SEARCH · Search NASA

Results for “Carbon Isotopes”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8

All sources NASA NTRS DOE OSTI

NASA NTRS1988

Characteristics and carbon stable isotopes of fluids in the Southern Kerala granulites and their bearing on the source of CO2

Carbon dioxide-rich inclusions commonly occur in the banded charnockites and khondalites of southern Kerala as well as in the incipient charnockites formed by desiccation of gneisses along oriented zones. The combined high density fluid inclusion isochores and the range of thermometric estimates from mineral assemblages indicate entrapment pressures in the range of 5.4 to 6.1 Kbar. The CO2 equation of state barometry closely compares with the 5 plus or minus 1 Kbar estimate from mineral phases for the region. The isochores for the high density fluid inclusions in all the three rock types pass through the P-T domain recorded by phase equilibria, implying that carbon dioxide was the dominating ambient fluid species during peak metamorphic conditions. In order to constrain the source of fluids and to evaluate the mechanism of desiccation, researchers undertook detailed investigations of the carbon stable isotope composition of entrapped fluids. Researchers report here the results of preliminary studies in some of the classic localities in southern Kerala namely, Ponmudi, Kottavattom, Manali and Kadakamon.

Santosh, M.↗

NASA NTRS1995

Integrated approaches to terminal Proterozoic stratigraphy: an example from the Olenek Uplift, northeastern Siberia

In the Olenek Uplift of northeastern Siberia, the Khorbusuonka Group and overlying Kessyusa and Erkeket formations preserve a significant record of terminal Proterozoic and basal Cambrian Earth history. A composite section more than 350 m thick is reconstructed from numerous exposures along the Khorbusuonka River. The Khorbusuonka Group comprises three principal sedimentary sequences: peritidal dolomites of the Mastakh Formation, which are bounded above and below by red beds; the Khatyspyt and most of the overlying Turkut formations, which shallow upward from relatively deep-water carbonaceous micrites to cross-bedded dolomitic grainstones and stromatolites; and a thin upper Turkut sequence bounded by karst surfaces. The overlying Kessyusa Formation is bounded above and below by erosional surfaces and contains additional parasequence boundaries internally. Ediacaran metazoans, simple trace fossils, and vendotaenids occur in the Khatyspyt Formation; small shelly fossils, more complex trace fossils, and acritarchs all appear near the base of the Kessyusa Formation and diversify upward. The carbon-isotopic composition of carbonates varies stratigraphically in a pattern comparable to that determined for other terminal Proterozoic and basal Cambrian successions. In concert, litho-, bio-, and chemostratigraphic data indicate the importance of the Khorbusuonka Group in the global correlation of terminal Proterozoic sedimentary rocks. Stratigraphic data and a recently determined radiometric date on basal Kessyusa volcanic breccias further underscore the significance of the Olenek region in investigations of the Proterozoic-cambrian boundary.

Non-NASA Center↗

NASA NTRS1999

Interchange for Joint Research Entitled: Miniature Laser Spectrometer for Stable Isotope Measurements

As a first step in successfully measuring carbon isotopes optically we have previously demonstrated the measurement of C-13/C-12 to a precision of 0.1% using a tunable diode laser and CO2 spectral lines in the 2300/cm spectral region. This precision of 0.1% (1 per mil) for carbon isotopes is a value sufficiently precise to provide important isotopic data of interest to astrobiologists. The precision presently attainable in gases is sufficient to permit our instrument to be used in the measurement of isotopic ratios of interest to astrobiologists as well as geologists and planetary scientists. A small stable isotope laser spectrometer with a 10 cm path gas cell was designed and constructed. The cell was integrated with a liquid nitrogen cooled tunable diode laser and indium antimonide detector for evaluation. Using the small gas cell, preliminary measurements of 13C/12C in CO2 were made employing single-beam sequential acquisitions of the required spectral data. The results indicate an accuracy of 0.1% which is sufficiently high to make meaningful measurements of martian samples. In addition, improvements in the spectrometer gas handling system have been made to markedly reduce C-13/C-12 isotopic fractionation during sample gas cell loading which we expect will lead to further improvements in precision and accuracy. An important part of making isotopic ratio measurements in solid samples using diode lasers is the conversion of the elements of interest to molecules that have absorption spectra in the mid-ir spectral range accessible by tunable diode lasers. In this project we have investigated the necessary sample preparation procedures to extract carbon, an element of astrobiological importance, from model soil compounds and to convert it to CO2, a molecule with appropriate optical absorption characteristics for reliable laser spectrometer isotopic ratio measurements of 13C/12C. We have considered calcium carbonate as a model for a component of the martian regolith, and we have formulated a simple heating protocol for extracting carbon in the form of CO2.

