These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Carbonate abundances and isotopic compositions in chondrites  

NASA Astrophysics Data System (ADS)

We report the bulk C abundances, and C and O isotopic compositions of carbonates in 64 CM chondrites, 14 CR chondrites, 2 CI chondrites, LEW 85332 (C2), Kaba (CV3), and Semarkona (LL3.0). For the unheated CMs, the total ranges of carbonate isotopic compositions are ?13C ? 25-75‰ and ?18O ? 15-35‰, and bulk carbonate C contents range from 0.03 to 0.60 wt%. There is no simple correlation between carbonate abundance and isotopic composition, or between either of these parameters and the extent of alteration. Unless accretion was very heterogeneous, the uncorrelated variations in extent of alteration and carbonate abundance suggests that there was a period of open system behavior in the CM parent body, probably prior to or at the start of aqueous alteration. Most of the ranges in CM carbonate isotopic compositions can be explained by their formation at different temperatures (0-130 °C) from a single fluid in which the carbonate O isotopes were controlled by equilibrium with water (?18O ? 5‰) and the C isotopes were controlled by equilibrium with CO and/or CH4 (?13C ? -33‰ or -20‰ for CO- or CH4-dominated systems, respectively). However, carbonate formation would have to have been inefficient, otherwise carbonate compositions would have resembled those of the starting fluid. A quite similar fluid composition (?18O ? -5.5‰, and ?13C ? -31‰ or -17‰ for CO- or CH4-dominated systems, respectively) can explain the carbonate compositions of the CIs, although the formation temperatures would have been lower (~10-40 °C) and the relative abundances of calcite and dolomite may play a more important role in determining bulk carbonate compositions than in the CMs. The CR carbonates exhibit a similar range of O isotopes, but an almost bimodal distribution of C isotopes between more (?13C ? 65-80‰) and less altered samples (?13C ? 30-40‰). This bimodality can still be explained by precipitation from fluids with the same isotopic composition (?18O ? -9.25‰, and ?13C ? -21‰ or -8‰ for CO- or CH4-dominated systems, respectively) if the less altered CRs had higher mole fractions of CO2 in their fluids. Semarkona and Kaba carbonates have some of the lightest C isotopic compositions of the meteorites studied here, probably because they formed at higher temperatures and/or from more CO2-rich fluids. The fluids responsible for the alteration of chondrites and from which the carbonates formed were almost certainly accreted as ices. By analogy with cometary ices, CO2 and/or CO would have dominated the trapped volatile species in the ices. The chondrites studied are too oxidized for CO-dominated fluids to have formed in their parent bodies. If CH4 was the dominant C species in the fluids during carbonate formation, it would have to have been generated in the parent bodies from CO and/or CO2 when oxidation of metal by water created high partial pressures of H2. The fact that the chondrite carbonate C/H2O mole ratios are of the order predicted for CO/CO2-H2O ices that experienced temperatures of >50-100 K suggests that the chondrites formed at radial distances of <4-15 AU.

Alexander, C. M. O'd.; Bowden, R.; Fogel, M. L.; Howard, K. T.

2015-04-01

2

Carbonate abundances and isotopic compositions in chondrites  

NASA Astrophysics Data System (ADS)

We report the bulk C abundances, and C and O isotopic compositions of carbonates in 64 CM chondrites, 14 CR chondrites, 2 CI chondrites, LEW 85332 (C2), Kaba (CV3), and Semarkona (LL3.0). For the unheated CMs, the total ranges of carbonate isotopic compositions are ?13C ? 25-75‰ and ?18O ? 15-35‰, and bulk carbonate C contents range from 0.03 to 0.60 wt%. There is no simple correlation between carbonate abundance and isotopic composition, or between either of these parameters and the extent of alteration. Unless accretion was very heterogeneous, the uncorrelated variations in extent of alteration and carbonate abundance suggests that there was a period of open system behavior in the CM parent body, probably prior to or at the start of aqueous alteration. Most of the ranges in CM carbonate isotopic compositions can be explained by their formation at different temperatures (0-130 °C) from a single fluid in which the carbonate O isotopes were controlled by equilibrium with water (?18O ? 5‰) and the C isotopes were controlled by equilibrium with CO and/or CH4 (?13C ? -33‰ or -20‰ for CO- or CH4-dominated systems, respectively). However, carbonate formation would have to have been inefficient, otherwise carbonate compositions would have resembled those of the starting fluid. A quite similar fluid composition (?18O ? -5.5‰, and ?13C ? -31‰ or -17‰ for CO- or CH4-dominated systems, respectively) can explain the carbonate compositions of the CIs, although the formation temperatures would have been lower (~10-40 °C) and the relative abundances of calcite and dolomite may play a more important role in determining bulk carbonate compositions than in the CMs. The CR carbonates exhibit a similar range of O isotopes, but an almost bimodal distribution of C isotopes between more (?13C ? 65-80‰) and less altered samples (?13C ? 30-40‰). This bimodality can still be explained by precipitation from fluids with the same isotopic composition (?18O ? -9.25‰, and ?13C ? -21‰ or -8‰ for CO- or CH4-dominated systems, respectively) if the less altered CRs had higher mole fractions of CO2 in their fluids. Semarkona and Kaba carbonates have some of the lightest C isotopic compositions of the meteorites studied here, probably because they formed at higher temperatures and/or from more CO2-rich fluids. The fluids responsible for the alteration of chondrites and from which the carbonates formed were almost certainly accreted as ices. By analogy with cometary ices, CO2 and/or CO would have dominated the trapped volatile species in the ices. The chondrites studied are too oxidized for CO-dominated fluids to have formed in their parent bodies. If CH4 was the dominant C species in the fluids during carbonate formation, it would have to have been generated in the parent bodies from CO and/or CO2 when oxidation of metal by water created high partial pressures of H2. The fact that the chondrite carbonate C/H2O mole ratios are of the order predicted for CO/CO2-H2O ices that experienced temperatures of >50-100 K suggests that the chondrites formed at radial distances of <4-15 AU.

Alexander, C. M. O'd.; Bowden, R.; Fogel, M. L.; Howard, K. T.

2015-01-01

3

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

NASA Technical Reports Server (NTRS)

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.

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

1987-01-01

4

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

NASA Astrophysics Data System (ADS)

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 ?13C 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.

Yang, Weifeng; Guo, Laodong

2014-11-01

5

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

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

6

Solar Carbon Monoxide, Thermal Profiling, and the Abundances of C, O, and their Isotopes  

E-print Network

A solar photospheric "thermal profiling" analysis is presented, exploiting the infrared rovibrational bands of carbon monoxide (CO) as observed with the McMath-Pierce Fourier transform spectrometer (FTS) at Kitt Peak, and from above the Earth's atmosphere by the Shuttle-borne ATMOS experiment. Visible continuum intensities and center-limb behavior constrained the temperature profile of the deep photosphere, while CO center-limb behavior defined the thermal structure at higher altitudes. The oxygen abundance was self consistently determined from weak CO absorptions. Our analysis was meant to complement recent studies based on 3-D convection models which, among other things, have revised the historical solar oxygen (and carbon) abundance downward by a factor of nearly two; although in fact our conclusions do not support such a revision. Based on various considerations, an oxygen abundance of 700+/-100 ppm (parts per million relative to hydrogen) is recommended; the large uncertainty reflects the model sensitivity of CO. New solar isotopic ratios also are reported for 13C, 17O, and 18O.

Thomas R. Ayres; Claude Plymate; Christoph U. Keller

2006-06-07

7

Natural Abundance Carbon Isotope Composition of Isoprene Reflects Incomplete Coupling between Isoprene Synthesis and Photosynthetic Carbon Flow  

PubMed Central

Isoprene emission from leaves is dynamically coupled to photosynthesis through the use of primary and recent photosynthate in the chloroplast. However, natural abundance carbon isotope composition (?13C) measurements in myrtle (Myrtus communis), buckthorn (Rhamnus alaternus), and velvet bean (Mucuna pruriens) showed that only 72% to 91% of the variations in the ?13C values of fixed carbon were reflected in the ?13C values of concurrently emitted isoprene. The results indicated that 9% to 28% carbon was contributed from alternative, slow turnover, carbon source(s). This contribution increased when photosynthesis was inhibited by CO2-free air. The observed variations in the ?13C of isoprene under ambient and CO2-free air were consistent with contributions to isoprene synthesis in the chloroplast from pyruvate associated with cytosolic Glc metabolism. Irrespective of alternative carbon source(s), isoprene was depleted in 13C relative to mean photosynthetically fixed carbon by 4‰ to 11‰. Variable 13C discrimination, its increase by partially inhibiting isoprene synthesis with fosmidomicin, and the associated accumulation of pyruvate suggested that the main isotopic discrimination step was the deoxyxylulose-5-phosphate synthase reaction. PMID:12692331

Affek, Hagit P.; Yakir, Dan

2003-01-01

8

Isotopic abundances of carbon and nitrogen in Jupiter-family and Oort Cloud comets  

Microsoft Academic Search

The 12C14N\\/12C15N and 12C14N\\/13C14N isotopic ratios are determined for the first time in a Jupiter-family comet, 88P\\/1981 Q1 Howell, and in the chemically peculiar Oort Cloud comet C\\/1999 S4 (LINEAR). By comparing these measurements to previous ones derived for six other Oort Cloud comets (including one of Halley-type), we find that both the carbon and nitrogen isotopic ratios are constant

D. Hutsemékers; J. Manfroid; E. Jehin; C. Arpigny; A. Cochran; R. Schulz; J. A. Stüwe; J.-M. Zucconi

2005-01-01

9

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

NASA Technical Reports Server (NTRS)

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.

Kerridge, J. F.

1985-01-01

10

Carbon, nitrogen and sulfur in lunar fines 15012 and 15013 - Abundances, distributions and isotopic compositions  

NASA Technical Reports Server (NTRS)

Lunar fines 15012,16 and 15013,3 were analyzed by stepwise pyrolysis and acid hydrolysis as well as complete combustion in oxygen to determine carbon, nitrogen and sulfur. In addition, hydrogen was analysed during pyrolysis as well as during hydrolysis. By comparison of the distribution frequencies of C, N, S, H2 and Fe with He-4, considered to have arisen from solar wind contribution, it is concluded that nitrogen and hydrogen have largely a solar origin. Carbon has a significant solar contribution, and metallic iron may have resulted from solar wind interaction with ferrous minerals on the lunar surface. Sulfur probably has a predominantly lunar origin. There is no direct evidence for meteorotic contribution to these samples. Solar wind interaction also has a marked effect on the stable isotope distribution of C-13/C-12, N-15/N-14, and S-34/S-32. In all cases, the heavy isotope was most enriched in the smallest grain-size fraction.

Chang, S.; Lawless, J.; Romiez, M.; Kaplan, I. R.; Petrowski, C.; Sakai, H.; Smith, J. W.

1974-01-01

11

Isotopic abundances of carbon and nitrogen in Jupiter-family and Oort Cloud comets  

E-print Network

The 12C14N/12C15N and 12C14N/13C14N isotopic ratios are determined for the first time in a Jupiter-family comet, 88P/1981 Q1 Howell, and in the chemically peculiar Oort Cloud comet C/1999 S4 (LINEAR). By comparing these measurements to previous ones derived for six other Oort Cloud comets (including one of Halley-type), we find that both the carbon and nitrogen isotopic ratios are constant within the uncertainties. The mean values are 12C/13C ~ 90 and 14N/15N \\~ 145 for the eight comets. These results strengthen the view that CN radicals originate from refractory organics formed in the protosolar molecular cloud and subsequently incorporated in comets.

D. Hutsemekers; J. Manfroid; E. Jehin; C. Arpigny; A. Cochran; R. Schulz; J. A. Stuwe; J. -M. Zucconi

2005-08-01

12

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

PubMed

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. PMID:25382295

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

2015-02-01

13

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

PubMed

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 ?(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 ?(13)C values and C(14)/C(18) ratios can be used to distinguish clean commercial cooking oils from illegal swill-cooked oils. PMID:22813234

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

2012-08-15

14

Carbon and O Isotopic Ratios, Trace Element Abundances and Cathodoluminescence Observation of Calcite in Murchison  

NASA Astrophysics Data System (ADS)

We found two types of calcite in Murchison with respect to C isotopic ratios, trace element concentrations and CL intensities. In contrast, they have similar O isotopic ratios, suggesting the presence of at least two C sources for calcite.

Fujiya, W.; Sugiura, N.; Marrocchi, Y.; Takahata, N.; Hoppe, P.; Shirai, K.; Sano, Y.; Hiyagon, H.

2014-09-01

15

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

NASA Astrophysics Data System (ADS)

Natural abundance stable (?13C) and radiocarbon (?14C) 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 ?13C 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 ?14C 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. Further research needs to examine the role which priming processes play in controlling the fate of organic contaminants in Athabasca oil sands tailings ponds, such as understanding to what extent the addition of labile material may hinder or enhance microbial uptake of fossil carbon. This knowledge can be subsequently used to optimize conditions which favour natural attenuation processes in reclamation sites following mine closure.

Ahad, J. M.; Pakdel, H.

2013-12-01

16

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

NASA Astrophysics Data System (ADS)

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 (?13C) 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 ?13C ~ -5 ‰ (vs. PDB). These values are high compared to N-MORB mantle source estimates (72-134 ppm) based upon CO2/Nb ratios [2, 3]; however, they are in good agreement with those from submarine glasses on adjacent segments from the Reykjanes and Kolbeinsey ridges [4,5]. Significantly, the model-derived ?13C estimate is close to the mean Icelandic geothermal value, implying that fluids closely resemble source values, i.e. they likely represent the exsolved component. Integrating the estimated source CO2 content with magma production values of 0.079 km3/yr [6] yields a CO2 flux of ~1.2 x 1011 mol CO2 yr-1for Iceland, representing ~ 5.4 % of the total carbon ridge flux of 2.2 x 1012 mol CO2 yr-1 [7]. Thus, the average CO2 flux estimate for Iceland is ~2.2 x 108 mol CO2 yr-1km-1 strike of ridge axis, which compares to an overall ridge flux (including Iceland) of ~2.9 x 107 mol CO2 yr-1km-1. This difference highlights both heterogeneity in source volatile contents and magma production rates as important controls for determining mantle CO2 fluxes. [1] Poreda et al., 1992 [2] Saal et al., 2002. [3] Shaw et al., 2010. [4] de Leeuw, 2007 [5] Macpherson et al., 2005. [6] Thordarson et al., 2007 [7] Marty et al., 1998.

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

2010-12-01

17

Carbon isotopes in oil-gas geology  

Microsoft Academic Search

Analysis of variations in the natural abundances of the carbon isotopes C12 and C13 in petroleum, gases, bitumens, and other materials is treated. A theoretical-calculation division gives data on the thermodynamic isotope effects of organic compounds, and presents a theory of biogenic isotope equilibria and intramolecular isotope nonuniformity of bio-organic compounds. Laboratory studies of processes simulating natural fractionation of carbon

E. M. Galimov

1975-01-01

18

Stellar Isotopic Abundances in the Milky Way: Insights into the Origin of Carbon and Neutron-Capture Elements  

NASA Astrophysics Data System (ADS)

Elements heavier than iron are formed by the capture of neutrons onto lighter nuclei. Neutron capture happens via two separate processes: the rapid neutron capture process (r-process) that occurs in supernovae, and slow neutron capture process (s-process) that occurs in less-massive stars. This work used high-resolution spectroscopy, synthetic model spectra, and a least-squares fit to show that the ratio of 12C to 13C increases proportionally with [Fe/H]. The new results agree with the conclusions of Lucatello et al. (2006) and Frebel (2008), and show significant improvement that contains less scattering of data points. Analysis of the obtained isotope ratios suggests that the carbon in most stars of the sample originated in supernovae. This paper also presents a method to calculate the europium isotope ratio by modeling the shapes of absorption lines. The range of europium isotopic ratios agrees with previous theoretical predictions about the classical model of heavy element nucleosynthesis, and the work presents new insight into the origins of life in the universe. We thank the US National Science Foundation, the UCSC Science Internship Program, and the Lick Observatory where the spectra were obtained.

Guo, Michelle; Zhang, A.; Kirby, E. N.; Guhathakurta, P.

2014-01-01

19

Site-specific responses to short-term environmental variation are reflected in leaf and phloem-sap carbon isotopic abundance of field grown Eucalyptus globulus.  

PubMed

The carbon isotopic composition (?(13) C) of plant material has been used extensively as an indirect measure of carbon fixation per volume of water used. More recently, the ?(13) C of phloem sap (?(13) C(phl) ) has been used as a surrogate measure of short-term, canopy scale ?(13) C. Using a combination of ?(13) C physiological, structural and chemical indices from leaves and phloem sap of Eucalyptus globulus at sites of contrasting water availability, we sought to identify short-term, canopy scale resource limitations. Results illustrate that ?(13) C(phl) offers valid reflections of short-term, canopy scale values of leaf ?(13) C and tree water status. Under conditions limited by water, leaf and phloem sap photoassimilates differ in (13) C abundance of a magnitude large enough to significantly influence predictions of water use efficiency. This pattern was not detected among trees with adequate water supply indicating fractionation into heterotrophic tissues that may be sensitive to plant water status. Trees employed a range of physiological, biochemical and structural adaptations to acclimate to resource limitation that differed among sites providing a useful context upon which to interpret patterns in ?(13) C. Our results highlight that such easily characterized properties are ideal for use as minimally invasive tools to monitor growth and resilience of plants to variations in resource availability. PMID:22568657

Merchant, Andrew; Buckley, Thomas N; Pfautsch, Sebastian; Turnbull, Tarryn L; Samsa, Glen A; Adams, Mark A

2012-12-01

20

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

PubMed

A 16-year field experiment was conducted in a ridge culture paddy field in the hilly region of Sichuan Basin, aimed to investigate the distribution characteristics of stable carbon isotope natural abundance (delta 13C) in soil humus fractions. The soil organic carbon (SOC) content in the paddy field under different cultivation modes ranked in the order of wide ridge culture > ridge culture > paddy and upland rotation. In soil humus substances (HS), humin (HU) was the main composition, occupying 21% - 30% of the total SOC. In the extracted soil carbon, humic acid (HA) dominated, occupying 17% - 21% of SOC and 38% - 65% of HS. The delta 13C value of SOC ranged from -27.9 per thousand to -25.6 per thousand, and the difference of the delta 13C value between 0-5 cm and 20-40 cm soil layers was about 1.9 per thousand. The delta 13C value of HA under different cultivation modes was 1 per thousand - 2 per thousand lower than that of SOC, and more approached to the delta 13C value of rapeseed and rice residues. As for fulvic acid (FA), its delta 13C value was about 2 per thousand and 4 per thousand higher than that of SOC and HA, respectively. The delta 13C value of HU in plough layer (0-20 cm) and plow layer (20-40 cm) ranged from -23.7 per thousand - -24.9 per thousand and -22.6 per thousand - -24.2 per thousand, respectively, reflecting the admixture of young and old HS. The delta 13C value in various organic carbon fractions was HU>FA>SOC>rapeseed and rice residues>HA. Long-term rice planting benefited the increase of SOC content, and cultivation mode played an important role in affecting the distribution patterns of soil humus delta 13C in plough layer and plow layer. PMID:21774322

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

2011-04-01

21

Isotopic abundance variations in interstellar HCN  

NASA Astrophysics Data System (ADS)

A study of the relative abundances of the rare isotopic species H(C-12)(N-15) and H(C-13)(N-14) has been made in six dense molecular clouds through observations of the 3.5-mm rotational transitions. The data indicate that in all sources the HC(N-15)/H(C-13)N integrated line-intensity ratio is smaller than that implied by terrestrial isotopic abundances. The excitation of HCN is discussed with special attention to the conditions which permit accurate abundance determination even when optical depths are large. A quantitative estimate of the line saturation shows this to be a small effect for the present measurements. There appears to be at least a factor of 6 between the average ratio for the sources in the galactic disk and that for two sources associated with the galactic center. This result is discussed in terms of increased nuclear processing in the galactic center region.

Linke, R. A.; Goldsmith, P. F.; Wannier, P. G.; Wilson, R. W.; Penzias, A. A.

1977-05-01

22

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

NASA Technical Reports Server (NTRS)

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.

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

1983-01-01

23

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

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.

Piper, Stephen C; Keeling, Ralph F

2012-01-03

24

Carbon isotopic fractionation in heterotrophic microbial metabolism  

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

25

Helium isotopic abundance variation in nature  

SciTech Connect

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.

Holden, N.E.

1993-08-01

26

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

USGS Publications Warehouse

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.

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

1983-01-01

27

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

NASA Astrophysics Data System (ADS)

We report new carbon dioxide (CO2) abundance and isotope data for 71 geothermal gases and fluids from both high-temperature (HT > 150 °C at 1 km depth) and low-temperature (LT < 150 °C at 1 km depth) geothermal systems located within neovolcanic zones and older segments of the Icelandic crust, respectively. These data are supplemented by CO2 data obtained by stepped heating of 47 subglacial basaltic glasses collected from the neovolcanic zones. The sample suite has been characterized previously for He-Ne (geothermal) and He-Ne-Ar (basalt) systematics (Füri et al., 2010), allowing elemental ratios to be calculated for individual samples. Geothermal fluids are characterized by a wide range in carbon isotope ratios (?13C), from -18.8‰ to +4.6‰ (vs. VPDB), and CO2/3He values that span eight orders of magnitude, from 1 × 104 to 2 × 1012. Extreme geothermal values suggest that original source compositions have been extensively modified by hydrothermal processes such as degassing and/or calcite precipitation. Basaltic glasses are also characterized by a wide range in ?13C values, from -27.2‰ to -3.6‰, whereas CO2/3He values span a narrower range, from 1 × 108 to 1 × 1012. The combination of both low ?13C values and low CO2 contents in basalts indicates that magmas are extensively and variably degassed. Using an equilibrium degassing model, we estimate that pre-eruptive basaltic melts beneath Iceland contain ?531 ± 64 ppm CO2 with ?13C values of -2.5 ± 1.1‰, in good agreement with estimates from olivine-hosted melt inclusions (Metrich et al., 1991) and depleted MORB mantle (DMM) CO2 source estimates (Marty, 2012). In addition, pre-eruptive CO2 compositions are estimated for individual segments of the Icelandic axial rift zones, and show a marked decrease from north to south (Northern Rift Zone = 550 ± 66 ppm; Eastern Rift Zone = 371 ± 45 ppm; Western Rift Zone = 206 ± 24 ppm). Notably, these results are model dependent, and selection of a lower ?13C fractionation factor will result in lower source estimates and larger uncertainties associated with the initial ?13C estimate. Degassing can adequately explain low CO2 contents in basalts; however, degassing alone is unlikely to generate the entire spectrum of observed ?13C variations, and we suggest that melt-crust interaction, involving a low ?13C component, may also contribute to observed signatures. Using representative samples, the CO2 flux from Iceland is estimated using three independent methods: (1) combining measured CO2/3He values (in gases and basalts) with 3He flux estimates (Hilton et al., 1990), (2) merging basaltic emplacement rates of Iceland with pre-eruptive magma source estimates of ?531 ± 64 ppm CO2, and (3) combining fluid CO2 contents with estimated regional fluid discharge rates. These methods yield CO2 flux estimates from of 0.2-23 × 1010 mol a-1, which represent ?0.1-10% of the estimated global ridge flux (2.2 × 1012 mol a-1; Marty and Tolstikhin, 1998).

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

2014-06-01

28

Exploring Marine Carbon Isotope Excursions  

NSDL National Science Digital Library

David Jones, Geology Department, Amherst College Topic: stable isotopes, geochemistry, oceanography, carbon cycle Course type: Upper level undergraduate course Description The exercise is designed to introduce ...

29

RELATIVE CHIRAL ABUNDANCES OF CARBON NANOTUBES DETERMINED BYRELATIVE CHIRAL ABUNDANCES OF CARBON NANOTUBES DETERMINED BYRELATIVE CHIRAL ABUNDANCES OF CARBON NANOTUBES DETERMINED BYRELATIVE CHIRAL ABUNDANCES OF CARBON NANOTUBES DETERMINED BY RESONANT RAMAN  

E-print Network

RELATIVE CHIRAL ABUNDANCES OF CARBON NANOTUBES DETERMINED BYRELATIVE CHIRAL ABUNDANCES OF CARBON NANOTUBES DETERMINED BYRELATIVE CHIRAL ABUNDANCES OF CARBON NANOTUBES DETERMINED BYRELATIVE CHIRAL ABUNDANCES OF CARBON NANOTUBES DETERMINED BY RESONANT RAMAN SPECTROSCOPY USING A TUNABLE DYE LASERRESONANT

Mellor-Crummey, John

30

Carbon Isotope Chemistry in Molecular Clouds  

NASA Technical Reports Server (NTRS)

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.

Robertson, Amy N.; Willacy, Karen

2012-01-01

31

THE ATOMIC WEIGHTS COMMISSION AND ISOTOPIC ABUNDANCE RATIO DETERMINATIONS.  

SciTech Connect

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).

HOLDEN, N.E.

2005-08-07

32

Climatic/Hydrologic Oscillations since 155,000 yr B.P. at Owens Lake, California, Reflected in Abundance and Stable Isotope Composition of Sediment Carbonate  

USGS Publications Warehouse

Sediment grain size, carbonate content, and stable isotopes in 70-cm-long (???1500-yr) channel samples from Owens Lake core OL-92 record many oscillations representing climate change in the eastern Sierra Nevada region since 155,000 yr B.P. To first order, the records match well the marine ??18O record. At Owens Lake, however, the last interglaciation appears to span the entire period from 120,000 to 50,000 yr B.P., according to our chronology, and was punctuated by numerous short periods of wetter conditions during an otherwise dry climate. Sediment proxies reveal that the apparent timing of glacial-interglacial transitions, notably the penultimate one, is proxy-dependent. In the grain-size and carbonate-content records this transition is abrupt and occurs at ??? 120,000 yr B.P. In contrast, in the isotopic records the transition is gradual and occurs between 145,000 and 120,000 yr B. P. Differences in timing of the transition are attributed to variable responses by proxies to climate change. ?? 1997 University of Washington.

Menking, K.M.; Bischoff, J.L.; Fitzpatrick, J.A.; Burdette, J.W.; Rye, R.O.

1997-01-01

33

Carbon isotopes in mollusk shell carbonates  

NASA Astrophysics Data System (ADS)

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 ?13C reflects the local mix of C3 and C4 plants consumed. Shell ?13C 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 ?13C is typically a few ‰ lower than ambient DIC, and often decreases with age. Shell ?13C 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.

McConnaughey, Ted A.; Gillikin, David Paul

2008-10-01

34

The abundances of elements and isotopes in the solar wind  

NASA Technical Reports Server (NTRS)

Studies of the chemical and isotopic composition of the solar wind are reviewed. Solar wind abundance measurements are discussed and solar wind, coronal, and photospheric abundances for elements between H and Fe are presented. Also, consideration is given to the determination of the solar wind isotopic composition of the noble gases using foil collection techniques and the observation of solar wind heavy ions with the mass per charge spectrometer on ISEE-3. Other topics include solar wind observations with solid state detectors, solar wind abundances in the magnetosheath and the plasma sheet, and high-mass resolution measurements of chemical elements and isotopes in the solar wind.

Gloeckler, George; Geiss, Johannes

1988-01-01

35

Interpreting carbon-isotope excursions: carbonates and organic matter  

Microsoft Academic Search

Variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon. Paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon

Lee R. Kump; Michael A. Arthur

1999-01-01

36

(Carbon isotope fractionation inplants)  

SciTech Connect

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.

O'Leary, M.H.

1990-01-01

37

Lithium Isotopic Abundances in Metal-poor Halo Stars  

Microsoft Academic Search

Very high quality spectra of 24 metal-poor halo dwarfs and subgiants have been acquired with ESO's VLT\\/UVES for the purpose of determining Li isotopic abundances. The derived one-dimensional, non-LTE 7Li abundances from the Li I 670.8 nm line reveal a pronounced dependence on metallicity but with negligible scatter around this trend. Very good agreement is found between the abundances from

Martin Asplund; David L. Lambert; Poul Erik Nissen; Francesca Primas; Verne V. Smith

2006-01-01

38

LITERATURE SURVEY ON ISOTOPIC ABUNDANCE RATIO MEASUREMENTS - 2001-2005  

SciTech Connect

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.

HOLDEN, N.E.

2005-08-13

39

Isotopic abundance in atom trap trace analysis  

DOEpatents

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.

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

2014-03-18

40

Europium Isotopic Abundances in Very Metal-poor Stars  

E-print Network

Europium isotopic abundance fractions are reported for the very metal-poor, neutron-capture-rich giant stars CS 22892-052, HD 115444, and BD +17 3248. The abundance fractions, derived from analysis of several strong Eu II lines appearing in high-resolution spectra of these stars, are in excellent agreement with each other and with their values in the Solar System: fraction(\\iso{Eu}{151}) ~= fraction(\\iso{Eu}{153}) ~= 0.5. Detailed abundance studies of very metal-poor stars have previously shown that the total elemental abundances of stable atoms with atomic numbers z >= 56 typically match very closely those of a scaled solar-system r-process abundance distribution. The present results for the first time extend this agreement to the isotopic level.

Christopher Sneden; John J. Cowan; James E. Lawler; Scott Burles; Timothy C. Beers; George M. Fuller

2002-01-28

41

Evidence for isotopic fractionation of carbon monoxide in dark clouds  

NASA Astrophysics Data System (ADS)

Chemical fractionation of the various isotopes of carbon monoxide has been studied in four isolated dark clouds. At positions away from the centers of three of the objects - B5, B335, and L1262 - the abundance of (CO-13) relative to C(O-18) is at least a factor of 4 greater than at the central positions. This detection of carbon isotope fractionation is consistent with theoretical predictions of (CO-13) enhancement in the outer parts of cool clouds. Combined observations of the J = 2 to 1 and J = 1 to 0 transitions of several CO isotopes have enabled us to derive molecular hydrogen densities and to assess the effect of saturation and resonant scattering. Abundance ratios of the rarer isotopic species in the cloud centers have also been determined.

Langer, W. D.; Goldsmith, P. F.; Carlson, E. R.; Wilson, R. W.

1980-01-01

42

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

SciTech Connect

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.

Stevens, C.M. [Argonne National Lab., IL (United States); Sepanski; Morris, L.J. [Univ. of Tennessee, Knoxville, TN (United States). Energy, Environment, and Resources Center

1995-03-01

43

Literature survey of isotopic abundance data for 1987-1989  

SciTech Connect

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.

Holden, N.E. (Brookhaven National Lab., Upton, NY (USA))

1989-08-09

44

The separation of stable isotopes of carbon  

Microsoft Academic Search

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

E. D. Oziashvili; A. S. Egiazarov

1989-01-01

45

Carbon and nitrogen stable isotopic inventory of the most abundant demersal fish captured by benthic gears in southwestern Iceland (North Atlantic)  

NASA Astrophysics Data System (ADS)

Stable isotopes (?13C and ?15N) were used to examine the origin of organic matter for the most representative demersal species of the SW Icelandic fishery, accounting for over 70% of landings of those species in the North Atlantic. Samples were collected during a 2-week period in early September 2004 from landings and directly during fishing cruises. Stable isotopes showed that particulate organic matter and sedimentary organic matter were at the base of the food web and appeared to fill two different compartments: the pelagic and the benthic. The pelagic realm was composed of only capelin and sandeel; krill and redfish occupied an intermediate position between pelagic and benthic realms; while anglerfish, haddock, cod and ling resulted as the true demersal species while tusk, rays and plaice were strongly linked to the benthic habitat.

Sarà, Gianluca; de Pirro, Maurizio; Sprovieri, Mario; Rumolo, Paola; Halldórsson, Halldór Pálmar; Svavarsson, Jörundur

2009-12-01

46

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

SciTech Connect

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.

Keeling, Ralph [UCSD-SIO

2014-12-12

47

Isotope tracers of organic carbon during artificial recharge  

SciTech Connect

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.

Davisson, M.L.

1998-02-09

48

Elemental, isotopic and molecular abundances in comets  

NASA Technical Reports Server (NTRS)

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

Delsemme, A. H.

1986-01-01

49

Probing the Isotopic Composition of Surface Waters Across Isotopic Extremes of Cryogenian Carbonates  

NASA Astrophysics Data System (ADS)

Neoproterozoic carbonate strata record unusually large and positive carbon isotope values (?13Ccarb from 4 to 10 per mil), and stratigraphically extensive large negative carbon isotope excursions (?13Ccarb < -5 per mil). Mechanisms that account for the magnitude, the facies distribution and the global abundance of these isotopically extreme carbonates in Neoproterozoic successions remain poorly understood. Little is also known about organisms and metabolisms that cycled carbon in these carbonate strata, because they rarely contain well-preserved organic-rich fossils. To better understand the cycling of carbon during the deposition of the 715-635 Ma Tayshir member of the Tsagaan Oloom Formation, Mongolia, we analyzed ?13Cfossil of two types of organic fossils that occur in 13C- enriched carbonates (+ 5 to 9.9 per mil) and within 13C-depleted carbonates of the Tayshir anomaly (-3 to -6 per mil). Because these organic microfossils are remarkably similar to the tests of modern planktonic, herbivorous tintinnid ciliates and benthic macroscopic red algae, respectively, they can be used as tracers of organic matter production in surface waters. Fossil tests were extracted by acid maceration, cleaned and analyzed morphologically and microscopically. Their carbon isotopic composition was measured using a nano-scaled elemental analyzer inlet (nano-EA-IRMS), with ±1 per mil analytical precision. To date, we analyzed 12 samples of 100-150 organic tests, representing 3 different fossiliferous parts of the Tayshir anomaly (?13Ccarb < -3 per mil) and 3 different strata predating the Tayshir anomaly (?13Ccarb > +5 per mil), respectively. More samples, including those of fossil algae and tests from the carbonate strata overlying the Tayshir anomaly, are currently being analyzed. Initial data reveal a rather constant isotopic composition of organic carbon in fossil tests (?13Cfossil), with values of -23 ±1 per mil both within 13C-enriched and 13C-depleted carbonates. The isotopic difference between ?13Cfossil and 13C-enriched carbonates is 28 to 30 per mil, suggesting maximal isotopic fractionation by primary producers, and little environmental (or diagenetic) processing of primary photosynthetic carbon. The carbonates of the Tayshir anomaly preserve two organic materials: matrix or bulk carbon characterized by a ?13Corg that covaries with ?13Ccarb, and a small, but morphologically diagnostic component whose ?13Cfossil values do not covary with ?13Ccarb. The stratigraphic thickness (~ 50 m) and isotopic heterogeneity of the organic matter within the Tayshir anomaly (~ 50 m) suggest a prolonged and large contribution of organic carbon remineralization.

Bosak, T.; Matys, E. D.; Bird, L. R.; Macdonald, F. A.; Freeman, K. H.

2012-12-01

50

Carbon isotope controlled molecular switches  

NASA Astrophysics Data System (ADS)

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.

Foster, Brian K.

51

Carbon Isotope Ratios in Belowground Carbon Cycle Processes  

Microsoft Academic Search

Abstract Analyses of carbon isotope ratios (?,C values of CO2effluxing from soils, but asof,yet a global,database,is lacking,with which,to test this prediction. Such a global,database,would be a useful input for global carbon cycle models,which,rely on ?values,to constrain source and sink relations. Keywords: global change, ecosystem processes, soil organic carbon, carbon isotope ratio, carbon cycle,

James R. Ehleringer; Nina Buchmann; Lawrence B. Flanagan

2000-01-01

52

Separation of carbon isotopes. [Patent application  

Microsoft Academic Search

An object of the present invention is to separate carbon isotopes by using a relatively inexpensive and readily available feedstock by a highly energy efficient, pressure-scalable process having a high enrichment factor. A further object of the present invention is to separate carbon isotopes through a substantially more energy efficient endothermic reaction, of approximately 15 kcal\\/mole. A still further object

D. S. Y. Hsu; T. J. Jr. Manuccia

1981-01-01

53

The Abundance and Isotopic Composition of Hg in Extraterrestrial Materials  

NASA Technical Reports Server (NTRS)

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.

Lauretta, D. S.

2004-01-01

54

Mass Spectrometric Measurement of Martian Krypton and Xenon Isotopic Abundance  

NASA Technical Reports Server (NTRS)

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.

Mahaffy, P.; Mauersberger, K.

1993-01-01

55

Carbon and nitrogen isotope studies in an arctic ecosystem  

SciTech Connect

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.

Schell, D.M.

1989-01-01

56

Carbon and nitrogen isotope studies in an arctic ecosystem  

SciTech Connect

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.

Schell, D.M.

1989-12-31

57

Low Carbon Abundance in Type Ia Supernovae  

E-print Network

We investigate the quantity and composition of unburned material in the outer layers of three normal Type Ia supernovae (SNe Ia): 2000dn, 2002cr and 20 04bw. Pristine matter from a white dwarf progenitor is expected to be a mixture of oxygen and carbon in approximately equal abundance. Using near-infrared (NIR, 0.7-2.5 microns) spectra, we find that oxygen is abundant while carbon is severely depleted with low upper limits in the outer third of the ejected mass. Strong features from the OI line at rest wavelength = 0.7773 microns are observed through a wide range of expansion velocities approx. 9,000 - 18,000 km/s. This large velocity domain corresponds to a physical region of the supernova with a large radial depth. We show that the ionization of C and O will be substantially the same in this region. CI lines in the NIR are expected to be 7-50 times stronger than those from OI but there is only marginal evidence of CI in the spectra and none of CII. We deduce that for these three normal SNe Ia, oxygen is more abundant than carbon by factors of 100 - 1,000. MgII is also detected in a velocity range similar to that of OI. The presence of O and Mg combined with the absence of C indicates that for these SNe Ia, nuclear burning has reached all but the extreme outer layers; any unburned material must have expansion velocities greater than 18,000 km/s. This result favors deflagration to detonation transition (DD) models over pure deflagration models for SNe Ia.

