THE ORIGIN OF PRESENT-DAY ANTARCTIC PRECIPITATION FROM SURFACE SNOW DEUTERIUM EXCESS DATA

The deuterium excess (d) is defined as a linear combination of the D/H and O-18/O-16 ratios in natural waters. We present an interpretation of deuterium excess data in surface Antarctic snow, using an isotopic model to derive information on the origin of present-day Antarctic precipitation. The data come from near the coast (D47, Adelie Land) and from inland (south pole, 1000 km from the sea). The one-dimensional isotopic model belongs to the Rayleigh family but fully accounts for mixed cloud processes between 0 degrees C and -30 degrees C. Modeling d in polar snowfalls meets the problem of a large sensitivity tp the saturation conditions prevailing at snow formation. Therefore we decided to tune the saturation in the model in order to yield realistic mean d values, but we use the seasonal phase of d versus delta, which is less sensitive to the saturation conditions, as an independent validation of the model predictions. Both inland and near the coast, our model can simulate the observed phase between d and delta in snow with moisture of subtropical origin (40 degrees-20 degrees S). Although we do not treat specifically storm precipitation near the coast, this study indicates that the observed phase between d and delta brings up a new validation of isotopic models. It supports a distant vapor source for large-scale precipitation delivered to the Antarctic continent.