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1

Isotopic abundance ratios in interstellar carbon monosulfide  

SciTech Connect

A survey of the relative abundances of the isotopic species, /sup 12/C/sup 32/S, /sup 12/C/sup 34/S, and /sup 13/C/sup 32/S has been made in 14 dense molecular clouds through observations of the J=3-1 rotational transitions at 3 mm. The abundance ratio, (/sup 13/C/sup 32/S)/(/sup 12/C/sup 34/S), is found to be 1.9 times greater in the galactic center sources than in the galactic disk sources. The average ratio for the galactic disk sources is 0.35 +- 0.10 where the quoted error is the rms of the source-to-source fluctuations. The average disk value for (/sup 13/C)/(/sup 12/C) is 0.015, if (/sup 32/S)/(/sup 34/S) is terrestrial. No evidence is found for a systematic variation of the ratio within the disk itself. Terrestrial sulfur abundances would imply that either the observations in CS are spatially unresolved or the kinetic temperature for CS is lower than that for CO. Beam dilution factors are derived for the sources studied. In addition, values for the molecular hydrogen densities and CS fractional abundances are obtained for these sources.

Frerking, M.A.; Wilson, R.W.; Linke, R.A.; Wannier, P.G.

1980-08-15

2

Carbon Isotope Abundance Ratios in Comets  

NASA Astrophysics Data System (ADS)

High resolution (lambda /Delta lambda ~ 10(5) ) spectra of the CN B-X (0-0) band at 3883 Angstroms have been obtained of four comets using the Mt. Stromlo 1.8-m telescope echelle spectrograph. The resolution and the S/N ratios of the spectra are of sufficient quality that (13) C(14) N lines have been identified in two of the comets. A fluorescence equilibrium model has been developed to compute the rotational line populations in the four lowest vibrational levels of the ground electronic state of the CN B-X (0-0) band. Line fluorescence efficiencies and rotational line intensities for all isotopic combinations of (12) C, (13) C, (14) N and (15) N have been computed for a range in heliocentric velocites. The computed CN spectra generated at the observed resolution are compared with the observations, and (12) C/(13) C ratios are derived. We show for the first time that collisions in the inner coma significantly affect the rotational line populations in the lowest vibrational levels of the ground electronic state. We find that the carbon isotope ratios are consistent with terrestrial values in all four comets.

Kleine, M.; Wyckoff, S.; Wehinger, P. A.; Peterson, B.

1992-12-01

3

Investigating microbial carbon cycling using natural abundance isotope analysis of PLFA  

NASA Astrophysics Data System (ADS)

Understanding microbial carbon sources and cycling is fundamental to our conceptualization of microbial ecosystems and their role in biogeochemical cycling in natural systems. Achieving this understanding requires application of a wide range of approaches. Natural abundance isotope analysis of individual compounds, particularly cellular components such as Phospholipids Fatty Acids (PLFA) can provide insights into the carbon sources and metabolic activities of the in situ microbial community from environmental samples. This is primarily because specific PLFA can be well resolved by gas chromatography even from complex matrices where confounding biological/organic compound abound. These PLFA can then be attributed to the viable microbial community, in some cases to specific components of this community and due to characteristic biosynthetic fractionations of stable isotope ratios, ?13C analysis of PLFA can: differentiate isotopically distinct primary carbon sources of heterotrophic communities; identify isotopic patterns characteristic of autotrophic versus heterotrophic processes; and elucidate microbial biosynthetic pathways. In cases where there ?13C cannot provide resolution of carbon sources, new approaches in ?14C of PLFA can be applied. The vast range in ?14C of ancient and modern carbon provides an easily traceable signal that can differentiate uptake and utilization of these carbon sources. This is particularly useful in cases such as contaminated sites where petroleum based contamination has occurred, or in natural systems where microbial communities may be utilizing geologic versus recently photosynthetically fixed carbon. This talk will present several examples demonstrating the utility of this approach.

Slater, G. G.; Brady, A.; Cowie, B.

2008-12-01

4

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

NASA Astrophysics Data System (ADS)

A solar photospheric ``thermal profiling'' analysis is presented, exploiting the infrared (2.3-4.6 ?m) 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 (for C/O?0.5). Our analysis was meant to complement recent studies based on three-dimensional (3D) convection models, which, among other things, have revised the historical solar oxygen (and carbon) abundance downward by a factor of nearly 2, although in fact our conclusions do not support such a revision. Based on various considerations, an ?O=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: 12C/13C=80+/-1, 16O/17O=1700+/-220, and 16O/18O=440+/-6-all significantly lower than terrestrial. CO synthesis experiments utilizing a stripped down version of the 3D model-which has large temperature fluctuations in the middle photosphere, possibly inconsistent with CO ``movies'' from the Infrared Imaging Spectrometer (IRIS), and a steeper mean temperature gradient than matches visible continuum center-limb measurements-point to a lower oxygen abundance (~500 ppm) and isotopic ratios closer to terrestrial. A low oxygen abundance from CO-and other molecules like OH-thus hinges on the reality of the theoretically predicted midphotospheric convective properties.

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

2006-08-01

5

Carbon abundance and isotopic studies of Shergotty and other shergottite meteorites  

NASA Astrophysics Data System (ADS)

Consortium samples of the Shergotty meteorite have been measured for C abundance and isotopic composition by stepped combustion and the results compared to different samples of the same meteorite and the other known shergottites. Clearly, the shergottite meteorites have a complex C chemistry and contain components of both low and high thermal stability. Two components labile at low temperature can be tentatively identified. One is enriched in C-13 and may be related to the carbonate thought to be produced by preterrestrial weathering in Nakhla. The other, which is isotopically light, is of unknown origin but might be related to shock effects. At high temperatures, two of the samples examined show evidence for a component of CO2 trapped from the Martian atmosphere, possibly indicating that shock-produced glass is heterogeneously distributed throughout the shergottite group. This interpretation is corroborated by N-isotope measurements made on one of the specimens. All samples appear to contain evidence of a high temperature magmatic component of C.

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

1986-06-01

6

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.

Affek, Hagit P.; Yakir, Dan

2003-01-01

7

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

Microsoft Academic Search

We report measurements of the susceptibility of a variety of elemental and organic carbon samples to oxidative degradation using both acid dichromate and basic peroxide reagents. Organic carbon is rapidly oxidized using either reagent, or both reagents sequentially. Elemental carbon exhibits a wide range of susceptibilities to oxidation related both to the degree to which the precursor plant material was

Michael I. Bird; Darren R. Gröcke

1997-01-01

8

Carbon, hydrogen and nitrogen in carbonaceous chondrites: abundances and isotopic compositions in bulk samples.  

PubMed

Whole-rock samples of 25 carbonaceous chondrites were analysed for contents of C, H and N and delta 13C, delta D and delta 15N. 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% 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. PMID:11539652

Kerridge, J F

1985-01-01

9

C, N, O abundances and carbon isotope ratios in evolved stars of the open clusters Collinder 261 and NGC 6253  

NASA Astrophysics Data System (ADS)

Context. Investigations of abundances of carbon and nitrogen in the atmospheres of evolved stars of open clusters may provide comprehensive information on chemical composition changes caused by stellar evolution. Aims: Our main aim is to increase the number of open clusters with determined carbon-to nitrogen and carbon isotope ratios. Methods: High-resolution spectra were analysed using a differential model atmosphere method. Abundances of carbon were derived using the C2 Swan (0, 1) band head at 5635.5 Å (FEROS spectra) and the C2 Swan (1, 0) band head at 4737 Å (UVES spectra). The wavelength interval 7980-8130 Å, with strong CN features was analysed to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen abundances were determined from the [O i] line at 6300 Å. Results: The average value of 12C/13C isotope ratios of Cr 261 is equal to 18 ± 2 in four giants and to 12 ± 1 in two clump stars; it is equal to 16 ± 1 in four clump stars of the open cluster NGC 6253. The mean C/N ratios in Cr 261 and NGC 6253 are equal to 1.67 ± 0.06 and 1.37 ± 0.09, respectively. Conclusions: The 12C/13C and C/N values in Cr 261 and NGC 6253 within limits of uncertainties agree with the theoretical model of thermohaline-induced mixing as well as with the cool-bottom processing model. Based on observations collected at ESO telescopes under programmes 65.N-0286, 169.D-0473.

Mikolaitis, Š.; Tautvaišien?, G.; Gratton, R.; Bragaglia, A.; Carretta, E.

2012-05-01

10

Infrared spectroscopy of symbiotic stars - Carbon abundances and C-12/C-13 isotopic ratios  

NASA Astrophysics Data System (ADS)

Intermediate-resolution spectra of a sample of symbiotic stars in the K and L bands are obtained. Pfund and Brackett emission lines as well as the first-overtone CO absorption bands are detected. Synthetic spectra are used to fit the CO absorption features and to obtain carbon abundances and C-12/C-13 ratios. Subsolar carbon abundances are found in the symbiotic red giants with little scatter from star to star. The C-12/C-13 ratios are also lower than the solar value. No modifications due to binarity are detected. The synthetic spectra were used to obtain angular diameters for some of the symbiotic red giants. A modified scheme applicable to symbiotic stars is given which enables accurate spectral classification of red giants embedded in strong nebular emission.

Schild, H.; Boyle, S. J.; Schmid, H. M.

1992-09-01

11

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

NASA Astrophysics Data System (ADS)

Small-subunit ribosomal RNA (SSU rRNA) is a phylogenetically informative molecule found in all species. Because it is poorly preserved in most environments, it is a useful marker for active microbial populations. We are using the natural-abundance stable carbon isotopic composition of specific microbial groups to help identify the carbon substrates contributing to microbial biomass in a variety of marine environments. At Guaymas Basin, hydrothermal fluids interact with abundant sedimentary organic carbon to produce natural gas and petroleum. Where this reaches the sediment surface, it can support dense patches of seafloor life, including Beggiatoa mats. We report here on the stable carbon isotopic composition of SSU rRNA from a Beggiatoa mat transect, a cold background site, a warm site with high oil concentration, and a second Beggiatoa mat. The central part of the transect mat overlay the steepest temperature gradient, and was visually dominated by orange Beggiatoa. This was fringed by white Beggiatoa mat and bare, but still warm, sediment. Methane concentrations were saturating beneath the orange and white mats and at the oily site, lower beneath bare sediment, and below detection at the background site. Our initial hypotheses were that rRNA isotopic composition would be strongly influenced by methane supply, and that archaeal rRNA might be lighter than bacterial due to contributions from methanogens and anaerobic methane oxidizers. We used biotin-labeled oligonucleotides to capture Bacterial and Archaeal SSU rRNA for isotopic determination. Background-site rRNA was isotopically heaviest, and bacterial RNA from below 2 cm at the oily site was lightest, consistent with control by methane. Within the transect mat, however, the pattern was more complicated; at some sediment depths, rRNA from the mat periphery was isotopically lightest. Part of this may be due to the spatially and temporally variable paths followed by hydrothermal fluid, which can include horizontal flow. There was no consistent isotopic difference between rRNAs captured by the two probes, although RNA recoveries were too low for isotopic determinations at depths where methanogens and methane oxidizers are expected. Our prediction that rRNA stable carbon isotopic composition would correlate with methane supply was borne out by the comparison between background and mat sediments, but may be an oversimplification for sites within hydrothermal features. Future work will include the isotopic characterization of other potential carbon substrates, such as acetate. We are also investigating cold-seep sediments and brine pools in the Gulf of Mexico, where methane is significantly more 13C-depleted than at Guaymas Basin and may therefore leave a stronger imprint on microbial biomass.table carbon isotopes of rRNA captured with Bacterial and Archaeal probes at mat transect and background sites.

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

2012-12-01

12

Geographical trends of carbon and sulphur isotope abundances in human kidney stones  

NASA Astrophysics Data System (ADS)

? 13C values and ? 34S values in human kidney stones range from -24 to -10 and -10 to + 20 %., respectively, and depend upon geographical location. Although the distributions overlap, the mean ? 13C values in oxalate stones from North America become less negative with decreasing latitude. For Mexico and Hawaii, the distributions appear to be bimodal. Uric acid stones are generally enriched in 13C by up to 7%. in comparison to oxalates from the same location, whereas cystine stones tend to span the ranges of both stone types. The geographical trends can be explained by the relative proportions of dietary carbon derived ultimately from plants undergoing various established photosynthetic mechanisms (C 3, C 4, CAM). The differences among the various major stone types may reflect isotope fractionation during biochemical conversions. Exogenic oxalates and uric acid are considered to have little role in precipitating the respective minerals. Whereas, the currently available C isotope data support this contention, more data are desirable, particularly for ingested oxalates. In contrast, S isotope data provide strong evidence that cystine stones are derived from ingested organo-S compounds and bear no relation to inorganic sulphate consumed by the individual. In turn, these organic-S compounds were probably derived from sulphate in the hydrosphere at lower levels in the food chain, e.g., by bacterial assimilation.

Krouse, H. R.; Levinson, A. A.

1984-01-01

13

Lithium Isotopic Abundances in Stars  

NASA Astrophysics Data System (ADS)

The Li isotope ratio, 6Li/7Li, in stars can be determined from the isotopic shift in the Li I 670.8 nm resonance line. Because of the small effect this however requires truly precision spectroscopy: spectral resolving power R ? 105 and S/N ? 500. In this review we discuss the method and what one can learn from Li isotopic abundances in terms of Big-Bang nucleosynthesis, cosmic ray production of Li, stellar structure, and planet formation. Some instrumental problems and the need for new instrumentation are briefly discussed.

Nissen, Poul Erik; Asplund, Martin

14

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

15

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

PubMed

Several diamond drill cores from formations within the Hamersley Group of Western Australia have been studied for evidence of short-range variations in the isotopic compositions of the carbonates. For a set of 32 adjacent microbands analyzed in a specimen from the Marra Mamba Iron Formation, carbon isotope compositions of individual microbands ranged from -2.8 to -19.8 per mil compared to PDB and oxygen isotope compositions ranged from 10.2 to 20.8 per mil compared to SMOW. A pattern of alternating abundances was present, with the average isotopic contrasts between adjacent microbands being 3.0 per mil for carbon and 3.1 per mil for oxygen. Similar results were obtained for a suite of 34 microbands (in four groups) from the Bruno's Band unit of the Mount Sylvia Formation. Difficulties were experienced in preparing samples of single microbands from the Dales Gorge Member of the Brockman Iron Formation, but overall isotopic compositions were in good agreement with values reported by previous authors. Chemical analyses showed that isotopically light carbon and oxygen were correlated with increased concentrations of iron. The preservation of these millimeter-scale variations in isotopic abundances is interpreted as inconsistent with a metamorphic origin for the isotopically light carbon in the BIF carbonates. A biological origin is favored for the correlated variations in 13C and Fe, and it is suggested that the 13C-depleted carbonates may derive either from fermentative metabolism or from anaerobic respiration. A model is presented in which these processes occur near the sediment-water interface and are coupled with an initial oxidative precipitation of the iron. PMID:11539027

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

1985-01-01

16

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

17

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

18

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

NASA Astrophysics Data System (ADS)

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

Erba, E.

2005-12-01

19

Testing the use of septum-capped vials for 13C-isotope abundance analysis of carbon dioxide.  

PubMed

Studying ecosystem processes in the context of carbon cycling and climate change has never been more important. Stable carbon isotope studies of gas exchange within terrestrial ecosystems are commonly undertaken to determine sources and rates of carbon cycling. To this end, septum-capped vials ('Exetainers') are often used to store samples of CO(2) prior to mass spectrometric analysis. To evaluate the performance of such vials for preserving the isotopic integrity (delta(13)C) and concentration of stored CO(2) we performed a rigorous suite of tests. Septum-capped vials were filled with standard gases of varying CO(2) concentrations (approximately 700 to 4000 ppm), delta(13)C values (approx. -26.5 to +1.8 per thousand(V-PDB)) and pressures (33 and 67% above ambient), and analysed after a storage period of between 7 and 28 days. The vials performed well, with the vast majority of both isotope and CO(2) concentration results falling within the analytical uncertainty of chamber standard gas values. Although the study supports the use of septum-capped vials for storing samples prior to mass spectrometric analysis, it does highlight the need to ensure that sampling chamber construction is robust (air-tight). PMID:20499326

Hardie, S M L; Garnett, M H; Fallick, A E; Stott, A W; Rowland, A P; Ostle, N J

2010-06-30

20

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

21

Absolute isotopic abundances of TI in meteorites  

NASA Astrophysics Data System (ADS)

The absolute isotope abundance of Ti has been determined in Ca-Al-rich inclusions from the Allende and Leoville meteorites and in samples of whole meteorites. The absolute Ti isotope abundances differ by a significant mass dependent isotope fractionation transformation from the previously reported abundances, which were normalized for fractionation using 46Ti/48Ti. Therefore, the absolute compositions define distinct nucleosynthetic components from those previously identified or reflect the existence of significant mass dependent isotope fractionation in nature. The authors provide a general formalism for determining the possible isotope compositions of the exotic Ti from the measured composition, for different values of isotope fractionation in nature and for different mixing ratios of the exotic and normal components.

Niederer, F. R.; Papanastassiou, D. A.; Wasserburg, G. J.

1985-03-01

22

Characterizing the Spatial and Temporal Variations in Organic Carbon Abundance and Stable Isotope Ratios in Lake Sediments Containing Evidence of Prehistoric Agriculture  

NASA Astrophysics Data System (ADS)

Intra-basin spatial variability in lake sediments has the potential to limit the utility of interpretations based on the analysis of a single sediment core. We analyzed a network of five sediment cores to assess geochemical and isotopic spatial variability across a lake in southern Costa Rica. Laguna Zoncho (8.813°N, 82.963°W) provides an excellent opportunity to detect spatial variability because it is a small lake (0.75 ha) with a known history of prehistoric maize agriculture in its watershed. During the agricultural period (1770-570 cal BP) at Zoncho, stable carbon isotope values in the five cores average -23 ‰ V-PDB; these values increase to -27 ‰ V-PDB during the subsequent period of forest recovery. In prior work at the lake, this forest recovery was assumed to have been initiated by the Spanish Conquest about AD 1500, but our new findings suggest it may have occurred earlier and have been driven by a different set of circumstances. We attribute the more positive values during the agricultural period to a greater abundance of C4 vegetation in the watershed as the result of agricultural activity that removed native C3 forest vegetation and created fields and disturbed environments that favor C4 plants. Organic carbon contents during the agricultural period average 5 % and increase to an average of 16 % post-Conquest. Molar C/N ratios range from 13 during the agricultural period to 16 after the cessation of agriculture in the watershed. The cores may indicate a non-simultaneous end to agriculture in the watershed. Stable carbon isotope values and organic carbon contents in three of the four cores collected closer to shore contain evidence of an abrupt end of agriculture around 1000 cal. BP. In these cores, stable carbon isotope values indicate a dramatic shift from C4 to C3 inputs and a rapid increase in organic contents. The fourth core shows this shift around 700 cal. BP. The core recovered from the center of the lake records a gradual end to agriculture in the watershed from 1000 to 700 cal. BP, suggesting that the central core contains reworked material from refocusing of intra-basinal sediments. Spatial variations in organic carbon content and stable carbon isotopic values in a lake as small as Laguna Zoncho highlights the importance of core site selection.

Taylor, Z. P.; Finkelstein, D. B.; Horn, S. P.

2009-12-01

23

A redetermination of the isotopic abundances of atmospheric Ar  

Microsoft Academic Search

Atmospheric argon measured on a dynamically operated mass spectrometer with an ion source magnet, indicated systematically larger 40Ar\\/36Ar ratios compared to the generally accepted value of Nier [Nier A.O., 1950. A redetermination of the relative abundances of the isotopes of carbon, nitrogen, oxygen, argon, and potassium. Phys. Rev. 77, 789–793], 295.5±0.5, which has served as the standard for all isotopic

Jee-Yon Lee; Kurt Marti; Jeffrey P. Severinghaus; Kenji Kawamura; Hee-Soo Yoo; Jin Bok Lee; Jin Seog Kim

2006-01-01

24

The carbon abundance and 12C/13C isotopic ratio in the atmosphere of Arcturus from 2.3 µm CO bands  

NASA Astrophysics Data System (ADS)

We have modeled absorption lines of the 12CO and 13CO (? ? = 2) molecular bands at ?? 2.29 2.45 µm in the spectrum of Arcturus (K2III). A grid of model atmospheres and synthetic spectra were computed for the red giant using T eff = 4300, log g = 1.5, and the elemental abundances of Peterson et al. (1993), with the exception of the abundances of carbon, log N(C), and oxygen, log N(O) and the carbon isotopic ratio, 12C/13C, which were varied in our computations. The computed spectra were compared to the observed spectrum of Arcturus from the atlas of Hinkle et al. (1976). The best fit between the synthetic and observed spectra is achieved for log N(C) = -3.78, 12C/13C = 8 ± 0.5. We discuss the dependence of 12C/13C on log N(C) and log N(O) in the atmosphere of the red giant.

Pavlenko, Ya. V.

2008-09-01

25

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

NASA Astrophysics Data System (ADS)

The Lau Basin has multiple mantle source components including contributions from the Indian and Pacific MORB sources, Tonga-Kermadec Arc and Samoan plume. In order to characterize the volatile systematics of these various sources and to map their spatial distribution, we have sampled basaltic glasses from over 50 dredge sites covering all known spreading centers in the basin as well as many off-axis seamounts. Here, we report He abundance and isotope results obtained by crushing, in addition to CO2 released through stepped heating, from sites at the Mangatolu Triple Junction (MTJ), Rochambeau Bank (RB), Peggy Ridge, and the Northern, Eastern and Central Lau Spreading Centers. High 3He/4He ratios from RB (up to 23 RA, where RA = air 3He/4He) confirm the presence of a plume component in the northwestern Lau Basin (Poreda, EPSL, 1985). Central and Eastern Lau Spreading Center basalts have 3He/4He ratios between 8.3 and 9.4 RA, consistent with a depleted, MORB-like mantle source with little influence from slab or crustal helium. In contrast, the large range in helium isotope ratios of MTJ samples (0.85 to 7.9 RA) and the correlation between low He abundances (~2 - 3 × 10-9 cm3/g) and low helium isotope ratios suggests the volatiles in this region have been severely affected by degassing and additions of radiogenic (crustal) He. CO2 abundances and carbon isotopes for samples from RB vary from 70 to 119 ppm ([CO2]total) with ?13Cvesicle falling between -12.3 to -14.8 ‰ and ?13Cdissolved lying between -9.3 to -10.7 ‰. In the MTJ, low helium concentration samples have ?13C as low as -27.4 ‰ and [CO2]total as low as 7.6ppm; interestingly, this region also has samples with the highest measured values (up to -6.3 ‰ and 132ppm total C). Combining the carbon and helium data, CO2/3He ratios in the MTJ range from arc-like values (~1010) to sediment or crustal values (~1013) showing the superimposition of degassing and/or contamination effects on a predominant slab-like signature. High 3He/4He samples from RB have CO2 /3He ratios similar to the upper mantle value (2 × 109), as at other back-arc localities exhibiting a high 3He/4He (plume) component (e.g. the Manus Basin; Shaw et al., GCA, 2004). Continuing analytical work will complete our He-C survey of the Lau Basin, identifying samples suitable for further effort involving Ne, Ar, H2O plus other tracers of interest. Presently, we are modeling degassing/contamination effects to identify the nature and distribution of mantle source components throughout the Lau Basin. The volatile characteristics of the high 3He/4He samples are of particular interest as they provide insight into the different recycling and storage histories of volatiles between distinct mantle reservoirs.

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

2005-12-01

26

ISOTOPIC TITANIUM ABUNDANCES IN LOCAL M DWARFS  

SciTech Connect

Relative abundances of the five stable isotopes of titanium ({sup 46}Ti to {sup 50}Ti) are measured for 11 M dwarfs belonging to the thin disk (four stars), thick disk (three stars), the halo (one star), and either the thick or the thin disk (three stars). Over the metallicity range of the sample (-1< [Fe/H] <0), the isotopic ratios are approximately constant at the solar system ratios. There is no discernible difference between the isotopic ratios for thin and thick disk stars. Isotopic ratios are in fair accord with recent calculations of Galactic chemical evolution despite the fact that such calculations underpredict [Ti/Fe] by about 0.4 dex at all metallicities.

Chavez, Joy [Department of Astronomy, University of Texas, 1 University Station, C1400 Austin, TX 78712-0259 (United States); Lambert, David L. [McDonald Observatory, University of Texas at Austin, 1 University Station, C1402 Austin, TX 78712-0259 (United States)], E-mail: jchavez@astro.as.utexas.edu, E-mail: dll@astro.as.utexas.edu

2009-07-10

27

Carbon isotope techniques  

SciTech Connect

This book is a hands-on introduction to using carbon isotope tracers in experimental biology and ecology. It is a bench-top reference with protocols for the study of plants, animals, and soils. The {sup 11}C, {sup 12}C, {sup 13}C, and {sup 14}C carbon isotopes are considered and standard techniques are described by established authors. The compilation includes the following features: specific, well-established, user-oriented techniques; carbon cycles in plants, animals, soils, air, and water; isotopes in ecological research; examples and sample calculations.

Coleman, D.C. (ed.) (Univ. of Georgia, Athens (United States)); Fry, B. (ed.) (Marine Biological Lab., Woods Hole, MA (United States))

1991-01-01

28

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

EPA Science Inventory

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

29

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

30

The abundance of 13 C in marine organic matter and isotopic fractionation in the global biogeochemical cycle of carbon during the past 800 Ma  

Microsoft Academic Search

New records of the abundance of 13C in marine organic matter have been compiled for (i) the later Neoproterozoic, from 800 to 543 Ma (346 analyses), (ii) the Cambrian through the Jurassic (1616 analyses), and (iii) the Cretaceous and Cenozoic (2493 analyses). Comparison of these to existing compilations of the abundance of 13C in sedimentary carbonates has allowed development of

John M. Hayes; Harald Strauss; Alan J. Kaufman

1999-01-01

31

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

32

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

NASA Astrophysics Data System (ADS)

We report H and C contents and ?D and ? 13C values of apatites from 15 alkaline intrusive complexes ranging in age from 110 Ma to 2.6 Ga. Sampling focused on carbonatites, but included silicate rocks as well. Heating at temperatures up to 1500°C is needed to extract fully H 2O and CO 2 from these apatites. Apatites from carbonatite-rich intrusive complexes contain 0.2-1.1 wt% H 2O and 0.05-0.70 wt% CO 2; apatites from two silicate-rich alkaline complexes with little or no carbonatite are generally poorer in both volatile components (0.1-0.2% H 2O and 0.01-0.11% CO 2). D/H ratios in apatites from these rocks are bimodally distributed: group I (?D = -51 to -74‰) and group II (?D = -88 to -104‰). We suggest that the ?D values of group I apatites represent primitive, mantle-derived values and that the group II apatites crystallized from degassed magmas, resulting in lower H 2O contents and ?D values. Although many factors influence the extent of degassing, the depth of emplacement could represent a major control. In contrast to H 2O contents and ?D values, CO 2 contents and ? 13C values of gas released at high temperatures from multiple aliquots of these apatite samples are variable. This suggests the presence of more than one C-bearing component in these apatites, one of which is proposed to be dissolved carbonate; the other, with ? 13C ˜<-25‰, could be associated with hydrocarbons. Group I apatites have ?D values similar to those of primitive, mantle-derived basaltic magmas and overlap with (but cover a narrower range than) mantle-derived mica, amphibole, and whole rocks. ? 13C values also overlap typical upper mantle. These results suggest that igneous apatites can retain their primary ?D and ? 13C values.

Nadeau, Serge L.; Epstein, Samuel; Stolper, Edward

1999-06-01

33

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.

Stephen C. Piper; Ralph F. Keeling

2012-01-03

34

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

35

Accumulation and isotopic evolution of carbon on the lunar surface  

NASA Technical Reports Server (NTRS)

The processes of hydrogen stripping, agglutination and impact comminution, acting upon a regolith containing both indigenous and solar wind-implanted carbon, provide a quantitative explanation for the relationship between carbon abundance and isotopic composition observed for Apollo 16 soils.

Kerridge, J. F.; Kaplan, I. R.; Lesley, F. D.

1974-01-01

36

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

Microsoft Academic Search

238U and 232Th concentrations and the extent of 238U-234U-230Th radioactive equilibrium have been measured in a suite of Precambrian carbonates and black shales from the Lesser Himalaya. These measurements were made to determine their abundances in these deposits, their contributions to dissolved uranium budget of the headwaters of the Ganga and the Indus in the Himalaya and to assess the

S. K. Singh; Tarun K. Dalai; S. Krishnaswami

2003-01-01

37

A Redetermination of the Relative Abundances of the Isotopes of Neon, Krypton, Rubidium, Xenon, and Mercury  

Microsoft Academic Search

A careful redetermination of isotopic abundance ratios in neon, krypton, rubidium, xenon, and mercury has been made. The mass spectrometer employed was calibrated for mass discriminative effects with a synthetic argon isotope mixture made from essentially pure samples of A36 and A40. The present results together with those obtained from an earlier study on carbon, nitrogen, oxygen, argon, and potassium

Alfred O. Nier

1950-01-01

38

Carbon isotopic composition of atmospheric methane  

Microsoft Academic Search

Recent measurements of the carbon isotopic abundance of atmospheric methane give a value of delta(¹³C\\/¹²C) = -47.0 +- 0.3%â, which is significantly different from earlier values measured by others between 1950 and 1970. The isotopic composition of various sources and the possibility of a temporal trend are discussed. The average methane concentration measured was 1.66 ppm, which is in accord

C. M. Stevens; F. E. Rust

1982-01-01

39

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

40

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

PubMed

238U and (232)Th concentrations and the extent of (238)U-(234)U-(230)Th radioactive equilibrium have been measured in a suite of Precambrian carbonates and black shales from the Lesser Himalaya. These measurements were made to determine their abundances in these deposits, their contributions to dissolved uranium budget of the headwaters of the Ganga and the Indus in the Himalaya and to assess the impact of weathering on (238)U-(234)U-(230)Th radioactive equilibrium in them. (238)U concentrations in Precambrian carbonates range from 0.06 to 2.07 microg g(-1). The 'mean' U/Ca in these carbonates is 2.9 ng U mg(-1) Ca. This ratio, coupled with the assumption that all Ca in the Ganga-Indus headwaters is of carbonate origin and that U and Ca behave conservatively in rivers after their release from carbonates, provides an upper limit on the U contribution from these carbonates, to be a few percent of dissolved uranium in rivers. There are, however, a few streams with low uranium concentrations, for which the carbonate contribution could be much higher. These results suggest that Precambrian carbonates make only minor contributions to the uranium budget of the Ganga-Indus headwaters in the Himalaya on a basin wide scale, however, they could be important for particular streams. Similar estimates of silicate contribution to uranium budget of these rivers using U/Na in silicates and Na* (Na corrected for cyclic and halite contributions) in river waters show that silicates can contribute significantly (approximately 40% on average) to their U balance. If, however, much of the uranium in these silicates is associated with weathering resistant minerals, then the estimated silicate uranium component would be upper limits. Uranium concentration in black shales averages about 37 microg g(-1). Based on this concentration, supply of U from at least approximately 50 mg of black shales per liter of river water is needed to balance the average river water U concentration, 1.7 microg L(-1) in the Ganga-Indus headwaters. Data on the abundance and distribution of black shales in their drainage basin are needed to test if this requirement can be met. (234)U/(238)U activity ratios in both carbonates and black shales are at or near equilibrium, thus preferential mobilization of (234)U from these deposits, if any, is within analytical uncertainties. (230)Th is equivalent to or in excess of (238)U in most of the carbonates. (230)Th/(238)U>1 indicates that during weathering, uranium is lost preferentially over Th. (232)Th concentrations in carbonates are generally quite low, <0.5 microg g(-1), though with a wide range, 0.01-4.8 microg g(-1). The variation in its concentrations seem to be regulated by aluminosilicate content of the carbonates as evident from the strong positive correlation between (232)Th and Al. PMID:12634002

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

2003-01-01

41

Ce isotope abundance in chondritic and HED meteorites  

NASA Astrophysics Data System (ADS)

138La, 136Ce and 138Ce are p-process nuclides, and their isotopic abundances are generally low due to their modes of nucleosynthesis compared with other isotopes of La and Ce (139La, 140Ce and 142Ce). Tanimizu et al. (2004) mentioned that, using the 140Ce/142Ce ratio as the normalizing value, 136Ce isotope abundance could be acted as an indicator of p-process nuclide anomaly for extra-terrestrial materials to understand the nucleosynthetic origins of solar system matter. Then, meteoritic primordial composition of Ce isotope provides useful information related with 138La decay system. Especially, combined Ce/Nd isotope data in geological and cosmological materials enable us the modeling of the light REE profiles of the source material. We measured Ce isotope ratio for fifteen meteorites, using 140Ce/142Ce=7.941 as the normalizing value, in order to compare Ce isotope abundance between chondritic and HED meteorites. Of them, Ce isotope abundances from two chondritic meteorites were deviated from the average abundances of other 13 meteorites. In this report, we will discuss cosmochemical significance of Ce isotope anomaly.