G. H. Marion; P. Hoeflich; J. C. Wheeler; E. L. Robinson; C. L. Gerardy; W. D. Vacca

2006-01-26

58

Low Carbon Abundance in Type Ia Supernovae  

E-print Network

We investigate the quantity and composition of unburned material in the outer layers of three normal Type Ia supernovae (SNe Ia): 2000dn, 2002cr and 20 04bw. Pristine matter from a white dwarf progenitor is expected to be a mixture of oxygen and carbon in approximately equal abundance. Using near-infrared (NIR, 0.7-2.5 microns) spectra, we find that oxygen is abundant while carbon is severely depleted with low upper limits in the outer third of the ejected mass. Strong features from the OI line at rest wavelength = 0.7773 microns are observed through a wide range of expansion velocities approx. 9,000 - 18,000 km/s. This large velocity domain corresponds to a physical region of the supernova with a large radial depth. We show that the ionization of C and O will be substantially the same in this region. CI lines in the NIR are expected to be 7-50 times stronger than those from OI but there is only marginal evidence of CI in the spectra and none of CII. We deduce that for these three normal SNe Ia, oxygen is mor...

Marion, G H; Höflich, P; Robinson, E L; Vacca, W D; Wheeler, J C

2006-01-01

59

Carbon and its isotopes in mid-oceanic basaltic glasses  

USGS Publications Warehouse

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.

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

1984-01-01

60

Metallicity-Dependent Isotopic Abundances and the Impact of Helium Rate Uncertainties in Massive Stars  

NASA Astrophysics Data System (ADS)

All stellar evolution models for nucleosynthesis require an initial isotopic abundance set to use as a starting point, because nuclear reactions occur between isotopes. Generally, our knowledge of isotopic abundances of stars is fairly incomplete except for the Solar System. We develop a first model for a complete average isotopic decomposition as a function of metallicity. Our model is based on the underlying nuclear astrophysics processes, and is fitted to observational data, rather than traditional forward galactic chemical evolution modeling which integrates stellar yields beginning from big bang nucleosynthesis. We first decompose the isotopic solar abundance pattern into contributions from astrophysical sources. Each contribution is then assumed to scale as a function of metallicity. The resulting total isotopic abundances are summed into elemental abundances and fitted to available halo and disk stellar data to constrain the model's free parameter values. This procedure allows us to use available elemental observational data to reconstruct and constrain both the much needed complete isotopic evolution that is not accessible to current observations, and the underlying astrophysical processes. Our model finds a best fit for Type Ia supernovae contributing ˜0.7 to the solar Fe abundance, and Type Ia onset occurring at [Fe/H]~1.2, in agreement with typical values. The completed model can be used in future nucleosynthesis studies. We also perform a preliminary analysis to assess the impact of our isotopic scaling model on the resulting nucleosynthesis of massive stars, compared to a linear interpolation method. Using these two input methods we compute a limited grid of stellar models, and compare the final nucleosynthesis to observations. The compactness parameter was first used to assess which models would likely explode as successful supernovae, and contribute explosive nucleosynthesis yields. We find a better agreement to solar observations using the scaling model compared to the linear interpolation method, for the six s--only isotopes along the weak s--process path. As a second project, we study the sensitivity of presupernova evolution and supernova nucleosynthesis yields of massive stars to variations of the helium-burning reaction rates within the range of their uncertainties. The current solar abundances from Lodders (2010) are used for the initial stellar composition. We compute a grid of 12 initial stellar masses and 176 models per stellar mass to explore the effects of independently varying the 12C(alpha,gamma)16O and 3alpha reaction rates, denoted Ralpha,12 and R3alpha, respectively. The production factors of both the intermediate-mass elements (A=16--40) and the s--only isotopes along the weak s--process path ( 70Ge, 76Se, 80Kr, 82Kr, 86Sr, and 87Sr) were found to be in reasonable agreement with predictions for variations of R3alpha and Ralpha,12 of +/-25%; the s--only isotopes, however, tend to favor higher values of R3alpha than the intermediate-mass isotopes. The experimental uncertainty (one standard deviation) in R3alpha(Ralpha,12 ) is approximately +/-10%(+/-25%). The results show that a more accurate measurement of one of these rates would decrease the uncertainty in the other as inferred from the present calculations. We also observe sharp changes in production factors and standard deviations for small changes in the reaction rates, due to differences in the convection structure of the star. The compactness parameter was used to assess which models would likely explode as successful supernovae, and hence contribute explosive nucleosynthesis yields. We also provide the approximate remnant masses for each model and the carbon mass fractions at the end of core-helium burning as a key parameter for later evolution stages.

West, Christopher

2013-03-01

61

ORIGINAL RESEARCH Hydrogen and carbon isotope fractionation during  

E-print Network

ORIGINAL RESEARCH Hydrogen and carbon isotope fractionation during degradation of chloromethane, hydrogen isotope fractionation, methylotrophic bacteria. Correspondence Thierry Nadalig, Universite de and abiotic processes. In this study, we measured hydrogen and carbon isotope fractionation of the remaining

Paris-Sud XI, Université de

62

Clumped isotope thermometry of cryogenic cave carbonates  

NASA Astrophysics Data System (ADS)

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 ?18O 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 temperatures indicate incomplete isotopic equilibration during precipitation of CCC. Fine-crystalline carbonate powder (<50 ?m, CCCfine) is thought to have formed in thin water films. Fast freezing causes strong isotopic disequilibrium effects related to rapid reaction rates, fast CO2 degassing, and limited isotopic equilibration (Clark and Lauriol, 1992) resulting in very positive ?13C (up to +18‰) and ?18O values (up to -2‰; Lacelle, 2007; Spötl, 2008; Žák et al., 2008). Larger crystals (mm to cm size, CCCcoarse) are thought to have formed in slow gradually freezing pool water (Žák et al., 2008), where super-saturation is created through ion rejection from the forming ice. This leads to slow mineral growth and strongly 18O-depleted CaCO3 (?18O: -24‰ to -10‰; Žák et al., 2012), but it is unknown whether CCCcoarse grows at isotopic equilibrium. Carbonate clumped isotope analyses (reported as ?47) are typically used to determine the formation temperature of carbonate minerals (Eiler, 2007, 2011; Affek, 2012). However, the sensitivity of ?47 to degassing makes it valuable also for the investigation of isotopic disequilibrium (Guo, 2008; Kluge and Affek, 2012). The carbonate clumped isotope thermometry is based on the temperature-dependent overabundance of 13C-18O bonds in the crystal lattice compared to a stochastic distribution.Depending on the conditions during carbonate formation, a varying degree of disequilibrium has been observed in clumped and oxygen isotopes of 'normal' speleothems (e.g., Mickler et al., 2006; Tremaine et al., 2011) complicating their interpretation. For stalagmites, an offset in ?18O of about 1‰ with respect to the isotopic equilibrium value is typically observed (McDermott et al., 2011) with a corresponding large offset in clumped isotopes (Affek et al., 2008; Daëron et al., 2011; Kluge and Affek, 2012). Initial degassing of CO2 from water that enters the low pCO2 cave environment (compared to the high CO2 levels found in soils) leads to an enrichment in 13C and 18O in DIC and depletion in ?47. Oxygen isotope e

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

2014-02-01

63

The isotopic composition of carbonatite and kimberlite carbonates and their bearing on the isotopic composition of deep-seated carbon  

Microsoft Academic Search

New carbon and oxygen isotopic compositions of carbonates from 14 carbonatite and 11 kimberlite occurrences are reported. A review of the available data on the carbon isotopic composition ranges of carbonatite and kimberlite carbonates shows that they are similar and overlap that of diamonds. The mean carbon isotopic composition of carbonates from 22 selected carbonatite complexes (-5.1%., S = ±

P. Deines; D. P. Gold

1973-01-01

64

[Abundance and activity of microorganisms at the water-sediment interface and their effect on the carbon isotopic composition of suspended organic matter and sediments of the Kara Sea].  

PubMed

At ten stations of the meridian profile in the eastern Kara Sea from the Yenisei estuary through the shallow shelf and further through the St. Anna trough, total microbial numbers (TMN) determined by direct counting, total activity of the microbial community determined by dark CO2 assimilation (DCA), and the carbon isotopic composition of organic matter in suspension and upper sediment horizons (?13C, per thousand) were investigated. Three horizons were studied in detail: (1) the near-bottom water layer (20-30 cm above the sediment); (2) the uppermost, strongly hydrated sediment horizon, further termed warp (5-10 mm); and (3) the upper sediment horizon (1-5 cm). Due to decrease in the amount of isotopically light carbon of terrigenous origin with increasing distance from the Yenisei estuary, the TMN and DCA values decreased, and the ?13C changed gradually from -29.7 to -23.9 per thousand. At most stations, a noticeable decrease in TMN and DCA values with depth was observed in the water column, while the carbon isotopic composition of suspended organic matter did not change significantly. Considerable changes of all parameters were detected in the interface zone: TMN and DCA increased in the sediments compared to their values in near-bottom water, while the 13C content increased significantly, with ?13C of organic matter in the sediments being at some stations 3.5- 4.0 per thousand higher than in the near-bottom water. Due to insufficient illumination in the near-bottom zone, newly formed isotopically heavy organic matter (?13C(-) -20 per thousand) could not be formed by photosynthesis, active growth of chemoautotrophic microorganisms in this zone is suggested, which may use reduced sulfur, nitrogen, and carbon compounds diffusing from anaerobic sediments. High DCA values for the interface zone samples confirm this hypothesis. Moreover, neutrophilic sulfur-oxidizing bacteria were retrieved from the samples of this zone. PMID:25509411

Ivanov, M V; Lein, A Iu; Savvichev, A S; Rusanov, I I; Veslopolova, E F; Zakharova, E E; Prusakova, T S

2013-01-01

65

The Abundance and Isotopic Composition of Hg in Extraterrestrial Materials  

NASA Technical Reports Server (NTRS)

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.

Blum, J. D.; Klaue, Bjorn

2005-01-01

66

Evidence from carbon isotope measurements for diverse origins of sedimentary hydrocarbons  

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

67

Spatial isotopic heterogeneity during the Guttenberg isotopic carbon excursion: Mechanisms and implications for craton-wide isotope gradients  

NASA Astrophysics Data System (ADS)

The carbon isotopic compositions of carbonate carbon (?13Ccarb) and organic carbon (?13Corg) in marine limestones are frequently used as paleoenvironmental proxies and as chemostratigraphic tools for aligning strata. These functions are predicated upon the assumption that isotopic variability in these strata reflects the secular variation in the marine reservoir of dissolved inorganic carbon (DIC). As such, the utility of these isotopic systems largely depends on the assumed spatial homogeneity of marine ?13CDIC. While other isotope systems such as sulfate and strontium have been shown to be extremely well mixed in the modern ocean, a 1-2‰ range in ?13CDIC exists over the entire depth and latitude range of the ocean. This variability in ?13CDIC is largely the result of differences in the local balance of organic carbon fixation and export (increasing ?13CDIC) and/or organic carbon oxidation (decreasing ?13CDIC). The preservation of such isotopic variability in the geologic record has been advocated on several occasions. In particular, previous workers have argued for an ocean-to-interior seaway isotopic gradient in ?13Ccarb, ?13Corg, and ?Nd across Laurentia during the Late Ordovician across the interval that spans the Guttenberg Isotopic Carbon Excursion (GICE). Here we examine two Late Ordovician-aged sections from Missouri, USA that contain the GICE. At first glace, our data showed high degree of stratigraphic and lateral variability. Detailed petrographic and geochemical (e.g., trace element abundance) screening reveals that the majority of the isotopic heterogeneity in our sections is the result of local syndepositional/diagenetic alteration - and not the result of primary gradients in ?13CDIC between the localities examined. Our 'least-altered' ?13Ccarb profile matches closely with previously published records from Iowa; however, sections adjacent both to our locations in Missouri and to the similar ?13Ccarb profile in Iowa are characterized by variable and more depleted ?13Ccarb profiles. This pattern of long-range reproducibility (several hundred km) and short-range (~10s of km) heterogeneity is not consistent with a craton-scale gradient in ?13CDIC. Rather, these observations suggest local depositional conditions and diagenetic alteration are the sources of substantial ?13Ccarb heterogeneity. Detailed petrographic and geochemical analyses are necessary to constrain the mechanisms that give rise to isotopic heterogeneity and, in particular to support interpretations of primary (i.e., water column) gradients in ocean chemistry.

Metzger, J. G.; Fike, D. A.

2012-12-01

68

The clumped isotopic record of Neoproterozoic carbonates, Sultanate of Oman  

NASA Astrophysics Data System (ADS)

The Huqf Supergroup of the Sultanate of Oman records several important events in latest Precambrian time, including two glaciations in the Abu Mahara Group (ca. 725 - <645 Ma), the enigmatic Shuram carbon isotope excursion in the Nafun Group (ca. <645-547 Ma), and the Precambrian-Cambrian boundary in the Ara Group (ca. 547-540 Ma). This interval contains several extreme isotopic excursions, hypothesized to record perturbations of the surficial Earth carbon cycle or post-depositional diagenetic processes. Rigorous interpretation of these records requires a more thorough assessment of diagenetic processes. To better understand the significance and cause of these large amplitude isotopic excursions, we employed carbonate clumped isotope thermometry. This method allows us to estimate the absolute temperature of carbonate precipitation, including recrystallization, based on the temperature dependent abundance of carbonate ions containing both 13C and 18O. These estimates are accompanied by a measurement of carbonate ?18O, which in conjunction with temperature, can be used to calculate the oxygen isotopic composition of the fluid from which the carbonate precipitated. We analyzed stratigraphically constrained samples from a range of paleoenvironments with differing burial histories (1 - >10km maximum burial depth) to constrain the temperature and fluid composition of recrystallization. Clumped isotope temperatures from Huqf Supergroup samples range from 35-175°C. The isotopic composition of the fluid these rocks equilibrated with ranges from -3.7 to 15.7% VSMOW. This large range in temperature and fluid composition separates into distinct populations that differ systematically with independent constraints on petrography, stratigraphy and burial history. The data indicate the Abu Mahara, Nafun and Ara groups have unique diagenetic histories. In central Oman, the post-glacial Abu Mahara cap dolostone shows high temperature, rock buffered diagenesis (Tavg = 176°C; ?18Ofluid = 15% VSMOW), the Nafun Group generally experienced lower temperature, fluid buffered diagenesis (Tavg = 69°C; ?18Ofluid = 1% VSMOW) and the Ara Group exhibits higher temperature, rock buffered diagenesis (Tavg = 85°C; ?18Ofluid = 6% VSMOW). Together these data help constrain the differential influence of carbonate diagenesis on the profound isotope excursions of the latest proterozoic.

Bergmann, K. D.; Eiler, J. M.; Fischer, W. W.; Osburn, M. R.; Grotzinger, J. P.

2011-12-01

69

Carbon Isotopes in an Earth System Model  

Microsoft Academic Search

We present first calculations of the carbon isotopic composition of carbon dioxide in the Earth System Model (ESM) COSMOS. Earth System models consist of coupled models of the ocean, the atmosphere, the land surface, the biosphere (marine and terrestrial, plants and soils), and the cryosphere (snow and ice). In COSMOS from the Max Planck Institute for Meteorology, Hamburg, Germany, these

M. Cuntz; C. H. Reick; E. Maier-Reimer; M. Heimann; M. Scholze; T. Naegler

2009-01-01

70

On the isotopic composition of carbon in soil carbon dioxide  

Microsoft Academic Search

In this study it is shown that the isotopic composition of carbon in soil Coâ differs from the isotopic composition of carbon in soil-respired COâ. Soil COâ collected from a montane soil has an endmember δ¹³C value of -23.3% whereas soil-respired COâ in this system has a δ¹³C value of -27.5%. This difference is very close to the theoretical difference

T. E. Cerling; D. K. Solomon; J. Quade; J. R. Bowman

1991-01-01

71

Potassium isotope abundances in Australasian tektites and microtektites.  

NASA Astrophysics Data System (ADS)

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

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

2008-10-01

72

STABLE CARBON ISOTOPE ANALYSIS OF NUCLEIC ACIDS TO TRACE SOURCES OF DISSOLVED SUBSTRATES USED BY ESTUARINE BACTERIA  

EPA Science Inventory

The natural abundance of stable carbon isotopes measured in bacterial nucleic acids that were extracted from estuarine bacterial concentrates were used to trace sources of organic matter for bacteria in.aquatic environments. he stable carbon isotope ratios of P. aeruginosa and nu...

73

Insights into nitrogen and carbon dynamics of ectomycorrhizal and saprotrophic fungi from isotopic evidence  

Microsoft Academic Search

The successful use of natural abundances of carbon (C) and nitrogen (N) isotopes in the study of ecosystem dynamics suggests\\u000a that isotopic measurements could yield new insights into the role of fungi in nitrogen and carbon cycling. Sporocarps of mycorrhizal\\u000a and saprotrophic fungi, vegetation, and soils were collected in young, deciduous-dominated sites and older, coniferous-dominated\\u000a sites along a successional sequence

Erik A. Hobbie; Stephen A. Macko; Herman H. Shugart

1999-01-01

74

The abundances of elements and isotopes in the solar wind  

NASA Technical Reports Server (NTRS)

Solar wind abundances have now been measured for eleven elements and the isotopes of the noble gases. Aside from solar wind protons and alpha particles, which have been studied extensively since the 1960's, information for heavier elements is limited. Nevertheless, two effects stand out. First is the enrichment of abundances of elements with low first ionization potential (FIP), most likely the combined result of an atom-ion separation process in the upper chromosphere, and a marginal coupling of low-charge-state heavy ions to protons and alphas during the acceleration of the solar wind. Second, there is variability in the solar wind composition over a whole range of time scales. Recent measurements carried out in the earth's magnetosheath during times that included high-speed coronal-hole-associated flows indicate a significantly lower overabundance of low FIP elements. Given the fact that the He/H ratio is remarkably constant in the coronal hole solar wind, this result suggests that both enrichment and variability are reduced in such flows.

Gloeckler, George; Geiss, Johannes

1989-01-01

75

Site-Specific Carbon Isotopes in Organics  

NASA Astrophysics Data System (ADS)

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 ?m. 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 ?13C and the difference in ?13C between the terminal and central carbon position. We tested this method by analyzing mixtures between natural propane and labeled propane (13CH3-12CH2-12CH3). Results are consistent with the expected relative fractionations between the two fragments, indicating limited 'scrambling' of carbon positions of less than 2% in the source. The limits of precision of this method are currently ~0.5 ‰, sufficient to resolve known or suspected position-specific isotope effects in propane. We have explored the expected temperature-dependent equilibrium isotopic distributions of propane using density functional theory and quantum mechanical models of vibrational isotope effects. These models predict the homogeneous isotope exchange equilibria among the various isotopologues of propane, which include several of a wide range of effects that should be measurable by our methods. At 300 K we predict that the central carbon site is 15‰ higher in ?13C and 95 ‰ higher in ?D than the terminal carbon site; similarly the molecule containing both a 13C and D in the central site is enriched by ~120 ‰ relative to a random isotopic distribution at 300 K. These predictions present targets for future experimental and empirical studies of the temperature dependence of isotopic ordering in propane. More generally, the methods we are developing for the study of intramolecular isotopic distributions in propane will serve as a model for future study of similar effects in other organic compounds. [1]DeNiro, Epstein (1977) Science Volume 197, 261-263.

Piasecki, A.; Eiler, J. M.

2012-12-01

76

Isotopic fronts in hydrothermally mineralized carbonate rocks  

Microsoft Academic Search

Advective-dispersive fluid flow through permeable and porous rock causes systematic alteration of the infiltrated rock. O and Sr isotopes can be used as tracers to monitor exchange processes between mineralizing hydrothermal solutions and carbonate host rocks. Fluid infiltration into rock of initially uniform isotopic composition leads to characteristic changes in delta18O and ?87Sr in the rock, that depend on infiltration

H. E. Frimmel

1992-01-01

77

Isotopic fronts in hydrothermally mineralized carbonate rocks  

Microsoft Academic Search

Advective-dispersive fluid flow through permeable and porous rock causes systematic alteration of the infiltrated rock. O and Sr isotopes can be used as tracers to monitor exchange processes between mineralizing hydrothermal solutions and carbonate host rocks. Fluid infiltration into rock of initially uniform isotopic composition leads to characteristic changes in d18O and ?87Sr in the rock, that depend on infiltration

H. E. Frimmel

1992-01-01

78

The effect of rising atmospheric oxygen on carbon and sulfur isotope anomalies in the Neoproterozoic Johnnie Formation, Death Valley, USA  

Microsoft Academic Search

Carbonates within the Rainstorm Member in the terminal Neoproterozoic Johnnie Formation of Death Valley, California record a remarkable negative carbon isotope anomaly – to a nadir of near ?11‰ – that accompanies a dramatic rise in trace sulfate abundance and fall of carbonate associated sulfate ?34S values. The carbonates, including the laterally extensive Johnnie Oolite, were deposited during marine flooding

Alan J. Kaufman; Frank A. Corsetti; Michael A. Varni

2007-01-01

79

On the enrichment of low-abundant isotopes of light chemical elements by gas centrifuges  

Microsoft Academic Search

A brief review of the main areas for the application of the isotopes 15N and 13C is made. Separation of the nitrogen isotopes in a single gas centrifuge in the form of pure nitrogen, ammonia, and trifluoride of nitrogen as well as the carbon isotopes in the form of carbon dioxide has been studied by means of numerical simulation. The

V. D Borisevich; O. E Morozov; Yu. P Zaozerskiy; G. M Shmelev; Yu. D Shipilov

2000-01-01

80

Carbon isotope ratios of organic compound fractions in oceanic suspended particles  

Microsoft Academic Search

To study cycling of organic fractions in the ocean, relative abundances and radio- and stable-carbon isotope measurements of total lipid extract, acid-soluble, and acid-insoluble fractions of suspended particulate organic carbon (POC) were made. Changes in relative abundances occurred mostly in the upper 1000 m of the water column, with a decrease in total lipid extract and the acid-soluble fraction and

Jeomshik Hwang; Ellen R. M. Druffel

2006-01-01

81

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

NASA Technical Reports Server (NTRS)

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.

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

1983-01-01

82

Coprecipitation and isotopic fractionation of boron in modern biogenic carbonates  

SciTech Connect

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.

Vengosh, A. (Australian National Univ., Canberra (Australia) Hebrew Univ., Jerusalem (Israel)); Chivas, A.R.; McCulloch, M.T. (Australian National Univ., Canberra (Australia)); Kolodny, Y.; Starinsky, A. (Hebrew Univ., Jerusalem (Israel))

1991-10-01

83

Carbon dioxide solubility and carbon isotope fractionation in basaltic melt  

SciTech Connect

Carbon dioxide solubility and isotope fractionation data for a MORB composition at 1,200-1,400C and 5-20 kbar have been obtained using piston-cylinder apparatus and stepped-heating mass spectrometry. Carbon dioxide solubility in basalt melt at 5, 10 and 20 kbar is 0.15-0.17%, 0.45-0.51%, and 1.49%, respectively. Values for {Delta}Co{sub 2}(vap) - CO 2/3{sup {minus}} (basalt melt), obtained from the difference between the isotopic compositions for coexisting vapor and melt, vary from 1.8% to 2.2%. A review of measured and estimated values for carbon isotope fractionation between CO{sub 2} vapor and carbon dissolved in basic melts shows variation from 1.8% to 4.6%. Results of this study and other considerations favor relatively small equilibrium CO{sub 2} vapor melt fractionation factors around 2%.

Mattey, D.P. (Univ. of London, Egham Hill (United Kingdom) Univ. of Tasmania, Hobart (Australia))

1991-11-01

84

Abundance and Isotopic Composition of Solar-Wind-Implanted Methane in Lunar Soil and Breccias  

NASA Astrophysics Data System (ADS)

Early analyses of lunar soils have revealed the presence of ppm amounts of indigenous methane and ethane thought to originate from the interaction of carbon and hydrogen in the solar wind [1]. The carbon abundance of lunar soils are typically between 50 to 300 ppm with isotopic compositions ranging from 0 to +20 per mil [2]. Solar wind hydrogen is generally accepted to contain delta D = -1000 per mil i.e. O ppm deuterium content; as indicated from D/H measurements of lunar hydrogen, after correction for contamination effects of terrestrial water from the sample [3]. In addition, recent solar spectroscopic measurements have detected hydrogen bearing molecules e.g. water [4]. Hence, isotopic analyses of methane in lunar samples can provide valuable information about isotopic composition of solar wind implanted species. For this study, we have analyzed methane from lunar soil A12023 and a breccia fragment taken from soil A10086. The methane from these samples was released by stepped pyrolysis and introduced into a new static vacuum mass spectrometer, MIRANDA (capable of measuring the delta l3C of ng amounts of methane to a precision of +/- 0.2 per mil. Isotopic compositions and abundances are calculated from 17M/l6M ratios in methane from which the delta 13C values can be determined assuming that solar wind hydrogen is delta D = -1000 per mil. Results from A12023 are presented in Figure 1, results from A10086 are discussed elsewhere [5]. Both samples displayed a broad release of methane between 400 degrees C and 800 degrees C with yields of 1.3 ppm and 1.9 ppm for the soil and the breccia respectively, consistent with previous measurements of ppm amounts of methane [1]. Figure 1 illustrates that methane in A12023 is isotopically heavy with a plateau of delta 13C = +55 per mil at a temperature between 500 degrees C and 600 degrees C. This is consistent with the previous measurement of A10086 [5] which also revealed isotopically heavy carbon with delta 13C approximately of +60 per mil. There is a possibility of hydrogen isotope exchange between water in the sample and methane, although unlikely below 600 degrees C. The delta l3C values have also been recalculated using a delta D of -360 per mil, the average delta D of water extracted from lunar material [6]. In this case a delta l3C of +20 per mil is obtained for the methane, in closer agreement to previous analyses which have a maximum delta 13C = +15 per mil [7]. Our preliminary investigations have indicated that the carbon in the methane is isotopically distinct from other lunar carbon sources. However further analyses are required to measure both delta 13C and delta D in a variety of lunar samples to verify the hypothesis that the methane is of solar wind origin. References: [1] Abell P. I. et al. (1970) Nature, 226, 251-252. [2] Epstein S. and Taylor H. P.(1973) Proc. LSC 4th, 1559-1575. [3] Epstein S. and Taylor H. P. (1972) Proc. LSC 3rd, 1429-1454. [4] Wallace L. et al. (1995) Science, 268, 1155-1158. [5] Brilliant D. R. et al. (1994) LPS XXV, 173-174. [6] Merlivat L. et al. (1972) Proc. LSC 3rd, 1473-1477. [7] Chang S. et al. (1974) GCA, 38, 853-872.

Lecluse, C.; Morse, A. D.; Butterworth, A. L.; Brilliant, D. R.; Pillinger, C. T.

1995-09-01

85

Isotope abundance of {sup 180}Ta{sup m} and p-process nucleosynthesis  

SciTech Connect

The p-process of stellar nucleosynthesis produces the stable neutron-deficient nuclides heavier than the iron peak elements. An accurate determination of the isotopic composition of tantalum is required to enable p-process nucleosynthetic calculations to be evaluated in terms of an accurate isotope abundance for {sup 180}Ta. This odd-odd nuclide has the remarkable property of having a long-lived isomeric state and a short-lived ground state, so that in reality one is measuring the isotope abundance of {sup 180}Ta{sup m}, which is a unique situation in nature. {sup 180}Ta{sup m} is the rarest isotope of nature's rarest element and is therefore an important isotope in deciphering the origin of the p-process. Because the isotopic composition of tantalum has only been measured on two occasions with relatively large uncertainties, an accurate determination is required to provide a better basis for p-process production calculations. A thermal ionization mass spectrometer was used to measure the isotope abundance of {sup 180}Ta{sup m} with high precision. The linearity of this instrument was verified by measuring the isotopically certified reference material for potassium (NIST 985), whose isotopes span a wide range of isotope ratios. The abundance sensitivity of the mass spectrometer for the measured ion beams has been examined to ensure the absence of tailing effects and interfering isotopes. These procedures are essential because of the extremely low isotope abundance of {sup 180}Ta{sup m}. The isotope fractionation of the tantalum isotopes was estimated by reference to the isotope fractionation of the isotopically certified reference material for rhenium (NIST 989). The isotopic composition of tantalum has been determined to be {sup 181}Ta/{sup 180}Ta{sup m}=8325 {+-} 43, which gives isotope abundances for {sup 180}Ta{sup m}=0.0001201 {+-} 0.0000008 and {sup 181}Ta=0.9998799 {+-} 0.0000008. This gives a Solar System abundance of {sup 180}Ta{sup m} of 2.49 x 10{sup -6} with reference to silicon=10{sup 6}. These isotope abundances, together with the relative atomic masses, give an atomic weight for tantalum of 180.947878 {+-} 0.000002.

Laeter, J.R. de; Bukilic, N. [Department of Applied Physics, Curtin University of Technology, GPO Box U1987, Perth, Western Australia 6845 (Australia)

2005-08-01

86

Carbon isotope fractionation during microbial methane oxidation  

NASA Astrophysics Data System (ADS)

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.

Barker, James F.; Fritz, Peter

1981-09-01

87

Carbon isotopic exchange between dissolved inorganic and organic carbon  

NASA Astrophysics Data System (ADS)

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. DOC observed in the deep ocean might therefore have a terrestrial DOC carbon skeleton with a carboxyl-rich component that is marine in origin.

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

2009-12-01

88

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

NASA Astrophysics Data System (ADS)

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 (?13C) between HCHO and fuel isotopic ratios was 7.4 ± 0.7‰, which was higher than that of HCHO from stand-alone gasoline engine (?13Cmax = 2.7‰), suggesting additional consumption by the catalytic converter. For diesel vehicle without catalytic converter, ?13C 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 the accordance of carbon isotopic data.

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

2014-04-01

89

Carbon and nitrogen abundances determined from transition layer lines  

NASA Technical Reports Server (NTRS)

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.

Boehm-Vitense, Erika; Mena-Werth, Jose

1992-01-01

90

Interpretation of the carbon abundance in Saturn measured by Cassini  

NASA Astrophysics Data System (ADS)

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 measured in Jupiter by Galileo.

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

2008-06-01

91

The geochemistry of the stable carbon isotopes  

Microsoft Academic Search

Several hundred samples of carbon from various geologic sources have been analyzed in a new survey of the variation of the ratio C 13 \\/C 12 in nature. Mass spectrometric determinations were made on the instruments developed by H. C. and his co-workers utilizing two complete feed systems with magnetic switching to determine small differences in isotope ratios between samples

Harmon Craig

1953-01-01

92

Carbon abundance and silicate mineralogy of anhydrous interplanetary dust particles  

NASA Astrophysics Data System (ADS)

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.

Thomas, K. L.; Blanford, G. E.; Keller, L. P.; Klock, W.; McKay, D. S.

1993-04-01

93

Carbon isotopes in biological carbonates: Respiration and photosynthesis  

USGS Publications Warehouse

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.

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

1997-01-01

94

Daily Variation of Isotope Ratios in Mars Atmospheric Carbon Dioxide  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

95

Contributions to the carbon isotopic composition of pedogenic carbonate in Aridisols  

NASA Astrophysics Data System (ADS)

Pedogenic carbonate is a common feature of arid and semi-arid soils. The stable carbon isotopic composition of soil carbonate is widely used for paleoenvironment reconstruction. The use of soil carbonate as a paleo-proxy depends on the applicability of the diffusion-production model of the isotopic composition of soil CO2 under conditions that may be highly variable, and unconstrained in the fossil record. In order to assess the applicability and appropriate model parameters of the diffusion-production model, we studied pedogenic clast coatings from Aridisols on alluvial fans across west-central Utah. To maximize potential variation in lithogenic vs. biogenic carbon, we selected sites from eight alluvial fans with different drainage basin lithologies, which included quartz sandstone, rhyolite, marine carbonate, and sulfide-rich black shale and marine carbonate. We targeted sites with abundant juniper vegetation to minimize variation in the isotopic composition of biogenic carbon and obtain ?13C values of C3-dominated vegetation. To constrain variation in the ?13C values of soil organic carbon (SOC) with elevation, we collected soil organic matter from vegetation zones along an elevation transect along the Stansbury Range. We observed decreasing ?13C values with increasing elevation with each vegetation zone having a characteristic ?13C value. In order to minimize variation in the atmospheric carbon contribution to soil carbonate, all clast coatings were collected from ~60cm depth. The ?13C values of SOC from the 8 sites had a narrow range from -25.4 to -23.8‰, suggesting we successfully minimized variation in the isotopic composition of biogenic carbon by targeting the juniper vegetation zone. The ?13C values of soil carbonate from all sites ranged from -6.6 to -3.3‰. We expected to see lithogenic carbon contribution in soils with sulfide-rich black shale, however the limited variation in ?13CPC suggests that biogenic carbon is the dominant contribution to the carbon isotopic composition of soil carbonate. However, the observed ~20‰ difference between ?13CSOC and ?13CPC indicates that assuming a cumulative ~15‰ fractionation to estimate ?13C of paleo-biomass from ?13CPC may be problematic. Soil respiration rates must be lower than is generally assumed to account for this difference under the assumptions of the diffusion-production model of soil CO2-carbonate. Respiration rates between 1x10-11 to 2x10-11 mol cm-2 s-1 would account for the observed difference in the carbon isotopic composition of soil carbonate and SOC. Measured respiration rates peak (~1.4x10-10 mol cm-2 s-1) early in the morning and decrease during the day to ~2x10-11 mol cm-2 s-1. Our results suggest caution if using pedogenic clast coatings from Aridisols to reconstruct paleo-vegetation. Lithogenic carbon does not contribute to the carbon isotopic composition of soil carbonate but without accounting for low respiration rates the ?13C values of soil carbonate would suggest a greater C4 contribution when using assumptions of respiration rates on the order of 1.5x10-10 mol cm-2 s-1 or greater.

Wilson, J. N.; Powell, R.; Wynn, J. G.

2013-12-01

96

Photosynthetic isotope fractionation: oxygen and carbon  

SciTech Connect

Isotopic carbon analyses of plant tissue and carbon dioxide from air samples and plant and soil respiration were made. Soil respiratory CO/sub 2/ is about 15/sup 0///sub 00/ lighter than atmospheric CO/sub 2/. Plant isotopic ratios were found to be influenced by (1) plant photosynthetic efficiency, (2) source CO/sub 2/, (3) airflow, and (4) CO/sub 2/ concentrations. Etiolated bean plants have nearly the same delta/sup 13/C value as seed carbon and seed dark respiratory CO/sub 2/. Mature leaves from greenhouse grown beans, however, are some 5 /sup 0///sub 00/ lighter than seed carbon. This is a result of CO/sub 2/ source, i.e., plant or soil respiratory CO/sub 2/. Leaves which are generally lighter than other plant organs becomes still lighter during the growing season. As a consequence of increasingly light leaf carbon, photorespired CO/sub 2/ also becomes lighter during the growing season. Oxygen isotopic values were measured for (1) photorespiratory CO/sub 2/, which reflects equilibration with leaf water, and (2) photosynthetic O/sub 2/, which is enriched in /sup 18/O, perhaps due to respiratory or photorespiratory /sup 16/O preference.

Martin, G.E. II

1982-01-01

97

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

NASA Astrophysics Data System (ADS)

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.

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

2014-02-01

98

Carbonate Ion Effects on Coccolith Carbon and Oxygen Isotopes  

NASA Astrophysics Data System (ADS)

The stable oxygen and carbon isotopic composition of biogenic calcite constitutes one of the primary tools used in paleoceanographic reconstructions. The ?18O of shells of ocean floor microfossils and corals reflects the composition of the paleo-seawater as they use the oxygen to build up their calcite and aragonite shells. The ?13C is used to reconstruct variations in the carbon isotopic composition of dissolved inorganic carbon in the ocean, which is controlled by biological productivity through the removal of isotopically light carbon in organic matter. To be effective and sensitive tools for understanding photic zone processes it is first necessary to understand the various biological fractionations associated with carbonate precipitation. To date, isotopic fractionation models are mainly based on foraminifera and corals but not on coccoliths, tiny plates produced by coccolithophore algae, which are often the most dominant carbonate contributors to pelagic sediments. As photosynthetic organisms, their chemistry can provide a sensitive tool for understanding photic zone processes. Coccoliths may be the most important carbonate phase for geochemical analysis in sediments where foraminifera are less common and/or core material is limited, such as in subpolar regions and for Early Cenozoic and Mesozoic sediments. Here we report experimental results on a common living coccolithophore species showing that the 13C/12C and 18O/16O ratios decrease with the increase of HCO^{3-} (CO32-). The selected species are among the heaviest calcifying extant coccolithophores and are major contributors to present coccolith carbonate export production. Because coccolithophores are photosynthetic organisms that calcify intracellularly in specialized vesicles, the challenge lies in ascertaining how kinetic and thermodynamic processes of isotopic fractionation are linked to cellular carbon "transport" and carbonate precipitation. This is a daunting challenge since studies have not conclusively distinguished whether C is taken up only as CO2 by passive diffusion or also by active transport of CO2 or HCO^{3-} . In reality, the patterns of stable isotopic variations in coccoliths may provide more constraints for unraveling the cellular C transport and the calcification mechanisms. We will present latest findings on these issues, both from culture experiments and sediment traps located in the Bay of Bengal. Coccolith species separated from these sediment traps also show evidence of carbonate ion effects.

Ziveri, P.; Probert, I.; Stoll, H. M.

2006-12-01

99

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

NASA Technical Reports Server (NTRS)

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.

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

2006-01-01

100

Carbon and Strontium Abundances of Metal-Poor Stars  

E-print Network

We present carbon and strontium abundances for 100 metal-poor stars measured from R$\\sim $7000 spectra obtained with the Echellette Spectrograph and Imager at the Keck Observatory. Using spectral synthesis of the G-band region, we have derived carbon abundances for stars ranging from [Fe/H]$=-1.3$ to [Fe/H]$=-3.8$. The formal errors are $\\sim 0.2$ dex in [C/Fe]. The strontium abundance in these stars was measured using spectral synthesis of the resonance line at 4215 {\\AA}. Using these two abundance measurments along with the barium abundances from our previous study of these stars, we show it is possible to identify neutron-capture-rich stars with our spectra. We find, as in other studies, a large scatter in [C/Fe] below [Fe/H]$ = -2$. Of the stars with [Fe/H]$<-2$, 9$\\pm$4% can be classified as carbon-rich metal-poor stars. The Sr and Ba abundances show that three of the carbon-rich stars are neutron-capture-rich, while two have normal Ba and Sr. This fraction of carbon enhanced stars is consistent with other studies that include this metallicity range.

