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1

Carbon isotopes and light element abundances in carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

A stepped combustion technique was used to measure the abundance of C, N, SO2 and H2O in seven carbonaceous chondrites. Details of the experimental procedures are provided, noting the necessity of adding fresh material at several of the 50 C increments (from 200-1200 C) to compensate for the small sizes of the samples. Samples from the Orgueil, Murchison, Cold Bokkeveld and Murray, Renazzo, Allende and Mokoia meteorites were examined. An extensive tabulation is provided of the elemental releases over various temperature intervals and comparisons are made between the release characteristics observed for the different samples. Emphasis is placed on the types and enrichments of carbon compounds detected and the compositions of the sites where releases occurred.

Halbout, Jerome; Mayeda, Toshiko K.; Clayton, Robert N.

1986-10-01

2

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

NASA Astrophysics Data System (ADS)

exists increasing evidence supporting the important role of black carbon in global carbon cycles. Particulate black carbon (PBC) is allochthonous and has distinct reactivities compared to the bulk particulate organic carbon (tot-POC) in marine environments. However, the abundance, geochemical behavior of PBC and its importance in oceanic carbon budget remain poorly understood. Here we report the abundance, distribution, and stable isotopic signatures of BC derived from the chemo-thermal oxidation (CTO-375) method (BCCTO) in the Gulf of Mexico. Our results show that BCCTO abundance decreased from shelf to basin, and more than a half of riverine BCCTO could be removed over the shelf. Moreover, BCCTO is much more refractory compared to the tot-POC and has ?13C values lower than those of BC-excluded POC. These results highlight the significance of PBC in marine carbon cycles and potentially suggest the need for a new end-member term in quantifying POC sources in the ocean.

Yang, Weifeng; Guo, Laodong

2014-11-01

3

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

E-print Network

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

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

2006-06-07

4

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

PubMed Central

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

Affek, Hagit P.; Yakir, Dan

2003-01-01

5

Stable-carbon isotope composition of Poaceae pollen: an assessment for reconstructing C3 and C4 grass abundance  

Microsoft Academic Search

Plants using the C3 and C4 photosynthetic pathways differ in carbon-isotope composition, and this difference offers a means to estimate the relative abundance of these two functional groups in the palaeorecord. We report here results of a study aiming to evaluate pollen &dgr;13C(&dgr;13Cp) of Poaceae (the grass family) as a proxy indicator for palaeoecological studies. On average &dgr;13Cp differs by

David M. Nelson; Feng Sheng Hu; Robert H. Michener

2006-01-01

6

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

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

7

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

8

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

9

The Solar Oxygen Abundance, and the Rare Isotopes of C and O, Derived from Infrared Spectra of Carbon Monoxide  

NASA Astrophysics Data System (ADS)

A detailed abundance analysis is presented for solar oxygen based on the ?V=1 fundamental (4.6~?m) and ?V=2 (2.3~?m) first-overtone rovibrational bands of carbon monoxide observed above the Earth's atmosphere at very high spectral resolution and high signal-to-noise by the Shuttle-borne ATMOS Fourier transform spectrometer (FTS). Additional observations to define the reference photospheric thermal structure were taken of the CO fundamental bands in an atmospheric window at 2145~cm-1 (4.6~?m) using the 1~m FTS of the McMath-Pierce telescope at Kitt Peak and a fast tip/tilt image stabilization system. The latter allowed measurements at the extreme limb where the highly slanted rays probe into the outer layers of the photosphere. High spatial resolution "movies" of weak CO lines at disk center taken under excellent seeing conditions with the Infrared Imaging Spectrometer (IRIS), also on the McMath-Pierce telescope, further constrained thermal and velocity fluctuations in the layers in which the abundance-sensitive CO lines form. This work is meant to complement a series of recent studies which have revised the previously recommended solar oxygen abundance downward by nearly a factor of two; although in fact our conclusions do not support such a revision. The oxygen abundance recovered in the present work is 70070~ppm (parts per million relative to hydrogen) compared with the proposed downward revision to 46060~ppm, and the recommended value of 650100~ppm of a decade ago. In our analysis, a fixed C/O ratio of 0.5, derived in independent work, was assumed; so the associated carbon abundance is 350~ppm. New accurate values for the solar abundance ratios of the rare isotopes of C and O also are reported: 12C/13C= 70, 16O/17O= 400, and 16O/18O= 2000. All three ratios are lower than terrestrial or meteoritic values (indicating higher isotopic abundances). We find no evidence in the ATMOS3 spectra for measurable 14C16O lines.

Ayres, T. R.; Plymate, C.; Keller, C.; Kurucz, R. L.

2005-05-01

10

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

11

Natural Abundance Carbon Isotope Composition of Isoprene Reflects Incomplete Coupling between Isoprene  

E-print Network

leaves is dynamically coupled to photosynthesis through the use of primary and recent photosyn- thate, carbon source(s). This contribution increased when photosynthesis was inhibited by CO2-free air) is emitted from leaves of various plant species (Kesselmeier and Staudt, 1999) and influences the trace

12

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. FRI1, S.A. HALLDRSON1, 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

13

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

14

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

15

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 (8.813N, 82.963W) 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

16

Carbon13 kinetic isotope effects in the decarbonylations of lactic acid containing 13 C at the natural abundance level  

Microsoft Academic Search

The13C kinetic isotope fractionation in the decarbonylation of lactic acid of natural isotopic composition by sulfuric acid has been studied in the temperature range of 2080C. The13C(1) isotope separation in the decarbonylation of lactic acid by concentrated sulfuric acid depends strongly on the temperature above 40C. Below this temperature the13C isotope effect in the decarbonylation of lactic acid by concentrated

M. Zielinski; G. Czarnota; H. Papiernik-Zielinska

1992-01-01

17

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

NASA Astrophysics Data System (ADS)

The internal structure and growth history of six macro-diamonds from kimberlite pipes in Yakutia (Russia) were investigated with cathodoluminescence imaging and coupled carbon isotope and nitrogen abundance analyses along detailed core to rim traverses. The diamonds are characterised by octahedral zonation with layer-by-layer growth. High spatial resolution SIMS profiles establish that there is no exchange of the carbon isotope composition across growth boundaries at the ?m scale and that isotopic variations observed between (sub)zones within the diamonds are primary. The macro-diamonds have ?13C values that vary within 2 of -5.3 and their nitrogen contents range between 0-1334 at. ppm. There are markedly different nitrogen aggregation states between major growth zones within individual diamonds that demonstrate Yakutian diamonds grew in multiple growth events. Growth intervals were punctuated by stages of dissolution now associated with <10 ?m wide zones of nitrogen absent type II diamond. Across these resorption interfaces carbon isotope ratios and nitrogen contents record shifts between 0.5-2.3 and up to 407 at. ppm, respectively. Co-variation in ?13C value-nitrogen content suggests that parts of individual diamonds precipitated in a Rayleigh process from either oxidised or reduced fluids/melts, with two single diamonds showing evidence of both fluid types. Modelling the co-variation establishes that nitrogen is a compatible element in diamond relative to its growth medium and that the nitrogen partition coefficient is different between oxidised (3-4.1) and reduced (3) sources. The reduced sources have ?13C values between -7.3 and -4.6, while the oxidised sources have higher ?13C values between -5.8 and -1.8 (if grown from carbonatitic media) or between -3.8 and +0.2 (if grown from CO2-rich media). It is therefore concluded that individual Yakutian diamonds originate from distinct fluids/melts of variable compositions. The diamond-forming fluids within the cratonic mantle beneath the Siberian Craton record significant variations in composition and volume and include both oxidised and reduced sources. These observations suggest that dating diamond inclusions using an isochron approach will best provide geologically meaningful ages if inclusions can be shown to be genetically (spatially) related.

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

2013-01-01

18

Nitrogen and carbon stable isotope abundances support the myco-heterotrophic nature and host-specificity of certain achlorophyllous plants  

Microsoft Academic Search

Summary Over 400 species of achlorophyllous vascular plants are thought to obtain all C 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 patterns of N and C stable isotopes of various eco- system pools in two old-growth conifer forests, we sampled six species

Steven A. Trudell; Paul T. Rygiewicz; Robert L. Edmonds

2003-01-01

19

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

20

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...

21

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

22

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

23

1, 393412, 2004 Carbon isotope  

E-print Network

BGD 1, 393­412, 2004 Carbon isotope anomaly in the major plant C1 pool F. Keppler et al. Title Page Biogeosciences Discussions is the access reviewed discussion forum of Biogeosciences Carbon isotope anomaly.keppler@qub.ac.uk) 393 #12;BGD 1, 393­412, 2004 Carbon isotope anomaly in the major plant C1 pool F. Keppler et al. Title

Boyer, Edmond

24

NATURAL ABUNDANCES OF CARBON ISOTOPES (14C, 13C) IN LICHENS AND CALCIUM OXALATE PRUINA: IMPLICATIONS FOR ARCHAEOLOGICAL AND PALEOENVIRONMENTAL STUDIES  

Microsoft Academic Search

Radiocarbon ages of calcium oxalate that occurs naturally on rock surfaces have been used recently in archae- ological and paleoenvironmental studies. Oxalate rock coatings are found globally, with most appearing to be residues from epilithic lichens. To explore the source(s) of carbon used by these organisms for the production of oxalate we measured the natural abundances of 14C and 13C

Melanie J Beazley; Richard D Rickman; Debra K Ingram; Thomas W Boutton; Jon Russ

25

Estimating Rates of Denudation Using Cosmogenic Isotope Abundances in Sediment  

Microsoft Academic Search

We propose, as a testable hypothesis, a basin-scale approach for interpreting the abundance of in situ produced cosmogenic isotopes, an approach which considers explicitly both the isotope and sediment flux through a drainage basin. Unlike most existing models, which are appropriate for evaluating in situ produced cosmogenic isotope abundance at discrete points on Earth's surface, our model is designed for

Paul Bierman; Eric J. Steig

1996-01-01

26

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 (Fri 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.; Fri, E.; Halldrsson, S. A.; Grnvold, K.

2014-06-01

27

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%, 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

28

THE ATOMIC WEIGHTS COMMISSION AND ISOTOPIC ABUNDANCE RATIO DETERMINATIONS.  

SciTech Connect

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

HOLDEN, N.E.

2005-08-07

29

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

30

Land plants, carbon isotopes and the late Paleozoic carbon cycle  

Microsoft Academic Search

Two parameters determine the carbon isotopic composition of plant tissue: the carbon isotopic composition of atmospheric carbon dioxide and the carbon isotopic fractionation associated with plant metabolism. Based on a systematic survey of terrestrial organic matter, we present a carbon isotope record for the late Paleozoic. Investigations directed towards sample type, maturity and host lithology indicate that near primary isotopic

W. Peters-Kottig; H. Strauss; H. Kerp

2003-01-01

31

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

32

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

33

Lithium Isotopic Abundances in Metal-poor Halo Stars  

Microsoft Academic Search

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

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

2006-01-01

34

Mercury Elemental and Isotopic Abundances in Mercury-Manganese Stars  

NASA Astrophysics Data System (ADS)

Hg II abundances have been determined for 42 mercury-manganese (HgMn) stars by fitting synthetic spectra to observed spectra of the 3984 A Hg II line. Nine of the stars had lines sharp enough to allow their Hg isotopic abundance mixes to be found. The Hg abundance is reported for more HgMn stars here than in any other single work. No correlation was found between Hg II abundance and Teff or the central wavelength of the 3984 A line. There may be a weak correlation between logg and the derived Hg II abundance. The mean central wavelength of the 3984 A line, an indicator of the Hg isotopic mix, is loosely correlated with T eff: stars with primarily heavy Hg isotopes tend to be cooler. I find that there is no evidence that any of the HgMn stars have 196Hg or 198Hg. For the sharp-lined stars, the 204Hg abundance decreases with increasing T eff. No correlation is seen between mean central wavelength and logg or between vsini and A(Hg) or the central wavelength of the 3984 A line. The 4358 A Hg I line was measured at high spectral resolution for seven HgMn stars. The isotopic shifts are too small and the hyperfine components are too weak to allow unambiguous isotopic abundance ratios to be found. Hg I abundances match Hg II abundances fairly well. Some Hg isotopic mixtures are difficult to explain using only diffusion. HR 7245 has approximately equal abundances of 199Hg, 200Hg, 202Hg, and 204Hg but very little 201Hg and 11 Per has Hg that is mostly 199Hg and 204Hg. My calculations show that the effect of hyperfine splitting of the 201Hg line on diffusion may partly explain the Hg isotopic mix found in HR 7245, but I found no explanation for that of 11 Per. These were the first very high resolution measurements of the 3984 A line for HR 7245 and 11 Per. Although diffusion may be acting in HgMn stars, there must be one or more other mechanisms acting to produce the abundances seen, or our understanding of diffusion is lacking on some important point.

Woolf, Vincent Martell

1998-10-01

35

(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

36

Some isotopic abundances in the cosmic radiation  

NASA Technical Reports Server (NTRS)

Cosmic ray nuclei with Z not less than 10 have been observed in a detector which measures charge with a double scintillator-Cherenkov array and mass by combining the Cherenkov signal with residual range measured in nuclear emulsions. Results are presented for the isotopic analyses of Al, Ca, Sc, Mn, Fe, Co, Ni and Cu in the energy range 300-800 MeV/amu.

Young, J. S.; Freier, P. S.; Waddington, C. J.

1980-01-01

37

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

38

Literature survey of isotopic abundance data for 1987-1989  

SciTech Connect

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

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

1989-08-09

39

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

40

Variable Carbon Isotopes in ALH84001 Carbonates  

Microsoft Academic Search

The Martian meteorite ALH84001 contains a small amount of carbonate that was deposited from aqueous fluids on the Martian surface approximately 3.9 Ga.. McKay et al. (1996) proposed evidence for the existence of life preserved within the carbonate grains. In order to determine the nature of the ancient Martian aqueous system we have combined previously collected oxygen isotopic data with

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

2002-01-01

41

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

42

The abundances of isotopes in the cosmic radiation  

NASA Technical Reports Server (NTRS)

Studies of the isotopic composition of nuclei in the cosmic radiation are reviewed, including abundances of the isotopes of elements from H to Ni, together with their implications for cosmic ray origin, acceleration, and transport in the Galaxy. The review focuses on determinations of the composition of cosmic ray source material, and the extent to which the isotopic composition of this material is different from, or similar to, typical solar system material and other samples of Galactic matter. Theoretical models that have been advanced to explain the observed overabundance of neutron-rich isotopes in cosmic rays are described. Also discussed are studies of various radioactive clocks that record the time-scales associated with the nucleosynthesis, acceleration, and transport of cosmic ray nuclei, and studies of the so-called anomalous cosmic ray component, thought to represent a sample of the neutral interstellar medium.

Mewaldt, R. A.

1989-01-01

43

Carbon and oxygen isotope microanalysis of carbonate.  

PubMed

Technical modification of the conventional method for the delta(13)C and delta(18)O analysis of 10-30 microg carbonate samples is described. The CO(2) extraction is carried out in vacuum using 105% phosphoric acid at 95 degrees C, and the isotopic composition of CO(2) is measured in a helium flow by gas chromatography/isotope ratio mass spectrometry (GC/IRMS). The feed-motion of samples to the reaction vessel provides sequential dropping of only the samples (without the sample holder) into the acid, preventing the contamination of acid and allowing us to use the same acid to carry out very large numbers of analyses. The high accuracy and high reproducibility of the delta(13)C and delta(18)O analyses were demonstrated by measurements of international standards and comparison of results obtained by our method and by the conventional method. Our method allows us to analyze 10 microg of the carbonate with a standard deviation of +/-0.05 per thousand for delta(13)C and delta(18)O. The method has been used successfully for the analyses of the oxygen and carbon isotopic composition of the planktonic and benthic foraminifera in detailed palaeotemperature reconstructions of the Okhotsk Sea. PMID:19603476

Velivetskaya, Tatiana A; Ignatiev, Alexander V; Gorbarenko, Sergey A

2009-08-30

44

The isotope abundances and the atomic weight of cadmium by a metrological approach  

Microsoft Academic Search

Gravimetric synthetic mixtures of seven enriched, purified cadmium isotope materials were used to determine the correction factors for mass fractionation (MC-TIMS) and mass discrimination (MC-ICP-MS). The isotope abundance ratios determined for various natural cadmium materials represents the isotope composition for natural cadmium materials. Correction of the isotope abundance ratios observed yielded isotope abundances of 106Cd 0.012450(8), 108Cd 0.008884(4), 110Cd 0.124846(16),

W. Pritzkow; S. Wunderli; J. Vogl; G. Fortunato

2007-01-01

45

The Abundance and Isotopic Composition of Hg in Extraterrestrial Materials  

NASA Technical Reports Server (NTRS)

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

Lauretta, D. S.

2004-01-01

46

The abundance and isotopic composition of Cd in iron meteorites  

NASA Astrophysics Data System (ADS)

Cadmium is a highly volatile element and its abundance in meteorites may help better understand volatility-controlled processes in the solar nebula and on meteorite parent bodies. The large thermal neutron capture cross section of 113Cd suggests that Cd isotopes might be well suited to quantify neutron fluences in extraterrestrial materials. The aims of this study were (1) to evaluate the range and magnitude of Cd concentrations in magmatic iron meteorites, and (2) to assess the potential of Cd isotopes as a neutron dosimeter for iron meteorites. Our new Cd concentration data determined by isotope dilution demonstrate that Cd concentrations in iron meteorites are significantly lower than in some previous studies. In contrast to large systematic variations in the concentration of moderately volatile elements like Ga and Ge, there is neither systematic variation in Cd concentration amongst troilites, nor amongst metal phases of different iron meteorite groups. Instead, Cd is strongly depleted in all iron meteorite groups, implying that the parent bodies accreted well above the condensation temperature of Cd (i.e., ?650 K) and thus incorporated only minimal amounts of highly volatile elements. No Cd isotope anomalies were found, whereas Pt and W isotope anomalies for the same iron meteorite samples indicate a significant fluence of epithermal and higher energetic neutrons. This observation demonstrates that owing to the high Fe concentrations in iron meteorites, neutron capture mainly occurs at epithermal and higher energies. The combined Cd-Pt-W isotope results from this study thus demonstrate that the relative magnitude of neutron capture-induced isotope anomalies is strongly affected by the chemical composition of the irradiated material. The resulting low fluence of thermal neutrons in iron meteorites and their very low Cd concentrations make Cd isotopes unsuitable as a neutron dosimeter for iron meteorites.

Kruijer, Thomas S.; Sprung, Peter; Kleine, Thorsten; Leya, Ingo; Wieler, Rainer

2013-12-01

47

Carbon and oxygen abundances in stellar populations  

E-print Network

Abundances of C, O, and Fe are determined for F and G main-sequence stars in the solar neighborhood in order to study trends and systematic differences in the C/Fe, O/Fe, and C/O ratios for stellar populations. Carbon abundances are determined from the CI lines at 5052 and 5380 AA and oxygen abundances from the OI triplet at 7774 AA and the [OI] line at 6300 AA. MARCS model atmospheres are applied and non-LTE corrections for the OI triplet are included. Systematic differences between high- and low-alpha halo stars and between thin- and thick-disk stars are seen in the trends of [C/Fe] and [O/Fe]. The two halo populations and thick-disk stars show the same trend of [C/O] versus [O/H], whereas thin-disk stars are shifted to higher [C/O]. Furthermore, we find some evidence of higher C/O and C/Fe ratios in stars hosting planets than in stars for which no planets have been detected. The results suggest that C and O in both high- and low-alpha halo stars and in thick-disk stars are made mainly in massive stars, whe...

Nissen, P E; Carigi, L; Schuster, W J; Zhao, G

2014-01-01

48

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

49

Carbon and oxygen abundances in stellar populations  

NASA Astrophysics Data System (ADS)

Context. Carbon and oxygen abundances in stars are important in many fields of astrophysics including nucleosynthesis, stellar structure, evolution of galaxies, and formation of planetary systems. Still, our knowledge of the abundances of these elements in different stellar populations is uncertain because of difficulties in observing and analyzing atomic and molecular lines of C and O. Aims: Abundances of C, O, and Fe are determined for F and G main-sequence stars in the solar neighborhood with metallicities in the range -1.6 < [Fe/H] < +0.4 in order to study trends and possible systematic differences in the C/Fe, O/Fe, and C/O ratios for thin- and thick-disk stars as well as high- and low-alpha halo stars. In addition, we investigate if there is any connection between C and O abundances in stellar atmospheres and the occurrence of planets. Methods: Carbon abundances are determined from the ?? 5052,5380 C i lines and oxygen abundances from the ?7774 O i triplet and the forbidden [O i] line at 6300 . MARCS model atmospheres are applied and non-LTE corrections for the O i triplet are included. Results: Systematic differences between high- and low-alpha halo stars and between thin- and thick-disk stars are seen in the trends of [C/Fe] and [O/Fe]. The two halo populations and thick-disk stars show the same trend of [C/O] versus [O/H], whereas the thin-disk stars are shifted to higher [C/O] values. Furthermore, we find some evidence of higher C/O and C/Fe ratios in stars hosting planets than in stars for which no planets have been detected. Conclusions: The results suggest that C and O in both high- and low-alpha halo stars and in thick-disk stars are made mainly in massive (M> 8 M?) stars, whereas thin-disk stars have an additional carbon contribution from low-mass AGB and massive stars of high metallicity causing a rising trend of the C/O ratio with increasing metallicity. However, at the highest metallicities investigated ([Fe/H] ? + 0.4), C/O does not exceed 0.8, which seems to exclude formation of carbon planets if proto-planetary disks have the same composition as their parent stars. Based on observations made with the Nordic Optical Telescope and on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programs given in Table 2 and in Tables 1 and 2 of Nissen & Schuster (2010).Tables 2-5 are available in electronic form at http://www.aanda.org, and also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/568/A25

Nissen, P. E.; Chen, Y. Q.; Carigi, L.; Schuster, W. J.; Zhao, G.

2014-08-01

50

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

51

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

52

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

53

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

54

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

55

Carbon and nitrogen isotope studies in an arctic ecosystem  

SciTech Connect

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

Schell, D.M.

1989-01-01

56

Carbon and nitrogen isotope studies in an arctic ecosystem  

SciTech Connect

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

Schell, D.M.

1989-12-31

57

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

58

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

59

Carbon isotope geochemistry of the Precambrian Lomagundi carbonate province, Rhodesia  

Microsoft Academic Search

Carbon isotope measurements carried out on 67 dolomite samples from the Middle Precambrian Lomagundi Group (Rhodesia) have yielded a 13 C mean of +8.2 2.6%. vs PDB. With the outcrop of these dolomites extending over a distance of almost 300 km, the Lomagundi dolomite faces is likely to represent the largest isotopically anomalous sedimentary carbonate province ever recorded. It

Manfred Schidlowski; Rudolf Eichmann; Christian E. Junge

1976-01-01

60

Preliminary report on isotope abundance measurements in groundwater samples from the Talbert Injection Barrier Area, Orange County Water District  

SciTech Connect

This report discusses isotope abundance measurements made on a collection of groundwater samples from the Orange County Water District. The water samples were collected in May, 1994 as part of a preliminary study conducted by LLNL to assess the feasibility of tracing and dating reclaimed water used in the Talbert Injection Barrier. A set of samples were collected both near to and far from the barrier and also at different depths in available monitoring wells. A variety of elements were selected for isotopic analysis; hydrogen (tritium), helium, neon, carbon, chlorine and strontium. The tritium abundance combined with the {sup 3}He and {sup 20}Ne abundance provides a method for age dating young (< 40 yr.) groundwater. The abundance of {sup 14}C provides an age dating technique for older (1,000--50,000 yr.) groundwater. The concentrations of {sup 36}Cl and {sup 87}Sr/{sup 86}Sr give information on sea water mixing and water-rock chemical interactions.

Hudson, G.B.; Davisson, M.L.; Velsko, C.; Niemeyer, S.; Esser, B.; Beiriger, J. [Lawrence Livermore National Lab., CA (United States). Isotope Sciences Div.

1995-02-01

61

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

62

14. CARBON AND OXYGEN ISOTOPE ANALYSIS OF LAKE SEDIMENT CELLULOSE  

E-print Network

14. CARBON AND OXYGEN ISOTOPE ANALYSIS OF LAKE SEDIMENT CELLULOSE: METHODS AND APPLICATIONS BRENT B isotopes, carbon isotopes, paleohydrology, paleoclimate Introduction Carbon and oxygen isotope analysis and interpretation of stable isotope data from lake sediments, various intriguing questions remain to be addressed

Edwards, Thomas W.D.

63

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

64

Martian carbon dioxide: Clues from isotopes in SNC meteorites  

NASA Technical Reports Server (NTRS)

Attempts to unravel the origin and evolution of the atmosphere and hydrosphere on Mars from isotopic data have been hampered by the impreciseness of the measurements made by the Viking Lander and by Earth-based telescopes. The SNC meteorites which are possibly pieces of the Martian surface offer a unique opportunity to obtain more precise estimates of the planet's volatile inventory and isotopic composition. Recently, we reported results on oxygen isotopes of water extracted by pyrolysis from samples of Shergotty, Zagami, Nakhla, Chassigny, Lafayette, and EETA-79001. Now we describe complementary results on the stable isotopic composition of carbon dioxide extracted simultaneously from those same samples. We will also report on C-14 abundances obtained by accelerator mass spectrometry (AMS) for some of these CO2 samples.