Becker, J. F.↗

NASA NTRS1995

Carbon Monoxide Isotopes: On the Trail of Galactic Chemical Evolution

From the early days of the discovery of radio emission from carbon monoxide it was realized that it offered unusual potential for under- standing the chemical evolution of the Galaxy and external galaxies through measurements of molecular isotopes. These results bear on stellar nucleosynthesis, star formation, and gases in the interstellar medium. Progress in isotopic radio measurements will be reviewed.

isotopes nucleosynthesis↗

NASA NTRS1999

Miniature Laser Spectrometer for Stable Isotope Measurements

Becker, J. F.↗

NASA NTRS2012

Analyzers Measure Greenhouse Gases, Airborne Pollutants

In complete darkness, a NASA observatory waits. When an eruption of boiling water billows from a nearby crack in the ground, the observatory s sensors seek particles in the fluid, measure shifts in carbon isotopes, and analyze samples for biological signatures. NASA has landed the observatory in this remote location, far removed from air and sunlight, to find life unlike any that scientists have ever seen. It might sound like a scene from a distant planet, but this NASA mission is actually exploring an ocean floor right here on Earth. NASA established a formal exobiology program in 1960, which expanded into the present-day Astrobiology Program. The program, which celebrated its 50th anniversary in 2010, not only explores the possibility of life elsewhere in the universe, but also examines how life begins and evolves, and what the future may hold for life on Earth and other planets. Answers to these questions may be found not only by launching rockets skyward, but by sending probes in the opposite direction. Research here on Earth can revise prevailing concepts of life and biochemistry and point to the possibilities for life on other planets, as was demonstrated in December 2010, when NASA researchers discovered microbes in Mono Lake in California that subsist and reproduce using arsenic, a toxic chemical. The Mono Lake discovery may be the first of many that could reveal possible models for extraterrestrial life. One primary area of interest for NASA astrobiologists lies with the hydrothermal vents on the ocean floor. These vents expel jets of water heated and enriched with chemicals from off-gassing magma below the Earth s crust. Also potentially within the vents: microbes that, like the Mono Lake microorganisms, defy the common characteristics of life on Earth. Basically all organisms on our planet generate energy through the Krebs Cycle, explains Mike Flynn, research scientist at NASA s Ames Research Center. This metabolic process breaks down sugars for energy to fuel cellular functions. "We think this chemical process did not exist when life first formed on Earth," he says, "because it is based on oxygen being available, and there was little oxygen available on the early Earth." It is possible that there are anaerobic regions beneath the sea floor in which life forms like those early non-Krebs Cycle microbes may yet exist. To detect and potentially collect samples of life emerging from hydrothermal vents, Flynn and his colleagues created Medusa, a multi-sensor instrument designed for long-term observation of diked vents on the ocean floor. When the vents erupt, Medusa assesses indicators of life within the expelled water. If the results are positive, the observatory collects samples and detaches from the ocean floor, making the long journey to the surface for retrieval by scientists. One of the indicators Medusa measures is the ratio of carbon isotopes in the water, namely carbon-12 and carbon-13. Living organisms preferentially take up carbon-12, Flynn says, so examining the ratio of these isotopes can help to determine the source of carbon in an environment as either biological or non-biological. "On Mars, there is evidence of localized methane in the atmosphere, and that methane could come from biological sources or from geochemical ones," Flynn says. "Determining the background planetary carbon isotope ratios and then evaluating the specific carbon ratios in this methane would help to determine how it was formed." A long-duration observatory similar to Medusa could one day provide essential evidence for or against the presence of life on the Red Planet or beneath the ice-crusted oceans of Europa.