David K. Lai; Jennifer A. Johnson; Michael Bolte; Sara Lucatello

2007-06-20

101

Abundances of Linear Carbon-Chain Molecules in Supernovae  

NASA Technical Reports Server (NTRS)

This paper evaluates the condensation of carbon solids in a gas of pure C and O atoms when these exist within the interior of an expanding young supernova. We calculate the abundances of large carbon molecules, which serve as nucleations for condensation of graphites. Additional information is contained in the original extended abstract.

Clayton, D. D.; Deneault, E.; Meyer, B. S.; The, L.-S.

2001-01-01

102

Precision performance of a Cavity Ring-down isotope spectrometer for carbon and oxygen isotopes of carbonate materials  

NASA Astrophysics Data System (ADS)

We have developed a novel laser spectrometer intended specifically for the measurement of ?18O and ?13C in solid carbonate material. Carbonate carbon and oxygen isotopes provide key contributions into our understanding of climate, biogeochemical processes and the carbon cycle. For this reason, the isotopic measurements of carbonates are one of the most abundant measures made by Earth scientists today. Conventional measurement techniques using isotope ratio mass spectrometry (IRMS), although optimized and prevalent, require dedicated personnel and can be expensive to operate. Here we present a new laser-based technique that will simplify measurements of ?18Ocarb and ?13Ccarb without compromising precision. To date, there have been no laser-based instruments with a demonstrated ability to meet the requirements of the carbonates community -- typically better than 0.1 ‰ for ?13C and ?18O for CO2 evolved from 1 mg of pure CaCO3. We will present data showing that the new Picarro G2171-i spectrometer meets these requirements. The spectrometer uses the laser-based spectroscopy technique of Cavity Ring-Down Spectroscopy (CRDS), a technology that has been successfully applied to many other isotopic ratio measurements including ?13C of CO2, ?13C of CH4, and ?18O and ?D of H2O. The spectrometer has been optimized to analyze the absorption spectra of concentrated CO2, specifically the isotopologues 12C16O16O, 13C16O16O, 12C16O18O, and 12C18O16O. We employ a new sample delivery technique that enables a longer integration time period, and hence more precise data. Long-term results for a run of 540 pulses of tank CO2 (90 hours) records a 1? standard deviation precision for ?18O and ?13C of < 0.08 ‰ and < 0.055 ‰, respectively. We coupled the CRDS spectrometer to an optimized sample acidification system and analyzed standards to assess the accuracy of the CRDS. We will present an inter-comparison between CRDS and IRMS for carbonates using standards commonly used as isotopic reference material for the calibration of IRMS instruments. The new CRDS spectrometer will provide researchers with a simplified option to accelerate the pace and breadth of carbonates-based research.

Cunningham, K. L.; Hoffnagle, J.; He, Y.; Fleck, D.; Saad, N.; Dennis, K.

2013-12-01

103

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

NASA Technical Reports Server (NTRS)

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 studies form the necessary precursors to the development of compact, lightweight stable isotope/trace gas sensors for future planetary missions.

Blake, Geoffrey A.

2004-01-01

104

Carbon isotopic composition of individual Precambrian microfossils  

NASA Technical Reports Server (NTRS)

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.

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

2000-01-01

105

Variations in Lead Isotopic Abundances in Sprague-Dawley Rat Tissues: Possible Reason of Formation  

PubMed Central

It has been reported in previous research that the lead isotopic composition of blood, urine and feces samples statistically differed from the given lead sources in Sprague-Dawley (SD) rats. However, the reason for this phenomenon is still unclear. An animal experiment was performed to investigate the lead isotope fractionation in diverse biological samples (i.e., lungs, liver, kidneys, bone) and to explore the possible reasons. SD rats were intratracheally instilled with lead acetate at the concentrations of 0, 0.02, 0.2, and 2 mg/kg body weight. Biological samples were collected for lead isotope analysis using an inductively coupled plasma mass spectrometry (ICP-MS). Significant differences are observed in lead isotope abundances among the diverse biological samples. The lead isotope abundances (206Pb, 207Pb and 208Pb) in diverse biological samples show different degrees and directions of departure from the given lead source. The results suggest that differences in enrichment or depletion capacity for each lead isotope in the various tissues might lead to the variation in lead isotopic abundances in tissues. Moreover, a nonlinear relationship between the blood lead level and the lead isotope abundances in liver and bone is observed. When the whole-blood level is higher than 50 ng/mL, the lead isotopic compositions of biological samples tend to be the same. Thus, the data support the speculation of a fractionation functional threshold. PMID:24587048

Liu, Duojian; Wu, Jing; Ouyang, Li; Wang, Jingyu

2014-01-01

106

Carbon and hydrogen isotope fractionation by moderately thermophilic methanogens1  

Microsoft Academic Search

is enriched in 13C when compared with other natural sources of methane; the magnitude of this isotope effect raises the possibility that methane produced at elevated temperature by the aceticlastic reaction could be mistaken for thermogenic methane based on carbon isotopic content. Studies of H2\\/CO2 methanogenesis were conducted with Methanothermobacter marburgensis . The fractionation of carbon isotopes between CO2 and

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

2004-01-01

107

BOREAS TE-5 Leaf Carbon Isotope Data  

NASA Technical Reports Server (NTRS)

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).

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

2000-01-01

108

(Carbon isotope fractionation in plants: Progress report)  

SciTech Connect

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.

Not Available

1987-01-01

109

Carbon isotope fractionation in autotrophic Chromatium  

E-print Network

) August 1974 ABSTRACT Carbon Isotope Fractionation in Autotrophic Chromatium (August 1974) blilliam Wai-Lun Wang, B. S. , Texas Lutheran College Co-Chairmen of Advisory Committee: Dr. Isilliam N. Sackett Dr. Chauncey P. . Benedict Bacterial cells... cellular constituents and 13 metabolic intermediates of autotrophic Chroma- tium 5 A comparison of the 6 C values of cottc n, 13 sorghum and autotrophic Chromatium 51 jx LIST OF FIGURES Figure Page 1 The Calvin Cycle (BASSHAN and CALVIN, 1957) . . 5...

Wong, William Wai-Lun

1974-01-01

110

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

USGS Publications Warehouse

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.

Meier, A.L.

1982-01-01

111

Low temperature Rosseland opacities with varied abundances of carbon and nitrogen  

E-print Network

We attempt to produce low temperature opacity data incorporating the effects of varied abundances of the elements carbon and nitrogen. For our temperature range of interest, molecules represent the dominant opacity source. Our dataset covers a wide metallicity range and is meant to provide important input data for stellar evolution models and other applications. We conduct chemical equilibrium calculations to evaluate the partial pressures of neutral atoms, ions, and molecules. Based on a large dataset containing atomic line and continuum data and, most importantly, a plethora of molecular lines, we calculate Rosseland mean opacity coefficients not only for a number of different metallicities, but also for varied abundances of the isotopes ^{12}C and ^{14}N at each metallicity. The molecular data comprise the main opacity sources for either an oxygen-rich or carbon-rich chemistry. We tabulate the opacity coefficients as a function of temperature and, basically, density. Due to the special role of the CO molecule, within a certain chemistry regime an alteration to the carbon abundance causes considerable changes in the Rosseland opacity. The transition from a scaled solar (i. e. oxygen-rich) mixture to a carbon-rich regime results in opacities that can, at low temperatures, differ by orders of magnitude from to the initial situation. The reason is that the mean opacity in either case is due to different molecular absorbers. Variations in the abundance of nitrogen have less pronounced effects but, nevertheless, cannot be neglected. [abridged

Michael T. Lederer; Bernhard Aringer

2008-12-09

112

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

PubMed Central

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

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

2014-01-01

113

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

NASA Technical Reports Server (NTRS)

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.

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

1981-01-01

114

ORIGINAL PAPER Carbon isotope ratio measurements of glyphosate  

E-print Network

ORIGINAL PAPER Carbon isotope ratio measurements of glyphosate and AMPA by liquid chromatography chromatography coupled to isotope ratio mass spectrometry. We demon- strate that this analysis can be carried out

115

Stable Carbon Isotope Ratios for Giant Stars in the Globular Cluster M13  

NASA Astrophysics Data System (ADS)

Recently, our paradigm for the formation and evolution of globular clusters has shifted. We now understand that the majority of present-day stars in globular clusters formed as second-generation stars, primarily from the ejecta of first-generation AGB stars, while the majority of first generation, less centrally concentrated stars, have been dynamically lost to the cluster (D'Ercole et al. 2011). This paradigm explains the observed star-to-star variations in the abundances of light element observed in globular clusters, and suggests that the carbon isotope ratio should be similarly differentiated between first and second generation stars. In an effort to verify this scenario, we have recently utilized the Gemini/NIFS to determine carbon isotope abundances (12C and 13C) for 18 giant stars in the globular clusters M13 through medium-resolution (R ˜ 5300) infrared spectroscopy of the first-overtone CO bands near 2.3 ?m. Our program stars are distributed from the tip of the RGB to the BLF (the bump in the luminosity function) of M13, and their Na, Mg, and Al abundances are already known from homogeneous data set analysis. Therefore, adding reliable abundances of the stable carbon isotopes to this homogeneous spectroscopic sample permits systematic tests of cluster chemical evolution models. We report preliminary results of the carbon abundance analysis for our NIFS K-band spectra and present an overview of our ongoing effort with other globular clusters.

Rhee, Jaehyon; Pilachowski, C. A.

2013-01-01

116

Carbon Abundances in the Small Magellanic Cloud Planetary Nebulae  

E-print Network

As an ongoing study of Magellanic Cloud PNe we have obtained UV spectra of 9 PNe in the SMC to measure their carbon abundances. The spectra have been acquired with ACS HRC/PR200L and SBC/PR130L. The ACS prisms give a reasonable resolution in the range of 1200 -- 2500 A to detect the C IV, C III], and C II] nebular emission, essential for chemical studies of the PNe. The carbon abundances of SMC PNe, together with those of the LMC previously determined with STIS spectroscopy, will allow a comparative study of nebular enrichment and provide the basis for comparison with stellar evolution models at various metallicity.

T. -H. Lee; L. Stanghellini; R. A. Shaw; B. Balick; E. Villaver

2006-05-31

117

Mechanism of Carbon Isotope Fractionation Associated with Lipid Synthesis  

Microsoft Academic Search

The low carbon-13\\/carbon-12 ratio of lipids is shown to result from isotopic fractionation during the oxidation of pyruvate to acetyl coenzyme A. In vitro analysis of the kinetic isotope effects of this reaction indicates that there will be a large, temperature-dependent difference in the carbon-13\\/carbon-12 ratio between the methyl and carbonyl carbon atoms of acetyl coenzyme A and between those

Michael J. Deniro; Samuel Epstein

1977-01-01

118

Carbon isotope labelling in graphene research  

NASA Astrophysics Data System (ADS)

The large scale production of graphene for any potential application relies on catalytic chemical vapour deposition (CVD). Despite much effort put into the graphene CVD research, there are still many challenges to be solved, not only concerning the growth itself, but also the subsequent treatment, i.e. transfer from the catalyst to a desired substrate. The need for fast progress naturally necessitates easy-to-use, versatile and efficient characterization methods. This perspective reviews the recent advances and potential of probably the most prospective one - Raman spectroscopy in connection with carbon isotope labelling of the CVD grown graphene layers. We discuss its use for the explanation and optimization of the growth process, followed by examples of employing isotope engineering in the studies of fundamental properties of graphene, not only by Raman spectroscopy.

Frank, O.; Kavan, L.; Kalbac, M.

2014-05-01

119

Carbon Abundances in the Galactic Thin and Thick Disks  

E-print Network

Although carbon is, together with oxygen and nitrogen, one of the most important elements in the study of galactic chemical evolution its production sites are still poorly known and have been much debated (see e.g. Gustafsson et al. 1999; Chiappini et al. 2003). To trace the origin and evolution of carbon we have determined carbon abundances from the forbidden [C I] line at 8727 A and made comparisons to oxygen abundances from the forbidden [O I] line at 6300 A in a sample of 51 nearby F and G dwarf stars. These data and the fact that the forbidden [C I] and [O I] lines are very robust abundance indicators (they are essentially insensitive to deviations from LTE and uncertainties in the stellar parameters, see, e.g., Gustafsson et al. 1999; Asplund et al. 2005) enable us to very accurately measure the C/O ratio as well as individual C and O abundances. Our first results indicate that the time-scale for the main source that contribute to the carbon enrichment of the interstellar medium operate on the same time-scale as those that contribute to the iron enrichment (and can possibly be AGB stars...)

T. Bensby; S. Feltzing

2005-06-07

120

The Abundances of Oxygen and Carbon in the Solar Photosphere  

Microsoft Academic Search

A series of recent studies has placed the best estimates of the photospheric abundances of carbon and oxygen at log ? =8.39 and 8.66, respectively. These values are ˜ 40 % lower than earlier estimates. A coalition of corrections due to the adoption of an improved model atmosphere, updated atomic data and non-LTE corrections, and a reevaluation of the effect

C. Allende Prieto

2008-01-01

121

Carbon and nitrogen stable isotope ratios in body tissue and mucus of feeding and fasting earthworms ( Lumbricus festivus )  

Microsoft Academic Search

We used natural abundance stable isotope techniques to estimate carbon and nitrogen turnover rates in body tissue and mucus\\u000a of earthworms. Isotope ratios of carbon (?13C) and nitrogen (?15N) were monitored simultaneously in body tissue and mucus for up to 101?days in feeding or fasting Lumbricus festivus kept in an artificial substrate. When the diet of the earthworms was switched

Olaf Schmidt; Charles M. Scrimgeour; James P. Curry

1999-01-01

122

Primary and diagenetic controls of isotopic compositions of iron-formation carbonates  

NASA Technical Reports Server (NTRS)

Results are presented on parallel analyses of carbonate and chert microbands in segments from the early Proterozoic Dales Gorge Member of the Brockman Iron Formation (western Australia), including data on isotopic, chemical, and mineralogic variations in microbanded carbonates, cherts, and coexisting minerals in four core segments from Paraburdoo and one from Wittenoom. It is shown that patterns of variation observed in isotopic abundance and mineral composition can be consistently explained in terms of diagenetic replacement of fine-grained primary precipitates by secondary ones, rather than by mineral-dependent fractionations, metamorphism, or the influence of large volumes of water in an open system.

Kaufman, Alan J.; Hayes, J. M.; Klein, C.

1990-01-01

123

Barium even-to-odd isotope abundance ratios in thick disk and thin disk stars  

E-print Network

We present the Ba even-to-odd isotope abundance ratios in 25 cool dwarf stars with the metallicity [Fe/H] ranged between 0.25 and --1.35. Our method takes advantage of the hyperfine structure (HFS) affecting the \\ion{Ba}{ii} resonance line of the odd isotopes. The fractional abundance of the odd isotopes of Ba is derived from a requirement that Ba abundances from the resonance line $\\lambda 4554$ and subordinate lines $\\lambda 5853$ and $\\lambda 6496$ must be equal. The results are based on NLTE line formation and analysis of high resolution (R $\\sim60000$) high signal-to-noise (S/N $\\ge 200$) observed spectra. We find that the fraction of the odd isotopes of Ba grows toward the lower Ba abundance (or metallicity) and the mean value in the thick disk stars equals 33 $\\pm$ 4%. This indicates the higher contribution of the $r-$process to barium in the thick disk stars compared to the solar system matter. The obtained fraction increases with the [Eu/Ba] abundance ratio growth in agreement with expectations. A significant fraction of the \\emph{even} isotopes of Ba found in old Galactic stars (the thick disk stars), $\\sim67$%, is in contrast to the prediction of the "classical" model of the $s-$process and favors the value predicted by the "stellar" models of Arlandini et al. (1999) and Travaglio et al. (1999).

L. Mashonkina; G. Zhao

2006-07-06

124

Carbon chain abundance in the diffuse interstellar medium  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

125

13C isotope separation using multiphoton excitation of carbon monoxide  

NASA Astrophysics Data System (ADS)

We report a possible means to selectively isolate 13C from carbon monoxide (CO) exploiting multiphoton dissociation near 199 nm. At ?=199.363 nm we observed mass spectra with greater than 95% 13C+ ions produced from CO with normal isotopic abundance. The technique of velocity map ion imaging was applied to explore this effect. The complete mechanism for the 13C+ detection reads as follows: CO( X1? +)+h?? CO( a3? 1), CO( a3? 1)+h?? C( 1D2)+ O( 3P0), C( 1D2)+h?? C( 3P1), C( 3P1)+h?? C++ e-. We also report the molecular constants for the CO h 3? + state for 12CO(? 00=100 385 .5 cm-1, B=1.97 1 cm-1) .

Hansen, Nils; Wodtke, Alec M.

2002-04-01

126

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

SciTech Connect

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.

McConnaughey, T.A.

1986-01-01

127

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)

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 same strength (LmaxHe ˜3 × 106 Lsun, LminHe ˜ 100 Lsun) as in AGB models with CO cores of mass ˜1 Msun, but the time between flashes (˜200 yr) and the mass of helium fuel built up between flashes (˜1.3 x 10-4 Msun) are much smaller. The amount of energy released in a flash is not enough to propel matter at the hydrogen-helium discontinuity far enough outward that associated cooling extinguishes hydrogen burning LminH ˜ 6 × 104 Lsun, (LmaxH ˜ 6 × 104 Lsun). The temperature at the base of the convective shell forced by helium burning attains a maximum of TmaxCSB ˜ 360 × 106 K. Depending on the choice of cross section for the 22Ne(?, n)25Mg reaction, 50%-80% the 22Ne initially in the convective shell is converted into 25Mg, providing 20-30 neutrons for every 56Fe seed nucleus. The neutron density (˜6 x 1012 cm-3) is presumably much larger than is appropriate for producing s-process isotopes in the solar system distribution at critical branch points. During pulse powerdown, at least 7% and perhaps as much as 30% of the matter which has been in the convective shell is dredged up into the convective envelope. Thus, an observational counterpart of the model may exhibit an enhancement of heavy s-process isotopes in a nonsolar distribution and Mg isotopes in a distinctly nonsolar distribution, but because of the large mass of the convective envelope, these anomalies may not be detectable in a typical TPSAGB star. The abundance of Li relative to H in a model may be much larger or much smaller than Li/H ˜ 10-10, depending on the treatment of convection and on where the model is in the TPSAGB phase. At the beginning of the TPSAGB phase, the surface abundances by number of CNO elements are in the ratio (C:N:0) = (2.4:4.3:6.3), compared with the initial ratios (C:N:0) = (3.6:1.0:8.0). During the TPSAGB phase, the ratio of C to N decreases, and the ratio of 12C to 13C decreases from ˜25 to ˜4. A test of these predictions involves abundance estimates of the brightest long-period variables in the Galaxy and in the Magellanic Clouds. Perhaps the major signature

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

1996-03-01

128

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

PubMed

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 rate of stable carbon isotopes in hair was low in L. curasoae and undetectable in G. soricina, which may be explained by the seasonal growth of the hair in these two species. Because both species are small (10 and 25 g, respectively) and nectar-feeding bats have higher mass-specific metabolic rates than bats in temperate regions or similar sized terrestrial mammals, our findings of low turnover rates were unexpected. PMID:12624176

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

2003-04-01

129

Degradation changes stable carbon isotope depth profiles in palsa peatlands  

NASA Astrophysics Data System (ADS)

Palsa peatlands are a significant carbon pool in the global carbon cycle and are projected to change by global warming due to accelerated permafrost thaw. Our aim was to use stable carbon isotopes as indicators of palsa degradation. Depth profiles of stable carbon isotopes generally reflect organic matter dynamics in soils with an increase of ?13C values during aerobic decomposition and stable or decreasing ?13C values with depth during anaerobic decomposition. Stable carbon isotope depth profiles of undisturbed and degraded sites of hummocks as well as hollows at three palsa peatlands in northern Sweden were used to investigate the degradation processes. The depth patterns of stable isotopes clearly differ between intact and degraded hummocks at all sites. Erosion and cryoturbation at the degraded sites significantly changes the stable carbon isotope depth profiles. At the intact hummocks the uplifting of peat material by permafrost is indicated by a turning in the ?13C depth trend, and this assessment is supported by a change in the C / N ratios. For hollows isotope patterns were less clear, but some hollows and degraded hollows in the palsa peatlands show differences in their stable carbon isotope depth profiles indicating enhanced degradation rates. We conclude that the degradation of palsa peatlands by accelerated permafrost thawing can be identified with stable carbon isotope depth profiles. At intact hummocks ?13C depth patterns display the uplifting of peat material by a change in peat decomposition processes.

Krüger, J. P.; Leifeld, J.; Alewell, C.

2014-06-01

130

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

NASA Technical Reports Server (NTRS)

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.

Boehme, Susan E.

1993-01-01

131

s-process studies - Xenon and krypton isotopic abundances  

NASA Technical Reports Server (NTRS)

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.

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

1978-01-01

132

Measurement of isotopic abundances in collected stratospheric ozone samples  

SciTech Connect

Enrichment of heavy O{sub 3} isotopes has been measured in collected stratospheric samples. A balloon-borne cryogenic sampler was used to gather six O{sub 3} samples between 26 and 35 km in three flights. Subsequent laboratory mass spectrometer analysis of rare O{sub 3} isotopes at both mass 49 and 50 has resulted in more precise measurements than have previously been reported with in situ and ground-based techniques. In one flight, {sup 50}O{sub 3} was enriched by 12-16% and {sup 49}O{sub 3} by 9-11%, both increasing with altitude. In the remaining two flights, the isotope enrichment was nearly mass-independent at 8-9%. The enrichments in O{sub 3} at mass 50 are less than the large 40% value observed in some stratospheric measurements but similar to {sup 49}O{sub 3} and {sup 50}O{sub 3} fractionations produced in laboratory-generated ozone.

Schueler, B.; Morton, J.; Mauersberger, K. (Univ. of Minnesota, Minneapolis (USA))

1990-08-01

133

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

NASA Technical Reports Server (NTRS)

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.

Marti, K.

1980-01-01

134

Isotopic Simple Global Carbon Model: the Use of Carbon Isotopes for Model Development  

NASA Astrophysics Data System (ADS)

Carbon dioxide is a major greenhouse gas in the atmosphere. Anthropogenic CO_2 emissions from fossil fuel use and deforestation have perturbed the natural global carbon cycle. As a result, the atmospheric CO_2 concentration has rapidly increased, causing the potential for global warming. A twenty four compartment isotopic simple global carbon model (ISGCM) has been developed for scenario analysis, research needs prioritization, and for recommending strategies to stabilize the atmospheric CO_2<=vel. CO_2 fertilization and temperature effects are included in the terrestrial biosphere, and the ocean includes inorganic chemistry which, with ocean water circulation, enables the calculation of time-variable oceanic carbon uptake. The eight compartment simple global carbon model (SGCM) served as the basis of the ISGCM model development. Carbon isotopes, ^{13}C (stable carbon) and ^{14}C (radiocarbon), were used for model constraints as well as results from SGCM that led to multiple compartments in ISGCM. ISGCM was calibrated with the observed CO _2 concentration, delta^ {13}C, and Delta^ {14}C in the atmosphere, Delta ^{14}C in the soil, and delta^{13}C and Delta^{14}C in the ocean. Also, ISGCM was constrained by literature values of oceanic carbon uptake (gas exchange) and CO_2 emissions from deforestation. Inputs (forcing functions in the model) were the CO_2 emissions from fossil fuel use and deforestation. Scenario analysis, together with emission strategies tests, indicate that urgent action to reduce anthropogenic emissions would need to be taken to stabilize atmospheric CO_2. Results showed that quantitatively, forest management is just as effective as the reduction of fossil fuel emissions in controlling atmospheric CO _2. Sensitivity analysis of temperature feedback suggests that future global warming would cause an additional perturbation in the global carbon cycle, resulting in depletion of soil organic carbon, accumulation of plant biomass, and the increase of atmospheric CO_2.

Kwon, O. Yul

135

Global simulation of the carbon isotope exchange of terrestrial ecosystems  

NASA Astrophysics Data System (ADS)

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 primarily dominated by C3/C4 plant composition and then ancillary environmental conditions. Along latitude, plant and litter carbon pools in northern ecosystems have slower turnover rates (i.e., higher 14C/12C) than those in tropical ecosystems. However, humus carbon in northern ecosystems with very long mean residence times has lower 14C/12C ratio, most of bomb-derived radioactive carbon lingered still in plant biomass. Now, we are attempting to examine the model estimations by comparing with atmospheric measurements.

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

2009-12-01

136

The isotopic and elemental abundances of neon nuclei accelerated in solar flares  

NASA Technical Reports Server (NTRS)

The relative isotopic abundances of Ne-20 and Ne-22 in seven solar flares were determined from measurements of the satellite IMP 8, yielding the ratio Ne-20/Ne-22 = 7.7 (+2.3, -1.5) for solar chromospheric matter. This value is in agreement with the ratio for the component neon-A (the 'primordial' component) found in carbonaceous chondrites. An elemental abundance ratio Ne/O = 0.14 + or - 0.01 also has been obtained which agrees closely with earlier reported measurements. It is shown that the effects of preferential acceleration relative to solar-system abundances with increasing charge number observed for some solar flares - though biasing the elemental ratio - does not appear to influence the neon isotopic abundances.

Dietrich, W. F.; Simpson, J. A.

1979-01-01

137

Carbon Isotope Stratigraphy of the Triassic-Jurassic Boundary, Northern Calcareous Alps, Southern Bavaria.  

NASA Astrophysics Data System (ADS)

The end Triassic is recognized as a period of increased marine biotic turnover, culminating in one of the five major mass extinction events of the Phanerozoic at the Triassic-Jurassic boundary. Carbon isotope excursions have been reported globally that may be in response to a perturbation to the earth system. Here we present findings from a succession of early Mesozoic Tethyan carbonate strata from the Northern Calcareous Alps (NCA) of southern Bavaria, Germany. The succession ranges from Carnian to Middle Jurassic in age and is part of the Bavarian Syncline, which trends East-West along the northern extent of the NCA. The two field areas studied, Wallberg and Buchstein, contain the Tr-J boundary, which is marked by an abrupt change from underlying reefal carbonate rocks to a deeper basinal setting dominated by marls, as well as the disappearance of abundant brachiopod, bivalve and colonial coral populations. The boundary is also characterized by a carbonate carbon isotope excursion. Carbonate C isotope values in the underlying reefal carbonate rocks are marked by values of 2.0 to 2.5‰. Above the contact, the carbonate C isotopes show a 1.5 - 2.0‰ decline, which coincides with the change from shallow to deeper marine carbonate sedimentation. Following the excursion, and whilst the succession maintains a basinal palaeoenvironmental setting, the C isotopes return to values similar to those present beneath the Tr-J boundary ranging from 2.0 - 2.5‰. The negative excursion may be recording a global perturbation to the carbon cycle, however the change from a shallow to deep marine depositional environment must also be considered as a possible influence on isotopic composition. Cross-plots of C and O isotopes show no correlation hence we prefer to interpret the carbonate C isotopic data to record original seawater values. Post-depositional diagenetic and lithification processes, however, likely modified the O isotope values. Our results urge caution in identifying C isotopic excursions as global until potential palaeoenvironmental-related changes can be excluded.

Blom, Vincent P. C.; Prave, Anthony R.; Raub, Timothy D.

2014-05-01

138

Isotope Dependence of Chemical Erosion of Carbon  

SciTech Connect

We study the chemical erosion of hydrogen-supersaturated carbon due to bombardment by hydrogen isotopes H, D, and T at energies of 1 30 eV using classical molecular dynamics simulations. The chemical structure at the hydrogen-saturated interface (the distribution of terminal hydrocarbon moieties, in particular) shows a weak dependence on the mass of the impinging atoms. However the sputtering yields increase considerably with increasing projectile mass. We analyze the threshold energies of chemical sputtering reaction channels and show that they are nearly mass independent, as expected from elementary bond-breaking chemical reactions involving hydrocarbons. Chemical sputtering yields for D impact are compared with new experimental data. Good agreement is found for small hydrocarbons but the simulations overestimate the production of large hydrocarbons for energies larger than 15 eV. We present a thorough analysis of the dependence of our simulations on the parameters of the bombardment schemes and discuss open questions and possible avenues for development.

Reinhold, Carlos O [ORNL; Krstic, Predrag S [ORNL; Stuart, S. J. [Clemson University; Zhang, Hengda [ORNL; Harris, Peter R [ORNL; Meyer, Fred W [ORNL

2010-01-01

139

"Carbon Isotope Anomaly in the major Plant C1 Pool and its Biogeochemical Implications"  

E-print Network

;-notation definition Relative Isotope Abundance: Isotopic compositions are usually expressed in term (carbohydrates including cellulose, hemicellulose, pectin) that are combined with lignin with lesser amounts

140

Fractionation between inorganic and organic carbon during the Lomagundi (2.222.1 Ga) carbon isotope excursion  

E-print Network

April 2008 Editor: H. Elderfield Keywords: Precambrian carbon cycle Lomagundi Event carbon isotope. carbonate carbon isotopic values on the shallow-marine carbonate platform suggests that the carbon cyclingFractionation between inorganic and organic carbon during the Lomagundi (2.22­2.1 Ga) carbon

Bekker, Andrey

141

Mass transfer and carbon isotope evolution in natural water systems  

USGS Publications Warehouse

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.

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

1978-01-01

142

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

NASA Technical Reports Server (NTRS)

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.

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

1975-01-01

143

Stable carbon and sulfur isotopes as records of the early biosphere  

NASA Technical Reports Server (NTRS)

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

Desmarais, David J.

1989-01-01

144

Carbon isotopes of hydrocarbons and carbon dioxide in natural gases in China  

NASA Astrophysics Data System (ADS)

130 natural gases in the continent of China were determined for the abundance and carbon isotopes of hydrocarbons and carbon dioxide. The ?13C (PDB) values of methane range from -68 to - 24.4%, and the largest isotopic variability for hydrocarbons is of ?13C 1 < ?13C; < ?13C; < ?13C 4 < ?13C 5. These characteristics suggest that the gaseous hydrocarbons originated principally from thermal and or microbial decomposition of organic matter. The wide variations of ?13C 0 distribution patterns (n = 1, 2, 3, 4 and 5) can be explained by (1) extensive mixture between thermogenic and microbial gases, or between thermogenic gases produced during different thermal stage, and or (2) preferential microbial oxidation. There is no direct evidence for the presence of abiogenic hydrocarbon in natural gases in China. One sample from Songliao basin shows a heavier ?13C 1 ( - 24‰) and reverse isotopic distribution pattern ( ?13C 1 > ?13C 2 > ?13C 3). Concerning the occurrence of mantle-derived He, Ne, Ar and Xe in the south Songliao basin, we propose that the methane mantle derived and heavy hydrocarbons (ethane, propane, butane, etc.) formed from polymerization of the mantle-derived methane. The ?13C values for carbon dioxide range from - 13.9 to + 13.5‰ suggesting the multiple origins. Gases with CO 2 concentrations greater than 10% have a narrow range of ?13C values, from - 8 to - 2‰, and show higher 1He 4He ratios ( > 0.1 times the atmospheric value), suggesting that a mantle-derived component is diluted by CO 2 derived from carbonate and or organic matter. Positive ?13C values ( + 4 - + 14‰) indicate CO 2 reduction to CH 2, CO 2 with trace concentration in CH 4-rich gases can be attributed to microbial decomposition of organic matter in sedimentary rocks.

Sheng, Xu; Nakai, Shun'ichi; Wakita, Hiroshi; Yongchang, Xu; Wang, Xianbin

1997-02-01

145

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

NASA Astrophysics Data System (ADS)

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 ?13C 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 ?13C 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.

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

2012-05-01

146

Molecular and stable carbon isotopic compositions of hopanoids in seep carbonates from the South China Sea continental slope  

NASA Astrophysics Data System (ADS)

The lipid biomarkers of hopanoids in cold seep carbonates from the South China Sea continental slope were investigated by gas chromatography-mass spectrometer (GC-MS) and gas chromatography-isotope ratio-mass spectrometer (GC-ir-MS). The distribution of hopanes/hopenes shows a preference for the ‘biological’ 17?(H), 21?(H)-over the ‘geological’ 17?(H), 21?(H)-configuration. This interpretation is in agreement with the strong odd-even preference of long-chain n-alkanes in those samples, suggesting that the ?? hopanes may be the early diagenetic products of biohopanoids and the ??, ?? configurations of hopanes were mainly derived from allochthonous sources contributing to the organic matter of the carbonates. In terms of hopanoid acids, the C30 to C33 17?(H), 21?(H)-hopanoid acids were detected with C32 17?(H), 21?(H)-hopanoid acid being the most abundant. However, there is a significant difference in stable carbon isotopic compostions of the C32 17?(H), 21?(H)-hopanoic acid among samples (-30.7‰ to -69.8‰). The ?13C values match well with the carbon isotopic compositions of SRB-derived iso-/anteiso-C15:0 fatty acids in the samples, which strongly depend on the carbon utilization types by microbe. The most abundant compound of hopanols detected in the samples, C30-17?(H), 21?(H)-hopanol, may be a good indicator of diagenetic product of type I methanotrophs. The molecular and carbon isotopic compositions of hopanoids demonstrate clearly that there is a combination contribution of both SRB and type I or type X methanotrophs to the source organism in the seep carbonates from the South China Sea continental slope.

Guan, Hongxiang; Sun, Yongge; Mao, Shengyi; Zhu, Xiaowei; Wu, Nengyou

2014-10-01

147

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

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

148

Investigation of four carbon monoxide isotopomers in natural abundance by laser-induced fluorescence in a supersonic jet  

Microsoft Academic Search

The four carbon monoxide (CO) isotopomers 12C16O, 13C16O, 12C18O and 12C17O have been detected simultaneously in a CO gas sample of natural isotopic abundance by measuring rovibronic excitation spectra of six vibronic bands in the Fourth Positive System. The CO sample was flow cooled by adiabatic expansion in a pulsed supersonic jet. The rovibronic excitation spectra were obtained using a

Anton Du Plessis; Erich G. Rohwer; Christine M. Steenkamp

2007-01-01

149

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

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

150

Isotope composition of carbon in amino acids of solid bitumens  

NASA Astrophysics Data System (ADS)

Primary data are presented on the isotope composition of carbon in individual amino acids from solid bitumens and several biological objects. The amino acids of biological objects are characterized by wide variations of the isotope composition of carbon. This fact occurs owing to the difference in biochemical paths of metabolism resulting in the synthesis of individual amino acids. The ?13C values are somewhat decreased for individual amino acids in asphaltenes, varying from -7.7 to -31.7‰. The carbon of amino acids is weighted in kerits from Bad'el' compared to asphaltenes. All the natural bitumens retain the characteristic trend for natural substances: the isotopically heavy and light amino acids by carbon are glycine and leucine, respectively. The isotope composition of amino-acid carbon is lightened compared to natural bitumens in the samples formed under a pronounced thermal impact (asphalt-like crust and kirishite).

Shanina, S. N.; Bushnev, D. A.

2014-06-01

151

Paleodietary reconstruction of Miocene faunas from Pa?alar, Turkey using stable carbon and oxygen isotopes of fossil tooth enamel  

Microsoft Academic Search

Miocene-age (? 15 Ma) deposits at Pa?alar in northwest Turkey contain abundant and well-preserved dental remains from a variety of herbivores. We used the carbon and oxygen isotopic compositions of inorganic carbonate in enamel from these teeth to reconstruct the paleodiet and sources of body water, respectively, of Miocene mammals. The ?13C (PDB) values of carbonate in the enamel fall

Jay Quade; Thure E. Cerling; Peter Andrews; Berna Alpagut

1995-01-01

152

Carbon isotopic characterisation of dissolved organic matter during water treatment.  

PubMed

Water treatment is a series of physio-chemical processes to aid organic matter (OM) removal, which helps to minimise the formation of potentially carcinogenic disinfection by-products and microbial regrowth. Changes in OM character through the treatment processes can provide insight into the treatment efficiency, but radiogenic isotopic characterisation techniques have yet to be applied. Here, we show for the first time that analysis of (13)C and (14)C of dissolved organic carbon (DOC) effectively characterises dissolved OM through a water treatment works. At the sites investigated: post-clarification, DOC becomes isotopically lighter, due to an increased proportion of relatively hydrophilic DOC. Filtration adds 'old' (14)C-DOC from abrasion of the filter media, whilst the use of activated carbon adds 'young' (14)C-DOC, most likely from the presence of biofilms. Overall, carbon isotopes provide clear evidence for the first time that new sources of organic carbon are added within the treatment processes, and that treated water is isotopically lighter and typically younger in (14)C-DOC age than untreated water. We anticipate our findings will precipitate real-time monitoring of treatment performance using stable carbon isotopes, with associated improvements in energy and carbon footprint (e.g. isotopic analysis used as triggers for filter washing and activated carbon regeneration) and public health benefits resulting from improved carbon removal. PMID:24075722

Bridgeman, John; Gulliver, Pauline; Roe, Jessie; Baker, Andy

2014-01-01

153

The Abundances of Oxygen and Carbon in the Solar Photosphere  

E-print Network

A series of recent studies has placed the best estimates of the photospheric abundances of carbon and oxygen at log epsilon = 8.39 and 8.66, respectively. These values are ~ 40 % lower than earlier estimates. A coalition of corrections due to the adoption of an improved model atmosphere, updated atomic data and non-LTE corrections, and a reevaluation of the effect of blending features, is responsible for the change. The adopted hydrodynamical model of the solar surface is an important element to the update, but using a theoretical 1D model atmosphere leads to an average oxygen abundance modestly increased by 0.09 dex, and a carbon abundance only 0.02 dex higher. Considering a state-of-the-art 3D hydrodynamical model of the solar surface yields consistent results from different sets of atomic and molecular lines. Systematic errors are likely to dominate the final uncertainties, but the available information indicates they are limited to solar convection zone, is still lacking.

Carlos Allende Prieto

2007-02-16

154

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

NASA Technical Reports Server (NTRS)

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.