Lee, S.; Asahara, Y.; Tanaka, T.; Lee, S. R.

2011-12-01

42

A large area experiment to determine cosmic ray isotopic abundances  

NASA Technical Reports Server (NTRS)

Measurements of the isotopic composition of cosmic rays have shown that the cosmic ray isotope ratios, Ne-22/Ne-20 and (Mg-25 + Mg-26)/Mg-24, exceed the solar abundance ratios by factors of 2.7 and 1.8, respectively. There are several processes which could be responsible for the observed excess of neutron-rich isotopes. The considered models imply neutron enrichment in the case of other, less abundant species, and a measurement of the involved isotopic abundances could provide a basis for the determination of the dominating processes occurring in cosmic ray sources. However, an experiment utilizing special equipment is necessary to conduct the required measurements. Such an experiment, the Aluminum Isotopic Composition Experiment (Alice), is being designed in a joint effort involving NASA and a West German university. Alice uses a Cherenkov-range technique to determine the isotopic composition of elements from oxygen through argon.

Mauger, B. G.; Balasubrahmanyan, V. K.; Ormes, J. F.; Streitmatter, R. E.; Heinrich, W.; Simon, M.; Tittel, H. O.

1983-01-01

43

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 ...

44

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

45

Organic chemistry of Murchison meteorite: Carbon isotopic fractionation  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

46

Stable Isotopes in Foraminiferal Carbonate  

Microsoft Academic Search

Analyses of stable oxygen and carbon isotopes from foraminiferal shells have played a pivotal role in palaeoceanography since Emiliani (1955) interpreted the isotopic record from deep-sea cores as a series of Pleistocene climate\\/temperature cycles. Oxygen isotope stratigraphy has become a global correlation tool, and an established dating tool. The primary ice-volume control on (benthic) oxygen isotope records has led to

Steve Cooke; Eelco J. Rohling

47

Silicon Reference Materials Certified for Isotope Abundances.  

National Technical Information Service (NTIS)

In a series of gas mass-spectrometric measurements performed near the highest attainable accuracy, samples from two highly homogeneous batches of silicon crystals and silica powder were compared directly with a synthetic mixture of the three stable isotop...

S. Valkiers P. De Bievre G. Lenaers H. S. Peiser

1991-01-01

48

Elemental Abundance Analysis in Carbon Stars  

NASA Astrophysics Data System (ADS)

We present an analysis of the elemental abundances of carbon, nitrogen, and oxygen in three carbon stars (TX Psc, BL Ori, and V Aql), based on high-resolution infrared spectra. We first compute a grid of model atmospheres in which the effect of molecular absorption is incorporated, using the Band Model method (Tsuji 1994). With the interplay between the atmospheric structure and the chemical composition properly taken into account, we determine the elemental abundances self-consistently. The derived abundances are discussed from a viewpoint of the nucleosynthesis in AGB stars. The oxygen abundances in the three stars are solar or slightly subsolar, showing fairly good agreement with the result by Lambert et al. (1986). However, the carbon abundances derived here show marked disagreement with those derived by Lambert et al: carbon abundance is higher than their result, therefore, C/O ratios are higher than believed. The 12C/13C ratios derived in our previous work (Ohnaka & Tsuji 1996) and the C/O ratios derived here show a very clear correlation. It strongly supports the scenario in which K and M giants evolve to carbon stars by addition of 12C synthesized in thermal pulses.

Ohnaka, K.; Tsuji, T.

49

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

50

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

PubMed

The stable isotope composition of dissolved organic carbon (delta(13)C-DOC) provides powerful information toward understanding carbon sources and cycling, but analytical limitations have precluded its routine measurement in natural samples. Recent interfacing of wet oxidation-based dissolved organic carbon analyzers and isotope ratio mass spectrometers has simplified the measurement of delta(13)C-DOC in freshwaters, but the analysis of salty estuarine/marine samples still proves difficult. Here we describe the coupling of the more widespread high-temperature catalytic oxidation-based total organic carbon analyzer to an isotope ratio mass spectrometer (HTC-IRMS) through cryogenic trapping of analyte gases exiting the HTC analyzer for routine analysis of delta(13)C-DOC in aquatic and marine samples. Targeted elimination of major sources of background CO2 originating from the HTC analyzer allows for the routine measurement of samples over the natural range of DOC concentrations (from 40 microM to over 2000 microM), and salinities (<0.1-36 g/kg). Because consensus reference natural samples for delta(13)C-DOC do not exist, method validation was carried out with water-soluble stable isotope standards as well as previously measured natural samples (IAEA sucrose, Suwannee River Fulvic Acids, Deep Sargasso Sea consensus reference material, and St. Lawrence River water) and result in excellent delta(13)C-DOC accuracy (+/-0.2 per thousand) and precision (+/-0.3 per thousand). PMID:18529015

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

2008-07-01

51

Carbon isotopes in mollusk shell carbonates  

Microsoft Academic Search

Mollusk shells contain many isotopic clues about calcification physiology and environmental conditions at the time of shell\\u000a formation. In this review, we use both published and unpublished data to discuss carbon isotopes in both bivalve and gastropod\\u000a shell carbonates. Land snails construct their shells mainly from respired CO2, and shell ?13C reflects the local mix of C3 and C4 plants

Ted A. McConnaughey; David Paul Gillikin

2008-01-01

52

Interstellar Carbon Abundances Along Translucent Sightlines  

NASA Astrophysics Data System (ADS)

We report interstellar C ii column densities or upper limits determined from weak absorption of the ? 2325.403Å intersystem transition in 6 translucent sightlines (AV > ˜ 1) observed with STIS. Carbon abundances are essential for understanding the ISM because, depending on whether it is in the gas or dust, interstellar C may play substantial roles in heating or cooling, molecular chemistry and extinction. Singly ionized carbon is an important species to measure because it represents the dominant ion state of this abundant element in neutral interstellar regions. The eight previous absorption measurements of interstellar C ii, seven in diffuse sightlines and one in a translucent sightline, have been consistent with a single gas-phase carbon-to-hydrogen ratio. Carbon, however, should be more readily incorporated into dust in denser interstellar regions. The targets observed for this study were chosen to maximize the chance of finding variation in the interstellar gas-phase C/H; enhanced oxygen depletions (compared to diffuse sightlines) have previously been found toward each of the stars. We find that carbon in forms other than C ii is usually insignificant, although one sightline may show a substantial abundance of excited C ii. This work is supported by grants from the Space Telescope Science Institute to Whitman College and Northwestern University.

Sofia, U. J.; Lauroesch, J. T.; Meyer, D. M.; Cartledge, S. I. B.

2003-12-01

53

(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

54

Decrease in Carbon Isotope Rations  

NSDL National Science Digital Library

This three-panel figure is an infographic showing how carbon and oxygen isotope ratios, temperature, and carbonate sediments have changed during the Palaeocene-Eocene Thermal Maximum. The figure caption provides sources to scientific articles from which this data was derived. A graphic visualization from the Intergovernmental Panel on Climate Change shows the rapid decrease in carbon isotope ratios that is indicative of a large increase in the atmospheric greenhouse gases CO2 and CH4, which was coincident with approximately 5C of global warming.

Intergovernmental Panel on Climate Change (IPCC)

55

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

56

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

57

Literature Survey on Isotopic Abundance Ratio Measurements 2001-2005.  

National Technical Information Service (NTIS)

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 Rese...

N. E. Holden

2005-01-01

58

Report on carbon and nitrogen abundance studies  

NASA Technical Reports Server (NTRS)

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

Boehm-Vitense, Erika

1991-01-01

59

Carbon and nitrogen isotopic analysis of atmospheric organic matter  

NASA Astrophysics Data System (ADS)

A new method is presented to analyse the isotopic abundance of organic matter in aerosols. The method involves water extraction of aerosol filters, elution through an ion retardation resin to remove inorganic components and lyophilising the eluent to concentrate the fraction prior to isotopic analysis. Results of analyses of a series of aerosol samples collected in the UK, for the fraction of organic matter passing through the resin, are presented. Carbon and nitrogen isotopic abundances ranged from -23.0‰ to -35.5‰ (versus PDB) and -14.6‰ to +12.5‰ (versus AIR), respectively.

Kelly, S. D.; Stein, C.; Jickells, T. D.

60

The carbon monoxide abundance in interstellar clouds  

NASA Technical Reports Server (NTRS)

The steady-state abundance of carbon monoxide in interstellar clouds is calculated as a function of optical depth, density, and temperature. The molecular reactions which lead to CO can be initiated by the following ion-molecule reactions: H(+) + O yields O(+) + H, C(+) + H2 yields CH2(+) + a photon, and H3(+) + C and O. As the ultraviolet radiation field is attenuated, C(+) is transformed primarily into CO and C I. There are characteristic column densities for the transition to CO corresponding to the optical depths for attenuating this field at different wavelengths. For thick, low-temperature clouds the attenuation of the fields which ionize carbon, sulfur, and heavy metals is important for CO production initiated by H3(+). Complete conversion to CO does not necessarily occur, and considerable neutral carbon may be expected even in optically thick clouds. Comparison of integrated column densities of CO with extinction are in reasonable agreement with observations.

Langer, W.

1976-01-01

61

Stable Carbon and Nitrogen Isotopic  

Microsoft Academic Search

The perennially ice-covered lakes in the McMurdo Dry Valleys, Antarctica, are part of the coldest and driest ecosystem on earth. To understand lacustrine carbon and nitrogen cycling in this end-member ecosystem, and to define paleolimnological proxies for ice-covered lakes, we measured the stable carbon and nitrogen isotopic composition of particulate organic matter (POM) and benthic organic matter (BOM) within the

Jennifer Lawson; PETER T. DORAN; Fabien Kenig; DAVID J. DES MARAIS; JOHN C. PRISCU

2004-01-01

62

Isotopic Abundances as Tracers of the Processes of Lunar Formation  

NASA Astrophysics Data System (ADS)

Ever since Apollo, isotopic abundances have been used as tracers to study lunar formation, in particular, to study the sources of the lunar material. In the last decade, however, a number of isotopic similarities have been observed between the lunar samples and the Earth's mantle such that these two reservoirs are now known to be indistinguishable from one another to high precision for a variety of isotopic tracers. This occurs against the backdrop of a Solar System that exhibits widespread heterogeneity with respect to these tracers, a situation that strongly argues that the source of the lunar material is the silicate Earth. To reconcile this observation with the fact that the Moon is thought to result from the collision of two isotopically distinct planetary bodies, a scenario has emerged in which the material from the Moon-forming impactor and the proto-Earth are homogenized in the aftermath of the giant impact. This takes place via turbulent mixing in the time after the giant impact but before lunar accretion while the Earth-Moon system exists in the form of a continuous, high-temperature fluid. Importantly, this high-temperature phase of the evolution occurs in the presence of at least two phases (liquid + vapor) making possible chemical and isotopic fractionation. While equilibrium isotopic fractionation tends to zero at high temperatures, and the post giant impact environment experiences some of the highest temperatures encountered in the Earth sciences, there are several factors that nevertheless make equilibrium isotope effects important probes of this early evolution. (1) Because the vaporization of silicates involves decomposition reactions, the bonding environment for elements in the liquid is often very different from that in the vapor. This difference makes the magnitude of isotopic fractionation intrinsically large, even at the relevant temperatures. (2) Since the isotopic composition of a silicate liquid and co-existing vapor are distinctly different, if the Moon preferentially forms from the liquid or vapor relative to the Earth, mass-dependent isotopic differences at the planetary scale may arise. The large density contrast between liquid and vapor makes phase separation possible. (3) The precision with which planetary isotopic compositions can be determined has increased such that measurements are sensitive to even small degrees of high-temperature phase separation. Using thermodynamic models of silicate liquids to determine the partial vaporization behavior of the major elements, we will present calculations of isotopic fractionation due to liquid-vapor separation for the elements iron, magnesium, silicon, and oxygen. Improvements in analytical precision have largely settled the question of the source of the lunar material - the Earth's mantle - and isotopic measurements are now beginning to yield insight into the high-temperatures processes operating during lunar formation.

Pahlevan, K.

2011-12-01

63

Automated determination of silicon isotope natural abundance by the acid decomposition of cesium hexafluosilicate.  

PubMed

A procedure for the automated determination of isotopic abundances of silicon from biogenic and lithogenic particulate matter and from dissolved silicon in fresh or saltwaters is reported. Samples are purified using proven procedures through the reaction of Si with acidified ammonium molybdate, followed by precipitation with triethylamine and combustion of the precipitate to yield silicon dioxide. The silicon dioxide is converted to cesium hexafluosilicate by dissolution in hydrogen fluoride and the addition of cesium chloride. Isotopic analysis is accomplished by decomposing the cesium hexafluosilicate with concentrated sulfuric acid to generate silicon tetrafluoride gas. Silicon tetrafluoride is purified cryogenically and analyzed on a gas source isotope ratio mass spectrometer. Yields of silicon tetrafluoride are >99.5%. The procedure can be automated by modifying commercial inlet systems designed for carbonate analysis. The procedure is free of memory effects and isotopic biases. Reproducibility is +/-0.03-0.10 per thousand for a variety of natural and synthetic materials. PMID:16944891

Brzezinski, Mark A; Jones, Janice L; Beucher, Charlotte P; Demarest, Mark S; Berg, Howard L

2006-09-01

64

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

PubMed

Subtle variations in the isotopic composition of elements carry unique information about physical and chemical processes in nature and are now exploited widely in diverse areas of research. Reliable measurement of natural isotope abundance variations is among the biggest challenges in inorganic mass spectrometry as they are highly sensitive to methodological bias. For decades, double spiking of the sample with a mix of two stable isotopes has been considered the reference technique for measuring such variations both by multicollector-inductively coupled plasma mass spectrometry (MC-ICPMS) and multicollector-thermal ionization mass spectrometry (MC-TIMS). However, this technique can only be applied to elements having at least four stable isotopes. Here we present a novel approach that requires measurement of three isotope signals only and which is more robust than the conventional double spiking technique. This became possible by gravimetric mixing of the sample with an isotopic spike in different proportions and by applying principles of isotope dilution for data analysis (GS-IDA). The potential and principle use of the technique is demonstrated for Mg in human urine using MC-TIMS for isotopic analysis. Mg is an element inaccessible to double spiking methods as it consists of three stable isotopes only and shows great potential for metabolically induced isotope effects waiting to be explored. PMID:23419016

Chew, Gina; Walczyk, Thomas

2013-04-01

65

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

66

Isotopic r-process abundances produced by supernova explosions  

NASA Astrophysics Data System (ADS)

The rapid neutron capture process (r-process) is one of the major nucleosynthesis processes responsible for the synthesis of heavy nuclei beyond iron. Isotopes beyond Fe are most exclusively formed in neutron capture processes and more heavier ones are produced by the r-process. Approximately half of the heavy elements with mass number A>70 and all of the actinides in the solar system are believed to have been produced in the r-process. We have studied the r-process in supernovae for production of heavy elements beyond A=40 with the newest mass values available. The supernovae envelopes at a temperature >109 K and neutron density of 1024 cm-3 are considered to be one of the most potential sites for the r-process. We investigate the r-process in a site-independent, classical approach which assumes a chemical equilibrium between neutron captures and photodisintegrations followed by a ?-flow equilibrium. We have studied the r-process path corresponding to temperatures ranging from 1.0×109 K to 3.0×109 K and neutron density ranging from 1020 cm-3 to 1030 cm-3. The primary goal of the r-process calculations is to fit the global abundance curve for solar system r-process isotopes by varying time dependent parameters such as temperature and neutron density. This method aims at comparing the calculated abundances of the stable isotopes with observation. The abundances obtained are compared with supernova explosion condition and found in good agreement. The elements obtained along the r-process path are compared with the observed data at all the above temperature and density range.

Baruah, Rulee; Duorah, Kalpana; Duorah, H. L.

2012-08-01

67

Carbon isotope fractionation in wood during carbonization  

NASA Astrophysics Data System (ADS)

A significant uncertainty exists as to whether ? 13C values in charcoal meaningfully represent the stable isotopic content of the original material, with studies suggesting variable responses to both natural and laboratory heating. An extensive study was undertaken using fully homogenised samples of wood taken from Eucalyptus spp., Quercus robur and Pinus radiata. The results demonstrate that the duration of heating had no tangible effect on the final composition of the charred material, with the ? 13C and carbon content of wood fixed after 30 min of heating. Furthermore, all three wood types become progressively depleted in 13C with increasing temperature. The results demonstrate that even at temperatures commonly reached in natural fires (<450 °C) isotopic fractionation of up to 1.3‰ can take place indicating that the absolute values obtained from charcoal extracted for paleoenvironmental reconstruction must be interpreted with caution.

Turney, C. S. M.; Wheeler, D.; Chivas, Allan R.

2006-02-01

68

Elemental and isotopic abundances in the solar wind  

NASA Technical Reports Server (NTRS)

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

Geiss, J.

1972-01-01

69

Carbon isotopic composition of Amazon shelf sediments  

SciTech Connect

The distribution of carbon isotopes in Amazon shelf sediment is controlled by the same processes that are forming the modern subaqueous delta. The terrestrial (-27 to -25 per thousand) isotopic carbon signal observed in surficial sediments near the river mouth extends over 400 km northwest along the shelf. Terrestrial carbon is associated with areas of rapid sediment accumulation (topset and foreset regions). A sharp boundary between terrestrial (-27 to -25 per thousand) and marine (-23 to -22 per thousand) isotopic carbon values in surficial sediments is associated with a change in depositional conditions (foreset to bottomset regions) and a decrease in sediment accumulation rate. POC water-column isotopic values (-27 per thousand) near the river mouth are similar to the underlying surficial-sediment TOC isotopic values, but POC water-column samples collected 20 km off the river mouth have marine carbon isotopic values (-22 to -19 per thousand) and differ from the underlying surficial-sediment TOC isotopic values. These water column observations are related to variations in turbidity and productivity. Down-core isotopic variation is only observed in cores taken in areas of lower sediment accumulation rates. These observations indicate that the organic carbon in Amazon shelf sediment is dominantly terrestrial in composition, and the location of deposition of this carbon is controlled by modern processes of sediment accumulation. The modern Amazon shelf is similar to large clinoform shale deposits of the Cretaceous in North America. Thus, the stratigraphic setting may help predict the isotopic variations of carbon in ancient deposits.

Showers, W.J.; Angle, D.G.; Nittrouer, C.A.; Demaster, D.J.

1985-02-01

70

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

71

Biomarker and Carbon Isotope Signals from Leaf to Terrestrial Archive  

NASA Astrophysics Data System (ADS)

Biomarker and isotopic signatures of terrestrial organic matter are increasingly used to discern organic matter provenance in transport systems as well as to reconstruct environmental conditions of ancient landscapes. Such tools help scholars evaluate river transport and the influence of climate on terrestrial biomass and soil carbon, the largest reduced carbon inventories within the global surface environment. These signals reflect isotopic fractionation during photosynthesis and the abundance and composition of plant lipids, which are ultimately influenced by plant community, ecosystem structure and climate. Case studies and literature data for plants, biomarkers, litter carbon and soil organic matter refine the framework for evaluating and interpreting ancient terrestrial environments. Such studies reveal isotopic and biomarker patterns primarily track woody cover and moisture gradients in ancient landscapes. This emerging approach is currently limited by a lack of supporting and critical information about carbon isotopic differences between lipids and leaves, which appear to vary with environment as well as plant type. Environmental reconstructions and carbon-cycle studies are also limited by incomplete understanding of carbon isotopic relationships between modern litter, mineral soil, leaf waxes, and ancient archives of these properties. The net imprint of diagenesis on bulk carbon archives can potentially be constrained with companion biomarker studies, provided biomass production, litter delivery and lipid isotopic characteristics are constrained. Soil organic matter isotopic diagenesis is not fully understood, especially on geologic timescales, but appears to vary with both climate and ecosystem properties. This presentation will highlight recent findings and current knowledge gaps in understanding biomarker and ancient soil organic carbon as landscape tracers of past vegetation and climate.

Freeman, K. H.

2012-12-01

72

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

73

Carbon isotope effects associated with aceticlastic methanogenesis  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

74

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

75

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

76

Carbon isotope effects associated with autotrophic acetogenesis  

USGS Publications Warehouse

The carbon kinetic isotope effects associated with synthesis of acetate from CO2 and H2 during autotrophic growth of Acetobacterium woodii at 30??C have been measured by isotopic analyses of CO2, methyl-carbon, and total acetate. Closed systems allowing construction of complete mass balances at varying stages of growth were utilized, and the effects of the partitioning of carbon between CO2 and HCO3- were taken into account. For the overall reaction, total carbonate ??? total acetate, isotope effects measured in replicate experiments ranged from -59.0 ?? 0.9% to - 57.2 ?? 2.3z%. Taking into account all measurements, the weighted mean and standard deviation are -58.6 ?? 0.7%. There is no evidence for intramolecular ordering in the acetate. The carbon isotopic composition of sedimentary acetate, otherwise expected to be near that of sedimentary organic carbon, is likely to be depleted in environments in which autotrophic acetogenesis is occurring. ?? 1989.

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

1989-01-01

77

Total carbon and sulfur abundances in Antarctic meteorites  

NASA Technical Reports Server (NTRS)

Total carbon and sulfur abundances have been measured in five Antarctic meteorites. Two C2 carbonaceous chondrites Yamato 74662 and Allan Hills 77306 have sulfur abundances (3.490 plus or minus .040% and 3.863 plus or minus 0.050% respectively) similar to other C2 chondrites but their carbon abundances (1.514 plus or minus 0.050% and 1.324 plus or minus .040% respectively) are lower than previously measured C2 chondrites. The decreased carbon abundances may reflect the effects of weathering in cold environments. Carbon and sulfur abundances for one C4 carbonaceous chondrite, one E4 enstatite chondrite and one ureilite are similar to values reported previously for meteorites of the same petrologic grades.

Gibson, E. K., Jr.; Yanai, K.

1979-01-01

78

A NEW CALCULATION FOR THE AGE OF THE EARTH FROM ABUNDANCES OF LEAD ISOTOPES  

Microsoft Academic Search

A new method, basically distinct from the two most common methods, is ; suggested for calculating the age of the Earth from lead isotope abundances. In ; common with other methods, the new method assumes that the samples used in the ; calculation can be interpreted by equations appropriate to evolution of the lead ; isotope abundances in a single

R. G. Ostic; R. D. Russell; P. H. Reynolds

1963-01-01

79

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

80

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

81

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

82

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

83

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

84

Carbon isotopic characterization of hydrophobic dissolved organic carbon in rainwater  

NASA Astrophysics Data System (ADS)

The 14C and 13C content of the hydrophobic fraction (C18 extractable) of dissolved organic carbon (DOC) in Wilmington North Carolina USA rainwater was determined for six rain events to elucidate potential sources. A two end member mass-balance calculation indicated that 42-61% of the hydrophobic DOC was of fossil fuel origin compared to previously published values (4-24%) for bulk rain DOC indicating a strong anthropogenic contribution to the hydrophobic component. All fossil fuel derived organic carbon in the bulk DOC (˜15% fossil fuel derived) could be accounted for in the hydrophobic fraction (˜52% fossil fuel derived) which represents approximately 1/3 of the bulk DOC. The ?13C values of the hydrophobic DOC were consistent (-28.8 ± 0.9‰) similar to that for terrestrial and fossil fuel derived organic carbon. This is in contrast to previously published bulk rain DOC ?13C values that displayed a strong influence of air-mass back-trajectory with ?13C values ranging from -20.8‰ (typical of marine organic carbon) for marine air-mass back-trajectory rain to -28.2‰ (typical of terrestrial or fossil fuel derived organic carbon) for terrestrial air-mass back-trajectory rain. The combination of 14C and 13C isotopic data strongly suggests that a large fraction of hydrophobic organic material in rain comes from incompletely combusted fossil fuels. Changes in energy usage patterns and efforts to reduce fossil fuel emissions will alter the abundance of this hydrophobic material in the atmosphere which may impact the spectral distribution of sunlight reaching the earth's surface as well as the degree of oceanic primary productivity.

Avery, G. Brooks; Biswas, K. Farhana; Mead, Ralph; Southwell, Melissa; Willey, Joan D.; Kieber, Robert J.; Mullaugh, Katherine M.

2013-04-01

85

Carbon abundances of sdO stars from SPY  

NASA Astrophysics Data System (ADS)

Ströer et al. (2007) recently suggested a classification of sdOs according to supersolar and subsolar helium abundances, with only the helium-enriched stars showing signes of carbon and/or nitrogen in their optical spectra. We aim to derive reliable carbon and nitrogen abundances by fitting synthetic spectra to data obtained with the UVES spectrograph at ESO. Here we present our first results of the analysis of carbon abundances in hot subdwarf O stars. By constructing a grid of model atmospheres consisting of hydrogen, helium and carbon we were able to derive atmospheric parameters of nine carbon rich sdOs. We find log(NC/Ntotal) up to ten times higher than the solar value, while the mean value for the effective temperature and the surface gravity is slightly lower than derived by helium-hydrogen models only. Surprisingly, we also find three fast rotators among our program stars.

Hirsch, Heiko; Heber, Uli

2009-06-01

86

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

87

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

88

Clumped Isotopes Applied to Carbonate Diagenesis and High Temperature Systems  

NASA Astrophysics Data System (ADS)

The field of clumped isotopes is concerned with the state of ordering of natural substances and aims at constraining the abundance of 18O-13C bonds (i.e. a 'clump') within the lattice of carbonate minerals. Measuring the difference between the abundance of 18O-13C bonds in a sample relative to a stochastic distribution of isotopologues offers a single-phase paleothermometer applicable to all carbonate phases. Most of the applications of clumped isotopes to date have been in the field of paleoclimate, but applications to diagenetic systems are becoming more common. The independence of clumped isotopes from the isotopic composition of the diagenetic fluid reduces ambiguities when interpreting paragenesis, fluid flow history, and thermal history of basins. This presentation will synthesize the results of several projects within our group that collectively aim at understanding and applying clumped isotopes to diagenetic systems. One example of project including diagenesis and clumped isotope is a study of low-temperature diagenetic calcite in a salt dome in Oman (Jebel Madar). Jebel Madar is an ideal case study as large fracture-related crystals can be sampled for both clumped isotopes and fluid inclusions. Results show a good match between single-phase fluid inclusions suggesting temperature of precipitations below 90-50°C, and clumped isotope data measured on the same crystals. The low-temperature study reveals the history of gradual cooling and progressive mixing between two sources of diagenetic fluids in the fracture of Jebel Madar, and highlights the potential of clumped isotope for diagenetic studies. However, applications at high-temperatures are currently more challenging because of the lack of empirical calibrations above 50°C. A second project is thus focused on a series of high-temperature lab precipitation experiments for calibrations at high temperature, while a third project explores applicability of clumped isotopes to cemented siliciclastic units. The long-term aim of our research efforts is thus calibration at subsurface conditions, and application of clumped isotope to unravel the diagenetic history of both carbonate and siliciclastic sequences. We would like to acknowledge the financial support of QCCSRC (funded jointly by Qatar Petroleum, Shell and the Qatar Science & Technology Park) and a BP Case studentship from the EPSRC.

John, C. M.; Jourdan, A.; Kluge, T.; Dale, A.; Davis, S.; Vandeginste, V.

2012-12-01

89

Carbon isotopic fractionation between CO 2 vapour, silicate and carbonate melts: an experimental study to 30 kbar  

Microsoft Academic Search

The carbon isotopic fractionation between CO2 vapour and sodamelilite (NaCaAlSi2O7) melt over a range of pressures and temperatures has been investigated using solid-media piston-cylinder high pressure apparatus. Ag2C2O4 was the source of CO2 and experimental oxygen fugacity was buffered at hematite-magnetite by the double capsule technique. The abundance and isotopic composition of carbon dissolved in sodamelilite (SM) glass were determined

David P. Mattey; W. R. Taylor; D. H. Green; C. T. Pillinger

1990-01-01

90

Carbon isotopic fractionation between CO2 vapour, silicate and carbonate melts: an experimental study to 30 kbar  

Microsoft Academic Search

The carbon isotopic fractionation between CO2 vapour and sodamelilite (NaCaAlSi2O7) melt over a range of pressures and temperatures has been investigated using solid-media piston-cylinder high pressure apparatus. Ag2C2O4 was the source of CO2 and experimental oxygen fugacity was buffered at hematite-magnetite by the double capsule technique. The abundance and isotopic composition of carbon dissolved in sodamelilite (SM) glass were determined

David P. Mattey; W. R. Taylor; D. H. Green; C. T. Pillinger

1990-01-01

91

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

92

Variations in lead isotopic abundances in Sprague-Dawley rat tissues: possible reason of formation.  