Source record↗

NASA NTRS2000

Abrupt Changes at the Permian/Triassic Boundary: Tempo of Events from High-Resolution Cyclostratigraphy

The Permian/Triassic (P/Tr) boundary (251.4 +/- 3 Myr) is marked by the most severe mass extinction in the geologic record. Recently, precise absolute dating has bracketed the marine extinctions and associated carbon-isotope anomaly within less than 1 Myr. We improve this resolution through high-resolution stratigraphy across the P/Tr boundary in the 331-m Gartnerkofel-1 core and nearby Reppwand outcrop section (Carnic Alps, Austria) utilizing FFT and wavelet timeseries analyses of cyclic components in down-hole core logs of density and natural gamma-ray intensity, and carbon-isotopic ratios of bulk samples. The wavelet analysis indicates continuity of deposition across the P/Tr boundary interval, and the timeseries analyses show evidence for persistent cycles in the ratio of approximately 40: 10: 4.7: 2.3 meters, correlated with Milankovitch-band orbital cycles of approximately 412: 100: 40: 20 kyr (eccentricity 1 and 2, obliquity, and precession), and giving a consistent average sedimentation rate of approximately 10 cm/1,000 yr. Milankovitch periods in delta C-13 and density in these shallow-water carbonates were most likely the result of climatically induced oscillations of sea level and climate, coupled with changes in ocean circulation and productivity, that affected sedimentation. Fluctuations in gamma radiation reflect varying input of clay minerals and the presence of shaly interbeds. Throughout the P/Tr boundary interval in the core, the 100,000-year eccentricity cycle seems to be dominant. Weaker obliquity and precession cycles are in line with the location of the Austrian section in the latest Permian, close to the Equator in the western bight of the Tethys, where obliquity and precessional effects on seasonal contrast might be subdued. Using the improved resolution provided by cycle analysis in the GK-1 core, we find that the dramatic change in the faunal record that marks the P/Tr boundary takes place over less than 6m, or less than 60,000 years. In the nearby Reppwand outcrop section, the same faunal changes occurs over only 0.8 m or about 8,000 years, close to the limit of time-resolution induced by bioturbation and reworking in these sediments. The sharp negative global carbon-isotope shift took place within less than or equal to 40,000 yr, and the isotope excursions persisted for approximately 480,000 yr into the Early Triassic. The results indicate that the severe marine faunal event that marks the P/Tr boundary was very sudden, perhaps less than the resolution window in the GK-1 core, and suggest a catastrophic cause. The wavelet-analysis approach to high-resolution cyclostratigraphy can be applied to other P/Tr boundary sections, and when combined with precise absolute dating and magnetostratigraphic methods promises a significant increase in resolution in determining the correlation and tempo of the end-Permian extinctions and related events worldwide.

Rampino, M. R.↗

NASA NTRS1992

Methane transport mechanisms and isotopic fractionation in emergent macrophytes of an Alaskan tundra lake

The stable carbon isotopic composition of methane associated with and emitted by the two dominant emergent macrophytes abundant in the many Alaskan tundra lakes, Carex rostrata and Arctophila fulva, is determined. The carbon isotopic composition of the methane was -58.6 +/- 0.5 (n=2) for Arctophila and -66.6 +/- 2.5 (n=6) for Carex. The methane emitted by these species is depleted in C-13 by 12 per mil for Arctophila and 18 per mil for Carex relative to methane withdrawn from plant stems 1-2 cm below the waterline. The results suggest more rapid transport of (C-12)H4 relative to (C-13)H4 through plants to the atmosphere. Plant stem methane concentrations ranged from 0.2 to 4.0 percent in Arctophila, with an isotopic composition of -46.1 +/- 4.3 percent (n=8). Carex stem methane concentrations ranged from 150 to 1200 ppm, with an isotopic composition of -48.3 +/- 1.4 per mil (n=3).

