils.

  12. 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.

  13. 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

  14. 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

  15. Evolution, Abundance and Biocalcification of Calcareous Nannoplankton During the Aptian (Early Cretaceous): Causes and Consequences for C Isotopic Anomalies, Climate Changes and the Carbon Cycle.

    NASA Astrophysics Data System (ADS)

    Erba, E.

    2005-12-01

    The mid Cretaceous is marked by extreme greenhouse conditions, coeval with emplacement of large igneous provinces, C isotopic anomalies, major changes in structure and composition of the oceans, and accelerated rates in the evolutionary history of calcareous plankton. The Aptian is a crucial interval to decipher links between biotic evolution and environmental pressure: it is appealing for understanding nannofloral biocalcification and feedbacks in the carbonate system and in the global carbon cycle. Ontong Java, Manihiki and Kerguelen Plateaus formed in the Aptian affecting the ocean-atmosphere system with excess CO2, changes in Ca2+ and Mg2+ concentrations, and varying nutrient cycling. Two large C isotopic anomalies are associated with episodes of prolonged high primary productivity, changes in alkality, global warming and cooling, anoxia, speciations and extinctions in planktonic communities. Nannofossil diversity, abundance and biocalcification are quantified in continuous, complete, pelagic sections to derive biosphere-geosphere interactions at short and long time scales. The early Aptian C isotopic anomaly interrupts a speciation episode in calcareous nannoplankton paralleled by a drastic reduction in nannofossil paleofluxes culminating in the nannoconid crisis preceding the Oceanic Anoxic Event 1a and the negative C isotopic spike linked to clathrate melting presumably triggered by the thermal maximum at the onset of the mid Cretaceous greenhouse climate. No extinctions are recorded. In the early late Aptian resumption of nannoconid production and appearance of several taxa are coeval with a return to normal C isotopic values. The occurrence of calpionellids and diversified planktonic foraminifers indicate successful biocalcification and restoration of the thermocline. In the late Aptian a drop in nannofossil abundance and accelerated extinction rates are associated with another C isotopic excursion under cool conditions possibly due to a prolonged volcanic

  16. 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.

  17. Carbon isotopes in comets

    NASA Technical Reports Server (NTRS)

    Wehinger, Peter A.

    1990-01-01

    The progress is reported of high resolution spectra of selected bright comets with the aim of determining the carbon isotope abundance ratio, C-12/C-13. The ratio was determined for various Solar System objects (in the atmospheres of the giant planets, meteorites, the Earth, and the solar photosphere), where the C-12/C-13 = 89/1. In the interstellar medium, optical and radio observations give a range of C-12/C-13 = 43-67/1 depending on the observing techniques used and the specific interstellar cloud observed. The echelle spectra is presented of the CN(0,0) violet system in three comets: P/Brorsen-Metcalf, C/Okazaki-Levy-Rudenko, and C/Austin. P/Brorsen-Metcalf has a period of 70 y (prograde) compared with P/Halley which is 76 y (retrograde). The similar periods made P/Brorsen-Metcalf of special interest for comparison with P/Halley.

  18. Tracing magma sources in an arc-arc collision zone: Helium and carbon isotope and relative abundance systematics of the Sangihe Arc, Indonesia

    NASA Astrophysics Data System (ADS)

    Jaffe, Lillie A.; Hilton, David R.; Fischer, Tobias P.; Hartono, Udi

    2004-04-01

    The Sangihe Arc is presently colliding with the Halmahera Arc in northeastern Indonesia, forming the world's only extant example of an arc-arc collision zone. We report the first helium and carbon isotopic and relative abundance data from the Sangihe Arc volcanoes as a means to trace magma origins in this complicated tectonic region. Results of this study define a north-south trend in 3He/4He, CO2/3He, and δ13C, suggesting that there are variations in primary magma source characteristics along the strike of the arc. The northernmost volcanoes (Awu and Karangetang) have higher CO2/3He and δ13C (up to 179 × 109 and -0.4‰, respectively) and lower 3He/4He (˜5.4 RA) than the southernmost volcanoes (Ruang, Lokon, and Mahawu). Resolving the arc CO2 into component structures (mantle-derived, plus slab-derived organic and carbonate CO2), the northern volcanoes contain an unusually high (>90%) contribution of CO2 derived from isotopically heavy carbonate associated with the subducting slab (sediment and altered oceanic basement). Furthermore, the overall slab contribution (CO2 of carbonate and organic origin) relative to carbon of mantle wedge origin is significantly enhanced in the northern segment of the arc. These observations may be caused by greater volumes of sediment subduction in the northern arc, along-strike variability in subducted sediment composition, or enhanced slab-derived fluid/melt production resulting from the superheating of the slab as collision progresses southward.

  19. Micron-scale coupled carbon isotope and nitrogen abundance variations in diamonds: Evidence for episodic diamond formation beneath the Siberian Craton

    NASA Astrophysics Data System (ADS)

    Wiggers de Vries, D. F.; Bulanova, G. P.; De Corte, K.; Pearson, D. G.; Craven, J. A.; Davies, G. R.

    2013-01-01

    The internal structure and growth history of six macro-diamonds from kimberlite pipes in Yakutia (Russia) were investigated with cathodoluminescence imaging and coupled carbon isotope and nitrogen abundance analyses along detailed core to rim traverses. The diamonds are characterised by octahedral zonation with layer-by-layer growth. High spatial resolution SIMS profiles establish that there is no exchange of the carbon isotope composition across growth boundaries at the μm scale and that isotopic variations observed between (sub)zones within the diamonds are primary. The macro-diamonds have δ13C values that vary within 2‰ of -5.3‰ and their nitrogen contents range between 0-1334 at. ppm. There are markedly different nitrogen aggregation states between major growth zones within individual diamonds that demonstrate Yakutian diamonds grew in multiple growth events. Growth intervals were punctuated by stages of dissolution now associated with <10 μm wide zones of nitrogen absent type II diamond. Across these resorption interfaces carbon isotope ratios and nitrogen contents record shifts between 0.5-2.3‰ and up to 407 at. ppm, respectively. Co-variation in δ13C value-nitrogen content suggests that parts of individual diamonds precipitated in a Rayleigh process from either oxidised or reduced fluids/melts, with two single diamonds showing evidence of both fluid types. Modelling the co-variation establishes that nitrogen is a compatible element in diamond relative to its growth medium and that the nitrogen partition coefficient is different between oxidised (3-4.1) and reduced (3) sources. The reduced sources have δ13C values between -7.3‰ and -4.6‰, while the oxidised sources have higher δ13C values between -5.8‰ and -1.8‰ (if grown from carbonatitic media) or between -3.8‰ and +0.2‰ (if grown from CO2-rich media). It is therefore concluded that individual Yakutian diamonds originate from distinct fluids/melts of variable compositions. The

  20. 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.

  1. Helium isotopic abundance variation in nature

    SciTech Connect

    Holden, N.E.

    1993-08-01

    The isotopic abundance of helium in nature has been reviewed. This atomic weight value is based on the value of helium in the atmosphere, which is invariant around the world and up to a distance of 100,000 feet. Helium does vary in natural gas, volcanic rocks and gases, ocean floor sediments, waters of various types and in radioactive minerals and ores due to {alpha} particle decay of radioactive nuclides.

  2. 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.

  3. 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.

  4. Study of the Role of Terrestrial Processes in the Carbon Cycle Based on Measurements of the Abundance and Isotopic Composition of Atmospheric CO2

    SciTech Connect

    Piper, Stephen C; Keeling, Ralph F

    2012-01-03

    The main objective of this project was to continue research to develop carbon cycle relationships related to the land biosphere based on remote measurements of atmospheric CO2 concentration and its isotopic ratios 13C/12C, 18O/16O, and 14C/12C. The project continued time-series observations of atmospheric carbon dioxide and isotopic composition begun by Charles D. Keeling at remote sites, including Mauna Loa, the South Pole, and eight other sites. Using models of varying complexity, the concentration and isotopic measurements were used to study long-term change in the interhemispheric gradients in CO2 and 13C/12C to assess the magnitude and evolution of the northern terrestrial carbon sink, to study the increase in amplitude of the seasonal cycle of CO2, to use isotopic data to refine constraints on large scale changes in isotopic fractionation which may be related to changes in stomatal conductance, and to motivate improvements in terrestrial carbon cycle models. The original proposal called for a continuation of the new time series of 14C measurements but subsequent descoping to meet budgetary constraints required termination of measurements in 2007.

  5. Hydrogen and carbon abundances and isotopic ratios in apatite from alkaline intrusive complexes, with a focus on carbonatites

    SciTech Connect

    Nadeau, S.L.; Epstein, S.; Stolper, E.

    1999-06-01

    The authors report H and C contents and {delta}D and {delta}{sup 13}C values of apatites from 15 alkaline intrusive complexes ranging in age from 110 Ma to 2.6 Ga. Sampling focused on carbonatites, but included silicate rocks as well. Heating temperatures up to 1,500 C is needed to extract fully H{sub 2}O and CO{sub 2} from these apatites. Apatites from carbonatite-rich intrusive complexes contain 0.2--1.1 wt% H{sub 2}O and 0.05--0.70 wt% CO{sub 2}; apatites from two silicate-rich alkaline complexes with little or no carbonatite are generally poorer in both volatile components (0.1--0.2% H{sub 2}O and 0.01--0.11% CO{sub 2}). D/H ratios in apatites from these rocks are bimodally distributed. The authors suggest that the {delta}D values of group I apatites represent primitive, mantle-derived values and that the group II apatites crystallized from degassed magmas, resulting in lower H{sub 2}O contents and {delta}D values. In contrast to H{sub 2}O contents and {delta}D values, CO{sub 2} contents and {delta}{sup 13}C values of gas released at high temperatures from multiple aliquots of these apatite samples are variable. This suggests the presence of more than one C-bearing component in these apatites, one of which is proposed to be dissolved carbonate; the other could be associated with hydrocarbons.

  6. 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.

  7. Carbon isotopic fractionation in heterotrophic microbial metabolism.

    PubMed Central

    Blair, N; Leu, A; Muñoz, 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% depleted in 13C relative to the glucose used as the carbon source, whereas the acetate was 12.3% enriched in 13C. The acetate 13C enrichment was solely in the carboxyl group. Even though the total cellular carbon was only 0.6% depleted in 13C, intracellular components exhibited a significant isotopic heterogeneity. The protein and lipid fractions were -1.1 and -2.7%, respectively. Aspartic and glutamic acids were -1.6 and +2.7%, respectively, yet citrate was isotopically identical to the glucose. Probable sites of carbon isotopic fractionation include the enzyme, phosphotransacetylase, and the Krebs cycle. PMID:2867741

  8. 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.

  9. Carbon isotopic fractionation in heterotrophic microbial metabolism

    SciTech Connect

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

    1985-10-01

    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. 38 references.

  10. THE ATOMIC WEIGHTS COMMISSION AND ISOTOPIC ABUNDANCE RATIO DETERMINATIONS.

    SciTech Connect

    HOLDEN, N.E.

    2005-08-07

    Following Thomson's discovery of stable isotopes in non-radioactive chemical elements, the derivation of atomic weight values from mass spectrometric measurements of isotopic abundance ratios moved very slowly. Forty years later, only 3 1/2 % of the recommended values were based on mass spectrometric measurements and only 38% in the first half century. It might be noted that two chemical elements (tellurium and mercury) are still based on chemical measurements, where the atomic weight value calculated from the relative isotopic abundance measurement either agrees with the value from the chemical measurement or the atomic weight value calculated from the relative isotopic abundance measurement falls within the uncertainty of the chemical measurement of the atomic weight. Of the 19 chemical elements, whose atomic weight is based on non-corrected relative isotopic abundance measurements, five of these are two isotope systems (indium, iridium, lanthanum, lutetium and tantalum) and one is a three-isotope system (oxygen).

  11. 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.

  12. 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.

  13. 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.

  14. 238U series isotopes and 232Th in carbonates and black shales from the Lesser Himalaya: implications to dissolved uranium abundances in Ganga-Indus source waters.

    PubMed

    Singh, S K; Dalai, Tarun K; Krishnaswami, S

    2003-01-01

    238U and (232)Th concentrations and the extent of (238)U-(234)U-(230)Th radioactive equilibrium have been measured in a suite of Precambrian carbonates and black shales from the Lesser Himalaya. These measurements were made to determine their abundances in these deposits, their contributions to dissolved uranium budget of the headwaters of the Ganga and the Indus in the Himalaya and to assess the impact of weathering on (238)U-(234)U-(230)Th radioactive equilibrium in them. (238)U concentrations in Precambrian carbonates range from 0.06 to 2.07 microg g(-1). The 'mean' U/Ca in these carbonates is 2.9 ng U mg(-1) Ca. This ratio, coupled with the assumption that all Ca in the Ganga-Indus headwaters is of carbonate origin and that U and Ca behave conservatively in rivers after their release from carbonates, provides an upper limit on the U contribution from these carbonates, to be a few percent of dissolved uranium in rivers. There are, however, a few streams with low uranium concentrations, for which the carbonate contribution could be much higher. These results suggest that Precambrian carbonates make only minor contributions to the uranium budget of the Ganga-Indus headwaters in the Himalaya on a basin wide scale, however, they could be important for particular streams. Similar estimates of silicate contribution to uranium budget of these rivers using U/Na in silicates and Na* (Na corrected for cyclic and halite contributions) in river waters show that silicates can contribute significantly (approximately 40% on average) to their U balance. If, however, much of the uranium in these silicates is associated with weathering resistant minerals, then the estimated silicate uranium component would be upper limits. Uranium concentration in black shales averages about 37 microg g(-1). Based on this concentration, supply of U from at least approximately 50 mg of black shales per liter of river water is needed to balance the average river water U concentration, 1.7 microg L

  15. Isotopic abundance in atom trap trace analysis

    SciTech Connect

    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.

  16. (Carbon isotope fractionation inplants)

    SciTech Connect

    O'Leary, M.H.

    1990-01-01

    The objectives of this research are: To develop a theoretical and experimental framework for understanding isotope fractionations in plants; and to develop methods for using this isotope fractionation for understanding the dynamics of CO{sub 2} fixation in plants. Progress is described.

  17. Coupling a high-temperature catalytic oxidation total organic carbon analyzer to an isotope ratio mass spectrometer to measure natural-abundance delta13C-dissolved organic carbon in marine and freshwater samples.

    PubMed

    Panetta, Robert J; Ibrahim, Mina; Gélinas, Yves

    2008-07-01

    The stable isotope composition of dissolved organic carbon (delta(13)C-DOC) provides powerful information toward understanding carbon sources and cycling, but analytical limitations have precluded its routine measurement in natural samples. Recent interfacing of wet oxidation-based dissolved organic carbon analyzers and isotope ratio mass spectrometers has simplified the measurement of delta(13)C-DOC in freshwaters, but the analysis of salty estuarine/marine samples still proves difficult. Here we describe the coupling of the more widespread high-temperature catalytic oxidation-based total organic carbon analyzer to an isotope ratio mass spectrometer (HTC-IRMS) through cryogenic trapping of analyte gases exiting the HTC analyzer for routine analysis of delta(13)C-DOC in aquatic and marine samples. Targeted elimination of major sources of background CO2 originating from the HTC analyzer allows for the routine measurement of samples over the natural range of DOC concentrations (from 40 microM to over 2000 microM), and salinities (<0.1-36 g/kg). Because consensus reference natural samples for delta(13)C-DOC do not exist, method validation was carried out with water-soluble stable isotope standards as well as previously measured natural samples (IAEA sucrose, Suwannee River Fulvic Acids, Deep Sargasso Sea consensus reference material, and St. Lawrence River water) and result in excellent delta(13)C-DOC accuracy (+/-0.2 per thousand) and precision (+/-0.3 per thousand).

  18. 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.

  19. LITERATURE SURVEY ON ISOTOPIC ABUNDANCE RATIO MEASUREMENTS - 2001-2005

    SciTech Connect

    HOLDEN, N.E.

    2005-08-13

    Along with my usual weekly review of the published literature for new nuclear data, I also search for new candidates for best measurements of isotopic abundances from a single source. Most of the published articles, that I previously had found in the Research Library at the Brookhaven Lab, have already been sent to the members of the Atomic Weights Commission, by either Michael Berglund or Thomas Walczyk. In the last few days, I checked the published literature for any other articles in the areas of natural variations in isotopic abundance ratios, measurements of isotopic abundance ratios on samples of extra-terrestrial material and isotopic abundance ratio measurements performed using ICPMS instruments. Hopefully this information will be of interest to members of the Commission, the sub-committee on isotopic abundance measurements (SIAM), members of the former sub-committee on natural isotopic fractionation (SNIF), the sub-committee on extra-terrestrial isotope ratios (SETIR), the RTCE Task Group and the Guidelines Task Group, who are dealing with ICPMS and TIMS comparisons. In the following report, I categorize the publications in one of four areas. Measurements performed using either positive or negative ions with Thermal Ionization Mass Spectrometer, TIMS, instruments; measurements performed on Inductively Coupled Plasma Mass Spectrometer, ICPMS, instruments; measurements of natural variations of the isotopic abundance ratios; and finally measurements on extra-terrestrial samples with instrumentation of either type. There is overlap in these areas. I selected out variations and ET results first and then categorized the rest of the papers by TIMS and ICPMS.

  20. 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.

  1. The new face of isotopic NMR at natural abundance.

    PubMed

    Jézéquel, Tangi; Joubert, Valentin; Giraudeau, Patrick; Remaud, Gérald S; Akoka, Serge

    2017-02-01

    The most widely used method for isotope analysis at natural abundance is isotope ratio monitoring by Mass Spectrometry (irm-MS) which provides bulk isotopic composition in (2) H, (13) C, (15) N, (18) O or (34) S. However, in the 1980s, the direct access to Site-specific Natural Isotope Fractionation by Nuclear Magnetic Resonance (SNIF-NMR(TM) ) was immediately recognized as a powerful technique to authenticate the origin of natural or synthetic products. The initial - and still most popular - application consisted in detecting the chaptalization of wines by irm-(2) H NMR. The approach has been extended to a wide range of methodologies over the last decade, paving the way to a wide range of applications, not only in the field of authentication but also to study metabolism. In particular, the emerging irm-(13) C NMR approach delivers direct access to position-specific (13) C isotope content at natural abundance. After highlighting the application scope of irm-NMR ((2) H and (13) C), this article describes the major improvements which made possible to reach the required accuracy of 1‰ (0.1%) in irm-(13) C NMR. The last part of the manuscript summarizes the different steps to perform isotope analysis as a function of the sample properties (concentration, peak overlap) and the kind of targeted isotopic information (authentication, affiliation). Copyright © 2016 John Wiley & Sons, Ltd.

  2. Literature survey of isotopic abundance data for 1987-1989

    SciTech Connect

    Holden, N.E. )

    1989-08-09

    I have compiled all of the data on isotopic abundance measurements and their variation in nature for the time period since the last General Assembly. Most of the data deals with the variations in the abundances as given by per mil deviations from some standard. As such, they are not of major interest to the Atomic Weights Commission. However, there were some measurements which are of general interest in this list.

  3. Carbon-13 isotopic abundance and concentration of atmospheric methane for background air in the Southern and Northern Hemispheres from 1978 to 1989

    SciTech Connect

    Stevens, C.M.; Sepanski; Morris, L.J.

    1995-03-01

    Atmospheric methane (CH{sub 4}) may become an increasingly important contributor to global warming in future years. Its atmospheric concentration has risen, doubling over the past several hundred years, and additional methane is thought to have a much greater effect on climate, on a per molecule basis, than additional C0{sub 2} at present day concentrations (Shine et al. 1990). The causes of the increase of atmospheric CH{sub 4} have been difficult to ascertain because of a lack of quantitative knowledge of the fluxes (i.e., net emissions) from the numerous anthropogenic and natural sources. The goal of CH{sub 4} isotopic studies is to provide a constraint (and so reduce the uncertainties) in estimating the relative fluxes from the various isotopically distinct sources, whose combined fluxes must result in the measured atmospheric isotopic composition, after the fractionating effect of the atmospheric removal process is considered. In addition, knowledge of the spatial and temporal changes in the isotopic composition of atmospheric CH{sub 4}, along with estimates of the fluxes from some of the major sources, makes it possible to calculate growth rates for sources whose temporal emissions trends would be difficult to measure directly.

  4. The abundance and isotopic composition of water in eucrites

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    Volatile elements play a key role in the dynamics of planetary evolution. Extensive work has been carried out to determine the abundance, distribution, and source(s) of volatiles in planetary bodies such as the Earth, Moon, and Mars. A recent study showed that the water in apatite from eucrites has similar hydrogen isotopic compositions compared to water in terrestrial rocks and carbonaceous chondrites, suggesting that water accreted very early in the inner solar system given the ancient crystallization ages (~4.5 Ga) of eucrites. Here, the measurements of water (reported as equivalent H2O abundances) and the hydrogen isotopic composition (δD) of apatite from five basaltic eucrites and one cumulate eucrite are reported. Apatite H2O abundances range from ~30 to ~3500 ppm and are associated with a weighted average δD value of -34 ± 67‰. No systematic variations or correlations are observed in H2O abundance or δD value with eucrite geochemical trend or metamorphic grade. These results extend the range of previously published hydrogen isotope data for eucrites and confirm the striking homogeneity in the H-isotopic composition of water in eucrites, which is consistent with a common source for water in the inner solar system.

  5. Developing Model Constraints on Northern Extra-Tropical Carbon Cycling Based on measurements of the Abundance and Isotopic Composition of Atmospheric CO2

    SciTech Connect

    Keeling, Ralph

    2014-12-12

    The objective of this project was to perform CO2 data syntheses and modeling activities to address two central questions: 1) how much has the seasonal cycle in atmospheric CO2 at northern high latitudes changed since the 1960s, and 2) how well do prognostic biospheric models represent these changes. This project also supported the continuation of the Scripps time series of CO2 isotopes and concentration at ten baseline stations distributed globally.

  6. The separation of stable isotopes of carbon

    NASA Astrophysics Data System (ADS)

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

    1989-04-01

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

  7. Mass Spectrometric Measurement of Martian Krypton and Xenon Isotopic Abundance

    NASA Technical Reports Server (NTRS)

    Mahaffy, P.; Mauersberger, K.

    1993-01-01

    The Viking gas chromatograph mass spectrometer experiment provided significant data on the atmospheric composition at the surface of Mars, including measurements of several isotope ratios. However, the limited dynamic range of this mass spectrometer resulted in marginal measurements for the important Kr and Xe isotopic abundance. The Xe-129 to Xe-132 ratio was measured with an uncertainty of 70%, but none of the other isotope ratios for these species were obtained. Accurate measurement of the Xe and Kr isotopic abundance in this atmosphere provides an important data point in testing theories of planetary formation and atmospheric evolution. The measurement is also essential for a stringent test for the Martian origin of the SNC meteorites, since the Kr and Xe fractionation pattern seen in gas trapped in glassy nodules of an SNC (EETA 79001) is unlike any other known solar system resevoir. Current flight mass spectrometer designs combined with the new technology of a high-performance vacuum pumping system show promise for a substantial increase in gas throughput and the dynamic range required to accurately measure these trace species. Various aspects of this new technology are discussed.

  8. 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.

  9. 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.

  10. Isotope tracers of organic carbon during artificial recharge

    SciTech Connect

    Davisson, M.L.

    1998-02-09

    This project developed an analytical technique for measuring the isotope abundance for 14C and 13C in total organic carbon (TOC) in order to test whether these measurements can trace TOC interaction with sedimentary material at the bottom of rivers and lakes, soils, and subsurface aquifer rocks.

  11. 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.

  12. Resonance ionization mass spectrometry for isotopic abundance measurements

    NASA Technical Reports Server (NTRS)

    Miller, C. M.

    1986-01-01

    Resonance ionization mass spectrometry (RIMS) is a relatively new laser-based technique for the determination of isotopic abundances. The resonance ionization process depends upon the stepwise absorption of photons from the laser, promoting atoms of the element of interest through progressively higher electronic states until an ion is formed. Sensitivity arises from the efficiency of the resonant absorption process when coupled with the power available from commercial laser sources. Selectivity derives naturally from the distinct electronic structure of different elements. This isobaric discrimination has provided the major impetus for development of the technique. Resonance ionization mass spectrometry was used for analysis of the isotopic abundances of the rare earth lutetium. Isobaric interferences from ytterbium severely effect the ability to measure small amounts of the neutron-deficient Lu isotopes by conventional mass spectrometric techniques. Resonance ionization for lutetium is performed using a continuous-wave laser operating at 452 nm, through a sequential two-photon process, with one photon exciting the intermediate resonance and the second photon causing ionization. Ion yields for microgram-sized quantities of lutetium lie between 10(6) and 10(7) ions per second, at overall ionization efficiencies approaching 10(-4). Discrimination factors against ytterbium greater than 10(6) have been measured. Resonance ionization for technetium is also being explored, again in response to an isobaric interference, molybdenum. Because of the relatively high ionization potential for Tc, three-photon, two-color RIMS processes are being developed.

  13. Carbon isotope controlled molecular switches

    NASA Astrophysics Data System (ADS)

    Foster, Brian K.

    Single molecules represent one fundamental limit to the downscaling of electronics. As a prototype element for carbon-based nanoscale science and technology, the detailed behavior of carbon monoxide (CO) on the copper surface Cu(111) has been investigated. These investigations span from individual carbon isotope resolution, to single molecules, to compact clusters assembled by molecular manipulation via a homemade scanning tunneling microscope (STM). Sub-nanoscale devices, composed of only a few molecules, which exploit both lone CO properties and molecule-molecule interaction, have been designed and assembled. The devices function as bi-stable switches and can serve as classical bits with densities > 50 Tbits/cm2. Operated in the nuclear mass sensitive regime, each switch can also function as a molecular "centrifuge" capable of identifying the isotope of a single carbon atom in real-time. A model, based on electron-vibron couping and inelastic tunneling, has been developed and explains the dynamic behavior of the switch. The interaction between pairs of switches was also explored and it was found that their behavior ranges from completely independent to strongly coupled. Larger nanostructures, which were composed of many sub-switches organized to leverage the fully coupled interaction, link two spatially separated "bits" on the surface. Such a linked system can set or read a state non-locally, which is equivalent to bidirectional information transfer. The linked system has also exhibited logic functionality. These experiments demonstrate scalable molecular cells for information storage, and for information processing through cellular automata logic schemes.

  14. Stable carbon isotope analysis of coprocessing materials

    SciTech Connect

    Winschel, R.A.; Lancet, M.S.; Burke, F.P.

    1991-04-01

    This is the final report which was a thirty-four month project conducted to develop and demonstrate stable carbon isotope analysis as a method to quantitatively distinguish the source of carbon in products of coal/petroleum coprocessing. The work included assessing precision, accuracy, the range of application and the significance of selective isotopic fractionation effects. A method was devised to correct for selective isotopic fractionation errors. The method was demonstrated through application with samples from twelve continuous-unit coprocessing tests. A data base of carbon isotope analyses is appended. 21 refs.

  15. A Clumped Isotope Calibration for Lacustrine Carbonates

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  16. Carbon isotope effects associated with aceticlastic methanogenesis

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    The carbon isotope effects associated with synthesis of methane from acetate have been determined for Methanosarcina barkeri 227 and for methanogenic archaea in sediments of Wintergreen Lake, Michigan. At 37 degrees C, the 13C isotope effect for the reaction acetate (methyl carbon) --> methane, as measured in replicate experiments with M. barkeri, was - 21.3% +/- 0.3%. The isotope effect at the carboxyl portion of acetate was essentially equal, indicating participation of both positions in the rate-determining step, as expected for reactions catalyzed by carbon monoxide dehydrogenase. A similar isotope effect, - 19.2% +/- 0.3% was found for this reaction in the natural community (temperature = 20 degrees C). Given these observations, it has been possible to model the flow of carbon to methane within lake sediment communities and to account for carbon isotope compositions of evolving methane. Extension of the model allows interpretation of seasonal fluctuations in 13C contents of methane in other systems.

  17. 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.

  18. 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.

  19. Carbon isotope effects associated with autotrophic acetogenesis

    USGS Publications Warehouse

    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??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 into account. For the overall reaction, total carbonate ??? total acetate, isotope effects measured in replicate experiments ranged from -59.0 ?? 0.9% to - 57.2 ?? 2.3z%. 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. ?? 1989.

  20. Stable carbon isotope analysis of coprocessing materials

    SciTech Connect

    Lancet, M.S.; Winschel, R.A.; Burke, F.P.

    1991-01-01

    Consol R D is developing and demonstrating stable carbon isotope analysis as a method to quantitatively distinguish coal-derived and petroleum-derived carbon in products from coal/petroleum coprocessing. The approach taken is to develop the method, then demonstrate its application an authentic continuous-unit products. The experimental details used for stable carbon isotope analyses by the organization that performs most of those analyses under this contract are described. A method was developed previously under this contract to correct the carbon sourcing calculations performed from stable carbon isotope analyses for selective isotopic fractionation. The method relies on three assumptions. This quarter, a study was completed to define the sensitivity of the carbon sourcing results to errors in the assumptions. Carbon contents and carbon isotope ratios were determined for the available feeds and product fractions from HRI bench-scale coprocessing Run 238-10 (Texas lignite/Hondo vacuum still bottoms (VSB), Texas lignite/Cold Lake VSB and Westerholt coal/Cold Lake VSB). These data were used for carbon sourcing calculations and individual feedstock conversion calculations. A previously devised means for correcting for selective isotope fractionation was applied. 6 refs., 30 figs., 16 tabs.

  1. Carbon and nitrogen isotope studies in an arctic ecosystem

    SciTech Connect

    Schell, D.M.

    1989-01-01

    This proposal requests funding for the completion of our current ecological studies at the MS-117 research site at Toolik Lake, Alaska. We have been using a mix of stable and radioisotope techniques to assess the fluxes of carbon and nitrogen within the ecosystem and the implications for long-term carbon storage or loss from the tundra. Several tentative conclusions have emerged from our study including: Tundra in the foothills is no longer accumulating carbon. Surficial radiocarbon abundances show little or no accumulation since 1000--2500 yrs BP. Coastal plain tundra is still accumulating carbon, but the rate of accumulation has dropped in the last few thousand years. Carbon export from watersheds in the Kuparuk and Imnavait Creek drainages are in excess of that expected from estimated primary productivity; and Nitrogen isotope abundances vary between species of plants and along hydrologic gradients.

  2. Carbon and nitrogen isotope studies in an arctic ecosystem

    SciTech Connect

    Schell, D.M.

    1989-12-31

    This proposal requests funding for the completion of our current ecological studies at the MS-117 research site at Toolik Lake, Alaska. We have been using a mix of stable and radioisotope techniques to assess the fluxes of carbon and nitrogen within the ecosystem and the implications for long-term carbon storage or loss from the tundra. Several tentative conclusions have emerged from our study including: Tundra in the foothills is no longer accumulating carbon. Surficial radiocarbon abundances show little or no accumulation since 1000--2500 yrs BP. Coastal plain tundra is still accumulating carbon, but the rate of accumulation has dropped in the last few thousand years. Carbon export from watersheds in the Kuparuk and Imnavait Creek drainages are in excess of that expected from estimated primary productivity; and Nitrogen isotope abundances vary between species of plants and along hydrologic gradients.

  3. Isotopic abundances - Inferences on solar system and planetary evolution

    NASA Astrophysics Data System (ADS)

    Wasserburg, G. J.

    1987-12-01

    For matter that has been removed from a region of nucleosynthetic activity and the effects of interactions with nuclear active particles, the only changes in nuclear abundances that can occur in an isolated system derive from the decay of radioactive nuclei of an element to yield the nucleus of another element. These two related nuclei furnish the absolute chronometers of geologic and cosmic time, through the decay of spontaneously radioactive parent nuclei and the accumulation of daughter nuclei. For systems related to such cosmic processes as the formation of the solar system from the precursor interstellar medium, and involving the very early evolution of the sun, there may arise considerable complexity, due to the intrinsic isotopic heterogeneity of the medium and the presence of short-lived nuclei.

  4. Stable carbon isotope analysis of coprocessing materials

    SciTech Connect

    Lancet, M.S.; Winschel, R.A.; Burke, F.P.

    1991-01-01

    The purpose of obtaining stable carbon isotope analyses of coprocessing products is to determine the amount of coal (or petroleum) carbon that is present in any reaction product. This carbon-sourcing of distillate fractions, soluble resid, and insoluble organic matter, etc. is useful in modeling reactions, and evaluating synergistic effects if they exist.

  5. Stable carbon isotope analysis of coprocessing materials

    SciTech Connect

    Lancet, M.S.; Winschel, R.A.; Burke, F.P.

    1991-12-31

    The purpose of obtaining stable carbon isotope analyses of coprocessing products is to determine the amount of coal (or petroleum) carbon that is present in any reaction product. This carbon-sourcing of distillate fractions, soluble resid, and insoluble organic matter, etc. is useful in modeling reactions, and evaluating synergistic effects if they exist.

  6. Isotope Engineering of Carbon Nanotube Systems

    NASA Astrophysics Data System (ADS)

    Simon, F.; Kramberger, Ch.; Pfeiffer, R.; Kuzmany, H.; Zólyomi, V.; Kürti, J.; Singer, P. M.; Alloul, H.

    2005-06-01

    The synthesis of a unique isotope engineered system, double-wall carbon nanotubes with natural carbon outer and highly 13C enriched inner walls, is reported from isotope enriched fullerenes encapsulated in single-wall carbon nanotubes (SWCNTs). The material allows the observation of the D line of the highly defect-free inner tubes that can be related to a curvature induced enhancement of the electron-phonon coupling. Ab initio calculations explain the inhomogeneous broadening of inner tube Raman modes due to the distribution of different isotopes. Nuclear magnetic resonance shows a significant contrast of the isotope enriched inner SWCNTs compared to other carbon phases and provides a macroscopic measure of the inner tube mass content. The high curvature of the small diameter inner tubes manifests in an increased distribution of the chemical shift tensor components.

  7. Stable carbon isotope analysis of coprocessing materials

    SciTech Connect

    Burke, F.P.; Winschel, R.A.; Lancet, M.S.

    1990-05-01

    Consol R D is developing and demonstrating stable carbon isotope analysis as a method quantitatively distinguish coal-derived and petroleum-derived carbon in products from coal/petroleum coprocessing. The approach taken is to develop the method, then demonstrate its application on authentic continuous-unit products. The significance of selective isotopic fractionation is being determined and, if necessary, corrections will be applied to account for it. Activities for this quarter include: method development -- investigation of selective fractionation. Three petroleum atmospheric still bottoms (ASBs) were separated by distillation and solubility fractionation to determine the homogeneity of the carbon isotope ratios of the separated fractions. These same three petroleum ASBs and three geographically distinct coals were pyrolyzed at 800{degree}F for 30 min and hydrogenated over a CoMo catalyst at 750{degree}F for 60 min to determine the effects of these treatments on the isotopic compositions of the produce fractions. Twelve coal liquefaction oils were analyzed for carbon isotope ratios. These oils were derived from subbituminous and bituminous coals from the first- and second-stage reactors in the thermal/catalytic and modes; validation and application, analysis. Carbon isotope analyses of samples from HRI bench unit coprocessing run 238-2 (Taiheiyo coal/Maya VSB) were analyzed. A method to correct for selective isotopic fractionation was developed and applied to the data. Five coprocessing samples were analyzed at the request of SRI International. 12 refs., 15 figs., 24 tabs.

  8. 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.

  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. On the abundances of carbon dioxide isotopologues in the atmospheres of mars and earth

    NASA Astrophysics Data System (ADS)

    Shved, G. M.

    2016-03-01

    The isotopic composition of carbon dioxide in the Martian atmosphere from the measurements of Mars Science Laboratory have been used to estimate the relative abundances of CO2 isotopologues in the Martian atmosphere. Concurrently, this study has revealed long-standing errors in the amounts of some of low-abundance CO2 isotopologues in the Earth's atmosphere in the databases of spectroscopic parameters of gases (HITRAN, etc.).

  11. Oxygen isotope fractionation in double carbonates.

    PubMed

    Zheng, Yong-Fei; Böttcher, Michael E

    2016-01-01

    Oxygen isotope fractionations in double carbonates of different crystal structures were calculated by the increment method. Synthesis experiments were performed at 60 °C and 100 °C to determine oxygen and carbon isotope fractionations involving PbMg[CO3]2. The calculations suggest that the double carbonates of calcite structure are systematically enriched in (18)O relative to those of aragonite and mixture structures. Internally consistent oxygen isotope fractionation factors are obtained for these minerals with respect to quartz, calcite and water at a temperature range of 0-1200 °C. The calculated fractionation factors for double carbonate-water systems are generally consistent with the data available from laboratory experiments. The experimentally determined fractionation factors for PbMg[CO3]2, BaMg[CO3]2 and CaMg[CO3]2 against H2O not only fall between fractionation factors involving pure carbonate end-members but are also close to the calculated fractionation factors. In contrast, experimentally determined carbon isotope fractionation factors between PbMg[CO3]2 and CO2 are much closer to theoretical predictions for the cerussite-CO2 system than for the magnesite-CO2 system, similar to the fractionation behavior for BaMg[CO3]2. Therefore, the combined theoretical and experimental results provide insights into the effects of crystal structure and exchange kinetics on oxygen isotope partitioning in double carbonates.

  12. Clumped isotope thermometry of cryogenic cave carbonates

    NASA Astrophysics Data System (ADS)

    Kluge, Tobias; Affek, Hagit P.; Zhang, Yi Ge; Dublyansky, Yuri; Spötl, Christoph; Immenhauser, Adrian; Richter, Detlev K.

    2014-02-01

    Freezing of cave pool water that is increasingly oversaturated with dissolved carbonate leads to precipitation of a very specific type of speleothems known as cryogenic cave carbonates (CCC). At present, two different environments for their formation have been proposed, based on their characteristic carbon and oxygen isotope ratios. Rapidly freezing thin water films result in the fast precipitation of fine-grained carbonate powder (CCCfine). This leads to rapid physicochemical changes including CO2 degassing and CaCO3 precipitation, resulting in significantly 13C-enriched carbonates. Alternatively, slow carbonate precipitation in ice-covered cave pools results in coarse crystalline CCC (CCCcoarse) yielding strongly 18O-depleted carbonate. This is due to the formation of relatively 18O-enriched ice causing the gradual depletion of 18O in the water from which the CCC precipitates. Cryogenic carbonates from Central European caves were found to have been formed primarily during the last glacial period, specifically during times of permafrost thawing, based on the oxygen isotope ratios and U-Th dating. Information about the precise conditions of CCCcoarse formation, i.e. whether these crystals formed under equilibrium or disequilibrium conditions with the parent fluid, however, is lacking. An improved understanding of CCCcoarse formation will increase the predictive value of this paleo-permafrost archive. Here we apply clumped isotopes to investigate the formation conditions of cryogenic carbonates using well-studied CCCcoarse from five different cave systems in western Germany. Carbonate clumped isotope measurements yielded apparent temperatures between 3 and 18 °C and thus exhibit clear evidence of isotopic disequilibrium. Although the very negative carbonate δ18O values can only be explained by gradual freezing of pool water accompanied by preferential incorporation of 18O into the ice, clumped isotope-derived temperatures significantly above expected freezing

  13. 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.

  14. 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.

  15. Carbonate clumped isotope thermometry in continental tectonics

    NASA Astrophysics Data System (ADS)

    Huntington, Katharine W.; Lechler, Alex R.

