1 Evaporation from the ocean surface into the free atmosphere is a non-equilibrium process. After equilibrium evaporation into a microskin layer above the sea surface the turbulent/diffusive transport into the atmosphere is affected by kinetic diffusion. The latter depends strongly on the saturation of the atmospheric planetary boundary layer, that is, principally on temperature and relative humidity. This is the reason for using deuterium excess records from polar ice to reconstruct past source conditions (Merlivat & Jouzel, 1979; Jouzel et al., 1982).
2 Further non-equilibrium processes take place during evaporation of rain drops falling through an undersaturated atmosphere (Stewart, 1975) and during the formation of ice crystals at very low temperatures (Jouzel & Merlivat, 1984).
In addition to these actual kinetic processes the relationship of the equilibrium fractionation coefficients of H218O and HD16O is temperature dependent, which is why site temperature has an additional influence on the deuterium excess.
Here we report on the major progress that has been made in recent years both in understanding the kinetic processes at the sea surface during evaporation and in interpreting deuterium excess records from Antarctica in terms of climatic variability during the past 400 kyr.
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