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1

Carbon Isotope Abundances in Comets  

Microsoft Academic Search

Rotational lines of 13C14N have been identified in high-resolution (lambda\\/Deltalambda~60,000) echelle spectra of the CN B2Sigma+-X2Sigma+ (0-0) band in three comets. The 12C\\/13C abundance ratios determined using a full fluorescence excitation model for comets Levy (C\\/1990 K1), Austin (C\\/1989 X1), and Okazaki-Levy-Rudenko (C\\/1989 XIX) are 90+\\/-10, 85+\\/-20, and 93+\\/-20, respectively, consistent with the solar system ratio, 90. A lower limit

Susan Wyckoff; Marvin Kleine; Bruce A. Peterson; Peter A. Wehinger; Lucy M. Ziurys

2000-01-01

2

Investigating microbial carbon cycling using natural abundance isotope analysis of PLFA  

Microsoft Academic Search

Understanding microbial carbon sources and cycling is fundamental to our conceptualization of microbial ecosystems and their role in biogeochemical cycling in natural systems. Achieving this understanding requires application of a wide range of approaches. Natural abundance isotope analysis of individual compounds, particularly cellular components such as Phospholipids Fatty Acids (PLFA) can provide insights into the carbon sources and metabolic activities

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

2008-01-01

3

Investigating microbial carbon cycling using natural abundance isotope analysis of PLFA  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

4

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

PubMed

Soil samples were collected from an experimental paddy field with long-term (26 years) fertilization in Taihu Lake region of Jiangsu Province to study the effects of different fertilization on the organic carbon distribution and stable carbon isotope natural abundance (delta 13C) in the soil profile, and on the humus composition. The results showed that long-term fertilization increased the organic carbon content in top soil significantly, and there was a significantly negative exponential correlation between soil organic carbon content and soil depth (P < 0.01). The organic carbon content in 10-30 cm soil layer under chemical fertilizations and in 20-40 cm soil layer under organic fertilizations was relatively stable. Soil delta 13C increased gradually with soil depth, its variation range being from -24% per thousand to -28 per thousand, and had a significantly negative linear correlation with soil organic carbon content (P < 0.05). In 0-20 cm soil layer, the delta 13C in treatments organic manure (M), M + NP, M + NPK, M + straw (R) + N, and R + N decreased significantly; while in 30-50 cm soil layer, the delta 13C in all organic fertilization treatments except R + N increased significantly. Tightly combined humus (humin) was the main humus composition in the soil, occupying 50% or more, and the rest were loosely and stably combined humus. Long-term fertilization increased the content of loosely combined humus and the ratio of humic acid (HA) to fulvic acid (FA). PMID:19102308

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

2008-09-01

5

Partitioning Respiration Fluxes in a Forested Mountainous Ecosystem Using Natural Abundance of Stable Carbon Isotopes  

NASA Astrophysics Data System (ADS)

Isotopic mass balance techniques can help overcome challenges to studying ecosystem fluxes in complex terrain. Because scaling up measurements made at the leaf level compounds and magnifies measurement errors, it is desirable that ecosystem fluxes be measured using an integrative technique, such as eddy covariance. However, advective forcing complicates the use of eddy covariance in complex terrain, so we used an isotopic mass balance approach to partition ecosystem respiration flux in a forested site in a mountainous region of northern Idaho, USA. In 2006 and 2007, we analyzed the carbon-13 composition (?13C) of ecosystem respiration and both the ?13C and magnitude of soil, foliar, and stem component fluxes of ecosystem respiration. Soil- and stem-respired ?13C values were similar, from -27.24 (2.63)‰ (stem) to -26.9 (1.11)‰ (soil). Foliar respiration was consistently more enriched by up to 8‰. We took advantage of nighttime advection to collect samples of air from the forest, then used a Keeling plot approach to determine the isotopic composition of respired CO2. Ecosystem-respired CO2 had a seasonal range from -27.3 (0.67)‰ to -23.5 (1.0)‰. Using a mixing model, we then determined a ratio of soil respiration to ecosystem respiration for the forest. We compared this ratio to a ratio obtained independently by scaling up soil, foliar, and stem respiration rate measurements to the forest level. This work shows that, in the absence of eddy covariance techniques, whole-ecosystem gas exchange can be examined using the natural abundance of stable isotopes. This approach can be further used to test the accuracy of ecosystem carbon models or scaling techniques.

Berryman, E. M.; López, N. U.; Gag, P.; Kavanagh, K.; Marshall, J. D.

2008-12-01

6

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

PubMed Central

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

Affek, Hagit P.; Yakir, Dan

2003-01-01

7

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

Microsoft Academic Search

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

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

2005-01-01

8

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

Microsoft Academic Search

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

Michael I. Bird; Darren R. Gröcke

1997-01-01

9

Natural Carbon Isotope Abundance of Plasma Metabolites and Liver Tissue Differs between Diabetic and Non-Diabetic Zucker Diabetic Fatty Rats  

PubMed Central

Background ‘You are what you eat’ is an accurate summary for humans and animals when it comes to carbon isotope abundance. In biological material, natural13C/12C ratio is subject to minute variations due to diet composition (mainly from ingestion of C3 and C4 metabolism plants) and to the discrimination between ‘light’ and ‘heavy’ isotopes during biochemical reactions (isotope effects and isotopic fractionation). Methodology/Principal Findings Carbon isotopic abundance was measured in ZDF (fa/+) and ZDF (fa/fa), (lean and obese-diabetic rats respectively) fed the same diet. By analysing plasma metabolites (glucose and non-esterified fatty acids), breath and liver tissue by high-precision isotope ratio mass spectrometry, we demonstrate for the first time statistically distinguishable metabolic carbon isotope abundance between ZDF (fa/+) and ZDF (fa/fa) rats based on plasma glucose, palmitic, oleic, linoleic, arachidonic acids and bulk analysis of liver tissue (P<0.005) resulting into clear isotopic fingerprints using principal component analysis. We studied the variation of isotopic abundance between both groups for each metabolite and through the metabolic pathways using the precursor/product approach. We confirmed that lipids were depleted in 13C compared to glucose in both genotypes. We found that isotopic abundance of linoleic acid (C18: 2n-6), even though both groups had the same feed, differed significantly between both groups. The likely reason for these changes between ZDF (fa/+) and ZDF (fa/fa) are metabolic dysregulation associated with various routing and fluxes of metabolites. Conclusion/Significance This work provides evidence that measurement of natural abundance isotope ratio of both bulk tissue and individual metabolites can provide meaningful information about metabolic changes either associated to phenotype or to genetic effects; irrespective of concentration. In the future measuring the natural abundance ?13C of key metabolites could be used as endpoints for studying in vivo metabolism, especially with regards to metabolic dysregulation, and development and progression of metabolic diseases.

Godin, Jean-Philippe; Ross, Alastair B.; Cleroux, Marilyn; Pouteau, Etienne; Montoliu, Ivan; Moser, Mireille; Kochhar, Sunil

2013-01-01

10

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

11

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

Microsoft Academic Search

The Sangihe Arc is presently colliding with the Halmahera Arc in northeastern Indonesia, forming the world's only extant example of an arc-arc collision zone. We report the first helium and carbon isotopic and relative abundance data from the Sangihe Arc volcanoes as a means to trace magma origins in this complicated tectonic region. Results of this study define a north-south

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

2004-01-01

12

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

13

Carbon Isotopes: Variations of Their Natural Abundance. Application to Correction of Radiocarbon Dates, to the Study of Plant Metabolism and to Paleoclimate.  

National Technical Information Service (NTIS)

The radiocarbon activity of contemporaneous samples shows: i) variations in the specific activity of the atmospheric C14, which varies with time and locality. ii) variations due to isotope discrimination, or fractionation, of the carbon isotope ratio duri...

J. C. Lerman

1974-01-01

14

Detection of Correlations in Stellar Isotopic Abundances  

NASA Astrophysics Data System (ADS)

The composition of a star changes with time via sequences of thermonuclear reactions. These sequences strongly couple the abundances of all elements to each other. The resulting complex interdependencies often make it difficult to ascertain which isotopic abundances most influence one another. To investigate this, a FORTRAN program has been written which analyzes these abundances over time as predicted by a simulation to determine if they may be correlated. This is accomplished via a looping over all possible pairs of tracked isotopes, quantitatively ascertaining the shapes of the abundance versus time curves for each, and assigning numerical scores to determine if these pairs of curves are correlated, anticorrelated, or uncorrelated. Preliminary results from this study will be presented.

Thomsen, K. A.; Smith, M. S.

2012-10-01

15

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

16

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

PubMed

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

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

2012-05-29

17

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

18

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

PubMed

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

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

2011-04-01

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

Helium isotopic abundance variation in nature  

SciTech Connect

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

Holden, N.E.

1993-08-01

21

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

USGS Publications Warehouse

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

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

2002-01-01

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

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

SciTech Connect

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

Stephen C. Piper; Ralph F. Keeling

2012-01-03

24

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

National Technical Information Service (NTIS)

The main objective of this project was to continue research to develop carbon cycle relationships related to the land biosphere based on remote measurements of atmospheric CO2 concentration and its isotopic ratios 13C/12C, 18O/16O, and 14C/12C. The projec...

R. F. Keeling S. C. Piper

2012-01-01

25

A Study of the Decomposition of Reed (Phragmites australis ) as a Possible Source of Aquatic Humic Substances by Measuring the Natural Abundance of Stable Carbon Isotopes  

NASA Astrophysics Data System (ADS)

The decomposition of leaf and steam litter of reed (P. australis) was measured both in the field and in the laboratory. The breakdown rates, the total carbon and the stable carbon isotope dynamics of reed litter were determined. The stable carbon isotope ratios of isolated humic substances (fulvic and humic acids) were also analysed. The 13C value in reed remains increased from -26 to -24 for stems and from -27 to -26 for leaves. The dissolved fulvic and humic acids isolated from the experimental bottles (mean 13C was -27.6) and the reservoir water were depleted in 13C (mean 13C was -28.6) relative to the reed remains. The results show that reed litter is an important source of coloured aquatic humic substances.

Balogh, Katalin V.; Présing, Mátyás; Vörös, Lajos; Tóth, Noémi

2006-02-01

26

Carbon isotopic fractionation in heterotrophic microbial metabolism  

SciTech Connect

Differences in the natural-abundance carbon stable isotopic compositions between products from aerobic cultures of Escherichia coli K-12 were measured. Respired CO2 was 3.4 percent depleted in C-13 relative to the glucose used as the carbon source, whereas the acetate was 12.3 percent enriched in C-13. The acetate C-13 enrichment was solely in the carboxyl group. Even though the total cellular carbon was only 0.6 percent depleted in C-13, intracellular components exhibited a significant isotopic heterogeneity. The protein and lipid fractions were -1.1 and -2.7 percent, respectively. Aspartic and glutamic acids were -1.6 and +2.7 percent, respectively, yet citrate was isotopically identical to the glucose. Probable sites of carbon isotopic fractionation include the enzyme, phosphotransacetylase, and the Krebs cycle. 38 references.

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

1985-10-01

27

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

28

Carbon isotopic composition of atmospheric methane  

Microsoft Academic Search

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

C. M. Stevens; F. E. Rust

1982-01-01

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

Use of carbon and nitrogen isotope ratios in termite research  

Microsoft Academic Search

In this paper, I review carbon and nitrogen isotopic (natural abundance levels) studies of termites. The carbon isotope ratio of CH 4 emitted from termites, together with the emission rates of CO 2, CH 4 and H 2, showed several trends corresponding to the kinds of symbiotic microbes and feeding habits. The fraction of methane oxidized in the nest structure

Ichiro Tayasu

1998-01-01

31

Ce isotope abundance in chondritic and HED meteorites  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

32

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

PubMed

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

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

2003-01-01

33

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

34

THE ATOMIC WEIGHTS COMMISSION AND ISOTOPIC ABUNDANCE RATIO DETERMINATIONS  

Microsoft Academic Search

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

2005-01-01

35

The abundances of isotopes in the cosmic radiation. [Milky way  

Microsoft Academic Search

Studies of the isotopic composition of nuclei in the cosmic radiation are reviewed, including abundances of the isotopes of elements from H to Ni (nuclear charge 1>{ital Z}>28), and 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

Mewaldt

1989-01-01

36

Mass Spectrometric Investigations on Ruthenium Isotopic Abundances.  

National Technical Information Service (NTIS)

Ruthenium isotopic compositions were measured on various terrestrial samples. One measurement was made on meteoritic material and assumed to be representative of primordial ruthenium. These measurements were made possible after a careful investigation of ...

C. Devillers T. Lecomte M. Lucas R. Hagemann

1976-01-01

37

Silicon Reference Materials Certified for Isotope Abundances.  

National Technical Information Service (NTIS)

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

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

1991-01-01

38

Relative isotopic abundances of zirconium in S-type stars  

Microsoft Academic Search

The relative abundances of the six stable or nearly stable isotopes of zirconium were measured for three S stars, R Cyg, V Cnc, and R Gem. The method of analysis is described with the abundances determined by comparing the observed stellar profile of intensity vs wavelength with synthetic spectra calculated by the Minnaert interpolation scheme for a single slab LTE

A. C. Zook

1978-01-01

39

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

40

LITERATURE SURVEY ON ISOTOPIC ABUNDANCE RATIO MEASUREMENTS - 2001-2005  

SciTech Connect

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

HOLDEN, N.E.

2005-08-13

41

The carbon isotopic composition of atmospheric methane  

NASA Astrophysics Data System (ADS)

Recent measurements of the carbon isotopic abundance of atmospheric methane give a value of sigma(C-13/C-12) = -47.0 within 0.3 parts per thousand, which is significantly different from earlier values measured 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 with the increase in concentration since 1965-1970 observed in other studies.

Stevens, C. M.; Rust, F. E.

1982-06-01

42

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

NASA Astrophysics Data System (ADS)

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

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

2004-07-01

43

GCR neon isotopic abundances: Comparison with wolf-rayet star models and meteoritic abundances  

NASA Astrophysics Data System (ADS)

Measurements of the neon isotopic abundances from the ACE-CRIS experiment are presented. These abundances have been obtained in seven energy intervals over the energy range of ~80<=E<=280 MeV/nucleon. The 22Ne/20Ne source ratio is derived using the measured 21Ne/20Ne abundance as a ``tracer'' of secondary production of the neon isotopes. We find that the 22Ne/20Ne abundance ratio at the cosmic-ray source is a factor of 5.0+/-0.2 greater than in the solar wind. The GCR 22Ne/20Ne ratio is also shown to be considerably larger than that found in anomalous cosmic rays, solar energetic particles, most meteoritic samples of matter, and interplanetary dust particles. Recent two-component Wolf-Rayet models provide predictions for the 22Ne/20Ne ratio and other isotope ratios. Comparison of the CRIS neon, iron, and nickel isotopic source abundance ratios with predictions indicate possible enhanced abundances of some neutron-rich nuclides that are expected to accompany the 22Ne excess. .

Binns, W. R.; Wiedenbeck, M. E.; Christian, E. R.; Cummings, A. C.; George, J. S.; Israel, M. H.; Leske, R. A.; Mewaldt, R. A.; Stone, E. C.; von Rosenvinge, T. T.; Yanasak, N. E.

2001-11-01

44

Stable Carbon and Sulfur Isotopes as Records of the Early Biosphere. Abstract Only.  

National Technical Information Service (NTIS)

The abundance ratios of the stable isotopes of light elements such as carbon and sulfur can differ between various naturally-occurring chemical compounds. If coexisting compounds have achieved mutual chemical and isotopic equilibrium, then the relative is...

D. J. Desmarais

1989-01-01

45

(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

46

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

47

Literature Survey on Isotopic Abundance Ratio Measurements 2001-2005.  

National Technical Information Service (NTIS)

Along with my usual weekly review of the published literature for new nuclear data, I also search for new candidates for best measurements of isotopic abundances from a single source. Most of the published articles, that I previously had found in the Rese...

N. E. Holden

2005-01-01

48

Some natural variations in the relative abundance of copper isotopes  

USGS Publications Warehouse

The relative isotopic abundance of copper has been measured in a number of minerals and a few plant materials. Suites of samples from Michigan and the Colorado Plateau have been examined in more detail to determine if local variations due to isotopic exchange or diffusion could be found. The relative isotopic abundance of copper in specimens from several other localities was also determined. The variations noted were small but in some cases were felt to be significant because they were larger than the experimental error (0??1 per cent in the ratio). A total spread of -1 to +8 parts per mil compared to the standard was found in the specimens tested. ?? 1958.

Walker, E. C.; Cuttitta, F.; Senftle, F. E.

1958-01-01

49

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

50

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

PubMed

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

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

2006-09-01

51

The separation of stable isotopes of carbon  

NASA Astrophysics Data System (ADS)

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

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

1989-04-01

52

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

PubMed

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

Chew, Gina; Walczyk, Thomas

2013-03-19

53

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

54

Determination of minor isotope abundances in naturally occurring uranium materials. The tracing power of isotopic signatures for uranium.  

National Technical Information Service (NTIS)

The mass spectrometric determination of minor abundant isotopes, (sup 234)U and (sup 236)U in naturally occurring uranium materials requires instruments of high abundance sensitivity and the use of highly sensitive detection systems. In this study the the...

R. Ovaskainen

1999-01-01

55

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

56

Carbon isotope effects in carbonate systems  

NASA Astrophysics Data System (ADS)

Global carbon cycle models require a complete understanding of the ? 13C variability of the Earth's C reservoirs as well as the C isotope effects in the transfer of the element among them. An assessment of ? 13C changes during CO 2 loss from degassing magmas requires knowledge of the melt-CO 2 carbon isotope fractionation. In order to examine the potential size of this effect for silicate melts of varying composition, 13C reduced partition functions were computed in the temperature range 275 to 4000 K for carbonates of varying bond strengths (Mg, Fe, Mn, Sr, Ba, Pb, Zn, Cd, Li, and Na) and the polymorphs of calcite. For a given cation and a given pressure the 13C content increases with the density of the carbonate structure. For a given structure the tendency to concentrate 13C increases with pressure. The effect of pressure (‰/10 kbar) on the size of the reduced partition function of aragonite varies with temperature; in the pressure range 1 to 10 5 bars the change is given by: ? 13C p average=-0.01796+0.06635? 10 3/T+0.006875? 10 6/T2 For calcite III the pressure effect is on average 1.4× larger than that for aragonite at all temperatures. The nature of the cation in a given structure type has a significant effect on the carbon isotope fractionation properties. The tendency to concentrate 13C declines in the series magnesite, aragonite, dolomite, strontianite, siderite, calcite, smithonite, witherite, rhodochrosite, otavite, cerrusite. For divalent cations a general expression for an estimation of the reduced partition function (?) from the reduced mass (? = [M Cation × M Carbonate]/[M Cation + M Carbonate]) is: 1000 ln?=(0.032367-0.072563? 10 3/T-0.01073? 10 6/T2)??-14.003+29.953? 10 3/T+9.4610? 10 6/T2 For Mg-calcite the 13C content varies with the Mg concentration. The fractionation between Mg-calcite (X = mole fraction of MgCO 3) and calcite is given by: 1000 ln(? MgCalite- Calcite)=[0.013702-0.10957× 10 3/T+1.35940× 10 6/T2-0.329124× 10 9/T3+0.0304160× 10 12/T4]× X1.5 The results of the computations were used together with previously published experimental vaporous CO 2-silicate melt fractionations to determine, at 1200°C, a relationship between melt-CO 213C fractionation and melt composition, expressed as molecular proportions of the cations Mg, Fe, Mn, Ca, Na, K and Si and Al: 1000 ln? Melt- CO2=5.14× Mg+ Fe+ Mn+ Ca+ Na+ K/Si+ Al+0.86 A conceptual model to understand this relationship was developed. The results of the computations approximate closely the experimentally determined vaporous CO 2-CaCO 3 fractionations at high temperatures. Empirically derived dolomite-calcite and calcite-graphite 13C isotope geothermometers agree with results of the present work.

Deines, Peter

2004-06-01

57

Carbon isotope controlled molecular switches  

NASA Astrophysics Data System (ADS)

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

Foster, Brian K.

58

Isotopic Abundances of Eu, Ba, and Sm in Metal-Poor Stars  

NASA Astrophysics Data System (ADS)

We have examined the isotopic mix of the heavy neutron-capture elements Eu, Ba, and Sm in three metal-poor stars with different enrichment histories. Isotopic abundances are more fundamental than elemental abundances as probes of the contributions from the rapid and slow nucleosynthesis reactions. We show preliminary results from our study, the first to examine isotopic abundances of three elements simultaneously in the same star.

Roederer, Ian U.; Sneden, Chris; Lawler, James E.; Sobeck, Jennifer S.; Pilachowski, Catherine A.; Cowan, John J.

59

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

60

Isotopic abundances - Inferences on solar system and planetary evolution  

NASA Astrophysics Data System (ADS)

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

Wasserburg, G. J.

1987-12-01

61

Carbon isotope effects associated with aceticlastic methanogenesis.  

PubMed Central

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

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

1994-01-01

62

Potassium isotope abundances in Australasian tektites and microtektites.  

NASA Astrophysics Data System (ADS)

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

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

2008-10-01

63

Stable carbon isotope ratios of rock varnish organic matter: a new paleoenvironmental indicator.  

PubMed

Stable carbon isotope ratios of organic matter in rock varnishes of Holocene age from western North America and the Middle East show a strong association with the environment. This isotopic variability reflects the abundance of plants with different photosynthetic pathways in adjacent vegetation. Analyses of different layers of varnish on late Pleistocene desert landforms indicate that the carbon isotopic composition of varnish organic matter is a paleoenvironmental indicator. PMID:17777781

Dorn, R I; Deniro, M J

1985-03-22

64

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

65

The carbon isotopic composition of ecosystem breath  

NASA Astrophysics Data System (ADS)

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

Ehleringer, J.

2008-05-01

66

Effects of biosynthesis and physiology on relative abundances and isotopic compositions of alkenones  

NASA Astrophysics Data System (ADS)

The number of double bonds in long-chain, unsaturated ketones (alkenones) produced by some members of the Haptophyceae is correlated with the ambient temperature at the time of synthesis. For these same organisms the depletion of carbon-13 in biosynthetic products relative to dissolved inorganic carbon is related directly to the specific growth rate and inversely to the concentration of dissolved carbon dioxide. This report summarizes issues relating to the physiology, metabolism, and biochemistry of alkenone producers and how they affect the abundances and isotopic compositions of alkenones. These considerations show that an understanding of cellular responses to parameters governing uptake of inorganic carbon (Ci), isotopic fractionation, growth under diverse nutrient conditions, and genetic variability, both in the field and in culture, is necessary for developing a conceptual understanding of the biological significance of the ?P and U37K' indices. Emiliana huxleyi is the best known alkenone producer and can serve as a model organism for these studies. This report identifies knowledge gaps and appropriate objectives for both field- and laboratory-based research.

GonzáLez, Elma L.; Riebesell, Ulf; Hayes, John M.; Laws, Edward A.

2001-01-01

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

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

Microsoft Academic Search

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

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

2000-01-01

69

Carbon Isotope and Isotopomer Fractionation in Dense Molecular Cloud Cores  

NASA Astrophysics Data System (ADS)

Observations of 13C species would be useful to investigate chemistry of carbon-bearing species. Recent observations in TMC-1 indicate that the abundances are different among carbon isotopomers of the same species. For instance, Takano et al. (1998) found that HCC13CN is more abundant than HC13CCN and H13CCCN, which indicates the three carbon atoms are not equivalent in HC_3N. Sakai et al. (2007; 2010) reported the abundance ratios of C13CS/13CCS and CCH/13CCH to be 4.2 and 1.6, respectively. Again, two carbon atoms are not equivalent in CCS and CCH. Sakai et al. (2007; 2010) discussed an origin of these anomalies and pointed out two possibilities: (i) fractionation during the formation of the species and (ii) rearrangements of the 13C position after the formation of molecules by isotopomer-exchange reactions. We construct a gas-grain chemical network model which includes carbon isotopes (12C and 13C) and isotopomers in order to investigate the evolution of molecular abundances, the carbon isotope ratios (12CX/13CX) and the isotopomer ratios (12C13CX/13C12CX) of CCH and CCS in dense molecular cores. We confirm that the isotope ratios of molecules, both in the gas phase and on grain surfaces, mostly depend on whether the species is formed from the carbon atom (ion) or the CO molecule; the isotope ratio is larger than the elemental abundance ratio of 12C/13C if the species is formed from the carbon atom, while the ratio is smaller if the species is formed from the CO molecule (cf. Langer et al. 1984). We successfully reproduce the observed C13CH/13CCH ratio in TMC-1 by considering the isotopomer-exchange reaction, 13CCH + H rightleftharpoons C13CH + H + 8.1 K. However, the C13CS/13CCS ratio remains lower than observed in TMC-1. We then assume the isotopomer-exchange reaction catalyzed by the H atom, 13CCS + H rightleftharpoons C13CS + H + 17.4 K. In the model with this reaction, the observed C13CS/13CCS, CCS/C13CS and CCS/13CCS ratios can be reproduced simultaneously.

Furuya, K.; Aikawa, Y.; Sakai, N.; Yamamoto, S.

2011-05-01

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 Isotope and Isotopomer Fractionation in Cold Dense Cloud Cores  

NASA Astrophysics Data System (ADS)

We construct a gas-grain chemical network model which includes carbon isotopes (12C and 13C) with an emphasis on isotopomer-exchange reactions. Temporal variations of molecular abundances, the carbon isotope ratios (12CX/13CX), and the isotopomer ratios (12C13CX/13C12CX) of CCH and CCS in cold dense cloud cores are investigated by numerical calculations. We confirm that the isotope ratios of molecules, both in the gas phase and grain surfaces, are significantly different depending on whether the molecule is formed from the carbon atom (ion) or the CO molecule. Molecules formed from carbon atoms have CX/13CX ratios greater than the elemental abundance ratio of [12C/13C]. On the other hand, molecules formed from CO molecules have CX/13CX ratios smaller than the [12C/13C] ratio. We reproduce the observed C13CH/13CCH ratio in TMC-1, if the isotopomer-exchange reaction, 13CCH + H \\rightleftharpoons C13CH + H + 8.1 K, proceeds with the forward rate coefficient kf > 10-11 cm3 s-1. However, the C13CS/13CCS ratio is lower than that observed in TMC-1. We then assume the isotopomer-exchange reaction catalyzed by the H atom, 13CCS + H \\rightleftharpoons C13CS + H + 17.4 K. In the model with this reaction, we reproduce the observed C13CS/13CCS, CCS/C13CS, and CCS/13CCS ratios simultaneously.

Furuya, Kenji; Aikawa, Yuri; Sakai, Nami; Yamamoto, Satoshi

2011-04-01

72

Carbon isotopic characterization of hydrophobic dissolved organic carbon in rainwater  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

73

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

NASA Astrophysics Data System (ADS)

Carbon-isotopic compositions of total carbonate, inoceramid carbonate, micritic carbonate, secondary cements, total organic carbon, and geoporphyrins have been measured in 76 different beds within a 17-m interval of a core through the Greenhorn Formation, an interbedded limestone and calcareous shale unit of Cretaceous age (Cenomanian-Turonian) from the Western Interior Seaway of North America. Results are considered in terms of variations in the processes of primary production (which led to the biosynthesis of the molecular precursors of the geoporphyrins) and in secondary processes (those mediating the transformation of primary organic material into sedimentary total organic carbon). It is shown that the porphyrin isotopic record reflects primary isotopic variations more closely than the TOC isotopic record, and that, in these sediments, TOC is enriched in 13C relative to its primary precursor by 0.6 to 2.8%.. This enrichment is attributed to isotope effects within the consumer foodweb and is associated with respiratory heterotrophy. Variations in this secondary enrichment are correlated with variations in the isotopic composition of marine carbonate. This correlation is attributed to effects of environmental changes on the marine foodweb. These may have included increased atmospheric oxygen associated with the Cenomanian-Turonian oceanic anoxic event. The isotopic fractionation associated with fixation of carbon by primary producers is observed to have varied by 1.5%. during the interval of deposition. It is suggested that this change is due to a variation in the makeup of the community of primary producers and/or to a decrease in the atmospheric abundance of CO 2 during the oceanic anoxic event.

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

1989-11-01

74

Production of carbon isotopes by laser separation  

NASA Astrophysics Data System (ADS)

Since the advent of lasers, these unique sources of highly intense and monochromatic radiation have been proposed as excellent tools to induce or catalyze chemical reactions. Due to the great interest to the problem of isotope production, investigation and application, the laser method of isotope separation has received the most attention worldwide and may be the first major commercial application of lasers to chemistry. Laser methods of isotope separation are based on high selectivity and power of laser sources of radiation. One of the most prominent method is based on the effect is isotope-selective multiphoton dissociation of molecules by IR-radiation (MLIS-method). This phenomena was discovered in Russia in 1974 and developed from scientific investigations to industrial scale production of 13C isotopes in collaboration between the Kurchatov Institute of Atomic Energy, TRINITI and Institute of Spectroscopy of RAS. Demonstration facilities for sulfur and carbon isotope separation with average productivity up to 2 g/h have been created as a result of collaboration and these systems are aimed at optimization of MLIS process and evaluation of its cost efficiency. Experiments show that laser produced isotopes are far cheaper as compared to any conventional technique. Results of basic scientific research, existing technological cooperation allow to start building a laser isotope separation plant. Light element isotopes produced there can answer a wide variety of demands in many technologies. These isotopes can be readily used in medicine, agriculture, environmental monitoring, etc.

