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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Stable water isotope behavior during the last glacial maximum: A general circulation model analysis

Global water isotope geochemisty during the last glacial maximum (LGM) is simulated with an 8 deg x 10 deg atmospheric general circulation model (GCM). The simulation results suggest that the spatial delta O-18/temperature relationships observed for the present day and LGM climates are very similar. Furthermore, the temporal delta O-18/temperature relationship is similar to the present-day spatial relationship in regions for which the LGM/present-day temperature change is significant. This helps justify the standard practice of applying the latter to the interpretation of paleodata, despite the possible influence of other factors, such as changes in the evaportive sources of precipitation or in the seasonality of precipitation. The model suggests, for example, that temperature shifts inferred from ice core data may differ from the true shifts by only about 30%.

Jouzel, Jean↗
NASA NTRS2016

How Will Sea Ice Loss Affect the Greenland Ice Sheet? On the Puzzling Features of Greenland Ice-Core Isotopic Composition

The modern cryosphere, Earth's frozen water regime, is in fast transition. Greenland ice cores show how fast theses changes can be, presenting evidence of up to 15 C warming events over timescales of less than a decade. These events, called Dansgaard/Oeschger (D/O) events, are believed to be associated with rapid changes in Arctic sea ice, although the underlying mechanisms are still unclear. The modern demise of Arctic sea ice may, in turn, instigate abrupt changes on the Greenland Ice Sheet. The Arctic Sea Ice and Greenland Ice Sheet Sensitivity (Ice2Ice Chttps://ice2ice.b.uib.noD) initiative, sponsored by the European Research Council, seeks to quantify these past rapid changes to improve our understanding of what the future may hold for the Arctic. Twenty scientists gathered in Copenhagen as part of this initiative to discuss the most recent observational, technological, and model developments toward quantifying the mechanisms behind past climate changes in Greenland. Much of the discussion focused on the causes behind the changes in stable water isotopes recorded in ice cores. The participants discussed sources of variability for stable water isotopes and framed ways that new studies could improve understanding of modern climate. The participants also discussed how climate models could provide insights into the relative roles of local and nonlocal processes in affecting stable water isotopes within the Greenland Ice Sheet. Presentations of modeling results showed how a change in the source or seasonality of precipitation could occur not only between glacial and modern climates but also between abrupt events. Recent fieldwork campaigns illustrate an important role of stable isotopes in atmospheric vapor and diffusion in the final stable isotope signal in ice. Further, indications from recent fieldwork campaigns illustrate an important role of stable isotopes in atmospheric vapor and diffusion in the final stable isotope signal in ice. This feature complicates the quantitative interpretation of ice core signals but also makes the stable ice isotope signal a more robust regional indicator of climate, speakers noted. Meeting participants agreed that to further our understanding of these relationships, we need more process-focused field and laboratory campaigns.

Greenland↗
NASA NTRS1997

Validity of the Temperature Reconstruction from Water Isotopes in Ice Cores

Well-documented present-day distributions of stable water isotopes (HDO and others) show the existence, in middle and high latitudes, of a linear relationship between the mean annual isotope content of precipitation (SD and 51"0) and the mean annual temperature at the precipitation site. Paleoclimatologists have used this relationship, which is particularly well obeyed over Greenland and Antarctica, to infer paleotemperatures from ice core data. There is, however, growing evidence that spatial and temporal isotope/ surface temperature slopes differ, thus complicating the use of stable water isotopes as paleothermometers. In this paper we review empirical estimates of temporal slopes in polar regions and relevant information that can be inferred from isotope models: simple, Rayleigh-type distillation models and (particularly over Greenland) general circulation models (GCMS) fitted with isotope tracer diagnostics. Empirical estimates of temporal slopes appear consistently lower than present-day spatial slopes and are dependent on the timescale considered. This difference is most probably due to changes in the evaporative origins of moisture, changes in the seasonality of the precipitation, changes in the strength of the inversion layer, or some combination of these changes. Isotope models have not yet been used to evaluate the relative influences of these different factors. The apparent disagreement in the temporal and spatial slopes clearly makes calibrating the isotope paleothermometer difficult. Nevertheless, the use of a (calibrated) isotope paleothermometer appears justified; empirical estimates and most (though not all) GCM results support the practice of interpreting ice core isotope records in terms of local temperature changes.