Chanton, Jeffrey P.↗

NASA NTRS2011

delta C-13 Analysis of Mars Analog Carbonates Using Evolved Gas Cavity - Ringdown Spectrometry on the 2010 Arctic Mars Analog Svalbard Expedition (AMASE)

The 2010 Arctic Mars Analog Svalbard Expedition (AMASE) investigated two distinct geologic settings on Svalbard, using instrumentation and techniques in development for future Mars missions, such as the Mars Science Laboratory (MSL), ExoMars, and Mars Sample Return (MSR). The Sample Analysis at Mars (SAM) instrument suite, which will fly on MSL, was developed at Goddard Space Flight Center (GSFC), together with several partners. SAM consists of a quadrupole mass spectrometer (QMS), a gas chromatograph CGC), and a tunable laser spectrometer (TLS), which all analyze gases created by evolved gas analysis (EGA). The two sites studied represent "biotic" and "abiotic" analogs; the "biotic" site being the Knorringfjell fossil methane seep, and the "abiotic" site being the basaltic Sigurdfjell vent complex. The data presented here represent experiments to measure the carbon isotopic composition of carbonates from these two analogs using evolved gas analysis coupled with a commercial cavity ringdown CO2 isotopic analyzer (Picarro) as a proxy for the TLS on SAM.

Stern, J. C.↗

NASA NTRS1989

The formation of weathering products on the LEW 85320 ordinary chondrite - Evidence from carbon and oxygen stable isotope compositions and implications for carbonates in SNC meteorites

Isotopic analysis of nesquehonite recovered from the surface of the LEW 85320 H5 ordinary chondrite shows that the delta C-13 and delta O-18 values of the two generations of bicarbonate (Antarctic and Texas) are different: delta C-13 = + 7.9 per mil and + 4.2 per mil; delta O-18 = + 17.9 per mil and + 12.1 per mil, respectively. Carbon isotopic compositions are consistent with equilibrium formation from atmospheric carbon dioxide at - 2 + or - 4 C (Antarctic) and + 16 + or - 4 C (Texas). Oxygen isotopic data imply that the water required for nesquehonite precipitation was derived from atmospheric water vapor or glacial meltwater which had locally exchanged with silicates, either in the meteorite or in underlying bedrock. Although carbonates with similar delta C-13 values have been identified in the SNC meteorites EETA 79001 and Nakhla, petrographic and temperature constraints argue against their simply being terrestrial weathering products.

Grady, Monica M.↗

NASA NTRS2007

Processes in Early Planetesimals: Evidence from Ureilite Meteorites

Ureilites are primitive ultramafic achondrites composed largely of olivine and pigeonite, with minor augite, carbon, sulphide and metal. They represent very early material in the history of the Solar System and form a bridge between undifferentiated chondrites and fully differentiated asteroids. They show a mixture of chemical characteristics, some of which are considered to be nebula-derived (e.g. a negative correlation between Mg/Fe and Delta O-17 that resembles that of the ordinary chondrites but at lower Delta O-17 values) whereas others have been imposed by asteroidal differentiation. Carbon isotope data show a striking negative correlation of delta C-13 values with mg# in olivine. delta C-13 also correlates positively with Delta O-17, and therefore this isotopic variation was probably also nebula-derived. Thus, oxygen and carbon isotope compositions and Fe-Mg systematics of each monomict ureilite were established before differentiation processes began. Heated by decay of short-lived radioactive isotopes, the ureilite asteroid started to melt. Metal and sulphide would have melted first, forming a Fe-S eutectic liquid, which removed chalcophile elements and incompatible siderophile elements, and basaltic melts that removed Al, Ca and the LREE. Several elements show different abundances and/or correlations with Fo content in olivine, e.g. carbon shows a positive correlation in ferroan ureilites, and a weak or even negative correlation in more magnesian compositions. HSE such as Os and Ir also show different distributions, i.e. ureilites with Fo < 82 have very scattered Os and Ir concentrations, which reach high values, whereas ureilites with Fo > 82 tend to have much less scattered and overall lower Os and Ir abundances. A similar change in elemental behaviour is shown by the Fe-Mn relations in ureilitic olivines: those with Fo contents < 85 show a good negative correlation, whereas those with Fo > 85 show much greater scatter. This suggests that a major change affected the parent body at a time when melting had reached relatively magnesian bulk compositions. We consider that this event may have been a hit and run collision in which the ureilite parent body collided with a larger object. During the collision, the ureilite mantle broke up catastrophically but re-accreted in a jumbled state around the still-intact core. Mg-rich basaltic melts that were in the process of being formed at the time of break-up were retained in part as melt clasts that re-accreted to the regolith and are found in polymict ureilites.