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

2000-07-01

75

Abundances of Linear Carbon-Chain Molecules in Supernovae  

NASA Astrophysics Data System (ADS)

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

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

2001-03-01

76

Carbon and nitrogen abundance variations in globular cluster red giants  

NASA Astrophysics Data System (ADS)

This dissertation describes investigations into two of the persistent questions of elemental abundances in Galactic globular clusters: the phenomenon of deep mixing, observed through the progressive depletion of surface carbon abundance as stars evolve along the red giant branch, and abundance bimodality, a phenomenon observed only in globular clusters, in which a subset of stars in a given globular cluster have a distinctive pattern of elemental enhancements and depletions relative to the Solar pattern. The first chapter gives an introduction to the history of globular cluster abundance studies, with particular focus on low-resolution spectroscopy. For both deep mixing and abundance bimodality, the leading theoretical models and the data which support and challenge them are laid out. Each section ends with a description of presently-unanswered questions; these are the motivation for the various projects contained in this dissertation. The second chapter describes the use of molecular handstrengths for determining elemental abundances from low-resolution spectra, and introduces a new CH bandstrength index that is designed to be sensitive to carbon abundance and insensitive to nitrogen abundance in Pop. II red giants over a wide range of metallicity. Various CH indices defined elsewhere in the literature are also discussed, and are shown to have comparable accuracy to the new index only over a limited range of stellar properties. Carbon abundances determined using the new CH index are compared to literature abundances for a few stars, and general concordance with published abundances is found. The third chapter contains a large-scale application of the new CH index: a survey of present-day carbon abundances and calculated carbon depletion rates in bright red giants belonging to eleven Galactic globular clusters spanning the full metallicity range of halo globular clusters. Targets were selected with similar evolutionary states, were observed with one instrument on one telescope, and were analyzed in a uniform manner, to eliminate potential sources of significant systematic error. In keeping with present theoretical models of the deep mixing process, red giants in low-metallicity globular clusters undergo more rapid carbon depletion, and therefore more efficient deep mixing, than their high-metallicity counterparts. The fourth chapter investigates the apparent disappearance of abundance bimodality at low overall metallicity by determining carbon abundances along the full red giant branch of the globular cluster M53. I find that the mild variation of CN bandstrength observed is consistent with a mildly bimodal distribution in carbon abundance, in agreement with previous work on the subject. However, this result raises the question of whether all low- metallicity clusters should have only mild star-to-star abundance variations, or whether M53 is unusual in this regard. I discuss previous investigations into this same question using other low-metallicity globular clusters, and conclude that M53 may have milder abundance variations than the well-studied clusters M92 and M15. The fifth chapter describes a study of CN bandstrength behavior in high- metallicity star clusters. While abundance bimodality, observed from a bimodal CN bandstrength distribution and anticorrelated CN and CH bandstrengths, is universal among Galactic globular clusters, it is not observed in Galactic open clusters. It is also unobserved among stars in the general halo field, an observation which places strong constraints on the process which produces the abundance bimodality. I find that the high-metallicity disk globular clusters NGC 6356 and NGC 6528 show clear CN bimodality, indicating that they are more similar to other (low-metallicity) globular clusters than to the old open clusters NGC 188, NGC 2158, and NGC 7789. The final chapter summarizes the questions addressed and the conclusions reached in the various projects described in this dissertation. Possible future work, which would help to clarify or extend those results, is also briefly outlined.

Martell, Sarah L.

2008-06-01

77

On the isotopic composition of carbon in soil carbon dioxide  

Microsoft Academic Search

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

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

1991-01-01

78

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

EPA Science Inventory

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

79

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

Microsoft Academic Search

We analyze recently published nitrogen and hydrogen isotopic data to constrain the initial volatile abundances on Saturn’s giant moon Titan. The nitrogen data are interpreted in terms of a model of non-thermal escape processes that lead to enhancement in the heavier isotope. We show that these data do not, in fact, strongly constrain the abundance of nitrogen present in Titan’s

Jonathan I. Lunine; Yuk L. Yung; Ralph D. Lorenz

1999-01-01

80

Isotopic fronts in hydrothermally mineralized carbonate rocks  

Microsoft Academic Search

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

H. E. Frimmel

1992-01-01

81

Abundance of solar wind magnesium isotopes determined with WIND/MASS  

NASA Astrophysics Data System (ADS)

We present first results of the abundance ratios of Mg isotopes in the solar wind using the high resolution mass spectrometer on the WIND spacecraft. The isotopic composition of Mg in the solar wind is consistent with terrestrial values. Our preliminary result is 24Mg:25Mg:26Mg=(0.792+/-0.006):(0.095+/-0.005):(0.113+/-0.005).

Bochsler, P.; Gonin, M.; Sheldon, R. B.; Zurbuchen, Th.; Gloeckler, G.; Hamilton, D. C.; Collier, M. R.; Hovestadt, D.

1996-07-01

82

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

NASA Astrophysics Data System (ADS)

CO spectral line formation in the Sun has long been a source of consternation for solar physicists, as have the elemental abundances it seems to imply. We modelled solar CO line formation using a realistic, ab initio, time-dependent 3D radiative-hydrodynamic model atmosphere. Results were compared with space-based observations from the ATMOS space shuttle experiment. We employed weak 12C16O, 13C16O and 12C18O lines from the fundamental (? v = 1) and first overtone (? v = 2) bands to determine the solar carbon abundance, as well as the 12C/13C and 16O/18O isotopic ratios. A weighted solar carbon abundance of log?_C=8.39 ± 0.05 was found. We note with satisfaction that the derived abundance is identical to our recent 3D determination based on C i, [C i], C2 and CH lines, increasing our confidence in the accuracy of both results. Identical calculations were carried out using 1D models, but only the 3D model was able to produce abundance agreement between different CO lines and the other atomic and molecular diagnostics. Solar 12C/13C and 16O/18O ratios were measured as 86.8+3.9-3.7 (?13C = 30+46-44) and 479+29-28 (?18O = 41+67-59), respectively. These values may require current theories of solar system formation, such as the CO self-shielding hypothesis, to be revised. Excellent agreement was seen between observed and predicted weak CO line shapes, without invoking micro- or macroturbulence. Agreement breaks down for the strongest CO lines however, which are formed in very high atmospheric layers. Whilst the line asymmetries (bisectors) were reasonably well reproduced, line strengths predicted on the basis of C and O abundances from other diagnostics were weaker than observed. The simplest explanation is that temperatures are overestimated in the highest layers of the 3D simulation. Thus, our analysis supports the presence of a COmosphere above the traditional photospheric temperature minimum, with an average temperature of less than 4000 K. This shortcoming of the 3D model atmosphere is not surprising, given that it was never intended to properly describe such high layers.

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

2006-09-01

83

Carbon, nitrogen, and oxygen abundances in Sirius and Vega  

SciTech Connect

Carbon, nitrogen, and oxygen abundances are obtained from C I, N I, and O I high excitation permitted lines in the spectra of the standard A star Vega and the ''hot'' Am star Sirius. Vega has normal abundances. Relative to Vega, Sirius is C deficient by 0.60 dex, N enhanced by 0.22 dex, and O deficient by 0.27 dex.

Lambert, D.L.; Roby, S.W.; Bell, R.A.

1982-03-15

84

Coprecipitation and isotopic fractionation of boron in modern biogenic carbonates  

SciTech Connect

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

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

1991-10-01

85

Stable isotope analysis of carbon and nitrogen in angrites  

NASA Astrophysics Data System (ADS)

Angrites are a small group of ancient basaltic achondrites, notable for their unusual chemistry and extreme volatile depletion. No comprehensive study of indigenous light elements currently exists for the group. Measurement of the abundances and isotopic composition of carbon and nitrogen could provide information pertaining to the evolution of the angrite parent body. Bulk-sample stepped combustion analyses of five angrites and a glass separate from D'Orbigny were combined with earlier data and acid dissolution experiments of carbonates found in D'Orbigny to compile an inventory of indigenous carbon and nitrogen. Indigenous carbon combusted between 700 °C and 1200 °C, with abundances of 10-140 ppm and a mass-weighted ?13C of -25 to -20‰ with the exception of D'Orbigny (?13C approximately -5‰). Nitrogen was released at 850-1200 ºC, 1-20 ppm with a ?15N -3‰ to +4‰; again, D'Orbigny (?15N approximately +20 to +25‰) was an exception. We interpret these components as largely indigenous and decoupled; the carbon in graphitic or amorphous form, while the nitrogen is present as a dissolved component in the silicates. No relationship with the textural sub-classification of angrites is apparent. We suggest that the angrite parent body contains a reservoir of reduced carbon and thus may have undergone a change in redox conditions, although the timing and mechanism for this remain unclear.

Abernethy, F. A. J.; Verchovsky, A. B.; Starkey, N. A.; Anand, M.; Franchi, I. A.; Grady, Monica M.

2013-09-01

86

Relative isotopic abundances of zirconium in R Cygni and V Cancri  

SciTech Connect

The relative abundances of the isotopes of zirconium, determined from the isotopic splitting of the /sup 1/Pi-/sup 1/..sigma.. (0,1) band head of ZrO, have been found for the two S stars R Cygni and V Cancri to be /sup 90/Zr:/sup 91/Zr:/sup 92/Zr:/sup 93/Zr:/sup 94/Zr:/sup 96/Zr = 0.47:0.10: 0.17:0.06:0.20:0.00. The nonzero abundance of /sup 93/Zr indicates that nucleosynthesis has taken place in these two stars within the recent past. Assuming that all of the above isotopes with the exception of /sup 96/Zr have been synthesized in the s-process, these abundances are consistent with all of the most common scenarios of s-process nucleosynthesis. Subject headings: nucleosynthesis--stars: abundances--stars: individual--stars: S-type

Zook, A.C.

1985-02-01

87

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

88

Carbon isotopic exchange between dissolved inorganic and organic carbon  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

89

The carbon stable isotope composition of pollen  

Microsoft Academic Search

The d13C value of plant tissue is increasingly used to infer environmental and ecological conditions in modern and ancient environments. Isolation techniques and morphological descriptions have been established that characterize plant pollen for the greater part of the Phanerozoic eon. If the d13C value of fossil pollen could be used as an indicator of the carbon isotope composition of ancient

A. Hope Jahren

2004-01-01

90

High Carbon Abundances in IDPs: Hydrated Particles from Cometary Sources?  

Microsoft Academic Search

Hydrated interplanetary dust particles (IDPs) may comprise up to 50% of all collected IDPs [Schramm et al., 1990]. However, controversies still exist regarding their formation, history, and relationship to other primitive solar system materials [e.g., Germani et al., 1990; Thomas et al., 1990]. We have examined six hydrated IDPs and determined their mineralogy and bulk chemical compositions, including carbon abundances,

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

1992-01-01

91

Stable isotope abundances ( 13C, 15N) in collagen and soft tissues from Pleistocene mammals from Yakutia: Implications for the palaeobiology of the Mammoth Steppe  

Microsoft Academic Search

A suite of skeletons and frozen carcasses of upper Pleistocene mammals from Yakutia (Sakha Republic, Russia) has been analyzed for their stable isotopic abundances in carbon and nitrogen. Results from bone collagen and soft tissues have been compared. The samples studied belong to herbivorous (mammoths, woolly rhinoceros, horse, bison, muskox) and carnivorous (wolf, lion) species. Bone collagen of herbivorous and

Hervé Bocherens; Gilles Pacaud; Petr A. Lazarev; André Mariotti

1996-01-01

92

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

93

Carbon chain abundance in the diffuse interstellar medium.  

PubMed

Thanks to the mid-IR sensitivities of the ISO and IRTS orbiting spectrometers it is now possible to search the diffuse interstellar medium for heretofore inaccessible molecular emission. In view of the recent strong case for the presence of C(7-) (Kirkwood et al. 1998, Tulej et al. 1998),and the fact that carbon chains possess prominent infrared active modes in a very clean portion of the interstellar spectrum, we have analyzed the IRTS spectrum of the diffuse interstellar medium for the infrared signatures of these species. Theoretical and experimental infrared band frequencies and absolute intensities of many different carbon chain species are presented. These include cyanopolyynes, neutral and anionic linear carbon molecules, and neutral and ionized, even-numbered, hydrogenated carbon chains. We show that--as a family--these species have abundances in the diffuse ISM on the order of 10(-10) with respect to hydrogen, values consistent with their abundances in dense molecular clouds. Assuming an average length of 10 C atoms per C-chain implies that roughly a millionth of the cosmically available carbon is in the form of carbon chains and that carbon chains can account for a few percent of the visible to near-IR diffuse interstellar band (DIB) total equivalent width (not DIB number). PMID:11543325

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

1999-12-10

94

Deconvolving the Carbon Isotope Record  

NASA Astrophysics Data System (ADS)

The evolution of the whole-ocean ? 13C value, under an assumption of steady state with respect to mass, can be modeled as: \\[ {d \\over dt}\\delta_\\Sigma(t)+{\\delta_\\Sigma(t) \\over \\tau_C}={1 \\over \\tau_C}\\delta_F(t) \\] where ? ? is the whole-ocean ? 13C value, ? C is the residence time of carbon and a net instantaneous ? 13C forcing function is defined: \\[ \\delta_F=\\delta_i-f_{carb}\\Delta_{carb}-\\(1-f_{carb}\\)\\Delta_{org} \\] where ? i is the ? 13C value of carbon input (e.g. weathering and volcanism), fcarb is the fraction of carbon removed through burial of carbonates as opposed to organic carbon, and ? carb and ? org are the differences between ? ? and ? 13C values for buried carbonate and organic carbon. The solution to this differential equation is: \\[ \\delta_\\Sigma\\(t\\)={1 \\over \\tau_C}\\int_0^t{{\\delta_F\\(t^\\prime\\)}e^{\\(-{t-t^\\prime \\over \\tau_C}\\)}dt^\\prime} \\] which can be expressed as a convolution \\[ \\delta_\\Sigma\\(t\\)={1 \\over \\tau_C} {{\\delta_F\\(t^\\prime\\)} \\otimes e^{\\(-{t-t^\\prime \\over \\tau_C}\\)}} \\] revealing that the evolution of the whole ocean ? 13C value is determined by the instantaneous ? 13C forcing (? F) subjected to a causal (i.e. phase-shifting) low-pass filter whose frequency response is dependent only on the carbon residence time. One consequence of this observation is that variance in ? 13C records should be concentrated at wavelengths >0.1 m.y., thereby explaining the persistent appearance of cyclicity dependent on orbital eccentricity ( ˜0.1~and ˜0.4 m.y.~periods) in ? 13C records. I demonstrate that an assumption of non-linear forcing of fcarb by orbitally-forced variations in insolation can explain most of the structure of high-resolution ? 13C records throughout the Cenozoic. A second consequence is that ? C and ? F should be separable by numerical manipulation of ? 13C records. Two applications are 1) estimation of the residence time of carbon at various times in the past and 2) investigation of changes in the instantaneous forcing through time.

Cramer, B. S.

2003-12-01

95

A Modern Analogue for Proterozoic Inverse Carbon Isotope Signatures  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

96

Oxygen and Carbon Isotope Ratios in CO2on Mars  

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

97

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

98

Carbon isotopic composition of individual Precambrian microfossils  

NASA Astrophysics Data System (ADS)

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

House, Christopher H.; Schopf, J. William; McKeegan, Kevin D.; Coath, Christopher D.; Harrison, T. Mark; Stetter, Karl O.

2000-08-01

99

Relative isotopic abundances of zirconium in R Cygni and V CANCRI  

Microsoft Academic Search

The relative abundances of the isotopes of Zr in the S stars R Cyg and V Cnc are calculated by determining isotopic splitting at the head of the 1Pi - 1Sigma (0, 1) band of ZrO in spectra obtained at resolution 30 pm on hypersensitized 127-O4 plates with a Varo tube on the 51-cm camera at the Coude focus of

A. C. Zook

1985-01-01

100

Measurement of plutonium and uranium isotopic abundances by gamma-ray spectrometry  

SciTech Connect

The isotopic composition of plutonium and uranium is needed for purposes of sample confirmation, or for interpreting results from calorimeters or neutron-coincidence measurement instruments to determine nuclear material mass. The authors have developed measurement methods and computer codes utilizing high-resolution gamma-ray spectrometry to measure the relative isotopic abundances of plutonium and uranium in various forms nondestructively. The computer codes, known as MGA and MGAU, have unique analysis methodologies that the authors briefly describe in this paper.

Ruhter, W.D. [Lawrence Livermore National Lab., CA (United States); Gunnink, R. [Gunnink (Ray), Fremont, CA (United States)

1996-02-01

101

Hyperfiltration-induced fractionation of carbon isotopes  

SciTech Connect

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

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

1987-05-01

102

Noble gas isotopic compositions of deep carbonate rocks from the Tarim Basin  

Microsoft Academic Search

Abundances and isotopic compositions of noble gases (He, Ne, Ar, Kr) with various existence states in carbonate rocks from\\u000a the Tacan1 Well have been investigated by means of the stepwise heating technique. The elemental abundance patterns of noble\\u000a gases in the samples show the enrichment of heavy noble gases and depletion of 20Ne relative to the atmosphere, which are designated

Shixin Zhou; Xianren Ye

2002-01-01

103

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

PubMed

Chemical, biological, and physical processes lead to distinctive "isotopic signatures" in biological materials that allow tracing of the origins of organic substances. Isotopic variation has been extensively used by plant physiological ecologists and by paleontologists, and recently ecologists have adopted the use of stable isotopes to measure ecosystem patterns and processes. To date, animal physiological ecologists have made minimal use of naturally occurring stable isotopes as tracers. Here we provide a review of the current and potential uses of naturally occurring stable isotopes in animal physiological ecology. We outline the physical and biological processes that lead to variation in isotopic abundance in plants and animals. We summarize current uses in animal physiological ecology (diet reconstruction and animal movement patterns), and suggest areas of research where the use of stable isotopes can be fruitful (protein balance and turnover and the allocation of dietary nutrients). We argue that animal physiological ecologists can benefit from including the measurement of naturally occurring stable isotopes in their battery of techniques. We also argue that animal physiologists can make an important contribution to the emerging field of stable isotopes in biology by testing experimentally the plethora of assumptions upon which the techniques rely. PMID:9683412

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

1998-03-01

104

Isotope fractionations in the terrestrial carbon cycle: a brief overview.  

PubMed

The bias in favour of isotopically light carbon inherent in biological carbon fixation has brought about an isotopic disproportionation of primordial (mantle-derived) carbon on a global scale, causing an enrichment of 12C in reduced (biogenic) carbon and a concomitant accumulation of the heavy complement (13C) in the residual oxidized (inorganic) carbon pool. As a result, the terrestrial carbon cycle has gone bipartite, comprising an organic branch of isotopically light carbon, and an inorganic branch made up of 13C-enriched carbon (mostly in the form of carbonate). The isotopic disparity between the two principal terrestrial carbon species can be traced back over 3.8 Gyr of Earth history, attesting to a biological modulation of the carbon cycle since the time of formation of the oldest sediments. PMID:11539258

Schidlowski, M

1995-03-01

105

Studies of Isotopic Abundances through Gamma-Ray Lines  

SciTech Connect

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

Diehl, Roland [Max Planck Institut fuer extraterrestrische Physik, D-85748 Garching (Germany)

2006-07-12

106

Abundances of light isotopes in galactic cosmic rays and the interstellar gas density  

Microsoft Academic Search

The fluxes of the light isotopes in the galactic cosmic rays are calculated in the energy range from 10 MeV to 5 GeV. The mean amount of matter traversed is taken to increase with decreasing energy, and various forms of the source spectrum are assumed. It is shown that it is possible to reconcile all observed abundance ratios including the

N. J. Westergaard

1979-01-01

107

Relative isotopic abundances of zirconium in R Cygni and V CANCRI  

NASA Astrophysics Data System (ADS)

The relative abundances of the isotopes of Zr in the S stars R Cyg and V Cnc are calculated by determining isotopic splitting at the head of the 1Pi - 1Sigma (0, 1) band of ZrO in spectra obtained at resolution 30 pm on hypersensitized 127-O4 plates with a Varo tube on the 51-cm camera at the Coude focus of the 3-m telescope at Lick Observatory. The data reduction techniques and the fit to the model synthetic spectra of Kurucz (1970) are described, and the ratio (Zr-90):(Zr-91):(Zr-92):(Zr-93):(Zr-94):(Zr-96) is given as 47:10:17:6:20:00 percent. The presence of the long-lived unstable isotope Zr-93 is interpreted as evidence for recent nucleosynthesis, and the abundances found are shown to be consistent with s-process nucleosynthesis.

Zook, A. C.

1985-02-01

108

Use of carbon isotope composition in monitoring environmental changes  

Microsoft Academic Search

In this work we will discuss the suitability of carbon isotope analysis in plants for the assessment of environmental changes and their effects on crops and natural systems. For C3 species, carbon isotope composition (?13C) of plant tissues constitutes an integrated record of the miscellaneous climatic and physiological factors that affect carbon assimilation and\\/or stomatal conductance. Here we present a

J. P. Ferrio; J. Voltas; J. L. Araus

2003-01-01

109

Oxygen Isotope Composition of Stratospheric Carbon Dioxide  

NASA Astrophysics Data System (ADS)

In the stratosphere, carbon dioxide gradually obtains an anomalous oxygen isotope enrichment, which generally increases with altitude. This enrichment has been related to transfer of anomalously fractionated oxygen from ozone to CO2 via a short-lived CO3* complex, which CO2 forms with O(1D) produced in the photolysis of ozone, al- though the precise transfer mechanism is still being debated. We present CO2 and O3 isotope measurements from 8 stratospheric balloon flights at two latitudes that provide now a complete oxygen isotope analysis of both gases. The results show an unambigu- ous, very tight correlation between 17O and 18O in CO2, which passes through the tropospheric values at the tropopause. The large ratio 17O/18O of 1.7 shows a faster transfer of 17 O than of 18 O into CO2 and establishes a standard throughout the lower and middle stratosphere. Ozone isotope transfer can now be treated in models with re- liable atmospheric data. Additional laboratory exchange experiments are being carried out to investigate the oxygen transfer process in detail.

Röckmann, T.; Brenninkmeijer, C. A. M.; Assonov, S. S.; Lämmerzahl, P.; Krankowsky, D.; Mauersberger, K.

110

Mg Isotopic Compositions of Modern Marine Carbonates  

NASA Astrophysics Data System (ADS)

We have used a MC-ICP-MS to measure the isotopic composition of magnesium in a number of samples of modern marine carbonate. Due to the large mass difference between 26Mg and 24Mg (similar to that between 13C and 12C), there is potential for mass fractionation during geologic and biologic processes that may make this isotope system useful for geochemical studies. These samples are from the study of Hemming and Hanson (1992, GCA 56: 537-543). The carbonate minerals analyzed include aragonite, low-Mg calcite, and high-Mg calcite. The samples include corals, echinoderms, ooids, etc., from subtropical to Antarctic settings. Mg purification was accomplished by ion-exchange chromatography, using Bio-Rad AG50W-X12 resin on which greater than 99 percent recovery of Mg is achieved. Samples were introduced into the MC-ICP-MS (VG Axiom) using a Cetac MCN-6000 nebuliser. We use a standard-sample-standard bracketing technique, and samples are analysed at least three times. For lab standards we find that the reproducibility on the 26Mg/24Mg to be about ñ 0.12 permil (2 s.d.). We monitored our separated samples for Na and Ca, as we have found that high Ca/Mg and Na/Mg produce variable magnesium isotopic fractionation during mass spectrometry due to as yet unclear matrix effects. We have normalized our results to our measured values for seawater. We observed a d26Mg(s.w.) range of -1.4 to -2.4 permil in our modern carbonate samples relative to present day seawater. Due to the long residence time of Mg in the oceans (ca. 50 my), this must be due to kinetic or biologic effects. Our d25Mg(s.w.) variations as a function of d26Mg(s.w.) plot along the terrestrial fractionation trend. With an average d26Mg(s.w.) of ca. +0.5 permil in all samples of mantle lithologies and mantle-derived igneous rocks (Bizzarro et al., Goldschmidt abs., 2003), we can assume that the Mg isotopic composition of Earth's river water lies between ca. -2.4 and +0.5 permil (relative to seawater). The actual value will vary according to the d26Mg of provenance carbonates and silicic crust, and the relative rates of chemical weathering and physical denudation. It is unlikely therefore that the Mg isotopic composition of seawater has remained constant through time.

Krogstad, E.; Bizzarro, M.; Hemming, N.

2003-12-01

111

Isotopes and atomic absorption spectrometry. Computer simulations, Part I: Evaluation of the simulation model using the flame atomic absorption determination of lithium isotope abundances  

Microsoft Academic Search

An evaluation of a computer model developed to calculate absorbances involving multi-isotopic elements is presented. With the use of the model, an independently peformed flame aotmic absorption experiment to determine isotope abundances of lithium is simulated. The necessity of having accurate values of the critical model parameters (damping constant, isotope shift, fine structure separation, and collisional shift) is demonstrated. The

K. A. S. Pathiratne; R. J. Lovett

1987-01-01

112

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

113

Biogenic vs. Abiogenic Isotope Signatures of Reduced Carbon Compounds: A Lesson from Hydrothermal Synthesis Experiments  

Microsoft Academic Search

With growing interest in and demonstrated cases of inorganic hydrothermal synthesis of reduced or organic carbon compounds from CO and COâ, it becomes crucial to establish geochemical criteria to distinguish reduced\\/organic carbon compounds of abiogenic origin from those of biogenic origin with overwhelming abundances on the surface and in subsurface of the Earth. Chemical and isotopic compositions, particularly ¹³C\\/¹²C ratios,

J. Horita; D. E. Allen; M. E. Berndt; W. E. Seyfried Jr.

2001-01-01

114

[Fractionation of carbon isotopes in the cell with stationary currents of carbon substrates].  

PubMed

A model of isotope fractionation of carbon with stationary current of carbon substrates was studied. The model is shown to give a satisfactory description of fractionation of carbon isotopes in heterotrophs and to be insufficient for describing isotope fractionation in autotrophs. PMID:7126666

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

115

Isotopic Abundances of Eu, Ba, and Sm in Metal-Poor Stars  

NASA Astrophysics Data System (ADS)

We have examined the isotopic mix of the heavy neutron (n)-capture elements Eu, Ba, and Sm in three metal-poor stars with different enrichment histories. Isotopic abundances are more fundamental than elemental abundances as probes of the contributions from the rapid (r) and slow (s) nucleosynthesis reactions. We use our isotopic abundances in conjunction with elemental abundances of many heavy n-capture elements to constrain the nucleosynthetic history of these metal-poor stars. HD 122563 is a very metal-poor giant that has a clear underabundance of n-capture elements ([Fe/H]=-2.7, [Eu/Fe]=-0.5, [Ba/Fe]=-1.0). HD 175305 is a metal-poor giant that is enriched in r-process material ([Fe/H]=-1.5, [Eu/Fe]=+0.5). HD 196944 is a very metal-poor giant star that is enriched in s-process material ([Fe/H]=-2.3, [Ba/Fe]=+1.1). We have acquired new high-resolution (R 130,000) and high-S/N (S/N 160-1000) observations of these three stars with the 2.7m Harlan J. Smith Telescope at McDonald Observatory using the 2dcoude spectrograph. We present our measurements of the isotopic abundances of Eu, Ba, and Sm in these three stars. This research has been supported by U.S. National Science Foundation grants AST 03-07495 and AST 06-07708.

Roederer, Ian U.; Sneden, C.; Lawler, J. E.; Sobeck, J. S.; Pilachowski, C. A.; Cowan, J. J.

2006-12-01

116

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

117

Investigating the Formation of Pedogenic Carbonate Using Stable Isotopes  

Microsoft Academic Search

The stable isotope composition of pedogenic carbonate has been used as a paleoenvironmental proxy because it is thought to form in isotopic equilibrium with soil CO2 and soil water, which are influenced by vegetation type and atmospheric circulation patterns, respectively. However, the isotopic composition of soil CO2 and soil water change seasonally and it is not known what portion of

D. O. Breecker; Z. D. Sharp; L. McFadden

2006-01-01

118

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

119

Carbon isotope ratios in giant stars of the old galactic cluster NGC 7789  

NASA Astrophysics Data System (ADS)

Carbon isotope ratios have been derived for seven giant stars in the old open cluster NGC 7789. High-resolution, high signal-to-noise spectra of the CN red system bands in these stars were obtained with the KPNO 4 m Cassegrain echelle spectrograph and a CCD camera. (C-13)N features were detected easily in all cluster stars, and isotope ratios in the range C-12/C-13 = 10-30 were derived. The isotope ratios of most stars are normal for K giants possessing convective envelopes and show no correlations with effective temperatures and with lithium abundances. However, one cluster star has both very high lithium and the lowest carbon isotope ratio. It is speculated that this star either is an asymptotic giant branch star or a weak G-band star.

Sneden, C.; Pilachowski, C. A.

1986-02-01

120

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

121

Biological control of calcium isotopic abundances in the global calcium cycle  

NASA Astrophysics Data System (ADS)

Measurements of 44 Ca/ 40 Ca, expressed as 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 in 44 Ca, measured with the double spike technique to a precision of ±0.15 . Volcanic rocks, including basalt and rhyolite, show little variability and cluster near 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 44 Ca about 1.0 . lower than seawater; this fractionation causes seawater to be enriched in heavy calcium ( 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.

Skulan, Joseph; Depaolo, Donald J.; Owens, Thomas L.

1997-06-01

122

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

1997-06-01

123

Carbon isotopic variations in fluid?deposited graphite: evidence for multicomponent Rayleigh isotopic fractionation  

Microsoft Academic Search

Carbon isotopic composition of fluid?deposited graphite in a metamorphic terrain can be used as a tracer for sources of fluids, their compositions and temperatures of graphitization. However, ?C of graphite almost always shows a large spread, mostly because of isotope fractionation during precipitation, making it necessary to understand these processes. In this work, a novel quantitative approach, involving Rayleigh isotope

Jyotiranjan S. Ray

2009-01-01

124

Sources of iron-formations in the archean isua and malene supracrustals, West Greenland: Evidence from LaCe and sm-nd isotopic data and REE abundances  

Microsoft Academic Search

Isotopic ratios of Ce and Nd and abundances of rare earth elements (REEs) and Ba are reported for the iron-formations of the Archean Isua and Malene supracrustals, West Greenland. It is suggested that the Sm-Nd system of the Isua iron-formations was disturbed by metamorphisms at 1680 Ma (oxide facies iron-formation) and 2740 Ma (carbonate facies iron-formation). However, the Malene iron-formation

H. Shimizu; N. Umemoto; A. Masuda; P. W. U. Appel

1990-01-01

125

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

Microsoft Academic Search

Through investigations of the isotope composition of carbon of various generations and carbonates from marbles, skarns, and nested and vein scheelite orebodies, the probable source of carbon of these carbonates has been established as a mixture of sedimentary carbonates, carbon dioxide with carbonic acid that was formed by oxidation of the organic matter from sedimentary terrane (..delta..C¹³ - 0.05 to

A. F. Korzhinskiy; G. P. Mamchur; O. A. Yarynych

1980-01-01

126

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

NASA Astrophysics Data System (ADS)

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

Dreibus, G.; Jagoutz, E.

127

Boron isotopic composition and concentration in modern marine carbonates  

Microsoft Academic Search

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

N. G. Hemming; G. N. Hanson

1992-01-01

128

Tritium isotope effects on carbon-13 NMR chemical shifts  

SciTech Connect

Deuterium isotope effects on carbon-13 NMR chemical shifts can be useful in making spectral assignments, and they are also interesting in their own right. The authors report here the first determination of tritium isotope effects on carbon-13 NMR spectra. 11 references, 2 tables.

Arrowsmith, C.H.; Baitzer, L.; Kresge, A.J.; Powell, M.F.; Tang, Y.S.

1986-03-19

129

Multiple Group Analysis (MGA): A gamma-ray spectrum analysis code for determining plutonium isotopic abundances  

SciTech Connect

MGA calculates relative isotopic abundances of plutonium and other actinides in a sample. The code performs its analysis using data from a gamma-ray spectrum of the sample taken with a germanium detector. This volume describes the structure of the program and the procedures used for measuring samples and analyzing the spectra. It is assumed that the user is familiar with standard practices and equipment used in gamma-ray spectrometry.

Gunnink, R.; Ruhter, W.D.

1990-09-01

130

Improve accuracy and sensibility in glycan structure prediction by matching glycan isotope abundance.  

