Mathematics – Logic
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p52b..01e&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P52B-01
Mathematics
Logic
0330 Geochemical Cycles, 0343 Planetary Atmospheres (5405, 5407, 5409, 5704, 5705, 5707), 1040 Isotopic Composition/Chemistry, 6225 Mars
Scientific paper
The stable isotope geochemistry of light elements (H, C, N, O and S) is a tool in the search for evidence of life on bodies other than the earth for several reasons: the elements in question are used by all known or easily imagined life forms; several mass spectrometric and spectroscopic methods for measuring their isotopic compositions exist and are appropriate for in situ analysis on other planets; it is known that 'vital effects' generate large (percent) isotopic fractionations; and studies of extant and former life on earth provide models for interpreting such data. However, the evidence stable isotope geochemistry provides is generally interpretable as a signature for life only in the context of a rich understanding of isotopic variations produced by non biological processes in the same environments. Several candidates in the search for extra-terrestrial life (Mars and the Jovian satellites) are bodies having volatile-element geochemical cycles that operate at lower temperatures than the earth's surface and involve phase-changes that do not occur on the earth (e.g., condensation/sublimation of CO2). We review new experimental data (both recently published and unpublished) describing isotopic fractionations accompanying phase changes of CO2, H2O below 240 K, NH3 and CO, compile them with previous data to derive general principles of low-temperature stable isotope fractionations, and discuss their significance for the stable isotope geochemistry of the surface of Mars. One example of the issues constrained by these data (the Martian CO2 cycle) is discussed here. The Martian surface is strongly influenced by condensation/sublimation and adsorption/desorption of CO2. The isotopic consequences of these processes are an attractive goal for in situ observations of atmosphere, ice and/or adsorbed gas because they provide a record of Martian atmospheric dynamics and atmosphere-surface interactions over a range of time-scales. Furthermore, these isotopic signals naturally must be understood before one could confidently identify carbon or oxygen isotope evidence for life. Recent experiments indicate that both ice/vapor and adsorbate/vapor phase changes produce oxygen isotope fractionations of the same direction and magnitude as those for condensation/evaporation of water vapor in the earth's atmosphere. This suggests that seasonal and longer-term cycles of condensation and release of CO2 produce variations of-order 10 % in d18O. The current seasonal cycle of ice-cap formation and sublimation likely produces a similar-magnitude latitudinal gradient in the d18O of CO2. This gradient must be sensitive to mixing between high- and low-latitude air and therefore provides a constraint on martian atmospheric circulation. In contrast, carbon isotopes of CO2 are not measurably fractionated by condensation/sublimation of ice and should be invariant in a martian atmosphere in which this is the only major phase change. Adsorption significantly (ca. 1 to 2 %) concentrates 13CO2 into the vapor phase and 12CO2 into adsorbate. This is opposite in direction to all familiar vapor-pressure isotope effects. Thus, cycles of adsorption/desorption of CO2 have a unique isotopic signature that should be distinguishable for other processes influencing the Martian atmosphere. Measurements of the variation in d13C of CO2 would constrain the extent to which the atmosphere and surface interact by adsorption/desorption processes.
No associations
LandOfFree
Vapor Pressure Isotope Effects and the Stable Isotope Geochemistry of the Martian Surface does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Vapor Pressure Isotope Effects and the Stable Isotope Geochemistry of the Martian Surface, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Vapor Pressure Isotope Effects and the Stable Isotope Geochemistry of the Martian Surface will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1892191