Mittlefehldt, David W.↗

NASA NTRS1992

Sudbury project (University of Muenster-Ontario Geological Survey): Petrology, chemistry, and origin of breccia formations

Within the Sudbury Project of the University of Muenster and the Ontario Geological Survey special emphasis was put on the breccia formations exposed at the Sudbury structure (SS) because of their crucial role for the impact hypothesis. They were mapped and sampled in selected areas of the north, east, and south ranges of the SS. The relative stratigraphic positions of these units are summarized. Selected samples were analyzed by optical microscopy, SEM, microprobe, XRF and INAA, Rb-Sr and SM-Nd-isotope geochemistry, and carbon isotope analysis. The results of petrographic and chemical analysis for those stratigraphic units that were considered the main structural elements of a large impact basin are summarized.

Stoeffler, D.↗

NASA NTRS1985

Seasonal C-13 variations of methane from an anoxic marine sediment

Recent analyses of glacial ice suggest that the atmospheric concentration of methane has doubled in the last several hundred years, presumably due to anthropogenic perturbations of the relevant biogeochemical cycles. In principal, carbon isotopic measurements of atmospheric methane would provide information concerning changes in the sources and sinks of methane. The isotopic composition of methane is dependent on the source of the methane carbon, the mechanism of methane synthesis, and the degree and mode of oxidation which the methane has experienced. Unfortunately, few carbon isotopic measurements of atmospheric variations have been reported, so conclusions about temporal isotopic variations cannot be made. Also, before isotopic measurements of atmospheric methane can be used to identify changes in methane isotopic composition from different sources must be obtained. Methane bubbles from the anoxic sediments of Cape Lookout Bight, NC exhibit seasonal C-13 variations. The C-13 values ranged from -58 in August to -64 in the winter months with the evolution of the C-13 enriched gas occurring during periods of peak methane production. Even though a few intramolecular C-13 measurements of the pore water acetate have been made (methyl group, -26 per mil; carbonyl, -6 per mil), it is not clear how the acetate fermentation pathway affects the methane C-13/C-12 composition.

Blair, Neal↗

NASA NTRS2000

BOREAS TGB-12 Isotropic Carbon Dioxide Data over the NSA

The BOREAS TGB-12 team made measurements of soil carbon inventories, carbon concentration in soil gases, and rates of soil respiration at several sites to estimate the rates of carbon accumulation and turnover in each of the major vegetation types. This data set contains information on the carbon isotopic content of carbon dioxide sampled from soils in the NSA-OBS, NSA-YJP, and NSA-OJP sites. Data were collected from 14-Nov-1993 to 10-Oct-1996. The data are stored in tabular ASCII files.

Trumbore, Susan↗

NASA NTRS2015

Carbon and Sulfur Isotopic Signatures of Ancient Life and Environment at the Microbial Scale: Neoarchean Shales and Carbonates

An approach to coordinated, spatially resolved, in situ carbon isotope analysis of organic matter and carbonate minerals, and sulfur three- and four-isotope analysis of pyrite with an unprecedented combination of spatial resolution, precision, and accuracy is described. Organic matter and pyrite from eleven rock samples of Neoarchean drill core express nearly the entire range of delta(sup 13)C, delta(sup 34)S, Delta(sup 33)S, and Delta(sup 36)S known from the geologic record, commonly in correlation with morphology, mineralogy, and elemental composition. A new analytical approach (including a set of organic calibration standards) to account for a strong correlation between H/C and instrumental bias in SIMS delta(sup 13)C measurement of organic matter is identified. Small (2-3 microns) organic domains in carbonate matrices are analyzed with sub-permil accuracy and precision. Separate 20- to 50-micron domains of kerogen in a single approx. 0.5 cu cm sample of the approx. 2.7 Ga Tumbiana Formation have delta(sup 13)C = −52.3 +/- 0.1per mille and −34.4 +/- 0.1per mille, likely preserving distinct signatures of methanotrophy and photoautotrophy. Pyrobitumen in the approx. 2.6 Ga Jeerinah Formation and the approx. 2.5 Ga Mount McRae Shale is systematically 13C-enriched relative to co-occurring kerogen, and associations with uraniferous mineral grains suggest radiolytic alteration. A large range in sulfur isotopic compositions (including higher Delta(sup 33)S and more extreme spatial gradients in Delta(sup 33)S and Delta(sup 36)S than any previously reported) are observed in correlation with morphology and associated mineralogy. Changing systematics of delta(sup 34)S, Delta(sup 33)S, and Delta(sup 36)S, previously investigated at the millimeter to centimeter scale using bulk analysis, are shown to occur at the micrometer scale of individual pyrite grains. These results support the emerging view that the dampened signature of mass-independent sulfur isotope fractionation (S-MIF) associated with the Mesoarchean continued into the early Neoarchean, and that the connections between methane and sulfur metabolism affected the production and preservation of S-MIF during the first half of the planet's history.