Karlsson, H. R.; Clayton, R. N.; Mayeda, T. K.; Jull, A. J. T.; Gibson, E. K., Jr.

1993-01-01

65

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; Sptl, 2008; k et al., 2008). Larger crystals (mm to cm size, CCCcoarse) are thought to have formed in slow gradually freezing pool water (k 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; k 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; Daron 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; Sptl, Christoph; Immenhauser, Adrian; Richter, Detlev K.

2014-02-01

66

Helium and carbon isotopes in Indian diamonds  

Microsoft Academic Search

Helium and carbon isotope measurements in Indian diamonds (from Andhra Pradesh) were carried out using samples that included mined diamonds from primary kimberlite source rocks and alluvial diamonds from river gravel. The He and C isotope concentrations in diamonds from these two sources were compared, and the Indian diamonds were compared to those from other regions. Results indicate that most

R. Wiens; D. Lal; H. Craig

1990-01-01

67

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

68

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

69

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 90-50C, 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 50C. 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

70

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

71

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

72

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

73

Carbon and Strontium Abundances of Metal-Poor Stars  

E-print Network

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

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

2007-06-20

74

Deciphering Carbon Isotope Excursions in Separated Biogenic and Diagenetic Carbonates  

Microsoft Academic Search

The long-term evolution of the carbon-isotope ratio in the sedimentary archive is classically linked with changes in primary productivity and organic matter burial. There have been sudden and pronounced shifts, so-called Carbon Isotope Excursions (CIEs) in the long-term trends as evidenced by synchronous shifts from various basins. These geochemical perturbations may have various explanations such as changes of the efficiency

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

2008-01-01

75

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

76

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

PubMed Central

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

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

2014-01-01

77

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

78

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

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

79

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

80

Low temperature Rosseland opacities with varied abundances of carbon and nitrogen  

E-print Network

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

Michael T. Lederer; Bernhard Aringer

2008-10-31

81

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

82

Isotope abundances of solar coronal material derived from solar energetic particle measurements  

Microsoft Academic Search

Coronal isotopic abundances for the elements He, C, N, O, Ne, and Mg are derived from previously published measurements of the isotopic composition of solar energetic particles by first measuring, and then correcting for, the charge-to-mass-dependent fractionation due to solar flare acceleration and propagation processes. The resulting coronal composition generally agrees with that of other samples of solar system material,

R. A. Mewaldt; E. C. Stone

1989-01-01

83

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

USGS Publications Warehouse

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

Meier, A.L.

1982-01-01

84

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

Microsoft Academic Search

Biological carbonate skeletons are built largely from carbon dioxide, which reacts to form carbonate ion within thin extracellular solutions. The light isotopes of carbon and oxygen react faster than the heavy isotopes, depleting the resulting carbonate ions in ¹³C and ¹⁸O. Calcium carbonate precipitation occurs sufficiently fast that the skeleton remains out of isotopic equilibrium with surrounding fluids. This explanation

McConnaughey

1986-01-01

85

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

86

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

87

Carbon IsotopesCarbon Isotopes A Short Course VU March, 2009  

E-print Network

2/25/2009 1 Carbon IsotopesCarbon Isotopes The Basics A Short Course VU March, 2009 Peter Swart;2/25/2009 6 Oxidation CH2O + O2 = CO2 + H2O -20 Sulfate reduction CH2O + SO4 2- = HS- + HCO3 - -20 Diagenesis oxidation of organic material · Anoxic Basins ­ Enhanced preservation of organic material · High Rates

Miami, University of

88

Daily Variation of Isotope Ratios in Mars Atmospheric Carbon Dioxide  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

89

CARBON ISOTOPE STRATIGRAPHY AND DIAGENESIS OF PENNSYLVANIAN (DESMOINESIAN-MISSOURIAN) CARBONATES IN EAST-CENTRAL IDAHO  

E-print Network

Carbon isotope stratigraphy of carbonate sediments is instrumental in examining major perturbations in the global carbon cycle and in correlating strata. However, the primary isotopic signal recorded in these sediments can vary with depositional...

Wood, Stephanie

2011-05-10

90

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

91

Photosynthetic isotope fractionation: oxygen and carbon  

SciTech Connect

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

Martin, G.E. II

1982-01-01

92

Primordial Carbon Abundances in Extremely Metal-Poor Stars  

NASA Astrophysics Data System (ADS)

We propose a novel approach towards defining the intital carbon abundance of extremely metal-poor stars. We will observe the C I 1930.9A line, which is detectable in unevolved turnoff stars even for [Fe/H] < -3.0. COS 1941A spectra and ground-based echelle spectra of the CH bands at 3142A and 4315A will both be analyzed with theoretical spectral calculations, and the results compared to understand better the effect of atmospheric convective motions on the CH features normally used for carbon determinations. Because the low-excitation C I 1930.9A line is virtually immune from non-LTE effects, the results should place the carbon abundances of these stars on a firm footing, of importance for theoretical scenarios of single star formation at these low metallicities.

Peterson, Ruth

2011-10-01

93

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

94

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

95

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

96

A new method for carbon isotopic analysis of protein  

Microsoft Academic Search

The reaction of ninhydrin with amino acids can be used in carbon isotopic studies of protein. The reaction can be applied to extract as carbon dioxide only peptide-bonded carbon in proteinaceous material, thus avoiding most, if not all, contaminants. Test radiocarbon dates on ancient bone indicate that the method provides reliable ages, and stable carbon isotopic data suggest that our

D. Nelson

1991-01-01

97

A New Method for Carbon Isotopic Analysis of Protein  

Microsoft Academic Search

The reaction of ninhydrin with amino acids can be used in carbon isotopic studies of protein. The reaction can be applied to extract as carbon dioxide only peptide-bonded carbon in proteinaceous material, thus avoiding most, if not all, contaminants. Test radiocarbon dates on ancient bone indicate that the method provides reliable ages, and stable carbon isotopic data suggest that our

D. E. Nelson

1991-01-01

98

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 fr Radioastronomie (MPIfR), ESO, and Onsala Space Observatory (OSO).

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

2009-01-01

99

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

100

Oxygen isotopic composition of carbon dioxide in the middle atmosphere.  

PubMed

The isotopic composition of long-lived trace molecules provides a window into atmospheric transport and chemistry. Carbon dioxide is a particularly powerful tracer, because its abundance remains >100 parts per million by volume (ppmv) in the mesosphere. Here, we successfully reproduce the isotopic composition of CO(2) in the middle atmosphere, which has not been previously reported. The mass-independent fractionation of oxygen in CO(2) can be satisfactorily explained by the exchange reaction with O((1)D). In the stratosphere, the major source of O((1)D) is O(3) photolysis. Higher in the mesosphere, we discover that the photolysis of (16)O(17)O and (16)O(18)O by solar Lyman-alpha radiation yields O((1)D) 10-100 times more enriched in (17)O and (18)O than that from ozone photodissociation at lower altitudes. This latter source of heavy O((1)D) has not been considered in atmospheric simulations, yet it may potentially affect the "anomalous" oxygen signature in tropospheric CO(2) that should reflect the gross carbon fluxes between the atmosphere and terrestrial biosphere. Additional laboratory and atmospheric measurements are therefore proposed to test our model and validate the use of CO(2) isotopic fractionation as a tracer of atmospheric chemical and dynamical processes. PMID:17190796

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

2007-01-01

101

Equations for lipid normalization of carbon stable isotope ratios in aquatic bird eggs.  

PubMed

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

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

2014-01-01

102

Carbon isotope (13 Ccarb) stratigraphy of the LowerMiddle Ordovician  

E-print Network

Ordovician Biodiversification Event (GOBE) New stable carbon isotope data (13 Ccarb) from LowerCarbon isotope (13 Ccarb) stratigraphy of the Lower­Middle Ordovician (Tremadocian February 2014 Keywords: Carbon isotopes Ordovician Chemostratigraphy Carbon cycling Great Basin Great

Saltzman, Matthew R.

103

ORIGINAL RESEARCH Hydrogen and carbon isotope fractionation during  

E-print Network

ORIGINAL RESEARCH Hydrogen and carbon isotope fractionation during degradation of chloromethane, hydrogen isotope fractionation, methylotrophic bacteria. Correspondence Thierry Nadalig, Universite de-FID equipment by REALISE (http://realise. unistra.fr), the Alsace network for research and engineering

Paris-Sud XI, Université de

104

Carbon Isotope Chemostratigraphy, the Baby and the Bathwater  

Microsoft Academic Search

Secular variations in the carbon isotopic values of carbonate sediments and rocks and their individual components have been applied successfully to problems of stratigraphic correlation and for interpretation of past changes in the global carbon cycle. However, this methodology is not without problems. A major tenet of stable isotope chemostratigraphy involves sampling and analyzing multiple, widely separated sequences, and, if

M. A. Arthur

2008-01-01

105

Carbon Isotope Discrimination in Leaves of C3 Plants  

Microsoft Academic Search

Carbon isotope composition is regarded as a powerful tool in understanding carbon cycling, both as a tracer and as a process recorder. However, accurate predictions of, for example, partitioning the net carbon flux into its components or obtaining climate information from tree rings, requires a good understanding of plant metabolism and related isotopic fractionations. Mechanistic models have concentrated largely on

M. Cuntz; G. Gleixner

2009-01-01

106

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

107

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.

Gonzlez, Luis A.; Lohmann, Kyger C.

1985-11-01

108

Dramatic shifts in biomarker carbon isotopic compositions during the Late Ordovician: Evidence for lower than expected pCO2?  

NASA Astrophysics Data System (ADS)

Positive carbon isotope excursions (ca 1.5 permil) occur in North American and East European carbonates of Late Ordovician (Caradocian) age. However, bulk organic carbon isotope records in three North American localities (Iowa, Ontario and Pennsylvania) and one Estonian locality indicate that carbon isotope fractionation by marine photoautotrophs decreased during this event. Such a decrease is unexpected. During other parts of Earth history, carbon isotope excursions, typically ascribed to organic carbon burial events, are commonly associated with a decrease in carbon isotope fractionation. However, at predicted Ordovician pCO2 and O2 concentrations, marine photosynthesis is not expected to be carbon-limited and carbon isotope fractionation will be constant despite the inferred pCO2 decrease. To further evaluate whether this represents evidence for relatively lower pCO2 levels (<8 times modern pre-industrial level) than those predicted by geochemical models, we deconstructed the organic carbon isotopic records using compound-specific carbon isotope analysis. The most dramatic increase in bulk organic carbon isotopic compositions (8 permil) occurs in the Iowa Guttenberg Formation, while a 5 permil increase occurs in sediments from Southern Ontario. In both cases, the carbon isotope excursion is associated with a change in organic matter assemblage: from a predominance of amorphous, presumably algal and bacterial, marine organic matter to abundant remains of the organic-walled microfossil Gloeocapsomporpha prisca. Biomarker analyses reveal that this shift in organic matter assemblage has strongly influenced the bulk organic carbon isotope record, and biomarkers (steranes, high-molecular-weight n-alkanes) that do not derive from G. prisca exhibit only a 3 to 4 permil excursions, consistent with the bulk organic records from Pennsylvania and Estonia. However, even biomarker-based calculations indicate that carbon isotope fractionation decreased during the isotope event, consistent with a dramatic decrease in pCO2. Alternatively, doubling of phytoplankton growth rates could also account for the observed decrease. An increase in productivity, and thus growth rate, is consistent with proposed changes in ocean circulation and sedimentological evidence for an increase in terrigenous inputs. Moreover, dramatic changes in the distributions of algal and bacterial biomarkers in the Iowa section provide evidence for a change in oceanographic conditions associated with the event. In particular, a dramatic decrease in the abundance of cyanobacterial biomarkers across the boundary suggests that nitrate-limiting conditions could have prevailed prior to the carbon isotope excursion but ceased at that point due to increased nutrient inputs. If so, the productivity event must have been regionally widespread, potentially recording a significant input of terrigenous nutrients into marine settings during the Taconic orogeny.

Pancost, R.; Freeman, K. H.; Patzkowsky, M. E.; Ainsaar, L.; Martma, T.

2003-04-01

109

LIGHT ISOTOPE ABUNDANCES IN SOLAR ENERGETIC PARTICLES MEASURED BY THE SPACE INSTRUMENT NINA  

E-print Network

LIGHT ISOTOPE ABUNDANCES IN SOLAR ENERGETIC PARTICLES MEASURED BY THE SPACE INSTRUMENT NINA A source of 3He. The presence of such reactions was independently confirmed by the detection of the 2.2 Me was detected by many observers, solar deu- terium and tritium have proved to be very rare and difficult

Morselli, Aldo

110

Determination of 235U isotopic abundance by fission-yield difference method  

NASA Astrophysics Data System (ADS)

Based on neutron activation analysis, a new method was presented for the determination of uranium isotopic abundance, in which fast neutrons generated by T (d, n) 4He were used to induce fission in uranium samples. The exponential relation between different abundances of 235U and the average fission-yield ratios of specific fission products was employed in this method. Taking the fission-yield ratios of specific fission products, such as Y/, Y/, Y/ and Y/ as the subjects of research, the relation curves between the average yield ratios and the 235U isotopic abundance as well as the expressions (Y/Y=f(H0)) for the average yield ratio (Y/Y) as a function of the 235U isotopic abundance (H0) were obtained. To verify the precision and accuracy of this method, 5 tests using each working curve were conducted for simulated samples with a 235U abundance of 72.2%, and the relative standard deviation (RSD) of all tests was less than 2%. Compared to the ? energy spectrum method, the relative error of each measurement result was between 1.11% and 1.66%.

Qiao, Yahua; Zhang, Ming; Yang, Yi; Liu, Shilong; Wu, Jizong; Wang, Bo

2014-03-01

111

Isotopes in groundwater hydrology  

Microsoft Academic Search

Isotopes in groundwater hydrology give a direct insight into the movement and distribution processes within the aquifer. Groundwater in its natural state contains environmental isotopes and conclusions may be drawn from their abundance variations. The isotopes commonly employed in groundwater investigations are the heavy stable isotopes of the water molecule, deuterium and oxygen-18 and the radioactive isotopes, tritium and carbon-14.

J. L. TERWEY

112

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

Microsoft Academic Search

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

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

1999-01-01

113

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

USGS Publications Warehouse

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

1978-01-01

114

Atmospheric parameters and carbon abundance for hot DB white dwarfs  

E-print Network

Atmospheric parameters for hot DB (helium atmosphere) white dwarfs near effective temperatures of 25000K are extremely difficult to determine from optical spectroscopy. This is particularly unfortunate, because this is the range of variable DBV or V777 Her stars. Accurate atmospheric parameters are needed to help or confirm the asteroseismic analysis of these objects. Another important aspect is the new class of white dwarfs - the hot DQ - detected by Dufour et al. (2007), with spectra dominated by carbon lines. The analysis shows that their atmospheres are pure carbon. The origin of these stars is not yet understood, but they may have an evolutionary link with the hotter DBs as studied here. Our aim is to determine accurate atmospheric parameters and element abundances and study the implications for the evolution white dwarfs of spectral classes DB and hot DQ. High resolution UV spectra of five DBs are studied with model atmospheres. We determine stellar parameters and abundances or upper limits of C and Si....

Koester, Detlev; Gnsicke, Boris T

2014-01-01

115

Vegetation succession and carbon sequestration in a coastal wetland in northwest Florida: Evidence from carbon isotopes  

E-print Network

Vegetation succession and carbon sequestration in a coastal wetland in northwest Florida: Evidence from carbon isotopes Yonghoon Choi and Yang Wang Department of Geological Sciences, Florida State. Measurements of stable carbon isotopic ratios as well as carbon (C), nitrogen (N), and phosphorus (P) contents

Wang, Yang

116

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

PubMed

Stable isotopes of carbon are commonly used to characterize dietary preferences in animals. Because turnover rates of carbon isotopes are related to metabolic rate, we wanted to determine the rates at which carbon isotopes are exchanged in tissues of two species of nectar-feeding bats (Leptonycteris curasoae and Glossophaga soricina), both of which have relatively high mass-specific metabolic rates. To test the hypothesis that isotope turnover is higher in nectar-feeding bats, because of their high mass-specific metabolic rates, than in other eutherian mammals, we conducted diet-switching experiments and chose three target tissues (hair, wing membrane and blood) to evaluate the isotopic turnover rates. We made the following predictions: (1) isotopic composition should change towards higher delta(13)C-values due to the turnover of carbon isotopes of C(3) origin with those of C(4)/CAM origin; (2) the turnover rates of carbon isotopes would differ between the three types of tissues in the following order of decreasing turnover rates: blood>wing membrane>hair; and (3) turnover rates of nectar-feeding bats should exceed those reported for other small mammals because of the high mass-specific metabolic rate of nectar-feeding bats. Compared to the initial diet, target tissues were enriched in heavy carbon isotopes by 2.8 per thousand in L. curasoae and by 2.6 per thousand in G. soricina. After changing the diet from C(3) to C(4)/CAM origin we found an increase in abundance of (13)C in blood and wing membrane in all experimental subjects. The estimated half life of carbon isotope turnover ranged from 100 to 134 days and did not differ significantly between blood and wing membrane, nor did it differ between the two species. The low turnover rate in wing membrane may reflect its specific composition and the relatively low temperature of this tissue, and long-lived erythrocytes in bat blood may be responsible for the low turnover rate of carbon isotopes in blood. The turnover rate of stable carbon isotopes in hair was low in L. curasoae and undetectable in G. soricina, which may be explained by the seasonal growth of the hair in these two species. Because both species are small (10 and 25 g, respectively) and nectar-feeding bats have higher mass-specific metabolic rates than bats in temperate regions or similar sized terrestrial mammals, our findings of low turnover rates were unexpected. PMID:12624176

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

2003-04-01

117

Further Evidence of the Carbon Isotope, Mass 13  

Microsoft Academic Search

A FEW days ago Dr. King and I announced the discovery of an isotope of carbon, mass 13, appearing in the lambda4737 Swan band of neutral C2. Since then, have found this isotope in two additional sources, namely, in Hopfield's absorption spectrograms of carbon monoxide, and in King's furnace (emission) spectrogram of the lambda3883 CN band.

Raymond T. Birge

1929-01-01

118

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

Microsoft Academic Search

Calibrated values have been obtained for sulfur isotope abundance ratios of sulfur isotope reference materials distributed by the IAEA (Vienna). For the calibration of the measurements, a set of synthetic isotope mixtures were prepared gravimetrically from high purity Ag2S materials enriched in32S, 33S, and 34S. All materials were converted into SF6 gas and subsequently, their sulfur isotope ratios were measured

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

2001-01-01

119

Atmospheric parameters and carbon abundance for hot DB white dwarfs  

NASA Astrophysics Data System (ADS)

Atmospheric parameters for hot DB (helium atmosphere) white dwarfs near effective temperatures of 25 000 K are extremely difficult to determine from optical spectroscopy. The neutral He lines reach a maximum in this range and change very little with effective temperature and surface gravity. Moreover, an often unknown amount of hydrogen contamination can change the resulting parameters significantly. This is particularly unfortunate because this is the range of variable DBV or V777 Her stars. Accurate atmospheric parameters are needed to help or confirm the asteroseismic analysis of these objects. Another important aspect is the new class of white dwarfs - the hot DQ - whose spectra are dominated by carbon lines. The analysis shows that their atmospheres are pure carbon. The origin of these stars is not yet understood, but they may have an evolutionary link with the hotter DBs, as studied here. Our aim is to determine accurate atmospheric parameters and element abundances and study the implications for the evolution of white dwarfs of spectral classes DB and hot DQ. High-resolution UV spectra of five DBs were studied with model atmospheres. We determined stellar parameters and abundances or upper limits of C and Si. These objects were compared with cooler DBs below 20 000 K. We find photospheric C and no other heavy elements - with extremely high limits on the C/Si ratio - in two of the five hot DBs. We compare various explanations for this unusual composition that have been proposed in the literature: accretion of interstellar or circumstellar matter, radiative levitation, carbon dredge-up from the deeper interior below the helium layer, and a residual stellar wind. None of these explanations is completely satisfactory, and the problem of the origin of the hot DQ remains an open question.

Koester, D.; Provencal, J.; Gnsicke, B. T.

2014-08-01

120

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

121

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

122

Isotopic and elemental abundances of neon nuclei accelerated in solar flares  

Microsoft Academic Search

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

W. F. Dietrich; J. A. Simpson

1979-01-01

123

Biological control of calcium isotopic abundances in the global calcium cycle  

SciTech Connect

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

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

1997-06-01

124

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

Microsoft Academic Search

Photosynthetic carbon (C) isotope discrimination labels photosynthates (deltaA) and atmospheric CO2 (deltaa) 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 (deltaW), soil (deltaS) and

Lisa Wingate; Jrme Oge; Rgis Burlett; Alexandre Bosc; Marion Devaux; John Grace; Denis Loustau; Arthur Gessler

2010-01-01

125

Carbon isotope fractionation in protoplanetary disks  

E-print Network

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

Woods, Paul M

2008-01-01

126

LITHIUM ABUNDANCES IN CARBON-ENHANCED METAL-POOR STARS  

SciTech Connect

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

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

2012-05-20

127

Carbon isotopes and concentrations in mid-oceanic ridge basalts  

Microsoft Academic Search

In order to estimate carbon fluxes at mid-ocean ridges and carbon isotopic compositions in the convective mantle, we have studied carbon concentrations and isotopic compositions in tholeiitic glasses from the FAMOUS zone (Mid-Atlantic Ridge at 36N) and East Pacific Rise from 21N (RITA zone) to 20S. These samples correspond essentially to the whole spectrum of spreading rates (2-16 cm\\/yr). They

F. Pineau; M. Javoy

1983-01-01

128

Linking carbon isotopes and carbon-water exchange of plants across different scales  

NASA Astrophysics Data System (ADS)

The anthropogenic rise in atmospheric CO2 levels may lead to increased photosynthetic uptake while transpiration rates remain constant or are reduced. Changes in plant regulation of carbon uptake and water loss also affect the carbon isotope signatures of plant material. But environmental conditions may change in addition to CO2. The resulting combination of factors can have different effects on the carbon-water balance of plants, and their carbon isotope signatures. For example, changes in evaporative demand alter the ratio of total carbon gain to water loss of a plant, the parameter of interest from the point of view of the atmosphere. Isotope values, on the other hand, also reflect physiological properties, including C:N allocation to carboxylation and internal conductance. Here, we explore how these factors shape carbon isotope signatures as well as carbon and water fluxes from leaf to ecosystem levels, and across diurnal to decadal timescales. We present new data to illustrate that a correlation between carbon isotope signatures and carbon-water exchange at the leaf level may not be passed on to the whole plant level. We then use a simple coupled model to analyse the relationships between carbon-water fluxes and isotope values. The model calculates gas exchange and carbon isotope signatures at the leaf level (for comparison with leaf samples), and propagates both gas exchange and isotope values to long- term trends in carbon-water exchange and carbon isotope signatures at the canopy scale (for comparison with samples of annual resolution). This approach is useful for exploring the sensitivity of carbon isotope ratios and carbon-water exchange of plants to simultaneous changes in external and internal factors, for example when interpreting trends in carbon isotope signatures obtained from tree rings.

Seibt, U.; Rajabi, A.; Griffiths, H.; Berry, J.

2007-12-01

129

Carbon and its isotopes in mid-oceanic basaltic glasses  

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

130

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

131

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

USGS Publications Warehouse

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

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

2006-01-01

132

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

133

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

134

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

E-print Network

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

Bekker, Andrey

135

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

Microsoft Academic Search

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

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

1995-01-01

136

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

137

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

PubMed

The development of stable isotope techniques is one of the main methodological advances in ecology of the last decades of the 20th century. Many biogeochemical processes are accompanied by changes in the ratio between stable isotopes of carbon and nitrogen (12C/13C and 14N/15N), which allows different ecosystem components and different ecosystems to be distinguished by their isotopic composition. Analysis of isotopic composition makes it possible to trace matter and energy flows through biological systems and to evaluate the rate of many ecological processes. The main concepts and methods of stable isotope ecology and patterns of stable isotope fractionation during organic matter decomposition are considered with special emphasis on the fractionation of isotopes in food chains and the use of stable isotope studies of trophic relationships between soil animals in the field. PMID:17966909

Tiunov, A V

2007-01-01

138

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

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

139

Analysis of carbon isotopes in airborne carbonate and impli-cations for aeolian sources  

Microsoft Academic Search

Methods were developed to determine the mass ratios of carbon isotopes in trace amounts of aerosol carbon- ate. A Finnigan MAT 252 mass spectrometer fitted with an on-line Kiel device was to determine the 13C\\/12C ratio in CO2 produced from the carbonate. A study using these methods was conducted to characterize the carbonate carbon isotopes in aerosol samples collected in

Junji CAO; WANG Yaqiang; ZHANG Xiaoye

2004-01-01

140

Analysis of carbon isotopes in airborne carbonate and implications for aeolian sources  

Microsoft Academic Search

Methods were developed to determine the mass ratios of carbon isotopes in trace amounts of aerosol carbonate. A Finnigan MAT\\u000a 252 mass spectrometer fitted with an on-line Kiel device was to determine the13C\\/12C ratio in CO2 produced from the carbonate. A study using these methods was conducted to characterize the carbonate carbon isotopes in aerosol\\u000a samples collected in Xian on

Junji Cao; Yaqiang Wang; Xiaoye Zhang; Shuncheng Lee; Kinfai Ho; Yunning Cao; Yang Li

2004-01-01

141

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

142

The Evolution Of Carbon, Sulphur, and Titanium Isotopes from High-Redshift to the Local Universe  

E-print Network

Recent observations of carbon, sulphur, and titanium isotopes at redshifts z~1 and in the local stellar disc and halo have opened a new window into the study of isotopic abundance patterns and the origin of the chemical elements. Using our Galactic chemical evolution code GEtool, we have examined the evolution of these isotopes within the framework of a Milky Way-like system. We have three aims in this work: first, to test the claim that novae are required, in order to explain the carbon isotope patterns in the Milky Way; second, to test the claim that sulphur isotope patterns at high-redshift require an initial mass function biased towards massive stars; and third, to test extant chemical evolution models against new observations of titanium isotopes that suggest an anti-correlation between trace-to-dominant isotopes with metallicity. Based upon our dual-infall galactic chemical evolution modelling of a Milky Way-like system, and the subsequent comparison with these new and unique datasets, we conclude the f...