    2015-04-01

    Reconstructing the thermal history of minerals and fluids in continental environments is a cornerstone of tectonics research. Paleotemperature constraints from carbonate clumped isotope thermometry have provided important tests of geodynamic, structural, topographic and basin evolution models. The thermometer is based on the 13C-18O bond ordering in carbonates (mass-47 anomaly, Δ47) and provides estimates of the carbonate formation temperature independent of the δ18O value of the water from which the carbonate grew; Δ47 is measured simultaneously with conventional measurements of carbonate δ13C and δ18O values, which together constrain the isotopic composition of the parent water. Depending on the geologic setting of carbonate growth, this information can help constrain paleoenvironmental conditions or basin temperatures and fluid sources. This review examines how clumped isotope thermometry can shed new light on problems in continental tectonics, focusing on paleoaltimetry, basin evolution and structural diagenesis applications. Paleoaltimetry is inherently difficult, and the precision in carbonate growth temperature estimates is at the limit of what is useful for quantitative paleoelevation reconstruction. Nevertheless, clumped isotope analyses have enabled workers to address previously intractable problems and in many settings offer the best chance of understanding topographic change from the geologic record. The portion of the shallow crust residing at temperatures up to ca. 200 °C is important as host to economic resources and records of tectonics and climate, and clumped isotope thermometry is one of the few proxies that can access this critical range with sensitivity to temperature alone. Only a handful of studies to date have used clumped isotopes to investigate diagenesis and other sub-surface processes using carbonate crystallization temperatures or the sensitivity of Δ47 values to a sample's thermal history. However, the thermometer is

  16. 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

  17. 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

  18. Carbon isotope anomalies in carbonates of the Karelian series

    NASA Astrophysics Data System (ADS)

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

    1990-07-01

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

  19. Shear heating and clumped isotope reordering in carbonate faults

    NASA Astrophysics Data System (ADS)

    Siman-Tov, Shalev; Affek, Hagit P.; Matthews, Alan; Aharonov, Einat; Reches, Ze'ev

    2016-07-01

    Natural faults are expected to heat rapidly during seismic slip and to cool quite quickly after the slip event. Here we examine clumped isotope thermometry for its ability to identify such short duration elevated temperature events along frictionally heated carbonate faults. Our approach is based on measured Δ47 values that reflect the distribution of oxygen and carbon isotopes in the calcite lattice, measuring the abundance of 13Csbnd 18O bonds, which is affected by temperature. We examine three types of calcite rock samples: (1) crushed limestone grains that were rapidly heated and then cooled in static laboratory experiments, simulating the temperature cycle experienced by fault rock during an earthquake slip; (2) limestone samples that were experimentally sheared to simulate earthquake slip events; and (3) samples from Fault Mirrors (FMs) collected from principle slip surfaces of three natural carbonate faults. Extensive FM surfaces are believed to form during earthquake slip. Our experimental results show that Δ47 values decrease rapidly (in the course of seconds) with increasing temperature and shear velocity. On the other hand, carbonate shear zones from natural faults do not show such Δ47 decrease. We suggest that the Δ47 response may be controlled by nano-size grains, the high abundance of defects, and highly stressed/strained grain boundaries within the carbonate fault zone that can reduce the activation energy for diffusion, and thus lead to an increased rate of isotopic disordering during shear experiments. In our laboratory experiments the high stress and strain on grain contacts and the presence of nanograins thus allows for rapid disordering so that a change in Δ47 occurs in a very short and relatively low intensity heating events. In natural faults it may also lead to isotopic ordering after the cessation of frictional heating thus erasing the high temperature signature of Δ47.

  20. Stable carbon isotope analysis of coprocessing materials

    SciTech Connect

    Winschel, R.A.; Lancet, M.S.; Burke, F.P.

    1990-07-01

    Consol R D is developing and demonstrating stable carbon isotope analysis as a method to quantitatively distinguish coal-derived and petroleum-derived carbon in products from coal/petroleum coprocessing. The approach taken is to develop the method, then demonstrate its application on authentic continuous-unit products. The significance of selective isotopic fractionation is being determined and, if necessary, corrections will be applied to account for it. Precision, accuracy and range of applicability are being defined. The value of accessory analytical techniques also is being assessed. The program is designed to address a substantial, demonstrated need of coprocessing research (both exploratory and development) for a technique to quantitatively distinguish the contributions of the individual coprocessing feedstocks to the various products. The carbon isotope technique currently is in routine use for other applications. Progress is discussed. 7 refs., 7 figs., 12 tabs.

  1. The temperature and carbonate ion influence on Pleistocene high latitude planktonic foraminiferal carbon isotopic records

    NASA Astrophysics Data System (ADS)

    Charles, C.; Foreman, A. D.; Munson, J.; Slowey, N. C.; Hodell, D. A.

    2014-12-01

    Establishing a credible record of the carbon isotopic composition of high latitude surface ocean DIC over ice ages has been an enormous challenge, because the possible archives of this important variable in deep sea sediments all incorporate complex effects of the biomineralization process. For example, culture experiments (by Spero and colleagues) demonstrate a strong temperature and carbonate ion effect on the carbon isotopic composition of G. bulloides--the taxon of planktonic foraminifera that is most abundant in the majority of subpolar sediment sequences. Here we capitalize on the fortuitous observation of exceptionally strong covariation between the oxygen and carbon isotopic composition of G. bulloides in multiple sediment sequences from the Benguela upwelling region. The covariation is most clear during Marine Isotopic Stage 3 (an interval when the isotopic composition of the seawater was least variable) and undoubtedly results from the precipitation of tests under variable conditions of temperature and carbonate ion. The unusually clear isotopic relationship in planktonic foraminifera observed off Namibia constitutes a field calibration of the biomineralization effects observed in culture, and we apply it to previously published high latitude carbon isotopic records throughout the Southern Ocean. We find that many of the excursions toward lower planktonic foraminiferal δ13C that have been interpreted previously as the upwelling of nutrient rich water during deglaciations are better explained as increases in upper ocean temperature and carbonate ion. Conversely, the excursions toward high δ13C during ice age intervals that have been interpreted previously as increased export production (purportedly stimulated by dust) are also better explained by temperature and carbonate ion variability. After removal of the inferred temperature and carbonate ion signal from the planktonic foraminiferal time series, the residual is essentially (but not exactly) the same

  2. Carbon and Carbon Isotope Cycling in the Western Canadian Arctic

    NASA Astrophysics Data System (ADS)

    Mol, Jacoba; Thomas, Helmuth

    2016-04-01

    Increasing carbon dioxide levels in the atmosphere are having drastic effects on the global oceans. The Arctic Ocean is particularly susceptible to change as warming, sea-ice loss and a weak buffering capacity all influence this complicated semi-enclosed sea. In order to investigate the inorganic carbon system in the Canadian Arctic, water samples were collected in the Beaufort Sea, on the Alaskan shelf, at the Mackenzie river delta, and in Amundsen Gulf during the summer of 2014 and were analyzed for dissolved inorganic carbon (DIC), total alkalinity (TA), DI13C and 18O isotopes. Carbon isotopes are used to investigate the role of biological production on the uptake and transfer of inorganic carbon to depth. A preferential uptake of the lighter 12C relative to the heavier 13C isotope during biological production leads to a fractionation of the 13C/12C isotopes in both the organic matter and the water column. This results in an enrichment of DI13C in the high productivity surface waters and a depletion of DI13C at depth. Physical processes including freshwater input, brine rejection, and water mass mixing are investigated through the measurement of oxygen isotopes. Differences in the carbon system across the study area due to both biological and physical processes are assessed using depth profiles of DI13C and related carbon system parameters.

  3. 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.

  4. The stable carbon isotopes in enstatite chondrites and Cumberland Falls

    NASA Astrophysics Data System (ADS)

    Deines, P.; Wickman, F. E.

    1985-01-01

    The carbon-isotopic composition (CIC) of the total carbon in the enstatite chondrites Indarch, Abee, St. Marks, Pillistfer, Hvittis and Daniel's Kuil and the enstatite achondrite Cumberland Falls has been measured. The empirical relationship between CIC and total carbon content is distinct from that of carbonaceous and ordinary chondrites. Within the enstatite chondrite group the average C-13 content increases with petrographic type: E4 less than E5 less than E6. Daniel's Kuil shows the largest C-13 enrichment in the bulk carbon of any meteorite. The CIC is most clearly correlated with the abundance of the elements Zn, Cd, and In. Insofar as these elements may hold the key to the understanding of enstatite chondrites, more detailed combined CIC and trace-element studies of these meteorites will play an important role in the deciphering of their history.

  5. Stable carbon isotope analysis of coprocessing materials

    SciTech Connect

    Lancet, M.S.; Winschel, R.A.; Burke, F.P.

    1991-03-01

    Research on coprocessing materials/products continued. Major topics reported here are described below. Microautoclave runs are described in which gases and insoluble organic matter produced from five coals and gases produced from three petroleum resids were analyzed to study feedstock/product selective isotopic fractionation. Selective isotopic fractionation was further explored through isotope analysis of the feed New Mexico coal and products from a continuous coal liquefaction run (HRI CC-10 or 227-68). Feeds (Texas lignite/Maya VSB) and products from two HRI continuous coprocessing runs (227-54 and 238-12) were analyzed. The results were corrected for selective isotopic fractionation and carbon sourcing was performed for the product fractions. {sup 1}H-NMR and phenolic -OH determinations are reported for all continuous unit samples obtained under this contract. 13 refs., 17 figs., 40 tabs.

  6. 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.

  7. 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

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

    SciTech Connect

    Vengosh, A. Hebrew Univ., Jerusalem ); Chivas, A.R.; McCulloch, M.T. ); Kolodny, Y.; Starinsky, A. )

    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 the 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.

  9. Stable carbon isotope analysis of coprocessing materials

    SciTech Connect

    Burke, F.P.; Winschel, R.A.; Lancet, M.S.

    1989-06-01

    The program is designed to address a substantial, demonstrated need of the coprocessing community (both exploratory and development) for a technique to quantitatively distinguish the contributions of the individual coprocessing feedstocks to the various products. The carbon isotope technique is currently in routine use for other applications. Results achieved this quarter include: Feed and product fractions from a Kentucky 9 coal/Kentucky tar sand bitumen coprocessing bench unit run at the Kentucky Center for Applied Energy Research (CAER) were analyzed for carbon isotope ratios. Corrections were made to the coal carbon recoveries and selectivities from the products of HRI Run 227-53. Feeds (Westerholt coal/Cold Lake VSB) and products from two periods of HRI coprocessing Run 238-1 were analyzed. Three petroleum samples and three coal samples were pyrolyzed at 800{degree}F for 30 min to determine the effect of pyrolysis on the isotopic homogeneity of each petroleum and coal sample. Products from each pyrolysis test were separated into five fractions; an additional set of coprocessing samples and a set of two-stage coal liquefaction samples were obtained from HRI for future work; work performed by the Pennsylvania State University show that microscopy is a promising method for distinguishing coal and petroleum products in residual coprocessing materials; and coal and petroleums that have large differences in carbon isotope ratios were identified for Auburn University. 7 refs., 2 figs., 12 tabs.

  10. Soil Carbon: Compositional and Isotopic Analysis

    SciTech Connect

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

    2016-11-01

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

  11. Carbon isotopes as indicators of peatland growth?

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  12. 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.

  13. Carbon isotopic exchange between dissolved inorganic and organic carbon

    NASA Astrophysics Data System (ADS)

    Thomas, B.; Freeman, K. H.; House, C. H.; Arthur, M. A.

    2009-12-01

    The pools of inorganic and organic carbon are often considered to be separate and distinct. Isotopic exchange between the inorganic and organic carbon pools in natural waters is rarely considered plausible at low temperatures owing to kinetic barriers to exchange. In certain circumstances, however carboxyl carbon of dissolved organic matter (DOM) may be subject to exchange with the dissolved inorganic carbon (DIC) pool. We report results from an isotopic labeling experiment that resulted in rapid methanogen-catalyzed isotopic exchange between DIC and the carboxyl carbon of acetate. This exchange rapidly mixes the isotopic composition of the DIC pool into the dissolved organic carbon (DOC) acetate pool. This exchange is likely associated with the reversible nature of the carbon monoxide dehydrogenase enzyme. In nature, many decarboxylase enzymes are also reversible and some can be shown to facilitate similar exchange reactions. Those decarboxylase enzymes that are important in lignin decomposition and other organic carbon (OC) transformations may help to mask the isotopic composition of the precursor DOC with as much as 15% contribution from DIC. Though this dilution is unlikely to matter in soils where DOC and DIC are similar in composition, this exchange may be extremely important in systems where the stable or radioisotope composition of DOC and DIC differ significantly. As an example of the importance of this effect, we demonstrate that the stable and radiocarbon isotopic composition of fluvial DOC could be altered by mixing with marine DIC to produce a DOC composition similar to those observed in the deep marine DOC pool. We hypothesize that this exchange resolves the conundrum of apparently old (>5 kyr) marine-derived DOC. If most of the carboxyl carbon of pre-aged, terrestrial-derived DOC (15% of total carbon) is subject to exchange with marine DIC, the resulting carbon isotopic composition of deep DOC will be similar to that observed in deep marine studies

  14. Interpretation of the carbon abundance in Saturn measured by Cassini

    NASA Astrophysics Data System (ADS)

    Hersant, Franck; Gautier, Daniel; Tobie, Gabriel; Lunine, Jonathan I.

    2008-06-01

    Spectral observations of Saturn from the far infrared spectrometer aboard the Cassini spacecraft [Flasar, F.M., et al., 2005. Temperatures, winds, and composition in the Saturnian system. Science 307, 1247-1251] have revealed that the C/H ratio in the planet is in fact about twice higher than previously derived from ground based observations and in agreement with the C/H value derived from Voyager IRIS by Courtin et al. [1984. The composition of Saturn's atmosphere at northern temperate latitudes from Voyager IRIS spectra - NH 3, PH 3, C 2H 2, C 2H 6, CH 3D, CH 4, and the Saturnian D/H isotopic ratio. Astrophys. J. 287, 899-916] . The implications of this measurement are reanalyzed in the present report on the basis that volatiles observed in cometary atmospheres, namely CO2, CH4, NH3 and H2S may have been trapped as solids in the feeding zone of the planet. CH4 and H2S may have been in the form of clathrate hydrates while CO2 presumably condensed in the cooling solar nebula. Carbon may also have been incorporated in organics. Conditions of temperature and pressure ease the hydratation of NH3. Such icy grains were included in planetesimals which subsequently collapsed into the hydrogen envelope of the planet, then resulting in C, N and S enrichments with respect to the solar abundance. Our calculations are consistent, within error bars, with observed elemental abundances on Saturn provided that the carbon trapped in planetesimals was mainly in the form of CH4 clathrate and CO2 ice (and maybe as organics) while nitrogen was in the form of NH3 hydrate. Our approach has implications on the possible pattern of noble gases in Saturn, since we predict that contrary to what is observed in Jupiter, Ar and Kr should be in solar abundance while Xe might be strongly oversolar. The only way to verify this scenario is to send a probe making in situ mass spectrometer measurements. Our scenario also predicts that the 14N/ 15N ratio should be somewhat smaller in Saturn than

  15. 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.

  16. 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.

  17. Stable carbon isotope analysis of coprocessing materials

    SciTech Connect

    Lancet, M.S.; Winschel, R.A.; Burke, F.P.

    1991-02-01

    Consol R D is developing and demonstrating stable carbon isotope analysis as a method to quantitatively distinguish coal-derived and petroleum-derived carbon in products from coal/petroleum coprocessing. The approach taken is develop the method, then demonstrate its application on authentic continuous-unit products. The significance of selective isotopic fractionation is being determined and, when necessary, corrections are applied to account for it. Precision, accuracy and range of applicability are being defined. The value of accessory analytical techniques also is being assessed. Previously reported data on samples from HRI bench-scale coprocessing Runs 227-53 (Texas lignite/Maya ASB and Texas lignite/Maya VSB) and 238-1 (Westerholt coal/Cold Lake VSB) were corrected for selective isotopic fractionation. Carbon sourcing was performed on samples from HRI bench-scale coprocessing Run 227-60 (Texas lignite/Maya VSB) and samples from UOP bench-scale coprocessing Run 26 (Illinois 6 coal/Lloydminster vacuum resid); the latter data were corrected for isotopic fractionation, though the former could not be corrected. A paper presented at the 1990 DOE Direct Liquefaction Contractor's Review Meeting is appended. 15 refs., 21 figs., 22 tabs.

  18. Deconvolving the Carbon Isotope Record

    NASA Astrophysics Data System (ADS)

    Cramer, B. S.

    2003-12-01

    The evolution of the whole-ocean δ 13C value, under an assumption of steady state with respect to mass, can be modeled as: \\[ {d \\over dt}\\delta_\\Sigma(t)+{\\delta_\\Sigma(t) \\over \\tau_C}={1 \\over \\tau_C}\\delta_F(t) \\] where δ Σ is the whole-ocean δ 13C value, τ C is the residence time of carbon and a net instantaneous δ 13C forcing function is defined: \\[ \\delta_F=\\delta_i-f_{carb}\\Delta_{carb}-\\(1-f_{carb}\\)\\Delta_{org} \\] where δ i is the δ 13C value of carbon input (e.g. weathering and volcanism), fcarb is the fraction of carbon removed through burial of carbonates as opposed to organic carbon, and Δ carb and Δ org are the differences between δ Σ and δ 13C values for buried carbonate and organic carbon. The solution to this differential equation is: \\[ \\delta_\\Sigma\\(t\\)={1 \\over \\tau_C}\\int_0^t{{\\delta_F\\(t^\\prime\\)}e^{\\(-{t-t^\\prime \\over \\tau_C}\\)}dt^\\prime} \\] which can be expressed as a convolution \\[ \\delta_\\Sigma\\(t\\)={1 \\over \\tau_C} {{\\delta_F\\(t^\\prime\\)} \\otimes e^{\\(-{t-t^\\prime \\over \\tau_C}\\)}} \\] revealing that the evolution of the whole ocean δ 13C value is determined by the instantaneous δ 13C forcing (δ F) subjected to a causal (i.e. phase-shifting) low-pass filter whose frequency response is dependent only on the carbon residence time. One consequence of this observation is that variance in δ 13C records should be concentrated at wavelengths >0.1 m.y., thereby explaining the persistent appearance of cyclicity dependent on orbital eccentricity ( ˜0.1~and ˜0.4 m.y.~periods) in δ 13C records. I demonstrate that an assumption of non-linear forcing of fcarb by orbitally-forced variations in insolation can explain most of the structure of high-resolution δ 13C records throughout the Cenozoic. A second consequence is that τ C and δ F should be separable by numerical manipulation of δ 13C records. Two applications are 1) estimation of the residence time of carbon at

  19. 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.

  20. 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.

  1. Carbon abundance and silicate mineralogy of anhydrous interplanetary dust particles

    NASA Technical Reports Server (NTRS)

    Thomas, Kathie L.; Blanford, George E.; Keller, Lindsay P.; Kloeck, Wolfgang; Mckay, David S.

    1993-01-01

    We have studied nineteen anhydrous chondritic interplanetary dust particles (IDPs) using analytical electron microscopy. We have determined a method for quantitative light element EDX analysis of small particles and have applied these techniques to a group of IDPs. Our results show that some IDPs have significantly higher bulk carbon abundances than do carbonaceous chondrites. We have also identified a relationship between carbon abundance and silicate mineralogy in our set of anhydrous IDPs. In general, these particles are dominated by pyroxene, olivine, or a subequal mixture of olivine and pyroxene. The pyroxene-dominated IDPs have a higher carbon abundance than those dominated by olivines. Members of the mixed mineralogy IDPs can be grouped with either the pyroxene- or olivine-dominated particles based on their carbon abundance. The high carbon, pyroxene-dominated particles have primitive mineralogies and bulk compositions which show strong similarities to cometary dust particles. We believe that the lower carbon, olivine-dominated IDPs are probably derived from asteroids. Based on carbon abundances, the mixed-mineralogy group represents particles derived from either comets or asteroids. We believe that the high carbon, pyroxene-rich anhydrous IDPs are the best candidates for cometary dust.

  2. Carbon isotopic composition of individual Precambrian microfossils.

    PubMed

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

    2000-08-01

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

  3. 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.

  4. Ion Mobility Mass Spectrometry Direct Isotope Abundance Analysis

    SciTech Connect

    Manuel J. Manard, Stephan Weeks, Kevin Kyle

    2010-05-27

    The nuclear forensics community is currently engaged in the analysis of illicit nuclear or radioactive material for the purposes of non-proliferations and attribution. One technique commonly employed for gathering nuclear forensics information is isotope analysis. At present, the state-of-the-art methodology for obtaining isotopic distributions is thermal ionization mass spectrometry (TIMS). Although TIMS is highly accurate at determining isotope distributions, the technique requires an elementally pure sample to perform the measurement. The required radiochemical separations give rise to sample preparation times that can be in excess of one to two weeks. Clearly, the nuclear forensics community is in need of instrumentation and methods that can expedite their decision making process in the event of a radiological release or nuclear detonation. Accordingly, we are developing instrumentation that couples a high resolution IM drift cell to the front end of a MS. The IM cell provides a means of separating ions based upon their collision cross-section and mass-to-charge ratio (m/z). Two analytes with the same m/z, but with different collision cross-sections (shapes) would exit the cell at different times, essentially enabling the cell to function in a similar manner to a gas chromatography (GC) column. Thus, molecular and atomic isobaric interferences can be effectively removed from the ion beam. The mobility selected chemical species could then be introduced to a MS for high-resolution mass analysis to generate isotopic distributions of the target analytes. The outcome would be an IM/MS system capable of accurately measuring isotopic distributions while concurrently eliminating isobaric interferences and laboratory radiochemical sample preparation. The overall objective of this project is developing instrumentation and methods to produce near real-time isotope distributions with a modular mass spectrometric system that performs the required gas-phase chemistry and

  5. Line formation in solar granulation. VII. CO lines and the solar C and O isotopic abundances

    NASA Astrophysics Data System (ADS)

    Scott, P. C.; Asplund, M.; Grevesse, N.; Sauval, A. J.

    2006-09-01

    CO spectral line formation in the Sun has long been a source of consternation for solar physicists, as have the elemental abundances it seems to imply. We modelled solar CO line formation using a realistic, ab initio, time-dependent 3D radiative-hydrodynamic model atmosphere. Results were compared with space-based observations from the ATMOS space shuttle experiment. We employed weak 12C16O, 13C16O and 12C18O lines from the fundamental (Δ v = 1) and first overtone (Δ v = 2) bands to determine the solar carbon abundance, as well as the 12C/13C and 16O/18O isotopic ratios. A weighted solar carbon abundance of logɛ_C=8.39 ± 0.05 was found. We note with satisfaction that the derived abundance is identical to our recent 3D determination based on C i, [C i], C2 and CH lines, increasing our confidence in the accuracy of both results. Identical calculations were carried out using 1D models, but only the 3D model was able to produce abundance agreement between different CO lines and the other atomic and molecular diagnostics. Solar 12C/13C and 16O/18O ratios were measured as 86.8+3.9-3.7 (δ13C = 30+46-44) and 479+29-28 (δ18O = 41+67-59), respectively. These values may require current theories of solar system formation, such as the CO self-shielding hypothesis, to be revised. Excellent agreement was seen between observed and predicted weak CO line shapes, without invoking micro- or macroturbulence. Agreement breaks down for the strongest CO lines however, which are formed in very high atmospheric layers. Whilst the line asymmetries (bisectors) were reasonably well reproduced, line strengths predicted on the basis of C and O abundances from other diagnostics were weaker than observed. The simplest explanation is that temperatures are overestimated in the highest layers of the 3D simulation. Thus, our analysis supports the presence of a COmosphere above the traditional photospheric temperature minimum, with an average temperature of less than 4000 K. This shortcoming of

  6. Natural gas constituent and carbon isotopic composition in petroliferous basins, China

    NASA Astrophysics Data System (ADS)

    Zhu, Guangyou; Wang, Zhengjun; Dai, Jinxing; Su, Jing

    2014-02-01

    There are abundant gas resources in petroliferous basins of China. Large to midsize gas fields are found in Eastern, central and Western of China. However, origin, constituents and isotopic composition of natural gas in different gas fields are varied distinctly, and some present strong chemical secondary alteration and show variation both in age and space. Based on the systematic analysis of constituents and carbon isotope of a large number of gas samples, combined with the geological characteristics, this paper classifies the origins of the gases, explores the gas isotope characteristics and evolutionary regulation with the variation time and space, and further discusses the distinctive geochemistry of the gases in China. These gases are dominated by dry gas, its methane carbon isotope values range from -10‰ to -70‰, ethane from -16‰ to -52‰, propane from -13‰ to -43‰, and butane from -18‰ to -34‰. The carbon isotopes of most gases show the characteristics of humic-derived gas and crude oil cracked gas. In addition, large primary biogenic gas fields have been discovered in the Qaidam basin; inorganic-derived alkane gases have been discovered in deep of the Songliao Basin. Half of these gas fields are characterized by the alkane carbon isotope reversal in different degrees. Research indicates there are several reasons can result in carbon isotope reversal. Firstly, gas charge of different genetic types or different source in one gas reservoir may cause carbon isotope reversal. Besides, high-over mature evolution of gas can also lead to the carbon isotopic reversal of alkanes. Thirdly, secondary alteration of hydrocarbons may also result in abnormal distribution of carbon isotope, isotope transforms to unusual light and heavy.

  7. 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).

  8. (Carbon isotope fractionation in plants: Progress report)

    SciTech Connect

    Not Available

    1987-01-01

    The purpose of this work is to use carbon isotope fractionation as a means of studying photosynthetic efficiency in plants. During the past year we have developed a new short-term method for measuring the isotope fractionation over a period of about an hour. This method is being used to study a variety of environmental and developmental effects in both C/sub 3/ and C/sub 4/ plants, and these results are being compared with results of the traditional combustion method. We have made extensive studies of aspartic acid, malic acid, and citric acid as possible indicators of the functioning of phosphoenolpyruvate carboxylase in C/sub 3/ plants. We find that most of the aspartic acid in proteins in C/sub 3/ plants is synthesized by action of phosphoenolpyruvate carboxylase on atmospheric CO/sub 2/ and phosphoenolpyruvate produced by glycolysis. The metabolically active pool of malate, aspartate, and citrate, on the other hand, appear not to be principally synthesized by this route. Studies of C/sub 4/ plants are in progress. During deacidification, CAM plants lose CO/sub 2/ to the atmosphere, and this material is highly enriched in carbon-13. Field-grown and growth-chamber grown CAM plants show similar isotope fractionations. Ploidy effects on isotope fractionation in alfalfa are extremely small.

  9. 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).

  10. The abundance of the radioactive isotope Al-26 in galactic cosmic rays

    NASA Technical Reports Server (NTRS)

    Wiedenbeck, M. E.

    1983-01-01

    Satellite observations of the isotopic composition of aluminum in low energy cosmic rays (E/M = 200 MeV/amu) have been used to determine the abundance of the unstable isotope Al-26 (T1/2 = 0.87 Myr). The observed abundance ratio, Al-26/Al-27 = 0.036 (+0.037, -0.022), is in good agreement with previous balloon observations and yields a cosmic ray confinement time consistent with values based on the abundance of Be-10.

  11. 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.

  12. [Relationship of intramolecular carbon isotopes in pyruvate decarboxylation].

    PubMed

    Ivlev, A A; Kniazev, D A; Kaloshin, A G

    1982-01-01

    Relationships were obtained which made possible to calculate isotope content of carbon atoms in the products and reaction compound in the course of piruvate decarboxilation. Isotope composition was determined from kinetic isotope effect accompanying the destruction of carbon bonds. Some applications of the expressions obtained are presented.

  13. Diurnal and Interannual Variation in Absorption Lines of Isotopic Carbon Dioxide in Mars Atmosphere

    NASA Astrophysics Data System (ADS)

    Livengood, Timothy A.; Kostiuk, Theodor; Hewagama, Tilak; Kolasinski, John R.; Henning, Wade G.

    2015-11-01

    Groundbased observations of Mars in 2003, 2007, 2012, and 2014 have detected transitions of carbon dioxide containing the stable minor isotopes of oxygen and carbon as well as the primary isotopes, using the ultrahigh resolution spectrometer HIPWAC at the NASA Infrared Telescope Facility. The most well characterized minor isotope is O-18, due to strong lines and observational opportunities. The average estimated O-18/O-16 isotope ratio is roughly consistent with other in situ and remote spectroscopic measurements but demonstrates an additional feature in that the retrieved ratio appears to increase with greater ground surface temperature. These conclusions primarily come from analyzing a subset of the 2007 data. Additional observations have been acquired over a broad range of local time and meridional position to evaluate variability with respect to ground surface temperature. These additional observations include one run of measurements with C-13. These observations can be compared to local in situ measurements by the Curiosity rover to narrow the uncertainty in absolute isotope ratio and extend isotopic measurements to other regions and seasons on Mars. The relative abundance of carbon dioxide heavy isotopes on Mars is central to estimating the primordial atmospheric inventory on Mars. Preferential freeze-distillation of heavy isotopes means that any measurement of the isotope ratio can be only a lower limit on heavy isotope enrichment due to past and current loss to space.

  14. Isotopic abundances of magnesium in five G and K dwarfs

    NASA Astrophysics Data System (ADS)

    Tomkin, J.; Lambert, D. L.

    1980-02-01

    The paper reports on an analysis of high-resolution low-noise Reticon observations of MgH lines in the spectra of Mu Cas, Epsilon Eri, 61 Cyg A and B, and Gmb 1830 by spectrum synthesis. It is shown that the mixtures of the isotopes in Mu Cas, Epsilon Eri, and 61 Cyg A and B are not significantly different from the terrestrial mixture. Attention is also given to a nonterrestrial mixture which is found in Gmb 1830.

  15. s-process studies - Xenon and krypton isotopic abundances

    NASA Technical Reports Server (NTRS)

    Clayton, D. D.; Ward, R. A.

    1978-01-01

    We propose an analysis of the s-process contributions to the isotopes of xenon and krypton. The object is to aid studies of the possibility that meteorites may contain gas that was carried in presolar grains that were grown in stellar ejecta and that were not degassed prior to incorporation into parent bodies. That model suggests routine interstellar fractionation of s-isotopes from r-isotopes owing to differential incorporation into dust. We show that a deficiency of s-process nuclei cannot yield details of Xe-X, but the gross similarities are strong enough to lead one to think that such a deficiency may play a role in a more complicated explanation. We predict the existence of an s-rich complement somewhere if fractional separation of this type has played a role in Xe-X. We show that the analogous decomposition of krypton is more uncertain, and we call for measurements of neutron-capture cross sections to alleviate these uncertainties.

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

    PubMed

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

    2007-01-02

    The isotopic composition of long-lived trace molecules provides a window into atmospheric transport and chemistry. Carbon dioxide is a particularly powerful tracer, because its abundance remains >100 parts per million by volume (ppmv) in the mesosphere. Here, we successfully reproduce the isotopic composition of CO(2) in the middle atmosphere, which has not been previously reported. The mass-independent fractionation of oxygen in CO(2) can be satisfactorily explained by the exchange reaction with O((1)D). In the stratosphere, the major source of O((1)D) is O(3) photolysis. Higher in the mesosphere, we discover that the photolysis of (16)O(17)O and (16)O(18)O by solar Lyman-alpha radiation yields O((1)D) 10-100 times more enriched in (17)O and (18)O than that from ozone photodissociation at lower altitudes. This latter source of heavy O((1)D) has not been considered in atmospheric simulations, yet it may potentially affect the "anomalous" oxygen signature in tropospheric CO(2) that should reflect the gross carbon fluxes between the atmosphere and terrestrial biosphere. Additional laboratory and atmospheric measurements are therefore proposed to test our model and validate the use of CO(2) isotopic fractionation as a tracer of atmospheric chemical and dynamical processes.

  17. The Li isotope composition of modern biogenic carbonates

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  18. Determining the isotopic abundance of a labeled compound by mass spectrometry and how correcting for natural abundance distribution using analogous data from the unlabeled compound leads to a systematic error.

    PubMed

    Schenk, David J; Lockley, William J S; Elmore, Charles S; Hesk, Dave; Roberts, Drew

    2016-04-01

    When the isotopic abundance or specific activity of a labeled compound is determined by mass spectrometry (MS), it is necessary to correct the raw MS data to eliminate ion intensity contributions, which arise from the presence of heavy isotopes at natural abundance (e.g., a typical carbon compound contains ~1.1% (13) C per carbon atom). The most common approach is to employ a correction in which the mass-to-charge distribution of the corresponding unlabeled compound is used to subtract the natural abundance contributions from the raw mass-to-charge distribution pattern of the labeled compound. Following this correction, the residual intensities should be due to the presence of the newly introduced labeled atoms only. However, this will only be the case when the natural abundance mass isotopomer distribution of the unlabeled compound is the same as that of the labeled species. Although this may be a good approximation, it cannot be accurate in all cases. The implications of this approximation for the determination of isotopic abundance and specific activity have been examined in practice. Isotopically mixed stable-atom labeled valine batches were produced, and both these and [(14) C6 ]carbamazepine were analyzed by MS to determine the extent of the error introduced by the approach. Our studies revealed that significant errors are possible for small highly-labeled compounds, such as valine, under some circumstances. In the case with [(14) C6 ]carbamazepine, the errors introduced were minor but could be significant for (14) C-labeled compounds with particular isotopic distributions. This source of systematic error can be minimized, although not eliminated, by the selection of an appropriate isotopic correction pattern or by the use of a program that varies the natural abundance distribution throughout the correction.

  19. Empirical Solar Abundance Scaling Laws of Supernova {gamma} Process Isotopes

    SciTech Connect

    Hayakawa, Takehito; Iwamoto, Nobuyuki; Kajino, Toshitaka; Shizum, Toshiyuki; Umeda, Hideyuki; Nomoto, Ken'Ichi

    2008-11-11

    Analyzing the solar system abundances, we have found two empirical abundance scaling laws concerning the p- and s-nuclei with the same atomic number. They are evidence that the 27 p-nuclei are synthesized by the supernova {gamma}-process. The scalings lead to a novel concept of 'universality of {gamma}-process' that the s/p and p/p ratios of nuclei produced by individual {gamma}-processes are almost constant, respectively. We have calculated the ratios of materials produced by the {gamma}-process based on core-collapse supernova explosion models under various astrophysical conditions and found that the scalings hold for individual {gamma}-processes independent of the conditions assumed. The results further suggest an extended universality that the s/p ratios in the {gamma}-process layers are not only constant but also centered on a specific value of 3. With this specific value and the scaling of the s/p ratios, we estimate that the ratios of the s-process abundance contributions from the AGB stars to the massive stars are almost 6.7 for the s-nuclei of A>90 in the solar system.

  20. Equations for Lipid Normalization of Carbon Stable Isotope Ratios in Aquatic Bird Eggs

    PubMed Central

    Elliott, Kyle H.; Davis, Mikaela; Elliott, John E.

    2014-01-01

    Stable isotope ratios are biogeochemical tracers that can be used to determine the source of nutrients and contaminants in avian eggs. However, the interpretation of stable carbon ratios in lipid-rich eggs is complicated because 13C is depleted in lipids. Variation in 13C abundance can therefore be obscured by variation in percent lipids. Past attempts to establish an algebraic equation to correct carbon isotope ratios for lipid content in eggs have been unsuccessful, possibly because they relied partly on data from coastal or migratory species that may obtain egg lipids from different habitats than egg protein. We measured carbon, nitrogen and sulphur stable isotope ratios in 175 eggs from eight species of aquatic birds. Carbon, nitrogen and sulphur isotopes were enriched in lipid-extracted egg samples compared with non extracted egg samples. A logarithmic equation using the C∶N ratio and carbon isotope ratio from the non extracted egg tissue calculated 90% of the lipid-extracted carbon isotope ratios within ±0.5‰. Calculating separate equations for eggs laid by species in different habitats (pelagic, offshore and terrestrial-influenced) improved the fit. A logarithmic equation, rather than a linear equation as often used for muscle, was necessary to accurately correct for lipid content because the relatively high lipid content of eggs compared with muscle meant that a linear relationship did not accurately approximate the relationship between percent lipids and the C∶N ratio. Because lipid extraction alters sulphur and nitrogen isotope ratios (and cannot be corrected algebraically), we suggest that isotopic measurement on bulk tissue followed by algebraic lipid normalization of carbon stable isotope ratio is often a good solution for homogenated eggs, at least when it is not possible to complete separate chemical analyses for each isotope. PMID:24465384

  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. On krypton isotopic abundances in the sun and in the solar wind

    NASA Technical Reports Server (NTRS)

    Marti, K.

    1980-01-01

    The Kr isotopic systematics in the meteorite Pesyanoe which is known to contain solar-type gases, are reported. Discrepancies in the isotopic data of fractions released at stepwise increasing temperatures cannot be reconciled with spallation Kr components, although spallation effects are significant. Fractionation mechanisms on the parent body and in the solar wind source region are considered and the implications for solar abundances discussed.

  3. Evaluation of bioremediation systems utilizing stable carbon isotope analysis

    SciTech Connect

    Van de Velde, K.; Nowell, C.; Marley, M.C.

    1994-12-31

    Carbon, whether in an organic or inorganic form, is composed primarily of two stable isotopes, carbon-12 and carbon-13. The ratio of carbon-12 to carbon-13 is approximately 99:1. The stable carbon isotope ratios of most natural carbon materials of biological interest range from approximately 0 to {minus}110 per mil ({per_thousand}) versus the PDB standard. Utilizing stable carbon isotope analysis, it is often possible to determine the source(s) of the liberated carbon dioxide, thereby confirming successful mineralization of the targeted carbon compound(s) and, if the carbon dioxide results from multiple carbon compounds, in what ratio the carbon compounds are mineralized. Basic stable isotope `theory` recommended sampling procedures and analysis protocols are reviewed. A case study involving fuel oil presented on the application of stable carbon isotope analysis for the monitoring and evaluation of in situ bioremediation. At the site, where a field bioventing study was being conducted, multiple potential sources of carbon dioxide production existed. Additional potential applications of stable carbon isotope analysis for bioremediation evaluation and monitoring are discussed.

  4. Abundance of atomic carbon /C I/ in dense interstellar clouds

    NASA Technical Reports Server (NTRS)

    Phillips, T. G.; Huggins, P. J.

    1981-01-01

    The abundance of interstellar neutral atomic carbon is investigated by means of its ground state fine-structure line emission at 492 GHz using the 91.5 cm telescope of NASAs Kuiper Airborne Observatory. Atomic carbon is found to be very abundant in dense interstellar molecular clouds with column densities of about 10 to the 19th per sq cm. Because the observations have considerably greater column densities than current theories of carbon chemistry, it is suggested that the physical conditions of these clouds are not as simple as assumed in the models. Various situations are discussed which would lead to large C I abundances, including the possibility that the chemical lifetimes of the clouds are relatively short.

  5. Further carbon isotope measurements of LEW 88516

    NASA Technical Reports Server (NTRS)

    Wright, I. P.; Douglas, C.; Pillinger, C. T.