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

1993-01-01

155

Carbon Isotopic Ratios of Amino Acids in Stardust-Returned Samples  

NASA Technical Reports Server (NTRS)

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).

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

2009-01-01

156

Carbon Isotopic Measurements of Amino Acids in Stardust-Returned Samples  

NASA Technical Reports Server (NTRS)

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).

Elsila, Jamie

2009-01-01

157

Carbon and Nitrogen Abundances in Early-type Galaxies  

E-print Network

For the first time, we undertake a systematic examination of the nitrogen abundances for a sample of 35 early-type galaxies spanning a range of masses and local environment. The nitrogen-sensitive molecular feature at 3360\\AA has been employed in conjunction with a suite of atomic- and molecular-sensitive indices to provide unique and definitive constraints on the chemical content of these systems. By employing NH3360, we are now able to break the carbon, nitrogen, and oxygen degeneracies inherent to the use of the CN-index. We demonstrate that the NH3360 feature shows little dependency upon the velocity dispersion (our proxy for mass) of the galaxies, contrary to what is seen for carbon- and magnesium-sensitive indices. At face value, these results are at odds with conclusions drawn previously using indices sensitive to both carbon and nitrogen, such as cyanogen (CN). With the aid of stellar population models, we find that the N/Fe ratios in these galaxies are consistent with being mildly-enhanced with respect to the solar ratio. We also explore the dependence of these findings upon environment, by analyzing the co-added spectra of galaxies in the field and the Coma cluster. We confirm the previously found differences in carbon abundances between galaxies in low- and high-density environments, while showing that these differences do not seem to exist for nitrogen. We discuss the implications of these findings for the derivation of the star formation histories in early-type galaxies, and for the origin of carbon and nitrogen, themselves.

Elisa Toloba; Patricia Sanchez-Blazquez; Javier Gorgas; Brad K. Gibson

2008-11-21

158

Model-based estimation of the global carbon budget and its uncertainty from carbon dioxide and carbon isotope records  

E-print Network

Model-based estimation of the global carbon budget and its uncertainty from carbon dioxide and the terrestrial biosphere based on carbon dioxide and carbon isotope records, and prior information on model of carbon dioxide and the resulting atmospheric concentration of carbon dioxide determined from the behavior

Jain, Atul K.

159

Carbon isotope fractionation during calcium carbonate precipitation induced by ureolytic bacteria  

NASA Astrophysics Data System (ADS)

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 ?13C 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.

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

2012-12-01

160

The Barium Isotopic Abundance in the Metal-Poor Star HD140283  

E-print Network

We derive the mixture of odd to even barium isotopes in the atmosphere of the metal-poor subgiant HD140283 from the analysis of the Ba II transition at 455.4 nm in a high-resolution high signal-to-noise spectrum of the star. The detailed shape of this spectral line depends on the relative contributions of odd and even isotopes via isotopic and hyperfine splitting. We measure the fractional abundance of odd Ba isotopes by modelling the formation of the Ba II 455.4 nm line profile with the use of both a classical 1D hydrostatic and a 3D hydrodynamical model atmosphere of HD140283. We interpret the results in terms of contributions by the slow (s-) and rapid (r-) neutron-capture processes to the isotopic mix. While the result of the 1D analysis of the Ba II feature indicates a (64 +/- 36)% contribution of the r-process to the isotopic mix, the 3D analysis points toward a mere (15 +/- 34)% contribution from this process, that is consistent with a solar-like mixture of barium isotopes.

R. Collet; M. Asplund; P. E. Nissen

2008-11-27

161

Origin of petroporphyrins. 2. Evidence from stable carbon isotopes  

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

162

The PalaeoceneEocene carbon isotope excursion: constraints from individual  

E-print Network

. Keywords: methane; Palaeocene­Eocene boundary; carbon isotopes; global warming Phil. Trans. R. Soc. A (2007 of thousands of years before gradually abating. With a few exceptions, mainly along Antarctica and in coastal

Zachos, James

163

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

PubMed

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. PMID:11538479

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

1990-01-01

164

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,...

165

Carbon Monoxide Isotopes: On the Trail of Galactic Chemical Evolution  

NASA Technical Reports Server (NTRS)

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.

Langer, W.

1995-01-01

166

Collisionally assisted, highly selective laser isotope separation of carbon-13  

Microsoft Academic Search

We have further developed our recently reported two-laser technique for highly selective molecular isotope separation of carbon-13 [Boyarkin, Kowalczyk, and Rizzo, J. Chem. Phys. 118, 93 (2003)] with the objective of increasing the yield. An essential feature of this approach in its original conception is the significant increase of isotopic selectivity that occurs through collisions during the time between the

M. Polianski; O. V. Boyarkin; T. R. Rizzo

2004-01-01

167

14. CARBON AND OXYGEN ISOTOPE ANALYSIS OF LAKE SEDIMENT CELLULOSE  

E-print Network

14. CARBON AND OXYGEN ISOTOPE ANALYSIS OF LAKE SEDIMENT CELLULOSE: METHODS AND APPLICATIONS BRENT B in the interpretation of cellulose isotope data, briefly highlights key results from recent applications, and outlines and Environmental Sciences Wesleyan University, Middletown, CT USA 06459 Keywords: cellulose, lake sediment, oxygen

Edwards, Thomas W.D.

168

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...

169

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

NASA Technical Reports Server (NTRS)

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.

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

2012-01-01

170

Ar-39 Detection at the 10^-16 Isotopic Abundance Level with Atom Trap Trace Analysis  

E-print Network

Atom Trap Trace Analysis (ATTA), a laser-based atom counting method, has been applied to analyze atmospheric Ar-39 (half-life = 269 yr), a cosmogenic isotope with an isotopic abundance of 8x10^-16. In addition to the superior selectivity demonstrated in this work, counting rate and efficiency of ATTA have been improved by two orders of magnitude over prior results. Significant applications of this new analytical capability lie in radioisotope dating of ice and water samples and in the development of dark matter detectors.

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

2011-01-15

171

Eocene-Miocene carbon-isotope and floral record from brown coal seams in the Gippsland Basin of southeast Australia  

NASA Astrophysics Data System (ADS)

The carbon-isotope and palynological record through 580 m thick almost continuous brown coal in southeast Australia's Gippsland Basin is a relatively comprehensive southern hemisphere Middle Eocene to Middle Miocene record for terrestrial change. The carbon isotope ? 13C coal values of these coals range from - 27.7‰ to - 23.2. This isotopic variability follows gymnosperm/angiosperm fluctuations, where higher ratios coincide with heavier ?13C values. There is also long-term variability in carbon isotopes through time. From the Eocene greenhouse world of high gymnosperm-heavier ?13C coal values, there is a progressive shift to lighter ?13C coal values that follows the earliest (Oi1?) glacial events around 33 Ma (Early Oligocene). The overlying Oligocene-Early Miocene brown coals have lower gymnosperm abundance, associated with increased % Nothofagus (angiosperm), and lightening of isotopes during Oligocene cooler conditions. The Miocene palynological and carbon-isotope record supports a continuation to the Oligocene trends until around the late Early Miocene (circa 19 Ma) when a warming commenced, followed by an even stronger isotope shift around 16 Ma that peaked in the Middle Miocene when higher gymnosperm abundance and heavier isotopes prevailed. The cycle between the two major warm peaks of Middle Eocene and Middle Miocene was circa 30 Ma long. This change corresponds to a fall in inferred pCO 2 levels for the same period. The Gippsland data suggest a link between gymnosperm abundance, long-term plant ?13C composition, climatic change, and atmospheric pCO 2. Climatic deterioration in the Late Miocene terminated peat accumulation in the Gippsland Basin and no further significant coals formed in southeast Australia. The poor correspondence between this terrestrial isotope data and the marine isotope record is explained by the dominant control on ?13C by the gymnosperm/angiosperm abundance, although in turn this poor correspondence may reflect palaeoclimate control. From the brown coal seam dating, the coal appears to have accumulated during a considerable part of the allocated 30 Ma Cenozoic time period. These brown coal carbon isotope and palynological data appear to record a more gradual atmospheric carbon isotope change compared to the marine record.

Holdgate, Guy R.; McGowran, Brian; Fromhold, Tom; Wagstaff, Barbara E.; Gallagher, Stephen J.; Wallace, Malcolm W.; Sluiter, Ian R. K.; Whitelaw, Michael

2009-01-01

172

Observations of Carbon Isotopic Fractionation in Interstellar Formaldehyde  

NASA Technical Reports Server (NTRS)

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 it feasible to observe its less common isotopologues. As a step in our investigation of C-13 fractionation patterns in the ISM, we here present comparisons between observations of the C-13 fraction in formaldehyde, and chemical fractionation models.

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

2012-01-01

173

Biological control of calcium isotopic abundances in the global calcium cycle  

SciTech Connect

Measurements of {sup 44}Ca/{sup 40}Ca, expressed as {delta}{sup 44}Ca, were made on igneous rocks and on shell and bone material from modern organisms to investigate the magnitude and origins of calcium isotopic fractionation in nature. The results document a span of 4{per_thousand} in {delta}{sup 44}Ca, measured with the double spike technique to a precision of {+-}0.15{per_thousand}. Volcanic rocks, including basalt and rhyolite, show little variability and cluster near {delta}{sup 44}Ca = 0 {+-}0.2. Systematic analysis of biological samples indicates that biological processing of calcium discriminates against heavy isotopes, and that biological fractionation is the primary generator of calcium isotopic fractionation in nature. Preliminary data suggest that calcium becomes isotopically lighter as it moves through food chains. Calcium carbonate shells of marine microorganisms and deep-sea carbonate ooze have {delta}{sup 44}Ca about 1.0{per_thousand}, lower than seawater; this fractionation causes seawater to be enriched in heavy calcium ({delta}{sup 44}Ca = +0.9) relative to igneous rocks. Marine organisms consequently are isotopically heavier than their terrestrial counterparts at similar trophic level. The calcium isotopic composition of living and fossil organisms may record information on diet and environment. 22 refs., 3 figs., 2 tabs.

Skulan, J. [Univ. of California, Berkeley, CA (United States)] [Univ. of California, Berkeley, CA (United States); DePaolo, D.J.; Owens, T.L. [Lawrence Berkeley National Lab., CA (United States)] [Lawrence Berkeley National Lab., CA (United States); [Univ. of California, Berkeley, CA (United States)

1997-06-01

174

Modeling the carbon isotope composition of bivalve shells (Invited)  

NASA Astrophysics Data System (ADS)

The stable carbon isotope composition of bivalve shells is a valuable archive of paleobiological and paleoenvironmental information. Previous work has shown that the carbon isotope composition of the shell is related to the carbon isotope composition of dissolved inorganic carbon (DIC) in the ambient water in which a bivalve lives, as well as metabolic carbon derived from bivalve respiration. The contribution of metabolic carbon varies among organisms, but it is generally thought to be relatively low (e.g., <10%) in shells from aquatic organism and high (>90%) in the shells from terrestrial organisms. Because metabolic carbon contains significantly more C-12 than DIC, negative excursions from the expected environmental (DIC) signal are interpreted to reflect an increased contribution of metabolic carbon in the shell. This observation contrasts sharply with modeled carbon isotope compositions for shell layers deposited from the inner extrapallial fluid (EPF). Previous studies have shown that growth lines within the inner shell layer of bivalves are produced during periods of anaerobiosis when acidic metabolic byproducts (e.g., succinic acid) are neutralized (or buffered) by shell dissolution. This requires the pH of EPF to decrease below ambient levels (~7.5) until a state of undersaturation is achieved that promotes shell dissolution. This condition may occur when aquatic bivalves are subjected to external stressors originating from ecological (predation) or environmental (exposure to atm; low dissolved oxygen; contaminant release) pressures; normal physiological processes will restore the pH of EPF when the pressure is removed. As a consequence of this process, a temporal window should also exist in EPF at relatively low pH where shell carbonate is deposited at a reduced saturation state and precipitation rate. For example, EPF chemistry should remain slightly supersaturated with respect to aragonite given a drop of one pH unit (6.5), but under closed conditions, equilibrium carbon isotope fractionation relations dictate that shell carbonate should be preferentially enriched in C-13 by 3 to 5 per mill (from 30° to 0°C) compared to EPF at a pH of 7.5. Anomalous positive excursions are rarely, if ever, observed in shell carbonate and they have yet to be associated with growth cessation markers in bivalves. The most likely explanation for the lack of anomalous positive values is that the percentage of metabolic carbon increases in EPF when bivalves experience stressful condition. This influx of metabolic carbon is balanced to a measureable extent by the enhanced fractionation of carbon isotopes during shell deposition from EPF at relatively low pH. These two processes may be combined in a quantitative model to extract a historical record of metabolic activity from the carbon isotope profiles of bivalve shells.

Romanek, C.

2010-12-01

175

Isotopic and elemental abundances of neon nuclei accelerated in solar flares  

Microsoft Academic Search

The relative isotopic abundances of ²°Ne and ²²Ne in seven solar flares were determined from measurements on the satellite IMP 8, yielding the ratio ²°Ne\\/²²Ne=7.7 (+2.3, -1.5) for solar chromospheric matter. This value is in agreement with the ratio for the component Neon-A (the ''primordial'' component) found in carbonaceous chondrites. An elemental abundance ratio Ne\\/O=0.14 +- 0.01 also has been

W. F. Dietrich; J. A. Simpson

1979-01-01

176

Radiocarbon and stable carbon isotope compositions of organic compound classes in sediments from the NE Pacific and Southern Oceans  

Microsoft Academic Search

Radiocarbon (?14C) abundance and stable carbon isotope (?13C) compositions were measured for total lipid, total hydrolyzable amino acids (THAA), total carbohydrates (TCHO), and acid-insoluble organic fractions separated from phytoplankton, zooplankton, and sediment cores collected from two abyssal sites, one in the northeast (NE) Pacific Ocean and one in the Southern Ocean. These results are compared with those obtained for a

Xu-Chen Wang; Ellen R. M Druffel

2001-01-01

177

Glaciation, aridification, and carbon sequestration in the Permo-Carboniferous: The isotopic record from low latitudes  

E-print Network

Glaciation, aridification, and carbon sequestration in the Permo-Carboniferous: The isotopic record and carbon sequestration in the Late Paleozoic, we have compiled new and published oxygen and carbon isotopic

Grossman, Ethan L.

178

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

NASA Astrophysics Data System (ADS)

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 behavior of these compounds in terms of their sources, sinks, inter- and intramolecular processes, it was decided in 2006 to develop an instrument capable of selectively measuring NMHC mixing ratios and stable carbon isotope ratios for use in the laboratory of the Atmospheric Physics and Chemistry Group at Universiteit Utrecht. This thesis documents the successful development, construction, testing and first applications of this stable carbon isotope ratio instrument. It is divided into five chapters, representing the content of three publications and additional material: an introduction; a method section; and applications: analysis of NMHC stable carbon isotopes in urban ambient air, laboratory measurments of the isotope effects in UV degradation of monocarbon chlorofluorocarbons, isotope analysis of diverse gases from firn air samples from Greenland, plus a section on future perspectives

Zuiderweg, A. T.

2012-09-01

179

CARBON AND OXYGEN ISOTOPE COMPOSITION OF ORGANIC MATTER AND CARBONATES IN RECENT LACUSTRINE SEDIMENTS  

Microsoft Academic Search

Abstract: Abstract: Abstract: Abstract: The distribution of stable isotopes (18O and 13C) and radiocarbon in organic mate- rials, carbonates and water samples collected from the environment of lacustrine sediments in Gosci¹¿ Lake (Central Poland) and Wigry Lake (NE Poland) were investigated. The oxygen and carbon isotopic analysis of terrestrial semi submerged and submerged plants, shells and water samples were compared

TATJANA BÖTTGER; ANNA PAZDUR; NATALIA PIOTROWSKA; RALF WAGNER

180

First measurement of Mg isotope abundances at high redshifts and accurate estimate of Deltaalpha\\/alpha  

Microsoft Academic Search

Aims: Abundances of the Mg isotopes 24Mg, 25Mg, and 26Mg can be used to test models of chemical enrichment of interstellar\\/intergalactic gas clouds. Additionally, because the position of the Mg ii lambdalambda2796,2803 Å lines is often taken as a reference in computations of possible changes of the fine-structure constant alpha, it should be clarified to which extent these lines are

I. I. Agafonova; P. Molaro; S. A. Levshakov; J. L. Hou

2011-01-01

181

Variations in carbon and nitrogen stable isotopes of cryoconite  

NASA Astrophysics Data System (ADS)

Cryoconite is biogenic surface dust on snow and ice, and is commoly observed on glaciers worldwide. Because of their dark coloration, cryoconite substantially reduce surface albedo and accelerate melting of glaciers. Therefore, it is important to understand formation process of cryoconite to evaluate its effect on glacier melting. Although cryoconite consists of mineral particles and organic matter, organic fraction is more important in terms of albedo effect because it is usually darker color and accounts for major part of cryoconite in volume. The organic matter is derived from photosynthetic microbes such as cyanobacteria, and/or from windblown organic matter from ground soil around glaciers. Carbon (C) and nitrogen (N) stable isotopes of the organic matter could be useful to know their sources and to understand their cycles on glaciers. In this study, I analyzed carbon and nitrogen stable isotopes of cryoconite collected from 6 sites of different elevation from May to September on an Alaska glacier (Gulkana Glacier) to know their spatial and seasonal variations. I also analyze those collected from glaciers in Asia and Arctic to compare them among different geographical locations. Results on the Alaska glacier show that C and N stable isotopes of cryoconite organic mater significantly varied among elevations and seasons. C isotope was generally higher in lower elevation, probably due to higher photosynthetic activity in the lower elevation. In contrast, N isotope was constant on the ice area, but was lower in the snow area where the red snow algae were blooming. N isotope may be reflective of nitrogen availavility on the glacier surface. Geograpical comparison shows large variations in C and N isotopes among regions: higher C and N isotopes on Asian glaciers, lower C and N isotopes in Alaska, and lower C and higher N isotopes on Arctic glaciers. The isotope values suggest that algal production is a major carbon source on most of glaciers, but their productivity and nirotogen cycle largely varied among the regions.

Takeuchi, N.

2012-12-01

182

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

E-print Network

The influence of kinetics on the oxygen isotope composition of calcium carbonate James M. Watkins a and calcium carbonate. Although oxygen isotope separation is expected on theoretical grounds, the temperature on equilibrium fractionation of oxygen isotopes between calcium carbonate and water. Equili- brium oxygen isotope

Watkins, Jim

183

Carbon13 and Carbon14 Abundances in Alaskan Aquatic Organisms: Delayed Production from Peat in Arctic Food Webs  

Microsoft Academic Search

Inputs of terrestrial peat carbon to the nearshore Alaskan Beaufort Sea from erosion and fluvial transport are of the same magnitude as in situ primary production within 10 kilometers of shore. Nevertheless, carbon-13\\/carbon-12 ratios and carbon-14 abundances in marine organisms show that only small amounts of the terrestrial carbon are transferred beyond the microbial level. Freshwater organisms, however, are heavily

Donald M. Schell

1983-01-01

184

Carbon and oxygen isotope fractionation in dense interstellar clouds  

NASA Technical Reports Server (NTRS)

It is pointed out that isotope fractionation as a result of chemical reactions is due to the small zero-point energy differences between reactants and products of isotopically distinct species. Only at temperatures near absolute zero does this energy difference become significant. Favorable conditions for isotope fractionation on the considered basis exist in space within dense interstellar clouds. Temperatures of approximately 10 K may occur in these clouds. Under such conditions, ion-molecule reactions have the potential to distribute isotopes of hydrogen, carbon, oxygen unequally among the interstellar molecules. The present investigation makes use of a detailed model of the time-dependent chemistry of dense interstellar clouds to study cosmological isotope fractionation. Attention is given to fractionation chemistry and the calculation of rate parameters, the isotope fractionation results, and a comparison of theoretical results with observational data.

Langer, W. D.; Graedel, T. E.; Frerking, M. A.; Armentrout, P. B.

1984-01-01

185

Equilibrium and nonequilibrium oxygen isotope effects in synthetic carbonates  

Microsoft Academic Search

A suite of divalent metal (Ca, Cd, Ba) carbonates was synthesized over the temperature range 10–40°C by the classical method of slowly bubbling N2 through a bicarbonate solution. It was discovered that carbonates could be precipitated reproducibly in or out of isotopic equilibrium with the environmental solution by varying the concentrations of bicarbonate and cation. Precipitation rate had little or

Sang-Tae Kim; James R. O'Neil

1997-01-01

186

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

NASA Technical Reports Server (NTRS)

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 suggests that Hg is associated with S-bearing phases and, thus, that HgS is a major Hg-bearing phase in both meteorites. The Hg peak at 225 C for Allende is similar to release patterns of physically adsorbed Hg on silicate and metal grains.

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

2001-01-01

187

Production of carbon isotopes by laser separation  

Microsoft Academic Search

Since the advent of lasers, these unique sources of highly intense and monochromatic radiation have been proposed as excellent tools to induce or catalyze chemical reactions. Due to the great interest to the problem of isotope production, investigation and application, the laser method of isotope separation has received the most attention worldwide and may be the first major commercial application

Vladimir Y. Baranov; A. P. Dyad'kin; D. D. Maluta; V. A. Kuzmenko; S. V. Pigulskiy; Vladimir S. Mezhevov; Vladilen S. Letokhov; V. B. Laptev; E. A. Ryabov; I. V. Yarovoi; V. B. Zarin; A. S. Podoryashy

2000-01-01

188

[Carbon isotope fractionation inplants]. Final report  

SciTech Connect

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.

O`Leary, M.H.

1990-12-31

189

Kinetic Fractionation of Carbon Isotopes During Carbonate Weathering in Glaciated Catchments: Implications for the Detection of Subglacial Microbial Activity  

NASA Astrophysics Data System (ADS)

Microbes are abundant at the water-rock-ice interface beneath valley glaciers at Haut Glacier d'Arolla, Switzerland (HGA) and at John Evans Glacier, Ellesmere Island Nunavut, Canada (JEG). However, the importance of in-situ microbial activity in driving subglacial weathering reactions remains unknown. This is a key question when considering the potential role of microbes in mediating subglacial weathering and carbon cycling on a continental scale beneath the Pleistocene mid-latitude ice sheets. This study measured the chemical composition of meltwaters, including ? {13}C-DIC at the two glaciers to quantify microbial CO2 inputs to the DIC budget using isotope mass balance techniques. However, PCO2 data indicates that most of the glacial meltwaters are far from equilibrium with respect to atmospheric CO2 and thus kinetic processes are important in determining the water chemistry. Consequently, conventional equilibrium isotope mass balance techniques were inappropriate in this case. Hence, laboratory experiments were conducted with calcium carbonate and carbonate rich glacial sediments from JEG under simulated subglacial conditions (< 63 micron size fraction, sediment concentrations 0.01 to 5 g/l, 5° C) to investigate potential kinetic isotopic effects and aid in interpretation of the field data (? {13}C-DIC values ranging from -2.4 to -15.7 ‰ ). The laboratory experiments demonstrate previously unreported kinetic fractionation of carbon isotopes during the initial hydrolysis (closed system conditions) and early stages of carbonate dissolution driven by atmospheric CO2 (open system conditions). Preferential dissolution of Ca12CO3, results in ? {13}C-DIC values that are significantly isotopically lighter than the bulk carbonate. This kinetic isotopic effect (KIE) is more pronounced at higher sediment concentrations and can be up to -17.4 ‰ for glacial sediments under closed system conditions and sediment concentrations of 5g/l. The KIE is also significant during the first 6 hrs of carbonate dissolution driven by atmospheric CO2. Incorporating KIE into the geochemical weathering models and isotopic mass balance calculations allows identification of significant (> 10 %) microbial CO2 contributions to the DIC budget in glacial meltwaters. However, where weathering processes producing KIE dominate the DIC budget, small microbial CO2 contributions may be masked. Examples of subglacial environments from JEG and HGA exhibiting these contrasting weathering processes and differing levels of microbial CO2 input will be presented.

Skidmore, M.; Sharp, M.; Tranter, M.; Bottrell, S.

2003-12-01

190

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

NASA Technical Reports Server (NTRS)

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.

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

1993-01-01

191

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

PubMed

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. PMID:11537805

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

1993-01-01

192

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

NASA Technical Reports Server (NTRS)

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.

Wiedenbeck, M. E.

1977-01-01

193

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)

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 Proterozoic seawater. Within the Damara basin, carbon-isotopic compositions of carbonates provide a potentially useful tool for the correlation of units between the Kalahari and Congo cratons. Carbonates depleted in 13C were deposited during and immediately following three separate glacial episodes in Namibia. The correspondence between ice ages and negative delta 13C excursions may reflect the effects of lowered sea levels; enhanced circulation of deep, cold, O2-rich seawater; and/or the upwelling of 13C-depleted deep water. Iron-formation is additionally associated with one of the glacial horizons, the Chuos tillite. Carbon-13 enriched isotopic abundances in immediately pre-glacial carbonates suggest that oceanographic conditions favored high rates of organic burial. It is likely that marine waters were stratified, with deep waters anoxic. A prolonged period of ocean stratification would permit the build-up of ferrous iron, probably from hydrothermal sources. At the onset of glaciation, upwelling would have brought 13C-depleted and iron-rich deep water onto shallow shelves where contact with cold, oxygenated surface waters led to the precipitation of ferric iron.

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

1991-01-01

194

LITHIUM ABUNDANCES IN CARBON-ENHANCED METAL-POOR STARS  

SciTech Connect

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.

Masseron, Thomas; Johnson, Jennifer A. [Department of Astronomy, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210 (United States); Lucatello, Sara [INAF, Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, 35122 Padova (Italy); Karakas, Amanda [Research School of Astronomy and Astrophysics, Australian National University, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611 (Australia); Plez, Bertrand [LUPM cc072, Universite Montpellier II, F-34095 Montpellier cedex 5 (France); Beers, Timothy C. [Department of Physics and Astronomy and JINA: Joint Institute for Nuclear Astrophysics, Michigan State University, E. Lansing, MI 48824 (United States); Christlieb, Norbert, E-mail: masseron@astronomy.ohio-state.edu, E-mail: jaj@astronomy.ohio-state.edu [Zentrum fuer Astronomie der Universitaet Heidelberg, Landessternwarte, Koenigstuhl 12, 69117, Heidelberg (Germany)

2012-05-20

195

The abundances of carbon and nitrogen in I Zw 18  

NASA Technical Reports Server (NTRS)

The first measurements of the semiforbidden C III 1909 A and forbidden N II 6583 A emission lines in I Zw 18 are reported. These data are combined with previously published spectrophotometry in order to derive the carbon and nitrogen abundances in I Zw 18 with the aid of a nebular model. The CNO abundances in I Zw 18 are found to exceed those found in the Magellanic Clouds and other well-observed oxygen-poor irregular galaxies and are more similar to those in the sun and nearby Galactic H II regions. It is argued that I Zw 18 may be older and more chemically evolved than previously believed, and that its extremely low O/H results from escape of O-rich supernova ejecta from the Galaxy or from dilution by accretion of primordial gas. Alternatively, I Zw 18 may have formed from a preenriched intergalactic medium. Spectroscopic diagnostics for composite photoionization models to fit the spectrum of I Zw 18 are discussed.

Dufour, Reginald J.; Garnett, Donald R.; Shields, Gregory A.

1988-01-01

196

Carbon cycle for Lake Washington - a stable isotope study  

Microsoft Academic Search

The authors investigate the carbon cycle in Lake Washington for the year 1980 using monthly measurements of the dissolved inorganic carbon (DIC) and its ¹³C:¹²C isotopic composition. Mass balances of DIC and its ¹³C:¹²C yield estimates of COâ gas exchange rates and net organic carbon production rates. Between 24 June and 13 August, the calculated COâ gas invasion rate of

P. D. Quay; S. R. Emerson; B. M. Quay; A. H. Devol

1986-01-01

197

Coprecipitation and isotopic fractionation of boron in modern biogenic carbonates  

Microsoft Academic Search

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

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

1991-01-01

198

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

PubMed

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). PMID:15645502

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

2005-01-01

199

The link between assimilation and below-ground processes - stable isotopes as tools to assess carbon transfer  

NASA Astrophysics Data System (ADS)

At present, there is lack of 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 ecosystem-scale processes. On the background of global climate change, we need to mechanistically link plant physiology, CO2 net exchange between ecosystems and the atmosphere and plant biomass accumulation. This is the basis for predicting productivity of forests as well as their carbon sequestration potential in future. This paper will give an overview on how stable isotope studies can give insights into the fate of newly assimilated carbon transported within trees and transferred to the soil and atmosphere. The paper includes assessments characterizing temporal and spatial variation in the natural abundance of carbon and oxygen isotopes or applying isotopically enriched tracers. In addition, it highlights the fact that the stable isotope composition of assimilates transported within the plant contains important time integrated information on environmental conditions, leaf physiology, and post-photosynthetic metabolism. The paper on the one hand focuses on the fast turn over carbon pools, which fuel plant respiration and soil microbial activity and on the other hand explores the transfer of the isotope information to long-lived compounds in plant archives such as tree rings.

Gessler, A.; Wingate, L.; Ogeé, J.; Offermann, C.; Kodama, N.

2011-12-01

200

Yucca Mountain Area Saturated Zone Dissolved Organic Carbon Isotopic Data  

SciTech Connect

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 groundwater ages. The DIC calculated groundwater ages were compared with DOC calculated groundwater ages and both of these ages were compared to travel times developed in ground-water flow and transport models. If nuclear waste is stored in Yucca Mountain, the saturated zone is the final barrier against the release of radionuclides to the environment. The most recent rendition of the TSPA takes little credit for the presence of the saturated zone and is a testament to the inadequate understanding of this important barrier. If radionuclides reach the saturated zone beneath Yucca Mountain, then there is a travel time before they would leave the Yucca Mountain area and flow down gradient to the Amargosa Valley area. Knowing how long it takes groundwater in the saturated zone to flow from beneath Yucca Mountain to down gradient areas is critical information for potential radionuclide transport. Radionuclide transport in groundwater may be the quickest pathway for radionuclides in the proposed Yucca Mountain repository to reach land surface by way of groundwater pumped in Amargosa Valley. An alternative approach to ground-water flow and transport models to determine the travel time of radionuclides from beneath Yucca Mountain to down gradient areas in the saturated zone is by carbon-14 dating of both inorganic and organic carbon dissolved in the groundwater. A standard method of determining ground-water ages is to measure the carbon-13 and carbon-14 of DIC in the groundwater and then correct the measured carbon-14 along a flow path for geochemical reactions that involve carbon containing phases. These geochemical reactions are constrained by carbon-13 and isotopic fractionations. Without correcting for geochemical reactions, the ground-water ages calculated from only the differences in carbon-14 measured along a flow path (assuming the decrease in carbon-14 is due strictly to radioactive decay) could be tens of thousands of years too old. The computer program NETPATH, developed by the USGS, is the best geochemical program for correcting carbon-14 activities for geochemical r

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

2007-06-25

201

Isotopic composition of carbon and nitrogen in ureilitic fragments of the Almahata Sitta meteorite  

NASA Astrophysics Data System (ADS)

This study characterizes carbon and nitrogen abundances and isotopic compositions in ureilitic fragments of Almahata Sitta. Ureilites are carbon-rich (containing up to 7 wt% C) and were formed early in solar system history, thus the origin of carbon in ureilites has significance for the origin of solar system carbon. These samples were collected soon after they fell, so they are among the freshest ureilite samples available and were analyzed using stepped combustion mass spectrometry. They contained 1.2-2.3 wt% carbon; most showed the major carbon release at temperatures of 600-700 °C with peak values of ?13C from -7.3 to +0.4‰, similar to literature values for unbrecciated ("monomict") ureilites. They also contained a minor low temperature (?500 °C) component (?13C = ca -25‰). Bulk nitrogen contents (9.4-27 ppm) resemble those of unbrecciated ureilites, with major releases mostly occurring at 600-750 °C. A significant lower temperature release of nitrogen occurred in all samples. Main release ?15N values of -53 to -94‰ fall within the range reported for diamond separates and acid residues from ureilites, and identify an isotopically primordial nitrogen component. However, they differ from common polymict ureilites which are more nitrogen-rich and isotopically heavier. Thus, although the parent asteroid 2008TC3 was undoubtedly a polymict ureilite breccia, this cannot be deduced from an isotopic study of individual ureilite fragments. The combined main release ?13C and ?15N values do not overlap the fields for carbonaceous or enstatite chondrites, suggesting that carbon in ureilites was not derived from these sources.

Downes, H.; Abernethy, F. A. J.; Smith, C. L.; Ross, A. J.; Verchovsky, A. B.; Grady, M. M.; Jenniskens, P.; Shaddad, M. H.

2015-02-01

202

Carbon and hydrogen isotope fractionation resulting from anaerobic methane oxidation  

Microsoft Academic Search

Methane oxidation in the anoxic sediments of Skan Bay, Alaska resulted in fractionation of carbon and hydrogen isotopes in methane. Isotope fractionation factors were estimated by fitting methane concentration, delta C¹³-CHâ and delta-D-CHâ data with depth distributions predicted by an open system, steady state model. Assuming that molecular diffusion coefficients for C¹²-CHâ, C¹³-CHâ, and C¹²-CHâD are identical, the predicted fractionation

M. J. Alperin; W. S. Reeburgh; M. J. Whiticar

1988-01-01

203

Stable carbon isotope biogeochemistry of lakes along a trophic gradient  

NASA Astrophysics Data System (ADS)

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 ?13C 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 ?13C 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 ?13C at the base of the food web (both autochthonous and allochthonous carbon). Phytoplankton ?13C 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.

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

2014-11-01

204

Stable carbon isotope biogeochemistry of lakes along a trophic gradient  

NASA Astrophysics Data System (ADS)

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 ?13C 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 ?13C of DIC. All organic-carbon pools showed larger isotopic variability in eutrophic lakes compared to oligo-mesotrophic lakes because of the high variability in ?13C at the base of the food web (both autochthonous and allochthonous carbon). Phytoplankton ?13C 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.

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

2014-05-01

205

Carbon isotope indicators of catchment vegetation in the Brazilian Amazon  

NASA Astrophysics Data System (ADS)

Paniculate organic carbon (POC) samples from rivers draining wholly forested catchments in the Amazon Basin exhibit carbon isotope values (?13C) of generally between -27 and -30‰. These values are distinct from those of POC from rivers draining nonforested (grassland/woodland) catchments, which are generally higher than -26‰. The difference is due to the presence in the nonforested regions, of grasses which assimilate carbon via the C4 photosynthetic pathway (average ?13C = ˜-13‰), rather than the C3 pathway (average ?13C = ˜-28‰) utilized by forest vegetation, and to negligible utilization of low-?13C respired carbon dioxide in regions of open vegetation. A change in the area of the Basin covered by closed forest will lead to a modification in the carbon isotope composition of exported POC as a result of changing (1) the proportion of C4 carbon in the total biomass (2) the relative proportion of the total POC derived from upstream, high-altitude (Andean) sources, (3) erosion rates, and (4) productivity. All of these factors will tend to reinforce each other in their effect on the carbon isotope composition of POC exported from the Basin, with a decrease in forest area leading to an increase in the ?13C value of POC (and vice versa). There is a sufficient difference between the ?13C values of POC exported from forested and non- forested catchments to elucidate past vegetation and therefore climatic changes in the Amazon Basin (and other tropical river basins), using the ?13C record in POC from either terrestrial or offshore sedimentary sequences. The carbon isotope composition of POC in rivers draining recently deforested regions indicates that the isotopic composition of coarse (>63 ?m) riverine POC will respond to vegetation changes in a catchment within years to decades, whereas the ?13C value of fine-grained (<63 ?m) riverine POC may take longer to respond.

Bird, M. I.; Fyfe, W. S.; Pinheiro-Dick, D.; Chivas, A. R.

1992-09-01

206

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

NASA Astrophysics Data System (ADS)

Chromium (Cr) stable isotopes experience an increased interest as a tracer of Cr (VI) reduction in groundwater and thus showed their potential as a monitor of remediation of anthropogenic and natural contamination in water (Berna et al., 2009; Izbicki et al., 2008). Chromium stable isotopes in Fe-rich chemical sediments (BIFs and Fe-cherts) have recently also been used as a tracer for Earth's atmospheric oxygenation through time (Frei et al., 2009). We have applied the Cr isotope system to organic-rich carbonates from a late Ediacaran succession in Uruguay (Polanco Formation), from which we have previously analyzed BIFs with extremely fractionated (?53Cr up to 5.0 ‰) Cr isotope signatures that are part of an underlying deep water clastic sediment (shale-dominated) sequence (Yerbal Formation) deposited in a glacio-marine environment (Gaucher et al.,2004). ?53Cr values of organic rich carbonates correlate with positive and negative carbon isotope excursions (?13C PDB between -3 and +3 ‰) and with systematic changes in strontium isotope compositions, commonly interpreted as to reflect fluctuations in organic (photosynthetic algae) production related to fluctuations in atmospheric oxygen and weathering intensities, respectively. Slightly positively fractioned ?53Cr values (up to +0.25‰), paralleling positive (?13C PDB and 87Sr/86Sr ratio excursions would thereby trace elevated atmospheric oxygen levels/pulses possibly related to glacier retreat/melting stages that caused bioproductivity to increase. While the causal link between these multiple isotopic tracers and the mechanisms of Cr stripping into carbonates has to be further investigated in detail, the first indications from this study point to a potentially promising use of stable Cr isotopes in organic-rich carbonates to monitor fluctuations of atmospheric oxygen, particularly over the Neoproterozoic and Phanerozoic ice age periods. E.C. Berna et al. (2010) Cr stable isotopes as indicators of Cr(VI) reduction in groundwater: a detailed time-series study of a point-source plume. Environ. Sci. Technol., v. 44, p. 1043-1048. J.A. Izbicki et al. (2008) Chromium, chromium isotopes and selected trace elements, western Mojave Desert, USA. Applied Geochemistry, v.23, p. 1325-1352. R. Frei et al. (2009) Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes. Nature, v. 461, p. 250-253. C. Gaucher et al. (2004) Chemostratigraphy of the Lower Arroyo del Soldado Group (Vendian, Uruguay) and palaeoclimatic implications. Gondwana Research, v.7, p. 715-730

Frei, R.; Gaucher, C.