Jouzel, J.↗
NASA NTRS2004

Winds, Water Budgets and Stable Isotopes in Tropical Cyclones using TRMM and QUICKSCAT

Water vapor is the most abundant greenhouse gas in the atmosphere. Changes in its concentration and distribution are controlled by the hydrologic cycle. Because of its capacity to absorb and emit long wave radiation, release latent heat during condensation in storms and reflect short wave radiation when clouds form it has a major impact on Global climate change. The stable isotope ratios of water are H20 H2l6O and H0 H2l6O. These ratios change whenever water undergoes a phase change. They also change in both rain and water vapor whenever an air parcel is exposed to rain. In addition the relative changes in the two ratios differ as a &nction of the relative humidity. In short, the stable isotope ratios in water vapor in the atmosphere contain an integrated history of the processes affecting the concentration and distribution of water vapor in the atmosphere. Therefore the measurement and interpretation of changes in these stable isotope ratios are a powerful tool matched by no other method in tracing the transport history of water in the atmosphere. Our initial studies under this grant focused on the changes of the stable isotope ratios of precipitation and water vapor in tropical cyclones. The changes in time and space were found to be very large and to trace the transport of water in the storms reflecting changes in basic structural features. Because the stable isotope ratios of rains from tropical cyclones are so low flooding associated with land falling tropical cyclones introduces a negative isotopic spike into the coastal surface waters. In addition the stable isotope ratios of water vapor in the vicinity of tropical cyclones is anomalously low. This suggests that carbonate shelled organisms such as ostracoda living in coastal waters have the potential to record the isotopic spike and thereby provide a long term record of tropical storm activity in sediment cores containing fossil shells. Likewise, tree rings in coastal environments offer a similar potential. We have analyzed the oxygen isotopic composition of ostrcoda shells formed in the floodwaters of Tropical Storm Allison (2001) and discovered the negative isotopic 1 16 spike. Because we had learned that storm activity has a major impact on the stable isotope ratios of water vapor in the tropics and sub-tropics we decided to analyze the isotopic compositions of water vapor in different locations in the tropics. We did this in Puerto Escondido, Mexico in July 1998, near Kwajalein Island in the Pacific in 1999 as part of a TRMM summer field program and in 2001 in Key West, Florida as part of the CAMEX 4 summer field program. Our isotopic studies along with our earlier tropical cyclone studies showed that the low isotopic ratios in water vapor induced by exposure to rains the storms persisted for 48 hours often far away from the original storm site. We also noted that positive isotopic spikes were introduced into atmospheric water vapor if winds were high and extensive sea spray was present. These findings have a significant impact on the interpretation of the stable isotope studies of tropical ice cores found in the high mountain regions of the tropics. The assumption made in interpreting the ice core record is that the source water vapor evaporated from the sea surface is in near isotopic equilibrium with the seawater and undergoes a decrease during its transport that reflects the change in temperature from the sea surface to the site of the ice core. Because an additional isotopic depletion occurs at the sea surface source area that depends on the intensity, duration and size of the tropical rain system the isotopic variations found in the ice cores must take into account changes in past storm activity in the tropics. These systems must be an important source of water vapor to the ice cores because they charge the troposphere with water vapor to a far greater vertical height than evaporation in quiescent regions. Finally, an interest in increased heat transfer in thnterior of tropical cyclones resulting from greater amounts of sea spray is a topic of considerable interest to the research community. Increases in sea spray may be related to rapid changes in the intensity of hurricanes, a feature of hurricanes that currently is very poorly forecast. Project CBLAST of the Hurricane Research Division of NOAA is an active program that uses P3 research aircraft to evaluate this problem. An instrument has been designed and built at the University of Houston that will be placed on the P3 research aircraft during the 2004 hurricane season. It continuously measures the salt content of rain in hurricanes. Changes in the salt content of the rains should reflect the abundance of sea spray at the sea surface. In this way maps of sea spray intensity in hurricanes may be forthcoming. This should help computer modelers who simulate hurricanes to better understand the potential of changes in sea spray to change the intensity of hurricanes. The cost of designing, building and installing this instrument was borne largely by funding from this NASA grant. A list of presentations at national meetings and publications that were as the result of funding from this NASA grant are found in the report.