    1993-01-01

    Douglas et al. have previously analyzed the carbon content and isotopic composition of a crushed sample (sub-sample 13) of the shergottite, LEW 88516. The powder, which was from a relatively large portion of the meteorite in order to obtain a representative sample, was distributed amongst the scientific community. However, it is probable that the preparation procedure was not optimized for the purposes of carbon measurements. Indeed, it was found that LEW 88516,13 contained over 1200 ppm carbon, a concentration which is greater than that present in any other SNC meteorite. That a close relative, ALH A77005, contains only 141 ppm carbon seems to implicate the preparation procedure as being responsible for the apparently high carbon content of LEW 88516. However, it may also be the nature of the fine powder which has resulted in contamination. The observation of high carbon content in LEW 88516,13 highlights the extreme difficulty of trying to obtain representative samples of whole meteorites for this kind of investigation. Presented herein are some further measurements of LEW 88516 which should serve to clarify some of the issues raised by the previous investigation.

  6. On the Evolution of Stars That Form Electron-degenerate Cores Processed by Carbon Burning. II. Isotope Abundances and Thermal Pulses in a 10 Msun Model with an ONe Core and Applications to Long-Period Variables, Classical Novae, and Accretion-induced Collapse

    NASA Astrophysics Data System (ADS)

    Ritossa, Claudio; Garcia-Berro, Enrique; Iben, Icko, Jr.

    1996-03-01

    A 10 Msun model of Population I composition is evolved from the hydrogen-burning main sequence to the thermally pulsing `super' asymptotic giant branch (TPSAGB) stage, where it has an oxygen-neon (ONe) core of mass 1.196 Msun and is experiencing thermal pulses driven by helium-burning thermonuclear flashes. Interior abundance characteristics are relevant to an understanding of the core collapse of massive acereting white dwarfs in close binary star systems. At mass point 0.2 Msun., abundances by mass are X(16O) = 0.656, X(20Ne) = 0.215, X(23Na) = 0.0467, X(24Mg) = 0.0325, X(25Mg) = 0.0115, X(12 C)= 0.0112, X(22Ne) = 0.00893, X(21Ne) = 0.00689, X(26Mg) = 0.00560, and X(27Al) = 0.00528. Abundances near the surface of the core are relevant to an understanding of nova outbursts in cataclysmic variables. At mass point 1.17 Msun, abundances by mass are X(16O) = 0.511, X(20Ne) = 0.313, X(23Na) = 0.0644, X(24Mg) = 0.0548, X(25Mg) = 0.0158, X(27 Al)= 0.0108, X(12C) = 0.00916, X(26Mg) = 0.00989, X(21Ne) = 0.00598, and X(22Ne) = 0.00431. Carbon burning is quenched at the beginning of the thermally pulsing phase, and a layer of CO matter of mass 0.015 Msun separates the ONe core from overlying helium- and hydrogen-rich layers. The outer 0.01 M of the CO layer contains essentially no neon: very little new 20Ne has been made, and most of the 22Ne which has been made from the original CNO elements has been converted into 25Mg and neutrons which have been captured to form neutron-rich isotopes. If the observational counterpart of the model is in a close binary and fills its Roche lobe near the end of the carbon-burning phase, and if the binary evolves into a cataclysmic variable, one expects that the ejecta of approximately 1000 nova outbursts will exhibit an under- abundance of neon and overabundance of carbon, oxygen, and magnesium. During the TPSAGB phase, characteristics of a pulse cycle approach local limit-cycle values after ˜30 pulses. Helium-shell flashes are of about the

  7. Natural abundance variations in stable isotopes and their potential uses in animal physiological ecology.

    PubMed

    Gannes, L Z; Martínez del Rio, C; Koch, P

    1998-03-01

    Chemical, biological, and physical processes lead to distinctive "isotopic signatures" in biological materials that allow tracing of the origins of organic substances. Isotopic variation has been extensively used by plant physiological ecologists and by paleontologists, and recently ecologists have adopted the use of stable isotopes to measure ecosystem patterns and processes. To date, animal physiological ecologists have made minimal use of naturally occurring stable isotopes as tracers. Here we provide a review of the current and potential uses of naturally occurring stable isotopes in animal physiological ecology. We outline the physical and biological processes that lead to variation in isotopic abundance in plants and animals. We summarize current uses in animal physiological ecology (diet reconstruction and animal movement patterns), and suggest areas of research where the use of stable isotopes can be fruitful (protein balance and turnover and the allocation of dietary nutrients). We argue that animal physiological ecologists can benefit from including the measurement of naturally occurring stable isotopes in their battery of techniques. We also argue that animal physiologists can make an important contribution to the emerging field of stable isotopes in biology by testing experimentally the plethora of assumptions upon which the techniques rely.

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  9. Studies of Isotopic Abundances through Gamma-Ray Lines

    NASA Astrophysics Data System (ADS)

    Diehl, Roland

    2006-07-01

    Cosmic gamma-ray lines convey isotopic information from sites of nucleosynthesis and from their surrounding interstellar medium. With recent space-borne gamma-ray spectrometers of high resolution (INTEGRAL, RHESSI), new results have been obtained for 44Ti from the Cas A core-collapse supernova, from long-lived radioactive 26Al and 60Fe, and from positron annihilation in our Galaxy: 44Ti ejection from Cas A may be on the low side of previously-reported values, and/or at velocities >7000 km s-1. 26Al sources apparently share the Galactic rotation in the inner Galaxy, and thus allow to estimate a total mass of 26Al in the Galaxy of 2.8 Msolar from the measured flux. The 60Fe production in massive stars appears lower than predicted by standard models, as constrained by the recent, though marginal, 60Fe detections. Positron annihilation in the Galaxy shows a remarkable bulge component, which is difficult to understand in terms of nucleosynthetic production of the positrons.

  10. 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

  11. Carbon-isotopic analysis of dissolved acetate

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  12. Carbon-isotopic analysis of dissolved acetate.

    PubMed

    Gelwicks, J T; Hayes, J M

    1990-01-01

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

  13. DETERMINING INTERSTELLAR CARBON ABUNDANCES FROM STRONG-LINE TRANSITIONS

    SciTech Connect

    Sofia, U. J.; Parvathi, V. S.; Babu, B. R. S.; Murthy, J.

    2011-01-15

    Carbon is arguably the most important element in the interstellar medium, yet its abundance in gas and dust is poorly understood due to a paucity of data. We explore the possibility of substantially increasing our knowledge of interstellar carbon by applying and assessing a new method for determining the column density of the dominant ion of interstellar carbon in diffuse neutral lines of sight. The method relies on profile fitting of the strong transition of C II at 1334 A in spectra continuum normalized with stellar models. We apply our method to six sight lines for which the carbon abundance has previously been determined with a weak intersystem absorption transition. Our strong-line method consistently shows a significantly lower gas-phase C abundance than the measurements from the weak lines. This result implies that more carbon could reside in dust than was previously thought. This has implications for dust models, which often suffer from a lack of sufficient carbon to plausibly explain extinction. There is no immediately clear explanation for the difference found between the strong- and weak-line C II determinations, but there are indications that the results from the method presented here have advantages over the weak-line column densities. If this is the case, then the reported oscillator strength for the C II transition at 2325 A may be too small. Our findings further suggest that damping wings modeled with a single absorption component may not produce accurate abundances. This problem could affect a large number of H I abundances determined through absorption line analysis that are reported in the literature.

  14. 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 organic 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.

  15. 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.

  16. Biomarker and molecular isotope approaches to deconvolve the terrestrial carbon isotope record: modern and Eocene calibrations

    NASA Astrophysics Data System (ADS)

    Diefendorf, A. F.; Freeman, K. H.; Wing, S.; Currano, E. D.

    2010-12-01

    Climate, biome, and plant community are important predictors of carbon isotope patterns recorded in leaves and leaf waxes. However, signatures recorded by terrestrial organic carbon and lipids that have mixed floral sources (e.g., n-alkanes) potentially reflect both plant community changes and climate. More taxonomically specific proxies for plants (i.e., di- and tri-terpenoids for conifers and angiosperms, respectively), can help to resolve the relative influences of changing community and climate, provided differences in biomarker production and lipid biosynthetic fractionation among plants can be better constrained. We present biomarker abundance and carbon isotope values for lipids from leaves, branches and bark of 44 tree species, representing 21 families including deciduous and evergreen conifers and angiosperms. n-alkane production differs greatly between conifer and angiosperm leaves. Both deciduous and evergreen angiosperms make significantly more n-alkanes than conifers, with n-alkanes not detected in over half of the conifers in our study. Terpenoid abundances scale strongly with leaf habit: evergreen species have significantly higher abundances. We combine these relative differences in lipid production with published estimates of fluxes for leaf litter from conifer and angiosperm trees to develop a new proxy approach for estimating paleo plant community inputs to ancient soils and sediments. To test our modern calibration results, we have evaluated n-alkanes and terpenoids from laterally extensive (~18 km) carbonaceous shales and mudstones in Eocene sediments (52.6 Ma) at Fifteenmile Creek in the Bighorn Basin (WY, USA). Our terpenoid-based proxy predicts on average a 40% conifer community, which is remarkably close in agreement with a fossil-based estimate of 36%. n-alkane carbon isotope fractionation (leaf-lipid) differs among plant types, with conifer n-alkanes about 2-3‰ 13C enriched relative to those in angiosperms. Since conifer leaves are

  17. 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.

  18. Current and relic carbon using natural abundance carbon-13

    SciTech Connect

    layse,MF; Clapp,CE; Allmaras,RR; Linden,D.R; Molina, JAE.; Copeland,SM; Dowdy,RH

    2002-05-01

    The role of agricultural practices on soil carbon (C) dynamics is critical to improved soil management. The main objective was to examine the C interactions resulting from crop changes under different tillage and residue treatments.

  19. 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.

  20. 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.

  1. Global simulation of the carbon isotope exchange of terrestrial ecosystems

    NASA Astrophysics Data System (ADS)

    Ito, A.; Terao, Y.; Mukai, H.

    2009-12-01

    There remain large uncertainties in our quantification of global carbon cycle, which has close interactions with the climate system and is subject to human-induced global environmental change. Information on carbon isotopes is expected to reduce the uncertainty by providing additional constraints on net atmosphere-ecosystem exchange. This study attempted to simulate the dynamics of carbon isotopes at the global scale, using a process-based terrestrial ecosystem model: Vegetation Integrative SImulator for Trace gases (VISIT). The base-model of carbon cycle (Sim-CYCLE, Ito 2003) has already considered stable carbon isotope composition (13C/12C), and here radioactive carbon isotope (14C) was included. The isotope ratios characterize various aspects of terrestrial carbon cycle, which is difficult to be constrained by sole mass balance. For example, isotopic discrimination by photosynthetic assimilation is closely related with leaf stomatal conductance and composition of C3 and C4 plant in grasslands. Isotopic disequilibrium represents mean residence time of terrestrial carbon pools. In this study, global simulations (spatial resolution 0.5-deg, time-step 1-month) were conducted during the period 1901 to 2100 on the basis of observed and projected atmospheric CO2, climate, and land-use conditions. As anthropogenic CO2 accumulates in the atmosphere, heavier stable carbon isotope (13C) was diluted, while radioactive carbon isotope (14C) is strongly affected by atomic bomb experiments mainly in the 1950s and 1960s. The model simulated the decadal change in carbon isotope compositions. Leaf carbon with shorter mean residence time responded rapidly to the atmospheric change, while plant stems and soil humus showed substantial time-lag, leading to large isotopic disequilibrium. In the future, the isotopic disequilibrium was estimated to augment, due to accelerated rate of anthropogenic CO2 accumulation. Spatial distribution of stable isotope composition (12C/13C, or d13C) was

  2. Low turnover rates of carbon isotopes in tissues of two nectar-feeding bat species.

    PubMed

    Voigt, Christian C; Matt, Felix; Michener, Robert; Kunz, Thomas H

    2003-04-01

    Stable isotopes of carbon are commonly used to characterize dietary preferences in animals. Because turnover rates of carbon isotopes are related to metabolic rate, we wanted to determine the rates at which carbon isotopes are exchanged in tissues of two species of nectar-feeding bats (Leptonycteris curasoae and Glossophaga soricina), both of which have relatively high mass-specific metabolic rates. To test the hypothesis that isotope turnover is higher in nectar-feeding bats, because of their high mass-specific metabolic rates, than in other eutherian mammals, we conducted diet-switching experiments and chose three target tissues (hair, wing membrane and blood) to evaluate the isotopic turnover rates. We made the following predictions: (1) isotopic composition should change towards higher delta(13)C-values due to the turnover of carbon isotopes of C(3) origin with those of C(4)/CAM origin; (2) the turnover rates of carbon isotopes would differ between the three types of tissues in the following order of decreasing turnover rates: blood>wing membrane>hair; and (3) turnover rates of nectar-feeding bats should exceed those reported for other small mammals because of the high mass-specific metabolic rate of nectar-feeding bats. Compared to the initial diet, target tissues were enriched in heavy carbon isotopes by 2.8 per thousand in L. curasoae and by 2.6 per thousand in G. soricina. After changing the diet from C(3) to C(4)/CAM origin we found an increase in abundance of (13)C in blood and wing membrane in all experimental subjects. The estimated half life of carbon isotope turnover ranged from 100 to 134 days and did not differ significantly between blood and wing membrane, nor did it differ between the two species. The low turnover rate in wing membrane may reflect its specific composition and the relatively low temperature of this tissue, and long-lived erythrocytes in bat blood may be responsible for the low turnover rate of carbon isotopes in blood. The turnover

  3. Carbon allocation in plants and ecosystems - insights from stable isotope studies

    NASA Astrophysics Data System (ADS)

    Gessler, Arthur

    2014-05-01

    Trees are large global stores of carbon (C) that will be impacted by increased carbon dioxide levels and climate change. However, at present we cannot properly predict the carbon balance of forests in future as we lack knowledge on how plant physiological processes, the transfer of carbon within the plant, carbon storage, and remobilization in the plant tissues as well as the release of carbon from the roots to the soil interact with environmental drivers and ecosystem-scale processes. This paper will summarise how stable isotope techniques can give new insights in the fate of newly assimilated C in plants and ecosystems on time scales from hours to seasons and it will include studies either characterizing temporal and spatial variation in the natural abundance of carbon and oxygen isotopes or applying isotopically enriched tracers. It comprises the assessment of the mechanisms of C partitioning among specific metabolic pathways, between plant organs and into various ecosystem C pools with different residence times. Moreover stable isotopes are highly suitable tools to characterise the role of the phloem, which is the central long-distance conveyer distributing C from source to sinks and thus plays a central role in linking sites and structures of storage, growth and other metabolic activities. A deeper understanding of these processes and their interaction with environmental drivers is critical for predicting how trees and ecosystems will respond to coming global environmental changes, including increased temperature, altered precipitation, and elevated carbon dioxide concentrations.

  4. 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

  5. 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.

  6. [Stable isotopes of carbon and nitrogen in soil ecological studies].

    PubMed

    Tiunov, A V

    2007-01-01

    The development of stable isotope techniques is one of the main methodological advances in ecology of the last decades of the 20th century. Many biogeochemical processes are accompanied by changes in the ratio between stable isotopes of carbon and nitrogen (12C/13C and 14N/15N), which allows different ecosystem components and different ecosystems to be distinguished by their isotopic composition. Analysis of isotopic composition makes it possible to trace matter and energy flows through biological systems and to evaluate the rate of many ecological processes. The main concepts and methods of stable isotope ecology and patterns of stable isotope fractionation during organic matter decomposition are considered with special emphasis on the fractionation of isotopes in food chains and the use of stable isotope studies of trophic relationships between soil animals in the field.

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

    USGS Publications Warehouse

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

    1978-01-01

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

  8. Absolute Isotopic Abundance Ratios and Atomic Weight of a Reference Sample of Nickel

    PubMed Central

    Gramlich, J. W.; Machlan, L. A.; Barnes, I. L.; Paulsen, P. J.

    1989-01-01

    Absolute values have been obtained for the isotopic abundance ratios of a reference sample of nickel (Standard Reference Material 986), using thermal ionization mass spectrometry. Samples of known isotopic composition, prepared from nearly isotopically pure separated nickel isotopes, were used to calibrate the mass spectrometers. The resulting absolute isotopic ratios are: 58Ni/60Ni=2.596061±0.000728, 61Ni/60Ni=0.043469±0.000015,62Ni/60Ni=0.138600±0.000045, and 64Ni/60Ni=0.035295±0.000024, which yield atom percents of 58Ni=68.076886 ±0.005919, 60Ni = 26.223146±0.005144,61Ni=1.139894±0.000433, 62Ni =3.634528±0.001142, and 64Ni =0.925546±0.000599. The atomic weight calculated from this isotopic composition is 58.693353 ±0.000147. The indicated uncertainties are overall limits of error based on two standard deviations of the mean and allowances for the effects of known sources of possible systematic error. PMID:28053421

  9. Carbon isotopic fractionation in the biosynthesis of bacterial fatty acids. Ozonolysis of unsaturated fatty acids as a means of determining the intramolecular distribution of carbon isotopes

    NASA Astrophysics Data System (ADS)

    Monson, K. David; Hayes, J. M.

    1982-02-01

    Methods for the determination of 13C abundances at individual olefinic carbon positions have been developed, tested, and shown to perform accurately. (1) The double bond is oxidized with ozone; (2) silver oxide is used to cleave the resulting ozonide quantitatively to carboxylic-acid fragments; (3) a modified Schmidt decarboxylation is used to produce CO 2 quantitatively from the carboxyl groups of the separated cleavage products; (4) the CO 2 is utilized for mass spectrometric analysis. The results of intramolecular isotopic analyses are combined with molecular-average isotopic compositions determined by total combustion in order to show that fatty acids biosynthesized by Escherichia coli grown aerobically with glucose as the sole carbon source and harvested at late log phase are depleted by approximately 3%. in 13C relative to the glucose. This fractionation arises in the formation of acetylcoenzyme A by pyruvate dehydrogenase and is localized at the carboxyl position in the acetyl-CoA product. The isotopic order in that two-carbon subunit is carried through the biosynthesis of fatty acids so that alternate positions in the fatty-acid chains are depleted in 13C by an amount equal to twice the molecular-average depletion. The kinetic isotope effect at C-2 for pyruvate dehydrogenase in vivo is shown to be approximately 2.3%. While it appears that no other fractionation mechanism has controlled the overall depletion of 13C in these fatty acids, a separate process responsible for control of isotopic abundances in the carboxyl groups has been identified and described elsewhere [Monson K.D. and Hayes J.M. (1980) J. Biol. Chem. 255, 11435-11441]. It is concluded that kinetic, rather than thermodynamic, factors have controlled isotopic distributions in these cells and that kinetic factors will be dominant in most biological reactions.

  10. 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.

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

    PubMed

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

    2011-09-14

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

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

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

    Sample surface carbon, mantle carbon dioxide in vesicles, and mantle carbon dissolved in glasses, are the three carbon components evident in the 11 mid-oceanic basalts presently analyzed. The total carbon content may be controlled by the depth of the shallowest ridge magma chamber, and carbon isotopic fractionation accompanies magma degassing. Using He-3 and carbon data for submarine hydrothermal fluids, the present day midoceanic ridge carbon flux is approximately estimated to be 1.0 x 10 to the 13th g C/yr, requiring 8 Gyr to accumulate the earth's present crustal carbon inventory.

  13. 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

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

  16. An automated method for 'clumped-isotope' measurements on small carbonate samples.

    PubMed

    Schmid, Thomas W; Bernasconi, Stefano M

    2010-07-30

    Clumped-isotope geochemistry deals with the state of ordering of rare isotopes in molecules, in particular with their tendency to form bonds with other rare isotopes rather than with the most abundant ones. Among its possible applications, carbonate clumped-isotope thermometry is the one that has gained most attention because of the wide potential of applications in many disciplines of earth sciences. Clumped-isotope thermometry allows reconstructing the temperature of formation of carbonate minerals without knowing the isotopic composition of the water from which they were formed. This feature enables new approaches in paleothermometry. The currently published method is, however, limited by sample weight requirements of 10-15 mg and because measurements are performed manually. In this paper we present a new method using an automated sample preparation device coupled to an isotope ratio mass spectrometer. The method is based on the repeated analysis (n = 6-8) of 200 microg aliquots of sample material and completely automated measurements. In addition, we propose to use precisely calibrated carbonates spanning a wide range in Delta(47) instead of heated gases to correct for isotope effects caused by the source of the mass spectrometer, following the principle of equal treatment of the samples and standards. We present data for international standards (NBS 19 and LSVEC) and different carbonates formed at temperatures exceeding 600 degrees C to show that precisions in the range of 10 to 15 ppm (1 SE) can be reached for repeated analyses of a single sample. Finally, we discuss and validate the correction procedure based on high-temperature carbonates instead of heated gases.

  17. Can heavy isotopes increase lifespan? Studies of relative abundance in various organisms reveal chemical perspectives on aging

    PubMed Central

    2016-01-01

    Stable heavy isotopes co‐exist with their lighter counterparts in all elements commonly found in biology. These heavy isotopes represent a low natural abundance in isotopic composition but impose great retardation effects in chemical reactions because of kinetic isotopic effects (KIEs). Previous isotope analyses have recorded pervasive enrichment or depletion of heavy isotopes in various organisms, strongly supporting the capability of biological systems to distinguish different isotopes. This capability has recently been found to lead to general decline of heavy isotopes in metabolites during yeast aging. Conversely, supplementing heavy isotopes in growth medium promotes longevity. Whether this observation prevails in other organisms is not known, but it potentially bears promise in promoting human longevity. PMID:27554342

  18. Boron abundances and isotopic ratios of olivine grains on Itokawa returned by the Hayabusa spacecraft

    NASA Astrophysics Data System (ADS)

    Fujiya, Wataru; Hoppe, Peter; Ott, Ulrich

    2016-09-01

    We report the B abundances and isotopic ratios of two olivine grains from the S-type asteroid Itokawa sampled by the Hayabusa spacecraft. Olivine grains from the Dar al Gani (DaG) 989 LL6 chondrite were used as a reference. Since we analyzed polished thin sections in both cases, we expect the contribution from the solar wind B (rich in 10B) to be minimal because the solar wind was implanted only within very thin layers of the grain surface. The Itokawa and DaG 989 olivine grains have homogeneous B abundances (~400 ppb) and 11B/10B ratios compatible with the terrestrial standard and bulk chondrites. The observed homogeneous B abundances and isotopic ratios of the Itokawa olivine grains are likely the result of thermal metamorphism which occurred in the parent asteroid of Itokawa, which had a similar composition as LL chondrites. The chondritic B isotopic ratios of the Itokawa samples suggest that they contain little cosmogenic B (from cosmic-ray spallation reactions) rich in 10B. This observation is consistent with the short cosmic-ray exposure ages of Itokawa samples inferred from the small concentrations of cosmogenic 21Ne. If other Itokawa samples have little cosmogenic B as well, the enrichment in 10B found previously on the surface of another Itokawa particle (as opposed to the bulk grain study here) may be attributed to implanted solar wind B.

  19. 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.

  20. Carbon and Oxygen Abundances in Low Metallicity Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Berg, Danielle A.; Skillman, Evan D.; Henry, Richard B. C.; Erb, Dawn K.; Carigi, Leticia

    2016-08-01

    The study of carbon and oxygen abundances yields information on the time evolution and nucleosynthetic origins of these elements, yet they remain relatively unexplored. At low metallicities, (12+log(O/H) < 8.0), nebular carbon measurements are limited to rest-frame UV collisionally excited emission lines. Therefore, we present the UV spectrophotometry of 12 nearby low-metallicity high-ionization H ii regions in dwarf galaxies obtained using the Cosmic Origins Spectrograph on the Hubble Space Telescope. We present the first analysis of the C/O ratio in local galaxies based solely on simultaneous significant detections of the UV {{{O}}}+2 and {{{C}}}+2 collisionally excited lines in seven of our targets and five objects from the literature to create a final sample of 12 significant detections. Our sample is complemented by optical SDSS spectra, from which we measured the nebular physical conditions and oxygen abundances using the direct method. At low metallicity, (12+log(O/H) < 8.0), no clear trend is evident in C/O versus O/H for the present sample given the large dispersion observed. When combined with recombination line observations at higher values of O/H, a general trend of increasing C/O with increasing O/H is also viable but with some significant outliers. Additionally, we find the C/N ratio appears to be constant (but with significant scatter) over a large range in oxygen abundance, indicating that carbon is predominantly produced by similar nucleosynthetic mechanisms as nitrogen. If true, and our current understanding of nitrogen production is correct, this would indicate that primary production of carbon (a flat trend) dominates at low metallicity, but quasi-secondary production (an increasing trend) becomes prominent at higher metallicities. A larger sample will be needed to determine the true nature and dispersion of the relation.

  1. 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

  2. Distribution and carbon isotope patterns of diterpenoids and triterpenoids in modern temperate C3 trees and their geochemical significance

    NASA Astrophysics Data System (ADS)

    Diefendorf, Aaron F.; Freeman, Katherine H.; Wing, Scott L.

    2012-05-01

    Tricyclic diterpenoids and pentacyclic triterpenoids are nearly exclusively produced by gymnosperms and angiosperms, respectively. Even though both classes of terpenoids have long been recognized as plant biomarkers, their potential use as phylogenetically specific δ13C proxies remains largely unexplored. Little is known of how terpenoid abundance and carbon isotope composition vary either with plant phylogenetic position, functional group, or during synthesis. Here, we report terpenoid abundances and isotopic data for 44 tree species in 21 families, representing both angiosperms and gymnosperms, and both deciduous and evergreen leaf habits. Di- and triterpenoid abundances are significantly higher in evergreens compared to deciduous species, reflecting differences in growth strategies and increased chemical investment in longer-lived leaves. Carbon isotope abundances of terpenoid lipids are similar to leaf tissues, indicating biosynthetic isotope effects are small for both the MVA (-0.4‰) and MEP (-0.6‰) pathways. Leaf and molecular isotopic patterns for modern plants are consistent with observations of amber, resins and plant biomarkers in ancient sediments. The δ13C values of ancient diterpenoids are higher than triterpenoids by 2-5‰, consistent with observed isotopic differences between gymnosperms and angiosperms leaves, and support the relatively small lipid biosynthetic effects reported here. All other factors being equal, evergreen plants will dominate the abundance of terpenoids contributed to soils, sediments and ancient archives, with similar inputs estimated for angiosperm and gymnosperm trees when scaled by litter flux.

  3. 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.

  4. Bromine and carbon isotope effects during photolysis of brominated phenols.

    PubMed

    Zakon, Yevgeni; Halicz, Ludwik; Gelman, Faina

    2013-12-17

    In the present study, carbon and bromine isotope effects during UV-photodegradation of bromophenols in aqueous and ethanolic solutions were determined. An anomalous relatively high inverse bromine isotope fractionation (εreactive position up to +5.1‰) along with normal carbon isotope effect (εreactive position of -12.6‰ to -23.4‰) observed in our study may be attributed to coexistence of both mass-dependent and mass-independent isotope fractionation of C-Br bond cleavage. Isotope effects of a similar scale were observed for all the studied reactions in ethanol, and for 4-bromophenol in aqueous solution. This may point out related radical mechanism for these processes. The lack of any carbon and bromine isotope effects during photodegradation of 2-bromophenol in aqueous solution possibly indicates that C-Br bond cleavage is not a rate-limiting step in the reaction. The bromine isotope fractionation, without any detectable carbon isotope effect, that was observed for 3-bromophenol photolysis in aqueous solution probably originates from mass-independent fractionation.

  5. Chemical and Isotopic Study of Lab-formed Carbonates Under Cryogenic and Hydrothermal Conditions

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

    Aqueous environments on early Mars were probably relatively short-lived and localized, as evidenced by the lack of abundant secondary minerals detected by the TES instrument. In order to better understand the aqueous history of early Mars we need to be able to interpret the evidence preserved in secondary minerals formed during these aqueous events. Carbonate minerals, in particular, are important secondary minerals for interpreting past aqueous environments as illustrated by the carbonates preserved in ALH84001. Carbonates formed in short-lived, dynamic aqueous events often preserve kinetic rather than equilibrium chemical and isotopic processes, and predicting the behavior of such systems is facilitated by empirical data.

  6. 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.

  7. 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,...

  8. Carbon, nitrogen, and oxygen abundances in G and K giants

    NASA Astrophysics Data System (ADS)

    Ries, L. M.

    The abundance of carbon, nitrogen, and oxygen were determined in 32 bright G and K giants in order to test theoretical predictions of nucleosynthesis and convective mixing in evolved stars. Atmospheric parameters were determined from lines of neutral and ionized iron measured from photographic plates taken with the coude spectrograph on a 2.1 m telescope. These were supplemented by spectra obtained with the coude Reticon on the 2.7 m telescope. Excitation temperatures were determined using a curve of growth technique on the neutral iron lines. Empirical solar oscillator strengths were used. Lineblanketed model atmospheres provides the calibration with effective temperature ionization equilibrium yielded the gravity, while the microturbulence was found by demanding that the iron abundance be independent of line strength.

  9. Temperature and Oxygen Isotope Composition of The Ediacaran Ocean: Constraints From Clumped Isotope Carbonate Thermometry

    NASA Astrophysics Data System (ADS)

    Bonifacie, M.; Eiler, J. M.; Fike, D. A.

    2008-12-01

    The temperature and chemical variations of the early oceans on Earth are highly debated, particularly for periods associated with significant evolutionary change and/or extinction. The temperature of past oceans has been estimated based on conventional carbonate-water and/or silicate-water stable oxygen isotope thermometry. Precambrian carbonates and silicates both exhibit a long-term secular trend of increasing δ18O values with decreasing age. This trend has been used to support two opposite - though related - interpretations: the Earth's oceans gradually cooled over the course of the Proterozoic eon, from a maximum of ~ 60-90°C at ~ 2.5Ga (and were, on average, relatively warm during much of the Paleozoic era) [1]. This interpretation has been supported by Si-isotope proxies and the thermal tolerances of proteins in various classes of microbial organisms [2-3]. Alternatively, the δ18O value of the oceans has gradually increased through time [4-5], and mean Earth surface temperatures varied over a narrow range similar to modern conditions. In other terms, one either assumes an ocean of constant δ18O and infers that climate varied dramatically, or vise versa. Finally, it is possible that post- depositional processes (e.g., diagenesis, burial metamorphism, weathering) has modified the δ18O values of all or most Precambrian sedimentary carbonates and silicates, overprinting any paleoclimatic variations. Carbonate 'clumped isotope' thermometry provides a new way to independently test these hypotheses because it allows one to determine the apparent growth temperatures of carbonate minerals based on their abundances of 13C-18O bonds, as reflected by the 'Δ47' value of CO2 extracted by phosphoric acid digestion [6]. This method is thermodynamically based and independent of the δ18O of water from which the carbonate grew. We will report the initial results of measurements of 'Δ47 for a suite of carbonates from the Sultanate of Oman. This Ediacaran age (~ 635 to

  10. 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.

  11. 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.

  12. 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).

  13. 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).

  14. Carbon isotope fractionation during calcium carbonate precipitation induced by ureolytic bacteria

    NASA Astrophysics Data System (ADS)

    Millo, Christian; Dupraz, S.; Ader, M.; Guyot, F.; Thaler, C.; Foy, E.; Ménez, B.

    2012-12-01

    Ureolytic bacteria have been proposed as model organisms to investigate the potential of subsurface microorganisms to enhance carbon capture and storage through solubility- and mineral-trapping of CO2 induced by bacterial ureolysis and carbonate formation. Ideally, CO2 incorporation into carbonates can be readily traced using carbon isotope measurements. However, the carbon isotope systematics of bacterial ureolysis and associated carbonate precipitation is still poorly known. We determined the carbon isotope fractionations expressed during ureolysis and carbonate precipitation induced by Sporosarcina pasteurii at 30 °C. Our results indicate that bacterial ureolysis proceeds as a Rayleigh distillation characterized by a 13C-enrichment factor equal to -12.5‰. As precipitation proceeds, the δ13C value of CaCO3, initially 1-2.1‰ lower than that of dissolved inorganic carbon (DIC), evolves progressively until it is 0.5‰ higher than that of the DIC, i.e. close to the value predicted for isotopic equilibrium. The minor isotope disequilibrium at the onset of precipitation and its rapid evolution towards isotopic equilibrium point to bacterial carbonates as reliable recorders of the carbon isotope composition of DIC. This corroborates the potential utility of 13C-tracing for the quantification of microbially-induced CO2 sequestration into solid carbonates and DIC.

  15. 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.

  16. Identification and quantification of base flow using carbon isotopes.

    PubMed

    Meredith, Elizabeth L; Kuzara, Shawn L

    2012-01-01

    Six surface water samples from locations along Otter Creek in Southeastern Montana and a groundwater sample from a nearby monitoring well completed in the Knobloch coal were analyzed for stable carbon isotope ratios. Along the length of its perennial reach, between the towns of Otter and Ashland, Otter Creek crosses several coal outcrops, including the Knobloch coal zone. The carbon isotope ratio of the creek becomes progressively more similar to that of the Knobloch coal aquifer groundwater in samples collected downgradient from the town of Otter. The isotope ratio of the stream changes from -10.5 to -8.9‰ reflecting the influence of the coal-aquifer base flow contribution, as represented by Knobloch coal groundwater, which has a carbon isotope value of +3.9‰. The dissolved inorganic carbon concentrations of the groundwater and surface water are similar (~100 mg/L), which allowed the use of the simplified, first-order, two-end-member mixing equation. Using carbon isotope ratios, calculations of the fraction of water contributed by coal aquifers indicate that approximately 11% of the surface water in Otter Creek at its mouth near Ashland was supplied by groundwater from the coal aquifers that crop out between Otter and Ashland. This study was conducted in December, when Otter Creek is at low flow. At times of higher surface flow, the contribution from groundwater base flow will be correspondingly smaller. This study illustrates that carbon isotopes can be an effective, low-cost tool in base flow studies.

  17. Isotopic fractionation of alkali earth metals during carbonate precipitation

    NASA Astrophysics Data System (ADS)

    Yotsuya, T.; Ohno, T.; Muramatsu, Y.; Shimoda, G.; Goto, K. T.

    2014-12-01

    The alkaline earth metals such as magnesium, calcium and strontium play an important role in a variety of geochemical and biological processes. The element ratios (Mg/Ca and Sr/Ca) in marine carbonates have been used as proxies for reconstruction of the past environment. Recently several studies suggested that the study for the isotopic fractionation of the alkaline earth metals in marine carbonates has a potentially significant influence in geochemical research fields (e.g. Eisenhauer et al., 2009). The aim of this study is to explore the influence of carbonate polymorphs (Calcite and Aragonite) and environmental factors (e.g., temperature, precipitation rate) on the level of isotopic fractionation of the alkaline earth metals. We also examined possible correlations between the level of isotopic fractionation of Ca and that of other alkaline earth metals during carbonate precipitation. In order to determine the isotope fractionation factor of Mg, Ca and Sr during carbonate precipitation, calcite and aragonite were synthesized from calcium bicarbonate solution in which the amount of magnesium was controlled based on Kitano method. Calcium carbonates were also prepared from the mixture of calcium chlorite and sodium hydrogen carbonate solutions. The isotope fractionation factors were measured by MC-ICPMS. Results suggested that the level of isotopic fractionation of Mg during carbonate precipitation was correlated with that of Sr and that the change of the carbonate crystal structure could make differences of isotopic fractionations of Mg and Ca, however no difference was found in the case of Sr. In this presentation, the possible mechanism will be discussed.

  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.

    1979-01-01

    The heavy isotopic anomalies observed recently in the fractionation and unknown nuclear inclusions from the Allende meteorite are explained by neutron reactions during the explosive carbon burning (ECB). This model produces heavy anomalies in the same zone where Al-26 and O-16 are produced, thus reducing the number of source zones required for the isotopic anomalies. Unlike the classical r-process, the ECB n-process avoids the problem with the Sr anomaly and may resolve the problem of conflicting time scales between Al-26 and the r-process isotopes I-129 and Pu-244. Experimental studies of Zr and Ce isotopic composition are proposed to test this model.

  19. 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.

  20. Quantifying Carbonate and Serpentine Abundances through VSWIR Microspectroscopy

    NASA Astrophysics Data System (ADS)

    Leask, E.; Ehlmann, B. L.

    2015-12-01

    Visible and shortwave-infrared (VSWIR) reflectance spectroscopy has been used for large-scale mineral mapping on Earth and on Mars. A prototype instrument (UCIS—Ultra Compact Imaging Spectrometer), operating in microscopic mode, applies the same principles over an area the size of a traditional thin section (15-50 cm2), acquiring data over the 0.5-2.5 μm range at a spatial scale of 80 μm/pixel. This technique requires little to no sample preparation and is non-destructive, preserving rock texture. It can be used on future rovers/landers for in-situ petrology and in the lab to link spectral data acquired at large scale with rock mineralogy. We compare microscale mineral maps and abundance results from linear spectral unmixing to other techniques, including XRD, acid dissolution, and EDS/WDS mapping. Samples from the Semail Ophiolite (Oman) are used as an analogue for Martian carbonate and serpentine deposits to assess the capabilities of IR spectroscopy to discriminate carbonate from minerals with absorptions at similar wavelength positions, to determine carbonate composition and the composition of intermixed phases, and to determine their relative abundances. We find that UCIS infrared images can differentiate between carbonate phases not distinguished in XRD results. For example, in a magnesite vein sample, the bulk magnesite is spectrally distinct from another carbonate phase present only in cavities within the sample. Microprobe and EDS analyses of the sample confirm that calcite is present only as a coating within secondary porosity. Similar to SEM-EDS mapping at smaller scales, UCIS can identify rare phases contained within a few pixels (100s μm). For example, aluminum-bearing phyllosilicates in discrete clasts were found among more typical serpentine in a carbonate-cemented breccia. Signals from such rare phases are typically not detectable in XRD but are in spatially resolved microscale IR data. Collectively, data indicate that VSWIR microspectroscopy

  1. 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

  2. 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.

  3. 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.

  4. 13C and 15N natural isotope abundance reflects breast cancer cell metabolism

    PubMed Central

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

    2016-01-01

    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. PMID:27678172

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

    NASA Astrophysics Data System (ADS)

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

    2002-05-01

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

  6. The isotopic characterization of carbon monoxide in the troposphere

    NASA Astrophysics Data System (ADS)

    Conny, Joseph M.

    The distributions of stable isotopes in trace atmospheric species are controlled mainly by the isotopic compositions of precursor molecules and isotope fractionation effects during production and removal of the species. Distributions of radioactive isotopes are controlled mainly by the isotopic compositions of precursor molecules and radioactive decay processes. As a result, through their isotopic compositions, atmospheric species are traceable to sources and sinks. Thus, isotopic compositions provide useful information for estimating source strengths and for understanding the importance of removal processes in the cycling of the species. The use of radioactive 14C and the stable isotopes ( 13C and 18O) are reviewed here for understanding production and removal processes of CO in the troposphere. Carbon monoxide is a critical component in atmospheric chemistry because of its large effect on levels of OH, the principal oxidant in the atmosphere. In the troposphere, this is due to relatively high concentrations of CO and a short lifetime (2-4 months). Initially, 14CO measurements were instrumental in estimating accurately the tropospheric lifetime. Since seasonal 14CO variation is controlled largely by OH, 14CO serves as an important surrogate measure of tropospheric OH. Global 14CO measurements have also been used to estimate the biogenic component of the global CO budget, specifically contributions from biomass burning, oxidized non-methane hydrocarbon (NMHC) emissions, oceans and plants. Research using 14CO measurements is also active in quantifying fossil and non-fossil urban emissions. Kinetic isotopic fractionation during production of 13CO and C 18O from reduced precursors allows one to distinguish, at least qualitatively, different varieties of CO based on seasonal tropospheric isotopic measurements. Difficulties in interpreting the stable isotopic record arise from large fractionation effects that obscure source isotopic signatures (in particular the oxygen

  7. Biosynthesis of gallic acid in Rhus typhina: discrimination between alternative pathways from natural oxygen isotope abundance.

