Laucks Foundation Inc. Suite 2100, PMB 174, 1700 Seventh Ave., Seattle, WA 98101, USA
Received: 08 May 2011 – Discussion started: 21 Jun 2011
Abstract. The currently used "kinetic-fractionation" (KF) model of the differential incorporation of water-molecule isotopologues into vapor-grown ice omits surface processes on crystal facets that may be important in temperature reconstructions. This article introduces the "surface-kinetic" fractionation model, a model that includes such surface processes, and shows that differences in deposition coefficients for water isotopologues can produce isotopic fractionation coefficients that significantly differ from those of KF 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 KF value by up to about ±17‰, and even more at greater supersaturation. As a result, the surface-kinetic theory may significantly change how fractionation depends on supersaturation. Moreover, the model introduces possible new temperature dependencies from the deposition coefficients. These parameters need to be constrained by new laboratory measurements.
Revised: 15 Oct 2011 – Accepted: 30 Oct 2011 – Published: 16 Nov 2011
Nelson, J.: Theory of isotopic fractionation on facetted ice crystals, Atmos. Chem. Phys., 11, 11351-11360, doi:10.5194/acp-11-11351-2011, 2011.