2010-12-01

207

Distinct carbon isotope fractionation during anaerobic degradation of dichlorobenzene isomers.  

PubMed

Chlorinated benzenes are ubiquitous organic contaminants found in groundwater and soils. Compound specific isotope analysis (CSIA) has been increasingly used to assess natural attenuation of chlorinated contaminants, in which anaerobic reductive dechlorination plays an essential role. In this work, carbon isotope fractionation of the three dichlorobenzene (DCB) isomers was investigated during anaerobic reductive dehalogenation in methanogenic laboratory microcosms. Large isotope fractionation of 1,3-DCB and 1,4-DCB was observed while only a small isotope effect occurred for 1,2-DCB. Bulk enrichment factors (?bulk) were determined from a Rayleigh model: -0.8 ± 0.1 ‰ for 1,2-DCB, -5.4 ± 0.4 ‰ for 1,3-DCB, and -6.3 ± 0.2 ‰ for 1,4-DCB. ?bulk values were converted to apparent kinetic isotope effects for carbon (AKIE) in order to characterize the carbon isotope effect at the reactive positions for the DCB isomers. AKIE values are 1.005 ± 0.001, 1.034 ± 0.003, and 1.039 ± 0.001 for 1,2-DCB, 1,3-DCB, and 1,4-DCB, respectively. The large difference in AKIE values between 1,2-DCB and 1,3-DCB (or 1,4-DCB) suggests distinct reaction pathways may be involved for different DCB isomers during microbial reductive dechlorination by the methanogenic cultures. PMID:24758692

Liang, Xiaoming; Mundle, Scott O C; Nelson, Jennifer L; Passeport, Elodie; Chan, Calvin C H; Lacrampe-Couloume, Georges; Zinder, Stephen H; Sherwood Lollar, Barbara

2014-05-01

208

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

NASA Astrophysics Data System (ADS)

The mineralogical, compositional and stable isotopic variability of lacustrine carbonates are frequently used as proxies for ancient paleoenvironmental change in continental settings, under the assumption that precipitated carbonates reflect conditions and chemistry of ancient lake waters. In some saline and alkaline lake systems, however, authigenic clay minerals, forming at or near the sediment water interface, are a major sedimentary component. Often these clays are rich in Mg, influencing the geochemical budget of lake waters, and are therefore expected to influence the properties of contemporaneous authigenic carbonate precipitates (which may also contain Mg). This paper documents evidence for a systematic feedback between clay mineral and carbonate authigenesis through multiple precessionally driven, m-scale sedimentary cycles in lacustrine oil-shale deposits of the Eocene Green River Formation from the Uinta Basin (NE Utah). In the studied section, authigenic, Mg-rich, trioctahedral smectite content varies cyclically between 9 and 39 wt.%. The highest concentrations occur in oil-shales and calcareous mudstones deposited during high lake level intervals that favored sedimentary condensation, lengthening the time available for clay diagenesis and reducing dilution by other siliciclastic phases. An inverse relation between dolomite percentage of carbonate and trioctahedral smectite abundance suggests the Mg uptake during clay authigenesis provides a first order control on carbonate mineralogy that better explains carbonate mineralogical trends than the possible alternative controls of (1) variable Mg/Ca ratios in lake water and (2) degree of microbial activity in sediments. We also observe that cyclical change in carbonate mineralogy, believed to be induced by clay authigenesis, also causes isotopic covariation between ?13CPDB and ?18OPDB of bulk sediments because of differences in the equilibrium fractionation factors of dolomite and calcite (˜2‰ and ˜2.6%, respectively). This provides an alternative mechanism for the common pattern of isotopic covariation, which is typically attributed to the effect of simultaneous changes in water balance and biological activity on the carbon and oxygen isotopic composition of lake waters. These findings may help improve paleoenvironmental reconstructions based on lacustrine carbonate records by adding to the factors known to influence the mineralogical, compositional and stable isotopic signals recorded by lacustrine carbonates.

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

2012-08-01

209

Temperature dependence of carbon isotope fractionation in CAM plants  

SciTech Connect

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.

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

1985-09-01

210

Temperature Dependence of Carbon Isotope Fractionation in CAM Plants.  

PubMed

The carbon isotope fractionation associated with nocturnal malic acid synthesis in Kalanchoë 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 degrees C nights, 23 degrees C days), the isotope fractionation for both plants is -4 per thousand (that is, malate is enriched in (13)C relative to the atmosphere). For K. daigremontiana, the isotope fractionation decreases with increasing temperature, becoming approximately 0 per thousand at 27 degrees C/33 degrees 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. PMID:16664371

Deleens, E; Treichel, I; O'leary, M H

1985-09-01

211

Stable carbon isotope analysis of nucleic acids to trace sources of dissolved substrates used by estuarine bacteria.  

PubMed Central

The natural abundance of stable carbon isotopes measured in bacterial nucleic acids extracted from estuarine bacterial concentrates was used to trace sources of organic matter for bacteria in aquatic environments. The stable carbon isotope ratios of Pseudomonas aeruginosa and nucleic acids extracted from cultures resembled those of the carbon source on which bacteria were grown. The carbon isotope discrimination between the substrate and total cell carbon from bacterial cultures averaged 2.3% +/- 0.6% (n = 13). Furthermore, the isotope discrimination between the substrate and nucleic acids extracted from bacterial cultures was 2.4% +/- 0.4% (n = 10), not significantly different from the discrimination between bacteria and the substrate. Estuarine water samples were prefiltered through 1-micron-pore-size cartridge filters. Bacterium-sized particles in the filtrates were concentrated with tangential-flow filtration and centrifugation, and nucleic acids were then extracted from these concentrates. Hybridization with 16S rRNA probes showed that approximately 90% of the nucleic acids extracted on two sample dates were of eubacterial origin. Bacteria and nucleic acids from incubation experiments using estuarine water samples enriched with dissolved organic matter from Spartina alterniflora and Cyclotella caspia had stable carbon isotope values similar to those of the substrate sources. In a survey that compared diverse estuarine environments, stable carbon isotopes of bacteria grown in incubation experiments ranged from -31.9 to -20.5%. The range in isotope values of nucleic acids extracted from indigenous bacteria from the same waters was similar, -27.9 to -20.2%. Generally, the lack of isotope discrimination between bacteria and nucleic acids that was noted in the laboratory was observed in the field.(ABSTRACT TRUNCATED AT 250 WORDS) Images PMID:2389930

Coffin, R B; Velinsky, D J; Devereux, R; Price, W A; Cifuentes, L A

1990-01-01

212

Variability in the carbon isotopic composition of foliage carbon pools (soluble carbohydrates, waxes) and respiration fluxes  

E-print Network

Variability in the carbon isotopic composition of foliage carbon pools (soluble carbohydrates measured the d13 C of assimilated carbon (foliage organic matter (dCOM), soluble carbohydrates (d pools (soluble carbohydrates, waxes) and respiration fluxes in southeastern U.S. pine forests, J

Martin, Timothy

213

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

PubMed

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 ?(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. PMID:23869014

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

214

Abundance and Isotopic Composition of Gases in the Martian Atmosphere from the Curiosity Rover  

NASA Astrophysics Data System (ADS)

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 (40Ar), 0.0193(±0.0001); nitrogen (N2), 0.0189(±0.0003); oxygen, 1.45(±0.09) × 10-3; carbon monoxide, < 1.0 × 10-3; and 40Ar/36Ar, 1.9(±0.3) × 103. The 40Ar/N2 ratio is 1.7 times greater and the 40Ar/36Ar 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 40Ar/36Ar ratio is consistent with martian meteoritic values, which provides additional strong support for a martian origin of these rocks. The isotopic signature ?13C 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.

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; Kemppinen, Osku; Bridges, Nathan; Johnson, Jeffrey R.; Minitti, Michelle; Cremers, David; Bell, James F.; Edgar, Lauren; Farmer, Jack; Godber, Austin; Wadhwa, Meenakshi; Wellington, Danika; McEwan, Ian; Newman, Claire; Richardson, Mark; Charpentier, Antoine; Peret, Laurent; King, Penelope; Blank, Jennifer; Weigle, Gerald; Schmidt, Mariek; Li, Shuai; Milliken, Ralph; Robertson, Kevin; Sun, Vivian; Baker, Michael; Edwards, Christopher; Ehlmann, Bethany; Farley, Kenneth; Griffes, Jennifer; Grotzinger, John; Miller, Hayden; Newcombe, Megan; Pilorget, Cedric; Rice, Melissa; Siebach, Kirsten; Stack, Katie; Stolper, Edward; Brunet, Claude; Hipkin, Victoria; Léveillé, Richard; Marchand, Geneviève; Sánchez, Pablo Sobrón; Favot, Laurent; Cody, George; Steele, Andrew; Flückiger, Lorenzo; Lees, David; Nefian, Ara; Martin, Mildred; Gailhanou, Marc; Westall, Frances; Israël, Guy; Agard, Christophe; Baroukh, Julien; Donny, Christophe; Gaboriaud, Alain; Guillemot, Philippe; Lafaille, Vivian; Lorigny, Eric; Paillet, Alexis; Pérez, René; Saccoccio, Muriel; Yana, Charles; Armiens-Aparicio, Carlos; Rodríguez, Javier Caride; Blázquez, Isaías Carrasco; Gómez, Felipe Gómez; Gómez-Elvira, Javier; Hettrich, Sebastian; Malvitte, Alain Lepinette; Jiménez, Mercedes Marín; Martínez-Frías, Jesús; Martín-Soler, Javier; Martín-Torres, F. Javier; Jurado, Antonio Molina; Mora-Sotomayor, Luis; Caro, Guillermo Muñoz; López, Sara Navarro; Peinado-González, Verónica; Pla-García, Jorge; Manfredi, José Antonio Rodriguez; Romeral-Planelló, Julio José; Fuentes, Sara Alejandra Sans; Martinez, Eduardo Sebastian; Redondo, Josefina Torres; Urqui-O'Callaghan, Roser; Mier, María-Paz Zorzano; Chipera, Steve; Lacour, Jean-Luc; Mauchien, Patrick; Sirven, Jean-Baptiste; Fairén, Alberto; Hayes, Alexander; Joseph, Jonathan; Sullivan, Robert; Thomas, Peter; Dupont, Audrey; Lundberg, Angela; Melikechi, Noureddine; Mezzacappa, Alissa; DeMarines, Julia; Grinspoon, David; Reitz, Günther; Prats, Benito; Atlaskin, Evgeny; Genzer, Maria; Harri, Ari-Matti; Haukka, Harri; Kahanpää, Henrik; Kauhanen, Janne; Kemppinen, Osku; Paton, Mark; Polkko, Jouni; Schmidt, Walter; Siili, Tero; Fabre, Cécile; Wray, James; Wilhelm, Mary Beth; Poitrasson, Franck; Patel, Kiran; Gorevan, Stephen; Indyk, Stephen; Paulsen, Gale; Gupta, Sanjeev; Bish, David; Schieber, Juergen; Gondet, Brigitte; Langevin, Yves; Geffroy, Claude; Baratoux, David; Berger, Gilles; Cros, Alain; d'Uston, Claude; Forni, Olivier; Gasnault, Olivier; Lasue, Jérémie; Lee, Qiu-Mei; Maurice, Sylvestre; Meslin, Pierre-Yves; Pallier, Etienne; Parot, Yann; Pinet, Patrick; Schröder, Susanne; Toplis, Mike; Lewin, Éric; Brunner, Will; Heydari, Ezat; Achilles, Cherie; Oehler, Dorothy; Sutter, Brad; Cabane, Michel; Coscia, David; Israël, Guy; Szopa, Cyril; Dromart, Gilles; Robert, François; Sautter, Violaine; Le Mouélic, Stéphane; Mangold, Nicolas; Nachon, Marion; Buch, Arnaud; Stalport, Fabien; Coll, Patrice; François, Pascaline; Raulin, François; Teinturier, Samuel; Cameron, James; Clegg, Sam; Cousin, Agnès; DeLapp, Dorothea; Dingler, Robert; Jackson, Ryan Steele; Johnstone, Stephen; Lanza, Nina; Little, Cynthia; Nelson, Tony; Wiens, Roger C.; Williams, Richard B.; Jones, Andrea; Kirkland, Laurel; Treiman, Allan; Baker, Burt; Cantor, Bruce; Caplinger, Michael; Davis, Scott; Duston, Brian; Edgett, Kenneth; Fay, Donald; Hardgrove, Craig; Harker, David; Herrera, Paul; Jensen, Elsa; Kennedy, Megan R.; Krezoski, Gillian; Krysak, Daniel; Lipkaman, Leslie; Malin, Michael; McCartney, Elaina; McNair, Sean; Nixon, Brian; Posiolova, Liliya; Ravine, Michael; Salamon, Andrew; Saper, Lee; Stoiber, Kevin; Supulver, Kimberley; Van Beek, Jason; Van Beek, Tessa; Zimdar, Robert; French, Katherine Louise; Iagnemma, Karl; Miller, Kristen; Summons, Roger; Goesmann, Fred; Goetz, Walter; Hviid, Stubbe; Johnson, Micah; Lefavor, Matthew; Lyness, Eric; Breves, Elly; Dyar, M. Darby; Fassett, Caleb; Blake, David F.; Bristow, Thomas; DesMarais, David; Edwards, Laurence; Haberle, Robert; Hoehler, Tori; Hollingsworth, Jeff; Kahre, Melinda; Keely, Leslie; McKay, Christopher; Wilhelm, Mary Beth; Bleacher, Lora; Brinckerhoff, William; Choi, David; Dworkin, Jason P.; Eigenbrode, Jennifer; Floyd, Melissa; Freissinet, Caroline; Garvin, James; Glavin, Daniel; Jones, Andrea; Martin, David K.

2013-07-01

215

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

SciTech Connect

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.

HOLDEN,N.E.

2007-07-23

216

BOREAS TE-5 Tree Ring and Carbon Isotope Ratio Data  

NASA Technical Reports Server (NTRS)

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).

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

2000-01-01

217

Carbon isotope systematics of a mantle "hotspot": a comparison of Loihi Seamount and MORB glasses  

USGS Publications Warehouse

The carbon isotope geochemistry of glasses from Loihi Seamount has been compared with that of MORB glasses. Stepped heating shows two carbon components in both sample suites: (1) isotopically light carbon (avg. ??13C = -26.3???) released 600??C, regarded as indigenous. The high-temperature component in MORB samples varied from 52 to 169 ppm C, average ??13C = -6.6???, consistent with previous studies (overall MORD average ??13C = -6.4 ?? 0.9???), and new results for Indian Ocean glasses are similar to Atlantic and Pacific Ocean samples. Carbon release profiles produced by stepped heating may be typical of locality, but there are no significant differences in ??13C values between MORB samples from different areas. Lower yields (17-110 ppm C) correlated with depth in the Loihi samples suggest that they are partially degassed. This degassing has not affected ??13C values significantly (avg. -5.8???). Loihi tholeiites have higher ??13C (avg. -5.6???) than the alkali basalts (avg. -7.1???). Carbon abundances correlate well with He concentration data. Comparison of the ??13C values with trace element and He, Sr, Nd, and Pb isotope data from the literature suggests that the Loihi samples with highest ??13C have high 3He/4He and possibly the least depleted 143Nd/144Nd and 87Sr/86Sr. The carbon isotope data are consistent with previous models for Loihi involving several mantle sources, lithospheric contamination, and mixing. The slightly higher ??13C of Loihi tholeiites suggests that the undegassed "plume" component manifested by high 3He/4He values might have ??13C about 1??? higher than the MORB average. ?? 1986.

Exley, R.A.; Mattey, D.P.; Clague, D.A.; Pillinger, C.T.

1986-01-01

218

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

NASA Astrophysics Data System (ADS)

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 (? 13C), but the causes of this pattern are poorly understood. We compiled new and published high-resolution ? 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 ? 13C pattern. Across a broad range of latitude, temperature, and precipitation regimes, we found that the average, measured seasonal change in ? 13C (?? 13C meas, ‰) within tree rings of evergreen species reflects changes in the carbon isotopic composition of atmospheric carbon dioxide (?? 13C CO2) and changes in seasonal precipitation (? P) according to the following equation: ?? 13C meas = ?? 13C CO2 - 0.82(? P) + 0.73; R2 = 0.96. Seasonal changes in temperature, pCO 2, and light levels were not found to significantly affect ?? 13C meas. We propose that this relationship can be used to quantify seasonal patterns in paleoprecipitation from intra-ring profiles of ? 13C measured from non-permineralized, fossil wood.

Schubert, Brian A.; Jahren, A. Hope

2011-11-01

219

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

220

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

NASA Astrophysics Data System (ADS)

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<63? 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 about 8-10‰ below 500° C, 5-6‰ between 500-700° C, and 8-10‰ above 700° C. CI and oxygen isotopic compositions of carbonate and phosphate are not well correlated. Only modest CI changes are recorded from 25-675° C, compared with much larger changes in oxygen isotopic composition, especially above 300° C. On average, original isotopic compositions are largely preserved for both phosphate (+/-1‰ ) and carbonate (+/-2‰ ) oxygen at <300° C. At higher temperatures, however, both phosphate and carbonate oxygen in the bioapatite are systematically depleted of oxygen-18 relative to original values.

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

2003-12-01

221

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 ...

222

Influence of diet on the distribution of carbon isotopes in animals  

Microsoft Academic Search

The influence of diet on the distribution of carbon isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant carbon isotopic composition. The isotopic composition of the whole body of an animal reflects the isotopic composition of its diet, but the animal is on average enriched in 13 C by about 1 relative to

Michael J. Deniro; Samuel Epstein

1978-01-01

223

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

224

The isotopic abundances of neon, magnesium and silicon nuclei accelerated in solar flares  

NASA Technical Reports Server (NTRS)

Direct measurements of the relative abundance of the isotopes Ne-20 and Ne-22 are reported along with a preliminary value for the Mg-26/Mg-24 ratio and an upper limit to the abundance of Si-30 in solar flare accelerated nuclei. A Ne-20/Ne-22 ratio of 7.7 plus 2.3 or minus 1.7 is in agreement with the ratio for the component Neon-A found in carbonaceous chondrites, while a preliminary value of 0.22 plus or minus 0.07 for Mg-26/Mg-24 is larger by approximately one standard deviation than the expected ratio of 0.14 given by Cameron (1973).

Dietrich, W. F.; Simpson, J. A.

1980-01-01

225

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

Microsoft Academic Search

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‰ ?13C, +2‰ ?18O). The

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

2007-01-01

226

Evolution of carbon isotopes, agglutinates, and the lunar regolith  

NASA Technical Reports Server (NTRS)

Apollo 17 light-mantle soils and Apollo 15 Apennine Front soils are compared with respect to isotopic enrichment of C-13 and the maturity of the site. Analyses of soil-size fractions indicate that while the carbon concentration on particle surfaces remains relatively constant with increasing soil maturity, total surface-correlated carbon increases due to increasing total soil surface area. The role of agglutinates in the incorporation of surface-correlated carbon into aggregate grains is examined; agglutinates contain a major percentage of the carbon found in mature soil, and the volume-correlated carbon component in agglutinates apparently continues to increase after the surface-correlated carbon concentrations have reached a constant value. Constraints that may limit the carbon concentration in lunar soils to a value not greater than 300 micrograms/g are considered.

Desmarais, D. J.; Basu, A.; Hayes, J. M.; Meinschein, W. G.

1975-01-01

227

Carbon stars in local group dwarf galaxies: C and O abundances  

E-print Network

We present abundances of carbon and oxygen as well as abundance ratios 12C/13C for a sample of carbon stars in the LMC, SMC, Carina, Sculptor and Fornax dwarf galaxies. The overall metallicities in these dwarf galaxies are lower than in the galactic disc. The observations cover most of the AGB and we discuss the abundance patterns in different regions along the AGB. The abundances are determined from infrared spectra obtained with the ISAAC spectrometer on VLT (R=1500) and the Phoenix Spectrometer on Gemini South (R=50000). The synthetic spectra used in the analysis were computed with MARCS model atmospheres. We find that the oxygen abundance is decreasing with decreasing overall metallicity of the system while the C/O ratio at a given evolutionary phase is increasing with decreasing oxygen abundance. keywords Stars: abundances -- Stars: carbon -- Stars: AGB and post-AGB -- Galaxies: dwarf -- Local Group -- Infrared: stars

R. Wahlin; K. Eriksson; B. Gustafsson; K. H. Hinkle; D. L. Lambert; N. Ryde; B. Westerlund

2006-05-10

228

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

Microsoft Academic Search

Differential fractionation of stable isotopes of carbon during photosynthesis causes C 4 plants and C3 plants to have distinct carbon-isotope signatures. In addition, marine C 3 plants have stable-isotope ratios of carbon that are intermediate between C4 and terrestrial C3 plants. The direct incorporation of the carbon-isotope ratio ( 13C\\/12C) of plants into consumers' tissues makes this ratio useful in

Jeffrey F. Kelly

2000-01-01

229

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

NASA Astrophysics Data System (ADS)

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 ?13C 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.

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

2014-01-01

230

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

NASA Astrophysics Data System (ADS)

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 ?13C 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.

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

2014-09-01

231

Molecular and carbon isotopic composition of leaf wax in vegetation and aerosols in a northern prairie ecosystem.  

PubMed

We measured the molecular and carbon isotopic composition of major leaf wax compound classes in northern mixed mesic prairie species (Agropyron smithii, Stipa viridula, Bouteloua gracilis, Tragopogon dubius) and in selected crops (Triticum aestivum, Brassica napus, Hordeum vulgare, Medicago sativa) of southern Alberta and also in aerosols collected 4 m above the prairie canopy. Our aims were to better constrain the wax biosynthetic carbon isotopic fractionation relative to the plant's carbon isotopic discrimination and to quantitatively assess the correspondence between wax composition in vegetation and in boundary layer aerosols. Wax molecular composition of the C(3)prairie species and bulked vegetation was characterized by high abundance of C(28) n-alkanol and C(31) n-alkane compounds whereas the C(4) species B. gracilis had several co-dominant n-alkanol and n-alkane compounds. Wax molecular composition of crop species differed significantly from that of prairie vegetation and was often dominated by a single compound. Results indicate that leaf wax isotopic composition is quantitatively related to the plant's carbon isotopic discrimination. Although species variations were evident, n-alcohol, n-acid and n-alkane wax compounds were on average depleted in (13)C by approximately 6.0+/-1 per thousand relative to total plant carbon. The magnitude of the depletion in wax delta(13)C was unaffected by environmental factors which altered photosynthetic carbon isotopic discrimination. No consistent difference in the magnitude of wax biosynthetic fractionation was observed between C(3) and C(4) species, indicating that photosynthetic pathway has little influence on the isotopic fractionation of wax during biosynthesis. The isotopic composition of ablated waxes in aerosols collected above the canopy was similar to that of the grassland vegetation but the molecular composition differed significantly and indicated that the source "footprint" of the ablated leaf wax particles we sampled in boundary layer air masses was of a regional or larger spatial scale. PMID:12647105

Conte, Maureen H; Weber, John C; Carlson, Peter J; Flanagan, Lawrence B

2003-03-01

232

Carbon Reservoir History of Mars Constrained by Atmospheric Isotope Signatures  

NASA Astrophysics Data System (ADS)

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. Here we use a box model to trace the evolution of the carbon reservoir and its iso-topic signature on Mars, with carbonate deposition and atmospheric escape as the two sinks and magmatic activity as the sole source. We derive new quantitative constraints on the amount of carbonate deposition and the atmospher-ic 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 frac-tionation factor of 0.6 and hence, photochemical escape processes can effectively enrich 13C in the Mars’s atmos-phere during the Amazonian. As a result, modest carbonate deposition must have occurred early in Mars’s history to compensate the enrichment effects of photochemical processes and also sputtering, even when volcanic outgassing up to 200 mbar occurred during the Hesperian. For a photochemical escape flux that scales as the square of the solar EUV flux or more, at least 0.1 bar of CO2 must have been deposited as carbonates in the Noachian and Hesperian. More carbonate deposition would be required if carbonate deposition only occurred in the Noachian or with low fractionation factors.

Hu, Renyu; Kass, David M.; Ehlmann, Bethany L.; Yung, Yuk

2014-11-01

233

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

234

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

NASA Technical Reports Server (NTRS)

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.

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

235

PHYSIOLOGICAL ECOLOGY -ORIGINAL PAPER Carbon and hydrogen isotope fractionation under continuous  

E-print Network

PHYSIOLOGICAL ECOLOGY - ORIGINAL PAPER Carbon and hydrogen isotope fractionation under continuous intensity continuous light, e.g., in the High Arctic summer, on plant carbon and hydrogen isotope on both carbon and hydrogen isotope com- positions of three deciduous conifers whose fossil counterparts

236

Variation of Hydrogen, Carbon, Nitrogen, and Oxygen Stable Isotope Ratios in an American Diet  

E-print Network

Variation of Hydrogen, Carbon, Nitrogen, and Oxygen Stable Isotope Ratios in an American Diet: Fast isotopes of hydrogen, carbon, nitrogen, and oxygen provide insights into a heterotrophic organism's diet component within the diet. KEYWORDS: Stable isotope; hydrogen; carbon; nitrogen; oxygen; American diet; fast

Ehleringer, Jim

237

Parallel, high-resolution carbon and sulfur isotope records of the evolving Paleozoic marine sulfur reservoir  

E-print Network

Parallel, high-resolution carbon and sulfur isotope records of the evolving Paleozoic marine sulfur the biogeochemical cycles of carbon and sulfur are expressed in the evolving stable isotope composition of the ocean time, along with the sulfate sulfur isotope composition preserved as carbonate-associated sulfate (CAS

Saltzman, Matthew R.

238

Variations in the isotopic composition of particulate organic carbon and their relation with carbon dynamics in the western Arctic Ocean  

Microsoft Academic Search

The relation between the dissolved carbon dioxide (CO2) and the stable isotopic composition of particulate organic matter in the water column has not been well quantified, but this information could help provide a better understanding of carbon dynamics in a warmer Arctic Ocean. The stable carbon isotopic composition of suspended particulate organic carbon (?13CPOC) in the surface waters of the

Run Zhang; Min Chen; Laodong Guo; Zhongyong Gao; Qiang Ma; Jianping Cao; Yusheng Qiu; Yanping Li

239

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

PubMed

Carbon isotopes are often used to detect the addition of foreign sugars to foods. This technique takes advantage of the natural difference in carbon isotope ratio between C(3) and C(4) plants. Many foods are derived from C(3) plants, but the low-cost sweeteners corn and sugar cane are C(4) plants. Most adulteration studies do not take into account the secular shift of the carbon isotope ratio of atmospheric carbon dioxide caused by fossil fuel burning, a shift also seen in plant tissues. As a result statistical tests and threshold values that evaluate authenticity of foods based on carbon isotope ratios may need to be corrected for changing atmospheric isotope values. Literature and new data show that the atmospheric trend in carbon isotopes is seen in a 36-year data set of maple syrup analyses (n = 246), demonstrating that published thresholds for cane or corn sugar adulteration in maple syrup (and other foods) have become progressively more lenient over time. PMID:20121108

Peck, William H; Tubman, Stephanie C

2010-02-24

240

Carbon isotope discrimination by plants follows latitudinal and altitudinal trends  

Microsoft Academic Search

In an earlier paper we provided evidence that carbon isotope discrimination during photosynthesis of terrestrial C3 plants decreases with altitude, and it was found that this was associated with greater carboxylation efficiency at high altitudes. Changing partial pressures of CO2 and O2 and changing temperature are possible explanations, since influences of moisture and light were reduced to a minimum by

Ch. Körner; G. D. Farquhar; S. C. Wong

1991-01-01

241

Where is air-sea gas exchange happening? Carbon isotope  

E-print Network

Where is air-sea gas exchange happening? Carbon isotope evidence Nir Krakauer California Institute: An application of generalized cross validation · The regional distribution of air-sea gas exchange · Seasonality;Gas exchange in perspective Applications of gas exchange rates · To infer the space and time

Krakauer, Nir Y.

242

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

NASA Technical Reports Server (NTRS)

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.

Neumann, K.; DesMarais, D. J.

1998-01-01

243

Stable carbon isotope fractionation by sulfate-reducing bacteria  

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

244

PoS(NIC-IX)150 Present-Day Carbon Abundances  

E-print Network

and slightly sub-solar present-day carbon abundance from young stars in the solar vicinity of log C/H + 12 = 8PoS(NIC-IX)150 Present-Day Carbon Abundances of Early-Type Stars M. F. Nievaab and N. Przybillaa a. José Cristino 77, 20921-400, Rio de Janeiro, Brazil E-mail: nieva@sternwarte.uni-erlangen.de Carbon

Przybilla, Norbert

245

Carbon Stars in the Hamburg/ESO Survey: Abundances  

NASA Astrophysics Data System (ADS)

We have carried out a detailed abundance analysis using high-dispersion spectra from HIRES at Keck for a sample of 16 carbon stars found among candidate extremely metal-poor (EMP) stars from the Hamburg/ESO Survey (HES). We find that the Fe metallicities for the cooler C stars (Teff~5100 K) have been underestimated by a factor of ~10 by the standard HES tools. The results presented here provided crucial supporting data used recently by Cohen et al. to derive the frequency of C stars among EMP stars. C enhancement in these EMP C stars appears to be independent of Fe metallicity and approximately constant at ~1/5 the solar ?(C). The C enhancement shows some evidence of decreasing with decreasing Teff (increasing luminosity), presumably due to mixing and dredge-up of C-depleted material. The mostly low 12C/13C ratios (~4) and the high N abundances in many of these stars suggest that material that has been through proton burning via the CN cycle comprises most of the stellar envelope. C enhancement in this sample is associated with strong enrichment of heavy nuclei beyond the Fe peak for 12 of the 16 stars. The remaining C stars from the HES, which tend to be the most Fe-poor, show no evidence for enhancement of the heavy elements. Very high enhancements of lead are detected in some of the C stars with highly enhanced Ba. The strong lead lines, the high Ba/Eu ratios, and the high ratios of abundances of the diagnostic elements in the first and second s-process peaks demonstrate that the s-process is responsible for the enhancement of the heavy elements for the majority of the C stars in our sample. The low 12C/13C ratios and large C and N enhancements of the EMP C stars are more extreme than those of intrinsic asymptotic giant branch C stars of near-solar Fe metallicity, but closer to the composition of CH stars. Our subsample of EMP C stars without s-process enhancement is reminiscent of the R-type C stars in the solar neighborhood; thus, we expect that they are formed by similar mechanisms. We suggest that both the s-process-enhanced and Ba-normal C stars result from phenomena associated with mass transfer in binary systems. This leads directly to the progression from C stars to CH stars and then to Ba stars as the Fe metallicity increases. Based in part on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.

Cohen, Judith G.; McWilliam, Andrew; Shectman, Stephen; Thompson, Ian; Christlieb, Norbert; Melendez, Jorge; Ramirez, Solange; Swensson, Amber; Zickgraf, Franz-Josef

2006-07-01

246

Carbon isotope geochemistry of the Santa Clara River  

NASA Astrophysics Data System (ADS)

The Santa Clara River is a prototypical small mountainous river, with a headwater height greater than 1000 m and a basin area smaller than 10,000 m 2. Although individual small mountainous rivers export trivial amounts of sediment and carbon to the ocean, as a group these rivers may export a major fraction (as much as 50%) of the total global river sediment flux [Milliman and Syvitski, 1992], making their geochemistry relevant the study of the ocean's carbon cycle. In addition, many small rivers export sediment in a few high flux events, causing massive, sporadic discharge of carbon onto coastal shelves, discharge conditions very different from those of large rivers. This class of rivers is an end-member of the river-ocean carbon exchange system,. opposite the Earth's largest river, the Amazon. The carbon mass and isotopic properties of the Santa Clara River are significantly different from previously studied large rivers. During the 1997-1998 winter, all Santa Clara carbon pools were old, with flux-weighted average ?l4C values of-428±76‰ for particulate organic carbon, -73±31‰ for dissolved organic carbon, and-644±58‰ for black carbon. The age of exported carbon is primarily due to the deep erosion of old soils and not to inclusion of fossil fuel carbon. Additionally, the ?13C signatures of exported carbon pools were high relative to terrestrial carbon, bearing a signature quite similar to marine carbon (average particulate organic carbon (POC) ?13C = -22.2±0.8‰). The Santa Clara's estuary is small and drains onto the narrow eastern Pacific coastal margin, exporting this old soil organic matter directly into the ocean. If the Santa Clara export patterns are representative of this class of rivers, they may be a significant source of refractory terrestrial carbon to the ocean.

Masiello, Caroline A.; Druffel, Ellen R. M.

2001-06-01

247

Magnesium isotope fractionation in bacterial mediated carbonate precipitation experiments  

NASA Astrophysics Data System (ADS)

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 ?26Mg 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 ?m in diameter, but with the majority have diameters of ~100 ?m. 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). Geomicrobiol. J. 20, 85-98.

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

2012-12-01

248

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

NASA Astrophysics Data System (ADS)

The stable carbon isotopic composition (expressed as ? 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 ? 13C and C 4 relative abundance in extant ecosystems has not been thoroughly examined. We determined sources of variation in ? 13C of bone collagen and tooth enamel of kangaroos ( Macropus spp.) collected throughout Australia by measuring ? 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 ? 13C (68%) and enamel ? 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 ? 13C. While there was no relationship between collagen ? 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 ? 13C, enrichment factors ( ??) 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 ? 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.

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

2007-08-01

249

Carbon isotope signature of dissolved inorganic carbon (DIC) in precipitation and atmospheric CO 2  

Microsoft Academic Search

This paper describes results of chemical and isotopic analysis of inorganic carbon species in the atmosphere and precipitation for the calendar year 2008 in Wroc?aw (SW Poland). Atmospheric air samples (collected weekly) and rainwater samples (collected after rain episodes) were analysed for CO2 and dissolved inorganic carbon (DIC) concentrations and for ?13C composition. The values obtained varied in the ranges:

Maciej Górka; Peter E. Sauer; Dominika Lewicka-Szczebak; Mariusz-Orion J?drysek

2011-01-01

250

Carbon isotopic fractionation of CFCs during abiotic and biotic degradation.  

PubMed

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 (?(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 ?(1/2) = 17.3 h and k(SA) = -(1.2 ± 0.5) × 10(-4) L m(-2) h(-1). Significant kinetic isotope effects of ?(‰) = -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 ?(13)C ? -13‰ (HCFC-22), ?(13)C ? -35‰ (CFC-12) and ?(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. PMID:22191586

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

2012-02-01

251

Vibration-rotation bands of CH in the solar infrared spectrum and the solar carbon abundance  

NASA Technical Reports Server (NTRS)

High resolution solar spectra obtained from the ATMOS Fourier Transform Spectrometer (Spacelab 3 flight on April 29-May 6, 1985) have made it possible to identify and measure a large number of lines of the vibration-rotation fundamental bands of the X2 Pi state of CH. From about 100 lines of the 1-0, 2-1, and 3-2 bands and adopting theoretical transition probabilities, a solar carbon abundance of 8.60 + or - 0.05 is derived. This value is compared with new results inferred from other carbon abundance indicators. The final recommended solar abundance of carbon is 8.60 + or - 0.05.

Grevesse, N.; Lambert, D. L.; Sauval, A. J.; Van Dishoek, E. F.; Farmer, C. B.; Norton, R. H.

1991-01-01

252

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

PubMed

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, (13)C, or D, were developed for the validity of the simplified Rayleigh approach when using labelled compounds. PMID:16442790

Mahieu, Koenraad; Visscher, Alex De; Vanrolleghem, Peter A; Cleemput, Oswald Van

2006-01-01

253

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

PubMed

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. PMID:19768966

Ivlev, A A; Voronin, V I

2007-01-01

254

Triple oxygen isotopes in biogenic and sedimentary carbonates  

NASA Astrophysics Data System (ADS)

The 17O anomaly (?17O) 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 ?17O than primary meteoric waters. In animal body water, ?17O relates to the intake of evaporated waters, evaporative effluxes of water, and the ?17O 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 ?17O of carbonate. We describe optimized methods based on a sequential acid digestion/reduction/fluorination approach that yield ?17O data with the high precision (?0.010‰, 1?) needed to resolve subtle environmental signals. We report the first high-precision ?17O 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 ?18O and ?17O 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 ?17O values that are similar to or slightly lower than global precipitation. Our results suggest that ?17O will have useful application to paleoenvironmental studies of continental environments where the effects of evaporation are important, and where vertebrate body water may record an isotopic signal of evaporated water sources and atmospheric oxygen.

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

2014-09-01

255

In situ analysis of carbon isotopes in North American diamonds  

NASA Astrophysics Data System (ADS)

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 ?13C (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‰) ?13C values of the Lynx (and Wawa) diamonds may indicate a different carbon reservoir for the Superior craton mantle as compared to other cratons.

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

2010-12-01

256

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

NASA Astrophysics Data System (ADS)

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 ?47, 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 ?47-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 ?47-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 ?18O values of 0.5-1.5‰ when used in conjunction with published temperature-?18Ocarb-?18Osw calibrations. This ?18O range is higher than is traditionally assumed for high-latitude Cretaceous seawater. We argue, however, that such values are plausible and may be related to different basin- or global-scale hydrologies or belemnite body fluid that was in isotopic disequilibrium with the seawater. The paired ?47 and ?18O from the fossils rule out isotopic exchange with high temperature fluids or later diagenesis in 18O-depleted meteoric waters. We observe no textual or chemical evidence of recrystallization, and we hypothesize that these shells faithfully record early Cretaceous high-latitude seawater temperatures. The inferred temperature range of 20-26°C is substantially higher than 60-70°N modern mean annual sea surface temperature (˜-1.0 to 10.0°C) and mean summer surface temperatures (˜-0.5 to 14.5°C), implying a substantially shallower latitudinal temperature gradient during the early Cretaceous.