Hughes, G L; Carigi, L; Snchez-Blazquez, P; Chavez, J M; Lambert, D L

2008-01-01

143

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

144

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

E-print Network

Glaciation, aridification, and carbon sequestration in the Permo-Carboniferous: The isotopic record and carbon sequestration in the Late Paleozoic, we have compiled new and published oxygen and carbon isotopic Carboniferous Stable isotopes Carbon cycling Brachiopods To evaluate the isotopic record of climate change

Grossman, Ethan L.

145

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. Oge, 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.; Oge, J.; Burlett, R.; Bosc, A.; Devaux, M.; Grace, J.; Loustau, D.; Gessler, A.

2010-12-01

146

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

147

Heavy Element Abundances and Isotope Anomalies in HR7775 and Chi LUPI  

NASA Astrophysics Data System (ADS)

Over the past few years a GTO team project hasobtained extensive GHRS echelle data of UV transitionsof heavy elements in the Hg-Mn stars chi Lupi andKappa Cancri. Isotopic anomalies, in which only theheaviest isotope of Hg, Pt and Tl is present, havebeen observed in chi Lupi, but are apparently absentin Kappa Cancri. Kappa Cancri is distinguished fromchi Lupi by both its higher effective temperature andits larger Mn abundance. To help constraintheoretical interpretations of the abundance andisotope anomalies, this program will observe the Hg-Mnstar HR7775, which has the same effective temperatureas chi-Lupi, but also has substantially higher Mn andBi abundances. Observations of HR 7775 will includelines of B III, S I, Au II and III, Pt I, II, and III,Hg II and III, Ru II, Zr III, Ge I, As I, Cd II, Gd III,Ta II, Sb II and N I. Additional observations ofchi Lupi will also be obtained including observationsof Bi III, Tl III, Cu II and Ir II.

Brandt, John

1995-07-01

148

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

149

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

150

The PalaeoceneEocene carbon isotope excursion: constraints from individual  

E-print Network

driven thermal combustion of organic-rich sediment, dissociation of seafloor methane hydrates hydrate dissociation, whereas slower rates might implicate other processes. The PETM carbon flux, water depth or depositional facies. This suggests one of several possibilities: (i) the isotopic

Zachos, James

151

Bromine and carbon isotope effects during photolysis of brominated phenols.  

PubMed

In the present study, carbon and bromine isotope effects during UV-photodegradation of bromophenols in aqueous and ethanolic solutions were determined. An anomalous relatively high inverse bromine isotope fractionation (?reactiveposition up to +5.1) along with normal carbon isotope effect (?reactiveposition of -12.6 to -23.4) observed in our study may be attributed to coexistence of both mass-dependent and mass-independent isotope fractionation of C-Br bond cleavage. Isotope effects of a similar scale were observed for all the studied reactions in ethanol, and for 4-bromophenol in aqueous solution. This may point out related radical mechanism for these processes. The lack of any carbon and bromine isotope effects during photodegradation of 2-bromophenol in aqueous solution possibly indicates that C-Br bond cleavage is not a rate-limiting step in the reaction. The bromine isotope fractionation, without any detectable carbon isotope effect, that was observed for 3-bromophenol photolysis in aqueous solution probably originates from mass-independent fractionation. PMID:24245662

Zakon, Yevgeni; Halicz, Ludwik; Gelman, Faina

2013-12-17

152

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...

153

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; Khn, H; Hedberg, M; Aregbe, Y

2012-10-20

154

A New Approach to Paleoaltimetry Based on Abundances of 13C-18O Bonds in Soil Carbonates  

NASA Astrophysics Data System (ADS)

The elevation of the earth's surface is among the most difficult environmental variables to reconstruct from the geological record. We describe a new approach to paleoaltimetry based on independent and simultaneous determinations of soil temperatures and the oxygen isotope compositions of soil waters, constrained by measurements of abundances of 13C-18O bonds in paleosol carbonates. The concentration of 13C18O16O in CO2 produced by phosphoric acid digestion of carbonates is proportional to abundances of 13C-18O bonds in reactant carbonates, and abundances of those bonds increase with decreasing carbonate growth temperature due to the isotope exchange equilibrium: 13C16O3 + 12C18O16O2 = 13C18O16O2 + 12C16O3. The paleothermometer based on this reaction constrains carbonate growth temperature independent of the d18O of waters from which they grew because the reaction is a homogeneous equilibrium involving only isotopologues of the carbonate ion. We refer to this method as the `clumped isotope thermometer' because it measures the temperature-dependent `clumping' of 13C and 18O into bonds with each other in the carbonate mineral lattice. This thermometer can aid paleoaltimetry by: (1) constraining the growth temperatures of soil carbonate, which can be compared to a known altitudinal gradient in surface temperature; (2) by rigorously constraining the d18O of water from which carbonate grew, which can be compared to the altitude dependence of the d18O of meteoric water; and, in a new approach to this problem, (3) by constraining the correlation between soil temperature and the d18O of soil water. Such correlations can discriminate between the effects of altitude, climate, latitude and seasonality in driving changes in T and d18O of water, and thus provide an opportunity for quantifying the contributions from altitude changes alone. We use our approach to show that 3700 500 m of surface uplift occurred in the Bolivian Altiplano over 3.6 Ma between 10.3 Ma and 6.7 Ma, at an average rate of 1.03 0.14 mm/yr. This rate is most consistent with removal of dense lower lithosphere as the cause of elevation gain. Surface uplift of the Altiplano coincides with a decrease in the rate of contractional deformation in the Andean plateau, the eastward propagation of deformation into the Subandean zone, and a decrease in the convergence rate between the Nazca and South American plates.

Eiler, J. M.; Ghosh, P.; Garzione, C.

2005-12-01

155

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

156

Identification and quantification of base flow using carbon isotopes.  

PubMed

Six surface water samples from locations along Otter Creek in Southeastern Montana and a groundwater sample from a nearby monitoring well completed in the Knobloch coal were analyzed for stable carbon isotope ratios. Along the length of its perennial reach, between the towns of Otter and Ashland, Otter Creek crosses several coal outcrops, including the Knobloch coal zone. The carbon isotope ratio of the creek becomes progressively more similar to that of the Knobloch coal aquifer groundwater in samples collected downgradient from the town of Otter. The isotope ratio of the stream changes from -10.5 to -8.9 reflecting the influence of the coal-aquifer base flow contribution, as represented by Knobloch coal groundwater, which has a carbon isotope value of +3.9. The dissolved inorganic carbon concentrations of the groundwater and surface water are similar (~100 mg/L), which allowed the use of the simplified, first-order, two-end-member mixing equation. Using carbon isotope ratios, calculations of the fraction of water contributed by coal aquifers indicate that approximately 11% of the surface water in Otter Creek at its mouth near Ashland was supplied by groundwater from the coal aquifers that crop out between Otter and Ashland. This study was conducted in December, when Otter Creek is at low flow. At times of higher surface flow, the contribution from groundwater base flow will be correspondingly smaller. This study illustrates that carbon isotopes can be an effective, low-cost tool in base flow studies. PMID:22671689

Meredith, Elizabeth L; Kuzara, Shawn L

2012-01-01

157

The characterisation and origin of graphite in cratonic lithospheric mantle: a petrological carbon isotope and Raman spectroscopic study  

Microsoft Academic Search

Graphite-bearing peridotites, pyroxenites and eclogite xenoliths from the Kaapvaal craton of southern Africa and the Siberian craton, Russia, have been studied with the aim of: 1) better characterising the abundance and distribution of elemental carbon in the shallow continental lithospheric mantle; (2) determining the isotopic composition of the graphite; (3) testing for significant metastability of graphite in mantle rocks using

D. G. Pearson; F. R. Boyd; S. E. Haggerty; J. D. Pasteris; S. W. Field; P. H. Nixon; N. P. Pokhilenko

1994-01-01

158

A stable isotopic study to determine carbon and nitrogen cycling in a disturbed southern Californian forest ecosystem  

Microsoft Academic Search

This study utilized isotope analyses to contrast nitrogen and carbon dynamics at four sites located along an air pollution gradient in the San Bernardino National Forest in southern California. Natural 15N and 13C abundances along with nutritional and edaphic properties were determined in soil, litter, and vegetation samples. Mean bulk nitrogen delta15N values of soil and vegetation at Camp Paivika

Stefania Korontzi; Stephen A. Macko; Iris C. Anderson; Mark A. Poth

2000-01-01

159

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

160

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

E-print Network

BEHAVIOR OF CARBON ISOTOPES DURING THE HYPERFILTRATION OF CALCIUM CARBONATE SOLUTIONS THROUGH CALCIUM BENTONITES A Thesis DAVID WILLIAM HINZ Submitted to the Graduate College of Texas ASM University in partial fulfillment of the requirements... for the degree of MASTER OF SCIENCE May 1987 Major Subject: Geology BEHAVIOR OF CARBON ISOTOPES DURING THE HYPERFILTRATION OF CALCIUM CARBONATE SOLUTIONS THROUGH CALCIUM BENTONITES A Thesis by DAVID WILLIAM HINZ Approved as to style and content by...

Hinz, David William

2012-06-07

161

13 C natural abundance variations in carbonates and organic carbon from boreal forest wetlands  

Microsoft Academic Search

13C natural abundance variations were measured in peat soil and vegetation from two contrasting boreal forest wetlands: an upland\\u000a watershed basin and a permanently saturated lowland mire. Evidence of methane oxidation was shown in the permanently saturated\\u000a wetland with ?13C values as low as -97 in carbonate minerals found in floating peat mats. It is postulated that13C depleted CH4

H. M. Rask; J. J. Schoenau

1993-01-01

162

Relative abundance of the helium isotopes He-3 and He-4 in the cosmic radiation  

NASA Technical Reports Server (NTRS)

The geomagnetic field near the equator is used to measure the He-3/He-4 abundance ratio near 6 GeV/nucleon. This ratio is found to be 0.24 + or - 0.05, under the assumption that the helium rigidity spectrum has the form dI/dR = about R exp(-2.65). If all He-3 is of secondary origin, this implies an interstellar mean escape-path length of about 15 g/sq cm, a value considerably larger than that determined from observations of heavier elements but compatible with measurements of the helium isotopic ratio at lower energies.

Jordan, S. P.; Meyer, P.

1984-01-01

163

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 10-15CI-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

164

Variations in carbon and nitrogen stable isotopes of cryoconite  

NASA Astrophysics Data System (ADS)

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

Takeuchi, N.

2012-12-01

165

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

166

Fractionation of Sulfur and Carbon Isotopes in a Meromictic Lake  

Microsoft Academic Search

In the permanently stagnant depths of Green Lake (near Syracuse, N.Y.), sulfide made by bacteria is depleted in heavy sulfur (S34), and sulfate is enriched. The fractionation factor, 1.0575, is the greatest yet observed. Isotopic resemblance to salt-dome sulfur deposits is evident, and, like saltdome calcite, the lake's carbon dioxide is depleted in heavy carbon (C13).

Edward S. Deevey Jr.; Noboyuki Nakai; Minze Stuiver

1963-01-01

167

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

E-print Network

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

Watkins, Jim

168

Isotopic studies of Yucca Mountain soil fluids and carbonate pedogenesis  

SciTech Connect

Secondary carbonates occurring within the soils, faults, and subsurface fractures of Yucca Mountain contain some of the best available records of paleoclimate and paleohydrology for the potential radioactive waste repository site. This article discusses conceptual and analytical advances being made with regard to the interpretation of stable isotope data from pedogenic carbonates, specifically related to the {sup 13}C content of soil CO{sub 2}, CaCO{sub 3} precipitation mechanisms, and isotopic fractionations between parent fluids and precipitating carbonates. The {sup 13}C content of soil carbon dioxide from Yucca Mountain and vicinity shows most of the usual patterns expected in such contexts: decreasing {sup 13}C content with depth (due mainly to increased importance of respired CO{sub 2}), decreasing {sup 13}C with altitude (partially due to relatively more C-3 vegetation), and reduced {sup 13}C during spring (due again to higher rates of respiration, and reduced gas permeability of wet soils). These patterns exist within the domain of a noisy data set; soil and vegetational heterogeneities, weather, and other factors apparently contribute to isotopic variability in the system. Several soil calcification mechanisms appear to be important, involving characteristic physical and chemical environments and isotopic fractionations. When CO{sub 2} loss from thin soil solutions is an important driving factor, carbonates may contain excess heavy isotopes, compared to equilibrium precipitation with soil fluids. When root calcification serves as a proton generator for plant absorption of soil nutrients, heavy isotope deficiencies are likely. Successive cycles of dissolution and reprecipitation mix and redistribute pedogenic carbonates, and tend to isotopically homogenize and equilibrate pedogenic carbonates with soil fluids.

McConnaughey, T.A.; Whelan, J.F.; Wickland, K.P.; Moscati, R.J. [Geological Survey, Denver, CO (United States)

1994-12-31

169

[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

170

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

171

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

172

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

173

Opening the carbon isotope "vital effect" black box, 2, Quantitative model for interpreting foraminiferal carbon isotope data  

NASA Astrophysics Data System (ADS)

Interpretation of carbon isotope records from late Quaternary planktonic foraminifers are confounded due to the presence of a significant physiological component in the carbon isotopic signal. A quantitative carbon isotope (QC) model is presented which relates the carbon isotopic composition of a foraminiferal shell to the physiological processes of respiration and symbiont photosynthesis and to the ?13C value of seawater ?CO2. The QC model is calibrated with physiological and stable isotopic data from laboratory experiments with living planktonic foraminifers. Model simulations of chamber and shell ?13C values with the symbiont-bearing foraminifers, Orbulina universa and Globigerinoides sacculifer, suggest (1) variations in symbiont density and photosynthetic rate (light level or habitat depth) are the primary physiological parameters controlling intraspecific carbon isotopic variability in these species, (2) respiration has little effect on the ?13C of O. universa, and (3) each chamber in a multichambered foraminiferal test will have a distinct ?13C value depending on its position in the test whorl. Size:?13C value relationships reported for G. sacculifer from fossil assemblages can be explained as a function of increasing symbiont density during ontogenetic development.

Spero, Howard J.; Lerche, Ian; Williams, Douglas F.

1991-12-01

174

Absolute isotopic composition of molybdenum and the solar abundances of the p-process nuclides {sup 92,94}Mo  

SciTech Connect

The isotopic composition of molybdenum has been measured with high precision using a thermal ionization mass spectrometer, the linearity of which has been verified by measuring the isotopically-certified reference material for strontium (NIST 987). The abundance sensitivity of the mass spectrometer in the vicinity of the molybdenum ion beams has been carefully examined to ensure the absence of tailing effects. Particular care was given to ensuring that potential isobaric interferences from zirconium and ruthenium did not affect the measurement of the isotopic composition of molybdenum. Gravimetric mixtures of two isotopically enriched isotopes, {sup 92}Mo and {sup 98}Mo, were analyzed mass spectrometrically to calibrate the mass spectrometer, in order to establish the isotope fractionation of the spectrometer for the molybdenum isotopes. This enabled the ''absolute'' isotopic composition of molybdenum to be determined. An accurate determination of the isotopic composition is required in order to calculate the atomic weight of molybdenum, which is one of the least accurately known values of all the elements. The absolute isotope abundances (in atom %) of molybdenum measured in this experiment are as follows: {sup 92}Mo=14.5246{+-}0.0015; {sup 94}Mo=9.1514{+-}0.0074; {sup 95}Mo=15.8375{+-}0.0098; {sup 96}Mo=16.672{+-}0.019; {sup 97}Mo=9.5991{+-}0.0073; {sup 98}Mo=24.391{+-}0.018; and {sup 100}Mo=9.824{+-}0.050, with uncertainties at the 1s level. These values enable an atomic weight A{sub r}(Mo) of 95.9602{+-}0.0023 (1s) to be calculated, which is slightly higher than the current Standard Atomic Weight A{sub r}(Mo) =95.94{+-}0.02 and with a much improved uncertainty interval. These 'absolute' isotope abundances also enable the Solar System abundances of molybdenum to be calculated for astrophysical purposes. Of particular interest are the Solar System abundances of the two p-process nuclides--{sup 92}Mo and {sup 94}Mo, which are present in far greater abundance than p-process theory suggests. The Solar System abundances for {sup 92}Mo and {sup 94}Mo of 0.364{+-}0.012 and 0.230{+-}0.008 respectively, (with respect to silicon =10{sup 6} atoms), are the most accurate values measured to date, and should therefore be adopted in future p-process calculations, rather than the existing values of 0.378{+-}0.021 and 0.236{+-}0.013, respectively.

Wieser, M. E. [Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, T2N 1N4 (Canada); Laeter, J. R. De [Department of Applied Physics, Curtin University of Technology, GPO Box U1987, Perth 6845 (Australia)

2007-05-15

175

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 CO gas exchange rates and net organic carbon production rates. Between 24 June and 13 August, the calculated CO gas invasion rate of

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

1986-01-01

176

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

177

Cr isotopic composition of modern carbonates and seawater  

NASA Astrophysics Data System (ADS)

Recent development in MC-ICP-MS instrumentation, coupled with double-spike techniques has led to the improvement of stable Cr isotopes measurements and allows the determination of Cr isotopes in low concentration samples such as carbonates and seawater. Cr is a redox sensitive element and its isotopes are fractionated during the reduction of Cr(VI) to Cr(III) [1]. Chromium isotopic variations in BIFs have been linked to the redox conditions of ancient oceans[2]. However, in order to understand Cr isotopic fractionation in the past it is important to constrain the Cr isotopic composition of modern seawater. Chromium concentrations in seawater are between 2 and 5nM, and therefore the measurement of stable Cr isotopes in seawater is an analytical challenge. We have developed a new technique to measure Cr isotopes in seawater based on the Cr co-precipitation with Fe[3], the chemical purification of Cr using an anion exchange chromatography and analyses using the double-spike technique with a ThermoFisher Neptune MC-ICP-MS. Using this method, seawater samples from the Argentinean Basin and from Southampton Water (UK) have been analysed, which have Cr concentrations of ~6nM of Cr. Chromium isotopic composition of our seawater samples is consistently heavier than continental crust and mantle values (?53Cr -0.18)[4] with ?53Cr values of ~+0.5. We have also measured Cr isotopic compositions in ooids from the Bahamas Banks, which represent chemical precipitates from modern seawater. These also record consistently heavy ?53Cr values (0.6-0.8), which overlap the range of modern seawater. We conclude that heavy ?53Cr in seawater reflect either redox cycling of Cr in the oceans[3] or fractionation during the weathering of the continental crust. Moreover, Cr isotopes in modern carbonates are not significantly offset from seawater and therefore, these carbonates reflect the Cr composition of seawater. Thus, Cr isotopes in carbonates can be used to reconstruct the Cr isotopic composition variations in past oceans. [1]Ellis et al., Science, 2002, 295, 2060-2062. [2] Frei et al., Nature, 2009, 461, 250-253.[3] Conelly et al., Deep Sea Res. Part I, 2006, 53, 1975-1988. [4] Schoenberg et al., Chem. Geol. 2008, 249, 294-306.

Bonnand, P.; Parkinson, I. J.; James, R. H.; Fehr, M.; Connelly, D. P.

2010-12-01

178

Yucca Mountain Area Saturated Zone Dissolved Organic Carbon Isotopic Data  

SciTech Connect

Groundwater samples in the Yucca Mountain area were collected for chemical and isotopic analyses and measurements of water temperature, pH, specific conductivity, and alkalinity were obtained at the well or spring at the time of sampling. For this project, groundwater samples were analyzed for major-ion chemistry, deuterium, oxygen-18, and carbon isotopes of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC). The U.S. Geological Survey (USGS) performed all the fieldwork on this project including measurement of water chemistry field parameters and sample collection. The major ions dissolved in the groundwater, deuterium, oxygen-18, and carbon isotopes of dissolved inorganic carbon (DIC) were analyzed by the USGS. All preparation and processing of samples for DOC carbon isotopic analyses and geochemical modeling were performed by the Desert Research Institute (DRI). Analysis of the DOC carbon dioxide gas produced at DRI to obtain carbon-13 and carbon-14 values was conducted at the University of Arizona Accelerator Facility (a NSHE Yucca Mountain project QA qualified contract facility). The major-ion chemistry, deuterium, oxygen-18, and carbon isotopes of DIC were used in geochemical modeling (NETPATH) to determine groundwater sources, flow paths, mixing, and ages. The carbon isotopes of DOC were used to calculate groundwater ages that are independent of DIC model corrected carbon-14 ages. The DIC model corrected carbon-14 calculated ages were used to evaluate groundwater travel times for mixtures of water including water beneath Yucca Mountain. When possible, groundwater travel times were calculated for groundwater flow from beneath Yucca Mountain to down gradient sample sites. DOC carbon-14 groundwater ages were also calculated for groundwaters in the Yucca Mountain area. When possible, groundwater travel times were estimated for groundwater flow from beneath Yucca Mountain to down gradient groundwater sample sites using the DOC calculated groundwater ages. The DIC calculated groundwater ages were compared with DOC calculated groundwater ages and both of these ages were compared to travel times developed in ground-water flow and transport models. If nuclear waste is stored in Yucca Mountain, the saturated zone is the final barrier against the release of radionuclides to the environment. The most recent rendition of the TSPA takes little credit for the presence of the saturated zone and is a testament to the inadequate understanding of this important barrier. If radionuclides reach the saturated zone beneath Yucca Mountain, then there is a travel time before they would leave the Yucca Mountain area and flow down gradient to the Amargosa Valley area. Knowing how long it takes groundwater in the saturated zone to flow from beneath Yucca Mountain to down gradient areas is critical information for potential radionuclide transport. Radionuclide transport in groundwater may be the quickest pathway for radionuclides in the proposed Yucca Mountain repository to reach land surface by way of groundwater pumped in Amargosa Valley. An alternative approach to ground-water flow and transport models to determine the travel time of radionuclides from beneath Yucca Mountain to down gradient areas in the saturated zone is by carbon-14 dating of both inorganic and organic carbon dissolved in the groundwater. A standard method of determining ground-water ages is to measure the carbon-13 and carbon-14 of DIC in the groundwater and then correct the measured carbon-14 along a flow path for geochemical reactions that involve carbon containing phases. These geochemical reactions are constrained by carbon-13 and isotopic fractionations. Without correcting for geochemical reactions, the ground-water ages calculated from only the differences in carbon-14 measured along a flow path (assuming the decrease in carbon-14 is due strictly to radioactive decay) could be tens of thousands of years too old. The computer program NETPATH, developed by the USGS, is the best geochemical program for correcting carbon-14 activities for geochemical r

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

2007-06-25

179

Does burial diagenesis reset pristine isotopic compositions in paleosol carbonates?  

NASA Astrophysics Data System (ADS)

Sedimentological study of early Oligocene continental carbonates from the fluvial Dagshai Formation of the Himalayan foreland basin, India resulted in the recognition of four different types namely, soil, palustrine, pedogenically modified palustrine and groundwater carbonates. Stable oxygen and carbon isotopic ( ?18O and ?13C) analyses of fabric selective carbonate microsamples show that although the pristine isotopic compositions are largely altered during deep-burial diagenesis, complete isotopic homogenization does not occur. ?18O and ?13C analyses of ~ 200 calcrete and palustrine carbonates from different stratigraphic horizons and comparison with ?18O of more robust bioapatite (fossil vertebrate tooth) phase show that dense micrites (~ > 70% carbonate) invariably preserve the pristine ?18O value (mean) of ~ - 9.8, while altered carbonates show much lower ?18O value ~ - 13.8. Such inhomogeneity causes large intra-sample and intra-soil profile variability as high as > 5, suggesting that soils behave like a closed system where diagenetic overprinting occurs in local domains. A simple fluid-rock interaction model suggests active participation of clay minerals to enhance the effect of fluid-rock ratio in local domains during diagenesis. This places an upper limit of 70% micrite concentration above which the effect of diagenetic alteration is minimal. Careful sampling of dense micritic part of the soil carbonate nodules, therefore, does provide pristine isotopic composition and it is inappropriate, as proposed recently, to reject the paleoclimatic potential of all paleosol carbonates affected by burial diagenesis. Based on pristine ?13C value of - 8.8 0.2 in soil carbonates an atmospheric CO 2 concentration between ~ 764 and ~ 306 ppmv is estimated for the early Oligocene (~ 31 Ma) Dagshai time. These data show excellent agreement between two independent proxy records (viz. soil carbonate and marine alkenone) and support early Oligocene survival of the Antarctic ice sheet.