PubMed

Mass Spectrometry (MS) is a powerful technique for the determination of glycan structures and is capable of providing qualitative and quantitative information. Recent development in computational method offers an opportunity to use glycan structure databases and de novo algorithms for extracting valuable information from MS or MS/MS data. However, detecting low-intensity peaks that are buried in noisy data sets is still a challenge and an algorithm for accurate prediction and annotation of glycan structures from MS data is highly desirable. The present study describes a novel algorithm for glycan structure prediction by matching glycan isotope abundance (mGIA), which takes isotope masses, abundances, and spacing into account. We constructed a comprehensive database containing 808 glycan compositions and their corresponding isotope abundance. Unlike most previously reported methods, not only did we take into count the m/z values of the peaks but also their corresponding logarithmic Euclidean distance of the calculated and detected isotope vectors. Evaluation against a linear classifier, obtained by training mGIA algorithm with datasets of three different human tissue samples from Consortium for Functional Glycomics (CFG) in association with Support Vector Machine (SVM), was proposed to improve the accuracy of automatic glycan structure annotation. In addition, an effective data preprocessing procedure, including baseline subtraction, smoothing, peak centroiding and composition matching for extracting correct isotope profiles from MS data was incorporated. The algorithm was validated by analyzing the mouse kidney MS data from CFG, resulting in the identification of 6 more glycan compositions than the previous annotation and significant improvement of detection of weaker peaks compared with the algorithm previously reported. PMID:22882827

Xu, Guang; Liu, Xin; Liu, Qing Yan; Zhou, Yanhong; Li, Jianjun

2012-07-16

131

Molybdenum isotopic composition of modern and Carboniferous carbonates  

Microsoft Academic Search

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

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

2009-01-01

132

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

Microsoft Academic Search

Secular variation in microbial carbonate abundance may be reflected by stromatolite morphotype diversity and reefal microbial carbonate abundance. These datasets reveal long-term changes over the past 3000 Myr that include a peak of abundance 1250 Myr ago, Late Proterozoic decline, Cambrian resurgence, and fluctuating decline during the remainder of the Phanerozoic. It is conceivable that Proterozoic metazoan diversification coincided with

Robert Riding

2006-01-01

133

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

134

Absolute and Relative Isotope Abundances Measured by Tunable Diode Laser Spectroscopy  

NASA Astrophysics Data System (ADS)

The potential for measuring absolute and relative isotope abundances by high resolution spectroscopy with tunable diode lasers as sources was studied. In order to achieve the sensitivity necessary to determine the absolute abundances of molecules containing long-lived radionuclides such as ('14)C an ('129)I, a resonant spectrophone based on the photoacoustic effect was used for detection. For safety, NH(,3) was used as a sample with air as a buffer gas when characterizing the performance of the TDL-spectrophone system. Frequency modulation of the TDL was employed. The optimum operating pressure was found to be 6.6 kPa(50 Torr). Substitution of Kr as a buffer gas yielded a fourfold increase in signal. It is estimated that with currently available TDLs a photoacoustic spectrometer should be capable of detecting ('14)CO(,2) and CH('129)I at the levels present in nuclear reactor containment gases. An isotope shift of CH(,3)('129) I relative to CH(,3)('127)I in the (nu)(,6) band of (0.0135 (+OR-) 0.0006) cm('-1) was measured by TDL linear absorption spectroscopy. To perform relative isotope abundance measurements a TDL was tuned over two adjacent, but well-resolved, rotation -vibration absorption lines, one of each isotopic species, while the transmitted radiation was monitored with a HgCdTe detector. The P(26) line of the (nu)(,1) band of N(,2)('18)O at 1225.3671 cm('-1) and the P(63) line of the (nu)(,1) band of N(,2)('16)O at 1225.4879 cm('-1) were chosen, for their line strength ratio is inversely proportional to the ratio of their natural abundances, and thereby yielded approximately equal absorbance for each isotopic species. A double-beam, single-detector spectrometer with wavelength modulation to minimize the effects of laser power and cell temperature fluctuations, has been adapted for use with a TDL. After samples of known ('18)O enrichment were used to calibrate the spectrometer, the (delta)('18)O of tropospheric N(,2)O was measured to be (8.05 (+OR-) 0.17)('o)/oo relative to a laboratory standard, or approximately 42('o)/oo relative to standard mean ocean water. After 190 days at 24(DEGREES)C no oxygen isotope exchange was observed between N(,2)('16)O and H(,2)('18)O.

Tucker, George Franklin

135

Simulation of carbon isotope discrimination of the terrestrial biosphere  

Microsoft Academic Search

We introduce a multistage model of carbon isotope discrimination during C3 photosynthesis and global maps of C3\\/C4 plant ratios to an ecophysiological model of the terrestrial biosphere (SiB2) in order to predict the carbon isotope ratios of terrestrial plant carbon globally at a 1° resolution. The model is driven by observed meteorology from the European Centre for Medium-Range Weather Forecasts

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

2005-01-01

136

Mass transfer and carbon isotope evolution in natural water systems  

USGS Publications Warehouse

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

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

1978-01-01

137

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

138

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 palehydrology 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 decreasing {sup 13}C with altitude and reduced {sup 13}C during spring. 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.

1994-12-31

139

Intramolecular carbon isotope distribution of acetic acid in vinegar.  

PubMed

Compound-specific carbon isotope analysis of acetic acid is useful for origin discrimination and quality control of vinegar. Intramolecular carbon isotope distributions, which are each carbon isotope ratios of the methyl and carboxyl carbons in the acetic acid molecule, may be required to obtain more detailed information to discriminate such origin. In this study, improved gas chromatography-pyrolysis-gas chromatography-combustion-isotope ratio mass spectrometry (GC-Py-GC-C-IRMS) combined with headspace solid-phase microextraction (HS-SPME) was used to measure the intramolecular carbon isotope distributions of acetic acid in 14 Japanese vinegars. The results demonstrated that the methyl carbons of acetic acid molecules in vinegars produced from plants were mostly isotopically depleted in (13)C relative to the carboxyl carbon. Moreover, isotopic differences (?(13)C(carboxyl) - ?(13)C(methyl)) had a wide range from -0.3 to 18.2‰, and these values differed among botanical origins, C3, C4, and CAM plants. PMID:21830825

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

2011-08-18

140

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

141

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

142

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

143

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

Microsoft Academic Search

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.

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

2007-01-01

144

Sr and Nd isotope ratios and REE abundances of moraines in the mountain areas surrounding the Taklimakan Desert, NW China  

Microsoft Academic Search

The first systematic data of Sr and Nd isotopic ratios, REE abundances, major element and mineral compositions are reported for the Chinese moraines from the western Kunlun Mts. and southern and north- ern flanks of the Tianshan Mts. and soils from the Tibet Plateau. This study was conducted in order to characterize the isotopic and geochemical features of these moraines

QING CHANG; TAKASHI MISHIMA; SADAYO YABUKI; YOSHIO TAKAHASHI; HIROSHI SHIMIZU

145

Stepwise atmospheric carbon-isotope excursion during the Toarcian Oceanic Anoxic Event (Early Jurassic, Polish Basin)  

NASA Astrophysics Data System (ADS)

During the Mesozoic (250-64 Ma) intervals of about 0.5 Myr were subject to severe environmental changes, including high sea-surface temperature and very low oxygen content of marine water. These Oceanic Anoxic Events, or OAEs, occurred simultaneously with profound disturbance to the carbon cycle. The carbon-isotope anomaly in the Early Jurassic that marks the Toarcian Oceanic Anoxic Event (T-OAE) at ~ 182 Ma is characterized in marine sections by a series of dramatic steps towards lighter values. Herein we present new carbon-isotope data from terrestrial organic matter (phytoclast separates), collected through a Late Pliensbachian-Middle Toarcian coastal and marginal marine succession in the Polish Basin, a setting where hinterland climate and sea-level change are well recorded. The results show that the shift to light carbon-isotope values in the woody organic matter, and therefore also in atmospheric carbon dioxide, similarly occurred in major steps. The steps are here correlated with those identified from marine organic matter, where they have previously been attributed to 100 kyr eccentricity forcing of climate. The results provide strong support for orbitally and climatically controlled release of isotopically light carbon from gas hydrates into the ocean-atmosphere system in a series of rapid bursts. Additionally, a link between the carbon-isotope steps and shoreline movements can be demonstrated. Individual peaks of the negative excursion are mostly associated with facies indicative of sea-level rise (flooding surfaces). However, at the same time inferred higher atmospheric carbon-dioxide content may be expected to have resulted in increased rainfall and temperature, leading to accelerated weathering and erosion, and consequently increased sediment supply, progradation and regression, causing some mismatches between isotope shifts and inferred sea-level changes. Enhanced abundance of megaspores derived from hydrophilic plant groups, and marked increase in kaolinite, are coincident with the overall development of the negative isotope excursion. The combined data suggest that each 100-kyr cycle in carbon-isotope values was characterized by increasingly severe palaeoclimatic change, culminating in extremely hot and humid conditions co-incident with the peak of the final most negative carbon-isotope excursion. The chemostratigraphic correlation allows very precise dating of the Late Pliensbachian-Middle Toarcian coastal and marginal marine sedimentary succession in the Polish Basin.

Hesselbo, Stephen P.; Pie?kowski, Grzegorz

2011-01-01

146

Isotopic exchange of carbon-bound hydrogen over geologic timescales  

NASA Astrophysics Data System (ADS)

The increasing popularity of compound-specific hydrogen isotope (D/H) analyses for investigating sedimentary organic matter raises numerous questions about the exchange of carbon-bound hydrogen over geologic timescales. Important questions include the rates of isotopic exchange, methods for diagnosing exchange in ancient samples, and the isotopic consequences of that exchange. This article provides a review of relevant literature data along with new data from several pilot studies to investigate such issues. Published experimental estimates of exchange rates between organic hydrogen and water indicate that at warm temperatures (50-100°C) exchange likely occurs on timescales of 10 4 to 10 8 yr. Incubation experiments using organic compounds and D-enriched water, combined with compound-specific D/H analyses, provide a new and highly sensitive method for measuring exchange at low temperatures. Comparison of ?D values for isoprenoid and n-alkyl carbon skeletons in sedimentary organic matter provides no evidence for exchange in young (<1 Ma), cool sediments, but strong evidence for exchange in ancient (>350 Ma) rocks. Specific rates of exchange are probably influenced by the nature and abundance of organic matter, pore-water chemistry, the presence of catalytic mineral surfaces, and perhaps even enzymatic activity. Estimates of equilibrium fractionation factors between organic H and water indicate that typical lipids will be depleted in D relative to water by ˜75 to 140‰ at equilibrium (30°C). Thus large differences in ?D between organic molecules and water cannot be unambiguously interpreted as evidence against hydrogen exchange. A better approach may be to use changes in stereochemistry as a proxy for hydrogen exchange. For example, estimated rates of H exchange in pristane are similar to predicted rates for stereochemical inversion in steranes and hopanes. The isotopic consequences of this exchange remain in question. Incubations of cholestene with D 2O indicate that the number of D atoms incorporated during structural rearrangements can be far less than the number of C-H bonds that are broken. Sample calculations indicate that, for steranes in immature sediments, the D/H ratio imparted by biosynthesis may be largely preserved in spite of significant structural changes.

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

2004-04-01

147

Reconstructing grassland vegetation and paleotemperatures using carbon isotope ratios of bison tooth enamel  

Microsoft Academic Search

Carbon isotope ratios (delta13C values) of herbivores reflect the delta13C values of dietary plants, and the delta13C values of grazers (animals that consume >90% grass) reflect the local abundance of C3 versus C4 grasses. Because grassland C3\\/C4 ratios correlate with climate, the delta13C of fossil grazers may serve as a proxy for reconstructing paleoclimates and paleovegetation patterns. However, the accuracy

Kathryn A. Hoppe; Adina Paytan; Page Chamberlain

2006-01-01

148

Developing a methodology for carbon isotope analysis of lacustrine diatoms.  

PubMed

Stable isotope analysis of sedimentary carbon in lakes can help reveal changes in terrestrial and aquatic carbon cycles. A method based on a single, photosynthetic organism, where host effects are minimised, should offer more precision than carbon isotope studies of bulk lake sediments. Here we report the development of a systematic method for use on fossil lacustrine diatom frustules, adapted from previous studies in marine environments. A step-wise cleaning experiment on diatomaceous lake sediments from Lake Challa, near Mount Kilimanjaro, was made to demonstrate the necessary treatment stages to remove external sedimentary carbon. Changes in soluble carbon compounds during these cleaning experiments were measured using gas chromatography/mass spectrometry (GC/MS). The mass spectrometry methods were refined to measure the small percentage of carbon in these samples and details of these methods are presented. Samples of cleaned diatoms containing <1% carbon yielded robust results. Carbon isotope analyses of diatom samples containing different species mixtures were performed and suggested that differences existed, although the effects lay within current experimental error and require further work. Unlike what was found in work on oxygen and silicon isotopes from diatom frustules, mineral contamination had no discernible impact on the diatom carbon isotope ratios from these sediments. The range of values found in the lakes investigated thus far can be interpreted with reference to the supply and nature of carbon from the catchment as well as to the demand generated from lake primary productivity. PMID:21594931

Hurrell, Elizabeth R; Barker, Philip A; Leng, Melanie J; Vane, Christopher H; Wynn, Peter; Kendrick, Chris P; Verschuren, Dirk; Street-Perrott, F Alayne

2011-06-15

149

Low temperature Rosseland opacities with varied abundances of carbon and nitrogen  

NASA Astrophysics Data System (ADS)

Context: With certain assumptions, radiative energy transport can be modelled by the diffusion approximation. In this case, the Rosseland mean opacity coefficient characterises the interaction between radiation and matter. The opacity data are usually available in pre-tabulated form, and in the generation of the data one assumes a distinct heavy element mixture, which is usually a scaled solar one. Therefore, presently available data is unable to cover the full parameter range of some astrophysical problems, in which the chemical composition of the medium being considered varies. Aims: 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. Methods: 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 12C and 14N 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. Results: 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. Conclusions: In typical astrophysical applications, it is indispensable to take into account opacity variations due to chemistry changes. In this respect, the new data is superior to previous compilations, but is, however, still subject to uncertainties. Database of Rosseland opacities is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/494/403

Lederer, M. T.; Aringer, B.

2009-01-01

150

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

PubMed

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

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

2012-08-23

151

Carbon Isotope Fractionation of Benzene and Toluene by Progressive Evaporation  

NASA Astrophysics Data System (ADS)

Evaporation experiments were performed to investigate carbon isotope fractionation of benzene and toluene during progressive evaporation at room temperature. Considerable carbon isotope fractionation occurred during evaporative enrichment of benzene and toluene. Carbon isotope compositions of residual compounds increased exponentially with increasing evaporation. This result was compatible with the direction of isotopic changes associated with both microbial degradation and natural evaporation previously observed in oil fields, but was not consistent with previous equilibrium volatilization findings. Although the enrichment factors obtained from non-equilibrium evaporation were much smaller than those from microbial degradation, our data indicated that carbon isotope fractionation of benzene and toluene caused by microbial degradation can be complicated by kinetic evaporation effects if both processes occur together in unsaturated zones. However, in the natural environment, carbon isotope fractionation of BTEXs by evaporation can be virtually overwhelmed by microbial degradation because enrichment factors of BTEXs are much lower in non- equilibrium evaporation than in microbial degradation. Consequently, our data are fundamental for evaluating the carbon isotope fractionation of benzene and toluene by evaporation and for tracking their fate and transport mechanisms in subsurface environments.

Lee, K.; Han, S.; Shin, W.

2008-12-01

152

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

153

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

PubMed

Volume mixing and isotope ratios secured with repeated atmospheric measurements taken with the Sample Analysis at Mars instrument suite on the Curiosity rover are: carbon dioxide (CO2), 0.960(±0.007); argon-40 ((40)Ar), 0.0193(±0.0001); nitrogen (N2), 0.0189(±0.0003); oxygen, 1.45(±0.09) × 10(-3); carbon monoxide, < 1.0 × 10(-3); and (40)Ar/(36)Ar, 1.9(±0.3) × 10(3). The (40)Ar/N2 ratio is 1.7 times greater and the (40)Ar/(36)Ar ratio 1.6 times lower than values reported by the Viking Lander mass spectrometer in 1976, whereas other values are generally consistent with Viking and remote sensing observations. The (40)Ar/(36)Ar ratio is consistent with martian meteoritic values, which provides additional strong support for a martian origin of these rocks. The isotopic signature ?(13)C from CO2 of ~45 per mil is independently measured with two instruments. This heavy isotope enrichment in carbon supports the hypothesis of substantial atmospheric loss. PMID:23869014

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

2013-07-19

154

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

155

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

NASA Astrophysics Data System (ADS)

Secondary Ion Mass Spectrometry, SIMS or ion microprobe analysis, has become an important tool for geochemistry because of its ability study the distributions of elemental and isotopic abundances in situ on polished samples with high (typically a few microns to sub-micron) spatial resolution. In addition, SIMS exhibits high sensitivity for a wide range of elements (H to Pu) so that isotope analyses can sometimes be performed for elements that comprise only trace quantities of some mineral phase (e.g., Pb in zircon) or on major and/or minor elements in very small samples (e.g., presolar dust grains). Offsetting these positive attributes are analytical difficulties due to the complexity of the sputtering source of analyte ions: (1) relatively efficient production of molecular ion species (especially from a complex matrix such as most natural minerals) that cause interferences at the same nominal mass as atomic ions of interest, and (2) quantitation problems caused by variations in the ionization efficiencies of different elements and/or isotopes depending upon the chemical state of the sample surface during sputtering--the so-called "matrix effects". Despite the availability of high mass resolution instruments (e.g., SHRIMP II/RG, CAMECA 1270/1280/NanoSIMS), the molecular ion interferences effectively limit the region of the mass table that can be investigated in most samples to isotope systems at Ni or lighter or at Os or heavier. The matrix effects and the sensitivity of instrumental mass discrimination to the physical state of the sample surface can hamper reproducibility and have contributed to a view that SIMS analyses, especially for so- called stable isotopes, are most appropriate for extraterrestrial samples which are often small, rare, and can exhibit large magnitude isotopic effects. Recent improvements in instrumentation and technique have extended the scope of SIMS isotopic analyses and applications now range from geochronology to paleoclimatology to volcanology to biogeochemistry and cosmochemistry. Multiple collector (static magnetic field) measurements at high mass resolving power have enabled high precision (sub-permil) for several stable isotopes systems (e.g., C, O, Mg, S). Applied to geochronology, the multiple collector approach permits very rapid survey of zircon Pb-Pb ages to identify candidate Hadean grains for further detailed analysis. Ion imaging has been used to correlate isotope compositions with biochemistry (e.g., FISH-SIMS) or to search for especially rare samples among larger populations (e.g., supernova grains of Stardust). For favorable sample geometries with lateral homogeneity, SIMS isotope analyses may be conducted in depth-profiling mode which brings spatial resolution into the tens of nm range. Applications of this approach include experimental petrology, thermochronology, and isotopic analyses of shallowly-implanted solar wind ions. New approaches to removal of molecular ion interferences include reverse- geometry instrumentation and accelerator-based SIMS. There always exists trade-offs between microanalysis and trace analysis on the one hand, and high precision on the other. In this contribution, I will review current status for isotope precision and accuracy of SIMS for applications in stable and radiogenic isotopes as a function of spatial scale. A discussion of current limits and future prospects for improvement in understanding matrix effects will be given. Examples from ion imaging/ depth profiling/ geochronology and cosmochemistry will be provided.

McKeegan, K. D.

2007-12-01

156

Carbon isotope fractionation during calcium carbonate precipitation induced by ureolytic bacteria  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

157

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

158

Carbon Isotope Fractionation in Plants: Annual Technical Progress Report.  

National Technical Information Service (NTIS)

Plants fractionate carbon isotopes during photosynthesis in ways which reflect photosynthetic pathway and environment. The fractionation is product of contributions from diffusion, carboxylation and other factors which can be understood using models which...

M. H. O'Leary

1988-01-01

159

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

160

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

161

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

162

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

163

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

2012-06-06

164

THE SPONTANEOUS FISSION OF CALIFORNIUM254 IN TYPE I SUPERNOVAE AND ANOMALY IN THE ABUNDANCE OF THE ISOTOPES OF Te, Xe, AND Sm  

Microsoft Academic Search

The laws governlng the relative abundunce of isotopes and the anomaly in ; the abundance of the isotopes of tellurium and xenon are considered. An ; hypothesis is advanced explaining the anomalously great abundance of Te-128, Te-; 130, Xe-128, and Xe-131 by the addition of decay products of nuclei that arise ; due to the spontaneous fission of transuranium isotopes.

Selinov

1959-01-01

165

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

PubMed

The Palaeocene-Eocene thermal maximum (PETM) is characterized by a global negative carbon isotope excursion (CIE) and widespread dissolution of seafloor carbonate sediments. The latter feature supports the hypothesis that the PETM and CIE were caused by the rapid release of a large mass (greater than 2000Gt C) of 12C-enriched carbon. The source of this carbon, however, remains a mystery. Possible sources include volcanically driven thermal combustion of organic-rich sediment, dissociation of seafloor methane hydrates and desiccation and oxidation of soil/sediment organics. A key constraint on the source(s) is the rate at which the carbon was released. Fast rates would be consistent with a catastrophic event, e.g. massive methane hydrate dissociation, whereas slower rates might implicate other processes. The PETM carbon flux is currently constrained by high-resolution marine and terrestrial records of the CIE. In pelagic bulk carbonate records, the onset of the CIE is often expressed as a single- or multiple-step excursion extending over 10(4) years. Individual planktonic shell records, in contrast, always show a single-step CIE, with either pre-excursion or excursion isotope values, but no transition values. Benthic foraminifera records, which are less complete owing to extinction and diminutive assemblages, show a delayed excursion. Here, we compile and evaluate the individual planktonic shell isotope data from several localities. We find that the most expanded records consistently show a bimodal isotope distribution pattern regardless of location, water depth or depositional facies. This suggests one of several possibilities: (i) the isotopic composition of the surface ocean/atmosphere declined in a geologic instant (<500yr), (ii) that during the onset of the CIE, most shells of mixed-layer planktonic foraminifera were dissolved, or (iii) the abundances or shell production of these species temporarily declined, possibly due to initial pH changes. PMID:17513259

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

2007-07-15

166

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

NASA Astrophysics Data System (ADS)

Natural ammonium N isotopic abundance has been increasingly used in studies of marine and freshwater biogeochemistry. However, current methods are time-consuming, subject to interference from DON, and not reliable at low concentrations. Our new method for determining the ?15N of ammonium overcomes these difficulties by employing the oxidation of ammonium to nitrite followed by conversion of nitrite to nitrous oxide. In the first step, ammonium is quantitatively oxidized by hypobromite at pH~12. After the addition of sodium arsenite to consume excess hypobromite, yield is verified by colorimetric NO2-measurement using sulfanilamide and naphthyl ethylenediamine (NED). Nitrite is further reduced to N2O by a 1:1 sodium azide and acetic acid buffer solution using previously established procedures. Buffer concentration can be varied according to sample matrix to ensure that a reaction pH between 2 and 4 is reached. The product nitrous oxide is then isotopically analyzed using a continuous flow purge and cryogenic trap system coupled to an isotope ratio mass spectrometer. Reliable ?15N values (±0.31‰) are obtained over a concentration range of 0.5 ?M to 20 ?M using 20 ml volumes of either fresh or seawater samples. Reagent blanks are very low, about 0.05 ?M. There is no interference from any of the nitrogen containing compounds tested except short chain aliphatic amino acid (i.e. glycine) which typically are not present at sufficiently high environmental concentrations to pose a problem.

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

2006-12-01

167

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

NASA Astrophysics Data System (ADS)

Within the realm of volatile organic compounds, hydrocarbons and halocarbons form a sizable proportion of carbon input to the atmosphere. Within these compound categories, the light non-methane hydrocarbons (NMHC, two to seven carbon atoms) and monocarbon halocarbons have a special place as these have strong, if not exclusive, anthropogenic (human-caused) sources. With common atmospheric molar mixing ratios in the parts-per-trillion (10-12 mole/mole) to parts-per-billion (10-9 mole/mole) range, these trace gases, though decidedly minor constituants of the atmosphere, have diverse consequences due to their atmospheric presence and their removal processes. Effects range from causing ground level air pollution and resulting hazards to health, to contributing to anthropogenic climate change and the destruction of the ozone layer in the stratosphere, among many others. The existance of stable isotopes (otherwise identical atoms with varying amounts of neutrons that do not spontaneously disintegrate) in several elements relevant to atmospheric chemistry and physics is a boon to research. Their presence in molecules is detectable by mass and cause small intra- and intermolecular property changes. These changes range from the physical (e.g. boiling point variation) to the chemical (reaction rate variation) and can influence external interactions as well. The measurement of the ratio of a minor stable isotope of an element to the major one (the stable isotope ratio) can be used to establish source fingerprints, trace the interaction dynamics, and refine the understanding of the relative contribution of sources and sinks to the atmosphere as a whole. The stable minor stable isotope of carbon, 13C, has a natural abundance of approximately 1.1 %. It has a sufficient fractional mass difference from its major isotope as to cause significant effects, making it ideal for measuring the ratios and properties of hydro- and halocarbons. In order to enable a better understanding of the behavior of these compounds in terms of their sources, sinks, inter- and intramolecular processes, it was decided in 2006 to develop an instrument capable of selectively measuring NMHC mixing ratios and stable carbon isotope ratios for use in the laboratory of the Atmospheric Physics and Chemistry Group at Universiteit Utrecht. This thesis documents the successful development, construction, testing and first applications of this stable carbon isotope ratio instrument. It is divided into five chapters, representing the content of three publications and additional material: an introduction; a method section; and applications: analysis of NMHC stable carbon isotopes in urban ambient air, laboratory measurments of the isotope effects in UV degradation of monocarbon chlorofluorocarbons, isotope analysis of diverse gases from firn air samples from Greenland, plus a section on future perspectives

Zuiderweg, A. T.

2012-09-01

168

Oxygen Isotopic Composition of Secondary Carbonates in CR1 Chondrite GRO 95577  

NASA Astrophysics Data System (ADS)

CR1 chondrite GRO 95577 carbonates may be anomalously young. To verify that carbonate is extraterrestrial and interpret oxygen isotopic evolution during aqueous alteration, we report SIMS oxygen isotopic compositions of Ca-carbonate and siderite.

Tyra, M. A.; Brearley, A. J.; Guan, Y.

2011-03-01

169

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

NASA Astrophysics Data System (ADS)

The isotopic composition of molybdenum has been measured with high precision using a thermal ionization mass spectrometer, the linearity of which has been verified by measuring the isotopically-certified reference material for strontium (NIST 987). The abundance sensitivity of the mass spectrometer in the vicinity of the molybdenum ion beams has been carefully examined to ensure the absence of tailing effects. Particular care was given to ensuring that potential isobaric interferences from zirconium and ruthenium did not affect the measurement of the isotopic composition of molybdenum. Gravimetric mixtures of two isotopically enriched isotopes, Mo92 and Mo98, were analyzed mass spectrometrically to calibrate the mass spectrometer, in order to establish the isotope fractionation of the spectrometer for the molybdenum isotopes. This enabled the “absolute” isotopic composition of molybdenum to be determined. An accurate determination of the isotopic composition is required in order to calculate the atomic weight of molybdenum, which is one of the least accurately known values of all the elements. The absolute isotope abundances (in atom %) of molybdenum measured in this experiment are as follows: Mo92=14.5246±0.0015; Mo94=9.1514±0.0074; Mo95=15.8375±0.0098; Mo96=16.672±0.019; Mo97=9.5991±0.0073; Mo98=24.391±0.018; and Mo100=9.824±0.050, with uncertainties at the 1s level. These values enable an atomic weight Ar(Mo) of 95.9602±0.0023 (1s) to be calculated, which is slightly higher than the current Standard Atomic Weight Ar(Mo) =95.94±0.02 and with a much improved uncertainty interval. These “absolute” isotope abundances also enable the Solar System abundances of molybdenum to be calculated for astrophysical purposes. Of particular interest are the Solar System abundances of the two p-process nuclides—Mo92 and Mo94, which are present in far greater abundance than p-process theory suggests. The Solar System abundances for Mo92 and Mo94 of 0.364±0.012 and 0.230±0.008 respectively, (with respect to silicon =106 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.; de Laeter, J. R.

2007-05-01

170

Locations of marine animals revealed by carbon isotopes  

PubMed Central

Knowing the distribution of marine animals is central to understanding climatic and other environmental influences on population ecology. This information has proven difficult to gain through capture-based methods biased by capture location. Here we show that marine location can be inferred from animal tissues. As the carbon isotope composition of animal tissues varies with sea surface temperature, marine location can be identified by matching time series of carbon isotopes measured in tissues to sea surface temperature records. Applying this technique to populations of Atlantic salmon (Salmo salar L.) produces isotopically-derived maps of oceanic feeding grounds, consistent with the current understanding of salmon migrations, that additionally reveal geographic segregation in feeding grounds between individual philopatric populations and age-classes. Carbon isotope ratios can be used to identify the location of open ocean feeding grounds for any pelagic animals for which tissue archives and matching records of sea surface temperature are available.

MacKenzie, Kirsteen M.; Palmer, Martin R.; Moore, Andy; Ibbotson, Anton T.; Beaumont, William R. C.; Poulter, David J. S.; Trueman, Clive N.

2011-01-01

171

Mg Isotope Fractionation in Microbial Carbonates From the 2.5 Ga Gamohaan Formation, South Africa  

NASA Astrophysics Data System (ADS)

Mg isotopic fractionation in calcite and dolomite from microbialites in the 2.5 Ga Gamohaan Formation, South Africa, were explored to study the possible use of Mg isotopes as biomarkers. We measured Mg isotopes in microdrilled fibrous marine calcite and dolomite from four different samples. Between 10-200 ?g of powdered mineral were dissolved in ~6N HCl. Mg was subsequently purified on a cation-exchange column. Mg isotopes were measured at UC Davis using the Nu Plasma HR multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) in medium resolution mode. Samples are depleted in ^{26}Mg and ^{25}Mg relative to DSM 3, the standard reference material, by -1.5 to -3.7‰ and -0.8 to -2‰ respectively. Dolomite is systematically heavier in ?^{26}Mg and ?^{25}Mg by 0.5-2‰ and 0.3-1‰ respectively, than the calcite. Fibrous marine calcite values from nearly contemporaneous samples vary by ~1.8‰, suggesting that Mg isotopic values were significantly influenced by local processes. The abundance of evidence for microbial influences on carbonate precipitation in these rocks suggests a microbial influence on the preserved Mg isotopes, consistent with a recent study that showed that microbial activity can cause significant fractionation of Mg isotopes (Black et al. 2006).

Jacobsen, B.; Chavdarian, G. V.; Yin, Q.; Sumner, D. Y.

2006-12-01

172

Carbon Isotope Effect in Rb_3C_60  

NASA Astrophysics Data System (ADS)

We have synthesized single crystals of isotopically enriched Rb_3C_60. The very sharp superconducting transitions in single crystal superconducting fullerides allow us to determine the isotope effect on Tc very accurately. We find that the carbon isotope shift for 99% ^13C substitution is significantly smaller than other values reported in the literature. This, coupled with the near-zero rubidium isotope effect reported by B. Burk et. al.(B. Burk, V. H. Crespi, A. Zettl and M. L. Cohen, PRL 72, 3706 (1994).) , should place considerable restraints on any theoretical model of superconductivity in the alkali fullerides. Further experiments to investigate the anomalous isotope shift reported by C.-C. Chen et. al.(Chia-Chun Chen and C. M. Lieber, Science 259, 655 (1993).) for isotopically disordered systems will be discussed.