isotopic signatures↗

NASA NTRS1993

Stable isotopes as tracers of methane dynamics in Everglades marshes with and without active populations of methane oxidizing bacteria

The stable carbon isotopic composition of CH4 is used to study the processes that affect it during transport through plants from sediment to the atmosphere. The enhancement of CH4 flux from Cladium and Eleocharis over the flux from open water or clipped sites indicated that these plants served as gas conduits between the sediments and the atmosphere. Lowering of the water table below the sediment surface caused an Everglades sawgrass marsh to shift from emission of CH4 to consumption of atmospheric CH4. Cladium transported gases passively mainly via molecular diffusion and/or effusion instead of actively via bulk flow. Stable isotropic data gave no evidence that CH4 oxidation was occurring in the rhizosphere of Cladium. Both CH4 stable carbon isotope and flux data indicated a lack of CH4 oxidation at the sediment-water interface in Everglades marl soils and its presence in peat soils where 40 to 92 percent of the flux across the sediment-water interface was oxidized.

Happell, James D.↗

NASA NTRS1989

The post-Paleozoic chronology and mechanism of 13C depletion in primary marine organic matter

Carbon-isotopic compositions of geoporphyrins have been measured from marine sediments of Mesozoic and Cenozoic age in order to elucidate the timing and extent of depletion of 13C in marine primary producers. These results indicate that the difference in isotopic composition of coeval marine carbonates and marine primary photosynthate was approximately 5 to 7 permil greater during the Mesozoic and early Cenozoic than at present. In contrast to the isotopic record of marine primary producers, isotopic compositions of terrestrial organic materials have remained approximately constant for this same interval of time. This difference in the isotopic records of marine and terrestrial organic matter is considered in terms of the mechanisms controlling the isotopic fractionation associated with photosynthetic fixation of carbon. We show that the decreased isotopic fractionation between marine carbonates and organic matter from the Early to mid-Cenozoic may record variations in the abundance of atmospheric CO2.

Non-NASA Center↗

NASA NTRS2008

Detection of Abiotic Methane in Terrestrial Continental Hydrothermal Systems: Implications for Methane on Mars

The recent detection of methane in the Martian atmosphere and the possibility that its origin could be attributed to biological activity, have highlighted the importance of understanding the mechanisms of methane formation and its usefulness as a biomarker. Much debate has centered on the source of the methane in hydrothermal fluids, whether it is formed biologically by microorganisms, diagenetically through the decomposition of sedimentary organic matter, or inorganically via reduction of CO2 at high temperatures. Ongoing research has now shown that much of the methane present in sea-floor hydrothermal systems is probably formed through inorganic CO2 reduction processes at very high temperatures (greater than 400 C). Experimental results have indicated that methane might form inorganically at temperatures lower still, however these results remain controversial. Currently, methane in continental hydrothermal systems is thought to be formed mainly through the breakdown of sedimentary organic matter and carbon isotope equilibrium between CO2 and CH4 is thought to be rarely present if at all. Based on isotopic measurements of CO2 and CH4 in two continental hydrothermal systems, we suggest that carbon isotope equilibration exists at temperatures as low as 155 C. This would indicate that methane is forming through abiotic CO2 reduction at lower temperatures than previously thought and could bolster arguments for an abiotic origin of the methane detected in the martian atmosphere.

Socki, Richard A.↗