PubMed

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 ((206)Pb, (207)Pb and (208)Pb) 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

93

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

94

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

95

Carbon isotopes in continental weathering environments and variations in ancient atmospheric CO 2 pressure  

Microsoft Academic Search

Abundance and carbon isotope data from an Fe(CO3)OH component in apparent solid solution in oolitic goethites have been used to infer ancient atmospheric CO2 pressures. A test of the validity of these estimates might be comparisons of the carbon isotope compositions of Fe(CO3)OH in oolitic goethites with time-equivalent pedogenic calcites. Temporal trends of the oolitic goethite and pedogenic calcite ?13C

Crayton J. Yapp; Harald Poths

1996-01-01

96

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

97

Bulk Earth carbon and its isotopic value  

NASA Astrophysics Data System (ADS)

The carbon isotope distribution in the Earth today is the net product of several primary processes, including planetary accretion, segregation of the core, the Moon-forming giant impact, magma oceans, crustal recycling, and biological processes. Therefore carbon isotope fractionation under mantle pressure and temperature conditions is one of the most important factors in deciphering the messages recorded in mantle samples and will assist towards the greater understanding the geodynamic carbon system. The largest and most powerful geochemical differentiation event during Earth's geologic history was core formation. The behaviour of 13C during this process is little constrained and needs to be investigated to understand the potential effects that it may have had on the carbon isotope composition of the silicate Earth. Isotopic fractionation of carbon at mantle pressure and temperatures in laboratory experiments and for natural terrestrial and extra-terrestrial samples between coexisting elemental carbon and carbides (reducing conditions) are higher than other systems previously investigated and can exceed 12 ‰ in the cores of celestial bodies and observed in Fe-meteorites (Deines and Wickman, 1975; Mikhail et al., 2010). First we review the mean values for carbon in ordinary chondrites and other solar system meteorites (from Mars, Vesta and the Moon) with a value of ?13C ? -20 +/- 4 ‰ (Grady et al 2004). Then we review the notion that the bulk Earth ?13C is around -5 ‰ similar to enstatite and carbonaceous chondrites and reflected in the majority of peridotitic mantle materials. Our modelling demonstrates that in order to understand the core/mantle carbon ratio we need to constrain the bulk Earth's initial ?13C value. We can constrain the relative proportion of carbon in the core/mantle by using simple isotopic mass balance and produce a range of carbon contents for the Earth then apply this to the maximum and minimums for the core using geophysical constraints. The mantle dominates the terrestrial carbon reservoir from an initial ?13C value of -5 ‰, but is dwarfed by the core with an initial ?13C value of -20 ‰. REFERENCES: S. Mikhail 2010 AGU U21A-001 abstract; Deines, P., Wickman, F.E., 1975. A contribution to the stable carbon isotope geochemistry of iron meteorites. Geochimica Et Cosmochimica Acta 39, 547-557. Grady, M. Verchovsky A, Wright, I. 2004 Magmatic carbon in Martian meteorites: attempts to constrain the carbon cycle on Mars. Int. J. Astrobiol. 2004;3:117-124.

Jones, A. P.; Mikhail, S.; Basugupta, S.

2012-12-01

98

Present-day carbon abundances from early-type stars  

NASA Astrophysics Data System (ADS)

Carbon is one of the most abundant metals in the universe because of its synthesis in the funda- mental 3? reaction. The knowledge of carbon abundances in different environments is one key ingredient to our understanding of stellar and galactochemical evolution. Studies of luminous OB-type stars allow us to address both topics even in galaxies beyond our own. Unfortunately the history of carbon abundance determinations from these objects in the last three decades is one of limited success. Analyses of the strong and weak line spectra of C II as well as C III tend to be largely discrepant. We present results of quantitative spectral analyses based on a sophisticated model atom for non-LTE line-formation calculations of C II-IV. As a first application, carbon abundances in a sample of B-type dwarfs and giants in nearby associations and in the field are determined. Consistency is finally achieved for all measurable lines (up to 40) from the three ionization stages. This includes in particular the notorious C II ? ? 4267 and 6578/6582 Å fea- tures which are highly important for abundance determinations of fast-rotating and extragalactic objects. The long-standing problem of carbon line-formation can now be regarded as solved, with the previous difficulties related to the use of inaccurate atomic data and stellar parameters. A highly homogeneous and slightly sub-solar present-day carbon abundance from young stars in the solar vicinity of log C/H + 12 = 8.33±0.04 is derived.

Nieva, Maria-Fernanda; Przybilla, N.

99

The stable carbon isotopes in enstatite chondrites and Cumberland Falls  

NASA Astrophysics Data System (ADS)

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

Deines, P.; Wickman, F. E.

1985-01-01

100

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

NASA Technical Reports Server (NTRS)

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

Wiedenbeck, M. E.

1983-01-01

101

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

102

Carbon isotope composition of Antarctic plants  

NASA Astrophysics Data System (ADS)

Carbon isotope compositions of Antarctic land plants are first reported. The most interesting feature is the isotope specificity of the species. For example Usnea antarctica from different locations shows relatively narrow range of the ? 13C-values from -22.44 to -21.29‰ (7 samples), Drepanocladus sp. from -24.86 to -23.49‰ (8 samples), and Andreaea depressincrvis from -23.87 to -23.23‰ (3 samples) etc. Usually, in inhabited lands and parts of the world with rich flora and developed soil, isotopic specificity of species is masked by variations of carbon isotope composition of CO 2. In Antarctic conditions influence of local sources of CO 2 on the isotope composition of CO 2 is appeared to be minimal. Therefore the ? 13C-variations inherent to individual plant physiology and biochemistry can be distinguished on the background of the stable level of the atmospheric CO 2 ? 13C-value. The latter is best to reflect the global state of the carbon cycle.

Galimov, E. M.

2000-05-01

103

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

104

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

105

CARBON ISOTOPE AND ISOTOPOMER FRACTIONATION IN COLD DENSE CLOUD CORES  

SciTech Connect

We construct a gas-grain chemical network model which includes carbon isotopes ({sup 12}C and {sup 13}C) with an emphasis on isotopomer-exchange reactions. Temporal variations of molecular abundances, the carbon isotope ratios ({sup 12}CX/{sup 13}CX), and the isotopomer ratios ({sup 12}C{sup 13}CX/{sup 13}C{sup 12}CX) of CCH and CCS in cold dense cloud cores are investigated by numerical calculations. We confirm that the isotope ratios of molecules, both in the gas phase and grain surfaces, are significantly different depending on whether the molecule is formed from the carbon atom (ion) or the CO molecule. Molecules formed from carbon atoms have CX/{sup 13}CX ratios greater than the elemental abundance ratio of [{sup 12}C/{sup 13}C]. On the other hand, molecules formed from CO molecules have CX/{sup 13}CX ratios smaller than the [{sup 12}C/{sup 13}C] ratio. We reproduce the observed C{sup 13}CH/{sup 13}CCH ratio in TMC-1, if the isotopomer-exchange reaction, {sup 13}CCH + H {r_reversible} C{sup 13}CH + H + 8.1 K, proceeds with the forward rate coefficient k{sub f} > 10{sup -11} cm{sup 3} s{sup -1}. However, the C{sup 13}CS/{sup 13}CCS ratio is lower than that observed in TMC-1. We then assume the isotopomer-exchange reaction catalyzed by the H atom, {sup 13}CCS + H {r_reversible} C{sup 13}CS + H + 17.4 K. In the model with this reaction, we reproduce the observed C{sup 13}CS/{sup 13}CCS, CCS/C{sup 13}CS, and CCS/{sup 13}CCS ratios simultaneously.

Furuya, Kenji; Aikawa, Yuri [Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501 (Japan); Sakai, Nami; Yamamoto, Satoshi, E-mail: furuya@stu.kobe-u.ac.jp [Department of Physics and Research Center for the Early Universe, University of Tokyo, Bunkyo-ku, Tokyo 113-003 (Japan)

2011-04-10

106

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

107

Carbon isotopes in biological carbonates: Respiration and photosynthesis  

NASA Astrophysics Data System (ADS)

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

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

1997-02-01

108

Abundances and Isotope Ratios in the Magellanic Clouds: The Star-Forming Environment of N 113  

NASA Astrophysics Data System (ADS)

With the goal of deriving the physical and chemical conditions of star-forming regions in the Large Magellanic Cloud (LMC), a spectral line survey of the prominent star-forming region N 113 is presented. The observations cover parts of the frequency range from 85 GHz to 357 GHz and include 63 molecular transitions from a total of 16 species, among them are the spectra of rare isotopologues. Maps of selected molecular lines as well as the 1.2 mm continuum distribution are also presented. Molecular abundances in the core of the complex are consistent with a photon-dominated region in a nitrogen deficient environment. While carbon monoxide (CO) shows optical depths of the order of ? ~ 10, 13CO is optically thin. The most prominent lines of carbon monosulfide (CS), HCN, and HCO+show signs of weak saturation (? ~ 0.5). Densities range from 5 × 103 cm-3 for CO to almost 106 for CS, HCN, and a few other species, indicating that only the densest regions provide sufficient shielding, even for some of the most common species. An ortho- to para-formaldehyde (H2CO) ratio of ~ 3 hints at H2CO formation in a warm (gsim 40 K) environment. Isotope ratios are 12C/13C ~ 49 ± 5, 16O/18O ~2000 ± 250, 18O/17O ~ 1.7 ± 0.2, and 32S/34S ~ 15. Agreement with data from other star-forming clouds shows that the gas is well mixed in the LMC. The isotope ratios not only differ from those seen in the Galaxy, they also do not form a continuation of the trends observed with decreasing metallicity from the inner to the outer Galaxy. This implies that the outer Galaxy, even though showing an intermediate metallicity, is not providing a transition zone between the inner Galaxy and the metal-poor environment of the Magellanic Clouds. A part of this discrepancy is likely caused by differences in the age of the stellar populations in the outer Galaxy and the LMC. While, however, this scenario readily explains measured carbon and oxygen isotope ratios, nitrogen and sulfur still lack a self-consistent interpretation. Based on observations with the Swedish/ESO Submillimeter Telescope (SEST) at the European Southern Observatory (ESO; La Silla, Chile) and the Atacama Pathfinder EXperiment (APEX; Chajnantor, Chile) of the Max-Planck-Institut für Radioastronomie (MPIfR), ESO, and Onsala Space Observatory (OSO).

Wang, M.; Chin, Y.-N.; Henkel, C.; Whiteoak, J. B.; Cunningham, M.

2009-01-01

109

Detrital carbonate influences on bulk oxygen and carbon isotope composition of lacustrine sediments from the Mediterranean  

Microsoft Academic Search

Detrital carbonate contamination is one of the principal problems with the integrity of stable isotope data from authigenic lake carbonates. Here we investigate the origin and climatic implications of stable isotope data from carbonate minerals deposited in two Mediterranean lakes: Gölhisar Gölü (SW Turkey) and Lake Pamvotis (NW Greece). In Gölhisar Gölü the bulk carbonate oxygen and carbon isotope composition

Melanie J. Leng; Matthew D. Jones; Michael R. Frogley; Warren J. Eastwood; Chris P. Kendrick; C. Neil Roberts

2010-01-01

110

Current and relic carbon using natural abundance carbon-13  

SciTech Connect

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

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

2002-05-01

111

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

112

Oxygen isotope partitioning between phosphate and carbonate in mammalian apatite  

NASA Astrophysics Data System (ADS)

The oxygen isotope compositions of phosphate and structural carbonate in mammalian enamel and bone apatite are linked to that of body water at constant body temperature near 37°C, but the isotope systematics of oxygen in structural carbonate are not well understood. Using coupled measurements of the oxygen isotope composition of structural carbonate and phosphate from horse tooth enamel, the apparent oxygen isotope fractionation factor between structural carbonate and body water is estimated to be 1.0263 ± 0.0014. These estimates provide a quantitative basis for using the oxygen isotope composition of structural carbonate in mammalian biogenic apatite for ecological, climatological, and physiological reconstruction.

Bryant, J. Daniel; Koch, Paul L.; Froelich, Philip N.; Showers, William J.; Genna, Bernard J.

1996-12-01

113

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

114

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

115

Cosmic ray isotope abundances from chromium to nickel  

NASA Technical Reports Server (NTRS)

IRIS, a telescope consisting of a large-area precision Cerenkov detector, scintillators, spark chambers, and a passive stack of Lexan polycarbonate track detectors, was exposed to the primary cosmic radiation for 6.6 sq m sr hr in a balloon flight in 1976. This measurement has yielded the isotopic composition of the iron-group elements Cr, Mn, Fe, and Ni with an average mass resolution of 0.65 amu for the energies 320-500 MeV per amu at the detector. This experiment places the most severe constraints to date on deviation from solar-system composition of the source of the cosmic radiation. Upper limits of 10 percent are placed on the ratios Fe-54/Fe-56 and Fe-58/Fe-56, which are inconsistent with large departures from solar system source composition reported by other workers. The isotopic measurements of Fe and Ni preclude the possibility that these cosmic rays were produced in a single e-process zone. The mean mass of Mn is less than 55, indicating the presence of electron-capture species produced by spallation.

Tarle, G.; Ahlen, S. P.; Cartwright, B. G.

1979-01-01

116

Oxygen and Carbon Isotope Ratios in CO2on Mars  

NASA Astrophysics Data System (ADS)

The major problems in spectroscopic determinations of the oxygen and carbon isotope ratios on Mars are uncertainties associated with (1) equivalent widths of the observed absorption lines, (2) line strengths in spectroscopic databases, and (3) thermal structure of the Martian atmosphere during the observation. We have made special efforts to reduce all these uncertainties. We observed Mars using Fourier Transform Spectrometer at the Canada-France-Hawaii Telescope. While the previous measurements of the oxygen and carbon isotope ratios on Mars were byproducts in observations of other species, our observation was specifically aimed at the isotope ratios. The observation covered a range of 6020 to 6310 cm-1 with the highest resolving power of 400,000 and a signal-to-noise ratio of 180 in the middle of the spectrum. The chosen spectral range involves 512 lines of the main isotope, 197 lines of 13CO2, 184 lines of CO18O, and 120 lines of CO17O. (Lines with strengths exceeding 10-27 cm at 220 K are considered here.) Due to the high spectral resolution, most of the lines are not blended. Uncertainties of retrieved isotope abundances are in inverse proportion to resolving power, signal-to-noise ratio, and square root of the number of lines. One of us (R.A. Toth) is making laboratory studies of the CO2isotope line strengths in the range of our observation. This work is aimed to achieve an accuracy of ~1% in the line strengths. Detailed observations of temperature profiles and dust abundances using MGS/TES are used to simulate each absorption line at various heights in each part of the instrument field of view and then sum up the results. Thermal radiation of Mars' surface and atmosphere is negligible in the chosen spectral range, and this reduces errors associated with uncertainties in the thermal structure on Mars. Using a combination of all these factors, we plan to achieve the highest accuracy in measuring the CO2isotope ratios. The results will be reported.

Krasnopolsky, V. A.; Maillard, J.; Owen, T. C.; Toth, R. A.; Smith, M. D.

2007-05-01

117

Molecular abundances in carbon-rich circumstellar envelopes  

NASA Astrophysics Data System (ADS)

A millimetre molecular line survey of seven high mass-loss rate carbon stars in both the northern and southern skies is presented. A total of 196 emission lines (47 transitions) from 24 molecular species were detected. The observed CO emission is used to determine mass-loss rates and the physical structure of the circumstellar envelope, such as the density and temperature structure, using a detailed radiative transfer analysis. This enables abundances for the remaining molecular species to be determined. The derived abundances generally vary between the sources by no more than a factor of five indicating that circumstellar envelopes around carbon stars with high mass-loss rates have similar chemical compositions. However, there are some notable exceptions. The most striking difference between the abundances are reflecting the spread in the 12C/13C-ratio of about an order of magnitude between the sample stars, which mainly shows the results of nucleosynthesis. The abundance of SiO also shows a variation of more than an order of magnitude between the sources and is on average more than an order of magnitude more abundant than predicted from photospheric chemistry in thermal equilibrium. The over-abundance of SiO is consistent with dynamical modelling of the stellar atmosphere and the inner parts of the wind where a pulsation-driven shock has passed. This scenario is possibly further substantiated by the relatively low amount of CS present in the envelopes. The chemistry occurring in the outer envelope is consistent with current photochemical models. Figures A.1-A.13 are only available in electronic form at http://www.edpsciences.org

Woods, P. M.; Schöier, F. L.; Nyman, L.-Å.; Olofsson, H.

2003-05-01

118

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

119

Carbon isotopic composition of individual Precambrian microfossils  

NASA Astrophysics Data System (ADS)

Ion microprobe measurements of carbon isotope ratios were made in 30 specimens representing six fossil genera of microorganisms petrified in stromatolitic chert from the ˜850 Ma Bitter Springs Formation, Australia, and the ˜2100 Ma Gunflint Formation, Canada. The ?13CPDB values from individual microfossils of the Bitter Springs Formation ranged from -21.3 ± 1.7‰ to -31.9 ± 1.2‰, and the ?13CPDB 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, Christopher H.; Schopf, J. William; McKeegan, Kevin D.; Coath, Christopher D.; Harrison, T. Mark; Stetter, Karl O.

2000-08-01

120

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

121

Hyperfiltration-induced fractionation of carbon isotopes  

SciTech Connect

Hyperfiltration of CaCO3 and NaHCO3 solutions through smectites induces chemical and isotopic fractionation of dissolved inorganic carbon (DIC). Early effluent solutions are enriched in carbonic acid and have DIC concentrations higher than the stock solutions from which they were derived. These H2CO3-laden throughput solutions are enriched in TC by 1.5% relative to the TC of the influent DIC. Dynamic diffusion within the concentration polarization layer results in geometrically incongruent concentration profiles of a solute's light and heavy isotope-bearing species due to different diffusion coefficients of these species. The result is that the heavy/light ratio of a solute species is greater at the membrane's high pressure interface than in the stock solution being hyperfiltrated. Thus, early effluent solutions are enriched in heavy species relative to the stock solution.

Fritz, S.J.; Hinz, D.W.; Grossman, E.L.

1987-05-01

122

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

123

Carbon-isotopic analysis of dissolved acetate  

Microsoft Academic Search

Heating of dried, acetate-containing solids together with oxalic acid dihydrate conveniently releases acetic acid for purification by gas chromatography. For determination of the carbon-isotopic composition of total acetate, the acetate-containing zone of the chromatographic effluent can be routed directly to a combustion furnace coupled to a vacuum system allowing recovery, purification, and packaging of COâ for mass-spectrometric analysis. For analysis

Jeffrey T. Gelwicks; J. M. Hayes

1990-01-01

124

Phanerozoic and Neoproterozoic Negative Carbon Isotope Excursions, Diagenesis and Terrestrialization  

Microsoft Academic Search

Comprehensive data sets of Phanerozoic and late Precambrian carbon isotope data derived from carbonate rocks show a similar positive relation when cross-plotted with oxygen isotope values. The range and slope between the time periods is identical and the processes responsible for the relation have been well documented in Quaternary sediments. These processes include the stabilization of isotope values to ambient

K. Paul; M. J. Kennedy

2008-01-01

125

Intrapopulation variation in carbon and nitrogen stable isotope ratios in the earthworm Aporrectodea longa  

Microsoft Academic Search

The natural abundance variations in carbon and nitrogen stable isotope ratios in a population of the earthworm Aporrectodea longa, a species known to feed on both soil and plant litter, is reported in this paper. Worms were collected from a small land area of an old white clover field and body tissue and mucus were analyzed separately. The range of

Olaf Schmidt

1999-01-01

126

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

127

Carbon and Oxygen Isotopic Composition in Paleoenvironmental Determination.  

National Technical Information Service (NTIS)

This work reports that the carbon and oxygen isotopic composition separate the mollusks from marine environment of the mollusks from continental environment in two groups isotopically different, making the biological control outdone by environment control...

J. R. M. Silva

1978-01-01

128

Strontium Isotopes of Banded Iron Formation Carbonates: An Argument Against Iron Carbonates Precipitating from Sea Water  

Microsoft Academic Search

This is a study of the Sr isotopic composition coupled with previously determined Fe, O, and C isotopic data of banded iron formation carbonates to assess if such carbonates precipitated in equilibrium with seawater.

J. M. Ludois; A. Heimann; C. M. Johnson; B. L. Beard; J. W. Valley; E. E. Roden; M. J. Spicuzza

2010-01-01

129

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

130

Carbon isotope labelling in graphene research.  

PubMed

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. PMID:24817019

Frank, O; Kavan, L; Kalbac, M

2014-06-21

131

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

132

Oxygen isotope fractionation in divalent metal carbonates  

USGS Publications Warehouse

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

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

1969-01-01

133

Coprecipitation and isotopic fractionation of boron in modern biogenic carbonates  

NASA Astrophysics Data System (ADS)

The abundances and isotopic composition of boron in modern, biogenic calcareous skeletons from the Gulf of Elat, Israel, the Great Barrier Reef, Australia, and in deep-sea sediments have been examined by negative thermal-ionization mass spectrometry. The selected species (Foraminifera, Pteropoda, corals, Gastropoda, and Pelecypoda) yield large variations in boron concentration that range from 1 ppm in gastropod shells to 80 ppm in corals. The boron content of the biogenic skeletons is independent of mineralogical composition and is probably related to biological (vital) effects. The ?11B values of the carbonates range from 14.2 to 32.2%. (relative to NBS SRM 951) and overlap with the ?11B values of modern deep-sea carbonate sediments ( ?11B = 8.9 to 26.2%.). The variations of ?11B may be controlled by isotopic exchange of boron species in which 10B is preferentially partitioned into the tetrahedral species, and coprecipitation of different proportions of trigonal and tetrahedral species in the calcium carbonates. Carbonates with low ?11B values (~ 15%.) may indicate preferential incorporation of tetrahedral species, whereas the higher ?11B values (~30%.) may indicate (1) uptake of both boron species assuming equilibrium with seawater (2) preferential incorporation of B(OH) 4- from in situ high-pH internal fluids of organisms that are isolated from seawater. The B content and ?11B values of deep-sea sediments, Foraminifera tests, and corals are used to estimate the global oceanic sink of elemental boron by calcium carbonate deposition. As a result of enrichment of B in corals, a substantially higher biogenic sink of 6.4 ± 0.9 × 10 10 g/yr is calculated for carbonates. This is only slightly lower than the sink for desorbable B in marine sediments (10 × 10 10 g/yr) and approximately half that of altered oceanic crust (14 × 10 10 g/yr). Thus, carbonates are an important sink for B in the oceans being ~20% of the total sinks. The preferential incorporation of 10B into calcium carbonate results in oceanic 11B-enrichment, estimated as 1.2 ± 0.3 × 10 12 per mil · 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. The potential use of boron-isotope geochemistry in skeletons as a tracer for palaeoenvironments is demonstrated in Ostracoda and Foraminifera from the Gulf of Carpentaria, Australia. The ?11B values of glacial-age, buried skeletons (4.0 and 4.9%., respectively) are lower than that of their modern equivalents (17.6 and 13.3%., respectively). This may reflect a "terrestrial" boron-isotope signature of the water in the gulf during the Late Quaternary when it was isolated from the ocean.

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

1991-10-01

134

Carbon isotope anomaly in the major plant C1 pool and its global biogeochemical implications  

NASA Astrophysics Data System (ADS)

We report that the most abundant C1 units of terrestrial plants, the methoxyl groups of pectin and lignin, have a unique carbon isotope signature exceptionally depleted in 13C. Plant-derived C1 volatile organic compounds (VOCs) are also anomalously depleted in 13C compared with Cn+1 VOCs. The results confirm that the plant methoxyl pool is the predominant source of biospheric C1 compounds of plant origin such as methanol, chloromethane and bromomethane. Furthermore this pool, comprising ca 2.5% of carbon in plant biomass, could be an important substrate for methanogenesis and thus be envisaged as a possible source of isotopically light methane entering the atmosphere. Our findings have significant implications for the use of carbon isotope ratios in elucidation of global carbon cycling. Moreover methoxyl groups could act as markers for biological activity in organic matter of terrestrial and extraterrestrial origin.

Keppler, F.; Kalin, R. M.; Harper, D. B.; McRoberts, W. C.; Hamilton, J. T. G.

135

Carbon isotope anomaly in the major plant C1 pool and its global biogeochemical implications  

NASA Astrophysics Data System (ADS)

We report that the most abundant C1 units of terrestrial plants, the methoxyl groups of pectin and lignin, have a unique carbon isotope signature exceptionally depleted in 13C. Plant-derived C1 volatile organic compounds (VOCs) are also anomalously depleted in 13C compared with Cn+1 VOCs. The results confirm that the plant methoxyl pool is the predominant source of biospheric C1 compounds of plant origin such as methanol, chloromethane and bromomethane. Furthermore this pool, comprising ca. 2.5% of carbon in plant biomass, represents an important substrate for methanogenesis and could be a significant source of isotopically light methane entering the atmosphere. Our findings have significant implications for the use of carbon isotope ratios in elucidation of global carbon cycling. Moreover methoxyl groups could act as markers for biological activity in organic matter of terrestrial and extraterrestrial origin.

Keppler, F.; Kalin, R. M.; Harper, D. B.; McRoberts, W. C.; Hamilton, J. T. G.

2004-08-01

136

The influence of carbon source on abiotic organic synthesis and carbon isotope fractionation under hydrothermal conditions  

NASA Astrophysics Data System (ADS)

A series of laboratory experiments were performed to investigate the relative contributions of CO and other single-carbon compounds to abiotic synthesis of organic compounds in hydrothermal environments. Experiments were conducted by heating aqueous solutions of CO, CO 2, HCOOH, or CH 4 at 250 °C under reducing conditions, and observing production of CH 4 and other hydrocarbons. Native Fe was included in the experiments as a source of H 2 through reaction with water and as a potential catalyst. Experiments with CO or HCOOH as the carbon source resulted in rapid generation of CH 4 and other hydrocarbons that closely resembled typical products of Fischer-Tropsch organic synthesis. In contrast, experiments using CO 2 or CH 4 as the carbon source yielded no detectable hydrocarbon products. Carbon isotope measurements of reaction products from the CO experiments indicate that the CH 4 and other hydrocarbons were substantially depleted in 13C, with CH 4 ? 13C values 30 to 34‰ lighter than the initial CO. Most of the fractionation apparently occurs during attachment of CO to the catalyst surface and subsequent reduction to surface-bound methylene. The initial step in polymerization of these methylene units to form hydrocarbons involves a small, positive fractionation, so that ethane and ethene are slightly enriched in 13C relative to CH 4. However, subsequent addition of carbon molecules to the growing hydrocarbon chain proceeds with no net observable fractionation, so that the isotopic compositions of the C 3+ light hydrocarbons are controlled by isotopic mass balance. This result is consistent with a previously proposed model for carbon isotopic patterns of light hydrocarbons in natural samples. The abundance and isotopic composition of light hydrocarbons produced with HCOOH as the carbon source were similar to those generated with CO, but the isotopic compositions of non-volatile hydrocarbons diverged, suggesting that the higher hydrocarbons were formed by different mechanisms in the CO and HCOOH experiments. The experiments indicate that CO, and possibly HCOOH, may be critical intermediates in the abiotic formation of organic compounds in geologic environments, and suggest that the low levels of these compounds present in most hydrothermal systems could represent a bottleneck restricting the extent of abiotic organic synthesis in some circumstances.

McCollom, Thomas M.; Lollar, Barbara Sherwood; Lacrampe-Couloume, Georges; Seewald, Jeffrey S.

2010-05-01

137

Carbon and oxygen isotopic composition of Holocene reefal carbonates  

NASA Astrophysics Data System (ADS)

Carbon and oxygen isotopic compositions have been determined for Holocene reefal carbonate grains and cements in samples from Enewetak, Bikini, Bermuda, and Belize to identify components that exhibit systematic isotopic fractionation relationships. These findings are compared with fractionation relationships determined from experimentally precipitated low-magnesium calcite (LMC), aragonite, and high-magnesium calcite (HMC) to determine if these relationships are observed in naturally precipitated carbonates. Compositional variation within individual samples is extreme (up to 6‰ in ?13C PDB and 3‰ in ?18O PDB). Experimental fractionation relationships fail to predict the range of observed compositions. Aragonite cements are enriched 1.0‰ to 1.4‰ in 13C and 1.5‰ to 2.0‰ in 18O relative to calcite equilibrium compositions; HMC cements are enriched by 0.3‰ to 0.4‰ in 13C and by 1.8‰ to 1.9‰ to 18O. For carbon, these results are in agreement with the experimental work of Rubinson and Clayton. For oxygen, our results suggest that fractionation factors of both aragonite and HMC may have been underestimated. Skeletal components exhibit inconsistent fractionation relative to inorganically precipitated marine cements, suggesting that marine cement compositions are more reliable indicators of the physicochemical conditions of precipitation than co-occurring skeletal carbonates.

González, Luis A.; Lohmann, Kyger C.

1985-11-01

138

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

NASA Astrophysics Data System (ADS)

Climate, biome, and plant community are important predictors of carbon isotope patterns recorded in leaves and leaf waxes. However, signatures recorded by terrestrial organic carbon and lipids that have mixed floral sources (e.g., n-alkanes) potentially reflect both plant community changes and climate. More taxonomically specific proxies for plants (i.e., di- and tri-terpenoids for conifers and angiosperms, respectively), can help to resolve the relative influences of changing community and climate, provided differences in biomarker production and lipid biosynthetic fractionation among plants can be better constrained. We present biomarker abundance and carbon isotope values for lipids from leaves, branches and bark of 44 tree species, representing 21 families including deciduous and evergreen conifers and angiosperms. n-alkane production differs greatly between conifer and angiosperm leaves. Both deciduous and evergreen angiosperms make significantly more n-alkanes than conifers, with n-alkanes not detected in over half of the conifers in our study. Terpenoid abundances scale strongly with leaf habit: evergreen species have significantly higher abundances. We combine these relative differences in lipid production with published estimates of fluxes for leaf litter from conifer and angiosperm trees to develop a new proxy approach for estimating paleo plant community inputs to ancient soils and sediments. To test our modern calibration results, we have evaluated n-alkanes and terpenoids from laterally extensive (~18 km) carbonaceous shales and mudstones in Eocene sediments (52.6 Ma) at Fifteenmile Creek in the Bighorn Basin (WY, USA). Our terpenoid-based proxy predicts on average a 40% conifer community, which is remarkably close in agreement with a fossil-based estimate of 36%. n-alkane carbon isotope fractionation (leaf-lipid) differs among plant types, with conifer n-alkanes about 2-3‰ 13C enriched relative to those in angiosperms. Since conifer leaves are generally 2-3‰ enriched relative to angiosperm leaves, we project that the far more abundant angiosperm lipids will be about 4-6 ‰ depleted relative to small amounts of conifer n-alkanes in natural samples. In addition, we report carbon isotope values of the terpenoids from the MVA (triterpenoids) and MEP (diterpenoids) synthesis pathways for our plant sample set. Bulk leaf tissue-to-lipid fractionation factors for terpenoids are similar and generally small, -0.4 and -0.6‰, for MVA and MEP products, respectively. Estimates of precipitation from fossil leaves at the Fifteenmile site allow us to predict leaf fractionation values for different plant types (bulk) and for triterpenoid and diterpenoid compound classes. Our fractionation factors, when applied to an estimate for the ?13C value of late Eocene CO2, agree well with bulk and molecular data. An understanding of molecular production biases greatly improves our ability to reconstruct both paleovegetation and ?13C of atmospheric CO2.