Fuhrer, M. S.; Cherrey, K.; Zettl, A.

1997-03-01

173

Can gas chromatography combustion isotope ratio mass spectrometry be used to quantify organic compound abundance?  

PubMed

Quantifying the concentrations of organics such as phospholipid fatty acids (PLFAs) and n-alkanes and measuring their corresponding (13)C/(12)C isotope ratios often involves two separate analyses; (1) quantification by gas chromatography flame ionisation detection (GC-FID) or gas chromatography/mass spectrometry (GC/MS), and (2) (13)?C-isotope abundance analysis by gas chromatography/combustion/isotope ratio mass spectrometry (GC-C-IRMS). This requirement for two separate analyses has obvious disadvantages in terms of cost and time. However, there is a history of using the data output of isotope ratio mass spectrometers to quantify various components; including the N and C concentrations of solid materials and CO(2) concentrations in gaseous samples. Here we explore the possibility of quantifying n-alkanes extracted from sheeps' faeces and fatty acid methyl esters (FAMEs) derivatised from PLFAs extracted from grassland soil, using GC-C-IRMS. The results were compared with those from GC-FID analysis of the same extracts. For GC-C-IRMS the combined area of the masses for all the ions (m/z 44, 45 and 46) was collected, referred to as 'area all', while for the GC-FID analysis the peak area data were collected. Following normalisation to a common value for added internal standards, the GC-C-IRMS 'area all' values and the GC-FID peak area data were directly compared. Strong linear relationships were found for both n-alkanes and FAMEs. For the n-alkanes the relationships were 1:1 while, for the FAMEs, GC-C-IRMS overestimated the areas relative to the GC-FID results. However, with suitable reference material 1:1 relationships were established. The output of a GC-C-IRMS system can form the basis for the quantification of certain organics including FAMEs and n-alkanes. PMID:21818802

Thornton, Barry; Zhang, Zulin; Mayes, Robert W; Högberg, Mona N; Midwood, Andrew J

2011-09-15

174

Terrestrial carbon and nitrogen isotopic ratios from cretaceous-tertiary boundary nanodiamonds.  

PubMed

One hypothesis for the origin of the nanometer-size diamonds found at the Cretaceous-Tertiary (K-T) boundary is that they are relict interstellar diamond grains carried by a postulated asteroid. The (13)C/(12)C and (15)N/(14)N ratios of the diamonds from two sites in North America, however, show that the diamonds are two component mixtures differing in carbon and nitrogen isotopic composition and nitrogen abundance. Samples from a site from Italy show no evidence for either diamond component. All the isotopic signatures obtained from the K-T boundary are material well distinguished from known meteoritic diamonds, particularly the fine-grain interstellar diamonds that are abundant in primitive chondrites. The K-T diamonds were most likely produced during the impact of the asteroid with Earth or in a plasma resulting from the associated fireball. PMID:17742530

Gilmour, I; Russell, S S; Arden, J W; Lee, M R; Franchi, I A; Pillinger, C T

1992-12-01

175

Equilibrium and nonequilibrium oxygen isotope effects in synthetic carbonates  

Microsoft Academic Search

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

Sang-Tae Kim; James R. O'Neil

1997-01-01

176

Biogeochemical influence on carbon isotope signature in boreal lake sediments  

Microsoft Academic Search

The sources of dissolved inorganic carbon (DIC) were determined in Lake 658 at the Experimental Lakes Area in northwest Ontario, Canada. The study covered a period from June to October 2001 in five different locations in the lake. The pore water chemistry (concentration of DIC and dissolved organic carbon (DOC), pH, total alkalinity (TA), and isotopic composition of DIC (d13CDIC))

N. Ogrinc; H. Hintelmann; C. Eckley; S. Lojen

2003-01-01

177

Mass transfer and carbon isotope evolution in natural water systems  

Microsoft Academic Search

This paper presents a theoretical treatment of the evolution of the carbon isotopes C 13 and C 14 in natural waters and in precipitates which derive from such waters. The effects of an arbitrary number of sources (such as dissolution of carbonate minerals and oxidation of organic material) and sinks (such as mineral precipitation, CO 2 degassing and production of

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

1978-01-01

178

[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

179

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

180

Determination of the Isotopic Abundance of exp 235 U in Rocks in Search for an Oklo Phenomenon in Brazil by Activation Analysis.  

National Technical Information Service (NTIS)

Isotopic analyses of uranium are generally carried out by mass spectrometry, with a precision better than 1%. In nuclear laboratories it is often necessary to perform rapid determinations of exp 235 U isotopic abundances. Thermal neutron activation analys...

M. B. A. Vasconcellos M. J. A. Armelin R. Fulfaro F. W. Lima

1981-01-01

181

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

182

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

NASA Astrophysics Data System (ADS)

We propose a new diagnostics of isotope abundance ratios and electron densities for low density plasmas, in the form of J = 0 -> J(') = 0 radiative transitions. These are usually viewed as being allowed only through two-photon decay, but they may also be induced by the hyperfine (HPF) interaction in atomic ions. This predicts a companion line to the E1] and M2 lines in the UV0.01 multiplet of ions isoelectronic to beryllium (e.g. C III, N IV, O V and Fe XXII) or magnesium (e.g. Si II, Ca IX, Fe XV and Ni XVII). As an example the companion line to the well known lambda lambda 1906.7,1908.7 lines in C III will be at 1909.597 Angstroms, but only present in the (13) C isotope (which has nuclear spin different from zero). We present new and accurate decay rates for the nsnp (3P^oJ) -> ns(2) (1S_{J('}=0)) transitions in ions of the Be (n=2) and Mg (n=3) isoelectronic sequences. We show that the HPF induced decay rates for the J = 0 -> J(') = 0 transitions are many orders of magnitude larger than those for the competing two-photon processes and, when present, are typically one or two orders of magnitude smaller than the decay rates of the magnetic quadrupole ( J = 2-> J(') = 0) transitions for these ions. We show that several of these HPF-induced transitions are of potential astrophysical interest, in ions of C, N, Na, Mg, Al, Si, K, Cr, Fe and Ni. We highlight those cases that may be of particular diagnostic value for determining isotopic abundance ratios and/or electron densities from UV or EUV emission line data. We present our atomic data in the form of scaling laws so that, given the isotopic nuclear spin and magnetic moment, a simple expression yields estimates for HPF induced decay rates. We examine some UV solar and nebular data in the light of these new results and suggest possible cases for future study. We could not find evidence for the existence of HPF induced lines in the spectra we examined, but we demonstrate that existing data have come close to providing interesting upper limits. For the planetary nebula SMC N2 we derive an upper limit of (13) C/(12) C of 0.1 from GHRS data obtained by Clegg. It is likely that more stringent limits could be obtained with newer data with higher sensitivities in a variety of objects.

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

1996-05-01

183

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

PubMed

The carbon isotope geochemistry of carbonates and organic carbon in the late Proterozoic Damara Supergroup of Namibia, including the Nama, Witvlei, and Gariep groups on the Kalahari Craton and the Mulden and Otavi groups on the Congo Craton, has been investigated as an extension of previous studies of secular variations in the isotopic composition of late Proterozoic seawater. Subsamples of microspar and dolomicrospar were determined, through petrographic and cathodoluminescence examination, to represent the "least-altered" portions of the rock. Carbon-isotopic abundances in these phases are nearly equal to those in total carbonate, suggesting that 13C abundances of late Proterozoic fine-grained carbonates have not been significantly altered by meteoric diagenesis, although 18O abundances often differ significantly. Reduced and variable carbon-isotopic differences between carbonates and organic carbon in these sediments indicate that isotopic compositions of organic carbon have been altered significantly by thermal and deformational processes, likely associated with the Pan-African Orogeny. Distinctive stratigraphic patterns of secular variation, similar to those noted in other, widely separated late Proterozoic basins, are found in carbon-isotopic compositions of carbonates from the Nama and Otavi groups. For example, in Nama Group carbonates delta 13C values rise dramatically from -4 to +5% within a short stratigraphic interval. This excursion suggests correlation with similar excursions noted in Ediacaran-aged successions of Siberia, India, and China. Enrichment of 13C (delta 13C> +5%) in Otavi Group carbonates reflects those in Upper Riphean successions of the Akademikerbreen Group, Svalbard, its correlatives in East Greenland, and the Shaler Group, northwest Canada. The widespread distribution of successions with comparable isotopic signatures supports hypotheses that variations in delta 13C reflect global changes in the isotopic composition of late Proterozoic seawater. Within the Damara basin, carbon-isotopic compositions of carbonates provide a potentially useful tool for the correlation of units between the Kalahari and Congo cratons. Carbonates depleted in 13C were deposited during and immediately following three separate glacial episodes in Namibia. The correspondence between ice ages and negative delta 13C excursions may reflect the effects of lowered sea levels; enhanced circulation of deep, cold, O2-rich seawater; and/or the upwelling of 13C-depleted deep water. Iron-formation is additionally associated with one of the glacial horizons, the Chuos tillite. Carbon-13 enriched isotopic abundances in immediately pre-glacial carbonates suggest that oceanographic conditions favored high rates of organic burial. It is likely that marine waters were stratified, with deep waters anoxic. A prolonged period of ocean stratification would permit the build-up of ferrous iron, probably from hydrothermal sources. At the onset of glaciation, upwelling would have brought 13C-depleted and iron-rich deep water onto shallow shelves where contact with cold, oxygenated surface waters led to the precipitation of ferric iron. PMID:11538647

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

1991-01-01

184

Pb isotopic ratios and elemental abundances for selective leachates from near-surface till: implications for mineral exploration  

Microsoft Academic Search

Pb isotope ratios obtained from fine-grained fractions ( In this study, Pb isotopic measurements, and selective leaching of 6 near-surface till samples down-ice from the Chisel Lake (Manitoba) and Manitouwadge (Ontario) VMS deposits were carried out in order to determine the location and nature of the Pb within till. Elemental abundances from selective leachates for all 6 samples display similar

G. E. M. Hall; K. Bell

1996-01-01

185

Carbon cycle for Lake Washington - a stable isotope study  

Microsoft Academic Search

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

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

1986-01-01

186

Investigation of tubular handling of bicarbonate in man. A new approach utilizing stable carbon isotope fractionation.  

PubMed Central

Two alternative mechanisms have been proposed for tubular reabsorption of bicarbonate: (a) H+ secretion and CO2 reabsorption and (b) direct reabsorption of HCO-3. In an attempt to differentiate between the two mechanisms, the present study utilized the natural abundance of stable carbon isotopes (13C, 12C) in the urinary total CO2. This novel methodology used mass spectrometric analysis of 13C/12C ratios in urinary total CO2 under normal conditions and during acetazolamide treatment. Blood and respiratory CO2 were analyzed to yield reference values. The results demonstrate that alkaline urine is preferentially enriched with 13C relative to the blood. It is suggested that this fractionation results from reaction out of isotopic equilibrium in which HCO-3 converts to CO2 during the reabsorption process in the distal nephron. The presence of carbonic anhydrase in the proximal nephron results in rapid isotopic exchange between CO2 and HCO-3 and keeps them in isotopic equilibrium. The ratio of urinary 13C/12C increases strikingly after acetazolamide administration and consequent inhibition of carbonic anhydrase in the proximal tubule. Although it is possible that in the latter case high HCO-3 generates the CO2 (ampholyte effect), the isotope fractionation indicates that CO2 rather than HCO-3 is reabsorbed. In contrast, at low urinary pH and total CO2 values, the carbon isotope composition approaches that of blood CO2. This indicates rapid CO2 exchange between urine and blood, through luminal membrane highly permeable to CO2. These results could be anticipated by a mathematical model constructed to plot 13C concentration of urinary total CO2. It is concluded that the mechanism of HCO-3 reclamation in man (and, by inference, in other mammals as well) works by conversion of HCO-3 to CO2 and reabsorption of CO2.

Burbea, Z H; Luz, B; Lazar, B; Winaver, J; Better, O S

1983-01-01

187

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

188

The early Cretaceous carbon- and oxygen-isotope record  

NASA Astrophysics Data System (ADS)

Bulk-carbonate carbon- and oxygen-isotope analyses have been conducted on marlstones from a biostratigraphically-continuous section (Berriasian-Aptian) from Río Argos, SE Spain. The stratigraphic succession at Río Argos consists of rhythmic limestones with a bed thickness between 0.5-75cm that are inter-bedded with marlstones with a thickness between 0.005-1m. The limestone beds through the succession are considered to be the result of differential dissolution and cementation during diagenesis, and so only the marlstones have been analyzed for isotopic ratios. Carbon- and oxygen-isotope ratios through the entire section show both short- and long-term variation, although only the major shifts will be discussed in this abstract. Carbon-isotope ratios fluctuate between -1 ppm and +1.2 ppm during the Berriasian and Lower Valanginian, with a rapid positive excursion at the base of the Upper Valanginian to +2.6 ppm. Values subsequently decline gradually towards background values (+0.4 ppm to +1.6 ppm) during the Hauterivian. From the mid-Barremian carbon-isotope ratios fluctuate in two major cycles between -1 ppm to +2.2 ppm. The Lower Aptian records a major negative excursion from a background of +1.8 ppm to -2.5 ppm (that is equivalent to OAE1a), followed by a rapid shift to +3.3 ppm. No correlation is found between carbon- and oxygen-isotope ratios and although there may be some diagenetic overprint we interpret the oxygen-isotope curve in terms of temporal shifts in palaeotemperature; the oxygen-isotope range for the entire stratigraphic section is between -4.6 ppm to -1.8 ppm. The Berriasian has relatively positive oxygen-isotope ratios (cool), although by the Lower Valanginian the values become more negative (warm) peaking in the Upper Valanginian. Oxygen-isotope ratios gradually increase throughout the remainder of the stratigraphic section to a peak in the mid-Barremian (cool), followed by a rapid drop to more negative (warm) ratios and increase once again to more positive ratios (cool) in the Lower Aptian. Although global sea-level changes may also affect oxygen-isotope ratios it is intriguing to note that both warm periods coincide with the initiation of large igneous provinces (Paraná-Etendeka, Valanginian; Ontong Java Plateau, Late Barremian).

Grocke, D. R.; Coccioni, R.; Price, G. D.; Arthur, M. A.

2003-04-01

189

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

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

190

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

191

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

SciTech Connect

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

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

1986-10-24

192

Isotopic variation of carbonate cements sampled by different techniques  

NASA Astrophysics Data System (ADS)

Several studies have been carried out using the isotopic signature of carbonate cements in the marine-phreatic environment. This study aims to compare the isotopic composition of specific levels inside a carbonate formation like beachrock. In particular, samples from the same level were analyzed, differing from each other on the sampled material. Bulk rock sample, macroscopic and microscopic selection, stirred and dried material are some of the selected methods of sample extraction for isotopic analysis. The results are plotted on diagrams and compared, in order to evaluate the reliability and suitability of sampling methods for isotopic analysis. Samples were taken from the same level of the formation in order to avoid differences of values originated in different precipitation conditions.

Psomiadis, D.; Dotsika, E.; Albanakis, K.; Zisi, N.

2009-04-01

193

Stable carbon isotope fractionation by methylotrophic methanogenic archaea.  

PubMed

In natural environments methane is usually produced by aceticlastic and hydrogenotrophic methanogenic archaea. However, some methanogens can use C(1) compounds such as methanol as the substrate. To determine the contributions of individual substrates to methane production, the stable-isotope values of the substrates and the released methane are often used. Additional information can be obtained by using selective inhibitors (e.g., methyl fluoride, a selective inhibitor of acetoclastic methanogenesis). We studied stable carbon isotope fractionation during the conversion of methanol to methane in Methanosarcina acetivorans, Methanosarcina barkeri, and Methanolobus zinderi and generally found large fractionation factors (-83‰ to -72‰). We further tested whether methyl fluoride impairs methylotrophic methanogenesis. Our experiments showed that even though a slight inhibition occurred, the carbon isotope fractionation was not affected. Therefore, the production of isotopically light methane observed in the presence of methyl fluoride may be due to the strong fractionation by methylotrophic methanogens and not only by hydrogenotrophic methanogens as previously assumed. PMID:22904062

Penger, Jörn; Conrad, Ralf; Blaser, Martin

2012-08-17

194

Quantifying absolute carbon isotope ratios by AMS  

NASA Astrophysics Data System (ADS)

Our AMS produced a ratio of instrument transmissions for 14C and 13C equal to 13/14 to 0.22 ± 0.06% accuracy at a specific charge-changing energy of 235 keV and giving absolute isotope ratios with that mass correction. The ratio for 13C and 12C transmissions was 12/13 at 215 keV. A differential equation model of energetic ion and atom transport through the gas collision cell was constructed with functions representing experimental cross-sections for all collision effects. This model showed cation yield dependencies that were linear with energy for the monoenergetic isotopic ions at the energies that we measured, explaining the inverse mass dependence. The model predicted multiple lower energies that have this dependence and, more importantly, two low energies at which cation yields were equal for pairs of isotopes, presaging potential absolute isotope ratio measurements at low MS energies.

Vogel, John S.; Giacomo, Jason A.; Dueker, Stephen R.

2013-01-01

195

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

196

Enhanced Carbon Enrichment in Parasitoids (Hymenoptera): A Stable Isotope Study  

Microsoft Academic Search

By considering the magnitude of isotope enrichment associated with trophic transfers in biologically important elements such as carbon (13C\\/12C) and nitrogen (15N\\/14N), it is possible to infer trophic interactions in systems where direct observations are logistically difÞcult. Several recent reviews have estimated that consumers become enriched in the heavy nitrogen isotope on the order of 2.3 to 3.4‰ with each

Gail A. Langellotto; Jay A. Rosenheim; Megan R. Williams

2005-01-01

197

‘Clumped isotope’ paleothermometry of soil carbonates: a status report  

NASA Astrophysics Data System (ADS)

The carbonate ‘clumped isotope’ paleothermometer is a promising new tool for reconstructing continental paleoclimate and paleoecology through analysis of soil carbonates, but wider application of this tool awaits a clearer understanding of how the system works. Specific questions include: When does soil carbonate form during the seasonal cycle at a specific site? How does soil temperature at depth relate to air temperature? What is the influence of soil moisture, vegetation cover, and incident solar heating on soil temperature? Does isotopic clumping in soil carbonate reflect equilibrium or nonequilibrium mineralization processes? Can we reliably measure ?47 of CO2 (the analytical basis of carbonate clumped isotope thermometry) liberated from the complex soil carbonate matrix? Is isotopic clumping in soil carbonate resistant to redistribution during burial and exhumation processes? We are pursuing several lines of investigation to address these questions. Temperatures based on ?47 measurements of soil carbonates from tropical environments are similar to mean annual air temperatures, while those from higher latitudes are generally closer to warm season temperatures. We have installed soil temperature loggers in several locations in Kenya and western North America characterized by several combinations of temperature, precipitation and vegetation, and detailed investigations are underway involving measurements of soil CO2, soil moisture, and soil temperature to help constrain the temperature and timing of soil carbonate growth. In the laboratory, we have found that CO2 generated by acid digestion from certain suites of material can be challenging to purify to the extent necessary for accurate and precise determination of ?47, but our success rate is improving as we streamline the CO2 extraction and purification procedure and refine our use of contaminant traps and GC column packings. Clumped isotope temperatures of Neogene paleosol carbonates in Bolivia and Kenya display no correlation with maximum burial depth and give reasonable Earth-surface temperatures, and the temperatures of paleosol carbonates exhumed and reexposed over a range of prevailing climates show no clear relationship with present day mean annual temperature, suggesting that temperatures are not significantly reset during recent exhumation. These observations suggest that that the outlook is promising for the clumped isotope system in soil carbonates. Although the temperature signal is complicated by seasonality, vegetation cover, and other factors, and therefore will not typically yield the mean-annual temperatures sought by many paleothermometry studies, it appears to be a thermodynamically-straightforward system that is governed by quantifiable physical processes, faithfully recording the ground temperature at the time of soil carbonate growth.

Passey, B. H.; Eiler, J. M.; Daëron, M.; Quade, J.; Garzione, C. N.; Smith, J. J.; Cerling, T. E.; Levin, N.

2009-12-01

198

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

199

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

NASA Astrophysics Data System (ADS)

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

Frei, R.; Gaucher, C.

2010-12-01

200

Carbon isotopes in terrestrial ecosystem pools and CO2 fluxes.  

PubMed

Stable carbon isotopes are used extensively to examine physiological, ecological, and biogeochemical processes related to ecosystem, regional, and global carbon cycles and provide information at a variety of temporal and spatial scales. Much is known about the processes that regulate the carbon isotopic composition (delta(13)C) of leaf, plant, and ecosystem carbon pools and of photosynthetic and respiratory carbon dioxide (CO(2)) fluxes. In this review, systematic patterns and mechanisms underlying variation in delta(13)C of plant and ecosystem carbon pools and fluxes are described. We examine the hypothesis that the delta(13)C of leaf biomass can be used as a reference point for other carbon pools and fluxes, which differ from the leaf in delta(13)C in a systematic fashion. Plant organs are typically enriched in (13)C relative to leaves, and most ecosystem pools and respiratory fluxes are enriched relative to sun leaves of dominant plants, with the notable exception of root respiration. Analysis of the chemical and isotopic composition of leaves and leaf respiration suggests that growth respiration has the potential to contribute substantially to the observed offset between the delta(13)C values of ecosystem respiration and the bulk leaf. We discuss the implications of systematic variations in delta(13)C of ecosystem pools and CO(2) fluxes for studies of carbon cycling within ecosystems, as well as for studies that use the delta(13)C of atmospheric CO(2) to diagnose changes in the terrestrial biosphere over annual to millennial time scales. PMID:18179603

Bowling, David R; Pataki, Diane E; Randerson, James T

2008-01-07

201

Goddard High-Resolution Spectrograph Observations of the B III Resonance Doublet in Early B Stars: Abundances and Isotope Ratios  

NASA Astrophysics Data System (ADS)

Boron abundances and isotope ratios in two early B stars have been measured by using the Hubble Space Telescope's Goddard High-Resolution Spectrograph (GHRS) in order to observe the B III resonance doublet near 2066 Å. We also report new experimental and theoretical results for the wavelengths, isotope shift, and hyperfine structure of these boron lines. In HD 886 (gamma Pegasi; B2 IV), and HD 35299 (B1 V) the abundance of boron is about a factor of 2 lower than that inferred from solar system meteorites. The ^11B/^10B isotope ratio in HD 886 is determined to be 4.7^+1.1_-1.0, and for HD 35299 a value of 3.7^+0.8_-0.6 is found. These values are consistent with the solar system isotope ratio. In a third star, HD 3360 (zeta Cassiopeiae; B2 IV), our GHRS observations show that the boron abundance is a factor of 40 below the solar system abundance. Our results for HD 886 and HD 35299 appear to be consistent with little dispersion in the initial boron-to-oxygen ratio among Population I stars and a universal ^11B/^10B isotope ratio. However, the abundance measured for HD 3360 shows that either some stars suffer significant boron depletion while still in the core-hydrogen burning phase of their evolution, or there is indeed a very wide variation in initial Population I boron abundances. A much-improved understanding of boron astration in early B stars will be required before this question can be resolved.

Proffitt, Charles R.; Jönsson, Per; Litzén, Ulf; Pickering, Juliet C.; Wahlgren, Glenn M.

1999-05-01

202

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

PubMed Central

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

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

1990-01-01

203

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

204

The time has changed: Middle Triassic climate changes revealed by carbon isotopes  

NASA Astrophysics Data System (ADS)

The Middle Triassic stratigraphy in Europe can be subdivided into a marine section of the Germanic and Paris Basin and a continental red-bed succession of Western Europe (Irish Basin, Wessex Basin). The link between the marine and continental is uncertain due to a lack of biostratigraphic information but recent palaeomagnetic studies have given a better understanding of the two environments (Hounslow et. al, 2001). In this study we have produced geochemical evidence which emphasize the implications of the palaeomagnetic data. We show that the marine and continental strata can be correlated using carbon isotopes. Throughout Europe the Middle Triassic is characterized by limestone deposits of the Muschelkalk Formation that contain evidence of a hiatus in sedimentation due to sea-level fall in the Middle Muschelkalk with the consequent deposition of evaporites. The Sherwood Sandstone Group (SSG) characterizes the Middle Triassic of Western Europe. The SSG is dominated by fluvial deposits with intercalated floodplain deposits, sand-flats and playas, which are penetrated by dolocretes and calcretes. The abundance of fluvial channels and sandflats are dependent on the fluvial activity and the water table height. In both depositional environments water plays a major role in the type of sediment. The volume of water is controlled by the prevalent climate. Climate signals are stored in carbon isotopes in both the marine Muschelkalk and the continental SSG. Carbon isotopes from the SSG from the Corrib Field, Slyne Basin, west of Ireland and from the Muschelkalk of the Germanic Basin have thus been interpreted in terms of climate change linked to stratigraphy. The continental sediments show a distinct positive carbon isotope excursion (taken from dolocretes), which is interpreted to present a more arid climate. In contrast the marine limestones exhibit a negative carbon isotopes excursion from a sea level low stand for the same time interval. The plot of both carbon isotopes curves against depth (using the Anisian-Ladinian boundary as a correlation marker) with a correction of sediment thickness show the same general climatic conditions for the Middle Triassic in Europe. Carbon isotope data from the Muschelkalk of the Germanic Basin and the SSG of the Slyne Basin reveal that the Middle Triassic was a time that witnessed a change from a humid to an arid climate with less fluvial activity in the continental parts and evaporite deposition in the marine part of Europe. References: Hounslow, M.W., McIntosh, G. &Jenkins, G.(2001): Magnetostratigraphy of the Middle Triassic: Sherwood Sandstone Group, South Devon, UK, EGS Nice

Schmid, S.; Worden, R.; Fisher, Q.

2003-04-01

205

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

Microsoft Academic Search

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

Jonathan G. Wynn; Jennifer W. Harden; Terry L. Fries

2006-01-01

206

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

NASA Astrophysics Data System (ADS)

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

Schubert, Brian A.; Jahren, A. Hope

2011-11-01

207

Oceanic carbon isotope constraints on oxygen and carbon dioxide in the Cenozoic atmosphere  

Microsoft Academic Search

The carbon isotope record of carbonate sediments deposited on the ocean floor during the past 10 to the 8th years may be interpreted in terms of changes in the global organic carbon reservoir, which has diminished by about 10 to the 19th moles over the past few tens of millions of years, drawing down the atmospheric oxygen content from 0.25

N. J. Shackleton

1985-01-01

208

Evaluation of carbonate abundance in putative martian paleolake basins  

Microsoft Academic Search

Carbonate deposits have not been found so far on Mars, although there appears to have been sufficient water to have supported their formation. Many hypotheses have been proposed in order to explain this. In the present work we explore the possibility that the missed detection of carbonate deposits on the martian surface could be simply due to the fact that

V. Orofino; J. Goldspiel; I. Carofalo; A. Blanco; S. Fonti; G. A. Marzo

2009-01-01

209

Evaluation of Carbonate Abundance in Putative Martian Paleolake Basins  

Microsoft Academic Search

Carbonate deposits have not been found so far on Mars, although there appears to have been sufficient water to have supported their formation. Many hypotheses have been proposed in order to explain this. In the present work we explore the possibility that the missed detection of carbonate deposits on the Martian surface could be simply due to the fact that

Jules M. Goldspiel; V. Orofino; I. Carofalo; A. Blanco; S. Fonti; G. A. Marzo

2008-01-01

210

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

Microsoft Academic Search

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

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

1997-01-01

211

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

212

Development of a Field-Deployable Methane Carbon Isotope Analyzer  

NASA Astrophysics Data System (ADS)

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

Dong, Feng; Baer, Douglas

2010-05-01

213

Terrestrial carbon isotope excursions and biotic change during Palaeogene hyperthermals  

NASA Astrophysics Data System (ADS)

Pronounced transient global warming events between 60 and 50 million years ago have been linked to rapid injection of isotopically-light carbon to the ocean-atmosphere system. It is, however, unclear whether the largest of the hyperthermals, the Palaeocene-Eocene Thermal Maximum (PETM; ref. ), had a similar origin as the subsequent greenhouse climate events, such as the Eocene Thermal Maximum 2 and H2 events. The timing and evolution of these events is well documented in marine records, but is not well constrained on land. Here we report carbon isotope records from palaeosol carbonate nodules from the Bighorn Basin, Wyoming, USA that record the hyperthermals. Our age model is derived from cyclostratigraphy, and shows a similar structure of events in the terrestrial and marine records. Moreover, the magnitude of the terrestrial isotope excursions is consistently scaled with the marine records, suggesting that the severity of local palaeoenvironmetal change during each event was proportional to the size of the global carbon isotope excursion. We interpret this consistency as an indication of similar mechanisms of carbon release during all three hyperthermals. However, unlike during the PETM (refs , ), terrestrial environmental change during the subsequent hyperthermals is not linked to substantial turnover of mammalian fauna in the Bighorn Basin.

Abels, Hemmo A.; Clyde, William C.; Gingerich, Philip D.; Hilgen, Frederik J.; Fricke, Henry C.; Bowen, Gabriel J.; Lourens, Lucas J.