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

2010-12-01

257

HCNMBC - A pulse sequence for H-(C)-N Multiple Bond Correlations at natural isotopic abundance  

NASA Astrophysics Data System (ADS)

We propose a pulse sequence, HCNMBC for multiple-bond H-(C)-N correlation experiments via one-bond 1J(C,H) and one- or multiple bond nJ(N,C) coupling constants (typically n = 1-3) at the natural isotopic abundance. A new adiabatic refocussing sequence is introduced to provide accurate and robust refocussing of both chemical shift and J-evolution over wide ranges of C-13 and N-15 frequencies. It is demonstrated that the proposed pulse sequence provides high quality spectra even for sub-milligram samples. We show that when a 1.7 mm cryoprobe is available as little as 10 ?g of glycine in D2O is sufficient to obtain the HCNMBC spectrum in ca. 12 h. The preliminary results indicate that the pulse sequence has a great potential in the structure determination of nitrogen heterocycles especially in cases where synthesis produces regioisomers.

Cheatham, Steve; Gierth, Peter; Bermel, Wolfgang; Kup?e, ?riks

2014-10-01

258

Sr, Nd, and Pb isotope evidence for a mantle origin of alkali chlorides and carbonates in the Udachnaya kimberlite, Siberia  

NASA Astrophysics Data System (ADS)

The kimberlite rocks of the Udachnaya-East pipe (Siberia) are uniquely fresh and contain very high abundances of primary volatiles (Cl, CO2, S). Alkali elements and chlorine are extremely abundant in the reconstructed kimberlite melt compositions, and this enrichment is very important for our understanding of deep-mantle melting and melt transport. Here we present new isotopic data that confirm a mantle origin for these kimberlitic chlorides and carbonates, and constrain the kimberlite emplacement age as ca. 347 Ma. The initial Nd and Pb isotope ratios in a large salt aggregate, in a Cl-S enriched water leachate of the groundmass, and in the silicate fraction of the groundmass are very similar ( ? Nd = +3 to +4, 206Pb/204Pb = 18.6, 207Pb/204Pb = 15.53), implying a comagmatic origin of the chlorides and carbonates and the silicates. Combined Sr, Nd, and Pb isotope data are used to rule out any significant contributions to the kimberlite chlorine budget from crustal sources, such as the Cambrian evaporite sequences of the Siberian platform. Our data support the interpretation that exsolved Na-K chloride and Na-K-Ca carbonate formed directly from original uncontaminated kimberlite magma. High Cl abundances in kimberlites suggest the presence of a Cl-rich reservoir in the deep sublithospheric mantle.

Maas, Roland; Kamenetsky, Maya B.; Sobolev, Alexander V.; Kamenetsky, Vadim S.; Sobolev, Nikolai V.

2005-07-01

259

First measurement of Mg isotope abundances at high redshifts and accurate estimate of ??/?  

NASA Astrophysics Data System (ADS)

Aims: Abundances of the Mg isotopes 24Mg, 25Mg, and 26Mg can be used to test models of chemical enrichment of interstellar/intergalactic gas clouds. Additionally, because the position of the Mg ii ??2796,2803 Å lines is often taken as a reference in computations of possible changes of the fine-structure constant ?, it should be clarified to which extent these lines are affected by isotopic shifts. Methods: We use a high-resolution spectrum (pixel size ? 1.3 km s-1) of the quasar HE0001-2340 observed with the UVES/VLT to measure Mg isotope abundances in the intervening absorption-line systems at high redshifts. Line profiles are prepared taking into account possible shifts between the individual exposures. In the line-fitting procedure, the lines of each ion are treated independently. Because of the unique composition of the selected systems - the presence of several transitions of the same ion - we can test the local accuracy of the wavelength scale calibration, which is the main source of errors in the sub-pixel line position measurements. Results: In the system at zabs = 0.45, which is probably a fragment of the outflow caused by SN Ia explosion of high-metallicity white dwarf(s), we measured velocity shifts of Mg ii and Mg i lines with respect to other lines (Fe i, Fe ii, Ca i, Ca ii): ?VMg II = -0.44 ± 0.05 km s-1, and ?VMg I = -0.17 ± 0.17 km s-1. This translates into the isotopic ratio 24Mg:25Mg:26Mg = (19 ± 11):(22 ± 13):(59 ± 6) with a strong relative overabundance of heavy Mg isotopes, (25Mg+26Mg)/24Mg = 4, as compared to the solar ratio 24Mg:25Mg:26Mg = 79:10:11, and (25Mg+26Mg)/24Mg = 0.3. In the systems at zabs = 1.58 and zabs = 1.65 enriched by AGB-stars we find only upper limits on the content of heavy Mg isotopes (25Mg+ 26Mg)/24Mg ? 0.7 and (25Mg+ 26Mg)/24Mg ? 2.6, respectively. At zabs = 1.58, we also put a strong constraint on a putative variation of ?: ??/? = (-1.5 ± 2.6) × 10-6, which is one of the most stringent limits obtained from optical spectra of QSOs. We reveal that the wavelength calibration in the range above 7500 Å is subject to systematic wavelength-dependent drifts. Based on observations performed at the VLT Kueyen telescope (ESO, Paranal, Chile), the ESO programme No. 083.A-0733(A).Tables are only available in electronic form at http://www.aanda.org

Agafonova, I. I.; Molaro, P.; Levshakov, S. A.; Hou, J. L.

2011-05-01

260

Contrasting the CO2-He Isotope and Relative Abundance Systematics of the Central American and IBM Arcs  

NASA Astrophysics Data System (ADS)

We report CO2 and He isotope and relative abundance data obtained utilizing high-T fumaroles, geothermal wells, boiling mud pots, hot springs and phenocryst-bearing lavas from both MARGINS-targeted regions. In Central America, we collected ~140 fluid and ~30 lava samples covering a total of 41 volcanic centers in Costa Rica (7), Nicaragua (8), El Salvador (10), Honduras (9) and Guatemala (7). Along the IBM arc, we sampled the islands of Uracas, Agrigan, Pagan and Alamagan in the CNMI and Oshima, Niijima, Shikinajima, Hachijojima and Aogashima in the Izu islands. Helium isotope ratios (3He/4He) reach a maximum of 8RA (where RA = air 3He/4He) with most values > 5 RA. The majority of samples have CO2/3He ratios between 1010 and 1011, as at other arcs. The ?13C of the CO2 for the majority of samples fall between -5 and 0 ‰ (PDB) consistent with a major slab input to the carbon inventory. The entire database has been assessed to identify samples unmodified by localised crustal processes (~75% of total), thereby defining the He and C systematics of the underlying mantle source. At both arcs, we utilize along-strike He-C variations to consider the relative influence of various subduction zone forcing functions on the output C-flux. We show that subducted sediment lithology, particularly down-hole C distribution and the nature (oxidized/reduced) of the C, is a major control on the output as opposed to other factors such as angle of slab dip, convergence rate, and thickness of overlying arc crust.

Hilton, D. R.; Fischer, T. P.; Shaw, A. M.; Hauri, E.; Walker, J.

2006-12-01

261

Carbon isotope fractionation of methyl bromide during agricultural soil fumigations  

USGS Publications Warehouse

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???.

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

2002-01-01

262

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

SciTech Connect

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.

Schell, D.M.

1994-06-01

263

Descriptions of carbon isotopes within the energy density functional theory  

SciTech Connect

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.

Ismail, Atef [Fundamental and Applied Sciences Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia and Department of Physics, Al-Azhar University, 71524 Assiut (Egypt); Cheong, Lee Yen; Yahya, Noorhana [Fundamental and Applied Sciences Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak (Malaysia); Tammam, M. [Department of Physics, Al-Azhar University, 71524 Assiut (Egypt)

2014-10-24

264

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

USGS Publications Warehouse

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. Bitumens are always co-genetic with associated coals and kerogens. Isotopic data reveal that Sofer's genetic classification of oils is not applicable to organic matter in coals. ?? 2003 Elsevier B.V. All rights reserved.

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

2003-01-01

265

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

NASA Astrophysics Data System (ADS)

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 ?13C -4.72± 2.11, o and ?18O -9.46± 1.9, o ; Zervynos ?13C -4.79± 1.82, o and ?18O -9.57± 1.69, o ; Rudnia ?13C -4.94± 7.53, o and ?18O -9.3± 3.92, o ; Pauliai ?13C -4.15± 0.67, o and ?18O -9.94± 1.07, o : In other countries: Poland ?13C -1.07± 1.94, o and ?18O -7.69± 0.95, o ; Belarus ?13C 0.97± 1.94, o and ?18O -7.61± 1.42, o ; Kaliningrad ?13C -1.14± 1.43, o and ?18O -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 separate local, regional and even global environment condition impact to isotopic values in the past. 1. Hammarlund, Dan, et al. "Climate and environment during the Younger Dryas (GS-1) as reflected by composite stable isotope records of lacustrine carbonates at Torreberga, southern Sweden." Journal of Quaternary Science 14.1 (1999): 17-28. 2. Makhnach, N., et al. "Stable oxygen and carbon isotopes in Late Glacial-Holocene freshwater carbonates from Belarus and their palaeoclimatic implications." Palaeogeography, Palaeoclimatology, Palaeoecology 209.1 (2004): 73-101.

Skipityt?, Raminta; Stan?ikait?, Migl?

2014-05-01

266

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

PubMed

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. PMID:19123821

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

2009-01-28

267

Stable Carbon Isotopes As Indicators of Plant Water Use Efficiency  

Microsoft Academic Search

Stable carbon isotopes have been utilized to better understand how environmental variables influence the efficiency of photosynthesis, specifically what factors limit the uptake and absorption of CO2 during photosynthesis. An understanding of the controls over both gas exchange and stomatal conductance can provide an explanation for the possible environmental influences on plant WUE. The delta13C of extractive-free wood was used

E. M. Powers; J. D. Marshall; N. Ubierna Lopez

2007-01-01

268

Control strategies for laser separation of carbon isotopes  

Microsoft Academic Search

Laser isotope separation (LIS) by infrared laser chemistry of polyatomic molecules has come a long way since its discovery.\\u000a The last decade has seen considerable efforts in scaling up of the process for light elements like carbon, oxygen and silicon.\\u000a These efforts aim at ways to improve both the enrichment factor and the throughput. The achievement is quite significant especially

V. Parthasarathy; A. K. Nayak; S. K. Sarkar

2002-01-01

269

Efficient, highly selective laser isotope separation of carbon-13  

Microsoft Academic Search

We recently demonstrated an original approach to highly selective laser isotope separation of carbon-13 that employs vibrational overtone pre-excitation of CF3H together with infrared multiphoton dissociation [O.V. Boyarkin, M. Kowalczyk, T.R. Rizzo, J. Chem. Phys. 118, 93 (2003)]. The practical implementation of this approach was complicated by the long absorption path length needed for the overtone excitation laser beam. In

M. N. Polianski; T. R. Rizzo; O. V. Boyarkin

2006-01-01

270

Stable carbon and nitrogen isotope biogeochemistry in the Delaware estuary  

Microsoft Academic Search

,Qbstract Seasonal variability in stable carbon (S'XZ) and nitrogen (b15N) isotope ratios was observed in suspended particulate matter of the Delaware estuary. Two major pools of organic matter were found in the estuary-phytoplankton growing in situ and a mixture of planktonic and terrestrial detritus. In general, the 6°C and 615N of suspended particulate matter reflected planktonic dom- inance. With the

L. A. Cifuentesl; J. H. SHARP; MARILYN L. FOGEL

1988-01-01

271

The use of stable carbon isotope analysis in rooting studies  

Microsoft Academic Search

Stable carbon isotope analysis was evaluated as a means of predicting the relative proportions of C3 and C4 root phytomass in species mixtures. The following mixtures of C3 and C4 species were used: 1) big bluestem (Andropogon gerardii)\\/cheatgrass (Bromus tectorum), 2) little bluestem (Schizachyrium scoparium)\\/cheatgrass, and 3) sorghum (Sorghum bicolor)\\/sunflower (Helianthus annuus). There was a significant correlation (P4 phytomass and

Tony J. Svejcar; Thomas W. Boutton

1985-01-01

272

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

SciTech Connect

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.

Pineau, F. (Univ. de Paris (France)); Mathez, E.A. (American Museum of Natural History, New York (USA))

1990-01-01

273

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

SciTech Connect

This report describes method development and preliminary evaluation for analyzing castor samples for signatures of purifying ricin. Ricin purification from the source castor seeds is essentially a problem of protein purification using common biochemical methods. Indications of protein purification will likely manifest themselves as removal of the non-protein fractions of the seed. Two major, non-protein, types of biochemical constituents in the seed are the castor oil and various carbohydrates. The oil comprises roughly half the seed weight while the carbohydrate component comprises roughly half of the remaining “mash” left after oil and hull removal. Different castor oil and carbohydrate components can serve as indicators of specific toxin processing steps. Ricinoleic acid is a relatively unique fatty acid in nature and is the most abundant component of castor oil. The loss of ricinoleic acid indicates a step to remove oil from the seeds. The relative amounts of carbohydrates and carbohydrate-like compounds, including arabinose, xylose, myo-inositol fucose, rhamnose, glucosamine and mannose detected in the sample can also indicate specific processing steps. For instance, the differential loss of arabinose relative to mannose and N-acetyl glucosamine indicates enrichment for the protein fraction of the seed using protein precipitation. The methods developed in this project center on fatty acid and carbohydrate extraction from castor samples followed by derivatization to permit analysis by gas chromatography-mass spectrometry (GC-MS). Method descriptions herein include: the source and preparation of castor materials used for method evaluation, the equipment and description of procedure required for chemical derivatization, and the instrument parameters used in the analysis. Two types of derivatization methods describe analysis of carbohydrates and one procedure for analysis of fatty acids. Two types of GC-MS analysis is included in the method development, one employing a quadrupole MS system for compound identification and an isotope ratio MS for measuring the stable isotope ratios of deuterium and hydrogen (D/H) in fatty acids. Finally, the method for analyzing the compound abundance data is included. This study indicates that removal of ricinoleic acid is a conserved consequence of each processing step we tested. Furthermore, the stable isotope D/H ratio of ricinoleic acid distinguished between two of the three castor seed sources. Concentrations of arabinose, xylose, mannose, glucosamine and myo-inositol differentiated between crude or acetone extracted samples and samples produced by protein precipitation. Taken together these data illustrate the ability to distinguish between processes used to purify a ricin sample as well as potentially the source seeds.

Wunschel, David S.; Kreuzer-Martin, Helen W.; Antolick, Kathryn C.; Colburn, Heather A.; Moran, James J.; Melville, Angela M.

2009-12-01

274

The use of carbon stable isotope ratios in drugs characterization  

SciTech Connect

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 ?{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.

Magdas, D. A., E-mail: gabriela.cristea@itim-cj.ro; Cristea, G., E-mail: gabriela.cristea@itim-cj.ro; Bot, A., E-mail: gabriela.cristea@itim-cj.ro; Mirel, V., E-mail: gabriela.cristea@itim-cj.ro [National Institute for Research and Development of Isotopic and Molecular Technologies, 65-103 Donath Str., 400293 Cluj-Napoca (Romania)

2013-11-13

275

The use of carbon stable isotope ratios in drugs characterization  

NASA Astrophysics Data System (ADS)

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 ?13C 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.

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

2013-11-01

276

Kinetic fractionation of carbon and oxygen isotopes during hydration of carbon dioxide  

NASA Astrophysics Data System (ADS)

Kinetic isotope effects (KIEs) during the inorganic hydration of carbon dioxide (CO2) in aqueous solution cause reduced stable carbon and oxygen isotope ratios (13C/12C and 18O/16O) in the reaction product carbonic acid (H2CO3) or bicarbonate ion (HCO3-), relative to CO2. While such KIEs are of importance in various physicochemical, geochemical, and biological systems, very few experimental and theoretical studies have attempted to determine the magnitude of the carbon and oxygen kinetic isotope fractionation (KIF) during hydration of CO2. Here I use transition state theory (TST) and quantum chemistry calculations to investigate the reaction rates of isotopic reactants CO2+nH2O (n = 1-8) along the hydration pathway to H2CO3 or HCO3-. Locating transition states is difficult and the quantum chemistry calculations time-consuming at large n. My results suggest that the hydration mechanism for n = 1-3 is unlikely to be the dominant pathway producing KIFs during CO2 hydration in aqueous solution; hydration mechanisms for n ? 4 appear more likely. For n = 4-8, the predicted KIF based on MP2/aug-cc-pVDZ calculations at 25 °C is ?1.023-1.033 and ?1.013-1.015, for carbon and oxygen, respectively. However, these values are uncertain and the results of the present study suggest that new experimental work is required to accurately determine the KIF of carbon and oxygen during CO2 hydration.

Zeebe, Richard E.

2014-08-01

277

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

PubMed Central

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

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

1998-01-01

278

The cause of carbon isotope minimum events on glacial terminations.  

PubMed

The occurrence of carbon isotope minima at the beginning of glacial terminations is a common feature of planktic foraminifera carbon isotopic records from the Indo-Pacific, sub-Antarctic, and South Atlantic. We use the delta13C record of a thermocline-dwelling foraminifera, Neogloboquadrina dutertrei, and surface temperature estimates from the eastern equatorial Pacific to demonstrate that the onset of delta13C minimum events and the initiation of Southern Ocean warming occurred simultaneously. Timing agreement between the marine record and the delta13C minimum in an Antarctic atmospheric record suggests that the deglacial events were a response to the breakdown of surface water stratification, renewed Circumpolar Deep Water upwelling, and advection of low delta13C waters to the convergence zone at the sub-Antarctic front. On the basis of age agreement between the absolute delta13C minimum in surface records and the shift from low to high delta13C in the deep South Atlantic, we suggest that the delta13C rise that marks the end of the carbon isotope minima was due to the resumption of North Atlantic Deep Water influence in the Southern Ocean. PMID:11964477

Spero, Howard J; Lea, David W

2002-04-19

279

Stable carbon and nitrogen isotope enrichment in primate tissues.  

PubMed

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 (?*) 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 ?* values of proteinaceous tissues were small (?1‰), and uncorrelated with body size or phylogenetic relatedness. Additionally, ?* values did not vary by habitat, sex, age, or manner of death. The mean ?* 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. PMID:20628886

Crowley, Brooke E; Carter, Melinda L; Karpanty, Sarah M; Zihlman, Adrienne L; Koch, Paul L; Dominy, Nathaniel J

2010-11-01

280

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

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

281

Oxygen isotope ratio measurements on carbon dioxide generated by reaction of microliter quantities of biological fluids with guanidine hydrochloride  

SciTech Connect

Guanidine hydrochloride was used to convert water in biological fluids to carbon dioxide for oxygen isotope ratio measurements. Five 10-..mu..L aliquots each of five different saliva, urine, plasma, and human milk samples were allowed to react with 100 mg of guanidine hydrochloride at 260/sup 0/C to produce ammonia and carbon dioxide. Ammonia was removed with 100% phosphoric acid and carbon dioxide was cryogenically purified before isotope ratio measurement. At natural abundances, the delta/sup 18/O values of the biological fluids were reproducible to within 0.16% (standard deviation) and accurate to within 0.11 +/- 0.73% (x vector +/- SD) of the H/sub 2/O-CO/sub 2/ equilibration values. At a 250% enrichment level of /sup 18/O, the delta/sup 18/O values of the biological fluids were reproducible to within 0.95% and accurate to -1.27 +/- 2.25%.

Wong, W.W.; Lee, L.S.; Klein, P.D.

1987-03-01

282

Allochthonous carbon hypothesis for bulk OM and n-alkane PETM carbon isotope discrepancies  

NASA Astrophysics Data System (ADS)

The Paleocene-Eocene Thermal Maximum (PETM), a period of abrupt, transient, and large-scale global warming fueled by a large release of isotopically light carbon, is a relevant analogue for episodes of rapid global warming and recovery. The PETM is recorded in pedogenic carbonate, bulk organic matter, and n-alkanes as a prominent negative carbon isotope excursion (CIE) in paleosols exposed in the Bighorn Basin, WY. Here we present a composite stable carbon isotope record from n-alkanes and dispersed soil organic ?13C records from five individual sections that span the PETM in the southeastern Bighorn Basin. Four sections are from a 10km transect in the Cabin Fork area and one section was collected at Sand Creek Divide. These five new dispersed organic carbon (DOC) isotope records are compared to the previously published Polecat Bench (Magioncalda et al. 2004) and Honeycombs (Yans et al. 2006) isotope records. The high-resolution n-alkane curve shows an abrupt, negative shift in ?13C values, an extended CIE body, and a rapid recovery to more positive ?13C values. Although the five DOC records show similarly abrupt negative shifts in ?13C values, the DOC CIEs are compressed, smaller in magnitude, and return to more positive ?13C values more gradually relative to the n-alkane record. Moreover, the stratigraphic thickness of the body of the excursion and the pattern of the recovery phase are not consistent among the five DOC records. We modeled predicted DOC ?13C values from the n-alkane record by applying enrichment factors based on modern plants to the n-alkane ?13C values. The anomaly, difference between the expected and observed DOC ?13C values, was calculated for the PETM records and compared to weight percent carbon and grain size. There is no correlation between pre- and post-PETM anomaly values and grain size or weight percent carbon. PETM anomaly values, however, do trend with both grain size and weight percent carbon. The largest PETM anomaly values correspond to the highest grain sizes and lowest weight percent carbon. We hypothesize that the difference between the n-alkane and DOC ?13C records is due to contamination of the DOC ?13C signal by weathering of older, refractory Jurassic-Cretaceous carbon. According to this hypothesis, before and after the CIE the difference in the isotopic composition of autochthonous (Cenozoic) and allochthonous (Jurassic-Cretaceous) organic matter would have been small because C3 plants in the Jurassic-Cretaceous and pre- and post-PETM had relatively similar values. Thus, the ratio of autochthonous: allochthonous organic matter would be uncorrelated with isotopic composition. During the CIE, the isotopic composition of autochthonous organic carbon decreased dramatically. Therefore, autochthonous and allochthonous carbon pools were isotopically distinct and a correlation between weight percent carbon and isotopic composition is expected: the lower the weight percent carbon, the higher the proportion of allochthonous carbon, the larger the anomaly.

Baczynski, A. A.; McInerney, F. A.; Wing, S. L.; Kraus, M. J.; Fricke, H. C.

2011-12-01

283

Carbon and Oxygen Abundances across the Hertzsprung Gap  

NASA Astrophysics Data System (ADS)

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 ? 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 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.

Adamczak, Jens; Lambert, David L.

2014-08-01

284

Isotopic Composition and Trace Element Abundances of a Presolar SiC AB Grain Reconstructed by Atom-Probe Tomography  

NASA Astrophysics Data System (ADS)

C and Si isotopic ratios of a previously characterized SiC AB grain are consistent with earlier NanoSIMS results. N, Al and Ti are abundant and distributed uniformly throughout the grain; s-process elements such as Zr, Mo and Ba were not detected.

Lewis, J. B.; Isheim, D.; Floss, C.; Groopman, E.; Gyngard, F.; Seidman, D. N.

2014-09-01

285

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

ERIC Educational Resources Information Center

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)

O'Malley, Rebecca M.

1982-01-01

286

Noble gas abundance and isotope ratios in the atmosphere of Jupiter from the Galileo Probe Mass Spectrometer  

Microsoft Academic Search

The Galileo Probe Mass Spectrometer provided the first data on the noble gas mixing and isotope ratios in the Jovian atmosphere. These measurements and the comparison with solar values constrain models of Jupiter's formation. Significant refinements to the initially reported abundances of argon, krypton, and xenon have been enabled through post-encounter laboratory calibrations using a refurbished engineering unit mass spectrometer

P. R. Mahaffy; H. B. Niemann; A. Alpert; S. K. Atreya; J. Demick; T. M. Donahue; D. N. Harpold; T. C. Owen

2000-01-01

287

The Distribution of Carbon Abundances in Stars in the Milky Way’s Satellite Galaxies  

NASA Astrophysics Data System (ADS)

There is evidence that the Milky Way halo is comprised in part of disrupted dwarf satellite galaxies; however, the extent to which they contribute to the halo’s formation is unclear. To further examine the role of dwarf galaxies in building the halo, we compared the degrees of carbon enhancement of the dwarf spheroidal (dSph) galaxies and field halo populations. We generated a grid of high-resolution synthetic spectra for hypothetical stars of specific effective temperature, surface gravity, metallicity, alpha element abundance, and carbon abundance for comparison with medium-resolution observed spectra of dSph stars of unmeasured [C/Fe] but otherwise known properties. After smoothing, rebinning, and normalizing the two data sets, we varied carbon abundance to find the best carbon abundance by determining the synthetic spectrum that gave the minimal deviation. We found a lower Carbon-Enhanced Metal-Poor (CEMP) fraction in the dSph galaxies, which suggests that they have evolved over time. Whereas star formation and chemical evolution stopped for accreted galaxies, the surviving galaxies evolved to became less carbon enhanced and more metal rich. The variation in carbon abundances supports prior knowledge of dSph stars and provide a deeper understanding the formation of stars such as those of the Milky Way halo. We thank the US National Science Foundation, the UCSC Science Internship Program, and the W. M. Keck Observatory where the spectra were obtained.

Guo, Michelle; Zhang, A.

2013-01-01

288

Boron Isotope Intercomparison Project (BIIP): Development of a new carbonate standard for stable isotopic analyses  

NASA Astrophysics Data System (ADS)

Boron consists of only of two isotopes with a relatively large mass difference (~10 %). It is also volatile in acidic media and prone to contamination during analytical treatment. Nevertheless, an increasing number of isotope laboratories are successfully using boron isotope compositions (expressed in ?11B) in marine biogenic carbonates to reconstruct seawater pH. Recent interlaboratory comparison efforts [1] highlighted the existence of a relatively high level of disagreement between laboratories when measuring such material, so in order to further strengthen the validity of this carbonate system proxy, appropriate reference materials need to be urgently characterised. We describe here the latest results of the Boron Isotope Intercomparison Project (BIIP) where we aim to characterise the boron isotopic composition of two marine carbonates: Japanese Geological Survey carbonate standard materials JCp-1 (coral porites) [2] and JCt-1 (Giant Clam) [3]. This boron isotope interlaboratory comparison study has two aims: (i) to assess to what extent chemical pre-treatment, aimed at removing organic material, can influence the resulting carbonate ?11B; (ii) to determine the isotopic composition of the two reference materials with a number of analytical techniques to provide the community with reference ?11B values for JCp-1 and JCt-1 and to further explore any differences related to analytical technique. In total eight isotope laboratories participated, of which one determined ?11B via negative thermal ionisation mass spectrometry (NTIMS) and seven used multi collector inductively coupled plasma mass spectrometry (MC-ICPMS). For the latter several different introduction systems and chemical purification methods were used. Overall the results are strikingly consistent between the participating labs. The oxidation of organic material slightly lowered the median ?11B by ~0.1 ‰ for both JCp-1 and JCt-1, while the mean ?11B of all labs for both standards was lowered by 0.20 ‰ for JCp-1 and 0.15 ‰ for JCt-1, hence within uncertainty of the reported values. With the exception of one MC-ICPMS lab that provided significantly lower JCp-1 ?11B data for unoxidised material (1.7 ‰ below median), the remaining JCp-1 results reproduced within ± 0.54 ‰ for unoxidised (n=21) and ± 0.37 ‰ for oxidised standards (n=21). The JCt-1 standards did not reproduce as well, resulting in a 2 s.d. of 1.0 ‰ for both unoxidised and oxidised powders (n=21) and in places the effect of oxidation appeared to be laboratory dependent. Exclusion of one MC-ICPMS lab resulted in an improved reproducibility of 0.52 ‰ (n=18) for oxidised JCt-1 material. The mean difference for the two standard materials in the respective labs (i.e., ??11B = mean ?11B(JCp-1) - mean ?11B(JCt-1)) was 7.9 ± 0.9 ‰ for unoxidised (n=7) and 8.1 ± 0.7 ‰ for oxidised standards (n=7). In this presentation emphasis will also be placed on distinguishing factors leading to increased/decreased interlaboratory consistency during the preparation and analysis of biogenic carbonates for other isotopic systems. References [1] Foster, G.L. et al. (2013) Chemical Geology 358: p. 1-14. [2] Okai, T. et al. (2002) Geostandards Newsletter 26: p. 95-99. [3] Inoue, M. et al. (2004) Geostandards and Geoanalytical Research 28: p. 411-416.

Gutjahr, Marcus; Bordier, Louise; Douville, Eric; Farmer, Jesse; Foster, Gavin L.; Hathorne, Ed; Hönisch, Bärbel; Lemarchand, Damien; Louvat, Pascale; McCulloch, Malcolm; Noireaux, Johanna; Pallavicini, Nicola; Rodushkin, Ilia; Roux, Philippe; Stewart, Joseph; Thil, François; You, Chen-Feng

2014-05-01

289

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...

290

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

NASA Astrophysics Data System (ADS)

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.

Bright, Jordon; Kaufman, Darrell S.; Forester, Richard M.; Dean, Walter E.

2006-09-01

291

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

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.

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

2006-01-01

292

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

SciTech Connect

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.

Aravena, R. (Univ. of Waterloo, Ontario (Canada). Center for Groundwater Research and Wetlands Research Center); Warner, B.G. (Univ. of Waterloo, Ontario (Canada). Wetlands Research Center and Dept. of Geography); Charman, D.J. (Univ. of Plymouth, Devon (United Kingdom). Dept. of Geographical Sciences); Belyea, L.R. (Queen Mary and Westfield College, London (United Kingdom). School of Biological Sciences); Mathur, S.P. (Foxleigh Crescent, Kanata, Ontario (Canada)); Dinel, H. (Center for Land and Biological Resources Research, Agriculture Canada, Ontario (Canada))

1993-01-01

293

Stable carbon isotope ratios in Asian elephant collagen: implications for dietary studies  

Microsoft Academic Search

Summary  Stable carbon isotope ratios in bone collagen have been used in a variety of dietary studies in modern and fossil animals,\\u000a including humans. Inherent in the stable isotope technique is the assumption that the isotopic signature is a reflection of\\u000a the diet and is persistent in collagen because this is a relatively inert protein. Carbon isotope analyses of bones from

R. Sukumar; R. Ramesh

1992-01-01

294

Sensitivity analysis and quantification of uncertainty for isotopic mixing relationships in carbon cycle research  

E-print Network

relationships is critical to isotopic applications in carbon cycle studies at all spatial and temporal scales ecosystems represents one of the current challenges in carbon cycle research (Schimel et al., 1994, 2001Sensitivity analysis and quantification of uncertainty for isotopic mixing relationships in carbon

Keener, James P.

295

SIO269 Special Topics in Marine Chemistry Seminar Carbon Cycle from an Isotope Perspective  

E-print Network

SIO269 Special Topics in Marine Chemistry Seminar ­ Carbon Cycle from an Isotope Perspective 1 Changes in the ocean carbon cycle readings: Broecker et al. (2007) Quay et al. (2003) November 27th Stable Carbon Isotopes: A quick introduction (Reading: Gruber et al., 1999; Kroopnick, 1985) October 9th

Aluwihare, Lihini

296

UNCORRECTEDPROOF 2 The effect of rising atmospheric oxygen on carbon and sulfur isotope  

E-print Network

UNCORRECTEDPROOF 1 2 The effect of rising atmospheric oxygen on carbon and sulfur isotope 3 90089, United States 8 Accepted 8 June 2006 9 10 Editor: P. Deines 11 Abstract 12 Carbonates within a remarkable negative carbon isotope anomaly ­ to a nadir of near -11 ­ that accompanies a dramatic rise

Kaufman, Alan Jay

297

HYDROGEN ISOTOPE PROFILE OF METHYL GROUPS IN MILIACIN (OLEAN-18-EN-3OL ME) BY NATURAL ABUNDANCE DEUTERIUM 2D-NMR  

E-print Network

HYDROGEN ISOTOPE PROFILE OF METHYL GROUPS IN MILIACIN (OLEAN- 18-EN-3OL ME) BY NATURAL ABUNDANCE.lesot@u-psud.fr; jeremy.jacob@univ-orleans.fr Compound-specific hydrogen isotope analyses are gaining increasing interest to which extent these modifications can be accompanied by a hydrogen isotope fractionation process

Paris-Sud XI, Université de

298

Carbon and Nitrogen Isotope Variation in Sphagnum from Peat Bogs in the Midwestern Us: Implications for Holocene Climate Reconstruction  

NASA Astrophysics Data System (ADS)

A peat core taken from near the center of Minden Bog in Michigan, representing about 3500 years of accumulation was previously analyzed for plant macrofossils, colorimetric humification, and testate amoebae to yield three independent climate proxies. The data show the site to be sensitive to bog water table fluctuations and suggest that this may be related to regional climatic changes. We analyzed the carbon and nitrogen isotopes and the carbon-nitrogen ratios in the bulk peat samples and determined that the changes in these isotopes and ratios can be attributed to one or more of the following: (1) changes in the relative abundance of vegetation taxa in the site, (2) changes in the metabolism that impact isotope ratios in the vegetation contributing to the bulk organic, and (3) selective preservation and regeneration of specific organic compounds within the bulk organic matter. We analyzed the carbon and nitrogen isotopes and the carbon-nitrogen ratios in a specific taxum, Sphagnum, to differentiate between these mechanisms and relate the record to water level and climate in the region.

Wong, D.; Paytan, A.; Jackson, S. T.

2009-12-01

299

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...

300

Chemical method for nitrogen isotopic analysis of ammonium at natural abundance.  

PubMed

We report a new chemical method to determine the (15)N natural abundance (?(15)N) for ammonium (NH4(+)) in freshwater (e.g., precipitation) and soil KCl extract. This method is based on the isotopic analysis of nitrous oxide (N2O). Ammonium is initially oxidized to nitrite (NO2(-)) by hypobromite (BrO(-)) using previously established procedures. NO2(-) is then quantitatively converted into N2O by hydroxylamine (NH2OH) under strongly acid conditions. The produced N2O is analyzed by a commercially available purge and cryogenic trap system coupled to an isotope ratio mass spectrometer (PT-IRMS). On the basis of a typical analysis size of 4 mL, the standard deviation of ?(15)N measurements is less than 0.3‰ and often better than 0.1‰ (3 to 5 replicates). Compared to previous methods, the technique here has several advantages and the potential to be used as a routine method for (15)N/(14)N analysis of NH4(+): (1) substantially simplified preparation procedures and reduced preparation time particularly compared to the methods in which diffusion or distillation is involved since all reactions occur in the same vial and separation of NH4(+) from solution is not required; (2) more suitability for low volume samples including those with low N concentration, having a blank size of 0.6 to 2 nmol; (3) elimination of the use of extremely toxic reagents (e.g., HN3) and/or the use of specialized denitrifying bacterial cultures which may be impractical for many laboratories. PMID:24654992

Liu, Dongwei; Fang, Yunting; Tu, Ying; Pan, Yuepeng

2014-04-15

301

Dynamic and transfert of carbon in Loire catchment using carbon isotopes  

NASA Astrophysics Data System (ADS)

Rivers have a major role in carbon transfer between continent and ocean. The organic matter exported from land represents a major source of DOC and POC in oceans. The composition and reactivity of this matter will influence its behavior and fate within the coastal areas and continental shelf. It is thus important to characterize the exported matter and its temporal variability. Stable carbon isotope ratios (d13C) and 14C activity can provide unique information on carbon sources, turnover and exchange processes. We present here a study of the carbon cycle in the Loire River and its major tributaries by combining carbon isotopes measurements and classical biogeochemical parameters (DOC, POC, DIC, pH, Temperature, Alkalinity, pH, chlorophyll …). Three campaigns were performed in April, July and October 2013. The changes in 14C signature due to the controlled liquid release of five nuclear power plants are used to get additional information on the carbon dynamics within the river. First results show a conservative behavior of the organic carbon concentrations contrary to the inorganic carbon all along the Loire River. However, the reactivity of the organic matter varies with rivers catchments and seasons. An inventory of the distribution of the different carbon phases within the Loire River and its tributaries is presented.

Coularis, Cindy; Fontugne, Michel; Tisnérat-Laborde, Nadine; Pastor, Lucie; Siclet, Françoise

2014-05-01

302

Stable carbon isotopic analysis of pyrolysis products of kerogens  

SciTech Connect

The origin of insoluble organic matter in sediments is still a matter of debate. The application of isotope-ratio-monitoring gas chromatography-mass spectrometry (irm-CYC-MS) in combination with pyrolytic and chemolytic methods allows the determination of the 13C-content of products released from the kerogen and provides a tool to determine the structure and origin of kerogen. Analysis of the pyrolysis products of several marine kerogens revealed that the stable carbon isotopic compositions of the n-alkanes (C10-C25) are quite similar to those of the n-alkenes. This suggests that they have a common origin such as algal biopolymers. The isoprenoid alkanes (C13-C20) also have similar isotopic compositions but differ from the values of the n-alkanes and n-alkenes. These isoprenoids could be derived from an isoprenoid algaenan similar to that biosynthesised by the freshwater algae Botryococcus braunii race L. The analysis of products in the aromatic fraction of the pyrolysates, showed a wide range of isotopic values, which suggest multiple origins.

Hoeld, I.M.; Schouten, S.; Sinninghe Damste, J.S. [NIOZ, Texel (Netherlands)

1996-12-31

303

Collisionally assisted, highly selective laser isotope separation of carbon-13.  

PubMed

We have further developed our recently reported two-laser technique for highly selective molecular isotope separation of carbon-13 [Boyarkin, Kowalczyk, and Rizzo, J. Chem. Phys. 118, 93 (2003)] with the objective of increasing the yield. An essential feature of this approach in its original conception is the significant increase of isotopic selectivity that occurs through collisions during the time between the overtone preexcitation laser pulse and the multiphoton dissociation pulse. We demonstrate here that under certain conditions, this collisional enhancement of the selectivity works equally well when the two pulses are overlapped in time, allowing the overall isotopic selectivity of the process to remain high while achieving a significant increase in the absolute dissociation yield. We also find that proper shaping of the CO2 laser dissociation pulse makes the fluence required for dissociation sufficiently low to allow irradiation of a large reaction volume by unfocused laser beams. Together, these factors may make this laser isotope separation scheme competitive with existing separation methods. PMID:15634141

Polianski, M; Boyarkin, O V; Rizzo, T R

2004-12-15

304

A Comparison of Oxidized Carbon Abundances among Comets  

NASA Technical Reports Server (NTRS)

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).