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

2010-12-01

139

The Measurement of Iron-Group Isotopic Abundances in the Cosmic Rays Using the Magpie Detector  

NASA Astrophysics Data System (ADS)

This thesis details the analysis of data from the MAGPIE detector, a balloon-borne detector designed to measure cosmic ray isotope abundances between 300 and 900 MeV/a ? in the Fe group. MAGPIE consists of a magnetic spectrometer for measuring particle rigidity, and nine stacks of CR-39 plastic nuclear track detectors for measuring charge and velocity. After an Antarctic flight in December of 1991 during which ~2000 Fe nuclei were collected, damage occurred to the spectrometer during the landing of the balloon payload, limiting the analysis to cosmic ray particles that stop in the plastic stack. This limited the energy range of data to between 100 MeV/a ? and 400 MeV/a ? for Fe group elements. The measurement of Fe group isotopes is an important one. Because nuclei from this group have the highest binding energy of all the elements, they represent the primary products during late stellar nucleosynthesis. This characteristic makes Fe group isotopes unique in their ability to probe the interior environment during the final stages of stellar evolution. In addition, the primary decay channel by e- capture for some of the Ni and Co isotopes makes these isotopes ideal for probing the time delay between production of cosmic rays and their acceleration. Finally, the radioactive isotope 54Mn has a mean lifetime that is comparable to residence time of lighter elements in the galaxy, which has been measured using the 10Be isotopic abundance. Both of these abundances are produced primarily through spallation during propagation, and Mn can measure the average density of the propagation medium and residence time for Fe group elements with isotopic abundance measurements of stable spallation products. After etching, the MAGPIE CR-39 plastic was scanned for tracks using an automated microscope and image processing system. This system offers a data acquisition method that is as efficient and much quicker than techniques using a microscope and reticle. Cosmic ray data were separated from background noise pits using a sheet aligning algorithm that searched for tracks having similar shape and size. I performed an extensive error analysis on the MAGPIE detector, scanning system, and etching facilities. Contributions to mass resolution from the last two categories are neglible. I found that the intrinsic charge resolution of the plastic has been severely degraded over time. This resolution fundamentally limited the ability of this detector to resolve charges to ?Z>= 0.4 e. The data were successfully fit to a charge distribution, but mass resolution was not adequate to generate a mass distribution. There appears to be an underabundance of Fe data, possibly from a systematic error.

Yanasak, Nathan Eugene

140

Mechanisms for “Vital Effects” in Biogenic Carbonates: New Perspectives Based on Abundances of 13C-18O Bonds  

NASA Astrophysics Data System (ADS)

Many biogenic carbonates exhibit correlated depletions in ?18O and ?13C relative to the compositions expected for isotopic equilibrium with ambient waters and dissolved inorganic carbon (DIC). Such ‘vital effects’ complicate the use of biogenic carbonates in paleoclimate studies, particularly efforts to quantify carbonate growth temperature using carbonate-water oxygen isotope thermometry. Two general classes of models have been proposed to account for such vital effects: equilibrium models in which carbonate grows in isotope equilibrium with local body water, but at a pH and/or body water isotopic composition that differs from ambient environmental water; and kinetic models in which dissolved inorganic carbon and co-existing water do not achieve local isotope exchange equilibrium. Here we examine the constraints on this problem implied by measurements of proportions of 13C-18O bonds in biogenic carbonates, expressed as ?47, the abundance anomaly of mass 47 isotopologues of CO2 (mainly 13C18O16O) derived from phosphoric acid digestion of carbonate minerals [1]. Despite the significant differences in equilibrium carbon and oxygen isotope compositons between dissolved HCO3- and CO32- (i.e. ~2‰ in ?13C and ~7‰ in ?18O at 300 K), physical-chemistry models (based on ab initio and statistical thermodynamic theory) predict only subtle (~0.02‰) difference in their proportions of 13C-18O bonds, corresponding to a relatively low, positive slope of ~0.003 for ?(?47)/?(?18O) in carbonates in which vital effects reflect equilibrium processes with locally exotic pH. In contrast, we infer that kinetic vital effects should lead to relatively strong increases in proportions of 13C-18O bonds in precipitated carbonate relative to those expected for equilibrium growth. This is because random incorporation of an oxygen atom from H2O or OH- during the hydration or hydroxylation of CO2 will yield a relatively steep negative slope for ?(?47)/?(?18O) in the product HCO3- and thus in carbonates, on the order of -0.01 to -0.05 at 300K. We are currently elaborating on this relatively simple kinetic model to include kinetic isotope effects accompanying hydration or hydroxylation of aqueous CO2. Isotopic analyses of deep-sea corals having marked vital effects for ?13C and ?18O yield equilibrium ?47 over a significant range of ?18O disequilibrium (~4.5‰) [2]. This observation is so far most consistent with equilibrium models of vital effects, as are the isotopic analyses of a variety of other biogenic carbonates grown at known temperatures [3]. The absence of significant “vital effects” in the clumped isotope compositions of biogenic carbonates constitutes another advantage of carbonate clumped isotope thermometer in paleo-temperature reconstruction, compared to the conventional carbonate-water oxygen isotope thermometer. Reference: [1] Ghosh et. al.(2006) GCA, 70: 1439-1456; [2] Thiagarajan et. al. (2009), GCA, 73: A1324; [3] Eiler J. M. (2007) EPSL, 262: 309-327.

Guo, W.; Kim, S.; Thiagarajan, N.; Adkins, J. F.; Eiler, J. M.

2009-12-01

141

Carbon-isotopic analysis of dissolved acetate  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

142

Oxygen and Carbon Isotopic Growth Record in a Reef Coral from the Florida Keys and a Deep-Sea Coral from Blake Plateau  

NASA Astrophysics Data System (ADS)

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

Emiliani, Cesare; Hudson, J. Harold; Shinn, Eugene A.; George, Robert Y.

1978-11-01

143

Mercury abundances and isotopic compositions in the Murchison (CM) and Allende (CV) carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

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 ± 15 ng/g in Murchison and 30.0 ± 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 ? 196/202Hg values for the anomalous, thermal-release components from bulk samples ranging from -260 ‰ to +440 ‰ in Murchison and from -620 ‰ to +540 ‰ 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 ‰. On-line thermal-release experiments were performed by coupling a programmable oven with the single-collector 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 from the meteorites as a function 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 ‰, 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. Prior studies suggested that the isotopic anomalies reported from NAA resulted from interference between 203Hg and 75Se. However, the amount of Se released from both meteorites, relative to Hg, is insufficient to produce all of the observed anomalies.

Lauretta, Dante S.; Klaue, Bjoern; Blum, Joel D.; Buseck, Peter R.

2001-09-01

144

Tropylium, chlorine isotopic abundances, monomeric metaphosphate anion, and conestoga wagon theory  

Microsoft Academic Search

As I look back over a career in mass spectrometry, three high points stand out especially prominently. These are associated\\u000a with (1) the tropylium model for the CuH7+ ion in the mass spectra of toluene and other alkylbenzenes, (2) revision of the previously accepted value for the natural\\u000a abundance of the chlorine isotopes, and (3) the first direct observation of

Seymour Meyerson

1993-01-01

145

Lead Abundance In The Martian Mantle Deduced From The Isotopic Data In Snc Meteorites  

NASA Astrophysics Data System (ADS)

Isotopic data are a powerful tool for the study of planetary evolution. Assuming that the SNC meteorites are rocks from Mars their Sm-Nd-, Rb-Sr- and Pb-Pb-isotope systematics reveal the time scale for the chemical evolution of the Martian mantle. From the Rb -Sr isotopic systematic the existence of 3 isotopically distinct reservoirs on Mars was postulated, which remained isolated for a period of 4.3 +/- 0.2 Ga. The basaltic shergottites Shergotty, Zagami and Los Angeles have relatively high radiogenic Sr, which might come from a planetary crust. A second group, characterized by non radiogenic Sr, consists of the two mafic cumulates Nakhla and Chassigny, the olivine rich basaltic shergottites DaG 476, SaU 005, Dhofar 019and the basaltic shergottite QUE 94201, which may represent the depleted mantle. The depletion of this reservoir must have taken place during a very early process. as derived from the primitive Sr isotopes and the existence of Nd-142, the daughter product of the extinct Sm-146, found in Chassigny, the Nakhlites, SaU 005, and DaG476. A third group, with intermediate Sr isotopic composition, represented by the lherzolitic shergottites, could be derived from a primitive, unfractionated mantle. Our observed correlation of Sr-isotopes with Pb-isotopes in SNC's permits to estimate the Pb abundance for the Martian mantle. The Pb isotopes of all measured SNCs show a similar pattern as Sr isotopes. The initial Pb data of Los Angeles, Shergotty, and Zagami from the enriched crustal reservoir and of Nakhla and SaU 005 from the depleted mantle reservoir plot close to the 4.5 Ga Pb -Pb isochron.. We used this correlation to estimate the µ value (238U/204Pb) of 3.1 for the Martian mantle. This corresponds to 366 ppb Pb. Compared to the Earth with a µ = 8.8, Pb is enriched on Mars by at least a fact or of 2.5. The same enrichment was found for all other moderately volatile and volatile elements on Mars. From the high abundance of Pb in the sulfide phases of iron meteorites a chalcophile behavior of Pb was postulated. Contrary to the Earth the Martian core is sulfur rich. But, the more than 2 fold enrichment of Pb in the silicate phase of Mars compared to that of Earth might exclude its chalcophile behavior. Lead, with a condensation temperature from a solar gas lower than 600oK belongs to the group of volatile elements. Obviously, during planetary formation and evolution Pb behaves like a volatile and not like a chalcophile element.

Dreibus, G.; Jagoutz, E.

146

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

NASA Astrophysics Data System (ADS)

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

Gessler, Arthur

2014-05-01

147

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

148

Boron isotopic composition and concentration in modern marine carbonates  

Microsoft Academic Search

The boron isotopic compositions and boron concentrations of selected modern marine carbonates were analysed by negative thermal ionization mass spectrometry with a 2 reproducibility of standards and samples better than 0.7%. It was found that the boron isotopic compositions of modern marine carbonates fall within a relatively narrow range (+22.1 ± 3%. relative to NBS SRM951 boric acid standard) for

N. G. Hemming; G. N. Hanson

1992-01-01

149

Molybdenum isotopic composition of modern and Carboniferous carbonates  

Microsoft Academic Search

We investigate the redox-sensitive isotope system of molybdenum (Mo) in marine carbonates to evaluate their potential as archive of the Mo isotopic composition of coeval seawater. We present Mo isotope data (?98\\/95Mo) of modern skeletal and non-skeletal carbonates as well as a variety of precipitates from the mid and late Carboniferous. The external reproducibility is determined by repeated analyses of

Andrea R. Voegelin; Thomas F. Nägler; Elias Samankassou; Igor M. Villa

2009-01-01

150

Fractionation of Carbon Isotopes during Biogenesis of Atmospheric Isoprene.  

PubMed

The stable carbon isotope composition of isoprene emitted from leaves of red oak (Quercus rubra L.) was measured. Isoprene was depleted in (13)C relative to carbon recently fixed by photosynthesis. The difference in isotope composition between recently fixed carbon and emitted isoprene was independent of the isotopic composition of the source CO(2). beta-Carotene, an isoprenoid plant constituent, was depleted in (13)C relative to whole leaf carbon to the same degree as isoprene, but fatty acids were more depleted. Isoprene emitted from leaves fed abscisic acid was much less depleted in (13)C than was isoprene emitted from unstressed leaves. We conclude that isoprene is made from an isoprenoid precursor that is derived from acetyl-CoA made from recent photosynthate. The carbon isotope composition of isoprene in the atmosphere is likely to be slightly more negative (less (13)C) than C(3) plant material but when plants are stressed the isotopic composition could vary. PMID:16668410

Sharkey, T D; Loreto, F; Delwiche, C F; Treichel, I W

1991-09-01

151

Carbon pools and isotopic trends in a hypersaline cyanobacterial mat  

Microsoft Academic Search

The fine-scale depth distribution of major carbon pools and their stable carbon isotopic signatures ( ? 13 C) were determined in a cyanobacterial mat (Salin-de-Giraud, Camargue, France) to study early diagenetic alterations and the carbon preservation potential in hypersaline mat ecosystems. Particular emphasis was placed on the geochemical role of extracellular polymeric substances (EPS). Total carbon (C tot ), organic

A. WIELAND; T. PAPE; J. MÖBIUS; W. MICHAELIS

2008-01-01

152

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

153

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

154

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

155

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

156

Cryogenian glaciation and the onset of carbon-isotope decoupling.  

PubMed

Global carbon cycle perturbations throughout Earth history are frequently linked to changing paleogeography, glaciation, ocean oxygenation, and biological innovation. A pronounced carbonate carbon-isotope excursion during the Ediacaran Period (635 to 542 million years ago), accompanied by invariant or decoupled organic carbon-isotope values, has been explained with a model that relies on a large oceanic reservoir of organic carbon. We present carbonate and organic matter carbon-isotope data that demonstrate no decoupling from approximately 820 to 760 million years ago and complete decoupling between the Sturtian and Marinoan glacial events of the Cryogenian Period (approximately 720 to 635 million years ago). Growth of the organic carbon pool may be related to iron-rich and sulfate-poor deep-ocean conditions facilitated by an increase in the Fe:S ratio of the riverine flux after Sturtian glacial removal of a long-lived continental regolith. PMID:20431011

Swanson-Hysell, Nicholas L; Rose, Catherine V; Calmet, Claire C; Halverson, Galen P; Hurtgen, Matthew T; Maloof, Adam C

2010-04-30

157

Diffusive fractionation of carbon isotopes in ?-Fe: Experiment, models and implications for early solar system processes  

NASA Astrophysics Data System (ADS)

Carbon is an abundant element of planets and meteorites whose isotopes provide unique insights into both organic and inorganic geochemical processes. The identities of carbonaceous phases and their textural and isotopic characters shed light on dynamical processes in modern Earth systems and the evolution of the early solar system. In meteorites and their parent bodies, reduced carbon is often associated with Fe-Ni alloys, so knowledge of the mechanisms that fractionate C isotopes in such phases is crucial for deciphering the isotopic record of planetary materials. Here we present the results of a diffusion-couple experiment in which cylinders of polycrystalline Fe containing 11,500 and 150 ?g/g of C were juxtaposed at 1273 K and 1.5 GPa for a duration of 36 min. Diffusion profiles of total C concentration and 13C/12C were measured by secondary ion mass spectrometry (SIMS). The elemental diffusivity extracted from the data is ˜3.0 × 10-11 m2 s-1, where 13C/12C was observed to change significantly along the diffusion profile, reflecting a higher diffusivity of 12C relative to 13C. The maximum isotopic fractionation along the diffusion profile is ˜30-40‰. The relative diffusivities (D) of the carbon isotopes can be related to their masses (M) by D/D=(C/M)?; the exponent ? calculated from our data has a value of 0.225 ± 0.025. Similarly high ? values for diffusion of other elements in metals have been taken as an indication of interstitial diffusion, so our results are consistent with C diffusion in Fe by an interstitial mechanism. The high ?-value reported here means that significant fractionation of carbon isotopes in nature may arise via diffusion in Fe(-Ni) metal, which is an abundant component of planetary interiors and meteorites.

Mueller, Thomas; Watson, E. Bruce; Trail, Dustin; Wiedenbeck, Michael; Van Orman, James; Hauri, Erik H.

2014-02-01

158

Constraints on the Origin of Galactic Cosmic Rays from Direct Measurements of Isotopic and Elemental Abundances  

NASA Astrophysics Data System (ADS)

Recent measurements of galactic cosmic ray (GCR) isotopic and elemental abundances have resulted in constraints on models of the origin of GCRs. The measurement of ^{59}Ni by the Cosmic Ray Isotope Spectrometer (CRIS) on the NASA Advanced Composition Explorer (ACE) has shown that there must be >˜10^{5} years between nucleosynthesis and acceleration. Measurements of a range of isotope ratios, most importantly ^{22}Ne/^{20}Ne and ^{58}Fe/^{56}Fe, have shown that the composition is consistent with source material that is a mix of ˜80% ISM (with Solar System abundances) and 20% outflow from massive stars. Data from the Trans-Iron Galactic Element Recorder (TIGER) and the ACE-CRIS experiments both show that the ordering of refractory and volatile elements with atomic mass is greatly improved when compared to an ˜80%/20% mix rather than pure ISM, that they have similar slopes, and that refractory elements are preferentially accelerated by a factor of ˜4 over volatile elements. We discuss these observations and conclude that our constraints are consistent with a GCR origin in OB associations. This research was supported by NASA under Grants NNX08AI11G and NNX09AC17G, and by NSF under Grant 0807356

Rauch, Brian

2012-07-01

159

The carbon isotopic composition of diamonds: relationship to diamond shape, color, occurrence and vapor composition  

NASA Astrophysics Data System (ADS)

Three hundred and thirty new 13C analyses of diamonds are presented, indicating, in conjunction with earlier published work, a range of about 30%. in the carbon isotopic composition of diamonds. The frequency distribution of diamond ?13C analyses shows a very pronounced mode at -5 to -6%.vs PDB, a large negative skewness, and a sharp boundary at about -1%.. Analyses of diamonds from the Premier and Dan Carl mines, South Africa, demonstrate that: (1) differences in 13C content that can be related to diamond color and shape are smaller than 1%.; (2) the mean 13C content of kimberlite carbonates is 1-2%. lower than that of associated diamonds; (3) significant differences in 13C content exist between the mean isotopic compositions of diamonds from these two pipes; (4) the variability in ?13C differs from one mine to the other. Computations were carried out evaluating the effect on the 13C content of diamonds of: (i) various precipitation processes; (ii) the abundance of the species H 2, H 2O, CH 4, CO, CO 2 and O 2 in the vapor; (iii) the initial isotopic composition variability of the source carbon; (iv) variations of the carbon isotope effects resulting from changes in pressure and temperature and (v) reservoir effects (Rayleigh fractionation). Fifty-eight genetic models were investigated for compatibility with the 13C distribution in diamonds and associated carbonate. The modeling does not permit an unambiguous answer to the question whether or not a vapor participated in diamond formation, although the presence of methane during diamond formation is compatible with the carbon isotopic composition data, possible oxygen fugacities in the mantle and with the composition of gases liberated from diamonds. In all probability carbon isotope effects in the diamond formation process were small, and the very large range in ?13C observed was inherited from the source carbon.

Deines, Peter

1980-07-01

160

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, Jr. , F. J.

1978-01-01

161

Carbon-isotopic analysis of dissolved acetate  

SciTech Connect

Heating of dried, acetate-containing solids together with oxalic acid dihydrate conveniently releases acetic acid for purification by gas chromatography. For determination of the carbon-isotopic composition of total acetate, the acetate-containing zone of the chromatographic effluent can be routed directly to a combustion furnace coupled to a vacuum system allowing recovery, purification, and packaging of CO{sub 2} for mass-spectrometric analysis. For analysis of methyl carbon, acetic acid can be cryogenically trapped from the chromatographic effluent, then transferred to a tube containing excess NaOH. The tube is evacuated, sealed, and heated to 500{degree}C to produce methane by pyrolysis of sodium acetate. Subsequent combustion of the methane allows determination of the {sup 13}C content at the methyl position in the parent acetate. With typical blanks, the standard deviation of single analyses is less than 0.4{per thousand} for acetate samples larger than 5 {mu}mol. A full treatment of uncertainties is outlined.

Gelwicks, J.T. (Merck and Co., Inc., Rahway, NJ (USA)); Hayes, J.M. (Indiana Univ., Bloomington (USA))

1990-03-01

162

Tracing the source of Beijing soil organic carbon: a carbon isotope approach.  

PubMed

Bulk soil organic carbon concentration and isotopic composition characterize its sources and fate, identify the anthropogenic input of organic carbon into the soil, and trace soil carbon turnover. Coal and/or coal combustion products represent the prime anthropogenic input of organic carbon into three soil profiles located in the vicinity of a steel company. Three profiles positioned away from any direct industrial contribution display vertical pattern in soil organic carbon concentration and isotopic composition that resemble more commonly observed downward gradients in soil carbon chemistry and indicate microbial soil carbon turnover. Two additional profiles located outside of the immediate industrial area display vertical carbon isotope profiles between typical of those from industrial and non-industrial areas. Eight soil profiles and their vertical distribution of bulk organic carbon isotopic composition and concentration collected in the Beijing area reveal and distinguish both anthropogenic and natural contributions of carbon to these soils. PMID:23434575

Guo, Qingjun; Strauss, Harald; Chen, Tong-Bin; Zhu, Guangxu; Yang, Jun; Yang, Junxing; Lei, Mei; Zhou, Xiaoyong; Peters, Marc; Xie, Yunfeng; Zhang, Hanzhi; Wei, Rongfei; Wang, Chunyu

2013-05-01

163

Characterizing uranium oxide reference particles for isotopic abundances and uranium mass by single particle isotope dilution mass spectrometry.  

PubMed

Uranium and plutonium particulate test materials are becoming increasingly important as the reliability of measurement results has to be demonstrated to regulatory bodies responsible for maintaining effective nuclear safeguards. In order to address this issue, the Institute for Reference Materials and Measurements (IRMM) in collaboration with the Institute for Transuranium Elements (ITU) has initiated a study to investigate the feasibility of preparing and characterizing a uranium particle reference material for nuclear safeguards, which is finally certified for isotopic abundances and for the uranium mass per particle. Such control particles are specifically required to evaluate responses of instruments based on mass spectrometric detection (e.g. SIMS, TIMS, LA-ICPMS) and to help ensuring the reliability and comparability of measurement results worldwide. In this paper, a methodology is described which allows quantifying the uranium mass in single micron particles by isotope dilution thermal ionization mass spectrometry (ID-TIMS). This methodology is characterized by substantial improvements recently achieved at IRMM in terms of sensitivity and measurement accuracy in the field of uranium particle analysis by TIMS. The use of monodisperse uranium oxide particles prepared using an aerosol generation technique developed at ITU, which is capable of producing particles of well-characterized size and isotopic composition was exploited. The evidence of a straightforward correlation between the particle volume and the mass of uranium was demonstrated in this study. Experimental results have shown that the uranium mass per particle can be measured via the ID-TIMS method to a relative expanded uncertainty of about 10% (coverage factor k=2). The availability of reliable and validated methods for the characterization of uranium particles is considered to be essential for the establishment of SI-traceable measurement results. It is therefore expected that the method developed in this study is valuable for the certification of particulate materials in which the isotopic composition and the content of uranium must be accurately known. PMID:23021805

Kraiem, M; Richter, S; Erdmann, N; Kühn, H; Hedberg, M; Aregbe, Y

2012-10-20

164

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

165

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

166

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

167

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

168

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

169

Microbial influences on local carbon isotopic ratios and their preservation in carbonate.  

PubMed

Analysis of the carbon isotopic composition of carbonates is a valuable tool for studying microbial processes and looking for evidence of life. Microbial fixation of CO2 and conversion of organic carbon to CO2 can produce measurable delta 13C shifts in a microbial mat environment. Diffusion modeling demonstrates that substantial isotopic shifts can develop within the mat and in the diffusion boundary layer in the fluid when CO2 fixation is rapid and prolonged for several hours. Carbonates that precipitate during rapid CO2 fixation can preserve these microbially produced isotopic shifts. However, continued precipitation during intervals when respiration dominates or after the cessation of active microbial growth commonly dilutes autotrophic isotopic signatures. Thus, preserved isotopic signatures rarely reflect the magnitude of isotopic shifts within the mat. Interpretation of observed isotopic shifts in microbial mat carbonate depends on fully characterizing ambient delta 13C and eliminating other origins for isotopic shifts. The carbon isotopic composition of reservoirs can vary substantially, both on Earth and on other planets. Characterizing the reservoir composition and any changes through time is critical to evaluating microbially induced shifts. In addition, careful evaluation of non-microbial causes for shifts in isotopic composition is essential for a reliable interpretation. Complicating processes include recrystallization, calcite precipitation over extended periods of time, variable precipitation rates and water chemistry, and mixing of carbonates having different isotopic signatures. PMID:12448995

Sumner, D Y

2001-01-01

170

Hot bottom burning in asymptotic giant branch stars and its effect on oxygen isotopic abundances  

NASA Technical Reports Server (NTRS)

A self-consistent calculation of asymptotic giant branch (AGB) evolution was carried out, including nucleosynthesis at the base of the convective envelope (hot bottom burning). Hot bottom burning was found to occur for stars between approximately 4.5 and approximately 7 solar mass, producing envelopes with O-18/O-16 less than or equal to 10(exp -6) and 10(exp -3) approximately less than or equal O-17/O-16 approximately less than or equal to 10(exp -1). The O-17 abundance depends sensitively on the nuclear O-17-destruction rate; this rate is only loosely constrained by the requirement that first and second dredge-up models match O-isotope observations of red giant branch (RGB) stars (Boothroyd, Sackmann, & Wasserburg 1994). In some cases, high mass-loss rates can terminate hot bottom burning before further O-17 enrichment takes place or even before all O-18 is destroyed. These predictions are in accord with the very limited stellar observations of J type carbon stars on the AGB and with some of the circumstellar Al2O3 grains from meteorites. In contrast, precise data from a number of grains and data from most low-mass S and C AGB stars (approximately less than 1.7 solar mass) lie in a region of the O-18/O-16 versus O-17/O-16 diagram that is not accessible by first and second dredge-up or by hot bottom burning. We conclude that for AGB stars, the standard models of stellar evolution are not in accord with these observations. We surmise that an additional mixing mechanism must exist that transports material from the cool bottom of the stellar convective envelope to a depth at which O-18 is destroyed. This 'cool bottom processing' mechanism on the AGB is similar to extra mixing mechanisms proposed to explain the excess C-13 (and depleted C-12) observed in the earlier RGB stage of evolution and the large Li-7 depletion observed in low-mass main-sequence stars.

Boothroyd, Arnold I.; Sackmann, I.-JULIANA; Wasserburg, G. J.

1995-01-01

171

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

172

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

173

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

174

Detrital carbonate influences on bulk oxygen and carbon isotope composition of lacustrine sediments from the Mediterranean  

NASA Astrophysics Data System (ADS)

Detrital carbonate contamination is one of the principal problems with the integrity of stable isotope data from authigenic lake carbonates. Here we investigate the origin and climatic implications of stable isotope data from carbonate minerals deposited in two Mediterranean lakes: Gölhisar Gölü (SW Turkey) and Lake Pamvotis (NW Greece). In Gölhisar Gölü the bulk carbonate oxygen and carbon isotope composition has previously been interpreted in terms of significant climate variation related to the lake's hydrological balance. However, the origin of the carbonates was not investigated even though phases of high magnetic susceptibility suggest that there were several periods of increased soil erosion from the karstic catchment which could bring detrital limestone in to the lake. SEM evidence suggests that the carbonates in Gölhisar Gölü sediments of Holocene age are predominantly derived from forms of authigenic calcite (i.e. platelets, prismatic crystals), although periods of inwash clearly occurred which may have influenced parts of the isotope stratigraphy during the last two millennia. For comparison we also looked at data of Late Pleistocene to Holocene age from Lake Pamvotis. Here, there is an excellent correlation between the bulk carbonate oxygen isotope and magnetic susceptibility data, but no significant correlation between the bulk carbonate isotope data and ostracod isotope data from the same levels. SEM analyses confirmed the presence of detrital carbonates and the lack of significant authigenic carbonate. While the Gölhisar record records aspects of climate in most of its isotope data, in the Pamvotis record only the ostracod data are likely to contain meaningful information.

Leng, Melanie J.; Jones, Matthew D.; Frogley, Michael R.; Eastwood, Warren J.; Kendrick, Chris P.; Roberts, C. Neil

2010-04-01

175

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

176

Photosynthetic carbon isotope discrimination and its relationship to the carbon isotope signals of stem, soil and ecosystem respiration (Invited)  

NASA Astrophysics Data System (ADS)

Photosynthetic carbon (C) isotope discrimination labels photosynthates (?A) and atmospheric CO2 (?a) with variable C isotope compositions during fluctuating environmental conditions. In this context, the C isotope composition of respired CO2 within ecosystems is often hypothesized to vary temporally with photosynthetic discrimination. We investigated the relationship between photosynthetic discrimination and the C isotope signals from stem (?W), soil (?S) and ecosystem (?E) respired CO2 to environmental fluctuations, using novel tuneable diode laser absorption spectrometer instrumentation in a mature maritime pine forest. Broad seasonal changes in photosynthetic discrimination were reflected in ?W, ?S and ?E. However, respired CO2 signals had smaller short-term variations than photosynthetic discrimination and were offset and delayed by 2-10 d, indicating fractionation and isotopic mixing in a large C pool. Variations in ?S did not follow photosynthetic discrimination at all times, especially during rainy periods and when there is a strong demand for C allocation above ground. It is likely that future isotope-enabled vegetation models will need to develop transfer functions that can account for these phenomena in order to interpret and predict the isotopic impact of biosphere gas exchange on the C isotope composition of atmospheric CO2. L. Wingate, J. Ogée, R. Burlett, A. Bosc, M. Devaux, J. Grace, D. Loustau and A. Gessler. Photosynthetic carbon isotope discrimination and its relationship to the carbon isotope signals of stem, soil and ecosystem respiration. New Phytologist, doi: 10.1111/j.1469-8137.2010.03384.x

Wingate, L.; Ogée, J.; Burlett, R.; Bosc, A.; Devaux, M.; Grace, J.; Loustau, D.; Gessler, A.