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

2010-11-01

180

Carbon isotopic composition of particulate organic carbon in Ross Sea surface waters during austral summer  

SciTech Connect

Marine organic matter isotopic carbon 13 is increasingly used in studies of the global carbon cycle. As part of the Ross Sea flux experiment, a systematic survey of carbon 13 in total dissolved carbon dioxide as well as sinking, suspended, sea-ice and seafloor organic matter was done in the Ross Sea. The degree of uniformity of carbon 13 depletion in polar end-member' setting was assessed. 10 refs., 2 figs.

Rogers, J.C.; Dunbar, R.B. (Rice Univ., Houston, TX (United States))

1993-01-01

181

Clumped Isotopes Kinetic Effects: Insight from Synthetic Carbonate and its Implication for Speleothems  

NASA Astrophysics Data System (ADS)

Carbonate clumped isotopes is a new paleothermometer based on the relative abundance of 13C-18O bonds in CaCO3 (?47). Being an internal property of the carbonate lattice, it provides a temperature estimate that is independent of the isotopic composition of the water in which the carbonate was formed. As such it is most relevant on land where the complexity of water ?18O, associated with the hydrological cycle, makes temperature reconstruction difficult. A large variety of marine biogenic carbonates adheres to a common ?47-T calibration relationship, developed through calcite synthesized at known temperatures. This relationship is therefore assumed to reflect equilibrium conditions. The application of clumped isotopes on land, however, has been elusive due to non-equilibrium, kinetic isotope effects, that are observed primarily in speleothems. These effects are associated with the degassing of CO2, and reflect the long time required for the solution to regain isotopic equilibrium. We observe that the time required for regaining equilibrium through isotope exchange between DIC and water is similar for ?47 and ?18O; therefore ?47 non-equilibrium also implies ?18O non-equilibrium in speleothems. We hypothesize that these kinetic isotope effects are related to speleothems formation occurring from a thin film of solution, where fast degassing lead to an isotopic offset in DIC, that is recorded in CaCO3 which is forming soon thereafter. To gain further insight we synthesized CaCO3 from a stagnant solution, leading to crystals forming at the water-air interface, the site of CO2 degassing, thus mimicking carbonate formation in thin films. The temperature dependence of ?47 in these samples was significantly less steep than that observed in marine biogenic carbonates, consistent with a kinetic effect that offsets ?47 to lower values, especially at low temperatures. The observed ?47-T relationship, although not a direct calibration, is consistent with modern speleothems from two caves, Soreq (Israel) and Bunker (Germany). These observations support a mechanism associated with the competition between the rate of CO2 degassing and the rate of DIC-water exchange. It further suggests a stronger kinetic effect at lower temperature, consistent with slower DIC-water exchange at low temperatures. Preliminary results of ?47 in Porites corals show a deviation of the opposite sign from the common biogenic ?47-T relationship and may reflect a similar, though reversed, process.

Affek, H. P.; Zaarur, S.; Kluge, T.; Saenger, C. P.; Douglas, P. M.

2010-12-01

182

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

183

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

184

Carbon and Oxygen Abundances across the Hertzsprung Gap  

NASA Astrophysics Data System (ADS)

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

Adamczak, Jens; Lambert, David L.

2014-08-01

185

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

186

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

E-print Network

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

Martin, Timothy

187

Implications of a Carbonate Ion Effect on Shell Carbon and Oxygen Isotopes for Glacial Ocean Conditions  

Microsoft Academic Search

Experimental work demonstrates that the carbon and oxygen isotopic composition of planktic foraminifera shells is directly influenced by the carbonate equilibrium state of seawater (Spero et al. 1997). Because the pCO2 of the sea surface and the atmosphere must be in approximate equilibrium, the glacial drop in atmospheric carbon dioxide recorded in ice cores must have been accompanied by an

D. W. Lea; J. Bijma; H. J. Spero; D. Archer

188

BOREAS TE-5 Tree Ring and Carbon Isotope Ratio Data  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

189

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

190

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

191

Carbon isotopic thermometry calibrated by dolomite-calcite solvus temperatures  

NASA Astrophysics Data System (ADS)

The temperature dependence of carbon isotopic fractionations between calcite and graphite, and between dolomite and graphite are calibrated by the calcite-dolomite solvus geothermometry using marbles collected from the contact metamorphic aureole in the Kasuga area, central Japan. The carbon isotopic fractionations ( ?13CCc- Gr and ?13CDo? Gr) systematically decrease with increasing metamorphic temperature. The concordant relationships between the fractionations and solvus temperatures are approximately linear with T-2 over the temperature range. 400 to 680C: ?13CCc? Gr (%.) = 5.6 10 6 T-2 (K) - 2.4 ?13CDo? Gr (%.) = 5.9 10 6 T-2 ( K) - 1.9 These systematic relationships between fractionation and temperature suggest that carbon isotopic equilibria between carbonates and graphite were attained in many cases. The equation for the calcite-graphite system has a slope steeper than BOTTINGA'S (1969) results. It is, however, in good agreement with that of VALLEY and O'NEIL (1981) in the temperature range from 600 to 800C. Because of the relatively high sensitivity to temperature, these isotopic geothermometers are useful for determining the temperatures in moderate- to high-grade metamorphosed carbonate rocks.

Wada, Hideki; Suzuki, Kazuhiro

1983-04-01

192

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 ...

193

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

194

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

195

Carbon dioxide gasification of carbon black: isotope study of carbonate catalysis  

SciTech Connect

Temperature-programmed reaction was used with labeled isotopes (/sup 13/C and /sup 18/O) to study interactions between carbon black and potassium carbonate in pure He and 10% CO/sub 2//90% He atmospheres. Catalytic gasification precursor complexes were observed. Carbon and oxygen-bearing carbon surface groups interacted with the carbonate above 500 K to form surface complexes. Between 500 and 950 K, and in the presence of gaseous CO/sub 2/, the complexes participated in C and O exchange with the gas phase while oxygen atoms within the complexes also exchanged with those on the carbon surface. As the temperature rose, the complexes decomposed, with CO/sub 2/ the initial product. Decomposition started around 500 K in pure He, and around 950 K in CO/sub 2//He. Catalytic gasification began only after decomposition of significant portions of the complexes. Elemental potassium formed, and the active catalyst appears to alternate between being potassium metal and a potassium-oxygen-carbon complex. Potassium carbonate is not part of the catalytic cycle. 20 references, 10 figures.

Saber, J.M.; Falconer, J.L.; Brown, L.F.

1984-11-01

196

Combined carbonate carbon isotopic and cellular ultrastructural studies of individual benthic foraminifera: Method description  

Microsoft Academic Search

Carbon isotopes of foraminiferal tests provide a widely used proxy for past oceanographic environmental conditions. This proxy can be calibrated using live specimens, which are reliably identified with observations of cell ultrastructure. Observations of ultrastructures can also be used for studies of biological characteristics such as diet and presence of symbionts. Combining biological and isotopic studies on individual foraminifera could

Jonathan B. Martin; Joan M. Bernhard; Jason Curtis; Anthony E. Rathburn

2010-01-01

197

New data from the Valanginian carbon-isotope event: implications for glacioeustacy and the carbon cycle  

Microsoft Academic Search

This study presents new isotopic data from an early Cretaceous (Berriasian-Valanginian) interval from the Yatria River, subpolar Urals, Western Siberia. Oxygen and carbon isotopic compositions have been determined from well preserved belemnite genera Lagonibelus sp., Cylindroteuthis sp. and Acroteuthis sp. Data indicate a shift to cooler temperatures from the Berriasian through into the Late Valanginian, with some warmer phases recognised

G. D. Price; J. Mutterlose

2003-01-01

198

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

NASA Astrophysics Data System (ADS)

Amino sugars are quantitatively significant constituents of soil and marine sediment, but their sources and turnover in environmental samples remain poorly understood. The stable carbon isotopic composition of amino sugars can provide information on the lifestyles of their source organisms and can be monitored during incubations with labeled substrates to estimate the turnover rates of microbial populations. However, until now, such investigation has been carried out only with soil samples, partly because of the much lower abundance of amino sugars in marine environments. We therefore optimized a procedure for compound-specific isotopic analysis of amino sugars in marine sediment employing gas chromatography-isotope ratio mass spectrometry. The whole procedure consisted of hydrolysis, neutralization, enrichment, and derivatization of amino sugars. Except for the derivatization step, the protocol introduced negligible isotopic fractionation, and the minimum requirement of amino sugar for isotopic analysis was 20 ng, i.e. equivalent to ~ 8 ng of amino sugar carbon. Our results obtained from ?13C analysis of amino sugars in selected marine sediment samples showed that muramic acid had isotopic imprints from indigenous bacterial activities, whereas glucosamine and galactosamine were mainly derived from organic detritus. The analysis of stable carbon isotopic compositions of amino sugars opens a promising window for the investigation of microbial metabolisms in marine sediments and the deep marine biosphere.

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

2014-01-01

199

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

NASA Astrophysics Data System (ADS)

Amino sugars are quantitatively significant constituents of soil and marine sediment, but their sources and turnover in environmental samples remain poorly understood. The stable carbon isotopic composition of amino sugars can provide information on the lifestyles of their source organisms and can be monitored during incubations with labeled substrates to estimate the turnover rates of microbial populations. However, until now, such investigation has been carried out only with soil samples, partly because of the much lower abundance of amino sugars in marine environments. We therefore optimized a procedure for compound-specific isotopic analysis of amino sugars in marine sediment, employing gas chromatography-isotope ratio mass spectrometry. The whole procedure consisted of hydrolysis, neutralization, enrichment, and derivatization of amino sugars. Except for the derivatization step, the protocol introduced negligible isotopic fractionation, and the minimum requirement of amino sugar for isotopic analysis was 20 ng, i.e., equivalent to ~8 ng of amino sugar carbon. Compound-specific stable carbon isotopic analysis of amino sugars obtained from marine sediment extracts indicated that glucosamine and galactosamine were mainly derived from organic detritus, whereas muramic acid showed isotopic imprints from indigenous bacterial activities. The ?13C analysis of amino sugars provides a valuable addition to the biomarker-based characterization of microbial metabolism in the deep marine biosphere, which so far has been lipid oriented and biased towards the detection of archaeal signals.

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

2014-09-01

200

The Distribution of Carbon Abundances in Stars in the Milky Ways Satellite Galaxies  

NASA Astrophysics Data System (ADS)

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

Guo, Michelle; Zhang, A.

2013-01-01

201

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

202

Carbon Reservoir History of Mars Constrained by Atmospheric Isotope Signatures  

NASA Astrophysics Data System (ADS)

The evolution of the atmosphere on Mars is one of the most intriguing problems in the exploration of the Solar System, and the climate of Mars may have evolved from a warmer, wetter early state to the cold, dry current state. Because CO2 is the major constituent of Marss atmosphere, its isotopic signatures offer a unique window to trace the evolution of climate on Mars. Here we use a box model to trace the evolution of the carbon reservoir and its iso-topic signature on Mars, with carbonate deposition and atmospheric escape as the two sinks and magmatic activity as the sole source. We derive new quantitative constraints on the amount of carbonate deposition and the atmospher-ic pressure of Mars through time, extending into the Noachian, ~3.8 Gyr before present. This determination is based on recent Mars Science Laboratory (MSL) isotopic measurements of Marss atmosphere, recent orbiter, lander, and rover measurements of Marss surface, and a newly identified mechanism (photodissociation of CO) that efficiently enriches the heavy carbon isotope. In particular, we find that escape via CO photodissociation on Mars has a frac-tionation factor of 0.6 and hence, photochemical escape processes can effectively enrich 13C in the Marss atmos-phere during the Amazonian. As a result, modest carbonate deposition must have occurred early in Marss history to compensate the enrichment effects of photochemical processes and also sputtering, even when volcanic outgassing up to 200 mbar occurred during the Hesperian. For a photochemical escape flux that scales as the square of the solar EUV flux or more, at least 0.1 bar of CO2 must have been deposited as carbonates in the Noachian and Hesperian. More carbonate deposition would be required if carbonate deposition only occurred in the Noachian or with low fractionation factors.

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

2014-11-01

203

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

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

204

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

205

Carbon Isotope Discrimination in Leaves of C3 Plants  

NASA Astrophysics Data System (ADS)

Carbon isotope composition is regarded as a powerful tool in understanding carbon cycling, both as a tracer and as a process recorder. However, accurate predictions of, for example, partitioning the net carbon flux into its components or obtaining climate information from tree rings, requires a good understanding of plant metabolism and related isotopic fractionations. Mechanistic models have concentrated largely on photosynthetic pathways and their isotopic composition. This cannot be said for respiratory processes. The mechanistic models of leaf isotope discrimination hence do not describe dawn, dusk and night very realistically or not at all. A new steady-state approach of the carbon isotope distribution in glucose potentially addresses the time of twilight and night (Tcherkez et al. 2004). Here, a new model of 13C discrimination in leaves of C3 plants is presented. The model is based on the steady-state approach of Tcherkez et al. (2004) but with much reduced complexity while retaining its general characteristics. In addition, the model introduces some new concepts such as a day-length dependent starch synthesis, night-length dependent starch degradation, energy-driven biosynthesis rates, and continuous leaf discrimination calculation for the whole diel cycle. It is therefore well adapted for biosphere-atmosphere exchange studies. The model predicts enriched sucrose and starch pools in the leaf compared to assimilated CO2. Biosynthesis on the other hand acts as the sink of the remaining, depleted carbon. The model calculates slightly different absolute starch compositions from the Tcherkez et al. (2004) model but this depends on chosen fractionation factors. The greatest difference between the two models is during dawn, dusk and night. For example, while Tcherkez et al. has changing phloem sucrose isotope composition during night, the model here predicts constant sucrose export composition. Observations seem to support rather constant phloem isotope composition but no adequate assessment is possible based on current data. References Tcherkez G., Farquhar G.D., Badeck F.-W. & Ghashghaie J. (2004) Theoretical considerations about carbon isotope distribution in glucose of C3 plants, Functional Plant Biology 31, 857-877

Cuntz, M.; Gleixner, G.

2009-04-01

206

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

207

Turonian to Santonian carbon isotope data from the Tethys Himalaya, southern Tibet  

Microsoft Academic Search

New stable carbon and oxygen isotope data from an Upper Cretaceous section in Tibet are presented, and compared to carbon isotope records from England, Italy, and Germany. Together with a stratigraphic re-interpretation of published carbon isotope data from a nearby section in Tibet, our data can surprisingly well be correlated with the European sections. This indicates that, similar to the

I. Wendler; J. Wendler; K.-U. Grfe; J. Lehmann; H. Willems

2009-01-01

208

Calibration of the carbonate `clumped isotope' paleotemperature proxy using mollusc shells and benthic foraminiferal tests  

Microsoft Academic Search

It has recently been shown that the carbonate `clumped isotope' thermometer can provide temperature constraints that depend only on the isotopic composition of carbonate (in particular, on the proportion of 13C and 18O that form bonds with each other), and that do not require assumptions about the isotopic composition of the water in which the carbonate formed (Ghosh et al.,

R. E. Came; W. B. Curry; C. R. Weidman; J. M. Eiler

2007-01-01

209

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

E-print Network

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

Saltzman, Matthew R.

210

In situ analysis of carbon isotopes in North American diamonds  

Microsoft Academic Search

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

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

2010-01-01

211

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

212

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

213

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

214

Stable carbon isotope fractionation by sulfate-reducing bacteria  

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

215

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

Microsoft Academic Search

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

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

2010-01-01

216

The OAE1a Negative Carbon Isotope Spike: a Stepwise Transition Revealed by a High Resolution Biomarker Carbon Isotope Record  

Microsoft Academic Search

Oceanic anoxic events (OAEs) are time envelopes in the Cretaceous when ocean conditions favoured the episodic deposition of organic-rich black shale, associated to a positive carbon isotope (delta13C) excursion, on a global scale. The OAE1a (Early Aptian, ~120 Myr ago) is characterized by an enigmatic negative delta13C spike of up to 30\\/00 in marine carbonates and of 4 to 50\\/00

S. Mehay; C. E. Keller; S. M. Bernasconi; H. Weissert; E. Erba

2008-01-01

217

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

218

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

219

Carbon Isotope Ratios in Crassulacean Acid Metabolism Plants  

PubMed Central

A year round study of photosynthesis and carbon isotope fractionation was conducted with plants of Opuntia phaeacantha Engelm. and Yucca baccata Torr. occurring in natural stands at elevations of 525, 970, 1450 and 1900 m. Plant water potentials and the daytime pattern of 14CO2 photosynthesis were similar for all cacti along the elevational gradient, despite significant differences in temperature regime and soil water status. Carbon isotope ratios of total tissue and soluble extract fractions were relatively constant throughtout the entire year. Additionally, the ?13C values were similar in all plants of the same species along the elevational gradient, i.e. ?12.5 0.86 for O. phaeacantha and ?15.7 0.95 for Y. baccata. The results of this study indicate Crassulacean acid metabolism predominates as the major carbon pathway of these plants, which do not facultatively utilize the reductive pentose phosphate cycle of photosynthesis as the primary carboxylation reaction. PMID:16659680

Szarek, Stan R.; Troughton, John H.

1976-01-01

220

Silicon and carbon abundances in the Orion nebula  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

221

Carbon isotopes in three SNC meteorites  

NASA Astrophysics Data System (ADS)

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

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

1985-02-01

222

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

223

Experimental determination of carbon isotope fractionation between iron carbide melt and carbon: 12C-enriched carbon in the Earth's core?  

Microsoft Academic Search

We report here new experimental data on equilibrium carbon isotope fractionation between graphite\\/diamond and iron carbide melt at 5 and 10GPa and in the temperature range between 1200 and 2000C. Carbon isotope equilibrium was tested using morphological features of graphite and also by performing a longer duration experiment, both of which suggested that equilibrium carbon isotope fractionation is present. The

Madhusoodhan Satish-Kumar; Hayato So; Takashi Yoshino; Mutsumi Kato; Yoshikuni Hiroi

2011-01-01

224

Linking carbon isotopes and carbon-water exchange of plants across different scales  

Microsoft Academic Search

The anthropogenic rise in atmospheric CO2 levels may lead to increased photosynthetic uptake while transpiration rates remain constant or are reduced. Changes in plant regulation of carbon uptake and water loss also affect the carbon isotope signatures of plant material. But environmental conditions may change in addition to CO2. The resulting combination of factors can have different effects on the

U. Seibt; A. Rajabi; H. Griffiths; J. Berry

2007-01-01

225

Isotopic Hg in an Allende carbon-rich residue  

NASA Technical Reports Server (NTRS)

A carbon-rich residue from Allende subjected to stepwise heating yielded two isotopically resolvable types of Hg: one with an (Hg-196)/(Hg-202) concentration ratio the same as terrestrial (monitor) Hg; the other enriched in Hg-196 relative to Hg-202 by about 60 percent. Hg with the 202 isotope enriched relative to 196, as is found in bulk Allende, was not observed. Whether the result of mass fractionation or nucleosynthesis, the distinct types of Hg entered different carrier phases and were not thermally mobilized since the accretion of the Allende parent body.

Reed, G. W., Jr.; Jovanovic, S.

1990-01-01

226

Inhomogeneity of C13 isotope distribution in isotope engineered carbon nanotubes: Experiment and theory  

NASA Astrophysics Data System (ADS)

Vibrational modes of C13 isotope enriched single-walled carbon nanotubes are inhomogeneously broadened due to the random distribution of isotopes. We study this effect on the radial breathing mode theoretically using density-functional theory within the local-density approximation and compare the result with experiments on inner tubes in double-walled carbon nanotubes grown from C13 -enriched fullerenes. Increased inhomogeneity was achieved by growing inner tubes from a mixture of enriched and natural fullerenes, which is explained by the calculations. This shows the absence of carbon diffusion along the tube axis during inner tube growth, supporting the theory of inner tube growth by Stone-Wales transformations from interconnected fullerenes.

Zlyomi, V.; Simon, F.; Rusznyk, .; Pfeiffer, R.; Peterlik, H.; Kuzmany, H.; Krti, J.

2007-05-01

227

Triple oxygen isotopes in biogenic and sedimentary carbonates  

NASA Astrophysics Data System (ADS)

The 17O anomaly (?17O) of natural waters has been shown to be sensitive to evaporation in a way analogous to deuterium excess, with evaporated bodies of water (e.g., leaf waters, lake waters, animal body waters) tending to have lower ?17O than primary meteoric waters. In animal body water, ?17O relates to the intake of evaporated waters, evaporative effluxes of water, and the ?17O value of atmospheric O2, which itself carries signatures of global carbon cycling and photochemical reactions in the stratosphere. Carbonates have the potential to record the triple oxygen isotope compositions of parent waters, allowing reconstruction of past water compositions, but such investigations have awaited development of methods for high-precision measurement of ?17O of carbonate. We describe optimized methods based on a sequential acid digestion/reduction/fluorination approach that yield ?17O data with the high precision (?0.010, 1?) needed to resolve subtle environmental signals. We report the first high-precision ?17O dataset for terrestrial carbonates, focusing on vertebrate biogenic carbonates and soil carbonates, but also including marine invertebrates and high-temperature carbonates. We determine apparent three-isotope fractionation factors between the O2 analyte derived from carbonate and the parent waters of the carbonate. These in combination with appropriate temperature estimates (from clumped isotope thermometry, or known or estimated body temperatures) are used to calculate the ?18O and ?17O of parent waters. The clearest pattern to emerge is the strong 17O-depletion in avian, dinosaurian, and mammalian body water (from analyses of eggshell and tooth enamel) relative to meteoric waters, following expected influences of evaporated water (e.g., leaf water) and atmospheric O2 on vertebrate body water. Parent waters of the soil carbonates studied here have ?17O values that are similar to or slightly lower than global precipitation. Our results suggest that ?17O will have useful application to paleoenvironmental studies of continental environments where the effects of evaporation are important, and where vertebrate body water may record an isotopic signal of evaporated water sources and atmospheric oxygen.

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

2014-09-01

228

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

229

Variation of carbon isotopic composition of seawater DIC in Western Tethys for the Middle Jurassic  

Microsoft Academic Search

An accurate chronostratigraphic calibration of carbon-isotope stratigraphy is necessary to clarify the relationship between the paleocarbon cycle, ocean carbon reservoirs and the faunal evolutionary processes. Marine carbonate sequences with high macro and microfossil content coupled with carbon isotope investigations permit biostratigraphic dating at the subzone level, and thus achieve an accurate chronostratigraphic calibration. Mid-Jurassic age rhythmic marl and marly limestone

L. O'Dogherty; M. Bill; J. Sandoval; R. Aguado

2008-01-01

230

Elemental abundances of metal poor carbon rich lead star: CS29497-030  

Microsoft Academic Search

We present here the abundance analysis of a metal poor carbon rich lead star, CS29497-030. High resolution and high signal to noise spectra were obtained using the UVES spectrograph on the 8.2m VLT-Kueyen telescope. The observations were made as a part of the Large Programme 165.N-0276, P.I. R. Cayrel. Abundance analysis was done using the latest version of the MARCS

T. Sivarani; P. Bonifacio; P. Molaro; R. Cayrel; M. Spite; F. Spite; B. Plez; J. Andersen; B. Barbuy; T. C. Beers; E. Depagne; V. Hill; P. Francois; B. Nordstrom; F. Primas

2002-01-01

231

Ultimate Isotope Precision for Carbonates Thermo Scientific  

E-print Network

into the microvolume, the CO2 pressure is monitored and, if required, the CO2 sample size can be reduced by expansion Performance With a sample size of > 20 µg for MAT 253 or > 40 µg for DELTA V and MAT 253, the following and accuracy over a large dynamic range of sample size. The KIEL IV Carbonate Device coupled to either the 10-k

Lachniet, Matthew S.

232

{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

233

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

234

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

235

Paleoclimate studies in Brazil using carbon isotopes in soils  

NASA Astrophysics Data System (ADS)

This chapter presents carbon isotope data of soil organic matter (SOM), collected in natural forest ecosystems in different sites from Brazil. The studied areas are located in Londrina (Southern part of the country), Piracicaba (Southeast), Salitre (Central) and Altamira (Northern). This study is part of the research program on tropical and sub-tropical soils in Brazil, of which the main objective is to use carbon isotopes to provide information on vegetation changes and their relationships with climatic changes during the Holocene. 14C data of charcoal samples, the humin fraction and soil organic matter (SOM) contents, indicate that the organic matter of this area is at least of Holocene age. 13C data in SOM indicate that C4 plants were the dominant vegetation in Londrina and Piracicaba during the early and middle Holocene, while C3 plants were the dominant vegetation in Altamira and probably a mixture of C3 and C4 plants occurred in Salitre during the Holocene.

Pessenda, Luiz C. R.; Valencia, E. P. E.; Aravena, R.; Telles, E. C. C.; Boulet, R.

