Ice-liquid isotope fractionation factors for O-18 and H-2 deduced from the isotopic correction constants for the triple point of water

The stable isotopes of water are extensively used as tracers in many fields of research. For this use, it is essential to know the isotope fractionation factors connected to various processes, the most important of which being phase changes. Many experimental studies have been performed on phase change fractionation over the last decades. Whereas liquid-vapour fractionation measurements are relatively straightforward, vapour-solid and liquid-solid fractionation measurements are more complicated, as maintaining equilibrium conditions when a solid is involved is difficult. In this work, we determine the ice-liquid isotope fractionation factors in an indirect way, by applying the Van't Hoff equation. This equation describes the relationship of the fractionation factors with isotope-dependent temperature changes. We apply it to the recently experimentally determined isotope dependences of the triple point temperature of water [Faghihi V, Peruzzi A, Aerts-Bijma AT, et al. Accurate experimental determination of the isotope effects on the triple point temperature of water. I. Dependence on the H-2 abundance. Metrologia. 2015;52:819-826; Faghihi V, Kozicki M, Aerts-Bijma AT, et al. Accurate experimental determination of the isotope effects on the triple point temperature of water. II. Combined dependence on the O-18 and O-17 abundances. Metrologia. 2015;52:827-834]. This results in new values for the H-2 (deuterium) and O-18 fractionation factors for the liquid-solid phase change of water, which agree well with existing, direct experimental data [Lehmann M, Siegenthaler U. Equilibrium oxygen- and hydrogen-isotope fractionation between ice and water. J Glaciol. 1991;37:23-26]. For H-2, the uncertainty is improved by a factor of 3, whereas for O-18 the uncertainty is similar. Our final results are (S-L) (H-2/H-1)=1.02093(13), and (S-L) (O-18/O-16)=1.002909(25), where the latter is the weighted average of the previous experimental study and this work.