2010-12-01

177

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

178

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

NASA Astrophysics Data System (ADS)

The temperature and chemical variations of the early oceans on Earth are highly debated, particularly for periods associated with significant evolutionary change and/or extinction. The temperature of past oceans has been estimated based on conventional carbonate-water and/or silicate-water stable oxygen isotope thermometry. Precambrian carbonates and silicates both exhibit a long-term secular trend of increasing ?18O values with decreasing age. This trend has been used to support two opposite - though related - interpretations: the Earth's oceans gradually cooled over the course of the Proterozoic eon, from a maximum of ~ 60-90°C at ~ 2.5Ga (and were, on average, relatively warm during much of the Paleozoic era) [1]. This interpretation has been supported by Si-isotope proxies and the thermal tolerances of proteins in various classes of microbial organisms [2-3]. Alternatively, the ?18O value of the oceans has gradually increased through time [4-5], and mean Earth surface temperatures varied over a narrow range similar to modern conditions. In other terms, one either assumes an ocean of constant ?18O and infers that climate varied dramatically, or vise versa. Finally, it is possible that post- depositional processes (e.g., diagenesis, burial metamorphism, weathering) has modified the ?18O values of all or most Precambrian sedimentary carbonates and silicates, overprinting any paleoclimatic variations. Carbonate 'clumped isotope' thermometry provides a new way to independently test these hypotheses because it allows one to determine the apparent growth temperatures of carbonate minerals based on their abundances of 13C-18O bonds, as reflected by the '?47' value of CO2 extracted by phosphoric acid digestion [6]. This method is thermodynamically based and independent of the ?18O of water from which the carbonate grew. We will report the initial results of measurements of '?47 for a suite of carbonates from the Sultanate of Oman. This Ediacaran age (~ 635 to ~ 548 Myr) suite was buried to a range of depths that generally decrease with distance from the basin center. These Omanese dolomites vary in ?18OPDB from ~ -7 to +1 ‰, inversely correlated with their apparent crystallization temperatures from 28 to 76°C (using the unpublished calibration for temperature dependence of ?47 of dolomite). The lowest ?18O values and highest temperatures are measured for samples with petrographic evidence for post-depositional re-crystallization (e.g. coarse crystals and low porosity) and likely to have experienced the most intense burial metamorphism. The correlation we observe between ?18Ocarb. and temperature suggests that the maximum temperature of the Ediacaran oceans was 28°C and that burial metamorphism has systematically modified the ?18O values of most of the analyzed carbonates. The ?18OSMOW for seawater for this period was between -1‰ (if depositional temperatures were 28°C - the maximum permitted by our data) and -4‰ (in the unlikely case that the ocean was at its minimum possible temperature permitting the existence of liquid water). [1] Knauth and Lowe, EPSL. (1978), 41, 209-222. [2] Robert and Chaussidon (2006), Nature, 443, 969-972. [3] Gaucher et al. (2008), Nature, 451, 704-707. [4] Shields and Veizer (2002), G3, 3. [5] Jaffres et al., (2006), ESR, 83-122. [6] Ghosh et al., (2006), GCA, 70, 1439-1456.

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

2008-12-01

179

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

Microsoft Academic Search

A global carbon cycle model is used to reconstruct the carbon budget, balancing emissions from fossil fuel and land use with carbon uptake by the oceans, and the terrestrial biosphere. We apply Bayesian statistics to estimate uncertainty of carbon uptake by the oceans and the terrestrial biosphere based on carbon dioxide and carbon isotope records, and prior information on model

Haroon S. Kheshgi; Atul K. Jain; Donald J. Wuebbles

1999-01-01

180

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

181

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

182

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,...

183

Absolute and relative isotope abundances measured by tunable diode laser spectroscopy  

SciTech Connect

The potential for measuring absolute and relative isotope abundances by high resolution spectroscopy with tunable diode lasers as sources was studied. In order to achieve the sensitivity necessary to determine the absolute abundances of molecules containing long-lived radionuclides such as /sup 14/C and /sup 129/I, a resonant spectrophone based on the photoacoustic effect was used for detection. For safety, NH/sub 3/ was used as a sample with air as a buffer gas when characterizing the performance of the TDL-spectrophone system. Frequency modulation of the TDL was employed. The optimum operating pressure was found to be 6.6 kPa(50 Torr). Substitution of Kr as a buffer gas yielded a fourfold increase in signal. It is estimated that with currently available TDLs a photoacoustic spectrometer should be capable of detecting /sup 14/CO/sub 2/ and CH/sup 129/I at the levels present in nuclear reactor containment gases. An isotope shift of CH/sub 3//sup 129/I relative to CH/sub 3//sup 127/I in the nu/sub 6/ band of (0.0135 +/- 0.0006) cm/sup -1/ was measured by TDL linear absorption spectroscopy.

Tucker, G.F.

1984-01-01

184

Global warming leads the carbon isotope excursion at the Paleocene-Eocene thermal maximum  

NASA Astrophysics Data System (ADS)

The prominent negative carbon isotope excursion (CIE) at the Paleocene-Eocene thermal maximum (55.5 Ma) is generally accepted to reflect a transient, massive input of isotopically light carbon into the ocean- atmosphere system. Many authors have assumed that this carbon led to pronounced global greenhouse warming. Here we show, from an expanded record in New Jersey, that both the onset of the global abundance of the subtropical dinoflagellate Apectodinium and surface-ocean warming as recorded by TEX86 preceded the CIE by several thousands of years. The offset between Apectodinium and the CIE was confirmed in other sites from New Jersey, the North Sea and New Zealand. The approximately 3 kyrs time lag between the onset of warming and the CIE is consistent with the expected lag between bottom water warming and submarine methane hydrate dissociation, suggesting that the latter mechanism indeed caused the CIE.

Sluijs, A.; Brinkhuis, H.; Schouten, S.; Zachos, J. C.; Bohaty, S.; John, C.; Deltrap, R.; Reichart, G.; Sinninghe Damsté, J.; Crouch, E.

2006-12-01

185

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...

186

Atmospheric Trace Gases, Carbon Isotopes, Radionuclides, and Aerosols: Isotopes in Greenhouse Gases Data from the Carbon Dioxide Information Analysis Center (CDIAC)  

DOE Data Explorer

(Scroll down to find Isotopes in Greenhouse Gases, a subheading under the broader heading of Atmospheric Trace Gases, etc.) CDIAC products are indexed and searchable through a customized interface powered by ORNL's Mercury search engine. Products include numeric data packages, publications, trend data, atlases, models, etc. and can be searched for by subject area, keywords, authors, product numbers, time periods, collection sites, spatial references, etc. Some of the collections may also be included in the CDIAC publication Trends Online: A Compendium of Global Change Data. Most data sets, many with numerous data files, are free to download from CDIAC's ftp area. Information related to isotopes in greenhouse gases includes: • Monthly atmospheric 13C/12C isotopic ratios for 10 SIO stations, (2005) (Trends Online) • Mixing ratios of CO, CO2, CH4, and isotope ratios of associated 13C, 18O, and 2H in air samples from Niwot Ridge, Colorado, and Monta±a de Oro, California, USA (2004) • Estimates of Monthly CO2 Emissions and Associated 13C/12C Values from Fossil-Fuel Consumption in the U.S.A., (2004) (Trends Online) ?13C in CO2 from the CSIRO GASLAB Flask Sampling Network (Trends Online) • In Situ 13CO2 from Cape Grim, Tasmania, Australia: 1982-1993 (2001) (Trends Online) • In situ Carbon 13 and Oxygen 18 Ratios of Atmospheric CO2 from Cape Grim, Tasmania, Australia: 1982-1993 (1995) • Carbon-13 Isotopic Abundance and concentration of Atmospheric Methane for Background Air in the Southern and Northern Hemispheres from 1978 to 1989 (1995) • Measurements of Atmospheric Methane and 13C/12C of Atmospheric Methane from Flask Air Samples (1999) • 14CO 2 Observations from Schauinsland, Germany (1997) (Trends Online) • Carbon-14 Measurements in Atmospheric CO 2 from Northern and Southern Hemisphere Sites, 1962-1992 (1996) • Carbon-14 Measurements in Surface Water CO2 from the Atlantic, Indian and Pacific Oceans, 1965-1994 (1998) (Specialized Interface)

187

Isotope Fractionation in Photosynthetic Bacteria during Carbon Dioxide Assimilation 1  

PubMed Central

The ? PDB13C values have been determined for the cellular constituents and metabolic intermediates of autotrophically grown Chromatium vinosum. The isotopic composition of the HCO3- in the medium and the carbon isotopic composition of the bacterial cells change with the growth of the culture. The ? PDB13C value of the HCO3- in the media changes from an initial value of ?6.6‰ to +8.1‰ after 10 days of bacterial growth and the ? PDB13C value of the bacterial cells change from ?37.5‰ to ?29.2‰ in the same period. The amount of carbon isotope fractionation during the synthesis of hexoses by the photoassimilation of CO2 has a range of ?15.5‰ at time zero to ?22.0‰ after 10 days. This range of fractionation compares to the range of carbon isotope fractionation for the synthesis of sugars from CO2 by ribulose 1,5-diphosphate carboxylase and the Calvin cycle. The amount of carbon isotope fractionation during the synthesis of aspartic acid from CO2 is ?24.9‰ at time zero and ?15.0‰ after 10 days of bacterial growth. This amount of fractionation is in the range of carbon isotope fractionation for the synthesis of C4 amino acids by a double carboxylation through ribulose 1,5-diphosphate and phosphoenolpyruvate carboxylase.

Wong, William; Sackett, William M.; Benedict, C. Roy

1975-01-01

188

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

189

Carbon isotope fractionation and the acetyl-CoA pathway  

NASA Astrophysics Data System (ADS)

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

Blaser, Martin; Conrad, Ralf

2010-05-01

190

Experimental determination of carbon isotope fractionation between graphite and carbonated silicate melt under upper mantle conditions  

NASA Astrophysics Data System (ADS)

Carbon isotope fractionation between graphite and carbonated silicate melt was determined at 5 GPa and in the temperature range between 1400 and 1900?°C. High pressure experiments were carried out in the carbon-saturated model harzbergite system (Enstatite-Magnesite-Olivine-Graphite), where carbonated silicate melt and graphite were the two stable carbon-bearing phases in the run products. Carbonated silicate melting resulted in an isotopic fractionation between graphite and carbon in the silicate melt, where the carbon in the melt is 13C enriched than co-existing graphite. 13C enrichment in carbonate melt when compared to graphite was further confirmed in experiments where redox melting between olivine and graphite produced carbonate melt as well as carbonate reduction experiments to form graphite. Although a quantitative estimate of fractionation between carbonate melt and graphite could not be obtained, our results indicate that mantle melting in the presence of graphite can result in progressive 13C carbon isotope enrichment in carbonate melt and depletion in graphite, which can be an alternate explanation for the carbon isotopic heterogeneity observed in the mantle derived carbon.

Mizutani, Shogo; Satish-Kumar, M.; Yoshino, Takashi

2014-04-01

191

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

NASA Astrophysics Data System (ADS)

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

Riding, Robert

2006-03-01

192

Carbon and oxygen isotope variations in southern African carbonatites  

Microsoft Academic Search

The C and O isotope composition of 54 carbonate samples from 18 carbonatite localities throughout southern Africa was determined. Sample frequency distributions indicate a dependence of the ?13C and ?18O values of southern African carbonatites on their carbonate mineralogy. The calcite carbonatite samples fall into the range ?8% to ?4% for ?13C and 6% to + 10% for ?18O, which

Uwe E Horstmann; Wilhelm J Verwoerd

1997-01-01

193

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

194

[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

195

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

196

PHANEROZOIC REEFAL MICROBIAL CARBONATE ABUNDANCE: COMPARISONS WITH METAZOAN DIVERSITY, MASS EXTINCTION EVENTS, AND SEAWATER SATURATION STATE  

Microsoft Academic Search

Reefal microbial carbonate abundance data (Kiessling, 2002) show an oscillating and declining Phanerozoic trend that, very broadly, varies inversely with metazoan diversity and directly with cal- culated seawater saturation state. Reefal microbial carbonates responded most to metazoan diversity and saturation state when these influences reinforced one another. Thus, when metazoan diversity was low and saturation state high, reefal microbial carbonates

R. RIDING

2005-01-01

197

Carbon isotopic studies of organic matter in Precambrian rocks.  

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

198

Detection of exogenous hydrocortisone in horse urine by gas chromatography-combustion-carbon isotope ratio mass spectrometry.  

PubMed

A gas chromatography-combustion-isotope ratio mass spectrometry method for confirmation of hydrocortisone abuse in horseracing and equine sports is proposed. Urinary hydrocortisone was converted to a bismethylenedioxy derivative which presents good gas chromatographic properties and brings an extra carbon contribution of only two carbon atoms. Synthetic hydrocortisone has a different 13C abundance from that of natural urinary horse hydrocortisone and the difference is significant, therefore exogenous and endogenous hydrocortisone can be distinguished. PMID:9449559

Aguilera, R; Becchi, M; Mateus, L; Popot, M A; Bonnaire, Y; Casabianca, H; Hatton, C K

1997-11-21

199

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

200

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

201

Tropylium, chlorine isotopic abundances, monomeric metaphosphate anion, and conestoga wagon theory.  

PubMed

As I look back over a career in mass spectrometry, three high points stand out especially prominently. These are associated with (1) the tropylium model for the CuH 7 (+) ion in the mass spectra of toluene and other alkylbenzenes, (2) revision of the previously accepted value for the natural abundance of the chlorine isotopes, and (3) the first direct observation of the monomeric metaphosphate anion, which had been for a quarter of a century an elusive, suspected reaction intermediate. Studies of organic ions in the rarefied atmosphere of the mass spectrometer, where only unimolecular processes are allowed, have deepened my appreciation of the role and ubiquity of bimolecular processes in more conventional chemical contexts. Consideration of the two categories of molecular behavior has prompted me to seek and find, for a selected system in the mass spectrometer, parallels both in condensed-phase chemistry and, by an anthropomorphic extension, in human behavior. PMID:24227459

Meyerson, S

1993-10-01

202

The R Coronae Borealis stars: carbon abundances from forbidden carbon lines  

NASA Astrophysics Data System (ADS)

Spectra of several R Coronae Borealis (RCB) stars at maximum light have been examined for the [CI] 9850- and 8727-Åabsorption lines. The 9850-Åline is variously blended with an FeII and CN lines, but positive identifications of the [CI] line are made for RCrB and SUTau. The 8727-Åline is detected in the spectrum of the five stars observed in this wavelength region. Carbon abundances are derived from the [CI] lines using the model atmospheres and atmospheric parameters used by Asplund et al. Although the observed strength of a CI line is constant from cool to hot RCB stars, the strength is lower than predicted by an amount equivalent to a factor of 4 reduction of the gf-value of a line. Asplund et al. dubbed this `the carbon problem' and discussed possible solutions. The [CI] 9850-Åline seen clearly in RCrB and SUTau confirms the magnitude of the carbon problem revealed by the CI lines. The [CI] 8727-Åline measured in five stars shows an enhanced carbon problem. The gf-value required to fit the observed [CI] 8727-Åline is a factor of 15 less than the well-determined theoretical gf-value. We suggest that the carbon problem for all lines may be alleviated to some extent by a chromospheric-like temperature rise in these stars. The rise far exceeds that predicted by our non-local thermodynamic equilibrium calculations, and requires a substantial deposition of mechanical energy.

Pandey, Gajendra; Lambert, David L.; Rao, N. Kameswara; Gustafsson, Bengt; Ryde, Nils; Yong, David

2004-09-01

203

Carbon and oxygen isotope composition of carbonates from an L6 chondrite: Evidence for terrestrial weathering from the Holbrook meteorite  

NASA Technical Reports Server (NTRS)

Terrestrial weathering in meteorites is an important process which alters pristine elemental and isotopic abundances. The Holbrook L6 chondrite fell in 1912. Material was recovered at the time of the fall, in 1931, and 1968. The weathering processes operating on the freshly fallen meteorite in a semi-arid region of northeastern Arizona have been studied after a ground residence of 19 and 56 years. It has been shown that a large portion of the carbonate material in 7 Antarctic ordinary chondrites either underwent extensive isotopic exchange with atmospheric CO2, or formed recently in the Antarctic environment. In fact it has been demonstrated that hydrated Mg-carbonates, nesquehonite and hydromagnesite, formed in less than 40 years on LEW 85320. In order to help further constrain the effects of terrestrial weathering in meteorites, the carbon and oxygen isotopes extracted from carbonates of three different samples of Holbrook L6: a fresh sample at the time of the fall in 1912, a specimen collected in 1931, and a third specimen collected at the same site in 1968.

Socki, R. A.; Gibson, E. K.; Jull, A. J. T.; Karlsson, H. R.

1991-01-01

204

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

205

Abundance and isotopic composition of noble gases in metal and graphite of the Bohumilitz IAB iron meteorite  

NASA Astrophysics Data System (ADS)

Abundances and isotopic compositions of noble gases in metal and graphite of the Bohumilitz IAB iron meteorite were measured. The abundance ratios of spallogenic components in metal reveal a 3He deficiency which is due to the diffusive loss of parent isotopes, i.e., tritium (Tilles, 1963; Schultz, 1967). The diffusive loss likely has been induced by thermal heating by the Sun during cosmic ray exposure (( 160 My; Lavielle et al., 1999). Thermal process such as impact-induced partial loss may have affected the isotopic composition of spallogenic Ne. The 129Xe/131Xe ratio of cosmogenic components in the metal indicates an enhanced production of epi-thermal neutrons. The abundance ratios of spallogenic components in the graphite reveal that it contained small amounts of metal and silicates. The isotopic composition of heavy noble gases in graphite itself was obtained from graphite treated with HF/HCl. The isotopic composition of the etched graphite shows that it contains two types of primordial Xe, i.e., Q-Xe and El Taco Xe. The isotopic heterogeneity preserved in the Bohumilitz graphite indicates that the Bohumilitz graphite did not experience any high(temperature event and, consequently, must have been emplaced into the metal at subsolidus temperatures. This situation is incompatible with an igneous model as well as the impact melting models for the IAB-IIICD iron meteorites as proposed by Choi et al. (1995) and Wasson et al. (1980).

Maruoka, Teruyuki; Matsuda, Jun-Ichi; Kurat, Gero

2001-05-01

206

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

207

Pu abundances, concentrations, and isotopics by x- and gamma-ray spectrometry assay techniques  

SciTech Connect

Two x- and gamma-ray systems were recently installed at-line in gloveboxes and will measure Pu solution concentrations from 5 to 105 g/L. These NDA technique, developed and refined over the past decade, are now used domestically and internationally for nuclear material process monitoring and accountability needs. In off- and at-line installations, they can measure solution concentrations to 0.2%. The K-XRFA systems use a transmission source to correct for solution density. The gamma-ray systems use peaks from 59- to 208-keV to determine solution concentrations and relative isotopics. A Pu check source monitors system stability. These two NDA techniques can be combined to form a new, NDA measurement methodology. With the instrument located outside of a glovebox, both relative Pu isotopics and absolute Pu abundances of a sample located inside a glovebox can be measured. The new technique works with either single or dual source excitation; the former for a detector 6 to 20 cm away with no geometric corrections needed; the latter requires geometric corrections or source movement if the sample cannot be measured at the calibration distance. 4 refs., 7 figs., 2 tabs.

Camp, D.C.; Gunnink, R.; Ruhter, W.D.; Prindle, A.L.; Gomes, R.J.

1986-10-24

208

A high-spectral-resolution study of abundances and isotopic composition of BHB stars in NGC 6397 and NGC 6752  

NASA Astrophysics Data System (ADS)

Large abundance anomalies have previously been detected in horizontal-branch B-type stars. We present the first high-resolution study of isotopic anomalies and chemical abundances in six horizontal-branch B-type stars in the globular clusters NGC 6397 and NGC 6752, carried out with UVES on the VLT and compare them to those observed in chemically peculiar main-sequence stars.

Hubrig, S.; Castelli, F.; De Silva, G.; González, J. F.; Momany, Y.; Netopil, M.; Moehler, S.

2010-01-01

209

Oxygen and Carbon Isotope Ratios of Fresh-Water Carbonates as Climatic Indicators  

Microsoft Academic Search

The temperature dependence of the fractiona- tion of oxygen isotopes in the carbon-dioxide- water-carbonate system has been employed extensively for paleotemperature measurements since the method was first proposed by Urey (1947). The method is based on the observa- tion that the temperature of a solution from which carbonate is slowly precipitated is re- flected in the 80\\/n60 isotope ratio of

Minze Stuiver

1970-01-01

210

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

211

Stable Carbon Isotope Fractionation by Methylotrophic Methanogenic Archaea  

PubMed Central

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

Penger, Jorn; Conrad, Ralf

2012-01-01

212

Surface carbon abundances and compositional stratification of cool helium-rich white dwarfs  

NASA Astrophysics Data System (ADS)

From the ultraviolet lines of CI in IUE spectra of the DQ white dwarfs L 845-70, GD 84, and G 188-27 we determine a surface carbon abundance of log C/He = -7, and Teff = 9,250, 9,000 and 11,000 K. Comparison with the results for other stars of the same spectral class indicates variations in carbon abundance at the same temperature. If the carbon is the result of surface pollution by interior carbon dredged up by convection, we conclude that the variations cannot be caused by mass differences but probably by different outer helium layer thicknesses.

Weidemann, V.; Koester, D.

1995-05-01

213

Abundances of carbon, nitrogen, and oxygen in the atmospheres of Cepheid variables: Evidence for helium enrichment  

SciTech Connect

A model-atmosphere analysis of Reticon spectra of 14 Cepheid variables and several nonvariable supergiants provides the effective temperatures, surface gravities, and abundances of carbon, nitrogen, oxygen, and metals (Z>10). The internal accuracy of the results is +- 200 K in T/sub eff/, +- 0/3 in log g, and +- 0/2 dex in the abundances.

Luck, R.E.; Lambert, D.L.

1981-05-01

214

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

215

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

216

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

217

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

218

Isotopic anomalies from neutron reactions during explosive carbon burning  

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

219

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

220

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

221

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

222

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

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

1990-01-01

223

Effect of Phytoplankton Cell Geometry on Carbon Isotopic Fractionation  

NASA Astrophysics Data System (ADS)

The carbon isotopic compositions of the marine diatom Porosira glacialis and the marine cyanobacterium Synechococcus sp. were measured over a series of growth rates (?) in a continuous culture system in which the concentration and carbon isotopic composition of CO 2(aq) were determined. These data were compared with previously published isotopic results of growth rate experiments using the marine diatom Phaeodactylum tricornutum and the marine haptophyte Emiliania huxleyi. Systematic relationships were found to exist between ?/[CO 2(aq)] and carbon isotopic fractionation (? P) for each species. Maximum isotopic fractionation (? f) for P. glacialis, E. huxleyi, and P. tricornutum was ˜25‰, suggesting that this value may be typical for maximum fractionation associated with Rubisco and ?-carboxylases for marine eukaryotic algae. By contrast, ? f determined for Synechococcus clone CCMP838 was ˜7‰ lower. The slopes of the lines describing the relationship between ? P and ?/[CO 2(aq)] for eukaryotic algal species were different by a factor of more than 20. This result can be accounted for by differences in the surface area and cellular carbon content of the cells. Comparison of chemostat experimental results with calculated results using a diffusion based model imply that the algae in the experiments were actively transporting inorganic carbon across the cell membrane. Our results suggest that accurate estimates of paleo-[CO 2(aq)] from ? P measured in sediments will require knowledge of growth rate as well as cell surface area and either cell carbon quota or cell volume. Given growth rate estimates, our empirical relationship permits reliable calculations of paleo-[CO 2(aq)] using compound-specific isotopic analyses of C 37 alkadienones (select haptophytes) or fossilized frustules (diatoms).

Popp, Brian N.; Laws, Edward A.; Bidigare, Robert R.; Dore, John E.; Hanson, Kristi L.; Wakeham, Stuart G.

1998-01-01

224

Factors That Control the Stable Carbon Isotopic Composition of Methane Produced in an Anoxic Marine Sediment.  

National Technical Information Service (NTIS)

The carbon isotopic composition of methane produced in anoxic marine sediment is controlled by four factors: (1) the pathway of methane formation, (2) the isotopic composition of the methanogenic precursors, (3) the isotope fractionation factors for metha...

M. J. Alperin N. E. Blair D. B. Albert T. M. Hoehler C. S. Martens

1993-01-01

225

Natural abundance-level measurement of the nitrogen isotopic composition of oceanic nitrate: an adaptation of the ammonia diffusion method  

Microsoft Academic Search

We have adapted the “ammonia diffusion” method of nitrate extraction for natural-abundance level nitrogen isotopic measurement of oceanic nitrate. The method involves: (1) sample concentration (by boiling or evaporation); (2) conversion of nitrate to ammonia using Devarda's alloy; and (3) the gas-phase diffusion of ammonia onto an acidified glass fiber disk which is sandwiched between two porous Teflon membranes. We

D. M. Sigman; M. A. Altabet; R. Michener; D. C. McCorkle; B. Fry; R. M. Holmes

1997-01-01

226

Sulfur Multiple Isotopes of the Moon: 33S and 36S Abundances Relative to Canon Diablo Troilite  

NASA Astrophysics Data System (ADS)

We are measuring sulfur multiple isotope abundances in 10 lunar basalts, a suite of terrestrial igneous rocks, and samples of Canon Diablo Troilite (CDT). Ongoing measurements suggest that the acid volatile sulfur (AVS) in lunar basalts is only slightly enriched in 34S relative to CDT.

Farquhar, J.; Wing, B. A.

2005-03-01

227

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

228

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

229

Study of the Remineralization of Organic Carbon in Nearshore Sediments Using Carbon Isotopes.  

National Technical Information Service (NTIS)

Major processes affecting the carbon chemistry in the sediments of Buzzards Bay, MA were reflected by changes in the stable carbon isotope ratios of dissolved inorganic carbon sigma CO2 in sediment pore water. The delta (13)C (PDB) of Sigma CO2 varies fro...

A. P. McNichol

1986-01-01

230

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

231

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

232

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

233

Interpreting the Ca isotope record of marine biogenic carbonates  

NASA Astrophysics Data System (ADS)

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

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

2007-08-01

234

Aptian Carbon Isotope Stratigraphy in Sierra del Rosario, Northeastern Mexico  

NASA Astrophysics Data System (ADS)

In most recent years Aptian carbon isotope stratigraphy has been widely studied in Europe where isotopic stages have been developed to correlate global events. Two negative excursions have been recorded in the Lower Aptian, the older is OAE 1a in the middle part, and a younger negative excursion labeled "Aparein level", which occurs in the uppermost part of the Lower Aptian. In Mexico previous works reported a carbon isotope negative excursion in the lowermost part of the La Peña Formation that was assigned to the onset of Oceanic Anoxic Event 1a (=OAE 1a). In this work we study the isotopic record of the ?13Ccarb of 32 bulk rock samples of limestone from the uppermost part of the Cupido Formation and the lower part of the La Peña Formation at the Francisco Zarco Dam Section (=FZD), Durango State, northeastern Mexico. The isotopic data are calibrated using the latest ammonite biostratigraphic biozonation of the Aptian. This age calibration allows us to make a precise correlation between the carbon isotopic record of Mexico and several European sections (e.g. Spain and France). In the studied Francisco Zarco Dam section we recognize a negative carbon isotopic excursion in the Dufrenoyia justinae ammonite Zone that corresponds to the "Aparein level", which we correlate using the ammonite zonation of others European sections (Figure 1). This correlation allows us to see how the negative excursion that characterizes the "Aparein level" is consistent with the C7 segment. Thus, our recent stratigraphic study allows us to conclude that the ammonite record in the lowermost part of the La Peña Formation is regionally isochronous, and correlates with the Dufrenoyia justinae Zone and Lower Aptian isotope interval C7. In agreement to these biostratigraphic data, the supposed record of the OAE 1a in the lowermost part of the La Peña Formation is not correct, and the carbon isotope negative excursion must be assigned to the younger event "Aparein level". Taking this into account, other Lower Aptian negative excursions reported in the literature and assigned to the OAE 1a, perhaps, must be reconsidered to distinguish among the two Lower Aptian negative excursions.; Figure 1: Isotopic curve of the FZD section compared with one section of Spain. The sharp negative peak in the Mexican section is compared with the Spanish section (see the arrow).

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

2013-05-01

235

Nitrogen and carbon isotopic ratios of chlorophyll from marine phytoplankton  

NASA Astrophysics Data System (ADS)

The relationship between the nitrogen and carbon isotopic ratios of chlorophyll a and total biomass was explored in cultured marine phytoplankton to assess the utility of chlorophyll as an isotopic proxy for photoautotrophs. A near constant nitrogen isotopic depletion of 5.06 ± 1.13‰ (95% confidence interval) in chlorophyll a relative to total nitrogen was observed in 8 species. This value was similar to isotopic differences between chlorophyll a and marine particles (5.27 ± 1.48‰ (1?); n = 6) and sediments (5.39 ± 0.67‰ (1?); n = 4) in a variety of settings. These findings suggest that a 5.1‰ isotopic depletion of chlorophyll a relative to total algal nitrogen is a robust relationship that justifies the use of chlorophyll as a nitrogen isotopic surrogate for photoautotrophs. Although interspecies differences in ?? 15N cell-Chla exist, and growth rate has a small effect on this parameter, the field data suggest these factors are probably minimized in the ocean where multiple species and growth rates occur. The nitrogen isotopic depletion of chlorophyll a probably occurs during the transamination of glutamic acid in ?-aminolevulinic acid biosynthesis, the first committed precursor to chlorophyll. The carbon isotopic composition of chlorophyll from 12 batch cultures and 7 species of marine phytoplankton was elevated by 0.32 ± 1.61‰ (95% confidence interval) relative to total cellular carbon. No significant interspecies variance was observed that was not attributable to intraspecies variance. There was a moderate inverse correlation between growth rate and ?? 13C cell-Chla, and it is hypothesized that this parameter is largely responsible for the large range of intraspecies ?? 13C cell-Chla values observed in batch cultures.

Sachs, Julian P.; Repeta, Daniel J.; Goericke, Ralf

1999-05-01

236

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

237

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

238

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

239

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 ...

240

Organic Carbon Degradation in Anoxic Organic-Rich Shelf Sediments: Biogeochemical Rates and Microbial Abundance  

Microsoft Academic Search

Identifying and explaining bottlenecks in organic carbon mineralization and the persistence of organic matter in marine sediments remain challenging. This study aims to illuminate the process of carbon flow between microorganisms involved in the sedimentary microbial food chain in anoxic, organic-rich sediments of the central Namibian upwelling system, using biogeochemical rate measurements and abundances of Bacteroidetes, Gammaproteobacteria, and sulfate-reducing bacteria

Elsabé M. Julies; Bernhard M. Fuchs; Carol Arnosti; Volker Brüchert

2010-01-01

241

Microscale carbon isotope variability in ALH84001 carbonates and a discussion of possible formation environments  

NASA Astrophysics Data System (ADS)

The carbonates in martian meteorite ALH84001 preserve a record of aqueous processes on Mars at 3.9 Ga, and have been suggested to contain signatures of ancient martian life. The conditions of the carbonate formation environment are critical for understanding possible evidence for life on Mars, the history of water on Mars, and the evolution of the martian atmosphere. Despite numerous studies of petrographic relationships, microscale oxygen isotope compositions, microscale chemical compositions, and other minerals associated with the carbonates, formation models remain relatively unconstrained. Microscale carbon isotope analyses of ALH84001 carbonates reveal variable ? 13C values ranging from +27 to +64 ‰. The isotopic compositions are correlated with chemical composition and extent of crystallization such that the Mg-poor, early-formed carbonates are relatively 13C depleted and the Mg-rich, later forming carbonates, are 13C enriched. These data are inconsistent with many of the previously proposed environments for carbonate formation, and a new set of hypotheses are proposed. Specifically, two new models that account for the data involve low temperature (<100°C) aqueous processes: (1) the carbonates formed during mixing of two fluids derived from separate chemical and isotopic reservoirs; or (2) the carbonates formed from high pH fluids that are exposed to a CO 2-rich atmosphere and precipitate carbonate, similar to high pH springs on Earth.