2012-05-01

214

Evaluation of Oxygen, Carbon, and Nitrogen Isotopic Paleoenvironmental Proxies in Lake Erie Sediments  

Microsoft Academic Search

The oxygen isotopic composition of calcium carbonate that precipitates in hardwater lakes is affected by meteorologic factors whereas the inorganic and organic carbon and nitrogen isotopic compositions of lake sediments are influenced by biological productivity within the lake. All of these isotopic proxies are potentially subject to post-depositional diagenesis. We have measured the isotopic compositions at 1-cm intervals in four

P. A. Meyers; C. Knowlton; B. J. Eadie; J. A. Robbins; M. Lansing

2004-01-01

215

Comparison of bulk and n-alkane PETM carbon isotope trends from the Bighorn Basin, Wyoming  

Microsoft Academic Search

The Paleocene-Eocene Thermal Maximum (PETM), a period of abrupt, short-term, and large-scale global warming fueled by a large release of isotopically light carbon, is recorded in terrestrial and marine carbonates and organic carbon as a prominent negative carbon isotope excursion (CIE). Here we present a composite stable carbon isotope record from n-alkanes and four bulk organic carbon records from individual

A. A. Baczynski; F. A. McInerney; M. J. Kraus; S. Wing

2010-01-01

216

Oxygen and Carbon Isotope Ratios in Martian Carbon Dioxide: Measurements and Implications for Atmospheric Evolution  

Microsoft Academic Search

Our measurements of high-resolution spectra of Mars at 3.7 and 8 ?m revealed 200 lines of16O12C17O,16O12C18O, and16O13C18O isotopes. Among them are 38 lines which are absent in spectroscopic databases. Eighty lines of the three isotopes with closely equivalent widths were chosen to determine the oxygen and carbon isotope ratios in CO2. A radiation transfer code which coupled the reflected solar

V. A. Krasnopolsky; M. J. Mumma; G. L. Bjoraker; D. E. Jennings

1996-01-01

217

Oxygen and Carbon Isotope Ratios in Martian Carbon Dioxide: Measurements and Implications for Atmospheric Evolution  

Microsoft Academic Search

Our measurements of high-resolution spectra of Mars at 3.7 and 8 mum revealed 200 lines of ^16O^12C^17O, ^16O^12C^18O, and ^16O^13C^18O isotopes. Among them are 38 lines which are absent in spectroscopic databases. Eighty lines of the three isotopes with closely equivalent widths were chosen to determine the oxygen and carbon isotope ratios in CO_2. A radiation transfer code which coupled

V. A. Krasnopolsky; M. J. Mumma; G. L. Bjoraker; D. E. Jennings

1996-01-01

218

Controls on the carbon isotopic composition of Southern Ocean phytoplankton  

NASA Astrophysics Data System (ADS)

Carbon isotopic compositions of suspended organic matter and biomarker compounds were determined for 59 samples filtered from Southern Ocean surface waters in January 1994 along two north-south transects (WOCE SR3 from Tasmania to Antarctica, and across the Princess Elizabeth Trough (PET) east of Prydz Bay, Antarctica). Along the SR3 line, bulk organic matter show generally decreasing 13C contents southward, which are well correlated with increasing dissolved molecular carbon dioxide concentrations, CO2(aq). This relationship does not hold along the PET transect. Using concentrations and isotopic compositions of molecular compounds, we evaluate the relative roles of several factors affecting the ?13C of Southern Ocean suspended particulate organic matter. Along the WOCE SR3 transect, the concentration of CO2(aq) plays an important role. It is well described by a supply versus demand model for the extent of cellular CO2 utilization and its associated linear dependence of isotopic fractionation (EP) on the reciprocal of CO2(aq). An equally important factor appears to be changes in algal assemblages along the SR3 transect, with their contribution to isotopic fractionation also well described by the supply and demand model, when formulated to include the cell surface/volume control of supply. Changes in microalgal growth rates appear to have a minor effect on EP. Along the PET transect, algal assemblage changes and possibly changes in microalgal growth rates appear to strongly affect the carbon isotopic variations of suspended organic matter. These results can be used to improve the formulation of modern carbon cycle models that include phytoplankton carbon isotopic fractionation.

Popp, Brian N.; Trull, Tom; Kenig, Fabien; Wakeham, Stuart G.; Rust, Terri M.; Tilbrook, Bronte; Griffiths, F. Brian; Wright, Simon W.; Marchant, Harvey J.; Bidigare, Robert R.; Laws, Edward A.

1999-12-01

219

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

NASA Astrophysics Data System (ADS)

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

Guo, Michelle; Zhang, A.

2013-01-01

220

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

Microsoft Academic Search

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

Jeffrey F. Kelly

2000-01-01

221

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

PubMed

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

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

2010-07-20

222

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

223

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

224

Determination of porphyrin carbon isotopic composition using gas chromatography-isotope ratio monitoring mass spectrometry.  

PubMed

Carbon isotopic compositions of aetio I occurring in the form of free-base, nickel, demetallation, dihydroxysilicon(IV) and bis(tert.-butyldimethylsiloxy)silicon(IV) [(tBDMSO)2Si(IV)] have shown that it has experienced no obvious isotope fractionation during the synthesis of [(tBDMSO)2Si(IV)] porphyrin from aetio I. Here, aetio I porphyrin species such as free-base, nickel, demetallated and dihydroxysilicon were analyzed by the conventional method, namely it is combusted in sealed system, and followed by isotope ratio monitoring mass spectrometric analysis. [(tBDMSO)2Si(IV)] aetio I was assayed by gas chromatography-isotope ratio monitoring mass spectrometry (GC-IRMS). A porphyrin mixture of [(tBDMSO)2Si(IV)] aetio I and octaethylporphyrin was also prepared. Their carbon isotopic compositions measured by GC-IRMS indicate that no isotope exchange took place between the porphyrins during the synthesis of [(tBDMSO)2Si(IV)] porphyrins. This method is employed for delta13C determination of geoporphyrins from the Maoming and Jianghan oil shales. PMID:11153940

Yu, Z; Sheng, G; Fu, J; Peng, P

2000-12-01

225

Association genetics in Pinus taeda L. II. Carbon isotope discrimination  

Microsoft Academic Search

Dissection of complex traits that influence fitness is not only a central topic in evolutionary research but can also assist breeding practices for economically important plant species, such as loblolly pine (Pinus taeda L). In this study, 46 single nucleotide polymorphisms (SNPs) from 41 disease and abiotic stress-inducible genes were tested for their genetic association with carbon isotope discrimination (CID),

S C González-Martínez; D Huber; E Ersoz; J M Davis; D B Neale

2008-01-01

226

Carbon isotope behaviour in wood and cellulose during artificial aging  

Microsoft Academic Search

Modern wood was subjected to an artificial decay process to investigate its behaviour with respect to the stable carbon isotope composition of wood and the corresponding cellulose. Four different woods were used, namely: oak (Quercus robur), beech (Fagus sylvatica), pine (Pinus sylvestris), sequoia (Sequoiadendron giganteum) and pure spruce cellulose. The process of decay was simulated by heating samples in water

G. H. Schleser; J. Frielingsdorf; A. Blair

1999-01-01

227

Mathematical models for petroleum-forming processes: carbon isotope fractionation  

Microsoft Academic Search

A mathematical model has been developed in which carbon isotope fractionation during thermal cracking of n -paraffins can be simulated. The model has been calibrated based on data from laboratory cracking experiments carried out on n -octadecane. Relative rate constants for cleavage of C 12 -C 12 , C 12 -C 13 and C 13 -C 13 bonds agree with

Douglas W. Waples; Leonard Tornheim

1978-01-01

228

Carbon isotope evidence for CAM photosynthesis in the Mesozoic  

Microsoft Academic Search

Crassulacean acid metabolism (CAM) photosynthesis, a flexible adaptation to water-stress, has not been shown to occur before the Pleistocene, despite suggestions that CAM first evolved in the Mesozoic or earlier. Here we report on multiple (‡7) positive organic carbon isotope excursions (d13Corg > )20& )i n Late Triassic and Early Jurassic (c. 200 Ma) sedimentary rocks from an arid terrestrial

John E. Decker; Maarten J. de Wit

2005-01-01

229

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

Microsoft Academic Search

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

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

2010-01-01

230

Stable Carbon Isotope Fractionation by Sulfate-Reducing Bacteria  

PubMed Central

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 ?13C values were determined for gaseous CO2, organic substrates, and products such as biomass. For three of the four SRB, carbon isotope effects between the substrates, acetate or lactate and CO2, and the cell biomass were small, ranging from 0 to 2‰. However, for Desulfotomaculum acetoxidans, the carbon incorporated into biomass was isotopically heavier than the available substrates by 8 to 9‰. SRB grown lithoautotrophically consumed less than 3% of the available CO2 and exhibited substantial discrimination (calculated as isotope fractionation factors [?]), as follows: for Desulfobacterium autotrophicum, ? values ranged from 1.0100 to 1.0123; for Desulfobacter hydrogenophilus, the ? value was 0.0138, and for Desulfotomaculum acetoxidans, the ? value was 1.0310. Mixotrophic growth of Desulfovibrio desulfuricans on acetate and CO2 resulted in biomass with a ?13C 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., H2), ecological forces can also influence carbon isotope discrimination by SRB.

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

2003-01-01

231

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

232

Partitioning peat respiration with stable carbon isotopes  

NASA Astrophysics Data System (ADS)

Equimolar production of CO2 and CH4 is assumed with methanogenesis. However, in both field and incubation studies of peat respiration, CO2 is continually reported to be in higher concentrations than CH4. It was assumed that this is due to loss of methane with ebullition and additional CO2 production by HMW organic matter fermentation. To determine the proportions of CO2 formed from both organic matter fermentation and methanogenesis and to determine the percent loss of CH4 from ebullition, isotope mass balance equations were developed. The 13C-CO2 measured in pore water represents a mixture between the 13C-CO2 from organic matter decomposition and methanogenesis. By collecting and analyzing pore water samples for ?13C and concentrations of both CO2 and CH4, the proportion of CO2 formed from organic matter fermentation and methanogenesis was calculated. It was found that, at 0, 154, and 261 cm depths, the percent CO2 from methanogenesis was 56%, 88%, and 91%, and the percent CH4 loss due to ebullition was 69%, 79%, and 85%, respectively. These findings indicate that with increasing depth both the percent CO2 formed from methanogenesis and the percent CH4 lost increased. Incubation experiments consisting of peat from five depth intervals (30-40, 70-80, 130-140, 170-180, and 270-280cm) were used to determine the accuracy of the isotope mass balance equations based on in situ concentrations and isotopic values. Measurements were made biweekly for concentrations and ?13C of CO2 and CH4. The percents of CO2 formed from methanogenesis based on the isotope mass balance equations were found to be to be 53%, 44%, 12%, 51%, and 54% corresponding to the respective depth ranges. The ratios of CH4/CO2 measured were 51%, 39%, 4%, 41%, and 54%, respectively. The average standard deviation between these sample sets was found to be ± 3.5%. This indicates that the isotope mass balance equations are an appropriate model for determining in situ CO2 partitioning in these systems.

Chanton, J.; Corbett, J.; Burdige, D. J.; Glaser, P. H.; Cooper, W. T.; Tfaily, M. M.

2010-12-01

233

Temperature and diet affect carbon and nitrogen isotopes of fish muscle: can amino acid nitrogen isotopes explain effects?  

Microsoft Academic Search

Stable isotope ratios of carbon (?13C) and nitrogen (?15N) are widely used in food-web studies to determine trophic positioning and diet sources. However in order to accurately interpret stable isotope data the effects of environmental variability and dietary composition on isotopic discrimination factors and tissue turnover rates must be validated. We tested the effects of temperature and diet on tissue

Alexandra L. Bloomfield; Travis S. Elsdon; Benjamin D. Walther; Elizabeth J. Gier; Bronwyn M. Gillanders

2011-01-01

234

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

NASA Astrophysics Data System (ADS)

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 provide novel information, but standard isotopic methods destroy ultrastructures by desiccating specimens and observations of ultrastructure require removal of carbonate tests, preventing isotope measurements. The approach described here preserves cellular ultrastructure during isotopic analyses by keeping the foraminifera in an aqueous buffer (Phosphate Buffered Saline (PBS)). The technique was developed and standardized with 36 aliquots of NBS-19 standard of similar weight to foraminiferal tests (5 to 123 ?g). Standard errors ranged from ± 0.06 to ± 0.85‰ and were caused by CO2 contaminants dissolved in the PBS. The technique was used to measure ?13C values of 96 foraminifera, 10 of which do not precipitate carbonate tests. Calcareous foraminiferal tests had corrected carbon isotope ratios of -8.5 to +3.2‰. This new technique allows comparisons of isotopic compositions of tests made by foraminifera known to be alive at the time of collection with their biological characteristics such as prey composition and presence or absence of putative symbionts. The approach may be applied to additional biomineralizing organisms such as planktonic foraminifera, pteropods, corals, and coccolithophores to elucidate certain biological controls on their paleoceanographic proxy signatures.

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

2010-06-01

235

A carbon isotope challenge to the snowball Earth.  

PubMed

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

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

2011-10-05

236

Reconstructing grassland vegetation and paleotemperatures using carbon isotope ratios of bison tooth enamel  

NASA Astrophysics Data System (ADS)

Carbon isotope ratios (?13C values) of herbivores reflect the ?13C values of dietary plants, and the ?13C values of grazers (animals that consume >90% grass) reflect the local abundance of C3 versus C4 grasses. Because grassland C3/C4 ratios correlate with climate, the ?13C of fossil grazers may serve as a proxy for reconstructing paleoclimates and paleovegetation patterns. However, the accuracy of environmental reconstructions based on herbivore ?13C values is often uncertain, because the relationship between the ?13C of many animals and the abundance of C4 and C3 grasses has not been precisely quantified. We analyzed the ?13C of tooth enamel carbonate from modern bison (Bison bison bison) from nine localities in the United States. The C4 grass biomass at these sites ranged from <1% to ˜95% of the total grass biomass. The mean ?13C of enamel for each population correlated well with the local abundance of C4 grasses and with variations in mean annual temperatures. The variability of enamel ?13C values did not differ among habitats and was not correlated with the abundance of C4 grasses. These results demonstrate that analyses of the ?13C values of fossil bison can be used as a quantitative proxy for reconstructing grassland C3/C4 ratios and paleotemperatures, and they will serve as a baseline for interpreting the ?13C of fossil bison and other large herbivores in North America.

Hoppe, Kathryn A.; Paytan, Adina; Chamberlain, Page

2006-08-01

237

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.

Szarek, Stan R.; Troughton, John H.

1976-01-01

238

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

NASA Astrophysics Data System (ADS)

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

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

2007-04-01

239

{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

240

Investigating the variations in carbon and nitrogen isotopes in carbonaceous chondrites  

NASA Astrophysics Data System (ADS)

The carbonaceous chondrites contain significant amounts of carbon- and nitrogen-bearing components, the most abundant of which is organic matter. Stepped combustion data of whole rock and HF/HCl residues of carbonaceous chondrites reveal that the organic material can be subdivided operationally into three components: (1) free organic matter (FOM), which is readily extractable from whole-rock meteorites and is enriched in 13C and 15N; (2) labile organic matter (LOM), which has a macromolecular structure but is liberated by hydrous pyrolysis; LOM is the parent structure for some FOM and is also enriched in 13C and 15N; and (3) refractory organic matter (ROM), which is also macromolecular but is virtually unaffected by hydrous pyrolysis and is relatively depleted in 13C and 15N. The macromolecular entities (LOM and ROM) are by far the most abundant organic components present, and as such, the relative abundances of the 13C- and 15N-enriched LOM and the 13C- and 15N-depleted ROM will have a major influence on the overall isotopic composition of the whole-rock meteorite. Laboratory experiments designed to simulate the effects of parent body aqueous alteration indicate that this form of processing removes LOM from the macromolecular material, allowing ROM to exert a stronger influence on the overall isotopic compositions. Hence, aqueous alteration of macromolecular materials on the meteorite parent body may have a significant control on the stable isotopic compositions of whole-rock carbonaceous chondrites. The enstatite chondrites are also carbon rich but have been subjected to high levels of thermal metamorphism on their parent body. Stepped combustion data of HF/HCl residues of enstatite chondrites indicate, that if they and carbonaceous chondrites inherited a common organic progenitor, metamorphism under reducing conditions appears to incorporate and preserve some of the 13C enrichments in LOM during graphitisation. However, when metamorphism is at its most extreme, the 15N enrichments in LOM are lost.

Sephton, M. A.; Verchovsky, A. B.; Bland, P. A.; Gilmour, I.; Grady, M. M.; Wright, I. P.

2003-06-01

241

(Carbon isotope fractionation in plants): Annual technical progress report  

SciTech Connect

Plants fractionate carbon isotopes during photosynthesis in ways which reflect photosynthetic pathway and environment. The fractionation is product of contributions from diffusion, carboxylation and other factors which can be understood using models which have been developed in our work. The object of our work is to use this fractionation to learn about the factors which control the efficiency of photosynthesis. Unlike previous studies, we do not rely principally on combustion methods, but instead develop more specific methods with substantially higher resolving power. We have recently developed a new short-term method for studying carbon isotope fractionation which promises to provide a level of detail about temperature, species, and light intensity effects on photosynthesis which has not been available until now. We are studying the isotopic compositions of metabolites (particularly aspartic acid) in C/sub 3/ plants in order to determine the role of phosphoenolpyruvate carboxylase in C/sub 3/ photosynthesis. We are studying the relative roles of diffusion and carboxylation in nocturnal CO/sub 2/ fixation in CAM plants. We are studying the use of isotopic content as an index of water-use efficiency in C/sub 3/ plants. We are developing new methods for studying carbon metabolism in plants. 3 refs

O'Leary, M.H.

1988-01-01

242

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

NASA Astrophysics Data System (ADS)

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

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

1995-09-01

243

A novel carbon isotope biomarker for dietary sugar.  

PubMed

Light element isotope signatures have been used to study food webs in many ecological niches, including those of ancient humans, but to a far lesser extent in modern humans. A recent paper presented results from a pilot study testing the utility of carbon isotope ratio analysis of alanine to measure an individual's sugar intake in the United States. A strong correlation was found between the enrichment of (13)C in alanine and sugar-sweetened beverage consumption. This candidate biomarker of sugar consumption deserves further consideration as an objective marker for use in the study of the relationship between sugar intake and health. PMID:23616500

Schoeller, Dale A

2013-04-24

244

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

NASA Astrophysics Data System (ADS)

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 Ag 2S materials enriched in 32S, 33S, and 34S. All materials were converted into SF 6 gas and subsequently, their sulfur isotope ratios were measured on the SF 5+ species using a special gas source mass spectrometer equipped with a molecular flow inlet system (IRMM's Avogadro II amount comparator). Values for the 32S/ 34S abundance ratios are 22.650 4(20), 22.142 4(20), and 23.393 3(17) for IAEA-S-1, IAEA-S-2, and IAEA-S-3, respectively. The calculated 32S/ 34S abundance ratio for V-CDT is 22.643 6(20), which is very close to the calibrated ratio obtained by Ding et al. (1999). In this way, the zero point of the VCDT scale is anchored firmly to the international system of units SI. The 32S/ 33S abundance ratios are 126.942(47), 125.473(55), 129.072(32), and 126.948(47) for IAEA-S-1, IAEA-S-2, IAEA-S-3, and V-CDT, respectively. In this way, the linearity of the V-CDT scale is improved over this range. The values of the sulfur molar mass for IAEA-S-1 and V-CDT were calculated to be 32.063 877(56) and 32.063 911(56), respectively, the values with the smallest combined uncertainty ever reported for the sulfur molar masses (atomic weights).

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

2001-09-01

245

Stable carbon isotope records of carbonates tracing fossil seep activity off Indonesia  

Microsoft Academic Search

Stable isotope records of carbonates from up to 20 m long sediment cores from the forearc basin of the Sunda arc display significant 13C depletion, deviating from expected normal marine levels by 5 to 40‰ (Peedee belemnite (PDB)). This depletion is interpreted to be caused by methane seepage and associated authigenic carbonate precipitation in sediments near the seafloor. About 2-?m-sized

M. Wiedicke; W. Weiss

2006-01-01

246

Cavity Ring-down Spectroscopy for Carbon Isotope Analysis with 2 {mu}m Diode Laser  

SciTech Connect

We have made a prototype based on CRDS with 2 {mu}m diode laser for carbon isotope analysis of CO{sub 2} in air. The carbon isotope ratio was obtained to be (1.085{+-}0.012)x10{sup -2} which shows good agreement with the isotope ratio measured by the magnetic sector-type mass spectrometer within uncertainty. Hence, we demonstrated the carbon isotope analysis based on CRDS with 2 {mu}m tunable diode laser.

Hiromoto, K.; Tomita, H.; Watanabe, K.; Kawarabayashi, J.; Iguchi, T. [Graduate School of Engineering, Nagoya University, Nagoya, Aichi 464-8603 (Japan)

2009-03-17

247

Natural Abundance Variations in Stable Isotopes and their Potential Uses in Animal Physiological Ecology  

Microsoft Academic Search

Chemical, biological, and physical processes lead to distinctive “isotopic signatures” in biological materials that allow tracing of the origins of organic substances. Isotopic variation has been extensively used by plant physiological ecologists and by paleontologists, and recently ecologists have adopted the use of stable isotopes to measure ecosystem patterns and processes. To date, animal physiological ecologists have made minimal use

Leonard Z. Gannes; Carlos Mart??nez del Rio; Paul Koch

1998-01-01

248

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

NASA Astrophysics Data System (ADS)

Stable carbon isotope composition (?13C) of carbonate sediments and the molecular (biomarker) characteristics of a continuous Permian-Triassic (PT) layer in southern China were studied to obtain geochemical signals of global change at the Permian-Triassic boundary (PTB). Carbonate carbon isotope values shifted toward positive before the end of the Permian period and then shifted negative above the PTB into the Triassic period. Molecular carbon isotope values of biomarkers followed the same trend at and below the PTB and remained negative in the Triassic layer. These biomarkers were acyclic isoprenoids, ranging from C15 to C40, steranes (C27 dominates) and terpenoids that were all significantly more abundant in samples from the Permian layer than those from the Triassic layer. The Triassic layer was distinguished by the dominance of higher molecular weight (waxy) n-alkanes. Stable carbon isotope values of individual components, including n-alkanes and acyclic isoprenoids such as phytane, isop-C25, and squalane, are depleted in ?13C by up to 8-10‰ in the Triassic samples as compared to the Permian. Measured molecular and isotopic variations of organic matter in the PT layers support the generally accepted view of Permian oceanic stagnation followed by a massive upwelling of toxic deep waters at the PTB. A series of large-scale (global) outgassing events may be associated with the carbon isotope shift we measured. This is also consistent with the lithological evidence we observed of white thin-clay layers in this region. Our findings, in context with a generally accepted stagnant Permian ocean, followed by massive upwelling of toxic deep waters might be the major causes of the largest global mass extinction event that occurred at the Permian-Triassic boundary.

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

2012-07-01

249

Investigating the Formation of Pedogenic Carbonate Using Stable Isotopes  

NASA Astrophysics Data System (ADS)

The stable isotope composition of pedogenic carbonate has been used as a paleoenvironmental proxy because it is thought to form in isotopic equilibrium with soil CO2 and soil water, which are influenced by vegetation type and atmospheric circulation patterns, respectively. However, the isotopic composition of soil CO2 and soil water change seasonally and it is not known what portion of this variability is recorded by the isotopic composition of pedogenic carbonate. It is generally believed that carbonate precipitation in soils is driven by evaporative concentration of Ca ions and/or decreasing soil pCO2. We seek to improve the proxy by determining the seasonality of pedogenic carbonate formation, in particular whether pedogenic carbonate forms during the wet season after individual rainstorms or during seasonal drying following the wet season. This was done by comparing the variations in carbon and oxygen isotope composition of soil CO2 with the isotopic composition of proximally located, newly-formed carbonates. Soil CO2 and incipient pedogenic carbonate coatings were collected in a very young (< 500yrs) soil developing in an inset terrace on the piedmont of the Sandia Mountains, central New Mexico. We also measure soil temperatures at the same site. In May 2006, at the end of the driest 6-month period on record in central New Mexico, soil CO2 profiles displayed a 2‰ decrease in ?13C values with depth from 9 to 100 cm. In August 2006, the shapes of the profiles were similar, but the ?13C values were 3-4‰ lower at each depth than in May. These results can be explained by an increase in respiration rate during the latter half of the summer (the wettest on record) when monsoon rainfall maintained high moisture contents in soils across New Mexico. Calculated ?13C values of calcite in equilibrium with May (but not August) soil CO2 agree with measured carbonate ?13C values below 20 cm depth. Very shallow carbonate has anomalously high ?13C values. Measurements of the ?18O values of soil CO2 collected in May span a 16‰ range with the highest values and steepest gradient just below the surface. In August, the lowest ?18O values measured were just below the surface and there was little change with depth below 35 cm. These results can also be explained by August rainfall which likely lowers the ?18O value of near surface soil water and also near surface soil CO2 via oxygen exchange. Neither the May nor August CO2 values are in equilibrium with the pedogenic carbonate at measured temperatures, but the shape of the ?18O CO2 profiles from May more closely approximate the carbonate ?18O profile. Our results to date suggest that the majority of pedogenic carbonate in this soil forms when the soil is relatively dry. It is possible that the magnitude of soil water evaporation during the period between daily thunderstorms is insufficient to drive carbonate precipitation. Sufficient evaporation may primarily occur during seasonal drying in the autumn. We will test this hypothesis by continuing to sample soil CO2 at this site.

Breecker, D. O.; Sharp, Z. D.; McFadden, L.

2006-12-01

250

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

NASA Astrophysics Data System (ADS)

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

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

2005-07-01

251

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

NASA Astrophysics Data System (ADS)

The carbonate clumped isotope thermometer is based on the temperature sensitivity of the relative abundance of carbonate ion groups containing 13C-18O bonds. One application of clumped isotope thermometry is to determine the temperature of ancient seawater from the skeletal material of calcium carbonate-secreting marine organisms. The relationship between ?47, a parameter describing isotopic clumping, and the temperature of carbonate biomineralization has been well-defined for fish otoliths, corals, foraminifera, and coccolithophore tests, but few data have been published for brachiopods and bivalve mollusks. A comprehensive evaluation of the ?47-temperature relationship for mollusks is required for paleotemperature interpretations from the marine fossil record. Here we present a more comprehensive calibration for modern mollusks, including bivalves, cephalopods, and gastropods. Further, we focus on a subset of cold water, high-latitude species collected in the northern Barents Sea. The observed ?47-temperature relationship is similar to the theoretical relationship presented by Guo et al. (2009) but deviates at low temperatures from the original Ghosh et al. (2007) calibration curve. This divergence could be related to methodological differences or unaccounted differences in the biomineralization of mollusks versus that of other carbonate-secreting organisms at low temperature. One advantage of clumped isotope thermometry over traditional oxygen isotope thermometry is that it does not require assumptions about the isotopic composition of the water in which the carbonate formed. This may be particularly useful in Mesozoic paleoceanography where the oxygen isotope value of seawater is uncertain. Using clumped isotope thermometry applied to early Cretaceous (Valangian) belemnite carbonate from the Yatria River, sub-polar Urals, Siberia, we find shell growth temperatures of 20-26°C at a paleolatitude of ~60-65°N. Our data imply average seawater ?18O values of 0.5-1.5‰ when used in conjunction with published temperature-?18Ocarb-?18Osw calibrations. This ?18O range is higher than is traditionally assumed for high-latitude Cretaceous seawater. We argue, however, that such values are plausible and may be related to different basin- or global-scale hydrologies or belemnite body fluid that was in isotopic disequilibrium with the seawater. The paired ?47 and ?18O from the fossils rule out isotopic exchange with high temperature fluids or later diagenesis in 18O-depleted meteoric waters. We observe no textual or chemical evidence of recrystallization, and we hypothesize that these shells faithfully record early Cretaceous high-latitude seawater temperatures. The inferred temperature range of 20-26°C is substantially higher than 60-70°N modern mean annual sea surface temperature (˜-1.0 to 10.0°C) and mean summer surface temperatures (˜-0.5 to 14.5°C), implying a substantially shallower latitudinal temperature gradient during the early Cretaceous.

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

2010-12-01

252

The Carbon Monoxide Abundance in Comet 103P/Hartley  

NASA Astrophysics Data System (ADS)

We report the detection of several emission bands in the CO Fourth Positive Group (4PG) from comet 103P/Hartley during ultraviolet spectroscopic observations from the Hubble Space Telescope (HST). Our team was allocated a total of 15 orbits of HST time to observe 103P during the fall of 2010, which we divided into three 5-orbit observing runs: on September 25 (r = 1.15 AU, ? = 0.22 AU), on November 4 (r = 1.06 AU, ? = 0.16 AU; EPOXI closest approach was on Nov 4.5832 UT), and on November 28 (r = 1.14 AU, ? = 0.28 AU). On the latter two dates we detected CO 4PG emission near 1500 Å using the Cosmic Origins Spectrograph (COS) with the G160M grating (Figure 1). The CO emissions exhibited short-term temporal variability at the level of ?30%, apparently in phase with the rotation of the comet's nucleus. For the spectra taken at the time of the EPOXI flyby, we derived a CO/H2O ratio of 0.15-0.45% [3]. Our preliminary analysis gives a similar CO abundance on November 28; the final estimates will be presented at the meeting.

Weaver, H. A.; Feldman, P. D.; A'Hearn, M. F.; Dello Russo, N.; Stern, S. A.

2011-10-01

253

BIOGENIC VS. ABIOGENIC ISOTOPE SIGNATURES OF REDUCED CARBON COMPOUNDS: A LESSON FROM HYDROTHERMAL SYNTHESIS EXPERIMENTS  

SciTech Connect

With growing interest in and demonstrated cases of inorganic hydrothermal synthesis of reduced or organic carbon compounds from CO and CO{sub 2}, it becomes crucial to establish geochemical criteria to distinguish reduced/organic carbon compounds of abiogenic origin from those of biogenic origin with overwhelming abundances on the surface and in subsurface of the Earth. Chemical and isotopic compositions, particularly {sup 13}C/{sup 12}C ratios, of reduced/organic carbon compounds have been widely utilized for deducing the origins and formation pathways of these compounds. An example is isotopic and C{sub 1}/(C{sub 2}+C{sub 3}) ratios of natural gases, which have been used to distinguish bacterial, thermogenic, and possible abiogenic origins. Another example is that ancient graphitic carbon with {delta}{sup 13}C values c-25per thousand has been considered of biogenic origin. Although these criteria could be largely valid, growing data including those from our hydrothermal experiments suggest that a great caution must be exercised.

Horita, J.

2001-06-13

254

Estimation of the Error in Carbon Dioxide Column Abundances Retrieved from GOSAT Data  

Microsoft Academic Search

In this chapter, the estimation of error in the method used to retrieve carbon dioxide (CO2) column abundances obtained from the Greenhouse Gases Observing Satellite (GOSAT) is presented. GOSAT will be the first satellite\\u000a dedicated to primarily observe CO2 and methane (CH4), which are considered to be major greenhouse gases, from space. The column abundances of CO2 and CH4 can

Mitsuhiro Tomosada; Koji Kanefuji; Yukio Matsumoto; Hiroe Tsubaki; Tatsuya Yokota

255

13 C abundance, water-soluble and microbial biomass carbon as potential indicators of soil organic carbon dynamics in subtropical forests at different successional stages and subject to different nitrogen loads  

Microsoft Academic Search

Chronic atmospheric nitrogen deposition affects the cycling of carbon (C) and nitrogen (N) in forest ecosystems, and thereby\\u000a alters the stable C isotopic abundance of plant and soil. Three successional stages, disturbed, rehabilitated and mature forests\\u000a were studied for their responses to different nitrogen input levels. N-addition manipulative experiments were conducted at\\u000a low, medium and high N levels. To study

Hua-Jun Fang; Gui-Rui Yu; Shu-Lan Cheng; Jiang-Ming Mo; Jun-Hua Yan; Shenggong Li

2009-01-01

256

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

Microsoft Academic Search

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 delta66Zn (reported relative to the JMCLyon standard) and Zn\\/Si ratios from the Southern Ocean diatomopal samples range from

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

2011-01-01

257

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

Microsoft Academic Search

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

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

2011-01-01

258

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

Microsoft Academic Search

The carbon isotopic composition of mollusc shell carbonate has been used as a general environmental indicator in numerous studies, but relatively little is known of the factors which affect within-shell variation. Primary control of delta¹³C values in shell carbonate comes from the dissolved bicarbonate source, particularly as related to marine versus fresh water. Present models explain cyclic variations in the

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

1985-01-01

259

The Paleozoic to Mesozoic carbon cycle revisited: The carbon isotopic composition of terrestrial organic matter  

Microsoft Academic Search

Two thousand one hundred forty-eight carbon isotope values for terrestrial organic matter (plant fossils, coal, bulk terrestrial organic matter) provide a proxy record for temporal changes in the global carbon cycle. ?13CTOM, ?13Ccarb, and ?13CCO2 allow a full evaluation of carbon transfer in the atmosphere-ocean system as well as between the marine and the terrestrial realm. The temporal evolution of

Harald Strauss; Wolfgang Peters-Kottig

2003-01-01

260

The Paleozoic to Mesozoic carbon cycle revisited: The carbon isotopic composition of terrestrial organic matter  

Microsoft Academic Search

Two thousand one hundred forty-eight carbon isotope values for terrestrial organic matter (plant fossils, coal, bulk terrestrial organic matter) provide a proxy record for temporal changes in the global carbon cycle. delta13CTOM, delta13Ccarb, and delta13CCO2 allow a full evaluation of carbon transfer in the atmosphere-ocean system as well as between the marine and the terrestrial realm. The temporal evolution of

Harald Strauss; Wolfgang Peters-Kottig

2003-01-01

261

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

NASA Astrophysics Data System (ADS)

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

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

2009-05-01

262

Can the carbon isotopic composition of methane be reconstructed from multi-site firn air measurements?  