    PubMed

    Werner, Roland A; Rossmann, Andreas; Schwarz, Christine; Bacher, Adelbert; Schmidt, Hanns-Ludwig; Eisenreich, Wolfgang

    2004-10-01

    The biosynthetic pathway of gallic acid in leaves of Rhus typhina is studied by oxygen isotope ratio mass spectrometry at natural oxygen isotope abundance. The observed delta18O-values of gallic acid indicate an 18O-enrichment of the phenolic oxygen atoms of more than 30 per thousand above that of the leaf water. This enrichment implies biogenetical equivalence with oxygen atoms of carbohydrates but not with oxygen atoms introduced by monooxygenase activation of molecular oxygen. It can be concluded that all phenolic oxygen atoms of gallic acid are retained from the carbohydrate-derived precursor 5-dehydroshikimate. This supports that gallic acid is synthesized entirely or predominantly by dehydrogenation of 5-dehydroshikimate.

  8. 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 attempt 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.

  9. High Spatial Resolution Isotopic Abundance Measurements by Secondary Ion Mass Spectrometry: Status and Prospects

    NASA Astrophysics Data System (ADS)

    McKeegan, K. D.

    2007-12-01

    Secondary Ion Mass Spectrometry, SIMS or ion microprobe analysis, has become an important tool for geochemistry because of its ability study the distributions of elemental and isotopic abundances in situ on polished samples with high (typically a few microns to sub-micron) spatial resolution. In addition, SIMS exhibits high sensitivity for a wide range of elements (H to Pu) so that isotope analyses can sometimes be performed for elements that comprise only trace quantities of some mineral phase (e.g., Pb in zircon) or on major and/or minor elements in very small samples (e.g., presolar dust grains). Offsetting these positive attributes are analytical difficulties due to the complexity of the sputtering source of analyte ions: (1) relatively efficient production of molecular ion species (especially from a complex matrix such as most natural minerals) that cause interferences at the same nominal mass as atomic ions of interest, and (2) quantitation problems caused by variations in the ionization efficiencies of different elements and/or isotopes depending upon the chemical state of the sample surface during sputtering--the so-called "matrix effects". Despite the availability of high mass resolution instruments (e.g., SHRIMP II/RG, CAMECA 1270/1280/NanoSIMS), the molecular ion interferences effectively limit the region of the mass table that can be investigated in most samples to isotope systems at Ni or lighter or at Os or heavier. The matrix effects and the sensitivity of instrumental mass discrimination to the physical state of the sample surface can hamper reproducibility and have contributed to a view that SIMS analyses, especially for so- called stable isotopes, are most appropriate for extraterrestrial samples which are often small, rare, and can exhibit large magnitude isotopic effects. Recent improvements in instrumentation and technique have extended the scope of SIMS isotopic analyses and applications now range from geochronology to paleoclimatology to

  10. [Carbon isotope fractionation inplants]. Final report

    SciTech Connect

    O`Leary, M.H.

    1990-12-31

    The objectives of this research are: To develop a theoretical and experimental framework for understanding isotope fractionations in plants; and to develop methods for using this isotope fractionation for understanding the dynamics of CO{sub 2} fixation in plants. Progress is described.

  11. Measurement of stable carbon isotope ratios of non-methane hydrocarbons and halocarbons

    NASA Astrophysics Data System (ADS)

    Zuiderweg, A. T.

    2012-09-01

    Within the realm of volatile organic compounds, hydrocarbons and halocarbons form a sizable proportion of carbon input to the atmosphere. Within these compound categories, the light non-methane hydrocarbons (NMHC, two to seven carbon atoms) and monocarbon halocarbons have a special place as these have strong, if not exclusive, anthropogenic (human-caused) sources. With common atmospheric molar mixing ratios in the parts-per-trillion (10-12 mole/mole) to parts-per-billion (10-9 mole/mole) range, these trace gases, though decidedly minor constituants of the atmosphere, have diverse consequences due to their atmospheric presence and their removal processes. Effects range from causing ground level air pollution and resulting hazards to health, to contributing to anthropogenic climate change and the destruction of the ozone layer in the stratosphere, among many others. The existance of stable isotopes (otherwise identical atoms with varying amounts of neutrons that do not spontaneously disintegrate) in several elements relevant to atmospheric chemistry and physics is a boon to research. Their presence in molecules is detectable by mass and cause small intra- and intermolecular property changes. These changes range from the physical (e.g. boiling point variation) to the chemical (reaction rate variation) and can influence external interactions as well. The measurement of the ratio of a minor stable isotope of an element to the major one (the stable isotope ratio) can be used to establish source fingerprints, trace the interaction dynamics, and refine the understanding of the relative contribution of sources and sinks to the atmosphere as a whole. The stable minor stable isotope of carbon, 13C, has a natural abundance of approximately 1.1 %. It has a sufficient fractional mass difference from its major isotope as to cause significant effects, making it ideal for measuring the ratios and properties of hydro- and halocarbons. In order to enable a better understanding of the

  12. On the volatile inventory of Titan from isotopic abundances in nitrogen and methane.

    PubMed

    Lunine, J I; Yung, Y L; Lorenz, R D

    1999-01-01

    We analyze recently published nitrogen and hydrogen isotopic data to constrain the initial volatile abundances on Saturn's giant moon Titan. The nitrogen data are interpreted in terms of a model of non-thermal escape processes that lead to enhancement in the heavier isotope. We show that these data do not, in fact, strongly constrain the abundance of nitrogen present in Titan's early atmosphere, and that a wide range of initial atmospheric masses (all larger than the present value) can yield the measured enhancement. The enrichment in deuterated methane is now much better determined than it was when Pinto et al. (1986. Nature 319, 388-390) first proposed a photochemical mechanism to preferentially retain the deuterium. We develop a simple linear theory to provide a more reliable estimate of the relative dissociation rates of normal and deuterated methane. We utilize the improved data and models to compute initial methane reservoirs consistent with the observed enhancement. The result of this analysis agrees with an independent estimate for the initial methane abundance based solely on the present-day rate of photolysis and an assumption of steady state. This consistency in reservoir size is necessary but not sufficient to infer that methane photolysis has proceeded steadily over the age of the solar system to produce large quantities of less volatile organics. Our analysis indicates an epoch of early atmospheric escape of nitrogen, followed by a later addition of methane by outgassing from the interior. The results also suggest that Titan's volatile inventory came in part or largely from a circum-Saturnian disk of material more reducing than the surrounding solar nebula. Many of the ambiguities inherent in the present analysis can be resolved through Cassini-Huygens data and a program of laboratory studies on isotopic and molecular exchange processes. The value of, and interest in, the Cassini-Huygens data can be greatly enhanced if such a program were undertaken

  13. The Palaeocene-Eocene carbon isotope excursion: constraints from individual shell planktonic foraminifer records.

    PubMed

    Zachos, James C; Bohaty, Steven M; John, Cedric M; McCarren, Heather; Kelly, Daniel C; Nielsen, Tina

    2007-07-15

    The Palaeocene-Eocene thermal maximum (PETM) is characterized by a global negative carbon isotope excursion (CIE) and widespread dissolution of seafloor carbonate sediments. The latter feature supports the hypothesis that the PETM and CIE were caused by the rapid release of a large mass (greater than 2000Gt C) of 12C-enriched carbon. The source of this carbon, however, remains a mystery. Possible sources include volcanically driven thermal combustion of organic-rich sediment, dissociation of seafloor methane hydrates and desiccation and oxidation of soil/sediment organics. A key constraint on the source(s) is the rate at which the carbon was released. Fast rates would be consistent with a catastrophic event, e.g. massive methane hydrate dissociation, whereas slower rates might implicate other processes. The PETM carbon flux is currently constrained by high-resolution marine and terrestrial records of the CIE. In pelagic bulk carbonate records, the onset of the CIE is often expressed as a single- or multiple-step excursion extending over 10(4) years. Individual planktonic shell records, in contrast, always show a single-step CIE, with either pre-excursion or excursion isotope values, but no transition values. Benthic foraminifera records, which are less complete owing to extinction and diminutive assemblages, show a delayed excursion. Here, we compile and evaluate the individual planktonic shell isotope data from several localities. We find that the most expanded records consistently show a bimodal isotope distribution pattern regardless of location, water depth or depositional facies. This suggests one of several possibilities: (i) the isotopic composition of the surface ocean/atmosphere declined in a geologic instant (<500yr), (ii) that during the onset of the CIE, most shells of mixed-layer planktonic foraminifera were dissolved, or (iii) the abundances or shell production of these species temporarily declined, possibly due to initial pH changes.

  14. Enzymatic passaging of human embryonic stem cells alters central carbon metabolism and glycan abundance

    PubMed Central

    Badur, Mehmet G.; Zhang, Hui; Metallo, Christian M.

    2016-01-01

    To realize the potential of human embryonic stem cells (hESCs) in regenerative medicine and drug discovery applications, large numbers of cells that accurately recapitulate cell and tissue function must be robustly produced. Previous studies have suggested that genetic instability and epigenetic changes occur as a consequence of enzymatic passaging. However, the potential impacts of such passaging methods on the metabolism of hESCs have not been described. Using stable isotope tracing and mass spectrometry-based metabolomics, we have explored how different passaging reagents impact hESC metabolism. Enzymatic passaging caused significant decreases in glucose utilization throughout central carbon metabolism along with attenuated de novo lipogenesis. In addition, we developed and validated a method for rapidly quantifying glycan abundance and isotopic labeling in hydrolyzed biomass. Enzymatic passaging reagents significantly altered levels of glycans immediately after digestion but surprisingly glucose contribution to glycans was not affected. These results demonstrate that there is an immediate effect on hESC metabolism after enzymatic passaging in both central carbon metabolism and biosynthesis. HESCs subjected to enzymatic passaging are routinely placed in a state requiring re-synthesis of biomass components, subtly influencing their metabolic needs in a manner that may impact cell performance in regenerative medicine applications. PMID:26289220

  15. Enzymatic passaging of human embryonic stem cells alters central carbon metabolism and glycan abundance.

    PubMed

    Badur, Mehmet G; Zhang, Hui; Metallo, Christian M

    2015-10-01

    To realize the potential of human embryonic stem cells (hESCs) in regenerative medicine and drug discovery applications, large numbers of cells that accurately recapitulate cell and tissue function must be robustly produced. Previous studies have suggested that genetic instability and epigenetic changes occur as a consequence of enzymatic passaging. However, the potential impacts of such passaging methods on the metabolism of hESCs have not been described. Using stable isotope tracing and mass spectrometry-based metabolomics, we have explored how different passaging reagents impact hESC metabolism. Enzymatic passaging caused significant decreases in glucose utilization throughout central carbon metabolism along with attenuated de novo lipogenesis. In addition, we developed and validated a method for rapidly quantifying glycan abundance and isotopic labeling in hydrolyzed biomass. Enzymatic passaging reagents significantly altered levels of glycans immediately after digestion but surprisingly glucose contribution to glycans was not affected. These results demonstrate that there is an immediate effect on hESC metabolism after enzymatic passaging in both central carbon metabolism and biosynthesis. HESCs subjected to enzymatic passaging are routinely placed in a state requiring re-synthesis of biomass components, subtly influencing their metabolic needs in a manner that may impact cell performance in regenerative medicine applications.

  16. 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.

  17. Quantifying nitrogen process rates in a constructed wetland using natural abundance stable isotope signatures and stable isotope amendment experiments.

    PubMed

    Erler, Dirk V; Eyre, Bradley D

    2010-01-01

    This study describes the spatial variability in nitrogen (N) transformation within a constructed wetland (CW) treating domestic effluent. Nitrogen cycling within the CW was driven by settlement and mineralization of particulate organic nitrogen and uptake of NO3-. The concentration of NO3- was found to decrease, as the delta15N-NO3- signature increased, as water flowed through the CW, allowing denitrification rates to be estimated on the basis of the degree of fractionation of delta15N-NO3-. Estimates of denitrification hinged on the determination of a net isotope effect (eta), which was influenced byprocesses that enrich or deplete 15NO3- (e.g., nitrification), as well as the rate constants associated with the different processes involved in denitrification (i.e., diffusion and enzyme activity). The influence of nitrification on eta was quantified; however, it remained unclear how eta varied due to variability in denitrification rate constants. A series of stable isotope amendment experiments was used to further constrain the value of eta and calculate rates of denitrification, and nitrification, within the wetland. The maximum calculated rate of denitrification was 956 +/- 187 micromol N m(-2) h(-1), and the maximum rate of nitrification was 182 +/- 28.9 micromol N m(-2) h(-1). Uptake of NO3- was quantitatively more important than denitrification throughoutthe wetland. Rates of N cycling varied spatially within thewetland, with denitrification dominating in the downstream deoxygenated region of the wetland. Studies that use fractionation of N to derive rate estimates must exercise caution when interpreting the net isotope effect. We suggest a sampling procedure for future natural abundance studies that may help improve the accuracy of N cycling rate estimates.

  18. 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.

  19. 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

  20. 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, and 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.

  1. Paleodietary reconstruction using stable isotopes and abundance analysis of bovids from the Shungura Formation of South Omo, Ethiopia.

    PubMed

    Negash, Enquye W; Alemseged, Zeresenay; Wynn, Jonathan G; Bedaso, Zelalem K

    2015-11-01

    Preservation of the stable carbon isotopic composition of fossil tooth enamel enables us to estimate the relative proportion of C3 versus C4 vegetation in an animal's diet, which, combined with analysis of faunal abundance, may provide complementary methods of paleoenvironmental reconstruction. To this end, we analyzed stable carbon isotopic composition (δ(13)C values) of tooth enamel from four bovid tribes (Tragelaphini, Aepycerotini, Reduncini, and Alcelaphini) derived from six members of the Shungura Formation (Members B, C, D, F, G, and L; ages from ca. 2.90-1.05 Ma (millions of years ago) in the Lower Omo Valley of southwestern Ethiopia. The bovids show a wide range of δ(13)C values within taxa and stratigraphic members, as well as temporal changes in the feeding strategies of taxa analyzed throughout the middle to late Pliocene and early Pleistocene. Such variation suggests that the use of actualistic approaches for paleoenvironmental reconstruction may not always be warranted. Alcelaphini was the only taxon analyzed that retained a consistent dietary preference throughout the sequence, with entirely C4-dominated diets. Reduncini had a mixed C3/C4 to C4-dominated diet prior to 2.4 Ma, after which this taxon shifted to a largely C4-dominated diet. Aepycerotini generally showed a mixed C3/C4 diet, with a period of increased C4 diet from 2.5 to 2.3 Ma. Tragelaphini showed a range of mixed C3/C4 diets, with a median value that was briefly nearer the C4 end member from 2.9 to 2.4 Ma but was otherwise towards the C3 end member. These isotopic results, combined with relative abundance data for these bovids, imply that the environment of the Lower Omo Valley consisted of a mosaic of closed woodlands, with riverine forests and open grasslands. However, our data also signify that the overall environment gradually became more open, and that C4 grasses became more dominant. Finally, these results help document the range and extent of environments and potential diets

  2. Carbon isotope fractionation and the acetyl-CoA pathway

    NASA Astrophysics Data System (ADS)

    Blaser, Martin; Conrad, Ralf

    2010-05-01

    Homoacetogenic bacteria can catalyze the reductive synthesis of acetate from CO2 via the acetyl-CoA pathway. Besides this unifying property homoacetogenic bacteria constitute a metabolically and phylogenetically diverse bacteriological group. Therefore their environmental role is difficult to address. It has been recognized that in methanogenic environments homoacetogenic bacteria contribute to the degradation of organic matter. The natural abundance of 13C may be used to understand the functional impact of homoacetogenic bacteria in the soil environment. To distinguish the acetyl-CoA pathway from other dominant processes, the isotopic composition of acetate and CO2 can be determined and the fractionation factors of the individual processes may be used to discriminate between the dominant pathways. To characterize the fractionation factor associated with the acetyl-CoA pathway the phylogenetic and metabolic diversity needs to be considered. Therefore the fractionation factor of substrate utilization and product formation of different homoacetogens (Acetobacterium woodii, Sporomusa ovata, Thermoanaerobacter kivui, Morella thermoautotrophica) has been studied under pure culture conditions in two defined minimal medium with H2/CO2 as sole source of carbon and energy. It became obvious that the cultivation conditions have a major impact on the obtained fractionation factors.

  3. LITHIUM ABUNDANCES IN CARBON-ENHANCED METAL-POOR STARS

    SciTech Connect

    Masseron, Thomas; Johnson, Jennifer A.; Lucatello, Sara; Karakas, Amanda; Plez, Bertrand; Beers, Timothy C.; Christlieb, Norbert E-mail: jaj@astronomy.ohio-state.edu

    2012-05-20

    Carbon-enhanced metal-poor (CEMP) stars are believed to show the chemical imprints of more massive stars (M {approx}> 0.8 M{sub Sun }) that are now extinct. In particular, it is expected that the observed abundance of Li should deviate in these stars from the standard Spite lithium plateau. We study here a sample of 11 metal-poor stars and a double-lined spectroscopic binary with -1.8 < [Fe/H] < -3.3 observed with the Very Large Telescope/UVES spectrograph. Among these 12 metal-poor stars, there are 8 CEMP stars for which we measure or constrain the Li abundance. In contrast to previous arguments, we demonstrate that an appropriate regime of dilution permits the existence of 'Li-Spite plateau and C-rich' stars, whereas some of the 'Li-depleted and C-rich' stars call for an unidentified additional depletion mechanism that cannot be explained by dilution alone. We find evidence that rotation is related to the Li depletion in some CEMP stars. Additionally, we report on a newly recognized double-lined spectroscopic binary star in our sample. For this star, we develop a new technique from which estimates of stellar parameters and luminosity ratios can be derived based on a high-resolution spectrum alone, without the need for input from evolutionary models.

  4. Paleogene plants fractionated carbon isotopes similar to modern plants

    NASA Astrophysics Data System (ADS)

    Diefendorf, Aaron F.; Freeman, Katherine H.; Wing, Scott L.; Currano, Ellen D.; Mueller, Kevin E.

    2015-11-01

    The carbon isotope composition (δ13 C) of terrestrial plant biomarkers, such as leaf waxes and terpenoids, provides insights into past carbon cycling. The δ13 C values of modern plant biomarkers are known to be sensitive to climate and vegetation type, both of which influence fractionation during lipid biosynthesis by altering plant carbon supply and its biochemical allocation. It is not known if fractionation observed in living plants can be used to interpret fossil lipids because plant biochemical characteristics may have evolved during the Cenozoic in response to changes in global climate and atmospheric CO2. The goal of this study was to determine if fractionation during photosynthesis (Δleaf) in the Paleogene was consistent with expectations based on living plants. To study plant fractionation during the Paleogene, we collected samples from eight stratigraphic beds in the Bighorn Basin (Wyoming, USA) that ranged in age from 63 to 53 Ma. For each sample, we measured the δ13 C of angiosperm biomarkers (triterpenoids and n-alkanes) and, abundance permitting, conifer biomarkers (diterpenoids). Leaf δ13 C values estimated from different angiosperms biomarkers were consistently 2‰ lower than leaf δ13 C values for conifers calculated from diterpenoids. This difference is consistent with observations of living conifers and angiosperms and the consistency among different biomarkers suggests ancient εlipid values were similar to those in living plants. From these biomarker-based δ13Cleaf values and independent records of atmospheric δ13 C values, we calculated Δleaf. These calculated Δleaf values were then compared to Δleaf values modeled by applying the effects that precipitation and major taxonomic group in living plants have on Δleaf values. Calculated and modeled Δleaf values were offset by less than a permil. This similarity suggests that carbon fractionation in Paleogene plants changed with water availability and major taxonomic group to about the

  5. 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

  6. A method for carbon stable isotope analysis of methyl halides and chlorofluorocarbons at pptv concentrations.

    PubMed

    Archbold, Marie E; Redeker, Kelly R; Davis, Simon; Elliot, Trevor; Kalin, Robert M

    2005-01-01

    A pre-concentration system has been validated for use with a gas chromatography/mass spectrometry/isotope ratio mass spectrometer (GC/MS/IRMS) to determine ambient air (13)C/(12)C ratios for methyl halides (MeCl and MeBr) and chlorofluorocarbons (CFCs). The isotopic composition of specific compounds can provide useful information on their atmospheric budgets and biogeochemistry that cannot be ascertained from abundance measurements alone. Although pre-concentration systems have been previously used with a GC/MS/IRMS for atmospheric trace gas analysis, this is the first study also to report system validation tests. Validation results indicate that the pre-concentration system and subsequent separation technologies do not significantly alter the stable isotopic ratios of the target methyl halides, CFC-12 (CCl(2)F(2)) and CFC-113 (C(2)Cl(3)F(3)). Significant, but consistent, isotopic shifts of -27.5 per thousand to -25.6 per thousand do occur within the system for CFC-11 (CCl(3)F), although the shift is correctible. The method presented has the capacity to separate these target halocarbons from more than 50 other compounds in ambient air samples. Separation allows for the determination of stable carbon isotope ratios of five of these six target trace atmospheric constituents within ambient air for large volume samples (carbon isotope results similar to published values for (13)C/(12)C analysis of MeCl (-39.1 per thousand) and CFC-113 (-28.1 per thousand). However, this is the first paper reporting stable carbon isotope signatures for CFC-11 (-29.4 per thousand) and CFC-12 (-37.0 per thousand).

  7. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  9. Temperature dependence of carbon isotope fractionation in CAM plants

    SciTech Connect

    Deleens, E.; Treichel, I.; O'Leary, M.H.

    1985-09-01

    The carbon isotope fractionation associated with nocturnal malic acid synthesis in Kalanchoe daigremontiana and Bryophyllum tubiflorum was calculated from the isotopic composition of carbon-4 of malic acid, after appropriate corrections. In the lowest temperature treatment (17/sup 0/C nights, 23/sup 0/C days), the isotope fractionation for both plants is -4% per thousand (that is, malate is enriched in /sup 13/C relative to the atmosphere). For K. daigremontiana, the isotope fractionation decreases with increasing temperature, becoming approximately 0% per thousand at 27/sup 0/C/33/sup 0/C. Detailed analysis of temperature effects on the isotope fractionation indicates that stomatal aperture decreases with increasing temperature and carboxylation capacity increases. For B. tubiflorum, the temperature dependence of the isotope fractionation is smaller and is principally attributed to the normal temperature dependences of the rates of diffusion and carboxylation steps. The small change in the isotopic composition of remaining malic acid in both species which is observed during deacidification indicates that malate release, rather than decarboxylation, is rate limiting in the deacidification process. 28 references, 1 figure, 4 tables.

  10. Stable carbon isotope biogeochemistry of lakes along a trophic gradient

    NASA Astrophysics Data System (ADS)

    de Kluijver, A.; Schoon, P. L.; Downing, J. A.; Schouten, S.; Middelburg, J. J.

    2014-05-01

    The stable carbon (C) isotope variability of dissolved inorganic and organic C (DIC and DOC), particulate organic carbon (POC), glucose and polar-lipid derived fatty acids (PLFA) were studied in a survey of 22 North American oligotrophic to eutrophic lakes. The δ13C of different PLFA were used as proxy for phytoplankton producers and bacterial consumers. Lake pCO2 was primarily determined by autochthonous production (phytoplankton biomass), especially in eutrophic lakes, and governed the δ13C of DIC. All organic-carbon pools showed larger isotopic variability in eutrophic lakes compared to oligo-mesotrophic lakes because of the high variability in δ13C at the base of the food web (both autochthonous and allochthonous carbon). Phytoplankton δ13C was negatively related to lake pCO2 over all lakes and positively related to phytoplankton biomass in eutrophic lakes, which was also reflected in a large range in photosynthetic isotope fractionation (ϵCO2-phyto, 8-25 ‰). The carbon isotope ratio of allochthonous carbon in oligo-mesotrophic lakes was rather constant, while it varied in eutrophic lakes because of maize cultivation in the watershed.

  11. Stable carbon isotope biogeochemistry of lakes along a trophic gradient

    NASA Astrophysics Data System (ADS)

    de Kluijver, A.; Schoon, P. L.; Downing, J. A.; Schouten, S.; Middelburg, J. J.

    2014-11-01

    The stable carbon (C) isotope variability of dissolved inorganic and organic C (DIC and DOC), particulate organic carbon (POC), glucose and polar-lipid derived fatty acids (PLFAs) was studied in a survey of 22 North American oligotrophic to eutrophic lakes. The δ13C of different PLFAs were used as proxy for phytoplankton producers and bacterial consumers. Lake pCO2 was primarily determined by autochthonous production (phytoplankton biomass), especially in eutrophic lakes, and governed the δ13C of DIC. All organic-carbon pools showed overall higher isotopic variability in eutrophic lakes (n = 11) compared to oligo-mesotrophic lakes (n = 11) because of the high variability in δ13C at the base of the food web (both autochthonous and allochthonous carbon). Phytoplankton δ13C was negatively related to lake pCO2 over all lakes and positively related to phytoplankton biomass in eutrophic lakes, which was also reflected in a large range in photosynthetic isotope fractionation (ϵCO2-phyto, 8-25‰). The carbon isotope ratio of allochthonous carbon in oligo-mesotrophic lakes was rather constant, while it varied in eutrophic lakes because of maize cultivation in the watershed.

  12. 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.

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

    PubMed

    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.

  14. 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.

  15. Absolute isotopic composition of molybdenum and the solar abundances of the p-process nuclides Mo92,94

    NASA Astrophysics Data System (ADS)

    Wieser, M. E.; de Laeter, J. R.

    2007-05-01

    The isotopic composition of molybdenum has been measured with high precision using a thermal ionization mass spectrometer, the linearity of which has been verified by measuring the isotopically-certified reference material for strontium (NIST 987). The abundance sensitivity of the mass spectrometer in the vicinity of the molybdenum ion beams has been carefully examined to ensure the absence of tailing effects. Particular care was given to ensuring that potential isobaric interferences from zirconium and ruthenium did not affect the measurement of the isotopic composition of molybdenum. Gravimetric mixtures of two isotopically enriched isotopes, Mo92 and Mo98, were analyzed mass spectrometrically to calibrate the mass spectrometer, in order to establish the isotope fractionation of the spectrometer for the molybdenum isotopes. This enabled the “absolute” isotopic composition of molybdenum to be determined. An accurate determination of the isotopic composition is required in order to calculate the atomic weight of molybdenum, which is one of the least accurately known values of all the elements. The absolute isotope abundances (in atom %) of molybdenum measured in this experiment are as follows: Mo92=14.5246±0.0015; Mo94=9.1514±0.0074; Mo95=15.8375±0.0098; Mo96=16.672±0.019; Mo97=9.5991±0.0073; Mo98=24.391±0.018; and Mo100=9.824±0.050, with uncertainties at the 1s level. These values enable an atomic weight Ar(Mo) of 95.9602±0.0023 (1s) to be calculated, which is slightly higher than the current Standard Atomic Weight Ar(Mo) =95.94±0.02 and with a much improved uncertainty interval. These “absolute” isotope abundances also enable the Solar System abundances of molybdenum to be calculated for astrophysical purposes. Of particular interest are the Solar System abundances of the two p-process nuclides—Mo92 and Mo94, which are present in far greater abundance than p-process theory suggests. The Solar System abundances for Mo92 and Mo94 of 0.364±0

  16. Carbon and Hydrogen Stable Isotope Fractionation Associated with the Aerobic and Anaerobic Degradation of Saturated and Alkylated Aromatic Hydrocarbons.

    PubMed

    Musat, Florin; Vogt, Carsten; Richnow, Hans H

    2016-01-01

    Saturated hydrocarbons (alkanes) and alkylated aromatic hydrocarbons are abundant environmental compounds. Hydrocarbons are primarily removed from the environment by biodegradation, a process usually associated with moderate carbon and significant hydrogen isotope fractionation allowing monitoring of biodegradation processes in the environment. Here, we review the carbon and hydrogen stable isotope fractionation associated with the cleavage of C-H bonds at alkyl chains of hydrocarbons. Propane, n-butane and ethylbenzene were used as model components for alkyl moieties of aliphatic and aromatic hydrocarbons with emphasis on the cleavage of the C-H bond without the involvement of molecular oxygen. The carbon and hydrogen isotope fractionation factors were further used to explore the diagnostic potential for characterizing the mode of bond cleavage under oxic and anoxic conditions. x039B; factors, calculated to correlate carbon and hydrogen fractionation, allowed to distinguish between aerobic and anaerobic biodegradation processes in the environment.

  17. Carbon and Hydrogen Isotopic Fractionation during Anaerobic Biodegradation of Benzene

    PubMed Central

    Mancini, Silvia A.; Ulrich, Ania C.; Lacrampe-Couloume, Georges; Sleep, Brent; Edwards, Elizabeth A.; Sherwood Lollar, Barbara

    2003-01-01

    Compound-specific isotope analysis has the potential to distinguish physical from biological attenuation processes in the subsurface. In this study, carbon and hydrogen isotopic fractionation effects during biodegradation of benzene under anaerobic conditions with different terminal-electron-accepting processes are reported for the first time. Different enrichment factors (ɛ) for carbon (range of −1.9 to −3.6‰) and hydrogen (range of −29 to −79‰) fractionation were observed during biodegradation of benzene under nitrate-reducing, sulfate-reducing, and methanogenic conditions. These differences are not related to differences in initial biomass or in rates of biodegradation. Carbon isotopic enrichment factors for anaerobic benzene biodegradation in this study are comparable to those previously published for aerobic benzene biodegradation. In contrast, hydrogen enrichment factors determined for anaerobic benzene biodegradation are significantly larger than those previously published for benzene biodegradation under aerobic conditions. A fundamental difference in the previously proposed initial step of aerobic versus proposed anaerobic biodegradation pathways may account for these differences in hydrogen isotopic fractionation. Potentially, C-H bond breakage in the initial step of the anaerobic benzene biodegradation pathway may account for the large fractionation observed compared to that in aerobic benzene biodegradation. Despite some differences in reported enrichment factors between cultures with different terminal-electron-accepting processes, carbon and hydrogen isotope analysis has the potential to provide direct evidence of anaerobic biodegradation of benzene in the field. PMID:12513995

  18. Constraining paleotemperature and water isotope signals at Lake Bonneville using carbonate clumped isotopes

    NASA Astrophysics Data System (ADS)

    Mering, J. A.; Oviatt, C. G.; Petryshyn, V. A.; Canet, J.; Tripati, A.

    2013-12-01

    Lake Bonneville was the largest pluvial system in the Great Basin during the Last Glacial Maximum (23-19 ka BP), reaching nearly 50,000 square kilometers at its high stand. Carbonate clumped isotope paleothermometry provides a new avenue to evaluate lake and atmospheric conditions by constraining the temperature and oxygen isotope ratios of lake water. Here, we present estimates of lake temperature, the oxygen isotope composition of paleowater, and Mean Annual Air Temperature (MAAT) from LGM paleoshoreline sites in Utah and Eastern Nevada. Multiple phases of ancient carbonate were evaluated, including endogenic carbonate from the ubiquitous Bonneville marl stratigraphic unit, and aragonitic shells of two species of aquatic gastropods (genera Pyrgulopsis and Stagnicola) collected from littoral deposits adjacent to the marl. These phases should record surface water conditions. Preliminary results indicate that paleotemperature estimates from gastropods and marl are similar at any given site. However, the latitudinal water isotope gradient reconstructed using marls is steeper than that reconstructed from gastropods, indicating that perhaps carbonate precipitation in marl is more evaporation-driven than shell growth of aquatic snails. Comparison with recent climate data, and clumped isotope measurements of modern samples from the Great Salt Lake, supports moderate temperature change in the Great Basin from the Last Glacial Maximum to present.

  19. 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

  20. Magnesium isotopic compositions of the Mesoproterozoic dolostones: Implications for Mg isotopic systematics of marine carbonates

    NASA Astrophysics Data System (ADS)

    Huang, Kang-Jun; Shen, Bing; Lang, Xian-Guo; Tang, Wen-Bo; Peng, Yang; Ke, Shan; Kaufman, Alan J.; Ma, Hao-Ran; Li, Fang-Bing

    2015-09-01

    Available Mg isotope data indicate that dolostones of different ages have overlapping range of Mg isotopic composition (δ26Mg) and there is no systematic difference among different types of dolomites. To further explore the Mg isotopic systematics of dolomite formation, we measured Mg isotopic compositions of Mesoproterozoic dolostones from the Wumishan Formation in North China Block, because dolomite formation in Mesoproterozoic might have been fundamentally different from the younger counterparts. Based on petrographic observations, three texturally-different dolomite phases (dolomicrite, subhedral dolomite and anhedral dolomite) are recognized in the Wumishan dolostones. Nevertheless, these three types of dolomites have similar δ26Mg values, ranging from -1.35‰ to -1.72‰, which are indistinguishable from Neoproterozoic and Phanerozoic dolostones. To explain δ26Mg values of dolostones, we simulate the Mg isotopic system during dolomite formation by applying the one-dimensional Diffusion-Advection-Reaction (1D-DAR) model, assuming that the contemporaneous seawater is the Mg source of dolostone. The 1D-DAR modeling results indicate that the degree of dolomitization is controlled by sedimentation rate, seawater Mg concentration, temperature, and reaction rate of dolomite formation, whereas Mg isotopic composition of dolostone is not only dependent on these factors, but also affected by δ26Mg of seawater and isotope fractionation during dolomite formation. Moreover, the 1D-DAR model predicts that dolomite formation within sediments has limited range of variation in δ26Mg with respect to limestones. Furthermore, the modeling results demonstrate that dolostone is always isotopically heavier than Ca-carbonate precipitated from seawater, explaining the systematic isotopic difference between dolostones and limestones. Finally, we can infer from the 1D-DAR model that early-formed dolostone at shallower depth of sediments is always isotopically lighter than that

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

  2. 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.

  3. 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).

  4. 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

  5. Interpreting the Ca isotope record of marine biogenic carbonates

    NASA Astrophysics Data System (ADS)

    Sime, Neil G.; De La Rocha, Christina L.; Tipper, Edward T.; Tripati, Aradhna; Galy, Albert; Bickle, Michael J.

    2007-08-01

    An 18 million year record of the Ca isotopic composition (δ 44/42Ca) of planktonic foraminiferans from ODP site 925, in the Atlantic, on the Ceara Rise, provides the opportunity for critical analysis of Ca isotope-based reconstructions of the Ca cycle. δ 44/42Ca in this record averages +0.37 ± 0.05 (1 σ SD) and ranges from +0.21‰ to +0.52‰. The record is a good match to previously published Neogene Ca isotope records based on foraminiferans, but is not similar to the record based on bulk carbonates, which has values that are as much as 0.25‰ lower. Bulk carbonate and planktonic foraminiferans from core tops differ slightly in their δ 44/42Ca (i.e., by 0.06 ± 0.06‰ ( n = 5)), while the difference between bulk carbonate and foraminiferan values further back in time is markedly larger, leaving open the question of the cause of the difference. Modeling the global Ca cycle from downcore variations in δ 44/42Ca by assuming fixed values for the isotopic composition of weathering inputs (δ 44/42Ca w) and for isotope fractionation associated with the production of carbonate sediments (Δ sed) results in unrealistically large variations in the total mass of Ca 2+ in the oceans over the Neogene. Alternatively, variations of ±0.05‰ in the Ca isotope composition of weathering inputs or in the extent of fractionation of Ca isotopes during calcareous sediment formation could entirely account for variations in the Ca isotopic composition of marine carbonates. Ca isotope fractionation during continental weathering, such as has been recently observed, could easily result in variations in δ 44/42Ca w of a few tenths of permil. Likewise a difference in the fractionation factors associated with aragonite versus calcite formation could drive shifts in Δ sed of tenths of permil with shifts in the relative output of calcite and aragonite from the ocean. Until better constraints on variations in δ 44/42Ca w and Δ sed have been established, modeling the Ca 2+ content

  6. 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

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

    PubMed

    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

  8. The Carboniferous carbon isotope record from sedimentary organic matter: can we disentangle the carbon cycle?

    NASA Astrophysics Data System (ADS)

    Davies, S. J.; Bennett, C. E.; Leng, M. J.; Kearsey, T.; Marshall, J. E.; Millward, D.; Reeves, E. J.; Snelling, A.; Sherwin, J. E.

    2014-12-01

    A comprehensive analysis of the δ13C composition of sedimentary organic matter from Euramerican Carboniferous successions indicates there are significant shifts in δ13C through this key time interval. Our studies have revealed that, at an individual location, the source and delivery mechanism of the sediment contribute to the type of organic matter preserved and, in turn this influences the measured δ13C values from bulk sedimentary organic matter of organic matter. In general, where marine-derived organic matter is dominant in these Carboniferous successions then δ13C values are characteristically lower compared to the higher values encountered where terrestrial plant-derived material is most abundant. The implication of these observations is that an apparent carbon isotope excursion identified from the bulk organic matter may reflect a change in transport processes, or depositional environment, rather than a perturbation in the global carbon cycle. In our most recent studies, however, we compare δ13C values from specific wood fragments and bulk sedimentary organic matter from non-marine, marine basinal, and marine shelfal successions from the earliest Mississippian through to the early Pennsylvanian. These data indicate that early Mississippian δ13C of organic matter is far less negative (around -22%0) than material of Late Mississippian age (around -26%0), however by the early Pennsylvanian, δ13C values return to -22%0. There are some δ13C data from brachiopod carbonate from this time interval and similar shifts are indicated. Our data are beginning to address whether we can identify a primary carbon cycle signal from the Carboniferous record using δ13C from a range of sedimentary environments. If we can, there are still questions around what the record is telling us about the global carbon cycle during a period when plant groups, including lycopods and seed ferns, rapidly diversified.

  9. 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 ...

  10. 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

  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.

    2017-02-01

    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. 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.

  13. 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

  14. Element distribution and noble gas isotopic abundances in lunar meteorite Allan Hills A81005

    NASA Technical Reports Server (NTRS)

    Kraehenbuehl, U.; Eugster, O.; Niedermann, S.

    1986-01-01

    Antarctic meteorite ALLAN HILLS A81005, an anorthositic breccia, is recognized to be of lunar origin. The noble gases in this meteorite were analyzed and found to be solar-wind implanted gases, whose absolute and relative concentrations are quite similar to those in lunar regolith samples. A sample of this meteorite was obtained for the analysis of the noble gas isotopes, including Kr(81), and for the determination of the elemental abundances. In order to better determine the volume derived from the surface correlated gases, grain size fractions were prepared. The results of the instrumental measurements of the gamma radiation are listed. From the amounts of cosmic ray produced noble gases and respective production rates, the lunar surface residence times were calculated. It was concluded that the lunar surface time is about half a billion years.

  15. A robust method for ammonium nitrogen isotopic analysis in freshwater and seawater at natural abundance levels

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Altabet, M. A.; Wu, T.; Hadas, O.