Niles, P. B.; Leshin, L. A.; Guan, Y.

2005-06-01

242

High Resolution Carbon and Oxygen Isotope Measurements of Laminations in Pedogenic Carbonate  

NASA Astrophysics Data System (ADS)

Stable carbon and oxygen isotope ratios in pedogenic carbonate from buried soils provide a proxy for low-resolution Quaternary climate and environmental conditions. Samples of carbonate are taken from clast rinds, nodules or filaments in calcic soils. Most clast rinds exhibit micro-laminations that may preserve isotopic ratios of formation. The techniques typically utilized to sample pedogenic carbonate, however, are too coarse to sample individual laminations and likely result in time averages and therefore limit temporal resolution. We investigated the heterogeneity of both carbon and oxygen isotopes ratios in clast rinds at a 100 ?m scale using a rapid CO2 laser extraction technique (Sharp and Cerling, 1996). A single 20 msec burst at low power releases CO2 from polished carbonate slabs and the CO2 is then analyzed using continuous flow GC-IRMS. Analyses take less than 5 minutes with a reproducibility of better than ±0.3‰ (?13C) and ±0.4‰ (?18O). We have made a two dimensional map of a thick carbonate rind on a limestone clast from a stage V soil to explore the potential for preservation of isotopic ratios in well developed soils and plan to analyze additional rinds from less well developed calcic horizons for comparison. The isotopic map reveals heterogeneities in ?13C of up to 4‰ at a sub-millimeter scale, possibly corresponding to 30% changes in the fraction of C4 plants. Also imaged are abrupt changes in ?13C of approximately 2‰ across sub-100 ?m scale boundaries. One well-defined carbon isotope boundary is sub parallel to, but crosses, the lamination boundaries. Oxygen isotope compositions do not change systematically across the same boundary and generally appear more random. These observations are most easily explained by alteration of initial isotopic compositions. Alteration may preferentially affect oxygen isotope ratios leaving carbon isotope distributions relatively intact. It is also possible that both carbon and oxygen isotopes distributions are mostly primary but that variations in ?18O occur at a much smaller scale than variations in ?13C. The apparently random oxygen isotope zoning could then be explained as the result of sampling multiple homogeneous zones with 100 ?m laser pits. Detailed analyses of clast rinds from less well-developed soils may help resolve these questions.

Breecker, D.; Sharp, Z.

2005-12-01

243

Carbon-enhanced metal-poor stars abundances (Allen+, 2012)  

NASA Astrophysics Data System (ADS)

Abundances for 18 CEMP stars are presented: BS 15621-047, BS 16033-081, BS 16077-077, BS 16082-129, BS 16543-097, BS 16929-005, CS 22949-008, CS 29503-010, CS 29512-073, CS 29526-110, CS 29528-028, CS 31070-073, BS 16080-175, BS 17436-058, CS 22183-015, CS 22887-048, CS 22898-027, CS 29502-092. Our results were compared to data of 109 stars from the literature. (4 data files).

Allen, D. M.; Ryan, S. G.; Rossi, S.; Beers, T. C.; Tsangarides, S. A.

2012-11-01

244

Stable carbon isotopes: Possible clues to early life on mars  

Microsoft Academic Search

Organic and inorganic carbon in terrestrial near-surface environments are characterized by a marked difference in their 13C\\/12C ratios which can be traced back in the Earth's sedimentary record over almost 4 billion years. There is no doublt that the bias in favour of 12C displayed by biogenic matter derives, for the most part, from the isotope-selecting properties of the carbon-fixing

Manfred Schidlowski

1992-01-01

245

Isotopic investigations of carbonate growth on concrete structures  

Microsoft Academic Search

Stable C and O isotope ratios were measured in carbonate minerals, growing under concrete structures from two locations in the United States. These locations were under a bridge in Michigan and under an overpass in New York. The ?13C of the carbonate samples ranged from ?21.6 to ?31.4‰ (with respect to V-PDB) and clearly indicated precipitation under non-equilibrium conditions. Indeed,

R. V. Krishnamurthy; D. Schmitt; E. A. Atekwana; M. Baskaran

2003-01-01

246

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

PubMed

• Photosynthetic carbon (C) isotope discrimination (?(?)) labels photosynthates (?(A) ) and atmospheric CO(2) (?(a)) with variable C isotope compositions during fluctuating environmental conditions. In this context, the C isotope composition of respired CO(2) within ecosystems is often hypothesized to vary temporally with ?(?). • We investigated the relationship between ?(?) and the C isotope signals from stem (?(W)), soil (?(S)) and ecosystem (?(E)) respired CO(2) to environmental fluctuations, using novel tuneable diode laser absorption spectrometer instrumentation in a mature maritime pine forest. • Broad seasonal changes in ?(?) were reflected in ?(W,) ?(S) and ?(E). However, respired CO(2) signals had smaller short-term variations than ?(A) and were offset and delayed by 2-10 d, indicating fractionation and isotopic mixing in a large C pool. Variations in ?(S) did not follow ?(A) at all times, especially during rainy periods and when there is a strong demand for C allocation above ground. • It is likely that future isotope-enabled vegetation models will need to develop transfer functions that can account for these phenomena in order to interpret and predict the isotopic impact of biosphere gas exchange on the C isotope composition of atmospheric CO(2). PMID:20663061

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

2010-10-01

247

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

248

Biomarkers, carbon isotopic composition and source rock potentials of Awgu coals, middle Benue trough, Nigeria  

NASA Astrophysics Data System (ADS)

Coal and carbonaceous shale samples were collected from two boreholes (BH 94 and BH 120) in Awgu formation of Middle Benue Trough, Nigeria. Source rock potentials of the samples were studied using biomarkers and carbon isotopic composition. Biomarkers in the aliphatic fractions in the samples were studied using Gas Chromatography-Mass Spectrometry (GC-MS). The Carbon isotope analysis of individual n-alkanes in the aliphatic fraction was performed using Gas Chromatography-Combustion-Isotope Ratio Mass Spectrometer (GC-IRMS). The abundance of hopanes, homohopanes (C31-C35), and C29 steranes in the samples indicate terrestrial plant, phytoplankton and cyanobacteria contributions to the organic matter that formed the coal. High (Pr/Ph) ratio (3.04-11.07) and isotopic distribution of individual alkanes showed that the samples consisted of mixed terrestrial/marine organic matter deposited under oxic condition in lacustrine-fluvial/deltaic depositional environment. The maturity parameters derived from biomarker distributions showed that the samples are in the main phase of oil window.

Adedosu, Taofik A.; Sonibare, Oluwadayo O.; Tuo, Jincai; Ekundayo, Olusegun

2012-05-01

249

Low stable carbon isotope fractionation by coccolithophore RubisCO  

NASA Astrophysics Data System (ADS)

The 13C/ 12C ratio of carbon compounds is used to identify sources and sinks in the global carbon cycle. However, the relatively enriched 13C content observed for marine organic carbon remains enigmatic. The majority of oceanic carbon is fixed by algae and cyanobacteria via the Calvin-Benson-Bassham cycle, yet isotopic discrimination by the CO 2 fixation enzyme, RubisCO (ribulose 1,5-bisphosphate carboxylase/oxygenase), has only been measured for a single marine cyanobacterium. Different forms of RubisCO occur in different phytoplankton species (overall amino acid identity varying by as much as ˜75%) and thus may vary in the degree to which they fractionate carbon. Here we measured isotope discrimination by RubisCO from the coccolithophore Emiliania huxleyi, a cosmopolitan species used as a marine algal model .E. huxleyi RubisCO discriminated substantially less ( ? = 11.1‰) against 13CO 2 than other RubisCO enzymes (18-29‰), despite having Michaelis-Menten kinetic parameters ( K = 72 ?M; Vmax = 0.66 ?mol min -1 mg -1 protein) similar to those measured for RubisCO enzymes from different organisms. If widespread, decreased isotope discrimination of 13C by phytoplankton RubisCO may be a major factor influencing the enriched 13C content of marine organic carbon. This finding emphasizes the necessity of (a) determining ? values for RubisCOs of other marine phytoplankton and (b) re-evaluation of ?13C values from physiological, environmental, and geological studies.

Boller, Amanda J.; Thomas, Phaedra J.; Cavanaugh, Colleen M.; Scott, Kathleen M.

2011-11-01

250

Carbon and hydrogen isotope fractionation by moderately thermophilic methanogens  

NASA Astrophysics Data System (ADS)

A series of laboratory studies were conducted to increase understanding of stable carbon ( 13C/ 12C) and hydrogen (D/H) isotope fractionation arising from methanogenesis by moderately thermophilic acetate- and hydrogen-consuming methanogens. Studies of the aceticlastic reaction were conducted with two closely related strains of Methanosaeta thermophila. Results demonstrate a carbon isotope fractionation of only 7‰ (? = 1.007) between the methyl position of acetate and the resulting methane. Methane formed by this process is enriched in 13C when compared with other natural sources of methane; the magnitude of this isotope effect raises the possibility that methane produced at elevated temperature by the aceticlastic reaction could be mistaken for thermogenic methane based on carbon isotopic content. Studies of H 2/CO 2 methanogenesis were conducted with Methanothermobacter marburgensis. The fractionation of carbon isotopes between CO 2 and CH 4 was found to range from 22 to 58‰ (1.023 ? ? ? 1.064). Greater fractionation was associated with low levels of molecular hydrogen and steady-state metabolism. The fractionation of hydrogen isotopes between source H 2O and CH 4 was found to range from 127 to 275‰ (1.16 ? ? ? 1.43). Fractionation was dependent on growth phase with greater fractionation associated with later growth stages. The maximum observed fractionation factor was 1.43, independent of the ?D-H 2 supplied to the culture. Fractionation was positively correlated with temperature and/or metabolic rate. Results demonstrate significant variability in both hydrogen and carbon isotope fractionation during methanogenesis from H 2/CO 2. The relatively small fractionation associated with deuterium during H 2/CO 2 methanogenesis provides an explanation for the relatively enriched deuterium content of biogenic natural gas originating from a variety of thermal environments. Results from these experiments are used to develop a hypothesis that differential reversibility in the enzymatic steps of the H 2/CO 2 pathway gives rise to variability in the observed carbon isotope fractionation. Results are further used to constrain the overall efficiency of electron consumption by way of the hydrogenase system in M. marburgensis, which is calculated to be less than 55%.

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

2004-04-01

251

Oxygen and Carbon Isotope Ratios in CO2on Mars  

Microsoft Academic Search

The major problems in spectroscopic determinations of the oxygen and carbon isotope ratios on Mars are uncertainties associated with (1) equivalent widths of the observed absorption lines, (2) line strengths in spectroscopic databases, and (3) thermal structure of the Martian atmosphere during the observation. We have made special efforts to reduce all these uncertainties. We observed Mars using Fourier Transform

V. A. Krasnopolsky; J. Maillard; T. C. Owen; R. A. Toth; M. D. Smith

2007-01-01

252

Oxygen and carbon isotope ratios in the martian atmosphere  

Microsoft Academic Search

Oxygen and carbon isotope ratios in the martian CO2 are key values to study evolution of volatiles on Mars. The major problems in spectroscopic determinations of these ratios on Mars are uncertainties associated with: (1) equivalent widths of the observed absorption lines, (2) line strengths in spectroscopic databases, and (3) thermal structure of the martian atmosphere during the observation. We

Vladimir A. Krasnopolsky; Jean Pierre Maillard; Tobias C. Owen; Robert A. Toth; Michael D. Smith

2007-01-01

253

Carbon isotope exchange rate of DIC in karst groundwater  

Microsoft Academic Search

The kinetics of isotopic exchange between dissolved inorganic carbon (DIC) of groundwater and calcite of the matrix of karst aquifers of Cyrenaica, Libya, can be deduced from 13C and 14C data. The aquifers are mostly confined, and the majority of the wells do not show any occurrence of modern recharge: in 1976–1980, in fact, the tritium content was below 1

Roberto Gonfiantini; Gian Maria Zuppi

2003-01-01

254

Accuracy of relative isotopic abundance and mass measurements in a single-stage orbitrap mass spectrometer.  

PubMed

Orbitrap technology offers a combination of different technical specifications which have not yet been achieved by other high-resolution mass spectrometry instrumentation. This refers to the combination of sensitivity, dynamic range, mass accuracy, resolution and speed. The high stability of the mass axis and the general ease of use made the orbitrap instrumentation attractive for routine laboratories. However, there are circumstances where significantly deviating relative isotopic abundance (RIA) and shifting accurate masses can be observed. RIA becomes biased at low ion counts. Furthermore, two adjacent, only partially resolved near-isobaric ions are detected with a deviating RIA. The presence of a very intensive mass peak does not only induce Fourier transformation related artefacts (side-lobes) but can cause mass shifts of small adjacent near-isobaric mass peaks. These effects are not as drastic as known for Fourier transform ion cyclotron resonance instruments. Still, users trying to identify or quantify trace level compounds should be aware about such limitations in order to avoid possible pitfalls. PMID:22467458

Kaufmann, A; Walker, S

2012-05-15

255

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

256

Determination of organic milk authenticity using carbon and nitrogen natural isotopes.  

PubMed

Natural stable isotopes of carbon and nitrogen ((12)C, (13)C, (14)N, (15)N) have abundances unique to each living creature. Therefore, measurement of the stable isotope ratio of carbon and nitrogen (?(13)C=(13)C/(12)C, ?(15)N=(15)N/(14)N) in milk provides a reliable method to determine organic milk (OM) authenticity. In the present study, the mean ?(13)C value of OM was higher than that of conventional milk (CM), whereas the mean ?(15)N value of OM was lower than that of CM; nonetheless both ?(13)C and ?(15)N values were statistically different for the OM and CM (P<0.05). Furthermore, the values of ?(13)C and ?(15)N were found to differ statistically with the collection date and the milk brand (P<0.05). The combination of ?(13)C and ?(15)N values was more effective than either value alone in distinguishing between OM and CM. The results of the present study, which is based on preliminary data from a limited sample size and sampling period, could be highly valuable and helpful for consumers, the food industry, and/or government regulatory agencies as it can prevent fraudulent labelling of organic food. Further studies include additional analyses of other milk brands and analyses over longer time periods in order to accurately determine OM authenticity using stable isotopes of carbon and nitrogen. PMID:24799230

Chung, Ill-Min; Park, Inmyoung; Yoon, Jae-Yeon; Yang, Ye-Seul; Kim, Seung-Hyun

2014-10-01

257

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

258

The stable carbon isotope composition of soil organic carbon and pedogenic carbonates along a bioclimatic gradient in the Palouse region, Washington State, USA  

Microsoft Academic Search

Isotopic signatures of soil components are commonly used to infer past ecologic and climatic shifts in the soil record. The theory behind the fractionation of isotopes that occurs during ecosystem processes is well understood; however, few isotopic studies have explored ecosystem relationships in modern soils. We discuss relationships of stable carbon isotopic signatures in plant tissue, soil organic carbon (SOC),

B. A. Stevenson; E. F. Kelly; E. V. McDonald; A. J. Busacca

2005-01-01

259

{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

260

A carbon isotope challenge to the snowball Earth.  

PubMed

The snowball Earth hypothesis postulates that the planet was entirely covered by ice for millions of years in the Neoproterozoic era, in a self-enhanced glaciation caused by the high albedo of the ice-covered planet. In a hard-snowball picture, the subsequent rapid unfreezing resulted from an ultra-greenhouse event attributed to the buildup of volcanic carbon dioxide (CO(2)) during glaciation. High partial pressures of atmospheric CO(2) (pCO2; from 20,000 to 90,000?p.p.m.v.) in the aftermath of the Marinoan glaciation (?635?Myr ago) have been inferred from both boron and triple oxygen isotopes. These pCO2 values are 50 to 225 times higher than present-day levels. Here, we re-evaluate these estimates using paired carbon isotopic data for carbonate layers that cap Neoproterozoic glacial deposits and are considered to record post-glacial sea level rise. The new data reported here for Brazilian cap carbonates, together with previous ones for time-equivalent units, provide estimates lower than 3,200?p.p.m.v.--and possibly as low as the current value of ?400?p.p.m.v. Our new constraint, and our re-interpretation of the boron and triple oxygen isotope data, provide a completely different picture of the late Neoproterozoic environment, with low atmospheric concentrations of carbon dioxide and oxygen that are inconsistent with a hard-snowball Earth. PMID:21979050

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

2011-10-01

261

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

NASA Astrophysics Data System (ADS)

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 top of the member reveals an isotopic shift of ? 13C (-5‰) and ? 18O (-10‰), probably related to a descent in the sea level. The sandy Güemes Member has isotopically negative (-2‰ ? 13C, -1‰ ? 18O) limestones, principally controlled by water mixing, decreased organic productivity, and compositional changes in the carbonates. The isotopically lighter limestones are calcitic, with a greater terrigenous contribution and different geochemical composition (high Si-Mn-Fe-Na, low Ca-Mg-Sr). These isotopic and lithological changes relate to the Cretaceous-Palaeogene transition. The Alemanía Member, composed of dolomitic limestones and pelites, represents a return to marine conditions and shows a gradual increase in isotopic values, reaching values similar to those of the Amblayo Member. The Juramento Member, composed of stromatolite limestones, shows isotopic variations that can be correlated with the two well-defined, shallowing-upward sequences of the member.

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

2007-04-01

262

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

263

Stable carbon isotopes in bivalve shells as a salinity proxy  

NASA Astrophysics Data System (ADS)

Stable carbon isotopes of dissolved inorganic carbon (?13C-DIC) often vary with salinity in estuarine settings. Variations of salinity in estuaries also complicate temperature reconstructions based on oxygen isotope values in biological carbonates. Therefore having a salinity proxy could assist in estuarine temperature reconstruction as well as providing data on freshwater discharge into the estuary. Unfortunately, ?13C values in bivalve shells are potentially influenced by several sources of carbon including DIC, metabolic carbon and sediment pore-water DIC. This study first investigates the influence of these three potential carbon sources in the Manila clam (Ruditapes philippinarum) reared under laboratory conditions and then in the field during a two-year monitoring study. Metabolic carbon remained fairly constant in the laboratory (~12%) and we did not detect any difference between clams living in organic rich sediments and those in sediment free aquaria. There was a strong correlation between ?13C-shell and ?13C-DIC (r2=0.77) indicating that ?13C-shell can be used as a relative salinity indicator. In the field, calculated salinities were within the range of recorded salinities (± 5 salinity units), but there were significant differences between individuals. This study highlights the potential of using ?13C in bivalve shells as a salinity proxy, but also illustrates that large uncertainties are associated with this proxy.

Gillikin, D. P.; Poulain, C.; Mas, R.; Woule Ebongue, V.; Robert, R.; Paulet, Y.; Lorrain, A.

2010-12-01

264

Biosynthetic control of the natural abundance of carbon 13 at specific positions within fatty acids in Escherichia coli. Evidence regarding the coupling of fatty acid and phospholipid synthesis  

SciTech Connect

Stable carbon isotope ratios (/sup 13/C//sup 12/C) at natural abundance levels have been determined for individual carbon atoms in each of the major phospholipid fatty acids of Escherichia coli grown on glucose as the sole carbon source. Two models were constructed for the isotope effects and carbon flow pathways which must be responsible for the observed isotopic fractionations. Both models incorporate a branch in the carbon flow at which fatty acyl-acyl carrier protein (acyl-ACP) is utilized either for complex lipid synthesis or for elongation by fatty acid synthetase. Depletion of carbon 13 in the carboxyl groups of myristic and palmitoleic acids (relative to carbonyl groups in precursor acyl-ACP's) was observed to occur at this branching site. Only one of the models was consistent both with this observation and with the observation that exogenous fatty acids are incorporated into phospholipids but are not elongated. The successful model has free fatty acid as the intermediate product coupling fatty acid biosynthesis to phospholipid synthesis. Essential to this pathway are those reactions catalyzed by thioesterases I and II as well as acyl-ACP synthetase, enzymes whose roles have previously been unknown in vivo.

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

1980-12-10

265

Carbon Dynamics and Spatial Distribution of SOC and Stable Carbon Isotopes Related to Soil Redistribution  

NASA Astrophysics Data System (ADS)

There is growing recognition that soil redistribution (by water and tillage erosion) plays an important role in the global carbon budget. Recent work in this field highlighted the impact of soil redistribution on the spatial distribution of SOC storage on arable land. Erosion leaves soils depleted of carbon while subsequent deposition leads to burial of quantities of soil and SOC of relevance to the global carbon budget. By incorporating carbon dynamics into a spatially distributed soil erosion model (SPEROS-C), it is possible to quantify carbon fluxes between soil and atmosphere under water and tillage erosion. In this contribution we present the results of an extensive fieldwork campaign, conducted to confirm the previously gained insights, explained above, as well as to refine model calibration and validation. We hereby looked at detailed depth profiles of SOC, radionuclides (Cs-137) and stable carbon isotopes on different landscape positions (shoulder positions, footslope, plateau) in three agricultural fields in Belgium. The fields have a different soil redistribution history (grassland, reduced tillage and conventional tillage) but a similar rolling topography. The aim of this work is to i) get to know the history of erosion and deposition processes (using Cs-137 as a soil movement tracer) and its effect on SOC content within a landscape. ii) improve the SPEROS-C model to simulate carbon dynamics on the landscape scale and estimate C fluxes between soil and atmosphere. iii) explore the spatial and vertical patterns of stable carbon isotopes and their use for estimating SOC turnover and constraining landscape scale C budgets. Our study provides detailed information on the vertical distribution of total carbon and different carbon isotopes with depth at various landscape conditions. The results allow for a better calibration of coupled carbon-erosion models by not only considering total carbon inventories, but also the vertical distribution of total carbon and different carbon isotopes.

van Hemelryck, H.; van Oost, K.; Govers, G.; Merckx, R.

2006-12-01

266

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

267

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

SciTech Connect

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

Mahieu, Koenraad [Laboratory of Applied Physical Chemistry (ISOFYS), Ghent University, Coupure links 653, B-9000 Ghent (Belgium) and Department of Applied Mathematics, Biometrics and Process Control (BIOMATH), Ghent University, Coupure links 653, B-9000 Ghent (Belgium)]. E-mail: Koenraad.Mahieu@Ugent.be; Visscher, Alex De [Laboratory of Applied Physical Chemistry (ISOFYS), Ghent University, Coupure links 653, B-9000 Ghent (Belgium); Vanrolleghem, Peter A. [Department of Applied Mathematics, Biometrics and Process Control (BIOMATH), Ghent University, Coupure links 653, B-9000 Ghent (Belgium); Cleemput, Oswald Van [Laboratory of Applied Physical Chemistry (ISOFYS), Ghent University, Coupure links 653, B-9000 Ghent (Belgium)

2006-07-01

268

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

269

Biomineralization and the carbon isotope record  

Microsoft Academic Search

Summary The advent of biomineralization at the turn of the Precambrian\\/Cambrian boundary has been a major event in the Earth's evolutionary history. With this there has been a major shift from abiotic to biotic formation of minerals such as phosphates and carbonates and, subsequently, silica. The dominant factor which effected this shift is a change in ocean's chemistry with respect

E. T. Degens; J. Kazmierczak; V. Ittekkot

1986-01-01

270

Nitrogen Source Differentiation Through Carbon Isotopes.  

National Technical Information Service (NTIS)

Fifty-one groundwater samples and one Platte River surface water sample were analyzed for nitrate-N, dissolved organic carbon (DOC), and (13)C ratios. Ten samples containing sufficient NO3-N (>5.0ppm) were analyzed for (15)N. Water samples were pumped fro...

R. F. Spalding J. R. Gormly

1977-01-01

271

Noble gas content and isotope abundances in phases of the Saint-Aubin (UNGR) iron meteorite  

NASA Astrophysics Data System (ADS)

We analyzed the noble gas isotopes in the Fe-Ni metal and inclusions of the Saint-Aubin iron meteorite, utilizing the stepwise heating technique to separate the various components of noble gases. The light noble gases in all samples are mostly cosmogenic, with some admixture from the terrestrial atmosphere. Total abundances of noble gases in metal are one of the lowest found so far in iron meteorites and the 4He/21Ne ratio is as high as 503, suggesting that the Saint-Aubin iron meteorite was derived from a very large meteoroid in space. The exposure ages obtained from cosmogenic 3He were 9-16 Ma. Saint-Aubin is very peculiar because it contains very large chromite crystals, which—like the metal—contain only cosmogenic and atmospheric noble gases. The noble gases in all the samples do not reveal any primordial components. The only exception is the 1000 °C fraction of schreibersite which contained about 5% of the Xe-HL component. The Xe-Q and the El Taco Xe components were not found and only the Xe-HL is present in this fraction. Some presolar diamond, the only carrier for the HL component known today, must have been available during growth of the schreibersite. However, it is also possible that this excess is due to the addition of cosmogenic and fission components. In this case, all the primordial components are masked (or lost) by the later events such as cosmic-ray irradiation, heating, and radioactive decay.

Nishimura, Chikako; Matsuda, Jun-Ichi; Kurat, Gero

2008-08-01

272

MeV He3\\/He4 isotope abundances in solar energetic particle events: SOHO\\/COSTEP observations  

Microsoft Academic Search

We present first results based on a systematic survey of 4-41 MeV\\/N 3He\\/4He isotope abundances with ratios >0.01 detected by the COmprehensive SupraThermal and Energetic Particle analyzer (COSTEP) onboard the SOHO (SOlar and Heliospheric Observatory) spacecraft. More than about 25% of the identified events showed 3He\\/4He ratios in the range 0.1-1. For events with sufficiently high detector count rates the

V. Bothmer; H. Sierks; E. Böhm; H. Kunow

2001-01-01

273

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.

2014-04-01

274

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

275

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

276

Using natural isotopic abundances to determine the source of nitrous oxide (N2O) emissions  

NASA Astrophysics Data System (ADS)

Numerous greenhouse gas studies have focused on carbon dioxide (CO2), whereas nitrous oxide (N2O) also plays a major role in global warming. Indeed, while nitrous oxide is 1000 times less concentrated than CO2 in the atmosphere, it is 300 times more efficient in terms of global warming potential. In addition, its atmospheric concentration increases with 0,3 % per year. According to the literature, nitrous oxide is produced, in soils and sediments, by two major processes: (1) Nitrification, mediated by autotrophic nitrifying bacteria under oxic conditions; (2) Denitrification, mediated by heterotrophic denitrifying bacteria under anoxic conditions. Denitrification induces intensive, localized and instantaneous fluxes. N2O emissions can be easily measured and modeled. In contrast, nitrification induces weak emissions, but spatially and temporally extended. Therefore, this process could represent a large potential of N2O emissions from soils and sediments. The study of isotopomer's isotopic composition of N2O, i.e. the intramolecular distribution or site preference (SP) determined by 15N measurement allows the determination of the origin of N2O emissions (nitrification vs. denitrification). Recent studies on pure cultures have showed that SP associated with nitrification is 35 ‰ while SP associated with denitrification is 0 ‰. The aim of this study was to determine SP associated with denitrification in soils and sediments, taking into account the environmental denitrifying bacterial communities, and under different environmental variables. To this end, flow-through reactors were used to determine denitrification rates at different temperatures and varying substrate (nitrate) concentrations. Site preference was measured for the different experiments. Different experiments of denitrification were realized in sediment flow through reactors under denitrifying conditions (anoxia, presence of organic matter and nitrate). We used acetylene (25°C) to block the enzyme nitrous oxide reductase, resulting in accumulation of N2O originating only from denitrification. Despite the fact that the isotopic composition of the produced N2O (15N and 18O) varies, the SP did not change significantly (SP = 6 ‰). These results compared to those of chemical denitrification show that despite very different isotopic compositions, the SP value is independent of the type of denitrification. Different nitrate concentrations (5 mM, 3 mM, 1,5 mM and 1 mM) at ambient temperature (25°C). The results of N2O production kinetics were not related to nitrate concentrations. SP of N2O are currently being analyzed. Different temperatures (35°C, 25°C and 12°C) and a nitrate concentration of 5 mM. The results of N2O production kinetics at different temperatures show an increase in N2O emissions with increasing temperature. SP of N2O are currently being analyzed. The goal for future work is to study the SP in these systems relative to salinity, pH and carbon organic concentration in denitrifying conditions but also in nitrifying conditions.

Mothet, A.; Sebilo, M.; Laverman, A. M.; Vaury, V.; Mariotti, A.

2012-04-01

277

Resolving isotopic fine structure to detect and quantify natural abundance- and hydrogen/deuterium exchange-derived isotopomers.  

PubMed

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-(2)H-exchanged/zero-(13)C isotopomer, a one-(2)H-exchanged/one-(13)C isotopomer, and a zero-(2)H-exchanged/two-(13)C isotopomer. Notably, such isotopomers differ slightly in mass as a result of the ?3 mDa mass defect between (2)H and (13)C 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

278

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

NASA Technical Reports Server (NTRS)

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

Schmidt, Gavin A.

1999-01-01

279

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

280

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

281

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

282

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

283

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

284

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

285

Method for determination of stable carbon isotope ratio of methylnitrophenols in atmospheric particulate matter  

NASA Astrophysics Data System (ADS)

A technique for the measurement of the stable isotope ratio of methylnitrophenols in atmospheric particulate matter is presented. Atmospheric samples from rural and suburban areas were collected for evaluation of the procedure. Particulate matter was collected on quartz fibre filters using dichotomous high volume air samplers. Methylnitrophenols were extracted from the filters using acetonitrile. The sample was then purified using a combination of high-performance liquid chromatography and solid phase extraction. The final solution was then divided into two aliquots. To one aliquot, a derivatising agent, Bis(trimethylsilyl)trifluoroacetamide, was added for Gas Chromatography-Mass Spectrometry analysis. The second half of the sample was stored in a refrigerator. For samples with concentrations exceeding 1 ng ?l-1, the second half of the sample was used for measurement of stable carbon isotope ratios by Gas Chromatography-Isotope Ratio Mass Spectrometry. The procedure described in this paper provides a method for the analysis of methylnitrophenols in atmospheric particulate matter at concentrations as low as 0.3 pg m-3 and for stable isotope ratios with an accuracy of better than ±0.5‰ for concentrations exceeding 100 pg m-3. In all atmospheric particulate matter samples analysed, 2-methyl-4-nitrophenol was found to be the most abundant methylnitrophenol, with concentrations ranging from the low pg m-3 range in rural areas to more than 200 pg m-3 in some samples from a suburban location.