NASA Astrophysics Data System (ADS)

Methane is a strong greenhouse gas and large uncertainties exist concerning the future evolution of its atmospheric abundance. Analyzing methane atmospheric mixing and stable isotope ratios in air trapped in polar ice sheets helps in reconstructing the evolution of its sources and sinks in the past. This is important to improve predictions of atmospheric CH4 mixing ratios in the future under the influence of a changing climate. We present an attempt to reconcile methane carbon isotope (?13C(CH4)) records from 11 boreholes in firn from both Greenland and Antarctica to reconstruct a consistent ?13C(CH4) history over the last 50 years. In the firn, the atmospheric signal is altered mainly by diffusion and gravitation. These processes are taken into account by firn air transport models. We show that (?13C(CH4) reconstructions from individual sites are not always mutually consistent among the different sites. Therefore we apply for the first time a multisite isotope inversion to reconstruct an atmospheric isotope history that is constrained by all individual sites, generating a multisite ?13C(CH4) scenario. The comparison of this scenario with ice core data, atmospheric air archive results and direct atmospheric monitoring data shows that inconsistencies exist between the different types of profiles which may be explained by inter-laboratory calibration differences, by analytical errors or by the lack of constraints on the diffusive fractionation estimates.

Sapart, Célia Julia; Martinerie, Patricia; Chappellaz, Jérôme; van de Wal, Roderik; Witrant, Emmanuel; Sperlich, Peter; van der Veen, Carina; Bernard, Sophie; Sturges, Bill; Blunier, Thomas; Schwander, Jakob; Etheridge, David; Röckmann, Thomas

2013-04-01

263

Carbon isotopic enrichment in Titan's tholins? Implications for Titan's aerosols  

NASA Astrophysics Data System (ADS)

Since the discovery of the main composition of Titan's atmosphere, many laboratory experiments have been carried out to reproduce its chemical evolution, particularly the formation of organic haze particles found throughout this atmosphere. Some of these simulations have produced solid products - referred to as Titan's tholins - that are assumed to have properties similar to those of Titan's aerosols. In the present work, we focus on the possible isotopic fractionation of carbon during the processes involved in the formation of Titan's tholins. Initial 12C/ 13C isotopic ratios measured on tholins made in the laboratory using cold plasma discharges are presented. Measurements of isotopic enhancement in 13C ( ?13C), both on tholins and on the initial gas mixture (N 2:CH 4 (98:2)) used to produce them do not show any clear deficit or enrichment in 13C relative to 12C in the lab-made tholins compared to the initial gas mixture. Preliminary data recovered from the Aerosol Collector Pyrolyzer (ACP) experiment of the Huygens probe suggests that Titan's aerosols may also be exempt of carbon isotopic enrichment. This observation creates possibilities for deeper analysis of ACP experiment data.

Nguyen, M.-J.; Raulin, F.; Coll, P.; Derenne, S.; Szopa, C.; Cernogora, G.; Israël, G.; Bernard, J.-M.

2007-11-01

264

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

SciTech Connect

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

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

1990-01-01

265

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

266

Carbon abundances from SDSS globular clusters: exploring the origin in the large spread in [C/Fe  

NASA Astrophysics Data System (ADS)

Globular clusters were once thought to be chemically homogeneous systems with a single stellar population. However, recent results suggest the presence of more than one stellar population among most all globular clusters. These stars have a different abundance pattern compared to halo stars of similar metallicities. To understand globular cluster formation in the context of hierarchical Galaxy formation models, it is necessary to understand the origin of their abundance patterns. We have used the SDSS spectra from Data Release 8 to estimate the carbon abundances for member stars in 5 globular clusters. We find large spreads in the carbon abundances throughout the CMDs of the clusters, indicating multiple populations with different carbon abundances.

Fiorenza, S. L.; Sivarani, T.; Susmitha, A.; Lee, Y. S.; Beers, T. C.

267

Carbon isotopic variation in spectral type II diamonds  

Microsoft Academic Search

The results of a survey of type II diamonds to identify any systematic association between delta C-13 and the diamond type are reported. The sealed-tube technique was employed, with the type II classification verified by IR techniques. The delta C-13 values were spread from -31.9 to -0.5 per thousand, covering nearly the entire previous carbon isotope range measured for diamonds.

H. J. Milledge; M. J. Mendelssohn; M. Seal; J. E. Rouse; P. K. Swart; C. T. Pillinger

1983-01-01

268

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

269

Carbon Isotope Discrimination in Photosynthesis of CAM Plants  

Microsoft Academic Search

SUCCULENT plants capable of Crassulacean acid metabolism (CAM) show extremely variable carbon isotope discrimination ratios1,2. This ratio, usually expressed as a delta13C value referred to a standard3, has emerged as a useful diagnostic criterion to determine photosynthetic pathways in higher plants3-5. Species with the C4 photosynthetic pathway6 show less negative delta13C values than do species with the C3 photosynthetic pathway.

C. B. Osmond; W. G. Allaway; B. G. Sutton

1973-01-01

270

Insights from Stable Isotopes on the Role of Terrestrial Ecosystems in the Global Carbon Cycle  

Microsoft Academic Search

The use of isotopic tracers in organic matter, water, and atmospheric gases has become an important component of the study of ecology and global change. Physiological and physical processes discriminate against heavy isotopes in predictable ways, so that measurements of isotopes at natural abundance, i.e., naturally occurring concentrations as opposed to artificial labeling experiments, can provide useful information about biological

Diane E. Pataki; Chun-Ta Lai; Charles D. Keeling; James R. Ehleringer

271

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

PubMed

Organic and inorganic carbon in terrestrial near-surface environments are characterized by a marked difference in their 13C/12C ratios which can be traced back in the Earth's sedimentary record over almost 4 billion years. There is no doubt that the bias in favour of 12C displayed by biogenic matter derives, for the most part, from the isotope-selecting properties of the carbon-fixing enzyme (ribulose-1,5-bisphosphate carboxylase) that is operative in the principal photosynthetic pathway and promotes most of the carbon transfer from the non-living to the living realm. Postulating a universality of biological principles in analogy to the proven universality of the laws of physics and chemistry, we may expect enzymatic reactions in exobiological systems to be beset with B similar kinetic fractionation effects. Hence, the retrieval from the oldest Martian sediments of isotopic fractionations between reduced and oxidized (carbonate) carbon may substantially constrain current conjectures on the possible existence of former life on Mars. PMID:11538127

Schidlowski, M

1992-01-01

272

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 (5.6 ± 1.2‰) was consistent with values reported for omnivorous mammals consuming monoisotopic diets. These primate-specific apparent enrichment values will be a valuable tool for cross-species comparisons. Additionally, they will facilitate dietary comparisons between living and fossil primates. Electronic supplementary material The online version of this article (doi:10.1007/s00442-010-1701-6) contains supplementary material, which is available to authorized users.

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

2010-01-01

273

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

274

Plate Tectonics and Terrestrial Carbon Isotope Records  

NASA Astrophysics Data System (ADS)

In 2001, we reported a negative excursion in early-Aptian atmospheric ?13CO2 (? = -3.6 to -6.5‰), based on ?13C analyses of organic matter and land-plant isolates from coarsely-sampled Colombian estuarine and near-shore sediments. Here we present similar results for an Aptian section of the Arundel Clay (Potomac Group, central Maryland), which is well-known for its exceptional preservation of terrestrial plant materials. Sampling across 13 meters of sediment at ~10-cm intervals revealed a clear shift in the ?13C of terrestrial organic matter (n=153) and land-plant isolates (n=33) of ? = -2.3 and -2.9 ‰, respectively. The shift was observed within palynological Zone I, which is temporally well-correlated with our previous work. Using an empirical relationship between ?13Cplant and ?13Catm, we calculated ??13Catm = -2.1 to -2.6 ‰ during the early Aptian from the Arundel Clay shift. Given the probable composition of the early Cretaceous atmosphere, mass balance calculations favor a methane hydrate release as the cause of this excursion. In consideration of a mechanism for methane release, we calculated changes in global subduction indicated by the well-established and rapid 2-fold increase in seafloor production that was unique within the early Aptian compared to the last 144 million years. We show that increased frictional interaction between overriding and subducting plates caused uplift and compression sufficient to continuously destabilize a portion of the probable methane hydrate reservoir, thus creating a perturbation in the C-isotope record of the Aptian atmosphere, as reflected in the ?13C of terrestrial photosynthesizers. The Aptian methane release is a new example of mechanistic coupling between major tectonic events and the global biosphere.

Jahren, H.; Conrad, C.; Arens, N.

2005-12-01

275

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

NASA Astrophysics Data System (ADS)

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

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

1996-09-01

276

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

277

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 it’s dissolution in the hypolimnion. The purpose of the current project is to present extensive background study to form the framework for quantifying the carbon isotope evolution with multiple reaction pathways. Carbon isotope composition of dissolved inorganic carbon is being analyzed. Wigley-Plummer-Pearson mass transfer model will be used for the quantification of carbon isotope reaction pathways.

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

2010-12-01

278

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

SciTech Connect

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

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

1990-08-01

279

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...

280

Isotopic abundance measurements on solid nuclear-type samples by glow discharge mass spectrometry  

Microsoft Academic Search

A double-focusing Glow Discharge Mass Spectrometer (GDMS) installed in a glovebox for nuclear sample screening has been employed for isotopic measurements. Isotopic compositions of zirconium, silicon, lithium, boron, uranium and plutonium which are elements of nuclear concern have been determined. Interferences arising from the matrix sample and the discharge gas (Ar) for each of these elements are discussed. The GDMS

Maria Betti; Gert Rasmussen; Lothar Koch

1996-01-01

281

Natural Abundance Isotopic Fractionation in the Fermentation Reaction: Influence of the Fermentation Medium  

Microsoft Academic Search

The isotopic parameters of fermentation products provide reliable criteria for characterizing their carbohydrate precursors on the condition that the isotopic coefficients which relate individual sites in the products and in the reactants have strictly reproducible or predictible values. Since fermentation may be performed either in natural media (such as fruit juices) which exhibit variable compositions or in “synthetic” media prepared

Ben-Li Zhang; Yunianta; Claude Vallet; Maryvonne L. Martin

1997-01-01

282

Were carbon isotopic gradients in post-snowball oceans inverted?  

NASA Astrophysics Data System (ADS)

In the Otavi Group of Namibia, 900 m of platform carbonate strata above the 635-Ma post-glacial cap dolostone are consistently lighter in ?13C by up to 2.5 per mil than the adjacent 180-320 m of correlative, >0.6-km-deep, foreslope strat. Assuming the foreslope carbonate was equilibrated with deeper water, the normal isotopic gradient dynamically sustained by the biological 'pump' was inverted. Geochronology of isotopically correlative Doushantuo strata in South China suggests that the inverted gradient lasted for ~2 Myr after the glacial termination. Thereafter, the inverted gradient disappears. A similar transient inverse gradient follows the older Cryogenian glaciation in Arctic Alaska. We hypothesize that the inverse gradients reflect high pCO2 in the glacial aftermaths. This had two consequences. First, the size of the DIC pool was enlarged, reducing the isotopic effect of the biological pump. Second, isotopic fractionation was strongly temperature-dependent due to the large fractionation between CO2 and CO32- coupled with the dominance of CO2(gas) among carbon species at pH<7.2. A difference in SST of ~25° between the areas of air-sea equilibration is required to account for a 2.5 per mil gradient in ?13C. This is realized in non-upwelling zones of the southern hemisphere today, where warm subtropical surface waters are underlain by Antarctic Intermediate Water. For our hypothesis to be valid, a large meridional temperature gradient must have coexisted with strong CO2 radiative forcing.

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

2008-12-01

283

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

USGS Publications Warehouse

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

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

2006-01-01

284

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

NASA Astrophysics Data System (ADS)

We have carried out Os-isotope analyses, and major and trace element determinations, on samples from the Permo-Triassic section at Meishan B sections, adjacent to the GSSP, China, to assess environmental change at the P-Tr boundary (Bed 27) and the underlying main extinction horizon (Bed 25). Major and trace element abundances were determined by XRF on 38 samples from a 2.3-metre interval of limestone, shale and dolomitic marl from Bed 24a to Bed 32. Re, Os and Mo abundances, and Os-isotope compositions, were determined on a subset of 26 samples, predominantly dark-coloured mudrocks; new Mo-isotope data will be presented. Initial 187Os/188Os(t=250Ma) ranges from 0.3 to 2, with no obvious pattern of change up-section. The data thus provide no unambiguous evidence at Meishan for major perturbation of seawater 187Os/188Os in this region of Palaeotethys, at least at the scale of the sampling. This is unlike early Jurassic and end-Cretaceous boundary sections, and mid-Cretaceous OAE intervals, which record substantial shifts in seawater 187Os/188Os that clearly reflect the influence of LIP emplacement. Major changes in elemental abundances occur between Beds 24 and Bed 27, accompanying the documented excursion in d13C. Redox- and biologically-sensitive elements such as Cu, Ni, P, V and Zn show strong fluctuations in abundance throughout Bed 24, even when abundances are normalised using Al2O3 to minimise the effects of carbonate dilution. In the lower part of Bed 27, however, the Al2O3-normalised concentrations of these elements decrease by an order of magnitude, and remain consistently low in the overlying Triassic marls. The relative decreases in Re and Os abundances throughout Bed 27 are even more substantial. Whilst these decreases are partly an artefact of Al-normalisation, the changes are accompanied by large increases in ratios involving lithogenous elements such as REE, Nb, Zr, Th and Ti. The data thus record a dramatic change in the marine depositional environment at Meishan, particularly within Bed 27, although levels of redox-sensitive elements were also very low within the upper part of Bed 24. A possible cause of these changes may have been an increase in the flux of terrigenous material, but this is not reflected by any obvious changes in 187Os/188O. Alternatively, these observations may reflect the occurrence of widespread oceanic anoxia in distal but contiguous water masses that caused a sudden reduction in the abundance of redox-sensitive elements in seawater. If the Meishan seas were fully open with Paleotethys, then seawater anoxia was global, as suggested by other studies. These results, combined with new Mo-isotope data, will shed further light on the phenomenon of marine anoxia in the vicinity of the P-Tr boundary and its relationship to the largest mass extinction of the Phanerozoic.

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

2009-12-01

285

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

286

Stable isotope composition of the carbonate concretion in loess and climate change  

Microsoft Academic Search

Carbonate concretions are commonly found in the loess in China. Oxygen and carbon isotopic compositions of carbonate concretions collected from 14 different paleosols (S1–S14) in the Lishi Formation of Luochuan loess section, China were analysed. The isotopic compositions of concretion in loess are useful tools in paleoclimatic study. Usually the more developed the paleosol is, the less negative the ?18O

Jiamao Han; Edward Keppens; Tungsheng Liu; Roland Paepe; Wenying Jiang

1997-01-01

287

Carbon isotopes and the oldest record of life: potential and limits  

Microsoft Academic Search

The currently available sedimentary carbon isotope record goes back to 3.85 Ga and conveys a remarkably consistent isotopic signal of biological carbon fixation based on the bias for light carbon ((superscript 12)C) exercised by common photosynthetic pathways. This holds particularly for the time segment < 3.5 Ga, whereas the older (Isua) record is blurred by a metamorphic overprint. In spite

Manfred Schidlowski

1997-01-01

288

Contribution of isotopic biogeochemistry (C, N, O) to the paleoecology of mammoths (mammuthus primigenius)  

Microsoft Academic Search

Carbon isotopic abundances in Alaskan, Albertan and Russian mammoths indicate a diet of C3?plants. The relatively high nitrogen isotopic abundances suggest arid conditions in Alberta and Alaska during the last ice age, and similar conditions in Russia. Nitrogen isotopic abundances are higher in mammoths relative to coeval herbivores, which may be due to differences in protein content of their diet.

Hervé Bocherens; Marc Fizet; André Mariotti; Roland A. Gangloff; James A. Burns

1994-01-01

289

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

EPA Science Inventory

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

290

Hydrogen and carbon isotopic measurements of methane from agricultural combustion: Implications for isotopic signatures of global biomass burning sources  

Microsoft Academic Search

The hydrogen and carbon isotope ratios of CH4 emitted from one bonfire and two laboratory combustions of agricultural residues were determined in this study as ?196 to ?262‰ for ?D and ?19.9 to ?35.1‰ for ?13C. The isotopic difference between CH4 emitted from biomass burning and fuel biomass, that is, the apparent isotopic fractionation occurring during combustion ($\\\\varepsilon$Burn), was within

Keita Yamada; Yoko Ozaki; Fumiko Nakagawa; Shigeto Sudo; Haruo Tsuruta; Naohiro Yoshida

2006-01-01

291

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

292

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

293

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

294

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

Microsoft Academic Search

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

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

1994-01-01

295

Regime of carbon compounds in carbonatites in Uzbekistan: Evidence from carbon isotopic composition and thermodynamic simulations  

Microsoft Academic Search

Thermodynamic analysis of equilibria between minerals (with regard for their compositions) in carbonatites of the Chagatai\\u000a complex, Uzbekistan, provides us with the possibility of estimating the oxygen fugacity at which carbonates could occur in\\u000a equilibrium with elementary carbon. Isotopic studies and thermodynamic simulations show that graphite started to crystallize\\u000a at 775°C and an oxygen fugacity value approximately one logarithmic unit

L. N. Kogarko; I. D. Ryabchikov; F. K. Divaev; F. Wall

2010-01-01

296

Effect of progressive acidification on stable carbon isotopes of dissolved inorganic carbon in surface waters  

Microsoft Academic Search

Acidification of surface waters by acid mine drainage (AMD) contamination or atmospheric deposition perturbs the carbonate equilibrium, with unknown effects to the isotope ratio of dissolved inorganic carbon (DIC). We progressively acidified samples of NaHCO3, stream water, groundwater, and spring water contaminated by AMD (AMD spring) to a pH < 3 using H2SO4 under open conditions (exposed to the atmosphere)

Hendratta N. Ali; Eliot A. Atekwana

2009-01-01

297

(Invited Review Paper) Factors Affecting the Isotopic Composition of Organic Matter. (1) Carbon Isotopic Composition of Terrestrial Plant Materials  

Microsoft Academic Search

The stable isotope composition of the light elements (i.e., H, C, N, O and S) of organic samples varies significantly and, for C, is also unique and distinct from that of inorganic carbon. This is the result of (1) the isotope composition of reactants, (2) the nature of the reactions leading to formation and post-formational modification of the samples, (3)

HSUEH-WEN YEH; WEI-MIN WANG

298

A Study of the Abundances of Light Isotopes in Cosmic Rays with a Superconducting Magnet Instrument.  

NASA Astrophysics Data System (ADS)

The balloon-borne Superconducting Magnet Instrument for Light Isotopes flew for the second time on July 24 -25, 1991 at the altitude of 36 km during conditions of extremely high solar modulation. The detector was designed to measure the charge, rigidity, and velocity of cosmic rays heavier than hydrogen within the kinetic energy range 100-2000 MeV/nucleon. The helium spectrum measured over this wide energy range is consistent with an interstellar helium spectrum expressed as a power law in the rigidity with spectral index of -2.68 and modulated to a level given by the solar modulation parameter phi = 1.5 GV. The ^2H/^4 He ratio measured in the kinetic energy range 100 -200 MeV/nucleon at 1 A.U. is consistent with the previous measurements made at similar solar modulation levels, but the uncertainties related to the production of secondary deuterons by the primary cosmic ray protons in the medium above the detector make these results upper limits. The derived corrections for the secondary fluxes of protons and deuterons at low kinetic energies are compared with the published data. This comparison results in the conclusion that the kinematics of the nuclear interactions is very important in determining accurate fluxes of secondary protons and deuterons. The low kinetic energy ^3He/ ^4He ratio at 1 A.U. is determined more accurately due to a smaller contribution from secondary production to the ^3He flux measured at the atmospheric depth of 5 g/cm^2, but the energy dependence of this ratio depends on the ^3He production spectrum in emulsion used to derive the fluxes of secondary ^3 He in this energy range. The ^3He/^4 He ratio energy range 100-500 MeV/nucleon is consistent with the previous measurements at similar levels of solar activity. Comparison with previous data allows us to conclude that, at these energies, the ^3He/ ^4He ratio is not sensitive to the level of the solar modulation in agreement with the predictions from the cosmic ray propagation models. Moreover, these measurements demonstrate that the propagation of the helium cosmic ray component through the interstellar medium is the same as the propagation history of the medium elements, carbon, nitrogen, and oxygen.

Lijowski, Michal

299

Maize Residue Decomposition Measurement Using Soil Surface Carbon Dioxide Fluxes and Natural Abundance of Carbon13  

Microsoft Academic Search

organic matter content and nutrient cycling. We hypothesized that mation obtained is mostly relevant to aboveground crop natural abundance 13 C analyses could be used with soil CO2 flux measurements to quantify the short-term decomposition rates of residues. The natural abundance of 13 C has also been maize (Zea mays L.) residues under undisturbed field conditions. For used to study

Philippe Rochette; Denis A. Angers; Lawrence B. Flanagan

1999-01-01

300

Carbon Isotope Ratios Demonstrate Carbon Flux from C4 Host to C3 Parasite 1  

PubMed Central

Carbon isotope ratios of mature leaves from the C3 angiosperm root hemiparasites Striga hermonthica (Del.) Benth (?26.7‰) and S. asiatica (L.) Kuntze (?25.6‰) were more negative than their C4 host, sorghum (Sorghum bicolor [L.] Moench cv CSH1), (?13.5‰). However, in young photosynthetically incompetent plants of S. hermonthica this difference was reduced to less than 1‰. Differences between the carbon isotope ratios of two C3-C3 associations, S. gesnerioides (Willd.) Vatke—Vigna unguiculata (L.) Walp. and Oryza sativa L.—Rhamphicarpa fistulosa (Hochst.) Benth differed by less than 1‰. Theoretical carbon isotope ratios for mature leaves of S. hermonthica and S. asiatica, calculated from foliar gas exchange measurements, were ?31.8 and ?32.0‰, respectively. This difference between the measured and theoretical ?13C-values of 5 to 6‰ suggests that even in mature, photosynthetically active plants, there is substantial input of carbon from the C4 host. We estimate this to be approximately 28% of the total carbon in S. hermonthica and 35% in S. asiatica. This level of carbon transfer contributes to the host's growth reductions observed in Striga-infected sorghum.

Press, Malcolm C.; Shah, Nishith; Tuohy, Janet M.; Stewart, George R.

1987-01-01

301

Carbon isotope ratios demonstrate carbon flux from c(4) host to c(3) parasite.  

PubMed

Carbon isotope ratios of mature leaves from the C(3) angiosperm root hemiparasites Striga hermonthica (Del.) Benth (-26.7 per thousand) and S. asiatica (L.) Kuntze (-25.6 per thousand) were more negative than their C(4) host, sorghum (Sorghum bicolor [L.] Moench cv CSH1), (-13.5 per thousand). However, in young photosynthetically incompetent plants of S. hermonthica this difference was reduced to less than 1 per thousand. Differences between the carbon isotope ratios of two C(3)-C(3) associations, S. gesnerioides (Willd.) Vatke-Vigna unguiculata (L.) Walp. and Oryza sativa L.-Rhamphicarpa fistulosa (Hochst.) Benth differed by less than 1 per thousand. Theoretical carbon isotope ratios for mature leaves of S. hermonthica and S. asiatica, calculated from foliar gas exchange measurements, were -31.8 and -32.0 per thousand, respectively. This difference between the measured and theoretical delta(13)C-values of 5 to 6 per thousand suggests that even in mature, photosynthetically active plants, there is substantial input of carbon from the C(4) host. We estimate this to be approximately 28% of the total carbon in S. hermonthica and 35% in S. asiatica. This level of carbon transfer contributes to the host's growth reductions observed in Striga-infected sorghum. PMID:16665818

Press, M C; Shah, N; Tuohy, J M; Stewart, G R

1987-12-01

302

Carbon isotopic enrichment in Titan's tholins? Implications for Titan's aerosols  

NASA Astrophysics Data System (ADS)

Since the discovery of the main composition of Titan's atmosphere, many laboratory experiments have been carried out to mimic its chemical evolution, and more particularly the formation of the organic haze particles widespread in this atmosphere. Indeed, some of these simulation experiments produce a solid phase - named Titan's tholins - that is assumed to get properties analogous to the Titan's aerosols ones. We have studied the possible isotopic fractionation of carbon during the processes involved in the formation of Titan's tholins, using tholins obtained from different simulation experiments. It's an important issue because it can provide information on the processes of tholins formation. We will present the first results obtained on the 12 C/13 C isotopic ratios measured on Titan's tholins synthesized in laboratory with cold plasma discharges. Measurements of isotopic enhancement in 13 C (? 13 C), done both on tholins and on the initial gas mixture (N2 :CH4 (98:2)) used to produce them, do not show any clear deficit or enrichment in 13 C relatively to 12 C in the synthesised tholins, compared to the initial gas mixture. Preliminary retrieving of the data of the Aerosol Collector and Pyrolyzer (ACP) experiment of the Huygens probe suggests that Titan's aerosols may also not present carbon isotopic enrichment. This observation allows to go further in the analyses of the ACP experiment data. We are also focusing on the evolution of Titan's tholins under acid hydrolysis treatment. This strong treatment aims to reproduce the evolution of Titan's aerosols in contact with ice water under a longer time scale. Preliminary results on the analyses of the obtained products could give guides lines to identify the still unspecified matter that takes part to the Titan's surface reflectivity decrease as observed by the DISR instrument. This study is still in progress.

Nguyen, M.-J.; Raulin, F.; Coll, P.; Derenne, S.; Szopa, C.; Cernogora, G.; Israel, G.; Bernard, J.-M.

303

A general algorithm for the 17O abundance correction to 13C/12C determinations from CO2 isotopologue measurements, including CO2 characterised by ‘mass-independent’ oxygen isotope distributions  

NASA Astrophysics Data System (ADS)

It is widely recognised that a significant limitation to the ultimate precision of carbon stable isotope ratio measurements, as obtained from dual-inlet mass spectrometric measurements of CO2 isotopologue ion abundances at m/z 44, 45, and 46, is the correction for interference from 17O-bearing molecular ions. Two long-established, alternative procedures for determining the magnitude of this correction are in widespread use (although only one has IAEA approval); their differences lead to small but potentially significant discrepancies in the magnitude of the resulting correction. Furthermore, neither approach was designed to accommodate oxygen three-isotope distributions which do not conform to terrestrial mass-dependent behaviour. Stratospheric CO2, for example, contains a strongly ‘mass-independent’ oxygen isotope composition. A new strategy for determining the 17O-bearing ion correction is presented, for application where the oxygen three-isotope characteristics of the analyte CO2 are accurately known (or assigned) in terms of the slope ? of the three-isotope fractionation line and the ordinate axis intercept 103 ln(1 + k) on a 103 ln(1 + ?17O) versus 103 ln(1 + ?18O) plot. At the heart of the approach is the relationship between 17R, which is the 17O/16O ratio of the sample CO2, and other assigned or empirically determined parameters needed for the ?13C evaluation: 218R17R(1+k)17R1?-3(17R)+217R45R-46R=0 With 45R and 46R as the respective 45/44 and 46/44 ion abundance ratios of the sample, as obtained by measurement of ?45(CO2) and ?46(CO2) values reported relative to a reference material (usually VPDB-CO2), and 17Rref and 18Rref being the respective 17O/16O and 18O/16O ratios in the same reference material, 17R can readily be obtained by numerical methods, for given ? and k values. The correction procedure involves no approximations, in principle, and is equally applicable to CO2 of terrestrial, mass-dependent oxygen isotopic composition, as well as to more ‘exotic’ sources. Besides isotopic characterisation of stratospheric CO2, potential applications include high precision ?13C measurements of CO2 derived from the oxidation of tropospheric CO (also characterised by significantly ‘mass-independent’ oxygen isotopic composition); high precision isotopic monitoring of atmospheric CO2; the metrology of carbonate isotopic reference materials; and the isotopic characterisation of CO2 which has been equilibrated with waters artificially ‘labelled’ with known enrichments of 17O and 18O.

Miller, M. F.; Röckmann, T.; Wright, I. P.

2007-07-01

304

Reaction cross sections of carbon isotopes incident on a proton  

SciTech Connect

We systematically study total reaction cross sections of carbon isotopes with N=6-16 on a proton target for wide range of incident energies. An emphasis is put on the difference from the case of a carbon target. The calculations include the reaction cross sections of {sup 19,20,22}C at 40A MeV, the data of which have recently been measured at RIKEN. The Glauber theory is used to calculate the reaction cross sections. To describe the intrinsic structure of the carbon isotopes, we use a Slater determinant generated from a phenomenological mean-field potential, and construct the density distributions. To go beyond the simple mean-field model, we adopt two types of dynamical models: One is a core+n model for odd-neutron nuclei, and the other is a core+n+n model for {sup 16}C and {sup 22}C. We propose empirical formulas which are useful in predicting unknown cross sections.