    2006-12-01

    Natural ammonium N isotopic abundance has been increasingly used in studies of marine and freshwater biogeochemistry. However, current methods are time-consuming, subject to interference from DON, and not reliable at low concentrations. Our new method for determining the δ15N of ammonium overcomes these difficulties by employing the oxidation of ammonium to nitrite followed by conversion of nitrite to nitrous oxide. In the first step, ammonium is quantitatively oxidized by hypobromite at pH~12. After the addition of sodium arsenite to consume excess hypobromite, yield is verified by colorimetric NO2-measurement using sulfanilamide and naphthyl ethylenediamine (NED). Nitrite is further reduced to N2O by a 1:1 sodium azide and acetic acid buffer solution using previously established procedures. Buffer concentration can be varied according to sample matrix to ensure that a reaction pH between 2 and 4 is reached. The product nitrous oxide is then isotopically analyzed using a continuous flow purge and cryogenic trap system coupled to an isotope ratio mass spectrometer. Reliable δ15N values (±0.31‰) are obtained over a concentration range of 0.5 μM to 20 μM using 20 ml volumes of either fresh or seawater samples. Reagent blanks are very low, about 0.05 μM. There is no interference from any of the nitrogen containing compounds tested except short chain aliphatic amino acid (i.e. glycine) which typically are not present at sufficiently high environmental concentrations to pose a problem.

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

    PubMed Central

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

    2017-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

  18. Carbon Isotope Discrimination in Leaves of C3 Plants

    NASA Astrophysics Data System (ADS)

    Cuntz, M.; Gleixner, G.

    2009-04-01

    Carbon isotope composition is regarded as a powerful tool in understanding carbon cycling, both as a tracer and as a process recorder. However, accurate predictions of, for example, partitioning the net carbon flux into its components or obtaining climate information from tree rings, requires a good understanding of plant metabolism and related isotopic fractionations. Mechanistic models have concentrated largely on photosynthetic pathways and their isotopic composition. This cannot be said for respiratory processes. The mechanistic models of leaf isotope discrimination hence do not describe dawn, dusk and night very realistically or not at all. A new steady-state approach of the carbon isotope distribution in glucose potentially addresses the time of twilight and night (Tcherkez et al. 2004). Here, a new model of 13C discrimination in leaves of C3 plants is presented. The model is based on the steady-state approach of Tcherkez et al. (2004) but with much reduced complexity while retaining its general characteristics. In addition, the model introduces some new concepts such as a day-length dependent starch synthesis, night-length dependent starch degradation, energy-driven biosynthesis rates, and continuous leaf discrimination calculation for the whole diel cycle. It is therefore well adapted for biosphere-atmosphere exchange studies. The model predicts enriched sucrose and starch pools in the leaf compared to assimilated CO2. Biosynthesis on the other hand acts as the sink of the remaining, depleted carbon. The model calculates slightly different absolute starch compositions from the Tcherkez et al. (2004) model but this depends on chosen fractionation factors. The greatest difference between the two models is during dawn, dusk and night. For example, while Tcherkez et al. has changing phloem sucrose isotope composition during night, the model here predicts constant sucrose export composition. Observations seem to support rather constant phloem isotope composition

  19. Quantifying seasonal precipitation using high-resolution carbon isotope analyses in evergreen wood

    NASA Astrophysics Data System (ADS)

    Schubert, Brian A.; Jahren, A. Hope

    2011-11-01

    High-resolution natural abundance stable carbon isotope analyses across annual growth rings in evergreen trees reveal a cyclic increase and decrease in the measured carbon isotopic composition (δ 13C), but the causes of this pattern are poorly understood. We compiled new and published high-resolution δ 13C data from across annual growth rings of 33 modern evergreen trees from 10 genera and 15 globally distributed sites to quantify the parameters that affect the observed δ 13C pattern. Across a broad range of latitude, temperature, and precipitation regimes, we found that the average, measured seasonal change in δ 13C (Δδ 13C meas, ‰) within tree rings of evergreen species reflects changes in the carbon isotopic composition of atmospheric carbon dioxide (Δδ 13C CO2) and changes in seasonal precipitation (Δ P) according to the following equation: Δδ 13C meas = Δδ 13C CO2 - 0.82(Δ P) + 0.73; R2 = 0.96. Seasonal changes in temperature, pCO 2, and light levels were not found to significantly affect Δδ 13C meas. We propose that this relationship can be used to quantify seasonal patterns in paleoprecipitation from intra-ring profiles of δ 13C measured from non-permineralized, fossil wood.

  20. Major and trace element abundances, and Sr and Nd isotopic composition of Carbonatites from Amba Dongar, Gujarat, India

    NASA Astrophysics Data System (ADS)

    Chandra, Jyoti; Paul, Debajyoti; Viladkar, Shrinivas G.; Sensarma, Sarajit

    2015-04-01

    Despite significant progress during the last decade, the petrogenesis of carbonatites is still highly debated regarding the exact mechanism of carbonatite magma generation (fractional crystallization of carbonated-silicate magmas, liquid immiscibility of carbonated-silicate magmas, partial melting of carbonated mantle peridotite or carbonated lherzolitic mantle) and its evolution. The Amba Dongar carbonatite complex in Chhota Udaipur district, Gujarat is the youngest Indian carbonatite complex, which intruded into the ~ 90 Ma Bagh sandstones and limestone and 68-65 Ma Deccan flood basalts. The emplacement age (40Ar/39Ar age of 65±0.3 Ma; Ray and Pande, 1999) coincides with the age of main pulse of Deccan flood basalts at ca. 65 Ma. We report new geochemical data (major oxide and trace element abundances, and Sr and Nd isotopic ratios) on 23 carbonatite samples from Amba Dongar. The Amba Dongar carbonatite complex consists of carbonatite (sövite, and ankerite), and associated nephelinite, phonolite, and both pre- and post-carbonatite basalts. Detailed minerology of carbonatite include dominant calcite along with pyrochlore, apatite, magnetite, aegirine-augite and accessory phases. Apatite crystals are observed in carbonatite as well as in nephelinite. In sövites, apatite occur in various forms including cumulus, clusters and scattered within and along the boundary of calcite crystals. Two generation of apatite crystals are commonly observed in sövite and nephelinite; textural changes suggest presence of different five pulses of sövitic magma during the emplacement of the sövite ring dike. Bulk major oxides and trace element (including REEs) compositions of carbonatites and associated silicate rocks are determined by WD-XRF and ICP-MS, respectively. Major oxides abundances are consistent with the already available data on the Amba Dongar carbonatite complex. Trace element concentrations for the sövite reveals high concentrations of Sr (929-7476 ppm), Ba (344

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  2. 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.

  3. 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.

  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. 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

  6. 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.; Colburn, Heather A.; Moran, James J.; Melville, Angela M.

    2009-12-01

    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.

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

    SciTech Connect

    Thomas, James; Decker, David; Patterson, Gary; Peterman, Zell; Mihevc, Todd; Larsen, Jessica; Hershey, Ronald

    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) 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

  8. Carbon isotopes in three SNC meteorites

    NASA Astrophysics Data System (ADS)

    Carr, R. H.; Wright, I. P.; Pillinger, C. T.

    1985-02-01

    The presence of several carbonaceous components in SNC meteorites has been inferred from the analyses of samples of three SNC meteorites, Shergotty, Chassigny, and Elephant Moraine. The identification of the actual species involved, however, has not been possible except for that of the terrestrial materials known to contaminate extraterrestrial samples. Above 700 C, there is evidence of the presence of isotropically heavy and light components in all three meteorites, although there are notable differences in their isotopic compositions. The similarities observed may indicate a common origin for the meteorites, but the possibility that magmatic processes on different parent bodies have produced these features must be more fully explored.

  9. Carbon and sulfur isotopes as tracers of fluid-fluid and fluid-rock interaction in geothermal systems

    NASA Astrophysics Data System (ADS)

    Stefansson, A.; Keller, N. S.; Gunnarsson Robin, J.; Kjartansdottir, R.; Ono, S.; Sveinbjörnsdottir, A. E.

    2014-12-01

    Carbon and sulfur are among major components in geothermal systems. They are found in various oxidation state and present in solid phases and fluids (water and vapor). In order to study the reactions and mass movement within multiphase geothermal systems, we have combined geochemical fluid-fluid and fluid-rock modelling with sulfur and carbon isotope fractionation modelling and compared the results with measured carbon and sulfur isotopes in geothermal fluids (water and vapor) for selected low- and high-enthalpy geothermal systems in Iceland. In this study we have focused on δ34S for H2S in vapor and water and SO4 in water as well as δ13C for CO2 in vapor and water phases. Isotope fractionations for CO2 and H2S between vapor and liquid water, upon aqueous speciation and upon carbonate and sulfide mineral formation were revised. These were combined with reaction modelling involving closed system boiling and progressive water-rock interaction to constrain the mass movement and isotope abundance between various phases. The results indicate that for a closed system, carbon and sulfur isotope abundance is largely dependent on progressive fluid-fluid and fluid-rock interaction and the initial total δ34S and δ13C value of the system. Initially, upon progressive fluid rock interaction the δ34S and δ13C values for the bulk aqueous phase approach that of the host rocks. Secondary mineral formation may alter these values, the exact isotope value of the mineral and resulting aqueous phase depending on aqueous speciation and isotope fractionation factor. In turn, aqueous speciation and mineral saturation depends on progressive fluid-rock interaction, fluid-fluid interaction, temperature and acid supply to the system. Depressurization boiling also results in isotope fractionation, the exact isotope value of the vapor and aqueous phase depending on aqueous speciation and isotope fractionation fractor. In this way, carbon and sulfur isotopes may be used combined with

  10. 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.

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

    NASA Astrophysics Data System (ADS)

    Kimball, Justine; Eagle, Robert; Dunbar, Robert

    2016-12-01

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

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

    DOE PAGES

    Kimball, Justine; Eagle, Robert; Dunbar, Robert

    2016-12-12

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  15. Carbon isotopic fractionation of CFCs during abiotic and biotic degradation.

    PubMed

    Archbold, Marie E; Elliot, Trevor; Kalin, Robert M

    2012-02-07

    Carbon stable isotope ((13)C) fractionation in chlorofluorocarbon (CFC) compounds arising from abiotic (chemical) degradation using zero-valent iron (ZVI) and biotic (landfill gas attenuation) processes is investigated. Batch tests (at 25 °C) for CFC-113 and CFC-11 using ZVI show quantitative degradation of CFC-113 to HCFC-123a and CFC-1113 following pseudo-first-order kinetics corresponding to a half-life (τ(1/2)) of 20.5 h, and a ZVI surface-area normalized rate constant (k(SA)) of -(9.8 ± 0.5) × 10(-5) L m(-2) h(-1). CFC-11 degraded to trace HCFC-21 and HCFC-31 following pseudo-first-order kinetics corresponding to τ(1/2) = 17.3 h and k(SA) = -(1.2 ± 0.5) × 10(-4) L m(-2) h(-1). Significant kinetic isotope effects of ε(‰) = -5.0 ± 0.3 (CFC-113) and -17.8 ± 4.8 (CFC-11) were observed. Compound-specific carbon isotope analyses also have been used here to characterize source signatures of CFC gases (HCFC-22, CFC-12, HFC-134a, HCFC-142b, CFC-114, CFC-11, CFC-113) for urban (UAA), rural/remote (RAA), and landfill (LAA) ambient air samples, as well as in situ surface flux chamber (FLUX; NO FLUX) and landfill gas (LFG) samples at the Dargan Road site, Northern Ireland. The latter values reflect biotic degradation and isotopic fractionation in LFG production, and local atmospheric impact of landfill emissions through the cover. Isotopic fractionations of Δ(13)C ∼ -13‰ (HCFC-22), Δ(13)C ∼ -35‰ (CFC-12) and Δ(13)C ∼ -15‰ (CFC-11) were observed for LFG in comparison to characteristic solvent source signatures, with the magnitude of the isotopic effect for CFC-11 apparently similar to the kinetic isotope effect for (abiotic) ZVI degradation.

  16. Carbon and oxygen isotopes of Maastrichtian Danian shallow marine carbonates: Yacoraite Formation, northwestern Argentina

    NASA Astrophysics Data System (ADS)

    Marquillas, Rosa; Sabino, Ignacio; Nobrega Sial, Alcides; Papa, Cecilia del; Ferreira, Valderez; Matthews, Stephen

    2007-04-01

    The Maastrichtian-Danian limestones of the Yacoraite Formation (northwestern Argentina) show carbon and oxygen isotopic values consistent with shallow marine conditions. The members of the formation respond to different sedimentary environments and are characterised by distinctive stable isotopes and geochemistry. The basal Amblayo Member is composed of high-energy dolomitic limestones and limestones with positive isotopic values (+2‰ δ 13C, +2‰ δ 18O). The top of the member reveals an isotopic shift of δ 13C (-5‰) and δ 18O (-10‰), probably related to a descent in the sea level. The sandy Güemes Member has isotopically negative (-2‰ δ 13C, -1‰ δ 18O) limestones, principally controlled by water mixing, decreased organic productivity, and compositional changes in the carbonates. The isotopically lighter limestones are calcitic, with a greater terrigenous contribution and different geochemical composition (high Si-Mn-Fe-Na, low Ca-Mg-Sr). These isotopic and lithological changes relate to the Cretaceous-Palaeogene transition. The Alemanía Member, composed of dolomitic limestones and pelites, represents a return to marine conditions and shows a gradual increase in isotopic values, reaching values similar to those of the Amblayo Member. The Juramento Member, composed of stromatolite limestones, shows isotopic variations that can be correlated with the two well-defined, shallowing-upward sequences of the member.

  17. Alkane distribution and carbon isotope composition in fossil leaves: An interpretation of plant physiology in the geologic past

    NASA Astrophysics Data System (ADS)

    Graham, H. V.; Freeman, K. H.

    2014-12-01

    The relative chain-length distribution and carbon-isotope composition of n-alkanes extracted from sedimentary rocks are important geochemical tools for investigating past terrestrial ecosystems. Alkanes preserved in ancient sediments are assumed to be contemporaneous, derived from the same ecosystem, and integrated from the biomass present on the landscape at the time of deposition. Further, there is an underlying assumption that ancient plants exhibited the same metabolic and physiological responses to climate conditions that are observed for modern plants. Interpretations of alkane abundances and isotopic signatures are complicated by the strong influence of phylogenetic affiliation and ecological factors, such as canopy structure. A better understanding of how ecosystem and taxa influence alkane properties, including homologue abundance patterns and leaf-lipid carbon isotope fractionation would help strengthen paleoecological interpretations based on these widely employed plant biomarkers. In this study, we analyze the alkane chain-length distribution and carbon-isotope composition of phytoleim and alkanes (d13Cleaf and d13Clipid) extracted from a selection of Cretaceous and Paleocene fossil leaves from the Guaduas and Cerrejon Formations of Colombia. These data were compared with data for the same families in a modern analogue biome. Photosynthetic and biosynthetic fractionation (∆leaf and elipid) values determined from the fossil material indicate carbon metabolism patterns were similar to modern plants. Fossil data were incorporated in a biomass-weighted mixing model to represent the expected lipid complement of sediment arising from this ecosystem and compared with alkane measurements from the rock matrix. Modeled and observed isotopic and abundance patterns match well for alkane homologs most abundant in plants (i.e., n-C27 to n-C33). The model illustrates the importance of understanding biases in litter flux and taphonomic pressures inherent in the

  18. 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

  19. 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.

  20. 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)

  1. 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.

  2. The origin of aubrites: Evidence from lithophile trace element abundances and oxygen isotope compositions

    NASA Astrophysics Data System (ADS)

    Barrat, J. A.; Greenwood, R. C.; Keil, K.; Rouget, M. L.; Boesenberg, J. S.; Zanda, B.; Franchi, I. A.

    2016-11-01

    We report the abundances of a selected set of ;lithophile; trace elements (including lanthanides, actinides and high field strength elements) and high-precision oxygen isotope analyses of a comprehensive suite of aubrites. Two distinct groups of aubrites can be distinguished: (a) the main-group aubrites display flat or light-REE depleted REE patterns with variable Eu and Y anomalies; their pyroxenes are light-REE depleted and show marked negative Eu anomalies; (b) the Mount Egerton enstatites and the silicate fraction from Larned display distinctive light-REE enrichments, and high Th/Sm ratios; Mount Egerton pyroxenes have much less pronounced negative Eu anomalies than pyroxenes from the main-group aubrites. Leaching experiments were undertaken to investigate the contribution of sulfides to the whole rock budget of the main-group aubrites. Sulfides contain in most cases at least 50% of the REEs and of the actinides. Among the elements we have analyzed, those displaying the strongest lithophile behaviors are Rb, Ba, Sr and Sc. The homogeneity of the Δ17O values obtained for main-group aubrite falls [Δ17O = +0.009 ± 0.010‰ (2σ)] suggests that they originated from a single parent body whose differentiation involved an early phase of large-scale melting that may have led to the development of a magma ocean. This interpretation is at first glance in agreement with the limited variability of the shapes of the REE patterns of these aubrites. However, the trace element concentrations of their phases cannot be used to discuss this hypothesis, because their igneous trace-element signatures have been modified by subsolidus exchange. Finally, despite similar O isotopic compositions, the marked light-REE enrichments displayed by Mount Egerton and Larned suggest that they are unrelated to the main-group aubrites and probably originated from a distinct parent body.

  3. 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

  4. 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.

  5. 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.

  6. STABLE CARBON ISOTOPE ANALYSIS OF SUBFOSSIL WOOD FROM AUSTRIAN ALPS

    PubMed Central

    KŁUSEK, MARZENA; PAWEŁCZYK, SŁAWOMIRA

    2015-01-01

    The presented studies were carried out in order to check the usefulness of subfossil wood for stable isotope analysis. The aim of research was also to define the optimal method of subfossil samples preparation. Subfossil samples used during the presented studies are a part of the multi-century dendrochronological scale. This chronology originates in an area situated around a small mountain lake — Schwarzersee, in Austria. The obtained results of stable carbon isotope measurements confirmed that the method of α-cellulose extraction by the application of acidic sodium chlorite and sodium hydroxide solutions removes resins and other mobile compounds from wood. Therefore, in the case of the analysed samples, the additional chemical process of extractives removing was found to be unnecessary. Studied wood samples contained an adequate proportion of α-cellulose similar to the values characteristic for the contemporary trees. This proved an adequate wood preservation which is essential for the conduction of isotopic research. PMID:26346297

  7. Carbon isotopes in xenoliths from the Hualalai Volcano, Hawaii, and the generation of isotopic variability

    SciTech Connect

    Pineau, F. ); Mathez, E.A. )

    1990-01-01

    The isotopic composition of carbon has been determined in a suite of xenoliths from lava of the 1800-1801 Kaupulehu eruption of Hualalai Volcano, Hawaii. Several lithologies are represented in the suite, including websterite, dunite, wehrlite, pyroxenite, and gabbro. In addition, there are composite xenoliths in which contacts between lithologies are preserved. Most of the xenoliths represent deformed cumulates. The contact relations in the composite samples indicate that the lithologies originated from the same source region, which, based on pressures determined from fluid inclusions, is estimated to be at a depth of {approx}20 km, or near the crust-mantle boundary. The observations and isotopic results demonstrate that isotopic variability can be generated by multistage fractionation processes such as degassing of CO{sub 2} from magma and precipitation of CO{sub 2}-rich fluids to form graphitic compounds. Such processes operated over regions the scales of which were determined by style and intensity of deformation and by lithology.

  8. 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...

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  10. 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.

  11. 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

  12. 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

  13. Carbon isotope fractionation of methyl bromide during agricultural soil fumigations

    USGS Publications Warehouse

    Bill, M.; Miller, L.G.; Goldstein, Allen H.

    2002-01-01

    The isotopic composition of methyl bromide (CH3Br) has been suggested to be a potentially useful tracer for constraining the global CH3Br budget. In order to determine the carbon isotopic composition of CH3Br emitted from the most significant anthropogenic application (pre-plant fumigation) we directly measured the ??13C of CH3Br released during commercial fumigation. We also measured the isotopic fractionation associated with degradation in agricultural soil under typical field fumigation conditions. The isotopic composition of CH3Br collected in soil several hours after injection of the fumigant was -44.5??? and this value increased to -20.7??? over the following three days. The mean kinetic isotope effect (KIE) associated with degradation of CH3Br in agricultural soil (12???) was smaller than the reported value for methylotrophic bacterial strain IMB-1, isolated from previously fumigated agricultural soil, but was similar to methylotrophic bacterial strain CC495, isolated from a pristine forest litter zone. Using this fractionation associated with the degradation of CH3Br in agricultural soil and the mean ??13C of the industrially manufactured CH3Br (-54.4???), we calculate that the agricultural soil fumigation source has a carbon isotope signature that ranges from -52.8??? to -42.0???. Roughly 65% of industrially manufactured CH3Br is used for field fumigations. The remaining 35% is used for structural and post-harvest fumigations with a minor amount used during industrial chemical manufacturing. Assuming that the structural and post-harvest fumigation sources of CH3Br are emitted without substantial fractionation, we calculate that the ??13C of anthropogenically emitted CH3Br ranges from -53.2??? to -47.5???.

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

    NASA Astrophysics Data System (ADS)

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

    1990-12-01

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

  15. [The mechanism of carbon isotope fractionation in photosynthesis and carbon dioxide component of the greenhouse effect].

    PubMed

    Ivlev, A A; Voronin, V I

    2007-01-01

    The relationship between the global climate warming, which is largely induced by increased CO2 atmospheric concentration, and the changes in carbon isotope fractionation in plants was explained in terms of the previously proposed oscillatory mechanism of photosynthesis, according to which CO2 assimilation and photorespiration are two reciprocally coupled oscillating mechanisms controlled by ribulose bisphosphate carboxylase/oxygenase switches. This explanation is confirmed by the changes in carbon isotope fractionation in the annual rings of trees and demonstrates that the light carbon isotope 12C enrichment before 1990s resulted from increased photosynthetic assimilation of CO2. The subsequent sharp 13C enrichment of the tree ring carbon until the present time suggests that the compensatory role of photosynthesis in boreal forests has been lost for the global climate.

  16. 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

  17. Oxygen isotopic disequilibrium in coccolith carbonate from phytoplankton blooms

    NASA Astrophysics Data System (ADS)

    Paull, Charles K.; Balch, William M.

    1994-01-01

    Particulate carbonate was concentrated with a flow centrifuge out of the waters from a coccolithophore bloom in the Gulf of Maine for δ 18O CaCO 3 measurement. The particulate samples were composed of diverse organic materials, but most samples were observed to be dominated by Emiliana huxleyi CaCO 3. The oxygen isotopic fractionation associated with these E. huxleyi populations were determined by comparing oxygen isotope ratios in coccoliths with those of anbient waters at the time of collection. The observed isotopic fractionations were large (up to 2.8%), but did not match well with the expected values based on previous laboratory experiments. The temperatures calculated from the isotopic values of surface samples averaged 7.4°C cooler than the waters from which this carbonate was collected. These discrepancies may indicate that the coccoliths were precipatated in cooler water 10-20 m below the surface waters were they were captured, or that the waters had warmed since the coccoliths grew.

  18. Stable Carbon Isotope Fractionation by Methylotrophic Methanogenic Archaea

    PubMed Central

    Penger, Jörn; Conrad, Ralf

    2012-01-01

    In natural environments methane is usually produced by aceticlastic and hydrogenotrophic methanogenic archaea. However, some methanogens can use C1 compounds such as methanol as the substrate. To determine the contributions of individual substrates to methane production, the stable-isotope values of the substrates and the released methane are often used. Additional information can be obtained by using selective inhibitors (e.g., methyl fluoride, a selective inhibitor of acetoclastic methanogenesis). We studied stable carbon isotope fractionation during the conversion of methanol to methane in Methanosarcina acetivorans, Methanosarcina barkeri, and Methanolobus zinderi and generally found large fractionation factors (−83‰ to −72‰). We further tested whether methyl fluoride impairs methylotrophic methanogenesis. Our experiments showed that even though a slight inhibition occurred, the carbon isotope fractionation was not affected. Therefore, the production of isotopically light methane observed in the presence of methyl fluoride may be due to the strong fractionation by methylotrophic methanogens and not only by hydrogenotrophic methanogens as previously assumed. PMID:22904062

  19. Carbon and hydrogen isotope fractionation by microbial methane oxidation: Improved determination

    SciTech Connect

    Mahieu, Koenraad . E-mail: Koenraad.Mahieu@Ugent.be; Visscher, Alex De; Vanrolleghem, Peter A.; Cleemput, Oswald Van

    2006-07-01

    Isotope fractionation is a promising tool for quantifying methane oxidation in landfill cover soils. For good quantification an accurate determination of the isotope fractionation factor ({alpha}) of methane oxidation based on independent batch experiments with soil samples from the landfill cover is required. Most studies so far used data analysis methods based on approximations of the Rayleigh model to determine {alpha}. In this study, the two most common approximations were tested, the simplified Rayleigh approach and the Coleman method. To do this, the original model of Rayleigh was described in measurable variables, methane concentration and isotopic abundances, and fitted to batch oxidation data by means of a weighted non-linear errors-in-variables regression technique. The results of this technique were used as a benchmark to which the results of the two conventional approximations were compared. Three types of batch data were used: simulated data, data obtained from the literature, and data obtained from new batch experiments conducted in our laboratory. The Coleman approximation was shown to be acceptable but not recommended for carbon fractionation (error on {alpha} - 1 up to 5%) and unacceptable for hydrogen fractionation (error up to 20%). The difference between the simplified Rayleigh approach and the exact Rayleigh model is much smaller for both carbon and hydrogen fractionation (error on {alpha} - 1 < 0.05%). There is also a small difference when errors in both variables (methane concentration and isotope abundance) are accounted for instead of assuming an error-free independent variable. By means of theoretical calculations general criteria, not limited to methane, {sup 13}C, or D, were developed for the validity of the simplified Rayleigh approach when using labelled compounds.

  20. Clumped isotope thermometry of modern and early Cretaceous molluscan carbonate from high-latitude seas (Invited)

    NASA Astrophysics Data System (ADS)

    Henkes, G. A.; Price, G. D.; Ambrose, W. G.; Carroll, M. L.; Passey, B. H.

    2010-12-01

    The carbonate clumped isotope thermometer is based on the temperature sensitivity of the relative abundance of carbonate ion groups containing 13C-18O bonds. One application of clumped isotope thermometry is to determine the temperature of ancient seawater from the skeletal material of calcium carbonate-secreting marine organisms. The relationship between Δ47, a parameter describing isotopic clumping, and the temperature of carbonate biomineralization has been well-defined for fish otoliths, corals, foraminifera, and coccolithophore tests, but few data have been published for brachiopods and bivalve mollusks. A comprehensive evaluation of the Δ47-temperature relationship for mollusks is required for paleotemperature interpretations from the marine fossil record. Here we present a more comprehensive calibration for modern mollusks, including bivalves, cephalopods, and gastropods. Further, we focus on a subset of cold water, high-latitude species collected in the northern Barents Sea. The observed Δ47-temperature relationship is similar to the theoretical relationship presented by Guo et al. (2009) but deviates at low temperatures from the original Ghosh et al. (2007) calibration curve. This divergence could be related to methodological differences or unaccounted differences in the biomineralization of mollusks versus that of other carbonate-secreting organisms at low temperature. One advantage of clumped isotope thermometry over traditional oxygen isotope thermometry is that it does not require assumptions about the isotopic composition of the water in which the carbonate formed. This may be particularly useful in Mesozoic paleoceanography where the oxygen isotope value of seawater is uncertain. Using clumped isotope thermometry applied to early Cretaceous (Valangian) belemnite carbonate from the Yatria River, sub-polar Urals, Siberia, we find shell growth temperatures of 20-26°C at a paleolatitude of ~60-65°N. Our data imply average seawater δ18O values of 0

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

    SciTech Connect

    Ismail, Atef; Cheong, Lee Yen; Yahya, Noorhana; Tammam, M.

    2014-10-24

    Within the energy density functional (EDF) theory, the structure properties of Carbon isotopes are systematically studied. The shell model calculations are done for both even-A and odd-A nuclei, to study the structure of rich-neutron Carbon isotopes. The EDF theory indicates the single-neutron halo structures in {sup 15}C, {sup 17}C and {sup 19}C, and the two-neutron halo structures in {sup 16}C and {sup 22}C nuclei. It is also found that close to the neutron drip-line, there exist amazing increase in the neutron radii and decrease on the binding energies BE, which are tightly related with the blocking effect and correspondingly the blocking effect plays a significant role in the shell model configurations.

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

    SciTech Connect

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

    2013-11-13

    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 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.

  3. 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.

  4. 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

  5. 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

  6. 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.

  7. 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

  8. 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

  9. Microbial carbonate abundance compared with fluctuations in metazoan diversity over geological time

    NASA Astrophysics Data System (ADS)

    Riding, Robert

    2006-03-01

    Secular variation in microbial carbonate abundance may be reflected by stromatolite morphotype diversity and reefal microbial carbonate abundance. These datasets reveal long-term changes over the past 3000 Myr that include a peak of abundance 1250 Myr ago, Late Proterozoic decline, Cambrian resurgence, and fluctuating decline during the remainder of the Phanerozoic. It is conceivable that Proterozoic metazoan diversification coincided with inception of stromatolite decline ˜1250 Myr ago, but microbial carbonate increase during Cambrian metazoan radiation together with failure of microbial carbonates to increase in the aftermaths of the End-Ordovician, End-Triassic and End-Cretaceous Mass Extinctions suggest that factors in addition to metazoan competition significantly influenced long-term changes in microbial carbonate abundance.

  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. Local and regional oscillations of carbon and oxygen isotopes in terestrial carbonates

    NASA Astrophysics Data System (ADS)

    Skipitytė, Raminta; Stančikaitė, Miglė

    2014-05-01

    Stable isotope ratios of carbon and oxygen in sediment carbonates are used as a tool to identify climatic changes in the past [1], [2]. Carbon is more related to humidity whereas oxygen is thought to respond the temperature [2]. Nevertheless number of questions about local, regional and global scale impacts to these records is left. In this research work carbon and oxygen isotope ratios in lacustrine carbonates are used to identify palaeoenvironmental dynamics of different locations. Samples of lacutrine carbonates were obtained from 8 sequences of different sites in Lithuania (4), Poland (1), Belarus (1) and Kaliningrad (1). Every sequence was divided into 2 cm intervals. The study showed differences in average carbon and oxygen isotope ratios between Lithuania and other countries (Poland, Belarus and Kaliningrad). Carbon and oxygen isotope ratios in 4 sites in Lithuania are: ¯U la δ13C -4.72± 2.11, o and δ18O -9.46± 1.9, o ; Zervynos δ13C -4.79± 1.82, o and δ18O -9.57± 1.69, o ; Rudnia δ13C -4.94± 7.53, o and δ18O -9.3± 3.92, o ; Pauliai δ13C -4.15± 0.67, o and δ18O -9.94± 1.07, o : In other countries: Poland δ13C -1.07± 1.94, o and δ18O -7.69± 0.95, o ; Belarus δ13C 0.97± 1.94, o and δ18O -7.61± 1.42, o ; Kaliningrad δ13C -1.14± 1.43, o and δ18O -6.51± 1.00, o : Average stable carbon and oxygen isotope values from four sites in Lithuania were -4.65 o for carbon and -9.51 o for oxygen. Despite homogeneity of average isotope signals in these four sites there are relatively large oscillations of isotopic values in Rudnia and relatively small in Pauliai. These oscillations could be related to local characteristics of particular place such as environmental conditions, water balance, input of terrigenous materials into basin, etc. Total amount of CaCO3 could also play a significant role in reconstructing palaeoenvironment from stable isotopes and creating isomaps. The comparison of isotope records from different locations could enable to

  12. Fatty acid and stable carbon isotope characterization of Camelina sativa oil: implications for authentication.

    PubMed

    Hrastar, Robert; Petrisic, Marinka G; Ogrinc, Nives; Kosir, Iztok Joze

    2009-01-28

    The importance of authenticity characterization is an increasing and pressing requirement for all foods. Vegetable oil is one of the most studied foods because of its nutritional and medicinal properties in a correct diet. In this study, a total of 53 Camelina sativa samples, from all known growing areas, were chemically and isotopically characterized. The fatty acid content of camelina oil was determined by gas chromatography (GC), and the ratios of stable carbon isotopes ((13)C/(12)C) of individual fatty acids and seed/bulk oil were determined by gas chromatography-combustion-stable isotope ratio mass spectrometry (GC/C/IRMS) and elemental analysis-stable isotope ratio mass spectrometry (IRMS). A total of 17 different fatty acids were detected by GC, with omega3 R-linolenic acid (C(18:3n3)) being the most abundant (29.7-40.0 wt %). Oleic acid (C(18:1n9)), linoleic acid (C(18:2n6)) and eicosenoic acid (C(20:1n9)) all belong to the second group of major fatty acids. The stable carbon isotopic values (delta(13)C) fell into a range typical for C(3) plants. The use of delta(13)C(18:2n6) vs delta(13)C(18:3n3) correlation could show cases where impurity or adulteration is suspected, whereas principal component analysis clearly separates oil samples from different continents. Preliminary results on the camelina oil authentication procedure provide a basis for the investigation of geographical origin and the further distinction between camelina and camelina refined or other, less expensive oils.

  13. {sup 39}Ar Detection at the 10{sup -16} Isotopic Abundance Level with Atom Trap Trace Analysis

    SciTech Connect

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

    2011-03-11

    Atom trap trace analysis, a laser-based atom counting method, has been applied to analyze atmospheric {sup 39}Ar (half-life=269 yr), a cosmogenic isotope with an isotopic abundance of 8x10{sup -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.

  14. Carbon and oxygen abundances across the Hertzsprung gap

    SciTech Connect

    Adamczak, Jens; Lambert, David L. E-mail: dll@astro.as.utexas.edu

    2014-08-10

    We derived atmospheric parameters and spectroscopic abundances for C and O for a large sample of stars located in the Hertzsprung gap in the Hertzsprung-Russell diagram in order to detect chemical peculiarities and get a comprehensive overview of the population of stars in this evolutionary state. We have observed and analyzed high-resolution spectra (R = 60,000) of 188 stars in the mass range 2-5 M{sub ☉} with the 2.7 m Harlan J. Smith Telescope at the McDonald Observatory including 28 stars previously identified as Am/Ap stars. We find that the C and O abundances of the majority of stars in the Hertzsprung gap are in accordance with abundances derived for local lower-mass dwarfs but detect expected peculiarities for the Am/Ap stars. The C and O abundances of stars with T{sub eff} < 6500 K are slightly lower than for the hotter objects but the C/O ratio is constant in the analyzed temperature domain. No indication of an alteration of the C and O abundances of the stars by mixing during the evolution across the Hertzsprung gap could be found before the homogenization of their atmospheres by the first dredge-up.

  15. 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.

  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. Carbon Abundance Plateaus among Carbon-Enhanced Metal-Poor Stars

    NASA Astrophysics Data System (ADS)

    Yoon, Jinmi; He, Siyu; Placco, Vinicius; Carollo, Daniela; Beers, Timothy C.

    2016-01-01

    A substantial fraction of low-metallicity stars in the Milky Way, the Carbon-Enhanced Metal-Poor (CEMP) stars, exhibit enhancements of their carbon-to-iron relative to the solar value ([C/Fe] > +0.7). They can be divided into several sub-classes, depending on the nature and degree of the observed enhancements of their neutron-capture elements, providing information on their likely progenitors. CEMP-s stars (which exhibit enhanced s-process elements) are thought to be enhanced by mass transfer from an evolved AGB companion, while CEMP-no stars (which exhibit no over-abundances of neutron-capture elements) appear to be associated with explosions of the very first generations of stars. High-resolution spectroscopic analyses are generally required in order to make these sub-classifications.Several recent studies have suggested the existence of bimodality in the distribution of absolute carbon abundances among CEMP stars -- most CEMP-no stars belong to a low-C band ((A(C) ˜ 6.5), while most CEMP-s stars reside on a high-C band (A(C) ˜ 8.25). The number of CEMP stars considered by individual studies is, however, quite small, so we have compiled all available high-resolution spectroscopic data for CEMP stars, in order to further investigate the existence of the claimed carbon bi-modality, and to consider what can be learned about the progenitors of CEMP-s and CEMP-no stars based on the observed distribution of A(C) on the individual plateaus.We acknowledge partial support from the grant PHY 14-30152; Physics Frontier Center/JINA Center for the Evolution of the Elements (JINA-CEE), awarded by the US National Science Foundation.

  18. A stable carbon isotope and biological marker study of Polish bituminous coals and carbonaceous shales

    USGS Publications Warehouse

    Kotarba, M.J.; Clayton, J.L.

    2003-01-01

    Biological marker and carbon isotopic compositions of coals and carbonaceous shales from the Upper Carboniferous strata of the Upper Silesian (USCB), Lower Silesian (LSCB), and Lublin (LCB) coal basins were determined to assess depositional conditions and sources of the organic matter. n-Alkane, sterane, and isoprenoid distribution, and carbon isotope ratios are consistent with an origin from higher plants. In some cases, pristane/phytane (Pr/Ph) ratios of carbonaceous shales (roof and floor shales) are < 1.0, while the associated coals have high ratios (??? 1.0). This suggests that reducing conditions prevailed during deposition of the shales, but a period of oxidizing conditions accompanied deposition of the coals. Steranes present in coal extracts are dominated by the 14??(H)17??(H)20R C29 stereoisomers, typical, but not conclusive, of higher plant origin. Carbonaceous shales exhibit a wider range of sterane composition, suggesting local, significant input of algal organic matter. Significant amounts of benzohopanes and gammacerane are present in some coals. Although benzohopanes are present at least in small amounts in samples from many different environments, they have been reported to occur most commonly in marine environments. The present study seems to provide the first example where benzohopanes have been reported in significant amounts in terrestrial organic matter. Gammacerane is abundant in rocks or sediments deposited in carbonate or highly saline marine environments. The finding of high gammacerane concentrations in the coals expands the depositional settings in which it has been observed and questions its utility as an independent indicator of hypersaline carbonate environments. Stable carbon isotope composition of coals, and type III kerogen in carbonaceous shales as well as correlation of stable carbon isotope composition of saturated and aromatic hydrocarbons in carbonaceous shales from both the USCB and the LSCB indicate terrigenous origin

  19. Effects of Water on Carbonate Clumped Isotope Bond Reordering Kinetics

    NASA Astrophysics Data System (ADS)

    Brenner, D. C.; Passey, B. H.

    2015-12-01

    Carbonate clumped isotope geothermometry is a powerful tool for reconstructing past temperatures, both in surface environments and in the shallow crust. The method is based on heavy isotope "clumps" within single carbonate groups (e.g., 13C18O16O2-2), whose overabundance beyond levels predicted by chance is determined by mineralization temperature. The degree of clumped isotope overabundance can change at elevated temperatures (ca. >100ºC) owing to solid-state diffusion of C and O through the mineral lattice. Understanding the kinetics of this clumped isotope reordering process is a prerequisite for application to geological questions involving samples that have been heated in the subsurface. Thus far, the effect of water on reordering kinetics has not been explored. The presence of water dramatically increases rates of oxygen self-diffusion in calcite, but whether this water-enhanced diffusion is limited to the mineral surface or extends into the bulk crystal lattice is not clear. Here we present experimentally determined Arrhenius parameters for reordering rates in optical calcite heated under aqueous high pressure (100 MPa) conditions. We observe only marginal increases in reordering rates under these wet, high pressure conditions relative to rates observed for the same material reacted under dry, low pressure conditions. The near identical clumped isotope reordering rates for wet and dry conditions contrasts with the orders of magnitude increase in oxygen diffusivity at the mineral surface when water is present. This suggests the latter effect arises from surface reactions that have minimal influence on the diffusivity of C or O in the bulk mineral. Our results also imply that previously published reordering kinetics determined under dry, low pressure experimental conditions are applicable to geological samples that have been heated in the presence of water.

