A kinetic isotope effect during ice formation by water freezing

A kinetic isotope effect is known to occur during ice formation from water vapour in a cloud; it is due to the difference in molecular diffusivities i n air of HDO and (H2O)-O-18 molecules. A similar effect is likely during wa ter freezing since diffusion coefficients of HDO and (H2O)-O-18 are also di fferent in liquid water. Their values are however less different from each other than those in air. Therefore, such a kinetic isotope effect during wa ter freezing is less frequently observed in Nature. This paper describes a situation in Antarctica where this effect is conspicuous in icings (aufeis) . In this type of ice indeed there is no relationship between delta D (or d elta(18)O) and deuterium excess whereas a clear inverse relationship betwee n these parameters exists in ice formed by water freezing when equilibrium isotopic fractionation applies. This kinetic effect is potentiality present in hail within clouds, in infiltration ice (formed during sea ice growth) and in some kinds of ground ice.