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

2010-01-01

305

Rapid carbon-carbon bond formation and cleavage revealed by carbon isotope exchange between the carboxyl carbon and inorganic carbon in hydrothermal fluids  

NASA Astrophysics Data System (ADS)

The carbon isotopic composition of organic compounds in water-rock systems (e.g., hydrothermal vents, sedimentary basins, and carbonaceous meteorites) is generally interpreted in terms of the isotopic composition of the sources of such molecules, and the kinetic isotope effects of metabolic or abiotic reactions that generate or transform such molecules. This hinges on the expectation that the carbon isotopic composition of many organic compounds is conserved under geochemical conditions. This expectation is reasonable in light of the strength of carbon-carbon bonds (ca. 81 kcal/mol); in general, environmental conditions conducive to carbon-carbon bond cleavage typically lead to transformations of organic molecules (decarboxylation is a notable example). Geochemically relevant reactions that involve isotopic exchange between carbon atoms in organic molecules and inorganic forms of carbon with no change in molecular structure appear to be rare. Notwithstanding such rarity, there have been preliminary reports of relatively rapid carbon isotope exchange between the carboxyl group in carboxylic acids and carbon dioxide in hot water [1,2]. We have performed laboratory hydrothermal experiments to gain insights into the mechanism of this surprising reaction, using phenylacetate as a model structure. By mass spectrometry, we confirm that the carboxyl carbon undergoes facile isotopic exchange with 13C-labeled bicarbonate at moderate temperatures (i.e., 230 C). Detailed kinetic analysis reveals that the reaction rate is proportional to the concentrations of both reactants. Further experiments demonstrate that the exchange reaction only occurs if the carbon atom adjacent to the carboxyl carbon is bonded to a hydrogen atom. As an example, no carbon isotope exchange was observed for benzoate in experiments lasting up to one month. The requirement of an alpha C-H bond suggests that enolization (i.e., deprotonation of the H) is a critical step in the mechanism of the exchange reaction. We confirmed this by determining the exchange kinetics for various ring-substituted phenylacetates, and we find that the observed rate constants are consistent with the amount of negative charge that would be expected on the alpha carbon of the enolate. The emerging picture of the reaction mechanism is that enolization allows fixation of labeled carbon dioxide as a beta-carboxy group, where subsequent heterolytic decarboxylation of the unlabeled carboxy group completes the exchange process. Solvent stabilization of ionic reaction intermediates would lead to faster than expected rates of exchange, and ultimately to an isotopic equilibrium over even short geologic timescales. For enolizable carboxylic acids in natural systems, one has to consider this exchange mechanism when interpreting the carbon isotopic composition. [1] Dias R.F. (2000) Ph.D. Dissertation, Penn. State Univ. [2] Seewald J.S. & Boekelheide N. (2005) Goldschmidt Conf., A558.

Glein, C. R.; Cody, G. D.

2013-12-01

306

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

SciTech Connect

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.

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

1980-10-01

307

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

USGS Publications Warehouse

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)

Hassan, Afifa Afifi

1982-01-01

308

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...

309

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

SciTech Connect

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.

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

1985-01-01

310

Stable Isotopic Evidence for a Pedogenic Origin of Carbonates in Trench 14 Near Yucca Mountain, Nevada  

Microsoft Academic Search

Layered carbonate and silica encrust fault fractures exposed in Trench 14 near Yucca Mountain, site of the proposed high-level nuclear waste repository in southern Nevada. Comparison of the stable carbon and oxygen isotopic compositions of the fracture carbonates with those of modern soil carbonates in the area shows that the fracture carbonates are pedogenic in origin and that they likely

Jay Quade; Thure E. Cerling

1990-01-01

311

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

PubMed

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 (?(Cl) = -0.39 ± 0.03‰) and an inverse effect for carbon (?(C) = +0.75 ± 0.04‰). During diffusion-controlled vaporization in a sand column, no significant carbon isotope fractionation is observed (?(C) = +0.10 ± 0.05‰), whereas fairly strong chlorine isotope fractionation occurs (?(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. PMID:22313159

Jeannottat, Simon; Hunkeler, Daniel

2012-03-20

312

Correction of tree ring stable carbon isotope chronologies for changes in the carbon dioxide content of the atmosphere  

Microsoft Academic Search

Tree-ring stable carbon isotope ratios (?13C) often display a decline over the industrial period (post-AD1850) that is only partly explained by changes in the isotopic ratio of carbon dioxide (CO2) and may represent a response to increased atmospheric concentrations of CO2 (ca). If this is not addressed, reconstructions using long tree-ring stable isotope chronologies calibrated using the modern period, for

Danny McCarroll; Mary H. Gagen; Neil J. Loader; Iain Robertson; Kevin J. Anchukaitis; Sietse Los; Giles H. F. Young; Risto Jalkanen; Andreas Kirchhefer; John S. Waterhouse

2009-01-01

313

Mars regolith versus SNC meteorites: Evidence for abundant crustal carbonates  

NASA Technical Reports Server (NTRS)

Viking XRF analyses are compared with those for terrestrial and lunar basalt samples, and eucritic meteorites (of possible Mars origin). The comparison indicates depletion of Ca relative to Si in the Mars regolith. It is suggested that carbonate formation during a warmer, wetter epoch early in Mars' history could have been responsible.

Warren, Paul H.

1987-01-01

314

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

SciTech Connect

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.

Jiang, W.; Williams, W.; Bailey, K.; O'Connor, T. P.; Mueller, P. [Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Davis, A. M. [Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637 (United States)] [Department of Geophysical Sciences, University of Chicago, Chicago, Illinois 60637 (United States); Hu, S.-M.; Sun, Y. R. [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Lu, Z.-T. [Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)] [Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637 (United States)] [Department of Physics, University of Chicago, Chicago, Illinois 60637 (United States); Purtschert, R. [Climate and Environmental Physics, University of Bern, CH-3012 Bern (Switzerland); Sturchio, N. C. [Department of Earth and Environmental Sciences, University of Illinois at Chicago, Chicago, Illinois 60607 (United States)

2011-03-11

315

The abundances of solar accelerated nuclei from carbon to iron.  

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

316

Comparisons between Antarctic and non-Antarctic meteorites based on carbon isotope geochemistry  

SciTech Connect

The whole-rock C isotopic composition of a suite of ordinary chondrites indicates that there is a difference between Antarctic and non-Antarctic meteorites. However, this apparent distinction is not due to an inherent difference in the meteorite source populations, but is rather a result of the presence of Antarctic weathering products, mainly bicarbonates, which affect the overall {delta}{sup 13}C of these meteorites. When these weathering products are removed, either by acid-washing or combustion to 500{degree}C, the perceived division also disappears, leading to the conclusion that ordinary chondrites (both Antarctic and non-Antarctic) have similar {delta}{sup 13}C values. The C chemistry of CI, CM, and CR chondrites is also subject to problematic interpretation. Whilst the indigenous C abundance is too high to be compromised by the addition of terrestrial weathering products, the inhomogeneous distribution of an array of components with widely varying isotopic signatures leads to a random distribution of {delta}{sup 13}C values. Analyses of individual components (insoluble macromolecular material, carbonates, and silicon carbide) reveal that there are no gross differences in C chemistry between Antarctic and non-Antarctic chondrites. The few distinctions that do exist might readily be explained by weathering or isotopic exchange in Antarctic. Whilst not forming a separate population, Antarctic carbonaceous chondrites may extend the range of properties of non-Antarctic chondrites beyond the currently known limits.

Grady, M.M.; Wright, I.P.; Pillinger, C.T. (The Open Univ., Milton Keynes (England))

1991-01-01

317

Modeling Chemical and Isotopic Variations in Lab Formed Hydrothermal Carbonates  

NASA Technical Reports Server (NTRS)

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.

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

2005-01-01

318

CNO ABUNDANCES OF HYDROGEN-DEFICIENT CARBON AND R CORONAE BOREALIS STARS: A VIEW OF THE NUCLEOSYNTHESIS IN A WHITE DWARF MERGER  

SciTech Connect

We present high-resolution (R {approx} 50, 000) observations of near-IR transitions of CO and CN of the five known hydrogen-deficient carbon (HdC) stars and four R Coronae Borealis (RCB) stars. We perform an abundance analysis of these stars by using spectrum synthesis and state-of-the-art MARCS model atmospheres for cool hydrogen-deficient stars. Our analysis confirms reports by Clayton and colleagues that those HdC stars exhibiting CO lines in their spectrum and the cool RCB star S Aps are strongly enriched in {sup 18}O (with {sup 16}O/{sup 18}O ratios ranging from 0.3 to 16). Nitrogen and carbon are in the form of {sup 14}N and {sup 12}C, respectively. Elemental abundances for CNO are obtained from C I, C{sub 2}, CN, and CO lines. Difficulties in deriving the carbon abundance are discussed. Abundances of Na from Na I lines and S from S I lines are obtained. Elemental and isotopic CNO abundances suggest that HdC and RCB stars may be related objects, and that they probably formed from a merger of an He white dwarf with a C-O white dwarf.

Garcia-Hernandez, D. A. [Instituto de Astrofisica de Canarias, C/ Via Lactea s/n, 38200 La Laguna (Spain); Hinkle, K. H. [National Optical Astronomy Observatory (NOAO), Tucson, AZ 85726 (United States); Lambert, David L. [W. J. McDonald Observatory, University of Texas at Austin, 1 University Station, C1400. Austin, TX 78712-0259 (United States); Eriksson, K. [Department of Physics and Astronomy, Uppsala University, Box 515, 75120 Uppsala (Sweden)], E-mail: agarcia@iac.es, E-mail: hinkle@noao.edu, E-mail: dll@astro.as.utexas.edu, E-mail: Kjell.Eriksson@astro.uu.se

2009-05-10

319

CNO Abundances of Hydrogen-Deficient Carbon and R Coronae Borealis Stars: A View of the Nucleosynthesis in a White Dwarf Merger  

NASA Astrophysics Data System (ADS)

We present high-resolution (R ~ 50, 000) observations of near-IR transitions of CO and CN of the five known hydrogen-deficient carbon (HdC) stars and four R Coronae Borealis (RCB) stars. We perform an abundance analysis of these stars by using spectrum synthesis and state-of-the-art MARCS model atmospheres for cool hydrogen-deficient stars. Our analysis confirms reports by Clayton and colleagues that those HdC stars exhibiting CO lines in their spectrum and the cool RCB star S Aps are strongly enriched in 18O (with 16O/18O ratios ranging from 0.3 to 16). Nitrogen and carbon are in the form of 14N and 12C, respectively. Elemental abundances for CNO are obtained from C I, C2, CN, and CO lines. Difficulties in deriving the carbon abundance are discussed. Abundances of Na from Na I lines and S from S I lines are obtained. Elemental and isotopic CNO abundances suggest that HdC and RCB stars may be related objects, and that they probably formed from a merger of an He white dwarf with a C-O white dwarf.

García-Hernández, D. A.; Hinkle, K. H.; Lambert, David. L.; Eriksson, K.

2009-05-01

320

Ca isotope fractionation in modern and fossil bivalve shell carbonate  

NASA Astrophysics Data System (ADS)

Ca isotopes of bivalve carbonate, used in combination with light stable isotopes and metal/Ca ratios may provide a useful archive of annual and seasonal parameters such as temperature, salinity or nutrient level, and therefore for high-resolution palaeoclimate reconstructions, but the reliability of these proxies remains questionable given potential vital/ontogenetic and microenvironmental effects. Furthermore, in order to test the applicability of bivalve-based environmental proxies on geological time-scales, it is of crucial importance to assess the sensitivity of shell geochemistry to early diagenesis. We investigated these potential effects, first by using field cultured, intertidal and subtidal bivalve species cultured in the Dutch Wadden Sea, and second by using selected fossil bivalve shells from Pleistocene (MIS 5e) uplifted marine terraces located in the SE Gulf of Corinth area, Greece. Cultured individuals offer the chance to compare time series of instrumental environmental data directly to growth rate and shell chemistry, whereas fossil samples, which were exposed to meteoric conditions for an extended period, are perfect for studying potential diagenetic influences on the Ca isotope system. Ca isotope signatures of both cultured bivalve species are positively correlated with ambient seawater temperature. The slope of the temperature-fractionation relation is similar to inorganic calcite and aragonite precipitates. However, the Ca isotope values are offset from the inorganic curves of about 0.5 permil. The most likely explanation for this offset is a biological induced fractionation, which can be attributed to the active transport of calcium through different cell layers to the site of calcification. In contrast, the studied fossil shells show little variations in Ca isotope composition. We observed that fossil biogenic aragonite from the same chronostratigraphic unit is considerably less fractionated than fossil biogenic calcite, which can be either explained by an implausible temperature effect of approximately 10 degree Celsius or by weak diagenetic overprinting. To summarize, these results provide new insights into biomineralization processes and indicate however a limited use of Ca isotopes in bivalves as temperature proxy.

Hippler, D.; Witbaard, R.; Buhl, D.; Immenhauser, A.

2009-04-01

321

The relationship between total dissolved carbon dioxide and its stable carbon isotope ratio in aquatic sediments  

NASA Astrophysics Data System (ADS)

A model is constructed to predict the stable carbon isotope ratio of the total dissolved CO 2 in aquatic sediments and laboratory reactors. The major parameters of the model are the fractionation between CO 2 and CH 4 as well as the intra-molecular fractionation of acetate, the relative production of CH 4 from CO 2 reduction versus acetate fermentation, the net production ratio of CO 2 to CH 4 and the stable carbon isotope ratio of the source organic carbon. The model is fitted to published data and to date from the littoral sediments of Lake Memphremagog, Quebec, Canada. The inclusion of the intra-molecular fractionation factor of acetate in the model provides a good fit to the data; without this factor, the values of the other parameters necessary for a good fit appear unreasonable.

LaZerte, Bruce D.

1981-05-01

322

Isotopic variations of dissolved inorganic carbon in the Gulf of Mexico  

E-print Network

stations were analyzed for salinity, dissolved oxygen, total inorganic carbon and the isotopic composition of the total inorganic I 1 on a University of Washington type salinometer. The total dissolved inorganic carbon in sea water was measured by a...

Kan, David Lan-Rong

1970-01-01

323

Carbonate clumped isotope constraints on Silurian ocean temperature and seawater d18  

E-print Network

temperature is the carbonate-water oxygen isotope exchange thermometer, also known as the carbonate d18 O thermometer (Urey, 1947). This thermometer is based on the temperature dependence of the fractionation between

324

The Abundances of Oxygen and Carbon in the Solar Photosphere  

Microsoft Academic Search

A series of recent studies has placed the best estimates of the photospheric\\u000aabundances of carbon and oxygen at log epsilon = 8.39 and 8.66, respectively.\\u000aThese values are ~ 40 % lower than earlier estimates. A coalition of\\u000acorrections due to the adoption of an improved model atmosphere, updated atomic\\u000adata and non-LTE corrections, and a reevaluation of the

Carlos Allende Prieto

2007-01-01

325

Depletion of 13C in lignin and its implications for stable carbon isotope studies  

NASA Astrophysics Data System (ADS)

Stable carbon isotope compositions of organic matter are now widely used to trace carbon flow in ecosystems, and have been instrumental in shaping current perceptions of the importance of terrestrial vegetation to estuarine and coastal marine environments. A general assumption in these and other studies relying on carbon isotope compositions for source identification of organic matter has been that the major biochemical components of plant tissues are isotopically invariant. We report here large differences between the carbon isotope compositions of the polysaccharide and lignin components of a variety of vascular plants, including the salt-marsh grass Spartina alterniflora, and demonstrate that the carbon isotope composition of Spartina detritus gradually changes during biogeochemical processing as polysaccharides are preferentially removed, leaving a material that is relatively enriched in lignin-derived carbon and depleted in 13C.

Benner, Ronald; Fogel, Marilyn L.; Sprague, E. Kent; Hodson, Robert E.

1987-10-01

326

Zn Isotope Abundances of Lunar Soils 64801, 68841, 69941, and 69961  

NASA Astrophysics Data System (ADS)

Mass fractionation is well established for the isotopes of several elements in lunar soils, notably O, Si, K, Ca (to a lesser extent), and S (see [1,2]). Zinc is nearly as volatile as S and is associated with it in the coatings of pyroclastic deposits (see [3]). It therefore seemed plausible that zinc might also be fractionated and that the degree of fractionation might be correlated with that of sulfur. To test this inference, we have begun to measure Zn isotopic abundances in lunar soils. Here we report results for four Apollo 16 samples from which the magnetic fraction had been previously removed. The samples were ground, weighed, and dissolved in HF, HNO3 and HCl in a Teflon bomb. Zn was separated by anion exchange and analyzed isotopically by using ICP/MS. Only the data for 64Zn, 66Zn, and 68Zn are reported: The molecular ion ^35Cl^16O(sub)2+ interfered with the measurement of 67Zn and counting statistics for 70Zn gave only %-level precision. We used Zn atomic absorption solutions as standards with a known concentration of Ga added to control for instrumental drift. Measured elemental Zn contents are consistent with literature values [4-6]. The isotopic ratios of the samples were expressed as delta-values calculated relative to the corresponding isotopic ratios of the standards. No fractionation (i.e., < 0.2%/AMU) was observed for any of several ordinary chondrites, among them Suizhou and Dhajala. In all four lunar soils, however, we found delta 68Zn~2xdelta 66Zn and delta 66Zn>0 at the one-sigma level. These results indicate mass dependent fractionation. If we make the oversimplified assumption that the Zn isotopic fractionation reflects Rayleigh distillation from a single well-mixed reservoir of material from which Zn evaporated as the atom, then the fraction of Zn retained is given approximately by (1+delta ^YZn/1000)^(-2M(sub)Y/Delta M where Y=66 or 68, M is mass, and Delta M is the mass difference M(sub)Y - M(sub)64. The computations suggest that the lunar soils analyzed lost 20 to 40% of their Zn. The calculated losses of Zn are comparable to those estimated for sulfur by [1]. The degree of S mass fractionation in lunar soils appears to correlate with S content and exposure age [7,8]; Kerridge [8,9] has therefore proposed that meteorite impact vaporizes some S but delivers even more. So far, we do not see a similar correlation with exposure age in the Zn data, but the number of samples analyzed is small. The nominal losses of potassium calculated by [1] are also in the neighborhood of 30%, but may actually be much higher for certain fractions of the soil [2]. To explain the K isotopic enrichments, and in particular the contrast to Mg and Ca in which any fractionations are much smaller, Humayun and Clayton [2] point to K's volatility and tendency to concentrate in the fine fractions. Zn has higher volatility than K and is also enriched in small grains [10]. References: [1] Clayton et al. (1974) Proc. LSC 5th, 1801-1809. [2] Humayun M. and Clayton R. N. (1995) GCA, 59, 2115-2130. [3] Haskin L. and Warren P. (1991) Lunar Sourcebook: A User's Guide to the Moon (G. Heiken et al., eds.), pp. 357-474, Cambridge Univ. [4] Kr henb hl et al. (1973) Proc. LSC 4th, 1325-1348. [5] Rose et al. (1973) Proc. LSC 4th, 1149-1158. [6] Finkelman et al. (1975) Proc. LSC 6th, 1385-1398. [7] Cripe J. D. and Moore C. B. (1976) Proc. LSC 7th, 469-479. [8] Kerridge et al. (1975) GCA, 39, 137-162. [9] Kerridge et al. (1975) Proc. LSC 6th, 2151-2162. [10] Kr henb hl et al. (1977) Proc. LSC 8th, 3901-3916.

Xue, S.; Herzog, G. F.; Hall, G. S.

1995-09-01

327

Carbon isotope discrimination varies genetically in c(4) species.  

PubMed

Carbon-isotope discrimination (Delta) is used to distinguish between different photosynthetic pathways. It has also been shown that variation in Delta occurs among varieties of C(3) species, but not as yet, in C(4) species. We now report that Delta also varies among genotypes of sorghum (Sorghum bicolor Moench), a C(4) species. The discrimination in leaves of field-grown plants of 12 diverse genotypes of sorghum was measured and compared with their grain yields. Discrimination varied significantly among genotypes, and there was a significant negative correlation between grain yield and Delta. The variation in Delta may be caused by genetic differences in either leakiness of the bundle-sheath cells or by differences in the ratio of assimilation rate to stomatal conductance. At the leaf level, the former should be related to light-use efficiency of carbon fixation and the latter should be related to transpiration efficiency. Both could relate to the yield of the crop. PMID:16667310

Hubick, K T; Hammer, G L; Farquhar, G D; Wade, L J; von Caemmerer, S; Henderson, S A

1990-02-01

328

Resolving Isotopic Fine Structure to Detect and Quantify Natural Abundance- and Hydrogen/Deuterium Exchange-Derived Isotopomers  

PubMed Central

Hydrogen/deuterium exchange (HDX) mass spectrometry (MS) is used for analyzing protein dynamics, protein folding/unfolding, and molecular interactions. Until this study, HDX MS experiments employed mass spectral resolving powers that afforded only one peak per nominal mass in a given peptide’s isotope distribution, and HDX MS data analysis methods were developed accordingly. A level of complexity that is inherent to HDX MS remained unaddressed, namely, various combinations of natural abundance heavy isotopes and exchanged deuterium shared the same nominal mass and overlapped at previous resolving powers. For example, an A + 2 peak is comprised of (among other isotopomers) a two-2H-exchanged/zero-13C isotopomer, a one-2H-exchanged/one-13C isotopomer, and a zero-2H-exchanged/two-13C isotopomer. Notably, such isotopomers differ slightly in mass as a result of the ~3 mDa mass defect between 2H and 13C atoms. Previous HDX MS methods did not resolve these isotopomers, requiring a natural-abundance-only (before HDX or “time zero”) spectrum and data processing to remove its contribution. It is demonstrated here that high-resolution mass spectrometry can be used to detect isotopic fine structure, such as in the A + 2 profile example above, deconvolving the isotopomer species resulting from deuterium incorporation. Resolving isotopic fine structure during HDX MS therefore permits direct monitoring of HDX, which can be calculated as the sum of the fractional peak magnitudes of the deuterium-exchanged isotopomers. This obviates both the need for a time zero spectrum as well as data processing to account for natural abundance heavy isotopes, saving instrument and analysis time. PMID:24328359

Liu, Qian; Easterling, Michael L.; Agar, Jeffrey N.

2014-01-01

329

Mass accuracy and isotopic abundance measurements for HR-MS instrumentation: capabilities for non-targeted analyses.  

PubMed

The development of automated non-targeted workflows for small molecule analyses is highly desirable in many areas of research and diagnostics. Sufficient mass and chromatographic resolution is necessary for the detectability of compounds and subsequent componentization and interpretation of ions. The mass accuracy and relative isotopic abundance are critical in correct molecular formulae generation for unknown compounds. While high-resolution instrumentation provides accurate mass information, sample complexity can greatly influence data quality and the measurement of compounds of interest. Two high-resolution instruments, an Orbitrap and a Q-TOF, were evaluated for mass accuracy and relative isotopic abundance with various concentrations of a standard mixture in four complex sample matrices. The overall average ± standard deviation of the mass accuracy was 1.06 ± 0.76 ppm and 1.62 ± 1.88 ppm for the Orbitrap and the Q-TOF, respectively; however, individual measurements were ± 5 ppm for the Orbitrap and greater than 10 ppm for the Q-TOF. Relative isotopic abundance measurements for A + 1 were within 5% of the theoretical value if the intensity of the monoisotopic peak was greater than 1E7 for the Orbitrap and 1E5 for the Q-TOF, where an increase in error is observed with a decrease in intensity. Furthermore, complicating factors were found in the data that would impact automated data analysis strategies, including coeluting species that interfere with detectability and relative isotopic abundance measurements. The implications of these findings will be discussed with an emphasis on reasonable expectations from these instruments, guidelines for experimental workflows, data analysis considerations, and software design for non-targeted analyses. PMID:24729191

Knolhoff, Ann M; Callahan, John H; Croley, Timothy R

2014-07-01

330

Mass Accuracy and Isotopic Abundance Measurements for HR-MS Instrumentation: Capabilities for Non-Targeted Analyses  

NASA Astrophysics Data System (ADS)

The development of automated non-targeted workflows for small molecule analyses is highly desirable in many areas of research and diagnostics. Sufficient mass and chromatographic resolution is necessary for the detectability of compounds and subsequent componentization and interpretation of ions. The mass accuracy and relative isotopic abundance are critical in correct molecular formulae generation for unknown compounds. While high-resolution instrumentation provides accurate mass information, sample complexity can greatly influence data quality and the measurement of compounds of interest. Two high-resolution instruments, an Orbitrap and a Q-TOF, were evaluated for mass accuracy and relative isotopic abundance with various concentrations of a standard mixture in four complex sample matrices. The overall average ± standard deviation of the mass accuracy was 1.06 ± 0.76 ppm and 1.62 ± 1.88 ppm for the Orbitrap and the Q-TOF, respectively; however, individual measurements were ± 5 ppm for the Orbitrap and greater than 10 ppm for the Q-TOF. Relative isotopic abundance measurements for A + 1 were within 5% of the theoretical value if the intensity of the monoisotopic peak was greater than 1E7 for the Orbitrap and 1E5 for the Q-TOF, where an increase in error is observed with a decrease in intensity. Furthermore, complicating factors were found in the data that would impact automated data analysis strategies, including coeluting species that interfere with detectability and relative isotopic abundance measurements. The implications of these findings will be discussed with an emphasis on reasonable expectations from these instruments, guidelines for experimental workflows, data analysis considerations, and software design for non-targeted analyses.

Knolhoff, Ann M.; Callahan, John H.; Croley, Timothy R.

2014-07-01

331

First measurement of Mg isotope abundances at high redshifts and accurate estimate of Delta alpha\\/alpha  

Microsoft Academic Search

(Abridged) We use a high-resolution spectrum of the quasar HE0001-2340\\u000aobserved with the UVES\\/VLT to measure Mg isotope abundances in the intervening\\u000aabsorption-line systems at high redshifts. Line profiles are prepared\\u000aaccounting for possible shifts between the individual exposures. Due to unique\\u000acomposition of the selected systems - the presence of several transitions of\\u000athe same ion - we can

I. I. Agafonova; P. Molaro; S. A. Levshakov; J. L. Hou

2011-01-01

332

Contrasting the CO2He Isotope and Relative Abundance Systematics of the Central American and IBM Arcs  

Microsoft Academic Search

We report CO2 and He isotope and relative abundance data obtained utilizing high-T fumaroles, geothermal wells, boiling mud pots, hot springs and phenocryst-bearing lavas from both MARGINS-targeted regions. In Central America, we collected ~140 fluid and ~30 lava samples covering a total of 41 volcanic centers in Costa Rica (7), Nicaragua (8), El Salvador (10), Honduras (9) and Guatemala (7).

D. R. Hilton; T. P. Fischer; A. M. Shaw; E. Hauri; J. Walker

2006-01-01

333

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

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

334

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

NASA Astrophysics Data System (ADS)

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 ?13C values (and so greatest fractionation between methane and TMA) occurred when the most TMA was added (1000 µM final concentration). This change in the isotopic composition of the methane produced with varying TMA concentrations, along with the high in situ methane ?13C values, suggest that the methanogens in these environments are operating at low substrate concentrations. Apparently, substrate limitation decreases isotopic fractionation during methanogenesis, which results in the abnormally high biogenic methane ?13C values.

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

2010-12-01

335

Carbon Dioxide Stable Isotope Detection of Geological Sequestration Seepage  

NASA Astrophysics Data System (ADS)

A priority for geological sequestration measurement, mitigation and verification (MMV) is a means of tracking seepage at concentrations at or below ambient CO2 concentrations. The carbon stable isotope ratio (13C16O2/12C16O2) is a sensitive diagnostic signature of anthropogenic and natural sources of CO2. However, the concentration of 13CO2 is approximately 100 times smaller than 12CO2 and sensitive analytical tools are required to measure the ratio in the field. Frequency modulated spectroscopy (FMS) is an ultra sensitive means of detecting the stable isotopes of CO2 that is conservatively 100x more sensitive than standard absorption spectroscopy. FMS involves directing a tunable diode laser (TDL) through an electro- optical modulator operating in the radio frequency regime producing the original carrier frequency from the TDL (wc) and evenly spaced sidebands (wc plus,minus wm). The species of interest is detected by tuning the TDL and the modulation frequency such that one of the sidebands (wc) interacts with a specific spectral feature. This paper will include experiments involving field measurements using both an in situ and remote FMS prototype instruments. The field site is located in a remote location on the Los Alamos National Laboratory campus were the instruments could monitor natural fluctuations. The in situ instrument was placed in the field site next to the remote instrument. The remote instrument was directed towards a retroreflector located 50m from the laser source signal and back to detector positioned next to the laser. The stable isotope ratio is monitored as the carrier frequency is scanned and the sidebands interact with both CO2 isotopes.

Fessenden, J. E.; Clegg, S. M.

2008-12-01

336

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

NASA Astrophysics Data System (ADS)

: The western Arabian Sea responds to the southwest monsoon winds by upwelling colder and nutrient rich waters from the deeper layers, causing a reduction in the sea surface temperature and enhanced biological productivity. A number of paleoclimatic studies have been carried out in this region to elucidate past monsoon variability (Sirocco et al., 1993; Gupta et al, 2003; Tiwari, 2005; Saher et.al.; 2007). Globigerina bulloides, a planktic foraminiferal species normally inhabiting surface ocean waters in temperate latitudes ( Be and Tolderlund , 1977) also becomes abundant at tropical latitudes upwelling occurs, and in these cases its abundance can exceed considerably. The conspicuous fluctuation in the abundance of Gg.bulloides during upwelling and non upwelling intervals is established through several studies ( Thiede and Junger, 1980, Gupta et al, 2003) This robust relation has been used as a proxy for wind velocity at several different times in the past in the Arabian Sea (Anderson et.al., 2002). A significant result from some of these centennially resolved Holocene records is declining abundance of Globigerina bulloides which is paralleled by reduced insolation record and this has been inferred as declining strength of Asian Monsoon. We are presenting here the data from the core SS4018 from near the Gulf of Aden, Western Arabian Sea taken at a water depth of 2830 m, precisely dated by the radiocarbon method using Accelerator Mass Spectrometry on planktonic foraminiferal separates. We have carried out the planktic foraminiferal census counts for each sample to know the relative abundance of key species. In addition to this, we have also employed multi- proxy approach such as oxygen and carbon isotopes of planktic foraminiferal tests, TOC, CaCO3 (%) to strengthen our interpretation and also to understand the relationships amongst the proxies themselves. Abundance of the key planktic foraminiferal species and other proxy records reveal at least 3 major climatic events (M-1, M-2 and M-3) during the last 10,000yrs. The earliest one (M-1) is a major decline in the upwelling intensity during 7.9.-5.6 kyBP. We have observed the lowest abundance of upwelling indicator species (UIS), it goes down from 70(%) to 30(%), mixed dweller (MD) and thermocline dweller (TD) species were showing their maximum abundance and at that time Organic carbon (OC) value revealed the lowest amount. Oxygen stable isotope records were also suggesting the same results. The second event at 5.5-2.2 kyBP (M-2) corresponds to average upwelling. We have observed the 2-3 high peaks of (UIS), on average UIS were showing around 50-55(%) of their abundance during this period, thus we have concluded the moderate intensity of SWM winds during M-2. The third event at last 2ky (M-3), decreasing trend in the strength of the SWM has been observed on the basis of sharp decline in the abundance of UIS and OC amount. For this interval, we have observed the increasing trend in the MD and TD planktic foraminiferal species.

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

2007-12-01

337

Neutrino Fluence after r-Process Freezeout and Abundances of TE Isotopes in Presolar Diamonds  

NASA Astrophysics Data System (ADS)

Using the data of Richter, Ott, & Begemann on Te isotopes in diamond grains from a meteorite, we derive bounds on the neutrino fluence and the decay timescale of the neutrino flux relevant for the supernova r-process. Our new bound on the neutrino fluence \\Fscr after freezeout of the r-process peak at mass number A~130 is more stringent than the previous bound \\Fscr<~0.045 (in units of 1037 ergs cm-2) of Qian et al. and Haxton et al., if the neutrino flux decays on a timescale ??>~0.65 s. In particular, it requires that a fluence of \\Fscr=0.031 be provided by a neutrino flux with ??<~0.84 s. Such a fluence may be responsible for the production of the solar r-process abundances at A=124-126. Our results are based on the assumption of Ott that only the stable nuclei implanted into the diamonds are retained, while the radioactive nuclei are lost from the diamonds upon decay after implantation. We consider that the nanodiamonds are condensed in an environment with C/O>1 in the expanding supernova debris or from the exterior H envelope. This environment need not have the 13C/12C ratio of the bulk diamonds, since the Te- and Xe-containing nanodiamond grains are too rare to affect that ratio. The implantation of nuclei would have occurred ~104-106 s after r-process freezeout. This time interval may be marginally sufficient to permit adequate cooling upon expansion for the formation of diamond grains. The mechanisms of preferential retention/loss of the implanted nuclei are not well understood.

Qian, Y.-Z.; Vogel, P.; Wasserburg, G. J.

1999-03-01

338

Investigating Deglacial Climate Records: The Carbon Isotope Minimum Event and High Resolution Radiocarbon Ages  

Microsoft Academic Search

The most recent transition from the Last Glacial Maximum (LGM) into the deglaciation was associated with an abrupt decrease in the carbon isotope composition of planktonic foraminifera. These low 13C\\/12C ratios, referred to as the carbon isotope minimum event (CIME), have been linked to changes in Southern Ocean circulation at the end of the LGM (Spero & Lea, 2002). One

K. Rose; E. L. Sikes; T. P. Guilderson; R. Zahn; T. M. Hill; H. J. Spero

2006-01-01

339

Associations between carbon isotope ratios of ecosystem respiration, water availability and canopy conductance  

E-print Network

important during rain-free periods. Keywords: carbon isotopes, climate, ecosystem respiration, Keeling plotAssociations between carbon isotope ratios of ecosystem respiration, water availability and canopy for Environmental Research, Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112

Ehleringer, Jim

340

Fractionation of carbon and hydrogen isotopes by methane-oxidizing bacteria  

Microsoft Academic Search

Carbon isotopic analysis of methane has become a popular technique in the exploration for oil and gas because it can be used to differentiate between thermogenic and microbial gas and can sometimes be used for gas-source rock correlations. Methane-oxidizing bacteria, however, can significantly change the carbon isotopic composition of methane; the origin of gas that has been partially oxidized by

Dennis D. Coleman; M SCHOELL

1981-01-01

341

Covariant C and O Isotope Trends in Some Terrestrial Carbonates and ALH 84001: Possible Linkage Through Similar Formation Processes  

Microsoft Academic Search

In this study we sought to identify discrete micro-scale isotopic variation within the carbonate crusts in Sunset Crater to see if they resembled the micro-scale isotope variation found in ALH 84001 carbonates.

K. E. Volk; P. B. Niles; R. A. Socki

2011-01-01

342

Stable Isotopes James R Ehleringer and Thure E Cerling  

E-print Network

for introduction into the mass spectrometer. The most commonly used approaches involve introducing hydrogen as H2 Element Isotope Abundance (%) Hydrogen 1 H 99.985 2 H 0.015 Carbon 12 C 98.89 13 C 1.11 Nitrogen 14 N 99? Of particular interest for global change studies are vari- ations in the isotopic abundances of hydrogen, carbon

Ehleringer, Jim

343

The influence of fertilizer nitrogen and season on the carbon-13 abundance of wheat straw  

Microsoft Academic Search

Carbon-13 abundance, expressed as ?13C in ‰, was measured in wheat straw grown between 1984 and 1989 on the Broadbalk Continuous Wheat Experiment at Rothamsted.\\u000a In all six years, straw grown without fertilizer N contained less carbon-13 (i.e.?13C was more negative) than straw grown with fertilizer, although the magnitude of this difference varied with year. In a dry\\u000a year, when

D. S. Jenkinson; K. Coleman; D. D. Harkness

1995-01-01

344

Elemental and isotopic abundance measurements of nuclei with Z>28 from the ACE-CRIS experiment and the OB association origin of galactic cosmic rays  

NASA Astrophysics Data System (ADS)

We summarize measurements made of the elemental and isotopic abundances of galactic cosmic ray nuclei by the Cosmic Ray Isotope Spectrometer (CRIS) on the NASA Advanced Composition Explorer (ACE) satellite over a period of 14 years in space. We have measured the isotopic abundances of Ga (Z=31) and Ge (Z=32) for the first time and have obtained greatly improved measurements of the Cu (Z=29) and Zn (Z=30) isotopes. We have also measured the elemental abundances of nuclei up to Sr (Z=38). A total of ˜700 nuclei heavier than Ni (Z=28) have been collected with energies in the range of ˜150 to 600 MeV/nucleon. Our earlier published work on isotopes with Z<28 has shown abundances consistent with an OB association origin of a substantial fraction of galactic cosmic rays. This is based primarily on the enhanced ^22Ne/^20Ne and ^58Fe/^56Fe ratios relative to solar system abundances. ^22Ne and ^58Fe are copiously produced in Wolf-Rayet stars, which are found primarily in OB associations. The elemental abundances of Z>29 nuclei provide completely independent evidence that also points to an OB association origin. The isotopic abundances of Cu, Zn, Ga, and Ge are consistent with either an OB association or normal interstellar medium origin. This research was supported by NASA under grant NNX11AC49G.

Binns, W. R.; Israel, M. H.; Christian, E. R.; de Nolfo, G. A.; von Rosenvinge, T. T.; Cummings, A. C.; Leske, R. A.; Mewaldt, R. A.; Stone, E. C.; Wiedenbeck, M. E.

2012-03-01

345

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

NASA Astrophysics Data System (ADS)

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.

Crowley, B. E.; Samonds, K.