Lawrence, James R.↗
NASA NTRS2022

Investigating Stable Oxygen and Carbon Isotopic Variability in Speleothem Records Over the Last Millennium Using Multiple Isotope-Enabled Climate Models

The incorporation of water isotopologues into the hydrology of general circulation models (GCMs) facilitates the comparison between modeled and measured proxy data in paleoclimate archives. However, the variability and drivers of measured and modeled water isotopologues, as well as the diversity of their representation in different models, are not well constrained. Improving our understanding of this variability in past and present climates will help to better constrain future climate change projections and decrease their range of uncertainty. Speleothems are a precisely datable terrestrial paleoclimate archives and provide well-preserved (semi-)continuous multivariate isotope time series in the lower latitudes and mid-latitudes and are therefore well suited to assess climate and isotope variability on decadal and longer timescales. However, the relationships of speleothem oxygen and carbon isotopes to climate variables are influenced by site-specific parameters, and their comparison to GCMs is not always straightforward. Here we compare speleothem oxygen and carbon isotopic signatures from the Speleothem Isotopes Synthesis and Analysis database version 2 (SISALv2) to the output of five different water-isotope-enabled GCMs (ECHAM5-wiso, GISS-E2-R, iCESM, iHadCM3, and isoGSM) over the last millennium (850–1850 CE). We systematically evaluate differences and commonalities between the standardized model simulation outputs. The goal is to distinguish climatic drivers of variability for modeled isotopes and compare them to those of measured isotopes. We find strong regional differences in the oxygen isotope signatures between models that can partly be attributed to differences in modeled surface temperature. At low latitudes, precipitation amount is the dominant driver for stable water isotope variability; however, at cave locations the agreement between modeled temperature variability is higher than for precipitation variability. While modeled isotopic signatures at cave locations exhibited extreme events coinciding with changes in volcanic and solar forcing, such fingerprints are not apparent in the speleothem isotopes. This may be attributed to the lower temporal resolution of speleothem records compared to the events that are to be detected. Using spectral analysis, we can show that all models underestimate decadal and longer variability compared to speleothems (albeit to varying extents). We found that no model excels in all analyzed comparisons, although some perform better than the others in either mean or variability. Therefore, we advise a multi-model approach whenever comparing proxy data to modeled data. Considering karst and cave internal processes, e.g., through isotope-enabled karst models, may alter the variability in speleothem isotopes and play an important role in determining the most appropriate model. By exploring new ways of analyzing the relationship between the oxygen and carbon isotopes, their variability, and co-variability across timescales, we provide methods that may serve as a baseline for future studies with different models using, e.g., different isotopes, different climate archives, or different time periods.

isotope-enabled simulations↗
NASA NTRS1991

Simulations of the HDO and H2O-18 atmospheric cycles using the NASA GISS general circulation model - Sensitivity experiments for present-day conditions

Incorporating the full geochemical cycles of stable water isotopes (HDO and H2O-18) into an atmospheric general circulation model (GCM) allows an improved understanding of global delta-D and delta-O-18 distributions and might even allow an analysis of the GCM's hydrological cycle. A detailed sensitivity analysis using the NASA/Goddard Institute for Space Studies (GISS) model II GCM is presented that examines the nature of isotope modeling. The tests indicate that delta-D and delta-O-18 values in nonpolar regions are not strongly sensitive to details in the model precipitation parameterizations. This result, while implying that isotope modeling has limited potential use in the calibration of GCM convection schemes, also suggests that certain necessarily arbitrary aspects of these schemes are adequate for many isotope studies. Deuterium excess, a second-order variable, does show some sensitivity to precipitation parameterization and thus may be more useful for GCM calibration.

Jouzel, Jean↗
NASA NTRS1993

Continental water recycling and H2(18)-O concentrations

Using a General Circulation Model (GCM) fitted with tracer diagnostics, we examine how continental moisture recycling affects the stable water isotope content of precipitation, focusing on its contribution to the 'noise' in the well-established relationship between temperature and delta O-18. On a global basis, for temperatures between -30 and 15 C, continental recycling explains more than a third of the variability in annual delta O-18 that is not explained by temperature. Recycling appears almost as important as temperature in defining delta O-18 distributions during northern hemisphere summer.

