Deuterium and oxygen 18 in precipitation: Modeling of the isotopic effects during snow formation

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Abstract
The classical Rayleigh model assuming isotopic equilibrium fails to explain the deuterium and oxygen 18 contents of polar snow. This model leads to too high temperature‐isotope gradients (both for δD and δ18O), to too low δD ‐ δ18O slopes, and consequently to an excessively large range of deuterium excess values (d = δD ‐ 8δ18O). We present a new model that takes into account the existence of an isotopic kinetic effect at snow formation as a result of the fact that vapor deposition occurs in an environment supersaturated over ice. This kinetic effect is thoroughly discussed from a microphysical point of view and tested against experimental data and field observations. This new formulation reconciles predicted and observed values both for the temperature‐isotope and δD ‐ δD18O relationships for reasonable values of supersaturation over ice.