Abu-Ibrahim, B. [RIKEN Nishina Center, RIKEN, Wako-shi, Saitama 351-0198 (Japan); Department of Physics, Cairo University, Giza 12613 (Egypt); Horiuchi, W. [Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan); Kohama, A. [RIKEN Nishina Center, RIKEN, Wako-shi, Saitama 351-0198 (Japan); Suzuki, Y. [Department of Physics, Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan)

2008-03-15

305

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

USGS Publications Warehouse

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

Hassan, Afifa Afifi

1982-01-01

306

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

307

Oxygen and carbon isotopes in Jordanian phosphorites and associated fossils  

NASA Astrophysics Data System (ADS)

Stable isotopes have proven to be efficient tools for paleoenvironmental analysis and interpretation of paleotemperature. Oxygen and carbon isotopes were analyzed in carbonate flourapatite (francolite), oyster shells, tests of foraminifera and ostracods from the Phosphorite Unit throughout Jordan. Isotopic analysis showed ?18O to be enriched in authigenic francolite in Upper Cretaceous in NW Jordan, indicating lower temperatures, a deeper depositional environment and lower salinity than Central Jordan. In Central Jordan, the local basin of Hafira shows enrichment of ?18O indicating a deeper depositional environment than shallower highs in Mutarammil and Wadi El-Hasa. The ?13C shows that the depositional environment was oxic to suboxic and may have reached the suboxic to anoxic interface in the deeper environment in NW Jordan. ?18O values in tests of foraminifera and ostracods are similar to ?18O values of authigenic phosphate, which is enriched in NW Jordan, indicating lower temperature, lower salinity and a deeper environment than Central Jordan. In Central Jordan, ?13C shows more depletion in the Sultani section due to land derived organic carbon (food web supply) carried by terrestrial water draining to the sea. The ?18O in oyster shells show an upward enrichment in the Wadi El-Hasa section, which indicate an increase of intense upwelling, enrichment of nutrients, development of productivity and growth of oyster buildups. Meanwhile, Hafira shows enrichment of ?18O and lower temperature, in agreement with foraminifera and ostracods. The two samples of oysters from SE Jordan, although affected by diagenesis, show heavier oxygen to the north, indicating a deeper water environment and lower salinity in the same basin.

Sadaqah, Rushdi M.; Abed, Abdulkader M.; Grimm, Kurt A.; Pufahl, Peir K.

2007-03-01

308

Multicomponent Isotope Separation in Matched Abundance Ratio Cascades Composed of Stages with Large Separation Factors.  

National Technical Information Service (NTIS)

The concept of the matched abundance ratio cascade and the system of equations for performing multicomponent productivity calculations upon them has proven extremely useful for analyzing the behavior of gaseous diffusion plants in which the stage separati...

E. Von Halle

1987-01-01

309

Measurement of 15N\\/ 14N Isotopic Composition in Individual Plasma Free Amino Acids of Human Adults at Natural Abundance by Gas Chromatography–Combustion Isotope Ratio Mass Spectrometry  

Microsoft Academic Search

We describe a high-precision methodology to determine the15N\\/14N isotopic composition of 13 plasma free amino acids out of 500 ?l plasma, measured asN-pivaloyl-i-propyl amino acid esters by gas chromatography–isotope ratio mass spectrometry. It is now possible to measure15N isotopic natural abundances in plasma free amino acids, which has not been the case previously because of the minimum requirement of 60

Cornelia C. Metges; Klaus J. Petzke

1997-01-01

310

Carbon Isotope Discrimination Varies Genetically in C4 Species  

PubMed Central

Carbon-isotope discrimination (?) is used to distinguish between different photosynthetic pathways. It has also been shown that variation in ? occurs among varieties of C3 species, but not as yet, in C4 species. We now report that ? also varies among genotypes of sorghum (Sorghum bicolor Moench), a C4 species. The discrimination in leaves of field-grown plants of 12 diverse genotypes of sorghum was measured and compared with their grain yields. Discrimination varied significantly among genotypes, and there was a significant negative correlation between grain yield and ?. The variation in ? may be caused by genetic differences in either leakiness of the bundle-sheath cells or by differences in the ratio of assimilation rate to stomatal conductance. At the leaf level, the former should be related to light-use efficiency of carbon fixation and the latter should be related to transpiration efficiency. Both could relate to the yield of the crop.

Hubick, Kerry T.; Hammer, Graeme L.; Farquhar, Graham D.; Wade, Len J.; von Caemmerer, Susanne; Henderson, Sally A.

1990-01-01

311

Micropowder collecting technique for stable isotope analysis of carbonates.  

PubMed

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

Sakai, Saburo; Kodan, Tsuyoshi

2011-05-15

312

Isotope Tutorial (title provided or enhanced by cataloger)  

NSDL National Science Digital Library

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

Pataki, Diane

313

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

314

Method for the identification and elimination of contamination during carbon isotopic analyses of extraterrestrial samples  

SciTech Connect

A stepped combustion method for the elimination of carbon-containing contamination and weathering products from meteorite and lunar samples is presented. Samples of the Allende CV3 chondrite, the Sharps and Weston ordinary chondrite falls, one ordinary and five Antarctic finds, and lunar soils from Apollo 11 were oxidized in pure O2 at increasing temperatures, from 200 to 1200 C in 100-C, 30-min steps and C yield and delta-(C-13) were measured after each step. It is found that some C contamination is present in all samples and can adversely affect C-isotopic-abundance measurements. Except for C1 and C2 carbonaceous chondrites, C combustion below 425 + or - 25 C is limited to the terrestrial contaminants, demonstrating the usefulness of stepped combustion in removing them. Graphs and tables of the results are presented and discussed. 34 references.

Swart, P.K.; Grady, M.M.; Pillinger, C.T.

1983-06-30

315

An annually resolved bristlecone pine carbon isotope chronology for the last millennium  

Microsoft Academic Search

We present the first near millennium-length, annually resolved stable isotope record from bristlecone pines (Pinus longaeva, D.K Bailey). The carbon isotope ratios from the cellulose of seven trees from the White Mountains of California, corrected for anthropogenic changes in atmospheric chemistry, are used to reconstruct growing season (June through August) precipitation back to AD 1085. Extremely negative isotope results are

Roderick J. Bale; Iain Robertson; Matthew W. Salzer; Neil J. Loader; Steven W. Leavitt; Mary Gagen; Thomas P. Harlan; Danny McCarroll

2011-01-01

316

The Effects of Sample Treatment and Diagenesis on the Isotopic Integrity of Carbonate in Biogenic Hydroxylapatite  

Microsoft Academic Search

The study of the isotopic composition of structural carbonate in fossil vertebrate hydroxylapatite has been hampered by uncertainty concerning sample treatment and arguments about the susceptibility of this material to diagenetic alteration. Our investigation of sample treatment reveals that some methods commonly used to remove organic matter and secondary minerals induce significant isotopic offsets, particularly for oxygen isotopes in bone

Marilyn L. Fogel

1997-01-01

317

Nondestructive, in situ, cellular-scale mapping of elemental abundances including organic carbon in permineralized fossils  

Microsoft Academic Search

The electron microprobe allows elemental abundances to be mapped at the mum scale, but until now high resolution mapping of light elements has been challenging. Modifications of electron microprobe procedure permit fine-scale mapping of carbon. When applied to permineralized fossils, this technique allows simultaneous mapping of organic material, major matrix-forming elements, and trace elements with mum-scale resolution. The resulting data

C. K. Boyce; R. M. Hazen; A. H. Knoll

2001-01-01

318

Effect of magnesium ions on the stable oxygen isotope equilibrium between dissolved inorganic carbon species and water.  

NASA Astrophysics Data System (ADS)

Stable oxygen isotope (?18O) values of foraminiferal calcites, which represent one of the most fundamental paleoceanographic tools to reconstruct ancient seawater temperatures, are influenced by seawater pH variations. Understanding the driving mechanism for such phenomenon requires precise knowledge of the equilibrium 18O fractionation factors between dissolved inorganic carbon (DIC) species and water. An experimental study by Beck et al. (2005) successfully refined the 18O fractionation factors between DIC components and water. Based on these results, the overall 18O fractionation between total DIC and water as a function of pH can be readily calculated (e.g., Zeebe, 2007). However, these calculations may not be applicable to seawater because the fractionation factors were measured in freshwater. Natural seawater contains numerous ionic species and other dissolved constituents, which may affect the fractionation factors. For example, it has been experimentally demonstrated that the presence of magnesium ions (Mg2+) in solutions affect equilibrium carbon isotope (13C) fractionation between aqueous CO2 and carbonate ions presumably due to the enrichment of 13C isotopes in Mg-CO30 complexes (Thode et al., 1965). This suggests that the presence of Mg2+ in solutions similarly affects the 18O fractionation factors between DIC species and water. On the other hand, Beck et al. (2005) concluded that the effect of ion pairs on the ?18O equilibrium appears to be negligible. However, this conclusion may not apply to ion paring in general, because experiments were not conducted for metal ions other than Na+. Given that Mg2+ has a marked effect on the equilibrium ?13C fractionation factors and Mg-CO30 is the most abundant form of metal-CO3-complexes in natural seawater, the potential effect of Mg2+ on the 18O fractionation factors between DIC components and water needs to be examined. Here, we will present preliminary results from quantitative carbonate precipitation experiments to evaluate the influence of Mg2+ on the ?18O equilibrium in the DIC-water system. REFERENCES Beck, W.C., Grossman, E.L., and Morse, J.W. (2005). Experimental studies of oxygen isotope fractionation in the carbonic acid system at 15° , 25° and 40° C. Geochim. Cosmochim. Acta, 69, 3493-3503. Thode, H.G., Shima, M., Rees, C.E., and Krishnamurty, K.V. (1965). Carbon-13 isotope effects in systems containing carbon dioxide, bicarbonate, carbonate, and metal ions. Canad. J. Chem., 43, 582-595. Zeebe, R.E. (2007). An expression for the overall oxygen isotope fractionation between the sum of dissolved inorganic carbon and water. Geochem. Geophys. Geosyst., 8, Q09002, doi: 10.1029/2007GC001663.

Uchikawa, Joji; Zeebe, Richard

2010-05-01

319

Comparing Deep Mixing in Globular Cluster and Halo Field Giants: Carbon Abundance Data from the Literature  

NASA Astrophysics Data System (ADS)

The behavior of carbon abundance as a function of luminosity is used to compare the rates of deep mixing within red giants of four globular clusters and the Galactic halo field population. Measurements of [C/Fe] for the clusters M92, NGC 6397, M3, and M13 have been compiled from the literature, together with the Gratton et al. data for halo field stars. Plots of [C/Fe] versus absolute visual magnitude show that for MV<+1.6 the rate of decline of carbon abundance with increasing luminosity on the red giant branch is d[C/Fe]/dMV~0.22+/-0.03 among the field stars, as well as in M92, NGC 6397, and M3. Among giants fainter than MV=+1.6 the variation of [C/Fe] with absolute magnitude is much less. The data indicate that the rate at which deep mixing introduces carbon-depleted material into the convective envelopes of field halo stars during the upper red giant branch phase of evolution is similar to that of many globular cluster giants. The notable exception appears to be M13, in which stars exhibit deep mixing at a greater rate; this may account for the high incidence of very low oxygen abundances among the most luminous giants in M13 in comparison to M3.

Smith, Graeme H.; Martell, Sarah L.

2003-10-01

320

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

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

321

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

322

Lithium abundances and isotopic compositions in mantle xenoliths from subduction and intra-plate settings: Mantle sources vs. eruption histories  

NASA Astrophysics Data System (ADS)

We report Li concentrations and isotopic compositions for olivine and pyroxene separates and bulk rocks of variably metasomatised harzburgite xenoliths hosted by andesitic tuffs of the active Avacha volcano in the Kamchatka arc, and for a single lava-hosted harzburgite from the intra-plate Vitim volcanic field, Siberia. The Li-isotope data on the Avacha samples ( ?7Li = 0 to + 5‰) mainly fall within the range reported previously for 'normal', MORB-type mantle (+ 2 to + 6‰) and show no significant inter-mineral disequilibria. These results indicate that the shallow mantle in the active Kamchatka arc, and probably in other subduction zones, has roughly (i.e. within ± 2‰) MORB-type Li isotopic signatures. By contrast, pyroxenes from the Vitim xenolith yield extremely low ?7Li (- 17‰ and - 18‰) and are out of equilibrium with coexisting olivine, which has high ?7Li (+ 6‰). Taken together, these results indicate that anomalous Li elemental and isotopic compositions in mantle xenoliths cannot be considered signatures of shallow sub-arc mantle or evidence for recent or ancient slab-related metasomatism. We review published data on Li abundances and isotopic compositions in intra-plate mantle xenoliths to show that the inter-mineral disequilibria do not appear to be related to characteristics of the xenoliths themselves (tectonic settings, rock types, chemical compositions) but rather depend on what kind of volcanic rocks host the xenoliths. The disequilibria are extremely rare in xenoliths from pyroclastic rocks, which cooled almost instantaneously on eruption, but are common in xenoliths found in massive basalts (which took longer to cool down after the eruption). The anomalous Li elemental and isotopic compositions in lava-hosted xenoliths may be related to re-distribution of Li between minerals during the long cooling driven by temperature-controlled variations of inter-mineral partition coefficients and/or infiltration of residual fluids produced by crystallization of host lava. The diffusive re-distribution of Li can be accompanied by isotopic fractionation whose magnitude, in addition to cooling time, may depend on modal ratios of olivine and pyroxenes, grain size and other factors. We further speculate that significant variations of ?7Li in lava-hosted suites may be related to different cooling times for thicker and thinner flows.

Ionov, Dmitri A.; Seitz, Hans-Michael

2008-02-01

323

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

SciTech Connect

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

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

2005-01-31

324

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

325

Stable carbon and nitrogen isotope signatures indicate recovery of marine biota from sewage pollution at Moa Point, New Zealand.  

PubMed

Stable carbon and nitrogen isotopes have been used to assess sewage contamination of a sewage outfall, discharging milli-screened effluent into Moa Point Bay, New Zealand, and monitor the recovery of flora and fauna after the outfall's closure. An initial study characterising the extent of the discharge and the effects on seaweed (Ulva lactuca L.), blue mussels (Mytilus galloprovincialis) and limpets (Cellana denticulata) from the area, showed effects of the sewage discharge on flora and fauna were localised within in the bay. The immediate area surrounding the discharge area was found to contain limited biodiversity, with an abundance of Ulva lactuca, a bright green lettuce-like seaweed, typically found in areas with high nutrient input, limpets and small blue mussels. The nitrogen isotopic signature (delta15N) is shown to be a good tracer of sewage pollution in seaweed and associated grazers (i.e. limpets) as a result of the increased contribution of urea and ammonia to seawater nitrogen derived from the effluent. The carbon isotopic signature (delta13C) is suggested as a more appropriate sewage tracer for mussels, which filter feed the effluent's particulate organic matter from the water. Lower carbon:nitrogen ratios were found in Ulva lactuca sampled from around the outfall region compared to uncontaminated control sites. However carbon:nitrogen ratios do not vary significantly amongst shellfish species. After closure, monitoring continued for 9 months and showed that the carbon and nitrogen isotopic signatures of algae (Ulva lactuca L.) returned to similar control site levels within 3 months. Limpet and blue mussels (Cellana denticulata and Mytilus galloprovincialis) showed slower recovery times than the Ulva lactuca, with detectable levels of the sewage-derived carbon and nitrogen remaining in the animal's tissue for up to 9 months. PMID:12837300

Rogers, Karyne M

2003-07-01

326

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

PubMed Central

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

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

1984-01-01

327

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

PubMed Central

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

2010-01-01

328

Simulation of carbon isotope discrimination of the terrestrial biosphere  

NASA Astrophysics Data System (ADS)

We introduce a multistage model of carbon isotope discrimination during C3 photosynthesis and global maps of C3/C4 plant ratios to an ecophysiological model of the terrestrial biosphere (SiB2) in order to predict the carbon isotope ratios of terrestrial plant carbon globally at a 1° resolution. The model is driven by observed meteorology from the European Centre for Medium-Range Weather Forecasts (ECMWF), constrained by satellite-derived Normalized Difference Vegetation Index (NDVI) and run for the years 1983-1993. Modeled mean annual C3 discrimination during this period is 19.2‰; total mean annual discrimination by the terrestrial biosphere (C3 and C4 plants) is 15.9‰. We test simulation results in three ways. First, we compare the modeled response of C3 discrimination to changes in physiological stress, including daily variations in vapor pressure deficit (vpd) and monthly variations in precipitation, to observed changes in discrimination inferred from Keeling plot intercepts. Second, we compare mean ?13C ratios from selected biomes (Broadleaf, Temperate Broadleaf, Temperate Conifer, and Boreal) to the observed values from Keeling plots at these biomes. Third, we compare simulated zonal ?13C ratios in the Northern Hemisphere (20°N to 60°N) to values predicted from high-frequency variations in measured atmospheric CO2 and ?13C from terrestrially dominated sites within the NOAA-Globalview flask network. The modeled response to changes in vapor pressure deficit compares favorably to observations. Simulated discrimination in tropical forests of the Amazon basin is less sensitive to changes in monthly precipitation than is suggested by some observations. Mean model ?13C ratios for Broadleaf, Temperate Broadleaf, Temperate Conifer, and Boreal biomes compare well with the few measurements available; however, there is more variability in observations than in the simulation, and modeled ?13C values for tropical forests are heavy relative to observations. Simulated zonal ?13C ratios in the Northern Hemisphere capture patterns of zonal ?13C inferred from atmospheric measurements better than previous investigations. Finally, there is still a need for additional constraints to verify that carbon isotope models behave as expected.

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

2005-03-01

329

Stable carbon isotope fractionation between substrates and products of Methanosarcina barkeri  

Microsoft Academic Search

Stable carbon isotope ratios are an important tool for understanding methanogenesis in the environment. When applied to biological methanogenesis, interpretation of carbon isotope ratios requires a thorough understanding of how the availability of different substrates affects the eventual ?13C of methane, biomass and lipids. Methanosarcina barkeri was grown on four substrates: methanol, trimethylamine (TMA), acetate, and H2\\/CO2, under variable conditions

Kathleen L. Londry; Kathleen G. Dawson; Heather D. Grover; Roger E. Summons; Alexander S. Bradley

2008-01-01

330

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 Angerbjörn; Pall Hersteinsson; Kerstin Lidén; Erle Nelson

1994-01-01

331

Groundtruthing the CSIA-aerosol technique for estimation of carbon isotopic discrimination of terrestrial photosynthesis  

Microsoft Academic Search

The carbon isotopic composition of vascular plant-derived leaf wax compounds present in aerosols can potentially provide a highly temporally resolved estimate of terrestrial photosynthetic fractionation of carbon dioxide on ecosystem and larger spatial scales. A central assumption of this approach is that the isotopic signal of the leaf waxes ablated off living vegetation by wind and dust scouring and accumulating

M. H. Conte; J. C. Weber; L. P. Flanagan

2001-01-01

332

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

333

Leaf carbon isotope and mineral composition in subtropical plants along an irradiance cline  

Microsoft Academic Search

Leaf carbon isotope ratios and leaf mineral composition (Ca, K, Mg, Mn, N, and P) were measured on the dominant species along an irradiance cline in a subtropical monsoon forest of southern China. This irradiance cline resulted from disturbance caused by fuel-harvesting. Leaf carbon isotope ratios increased from undisturbed to disturbed sites for all species, indicating that leaf intercellular CO2

J. R. Ehleringer; C. B. Field; Zhi-fang Lin; Chun-yen Kuo

1986-01-01

334

Remote Detection of Carbon Stable Isotope of CO2 for Carbon Sequestration  

NASA Astrophysics Data System (ADS)

Carbon storage in geologic formations is one method to prevent carbon dioxide (CO2), produced by fossil fuel combustion, from entering the Earth's atmosphere. The monitoring, verification and accounting (MVA) of geologically sequestered CO2 is critical to measure the operation and functioning of a geologic storage site. Surface monitoring techniques need to identify seepage from the sequestration reservoir at or below ambient CO2 concentrations. The Zero Emissions Research & Technology (ZERT) group at Montana State University established a field test site where controlled amounts of CO2 are released to test the performance of CO2 detection instruments and measurement techniques. The field site allows a controlled flow rate of CO2 to be released into the near surface, just below the water table, through a 100 m long horizontal pipe. In July of 2009, a release was conducted, with a uniform flow rate of 0.2 tons per day, and the seepage rate was measured. The carbon stable isotope ratio of CO2 is a sensitive diagnostic signature to distinguish between anthropogenic and natural sources of CO2. However, natural concentrations of 13C16O2 are approximately 100 times smaller than 12C16O2. Frequency-modulated spectroscopy (FMS) is an ultra-sensitive technique developed to detect the CO2 stable carbon isotopes. An instrument has been developed that uses this FMS technique and an integrated volume over a long, open-air path to detect changes in the carbon isotope ratio. This paper will briefly describe the FMs technique and present results from instrument deployment to the ZERT field site to monitor the 13C16O2/12C16O2 stable isotope ratio. LA-UR 09-05648

Humphries, S. D.; Clegg, S. M.; Fessenden, J. E.; Dobeck, L.; Spangler, L.

2009-12-01

335

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

PubMed

The stable isotope composition of the light elements (i.e., H, C, N, O and S) of organic samples varies significantly and, for C, is also unique and distinct from that of inorganic carbon. This is the result of (1) the isotope composition of reactants, (2) the nature of the reactions leading to formation and post-formational modification of the samples, (3) the environmental conditions under which the reactions took place, and (4) the relative concentration of the reactants compared to that of the products (i.e., [products]/[reactants] ratio). This article will examine the carbon isotope composition of terrestrial plant materials and its relationship with the above factors. delta13C(PDB) values of terrestrial plants range approximately from -8 to -38%, inclusive of C3-plants (-22 to -38%), C4-plants (-8 to -15%) and CAM-plants (-13 to -30%). Thus, the delta13C(PDB) values largely reflect the photosynthesis pathways of a plant as well as the genetics (i.e., species difference), delta13C(PDB) values of source CO2, relevant humidity, CO2/O2 ratios, wind and light intensity etc. Significant variations in these values also exist among different tissues, different portions of a tissue and different compounds. This is mainly a consequence of metabolic reactions. Animals mainly inherit the delta13C(PDB) values of the foods they consume; therefore, their delta13C(PDB) values are similar. The delta13C(PDB) values of plant materials, thus, contain information regarding the inner workings of the plants, the environmental conditions under which they grow, the delta13C(PDB) values of CO2 sources etc., and are unique. Furthermore, this uniqueness is passed on to their derivative matter, such as animals, humus etc. Hence, they are very powerful tools in many areas of research, including the ecological and environmental sciences. PMID:11480769

Yeh, H W; Wang, W M

2001-07-01

336

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

337

Genetic differences in water-use efficiency, stomatal conductance and carbon isotope fractionation in potato  

Microsoft Academic Search

Summary  Potato (Solanum tuberosum L.) cultivars were grown in pots and containers under a rain shelter to examine differences in stomatal conductance, water-use\\u000a efficiency, and carbon isotope fractionation. Conductance was measured on abaxial leaf surfaces with a steady state diffusion\\u000a porometer. Carbon isotopic analyses were made with an isotope ratio mass spectrometer. Water-use efficiency (WUE) was obtained\\u000a by dividing total dry

J. Vos; J. Groenwold

1989-01-01

338

On the Carbon and Nitrogen Abundances of Bright Giants in Three Galactic Globular Clusters  

NASA Astrophysics Data System (ADS)

We report on an analysis of CN and CH band strengths of 42 bright (Mv < 0) giants in the globular clusters M13, M10, and NGC 7006. The clusters are all of similar metallicity ([Fe/H] = -1.5), however NGC 7006 is a classic second parameter cluster with a far redder HB morphology compared to M13 and M10. Our spectra, taken over several observing campaigns at the Lick 3-m Shane and McDonald 2.7-m Smith telescopes, have been flux calibrated and the resulting C and N abundances compare well for stars in common with previous studies in the literature. In all three clusters significant (approximately 1 dex) depletions of carbon with increasing evolutionary state are evident. At the same time, large (0.3 dex or more) star to star variations in carbon are also present. An even larger (1 dex) scatter exists among the nitrogen abundances of the least luminous program stars and a tendency towards high nitrogen abundance stars with greater luminosity is observed. We interpret these results as the operation of an extra-mixing process during the later stages of RGB ascent in which C-poor/N-rich material is mixed to the surface from a region just above the H-burning shell. The extent of mixing among the giants of NGC 7006 appears comparable to that of both M13 and M10, despite its redder HB morphology. Moreover, as has been demonstrated by Briley, Cohen & Stetson (2004 AJ, 127, 1579) for M13, the intrinsic scatter in C and N abundances of the giants in both M10 and NGC 7006 is also consistent with the presence of primordial star to star abundance differences that are being modified by this extra mixing. Partial support for this work was provided by the NSF under grant AST-0098489 and the UWO Faculty Development Program (to MMB).

Briley, M. M.; Harbeck, D.; Smith, G. H.

2004-05-01

339

Oxygen-18 Carbon Dioxide Isotope Ratio in Mars Atmosphere  

NASA Astrophysics Data System (ADS)

The determination of isotopic ratios on Mars is important to the study of atmospheric evolution [1]. The relative abundance of isotopes of CO2 provides insight into the loss of Mars' primordial atmosphere. Isotopic ratios also provide markers in the study of geochemistry of Mars meteorites and future returned samples formed in equilibrium with ambient atmosphere, and are probes of biogenic and abiotic chemistry, which differ in isotope fractionation. Due to its lesser gravity and relatively thin residual atmosphere, Mars' atmosphere should be enriched in heavy isotopes [1]. However Viking [2] results indicated an Earth-like singly substituted oxygen-18 CO2 isotopic ratio, 18OCO/OCO, with ?18O = 0±50‰ relative to Vienna Standard Mean Ocean Water (VSMOW). By comparison, isotopic ratios in Earth atmospheric CO2 are not uniquely defined due to seasonal and biotic variability, but have a range 0-41‰ relative to VSMOW [3, 4]. Phoenix lander TEGA [3] measurements found a modest enrichment of ?18O = 31.0±5.7‰. Only the Viking and Phoenix landers have carried a mass spectrometer to Mars, so far, until the arrival of Mars Science Laboratory in August 2012. Using ground-based spectroscopic techniques Krasnopolsky et al. [5] also found modest enrichment ?18O = 18±18‰. We present results from fully resolved spectroscopic measurements near 10.6 ?m of both the normal and singly substituted oxygen- 18 CO2 lines, taken with the Goddard Space Flight Center Heterodyne Instrument for Planetary Winds And Composition (HIPWAC) at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. Measurements with spectral resolving power ?/??=107 were obtained in October 2007 with an instantaneous field-of-view on the planet of ~1 arcsec, at the locations shown in Fig. 1 as open squares. The solid and broken line tracks show Mars SPICAM measurements of ozone corresponding to ozone measurements also obtained with HIPWAC and shown as hatched and solid regions [6]. Figure 1: Locations of measured 18O12C16O fractional abundance on Mars (open squares). The colored tracks are Mars Express SPICAM measurements of ozone; the solid and hatched areas show contemporaneous HIPWAC measurements of ozone [6]. Figure 2 illustrates the CO2 normal-isotope and O-18 isotopologue lines measured on Mars at ~1 MHz (0.0003 cm-1) spectral resolution. The strong absorption line constrains the temperature simultaneously at the position of the measurement. The narrow mesospheric non- LTE line emission is also seen at the core of the absorption. The standard Mars Global Surveyor temperature profile was used to obtain the modeled emergent spectrum in blue. It clearly does not fit as well as the thermal profile retrieved from the CO2 absorption line profile (red fit). EPSC Abstracts Vol. 7 EPSC2012-432 2012 European Planetary Science Congress 2012 c Author(s) 2012 EPSC European Planetary Science Congress Figure 2: HIPWAC measurements of CO2 spectrum on Mars near 10.5 ?m. The broad absorption retrieves the temperature. The fitted model spectra correspond to using the standard MGS thermal profile (blue), and our retrieved profile (red). The fit to the isotopic line is excellent and yields ?18O = +9±14‰. Radiative-transfer software developed in-house at GSFC to be compatible with very high spectral resolving power [7] was used to obtain the temperature profile and spectral fit. The fit on the 952.8629 cm-1 18OC16O line retrieves ?18O = +9±14‰. There appears to be no significant enhancement in the average over the extended region measured. Additional, more global, measurements were acquired in May 2012 and these data are being analyzed. These and additional high spectral resolution ground-based global measurements of ?18O can investigate Mars' atmospheric history; help define Mars Science Laboratory (MSL) protocols to sample isotopic ratios diurnally and seasonally, throughout its prime mission; and investigate possible meridional variability due to mass-fractionation in the polar freeze-sublimate cycle, similar to effects in terrestrial polar ice formation [

Kostiuk, T.; Livengood, T. A.; Hewagama, T.; Smith, R.; Fast, K. E.; Annen, J.; Sonnabend, G.; Sornig, M.

2012-09-01

340

Carbon isotope ratio measurements of glyphosate and AMPA by liquid chromatography coupled to isotope ratio mass spectrometry.  

PubMed

The interest in compound-specific isotope analysis for product authenticity control and source differentiation in environmental sciences has grown rapidly during the last decade. However, the isotopic analysis of very polar analytes is a challenging task due to the lack of suitable chromatographic separation techniques which can be used coupled to isotope ratio mass spectrometry. In this work, we present the first method to measure carbon isotope compositions of the widely applied herbicide glyphosate and its metabolite aminomethylphosphonic acid (AMPA) by liquid chromatography coupled to isotope ratio mass spectrometry. We demonstrate that this analysis can be carried out either in cation exchange or in reversed-phase separation modes. The reversed-phase separation yields a better performance in terms of resolution compared with the cation exchange method. The measurement of commercial glyphosate herbicide samples show its principal applicability and reveals a wide range of ?(13)C values between -24 and -34 ‰ for different manufacturers. The absolute minimum amounts required to perform a precise and accurate determination of carbon isotope compositions of glyphosate and AMPA were in the sub-microgram range. The method proposed is sensitive enough to further perform the experiments that are necessary to better understand the carbon isotope fractionation associated to the natural degradation of glyphosate into AMPA. Furthermore, it can be used for contaminant source allocation and product authenticity as well. PMID:23322349

Kujawinski, Dorothea M; Wolbert, J Benjamin; Zhang, Lijun; Jochmann, Maik A; Widory, David; Baran, Nicole; Schmidt, Torsten C

2013-01-16

341

Biological control of calcium isotopic abundances in the global calcium cycle  

Microsoft Academic Search

Measurements of 44Ca\\/40Ca, expressed as ?44Ca, 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‰ in ?44Ca, measured with the double spike technique to a precision of ±0.15‰. Volcanic rocks, including basalt and rhyolite, show little

Joseph Skulan; Donald J. DePaolo; Thomas L. Owens

1997-01-01

342

Hydrogen isotope abundances in the solar system. Part I. Unequilibrated chondrites  

SciTech Connect

Concentrations and isotopic compositions of H extracted by pyrolysis under a He flow were determined in three unequilibrated type 3 ordinary chondrites: Chainpur, Bishunpur and Ngawi. In Chainpur, a D-depleted component is removed at low temperature (200 to 400/sup 0/C), whereas at temperatures ranging between 450/sup 0/C and 900/sup 0/C, a D-rich component is evolved with a bimodal release pattern. The isotopic composition patterns reported as a function of temperature are qualitatively similar in the three meteorites. Consequently, the bulk isotopic composition of each meteorite is interpreted as resulting from the mixing of two components, the low deltaD fraction constituting 80 to 90% of the total H. The assumption that a carbonaceous chondrite-like polymer is the carrier of the D-rich H is supported by two observations: (i) the D-rich H is released with bimodal patterns, and (ii) oxidation of whole-rock samples with H/sub 2/O/sub 2/ removes this D-rich hydrogen. For each meteorite the peak in H concentration associated with the marked increase in the deltaD patterns permits one to calculate an isotopic composition for the D-rich H. The calculated deltaD values never exceed ca. + 5500 per thousand and no experimental indication of the presence of any D-richer H was found. Uncertainties on these determinations do not permit one to establish the presence of a unique D-rich component, common to these three meteorites.