Koster, Randal D.↗
NASA NTRS2010

Evaluating the Historical Importance of Impact Induced Hydrothermal Systems on Mars Using the Stable Isotopic Composition of Martian Water

The importance of impact events during the early history of Mars is obvious through a simple examination of the character of the martian surface. This ancient, heavily cratered terrain has been shown to be associated with extensive phyllosilicate deposits. This geologic link could suggest that the extensive phyllosilicate-forming alteration may have occurred during early martian history through impact-induced hydrothermal alteration. However, examination of the oxygen isotopic composition of water on Mars suggests that the extensive phyllosilicate deposits were formed primarily through low temperature (<30 C) interactions, and that high temperature weathering in impact-induced hydrothermal systems have not been a dominant process on Mars. The average oxygen isotopic composition of water on Earth is dictated by the nature of water-rock interactions. If these interactions occur at higher temperatures then the water will contain a higher proportion of 18O, while lower temperature interactions will result in water with a lower proportion of 18O. Water on Earth today contains a higher proportion of 18O because of plate tectonics and hydrothermal interaction at mid-ocean ridges. The oxygen isotopic composition of water on early earth, however, may have been quite different, containing a smaller proportion of 18O suggesting much less hydrothermal interaction. Because there are not yet any direct measurements of the oxygen isotopic composition of water on Mars, it needs to be inferred through examination of carbonates preserved in martian meteorites and the isotopic composition of atmospheric CO2. This can be done because the oxygen incorporated into carbonates and CO2 is easily exchanged with liquid water if it is present. Independently, both measurements provide an estimate for the (Sigma)18O of water on Mars to be near -16%. This composition is consistent with low temperature weathering of the silicate crust, and indicates that impact hydrothermal systems did not play an important role in the early alteration of the planet. However, our understanding of impact-induced hydrothermal systems remains unclear. If most of the water mobilized by an impact event remained at relatively low temperatures (<30deg), low-temperature interactions could predominate in these environments. These conditions would be consistent with the isotopic constraints suggested in this study.

Niles, Paul B.↗
NASA NTRS2003

Water Vapor and its Isotopic Composition in the Upper Troposphere and Stratosphere

Any theory of water vapor in the tropical tropopause layer (TTL) must explain both the abundance and isotopic composition of water there. We have previously presented a model of the TTL that simulated the abundance of water vapor as well as the details of the vertical profile. That model included the effects of 'overshooting convection', which injects dry air directly into the TTL. Here, we present results for the model after modifying it to include water's stable isotope HDO. The model is capable of accurately simulating the recently observed, nearly uniform HDO depletion (delta D) in the TTL. We find that lofted ice is necessary to accurately simulate the profile of delta D in the TTL, as has been suggested previously. We also find that vertical mixing due to overshooting convection plays an important role in maintaining the observed profile. Finally, any theory of lofted ice requires a complementary source of dry air in the TTL; without that, the TTL will rapidly saturate and the lofted ice will not evaporate.

Dessler, A. E.↗
NASA NTRS1994

Carbonates and sulfates in the Chassigny meteorite: Further evidence for aqueous chemistry on the SNC parent planet

Scanning electron microscopy and energy-dispersive X-ray spectrometry of untreated interior chips from three different specimens of the Chassigny meteorite confirm the presence of discrete grains of Ca-carbonate, Mg-carbonate, and Ca-sulfate. Morphologies of these salt grains suggest that the Ca-carbonate is calcite (CaCO3) and that the Ca-sulfate is gypsum (CaSO4-2H2O) or bassanite (CaSO4-1/2H2O). The morphologic identification of the Mg-carbonate is equivocal, but rhombohedral and acicular crystal habits suggest magnesite and hydromagnesite, respectively. The salts in Chassigny occur as discontinuous veins in primary igneous minerals and are similar to those previously documented in the nakhlites, Nakhla and Lafayette, and in shergottite EETA79001. Unlike those in nakhlites, however, the Chassigny salts occur alone, without associated ferric oxides or aluminosilicates clays. Traces of Cl and P in Chassigny salts are consistent with precipitation of the salts from short-lived, saline, aqueous solutions that postdated igneous crystallization. In contrast with the clear case for nakhlites, stratigraphic evidence for a preterrestrial origin of the salts in Chassigny is ambiguous; however, a preterrestrial origin of the Chassigny salts best explains all available evidence. The water-precipitated salts provide clear physical evidence for the hypothesis, proposed by other workers, that the igneous amphiboles in Chassigny might have experienced isotope-exchange reactions with near-surface water, thereby compromising the original stable-isotope signature of any magmatic water in melt inclusions.