2012-12-01

346

Mineral-fluid partitioning and isotopic fractionation of boron in synthetic calcium carbonate  

Microsoft Academic Search

Aragonite, high-Mg calcite, and Mg-free calcite have been grown under monitored laboratory conditions to investigate mineral-fluid partitioning and isotopic fractionation of boron into carbonates. At pH ? 8, both polymorphs have boron isotopic compositions I6.5%0 lower than the boron isotopic composition of the experimental fluid (?11B = 0 ± 0.7?.). The isotopic composition of the synthetic minerals is identical to

N. G. Hemming; R. J. Reeder; G. N. Hanson

1995-01-01

347

Evidence for recurrent Early Triassic massive volcanism from quantitative interpretation of carbon isotope fluctuations  

Microsoft Academic Search

Carbon cycle disturbance associated with mass extinction at the end of the Permian Period continued through the Early Triassic, an interval of approximately 5 million years. Coincidence of carbon cycle stabilization with accelerated Middle Triassic biotic recovery suggests a link between carbon cycling and biodiversity, but the cause of Early Triassic carbon isotope excursions remains poorly understood. Previous modeling studies have

Jonathan L. Payne; Lee R. Kump

2007-01-01

348

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

PubMed

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. PMID:17510940

Mora, Germán; Raich, James W

2007-01-01

349

Lipid Biomarkers and Molecular Carbon Isotopes for Elucidating Carbon Cycling Pathways in Hydrothermal Vents  

NASA Astrophysics Data System (ADS)

Increasing molecular evidence suggests that hydrothermal vents in mid-ocean ridges harbor large populations of free-living bacteria, particularly the epsilon Proteobacteria. However, pathways for carbon metabolism by these bacteria are poorly known. We are addressing this question by analyzing the lipid biomarkers and their isotope signatures in environments where the epsilon Proteobacteria are likely predominant. Solid materials were collected from hydrothermal vents in the East Pacific Rise and at the Guaymas Basin in the Gulf of California. Fatty acids extracted from these samples are dominated by 16:0 (27-41%), 18:0 (16-48%), 18:1 (11-42%), 16:1 (7-12%), and 14:0 (5-28%). In addition, 15:0 and anteiso-15:0 are significantly present (2-3%) in samples from the Guaymas Basin. The isotopic compositions of these fatty acids range from -15.0\\permil to -33.1\\permil with the most positive values occurring only in monounsaturated fatty acids (16:1 and 18:1). We are currently unable to assign these biomarkers to any of the epsilon Proteobacteria because biomarkers are poorly known for these organisms isolated from the vents. However, no polyunsaturated fatty acids were detected in these samples, which are consistent with the absence of vent animals at the sampling sites. Signature biomarkers of 20:1 and cy21:0, which are characteristic of the thermophilic chemolithoautotrophs such as Aquificales, are also absent in these samples. These results imply that the deeply branched Aquificales species do not constitute the major microbial community in these vent environments. The large range of molecular isotopic compositions suggests that these lipids are synthesized from various carbon sources with different isotopic compositions or through different biosynthetic pathways, or both. We are currently measuring the isotopic compositions of the total organic carbon in the bulk samples and will determine the fractionations between lipid biomarkers and the total organic carbon. Molecular DNA data from these vent environments indicate that the reversed TCA cycle may be used for CO2 fixation by the epsilon Proteobacteria for chemolithoautotrophic growth. Isotopic fractionation patterns between lipid biomarkers and the bulk organic carbon can provide independent information on this unique biosynthetic pathway.

Zhang, C. L.; Dai, J.; Campbell, B.; Cary, C.; Sun, M.

2003-12-01

350

Modelling carbon isotope composition of dissolved inorganic carbon and methane in marine porewaters  

NASA Astrophysics Data System (ADS)

Carbon isotope compositions of dissolved inorganic carbon (DIC) and methane (CH4) in marine sedimentary porewaters at near surface temperatures show extremely large variation in apparent fractionation covering a range from -100 ‰ to +30 ‰. This fractionation is essentially the result of microbial activity, but the mechanisms and factors controlling this fractionation are still incompletely understood. This study provides a reaction transport model approach to evaluate the effects of the most important processes and factors on carbon isotope distribution with the goal to better understand carbon isotope distribution in modern sediment porewaters and in the geological record. Our model results show that kinetic fractionation during methanogenesis, both through the acetoclastic and autotrophic pathways, results in a nearly symmetrical distribution of ?13C values in DIC and CH4 with respect to the isotope value of buried organic matter. An increased fractionation factor during methanogenesis leads to a larger difference between ?13CDIC and ?13CCH4. Near the sulphate methane transition zone, DIC is more depleted in 13C due to diffusive mixing with DIC produced by anaerobic oxidation of methane (AOM) and organoclastic sulphate reduction. The model also shows that an upward decrease in ?13CCH4 near the SMT can only be caused by equilibrium fractionation during AOM including a backward "leakage" of carbon from DIC to CH4 through the enzymatic pathway. However, this effect of reversibility has no influence on the DIC pool as long as methane is completely consumed at the SMT. Only a release of methane at the sediment-water interface, due to a fraction of the methane escaping re-oxidation, results in a small shift towards more positive ?13CDIC values. Methane escape at the SMT is possible if either the methane flux is too high to be entirely oxidized by AOM, or if bubbles of methane gas by-pass the sulphate reduction zone and escape episodically into the water column. A small but significant isotope effect is also caused by differential diffusion of the 12C and 13C isotopes of CH4 leading to somewhat more positive ?13CCH4 values, while DIC remains unaffected by this process. The consideration of all these effects allows a relatively good reproduction of ?13CDIC and ?13CCH4 profiles in marine sediments in diffusive systems. However, the model cannot reproduce profiles measured in seep environments, where CH4 and DIC profiles are perturbed by upward advecting, possibly thermogenic methane from greater depth. The model is now available to be applied for non-steady state systems, which ultimately will help to understand past dynamics of ?13C compositions and their diagenetic records as a result of changing microbial activity.

Meister, Patrick; Liu, Bo; Khalili, Arzhang; Barker Jørgensen, Bo

2014-05-01

351

The Abundance of Very Large Hydrocarbons and Carbon Clusters in the Diffuse Interstellar Medium  

NASA Astrophysics Data System (ADS)

Two current gas-phase chemical models of interstellar clouds have been extended to include hydrocarbons and bare carbon clusters through 64 carbon atoms in size. The new molecules comprise linear, monocyclic, tricyclic, and fullerene/ane species but do not include polycyclic aromatic hydrocarbons (PARs). The reaction networks used to produce and destroy these species have been adopted from a laboratory synthesis of fullerenes. The models have been used to investigate the chemistry of complex molecules in a number of dispersive clouds, which begin as dense clouds but end up as diffuse material. The calculated abundances of large molecules are discussed in terms of candidates for the carriers of the diffuse interstellar bands (DIBs). We find that both gas-phase models utilized can produce large abundances of 64 carbon atom species, considered to represent molecules of this size and larger. Such species are DIB candidates only if the abundances are not spread too thinly over many species. One of the two gas-phase models used leads to large abundances of fullerenes and fulleranes. If this model is accurate, the fullerenes/anes represent reasonable candidates for the carriers of the DIBs. If small hydrocarbon "seeds" are assumed to be present on dust particles and to photodesorb during cloud dispersion, we find that large abundances of linear and monocyclic hydrocarbons can also be produced and maintained via gas-phase chemistry, so that these molecules become additional DIB-carrier candidates.

Bettens, R. P. A.; Herbst, Eric

1996-09-01

352

Carbon isotope effects during precipitation of barium carbonate: implications for environmental studies  

Microsoft Academic Search

Here we demonstrate that precipitation of dissolved inorganic carbon (DIC) to at pH 10.26, 11.38 and 12.11 does not cause\\u000a measurable carbon isotope fractionation. However, NaOH solution prepared under standard laboratory procedure and used to increase\\u000a pH value for precipitation of BaCO3 can be contaminated by atmospheric CO2. In our experiment, ?13C value in the contaminant DIC was ?24.30‰, which

Anna Szynkiewicz; Mariusz Orion J?drysek; Marta Kurasiewicz

2006-01-01

353

Behavior of carbon isotopes during the hyperfiltration of calcium carbonate solutions through calcium bentonites  

E-print Network

(aq) The 1sotopic ratio of the effluent gave no clue to the possible occurrence of any fractionation of carbon 1sotopes. The solution retained on the high pressure s1de of the membrane was found to have an increased calcium concentration, as would... the stock solution's COB(aq) concentration. This is interpreted as conversion of bicarbonate to CO7(aq) along or within the membrane, with subsequent transport of the C02~a ~ through the membrane. The carbon isotopic ratio of the throughput solution...

Hinz, David William

1987-01-01

354

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

NASA Technical Reports Server (NTRS)

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.

Mccluskey, Carolina P. S.

1990-01-01

355

Equilibrium carbon and hydrogen isotope fractionation in iron  

NASA Astrophysics Data System (ADS)

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 ?-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, ?-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 (2009) Nature Geoscience doi:10.1038/ngeo546; 3. Polyakov (2009) Science 323:912; 4. Polyakov & Kharlashina (1995) GCA 59:2561.

Schauble, E. A.

2009-12-01

356

The biodegradation of fluoranthene as monitored using stable carbon isotopes  

SciTech Connect

The measurement of stable isotope ratios of carbon ({delta}{sup 13}C 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, designated EPA505, was grown on fluoranthene. During growth of EPA505 on fluoranthene, bacterial biomass, respired CO{sub 2}, and dissolved organic carbon (DOC), as well as fluoranthene, were sampled over 8 days. The concentrations and {delta}{sup 13}C values of each of these carbon pools were determined. The concentration of fluoranthene decreased from 12.1 {+-} 2.0 (n = 2) to 3.0 {+-} 0.9 (n = 2) mg C per flask over 188 h, and CO{sub 2} increased from undetectable levels to 7.1 {+-} 0.3 (n = 4) mg C per flask. A total of 55.5% mineralization resulted. DOC concentrations remained fairly constant with time, averaging 2.2 to 3.6 mg C per flask. The {delta}{sup 13}C value of fluoranthene remained constant over the course of the experiment, averaging {minus}24.5 {+-} 0.2{per_thousand} (n = 8). Bacterial nucleic acids and respired CO{sub 2} took on {delta}{sup 13}C values similar to those of fluoranthene within 47 h, measuring {minus}22.6 and {minus}24.3{per_thousand}, respectively.

Trust, B.A. [National Research Council, Gulf Breeze, FL (United States); Mueller, J.G. [SBP Technologies Inc., Gulf Breeze, FL (United States); Coffin, R.B. [Environmental Protection Agency, Gulf Breeze, FL (United States). Environmental Research Lab.; Cifuentes, L.A. [Texas A and M Univ., College Station, TX (United States). Dept. of Oceanography

1995-12-31

357

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

PubMed

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 varia-tion 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 ?13C and ?15N 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 inte-grated in animals' isotope values will be crucial for developing reliable methods to use stable isotopes as dietary tracers. PMID:25700080

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

2015-01-01

358

The magnesium isotope record of cave carbonate archives  

NASA Astrophysics Data System (ADS)

Here we explore the potential of time-series magnesium (?26Mg) 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 ?26Mg 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 ?26Mg 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 ?26Mg: -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 ?26Mg: -4.01 ± 0.07 ‰; BU 4 mean ?26Mg: -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 German speleothems are shifted to higher values due to sampling in detrital layers (Mg-bearing clay minerals) of the speleothems. The data and their interpretation shown here highlight the potential but also the limitations of the magnesium isotope proxy applied in continental climate research. An obvious potential lies in its sensitivity for even subtle changes in soil-zone parameters, a hitherto rather poorly understood but extremely important component in cave archive research. Limitations are most obvious in the low resolution and high sample amount needed for analysis. Future research should focus on experimental and conceptual aspects including quantitative and well calibrated leaching and precipitation experiments.

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

359

The magnesium isotope record of cave carbonate archives  

NASA Astrophysics Data System (ADS)

Here we explore the potential of magnesium (?26Mg) 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 ?26Mg 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 ?26Mg 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 ?26Mg: -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 ?26Mg: -4.01 ± 0.07‰; BU 4 mean ?26Mg: -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 ?26Mg values of the Austrian and two ?26Mg values of the German speleothems are shifted to higher values due to sampling in detrital layers (Mg-bearing clay minerals) of the speleothems. The data and their interpretation shown here highlight the potential but also the limitations of the magnesium isotope proxy applied in continental climate research. An obvious potential lies in its sensitivity for even subtle changes in soil-zone parameters, a hitherto rather poorly understood but extremely important component in cave archive research. Limitations are most obvious in the low resolution and high sample amount needed for analysis. Future research should focus on experimental and conceptual aspects including quantitative and well-calibrated leaching and precipitation experiments.

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

360

Modeling Environmental Controls on the Carbon Isotope Composition of Ecosystem Respired Carbon Dioxide  

NASA Astrophysics Data System (ADS)

Our main objective was to test whether the carbon isotope composition of ecosystem respired CO2 varied in response to environmental conditions in a manner consistent with well-known leaf-level studies of photosynthetic 13C discrimination. We developed an ecosystem-scale model that calculated leaf CO2 assimilation, stomatal conductance and chloroplast CO2 concentration separately for sunlit and shaded leaves within multiple canopy layers. The stomatal conductance model was linked to differences in water potential and resistances in the hydraulic pathway between the soil and the tree foliage. This part of the ecosystem model was validated by comparison to leaf-level gas exchange measurements and estimates of ecosystem-scale photosynthesis (GEP). The estimates of GEP were based on eddy covariance measurements of net ecosystem CO2 exchange (NEE) and the Fluxnet-Canada Research Network standard protocol for partitioning NEE into GEP and total ecosystem respiration (TER). The carbon isotope composition of carbohydrate formed during photosynthesis was calculated based on the Farquhar model of isotope effects. Total ecosystem respiration was modeled, based on measured temperature and soil moisture, as the sum of four components (1) above-ground plant, (2) root, (3) litter, and (4) mineral soil. We applied a variety of techniques to allocate the contribution of these different components so that modeled TER was consistent with TER calculated from NEE measurements. The carbon isotope composition of CO2 released during above-ground plant and root respiration was calculated based on an assimilated-weighted average of carbohydrate fixed during a variable number of days previous to the day of respiration. The isotope composition of CO2 released by litter and mineral soil respiration was based on measurements of the ?13C values of these components (we assumed no isotope fractionation during respiration) and held constant in all calculations. The model was compared to measurements of the ?13C values of ecosystem respired CO2 made in a coastal Douglas-fir forest on Vancouver Island during May-October of 2003-2005. Excellent agreement was observed between the modeled and measured ?13C values of ecosystem respired CO2. These results indicate that the stable isotope composition of respired CO2 is a useful ecosystem-scale tool to study constraints to photosynthesis and acclimation of ecosystems to environmental stress.

Cai, T.; Flanagan, L. B.

2006-12-01

361

The Carbon Isotopic Composition of LEW88516, the Fifth Shergottite  

NASA Astrophysics Data System (ADS)

Lewis Cliffs 88516 is a shergottite of harzburgite composition similar in many respects to ALH A77005. A previous study of the carbon in this latter sample (Wright et al., 1986) has shown it to contain one of the lowest carbon contents of any SNC meteorite (140 ppm carbon). At the very least this suggests that ALH A77005 is not heavily contaminated with terrestrial organic compounds or Antarctic weathering products. On the basis of stepped combustion results, no evidence was found in ALH A77005 for the presence of ^13C-rich carbonates, as have been found in Antarctic and non- Antarctic meteorites alike (Carr et al., 1985; Wright et al., 1988, 1992). However, ALH A77005 was observed to liberate a discrete release of carbon at 500-600 degrees C, a temperature interval that would be consistent with the presence of carbonate minerals. Interestingly, the delta^13C value at 500-600 degrees C was -29o/oo, which is hardly different to the bulk value of -28.7o/oo. Thus, it remains a possibility that ALH A77005 contains carbonate minerals of relatively light carbon isotopic composition, a proposition that will have to be clarified by making further analyses of this meteorite. As a preliminary investigation of LEW 88516 we elected to use stepped combustion to analyse the subsample LEW 88516,13, a powder prepared specially at NASA-JSC, using ca. 1 g of the meteorite, in order to provide a representative and homogeneous sample. The total carbon content of LEW 88516,13 is 1215 ppm, which is in fact the highest measured so far for any SNC meteorite. In light of the similarities between LEW 88516 and ALH A77005 the largest excesses of carbon found in the former meteorite pose a problem of interpretation. Most of this carbon is released at low temperatures and is thus most likely to be organic in nature. It would seem to be a possibility that some of this carbon was introduced during the crushing procedure, highlighting the problem of trying to ascertain the true bulk carbon content of SNC meteorites. However, the bulk delta^13C value of LEW 88516,13 is -21.2o/oo, which is relatively high for normal terrestrial contaminants. The reason for the elevated delta^13C is the presence of a ^13C-rich component that is liberated between 400 and 900 degrees C, broadly the region that results in the decrepitation of carbonate minerals. In order to obtain the delta^13C value of these minerals it will be necessary to undertake an acid-dissolution extraction of the meteorite. On the basis of the stepped combustion data it is apparent that the delta^13C of the carbonates is at least -14.6o/oo (the most extreme result obtained, at 500-600 degrees C). If the delta^13C of any carbonates was +lOo/oo, LEW 88516 could contain 90 ppm of carbon as carbonate, a concentration that is considerably higher than any observed in other SNC meteorites (Wright et al., 1992). If the delta^13C value of the putative carbonates in LEW 88516 was lower than +10o/oo, then the meteorite would contain even more of these minerals. Clearly, in spite of the potential problems of contamination, LEW 88516 is worthy of further study. The Antarctic shergottite, EET A79001, has been found to contain enrichments of organic compounds accompanying deposits of carbonate minerals (Wright et al., 1989). Since LEW 88516 also contains high levels of both organics and carbonates, it is apparent that analyses of this meteorite will assist the understanding of this association. Although we cannot rule out the possibility that the carbon components observed in LEW 88516 are indigenous, in light of the small size of the sample (13.2 g) it is anticipated that Antarctic weathering will have played an important role in affecting the carbon inventory of the sample. References: Carr, R.H., Grady, M.M., Wright, I.P. and Pillinger, C.T. (1985) Nature, 314, 248-250. Wright, I.P., Carr, R.H. and Pillinger, C.T. (1986) Geochim. Cosmochim. Acta, 50, 983-991. Wright, I.P., Grady, M.M. and Pillinger, C.T. (1989) Nature, 340, 220-222. Wright, I.P., Grady, M.M. and Pillinger, C.T. (1992) Geochim. Cosmochim. Acta,

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

1992-07-01

362

Seasonal stable-carbon isotope variability in tree rings: possible paleoenvironmental signals  

Microsoft Academic Search

Leavitt, SW. and Long, A., 1991. Seasonal stable-carbon isotope variability in tree rings: possible paleoenvironmental signals. Chem. Geol. (Isot. Geosci. Sect.), 87: 59-70. Plant stable-carbon isotope fractionation models indicate that 613C of atmospheric C02, CO1 concentration, light and moisture stress, among other factors, may potentially affect the 613C of fixed carbon. Seasonal 613C variations in tree rings may therefore represent

Steven W. Leavitt; Austin Longb

2000-01-01

363

Carbon-isotope composition of sediments from the Gulf of Papua  

Microsoft Academic Search

Rivers draining into the Gulf of Papua (GOP) from the Papua New Guinea mainland deliver approximately 340 × 106 t yr-1 of sediment to the marine environment. The terrestrially derived sediment contains 1.1 ± 0.2% particulate organic carbon with a carbon-isotope composition of -26.5 ± 0.2‰, and amounts to 3.7 ± 0.7 × 106 t yr-1. The carbon-isotope composition of

M. I. Bird; A. R. Chivas; G. J. Brunskill

1995-01-01

364

Double-comparison method for mass spectrometric determination of hydrogen isotopic abundances  

Microsoft Academic Search

Hydrogen isotope ratio analysis is subject to interference from Hâ\\/sup +\\/, and the uncertainty in the Hâ\\/sup +\\/ correction is generally the limiting factor in the precision of hydrogen isotopic analyses. Mathematical modeling indicates that the precision of the analysis can be improved through the use of a double-comparison technique employing a second reference gas. In order to compare the

D. A. Schoeller; D. W. Peterson; J. M. Hayes

1983-01-01

365

Sr Incorporation and Calcium Isotopic Fractionation during Calcium Carbonate Precipitation  

NASA Astrophysics Data System (ADS)

Element substitution and calcium isotopic fractionation can provide information about the mechanisms of CaCO3 precipitation, precipitation rates, temperatures and solution chemistry. In the present study precipitation experiments for the formation of the CaCO3 polymorphs: calcite, aragonite and vaterite were carried out. Calcium carbonates are formed at various Mg/Ca ratios or in presence of polyaspartic acid at temperatures between 5 and 40Ë? C at pH 8.3 by using an advanced CO2-diffusion technique (Tang et al., 2008). The results indicate elevated Sr distribution coefficients (DSr) during calcite and vaterite formation at increasing precipitation rates, whereas DSr-values decrease only slightly with increasing rate during the formation of aragonite. 44Ca/40Ca fractionation increases for aragonite and calcite formation as precipitation rates increase. Preliminary results show less calcium isotopic fractionation for vaterite compared to calcite and aragonite. However, 44?40CaCaCO3(s)-Ca(aq)-values for the three modifications indicate an inverse correlation with DSr. Respective mechanisms and proposed models are discussed. Reference Tang J., Köhler S.J., and Dietzel M. (2008) Sr2+/Ca2+ and 44Ca/40Ca fractionation during inorganic calcite formation: I. Sr in corporation, Geochimica et Cosmochimica Acta, 72, 3718-3732.

Niedermayr, A.; Dietzel, M.; Köhler, S. J.; Böhm, F.; Kisakurek, B.; Eisenhauer, A.

2009-04-01

366

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

NASA Technical Reports Server (NTRS)

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.

Clayton, D. D.

1978-01-01

367

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

NASA Astrophysics Data System (ADS)

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. ?13C-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 phytoplankton is to be determined. The isotopic composition of different sulfur species, SO42- , S0 and S2-, and seasonal variation are being analyzed. Exploration of the potential role of PSB on sulfur isotopic composition and their affect on the sulfur isotopic distribution in the lake system is in progress. Currently, no sulfur isotopic composition measurements through PSB or systematic studies of the impact of fractionation between sulfate and sulfide by PSB exist in the literature. Since PSB affect the equilibrium of the system, more than just sulfate and sulfide should be considered.

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

2013-12-01

368

Carbon isotopic composition of Ambrosia and Artemisia pollen: assessment of a C?-plant paleophysiological indicator.  

PubMed

There is limited evidence on how shifts in plant physiological performance influence vegetation variations in the paleorecord. To evaluate ?¹³C of pollen from C? plants as an indicator of community-level physiology, small quantities (10-30 grains) of untreated pollen and sporopollenin from herbarium specimens of Ambrosia (A. tomentosa and A. psilostachya) and Artemisia (A. frigida, A. ludoviciana and A. dracunculus), genera abundant in grassland pollen profiles, were isolated by micromanipulation. Their ?¹³C values were measured using a spooling-wire microcombustion device interfaced with an isotope-ratio mass spectrometer. Leaf ?¹³C was also measured. Carbon isotope discrimination (?) for untreated pollen, sporopollenin and leaves was compared with historic records of seasonal precipitation amount, vapor pressure deficit and the Palmer Drought Severity Index (PDSI). Each species showed positive correlations between ? of untreated pollen and sporopollenin. Sporopollenin ? was most strongly correlated with PDSI. Correlations among leaf ? and moisture indicators were stronger for Ambrosia than Artemisia. These results suggest that sporopollenin ? indicates the level of moisture stress in C? plants. Therefore, ?¹³C analysis of pollen promises to help address important paleoecological questions, such as how community-level physiology contributes to shifts in vegetation composition. PMID:22742492

Nelson, David M

2012-09-01

369

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

PubMed

Rapid detection of shifts in substrate utilization and energy balance would provide a compelling biofeedback tool for individuals attempting weight loss. As a proof of concept, we tested whether the natural abundance of exhaled carbon stable isotope ratios (breath ?(13)C) reflects shifts between negative and positive energy balance. Volunteers (n=5) consumed a 40% energy-restricted diet for 6 days followed by 50% excess on day 7. Breath was sampled immediately before and 1?h and 2?h after breakfast, lunch and dinner. Exhaled breath ?(13)C values were measured by cavity ring-down spectroscopy. Using repeated measures analysis of variance (ANOVA) followed by Dunnett's contrasts, pre-breakfast breath values on days 2-6 were compared with day 1, and postprandial day 7 time points were compared with pre-breakfast day 7. Energy restriction diminished pre-breakfast breath ?(13)C by day 3 (P<0.05). On day 7, increased energy intake was first detected immediately before dinner (-23.8±0.6 vs -21.9±0.7‰, P=0.002 (means±s.d.)), and breath ?(13)C remained elevated at least 2?h post dinner. In conclusion, when shifting between negative and positive energy balance, breath ?(13)C showed anticipated isotopic changes. Although additional research is needed to determine specificity and repeatability, this method may provide a biomarker for marked increases in caloric intake. PMID:24441037

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

2014-09-01

370

Near-infrared spectroscopy of M dwarfs. I. CO molecule as an abundance indicator of carbon  

NASA Astrophysics Data System (ADS)

Based on the near-infrared spectra of 42 M dwarfs, carbon abundances are determined from the ro-vibrational lines of the CO (2-0) band. We apply Teff values based on the angular diameters if available or use the Teff values in a log Teff-M3.4 relation (M3.4 is the absolute magnitude at 3.4 ?m based on the WISE W1 flux and the Hipparcos parallax) to estimate Teff values of objects for which angular diameters are unknown. Also, we discuss briefly the HR diagram of low-mass stars. On the observed spectrum of the M dwarf, the continuum is depressed by the numerous weak lines of H2O and only the depressed continuum or the pseudo-continuum can be seen. On the theoretical spectrum of the M dwarf, the true continuum can be evaluated easily but the pseudo-continuum can also be evaluated accurately thanks to the recent H2O line database. Then spectroscopic analysis of the M dwarf can be done by referring to the pseudo-continuum both on the observed and theoretical spectra. Since the basic principle of the spectroscopic analysis should be the same whether the true- or pseudo-continuum is referred to, the difficulty related to the continuum in cool stars can in principle be overcome. Then, the numerous CO lines can be excellent abundance indicators of carbon, since almost all the carbon atoms are in stable CO molecules which suffer little effect of the uncertainties in photospheric structure, and carbon abundances in late-type stars can best be determined in M dwarfs rather than in solar type stars. The resulting C/Fe ratios for most M dwarfs are nearly constant at about the solar value based on the classical high carbon abundance rather than on the recently revised lower value. This result implies that the solar carbon abundance is atypical for its metallicity among the stellar objects in the solar neighborhood if the downward revised carbon abundance is correct.

Tsuji, Takashi; Nakajima, Tadashi

2014-10-01

371

Absolute quantification of protein and post-translational modification abundance with stable isotope–labeled synthetic peptides  

PubMed Central

In the analysis of biological systems, it is of interest to identify the components of the system and to monitor their changes in abundance under different conditions. The AQUA (for ‘absolute quantification’) method allows sensitive and specific targeted quantification of protein and post-translational modifications in complex protein mixtures using stable isotope–labeled peptides as internal standards. Each AQUA experiment is composed of two stages: method development and application to a biological scenario. In the method development stage, peptides from the protein of interest are chosen and then synthesized with stable isotopes such as 13C, 2H or 15N. The abundance of these internal standards and their endogenous counterparts can be measured by mass spectrometry with selected reaction monitoring or selected ion monitoring methods. Once an AQUA method is established, it can be rapidly applied to a wide range of biological samples, from tissue culture cells to human plasma and tissue. After AQUA peptide synthesis, the development, optimization and application of AQUA analyses to a specific biological problem can be achieved in ~1 week. Here we demonstrate the usefulness of this method by monitoring both Polo-like kinase 1 (Plk1) protein abundance in multiple lung cancer cell lines and the extent of Plk1 activation loop phosphorylation (pThr-210) during release from S phase. PMID:21293459

Kettenbach, Arminja N; Rush, John; Gerber, Scott A

2013-01-01

372

Stable Carbon Isotopes As Indicators of Plant Water Use Efficiency  

NASA Astrophysics Data System (ADS)

Stable carbon isotopes have been utilized to better understand how environmental variables influence the efficiency of photosynthesis, specifically what factors limit the uptake and absorption of CO2 during photosynthesis. An understanding of the controls over both gas exchange and stomatal conductance can provide an explanation for the possible environmental influences on plant WUE. The ?13C of extractive-free wood was used as an index of plant water use efficiency at Mica Creek Experimental Watershed, Shoshone County, ID. The ?13C values of tree rings were used to determine the effects of clear cut and partial cut harvesting practices, the effect of elevation, and species differences in intrinsic water use efficiency (WUE) among coniferous species including: Thuja plicata, Larix occidentalis, Picea engelmannii, Pseudotsuga menziesii, Abies lasiocarpa, and Abies grandis. We found significant effects of harvest treatments (p=0.0197), elevation (p= 0.0268), and species (p<0.001) on tree ?13C. The significantly more enriched isotopic signatures observed in Thuja plicata (?13C = -23.37 ±0.17‰), indicate that it is a more water use efficient species compared to Larix occidentalis (?13C = -25.66 ±0.43‰), and Abies grandis (?13C = -25.83 ±0.15‰). There was also an overall trend of ?13C enrichment with elevation. The isotopic composition of tree rings has been estimated to increase by 0.003 ‰ per meter of elevation gain, which may be related to a decrease in soil moisture with elevation. Finally, the mean ?13C values observed on partial cut (?13C = -24.73 ±0.10‰) and clear cut treatments (?13C = -24.45 ±0.29‰) were significantly more enriched than the mean value for the control treatment (?13C = -25.25 ±0.19‰). The more enriched isotopic signatures observed on the harvested treatments indicate that the trees are more water use efficient, which may be a result of increased photosynthetic capacity with an increase in the availability of water, foliar nitrogen, and light to individual trees on the harvested treatments. The reduction of stand density through harvesting may reduce the transpirational water losses on a stand level, thus increasing the water availability for individual trees.

Powers, E. M.; Marshall, J. D.; Ubierna Lopez, N.

2007-12-01

373

Assessment of carbonate-phosphoric acid analytical technique performed using GasBench II in continuous flow isotope ratio mass spectrometry  

Microsoft Academic Search

The commonly used online automated analytical method (in particular Thermo GasBench II) to determine stable carbon and oxygen isotope ratio composition of calcium carbonate in continuous flow isotope ratio mass spectrometry is evaluated. We have analyzed the isotopic composition of three in-house calcium carbonate standards as unknown samples for assessment of speed, accuracy and precision of isotopic measurements. Isotopic analyses

Debajyoti Paul; Grzegorz Skrzypek

2007-01-01

374

Standard test method for uranium and plutonium concentrations and isotopic abundances by thermal ionization mass spectrometry  

E-print Network

1.1 This test method covers the determination of the concentration and isotopic composition of uranium and plutonium in solutions. The purified uranium or plutonium from samples ranging from nuclear materials to environmental or bioassay matrices is loaded onto a mass spectrometric filament. The isotopic ratio is determined by thermal ionization mass spectrometry, the concentration is determined by isotope dilution. 1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish safety and health practices and determine the applicability of regulatory limitations prior to use.

American Society for Testing and Materials. Philadelphia

2005-01-01

375

Sniffing for Clues to the Dinosaurs Demise: Measurement of Osmium Isotope Compositions and Platinum Group Element Abundances in Volcanic Emissions  

NASA Astrophysics Data System (ADS)

Platinum Group Elements (PGE: Os, Ir, Rh, Ru, Pt, Pd) and osmium isotopes measured in marine and terrestrial sediment, snow and ice records are important paleo-tracers of riverine, hydrothermal, extraterrestrial, volcanic and anthropogenic inputs into the global surficial environment. For instance, the marine Os isotope record across the Cretaceous-Tertiary Boundary (KTB) indicates that the onset of the main phase of Deccan volcanism and the transient late Maastrichtian warming preceded the large extraterrestrial impact and the related KTB mass extinction by several hundred thousand years [Ravizza and Peucker-Ehrenbrink, 2003]. Distinguishing extraterrestrial from volcanic PGE sources has been difficult due to the similarity in Os isotopic compositions, complex PGE fractionations, and our lack of knowledge of the Os isotopic composition and PGE abundances in volcanic aerosols. These difficulties have fueled vigorous debate about extraterrestrial vs. volcanic triggers of mass extinctions in the geologic record. To assess the volcanic contribution to the global Re-Os-PGE cycle we have initiated a study of Os isotopic compositions and PGE abundances in volcanic emissions from volcanoes around the globe. Here we report preliminary data on PGE abundances and Os isotopes measured in gas and aerosol filter samples from Vulcan Masaya, Nicaragua and Mt Etna, Italy. Samples were analyzed by ID-ICPMS (ThermoFinnigan ELEMENT 2 and NEPTUNE) at the Woods Hole Oceanographic Institution. Osmium isotope compositions of the filters are unradiogenic (0.1272 to 0.187). Osmium concentrations range from 28 to 97 pg/cubic meter and are 3-4 orders of magnitude lower than those measured by Krahenbuhl et al. [1992] during the spring 1984 eruption of Mauna Loa just after the lava fountaining phase. Normalized PGE abundance patterns are fractionated relative to carbonaceous chondrites and two important features distinguish the pattern from other important PGE sources: 1) Os/Ir is much higher than that of the continental crust, the mantle and extraterrestrial matter; and 2) Pt/Pd is much lower than that of the continental crust, mantle, extraterrestrial matter and catalytic converters. If these PGE patterns from Masaya and Etna are typical of volcanic emissions worldwide they indicate that volcanic emission PGE patterns are distinct from the globally integrated KTB patterns [Tredoux et al. 1989; Evans et al., 1993] and that a volcanic source is not the cause of the elevated PGE abundances across the KTB. The PGE pattern of volcanic emissions is also different from catalytic converters enabling us to distinguish between volcanic sources and contamination from catalytic converters in places such as the Greenland Ice sheet [Barbante et al., 2001]. While these data have important implications for understanding the contribution of volcanic emissions to the global Re-Os-PGE cycles they need to be augmented with further analyses from other volcanoes.

Sims, K. W.; Peucker-Ehrenbrink, B.; Mather, T.; Pyle, D.; Martin, R.; Gauthier, P.; Aiuppa, A.

2005-12-01

376

Stable carbon isotope discrimination and microbiology of methane formation in tropical anoxic lake sediments  

NASA Astrophysics Data System (ADS)

Methane is an important end product of degradation of organic matter in anoxic lake sediments. Methane is produced by either reduction of CO2 or cleavage of acetate involving different methanogenic archaea. The contribution of the different methanogenic paths and of the diverse bacteria and archaea involved in CH4 production exhibits a large variability that is not well understood. Lakes in tropical areas, e.g. in Brazil, are wetlands with high potential impact on the global CH4 budget. However, they have hardly been studied with respect to methanogenesis. Therefore, we used samples from 16 different lake sites in the Pantanal and Amazon region of Brazil to measure production of CH4, CO2, analyze the content of 13C in the products and in intermediately formed acetate, determine the abundance of bacterial and archaeal microorganisms and their community composition and diversity by targeting the genes of bacterial and archaeal ribosomal RNA and of methyl coenzyme M reductase, the key enzyme of methanogenic archaea. These experiments were done in the presence and absence of methyl fluoride, an inhibitor of acetoclastic methanogenesis. While production rates of CH4 and CO2 were correlated to the content of organic matter and the abundance of archaea in the sediment, values of 13C in acetate and CH4 were related to the 13C content of organic matter and to the path of CH4 production with its intrinsic carbon isotope fractionation. Isotope fractionation was small (average 10‰) for conversion of C-org to acetate-methyl, which was hardly further fractionated during CH4 production. However, fractionation was strong for CO2 conversion to CH4 (average 75‰), which generally accounted for >50% of total CH4 production. Canonical correspondence analysis did not reveal an effect of microbial community composition, despite the fact that it exhibited a pronounced variability among the different sediments.

Conrad, R.; Noll, M.; Claus, P.; Klose, M.; Enrich-Prast, A.

2010-12-01

377

Stable carbon isotope discrimination and microbiology of methane formation in tropical anoxic lake sediments  

NASA Astrophysics Data System (ADS)

Methane is an important end product of degradation of organic matter in anoxic lake sediments. Methane is mainly produced by either reduction of CO2 or cleavage of acetate involving different methanogenic archaea. The contribution of the different methanogenic paths and of the diverse bacteria and archaea involved in CH4 production exhibits a large variability that is not well understood. Lakes in tropical areas, e.g. in Brazil, are wetlands with high potential impact on the global CH4 budget. However, they have hardly been studied with respect to methanogenesis. Therefore, we used samples from 16 different lake sediments in the Pantanal and Amazon region of Brazil to measure production of CH4, CO2, analyze the content of 13C in the products and in intermediately formed acetate, determine the abundance of bacterial and archaeal microorgansisms and their community composition and diversity by targeting the genes of bacterial and archaeal ribosomal RNA and of methyl coenzyme M reductase, the key enzyme of methanogenic archaea. These experiments were done in the presence and absence of methyl fluoride, an inhibitor of acetoclastic methanogenesis. While production rates of CH4 and CO2 were correlated to the content of organic matter and the abundance of archaea in the sediment, values of 13C in acetate, CO2, and CH4 were related to the 13C content of organic matter and to the path of CH4 production with its intrinsic carbon isotope fractionation. Isotope fractionation was small (average 10‰) for conversion of Corg to acetate-methyl, which was hardly further fractionated during CH4 production. However, fractionation was strong for CO2 conversion to CH4 (average 75‰), which generally accounted for >50% of total CH4 production. Canonical correspondence analysis did not reveal an effect of microbial community composition, despite the fact that it exhibited a pronounced variability among the different sediments.

Conrad, R.; Noll, M.; Claus, P.; Klose, M.; Bastos, W. R.; Enrich-Prast, A.

2011-03-01

378

Stable carbon isotope discrimination and microbiology of methane formation in tropical anoxic lake sediments  

NASA Astrophysics Data System (ADS)

Methane is an important end product of degradation of organic matter in anoxic lake sediments. Methane is mainly produced by either reduction of CO2 or cleavage of acetate involving different methanogenic archaea. The contribution of the different methanogenic paths and of the diverse bacteria