Robert, F.; Javoy, M.; Halbout, J.; Dimon, B.; Merlivat, L.

1987-07-01

343

Models of earth structure inferred from neodymium and strontium isotopic abundances  

PubMed Central

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

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

1979-01-01

344

Calcium isotopic ratios and rare earth element abundances in refractory inclusions from the Allende CV3 chondrite  

NASA Astrophysics Data System (ADS)

Refractory inclusions in primitive meteorites are the oldest objects formed in the Solar System. They exhibit large mass-dependent isotopic effects in many elements, including Si, Mg and Ca, indicative of their complex origin. We report data for both mass-dependent (?) and mass-independent (?) Ca isotopic effects, and rare earth element (REE) abundances in six refractory inclusions from the Allende CV3 meteorite. Our data reveal large mass-dependent Ca isotopic effects in these refractory inclusions, with ? 44/40Ca ranging from -5.60 to +0.35 (relative to NIST SRM 915a), which are significantly lower than that of the bulk silicate Earth (? 44/40Ca = 1.05 ± 0.04). Importantly, ? 44/40Ca is correlated with REE patterns: refractory inclusions with Group II REE patterns have lighter Ca isotope compositions compared to those with Group I REE patterns. Specifically, the studied refractory inclusions form negative 44Ca/ 40Ca-Tm/Er and 44Ca/ 40Ca-Nd/Er trends, implying segregation of up to 3% of an ultrarefractory evaporation residue from a chondritic reservoir prior to the formation of refractory inclusions. This residue would have to be characterized by high 44Ca/ 40Ca and low Tm/Er and Nd/Er. At 2 ? levels of ±0.5 and ±1.5 for ? 40/44Ca and ? 43/44Ca, respectively, the six refractory inclusions studied show no detectable 40Ca or 43Ca anomalies relative to the terrestrial standards. However, five out of the six refractory inclusions do show a 48Ca excess of several ?-units, clearly resolvable from the terrestrial standards.

Huang, Shichun; Farkaš, Juraj; Yu, Gang; Petaev, Michail I.; Jacobsen, Stein B.

2012-01-01

345

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

346

Stable carbon isotope fractionation in the search for life on early Mars.  

PubMed

Isotopic measurements and, more specifically, ratios of 13C to 12C in organic relative to inorganic deposits, are useful in reconstructing past biological activity on Earth. Organic matter has a lower ratio of 13C to 12C due largely to the preferential fixation of 12C over the heavier isotope by the major carbon-fixation enzyme, ribulose-1,5-bisphosphate carboxylase/oxygenase, although other factors (e.g., availability of source carbon, fixation by other carboxylating enzymes and diagenesis of organic material) also contribute to fractionation. Would carbon isotope discrepancies between inorganic and organic carbon indicate past biological activity on Mars? In order to answer this question, we analyse what is known about terrestrial biologic and abiologic carbon fixation and its preservation in the fossil record, and suggest what the isotope discrimination during possible biologic and abiologic carbon fixation on Mars might have been like. Primarily because isotopic signatures of abiotically fixed carbon overlap with those of biotic fixation, but also because heterotrophy does not significantly alter the isotopic signature of ingested carbon, fractionation alone would not be definitive evidence for life. However, a narrow range of fractionation, including no fractionation, would suggest biotic processes. Never-the-less, isotopic ratios in organic deposits on Mars would be extremely useful in analysing prebiotic, if not biotic, carbon transformations on Mars. PMID:11537367

Rothschild, L J; DesMarais, D

1989-01-01

347

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

Microsoft Academic Search

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

Jonathan L. Payne; Lee R. Kump

2007-01-01

348

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

Microsoft Academic Search

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

Jonathan L. Payne; Lee R. Kump

2007-01-01

349

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

350

Tree Species of the Central Amazon Affects Natural Abundance of Nitrous Oxide Isotopes  

NASA Astrophysics Data System (ADS)

The use of stable isotopes of N and O in N2O has been proposed as a way to better constrain the global budget of atmospheric N2O and to better understand relative contribution of the main microbial processes (nitrification and denitrification) responsible for N2O formation in soil. This study examined the effects of tree species used in plantation systems of the Brazilian Amazon in comparison to natural and secondary forests on the isotopic composition of N{2}O emitted from the soil. We also compared the effects of tree species with those of soil moisture, as we expected the latter to be the main factor regulating the proportion of nitrifier and denitrifier derived N2O and, consequently, isotopic signatures of N2O. To our knowledge, this is the first study to show that tree species significantly affect the 15N composition of nitrous oxide, likely due to tree-mediated changes in microbial communities. However, we found no evidence that varying contributions of nitrification and denitrification to N2O flux contributed to variation in the 15N composition of N2O. In our study, all N2O was likely produced by denitrification. We suspect that the differences in 15N observed were due to effect of nitrate immobilization on isotopes of N in nitrate, the substrate for denitrification. However, this explanation needs further verification. While tree species did affect the 15N composition of N2O, they did not affect the rate of N2O emission. We conclude that tree species contribute to a large isotopic variation in N2O observed in a range tropical forest soils. We found that soil water affects both 15N and 18O in N2O, with wetter soils producing N2O depleted in 15N and 18O. This is likely caused by increased activity of denitrification and/or decrease nitrate immobilization in case of 15N, and both by denitrification and by direct exchange of 18O-H2O and N2O with NO3-.

Menyailo, O. V.; Lehmann, J.; Gebauer, G.; Hungate, B. A.; Zech, W.

2001-05-01

351

The stable carbon isotope biogeochemistry of acetate and methane in freshwater environments  

SciTech Connect

Methane produced in freshwater sediments, where acetate is the major substrate utilized by methanogenic bacteria, is commonly depleted in {sup 13}C. Variations in the carbon-isotopic composition of methane have been related to flows of acetate carbon to various fates within microbial communities. To examine these processes, the isotopic compositions of biogenic methane and its sedimentary sources (acetate and CO{sub 2}) were considered along with related isotope effects. A method of preparation for carbon isotope analyses of both carbons in acetate was developed. Uncertainties in measurements are less than 0.4{per thousand} for samples greater than 5 {mu}mol of acetate. Advantages of this technique include good separation of acetate from other compounds and the applicability to samples containing micromolar quantities of acetate. Carbon kinetic isotope effects associated with synthesis of acetate from CO{sub 2} by Acetobacterium woodii were measured by isotopic analyses of CO{sub 2}, 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 CO{sub 2} and HCO{sub 3}{sup {minus}} were taken into account. For the overall reaction total carbonate {yields} total acetate, the isotope effect measured {minus}58.6 {plus minus} 0.7{per thousand}; there is no evidence for intramolecular isotopic ordering in the acetate. Carbon isotope effects associated with synthesis of methane from acetate by Methanosarcina barkeri and by a natural community of methanogens were measured in closed system experiments. For the process of methyl-carbon {yields} methane, the isotope effect measured {minus}21.5 {plus minus} 1.3{per thousand}.

Gelwicks, J.T.

1989-01-01

352

Binding of carbon dioxide to phosphoenolpyruvate carboxykinase deduced from carbon kinetic isotope effects.  

PubMed

Phosphoenolpyruvate carboxykinase [ATP:oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.49] from Chloris gayana Kunth has been purified by a combination of ammonium sulfate fractionation, ion exchange, gel filtration, and affinity chromatography on agarose-hexane-ATP. In the direction of OAA formation, the specific activity of the enzyme was 33 mumol/(min.mg of protein). The carbon isotope effect on carboxylation was measured by successive analysis of remaining CO2 over the course of the reaction. At 22 mM PEP and 1.3 mM MgADP, pH 7.5, the isotope effect is 1.024 +/- 0.001. When the concentration of PEP was reduced to 1 mM, the isotope effect rose to 1.034 +/- 0.004; when the concentration of MgADP was reduced to 60 microM, the value rose to 1.040 +/- 0.006. The variation of the carbon isotope effect on carboxylation with both substrate concentrations indicates that the enzyme operates by a random kinetic mechanism. This in turn requires that the enzyme have a binding site for substrate CO2; this is one of the first enzymes for which such a site has been demonstrated. PMID:1567882

Arnelle, D R; O'Leary, M H

1992-05-01

353

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

NASA Astrophysics Data System (ADS)

The stable carbon isotope ratio (? 13C) of respired CO2 has been used to partition soil respiration into root and microbial components by exploiting the different ? 13C signals from C3 plants growing in a previously C4 dominated system (Rouchette, Angers and Flanagan 1999). We extend this approach and present data that attempts to partition ecosystem respiration using ? 13C analyses of all of the ecosystem compartments in a mixed C3 annual grassland that has not experienced recent C4 inputs. From December 2000 to February 2001 we measured ? 13C-CO2 respired from leaves, roots and sieved soil collected from a winter-active grassland near Ione, California. Two-source mixing models were used to calculate the contribution of each source to total system respiration by comparing their isotope signals to those from whole ecosystem respiration and soil surface efflux. Isotope ratios were measured on 10mL air samples in septum-capped vials using a Finnigan MAT Delta PlusXL IRMS/Gas Bench II interfaced to an autosampler (after Tu et al. 2001). The vials were filled with sample air in the field using a double-holed needle connected in a closed loop to a LI-6200 IRGA and a bottle containing the isolated samples (leaf, root, sieved soil, etc.). Leaves were clipped at ground level and roots and soil were separated by sieving soil cores. Sample ? 13CO2 signatures were determined by plotting the change in ? 13C against the inverse of CO2 concentration. On average, CO2 respired from sieved soil (-27.4o/oo+/-1.4) was slightly more depleted than that from leaves (-27.2o/oo+/-0.5), but much more depleted than the whole ecosystem (-24.9o/oo+/-0.6), the soil surface efflux (-23.8o/oo+/-0.9), and plant roots (-20.5o/oo+/-0.8). Based on these isotope values, leaf respiration comprised 33% of ecosystem respiration with 36% from roots and 31% from soil microbial respiration. Thus, over two-thirds of ecosystem respiration was autotrophic (plant-based) in origin with roughly one-third being heterotrophic. Belowground respiration, comprised of both autotrophic (root) and heterotrophic (microbial) components, accounted for nearly two-thirds of total ecosystem respiration. Root and microbial respiration each contributed to nearly half of total belowground respiration (53% and 47%, respectively). Similarly, plant respiration was divided nearly equally between that from roots (52%) and leaves (48%). Partitioning using natural abundance stable carbon isotope ratios was made possible because of the relatively large differences in ? 13C values among the various sources in this entirely C3 system. To our knowledge, such large isotopic differences in respired CO2 among different plant tissues and belowground components have not been documented before. Further research is needed to determine how such differences may arise and to establish if similar differences exist in other ecosystems or at different times of the growing season. Our results also imply that interpretation of above-canopy Keeling plot intercepts may be complicated by both multiple (and isotopically distinct) sources and by isotopic fractionation that occurs either during the respiration process itself or during the transfer of carbon compounds prior to respiration.

Tu, K. P.

2001-12-01

354

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

PubMed

Temporal stable isotope records derived from animal tissues are increasingly studied to determine dietary and climatic histories. Despite this, the turnover times governing rates of isotope equilibration in specific tissues following a dietary isotope change are poorly known. The dietary isotope changes recorded in the hair and blood bicarbonate of two adult horses in this study are found to be successfully described by a model having three exponential isotope pools. For horse tail hair, the carbon isotope response observed following a dietary change from a C3 to a C4 grass was consistent with a pool having a very fast turnover rate ( t1/2 approximately 0.5 days) that made up approximately 41% of the isotope signal, a pool with an intermediate turnover rate ( t1/2 approximately 4 days) that comprised approximately 15% of the isotope signal, and a pool with very slow turnover rate ( t1/2 approximately 140 days) that made up approximately 44% of the total isotope signal. The carbon isotope signature of horse blood bicarbonate, in contrast, had a different isotopic composition, with approximately 67% of the isotope signal coming from a fast turnover pool ( t1/2 0.2 days), approximately 17% from a pool with an intermediate turnover rate ( t1/2 approximately 3 days) and approximately 16% from a pool with a slow turnover rate ( t1/2 approximately 50 days). The constituent isotope pools probably correspond to one exogenous and two endogenous sources. The exogenous source equates to our fast turnover pool, and the pools with intermediate and slow turnover rates are thought to derive from the turnover of metabolically active tissues and relatively inactive tissues within the body, respectively. It seems that a greater proportion of the amino acids available for hair synthesis come from endogenous sources compared to the compounds undergoing cellular catabolism in the body. Consequently, the isotope composition of blood bicarbonate appears to be much more responsive to dietary isotope changes, whereas the amino acids in the blood exhibit considerable isotopic inertia. PMID:14730442

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

2004-01-17

355

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 Å, 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

356

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

357

Stable-Isotope Analysis of Italian Shallow-Water Carbonates: the Response of Mesozoic Platform Carbonates to Oceanic Anoxic Events  

NASA Astrophysics Data System (ADS)

Many recent carbonate platforms have been observed to be in a phase of partial drowning. Factors responsible for degradation of shallow, reefal environments include sea-water temperature, salinity, light, sediment input, nutrients, bioerosion, and tempests. In particular, nutrient excess (eutrophication) has been observed to create environments lacking in carbonate producers and with benthic communities dominated by algal-cyanobacterial mats and bioeroders such as sponges. Sea-water temperatures in excess of 30° C have also led to coral and foraminiferal bleaching and death. The stratigraphic record shows that many carbonate platforms have been through the same process of partial and complete drowning throughout the Phanerozoic. Carbon-, strontium-, and oxygen-isotope analyses were undertaken on Italian platform carbonates and used alongside a poorly constrained biostratigraphy to identify the stratigraphic position of those intervals recording major changes in the Mesozoic carbon-cycle known as Oceanic Anoxic Events (Early Toarcian, Early Aptian, Cenomanian-Turonian) and to investigate the response of carbonate platforms to such events. In the Lower Toarcian sections studied (Trento Platform, Southern Alps, North Italy), bulk-rock \\delta13C(carb) shows a negative excursion with values lower than +1% followed by a positive excursion with values peaking at greater than +4%. This negative excursion has recently been ascribed to be the result of a massive methane gas-hydrate dissociation event and has not been previously recorded in shallow-water platform carbonates. Recent work on Lower Aptian deep- and shallow-water carbonates and organic marine and terrestrial carbon from sections around the world has revealed a similar negative followed by positive \\delta13C trend. In a section through the Friuli Platform (Southern Alps, North Italy), this study has given evidence of an Early Aptian negative excursion but without the presence of an obvious later positive \\delta13C(carb) event. This lack of a positive excursion is believed to be the result of "signal-dampening" due to deposition of carbonate in a restricted lagoonal environment affected by local processes such as the oxidation of organic matter. Previous work on Cenomanian-Turonian successions has shown a globally reproducible four-pronged positive \\delta13C excursion in pelagic carbonates and marine and terrestrial organic carbon across the stage boundary. Shallow-water carbonates in one section in Southern Italy (Southern Limestone Apennines), where the Cenomanian-Turonian boundary is preserved, show the same pattern with values again peaking above +4%. Associated with these three major Oceanic Anoxic Events, which are known to be periods of relative palaeotemperature maxima and increased nutrient cycling, are facies changes in the shallow-water carbonates indicating that the platforms struggled to keep up with relative sea-level rise. These periods of "carbonate crisis" are reflected in the stratigraphic record by the presence of laminated marls and/or abundant sponge-spicules and/or chert. This lithological evidence indicates that at these times the carbonate platforms were affected by some of the same degradative factors we see responsible for partial drowning today.

Woodfine, R. G.; Jenkyns, H. C.; Sarti, M.; Bruni, R.; Baroncini, F.

2001-12-01

358

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

Microsoft Academic Search

CO spectral line formation in the Sun has long been a source of consternation for solar physicists, as have the elemental abundances it seems to imply. We modelled solar CO line formation using a realistic, ab initio, time-dependent 3D radiative-hydrodynamic model atmosphere. Results were compared with space-based observations from the ATMOS space shuttle experiment. We employed weak 12C16O, 13C16O and

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

2006-01-01

359

The magnesium isotope record of cave carbonate archives  

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

360

The magnesium isotope record of cave carbonate archives  

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

361

Using SPIRAL (Single Pollen Isotope Ratio AnaLysis) to estimate C 3- and C 4-grass abundance in the paleorecord  

Microsoft Academic Search

C3 and C4 grasses differ greatly in their responses to environmental controls and influences on biogeochemical processes (e.g. water, carbon, and nutrient cycling). Difficulties in distinguishing between these two functional groups of grasses have hindered paleoecological studies of grass-dominated ecosystems. Stable carbon isotopic analysis of individual grains of grass pollen using a spooling-wire microcombustion device interfaced with an isotope-ratio mass

David M. Nelson; Feng Sheng Hu; Daniel R. Scholes; Neeraj Joshi; Ann Pearson

2008-01-01

362

Carbon fluxes, pCO 2 and substrate weathering in a large northern river basin, Canada: carbon isotope perspectives  

Microsoft Academic Search

Isotopic composition of dissolved inorganic carbon (?13CDIC) in the Ottawa River basin is about ?8 and ?16‰ for lowland carbonate and upland silicate tributaries, respectively. This suggests that (1) the source of DIC to the Ottawa River is soil respiration and carbonate weathering, (2) exchange with the atmosphere is unidirectional or volumetrically unimportant, and (3) in-river respiration and photosynthesis are

Kevin Telmer; Jan Veizer

1999-01-01

363

Genetic Effect on Carbon-Isotope Composition of a Plant  

NASA Astrophysics Data System (ADS)

Stable carbon isotopes of organic sediments are potential tools in investigating a wide spectrum of geological problems. These include paleoclimate, paleoecology, and the origin of life. The quality of the information the tools provides depends largely on our knowledge on the factors determining the isotopic composition of a plant. This is because most biogenic organic sediments are derived from plants. The factors can be grouped into internal and external. The internal factors are ultimately attributable to the genetic make-up of a plant. The most well known internal factor is the photosynthetic pathway. Others include structure of the leave tissue and metabolic characteristics of a plant. External factors are concentration and the isotopic composition of the source CO2 and the physical and chemical conditions of the plant's growth environments. This study addresses primarily the genetic effect, the internal factors. Based on the results of two suites of natural plant samples, it is concluded that the difference in photosynthetic pathway entails about 20.0 % of spread in terms of ä13CPDB values. Genetic effect is also accountable for up to 7.0 to 8.0 % spread in ä13CPDB values within a single category of photosynthetic pathway (i.e. the Calvin cycle). With constrains from the relevant known knowledge, it is concluded that the ä13CPDB values of terrestrial plants are probably ranging from - 8.0 to equal or less than -44.9 %. This range of ä13CPDB values may also be considered the bio-signature of organic sediments of great antiquity.

Yeh, H.

2005-05-01

364

Carbon isotopic enrichment in Titan's Tholins: implications for Titan's aerosols  

NASA Astrophysics Data System (ADS)

Since the discovery of the main composition of Titan s atmosphere many laboratory experiments have been carried out to mimic its chemical evolution and in particular the formation of the haze particles of this atmosphere Indeed the solid products obtained during these simulation experiments -- often named Titan s tholins -- are supposed to be analogues of Titan s aerosols and many studies have already been achieved on these tholins We have studied the possible isotopic fractionation of carbon during the processes involved in the formation of Titan s tholins using tholins obtained from different simulation experiments We will present the first results obtained on the isotopic ratios of 13 C 12 C measured on the analogues of Titan s aerosols synthesized in laboratory Measurement of delta 13 C leaded both on laboratory aerosols and on the initial gas mixture N 2 CH 4 98 2 used in the simulations doesn t show any evident deficit or enrichment of 13 C in comparison with 12 C in the aerosols synthesised compared to the initial gas mixture Preliminary retrieving of the data of the ACP instrument on the Huygens probe suggests that Titan s aerosols may present also no enrichment This allows us to go further in the analyses of the ACP data in comparison with the first conclusions newly published in Nature Isra e l et al Nature 2005

Nguyen, N.; Raulin, R.; Coll, C.; Derenne, D.; Szopa, S.; Israël, I.; Cernogora, C.; Bernard, B.

365

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

366

MGA (Multi-Group Analysis): A gamma-ray spectrum analysis code for determining plutonium isotopic abundances  

SciTech Connect

Nondestructive measurements of x-ray and gamma-ray emissions can be used to analyze a sample for plutonium. This report describes the methods and algorithms we have developed for analyzing gamma-ray spectra obtained by using a germanium detector system to accurately determine the relative abundances of various actinide isotopes in a sample. Our methodology requires no calibrations and can be used to measure virtually any size and type of plutonium sample. Measurement times can be as short as a few minutes; measurements are frequently accurate to within 1%. Our methods have been programmed into a computerized analysis code called MGA (Multi-Group Analysis). Our current versions can be run on personal computers (IBM type) and on the DEC VAX microcomputer. Spectral analysis times are usually far less than a minute. 28 refs., 26 figs., 1 tab.

Gunnink, R

1990-04-03

367

Stable-Carbon Isotope Ratios as a Measure of Marine Versus Terrestrial Protein in Ancient Diets  

Microsoft Academic Search

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 [sim] 7 per mil difference between oceanic and atmospheric carbon. This difference is passed on to human consumers. The carbon isotopic values {([dgr]13C)} for human collagen thus yield direct information on the relative amounts of

Brian S. Chisholm; D. Erle Nelson; Henry P. Schwarz

1982-01-01

368

MGA: A gamma-ray spectrum analysis code for determining plutonium isotopic abundances. Volume 3, FORTRAN listing of the GA code  

SciTech Connect

Nondestructive measurements of x-ray and gamma-ray emissions can be used to determine the abundances of various actinides in a sample. Volume 1 of this report describes the methods and algorithms we have developed to determine the relative isotopic abundances of actinides in a sample, by analyzing gamma-ray spectra obtained using germanium detector systems. Volume 2 is a guide to using the MGA (Multiple Group Analysis) computer program we have written to perform plutonium isotopic analyses. This report contains a listing of the FORTRAN instructions of the code.

Gunnink, R

1991-09-01

369

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

NASA Astrophysics Data System (ADS)

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 ?15N values of soil and vegetation at Camp Paivika (CP), the most polluted site, were at least 1.7‰ more enriched than the other, less polluted sites. Mean soil ?15NH4+ was also significantly enriched in 15N at CP compared to Barton Flats (BF), the least polluted site, by 3.8‰. Soil ?15NO3- signatures were not statistically different among sites. The litter ?15NH4+ values followed a trend similar to that of the soil. Furthermore, the litter ?15NO3- at CP was significantly depleted in 15N compared to the other sites. The isotopic discrimination for the eventual production of nitrate from organic nitrogen in soil and litter was maximized at CP and minimized at BF. A stable carbon isotopic gradient of decreasing soil, litter, and foliar ?13C was also observed with increasing site pollution level. These results support the hypothesis that chronic atmospheric deposition has enhanced nitrogen cycling processes and has affected carbon metabolism at CP.

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

2000-03-01

370

Carbon Abundances from SDSS Globular Clusters: Exploring the Origin in the Large Spread in [C/Fe  

NASA Astrophysics Data System (ADS)

Globular clusters are compact, massive, and the oldest bound stellar systems of the Galaxy. They were thought to be chemically homogeneous systems with a single stellar population. However, recent results based on precise photometry from HST suggests the presence of more than one stellar population among globular cluster stars. These stars have a different abundance pattern compared to halo stars of similar metallicities. To understand globular cluster formation, in the context of hierarchical Galaxy formation models, it is necessary to understand the origin of their abundance pattern. We have used the SDSS spectra from Data Release 8 to estimate the carbon abundances for 5 globular clusters. We find large spreads in the carbon abundances throughout the CMDs of the clusters, indicating multiple populations with different carbon abundances. For a subset of good S/N spectra, we derive Ba and Sr abundances to distinguish the changes in the carbon as due to any self-enrichment (during AGB or even helium core flash) or from depletion due to CN cycle and mixing processes. This will help in probing the origin of the actual spread in the carbon abundance due to different stellar populations.

Fiorenza, Stephanie; Sivarani, T.; Antony, S.; Lee, Y.; Beers, T. C.

2013-01-01

371

Carbon and hydrogen isotopic compositions of stratospheric methane: 2. Two-dimensional model results and implications for kinetic isotope effects  

NASA Astrophysics Data System (ADS)

New high-precision measurements of the carbon and hydrogen isotopic compositions of stratospheric CH4 made on whole air samples collected aboard the NASA ER-2 aircraft are compared with results from the Lawrence Livermore National Laboratory 2-D model. Model runs incorporating sets of experimentally determined kinetic isotope effects (KIEs) for the reactions of CH4 with each of the oxidants OH, O(1D), and Cl are examined with the goals of determining (1) how well the 2-D model can reproduce the observations for both the carbon and hydrogen isotopic compositions, (2) what factors are responsible for the observed increase in the apparent isotopic fractionation factors with decreasing methane mixing ratios, and (3) how sensitive the modeled isotopic compositions are to various experimentally determined KIEs. Bound by estimates of the effects of uncertainties in model chemistry and transport on isotopic compositions, we then examine the constraints the ER-2 observations place on values for the KIEs. For the carbon KIE for reaction of CH4 with O(1D), for example, the analysis of model results and observations favors the larger of the experimental values, 1.013, over a value of 1.001. These analyses also suggest that intercomparisons of results from different models using a given set of KIEs may be useful as a new diagnostic of model-model differences in integrated chemistry and transport.

McCarthy, M. C.; Boering, K. A.; Rice, A. L.; Tyler, S. C.; Connell, P.; Atlas, E.

2003-08-01

372

Carbon isotopic composition of Neoproterozoic glacial carbonates as a test of paleoceanographic models for snowball Earth phenomena  

NASA Astrophysics Data System (ADS)

Consistently positive carbon isotopic values were obtained from in situ peloids, ooids, and stromatolitic carbonate within Neoproterozoic glacial successions in northern Namibia, central Australia, and the North American Cordillera. Because positive values continue upward into the immediately overlying postglacial cap carbonates, the negative isotopic excursions widely observed in those carbonate rocks require an explanation that involves a short-term perturbation of the global carbon cycle during deglaciation. The data do not support the ecological consequences of complete coverage of the glacial ocean with sea ice, as predicted in the 1998 snowball Earth hypothesis of P.F. Hoffman et al. In the snowball Earth hypothesis, the postglacial cap carbonates and associated -5‰ negative carbon isotopic excursions represent the physical record of CO2 transfer from the high-pCO2 snowball atmosphere (˜0.12 bar) to the sedimentary reservoir via silicate weathering in the snowball aftermath. Stratigraphic timing constraints on cap carbonates imply weathering rates of ˜1000 times preglacial levels to be consistent with the hypothesis. The absence of Sr isotopic variation between glacial and postglacial deposits and calculations of maximum weathering rates do not support a post-snowball weathering event as the origin for cap carbonates and associated isotopic excursions.

Kennedy, Martin J.; Christie-Blick, Nicholas; Prave, Anthony R.

2001-12-01

373

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

Microsoft Academic Search

CO spectral line formation in the Sun has long been a source of consternation\\u000afor solar physicists, as have the elemental abundances it seems to imply. We\\u000amodelled solar CO line formation using a realistic, ab initio, time-dependent\\u000a3D radiative-hydrodynamic model atmosphere. Results were compared with\\u000aobservations from the space-based ATMOS experiment. We employed weak 12C16O,\\u000a13C16O and 12C18O lines

Patrick C. Scott; Martin Asplund; Nicolas Grevesse; A. Jacques Sauval

2006-01-01

374

3D H2BC: a novel experiment for small-molecule and biomolecular NMR at natural isotopic abundance.  

PubMed

3D H2BC is introduced for heteronuclear assignment on natural abundance samples even for biomolecules up to at least 10 kDa in low millimolar concentrations as an overnight experiment using the latest generation of cryogenically cooled probes. The short pulse sequence duration of H2BC is maintained in the 3D version due to multiple use of the constant-time delay. Applications ranging from a small lipid to a non-recombinant protein demonstrate the merits of 3D H2BC and the ease of obtaining assignments in chains of protonated carbons. PMID:19604710

Meier, Sebastian; Benie, Andrew J; Duus, Jens Ø; Sørensen, Ole W

2009-06-25

375

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

376

Effect of altitude on the carbon-isotope composition of forest and grassland soils from Papua New Guinea  

SciTech Connect

The stable isotope composition of carbon can be used to provide information on the origin of carbon in soil organic matter. This study looks at the effect of decreasing temperature and atmospheric pressure (altitude) on the carbon-isotope composition of soil organic carbon from forests and grasslands in tropical regions. Investigators examine whether a predictable relationship exists between vegetation type, the 13C value of surface soil organic matter, and altitude. The results provide a framework within which to more accurately constrain the carbon-isotope composition of terrestrial carbon ppls and to interpret the observed variations in the isotopic composition of rivere particulate organic carbon. 31 refs., 5 figs., 1 tab.

Bird, M.I.; Haberle, S.G.; Chivas, A.R. (Australian National Univ., Canberra (Australia))

1994-03-01

377

Natural abundance carbon 13 nuclear magnetic resonance spectroscopy of antifreeze glycoproteins  

SciTech Connect

Natural abundance /sup 13/C NMR spectroscopy (at 67.9 MHz) is used to study an aqueous solution of the antifreeze glycoproteins 3 to 6 from the Antarctic cod. Assignments of resonances to specific carbons of the known Ala-Ala-(..beta..Gal-(1 ..-->.. 3)-..cap alpha..-N-acetylgalactosamine)Thr repeating unit are presented. Some of the carbons of the proline residues of glycoprotein 6 are also identified. Spin-lattice relaxation times (at 30/sup 0/C), linewidths (at 35/sup 0/C), nuclear Overhauser enhancements (at 35/sup 0/C), and the temperature dependence of chemical shifts (from 0/sup 0/ to 75/sup 0/C) all strongly suggest that these antifreeze glycoproteins are predominantly or entirely flexible random coil polymers.

Berman, E. (Indiana Univ., Bloomington); Allerhand, A.; DeVries, A.L.

1980-05-25

378

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

379

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

380

Critique: measuring hydrogen stable isotope abundance of proteins to infer origins of wildlife, food and people.  

PubMed

Measurement of the relative abundance of (2)H (expressed in ?(2)H values) in tissues of plants, wildlife and people has evolved into a powerful forensic tool. The approach is based on the strong linkage between spatial patterns of ?(2)H values in precipitation at local and continental scales, and the tissues of plants and animals produced on these 'isoscapes'. Unfortunately, despite this exciting potential, difficulties inherent in the measurement of ?(2)H values in complex organic materials such as proteins, as well as the accuracy of such measurements, and a reluctance to adopt strict quality assurance/QC approaches to address challenges associated with these measurements, has clearly limited this potential. These challenges are entirely avoidable and techniques now exist for the routine reliable measurement of ?(2)H values in materials of forensic interest that will allow completely comparable data among laboratories. PMID:23534421