Wentworth, Susan J.↗
NASA NTRS1991

Method for determining stable isotope ratios of dissolved organic carbon in interstitial and other natural marine waters

A procedure is described for the analysis of the stable carbon isotopic composition of dissolved organic carbon (DOC) in natural waters from marine and higher-salinity environments. Rapid (less than 5 min) and complete oxidation of DOC is achieved using a modification of previous photochemical oxidation techniques. The CO2 evolved from DOC oxidation can be collected in less than 10 min for isotopic analysis. The procedure is at present suitable for oxidation and collection of 1-5 micromoles of carbon and has an associated blank of 0.1-0.2 micromole of carbon. Complete photochemical oxidation of DOC standards was demonstrated by quantitative recovery of CO2 as measured manometrically. Isotopic analyses of standards by photochemical and high-temperature sealed-tube combustion methods agreed to within 0.3%. Photochemical oxidation of DOC in a representative sediment pore-water sample was also quantitative, as shown by the excellent agreement between the photochemical and sealed-tube methods. The delta 13C values obtained for pore-water DOC using the two methods of oxidation were identical, suggesting that the modified photochemical method is adequate for the isotopically non-fractionated oxidation of pore-water DOC. The procedure was evaluated through an analysis of DOC in pond and pore waters from a hypersaline microbial mat environment. Concentrations of DOC in the water column over the mat displayed a diel pattern, but the isotopic composition of this DOC remained relatively constant (average delta 13C = -12.4%). Pore-water DOC exhibited a distinct concentration maximum in the mat surface layer, and delta 13C of pore-water DOC was nearly 8% lighter at 1.5-2.0-cm depth than in the mat surface layer (0-0.5-cm depth). These results demonstrate the effectiveness of the method in elucidating differences in DOC concentration and delta 13C over biogeochemically relevant spatial and temporal scales. Carbon isotopic analysis of DOC in natural waters, especially pore waters, should be a useful probe of biogeochemical processes in recent environments.

NASA Discipline Exobiology↗
NASA NTRS2016

Impact of Source Region on the delta18 O signal in snow: A case study from Mount Wrangell Alaska

The stable isotopic composition of water in ice cores is an important source of information on past climate variability. At its simplest level, the underlying assumption is that there is an empirical relationship between the normalized difference in the concentration for these stable isotopes and a specified local temperature at the ice core site. There are, however, nonlocal processes, such as a change in source region or a change in the atmospheric pathway, which can impact the stable isotope signal, thereby complicating its use as a proxy for temperature. In this paper, the importance of these nonlocal processes are investigated through the analysis of the synoptic-scale circulation during a snowfall event at the summit of Mount Wrangell (62 deg N, 144 deg W; 4300 m MSL) in south-central Alaska. During this event there was, over a 1-day period in which the local temperature was approximately constant, a change in delta18 O that exceeded half that normally seen to occur in the region between summer and winter. As shall be shown, this arose from a change in the source region, from the subtropical eastern Pacific to northeastern Asia, for the snow that fell on Mount Wrangell during the event.

Snow↗
NASA NTRS1999

On-line technique for measuring stable oxygen and hydrogen isotopes from microliter quantities of water

Detailed here is a method for extracting and analyzing oxygen and hydrogen isotopes from 10 microL-sized water samples. Based on the traditional CO2-H2O equilibration technique, the oxygen isotope exchange reaction is done exclusively in sealed 6-mm (o.d.) Pyrex tubes at 25 degrees C, with full isotope exchange completed in at least 28 h. Using the same water sample employed in the 18O equilibration, D/H extractions are done in separate sealed 6-mm (o.d.) Pyrex tubes by reaction with Zn at 450 degrees C to form H2(g). Provided that a correction factor is applied to 18O analyses, accuracy and precision for both 18O and D/H are comparable to standard techniques using much larger samples.