  20. Biogeochemistry of a mesotrophic lake and it's carbon isotope geochemistry

    NASA Astrophysics Data System (ADS)

    Cheng, S.; Ehresman, W.; Sadurski, S. E.

    2010-12-01

    Crystal Lake, located in west-central Ohio, is the main lake of a series of 4 interconnected lakes. The location and orientation indicate that they are most likely moulin-induced glacial lakes. Crystal Lake is about 5 hectares (12.5 acres). The maximum depth and mean depth are about 11.9 meters and 3.8 meters, respectively. As a result of this high depth-to-surface area ratio, it creates a strong thermal stratification during warm season. The lake was classified as eutrophic lake. However, the water quality has improved in the past decades. The chlorophyll in the epillimnion and upper metalimlion is about 4 μg/l and the Secchi disk depth is about 3.0 meters (10 feet). It is therefore reclassified as mesotrophic lake. Dissolved oxygen maximum (15.6 ppm) and pH peak (8.6) existed at 4.1 meter on August 16, 2010. At around 7.3 meter, where redox potential reading shows a sudden change from oxidizing to reducing , a ~half meter layer of dense purple sulfur bacteria coincides with turbidity, chlorophyll, and sulfate maxima. The chemical depth profiles are a result of thermal stratification, oxygenic photosynthesis by algae, non-oxygenic photosynthesis by purple sulfur bacteria, and respiration in the hypolimnion. Precipitation of calcium carbonate in the epilimnion and metalimnion is coupled by it’s dissolution in the hypolimnion. The purpose of the current project is to present extensive background study to form the framework for quantifying the carbon isotope evolution with multiple reaction pathways. Carbon isotope composition of dissolved inorganic carbon is being analyzed. Wigley-Plummer-Pearson mass transfer model will be used for the quantification of carbon isotope reaction pathways.

  1. Anomalous Oxygen Isotopic Fractionation in Vacuum Ultraviolet Photodissociation of Carbon Monoxide and Test of Self-Shielding: Relevance for Meteorite Oxygen Isotopes

    NASA Astrophysics Data System (ADS)

    Chakraborty, S.; Ahmed, M.; Jackson, T. L.; Thiemens, M. H.

    2008-12-01

    Oxygen is the predominant elemental constituent of rocky planets and asteroids. It is the third most abundant element in the solar system after hydrogen and helium. The isotopic compo-sition of oxygen in three-isotope space (δ18O vs. δ17O plot) exhibits large heterogeneity among different bodies formed from the same primordial gas and dust mixture, termed the solar nebula. It is not possible to fully understand the formation and evolution of our own planetary system, unless we resolve the source of the oxygen isotopes. At present, there are two models: self shielding photochemistry in the solar nebula, and symmetry driven gas-phase and/or surface chemistry in the solar nebula, which can also involve photochemistry, but isn't required. Photochemistry is a dominant process at the outer layers of the nebular disk and isotopically selective photodissociation (a process known as isotopic self-shielding) of carbon monoxide, the most abundant nebular oxygen bearing molecule, has been suggested as a source of isotopically anomalous oxygen in the solar reservoir [1-3]. However, these models have had no experimental verification of the relevant isotopic fractionation associated with VUV-CO photodissociation at the relevant wavelengths. Recently, we have performed a series of CO photodissociation experiment with a windowless flow chamber at the Advanced Light Source (LBNL) synchrotron at Berkeley. These experiments demonstrate an anomalously enriched atomic oxygen reservoir is generated through CO photo-dissociation, but, without requiring isotopic self shielding [4]. These results emphasize the importance of chemistry in the solar nebula as we have previously demonstrated through recent laboratory experiments [5]. It is clear that the mass- independent oxygen isotopic composition, as observed in some of the first condensed solids in the solar system (Calcium-Aluminum rich Inclusions- CAIs, Chondrules etc.), can be generated through symmetry driven gas-phase chemical

  2. 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.

  3. 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...

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

    SciTech Connect

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

    1993-01-01

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

  5. 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

  6. 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.

  7. Were carbon isotopic gradients in post-snowball oceans inverted?

    NASA Astrophysics Data System (ADS)

    Halverson, G. P.; Hoffman, P. F.; MacDonald, F. A.; Higgins, J. A.; Schrag, D. P.

    2008-12-01

    In the Otavi Group of Namibia, 900 m of platform carbonate strata above the 635-Ma post-glacial cap dolostone are consistently lighter in δ13C by up to 2.5 per mil than the adjacent 180-320 m of correlative, >0.6-km-deep, foreslope strat. Assuming the foreslope carbonate was equilibrated with deeper water, the normal isotopic gradient dynamically sustained by the biological 'pump' was inverted. Geochronology of isotopically correlative Doushantuo strata in South China suggests that the inverted gradient lasted for ~2 Myr after the glacial termination. Thereafter, the inverted gradient disappears. A similar transient inverse gradient follows the older Cryogenian glaciation in Arctic Alaska. We hypothesize that the inverse gradients reflect high pCO2 in the glacial aftermaths. This had two consequences. First, the size of the DIC pool was enlarged, reducing the isotopic effect of the biological pump. Second, isotopic fractionation was strongly temperature-dependent due to the large fractionation between CO2 and CO32- coupled with the dominance of CO2(gas) among carbon species at pH<7.2. A difference in SST of ~25° between the areas of air-sea equilibration is required to account for a 2.5 per mil gradient in δ13C. This is realized in non-upwelling zones of the southern hemisphere today, where warm subtropical surface waters are underlain by Antarctic Intermediate Water. For our hypothesis to be valid, a large meridional temperature gradient must have coexisted with strong CO2 radiative forcing.

  8. Maturation of Green River Shale Kerogen with Hydrous Pyrolysis: Characterization of Geochemical Biomarkers and Carbon Isotopes

    NASA Astrophysics Data System (ADS)

    Fu, Q.; Darnell, M.; Bissada, K. K.

    2014-12-01

    To fully understand controlling factors of organic compound generation during oil shale maturation, and systematically assess associated carbon isotope values, a series of hydrous pyrolysis experiments are performed. Kerogen was isolated from Green River shale by a set of acid treatment. Experiments are conducted at 350 °C and 300 bars of total pressure with running time of 24, 48 and 72 hours, respectively. In each experiment, the reactor contains 1.5 grams of kerogen and 30 grams of deionized water. After experiments, gaseous products are removed under cryogenic conditions for chemical and carbon isotope analyses (GC-IRMS). The bitumen product is retrieved and separated into saturated hydrocarbons, aromatics, resins, and asphaltenes (SARA) by HPLC before subsequent analyses (GC, GC-MS, and IRMS). The gaseous compounds from experiments consisted of CO2 and C1 to C4 hydrocarbons. Semiquantitative analysis indicates the yield of n-alkanes decreases with carbon number, with CO2 being more abundant than all alkanes. The δ13C value of alkanes increases with molecular weight, with CO2 having the highest value. Methane and ethane become enriched in 13C with time. In bitumen products, gravimetric analysis has shown that the abundance of aromatics increases with time, while that of asphaltenes decreases. After 72 hours, the weight percentages of saturated hydrocarbons, aromatics, resins and asphaltenes are 2.6, 42.3, 40.1, and 15.0, respectively. High resolution GC-MS results indicate low kerogen maturation after 72 hours using saturated biomarker compounds as thermal maturity indicator, such as 22S/(22S + 22R) of C31 to C35 homohopanes, tricyclics/17(H)-hopanes, and Ts/(Ts + Tm). Bulk carbon isotope value of bitumen decreases with time, with 2.5‰ lighter than original kerogen after 72 hours. In terms of different groups, saturated hydrocarbons and resins become depleted in 13C with longer reaction time, while aromatics and asphaltenes become enriched in 13C

  9. Carbon and nitrogen isotope studies in an arctic ecosystem. Final report

    SciTech Connect

    Schell, D.M.

    1994-06-01

    The dynamics of carbon fixation and storage in tundra soils has received considerable attention with respect to global carbon cycling. Recent findings by investigators using chamber measurements of fixation/respiration rates in arctic tundra have led to the conclusion that tundra is no longer storing carbon but is instead a source of carbon dioxide to the atmosphere. The author has sought to test these conclusions and to determine methods by which the long-term accumulation or loss of carbon in tundra can be determined. Little is known, however, of the processes that control storage and the current rates of carbon fixation and peat formation in arctic Alaska. This project focused on several aspects of carbon dynamics and the roles of decomposition and herbivory at the DOE research site at Imnavait Creek, Alaska. Through the use of natural abundance stable and radioisotope techniques, several conclusions emerged. Peat carbon continues to accumulate in wetter areas of foothill valleys and on the coastal plain of arctic Alaska. Radiocarbon profiles of bomb {sup 14}C were used to date layers of vegetation and litter to obtain decomposition rates and to extrapolate these values to intersection with the permafrost horizon where further decomposition is assumed to cease. Carbon storage in riparian moss at Imnavait Creek was estimated at 3 g C/m{sup 2}-yr. Profiles of {sup 137}Cs closely matched those of {sup 14}C and may provide a more expeditious means of assessing recent carbon accumulation rates in tundra. Carbon and nitrogen stable isotope ratios in tundra vegetation vary markedly over hydrologic gradients in apparent response to changing growth rates and sources of nitrogenous nutrients. Within a taxon, {delta}{sup 15}N values varied by several {per_thousand} over a tens of meters distance.

  10. Stable carbon isotope fractionation by acetotrophic sulfur-reducing bacteria.

    PubMed

    Goevert, Dennis; Conrad, Ralf

    2010-02-01

    Acetate is the most important intermediate in anaerobic degradation of organic matter. The carbon isotope effects associated with the oxidation of acetate (epsilon(ac)) were examined for four acetotrophic sulfur reducers, Desulfuromonas acetoxidans, Desulfuromonas thiophila, Desulfurella acetivorans, and Hippea maritima. During the consumption of acetate and sulfur, acetate was enriched in (13)C by 11.5 and 11.2 per thousand in Desulfuromonas acetoxidans and Desulfuromonas thiophila, respectively. By contrast, isotope fractionation in D. acetivorans and H. maritima resulted in isotope enrichment factors of epsilon(ac)=-6.3 per thousand and -8.4 per thousand, respectively. These sulfur-reducing bacteria all metabolize acetate via the tricarboxylic acid cycle, but have different mechanisms for the initial activation of acetate. In Desulfuromonas acetoxidans, acetyl-CoA is formed by succinyl-CoA : acetate-CoA-transferase, and in D. acetivorans by acetate kinase and phosphate acetyltransferase. Hence, values of epsilon(ac) seem to be characteristic for the type of activation of acetate to acetyl-CoA in acetotrophic sulfur reducers. Summarizing epsilon(ac)-values in anaerobic acetotrophic microorganisms, it appears that isotope fractionation depends on the mechanism of acetate activation to acetyl-CoA, on the key enzyme of the acetate dissimilation pathway, and on the bioavailability of acetate, which all have to be considered when using delta(13)C of acetate in environmental samples for diagnosis of the involved microbial populations.

  11. Hydrogen recycle and isotope exchange from dense carbon films

    SciTech Connect

    Clausing, R.E.; Heatherly, L.

    1987-03-01

    Dense carbon films were prepared by deposition from hydrogen plasmas to which methane was added. The initial hydrogen recycle coefficient from the films ranges from more than two to less than one. The films contain large amounts of hydrogen (up to 50 at. %). They adjust themselves to provide recycling coefficients near unity. Isotope changeover times tend to be long. The reservoir of hydrogen instantly available to the plasma to maintain or stabilize the recycle coefficient and isotopic composition of the plasma is 10/sup 15/ cm/sup -2/ or greater depending on film preparation, temperature, and prior plasma exposure conditions. Simulator observations tend to support and improve the understanding of the observations in TEXTOR and JET; however, they also point out the need for control of film deposition and operating parameters to provide desirable and reproducible properties. The films and the hydrogen isotopes they contain can be removed easily by plasma processes. Since the hydrogen in these films is relatively immobile except in the zone reached by energetic particles, or at temperatures above 400/sup 0/C, dense carbon films may be useful in managing the tritium recovery from near-term fusion experiments.

  12. Carbon and oxygen isotopes in apatite CO/sub 2/ and co-existing calcite

    SciTech Connect

    Kolodny, Y.; Kaplan, I. R.

    1981-04-01

    Carbon and oxygen isotopes were analyzed in carbonate apatite CO/sub 2/ and in co-existing calcite. Both C and O in apatite CO/sub 2/ are enriched in the respective light isotopes relative to calcite. These results confirm the proposition that carbonate is part of the apatite structure.

  13. Terrestrial and Meteorite Carbon Appear to Have the Same Isotopic Composition

    PubMed Central

    Libby, W. F.

    1971-01-01

    The carbon-isotope ratio recently obtained for the carbon found in the Murchison meteorite, which has been shown (by the racemic nature of twelve component amino acids) to be free of terrestrial contamination, agrees with that for average terrestrial sediments. This finding indicates that the earth and the stony meteorites contain carbon of the same isotopic composition. PMID:16591904

  14. A Comparison of Oxidized Carbon Abundances among Comets

    NASA Technical Reports Server (NTRS)

    DiSanti, M. A.; Mumma, M. J.; Bonev, B. P.; Villanueva, G. L.; Radeva, Y. L.; Magee-Sauer, K.; Gibb, E. L.

    2010-01-01

    Comets contain relatively well preserved icy material remaining from the epoch of Solar System formation, however the extent to which these ices are modified from their initial state remains a fundamental question in cometary science. As a comet approaches the Sun, sublimation of the ices contained in its nucleus (termed " native ices") releases parent volatiles into the coma, where they can be measured spectroscopically. One means of assessing the degree to which interstellar ices were processed prior to their incorporation into cometary nuclei is to measure the relative abundances of chemically-related parent volatiles. For example, formation of C2H6 by hydrogen atom addition (e.g., to C2H2) on surfaces of ice-mantled grains was proposed to explain the high C2H6 to CH4 abundance observed in C/1996 B2 (Hyakutake) [1]. The large C2H6/CH4 abundance ratios measured universally in comets, compared with those predicted by gas phase production of C2H6, establishes H-atom addition as an important and likely ubiquitous process. CO should also be hydrogenated on grain surfaces. Laboratory irradiation experiments on interstellar ice analogs indicate this to require very low temperatures (T approx. 10-25 K), the resulting yields of H2CO and CH3OH being highly dependent both on hydrogen density (i.e., fluence) and on temperature ([2],[3]). This relatively narrow range in temperature reflects a lack of mobility below 8-10 K on the one hand, and reduced sticking times for H-atoms as grain surfaces are warmed above 20 K on the other. The relative abundances of these three chemically-related molecules in comets provides one measure of the efficiency of H-atom addition to CO on pre-cometary grains (Fig. 1).

  15. Carbon isotopic composition of deep carbon gases in an ombrogenous peatland, northwestern Ontario, Canada

    SciTech Connect

    Aravena, R. . Center for Groundwater Research and Wetlands Research Center); Warner, B.G. . Wetlands Research Center and Dept. of Geography); Charman, D.J. . Dept. of Geographical Sciences); Belyea, L.R. . School of Biological Sciences); Mathur, S.P. ); Dinel, H. )

    1993-01-01

    Radiocarbon dating and carbon isotope analyses of deep peat and gases in a small ombrogenous peatland in northwestern Ontario reveals the presence of old gases at depth that are 1000-2000 yr younger than the enclosing peat. The authors suggest that the most likely explanation to account for this age discrepancy is the downward movement by advection of younger dissolved organic carbon for use by fermentation and methanogens bacteria. This study identifies a potentially large supply of old carbon gases in peatlands that should be considered in global carbon models of the terrestrial biosphere.

  16. Abundance Anomaly of the 13C Isotopic Species of c-C3H2 in the Low-mass Star Formation Region L1527

    NASA Astrophysics Data System (ADS)

    Yoshida, Kento; Sakai, Nami; Tokudome, Tomoya; López-Sepulcre, Ana; Watanabe, Yoshimasa; Takano, Shuro; Lefloch, Bertrand; Ceccarelli, Cecilia; Bachiller, Rafael; Caux, Emmanuel; Vastel, Charlotte; Yamamoto, Satoshi

    2015-07-01

    The rotational spectral lines of c-C3H2 and two kinds of the 13C isotopic species, c-{}13{{CCCH}}2 ({C}2v symmetry) and c-{{CC}}13{{CH}}2 (Cs symmetry), have been observed in the 1-3 mm band toward the low-mass star-forming region L1527. We have detected 7, 3, and 6 lines of c-C3H2, c-{}13{{CCCH}}2, and c-{{CC}}13{{CH}}2, respectively, with the Nobeyama 45 m telescope and 34, 6, and 13 lines, respectively, with the IRAM 30 m telescope, where seven, two, and two transitions, respectively, are observed with both telescopes. With these data, we have evaluated the column densities of the normal and 13C isotopic species. The [c-C3H2]/[c-{}13{{CCCH}}2] ratio is determined to be 310 ± 80, while the [c-C3H2]/[c-{{CC}}13{{CH}}2] ratio is determined to be 61 ± 11. The [c-C3H2]/[c-{}13{{CCCH}}2] and [c-C3H2]/[c-{{CC}}13{{CH}}2] ratios expected from the elemental 12C/13C ratio are 60-70 and 30-35, respectively, where the latter takes into account the statistical factor of 2 for the two equivalent carbon atoms in c-C3H2. Hence, this observation further confirms the dilution of the 13C species in carbon-chain molecules and their related molecules, which are thought to originate from the dilution of 13C+ in the gas-phase C+ due to the isotope exchange reaction: {}13{{{C}}}++{CO}\\to {}13{CO}+{{{C}}}+. Moreover, the abundances of the two 13C isotopic species are different from each other. The ratio of c-{}13{{CCCH}}2 species relative to c-{{CC}}13{{CH}}2 is determined to be 0.20 ± 0.05. If 13C were randomly substituted for the three carbon atoms, the [c-{}13{{CCCH}}2]/[c-{{CC}}13{{CH}}2] ratio would be 0.5. Hence, the observed ratio indicates that c-{{CC}}13{{CH}}2 exists more favorably. Possible origins of the different abundances are discussed. Based on observations carried out with the IRAM 30 m Telescope and the NRO 45 m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). NRO is a branch of the National Astronomical Observatory of Japan

  17. 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...

  18. Carbon isotope ratios and impurities in diamonds from Southern Africa

    NASA Astrophysics Data System (ADS)

    Kidane, Abiel; Koch-Müller, Monika; Morales, Luiz; Wiedenbeck, Michael; De Wit, Maarten

    2015-04-01

    We are investigating the sources of diamonds from southern Africa by studying both their carbon isotopic composition and chemical impurities. Our samples include macro-sized diamonds from River Ranch kimberlite in Zimbabwe and the Helam and Klipspringer kimberlitic deposits from South Africa, as well as micro-sized diamonds from Klipspringer and Premier kimberlites in South Africa. We have characterized the samples for their structurally bounded nitrogen, hydrogen and platelets defect using a Fourier Transmission Infrared Spectroscopy (FTIR). Using the DiaMap routine, open source software (Howell et al., 2012), IR spectra were deconvulated and quantified for their nitrogen (A, B and D components) and hydrogen contents. High to moderate nitrogen concentrations (1810 to 400 µg/g; 400 to 50 µg/g respectively) were found in diamonds from Klipspringer and Helam. Moderate to low (<50 µg/g) nitrogen concentrations were observed in diamonds from Premier and River Ranch. Type II diamonds, i.e. diamonds with no N impurities, which are presumed to have been derived from ultramafic sources, are found in the River Ranch deposit. The macro- and micro-size diamonds from the Klipspringer deposit display similar nitrogen defects, with higher nitrogen concentration and more frequent D components found in the macro-size diamonds. One of the first steps towards reliable carbon isotope studies is the development of calibration materials for SIMS carbon isotopic analyses. We have investigated candidate materials both from a polycrystalline synthetic diamond sheet and two natural gem quality diamonds from Juina (Brazil). Electron-based images of the synthetic diamond sheet, obtained using GFZ Potsdam's dual beam FIB instrument, show many diamond grains with diameters greater than 35 µm. SIMS testing of the isotopic homogeneity of the back and front sides of the synthetic sheets reveal similar 13C/12C ratio within a RSD of <1 ‰ . SIMS isotopic analyses of the two natural diamond RMs

  19. 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

  20. [Distribution of carbon isotopes ((13)C/(12)C) in cells and temporal organization of cellular processes].

    PubMed

    Ivlev, A A

    1991-01-01

    Recent studies on fractionation of carbon isotopes in biological systems are reviewed. It follows that direct experimental proofs have been obtained that 1) basic fractionation of carbon isotopes in the cell is related to isotope effect in pyruvate decarboxylation; 2) fractionation of carbon isotopes in the above reaction in vivo proceeds with exhausting substrate pool. The latter provides natural relationship between metabolites isotope distribution and sequence of their synthesis in the cell cycle, or with the temporal organization of cellular metabolism. The non-steady and periodic pattern of pyruvate decarboxylation due to the exhausting substrate pool well agrees with the existing notions on reciprocal oscillations in the cell glycolytic chain. Experimental data are presented corroborating indirectly the existence of oscillations in bacterial cells. Earlier proposed model of the mechanism of carbon isotope fractionation based on the above principles can be used for analysing changes in isotopic characteristics of the organisms and interpreting their relations with metabolic processes.

  1. Chlorine and carbon isotopes fractionation during volatilization and diffusive transport of trichloroethene in the unsaturated zone.

    PubMed

    Jeannottat, Simon; Hunkeler, Daniel

    2012-03-20

    To apply compound-specific isotope methods to the evaluation of the origin and fate of organic contaminants in the unsaturated subsurface, the effect of physicochemical processes on isotope ratios needs to be known. The main objective of this study is to quantify chlorine and carbon isotope fractionation during NAPL-vapor equilibration, air-water partitioning, and diffusion of trichloroethene (TCE) and combinations of these effects during vaporization in porous media. Isotope fractionation is larger during NAPL-vapor equilibration than air-water partitioning. During NAPL-vapor equilibration, carbon, and chlorine isotope ratios evolve in opposite directions although both elements are present in the same bond, with a normal isotope effect for chlorine (ε(Cl) = -0.39 ± 0.03‰) and an inverse effect for carbon (ε(C) = +0.75 ± 0.04‰). During diffusion-controlled vaporization in a sand column, no significant carbon isotope fractionation is observed (ε(C) = +0.10 ± 0.05‰), whereas fairly strong chlorine isotope fractionation occurs (ε(Cl) = -1.39 ± 0.06‰) considering the molecular weight of TCE. In case of carbon, the inverse isotope fractionation associated with NAPL-vapor equilibration and normal diffusion isotope fractionation cancel, whereas for chlorine both processes are accompanied by normal isotope fractionation and hence they cumulate. A source of contamination that aged might thus show a shift toward heavier chlorine isotope ratios.

  2. 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.

  3. Isotope-based Fluvial Organic Carbon (ISOFLOC) Model: Model formulation, sensitivity, and evaluation

    NASA Astrophysics Data System (ADS)

    Ford, William I.; Fox, James F.

    2015-06-01

    Watershed-scale carbon budgets remain poorly understood, in part due to inadequate simulation tools to assess in-stream carbon fate and transport. A new numerical model termed ISOtope-based FLuvial Organic Carbon (ISOFLOC) is formulated to simulate the fluvial organic carbon budget in watersheds where hydrologic, sediment transport, and biogeochemical processes are coupled to control benthic and transported carbon composition and flux. One ISOFLOC innovation is the formulation of new stable carbon isotope model subroutines that include isotope fractionation processes in order to estimate carbon isotope source, fate, and transport. A second innovation is the coupling of transfers between carbon pools, including algal particulate organic carbon, fine particulate and dissolved organic carbon, and particulate and dissolved inorganic carbon, to simulate the carbon cycle in a comprehensive manner beyond that of existing watershed water quality models. ISOFLOC was tested and verified in a low-gradient, agriculturally impacted stream. Results of a global sensitivity analysis suggested the isotope response variable had unique sensitivity to the coupled interaction between fluvial shear resistance of algal biomass and the concentration of dissolved inorganic carbon. Model calibration and validation suggested good agreement at event, seasonal, and annual timescales. Multiobjective uncertainty analysis suggested inclusion of the carbon stable isotope routine reduced uncertainty by 80% for algal particulate organic carbon flux estimates.

  4. A process-based model for non-equilibrium clumped isotope effects in carbonates

    NASA Astrophysics Data System (ADS)

    Watkins, J. M.; Hunt, J. D.

    2015-12-01

    The equilibrium clumped isotope composition of carbonate minerals is independent of the composition of the aqueous solution. However, many carbonate minerals grow at rates that place them in a non-equilibrium regime with respect to carbon and oxygen isotopes with unknown consequences for clumped isotopes. We develop a process-based model that allows one to calculate the oxygen, carbon, and clumped isotope composition of calcite as a function of temperature, crystal growth rate, and solution pH. In the model, carbon and oxygen isotope fractionation occurs through the mass-dependent attachment/detachment kinetics of the isotopologues of HCO-3 and CO2-3 to and from the calcite surface, which in turn, influence the clumped isotope composition of calcite. At experimental and biogenic growth rates, the mineral is expected to inherit a clumped isotopic composition that is similar to that of the DIC pool, which helps to explain (1) why different organisms share the same clumped isotope versus temperature calibration curves, (2) why many inorganic calibration curves are slightly different from one another, and (3) why foraminifera, coccoliths, and deep sea corals can have near-equilibrium clumped isotope compositions but far-from-equilibrium carbon and oxygen isotope compositions. Some aspects of the model can be generalized to other mineral systems and should serve as a useful reference in future efforts to quantify kinetic clumped isotope effects.

  5. On strontium isotopic anomalies and odd-A p-process abundances. [in solar system

    NASA Technical Reports Server (NTRS)

    Clayton, D. D.

    1978-01-01

    Several aspects of the nucleosynthesis of Sr isotopes are considered in an attempt to shed light on the problem of the Sr isotopic anomalies discovered in an inclusion of the Allende meteorite. Decomposition of the Sr isotopes into average r-, s-, and p-process nucleosynthetic classes is performed. It is suggested that the Allende inclusion most likely has an excess of s-process Sr and that the initial Sr-87/Sr-86 isotopic ratio is probably slightly more primitive than basaltic achondrites. The results also show that Sn-115 is mostly due to the r-process and that odd-A yields are very small. It is concluded that if the Sr anomaly in the inclusion is an average s enhancement, it argues somewhat in favor of a model of gas/dust fractionation of s and r isotopes during accumulation of the inclusion parent in the protosolar cloud.

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

    NASA Astrophysics Data System (ADS)

    Breecker, D.

    2015-12-01

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

  7. The concentration and isotopic composition of carbon in basaltic glasses from the Juan de Fuca Ridge, Pacific Ocean

    NASA Technical Reports Server (NTRS)

    Blank, Jennifer G.; Delaney, John R.; Des Marais, David J.

    1993-01-01

    The abundance and C-13/C-12 ratios of carbon were analyzed in basaltic glass from twenty locations along the Juan de Fuca Ridge using a 3-step combustion/extraction technique. Carbon released during the first two combustion steps at 400-500 C and 600-650 C is interpreted to be secondary, and only the carbon recovered during a final combustion step at about 1200 C is thought to be indigenous to the samples. For carbon released at about 1200 C, glasses analyzed as 1-2 mm chips contained 23-146 ppm C with delta C-13 values of -4.8 to -9.3 per mil, whereas samples crushed to 38-63 microns or 63-90 microns yielded 56-103 ppm C with delta C-13 values of -6.1 to -9.2 per mil. The concentrations and isotopic compositions of the primary carbon dissolved in the glasses and present in the vesicles are similar to those previously reported for other ocean-ridge basalts. The Juan de Fuca basaltic magmas were not in equilibrium with respect to carbon when they erupted and quenched on the sea floor. Evidence of disequilibrium includes (1) a large range of carbon contents among glasses collected at similar depths, (2) a highly variable calculated carbon isotopic fractionation between melt and vapor determined by comparing crushed and uncrushed splits of the same sample, and (3) a lack of correlation between vesicle abundance, carbon concentration, and depth of eruption. Variations in carbon concentration and delta C-13 ratios along the ridge do not correlate with major element chemistry. The observed relationship between carbon concentrations and delta C-13 values may be explained by late-stage, variable degrees of open-system (Rayleigh-like) degassing.

  8. 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.

  9. The carbon isotopic composition of Novo Urei diamonds

    NASA Technical Reports Server (NTRS)

    Fisenko, A. V.; Semjenova, L. F.; Verchovsky, A. B.; Russell, S. S.; Pillinger, C. T.

    1993-01-01

    The carbon isotopic composition of diamond grains isolated from the Novo Urei meteorite are discussed. A diamond separate was obtained from 2g of whole rock using the chemical treatments described aimed at obtaining very pure diamond. X ray diffraction of the residue, which represented 5000 ppm of the parent mass, indicated only the presence of the desired mineral. The diamond crystals were 1-30 microns in diameter, and some grains had a yellow color. The chemical treatments were followed by a size separation to give a 1-10 microns and a 5-30 microns fraction, which were named DNU-1 and DNU-2, respectively.

  10. Physiological and environmental factors related to carbon isotopic variations in mollusc shell carbonate

    SciTech Connect

    Krantz, D.E.; Williams, D.F.; Jones, D.S.

    1985-01-01

    The carbon isotopic composition of mollusc shell carbonate has been used as a general environmental indicator in numerous studies, but relatively little is known of the factors which affect within-shell variation. Primary control of delta/sup 13/C values in shell carbonate comes from the dissolved bicarbonate source, particularly as related to marine versus fresh water. Present models explain cyclic variations in the delta/sup 13/C profiles of mollusc shells due to upwelling, phytoplankton productivity and stratification, disequilibrium with rapid shell growth, and infaunal versus epifaunal habitat. Carbon and oxygen isotopic profiles in this study were obtained from specimens of Spisula solidissima (surf clam) and Placopecten magellanicus (sea scallop) collected alive from 14 to 57 m water depths off the Virginia coast. Three main factors appear to affect the delta/sup 13/C profiles in these specimens. Isotopically light values commonly associated with the spring and occasionally the fall correspond with seasonal phytoplankton productivity. A significant negative delta/sup 13/C offset of the infaunal Spisula relative to the epifaunal Placopecten probably relates to the inclusion of isotopically more negative pore-water bicarbonate by Spisula. Additionally, occasional transient spikes in both the delta/sup 18/O and delta/sup 13/C profiles correspond to intrusion of reduced-salinity water.

  11. 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...

  12. Silicon and carbon abundances in the Orion nebula

    NASA Technical Reports Server (NTRS)

    Rubin, Robert H.; Dufour, Reginald J.; Walter, Donald K.

    1993-01-01

    We assess the gas-phase abundances of Si and C from our recent measurements of Si(2+), C(2+), and C(+) in the Orion Nebula by expanding on our earlier 'blister' models. The C and Si abundances are derived from new IUE high-dispersion spectra of the C(2+) 1907, 1909 A and Si(2+) 1883, 1892 A lines and archival IUE data. Gas-phase Si/C = 0.016 in the Orion ionized volume and is particularly insensitive to uncertainties in extinction and temperature structure. The solar value is 0.098. Gas-phase C/H = 2.8 x 10 exp -4 and Si/H = 4.5 x 10 exp -6. Compared to solar, Si is depleted by a factor of about 8 in the ionized region, while C is much less depleted (factor of 1.3), if depleted at all. This suggests that most Si resides in dust grains even in the ionized volume. Thus, most of the observed forbidden Si II 34.8-micron emission in Orion does not arise in the H II region.

  13. Stable isotope mass balances versus concentration differences of dissolved inorganic carbon - implications for tracing carbon turnover in reservoirs.

    PubMed

    Barth, Johannes A C; Mader, Michael; Nenning, Franziska; van Geldern, Robert; Friese, Kurt

    2017-02-13

    The aim of this study was to identify sources of carbon turnover using stable isotope mass balances. For this purpose, two pre-reservoirs in the Harz Mountains (Germany) were investigated for their dissolved and particulate carbon contents (dissolved inorganic carbon (DIC), dissolved organic carbon, particulate organic carbon) together with their stable carbon isotope ratios. DIC concentration depth profiles from March 2012 had an average of 0.33 mmol L(-1). Increases in DIC concentrations later on in the year often corresponded with decreases in its carbon isotope composition (δ(13)CDIC) with the most negative value of -18.4 ‰ in September. This led to a carbon isotope mass balance with carbon isotope inputs of -28.5 ‰ from DOC and -23.4, -31.8 and -30.7 ‰ from algae, terrestrial and sedimentary matter, respectively. Best matches between calculated and measured DIC gains were achieved when using the isotope composition of algae. This shows that this type of organic material is most likely responsible for carbon additions to the DIC pool when its concentrations and δ(13)CDIC values correlate negatively. The presented isotope mass balance is transferable to other surface water and groundwater systems for quantification of organic matter turnover.

  14. Lithium isotopes and light lithophile element abundances in shergottites: Evidence for both magmatic degassing and subsolidus diffusion

    NASA Astrophysics Data System (ADS)

    Udry, Arya; McSween, Harry Y.; Hervig, Richard L.; Taylor, Lawrence A.

    2016-01-01

    Degassed magmatic water was potentially the major source of surficial water on Mars. We measured Li, B, and Be abundances and Li isotope profiles in pyroxenes, olivines, and maskelynite from four compositionally different shergottites—Shergotty, QUE 94201, LAR 06319, and Tissint—using secondary ion mass spectrometry (SIMS). All three light lithophile elements (LLE) are incompatible: Li and B are soluble in H2O-rich fluids, whereas Be is insoluble. In the analyzed shergottites, Li concentration decreases and Be concentration increases from cores to rims in pyroxenes. However, B concentrations do not vary consistently with Li and Be abundances, except in QUE 94201 pyroxenes. Additionally, abundances of these three elements in olivines show a normal igneous-fractionation trend consistent with the crystallization of olivine before magma ascent and degassing. We expect that kinetic effects would lead to fractionation of 6Li in the vapor phase compared to 7Li during degassing. The Li isotope profiles, with increasing δ7Li from cores to rims, as well as Li and B profiles indicate possible degassing of hydrous fluids only for the depleted shergottite QUE 94201, as also supported by degassing models. Conversely, Shergotty, LAR 06319, and Tissint appear to have been affected by postcrystallization diffusion, based on their LLE and Li isotope profiles, accompanied by diffusion models. This process may represent an overlay on a degassing pattern. The LLE profiles and isotope profiles in QUE 94201 support the hypothesis that degassing of some basaltic shergottite magmas provided water to the Martian surface, although evidence may be obscured by subsolidus diffusion processes.

  15. Environmental drivers of carbon and nitrogen isotopic signatures in peatland vascular plants along an altitude gradient.

    PubMed

    Gavazov, Konstantin; Hagedorn, Frank; Buttler, Alexandre; Siegwolf, Rolf; Bragazza, Luca

    2016-01-01

    Peatlands are important sinks of atmospheric carbon (C) that, in response to climate warming, are undergoing dynamic vegetation succession. Here we examined the hypothesis that the uptake of nutrients by different plant growth forms (PGFs) is one key mechanism driving changes in species abundance in peatlands. Along an altitude gradient representing a natural climate experiment, we compared the variability of the stable C isotope composition (δ(13)C) and stable nitrogen (N) isotope composition (δ(15)N) in current-year leaves of two major PGFs, i.e. ericoids and graminoids. The climate gradient was associated with a gradient of vascular plant cover, which was parallelled by different concentrations of organic and inorganic N as well as the fungal/bacterial ratio in peat. In both PGFs the (13)C natural abundance showed a marginal spatial decrease with altitude and a temporal decrease with progression of the growing season. Our data highlight a primary physical control of foliar δ(13)C signature, which is independent from the PGFs. Natural abundance of foliar (15)N did not show any seasonal pattern and only in the ericoids showed depletion at lower elevation. This decreasing δ(15)N pattern was primarily controlled by the higher relative availability of organic versus inorganic N and, only for the ericoids, by an increased proportion of fungi to bacteria in soil. Our space-for-time approach demonstrates that a change in abundance of PGFs is associated with a different strategy of nutrient acquisition (i.e. transfer via mycorrhizal symbiosis versus direct fine-root uptake), which could likely promote observed and predicted dwarf shrub expansion under climate change.

  16. 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)

  17. Isotope composition of carbon in the carbonates of the Gumbeykan scheelite deposits in the southern Urals

    SciTech Connect

    Korzhinskii, A.F.; Mamchur, G.P.; Yarynych, O.A.

    1980-10-01

    Through investigations of the isotope composition of carbon of various generations and carbonates from marbles, skarns, and nested and vein scheelite orebodies, the probable source of carbon of these carbonates has been established as a mixture of sedimentary carbonates, carbon dioxide with carbonic acid that was formed by oxidation of the organic matter from sedimentary terrane (..delta..C/sup 13/ - 0.05 to -0.62%). In the calcite and dolomite phenocrysts of marble and the coarse-grained dolostone, containing scheelite, the carbon was lighter (..delta..C/sup 13/ from -0.60 to -0.87%). For the dolomite and ankerite from scheelite pockets of the Balkan deposit and quartz veins of the Buranovo, ..delta..C/sup 13/ varied from -0.44 to -0.87%. The lightest carbon found in strontianite (..delta..C/sup 13/ = -1.32%), located near the coating of the organic matter (..delta..C/sup 13/ = -1.26%) in fractures of the quartz vein of the Buranovo deposit. In the section through the orebodies and near-ore diffusion-metasomatic zones of the Balkan deposit, the lessening of carbon in the carbonates was observed, with increasing distance away from the fracture. ..delta..C/sup 13/ in the altered granitoids ranged from -0.44 to -1.03%; while in the diopside-wollastonite hornfels, from -0.89 to 1.13%. The lessening in weight of the carbon is explained by diffusional fractionation of the isotopes caused apparently by the differential movement of volatile mixtures of carbon during ore-forming processes and the formation of their diffusion-metasomatic zones.

  18. Carbon stable isotopes as indicators of coastal eutrophication.

    PubMed

    Oczkowski, Autumn; Markham, Erin; Hanson, Alana; Wigand, Cathleen

    2014-04-01

    Coastal ecologists and managers have frequently used nitrogen stable isotopes (delta15N) to trace and monitor sources of anthropogenic nitrogen (N) in coastal ecosystems. However, the interpretation of delta15N data can often be challenging, as the isotope values fractionate substantially due to preferential retention and uptake by biota. There is a growing body of evidence that carbon isotopes may be a useful alternative indicator for eutrophication, as they may be sensitive to changes in primary production that result from anthropogenic nutrient inputs. We provide three examples of systems where delta13C values sensitively track phytoplankton production. First, earlier (1980s) mesocosm work established positive relationships between delta13C and dissolved inorganic nitrogen and dissolved silica concentrations. Consistent with these findings, a contemporary mesocosm experiment designed to replicate a temperate intertidal salt marsh environment also demonstrated that the system receiving supplementary nutrient additions had higher nutrient concentrations, higher chlorophyll concentrations, and higher delta13C values. This trend was particularly pronounced during the growing season, with differences less evident during senescence. And finally, these results were replicated in the open waters of Narragansett Bay, Rhode Island, USA, during a spring phytoplankton bloom. These three examples, taken together with the pre-existing body of literature, suggest that, at least in autotrophic, phytoplankton-dominated systems, delta13C values can be a useful and sensitive indicator of eutrophication.