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

2011-11-01

286

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

287

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

288

Continental-Scale Distributions of Vegetation Stable Carbon Isotope Ratios  

Microsoft Academic Search

\\u000a The stable carbon isotope composition (?13C) of terrestrial vegetation is important for a variety of applications in fields ranging from biogeochemistry to zoology\\u000a to paleoclimatology. To a large degree, spatial patterns in plant ?13C are imparted by variations in the photosynthetic pathway (C3\\/C4) composition of vegetation in topical and subtropical regions. Thus, the fractional coverage of each vegetation type must

Christopher J. Still; Rebecca L. Powell

289

Carbon Isotopic Evidence for Methane Hydrate Instability During Quaternary Interstadials  

Microsoft Academic Search

Large (about 5 per mil) millennial-scale benthic foraminiferal carbon isotopic oscillations in the Santa Barbara Basin during the last 60,000 years reflect widespread shoaling of sedimentary methane gradients and increased outgassing from gas hydrate dissociation during interstadials. Furthermore, several large, brief, negative excursions (up to -6 per mil) coinciding with smaller shifts (up to -3 per mil) in depth-stratified planktonic

James P. Kennett; Kevin G. Cannariato; Ingrid L. Hendy; Richard J. Behl

2000-01-01

290

Stable carbon and nitrogen isotope analysis of avian uric acid.  

PubMed

We report results obtained using a new technique developed to measure the stable-isotope composition of uric acid isolated from bird excreta (guano). Results from a diet-switch feeding trial using zebra finches suggest that the delta(13)C of uric acid in the guano equilibrates with the diet of the bird within 3 days of a change in diet, while the equilibration time for delta(15)N may be longer. The average carbon isotope discrimination between uric acid and food before the diet switch was +0.34 +/- 1 per thousand (1sigma) while after the diet switch this increased slightly to +0.83 +/- 0.7 per thousand (1sigma). Nitrogen isotope discrimination was +1.3 +/- 0.3 per thousand (1sigma) and +0.3 +/- 0.3 per thousand (1sigma) before and after the diet switch; however, it is possible that the nitrogen isotope values did not fully equilibrate with diet switch over the course of the experiment. Analyses of other chemical fractions of the guano (organic residue after uric acid extraction and non-uric acid organics solubilised during extraction) suggest a total range of up to 3 per thousand for both delta(13)C and delta(15)N values in individual components of a single bulk guano sample. The analysis of natural samples from a range of terrestrial and marine species demonstrates that the technique yields isotopic compositions consistent with the known diets of the birds. The results from natural samples further demonstrate that multiple samples from the same species collected from the same location yield similar results, while different species from the same location exhibit a range of isotopic compositions indicative of different dietary preferences. Given that many samples of guano can be rapidly collected without any requirement to capture specimens for invasive sampling, the stable-isotope analysis of uric acid offers a new, simple and potentially powerful tool for studying avian ecology and metabolism. PMID:18837063

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

2008-11-01

291

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.

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

1998-01-01

292

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

PubMed

The occurrence and abundance of microbial fatty acids have been used for the identification of microorganisms in microbial communities. However, these fatty acids can also be used as indicators of substrate usage. For this, a systematic investigation of the discrimination of the stable carbon isotopes by different microorganisms is necessary. We grew 11 strains representing major bacterial and fungal species with four different isotopically defined carbon sources and determined the isotope ratios of fatty acids of different lipid fractions. A comparison of the differences of delta13C values of palmitic acid (C16:0) with the delta13C values of the substrates revealed that the isotope ratio is independent of the growth stage and that most microorganisms showed enrichment of C16:0 with 13C when growing on glycerol. With the exception of Burkholderia gladioli, all microorganism showed depletion of 13C in C16:0 while incorporating the carbons of glucose, and most of them were enriched with 13C from mannose, with the exception of Pseudomonas fluorescens and the Zygomycotina. Usually, the glycolipid fractions are depleted in 13C compared to the phospholipid fractions. The delta13C pattern was not uniform within the different fatty acids of a given microbial species. Generally, tetradecanoic acid (C14:0) was depleted of 13C compared to palmitic acid (C16:0) while octadecanoic acid (C18:0) was enriched. These results are important for the calibration of a new method in which delta13C values of fatty acids from the environment delineate the use of bacterial substrates in an ecosystem. PMID:9797266

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

1998-11-01

293

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

294

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

295

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

NASA Astrophysics Data System (ADS)

We present a lake-wide investigation of Lake Superior carbon and organic matter biogeochemistry using radiocarbon, stable isotope, and carbon concentrations. Dissolved inorganic carbon (DIC) abundance in the lake was 121-122 Tg C, with offshore concentration and?13C values being laterally homogenous and tightly coupled to the physical and thermal regime and biochemical processes. Offshore ?14C of DIC (50-65‰) exhibited lateral homogeneity and was more 14C enriched than co-occurring atmospheric CO2 (˜38‰); nearshore ?14C of DIC (36-38‰) was similar to atmospheric CO2. Dissolved organic carbon (DOC) abundance was 14.2-16.4 Tg C. DOC's concentration and ?13C were homogenous in June (mixed lake), but varied laterally during August (stratification) possibly due to spatial differences in lake productivity. Throughout sampling, DOC had modern radiocarbon values (14-58‰) indicating a semilabile nature with a turnover time of ?60 years. Lake particulate organic carbon (POC, 0.9-1.3 Tg C) was consistently 13C depleted relative to DOC. The ?15N of epilimnetic particulate organic nitrogen shifted to more negative values during stratification possibly indicating greater use of nitrate (rather than ammonium) by phytoplankton in August. POC's radiocarbon was spatially heterogeneous (?14C range: 58‰ to -303‰), and generally 14C depleted relative to DOC and DIC. POC 14C depletion could not be accounted for by black carbon in the lake but, because of its spatial and temporal distribution, is attributed to sediment resuspension. The presence of old POC within the epilimnion of the open lake indicates possible benthic-pelagic coupling in the lake's organic carbon cycle; the ultimate fate of this old POC bears further investigation.

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

2012-03-01

296

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

297

The clumped isotope geothermometer in soil and paleosol carbonate  

NASA Astrophysics Data System (ADS)

We studied both modern soils and buried paleosols in order to understand the relationship of temperature (T°C(47)) estimated from clumped isotope compositions (?47) of soil carbonates to actual surface and burial temperatures. Carbonates from modern soils with differing rainfall seasonality were sampled from Arizona, Nevada, Tibet, Pakistan, and India. T°C(47) obtained from these soils shows that soil carbonate forms in the warmest months of the year, in the late morning to afternoon, and probably in response to intense soil dewatering. T°C(47) obtained from modern soil carbonate ranges from 10.8 to 39.5 °C. On average, T°C(47) exceeds mean annual temperature by 10-15 °C due to summertime bias in soil carbonate formation, and to summertime ground heating by incident solar radiation. Secondary controls on T°C(47) are soil depth and shading. Site mean annual air temperature (MAAT) across a broad range (0-30 °C) of site temperatures is highly correlated with T°C(47) from soils, following the equation: MAAT(°C)=1.20(T°C(47)0)-21.72(r2=0.92) where T°C(47)0 is the effective air temperature at the site estimated from T°C(47). The effective air temperature represents the air temperature required to account for the T°C(47) at each site, after consideration of variations in T°C(47) with soil depth and ground heating. The highly correlated relationship in this equation should now permit mean annual temperature in the past to be reconstructed from T°C(47) in paleosol carbonate, assuming one is studying paleosols that formed in environments generally similar in seasonality and ground cover to our calibration sites. T°C(47)0 decreases systematically with elevation gain in the Himalaya, following the equation: elevation(m)=-229(T°C(47)0)+9300(r2=0.95) Assuming that temperature varied similarly with elevation in the past, this equation can be used to reconstruct paleoelevation from clumped isotope analysis of ancient soil carbonates. We also measured T°C(47) from long sequences of deeply buried (?5 km) paleosol carbonate in the Himalayan foreland in order to evaluate potential diagenetic resetting of clumped isotope composition. We found that paleosol carbonate faithfully records plausible soil T°C(47) down to 2.5-4 km burial depth, or ˜90-125 °C. Deeper than this and above this temperature, T°C(47) in paleosol carbonate is reset to temperatures >40 °C. We observe ˜40 °C as the upper limit for T°C(47) in modern soils from soil depths >25 cm, and therefore that T°C(47) >40 °C obtained from ancient soil carbonate indicates substantially warmer climate regimes compared to the present, or non-primary temperatures produced by resetting during diagenesis. If representative, this limits the use of T°C(47) to reconstruct ancient surface temperature to modestly buried (<3-4 km) paleosol carbonates. Despite diagenetic resetting of ?47 values, ?18O and ?13C values of the same deeply buried paleosol carbonate appear unaltered. We conclude that solid-state reordering or recrystallization of clumping of carbon and oxygen isotopes can occur in the absence of open-system exchange of paleosol carbonate with significant quantities of water or other phases.

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

2013-03-01

298

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

299

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

300

Stable-isotope record of organic carbon from an evolving carbonate banktop, Bight of Abaco, Bahamas  

NASA Astrophysics Data System (ADS)

The stable-isotope composition (?13C) of total organic carbon (TOC) was measured as a function of depth throughout a 217-cm-thick sequence of Holocene carbonate sediment within the Bight of Abaco lagoon, Little Bahama Bank. Biofacies and lithofacies analyses indicate progressive banktop submergence and paleoenvironmental response during Holocene sea-level rise. Stable-isotope values shift markedly from -27.7‰ within the 7900 B.P. paleosol at the base of the core to -11.1‰ at the present-day sediment-water interface. An abrupt excursion toward heavy-isotope values records the first establishment of Thalassia seagrass upon open-marine flooding. A multitracer approach, combining biofacies, lithofacies, and stable-isotope analysis of TOC confirms that the dramatic +17‰ shift observed in ?13C was a direct result of sea-level rise and associated environmental changes over the banktop; there is little evidence of spurious diagenetic overprint. Stable-isotope analyses of organic carbon may enhance the reconstruction of carbonate sequences by revealing a distinctive geochemical signature of banktop flooding, including the onset of growth of otherwise unpreservable Thalassia seagrass.

Rasmussen, Kenneth A.; Haddad, Robert I.; Neumann, A. Conrad

1990-08-01

301

Stable-isotope record of organic carbon from an evolving carbonate banktop, Bight of Abaco, Bahamas  

SciTech Connect

The stable-isotope composition ({delta}{sup 13}C) of total organic carbon (TOC) was measured as a function of depth throughout a 217-cm-thick sequence of Holocene carbonate sediment within the Bight of Abaco lagoon, Little Bahama Bank. Biofacies and lithofacies analyses indicate progressive banktop submergence and paleoenvironmental response during Holocene sea-level rise. Stable-isotope values shift markedly from {minus}27.7{per thousand} within the 7900 B.P. paleosol at the base of the core to {minus}11.1{per thousand} at the present-day sediment-water interface. An abrupt excursion toward heavy-isotope values records the first establishment of Thalassia seagrass upon open-marine flooding. A multitracer approach, combining biofacies, lithofacies, and stable-isotope analysis of TOC confirms that the dramatic +17{per thousand} shift observed in {delta}{sup 13}C was a direct result of sea-level rise and associated environmental changes over the banktop; there is little evidence of spurious diagenetic overprint. Stable-isotope analyses of organic carbon may enhance the reconstruction of carbonate sequences by revealing a distinctive geochemical signature of banktop flooding, including the onset of growth of otherwise unpreservable Thalassia seagrass.

Rasmussen, K.A.; Neumann, A.C. (Univ. of North Carolina, Chapel Hill (USA)); Haddad, R.I. (NASA-Ames Research Center, Moffett Field, CA (USA))

1990-08-01

302

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...

303

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

2006-01-01

304

Perturbing phytoplankton: response and isotopic fractionation with changing carbonate chemistry in two coccolithophore species  

NASA Astrophysics Data System (ADS)

All species of coccolithophore appear to respond to perturbations of carbonate chemistry in a different way. Here, we show that the degree of malformation, growth rate and stable isotopic composition of organic matter and carbonate produced by two contrasting species of coccolithophore (Gephyrocapsa oceanica and Coccolithus pelagicus ssp. braarudii) are indicative of differences between their photosynthetic and calcification response to changing DIC levels (ranging from ~1100 to ~7800 ?mol kg-1) at constant pH (8.13 ± 0.02). Gephyrocapsa oceanica thrived under all conditions of DIC, showing evidence of increased growth rates at higher DIC, but C. braarudii was detrimentally affected at high DIC showing signs of malformation, and decreased growth rates. The carbon isotopic fractionation into organic matter and the coccoliths suggests that C. braarudii utilises a common internal pool of carbon for calcification and photosynthesis but G. oceanica relies on independent supplies for each process. All coccolithophores appear to utilize bicarbonate as their ultimate source of carbon for calcification resulting in the release of a proton. But, we suggest that this proton can be harnessed to enhance the supply of CO2(aq) for photosynthesis either from a large internal HCO3- pool which acts as a pH buffer (C. braarudii), or pumped externally to aid the diffusive supply of CO2 across the membrane from the abundant HCO3- (G. oceanica), likely mediated by an internal and external carbonic anhydrase respectively. Our simplified hypothetical spectrum of physiologies may provide a context to understand different species response to changing pH and DIC, the species-specific ?p and calcite "vital effects", as well as accounting for geological trends in coccolithophore cell size.

Rickaby, R. E. M.; Henderiks, J.; Young, J. N.

2010-12-01

305

Inorganic origin of carbon dioxide during low temperature thermal recovery of bitumen: Chemical and isotopic evidence  

NASA Astrophysics Data System (ADS)

Carbon dioxide, produced at low temperatures, is the dominant gaseous species evolved during steam-assisted thermal recovery of bitumen at the Tucker Lake pilot, Cold Lake, Alberta. Two possible sources for the produced CO 2 are considered: pyrolysis of bitumen and dissolution of carbonate minerals. Data from natural systems and experiments by other authors suggest that clay-carbonate reactions are the dominant source of CO 2. Carbon isotope and chemical analyses of produced gas and water reveal that CO 2 and HCO 3- become more enriched in 13C, and concentrations of Ca 2+ and HCO 3- rise during production. Temperatures in the producing zone are estimated to be between 70 and 220°C using the Na/K and chalcedony chemical geothermometers, and show that production of 13C-enriched CO 2 and HCO 3- occurs as temperature decreases during production. This extends the temperature range at which CO 2 is known to be produced from carbonates to lower levels than previously noted. The ? 13C of calcite in the reservoir is enriched in ? 13C, giving values as high as + 17.4%. When the calcite isotopic compositions are combined with temperature data and temperature fractionation equations for calcite, CO 2, and HCO 3-, they show calcite to be the only viable source of CO 2. Bitumen pyrolysis may contribute small amounts of CO 2, probably by decarboxylation, early in the production cycle but cannot contribute significant volumes. The recognition of production of CO 2 by reactive calcite destruction at temperatures between 70 and 220°C suggests that this process may be responsible for the production of large quantities of CO 2 in natural systems, particularly in lithofeldspathic sands and shales with high carbonate content and abundant clays. Organic acids have been suggested to be the source of CO 2 in diagenetic fluids, but the results presented here suggest that this hypothesis requires more complete investigation.

Hutcheon, Ian; Abercrombie, Hugh J.; Krouse, H. R.

1990-01-01

306

Carbon and nitrogen isotope fractionation during possible organic aerosol formation in Titan and the early Earth  

NASA Astrophysics Data System (ADS)

Abiotic formation of complex organic macromolecule aerosols is important not only for the potential for prebiotic chemical evolution, but also in the global elemental cycle. The direct clues of the habitable environment and biosphere on the early Earth are mostly obtained from geological records, such as isotope signatures and biomarkers in the ancient organic sediments. The recent Cassini-Huygens mission revealed the generation of complex organic aerosols in Titan's upper atmosphere, and similar processes could have lead to the formation of organic aerosols in the early Earth atmosphere. Understanding the formation reaction network and accompanying isotope fractionation processes of the organic aerosols is necessary to constrain the active organic environment on the early Earth from the available geological evidence. We have investigated the abiotic formation of organic aerosols in simulated atmospheres of Titan and the early, with particular focus on carbon and nitrogen isotope fractionation. Laboratory aerosol analogues, termed tholins, are generated with cold plasma irradiation of reduced gas mixtures, such as N2/CH4 and N2/H2/CO. Stable isotopic ratios of 15N/14N and 13C/12C for the generated tholins are measured with an elemental analysis-isotope ratio mass spectrometer (EA-IR-MS). Our preliminary data for tholins generated from an equivalent N2/CH4 (=90/10) gas mixture at various pressures suggests the 15N isotopic fractionation up to ?15N = -20~25 permil during tholin formation, while 13C isotopic fractionation seems almost negligible. This negative ?15N is even lighter than those observed in kerogens in the Archean sediments (Beaumont and Robert, 1999; Pinti et al., 2001), and the organic haze could have contributed to the source of 15N-depleted kerogens. Furthermore, the ?15N vary with deposition pressure. Previous works demonstrated that the resulted two types of tholin are very different in chemical structure and optical properties (Imanaka et al., 2004, 2012). Although the correlation of pressure might be just an apparent one, distinct type of chemistry could be the reason of such isotopic fractionation. The two distinct ?15N could be related to the difference of dominant functional groups, such as -NH2 and -CN. Since N-H functionality is more abundant in the tholins with depleted 15N, the observed isotopic fractionation could be related to the chemical bond change from N2 to -N-H functionality.

Imanaka, H.

2012-12-01

307

Experimental observations on carbon isotope exchange in carbonate-water systems  

NASA Astrophysics Data System (ADS)

This study presents data from experiments investigating carbon isotope exchange between carbonate solution and solid calcite using carbon-13 as a tracer. All experiments were done with calcite saturated solutions and results show that a two-step adsorption-recrystallization reaction takes place. Isotope effects are caused by exchange by carbonate on the solid surface with carbon in the aqueous phase. Adsorption reactions are characterized by a maximum isotopic exchange capacity (IEC) on crystal surfaces of about 10 11 reaction sites per cm 2, following a second order rate law with respect to 13C concentration in solution ( constant kex ? 10 6 cm 5 mole -1 s -1 and half-life t 1/2 = 700 s). The adsorption reaction was followed by a first order recrystallization which is characterized by a rate constant of the order of 10 -8 s -1 and a t 1/2 of 10 7 s. Negative isotopic gradient experiments and runs with calcite crystals in Mg 2+ spiked solutions provided the preliminary basis for the characterization of the mechanisms of both proposed reactions.

Mozeto, A. A.; Fritz, P.; Reardon, E. J.

1984-03-01

308

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

309

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

PubMed

The oxygen isotopic compositions of two calcium-aluminum-rich inclusions (CAIs) from the unequilibrated ordinary chondrite meteorites Quinyambie and Semarkona are enriched in 16O by an amount similar to that in CAIs from carbonaceous chondrites. This may indicate that most CAIs formed in a restricted region of the solar nebula and were then unevenly distributed throughout the various chondrite accretion regions. The Semarkona CAI is isotopically homogeneous and contains highly 16O-enriched melilite, supporting the hypothesis that all CAI minerals were originally 16O-rich, but that in most carbonaceous chondrite inclusions some minerals exchanged oxygen isotopes with an external reservoir following crystallization. PMID:9545215

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

1998-04-17

310

Terrestrial and Meteorite Carbon Appear to Have the Same Isotopic Composition  

PubMed Central

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

Libby, W. F.

1971-01-01

311

The calcareous nannofossil Prinsiosphaera achieved rock-forming abundances in the latest Triassic of western Tethys: consequences for the ?13C of bulk carbonate  

NASA Astrophysics Data System (ADS)

The onset of pelagic biomineralization was a milestone in the history of the long-term inorganic carbon cycle: as soon as calcareous nannofossils became major limestone producers, the pH and supersaturation state of the global ocean were stabilized (the so-called mid-Mesozoic revolution). But although it is known that calcareous nannofossils were abundant already by the end of the Triassic, no estimates exist on their contribution to hemipelagic carbonate sedimentation. With this work, we estimate the volume proportion of Prinsiosphaera, the dominant late Triassic calcareous nannofossil, in hemipelagic and pelagic carbonates of western Tethys. The investigated Upper Triassic lime mudstones are composed essentially of microspar and tests of calcareous nannofossils, plus minor bioclasts. Prinsiosphaera had become a significant component of lime mudstones since the late Norian, and was contributing up to ca. 60% of the carbonate by the late Rhaetian in periplatform environments with hemipelagic sedimentation. The increasing proportion of Prinsiosphaera in upper Rhaetian hemipelagic lime mudstones is paralleled by an increase of the ?13C of bulk carbonate. We interpreted this isotopic trend as related to the diagenesis of microspar, which incorporated respired organic carbon with a low ?13C when it formed during shallow burial. As the proportion of nannofossil tests increased, the contribution of microspar with low ?13C diminished, determining the isotopic trend. We suggest that a similar diagenetic effect may be observed in many Mesozoic limestones with a significant, but not yet dominant, proportion of calcareous plankton.

Preto, N.; Agnini, C.; Rigo, M.; Sprovieri, M.; Westphal, H.

2013-09-01

312

The calcareous nannofossil Prinsiosphaera achieved rock-forming abundances in the latest Triassic of western Tethys: consequences for the ?13C of bulk carbonate  

NASA Astrophysics Data System (ADS)

The onset of pelagic biomineralization marked a milestone in the history of the long term inorganic carbon cycle: as soon as calcareous nannofossils became major limestone producers, the pH and supersaturation state of the global ocean were stabilized (the so-called Mid Mesozoic Revolution). But although it is known that calcareous nannofossils were abundant already by the end of the Triassic, no estimates exist on their contribution to hemipelagic carbonate sedimentation. With this work, we estimate the volume proportion of Prinsiosphaera, the dominant Late Triassic calcareous nannofossil, in hemipelagic and pelagic carbonates of western Tethys. The investigated Upper Triassic lime mudstones are composed essentially of microspar and tests of calcareous nannofossils, plus minor bioclasts. Prinsiosphaera became a significant component of lime mudstones since the late Norian, and was contributing up to ca. 60% of the carbonate by the late Rhaetian in periplatform environments with hemipelagic sedimentation. The increasing proportion of Prinsiosphaera in upper Rhaetian hemipelagic lime mudstones is paralleled by a increase of the ?13C of bulk carbonate. We interpreted this isotopic trend as related to the diagenesis of microspar, which incorporated respired organic carbon with a low ?13C when it formed during shallow burial. As the proportion of nannofossil tests increased, the contribution of microspar with low ?13C diminished, determining the isotopic trend. We suggest that a similar diagenetic effect may be observed in many Mesozoic limestones with a significant, but not yet dominant, proportion of calcareous plankton.

Preto, N.; Agnini, C.; Rigo, M.; Sprovieri, M.; Westphal, H.

2013-05-01

313

The dating of impure carbonates with decay-series isotopes  

NASA Astrophysics Data System (ADS)

The uranium-series disequilibrium methods have been successfully applied to the dating of clean carbonate precipitates such as coralline and speleothem materials. Similar success has yet to be achieved for the widely occuring inorganically precipitated impure carbonates (e.g., travertine, tufa, and calcrete), of which there is an ever-increasing need for determining their chronology in Quaternary and archaeological studies. The main problem involves the presence of detrital materials which cannot be isolated from the carbonate fraction by simple physical means. Chemical separation using dilute acid leaching has been often attempted. This process may solubilize some of the uranium and thorium isotopes from the detrital component, and this detrital contamination must be corrected for. This paper reviews the principles and assumptions of the detrital correction schemes, discusses the theoretical and experimental aspects of the mixing-line plots as suggested by Rosholt and Szabo, and recommends analytical procedures pertinent to the use of such plots.

Ku, Teh-Lung; Liang, Zhuo-Cheng

1984-06-01

314

Measurement of Absolute Carbon Isotope Ratios: Mechanisms and Implications  

NASA Astrophysics Data System (ADS)

An accelerator mass spectrometer (AMS) produced absolute isotope ratio measurements for 14C/13C as tested against >500 samples of NIST SRM-4990-C (OxII 14C standard) to an accuracy of 2.2±0.6‰ over a period of one year with measurements made to 1% counting statistics. The spectrometer is not maximized for 13C/12C, but measured ?13C to 0.4±0.1‰ accuracy, with known methods for improvement. An AMS produces elemental anions from a sputter ion source and includes a charge-changing collision in a gas cell to isolate the rare 14C from the common isotopes and molecular isobars. Both these physical processes have been modeled to determine the parameters providing such absolute measures. Neutral resonant ionization in a cesium plasma produces mass-independent ionization, while velocity dependent charge-state distributions in gas collisions produce relative ion beam intensities that are linear in mass at specific collision energies. The mechanisms are not specific to carbon isotopes, but stand alone absolute IRMS (AIR-MS) instruments have not yet been made. Aside from the obvious applications in metrology, AIR-MS is particularly valuable in coupled separatory MS because no internal or external standards are required. Sample definition processes can be compared, even if no exact standard reference sample exists. Isotope dilution measurements do not require standards matching the dilution end-points and can be made over an extended, even extrapolated, range.

Vogel, J. S.; Giacomo, J. A.; Dueker, S. R.

2012-12-01

315

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

316

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

317

Determination of radium isotope ratios and abundances in geologic samples by thermal ionization mass spectrometry.  

PubMed

We describe chemical separation and mass spectrometric procedures for the measurement of radium isotopes in geologic samples. These methods provide 226Ra/228Ra ratio measurements for 1 g or less of rock sample containing subpicogram amounts of radium with precision better than 1.5% (95% confidence level). Radium-226 concentrations were measured by isotope dilution for smaller sample sizes (100-500 mg) containing as little as 1-10 fg of total 226Ra with similar high precision. PMID:1858983

Volpe, A M; Olivares, J A; Murrell, M T

1991-05-01

318

Ground penetrating radar measurements show a spatial relationship between coarse root biomass and soil carbon abundance  

NASA Astrophysics Data System (ADS)

In savanna ecosystems, the dynamics of soil organic carbon are complicated by multiple sources of inputs, created by the coexistance of trees and grasses, and by spatial heterogeneity induced by a patchy vegetation structure. A previous study on the spatial pattern of soil carbon abundance on the Kalahari Transect in Southern Africa found that for savannas with sparse woody cover the semivariogram of soil carbon abundance demonstrates periodicity. It is hypothesized that the periodicity is induced by the patchy spatial distribution of the canopies and root systems of woody plants. We tested this by mapping the abundance of coarse woody roots with ground penetrating radar. Spatial patterns of soil carbon abundance were measured at our research site in a previous study. The site is on the Botswana portion of the Kalahari Transect, and has deep, homogeneous, sandy soil. We ran the ground penetrating radar over three 20 by 20 meter square plots in two perpendicular directions. We filtered the radar images to remove background noise and applied a Hilbert transform to reduce echoes. In each plot, we also dug 20 root biomass sampling pits. Using the sampling pit data, we were able to verify that there is a log-linear relationship (r2 = 0.80) between radar signal return and coarse root biomass in the upper 50 cm of soil. Semivariograms of coarse root biomass inferred from radar returns showed periodicity at similar spatial scales to the periodicity in soil carbon abundance. Our results suggest that the belowground components of woody plants, which may extend well beyond their canopies, exert a stronger influence on soil carbon cycling than the aboveground components, illustrating a key issue with the common practice of dividing arid and semiarid landscapes into "under canopy" and "inter-canopy" components in analyses of soil biogeochemistry. We were able to show that a relationship exists between ground penetrating radar returns and coarse root biomass for dry, sandy soils. However, the large amount of information needed to determine a predictive relationship suggests that ground penetrating radar may be more useful in investigating spatial patterns of root biomass than as a tool for quantifying absolute biomass abundance.

O'Donnell, F. C.; Caylor, K. K.; Gerlein, C.; Bhattachan, A.

2013-05-01

319

Ground penetrating radar measurements show a spatial relationship between coarse root biomass and soil carbon abundance  

NASA Astrophysics Data System (ADS)

In savanna ecosystems, the dynamics of soil organic carbon are complicated by multiple sources of inputs, created by the coexistance of trees and grasses, and by spatial heterogeneity induced by a patchy vegetation structure. A previous study on the spatial pattern of soil carbon abundance on the Kalahari Transect in Southern Africa found that for savannas with sparse woody cover the semivariogram of soil carbon abundance demonstrates periodicity. It is hypothesized that the periodicity is induced by the patchy spatial distribution of canopies and root systems of woody plants. We tested this by mapping the abundance of coarse woody roots with ground penetrating radar. Spatial patterns of soil carbon abundance were measured at our research site in a previous study. The site is on the Botswana portion of the Kalahari Transect, and has deep, homogeneous, sandy soil. We ran the ground penetrating radar over three 20 by 20 meter square plots in two perpendicular directions. We filtered the radar images to remove background noise and applied a Hilbert transform to reduce echoes. In each plot, we also dug 20 root biomass sampling pits. Using the sampling pit data, we were able to verify that there is a log-linear relationship (r2 = 0.80) between radar signal return and coarse root biomass in the upper 50 cm of soil. Semivariograms of coarse root biomass inferred from radar returns showed periodicity at similar spatial scales to the periodicity in soil carbon abundance. Our results suggest that the belowground components of woody plants, which may extend well beyond their canopies, exert a stronger influence on soil carbon cycling than the aboveground components, illustrating a key issue with the common practice of dividing arid and semiarid landscapes into "under canopy" and "inter-canopy" components in analyses of soil biogeochemistry. We were able to show that a relationship exists between ground penetrating radar returns and coarse root biomass for dry, sandy soils. However, the large amount of information needed to determine a predictive relationship suggests that ground penetrating radar may be more useful in investigating spatial patterns of root biomass than as a tool for quantifying absolute biomass abundance.

O'Donnell, F. C.; Gerlein, C.; Bhattachan, A.; Caylor, K. K.

2012-12-01

320

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

321

The distribution and stable carbon isotopic composition of dissolved organic carbon in estuaries  

Microsoft Academic Search

The distributions of dissolved organic carbon (DOC) and the natural carbon isotope ratio of DOC (DO13C) in estuaries reflect the predominant sources and sinks of organic matter from both allochthonous and autochthonous origins.\\u000a The traditional view is that DOC in land-margin ecosystems reflects mainly the mixing of land-derived and oceanic DOC. However,\\u000a this view is not consistent with the bulk

Bruce Peterson; Brian Fry; Meredith Hullar; Susan Saupe; Richard Wright

1994-01-01

322

Contribution of stable isotopes to the understanding of the unsaturated zone of a carbonate aquifer (Nerja Cave, southern Spain)  

NASA Astrophysics Data System (ADS)

We analysed the stable isotopes ( 18O and 2H) of rainwater and drip water within a cave (Nerja Cave) located in the unsaturated zone of a carbonate aquifer. Rainfall is more abundant and presents lower isotopic content in winter, while the volume of drip water is greater and its isotopic content is lower in summer. The flow analysis of 18O through the unsaturated zone confirms the seasonal lag between rainfall and the appearance of drip water in the cave and reveals that the unsaturated zone of the aquifer, in the sector of the cave, behaves like an inertial system with a strong capability to modulate the input signal. To cite this article: F. Carrasco et al., C. R. Geoscience 338 (2006).

Carrasco, Francisco; Andreo, Bartolomé; Liñán, Cristina; Mudry, Jacques

2006-12-01

323

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...

