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Experimental constraints on the fractionation of ^(13)C/^(12)C and ^(18)O/^(16)O ratios due to adsorption of CO_2 on mineral substrates at conditions relevant to the surface of Mars

Rahn, T. and Eiler, J. M. (2001) Experimental constraints on the fractionation of ^(13)C/^(12)C and ^(18)O/^(16)O ratios due to adsorption of CO_2 on mineral substrates at conditions relevant to the surface of Mars. Geochimica et Cosmochimica Acta, 65 (5). pp. 839-846. ISSN 0016-7037. https://resolver.caltech.edu/CaltechAUTHORS:20121023-134520771

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Abstract

We report here measurements of fractionations of stable carbon and oxygen isotopes between CO_2 vapor and CO^2 adsorbed on kaolinite, basalt, or fluorite. Carbon-isotope fractionations between adsorbate and vapor (Δ^(13)C_(a-v) = 1000 · 1n (α_(a-v)), where α = ^(13)C/^(12)C_(adsorbate))/(^(13)C/^(12)C_(vapor)); ∼δ^(13)C_(adsorbate)-δ^(13)C_(vapor)) exhibit a ∼1‰ enrichment of ^(13)C in the vapor phase for all substrates and temperatures over the range 190 to 230 K. These fractionations are ‘reversed’ relative to the common expectation that heavy isotopomers should be concentrated into condensed phases relative to coexisting vapor (Lindemann, 1919). Oxygen-isotope fractionations between adsorbate and vapor are complex: Comparison of experiments using vacuum-baked substrates to those in which substrates were not vacuum-baked suggests that exchange between one or both phases of CO_2 and water adsorbed on the sample surfaces influences the ^(18)O/^(16)O fractionation between vapor and adsorbate and changes the ^(18)O/^(16)O composition of the total CO_2 in the experiment. In experiments on vacuum-baked substrates, oxygen results exhibited ‘normal’ fractionation of ∼1.8‰ (that is, ^(18)O preferentially partitioned into the adsorbed CO_2). No evidence was found for measurable exchange of oxygen isotopes between structural oxygen in mineral substrates and CO_2 adsorbed on those substrates. The observation that ^(13)C is enriched in the vapor phase may help account for subtle (per mil to tens of per mil) enrichments of ^(13)C estimated for the Martian atmosphere as compared to bulk terrestrial carbon.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/S0016-7037(00)00592-5DOIUNSPECIFIED
http://www.sciencedirect.com/science/article/pii/S0016703700005925PublisherUNSPECIFIED
Additional Information:© 2001 Elsevier Science Ltd. Received August 11, 2000; accepted in revised form October 20, 2000. We wish to thank Bruce Jakosky and two anonymous reviewers for their thoughtful comments and Nami Kitchen for invaluable assistance in the laboratory. Associate editor: S. M. McLennan.
Issue or Number:5
Record Number:CaltechAUTHORS:20121023-134520771
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20121023-134520771
Official Citation:T Rahn, J.M Eiler, Experimental constraints on the fractionation of 13C/12C and 18O/16O ratios due to adsorption of CO2 on mineral substrates at conditions relevant to the surface of Mars, Geochimica et Cosmochimica Acta, Volume 65, Issue 5, 1 March 2001, Pages 839-846, ISSN 0016-7037, 10.1016/S0016-7037(00)00592-5. (http://www.sciencedirect.com/science/article/pii/S0016703700005925)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35039
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:23 Oct 2012 21:08
Last Modified:03 Oct 2019 04:24

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