Atmos. Chem. Phys. Discuss., 11, 17423-17445, 2011
© Author(s) 2011. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Theory of isotope fractionation on facetted ice crystals
J. Nelson
Laucks Foundation Inc. Suite 2100, PMB 174, 1700 Seventh Ave., Seattle WA 98101, USA

Abstract. Present models of the differential incorporation of isotopic water molecules into vapor-grown ice omit surface processes that may be important in temperature reconstructions. This article introduces a model that includes such surface processes and shows that differences in deposition coefficients for water isotopes can produce isotope fractionation coefficients that significantly differ from those of existing theory. For example, if the deposition coefficient of H218O differs by just 5 % from that of ordinary water (H216O), the resulting fractionation coefficient at 20 % supersaturation may deviate from the kinetic fractionation (KF) prediction by up to about ±17 ‰. Like the KF model, this "surface-kinetic" fractionation model generally predicts greater deviation from the equilibrium prediction at higher supersaturations; indeed, the sensitivity to supersaturation far exceeds that to temperature. Moreover, the model introduces possible new temperature dependencies from the deposition coefficients. These parameters need to be constrained by new laboratory measurements; nevertheless, the theory suggests that observed δ18O changes in ice samples are unlikely to be due solely to temperature changes.

Citation: Nelson, J.: Theory of isotope fractionation on facetted ice crystals, Atmos. Chem. Phys. Discuss., 11, 17423-17445, doi:10.5194/acpd-11-17423-2011, 2011.
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