236

Descriptions of carbon isotopes within the energy density functional theory  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

237

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

238

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

PubMed

The importance of authenticity characterization is an increasing and pressing requirement for all foods. Vegetable oil is one of the most studied foods because of its nutritional and medicinal properties in a correct diet. In this study, a total of 53 Camelina sativa samples, from all known growing areas, were chemically and isotopically characterized. The fatty acid content of camelina oil was determined by gas chromatography (GC), and the ratios of stable carbon isotopes ((13)C/(12)C) of individual fatty acids and seed/bulk oil were determined by gas chromatography-combustion-stable isotope ratio mass spectrometry (GC/C/IRMS) and elemental analysis-stable isotope ratio mass spectrometry (IRMS). A total of 17 different fatty acids were detected by GC, with omega3 R-linolenic acid (C(18:3n3)) being the most abundant (29.7-40.0 wt %). Oleic acid (C(18:1n9)), linoleic acid (C(18:2n6)) and eicosenoic acid (C(20:1n9)) all belong to the second group of major fatty acids. The stable carbon isotopic values (delta(13)C) fell into a range typical for C(3) plants. The use of delta(13)C(18:2n6) vs delta(13)C(18:3n3) correlation could show cases where impurity or adulteration is suspected, whereas principal component analysis clearly separates oil samples from different continents. Preliminary results on the camelina oil authentication procedure provide a basis for the investigation of geographical origin and the further distinction between camelina and camelina refined or other, less expensive oils. PMID:19123821

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

2009-01-28

239

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

240

Stable isotope analysis of carbon cycling in the Perdido estuary, Florida  

Microsoft Academic Search

Stable carbon isotope (?13C) analysis was used in the Peridido Estuary, Florida U.S. to determine the predominant carbon source that supports the bacterial\\u000a assemblage. Stable carbon isotope values were measured in the suspended particulate matter (SPM), dissolved organic and inorganic\\u000a matter, and bacteria. Stable nitrogen isotope (?15N) ratios were measured in SPM and nitrate to assist in understanding carbon cycling

Richard B. Coffin; Luis A. Cifuentes

1999-01-01

241

The use of stable carbon isotope analysis in rooting studies  

Microsoft Academic Search

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

Tony J. Svejcar; Thomas W. Boutton

1985-01-01

242

Carbon Isotopic Signatures of Individual Archean Microfossils(?) from Western Australia  

Microsoft Academic Search

New types of carbonaceous filamentous microstructures have been identified in silica veins at two new localities in the ?3.5 Ga North Pole area of Western Australia. Their carbon isotopic compositions were measured in situ by secondary-ion mass spectrometry. The carbonaceous filaments are ?1?m wide, 10 to 100 ?m long, and are permineralized in a fine-grained (?1 ?m) silica matrix. They

Yuichiro Ueno; Yukio Isozaki; Hisayoshi Yurimoto; Shigenori Maruyama

2001-01-01

243

Stable Carbon Isotopes As Indicators of Plant Water Use Efficiency  

Microsoft Academic Search

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

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

2007-01-01

244

Carbon isotope and magnetostratigraphy of the Cretaceous (Barremian Aptian) Pabelln Formation, Chaarcillo Basin, Chile  

Microsoft Academic Search

New oxygen and carbon isotopic analyses of finefraction samples from the Pabelln Formation (Chaarcillo Basin, Chile), together with magnetostratigraphic data, are presented. The carbon isotope curve shows a distinctive pattern including a negative isotope excursion preceding a positive event. Within the Lower Aptian this chemostratigraphic event is widely used for correlation of marine and continental stratigraphic sections and confirms the

Gregory D. Price; Ben Dashwood; Graeme K. Taylor; Robert M. Kalin; Neil Ogle

2008-01-01

245

Isotopic analysis of tooth enamel carbonate from modern North American feral horses  

E-print Network

Isotopic analysis of tooth enamel carbonate from modern North American feral horses: implications and oxygen isotope values (N13 C and N18 O) of tooth enamel carbonate and the N13 C values of fecal samples isotope analyses of fecal material and tooth enamel suggest that horses consumed primarily grass, but some

Amundson, Ronald

246

Kinetic isotope effects during carbonate mineral formation Z. Sade*, R. Yam, A. Shemesh and I. Halevy  

E-print Network

Kinetic isotope effects during carbonate mineral formation Z. Sade*, R. Yam, A. Shemesh and I. Halevy Weizmann Institute of Science, Rehovot 76100, Israel *ziv.sade@weizmann.ac.il The oxygen isotopic ambient water to determine the temperature at which the carbonates formed and the oxygen isotope

Simon, Emmanuel

247

Isotope-induced elastic scattering of optical phonons in individual suspended single-walled carbon nanotubes  

E-print Network

Isotope-induced elastic scattering of optical phonons in individual suspended single-walled carbon 10, 2011) Isotope-induced scattering of optical phonons in individual single-walled carbon nanotubes (SWNTs) was investigated by resonance Raman scattering measurements of more than 600 sus- pended, isotope

Maruyama, Shigeo

248

Carbon isotope chemostratigraphy of the Middle Riphean type section (Avzyan Formation, Southern Urals, Russia)  

E-print Network

Carbon isotope chemostratigraphy of the Middle Riphean type section (Avzyan Formation, Southern preserve all or part of the mid- Mesoproterozoic isotopic shift. This shift represents a significant, the character of the carbon isotopic curve is most similar to that of the Dismal Lakes Group, arctic Canada

Perfect, Ed

249

From isotope labeled CH3CN to N2 inside single-walled carbon nanotubes  

E-print Network

From isotope labeled CH3CN to N2 inside single-walled carbon nanotubes Christian Kramberger to this peculiar place? We have used N15 and C13 isotope labeled acetonitrile during the synthesis of single-walled carbon nanotubes to investigate this process. The isotope shifts of phonons and vibrons are observed

Maruyama, Shigeo

250

The use of carbon stable isotope ratios in drugs characterization  

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

251

The use of carbon stable isotope ratios in drugs characterization  

SciTech Connect

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

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

2013-11-13

252

Isotope Effects on Heat Conduction of Carbon Nanotubes Shigeo Maruyama, Yuki Taniguchi and Yasushi Shibuta  

E-print Network

Isotope Effects on Heat Conduction of Carbon Nanotubes Shigeo Maruyama, Yuki Taniguchi and Yasushi that the inclusion of only 1 % of 13 C natural isotope dramatically reduces the thermal conductivity of diamond. However, isotope effects on heat conduction of SWNTs have not been elucidated. We estimated isotope

Maruyama, Shigeo

253

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

254

Stable carbon and nitrogen isotope enrichment in primate tissues  

PubMed Central

Isotopic studies of wild primates have used a wide range of tissues to infer diet and model the foraging ecologies of extinct species. The use of mismatched tissues for such comparisons can be problematic because differences in amino acid compositions can lead to small isotopic differences between tissues. Additionally, physiological and dietary differences among primate species could lead to variable offsets between apatite carbonate and collagen. To improve our understanding of the isotopic chemistry of primates, we explored the apparent enrichment (?*) between bone collagen and muscle, collagen and fur or hair keratin, muscle and keratin, and collagen and bone carbonate across the primate order. We found that the mean ?* values of proteinaceous tissues were small (?1), and uncorrelated with body size or phylogenetic relatedness. Additionally, ?* values did not vary by habitat, sex, age, or manner of death. The mean ?* value between bone carbonate and collagen (5.61.2) was consistent with values reported for omnivorous mammals consuming monoisotopic diets. These primate-specific apparent enrichment values will be a valuable tool for cross-species comparisons. Additionally, they will facilitate dietary comparisons between living and fossil primates. Electronic supplementary material The online version of this article (doi:10.1007/s00442-010-1701-6) contains supplementary material, which is available to authorized users. PMID:20628886

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

2010-01-01

255

Stable carbon and nitrogen isotope enrichment in primate tissues.  

PubMed

Isotopic studies of wild primates have used a wide range of tissues to infer diet and model the foraging ecologies of extinct species. The use of mismatched tissues for such comparisons can be problematic because differences in amino acid compositions can lead to small isotopic differences between tissues. Additionally, physiological and dietary differences among primate species could lead to variable offsets between apatite carbonate and collagen. To improve our understanding of the isotopic chemistry of primates, we explored the apparent enrichment (?*) between bone collagen and muscle, collagen and fur or hair keratin, muscle and keratin, and collagen and bone carbonate across the primate order. We found that the mean ?* values of proteinaceous tissues were small (?1), and uncorrelated with body size or phylogenetic relatedness. Additionally, ?* values did not vary by habitat, sex, age, or manner of death. The mean ?* value between bone carbonate and collagen (5.61.2) was consistent with values reported for omnivorous mammals consuming monoisotopic diets. These primate-specific apparent enrichment values will be a valuable tool for cross-species comparisons. Additionally, they will facilitate dietary comparisons between living and fossil primates. PMID:20628886

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

2010-11-01

256

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 (TC(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. TC(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. TC(47) obtained from modern soil carbonate ranges from 10.8 to 39.5 C. On average, TC(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 TC(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 TC(47) from soils, following the equation: MAAT(C)=1.20(TC(47)0)-21.72(r2=0.92) where TC(47)0 is the effective air temperature at the site estimated from TC(47). The effective air temperature represents the air temperature required to account for the TC(47) at each site, after consideration of variations in TC(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 TC(47) in paleosol carbonate, assuming one is studying paleosols that formed in environments generally similar in seasonality and ground cover to our calibration sites. TC(47)0 decreases systematically with elevation gain in the Himalaya, following the equation: elevation(m)=-229(TC(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 TC(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 TC(47) down to 2.5-4 km burial depth, or 90-125 C. Deeper than this and above this temperature, TC(47) in paleosol carbonate is reset to temperatures >40 C. We observe 40 C as the upper limit for TC(47) in modern soils from soil depths >25 cm, and therefore that TC(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 TC(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.; Daron, M.; Achyuthan, H.

2013-03-01

257

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

258

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

259

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

260

The Zn abundance and isotopic composition of diatom frustules, a proxy for Zn availability in ocean surface seawater  

NASA Astrophysics Data System (ADS)

We have developed cleaning methods for extracting diatomopal from bulk marine sediment samples, for measurement of both zinc (Zn) abundance and isotope composition. This cleaning technique was then applied to a set of Holocene core-top samples from the Southern Ocean. The measured ?66Zn (reported relative to the JMCLyon standard) and Zn/Si ratios from the Southern Ocean diatomopal samples range from 0.7 to 1.5, and from 14 to 0.9 ?mol/mol, respectively. The Zn abundance and isotope composition data show a clear correlation with opal burial rates and other oceanographic parameters. In common with previous work, we interpret the systematic changes in the Zn/Si ratio to be linked to the variability in the concentrations of bioavailable Zn in the ambient surface seawater where the diatom opal is formed. This variability is likely to be primarily controlled by the degree to which Zn is taken up into phytoplankton biomass. The observed systematic pattern in the ?66Zn compositions of the diatomopal core-top samples is, similarly, likely to reflect changes in the ?66Zn composition of the ambient Zn in the surface waters above the core-top sites, which is progressively driven towards isotopically heavier values by preferential incorporation of the lighter isotopes into phytoplankton organic material. Thus, the systematic relationship between Zn isotopes and abundance observed in the core-top diatomopal samples suggests a potential tool for investigating the biogeochemical cycling of Zn in the past surface ocean for down-core diatomopal material. In this respect, it may be possible to test hypotheses that attribute variations in atmospheric CO2 on glacial-interglacial timescales to the degree to which trace metals limited primary productivity in HNLC zones.

Andersen, Morten B.; Vance, Derek; Archer, Corey; Anderson, Robert F.; Ellwood, Michael J.; Allen, Claire S.

2011-01-01

261

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

NASA Astrophysics Data System (ADS)

Oxygen is the predominant elemental constituent of rocky planets and asteroids. It is the third most abundant element in the solar system after hydrogen and helium. The isotopic compo-sition of oxygen in three-isotope space (?18O vs. ?17O plot) exhibits large heterogeneity among different bodies formed from the same primordial gas and dust mixture, termed the solar nebula. It is not possible to fully understand the formation and evolution of our own planetary system, unless we resolve the source of the oxygen isotopes. At present, there are two models: self shielding photochemistry in the solar nebula, and symmetry driven gas-phase and/or surface chemistry in the solar nebula, which can also involve photochemistry, but isn't required. Photochemistry is a dominant process at the outer layers of the nebular disk and isotopically selective photodissociation (a process known as isotopic self-shielding) of carbon monoxide, the most abundant nebular oxygen bearing molecule, has been suggested as a source of isotopically anomalous oxygen in the solar reservoir [1-3]. However, these models have had no experimental verification of the relevant isotopic fractionation associated with VUV-CO photodissociation at the relevant wavelengths. Recently, we have performed a series of CO photodissociation experiment with a windowless flow chamber at the Advanced Light Source (LBNL) synchrotron at Berkeley. These experiments demonstrate an anomalously enriched atomic oxygen reservoir is generated through CO photo-dissociation, but, without requiring isotopic self shielding [4]. These results emphasize the importance of chemistry in the solar nebula as we have previously demonstrated through recent laboratory experiments [5]. It is clear that the mass- independent oxygen isotopic composition, as observed in some of the first condensed solids in the solar system (Calcium-Aluminum rich Inclusions- CAIs, Chondrules etc.), can be generated through symmetry driven gas-phase chemical reactions. We will present new oxygen isotope data of VUV photodissociation of CO and discuss the relevance of this data to address the anomalous oxygen isotopic compositions of meteorites. References: [1] Clayton R. N. (2002) Nature, 415, 860-861. [2] Yurimoto H. and Kuramoto K. (2004) Science, 305, 1763-1766. [3] Lyons J. R. and Young E. D. and (2005) Nature, 435, 317-320. [4] Chakraborty S., Ahmed M., Jackson, T. L. and Thiemens M.H. (2008) Science, 321, 1328-1331. [5] Kimura Y., Nuth J. A., Chakraborty S., and Thiemens M. H. (2007) Meteoritics and Planetary Science, 42, 1429-1439.

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

2008-12-01

262

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

263

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; Hnisch, Brbel; Lemarchand, Damien; Louvat, Pascale; McCulloch, Malcolm; Noireaux, Johanna; Pallavicini, Nicola; Rodushkin, Ilia; Roux, Philippe; Stewart, Joseph; Thil, Franois; You, Chen-Feng

2014-05-01

264

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...

265

A New Look at Carbon Abundances in Planetary Nebulae. IV. Implications for Stellar Nucleosynthesis  

Microsoft Academic Search

This paper is the fourth and final report on a project designed to study carbon abundances in a sample of planetary nebulae representing a broad range in progenitor mass and metallicity. We present newly acquired optical spectrophotometric data for three Galactic planetary nebulae, IC 418, NGC 2392, and NGC 3242, and combine them with UV data from the IUE Final

R. B. C. Henry; K. B. Kwitter; J. A. Bates

2000-01-01

266

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 220C 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 220C 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

267

Strontium isotopic composition of carbonates from the Sumbar KT boundary  

NASA Astrophysics Data System (ADS)

Studies on the Sr isotopic composition of ocean water through time have shown that anomalously high Sr-87/Sr-86 ratios occur at the time of the KT boundary (KTB) event. Studies on the Os isotopic composition of the KTB section of Sumbar, Turkmenistan, are consistent with enhanced weathering of continental crust. To see if there is any correlation between these two isotopic systems, the Sr isotopic composition (IC) was studied on splits of the same samples analyzed for the Os-IC. The sediments were leached with 5M CH3COOH to dissolve only the carbonate component. Because the radiogenic ingrowth of Sr-87 through the decay of Rb is insignificant, the leachates should represent the isotopic composition of seawater at the time of deposition. The abrupt increase of the Sr-87/Sr-86 ratio at the KTB and the smooth decrease of the ratio with stratigraphic height is in agreement with published data. The sudden increase toward a more radiogenic Sr signature is consistent with a catastrophic event. The last two Maastrichtian samples show slightly elevated Sr-87/Sr-86. But these two values are consistent with literature data of samples below the KTB. These ratios are indistinguishable from the 5.5-6.5 cm interval above the boundary clay. The slight increase of the Sr isotopic ratio before the KTB is in contradiction to a catastrophic event. Elemental mobilization could be the cause, but the increase in the Sr-87/Sr-86 goes parallel with a change of the Ir concentration and the Os IC in the last centimeter of the Maastrichtian. Since mobilization of Ir and Os are most unlikely, the possibility of a slight mechanical mixing of the enriched KTB clay with the underlying deposits has to be discussed.

Meisel, T.; Pettke, T.

1994-07-01

268

Photosynthetic fractionation of the stable isotopes of oxygen and carbon  

SciTech Connect

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

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

1993-01-01

269

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

270

New data from the Valanginian carbon-isotope event: implications for glacioeustacy and the carbon cycle  

NASA Astrophysics Data System (ADS)

This study presents new isotopic data from an early Cretaceous (Berriasian-Valanginian) interval from the Yatria River, subpolar Urals, Western Siberia. Oxygen and carbon isotopic compositions have been determined from well preserved belemnite genera Lagonibelus sp., Cylindroteuthis sp. and Acroteuthis sp. Data indicate a shift to cooler temperatures from the Berriasian through into the Late Valanginian, with some warmer phases recognised within the earliest Valanginian. A positive shift in carbon isotope values during the late Valanginian appear to correlate with carbon isotope profiles recorded from pelagic Tethyan successions. Surprisingly, these most positive carbon isotope values correspond with the most positive oxygen isotope values (and hence coldest palaeotemperatures) and a period characterised by inferred eustatic sea level fall. Primary productivity within Tethys is thought to have been driven by nutrients derived from upwelling and riverine influences and where temperatures at the Earths surface was presumably much higher. At higher latitudes climatic and environmental conditions are somewhat different whereby rates of weathering are much lower because of the prevalent cold climate and pulses of productivity may also be related to nutrients being released by the melting of ice and concurrent differences of under-ice light conditions. Furthermore, reduced poleward oceanic heat transport may be envisaged if cold climates were prevalent at high latitudes resulting in a relatively sluggish ocean circulation pattern. Hence in the absence of widespread Valanginian organic-rich black shale deposition within Tethys, organic carbon may have been stored in coastal areas and/or as a result of enhanced preservation within stratified waters in high latitude basins.

Price, G. D.; Mutterlose, J.

2003-04-01

271

Constraint of the CO2 rise by new atmospheric carbon isotopic measurements during the last deglaciation  

E-print Network

Click Here for Full Article Constraint of the CO2 rise by new atmospheric carbon isotopic increase of atmospheric carbon dioxide (CO2) during the last glacialinterglacial climatic transition remain debated. We analyzed the parallel evolution of CO2 and its stable carbon isotopic ratio (d13 CO2

Chappellaz, Jérôme

272

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

E-print Network

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

Aluwihare, Lihini

273

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

E-print Network

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

Keener, James P.

274

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

E-print Network

UNCORRECTEDPROOF 1 2 The effect of rising atmospheric oxygen on carbon and sulfur isotope 3 (Berner, 2001 and references therein). Strati- 34graphic fluctuations of carbon and sulfur isotopes in 35 occur when reduced carbon and 43sulfur, as pyrite, are sequestered through biological and Chemical

Kaufman, Alan Jay

275

Strontium isotopes in carbonate deposits at Crater Flat, Nevada  

SciTech Connect

Strontium isotope studies of carbonates from soils, veins, eolian dust and Paleozoic basement samples near Crater Flat, southwest of Yucca Mountain, provide evidence for the origins of these materials. Vein and soil carbonates have nearly identical ranges of {sup 87}Sr/{sup 86}Sr ratios at the lower end of the pedogenic range. The average {sup 87}Sr/{sup 86}Sr of Paleozoic basement from Black Marble Hill is similar to the {sup 87}Sr/{sup 86}Sr in the eolian dust, perhaps indicating a local source for this material. Possible spring deposits have generally higher {sup 87}Sr/{sup 86}Sr than the other carbonates. These data are compared with similar data from areas east of Yucca Mountain. 7 refs., 5 figs.

Marshall, B.D.; Futa, K.; Peterman, Z.E.; Stuckless, J.S.

1991-01-01

276

Studies of individual carbon sites of proteins in solution by natural abundance carbon 13 nuclear magnetic resonance spectroscopy. Relaxation behavior.  

PubMed

The aromatic regions in proton-decoupled natural abundance 13C Fourier transform nuclear magnetic resonance spectra (at 14.2 kG) of small native proteins contain broad methine carbon bands and narrow nonprotonated carbon resonances. Some factors that affect the use of natural abundance 13C Fourier transform NMR spectroscopy for monitoring individual nonprotonated aromatic carbon sites of native proteins in solution are discussed. The effect of protein size is evaluated by comparing the 13C NMR spectra of horse heart ferrocytochrome c, hen egg white lysozyme, horse carbon monoxide myoglobin, and human adult carbon monoxide hemoglobin. Numerous single carbon resonances are observed in the aromatic regions of 13C NMR spectra of cytochrome c, lysozyme, and myoglobin. The much larger hemoglobin yields few resolved individual carbon resonances. Theoretical and some experimental values are presented for the natural linewidths (W), spin-lattice relaxation times (T1), and nuclear Overhauser enhancements (NOE) of nonprotonated aromatic carbons and Czeta of arginine residues. In general, the 13C-1H dipolar mechanism dominates the relaxation of these carbons. 13C-14N dipolar relaxation contributes significantly to 1/T1 of C epsilon2 of tryptophan residues and Czeta of arginine residues of proteins in D2O. The NOE of each nonprotonated aromatic carbon is within experimental error of the calculated value of about 1.2. As a result, integrated intensities can be used for making a carbon count. Theoretical results are presented for the effect of internal rotation on W, T1, and the NOE. A comparison with the experimental T1 and NOE values indicates that if there is internal rotation of aromatic amino acid side chains, it is not fast relative to the over-all rotational motion of the protein. PMID:169239

Oldfield, E; Norton, R S; Allerhand, A

1975-08-25

277

Late Early Triassic climate change: Insights from carbonate carbon isotopes, sedimentary evolution and ammonoid paleobiogeography  

Microsoft Academic Search

The late Early Triassic sedimentaryfacies evolution and carbonate carbon-isotope marine record (?13Ccarb) of ammonoid-rich, outer platform settings show striking similarities between the South China Block (SCB) and the widely distant Northern Indian Margin (NIM). The studied sections are located within the Triassic Tethys Himalayan belt (Losar section, Himachal Pradesh, India) and the Nanpanjiang Basin in the South China Block (Jinya

Thomas Galfetti; Hugo Bucher; Arnaud Brayard; Peter A. Hochuli; Helmut Weissert; Kuang Guodun; Viorel Atudorei; Jean Guex

2007-01-01

278

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

NASA Astrophysics Data System (ADS)

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 by Doran et al. has shown that algal mats in these streams have delta C-13 values averaging -7.0%. 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. Additional information is contained in the original.

Neumann, K.; Lyons, W. B.; DesMarais, D. J.

1998-01-01

279

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

280

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

NASA Astrophysics Data System (ADS)

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

Tsuji, Takashi; Nakajima, Tadashi

2014-10-01

281

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...

282

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

Microsoft Academic Search

Hydrogen isotope ratio analysis is subject to interference from H\\/sup +\\/, and the uncertainty in the H\\/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

283

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

284

Interpreting carbonate and organic carbon isotope covariance in the sedimentary record  

NASA Astrophysics Data System (ADS)

Many negative ?13C excursions in marine carbonates from the geological record are interpreted to record significant biogeochemical events in early Earth history. The assumption that no post-depositional processes can simultaneously alter carbonate and organic ?13C values towards more negative values is the cornerstone of this approach. However, the effects of post-depositional alteration on the relationship between carbonate and organic ?13C values have not been directly evaluated. Here we present paired carbonate and organic ?13C records that exhibit a coupled negative excursion resulting from multiple periods of meteoric alteration of the carbonate ?13C record, and consequent contributions of isotopically negative terrestrial organic matter to the sedimentary record. The possibility that carbonate and organic ?13C records can be simultaneously shifted towards lower ?13C values during periods of subaerial exposure may necessitate the reappraisal of some of the ?13C anomalies associated with noteworthy biogeochemical events throughout Earth history.

Oehlert, Amanda M.; Swart, Peter K.

