REMARKS ON THE DEUTERIUM EXCESS IN PRECIPITATION IN COLD REGIONS

Jouzel and Merlivat developed and used an expression for the kinetic fractionation coefficient alpha-k, and greatly improved the predictions of delta(O-18) and d, (the deuterium excess) for East Antarctica. The alpha-k coefficient is re-derived in terms of ambient cloud temperatures and is used to re-calculate their single-source East Antarctic simulations. While the "improved" alpha-k produces virtually no change in the delta's, there is a small change in predicted d's. However, no matter which alpha-k is used, the simulated d's are very sensitive to the supersaturation history of the precipitating air mass. The single-source model is run for a wide range of supersaturation histories. Averaging the resulting suite of delta(O-18) and d solutions gives reasonable and stable d predictions. The temperature T(s) at which clouds switch from being supercooled water drops to ice crystals depends in part on the microparticle loading of the air. The value of T(s) significantly influences the d's and even delta's predicted. Thus ice-core microparticles, d and delta might be "process related".