  19. Dual carbon isotope characterization of total organic carbon in wintertime carbonaceous aerosols from northern India

    NASA Astrophysics Data System (ADS)

    Bikkina, Srinivas; Andersson, August; Sarin, M. M.; Sheesley, R. J.; Kirillova, E.; Rengarajan, R.; Sudheer, A. K.; Ram, K.; Gustafsson, Örjan

    2016-05-01

    Large-scale emissions of carbonaceous aerosols (CA) from South Asia impact both regional climate and air quality, yet their sources are not well constrained. Here we use source-diagnostic stable and radiocarbon isotopes (δ13C and Δ14C) to characterize CA sources at a semiurban site (Hisar: 29.2°N, 75.2°E) in the NW Indo-Gangetic Plain (IGP) and a remote high-altitude location in the Himalayan foothills (Manora Peak: 29.4°N, 79.5°E, 1950 m above sea level) in northern India during winter. The Δ14C of total aerosol organic carbon (TOC) varied from -178‰ to -63‰ at Hisar and from -198‰ to -1‰ at Manora Peak. The absence of significant differences in the 14C-based fraction biomass of TOC between Hisar (0.81 ± 0.03) and Manora Peak (0.82 ± 0.07) reveals that biomass burning/biogenic emissions (BBEs) are the dominant sources of CA at both sites. Combining this information with δ13C, other chemical tracers (K+/OC and SO42-/EC) and air mass back trajectory analyses indicate similar source regions in the IGP (e.g., Punjab and Haryana). These results highlight that CA from BBEs in the IGP are not only confined to the atmospheric boundary layer but also extend to higher elevations of the troposphere, where the synoptic-scale circulations could substantially influence their abundances both to the Himalayas and over the downwind oceanic regions such as the Indian Ocean. Given the vast emissions of CA from postharvest crop residue combustion practices in the IGP during early Northeast Monsoon, this information is important for both improved process and model understanding of climate and health effects, as well as in guiding policy decision aiming at reducing emissions.

  20. 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.

  1. Oxygen isotopic abundances in calcium- aluminum-rich inclusions from ordinary chondrites: implications for nebular heterogeneity.

    PubMed

    McKeegan, K D; Leshin, L A; Russell, S S; MacPherson, G J

    1998-04-17

    The oxygen isotopic compositions of two calcium-aluminum-rich inclusions (CAIs) from the unequilibrated ordinary chondrite meteorites Quinyambie and Semarkona are enriched in 16O by an amount similar to that in CAIs from carbonaceous chondrites. This may indicate that most CAIs formed in a restricted region of the solar nebula and were then unevenly distributed throughout the various chondrite accretion regions. The Semarkona CAI is isotopically homogeneous and contains highly 16O-enriched melilite, supporting the hypothesis that all CAI minerals were originally 16O-rich, but that in most carbonaceous chondrite inclusions some minerals exchanged oxygen isotopes with an external reservoir following crystallization.

  2. 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.

  3. 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.

  4. Small mammal tooth enamel carbon isotope record of C4 grasses in late Neogene China

    NASA Astrophysics Data System (ADS)

    Arppe, Laura; Kaakinen, Anu; Passey, Benjamin H.; Zhang, Zhaoqun; Fortelius, Mikael

    2015-10-01

    The spatiotemporal pattern of the late Cenozoic spread of C4 vegetation is an important indicator of environmental change that is intertwined with the uplift of the Himalaya and Tibetan Plateau, and the development of the East Asian monsoons. To explore the spread of C4 vegetation in China and shed new light on regional climatic evolution, we measured δ13C values of more than 200 small mammal teeth (primarily rodents and lagomorphs) using a laser ablation isotope ratio mass spectrometry approach. Small mammals are highly sensitive indicators of their environment because they have limited spatial ranges and because they have minimal time-averaging of carbon isotope signatures of dietary components. The specimens originate from four classic Late Miocene fossil localities, Lufeng, Yuanmou, Lingtai, and Ertemte, along a southwest-northeast transect from Yunnan Province to Inner Mongolia. In Yunnan (Lufeng, Yuanmou) and on the Loess Plateau (Lingtai), the small mammal δ13C values record nearly pure C3 ecosystems, and mixed but C3-based ecosystems, respectively, in agreement with previous studies based on carbon isotopes of large herbivores and soil carbonates. In Inner Mongolia, the micromammalian tooth enamel δ13C record picks up the presence of C4 vegetation where large mammal samples do not, indicating a mixed yet C3-dominated ecosystem at ~ 6 Ma. As a whole, the results support a scenario of northward increasing C4 grass abundance in a pattern that mirrors northward decreasing precipitation of the summer monsoon system. The results highlight differences between large and small mammals as indicators of C4 vegetation in ancient ecosystems, particularly the ability of small mammal δ13C values to detect the presence of minor components of the vegetation structure.

  5. Mathematical modeling of stable carbon isotope ratios in natural gases^@?

    NASA Astrophysics Data System (ADS)

    Tang, Y.; Perry, J. K.; Jenden, P. D.; Schoell, M.

    2000-08-01

    A new approach is presented for mathematical modeling of stable carbon isotope ratios in hydrocarbon gases based on both theoretical and experimental data. The kinetic model uses a set of parallel first-order gas generation reactions in which the relative cracking rates of isotopically substituted (k∗) and unsubstituted (k) bonds are represented by the equation k∗/k=(Af∗/Af) exp(-ΔEa/RT), where R is the gas constant and T is temperature. Quantum chemistry calculations have been used to estimate the entropic (A f∗/A f) and enthalpic (ΔEa) terms for homolytic bond cleavage in a variety of simple molecules. For loss of a methyl group from a short-chain n-alkane (≤ C 6), for example, we obtain an average ΔEa of 42.0 cal/mol and an average A f∗/A f of 1.021. Expressed differently, 13C-methane generation is predicted to be 2.4% (24‰) slower than 12C-methane generation (from a short-chain n-alkane) in a sedimentary basin at 200°C but only 0.7% (7‰) slower in a laboratory heating experiment at 500°C. Similar calculations carried out for homolytic bond cleavage in other molecules show that with few exceptions, ΔEa varies between 0 and 60 cal/mol and A f∗/A f between 1.00 and 1.04. Examination of this larger data set reveals: (1) a weak sigmoid relationship between ΔEa and bond dissociation energy; and (2) a strong positive correlation between ΔEa and A f∗/A f. The significance of these findings is illustrated by fitting a kinetic model to chemical and isotopic data for the generation of methane from n-octadecane under isothermal closed-system conditions. For a specific temperature history, the fitted model provides quantitative relationships among methane carbon isotope composition, total methane yield and methane generation rate which may have relevance to the cracking of oil-prone kerogens and crude oil. The observed variability of the kinetic reactivity of various methane source rocks highlights the need to apply and adequately calibrate such

  6. Abundance and Characterization of Dissolved Organic Carbon in Suburban Streams of Baltimore, Maryland, USA

    NASA Astrophysics Data System (ADS)

    Mora, G.; Fazekas, M.

    2014-12-01

    The contribution of streams and rivers to the carbon cycle is significant, transporting to the oceans ~1.4 Pg C/yr, with dissolved carbon corresponding to as much as 0.7 Pg C/yr. Changes in land use have the potential effect of modifying this flux, particularly in urban areas where impervious areas are common. To investigate the effect of urbanization on riverine carbon transport, we studied four first-order streams in Towson, a suburb of Baltimore, Maryland, USA. The watersheds from the studied streams exhibit different levels of urbanization as measured by the percentage of impervious areas. Samples from these four streams were taken weekly, and several chemical constituents were measured either in the field or in the laboratory. These constituents included nitrate, dissolved organic nitrogen, pH, dissolved organic carbon (DOC), total carbon, dissolved inorganic carbon (DIC), phosphate, the carbon isotopic compositions of DOC and DIC, and fluorescence intensity of the DOC. Results show that DOC concentrations were consistently below 5 mg C/L regardless of the level of imperviousness of the watershed. Similarly, carbon isotope ratios were consistent across the studied streams, with values centered around -26.4 per mil, thus suggesting a significant influx of soil-derived organic carbon originated from C3 plants that are common in the watersheds. Confirming this interpretation, fluorescence spectroscopy data suggest a humic-like origin for the DOC of the streams, thus pointing to the heterotrophic nature of the streams. The combined results suggest that the studied streams exhibit similar DOC concentrations, carbon isotopic values, and fluorescence spectra, despite their level of impervious surfaces in their watersheds.

  7. Carbon isotope variation in mid-continent Ordovician-type oils: relationship to a major middle Ordovician carbon isotope shift

    SciTech Connect

    Hatch, J.R.; Jacobson, S.R.; Witzke, B.J.; Anders, D.E.; Watney, W.L.; Newell, K.D.

    1985-05-01

    Detailed organic geochemical comparisons of Mid-Continent Ordovician oils with extracts of potential source rocks show that in the Forest City basin of northeastern Kansas and southeastern Nebraska, oil source rocks are Middle Ordovician shales of the Simpson Group. For the Keota Dome field, Washington County, Iowa, the oil source rock is the Middle Ordovician Glenwood Shale Member of the Platteville Formation. Analyses of saturated and aromatic hydrocarbon fractions of Ordovician-type oils from the Forest City basin, Keota Dome field, and the Michigan basin show that sigma TC of the two fractions are similar and that sigma T varies over a considerable range, from -32.5 per mil to -25.5 per mil (PDB). This large range in sigma TC reflects a major shift in the carbon isotope composition of organic matter during the Middle Ordovician. This shift is shown in a 62.5-ft (19 m) interval of core from the Decorah and Platteville Formations in the E.M. Greene 1 well in Washington County, Iowa, where organic carbon sigma TC changes regularly upward from -32.2 per mil to -22.7 per mil (PDB). The change in organic carbon sigma TC in this core is not related to variations in amount (0.13-41.4% TOC) or type (hydrogen index = 69 to 1000 mg HC/g TOC) of the marginally mature (T/sub max/ = 440 +/- 5C) organic matter. Ordovician-type oils in both the Forest City and Michigan basins show variable sigma TC, suggesting that the sigma TC shift displayed in the Middle Ordovician rocks of southeastern Iowa is a regional and possibly a global effect, related to changes in the sigma TC of the ocean-atmosphere carbon reservoir. Isotopic analyses of coexisting carbonate minerals support this interpretation.

  8. The interstellar carbon abundance. II - Rho Ophiuchi and Beta Scorpii

    NASA Technical Reports Server (NTRS)

    Welty, D. E.; York, D. G.; Hobbs, L. M.

    1986-01-01

    A procedure designed to obtain increased sensitivity from high-dispersion IUE spectra by using a flat-field spectrum to remove nonrandom noise due to the response pattern of the SEC vidicon detector is described. Application of this procedure to spectra of Rho Oph and Beta(1) Sco near the spin-forbidden interstellar 2325 line of C II yields 2 sigma upper limits on absorption of W (lambda) not greater than about 4 mA. The resulting depletion of carbon from the interstellar gas toward Rho Oph exceeds a factor of 1.4.

  9. 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

  10. Determination of the natural abundance δ15N of taurine by gas chromatography-isotope ratio measurement mass spectrometry.

    PubMed

    Tea, Illa; Antheaume, Ingrid; Besnard, Jorick; Robins, Richard J

    2010-12-15

    The measurement of the nitrogen isotope ratio of taurine (2-aminoethanesulphonic acid) in biological samples has a large number of potential applications. Taurine is a small water-soluble molecule which is notoriously difficult to analyze due to its polarity and functionality. A method is described which allows the determination of the natural abundance δ(15)N values of taurine and structural analogues, such as 3-amino-1-propanesulphonic acid (APSA), by isotope ratio mass spectrometry interfaced to gas chromatography (GC-irm-MS). The one-step protocol exploits the simultaneous derivatization of both functionalities of these aminosulphonic acids by reaction with triethylorthoacetate (TEOA). Conditions have been established which ensure quantitative reaction thus avoiding any nitrogen isotope fractionation during derivatization and workup. The differences in the δ(15)N values of derivatized and non-derivatized taurine and APSA all fall within the working range of 0.4‰ (-0.02 to 0.39‰). When applied to four sources of taurine with various δ(15)N values, the method achieved excellent reproducibility and accuracy. The optimized method enables the determination of the natural abundance δ(15)N values of taurine over the concentration range 1.5-7.84 µmol.mL(-1) in samples of biological origin.

  11. Factors affecting the isotopic composition of organic matter. (1) Carbon isotopic composition of terrestrial plant materials.

    PubMed

    Yeh, H W; Wang, W M

    2001-07-01

    The stable isotope composition of the light elements (i.e., H, C, N, O and S) of organic samples varies significantly and, for C, is also unique and distinct from that of inorganic carbon. This is the result of (1) the isotope composition of reactants, (2) the nature of the reactions leading to formation and post-formational modification of the samples, (3) the environmental conditions under which the reactions took place, and (4) the relative concentration of the reactants compared to that of the products (i.e., [products]/[reactants] ratio). This article will examine the carbon isotope composition of terrestrial plant materials and its relationship with the above factors. delta13C(PDB) values of terrestrial plants range approximately from -8 to -38%, inclusive of C3-plants (-22 to -38%), C4-plants (-8 to -15%) and CAM-plants (-13 to -30%). Thus, the delta13C(PDB) values largely reflect the photosynthesis pathways of a plant as well as the genetics (i.e., species difference), delta13C(PDB) values of source CO2, relevant humidity, CO2/O2 ratios, wind and light intensity etc. Significant variations in these values also exist among different tissues, different portions of a tissue and different compounds. This is mainly a consequence of metabolic reactions. Animals mainly inherit the delta13C(PDB) values of the foods they consume; therefore, their delta13C(PDB) values are similar. The delta13C(PDB) values of plant materials, thus, contain information regarding the inner workings of the plants, the environmental conditions under which they grow, the delta13C(PDB) values of CO2 sources etc., and are unique. Furthermore, this uniqueness is passed on to their derivative matter, such as animals, humus etc. Hence, they are very powerful tools in many areas of research, including the ecological and environmental sciences.

  12. 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.

  13. Carbon Reservoir History of Mars Constrained by Atmospheric Isotopic Measurements and Carbonate Remote Sensing

    NASA Astrophysics Data System (ADS)

    Hu, R.; Kass, D. M.; Ehlmann, B. L.; Yung, Y. L.

    2015-12-01

    The evolution of the atmosphere on Mars is one of the most intriguing problems in the exploration of the Solar System, and the climate of Mars may have evolved from a warmer, wetter early state to the cold, dry current state. Because CO2 is the major constituent of Mars's atmosphere, its isotopic signatures offer a unique window to trace the evolution of climate on Mars. We derive new quantitative constraints on the amount of carbonate deposition and the atmospheric pressure of Mars through time, extending into the Noachian, ~3.8 Gyr before present. This determination is based on recent Mars Science Laboratory (MSL) isotopic measurements of Mars's atmosphere, recent orbiter, lander, and rover measurements of Mars's surface, and a newly identified mechanism (photodissociation of CO) that efficiently enriches the heavy carbon isotope. In particular, we find that escape via CO photodissociation on Mars has a fractionation factor of 0.6 and hence, photochemical escape processes can effectively enrich 13C in the Mars's atmosphere during the Amazonian. This enrichment is partially compensated by moderate carbonate precipitation during the late Noachian and/or Hesperian. The current atmospheric 13C/12C and rock and soil carbonate measurements indicate an early atmosphere with a surface pressure less than 1 bar. Only scenarios with large amounts of carbonate formation in open lakes permit higher values up to 1.8 bars. The evolutionary scenarios are fully testable with data from the MAVEN mission and further studies of the isotopic composition of carbonate in the Martian rock record through time.

  14. Tunable Diode Laser Measurements of Leaf-scale Carbon Isotope Discrimination and Ecosystem Respired Carbon and Oxygen Isotope Ratios in a Semi-arid Woodland

    NASA Astrophysics Data System (ADS)

    McDowell, N.; Chris, B.; Hanson, D.; Kern, S.; Meyer, C.; Pockman, W.; Powers, H.

    2005-12-01

    We present results and speculative interpretation of leaf-level carbon isotope discrimination and ecosystem respired carbon and oxygen isotope ratios from a semi-arid, C3/C4 woodland located in northern New Mexico, USA. Overstory leaf area index (LAI) is dominated by live juniper (Juniperus monosperma) trees with an LAI value of approximately 1.0 m2 per m2 ground area, and has a seasonally dynamic understory of mixed C3 forbs and C4 grasses and cacti, with a maximum LAI of 0.30 m2 per m2 ground area. Ecosystem respired carbon isotope ratios showed values characteristic of C3 dominated photosynthesis (Keeling plot intercepts of -35 to -22 per mil). Seasonal variation was typical of that found in wetter, C3 dominated forests, as was the dependence on climate (e.g. relationships with vapor pressure deficit, soil water content, and canopy conductance). Leaf-level carbon isotope discrimination of the junipers, measured by coupling a Li-Cor 6400 photosynthesis system to the TDL, provided discrimination-Ci and discrimination-vpd relationships consistent with measured ecosystem respired carbon isotope ratios. The oxygen isotope ratio of ecosystem respiration was dependent on rain water isotope composition, but was correlated with soil water content during rain-free periods. The cumulative effect of vapor pressure deficit after a rain event was tightly correlated with the oxygen isotope ratio of ecosystem respiration, suggesting the primary drivers are evaporative enrichment of soil water and perhaps nocturnal leaf enrichment. Instrument precision for carbon and oxygen isotope ratios of carbon dioxide is 0.06 to 0.18 per mil; however, overall precision is somewhat lower due to pressure and sampling effects.

  15. 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

  16. 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 CH4 and CO2 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 CH4 as the source of carbon and treat CO2 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 CH4/CO2/N2 atmosphere. UMR results suggest that CH4 contributes 70-100% of carbon in the aerosol, while HR results constrain the value from 94% to 100%. We also confirm that CO2 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.

  17. Variations in Os- and Mo-isotope compositions and trace element abundances across the Permo-Triassic boundary, Meishan, China: Proxy evidence for large-scale oceanic anoxia?

    NASA Astrophysics Data System (ADS)

    Cohen, A. S.; Saunders, A.; Zhang, H.; Li, J.

    2009-12-01

    We have carried out Os-isotope analyses, and major and trace element determinations, on samples from the Permo-Triassic section at Meishan B sections, adjacent to the GSSP, China, to assess environmental change at the P-Tr boundary (Bed 27) and the underlying main extinction horizon (Bed 25). Major and trace element abundances were determined by XRF on 38 samples from a 2.3-metre interval of limestone, shale and dolomitic marl from Bed 24a to Bed 32. Re, Os and Mo abundances, and Os-isotope compositions, were determined on a subset of 26 samples, predominantly dark-coloured mudrocks; new Mo-isotope data will be presented. Initial 187Os/188Os(t=250Ma) ranges from 0.3 to 2, with no obvious pattern of change up-section. The data thus provide no unambiguous evidence at Meishan for major perturbation of seawater 187Os/188Os in this region of Palaeotethys, at least at the scale of the sampling. This is unlike early Jurassic and end-Cretaceous boundary sections, and mid-Cretaceous OAE intervals, which record substantial shifts in seawater 187Os/188Os that clearly reflect the influence of LIP emplacement. Major changes in elemental abundances occur between Beds 24 and Bed 27, accompanying the documented excursion in d13C. Redox- and biologically-sensitive elements such as Cu, Ni, P, V and Zn show strong fluctuations in abundance throughout Bed 24, even when abundances are normalised using Al2O3 to minimise the effects of carbonate dilution. In the lower part of Bed 27, however, the Al2O3-normalised concentrations of these elements decrease by an order of magnitude, and remain consistently low in the overlying Triassic marls. The relative decreases in Re and Os abundances throughout Bed 27 are even more substantial. Whilst these decreases are partly an artefact of Al-normalisation, the changes are accompanied by large increases in ratios involving lithogenous elements such as REE, Nb, Zr, Th and Ti. The data thus record a dramatic change in the marine depositional

  18. 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

  19. Unusually high stable carbon isotopic values of methane from low organic carbon Mars analog hypersaline environments

    NASA Astrophysics Data System (ADS)

    Kelley, C. A.; Poole, J. A.; Tazaz, A.; Chanton, J.; Bebout, B.

    2010-12-01

    Motivated by the Mars rovers’ findings of past hypersaline environments and the discovery of methane in the atmosphere of Mars, we examined methanogenesis in hypersaline ponds in Baja California Sur and in the Don Edwards National Wildlife Refuge in northern California. Methane-rich bubbles were observed to be released from below gypsum/halite crusts in these environments. The stable carbon isotopic composition of these bubbles ranged from about -30 to -40 ‰. Methane with these relatively high isotopic values would typically be considered non-biogenic, however incubations of crust and sediments samples over time resulted in the production of methane. We therefore undertook a series of measurements aimed at understanding the isotopic composition of methane in these environments. The concentrations and isotopic composition of the particulate organic carbon (POC) in these environments were measured. POC content was low (relative to most methane-producing sedimentary environments), generally less than 1%, and always less than 2% of the total mass. The isotopic composition of the POC ranged from -13 to -22 ‰. To determine the substrates used by the methanogens, 13C-labeled trimethylamine (TMA), monomethylamine, methanol, acetate and bicarbonate were added to incubation vials and the methane produced was monitored for 13C content. The main substrates used by the methanogens in these hypersaline environments were the non-competitive substrates, the methylamines and methanol. When unlabeled, but isotopically known, TMA was added to incubation vials in varying concentrations, the isotopic composition of the methane produced also varied. Little, if any, difference in the isotopic composition between the TMA and methane occurred at the lowest TMA concentration (10 µM final concentration). The lowest methane δ13C values (and so greatest fractionation between methane and TMA) occurred when the most TMA was added (1000 µM final concentration). This change in the

  20. The source charge and isotopic abundances of cosmic rays with Z = 9-16 - A study using new fragmentation cross sections

    NASA Technical Reports Server (NTRS)

    Webber, W. R.; Gupta, M.; Soutoul, A.; Ferrando, P.

    1990-01-01

    The cosmic ray source charge and isotopic abundances for charges with Z = 9-16 are reexamined using newly measured fragmentation cross sections in a standard Galactic propagation model. Compared with earlier studies, the cosmic-ray data are now consistent with no excess of Si-29 and Si-30 in the source relative to the solar coronal abundances. The excess of Mg-25 and Mg-26 is now about 1 sigma or less relative to solar coronal isotopic abundances, leaving Ne-22 as the only clearly established neutron-rich isotopic excess in the cosmic ray source. Better estimates of the source abundances of elements obtained using the new cross sections permit the conclusion that high first ionization potential (FIP) elements have a wide spread of compositional differences in the cosmic-ray source relative to solar coronal abundances, whereas elements with a low FIP have a composition similar to the solar corona.

  1. Turnover of carbon isotopes in tail hair and breath CO2 of horses fed an isotopically varied diet.

    PubMed

    Ayliffe, L K; Cerling, T E; Robinson, T; West, A G; Sponheimer, M; Passey, B H; Hammer, J; Roeder, B; Dearing, M D; Ehleringer, J R

    2004-03-01

    Temporal stable isotope records derived from animal tissues are increasingly studied to determine dietary and climatic histories. Despite this, the turnover times governing rates of isotope equilibration in specific tissues following a dietary isotope change are poorly known. The dietary isotope changes recorded in the hair and blood bicarbonate of two adult horses in this study are found to be successfully described by a model having three exponential isotope pools. For horse tail hair, the carbon isotope response observed following a dietary change from a C3 to a C4 grass was consistent with a pool having a very fast turnover rate ( t1/2 approximately 0.5 days) that made up approximately 41% of the isotope signal, a pool with an intermediate turnover rate ( t1/2 approximately 4 days) that comprised approximately 15% of the isotope signal, and a pool with very slow turnover rate ( t1/2 approximately 140 days) that made up approximately 44% of the total isotope signal. The carbon isotope signature of horse blood bicarbonate, in contrast, had a different isotopic composition, with approximately 67% of the isotope signal coming from a fast turnover pool ( t1/2 0.2 days), approximately 17% from a pool with an intermediate turnover rate ( t1/2 approximately 3 days) and approximately 16% from a pool with a slow turnover rate ( t1/2 approximately 50 days). The constituent isotope pools probably correspond to one exogenous and two endogenous sources. The exogenous source equates to our fast turnover pool, and the pools with intermediate and slow turnover rates are thought to derive from the turnover of metabolically active tissues and relatively inactive tissues within the body, respectively. It seems that a greater proportion of the amino acids available for hair synthesis come from endogenous sources compared to the compounds undergoing cellular catabolism in the body. Consequently, the isotope composition of blood bicarbonate appears to be much more responsive to

  2. On the Stability and Abundance of Single Walled Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Hedman, Daniel; Reza Barzegar, Hamid; Rosén, Arne; Wågberg, Thomas; Andreas Larsson, J.

    2015-11-01

    Many nanotechnological applications, using single-walled carbon nanotubes (SWNTs), are only possible with a uniform product. Thus, direct control over the product during chemical vapor deposition (CVD) growth of SWNT is desirable, and much effort has been made towards the ultimate goal of chirality-controlled growth of SWNTs. We have used density functional theory (DFT) to compute the stability of SWNT fragments of all chiralities in the series representing the targeted products for such applications, which we compare to the chiralities of the actual CVD products from all properly analyzed experiments. From this comparison we find that in 84% of the cases the experimental product represents chiralities among the most stable SWNT fragments (within 0.2 eV) from the computations. Our analysis shows that the diameter of the SWNT product is governed by the well-known relation to size of the catalytic nanoparticles, and the specific chirality is normally determined by the product’s relative stability, suggesting thermodynamic control at the early stage of product formation. Based on our findings, we discuss the effect of other experimental parameters on the chirality of the product. Furthermore, we highlight the possibility to produce any tube chirality in the context of recent published work on seeded-controlled growth.

  3. On the Stability and Abundance of Single Walled Carbon Nanotubes

    PubMed Central

    Hedman, Daniel; Reza Barzegar, Hamid; Rosén, Arne; Wågberg, Thomas; Andreas Larsson, J.

    2015-01-01

    Many nanotechnological applications, using single-walled carbon nanotubes (SWNTs), are only possible with a uniform product. Thus, direct control over the product during chemical vapor deposition (CVD) growth of SWNT is desirable, and much effort has been made towards the ultimate goal of chirality-controlled growth of SWNTs. We have used density functional theory (DFT) to compute the stability of SWNT fragments of all chiralities in the series representing the targeted products for such applications, which we compare to the chiralities of the actual CVD products from all properly analyzed experiments. From this comparison we find that in 84% of the cases the experimental product represents chiralities among the most stable SWNT fragments (within 0.2 eV) from the computations. Our analysis shows that the diameter of the SWNT product is governed by the well-known relation to size of the catalytic nanoparticles, and the specific chirality is normally determined by the product’s relative stability, suggesting thermodynamic control at the early stage of product formation. Based on our findings, we discuss the effect of other experimental parameters on the chirality of the product. Furthermore, we highlight the possibility to produce any tube chirality in the context of recent published work on seeded-controlled growth. PMID:26581125

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

    PubMed

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

    2015-11-01

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

  5. 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

  6. Using Carbon Isotopes in Cenozoic Soil Carbonates to Quantify Primary Productivity from Mid-Latitude Regions

    NASA Astrophysics Data System (ADS)

    Caves, J. K.; Kramer, S. H.; Ibarra, D. E.; Chamberlain, C. P.

    2015-12-01

    The carbon isotope composition of pedogenic carbonates (δ13Ccarb) from paleosols has been extensively used as a proxy to estimate atmospheric pCO2 over the Phanerozoic. However, a number of other factors - including the concentration of plant-respired CO2 and the isotopic composition of both atmospheric and plant-respired carbon - influence the δ13C of pedogenic carbonates. For example, δ13Ccarb records from the mid-latitudes in central Asia and western North America show increasing trends in δ13Ccarb despite decreasing pCO2 during the late Cenozoic, which suggests that other factors play an important role in determining the isotopic composition of pedogenic carbonates. Instead, we suggest that these records are primarily recording changes in primary productivity rather than changes in atmospheric pCO2 and therefore propose a novel use of paleosol carbonate records to understand paleo-ecosystem dynamics. Here, we compile existing paleosol carbonate records, and present three new records from Wyoming, to estimate soil respiration and primary productivity in western North America during the Paleogene and early Neogene. We observe both an overall increase in δ13Ccarb after the early Eocene, and spatially heterogeneous δ13Ccarb values across western US basins. We combine this δ13Ccarb data with compilations of atmospheric pCO2 to estimate soil respiration and plant productivity. The long-term increase in δ13Ccarb indicates a decrease in plant productivity as conditions became more arid across much of the western US, congruent with both records of regional uplift and of global cooling. Furthermore, significant spatial heterogeneity in δ13Ccarb indicates that regional factors, such as the presence of paleolakes and/or local paleotopography may have provided a second-order control on local and regional productivity. Thus, our results provide a first-order estimate linking changes in primary productivity with regional tectonics and global climatic change.

  7. 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.

  8. 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.

  9. 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.

  10. Seasonal variation in stable carbon and nitrogen isotope values of bats reflect environmental baselines.

    PubMed

    Popa-Lisseanu, Ana G; Kramer-Schadt, Stephanie; Quetglas, Juan; Delgado-Huertas, Antonio; Kelm, Detlev H; Ibáñez, Carlos

    2015-01-01

    The stable carbon and nitrogen isotope composition of animal tissues is commonly used to trace wildlife diets and analyze food chains. Changes in an animal's isotopic values over time are generally assumed to indicate diet shifts or, less frequently, physiological changes. Although plant isotopic values are known to correlate with climatic seasonality, only a few studies restricted to aquatic environments have investigated whether temporal isotopic variation in consumers may also reflect environmental baselines through trophic propagation. We modeled the monthly variation in carbon and nitrogen isotope values in whole blood of four insectivorous bat species occupying different foraging niches in southern Spain. We found a common pattern of isotopic variation independent of feeding habits, with an overall change as large as or larger than one trophic step. Physiological changes related to reproduction or to fat deposition prior to hibernation had no effect on isotopic variation, but juvenile bats had higher δ13C and δ15N values than adults. Aridity was the factor that best explained isotopic variation: bat blood became enriched in both 13C and 15N after hotter and/or drier periods. Our study is the first to show that consumers in terrestrial ecosystems reflect seasonal environmental dynamics in their isotope values. We highlight the danger of misinterpreting stable isotope data when not accounting for seasonal isotopic baselines in food web studies. Understanding how environmental seasonality is integrated in animals' isotope values will be crucial for developing reliable methods to use stable isotopes as dietary tracers.

  11. [Microbial community abundance and diversity in typical karst ecosystem to indicate soil carbon cycle].

    PubMed

    Jin, Zhen-Jiang; Tang, Hua-Feng; Li, Min; Huang, Bing-Fu; Li, Qiang; Zhang, Jia-Yu; Li, Gui-Wen

    2014-11-01

    The soil microbial characteristics were detected to clarify their indications in organic carbon cycle in karst system. Soil samples from three karst types (saddle, depression and slop) at 0-10 cm, 10-20 cm and 20-30 cm layers were collected in the Yaji Karst Experimental Site, a typical karst ecosystem. The microbial diversity and abundance were assayed using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and fluorescence quantitative PCR. The data showed that the highest abundance of 16S rRNA and 18S rRNA were in depression with 1.32 x 10(11) copies x g(-1) and in saddle with 1.12 x 10(10) copies x g(-1), respectively. The abundance of 16S rRNA in saddle and depression decreased from top to bottom, while that of 18S rRNA in three karst forms decreased, which showed that the abundance changed consistently with soil organic carbon (SOC). The 3 diversity indices of 16S rRNA and 6 diversity indices of 18S rRNA increased from top to bottom in soil profiles of three karst forms. These results showed that microbial diversity changed conversely with the abundance and SOC in soil profile. It can be concluded that the abundance was more important than the diversity index for soil carbon cycle in karst system.

  12. 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

  13. Carbon, Nitrogen, and Oxygen Abundances of Selected Stars in the Hertzsprung Gap

    NASA Astrophysics Data System (ADS)

    Vanture, Andrew D.; Wallerstein, George

    1999-01-01

    The iron, carbon, nitrogen, and oxygen abundances for several stars whose characteristics place them in the Hertzsprung gap have been derived from high-resolution spectra. These stars were selected based on the fact that previous studies have shown them to have peculiar carbon, nitrogen, or lithium abundances considering their position in the Hertzsprung-Russell diagram. When combined with the lithium abundances derived by Wallerstein and coworkers, the carbon, nitrogen, and oxygen abundances indicate that the sample of stars can generally be broken into two categories-lower luminosity dwarfs or subgiants that are unmixed and higher luminosity mixed giants. Among the sample are two stars, HR 7606 and HR 8626, which previously have been identified by Bidelman as ``low-velocity CH stars.'' These stars show metallicities of [Fe/H]~-0.5 and solar abundances of carbon, nitrogen, and oxygen. The strength of the CH band in these stars is probably an artifact of a mild metal deficiency and the absence of substantial mixing of CN processed materials to the surface of the star rather than an unusual nucleosynthetic history.

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

    SciTech Connect

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

    2014-12-31

    Carbon stable isotopes can be used in characterization and monitoring of CO2 sequestration sites to track the migration of the CO2 plume and identify leakage sources, and to evaluate the chemical reactions that take place in the CO2-water-rock system. However, there are few tools available to incorporate stable isotope information into flow and transport codes used for CO2 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 module of TOUGHREACT was modified to include separate isotopic species of CO2 gas and dissolved inorganic carbon (CO2, CO32-, HCO3-,…). 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 CO2 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.

  15. 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 CO2 sequestration sites to track the migration of the CO2 plume and identify leakage sources, and to evaluate the chemical reactions that take place in the CO2-water-rock system. However, there are few tools available to incorporate stable isotope information into flow and transport codes used for CO2 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 module of TOUGHREACT was modifiedmore » to include separate isotopic species of CO2 gas and dissolved inorganic carbon (CO2, CO32-, HCO3-,…). 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 CO2 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

  16. 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.

  17. Sources of carbon isotope variation in kangaroo bone collagen and tooth enamel

    NASA Astrophysics Data System (ADS)

    Murphy, Brett P.; Bowman, David M. J. S.; Gagan, Michael K.

    2007-08-01

    The stable carbon isotopic composition (expressed as δ 13C) of herbivore remains is commonly used to reconstruct past changes in the relative abundance of C 4 versus C 3 grass biomass (C 4 relative abundance). However, the strength of the relationship between herbivore δ 13C and C 4 relative abundance in extant ecosystems has not been thoroughly examined. We determined sources of variation in δ 13C of bone collagen and tooth enamel of kangaroos ( Macropus spp.) collected throughout Australia by measuring δ 13C of bone collagen (779 individuals) and tooth enamel (694 individuals). An index of seasonal water availability, i.e. the distribution of rainfall in the C 4 versus C 3 growing seasons, was used as a proxy for C 4 relative abundance, and this variable explained a large proportion of the variation in both collagen δ 13C (68%) and enamel δ 13C (68%). These figures increased to 78% and 77%, respectively, when differences between kangaroo species were accounted for. Vegetation characteristics, such as woodiness and the presence of an open forest canopy, had no effect on collagen or enamel δ 13C. While there was no relationship between collagen δ 13C and kangaroo age at death, tooth enamel produced later in life, following weaning, was enriched in 13C by 3.5‰ relative to enamel produced prior to weaning. From the observed relationships between seasonal water availability and collagen and enamel δ 13C, enrichment factors ( ɛ∗) for collagen-diet and enamel-diet (post-weaning) were estimated to be 5.2‰ ± 0.5 (95% CI) and 11.7‰ ± 0.6 (95% CI), respectively. The findings of this study confirm that at a continental scale, collagen and enamel δ 13C of a group of large herbivores closely reflect C 4 relative abundance. This validates a fundamental assumption underpinning the use of isotopic analysis of herbivore remains to reconstruct changes in C 4 relative abundance.

  18. Preparation of starch and other carbon fractions from higher plant leaves for stable carbon isotope analysis.

    PubMed

    Wanek, W; Heintel, S; Richter, A

    2001-01-01

    The measurement of the carbon isotope composition of starch and cellulose still relies on chemical isolation of these water-insoluble plant constituents and subsequent elemental analysis by isotope ratio mass spectrometry (EA/IRMS) of the purified fractions, while delta(13)C values of low-molecular-weight organic compounds are now routinely measured by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Here we report a simple and reliable method for processing milligram quantities of dried plant material for the analysis of the carbon isotope composition of lipids, soluble sugars, starch and cellulose from the same sample. We evaluated three different starch preparation methods, namely (1) enzymatic hydrolysis by alpha-amylase, (2) solubilization by dimethyl sulfoxide (DMSO) followed by precipitation with ethanol, and (3) partial hydrolysis by HCl followed by precipitation of the resulting dextrins by ethanol. Starch recovery for three commercially available native starches (from potato, rice and wheat) varied from 48 to 81% for the techniques based on precipitation, whereas the enzymatic technique exhibited yields between 99 and 105%. In addition, the DMSO and HCl techniques introduced a significant (13)C fractionation of up to 1.9 per thousand, while the carbon isotope composition of native starches analyzed after enzymatic digestion did not show any significant difference from that of untreated samples. The enzymatic starch preparation method was then incorporated into a protocol for determination of delta(13)C signatures of lipids, soluble carbohydrates, starch and crude cellulose. The procedure is based on methanol/chloroform/water extraction of dried and ground leaf material. After recovery of the chloroform phase (lipid fraction), the methanol/water phase was deionized by ion exchange (soluble carbohydrate fraction) and the pellet treated with heat-stable alpha-amylase (starch fraction). The remaining insoluble material was subjected

  19. Carbon-isotopic composition of soil-respired carbon dioxide in static closed chambers at equilibrium.

    PubMed

    Mora, Germán; Raich, James W

    2007-01-01

    The carbon-isotopic composition (delta13C) of soil-respired CO2 has been employed to evaluate soil carbon-cycling processes and the contribution of soil CO2 emissions to canopy and tropospheric air. These evaluations can be successful only when accurate isotope values of soil-respired CO2 are available. Here, we tested the robustness of delta13C values of soil-respired CO2 obtained after long incubations in static closed chambers that were initially flushed with soil air. The rationale of this approach is that the equilibrium carbon-isotope values of chamber-headspace CO2 are theoretically equal to those of CO2 produced within the soil. Static closed chambers were installed in replicated grass monocultures, and measurements of headspace CO2 concentrations and delta13C values were performed at regular time intervals for 24 h in July 2005. The results revealed no significant effects of grass species on headspace CO2 concentrations or delta13C values (repeated measures analysis of variance (ANOVA), P>0.1). As predicted by theory, isotope values asymptotically approached equilibrium conditions, which in our experimental setting occurred after 10 h. This good match between model predictions and our results suggests that an accurate determination of delta13C values of CO2 produced within soils is obtained through the isotopic measurement of chamber-headspace CO2 once equilibrium conditions have been reached with the underlying soils. An additional advantage of this approach is that only one sample per chamber is required, which, combined with the low uncertainties of these measurements, facilitates the investigation of the spatial (landscape) variability of soil-respired CO2.