324

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

325

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

Microsoft Academic Search

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

R. Aravena; B. G. Warner; D. J. Charman; L. R. Belyea; S. P. Mathur; H. Dinel

1993-01-01

326

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

327

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

328

Carbon cycle for Lake Washington - a stable isotope study  

SciTech Connect

The authors investigate the carbon cycle in Lake Washington for the year 1980 using monthly measurements of the dissolved inorganic carbon (DIC) and its /sup 13/C:/sup 12/C isotopic composition. Mass balances of DIC and its /sup 13/C:/sup 12/C yield estimates of CO/sub 2/ gas exchange rates and net organic carbon production rates. Between 24 June and 13 August, the calculated CO/sub 2/ gas invasion rate of 0.80 x 10/sup 6/ mol C d/sup -1/ is nearly equal to the river DIC inflow rate. The calculated epilimnetic net organic carbon production rate is 0.68 x 10/sup 6/ mol C d/sup -1/, about 20-30% of primary productivity estimated from /sup 14/C-fixation experiments and ETS-derived respiration rates. Metalimnetic and hypolimnetic DIC increase rates and porewater DIC gradients in hypolimnetic sediments indicate that remineralization of particulate organic carbon (POC) previously deposited in the sediments is a major (0.5 x 10/sup 6/ mol C d/sup -1/) DIC source to the lake during summer. For the whole year, summertime CO/sub 2/ gas invasion balances wintertime CO/sub 2/ gas evasion and DIC and POC outflow balance DIC and POC inflow rates, implying no net carbon burial in the sediments during 1980. This contrasts with the measured long term sedimentation-rate-derived carbon burial rate of 0.8 x 10/sup 6/ mol C d/sup -1/. Year-to-year variability in summertime primary production rates largely determines net gains or losses of carbon via CO/sub 2/ gas exchange and sedimentation.

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

1986-05-01

329

Metallicities and carbon abundances of 40 field red supergiants in the Small Magellanic Cloud  

Microsoft Academic Search

Low-resolution spectra (~5A) for 40 red supergiants in the Small Magellanic Cloud were compared with synthetic spectra, and their metallicities were derived. A mean metallicity of [Fe\\/He]=-0.71 is found for 38 stars cooler than T_eff_<4500K. Using the stellar parameters derived, the carbon abundances were determined by comparing synthetic spectra at the G-band region to the observed spectra. A mean ?(C)=7.85

M. T. Meliani; B. Barbuy; T. Richtler

1995-01-01

330

Helium-carbon isotopic composition of thermal waters from Tunisia  

NASA Astrophysics Data System (ADS)

Tunisia has numerous thermo-mineral springs. Previous studies have shown that their chemical composition and occurrence are strongly influenced by the regional geology, however little work has been conducted to date to investigate the isotopic composition of volatiles associated with these geothermal manifestations. Here, we report the results of an extensive survey of both natural hot springs and production wells across Tunisia aimed at investigating the spatial distribution of the 3He/4He ratio and associated carbon isotopic compositions. With respect to helium isotopes, not unexpectedly, the lowest 3He/4He values (0.01-0.02 Ra) are associated with the old groundwaters of the “Continental Intercalaire” aquifer of the stable Saharan Platform. The 3He/4He values are equal to the crustal production ratio, with no detectable amount of mantle-derived 3He, in agreement with previous studies of helium isotopes in sedimentary basin, which conclude that tectonically-stable regions are essentially impermeable to mantle volatiles. The low 3He/4He domain extends to the entire Atlasic domain of central Tunisia. This Atlasic domain also displays the highest helium concentrations : along the Gafsa Fault, helium concentrations of 1777 and 4723 x 10-8 cm3STP/g (the highest value of our data set) are observed in the production wells of Sidi Ahmed Zarrouk. This emphasizes the role of deep tectonic features in channelling and transporting deep crustal volatiles to shallow levels. The eastern margin of Tunisia displays higher 3He/4He values indicative of a substantial mantle volatile input. The highest value is recorded in the carbo-gaseous mineral water of Ain Garci (2.4 Ra). This northeastern part of the African plate commonly referred to as the Pelagian block extends from Tunisia to Sicily and is characterized by strong extensional tectonics (Pantelleria rift zone) and present-day magmatic activity. This lithospheric stretching and decompressional mantle melts production in the central portion of the Pelagian Block may facilitate the transport of mantle helium through the thinned crust away from the rift zone across the existing network of fractures and deep faults. Samples were also collected for water chemistry, ?D, ?18O, and carbon isotopic composition. ?13C(TDC) data are highly heterogeneous (ranging from -11.2 to +2.9 ‰ vs. V-PDB), in particular, revealing a complex origin for total dissolved carbon (TDC) in groundwaters. We interpret these variable isotopic compositions as reflecting mixture of biogenically derived carbon with abiogenic (mantle-derived or metamorphic) CO2. A detailed discussion of the whole chemistry and isotopic data set will be presented and the results will be examined in relation to the geological and structural framework of Tunisia.

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

2010-12-01

331

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

NASA Astrophysics Data System (ADS)

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

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

2008-11-01

332

Martian carbonates in ALH 84001: Textural, elemental, and stable isotopic compositional evidence on their formation. [Abstract only  

NASA Technical Reports Server (NTRS)

Martian orthopyroxenite ALH 84001 is unusual compared to other martian meteorites in its abundance of Mg-Fe-Ca carbonites. Becasue textural evidence indicates that these carbonates are undoubtedly of martian origin, we have undertaken stable isotopic studies to elucidate their origin by evaluating whether they represent primordial martian C that was outgassing from the mantle of Mars, or volatile additions to the ALH 84001 protolith that equilibrated with the martian atmosphere. If precipitation occurred in a closed system then the isotopic results are compatible with the observed chemical zonation. A unique temperature of formation can be calculated using the difference in C-13 and O-18 between the Fe and Mg carbonates, assuming that precipitation occurred at a constant temperature. Precipitation of approximately one-half of the CO2 reservoir at 320 C can account for the observed values, with the original CO2 reservoir having a delta C-13 of approximately 45% and delta O-18 of approximately 22%. If carbonate precipitated in equilibrium with a large isotopically homogeneous CO2 reservoir (open system), isotopic differences must be attributed to a change in temperature of at least several hundreds of degrees. This temperature change is compatible with a calculated range of temperatures based on carbonate geothermometry. Clearly, carbonate in ALH 84001 is in delta O-18 disequilibrium with orthopyroxene groundmass. Most likely, the carbonate precipitated from a fluid that equilibrated with the martian atmosphere. The deposits or fluids in equilibrium with these deposits were remobilized in the crust producing the carbonate in ALH 84001. This observation establishes a link for the first time between the atmospheric and lithospheric C and O pools that reside on Mars.

Romanek, C. S.; Mittlefehldt, D. W.; Gibson, E. K., Jr.; Socki, R. A.

1994-01-01

333

Chemical Abundances Of Carbon-enhanced Metal-poor Stars With X-shooter  

NASA Astrophysics Data System (ADS)

We present abundances of carbon-enhanced metal-poor (CEMP) stars observed with the X-Shooter spectrograph on the ESO VLT. With broad wavelength coverage, spanning from near-UV to near-IR, these moderate resolution spectra are used to estimate CNO abundances and neutron-capture-element abundances for a sample of 27 metal-poor stars. With these estimates in hand, we classify each CEMP star according to its chemical signature. The classes of CEMP stars that we identify are suggestive of different mechanisms that gave rise to their carbon enhancements. We discuss the likely sites of carbon production associated with these types of stars. This work was supported in part from grants AST 07-07776, as well as from PHY 02-15783 and PHY 08-22648; Physics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA), awarded by the US National Science Foundation. This work was also supported in part by the Danish Natural Science Research Council.

Kennedy, Catherine R.; Beers, T. C.; Nordstrom, B.; Hansen, C.

2012-01-01

334

CARBON ISOTOPE FRACTIONATION AND DEPLETION IN TMC1  

SciTech Connect

{sup 12}C/{sup 13}C isotopologue abundance anomalies have long been predicted for gas-phase chemistry in molecules other than CO and have recently been observed in the Taurus molecular cloud (TMC) in several species hosting more than one carbon atom, i.e., CCH, CCS, CCCS, and HC{sub 3}N. Here we work to ascertain whether these isotopologic anomalies actually result from the predicted depletion of the {sup 13}C{sup +} ion in an oxygen-rich optically shielded dense gas, or from some other more particular mechanism or mechanisms. We observed {lambda}3mm emission from carbon-, sulfur-, and nitrogen-bearing isotopologues of HNC, CS, and H{sub 2}CS at three positions in Taurus (TMC1, L1527, and the NH{sub 3} peak) using the ARO 12 m telescope. We saw no evidence of {sup 12}C/{sup 13}C anomalies in our observations. Although the pool of C{sup +} is likely to be depleted in {sup 13}C, {sup 13}C is not depleted in the general pool of carbon outside CO, which probably exists mostly in the form of C{sup 0}. The observed isotopologic abundance anomalies are peculiar to those species in which they are found.

Liszt, H. S. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475 (United States); Ziurys, L. M., E-mail: hliszt@nrao.edu [Arizona Radio Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

2012-03-01

335

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

USGS Publications Warehouse

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

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

2004-01-01

336

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

PubMed

This study demonstrates the advantage of a combined use of chemical and isotopic tools to understand the dissolved organic carbon (DOC) cycle in a regional confined methanogenic aquifer. DOC concentration and carbon isotopic data demonstrate that the soil zone is a primary carbon source of groundwater DOC in areas close to recharge zones. An in-situ DOC source linked to organic rich sediments present in the aquifer matrix is controlling the DOC pool in the central part of the groundwater flow system. DOC fractions, 13C-NMR on fulvic acids and 14C data on DOC and CH4 support the hypothesis that the in-situ DOC source is a terrestrial organic matter and discard the Ordovician bedrock as a source of DOC. PMID:15223664

Aravena, Ramon; Wassenaar, Leonard I; Spiker, Elliot C

2004-06-01

337

Carbon isotope fractionation of sapropelic organic matter during early diagenesis  

USGS Publications Warehouse

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

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

1984-01-01

338

Micropowder collecting technique for stable isotope analysis of carbonates.  

PubMed

Micromilling is a conventional technique used in the analysis of the isotopic composition of geological materials, which improves the spatial resolution of sample collection for analysis. However, a problem still remains concerning the recovery ratio of the milled sample. We constructed a simple apparatus consisting of a vacuum pump, a sintered metal filter, electrically conductive rubber stopper and a stainless steel tube for transferring the milled powder into a reaction vial. In our preliminary experiments on carbonate powder, we achieved a rapid recovery of 5 to 100?µg of carbonate with a high recovery ratio (>90%). This technique shortens the sample preparation time, improves the recovery ratio, and homogenizes the sample quantity, which, in turn, improves the analytical reproducibility. PMID:21488119

Sakai, Saburo; Kodan, Tsuyoshi

2011-05-15

339

New Methods for Fully Automated Isotope Ratio Determination from Hydrogen at the Natural Abundance Level  

Microsoft Academic Search

A variety of methods for measurement of H\\/H from H2 are evaluated for their ability to be fully automated and for applicability to automated isotopic analysis of water and organic compounds. Equilibration of water with H2 gas with the aid of a platinum catalyst has been commercialized into a fully automated sample preparation device. A second and newer technique, involving

W. A. Brand; H. Avak; R. Seedorf; D. Hofmann; Th. Conradi

1996-01-01

340

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

NASA Astrophysics Data System (ADS)

A new approach is presented for mathematical modeling of stable carbon isotope ratios in hydrocarbon gases based on both theoretical and experimental data. The kinetic model uses a set of parallel first-order gas generation reactions in which the relative cracking rates of isotopically substituted (k?) and unsubstituted (k) bonds are represented by the equation k?/k=(Af?/Af) exp(-?Ea/RT), where R is the gas constant and T is temperature. Quantum chemistry calculations have been used to estimate the entropic (A f?/A f) and enthalpic (?Ea) terms for homolytic bond cleavage in a variety of simple molecules. For loss of a methyl group from a short-chain n-alkane (? C 6), for example, we obtain an average ?Ea of 42.0 cal/mol and an average A f?/A f of 1.021. Expressed differently, 13C-methane generation is predicted to be 2.4% (24‰) slower than 12C-methane generation (from a short-chain n-alkane) in a sedimentary basin at 200°C but only 0.7% (7‰) slower in a laboratory heating experiment at 500°C. Similar calculations carried out for homolytic bond cleavage in other molecules show that with few exceptions, ?Ea varies between 0 and 60 cal/mol and A f?/A f between 1.00 and 1.04. Examination of this larger data set reveals: (1) a weak sigmoid relationship between ?Ea and bond dissociation energy; and (2) a strong positive correlation between ?Ea and A f?/A f. The significance of these findings is illustrated by fitting a kinetic model to chemical and isotopic data for the generation of methane from n-octadecane under isothermal closed-system conditions. For a specific temperature history, the fitted model provides quantitative relationships among methane carbon isotope composition, total methane yield and methane generation rate which may have relevance to the cracking of oil-prone kerogens and crude oil. The observed variability of the kinetic reactivity of various methane source rocks highlights the need to apply and adequately calibrate such models with laboratory data for specific study areas. With this approach isotope data of natural gases can be used not only to estimate the time of gas generation in a sedimentary basin, but also to evaluate the source rock maturities at which specific accumulations were generated, and place constraints on trap charging histories.

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

2000-08-01

341

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

342

Genesis of carbonates within Abalak and Bazhenov formations (West Siberia), revealed from stable carbon and oxygen isotopes distribution  

NASA Astrophysics Data System (ADS)

Upper Jurassic deposits of Bazhenov formation are the main source rocks of the West Siberia Basin. Now the Bazhenov suite is intensively investigated not only as a source rock, but as unconventional reservoir of oil due to its vertical and lateral heterogeneity. The rocks of Bazhenov formation are composed of four main units: silica minerals, clay (predominantly hydromica), kerogen and carbonates. To predict the distribution of different lithological units it is important to reveal their genesis and facial conditions during their formation. One of the reservoir types is presented by cavernous-porous carbonates. Stable carbon and oxygen isotopes investigations has been carried out to reveal origin of carbonate material in Late Abalak - Bazhenov time. Four genetic types of carbonates have been subdivided according to mineralogical composition and stable carbon and oxygen isotopes distribution: 1) belemnites and other faunal remains; 2) secondary dolomites of Bazhenov formation; 3) secondary calcite filling cracks and composing inclusions of Abalak deposits; 4) methane-derived authigenic carbonates of Abalak formation. The first three types are presented by normal marine carbonates according to their carbon isotopes composition. Light oxygen isotopes composition indicates high temperatures during their precipitation (diagenesis). The fourth type is characterized by light carbon isotopes composition, which indicates presence of isotopically light biogenic CO2 in the environment. According to oxygen isotopic composition the carbonate material is primary and precipitated in subsurface conditions. Such carbon and oxygen isotopes composition is characteristic for methane-derived carbonates formed in the areas of active fluids discharge to the seafloor (cold seeps) as a result of Anaerobic Oxidation of Methane (AOM). Thus in Late Jurassic time active fluid escape to the sea floor took place in the West Siberia Basin.

Yurchenko, A.; Blinova, V.; Kalmikov, G. A.; Balushkina, N. S.

2013-12-01

343

Construction of Confidence Regions for Isotopic Abundance Patterns in LC/MS Data Sets for Rigorous Determination of Molecular Formulas  

PubMed Central

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

2010-01-01

344

A Widely Tunable Infrared Laser Spectrometer for Measurements of Isotopic Ratios of Carbon Cycle Gases  

SciTech Connect

The atmospheric abundances of carbon dioxide and methane have increased dramatically during the industrial era. Measurements of the isotopic composition of these gases can provide a powerful tool for quantifying their sources and sinks. This report describes the development of a portable instrument for isotopic analysis CO{sub 2} and CH{sub 4} using tunable infrared laser absorption spectroscopy. This instrument combines novel optical design and signal processing methods with a widely tunable mid-infrared laser source based on difference frequency generation (DFG) which will can access spectral regions for all the isotopes of CO{sub 2} and CH{sub 4} with a single instrument. The instrument design compensates for the large difference in concentration between major and minor isotopes by measuring them with path lengths which differ by a factor of 100 within the same multipass cell. During Phase I we demonstrated the basic optical design and signal processing by determining {sup 13}CO{sub 2} isotopic ratios with precisions as small as 0.2{per_thousand} using a conventional lead salt diode laser. During Phase II, the DFG laser source was coupled with the optical instrument and was demonstrated to detect {sup 13}CH{sub 4}/{sup 12}CH{sub 4} ratios with a precision of 0.5{per_thousand} and an averaging time of 20 s using concentrated methane in air with a mixing ratio of 2700 ppm. Methods for concentrating ambient air for isotopic analysis using this technique have been evaluated. Extensions of this instrument to other species such as {sup 13}CO{sub 2}, C{sup 18}OO, and CH{sub 3}D are possible by substituting lasers at other wavelengths in the DFG source module. The immediate commercial application of this instrument will be to compete with existing mass spectrometric isotope instruments which are expensive, large and relatively slow. The novel infrared source developed in this project can be applied to the measurement of many other gas species and will have wide application in atmospheric monitoring, industrial process control, and medical research and diagnostic development.

Joanne H. Shorter; J. Barry McManus; David D. Nelson; Charles E. Kolb; Mark S. Zahniser; Ray Bambha; Uwe Lehmann; Tomas Kulp; Stanley C. Tyler

2005-01-31

345

On the determination of carbon isotopic ratios in cool carbon stars  

NASA Astrophysics Data System (ADS)

We discuss the determination of carbon isotopic ratios (12C) / (12C) iso in N-type Galactic carbon stars. Ohnaka & Tsuji (1996) reported (12C) / (12C) iso ratios smaller by a factor 2 or 3 than the determinations of Lambert et al. (1986). Using synthetic spectra of carbon stars, we analyse systematic errors in their iso-intensity method. It is found to be rather sensitive to model parameters and blends. Furthermore, there are large discrepancies between the effective temperatures adopted by these two studies (mean discrepancy close to 260 K for the 20 stars in common). That, together with uncertainties due to model atmospheres, to carbon enrichments and effects of the blends, could explain most of the discrepancies between these two studies. The LGEH86 analysis is, on the other hand, rather insensitive to model parameters. We therefore conclude that large (12C) / (12C) iso ratios in cool Galactic carbon stars should be favoured.

de Laverny, P.; Gustafsson, B.

1998-04-01

346

Isotope Tutorial (title provided or enhanced by cataloger)  

NSDL National Science Digital Library

This isotope tutorial explains what isotopes are and what units are used to express them, how measurements of isotopes are made, and how natural variation in stable isotope abundances come about. The site describes processes affecting isotope ratios such as photosynthesis, evapotranspiration, and respiration; biosphere-atmosphere exchange of isotopes in water and carbon; and how stable isotopes are used to study environmental history. There is information on courses in stable isotopes and the Biosphere - Atmosphere Stable Isotope Network (BASIN) project aimed at improving understanding of carbon cycle processes at the ecosystem, regional, and global scale. Links are provided to analytical labs.

Pataki, Diane

347

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

National Technical Information Service (NTIS)

MIL 090001 is a large (approximately 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 e...

K. D. McKeegan L. P. Keller Z. D. Sharp

2012-01-01

348

Element abundance patterns in carbonate globules and rims from ALH 84001  

NASA Astrophysics Data System (ADS)

Posssible evidence for ancient biological activity in carbonate globules and the rims on the carbonate globules from the ALH 84001 meteorite has been reported by McKay et al. (1996). Element abundance patterns have previously proven useful in constraining the formation temperatures and formation mechanisms of planetary materials and meteorites. In this study, both a carbonate globule sample and a rim sample were extracted from fresh fracture surfaces of ALH 84001 and were analyzed for major trace elements (S, Cl, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Ge, Se, Br, Rb, Sr, Y, and Zr) using an about six-micron analysis beamspot on the X-Ray Microprobe (XRF Microprobe) on Beamline X26A of the National Synchrotron Light Source at Brookhaven National Laboratory.

Flynn, G. J.; Sutton, S. R.; Keller, L. P.

1997-03-01

349

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

350

Models of earth structure inferred from neodymium and strontium isotopic abundances  

PubMed Central

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

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

1979-01-01

351

New methods for fully automated isotope ratio determination from hydrogen at the natural abundance level.  

PubMed

Abstract A variety of methods for measurement of (2)H/(1)H from H(2) are evaluated for their ability to be fully automated and for applicability to automated isotopic analysis of water and organic compounds. Equilibration of water with H(2) gas with the aid of a platinum catalyst has been commercialized into a fully automated sample preparation device. A second and newer technique, involving injecting water, methane, or other volatile organic compounds onto hot chromium in a reactor attached to the dual inlet system of a gas isotope ratio mass spectrometer, can be integrated with a conventional GC-autosampler to allow automated analysis of a variety of substrates. Both techniques result in precisions around 1‰ (? notation) on the VSMOW scale, and are fast and accurate, and with appropriate mass spectrometers require only negligible scaling for the SLAP/VSMOW difference. Several experimental methods which show considerable promise employ "isotope ratio monitoring" (irm) inlet systems, in which a carrier gas is used for transport of H(2) to the mass spectrometer. Any such method has to address the problem of He ions corrupting the measurement of the H(2) ions. One such approach uses a heated palladium membrane for selective introduction of H(2) into the mass spectrometer, and a second involves modifications to the ion optics to control the stray helium ions. Both approaches have significant limitations that must be overcome before irm techniques can be used in routine applications, in particular for measuring hydrogen isotopes from GC effluents (irm-GCMS). PMID:22088118

Brand, W A; Avak, H; Seedorf, R; Hofmann, D; Conradi, T

1996-08-01

352

CARBON ABUNDANCES FOR RED GIANTS IN THE DRACO DWARF SPHEROIDAL GALAXY  

SciTech Connect

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

Shetrone, Matthew D.; Stanford, Laura M. [McDonald Observatory, University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712-0259 (United States); Smith, Graeme H. [University of California ObservatoriesLick Observatory, Department of Astronomy and Astrophysics, UC Santa Cruz, 1156 High St., Santa Cruz, CA 95064 (United States); Siegel, Michael H. [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, State College, PA 16801 (United States); Bond, Howard E., E-mail: shetrone@astro.as.utexas.edu, E-mail: graeme@ucolick.org, E-mail: siegel@astro.psu.edu, E-mail: bond@stsci.edu [9615 Labrador Ln., Cockeysville, MD 21030 (United States)

2013-05-15

353

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

354

Fractionation of carbon isotopes by phytoplankton and estimates of ancient CO2 levels  

Microsoft Academic Search

Reports of the 13C content of marine particulate organic carbon are compiled and on the basis of GEOSECS data and temperatures, concentrations, and isotopic compositions of dissolved CO2 in the waters in which the related phytoplankton grew are estimated. In this way, the fractionation of carbon isotopes during photosynthetic fixation of CO2 is found to be significantly correlated with concentrations

Katherine H. Freeman; J. M. Hayes

1992-01-01

355

Carbon isotope fractionation during degradation of benzene, trichloroethene, and tetrachloroethene under ultraviolet light  

Microsoft Academic Search

Stable carbon isotope fractionation factors associated with the degradation of benzene, trichloroethene (TCE), and tetrachloroethene (PCE) under ultraviolet light (254 nm) have been measured experimentally using simple and inexpen- sive quartz reaction vessels equipped with a syringe valve and septum. Carbon isotope enrichment factors of ?benzene = -6.2 ± 0.3‰, ?TCE = -6.8 ± 0.2‰, and ?PCE = -4.1 ±

SIMON R. POULSON; HIROSHI NARAOKA

2006-01-01

356

Deglacial methane emission signals in the carbon isotopic record of Lake Baikal  

Microsoft Academic Search

Changes in the concentrations of atmospheric greenhouse gases constitute an important part of global climate forcing. Here we present the first continental evidence for climatically caused changes in a methane gas hydrate reservoir. The organic carbon stable isotope record from Lake Baikal during the past 130?000 years registers regular emissions of isotopically light carbon by the occurrence of distinct negative

Alexander A. Prokopenko; Douglas F. Williams

2004-01-01

357

Isotopic and elemental abundances of copper and zinc in lunar samples, Zagami, Pele’s hairs, and a terrestrial basalt  

NASA Astrophysics Data System (ADS)

We used ICP-MS to measure the elemental concentrations and isotopic abundances of Cu and Zn in: nine Ti-rich lunar basalts (10017, 10022, 10024, 10057, 70215, 71055, 74255, 75055, and 75075); size-separated samples prepared by sieving of pyroclastic black glass 74001, orange glass 74022, and the lunar soils 15021, 15231, 70181, and 79221; a basalt from the Piton des Neiges volcano, Reunion Island; two samples of Pele's hairs from the Nyiragongo volcano, Democratic Republic of Congo, and the martian meteorite Zagami. The isotopic fractionation of zinc in lunar basalts and Zagami is mass dependent relative to a terrestrial standard (JMC 400882B). These and published results imply that lunar, terrestrial, meteoritic, and perhaps martian zinc all come from one or more reservoirs linked by mass-dependent fractionation processes. Relative to terrestrial basalts, Ti-rich lunar basalts are enriched in the heavier isotopes of Cu and Zn: we find for Ti-rich lunar basalts the following ranges and averages ±1 - ? (‰): ? 65Cu/ 63Cu ? ? 65Cu, 0.1-1.4, 0.5 ± 0.1‰ ( N = 7); ? 66Zn/ 64Zn ? ? 66Zn = 0.2-1.9, 1.2 ± 0.2‰ ( N = 8; 10017 excluded). For two terrestrial samples, we find ? 66Zn ˜ +0.3‰ and ? 65Cu ˜ 0‰, which are consistent with published values. The differences between the lunar basalts and terrestrial basalts could reflect minor, planetary-scale vaporization or igneous processes on the Moon. Data for size separates of the pyroclastic glasses 74001 and 74220 confirm the well-known surface correlation of Cu and Zn, but modeling calculations reveal no sharp differences between either the elemental ratios or the isotopic composition of grain interiors and exteriors. The absence of such differences indicates that the isotopic compositions for bulk samples are dominated by a light-isotope-rich surface component. Data for size separates of lunar soils also confirm the surface correlation of Cu and Zn, but an enrichment of heavy rather than light isotopes. Averages for bulk lunar soils from this work and the literature are (‰): ? 65Cu, from 1.4 to 4.1, average 3.0 ± 0.3 ( N = 9); ? 66Zn, from 2.2 to 6.4, average 4.0 ± 0.3 ( N = 14). As with the glasses, in all but soil 15231 our data show no strong differences between the isotopic composition of soil sub-samples with small and large grains. The size of the isotopic fractionation inferred for the surface component in the soils is 3× smaller than predicted by a published model of sputtering primarily by solar particles. At the same time, the observed fractionation is larger than predicted by calculations based on a model of micrometeorite impact heating and hydrodynamic quenching. Because impact heating appears unable to explain the observations, we conclude that sputtering must be important even though samples with very large isotopic fractionation of Cu and Zn have not yet been found.

Herzog, G. F.; Moynier, F.; Albarède, F.; Berezhnoy, A. A.

2009-10-01

358

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

NASA Astrophysics Data System (ADS)

Studies of the isotopic content of atmospheric particulate matter are hampered by difficulties in chemically defining the pools of carbon and analytically isolating the different pools. We are conducting studies on reference materials and atmospheric aerosol samples to develop a method to measure stable and radio- carbon isotopes on the labile and refractory carbon. We are using a flow-through combustion system that allows us to combust, collect and measure the isotopic content of the gases produced at all stages of heating/oxidizing. We compare our results to those measured using a chemothermal oxidation method (CTO) (Gustafsson et al., 2001). In this method, refractory carbon is defined as the material remaining after pre- combusting a sample at 375°C in the presence of oxygen for 24 hours. The reference materials are diesel soot, apple leaves and a hybrid of the two (DiesApple), all from NIST. These provide carbon with two well-defined fractions -- the soot provides refractory carbon that is radiocarbon dead and the apple leaves provide organic carbon that is radiocarbon modern. Radiocarbon results from DiesApple indicate that the "refractory" carbon defined by the CTO method is actually a mixture of old and modern carbon that contains over 25% modern carbon. This suggests that charred material formed from the apples leaves during the pre-combustion step is contributing to the fraction we identify as refractory carbon. We are studying this by analyzing the individual materials and the mixture using our flow-through system. First results with this system indicate that the refractory fraction trapped from the DiesApple contains much less modern carbon than the CTO method, less than 7%. We will present detailed concentration and isotopic results of the generation of carbon dioxide during programmed combustion of each of the reference materials. We studied the radiocarbon content of both the total carbon (TC) and refractory carbon in the fine particulate matter (PM2.5) collected on quartz fiber filters as part of the Southeastern Aerosol Research and Characterization (SEARCH) program. The five samples were collected at two sites (Birmingham, AL and Atlanta, GA) with very different sources of atmospheric particulate matter. In all instances, the refractory carbon contained significantly less radiocarbon than the TC suggesting, not unexpectedly, a source of particulate carbon from the combustion of fossil material. We will present results from the analysis of the same filters in the flow-through system. The implication of our results for the use of radiocarbon in the quantitative apportionment of atmospheric particulate matter sources will be discussed. Gustafsson O., T. Bucheli, Z. Kukulska, M. Andersson, C. Largeau, J-N. Rouzaud, C. Reddy and T. Eglinton (2001) Evaluation of a protocol for the quantification of black carbon in sediments. GBD 15, 881-890.

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

2006-12-01

359

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

Microsoft Academic Search

To evaluate the isotopic record of climate change and carbon sequestration in the Late Paleozoic, we have compiled new and published oxygen and carbon isotopic measurements of more than 2000 brachiopod shells from Carboniferous through Middle Permian (359–260 Ma) strata. We focus on the isotopic records from the U.S. Midcontinent and the Russian Platform because these two regions provide well-preserved marine

Ethan L. Grossman; Thomas E. Yancey; Thomas E. Jones; Peter Bruckschen; Boris Chuvashov; S. J. Mazzullo; Horng-sheng Mii

2008-01-01

360

The origin of fluorine: The first determination of fluorine abundances in extragalactic AGB carbon stars  

NASA Astrophysics Data System (ADS)

Only for AGB stars does there exist observational evidence that nucleosynthesis of fluorine, as ^19F, is an ongoing process. However, we have recently derived F abundances in Galactic AGB carbon- stars and found much lower F enhancements than previously reported in the literature. This downward revision to the F abundances in Galactic stars results from much improved molecular data and model atmospheres adopted in our recent analyses. The lower F enhancements found places doubt on the real contribution of AGB stars to the chemical evolution of this element. Nevertheless, theoretical AGB models predict large primary F production at low metallicity, but this has not yet been tested observationally. Therefore, we propose to measure F abundances in extragalactic AGB C-stars covering a range in metallicity and belonging to nearby (metal-poor) galaxies. This will lead to the first derivation of F abundances in extragalactic AGB C-stars, to new constraints on nucleosynthetic models and to a better estimation of the contribution of AGB stars to the F inventory in stellar populations.

Abia, Carlos; Cunha, Katia; Smith, Verne V.

2010-08-01