2014-08-01

285

Precambrian Research 148 (2006) 145180 Carbon isotope record for the onset of the Lomagundi carbon isotope  

E-print Network

of the Mille Lacs Group (Trout Lake, Glen Township, and Denham formations) in Minnesota have 13 C values Group in the Lake Superior area, USA and the Gordon Lake Formation of the correlative upper Huronian carbonates of the basal Gordon Lake Formation and thick carbonate succession of the Kona Dolomite

Kaufman, Alan Jay

286

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

287

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

288

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

289

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

290

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

USGS Publications Warehouse

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

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

2008-01-01

291

A history of methane hydrate release and formation from the detailed carbon isotope stratigraphy of the apticore  

NASA Astrophysics Data System (ADS)

Oceanic Anoxic Event 1a (OAE 1a) is the longest and most pronounced OAE to take place on Earth in the past 200 m.y. Detailed ?13C records through expanded marine sections of OAE 1a, known in Italy as the Selli Event, present Earth Scientists with a number of mysteries to explain. Initially, marine sediments from around the globe became dramatically enriched in organic carbon and the carbon isotope record becomes sharply negative. Second, as the organic rich deposition continues, the global carbon isotopic record does not move above the initial values, as would be expected, for hundreds of thousands of years. And finally, as the excess organic carbon concentrations decline in marine sediments around the globe, only then does the carbon isotope record move to significantly positive values and persists at these unusual levels for more than a million years. In all, three of these phases in the ?13C record appear to contradict the sedimentary record. Here we can create a working hypothesis using a combination of stratigraphic records with outstanding age control from a cored section in northern Italy and a stable carbon isotope box model for the global ocean. The initial conundrum, the negative shift that begins the OAE, has been associated with the injection of isotopically negative carbon (-60 ppm) into the ocean/atmosphere system via the melting of marine methane hydrates (an approximate input of 1664Gt of methane over 65,000 years). The second phase is explained here by a slow "bleed" of methane from clathrates into the exogenic system for a million years in a "super green house" world. This accounts for a further 6830Gt of methane release. The third phase is the direct result of the end of the methane release episode. We suggest that in the million years following the OAE, the relatively labile and abundant organic matter in the shallowly buried organic carbon rich sediments was the source for about 8800Gt of new methane hydrate, which is then stored in the overlying hemipelagic sediment. This suggestion, along with a syncronous cooling in the ocean at the time, could explain the extended positive ?13C interval. This hypothesis can serve as a more general model to explain positive carbon isotope excursions that follow OAE emplacement.

Opdyke, B.; Erba, E.; Larson, R.; Herbert, T.

2003-04-01

292

A synthesis of tissue-preservation effects on carbon and nitrogen stable isotope signatures  

E-print Network

Helen C. Sarakinos, Michael L. Johnson, and M. Jake Vander Zanden Abstract: Stable-isotope analysis suggest that preserved specimens may be used for stable-isotope analysis and open up the possibilityNOTE A synthesis of tissue-preservation effects on carbon and nitrogen stable isotope signatures

Vander Zanden, Jake

293

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

294

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

295

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

Microsoft Academic Search

We present results and speculative interpretation of leaf-level carbon isotope discrimination and ecosystem respired carbon and oxygen isotope ratios from a semi-arid, C3\\/C4 woodland located in northern New Mexico, USA. Overstory leaf area index (LAI) is dominated by live juniper (Juniperus monosperma) trees with an LAI value of approximately 1.0 m2 per m2 ground area, and has a seasonally dynamic

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

2005-01-01

296

The Carbon Isotopic Content and Concentration of Ambient Formic and Acetic Acid  

Microsoft Academic Search

A direct method for source determination of atmospheric formic and acetic acid, through carbon isotopic analysis of the ambient acids and their potential sources, has been successfully developed and tested. These first carbon isotopic measurements of formic acid in the atmosphere were found to be fairly constant, regardless of location. This is consistent with a single dominating source of formic

Bryan Jay Johnson

1991-01-01

297

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

298

Carbon isotope discrimination of arctic and boreal biomes inferred from remote atmospheric measurements  

E-print Network

efficiency values that minimize the cost function covary. The optimal light use efficiency was 0.47 gC MJ?1 to Geographic Region: Arctic region; KEYWORDS: net primary production, light use efficiency, carbon isotopeCarbon isotope discrimination of arctic and boreal biomes inferred from remote atmospheric

299

Relationships Between Carbon Isotope Discrimination and Yield of Spring Wheat Under Different Water and Nitrogen Levels  

Microsoft Academic Search

A greenhouse experiment was conducted to investigate the relationships between foliar carbon isotope discrimination (?) and above ground dry matter (ADM) at different stages during a plant's life cycle, and grain carbon isotope discrimination and grain yield (GY) at maturity of spring wheat (Triticum aestivum L.) under different nitrogen (N) and water levels. Results showed that ADM and GY both

L. J. Zhao; H. L. Xiao; X. H. Liu

2007-01-01

300

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

301

A comparison of lignin and stable carbon isotope compositions in quaternary marine sediments  

Microsoft Academic Search

Heges, J.I. and van Geen, A., 1982. A comparison of lignin and stable carbon isotope compositions in quaternary marine sediments. Mar. Chem., 11: 43--53. Organic matter in four Quaternary sediment cores from the Gulf of Mexico and one core from the Washington State coast have been analyzed for lignin and stable carbon isotope compositions. Holocene sequences of all five cores

JOHN I. HEDGES; ALEXANDER VAN GEEN

1982-01-01

302

Dietary variation in arctic foxes ( Alopex lagopus )-an analysis of stable carbon isotopes  

Microsoft Academic Search

We used stable carbon isotopes to analyse individual variation in arctic fox diet. We extracted collagen from bones (the lower jaw), and measured stable carbon isotopes. The foxes came from three different localities: Iceland, where both microtines and reindeer are rare; west Greenland, where microtines are absent; and Sweden, where scat analyses showed the primary food to be microtine rodents

Anders Angerbjrn; Pall Hersteinsson; Kerstin Lidn; Erle Nelson

1994-01-01

303

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 375C 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

304

Carbon kinetic isotope effect in the reaction of CH4 with HO  

Microsoft Academic Search

The carbon kinetic isotope effect in the CH4 + HO reaction can enrich atmospheric methane in 13C relative to its sources. In the only previous measurement of the carbon kinetic isotope effect in this reaction, a value of k12\\/k13 of 1.003 was reported. In the present experimental determination we have found a significantly larger kinetic isotope effect of 1.010 +\\/-

J. A. Davidson; C. A. Cantrell; S. C. Tyler; R. E. Shetter; R. J. Cicerone

1987-01-01

305

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

Microsoft Academic Search

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

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

1995-01-01

306

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

Microsoft Academic Search

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

Jonathan L. Payne; Lee R. Kump

2007-01-01

307

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

308

Elemental abundances of metal poor carbon rich lead star: CS29497-030  

E-print Network

We present here the abundance analysis of a metal poor carbon rich lead star, CS29497-030. High resolution and high signal to noise spectra were obtained using the UVES spectrograph on the 8.2m VLT-Kueyen telescope. The observations were made as a part of the Large Programme 165.N-0276, P.I. R. Cayrel. Abundance analysis was done using the latest version of the MARCS model atmospheres (Plez et. al. 1992) and the turbospectrum spectrum synthesis code. We have derived Teff = 6650K from the FeI lines. Visible and infrared broad band colours using the Alonso et al. (1996) calibration, gives similar temperatures. A log g value of 3.5 was obtained from the ionisation equilibrium of FeI and FeII, we remark that this gravity also satisfies the MgI/MgII, TiI/TiII and MnI/MnII equilibria, within errors. The abundance analysis indicates a metallicity, [Fe/H] = --2.7. A large overabundance of carbon ([C/Fe]=2.7) was found. We have also found large enhancement in the s-process elements and in particular lead shows an extremely high abundance of [Pb/Fe]=3.5, which makes this the star with the highest Pb/Fe ratio, up to date. The Pb/Ba ratio is found to be high ([Pb/Ba]=1.2) and the same s true for other second-peak s-process elements(e.g La, Ce, Nd). The star is a known spectroscopic binary with a period of 346 days (Preston & Sneden 2000). The abundance pattern suggests that CS 29497-30 has accreted matter from its companion, when it was in the AGB phase.

T. Sivarani; P. Bonifacio; P. Molaro; R. Cayrel; M. Spite; F. Spite; B. Plez; J. Andersen; B. Barbuy; T. C. Beers; E. Depagne; V. Hill; P. Francois; B. Nordstrom; F. Primas

2002-12-18

309

Neodymium isotopes in biogenic carbonates: reliable archives of ?Nd  

NASA Astrophysics Data System (ADS)

Neodymium isotope (143Nd/144Nd) compositions from dispersed authigenic ferromanganese oxide fraction in marine sediments, ferromanganese crusts, foraminiferal shells and fossil fish teeth are employed to trace provenance and water mass mixing in the past, having the advantage of not being fractionated by biological processes in the water column. In the modern ocean the different water masses ultimately derive their ?Nd values through continental weathering, erosion and particle-seawater interactions. This geochemical tracer has been only recently applied to scleractinian deep-water coral skeletons sourced from various sites and depths in the Atlantic ocean. Aragonitic corals can be precisely dated by U-series, potentially providing century-long records of intermediate and bathyal zone variability at sub-decadal resolution. Motivated by these recent findings we have investigated the Nd isotopic compositions of living specimens of various calcifying organisms collected in two key locations of the Mediterranean Sea and in the Southern Ocean. In particular, we analyzed several specimens of the aragonitic deep-water corals Desmophyllum dianthus, Lophelia pertusa, Madrepora oculata, Flabellum impensum, the temperate coral Cladocora caespitosa, the calcitic gorgonian coral Corallium rubrum, the bivalves Glans aculeata and Karnekampia bruei and the polychate Serpula vermicularis. Most of the samples were retrieved from the Strait of Sicily and the Southern Adriatic Sea at different water depths. Ten seawater samples from three new profiles in the Mediterranean were also collected at the same locations and depths, offering a unique opportunity to compare the Nd isotopic composition of biogenic carbonates directly with the surrounding ambient seawater. The Mediterranean Sea is particularly suited for this comparison exercise since it is characterized by water masses displaying a large range of ?Nd values, from -10.5 in the Western Mediterranean to -4.8 in the Eastern Mediterranean. In addition, specimens of living and fossil Desmophyllum dianthus and Lophelia pertusa were analysed for Nd concentration at fine-scale resolution using a laser ablation ICP-MS, with the aim to understand the effect of the coral microstructures on the Nd distribution. Nd isotopes in the modern biogenic carbonates analyzed thus far match the surrounding seawater and unless diagenesis is significant, we expect that these calcifying organisms can serve as reliable archives for past ocean circulation.

Montagna, P.; Goldstein, S. L.; Taviani, M.; Frank, N.; McCulloch, M. T.

2010-12-01

310

Fossil-wood carbon-isotope stratigraphy of the non-marine Wealden Group (Lower Cretaceous, southern England)  

Microsoft Academic Search

Recent studies have shown that it is possible to use the carbon-isotopic composition of fossil wood as a chemostratigraphic tool and as a proxy for changes to the carbon-isotopic composition of palaeoatmospheres. We present new fossil-wood carbon-isotope data from the non-marine Wessex Formation (Wealden Group, Lower Cretaceous) of the Isle of Wight and Dorset (southern England). These carbon-isotope data have

S. A. Robinson; S. P. Hesselbo

2003-01-01

311

Uptake of Dissolved Sulfide by Spartina alterniflora: Evidence from Natural Sulfur Isotope Abundance Ratios  

Microsoft Academic Search

The difference in the stable sulfur isotope ratios of sulfate and sulfide in marsh pore water was used to verify the uptake of hydrogen sulfide by the salt marsh cordgrass Spartina alterniflora in a North Carolina salt marsh. Most of the plant sulfur derived from pore-water sulfide was recovered as sulfate, an indication that the sulfide had been oxidized within

Paul R. Carlson; Joseph Forrest

1982-01-01

312

Carbon Abundances for Red Giants in the Draco Dwarf Spheroidal Galaxy  

NASA Astrophysics Data System (ADS)

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 , 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 ?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. The data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.

Shetrone, Matthew D.; Smith, Graeme H.; Stanford, Laura M.; Siegel, Michael H.; Bond, Howard E.

2013-05-01

313

Elemental abundances of metal poor carbon rich lead star CS29497-030  

E-print Network

We present here the abundance analysis of a metal poor carbon rich lead star, CS29497-030. High resolution and high signal to noise spectra were obtained using the UVES spectrograph on the 8.2m VLT-Kueyen telescope. The observations were made as a part of the Large Programme 165.N-0276, P.I. R. Cayrel. Abundance analysis was done using the latest version of the MARCS model atmospheres (Plez et. al. 1992) and the turbospectrum spectrum synthesis code. We have derived Teff = 6650K from the FeI lines. Visible and infrared broad band colours using the Alonso et al. (1996) calibration, gives similar temperatures. A log g value of 3.5 was obtained from the ionisation equilibrium of FeI and FeII, we remark that this gravity also satisfies the MgI/MgII, TiI/TiII and MnI/MnII equilibria, within errors. The abundance analysis indicates a metallicity, [Fe/H] = --2.7. A large overabundance of carbon ([C/Fe]=2.7) was found. We have also found large enhancement in the s-process elements and in particular lead shows an extr...

Sivarani, T; Molaro, P; Cayrel, R; Spite, M; Spite, F; Plez, B; Andersen, J; Barbuy, B; Beers, T C; Depagne, E; Hill, V; Franois, P; Nordstrm, B; Primas, F

2002-01-01

314

The magnesium isotope record of cave carbonate archives  

NASA Astrophysics Data System (ADS)

Here we explore the potential of magnesium (?26Mg) isotope time-series data as continental climate proxies in speleothem calcite archives. For this purpose, a total of six Pleistocene and Holocene stalagmites from caves in Germany, Morocco and Peru and two flowstones from a cave in Austria were investigated. These caves represent the semi-arid to arid (Morocco), the warm-temperate (Germany), the equatorial-humid (Peru) and the cold-humid (Austria) climate zones. Changes in the calcite magnesium isotope signature with time are compared against carbon and oxygen isotope records from these speleothems. Similar to other proxies, the non-trivial interaction of a number of environmental, equilibrium and disequilibrium processes governs the ?26Mg fractionation in continental settings. These include the different sources of magnesium isotopes such as rainwater or snow as well as soil and host rock, soil zone biogenic activity, shifts in silicate versus carbonate weathering ratios and residence time of water in the soil and karst zone. Pleistocene stalagmites from Morocco show the lowest mean ?26Mg values (GDA: -4.26 0.07 and HK3: -4.17 0.15), and the data are well explained in terms of changes in aridity over time. The Pleistocene to Holocene stalagmites from Peru show the highest mean value of all stalagmites (NC-A and NC-B ?26Mg: -3.96 0.04) but only minor variations in Mg-isotope composition, which is consistent with the rather stable equatorial climate at this site. Holocene stalagmites from Germany (AH-1 mean ?26Mg: -4.01 0.07; BU 4 mean ?26Mg: -4.20 0.10) suggest changes in outside air temperature was the principal driver rather than rainfall amount. The alpine Pleistocene flowstones from Austria (SPA 52: -3.00 0.73; SPA 59: -3.70 0.43) are affected by glacial versus interglacial climate change with outside air temperature affecting soil zone activity and weathering balance. Several ?26Mg values of the Austrian and two ?26Mg values of the German speleothems are shifted to higher values due to sampling in detrital layers (Mg-bearing clay minerals) of the speleothems. The data and their interpretation shown here highlight the potential but also the limitations of the magnesium isotope proxy applied in continental climate research. An obvious potential lies in its sensitivity for even subtle changes in soil-zone parameters, a hitherto rather poorly understood but extremely important component in cave archive research. Limitations are most obvious in the low resolution and high sample amount needed for analysis. Future research should focus on experimental and conceptual aspects including quantitative and well-calibrated leaching and precipitation experiments.

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

2012-11-01

315

The magnesium isotope record of cave carbonate archives  

NASA Astrophysics Data System (ADS)

Here we explore the potential of time-series magnesium (?26Mg) isotope data as continental climate proxies in speleothem calcite archives. For this purpose, a total of six Pleistocene and Holocene stalagmites from caves in Germany, Morocco and Peru and two flowstones from a cave in Austria were investigated. These caves represent the semi-arid to arid (Morocco), the warm-temperate (Germany), the equatorial-humid (Peru) and the cold-humid (Austria) climate zones. Changes in the calcite magnesium isotope signature with time are placed against carbon and oxygen isotope records from these speleothems. Similar to other proxies, the non-trivial interaction of a number of environmental, equilibrium and non-equilibrium processes governs the ?26Mg fractionation in continental settings. These include the different sources of magnesium isotopes such as rain water or snow as well as soil and hostrock, soil zone biogenic activity, shifts in silicate versus carbonate weathering ratios and residence time of water in the soil and karst zone. Pleistocene stalagmites from Morocco show the lowest mean ?26Mg values (GDA: -4.26 0.07 and HK3: -4.17 0.15 ) and the data are well explained in terms of changes in aridity over time. The Pleistocene to Holocene stalagmites from Peru show the highest mean value (NC-A and NC-B ?26Mg: -3.96 0.04 ) but only minor variations in Mg-isotope composition, which is in concert with the rather stable equatorial climate at this site. Holocene stalagmites from Germany (AH-1 mean ?26Mg: -4.01 0.07 ; BU 4 mean ?26Mg: -4.20 0.10 ) record changes in outside air temperature as driving factor rather than rainfall amount. The alpine Pleistocene flowstones from Austria (SPA 52: -3.00 0.73 ; SPA 59: -3.70 0.43 ) are affected by glacial versus interglacial climate change with outside air temperature affecting soil zone activity and weathering balance. Several data points in the Austrian and two data points in the German speleothems are shifted to higher values due to sampling in detrital layers (Mg-bearing clay minerals) of the speleothems. The data and their interpretation shown here highlight the potential but also the limitations of the magnesium isotope proxy applied in continental climate research. An obvious potential lies in its sensitivity for even subtle changes in soil-zone parameters, a hitherto rather poorly understood but extremely important component in cave archive research. Limitations are most obvious in the low resolution and high sample amount needed for analysis. Future research should focus on experimental and conceptual aspects including quantitative and well calibrated leaching and precipitation experiments.

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

2012-05-01

316

Seasonal cycle of carbon dioxide and its isotopic composition in an urban atmosphere: Anthropogenic and biogenic effects  

E-print Network

Seasonal cycle of carbon dioxide and its isotopic composition in an urban atmosphere: Anthropogenic. Ehleringer, Seasonal cycle of carbon dioxide and its isotopic composition in an urban atmosphere burning, and fossil fuel combustion impart carbon and oxygen isotope signals to the atmosphere that can

Ehleringer, Jim

317

New Method for Isotopic Ratio Measurements of Atmospheric Carbon Dioxide Using a 4.3 m Pulsed Quantum Cascade  

E-print Network

1 New Method for Isotopic Ratio Measurements of Atmospheric Carbon Dioxide Using a 4.3 µm Pulsed of stable isotopic ratios of carbon dioxide using a near room temperature pulsed quantum cascade laser; 91.67.Rx 1. Introduction Real time methods to monitor the stable isotopic ratios of carbon dioxide

Saleska, Scott

318

Effect of photosynthetic light dosage on carbon isotope composition in the coral skeleton: Long-term culture of Porites spp  

Microsoft Academic Search

Whereas the oxygen isotope ratio of the coral skeleton is used for reconstruction of past information on seawater, the carbon isotope ratio is considered a proxy for physiological processes, principally photosynthesis and respiration. However, the fractionation of carbon isotopes in biogenic carbonate such as coral skeleton is still unclear. We conducted a long-term culture experiment of Porites spp. corals at

Tamano Omata; Atsushi Suzuki; Takanori Sato; Kayo Minoshima; Eriko Nomaru; Akio Murakami; Shohei Murayama; Hodaka Kawahata; Tadashi Maruyama

2008-01-01

319

Carbon Isotope Ratio in 12 CO/ 13 CO toward Local Molecular Clouds with Near-Infrared High Resolution Spectroscopy of  

E-print Network

Carbon Isotope Ratio in 12 CO/ 13 CO toward Local Molecular Clouds with Near-Infrared High@duke.ifa.hawaii.edu ABSTRACT We report the carbon monoxide isotope ratio in local molecular clouds toward LkH#11; 101, AFGL 490 The main isotope of carbon ( 12 C) is a primary product of the 3 #11; process in the stellar

Usuda, Tomonori

320

Plate tectonic trigger of changes in pCO2 and climate in the Oxfordian (Late Jurassic): Carbon isotope and modeling evidence  

E-print Network

in the C-isotope record. A prominent mid-Oxfordian positive excursion in bulk carbonate carbon isotope Tethys realm. In this study we present new bulk organic matter C-isotope data (13 Corg) from northwestern: carbon isotopes; pCO2; climate; carbon cycle; model simulation 1. Introduction The Late Jurassic carbon

Gilli, Adrian

321

Carbon isotopic evidence for methane hydrate instability during quaternary interstadials  

PubMed

Large (about 5 per mil) millennial-scale benthic foraminiferal carbon isotopic oscillations in the Santa Barbara Basin during the last 60,000 years reflect widespread shoaling of sedimentary methane gradients and increased outgassing from gas hydrate dissociation during interstadials. Furthermore, several large, brief, negative excursions (up to -6 per mil) coinciding with smaller shifts (up to -3 per mil) in depth-stratified planktonic foraminiferal species indicate massive releases of methane from basin sediments. Gas hydrate stability was modulated by intermediate-water temperature changes induced by switches in thermohaline circulation. These oscillations were likely widespread along the California margin and elsewhere, affecting gas hydrate instability and contributing to millennial-scale atmospheric methane oscillations. PMID:10753115

Kennett; Cannariato; Hendy; Behl

2000-04-01

322

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

NASA Technical Reports Server (NTRS)

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

Waddington, C. J.

1975-01-01

323

The Importance of Sulfur on Enriched Carbon Isotopes and Extreme Carbon Cycle Perturbations of the Cryogenian  

NASA Astrophysics Data System (ADS)

The Neoproterozoic carbon isotope record is unusual in that it is characterized by high ?13Ccarbonate values that persist for tens of millions of years and that are interrupted by large negative excursions that coincide with two global-scale glaciations: the Sturtian (~710 Ma) and the Marinoan (~635 Ma). While the mechanisms underpinning the negative carbon isotope excursions remain controversial, the prolonged intervals of 13C-enrichment have been attributed to increased primary production and organic carbon burial. Here, we present sulfur isotope data (sulfate and pyrite) from carbonate rocks deposited in northern Namibia spanning the interglacial interval (Cryogenian Period) in order to test the hypothesis that changes in marine sulfate concentrations impacted phosphorus recycling efficiency and played a role in regulating the Neoproterozoic carbon cycle. ?34Spyrite results through the interglacial interval are 34S-enriched (-5.65 to 39.17). These data suggest sulfate concentrations were very low during this time interval as a result of nearly complete reduction of sulfate via microbes (microbial sulfate reduction) while the major fluxes of sulfate into the ocean (riverine input) were restricted due to a reduction of the hydrologic cycle during glaciation. Importantly, positive swings in ?13Ccarbonate are accompanied by negative ?34Spyrite shifts. We interpret these negative ?34Spyrite shifts as intervals of increasing sulfate concentration. As sulfate concentrations rise, bacterial sulfate reduction results in more sulfide production, which then reacts with various iron phases to from pyrite. A major sink for phosphorus in the ocean is adsorption onto iron oxides and oxyhydroxides. Therefore, the consumption of iron oxides and oxyhydroxides during pyrite formation allows for more phosphorus to be recycled in marine waters, stimulating primary production.

Gouldey, J. C.; Hurtgen, M. T.; Halverson, G. P.

2012-12-01

324

Carbon Isotopic Constraints on Arctic Methane Sources, 2008-2010  

NASA Astrophysics Data System (ADS)

Arctic methane source strengths are particularly vulnerable to large changes with year-to year meteorological variations and with climatic change. A global increase in methane seen in 2007 (Dlugokencky et al., 2009) may have been in part be due to elevated wetland emissions caused by a warm, wet summer over large parts of Siberia. In 2010 wildfires over large areas of Russia will have added methane to the Arctic atmosphere. Carbon isotopic composition of methane in air from the Arctic arriving at a measurement station can be used to identify sources of the gas. Measurement of methane ?13C in air close to sources, including wetlands, permafrost, pine forest and submarine methane clathrate has extended the available data of source signatures of methane from northern sources. Keeling plot analysis of diurnal records from field campaigns in Arctic wetlands show that bulk wetland methane emissions are typically close to ?13CCH4 -691 . Air samples from Zeppelin (Spitsbergen, Norway), Pallas (Finland) and Barra (Outer Hebrides, Scotland) have been regularly analysed for methane ?13C. Summer campaigns at Zeppelin point to a 13C depleted bulk Arctic source of dominantly biogenic origin, at -67. In spring, while the wetlands are still frozen, the source signature is more enriched, -53, with trajectory analysis implying a large contribution from onshore gas fields. Arctic methane emissions respond rapidly to warming with strong positive feedbacks. With rapid warming there is the potential to release large stores of carbon from permafrost and methane hydrates. Isotopic data are powerful discriminants of sources. High frequency, ideally continuous, monitoring of methane ?13C from a number of Arctic sites, onshore and offshore, coupled with back-trajectory analysis and regional modelling, will be important if future changes in Arctic source strengths are to be quantified. Reference: Dlugokencky, E. J., et al. (2009), Observational constraints on recent increases in the atmospheric CH4 burden, Geophys. Res. Lett., 36, L18803, doi:10.1029/2009GL039780.

Fisher, R. E.; Lowry, D.; Lanoiselle, M.; Sriskantharajah, S.; Nisbet, E. G.

2010-12-01

325

Evaluation of TASTEX task H: measurement of plutonium isotopic abundances by gamma-ray spectrometry  

SciTech Connect

This report describes a computer-based gamma spectrometer system that was developed for measuring isotopic and total plutonium concentrations in nitric acid solutions. The system was installed at the Tokai reprocessing plant where it is undergoing testing and evaluation as part of the Tokai Advanced Safeguards Exercise (TASTEX). Objectives of TASTEX Task H, High-Resolution Gamma Spectrometer for Plutonium Isotopic Analysis, the methods and equipment used, the installation and calibration of the system, and the measurements obtained from several reprocessing campaigns are discussed and described. In general, we find that measurements for gamma spectroscopy agree well with those of mass spectrometry and of other chemical analysis. The system measures both freshly processed plutonium from the product accountability tank and aged plutonium solutions from storage tanks. 14 figures, 15 tables.