  20. Silver isotope variations in chondrites: Volatile depletion and the initial 107Pd abundance of the solar system

    NASA Astrophysics Data System (ADS)

    Schönbächler, M.; Carlson, R. W.; Horan, M. F.; Mock, T. D.; Hauri, E. H.

    2008-11-01

    The extinct radionuclide 107Pd decays to 107Ag (half-life of 6.5 Ma) and is an early solar system chronometer with outstanding potential to study volatile depletion in the early solar system. Here, a comprehensive Ag isotope study of carbonaceous and ordinary chondrites is presented. Carbonaceous chondrites show limited variations ( ɛ107Ag = -2.1 to +0.8) in Ag isotopic composition that correlate with the Pd/Ag ratios. Assuming a strictly radiogenic origin of these variations, a new initial 107Pd/ 108Pd of 5.9 (±2.2) × 10 -5 for the solar system can be deduced. Comparing the Pd-Ag and Mn-Cr data for carbonaceous chondrites suggests that Mn-Cr and Pd-Ag fractionation took place close to the time of calcium-aluminium-rich inclusion (CAI) and chondrule formation ˜4568 Ma ago. Using the new value for the initial 107Pd abundance, the revised ages for the iron-rich meteorites Gibeon (IVA, 8.5 +3.2/-4.6 Ma), Grant (IIIAB, 13.0 +3.5/-4.9 Ma) and Canyon Diablo (IA, 19.5 +24.1/-10.4 Ma) are consistent with cooling rates and the closure temperature of the Pd-Ag system. In contrast to carbonaceous chondrites, ordinary chondrites show large stable isotope fractionation of order of 1 permil for 107Ag/ 109Ag. This indicates that different mechanisms of volatile depletion were active in carbonaceous and ordinary chondrites. Nebular processes and accretion, as experienced by carbonaceous chondrites, did not led to significant Ag isotope fractionation, while the significant Ag isotope variations in ordinary chondrites are most likely inflicted by open system parent body metamorphism.

  1. First results on stable isotopes in fluid inclusions in cryogenic carbonates from Ural Mountains (Russia)

    NASA Astrophysics Data System (ADS)

    Dublyansky, Yuri; Luetscher, Mark; Spötl, Christoph; Töchterle, Paul; Kadebskaya, Olga

    2015-04-01

    Cryogenic cave carbonates (CCC) were found in a number of caves in the Ural. In contrast to the CCC previously reported from Central Europe, the Uralian CCC have larger sizes (up to 4-5 cm), which allows for more detailed petrographic and geochemical studies. CCCs from Uralian caves commonly show spherulitic shapes due to crystal splitting, supporting the model of calcite precipitating in a freezing water pond. δ18O values of studied CCCs are lower by 1 to 14 o compared to noncryogenic speleothems of Pleistocene and Holocene age from the same caves. δ18O and δ13C values are inversely correlated and typically show a fractionation between the core and the rim of individual samples. These trends are similar to those reported for CCCs from European caves (Žák et al., 2004). Petrographic observations performed on doubly polished, 100-150 micron-thick sections revealed abundant fluid inclusions, trapped between fibres of the spherulites. Petrographic relationships suggest that these inclusions are primary. The isotopic composition of water trapped in fluid inclusions in CCCs from two caves was analyzed following mechanical crushing at 120 °C, cryo-trapping of released water, pyrolysis on glassy carbon at 1400 °C (TC/EA device; Thermo), and analysis of the evolved gases on an isotope ratio mass spectrometer (Delta V Advantage; Thermo Fisher). The lack of peaks on the m/z 2 trace during the heating of the loaded crushing cell attests for a good sealing of the fluid inclusions. The measured δD values range between -136 o and -145 o VSMOW. The values measured in CCCs are more negative than the typical values of fluid inclusion water measured in the Holocene stalagmites from central Ural (-99 to -108 ). This shift toward more negative values is attributed to the isotopic fractionation between ice and water during the freezing. Reference: Žák et al., 2004, Chemical Geology, 2006, 119-136.

  2. 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

  3. 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

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

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

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

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

    NASA Astrophysics Data System (ADS)

    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 CH4 and CO2 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 CH4 as the source of carbon and treat CO2 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 CH4/CO2/N2 atmosphere. UMR results suggest that CH4 contributes 70-100% of carbon in the aerosol, while HR results constrain the value from 94% to 100%. We also confirm that CO2 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.

  6. 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.

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

    NASA Astrophysics Data System (ADS)

    Jost, H. J. H.; Stoltmann, T.; Stöbener, N.; Wapelhorst, E.; Mandic, M.; Aepfler, R.; Hinrichs, K. U.; Taubner, H.; Elvert, M.

    2015-12-01

    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.

  8. 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.

  9. Carbon isotopic evidence for methane hydrate instability during quaternary interstadials

    PubMed

    Kennett; Cannariato; Hendy; Behl

    2000-04-07

    Large (about 5 per mil) millennial-scale benthic foraminiferal carbon isotopic oscillations in the Santa Barbara Basin during the last 60,000 years reflect widespread shoaling of sedimentary methane gradients and increased outgassing from gas hydrate dissociation during interstadials. Furthermore, several large, brief, negative excursions (up to -6 per mil) coinciding with smaller shifts (up to -3 per mil) in depth-stratified planktonic foraminiferal species indicate massive releases of methane from basin sediments. Gas hydrate stability was modulated by intermediate-water temperature changes induced by switches in thermohaline circulation. These oscillations were likely widespread along the California margin and elsewhere, affecting gas hydrate instability and contributing to millennial-scale atmospheric methane oscillations.

  10. Stable carbon isotope values document how a Late Holocene expansion in grasslands impacted vertebrates in northwestern Madagascar

    NASA Astrophysics Data System (ADS)

    Crowley, B. E.; Samonds, K.

    2012-12-01

    Madagascar is home to some of the world's most distinctive plants and animals. Unfortunately, forest loss and habitat degradation has had a dramatic impact on both floral and faunal communities. Here we use carbon isotope values in radiocarbon-dated bones to examine how the vertebrate community at Anjohibe Cave, northwestern Madagascar, responded to a Late Holocene increase in C4 grass abundance. Our data demonstrate that major changes in the vegetation and animal community are recent phenomena at Anjohibe. Extinct lemurs and hippopotamuses were present until ca. 1500 years ago. These taxa relied exclusively on C3 resources. Locally extirpated fauna were present until 300 years ago. The majority of these species also relied on C3 resources. Their presence strongly suggests that the region surrounding the cave was more wooded than it is now, possibly as recently as 300 years ago. All introduced individuals are modern. Rats (Rattus sp.), shrews (Suncus murinus), and the giant frog Hoplobatrachus cf. tigrinus, have remarkably high carbon isotope values, implicating substantial ingestion of C4 foods. It is possible that grass abundance has increased dramatically in the past 100 years. Alternatively, opportunistically granivorous rats and shrews may selectively consume seeds from C4 grasses. In agreement with previous studies, stable isotope data reveal details of vegetation and faunal turnover in Northwestern Madagascar. Grasses have increased, forest dwelling species have vanished, and introduced taxa are exploiting a novel niche.

  11. Magnesium and calcium isotopic characteristics of Tengchong volcanics: Recycling of marine carbonates into the SE Tibetan mantle

    NASA Astrophysics Data System (ADS)

    Liu, F.; Zhang, Z.; Liu, Y.; Zhu, H.; Kang, J.; Zhang, C.; Sun, W.; Wang, G. Q.

    2015-12-01

    Post-collisional high-K calc-alkaline volcanic rocks are widely distributed in Tengchong in the southeastern margin of Tibetan Plateau. Previous considerable petrological and Sr-Nd-Pb isotopic researches undoubtedly indicate that the mantle beneath Tengchong is heterogeneous and enriched. However, the genesis of such a kind of mantle is still poor understood and needs more constrains. One of the key points lead to the answer to this question is that, is there any recycled carbonate involved? Therefore, Magnesium and calcium isotopic compositions of mantle-derived volcanics should be investigated because they are good candidates to be potentially used to trace recycling of ancient marine carbonates into the mantle. In this study, we report high-precision Mg and Ca isotopic compositions for calc-alkaline volcanic rocks in Tengchong. These volcanic rocks show significantly lighter δ26Mg values (-0.44 to -0.36‰) than the mantle value (-0.25±0.07‰). Similarly, they display lighter δ44Ca values (0.65-0.80‰) than the mantle value (1.05±0.04‰). Because neither δ26Mg nor δ44Ca are correlated with SiO2 (50.8-61.6 wt.%) contents, and there is no relationships between δ26Mg or δ44Ca and typical trace element abundance ratios (e.g. Sm/Yb, Ba/Y), we conclude that magma differentiation or partial melting would lead to limited Mg and Ca isotopes fractionation. Thus, low δ26Mg and δ44Ca signatures of Tengchong volcanic rocks probably reflect that the δ26Mg and δ44Ca characteristics of the underneath mantle source, and are resulted from adding ancient marine carbonates into the primitive mantle which has low Mg and Ca isotopic compositions. Our model simulation using a two end-member mixing between Mg-Ca isotopic compositions of primitive mantle and ancient marine carbonate indicates that carbonates involved in the mantle source is mainly dolostone with minor limestone. Combined with the geotectonic evolution history in Tengchong, we propose that the enriched

  12. 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.

  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. 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.

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

    PubMed

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

    2016-08-01

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

  16. Microfacies Analyses and Carbon Isotope Studies on Lower Triassic Microbialites from Armenia

    NASA Astrophysics Data System (ADS)

    Friesenbichler, Evelyn; Baud, Aymon; Krystyn, Leopold; Sahakyan, Lilit; Richoz, Sylvain

    2016-04-01

    After the end-Permian mass extinction the upper Paleozoic skeletal carbonate factory was abruptly replaced by a non-skeletal carbonate factory and Permian-Triassic boundary microbialites (PTBMs) were flourishing. These PTBMs were abundant in low-latitude shallow-marine carbonate shelves in central Tethyan continents and were present during at least four events in the Lower Triassic. The investigated PTBMs from three different sites in southern Armenia were formed in a distal open marine setting on a pelagic carbonate ramp. They grew during two microbial growth phases in Griesbachian times, whereas the microbialites from the first microbial growth phase co-occur with calcium carbonate crystal fans (CCFs). The microbes formed predominantly thrombolites that vary in size between 5 cm to 1.5 m. The biggest thrombolite has a cone-shaped build-up geometry and an asymmetrical growth, which indicates the influence of a steady bottom current. It consists of numerous thrombolite domes with a top head diameter of up to 8 m width and a total height of up to 12 m. The microbialites are surrounded by a bioclastic wackestone that mainly contains ostracods, foraminifers, microgastropods, thin-shelled bivalves and sponges. Carbon isotope studies were performed on both the microbialites and the surrounding sediment. A comparison between the δ13C values of the microbialites and the surrounding sediment revealed that there is little difference (<0.4‰) between these values in the microbialites that formed during the second microbial growth phase. In contrast, the microbialites and CCFs from the first microbial growth phase show differences in the δ13C values of up to 2.3‰ , which could be due to microbial activity.

  17. Carbon isotope systematics of individual hydrocarbons in hydrothermal petroleum from Escanaba Trough, Northeastern Pacific Ocean

    USGS Publications Warehouse

    Simoneit, B.R.T.; Schoell, M.; Kvenvolden, K.A.

    1997-01-01

    We submitted individual aliphatic and polycyclic aromatic hydrocarbons in samples of hydrothermal petroleum from Escanaba trough to compound specific isotope analysis to trace their origins. The carbon isotope compositions of the alkanes and polycyclic aromatic hydrocarbons (means -27.5 and -24.7%, respectively) reflect a primarily terrestrial organic matter source.We submitted individual aliphatic and polycyclic aromatic hydrocarbons in samples of hydrothermal petroleum from Escanaba Trough to compound specific isotope analysis to trace their origins. The carbon isotope compositions of the alkanes and polycyclic aromatic hydrocarbons (means -27.5 and -24.7 per mill, respectively) reflect a primarily terrestrial organic matter source.

  18. Theoretical effect of diffusion on isotopic abundance ratios in rocks and associated fluids

    USGS Publications Warehouse

    Senftle, F.E.; Bracken, J.T.

    1955-01-01

    Diffusion is considered as a possible process of isotope fractionation taking place throughout geologic time. Both diffusion in solids and diffusion in liquids are taken as possible mechanisms, the latter being more important. Arguments are presented to show that if significant fractionation takes place within a crystal by outward diffusion under solid-state conditions, enrichment will be evident only in elements of minor concentration. Similar conclusions are inferred for solid-state diffusion across a boundary or for diffusion in liquids. No isotopic enrichment can be expected in relatively large bodies of diffusion transported material. Although the necessary data to confirm these conclusions are scanty, it seems worth while to undertake further work in this direction. ?? 1955.

  19. 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

  20. The abundance and excitation of the carbon chains in interstellar molecular clouds

    NASA Technical Reports Server (NTRS)

    Bujarrabal, V.; Guelin, M.; Morris, M.; Thaddeus, P.

    1981-01-01

    Emission lines from the carbon chains HC3N, HC5N, HC7N and HC9N were observed at 3 mm, 7 mm, and 1.4 cm in a number of dark clouds, Orion A and IRC(plus)10216. Non-LTE models were constructed to describe excitation and column densities. Component models for the Taurus dark cloud TMC-1 suggested that relative molecular abundances do not vary substantially along the cloud ridge, whereas the H2 density does by a factor of three. Data available for other dark clouds showed that the decrease in abundance with length from one carbon chain to the next is nearly constant, being close to 2.3. The decline in carbon chain abundance with length is steeper in Orion KL than in dark clouds by a factor of approximately four. Abundance ratios derived for the carbon star IRC(plus)10216 are uncertain, due to difficulties in modeling excitation rates in this environment.

  1. 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.

  2. Influence of Purple Sulfur Bacteria on the biogeochemistry of Carbon and Sulfur Isotopes in Crystal Lake, OH

    NASA Astrophysics Data System (ADS)

    Meyer, A.; Nichols, D. L.; Cheng, S.

    2013-12-01

    Crystal Lakes are a series of four interconnected mesotrophic, moulin-induced glacial lakes in west-central Ohio. The study site, Main Lake (a.k.a. Crystal Lake), is the largest and deepest lake among them. It is about 5 ha with a maximum depth of 11.9 meters and a mean depth of 3.8 meters. Thermal stratification develops during the warmer months. Photosynthesis, which preferentially uptakes lighter isotopes, is the primary pathway for carbon and sulfur isotope fractionation in natural waters. Photosynthesizers present at Crystal Lake include green algae, diatoms, cyanobacteria, and purple sulfur bacteria (PSB). Phytoplankton growth is limited by nutrient availability, influencing the extent of fractionation. Purple sulfur bacteria (PSB) utilize sulfide as an electron donor instead of water. The layer of concentrated PSB population exists between oxic and anoxic water in lakes where sufficient light and sulfide are present. These bacteria impact the levels of several sulfur compounds and isotopic composition within lake systems by oxidizing sulfide to sulfate. Field parameters collected in warmer months show turbidity and chlorophyll peaks around 6 m with variations caused by temperature, light, and nutrient availability. The dissolved oxygen minimum and the redox and sulfate maxima generally correspond with the turbidity and chlorophyll peaks, indicating the presence of a PSB layer. This layer occurs at the boundary between the metalimnion and hypolimnion. Sulfide concentrations increased from a maximum of 0.02 mg/L in May to a maximum of 9.25 mg/L in August. In May sulfide was only found at 10.4 m and below while in August it was present at 6 m and below. Sulfate values remain relatively constant with a maximum at the layer of PSB, then decline with depth where Sulfide is abundant. δ13C-DIC values peak at 6 m corresponding with the layer of PSB. This peak may be due to the influence of PSB on carbon isotope fractionation. The carbon isotope composition of

  3. 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). The calibration lines of both experimental approaches overlap and agree in the slopes with theoretical estimates and with other calibration experiments in which carbonates were reacted with phosphoric acid at temperatures above 70 °C. Our study suggests a universal Δ47-T calibration (T in K, Δ47 in ‰):

  4. Abundance anomalies of carbon and nitrogen in the IUE spectra of Algol-type interacting binaries

    NASA Technical Reports Server (NTRS)

    Mccluskey, Carolina P. S.

    1990-01-01

    There are two primary ways in which the products of nucleosynthesis in stellar interiors may appear at the surface of a star. These are mixing and/or loss of the original unburned stellar envelope. In interacting binaries, overflow can contribute dramatically to envelope loss. The simplest abundance anomalies to be expected from nuclear burning of hydrogen, helium, or carbon would be under or over abundances H, He, C, O, Ne, and Mg. In addition, it is expected that carbon is initially severely depleted, while nitrogen is enhanced during hydrogen burning via the CNO cycle in stars above two solar masses. Other, more subtle anomalies are also expected, and elements heavier than magnesium can be created during very late evolution by nuclear burning in massive stars. Consequently, it is expected that abundance anomalies of various kinds should occur in interacting binaries where one or both stars have lost significant amounts of mass.

  5. Effects of environmental and biotic factors on carbon isotopic fractionation during decomposition of soil organic matter.

    PubMed

    Wang, Guoan; Jia, Yufu; Li, Wei

    2015-06-09

    Decomposition of soil organic matter (SOM) plays an important role in the global carbon cycle because the CO2 emitted from soil respiration is an important source of atmospheric CO2. Carbon isotopic fractionation occurs during SOM decomposition, which leads to (12)C to enrich in the released CO2 while (13)C to enrich in the residual SOM. Understanding the isotope fractionation has been demonstrated to be helpful for studying the global carbon cycle. Soil and litter samples were collected from soil profiles at 27 different sites located along a vertical transect from 1200 to 4500 m above sea level (a.s.l.) in the south-eastern side of the Tibetan Plateau. Their carbon isotope ratios, C and N concentrations were measured. In addition, fiber and lignin in litter samples were also analyzed. Carbon isotope fractionation factor (α) during SOM decomposition was estimated indirectly as the slope of the relationship between carbon isotope ratios of SOM and soil C concentrations. This study shows that litter quality and soil water play a significant role in isotope fractionation during SOM decomposition, and the carbon isotope fractionation factor, α, increases with litter quality and soil water content. However, we found that temperature had no significant impact on the α variance.

  6. Effects of environmental and biotic factors on carbon isotopic fractionation during decomposition of soil organic matter

    PubMed Central

    Wang, Guoan; Jia, Yufu; Li, Wei

    2015-01-01

    Decomposition of soil organic matter (SOM) plays an important role in the global carbon cycle because the CO2 emitted from soil respiration is an important source of atmospheric CO2. Carbon isotopic fractionation occurs during SOM decomposition, which leads to 12C to enrich in the released CO2 while 13C to enrich in the residual SOM. Understanding the isotope fractionation has been demonstrated to be helpful for studying the global carbon cycle. Soil and litter samples were collected from soil profiles at 27 different sites located along a vertical transect from 1200 to 4500 m above sea level (a.s.l.) in the south-eastern side of the Tibetan Plateau. Their carbon isotope ratios, C and N concentrations were measured. In addition, fiber and lignin in litter samples were also analyzed. Carbon isotope fractionation factor (α) during SOM decomposition was estimated indirectly as the slope of the relationship between carbon isotope ratios of SOM and soil C concentrations. This study shows that litter quality and soil water play a significant role in isotope fractionation during SOM decomposition, and the carbon isotope fractionation factor, α, increases with litter quality and soil water content. However, we found that temperature had no significant impact on the α variance. PMID:26056012

  7. Effects of environmental and biotic factors on carbon isotopic fractionation during decomposition of soil organic matter

    NASA Astrophysics Data System (ADS)

    Wang, Guoan; Jia, Yufu; Li, Wei

    2015-06-01

    Decomposition of soil organic matter (SOM) plays an important role in the global carbon cycle because the CO2 emitted from soil respiration is an important source of atmospheric CO2. Carbon isotopic fractionation occurs during SOM decomposition, which leads to 12C to enrich in the released CO2 while 13C to enrich in the residual SOM. Understanding the isotope fractionation has been demonstrated to be helpful for studying the global carbon cycle. Soil and litter samples were collected from soil profiles at 27 different sites located along a vertical transect from 1200 to 4500 m above sea level (a.s.l.) in the south-eastern side of the Tibetan Plateau. Their carbon isotope ratios, C and N concentrations were measured. In addition, fiber and lignin in litter samples were also analyzed. Carbon isotope fractionation factor (α) during SOM decomposition was estimated indirectly as the slope of the relationship between carbon isotope ratios of SOM and soil C concentrations. This study shows that litter quality and soil water play a significant role in isotope fractionation during SOM decomposition, and the carbon isotope fractionation factor, α, increases with litter quality and soil water content. However, we found that temperature had no significant impact on the α variance.

  8. 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

  9. The Suess Effect and Additional Impacts on the Carbon Isotope Composition of a Belizean Coral

    NASA Astrophysics Data System (ADS)

    Greer, L.; Bunn, S.; Humston, R.; Swart, P. K.; Curran, H.; Rose, L. E.

    2011-12-01

    Recent work has shown that the geochemistry of coral skeletons can reflect large-scale changes in the ocean carbon isotope budget as influenced by the anthropogenic influx of fossil fuel carbon to the atmosphere (the Suess Effect). Yet not all coral carbon records reflect just atmospheric controls on carbon. This study assesses the relative influence of the Suess Effect on carbon chemistry within a Belizean Montastrea faveolota colony and interprets deviations from the Suess Effect signal. The coral sample used for this study was collected off Wee Wee Caye, in South-Central Belize offshore of the Sittee River, Stann Creek District in 2003. Coral carbonate was sampled at an average resolution of 15 samples per coral year. Carbon isotope data from the Belizean coral were compared with mean annual carbon isotope data from Atlantic corals in a study by Swart et. al (2010) to analyze the relative contribution of the Suess Effect and competing controls on the carbon isotope composition of Belizean waters. The observed pattern in the Belize coral suggested two distinct trends in carbon isotopic composition, and segmented regression analysis indicated a significant breakpoint occurs in this record in approximately 1965. Deforestation rates in Belize after the 1960's have been almost double that for the rest of Central America (2.3% vs. 1.2% annually) corresponding with a general shift from rural farming to large scale agriculture in Belize. Consequently, increased rates of deforestation in Belize may have been an important factor in carbon isotope budgets of the area over the last several decades. Compared with data averaged from Atlantic coral samples, annual carbon isotope values in Belizean coral declined more rapidly since the 1960's. We attribute this sharper decline in the Belizean coral to enhanced influx of terrestrial 'light' organic carbon to the reef over the study period.

  10. A molecular organic carbon isotope record of miocene climate changes

    SciTech Connect

    Schoell, M. ); Schouten, S.; Sinninghe Damste', J.S.; Leeuw, J.W. de ); Summons, R.E. )

    1994-02-25

    The difference in carbon-13 ([sup 13]C) contents of hopane and sterane biomarkers in the Monterey formation (Naples Beach, California) parallels the Miocene inorganic record of the change in [sup 18]O ([delta][sup 18]O), reflecting the Miocene evolution from a well-mixed to a highly stratified photic zone (upper 100 meters) in the Pacific. Steranes ([delta][sup 13]C = 25.4 [+-] 0.7 per mil versus the Pee Dee belemnite standard) from shallow photic-zone organisms do not change isotopically throughout the Miocene. In contrast, sulfur-bound C[sub 35] hopanes (likely derived from bacterial plankton living at the base of the photic zone) have systematically decreasing [sup 13]C concentrations in Middle and Late Miocene samples ([delta][sup 13]C = 29.5 to [minus]31.5 per mil), consistent with the Middle Miocene formation of a carbon dioxide-rich cold water mass at the base of the photic zone.

  11. Construction of confidence regions for isotopic abundance patterns in LC/MS data sets for rigorous determination of molecular formulas.

    PubMed

    Ipsen, Andreas; Want, Elizabeth J; Ebbels, Timothy M D

    2010-09-01

    It has long been recognized that estimates of isotopic abundance patterns may be instrumental in identifying the many unknown compounds encountered when conducting untargeted metabolic profiling using liquid chromatography/mass spectrometry. While numerous methods have been developed for assigning heuristic scores to rank the degree of fit of the observed abundance patterns with theoretical ones, little work has been done to quantify the errors that are associated with the measurements made. Thus, it is generally not possible to determine, in a statistically meaningful manner, whether a given chemical formula would likely be capable of producing the observed data. In this paper, we present a method for constructing confidence regions for the isotopic abundance patterns based on the fundamental distribution of the ion arrivals. Moreover, we develop a method for doing so that makes use of the information pooled together from the measurements obtained across an entire chromatographic peak, as well as from any adducts, dimers, and fragments observed in the mass spectra. This greatly increases the statistical power, thus enabling the analyst to rule out a potentially much larger number of candidate formulas while explicitly guarding against false positives. In practice, small departures from the model assumptions are possible due to detector saturation and interferences between adjacent isotopologues. While these factors form impediments to statistical rigor, they can to a large extent be overcome by restricting the analysis to moderate ion counts and by applying robust statistical methods. Using real metabolic data, we demonstrate that the method is capable of reducing the number of candidate formulas by a substantial amount, even when no bromine or chlorine atoms are present. We argue that further developments in our ability to characterize the data mathematically could enable much more powerful statistical analyses.

  12. Stable isotope natural abundance of nitrous oxide emitted from Antarctic tundra soils: effects of sea animal excrement depositions.

    PubMed

    Zhu, Renbin; Liu, Yashu; Li, Xianglan; Sun, Jianjun; Xu, Hua; Sun, Liguang

    2008-11-01

    Nitrous oxide (N2O), a greenhouse gas, is mainly emitted from soils during the nitrification and denitrification processes. N2O stable isotope investigations can help to characterize the N2O sources and N2O production mechanisms. N2O isotope measurements have been conducted for different types of global terrestrial ecosystems. However, no isotopic data of N2O emitted from Antarctic tundra ecosystems have been reported although the coastal ice-free tundra around Antarctic continent is the largest sea animal colony on the global scale. Here, we report for the first time stable isotope composition of N2O emitted from Antarctic sea animal colonies (including penguin, seal and skua colonies) and normal tundra soils using in situ field observations and laboratory incubations, and we have analyzed the effects of sea animal excrement depositions on stable isotope natural abundance of N2O. For all the field sites, the soil-emitted N2O was 15N- and 18O-depleted compared with N2O in local ambient air. The mean delta values of the soil-emitted N2O were delta15N = -13.5 +/- 3.2 per thousand and delta18O = 26.2 +/- 1.4 per thousand for the penguin colony, delta15N = -11.5 +/- 5.1 per thousand and delta18O = 26.4 +/- 3.5 per thousand for the skua colony and delta15N = -18.9 +/- 0.7 per thousand and delta18O = 28.8 +/- 1.3 per thousand for the seal colony. In the soil incubations, the isotopic composition of N2O was measured under N2 and under ambient air conditions. The soils incubated under the ambient air emitted very little N2O (2.93 microg N2O--N kg(-1)). Under N2 conditions, much more N2O was formed (9.74 microg N2O--N kg(-1)), and the mean delta15N and delta18O values of N2O were -19.1 +/- 8.0 per thousand and 21.3 +/- 4.3 per thousand, respectively, from penguin colony soils, and -17.0 +/- 4.2 per thousand and 20.6 +/- 3.5 per thousand, respectively, from seal colony soils. The data from in situ field observations and laboratory experiments point to denitrification as the

  13. Determination of carbon isotopic measurement conditions for ceramide in skin using gas chromatography-combustion-isotope ratio mass spectrometry.

    PubMed

    Haraguchi, Hiroyuki; Yamada, Keita; Miyashita, Rumiko; Aida, Kazuhiko; Ohnishi, Masao; Gilbert, Alexis; Yoshida, Naohiro

    2014-01-01

    The ceramide (Cer) content of skin and glucosylceramide (GlcCer) intake affect skin moisture conditions, but their mutual relation in skin remains unclear. For clarification of that mutual relation, carbon stable isotopes ((12)C and (13)C) are useful as a tracer. However, carbon isotopic measurement has not been applied to the study of clarifying their skin moisturizing effects. Therefore, we used gas chromatography / combustion / isotope ratio mass spectrometry (GC-C-IRMS) to ascertain the appropriate conditions for carbon isotopic measurements using synthesized Cer (SCer) in substitution for very low concentrations of Cer in skin. SCer was derivatized to trimethylsilylated SCer (TMS-SCer) quantitatively using N-trimethylsilylimidazole (TMSI) depending on the amount of SCer. The derivatization rates were 75-85%. Excess TMSI was removed using three cycles of hexane-water distribution. Under these conditions, carbon isotopic measurements of TMS-SCer conducted using GC-C-IRMS showed high repeatability and good inter-day variation (S.D. < 0.3‰). The carbon stable isotope ratio value (δ(13)C) of SCer calculated using a mass balance equation was compared with δ(13)C of underivatized SCer, which was regarded as the actual δ(13)C of SCer obtained using sealed tube combustion method. The difference between the calculated δ(13)C of SCer and δ(13)C of the underivatized SCer depended on the TMSI reagent supplier and on the number of hydroxyl groups to be derivatized in SCer. For accurate δ(13)C of Cer in skin using GC-C-IRMS, the measured δ(13)C of a target TMS-Cer must be calculated using a correction factor representing the difference in δ(13)C of underivatized standard SCer from that of TMS-standard SCer having a structure resembling that of the target Cer in skin. In addition, we show that the same lot of TMSI reagent from a specific supplier must be used throughout the experiments.

  14. Carbon and hydrogen isotope fractionation of benzene and toluene during hydrophobic sorption in multistep batch experiments.

    PubMed

    Imfeld, G; Kopinke, F-D; Fischer, A; Richnow, H-H

    2014-07-01

    The application of compound-specific stable isotope analysis (CSIA) for evaluating degradation of organic pollutants in the field implies that other processes affecting pollutant concentration are minor with respect to isotope fractionation. Sorption is associated with minor isotope fractionation and pollutants may undergo successive sorption-desorption steps during their migration in aquifers. However, little is known about isotope fractionation of BTEX compounds after consecutive sorption steps. Here, we show that partitioning of benzene and toluene between water and organic sorbents (i.e. 1-octanol, dichloromethane, cyclohexane, hexanoic acid and Amberlite XAD-2) generally exhibits very small carbon and hydrogen isotope effects in multistep batch experiments. However, carbon and hydrogen isotope fractionation was observed for the benzene-octanol pair after several sorption steps (Δδ(13)C=1.6 ± 0.3‰ and Δδ(2)H=88 ± 3‰), yielding isotope fractionation factors of αC=1.0030 ± 0.0005 and αH=1.195 ± 0.026. Our results indicate that the cumulative effect of successive hydrophobic partitioning steps in an aquifer generally results in insignificant isotope fractionation for benzene and toluene. However, significant carbon and hydrogen isotope fractionation cannot be excluded for specific sorbate-sorbent pairs, such as sorbates with π-electrons and sorbents with OH-groups. Consequently, functional groups of sedimentary organic matter (SOM) may specifically interact with BTEX compounds migrating in an aquifer, thereby resulting in potentially relevant isotope fractionation.

  15. Stable carbon isotopic apportionment of individual PAH in sediments from marine and estuarine environments

    SciTech Connect

    O`Malley, V.P.; Abrajano, T.A. Jr.; Hellou, J.

    1995-12-31

    Much interest has recently focused on the quantitative apportionment of multiple sources of organic contaminants in natural aquatic systems. Polycyclic aromatic hydrocarbons (PAH) are of great interest in this regard because in addition to their suspected toxic and carcinogenic properties, they also have a wide range of potential natural and anthropogenic sources. Here we present the results of a study where the primary source inputs of PAH to sediments of a Harbor and Estuary are quantitatively assessed using a combination of molecular abundance and carbon isotope measurements of individual (4- and 5-ring) PAH. Mass balance calculations using a simple two-component mixing model show that approximately 50 to 80% of the PAH input to the Harbour sediments is of combustion origin, and likely dominated by vehicular emissions. Direct petrogenic contribution, possibly crankcase oil, accounts for the remaining 20 to 50% of the total PAH input. PAH inputs to the Estuary seemed to be predominately of wood combustion origin but the presence of an unidentified isotopically depleted PAH source was also apparent.

  16. 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.

  17. A chart of cosmic ray isotopes. [showing radioactive decay, abundance and nucleosynthesis

    NASA Technical Reports Server (NTRS)

    Waddington, C. J.

    1975-01-01

    A chart has been prepared that lists some of the properties relevant to cosmic ray studies of all the significant nuclides between lithium and nickel. On this chart there are shown all the possible decays that might be of interest in the unique conditions experienced by cosmic ray nuclei, various abundance figures and the probable nucleosynthesis processes of origin.

  18. 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.

  19. Carbon isotope separation and molecular formation in laser-induced plasmas by laser ablation molecular isotopic spectrometry.

    PubMed

    Dong, Meirong; Mao, Xianglei; Gonzalez, Jhanis J; Lu, Jidong; Russo, Richard E

    2013-03-05

    Laser ablation molecular isotopic spectrometry (LAMIS) recently was reported for rapid isotopic analysis by measuring molecular emission from laser-induced plasmas at atmospheric pressure. This research utilized the LAMIS approach to study C2 molecular formation from laser ablation of carbon isotopic samples in a neon gas environment at 0.1 MPa. The isotopic shift for the Swan system of the C2 Δν = 1 band was chosen for carbon isotope analysis. Temporal and spatial resolved measurements of (12)C2, (12)C(13)C, and (13)C2 show that C2 forms from recombination reactions in the plasma. A theoretical simulation was used to determine the temperature from the molecular bands and to extract the isotopic ratio of (12)C/(13)C derived from (12)C2, (12)C(13)C, and (13)C2. Our data show that the ratio of (12)C/(13)C varies with time after the laser pulse and with distance above the sample. (12)C/(13)C deviates from the nominal ratio (2:1) at early times and closest to the sample surface. These measurements provide understanding of the chemical processes in the laser plasma and analytical improvement using LAMIS.

  20. 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

  1. 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

  2. sup 13 C and sup 18 O isotopic disequilibrium in biological carbonates: II. In vitro simulation of kinetic isotope effects

    SciTech Connect

    McConnaughey, T. )

    1989-01-01

    Biological carbonates are built largely from CO{sub 2}, which diffuses across the skeletogenic membrane and reacts to form HCO{sub 3}{sup {minus}}. Kinetic discrimination against the heavy isotopes {sup 18}O and {sup 13}C during CO{sub 2} hydration and hydroxylation apparently causes most of the isotopic disequilibrium observed in biological carbonates. These kinetic isotope effects are expressed when the extracytosolic calcifying solution is thin and alkaline, and HCO{sub 3}{sup {minus}} precipitates fairly rapidly as CaCO{sub 3}. In vitro simulation of the calcifying environment produced heavy isotope depletions qualitatively similar to, but somewhat more extreme than, those seen in biological carbonates. Isotopic equilibration during biological calcification occurs through CO{sub 2} exchange across the calcifying membrane and by admixture ambient waters (containing HCO{sub 3}{sup {minus}}) into the calcifying fluids. Both mechanisms tend to produce linear correlations between skeletal {delta}{sup 13}C and {delta}{sup 18}O.

  3. Carbon, nitrogen, and oxygen abundances in main-sequence stars. II 20 F and G stars

    NASA Astrophysics Data System (ADS)

    Clegg, R. E. S.; Tomkin, J.; Lambert, D. L.

    1981-11-01

    High-resolution Reticon spectra of red and near-infrared C I, N I, and O I lines have been analyzed to determine C, N, and O abundances in a sample of 20 F and G main-sequence stars. Their iron abundances, which have been determined from analysis of additional Reticon spectra of red Fe I lines, cover the Fe/H range from -0.9 to 0.4. Sulfur abundances have also been obtained. It is found that the variations of the carbon and sulfur abundances closely follow those of iron. The oxygen abundance varies much more slowly than iron (O/Fe = 0.48 (+ or - 0.07) Fe/H). This result confirms an earlier conclusion that oxygen is overabundant in more metal-deficient stars. The behavior of the nitrogen abundance appears to be similar to that of iron (N/Fe = 0.0 + or - 0.2). However, the unavailability of nitrogen abundances for the most metal-deficient stars in the sample makes this result less certain than the results for the other elements. These results are discussed in the light of current theories of stellar nucleosynthesis of the elements.

  4. 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.

  5. Concentration and isotopic composition of carbon and sulfur in apollo 11 lunar samples.

    PubMed

    Kaplan, I R; Smith, J W

    1970-01-30

    The concentration of carbon and sulfur in six samples ranged between 20 to 200 and 650 to 2300 parts per million, respectively. Carbon was present in gaseous, volatilizable, and nonvolatile forms, and terrestrial contaminants were recognized. Sulfur appeared to exist only as acid-volatile sulfide. The bulk fines contain a high concentration of carbon and a low concentration of sulfur. They are always enriched in the heavier isotope carbon-13 or sulfur-34. The fine-grained basaltic rocks show the reverse relation; lowest carbon, highest sulfide concentrations, and no apparent enrichment in heavy isotopes. The breccias are of intermediate composition.

  6. 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

  7. 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

  8. Stable carbon isotope evidence for nitrogenous fertilizer impact on carbonate weathering in a small agricultural watershed.

    PubMed

    Brunet, F; Potot, C; Probst, A; Probst, J-L

    2011-10-15

    The isotopic signature of Dissolved Inorganic Carbon (DIC), δ(13)C(DIC), has been investigated in the surface waters of a small agricultural catchment on calcareous substratum, Montoussé, located at Auradé (south-west France). The Montoussé catchment is subjected to intense farming (wheat/sunflower rotation) and a moderated application of nitrogenous fertilizers. During the nitrification of the NH(4)(+), supplied by fertilization, nitrate and H(+) ions are produced in the soil. This anthropogenic acidity is combined with the natural acidity due to carbonic acid in weathering processes. From an isotopic point of view, with 'natural weathering', using carbonic acid, δ(13)C(DIC) is intermediate between the δ(13)C of soil CO(2) produced by organic matter oxidation and that of the carbonate rocks, while it has the same value as the carbonates when carbonic acid is substituted by another acid like nitric acid derived from nitrogen fertilizer. The δ(13)C(DIC) values range from -17.1‰ to -10.7‰ in Montoussé stream waters. We also measured the δ(13)C of calcareous molassic deposits (average -7.9‰) and of soil organic carbon (between -24.1‰ and -26‰) to identify the different sources of DIC and to estimate their contribution. The δ(13) C(DIC) value indicates that weathering largely follows the carbonic acid pathway at the springs (sources of the stream). At the outlet of the basin, H(+) ions, produced during the nitrification of N-fertilizer, also contribute to weathering, especially during flood events. This result is illustrated by the relationship between δ(13)C(DIC) and the molar ratio NO(3)(-)/(Ca(2+) + Mg(2+)). Consequently, when the contribution of nitrate increases, the δ(13)C(DIC) increases towards the calcareous end-member. This new isotopic result provides evidence for the direct influence of nitrogen fertilizer inputs on weathering, CO(2) consumption and base cation leaching and confirms previous results obtained using the chemistry of the

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

    NASA Astrophysics Data System (ADS)

    McCarroll, Danny

    2010-05-01

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

  10. Carbon isotopes in the ocean model of the Community Earth System Model (CESM1)

    NASA Astrophysics Data System (ADS)

    Jahn, A.; Lindsay, K.; Giraud, X.; Gruber, N.; Otto-Bliesner, B. L.; Liu, Z.; Brady, E. C.

    2015-08-01

    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 s