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

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.

A late-glacial high-resolution site and source temperature record derived from the EPICA Dome C isotope records (East Antarctica)

“…The model is run assuming a constant relationship between condensation and surface temperature [49]. The order of magnitude of the N 18 O sw correction has the same amplitude as the glacialî nterglacial deuterium excess signal (an LGM correction of +2.7x to compare with a glacial deuterium excess decrease of 4x) but only a weak impact on the deuterium (an LGM correction of 35x compared to a glacial deuterium decrease of 45x).…”

Airborne in situ vertical profiling of HDO / H<sub>2</sub><sup>16</sup>O in the subtropical troposphere during the MUSICA remote sensing validation campaign

“…Evaporation and condensation leave a fingerprint in the isotopologue ratios due to differences in vapor pressure and kinetic diffusion properties of the isotopologues (Dansgaard, 1964;Merlivat, 1978;Jouzel and Merlivat, 1984). This fingerprint is mainly depending on temperature (vapor pressure), but it also contains information of relative humidity (kinetic effect) during evaporation.…”

Characterizing moisture exchange between the Hawaiian convective boundary layer and free troposphere using stable isotopes in water

“…[19] To account for the presence of cloud within an adiabatic plume, the Rayleigh model may be modified so that conversion of condensate to precipitation is less than 100% [Dansgaard, 1964;Jouzel and Merlivat, 1984;Noone, 2012]. By defining a precipitation efficiency parameter ε, which varies from 0 if all condensate is held with the ascending vapor to 1 if all condensate is converted to precipitation, the isotope ratio of the vapor (R) can be written for discrete vertical points in the profile as…”