Gunnink, R.; Prindle, A.L.; Asakura, Y.; Masui, J.; Ishiguro, N.; Kawasaki, A.; Kataoka, S.

1981-10-01

326

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

USGS Publications Warehouse

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

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

1955-01-01

327

Carbon-isotope composition of sediments from the Gulf of Papua  

Microsoft Academic Search

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

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

1995-01-01

328

Stable-carbon isotope ratios as a measure of marine versus terrestrial protein in ancient diets  

SciTech Connect

The stable-carbon isotope ratios for the flesh of marine and terrestrial animals from Canada's Pacific coast differ by 7.9 +- 0.4 per mil, reflecting the approx. 7 per mil difference between oceanic and atmospheric carbon. This difference is passed on to human consumers. The carbon isotopic values (delta /sup 13/C) for human collagen thus yield direct information on the relative amounts of marine and terrestrial foods in prehistoric diets.

Chisholm, B.S. (Simon Fraser Univ., Burnaby, British Columbia); Nelson, D.E.; Schwarcz, H.P.

1982-06-04

329

Isotopic and elemental abundances of copper and zinc in lunar samples, Zagami, Peles 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.; Albarde, F.; Berezhnoy, A. A.

2009-10-01

330

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

PubMed

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

Nelson, David M

2012-09-01

331

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

PubMed

Rapid detection of shifts in substrate utilization and energy balance would provide a compelling biofeedback tool for individuals attempting weight loss. As a proof of concept, we tested whether the natural abundance of exhaled carbon stable isotope ratios (breath ?(13)C) reflects shifts between negative and positive energy balance. Volunteers (n=5) consumed a 40% energy-restricted diet for 6 days followed by 50% excess on day 7. Breath was sampled immediately before and 1?h and 2?h after breakfast, lunch and dinner. Exhaled breath ?(13)C values were measured by cavity ring-down spectroscopy. Using repeated measures analysis of variance (ANOVA) followed by Dunnett's contrasts, pre-breakfast breath values on days 2-6 were compared with day 1, and postprandial day 7 time points were compared with pre-breakfast day 7. Energy restriction diminished pre-breakfast breath ?(13)C by day 3 (P<0.05). On day 7, increased energy intake was first detected immediately before dinner (-23.80.6 vs -21.90.7, P=0.002 (meanss.d.)), and breath ?(13)C remained elevated at least 2?h post dinner. In conclusion, when shifting between negative and positive energy balance, breath ?(13)C showed anticipated isotopic changes. Although additional research is needed to determine specificity and repeatability, this method may provide a biomarker for marked increases in caloric intake. PMID:24441037

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

2014-09-01

332

Abundances relative to carbon of the elements silicon to nickel in the galactic cosmic radiation  

NASA Technical Reports Server (NTRS)

Discussion of the abundances relative to carbon of the elements from silicon to nickel in the galactic cosmic radiation as measured by cosmic ray telescopes on the IMP-5 and IMP-7 satellites, in energy ranges between 40 and 450 MeV/nucleon depending on the species. The IMP-7 measurements are still to be considered only preliminary and do not yet fully exploit the resolution capabilities of that instrument. Calculations of the abundances to be expected in this charge range if the cosmic radiation traverses 6 g/sq cm of material after acceleration are presented, and the consequences which follow both for propagation models and for the chemical composition of the sources of the cosmic radiation are discussed.

Cartwright, B.; Garcia-Munoz, M.; Simpson, J. A.

1974-01-01

333

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

334

The relationship between carbon monoxide abundance and visual extinction in interstellar clouds  

NASA Technical Reports Server (NTRS)

Carbon monoxide column densities are compared to visual extinctions toward field stars in the rho Oph and Taurus molecular cloud complexes. The relationship of C(0-18) column density to extinction is established, and new determinations for (C-13)O column densities are given for a range of visual extinctions extended to beyond 20 mag. A prescription for determining hydrogen column densities and masses of molecular clouds from observations of CO isotopes is presented and discussed critically. These measurements agree well with the predictions of gas phase chemistry models which include chemical fractionation and selective isotopic photodestruction. The functional dependence of the C(O-18) column density on extinction is characterized by two different regimes separated by a distinct transition observed to occur at 4 mag in both molecular cloud complexes, whereas the functional dependence of (C-13)O is quite different in the two regions. Some saturation is found to occur for C(O-18) emission at high visual extinction and use the rarer isotopic species C(O-17) and (C-13)(O-18) to correct for it.

Frerking, M. A.; Langer, W. D.; Wilson, R. W.

1982-01-01

335

Tracing carbonate-silicate interaction during subduction using magnesium and oxygen isotopes.  

PubMed

Subduction of carbonates and carbonated eclogites into the mantle plays an important role in transporting carbon into deep Earth. However, to what degree isotopic exchanges occur between carbonate and silicate during subduction remains unclear. Here we report Mg and O isotopic compositions for ultrahigh pressure metamorphic marbles and enclosed carbonated eclogites from China. These marbles include both calcite- and dolomite-rich examples and display similar O but distinct Mg isotopic signatures to their protoliths. Their ?(26)Mg values vary from -2.508 to -0.531, and negatively correlate with MgO/CaO ratios, unforeseen in sedimentary carbonates. Carbonated eclogites have extremely heavy ?(18)O (up to +21.1) and light ?(26)Mg values (down to -1.928 in garnet and -0.980 in pyroxene) compared with their protoliths. These unique Mg-O isotopic characteristics reflect differential isotopic exchange between eclogites and carbonates during subduction, making coupled Mg and O isotopic studies potential tools for tracing deep carbon recycling. PMID:25367068

Wang, Shui-Jiong; Teng, Fang-Zhen; Li, Shu-Guang

2014-01-01

336

Stable Carbon Isotopes As Indicators of Plant Water Use Efficiency  

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

337

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

USGS Publications Warehouse

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

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

1997-01-01

338

Carbon and nitrogen abundance determinations from transition layer lines. [giant stars  

NASA Technical Reports Server (NTRS)

For red giants a smooth increase in the nitrogen to carbon abundance ratio for increasing B-V as is expected for the first dredge up phase when the outer convection zone deepens is found. An average increase in the nitrogen to silicon ratio for B-V = 0.6 which goes back to almost solar values for cool giants with B - V approximately 1.0 is reported. It looks as if Si would be enriched for deeper mixing contrary to expectations from standard evolution theory.

Boehm-Vitense, Erika; Mena-Werth, Jose

1988-01-01

339

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

NASA Astrophysics Data System (ADS)

Stable carbon isotopes provide a powerful tool to assess carbon pools and their dynamics. Dissolved organic carbon (DOC) has been recognized to play an important role in ecosystem functioning and carbon cycling and has therefore gained increased research interest. However, direct measurement of 13C isotopic signature of carbon in the dissolved phase is technically challenging particularly using high temperature combustion. Until recently, mainly custom-made systems existed which were modified for coupling of TOC instruments with IRMS for simultaneous assessment of C content and isotopic signature. The variety of coupled systems showed differences in their analytical performances. For analysis of DOC high temperature combustion is recognized as best performing method, owing to its high efficiency of conversion to CO2 also for highly refractory components (e.g. humic, fulvic acids) present in DOC and soil extracts. Therefore, we tested high temperature combustion TOC coupled to IRMS (developed by Elementar Group) for bulk measurements of DOC concentration and 13C signature. The instruments are coupled via an Interface to exchange the carrier gas from O2 to He and to concentrate the derived CO2 for the isotope measurement. Analytical performance of the system was assessed for a variety of organic compounds characterized by different stability and complexity, including humic acid and DOM. We tested injection volumes between 0.2-3 ml, thereby enabling measurement of broad concentration ranges. With an injection volume of 0.5 ml (n=3, preceded by 1 discarded injection), DOC and 13C signatures for concentrations between 5-150 mg C/L were analyzed with high precision (standard deviation (SD) predominantly <0.1), good accuracy and linearity (overall SD <0.9). For the same settings, slightly higher variation in precision was observed among the lower concentration range and depending upon specific system conditions. Differences in 13C signatures of about 50 among samples did not affect the precision of the analysis of natural abundance and labeled samples. Natural DOM, derived from different soils and assessed at various concentrations, was measured with similar good analytical performance, and also tested for the effect of freezing and re-dissolving. We found good performance of TOC-IRMS in comparison with other systems capable of determining C concentration and isotopic signatures. We recognize the advantages of this system providing: - High sample throughput, short measurement time (15 minutes), flexible sample volume - Easy maintenance, handling, rapid sample preparation (no pretreatment) This preliminary assessment highlights wide-ranging opportunities for further research on concentrations and isotopic signatures by TOC-IRMS to elucidate the role of dissolved carbon in terrestrial and aquatic systems.

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

2013-04-01

340

Global synchronous changes in the carbon isotopic composition of carbonate sediments unrelated to changes in the global carbon cycle  

PubMed Central

The carbon isotopic (?13C) composition of bulk carbonate sediments deposited off the margins of four carbonate platforms/ramp systems (Bahamas, Maldives, Queensland Plateau, and Great Australian Bight) show synchronous changes over the past 0 to 10 million years. However, these variations are different from the established global pattern in the ?13C measured in the open oceans over the same time period. For example, from 10 Ma to the present, the ?13C of open oceanic carbonate has decreased, whereas platform margin sediments analyzed here show an increase. It is suggested that the ?13C patterns in the marginal platform deposits are produced through admixing of aragonite-rich sediments, which have relatively positive ?13C values, with pelagic materials, which have lower ?13C values. As the more isotopically positive shallow-water carbonate sediments are only produced when the platforms are flooded, there is a connection between changes in global sea level and the ?13C of sediments in marginal settings. These data indicate that globally synchronous changes in ?13C can take place that are completely unrelated to variations in the global carbon cycle. Fluctuations in the ?13C of carbonate sediments measured during previous geological periods may also be subject to similar processes, and global synchroniety of ?13C can no longer necessarily be considered an indicator that such changes are related to, or caused by, variations in the burial of organic carbon. Inferences regarding the interpretation of changes in the cycling of organic carbon derived from ?13C records should be reconsidered in light of the findings presented here. PMID:18772393

Swart, Peter K.

2008-01-01

341

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

NASA Technical Reports Server (NTRS)

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

Webster, Christopher R.; Mahaffy, Paul R.

2011-01-01

342

A molecular organic carbon isotope record of miocene climate changes  

SciTech Connect

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

Schoell, M. (Chevron Petroleum Technology Co., La Habra, CA (United States)); Schouten, S.; Sinninghe Damste', J.S.; Leeuw, J.W. de (Netherlands Institute of Sea Research, Texel (Netherlands)); Summons, R.E. (Australian Geological Survey Organization, Canberra (Australia))

1994-02-25

343

Short-term carbon isotopic fractionation in plants  

SciTech Connect

A system was developed for measuring carbon isotopic fractionation in plants over a time interval of 1-3 hours, in contrast to leaf combustion studies which give long-term, integrated discrimination measurements. The system was used to study environmental effects on soybean (Glycine max) and corn (Zea mays) discrimination. Changes in leaf temperature, photon flux density (PFD), O{sub 2} concentration, and CO{sub 2} concentration produced little or no change in measured discrimination ({Delta}). For soybean, {Delta} increased with decreasing PFD. For corn, {Delta} decreased with decreasing O{sub 2} concentration. For both soybean and corn, {Delta} increased with increasing CO{sub 2} concentration. These changes in {Delta} were interpreted as environmental effects on stomatal conductance and photosynthetic capacity, which indirectly affect {Delta} by altering C{sub i}/C{sub a}. Respiratory discrimination in the dark and light was also investigated. Respired CO{sub 2} was 5{per thousand} and 0-1{per thousand} more positive than leaf carbon for soybean and corn, respectively. Photorespiratory discrimination was 6-7{per thousand} for soybean, supporting the contention that glycine decarboxylase may be the source of discrimination in the photorespiratory pathway.

Rooney, M.A.

1988-01-01

344

Spatial Variability in Instantaneous Photosynthetic Carbon and Oxygen Isotope Discrimination  

NASA Astrophysics Data System (ADS)

Stable carbon and oxygen isotope ratios of CO2 are useful tracers in studies of carbon and water cycling between the terrestrial biosphere and the atmosphere. Interpretation of variation in 13CO2 and C16O18O relies on models describing physical and biochemical processes and their associated fractionations. A layer of complexity not currently quantified or accounted for in canopy models is spatial variation in photosynthetic discrimination within a single leaf. A new measurement technique, employing tunable diode laser absorption spectrometry coupled to an open gas exchange system, enables online measurement of photosynthetic discrimination at high temporal resolution. Using this system, photosynthetic 13C and 18O discrimination was measured along leaves of a C3 monocot. For the forage cereal Triticale, 13C discrimination increased by 2 and 18O by 20 from the base to the tip of mature leaves when measured at saturating irradiance. The increase in 13C discrimination was associated with an increase in the leaf internal conductance of CO2, and 18O discrimination with carry-forward of evaporative enrichment along the leaf. When numerical averages are compared to flux- and area-weighted averages, the portion of the leaf approximately one third of the way from the base can be shown to provide the most representative area for scaling up.

Barbour, M. M.

2007-12-01

345

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

NASA Astrophysics Data System (ADS)

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

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

2007-06-01

346

Estimation of riverine carbon and organic matter source contributions using time-based isotope mixing models  

NASA Astrophysics Data System (ADS)

Rivers transport globally significant amounts of carbon (C) from terrestrial ecosystems to ocean margins. Understanding and quantifying the sources and respective contributions to riverine C has emerged as an important biogeochemical problem that can be approached through natural-abundance isotope mass balance. Traditionally, the sources of riverine C have been identified either qualitatively or quantitatively through application of static mixing models. However, both source signatures and contributions can vary significantly with time. Here we apply two time-based mixing models to a study of six rivers draining the northeast U.S. In the first model, a time-averaged mixing model (TAMM), we vary only the source isotopic (?13C and ?14C) signatures. In the second model, a time-varying mixing model (TVMM), we allow both isotopic signatures and contributions to vary with time. Based on results from the TVMM, drivers of variation in riverine particulate organic C (POC), dissolved organic C (DOC), and dissolved inorganic C (DIC) include stream discharge, stream discharge and water temperature, and water temperature and vegetation phenology, respectively. Major sources include C3plant material, algal material and slow-turnover soil OC ("slow SOC"), which together account for 50%-100% (95% CI) of riverine POC; C3plant material and slow SOC, which together typically account for 60%-100% (95% CI) of DOC; and atmospheric exchange which alone typically accounts for 40%-60% (95% CI) of DIC. Seasonal change in relative contributions from algal material, slow SOC, and photosynthesis (in response to the identified drivers) dominates the observed variation in POC, DOC and DIC, respectively. The TVMM is a novel tool to identify component contributions under more realistic non-static conditions, and with potential application to a broad range of biogeochemical studies.

Hossler, Katie; Bauer, James E.

2012-09-01

347

Quantum-Chemical Calculations of Carbon-Isotope Fractionation in CO2(g), Aqueous Carbonate Species, and Carbonate Minerals  

SciTech Connect

Quantum chemical calculations on large supermolecular carbonate-water and carbonate mineral clusters are used to predict equilibrium constants for 13,12C-isotope-exchange reactions between CO2(g), aqueous carbonate species, and the common carbonate minerals. For the aqueous species, we evaluate the influence of the size and conformational variability of the solvation shell, the exchange-correlation functional, and the basis set. The choice of exchange-correlation functional (PBE vs B3LYP), the basis set (6-31G* vs aug-cc-pVDZ), and solvation shell size (first shell only vs first shell and a partial second shell) each produce changes of ~5-10 per mil in the reduced partition function ratio. Conformational variability gives rise to a standard error of ~0.5 per mil using ~10 solute-solvent conformations. The best results are obtained with the B3LYP/ aug-cc-pVDZ combination, but because the improvements in the basis set and exchange correlation functional drive the reduced partition function ratios in opposite directions, reasonably good results are also obtained with the PBE/6-31G* combination. To construct molecular clusters representative of mineral environments, a new method is introduced on the basis of conservation of Pauling bond strength. Using these clusters as models for minerals, calculations of mineral-gas and mineral-aqueous carbon-isotope fractionation factors, are in good agreement with experimental measurements. Carbon-isotope fractionation factors for gas, aqueous, and mineral phases are thus integrated into a single theoretical/computational framework.

Rustad, James R.; Nelmes, Sierra L.; Jackson, Virgil E.; Dixon, David A.

2008-01-24

348

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

PubMed

The application of compound-specific stable isotope analysis (CSIA) for evaluating degradation of organic pollutants in the field implies that other processes affecting pollutant concentration are minor with respect to isotope fractionation. Sorption is associated with minor isotope fractionation and pollutants may undergo successive sorption-desorption steps during their migration in aquifers. However, little is known about isotope fractionation of BTEX compounds after consecutive sorption steps. Here, we show that partitioning of benzene and toluene between water and organic sorbents (i.e. 1-octanol, dichloromethane, cyclohexane, hexanoic acid and Amberlite XAD-2) generally exhibits very small carbon and hydrogen isotope effects in multistep batch experiments. However, carbon and hydrogen isotope fractionation was observed for the benzene-octanol pair after several sorption steps (??(13)C=1.6 0.3 and ??(2)H=88 3), yielding isotope fractionation factors of ?C=1.0030 0.0005 and ?H=1.195 0.026. Our results indicate that the cumulative effect of successive hydrophobic partitioning steps in an aquifer generally results in insignificant isotope fractionation for benzene and toluene. However, significant carbon and hydrogen isotope fractionation cannot be excluded for specific sorbate-sorbent pairs, such as sorbates with ?-electrons and sorbents with OH-groups. Consequently, functional groups of sedimentary organic matter (SOM) may specifically interact with BTEX compounds migrating in an aquifer, thereby resulting in potentially relevant isotope fractionation. PMID:24726480

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

2014-07-01

349

Carbon isotope variation through the Neoproterozoic Doushantuo and Dengying Formations, South China: Implications for chemostratigraphy and paleoenvironmental change  

Microsoft Academic Search

Primary carbon isotope trends in marine carbonate rocks are particularly useful for chemostratigraphic correlation and paleoenvironmental reconstruction of the Neoproterozoic Earth System. Differences, however, exist between the published carbonate C-isotope profiles from the Neoproterozoic Yangtze platform and the global C-isotope record through the equivalent time interval. More C-isotope profiles are required for the Yangtze platform from where excellently preserved early

Hong-Fei Ling; Hong-Zhen Feng; Jia-Yong Pan; Shao-Yong Jiang; Yong-Quan Chen; Xi Chen

2007-01-01

350

Carbon fixed during fumigation with elevated [CO2] (which was depleted in stable 13C isotope,  

E-print Network

, Garten CT, Norby RJ (2012) Soil carbon and nitrogen cycling and storage throughout the soil profile, P = 0.26 Final FACE harvest reveals increased soil carbon and nitrogen storage under elevated [CO2 on soil carbon (C) and nitrogen (N) cycling. · Biogeochemical and isotopic analyses of soil samples to 90

351

M.R. Saltzman and E. Thomas Chapter 11 Carbon Isotope Stratigraphy  

E-print Network

derived from pelagic carbonates, and exhibit low amplitude d13 Ccarb variability (from ?1 to þ4&) relative OF CARBON ISOTOPE STRATIGRAPHY The potential of marine carbonate d13 C trends and excursions to date.g., Shackleton and Hall, 1984; Berner, 1990; Kump and Arthur, 1999; Falkowski, 2003; Sundquist and Visser, 2004

Saltzman, Matthew R.

352

Insights into early Earth from the Pt-Re-Os isotope and highly siderophile element abundance systematics of Barberton komatiites  

NASA Astrophysics Data System (ADS)

Highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundance and Pt-Re-Os isotopic data are reported for well-preserved komatiites from the Komati and Weltevreden Formations of the Barberton Greenstone Belt in South Africa. The Re-Os data for whole-rock samples and olivine and chromite separates define isochrons with ages of 3484 38 and 3263 12 Ma for the Komati and Weltevreden systems, respectively. The respective initial 187Os/188Os = 0.10335 15 (?187Os = +0.34 0.15) and 0.10442 4 (?187Os = -0.14 0.04) are well within the range defined by chondritic meteorites. When considered together with the Re-Os data for late Archean komatiite systems, these data indicate that the mantle sources of most Archean komatiites evolved with essentially uniform long-term Re/Os that is well within the chondritic range. By contrast, the initial 186Os/188Os = 0.1198283 9 (?186Os = -0.12 0.08) and 0.1198330 8 (?186Os = +0.22 0.07) for the Komati and Weltevreden systems, respectively, are outside of known chondritic evolution paths, indicating that the mantle sources of these two komatiite systems evolved with fractionated time-integrated Pt/Os. The new 186,187Os isotopic data for these early Archean komatiite systems, combined with published 142,143Nd and 176Hf isotopic data for these systems, are consistent with formation and long-term isolation of deep-seated mantle domains with fractionated time-integrated Sm/Nd, Lu/Hf, and Pt/Os ratios, at ca. 4400 Ma. These domains may have been generated as a result of late-stage crystallization of a primordial magma ocean involving Mg-perovskite, Ca-perovskite and Pt-alloys acting as the fractionating phases. The inferred fractionated mantle domains were sampled by the early Archean komatiites, but were largely mixed away by 2.7 Ga, as evidenced by uniform time-integrated Sm/Nd, Lu/Hf, and Pt/Os ratios inferred for the sources of most late Archean komatiite systems. The calculated total Pt + Pd abundances present in the sources of the early Archean komatiite systems fall only 7-14% short of those present in estimates for the modern primitive mantle. These are also within the range of the total Pt + Pd abundances present in the sources of late Archean komatiite systems, indicating little change in the HSE abundances in the Archean mantle between 3.5 and 2.7 Ga. The new HSE data for the early Archean komatiite systems may implicate late accretion of HSE to the mantle prior to completion of crystallization of a final terrestrial magma ocean, followed by sluggish mixing of diverse, post-magma ocean domains characterized by variably fractionated lithophile element and HSE abundances.

Puchtel, Igor S.; Walker, Richard J.; Touboul, Mathieu; Nisbet, Euan G.; Byerly, Gary R.

2014-01-01

353

Calculation of isotope shifts and relativistic shifts in C I, C II, C III, and C IV J. C. Berengut*  

E-print Network

Calculation of isotope shifts and relativistic shifts in C I, C II, C III, and C IV J. C. Berengut of calculating isotope shifts and relativistic shifts in atomic spectra. We test the method on neutral carbon the lifetime of the Universe. Carbon isotope shifts can be used to measure isotope abundances in gas clouds

Kozlov, Mikhail G

354

Evidence for deep mantle convection and primordial heterogeneity from nitrogen and carbon stable isotopes in diamond  

NASA Astrophysics Data System (ADS)

Diamond, as the deepest sample available for study, provides a unique opportunity to sample and examine parts of the Earth's mantle not directly accessible. In order to provide further constraints on mantle convection and deep volatile cycles, we analysed nitrogen and carbon isotopes and nitrogen abundances in 133 diamonds from Juina (Brazil) and Kankan (Guinea). Host syngenetic inclusions within these diamonds indicate origins from the lithosphere, the asthenosphere-transition zone and the lower mantle. Juina and Kankan diamonds both display overall carbon isotopic compositions within the current upper mantle range but the ?13C signatures of diamonds from the asthenosphere-transition zone extend toward very negative and positive values, respectively. Two Kankan diamonds with both lower mantle and asthenosphere-transition zone inclusions (KK-45 and KK-83) are zoned in ?13C, and have signatures consistent with multiple growth steps likely within both the lower mantle and the asthenosphere-transition zone illustrating the transfer of material through the 670 km seismic discontinuity. At a given locality, diamonds from the upper and the lower mantle show similar ?15N distributions with coinciding modes within the range defined by typical upper mantle samples, as one might expect for a well stirred reservoir resulting from whole mantle convection. Kankan diamonds KK-11 (lower mantle), KK-21 and KK-92 (both lithospheric) display the lowest ?15N values (-24.9%, -39.4% and -30.4%) ever measured in terrestrial samples, which we interpret as reflecting primordial heterogeneity preserved in an imperfectly mixed convective mantle. Our diamond data thus provide support for deeply rooted convection cells, together with the preservation of primordial volatiles in an imperfectly mixed convecting mantle, thereby reconciling the conflicting interpretations regarding mantle homogeneity derived from geochemical and geophysical studies.

Palot, M.; Cartigny, P.; Harris, J. W.; Kaminsky, F. V.; Stachel, T.