NASA Center JSC↗
NASA NTRS2013

Mars Atmospheric Escape Recorded by H, C and O Isotope Ratios in Carbon Dioxide and Water Measured by the Sam Tunable Laser Spectrometer on the Curiosity Rover

Stable isotope ratios in C, H, N, O and S are powerful indicators of a wide variety of planetary geophysical processes that can identify origin, transport, temperature history, radiation exposure, atmospheric escape, environmental habitability and biological activity [2]. For Mars, measurements to date have indicated enrichment in all the heavier isotopes consistent with atmospheric escape processes, but with uncertainty too high to tie the results with the more precise isotopic ratios achieved from SNC meteoritic analyses. We will present results to date of H, C and O isotope ratios in CO2 and H2O made to high precision (few per mil) using the Tunable Laser Spectrometer (TLS) that is part of the Sample Analysis at Mars (SAM) instrument suite on MSL s Curiosity Rover.

Webster, C. R.↗
NASA NTRS2014

Martian Cryogenic Carbonate Formation: Stable Isotope Variations Observed in Laboratory Studies

The history of water on Mars is tied to the formation of carbonates through atmospheric CO2 and its control of the climate history of the planet. Carbonate mineral formation under modern martian atmospheric conditions could be a critical factor in controlling the martian climate in a means similar to the rock weathering cycle on Earth. The combination of evidence for liquid water on the martian surface and cold surface conditions suggest fluid freezing could be very common on the surface of Mars. Cryogenic calcite forms easily from freezing solutions when carbon dioxide degasses quickly from Ca-bicarbonate-rich water, a process that has been observed in some terrestrial settings such as arctic permafrost cave deposits, lake beds of the Dry Valleys of Antarctica, and in aufeis (river icings) from rivers of N.E. Alaska. A series of laboratory experiments were conducted that simulated cryogenic carbonate formation on Mars in order to understand their isotopic systematics. The results indicate that carbonates grown under martian conditions show variable enrichments from starting bicarbonate fluids in both carbon and oxygen isotopes beyond equilibrium values.

Socki, Richard A.↗
NASA NTRS2013

Carbonate Mineral Formation on Mars: Clues from Stable Isotope Variation Seen in Cryogenic Laboratory Studies of Carbonate Salts

The geologic history of water on the planet Mars is intimately connected to the formation of carbonate minerals through atmospheric CO2 and its control of the climate history of Mars. Carbonate mineral formation under modern martian atmospheric conditions could be a critical factor in controlling the martian climate in a means similar to the rock weathering cycle on Earth. The combination of evidence for liquid water on the martian surface and cold surface conditions suggest fluid freezing could be very common on the surface of Mars. Cryogenic calcite forms readily when a rise in pH occurs as a result of carbon dioxide degassing quickly from freezing Ca-bicarbonate-rich water solutions. This is a process that has been observed in some terrestrial settings such as arctic permafrost cave deposits, lakebeds of the Dry Valleys of Antarctica, and in aufeis (river icings) from rivers of N.E. Alaska. We report here the results of a series of laboratory experiments that were conducted to simulate potential cryogenic carbonate formation on the planet Mars. These results indicate that carbonates grown under martian conditions (controlled atmospheric pressure and temperature) show enrichments from starting bicarbonate fluids in both carbon and oxygen isotopes beyond equilibrium values with average delta13C(DIC-CARB) values of ~20.5%0 which exceed the expected equilibrium fractionation factor of [10(sup 3) ln alpha = ~13%0] at 0 degC. Oxygen isotopes showed a smaller enrichment with delta18O(H2O-CARB) values of ~35.5%0, slightly exceeding the equilibrium fractionation factor of [10(sup 3) ln alpha = ~34%0 ] at 0degC. Large kinetic carbon isotope effects during carbonate precipitation could substantially affect the carbon isotope evolution of CO2 on Mars allowing for more efficient removal of 13C from the Noachian atmosphere enriched by atmospheric loss. This mechanism would be consistent with the observations of large carbon isotope variations in martian materials despite the relative paucity of carbonate minerals in the martian crust.

Socki, Richard↗
NASA NTRS1993

Martian carbon dioxide: Clues from isotopes in SNC meteorites

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

Karlsson, H. R.↗