2012-12-01

355

Carbon Isotope Records From Wetland Plants, and Implications for Paleohydrological Reconstructions  

NASA Astrophysics Data System (ADS)

The carbon isotopic record of temperate tree-rings, are controlled by changes in water stress, which causes an increase in water-use-efficiency that results in a relative carbon isotope enrichment. Hence a relative decrease in rainfall during the growing season, would result in a water-stressed condition. However, plants growing in wetland environments do not necessarily respond in a similar manner. In contrast, to terrestrial plants, initial carbon isotopic results indicated that wetland plants such as pond cypress have positive relationship with precipitation. One important plant in the greater Everglades ecosystems is sawgrass ( Cladium jamaicense), which comprises an important part of the regional ecosystem. To calibrate and understand the isotopic changes that may potentially be related to changes in water level, which corresponds to hydroperiod in a temporal manner, mesocosm experiments were used to grow these plants at different water levels. 24 mesocosms were randomly assigned 4 different water treatments to simulate changes in hydroperiod and water depth, similar to the typical Everglades wet season and dry season cycle. Our initial results from this work show a strong correlation between variations in water depth and plant carbon isotope values in the shallow water treatments vs. the deeper water treatments. Further analyses are presently underway to compare assimilation with the collected carbon isotopic data. These results confirm the observations from the cypress work, and set the stage for using carbon isotopes from preserved OM and/or biomarkers to reconstruct changes in water level from wetland settings.

Anderson, W. T.; Saunders, C.; Sternberg, L.; Childers, D. L.; Newman, S.

2007-12-01

356

Carbon, sulfur, and oxygen isotope evidence for a strong depth gradient and oceanic oxidation after the Ediacaran  

E-print Network

Carbon, sulfur, and oxygen isotope evidence for a strong depth gradient and oceanic oxidation after that likely hosted a large reservoir of dissolved organic carbon (DOC) to a Phanerozoic-style oxic deep ocean Ccarb), carbonate oxygen isotopes (d18 Ocarb), carbonate associated sulfate sulfur (d34 SCAS) and oxygen

Kaufman, Alan Jay

357

Carbon and Sulfur Stable Isotope Records of the Early Paleogene  

NASA Astrophysics Data System (ADS)

Secular records of stable carbon isotopes and stable sulfur isotopes from marine sediment provide primary tools for understanding past changes in global biogeochemical cycling. Over the Cenozoic, the most pronounced changes in ?13C and ?34S records happened during the late Paleocene and Early Eocene. The cause of these variations remains the source of debate, in part because the ?13C and ?34S records are not linked very well in the time domain. The early Cenozoic ?34S record principally comes from analyses of barite extracted from DSDP Sites 366 and 577 (Paytan et al., Science, 1996). However, Site 366 has no ?13C record and poorly preserved microfossil assemblages, and Site 577 has a problematic stratigraphy because of misplaced datums, and unrecognized core gaps and core overlaps. Here we generate a ?13C record at Site 366, realign the stratigraphy at Site 577, and place both records on a current time scale for the early Paleogene (Option 1; Westerhold et al., P3, 2008). There is now very little play in the relative and absolute timing of ?13C and ?34S changes across the early Paleogene. Between about 62 and 58 Ma, the ?13C of carbonate increased while the ? 34S of barite decreased. A marked change occurred at about 58 Ma: form this time to about 52 Ma, the ?13C of carbonate decreased but the ? 34S of barite continued to decrease. At about 52 Ma and a few million years after, both ?13C and ? 34S increased. Thus, the records are coupled but in a complex manner, and the series of hyperthermals happened when both ?13C and ? 34S decreased together. No model to date explains these basic observations satisfactorily. For example, volcanism as a cause for the ?34C drop does not explain the initial 4 Myr rise in ?13C and apparent coeval removal of carbon from the ocean and atmosphere; storage and release of terrestrial organic carbon as a cause for the rise and fall in ?13C does not explain the drop or subsequent rise in ?34S. Clearly, however, the idea that methane build-up in marine sediment during the late Paleocene and its subsequent discharge over the early Eocene is wrong, at least as presented (Dickens, Clim. Past, 2011). This is because such storage and release must drive significant anaerobic oxidation of methane (AOM) and the formation of Fe sulfides, which if depleted in 34S relative to seawater, would cause a positive ?34S excursion. Indeed, seafloor methane cannot be a significant player in global biogeochemical cycling during the early Paleogene, unless one invokes an unconventional notion: AOM leads to burial of 34S-enriched Fe sulfides.

Dickens, G.; Backman, J.

2012-12-01

358

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

PubMed

The measurement of the carbon isotope composition of starch and cellulose still relies on chemical isolation of these water-insoluble plant constituents and subsequent elemental analysis by isotope ratio mass spectrometry (EA/IRMS) of the purified fractions, while delta(13)C values of low-molecular-weight organic compounds are now routinely measured by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Here we report a simple and reliable method for processing milligram quantities of dried plant material for the analysis of the carbon isotope composition of lipids, soluble sugars, starch and cellulose from the same sample. We evaluated three different starch preparation methods, namely (1) enzymatic hydrolysis by alpha-amylase, (2) solubilization by dimethyl sulfoxide (DMSO) followed by precipitation with ethanol, and (3) partial hydrolysis by HCl followed by precipitation of the resulting dextrins by ethanol. Starch recovery for three commercially available native starches (from potato, rice and wheat) varied from 48 to 81% for the techniques based on precipitation, whereas the enzymatic technique exhibited yields between 99 and 105%. In addition, the DMSO and HCl techniques introduced a significant (13)C fractionation of up to 1.9 per thousand, while the carbon isotope composition of native starches analyzed after enzymatic digestion did not show any significant difference from that of untreated samples. The enzymatic starch preparation method was then incorporated into a protocol for determination of delta(13)C signatures of lipids, soluble carbohydrates, starch and crude cellulose. The procedure is based on methanol/chloroform/water extraction of dried and ground leaf material. After recovery of the chloroform phase (lipid fraction), the methanol/water phase was deionized by ion exchange (soluble carbohydrate fraction) and the pellet treated with heat-stable alpha-amylase (starch fraction). The remaining insoluble material was subjected to solvolysis by diglyme (cellulose fraction). The method was shown to be applicable to foliar tissues of a variety of different plant species (spruce, erect brome, maize and soybean). PMID:11445894

Wanek, W; Heintel, S; Richter, A

2001-01-01

359

Petrology, trace element abundances and oxygen isotopic compositions of a compound CAI-chondrule object from Allende  

NASA Astrophysics Data System (ADS)

We report the petrology, trace element abundances and oxygen isotopic characteristics of a compound CAI-chondrule object, WI-025, found in the Allende CV3 chondrite. The WI-025 is an irregularly shaped inclusion consisting of three texturally and chemically distinct portions: the interior portion, the igneous rim and the intermediate zone located between these two portions. The interior portion consists of anorthite, spinel, olivine and Al-bearing low-Ca pyroxene. The major element chemistry of the interior portion corresponds to that of Al-rich chondrules and is of intermediate character between fine-grained spinel-rich CAIs and ferromagnesian chondrules. The interior portion has abundant 16O-rich spinel (?17O = -14.2 to -24.7) and displays a group II CAI-like REE composition. These observations indicate that the interior portion contains a CAI component formed by fractional condensation. The major and trace element chemistry of the interior portion indicate that the CAI had subsequently assimilated chondrule materials through partial melting. The maximum heating temperature of the partial melting is estimated at approximately 1400 C, similar to the maximum heating temperature of Type-B CAIs. The oxygen isotopic compositions of the olivine and low-Ca pyroxene (?17O = -6.3) in the interior portion indicate that the partial melting and chondrule assimilation took place under a moderately 16O-poor nebular gas. The igneous rim is texturally and chemically similar to ferromagnesian chondrules and entirely surrounds the interior portion. The oxygen isotopic compositions of the olivine and low-Ca pyroxene in the igneous rim are indistinguishable from those of the interior olivine and Al-bearing low-Ca pyroxenes. These observations indicate that a chondrule material, which was melted in the same nebular gas as the interior portion, was accreted to the interior portion. The intermediate zone represents a reaction zone accompanying the igneous rim formation. The formation history of WI-025 can be summarized by the following processes: (1) original CAI formation, (2) partial melting and chondrule assimilation, (3) igneous rim formation and (4) secondary alteration on the parent body.

Wakaki, S.; Itoh, S.; Tanaka, T.; Yurimoto, H.

2013-02-01

360

Atmospheric Aerosol Investigation In Vilnius using Stable Carbon Isotopes  

NASA Astrophysics Data System (ADS)

The effects of aerosols on the atmosphere, climate, and public health are among the central topics in current environmental research. Spatially urban air pollution is a major public concern world-wide.In this study the results of experimental research are presented, the basis of which is the investigation of 13C/12C variations ?13C of stable carbon isotopes in total carbonaceous aerosols in Vilnius city, Lithuania. The main aim of the work is to identify the origin of carbonaceous aerosols. Two autumns and one spring sampling campaign were designed with the aim to determine the changes in the air caused by the beginning/end of the heating season. The experiment was performed during several sampling periods. The first period lasted from 26 November to 06 December 2010. The second was from 04 April to 16 May 2011. The third was from 12 to 29 October 2012. Atmospheric aerosols, according to their aerodynamic diameters, were collected with an eleven-stage impactor "MOUDI". The stages have 50% aerodynamic diameter cut-offs of 18.0, 10.0, 5.6, 3.2, 1.8, 1.0, 0.56, 0.32, 0.18, 0.1 and 0.056 ?m, for stages 1-11, respectively. The analysis proceeds essentially in two stages. In the first, MOUDI foils were analyzed with EA-IRMS (FlashEA 1112 coupled to ThermoFinnigan Delta Plus Advantage). Half of the foil was measured directly (TC ?13C values). The rest was heated in the oven (400 C) to remove organic part and measured EC+CC ?13C values (carbonates were not removed with acid). During the second stage of the analysis, corrections are made and OC ?13C values were calculated using isotopic balance equation: . As the main aim of the study was to identify the origin of incoming carbonaceous aerosols, air mass back trajectories were calculated using the HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model.

Masalaite, Agne; Garbaras, Andrius; Remeikis, Vidmantas

2013-04-01

361

Carbon13 kinetic isotope effects on pyruvate decarboxylation. II. Solvent effects in model systems  

Microsoft Academic Search

Carbon-13 kinetic isotope effects were determined for the decarboxylation of pyruvate by thiamin and for the decarboxylation of 2-(1-carboxy-1-hydroxyethyl)-3,4-dimethylthiazolium chloride (a covalent pyruvate-thiamin adduct) in water and in aqueous ethanol. The kinetic isotope effect for the decarboxylation step in the second system increased from 1.051 in HO to approximately 1.058 in 50% v\\/v ethanol. The isotope effect in the thiamin

Frank Jordan; Donald J. Kuo; Ernst U. Monse

1978-01-01

362

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

363

Progress and challenges in using stable isotopes to trace plant carbon and water relations across scales  

NASA Astrophysics Data System (ADS)

Stable isotope analysis is a powerful tool for assessing plant carbon and water relations and their impact on biogeochemical processes at different scales. Our process-based understanding of stable isotope signals, as well as technological developments, has progressed significantly, opening new frontiers in ecological and interdisciplinary research. This has promoted the broad utilisation of carbon, oxygen and hydrogen isotope applications to gain insight into plant carbon and water cycling and their interaction with the atmosphere and pedosphere. Here, we highlight specific areas of recent progress and new research challenges in plant carbon and water relations, using selected examples covering scales from the leaf to the regional scale. Further, we discuss strengths and limitations of recent technological developments and approaches and highlight new opportunities arising from unprecedented temporal and spatial resolution of stable isotope measurements.

Werner, C.; Schnyder, H.; Cuntz, M.; Keitel, C.; Zeeman, M. J.; Dawson, T. E.; Badeck, F.-W.; Brugnoli, E.; Ghashghaie, J.; Grams, T. E. E.; Kayler, Z. E.; Lakatos, M.; Lee, X.; Mguas, C.; Oge, J.; Rascher, K. G.; Siegwolf, R. T. W.; Unger, S.; Welker, J.; Wingate, L.; Gessler, A.

2012-08-01

364

Towards an understanding of the carbon isotopic changes across the Toarcian oceanic anoxic event  

E-print Network

A combination of bulk carbon, biomarker and compound specific isotopic analyses were used in order to investigate the changes which accompanied the deposition of black shales during the upper tenuicostatum and lower ...

Cohen, Alison Margaret

2005-01-01

365

SEASONAL VARIATIONS OF STABLE HYDROGEN AND CARBON ISOTOPE RATIOS OF METHANE IN SUBTROPICAL FRESHWATER SEDIMENTS  

EPA Science Inventory

Stable hydrogen (D) and carbon (13C) isotope ratios of sedimentary methane from five subtropical Florida freshwater sites exhibited smaller, less distinct seasonal variations than previously observed in temperate sediments, apparently due to the smaller range of temperatures forc...

366

Speleothems as proxy for the carbon isotope composition of atmospheric CO2  

NASA Astrophysics Data System (ADS)

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

Baskaran, M.; Krishnamurthy, R. V.

1993-12-01

367

Lipid correction for carbon stable isotope analysis of deep-sea fishes  

Microsoft Academic Search

Stable isotope analysis of fish tissue can aid studies of deep-sea food webs because sampling difficulties severely limit sample sizes of fish for traditional diet studies. The carbon stable isotope ratio (?13C) is widely used in food web studies, but it must be corrected to remove variability associated with varying lipid content in the tissue. A lipid correction has not

Joel C. Hoffman; Tracey T. Sutton

2010-01-01

368

The carbon isotopic composition of mosses and peat: record of temperature variations  

Microsoft Academic Search

The analysis of stable isotopic composition of peat bogs cores could be a valuable tool when reconstructing past climates. Better quantitative understanding of the potential relations between carbon isotope variations of plants and the temperature of vegetation, may result in a new means of paleoclimate reconstructions. The samples of mosses (Sphagnum Sp. and Polytrichum Sp.) and blocks of acrotelm (not

G. D. Skrzypek; M. O. Jedrysek

2006-01-01

369

Stable carbon isotope ratio variations in marine macrophytes along intertidal gradients  

Microsoft Academic Search

The hypothesis that relative water motion and boundary layer diffusion processes affect carbon isotope ratios of aquatic plants was tested in tidal pool and surge zone comparisons of the surfgrass Phyllospadix spp. No evidence was found that submerged plants growing in still upper tidal pools were isotopically different from those growing submerged in lower tidal surge zones. Significant decreases in

L. W. Cooper; C. P. McRoy

1988-01-01

370

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

E-print Network

An automated method for `clumped-isotope' measurements on small carbonate samples Thomas W. Schmid present a new method using an automated sample preparation device coupled to an isotope ratio mass spectrometer. The method is based on the repeated analysis (n ¼ 6­8) of 200 mg aliquots of sample material

Gilli, Adrian

371

Carbon isotope composition of low molecular weight hydrocarbons and monocarboxylic acids from Murchison meteorite  

Microsoft Academic Search

Carbon isotopic compositions have been measured for individual hydrocarbons and monocarboxylic acids from the Murchison meteorite, a C2 carbonaceous chondrite which fell in Australia in 1969. With few exceptions, notably benzene, the volatile products are substantially isotopically heavier than their terrestrial counterparts, signifying their extraterrestrial origin. For both classes of compounds, the ratio of C-13 to C-12 decreases with increasing

George Yuen; Neal Blair; D. J. Des Marais; Sherwood Chang

1984-01-01

372

Carbon and hydrogen isotopic fractionation of low molecular weight organic compounds during ultraviolet degradation  

Microsoft Academic Search

Ultraviolet (UV) radiation is a ubiquitous energy source for chemical reactions in nature. In particular, UV radiation provides an important pathway for degradation of organic compounds. Although isotopic change in organic compounds exposed to UV radiation may be an indicator for evaluating the extent of degradation, the isotope behavior has not been yet clarified. In this study, stable carbon and

Yasuhiro Oba; Hiroshi Naraoka

2008-01-01

373

Stable carbon and oxygen isotopes in Sphagnum fuscum peat from subarctic Canada: Implications for palaeoclimate studies  

Microsoft Academic Search

Stable carbon and oxygen isotope ratios in single plant components in Sphagnum peat have a good potential to reveal environmental changes in peat archives. Two peat profiles, covering the past ?6000years, and a Sphagnum hummock from a discontinuous permafrost area in west central Canada were studied in order to evaluate the effect of decomposition rate on isotope records and to

Pivi Kaislahti Tillman; Steffen Holzkmper; Peter Kuhry; A. Britta K. Sannel; Neil J. Loader; Iain Robertson

2010-01-01

374

Seasonality of stable carbon isotopes within the pelagic food web of Lake Kinneret  

Microsoft Academic Search

Seasonal variations in the carbon isotope composition of components of the pelagic food web in Lake Kinneret were recorded and compared with those recorded for bulk plankton from the lake in the early 1970s. Individual planktonic components as well as bulk plankton were isotopically lightest shortly after overturn in January and heaviest in May, after the peak of the annual

TAMAR ZOHARY; JONATHAN EREZ; Moshe Gophenl; ILANA BERMAN-FRANK; MARIANA STILLER

1994-01-01

375

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

EPA Science Inventory

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

376

Using Carbon and Nitrogen Isotopes in Lake Sediments to Detect Land Use Change  

NASA Astrophysics Data System (ADS)

Stable isotopes in lakes sediments are often used to reconstruct past environmental conditions. Carbon and nitrogen isotopes can provide information about both internal processes and terrestrial inputs to a lake. As such, they offer a powerful approach to detecting human impacts on aquatic systems. We investigated the potential of stable isotopes to trace anthropogenic land use changes by comparing stable isotopic composition of sedimentary organic matter at several river deltas in Lake Tanganyika, East Africa. Lake Tanganyika is a large rift valley lake draining watersheds that differ greatly in size, with land use patterns that vary from low-impact, protected areas (such as Gombe Steam National Park) to deforested and intensely cultivated regions. We found that carbon isotopes were related to both watershed disturbance and size, while nitrogen isotopes were related only to watershed disturbance. The direct relationship between 13C and C:N ratios across all watersheds suggests that differences in ? 13C may be attributed to terrestrial inputs rather than internal changes in the lake, such as increased productivity. Stable isotope analyses of cores taken at two sites were consistent with patterns seen in surface sediments. Our results suggest that nitrogen isotopes may be a better indicator of land use than carbon isotopes and that watershed size can be a confounding factor in the interpretation of geochemical signals in lake sediments.

O'Reilly, C. M.; Dettman, D. L.; Cohen, A. S.

2001-05-01

377

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

EPA Science Inventory

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

378

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

EPA Science Inventory

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

379

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

EPA Science Inventory

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

380

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

EPA Science Inventory

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

381

Stable carbon isotope ratios and the existence of a gas phase in the evolution of carbonate ground waters  

Microsoft Academic Search

The chemical and stable isotope compositions of unpolluted ground waters in carbonate terranes are a function of the pH, P CO 2 , 13 C content of the ground water recharge, the 13 C content of the carbonate rock, and the manner in which the rock is dissolved or precipitated. Physico-chemical models show that significantly different relationships exist between Ca

Peter Deines; Russell S. Harmon; Donald Langmuir

1974-01-01

382

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

PubMed

Carbon isotope ratio (CIR) analysis has been routinely and successfully applied to doping control analysis for many years to uncover the misuse of endogenous steroids such as testosterone. Over the years, several challenges and limitations of this approach became apparent, e.g., the influence of inadequate chromatographic separation on CIR values or the emergence of steroid preparations comprising identical CIRs as endogenous steroids. While the latter has been addressed recently by the implementation of hydrogen isotope ratios (HIR), an improved sample preparation for CIR avoiding co-eluting compounds is presented herein together with newly established reference values of those endogenous steroids being relevant for doping controls. From the fraction of glucuronidated steroids 5?-pregnane-3?,20?-diol, 5?-androst-16-en-3?-ol, 3?-Hydroxy-5?-androstane-11,17-dione, 3?-hydroxy-5?-androstan-17-one (ANDRO), 3?-hydroxy-5?-androstan-17-one (ETIO), 3?-hydroxy-androst-5-en-17-one (DHEA), 5?- and 5?-androstane-3?,17?-diol (5aDIOL and 5bDIOL), 17?-hydroxy-androst-4-en-3-one and 17?-hydroxy-androst-4-en-3-one were included. In addition, sulfate conjugates of ANDRO, ETIO, DHEA, 3?-hydroxy-5?-androstan-17-one plus 17?- and androst-5-ene-3?,17?-diol were considered and analyzed after acidic solvolysis. The results obtained for the reference population encompassing n = 67 males and females confirmed earlier findings regarding factors influencing endogenous CIR. Variations in sample preparation influenced CIR measurements especially for 5aDIOL and 5bDIOL, the most valuable steroidal analytes for the detection of testosterone misuse. Earlier investigations on the HIR of the same reference population enabled the evaluation of combined measurements of CIR and HIR and its usefulness regarding both steroid metabolism studies and doping control analysis. The combination of both stable isotopes would allow for lower reference limits providing the same statistical power and certainty to distinguish between the endo- or exogenous origin of a urinary steroid. PMID:23568614

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

2013-06-01

383

Carbonisotope stratigraphy and ammonite faunal turnover for the Middle Jurassic in the Southern Iberian palaeomargin  

Microsoft Academic Search

Variations in the stable carbonisotope ratio of marine and continental sediments can reflect changes in sink and flux modifications of the palaeocarbon cycle. Here we report carbonisotope compositions of Middle Jurassic marine carbonates from the Betic Cordillera (southern Spain), which represents an ideal region to link the stable carbonisotope curves directly to ammonite zones and subzones, and thereby for the

Luis O'Dogherty; Jos Sandoval; Annachiara Bartolini; Sbastien Bruchez; Markus Bill; Jean Guex

2006-01-01

384

Carbon isotope anomaly and other geochemical changes at the Triassic-Jurassic boundary from a marine section in Hungary  

Microsoft Academic Search

Most mass extinctions are linked with carbon isotope excursions, implying that biotic crises are coupled with changes in the global carbon cycle. The isotopic evolution during the end-Triassic extinction is far less documented than that for the other major Phanerozoic extinctions. Here we report a sharp and short-lived -3.50\\/00 excursion in carbon isotope values for carbonate (delta13Ccarb) corresponding to a

Jzsef Plfy; Attila Demny; Jnos Haas; Magdolna Hetnyi; Michael J. Orchard; Istvn Veto

2001-01-01

385

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

PubMed

Fractionation of carbon isotopes (13C/12C) by glycine decarboxylase (GDC) was investigated in mitochondrial preparations isolated from photosynthetic tissues of different plants (Pisum, Medicago, Triticum, Hordeum, Spinacia, Brassica, Wolffia). 20 mM glycine was supplied to mitochondria, and the CO2 formed was absorbed and analyzed for isotopic content. CO2 evolved by mitochondria of Pisum was enriched up to 8% in 12C compared to the carboxylic atom of glycine. CO2 evolved by mitochondria of the other plants investigated was enriched by 5-16% in 13C. Carbon isotope effects were sensitive to reaction conditions (pH and the presence of GDC cofactors). Theoretical treatment of the reaction mechanism enabled us to conclude that the value and even the sign of the carbon isotope effect in glycine decarboxylation depend on the contribution of the enzyme-substrate binding step and of the decarboxylation step itself to the overall reaction rate. Therefore, the fractionation of carbon isotopes in GDC reaction was revealed which provides essential isotopic effects in plants in addition to the well-known effect of carbon isotope fractionation by the central photosynthetic enzyme, ribulose-1,5-biphosphate carboxylase. PMID:8647275

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

1996-05-20

386

Insights into Belowground Processes from Carbon and Nitrogen Isotopes  

NASA Astrophysics Data System (ADS)

13C and 15N content generally increase with greater depth in the soil but no completely satisfactory explanation of this phenomenon has been advanced. Several explanations have been proposed, including discrimination against 13C and 15N during decomposition, preferential preservation of 13C-enriched compound classes, incorporation of soil CO2 into microbial biomass by anaplerotic reactions, enrichment in 13C and 15N of belowground plant and mycorrhizal fungal components compared to aboveground components, and preferential loss of 15N during nitrification, amonification, and denitrification reactions. Here, I examine the theoretical, experimental, and field evidence for the differing proposed hypotheses. The ratio of enrichment in 15N and 13C with depth is between 2 and 3, suggesting that the movement of carboxyl groups (-CO2) and amino groups (-NH2) during decomposition may control soil isotope patterns. Another important factor is the incorporation of 13C-enriched root and mycorrhizal carbon into deeper soil layers versus the incorporation of 13C-depleted above-ground plant litter at the soil surface. Anaplerotic fixation of soil CO2 appears unimportant as a contributing factor to 13C enrichment of soil profiles, based on the average efficiency of microbial metabolism (40%) and the relative proportion of microbial C attributed to anaplerotic reactions (3-5%). Because mycorrhizal fungi and plant roots appear generally enriched in 13C and 15N relative to above-ground plant components, I suggest that increasing 13C and 15N enrichment of soil relative to above-ground plant foliage should correlate with the relative carbon allocation belowground to roots and mycorrhizal fungi in many terrestrial systems.

Hobbie, E. A.

2005-12-01

387

Turnover of stable carbon isotopes in the muscle, liver, and breath CO2 of alpacas (Lama pacos)  

E-print Network

2005; Revised 21 February 2006; Accepted 25 February 2006 Stable carbon isotope analysis of animal a single-pool model. Copyright # 2006 John Wiley & Sons, Ltd. Stable isotope analysis is now frequentlyTurnover of stable carbon isotopes in the muscle, liver, and breath CO2 of alpacas (Lama pacos) M

Ehleringer, Jim