摘要：The use of water isotopes in polar regions is essential for reconstructing past climate over glacial-interglacial cycles. In addition to δD or δ 18 O, linearly related to condensation temperature, the second-order parameters, d-excess and 17 O-excess, provide important information on the climatic conditions of the source of precipitations. In order to best interpret the glacial-interglacial records of d-excess and 17 O-excess in polar ice cores, it is important to document their present variability, especially in remote and cold regions of East Antarctica. Indeed, the current climatic conditions encountered in these regions provide a good analogy with glacial climatic conditions in a large part of Antarctica. Here we present the first seasonal variations of 17 O-excess and d-excess at Vostok station on an event basis (i.e. samples were collected immediately after each precipitation event) over 1 year. These records show strong correlation between 17 O-excess and δ 18 O over the course of the year, with an amplitude 40 per meg (10 -3 %) in the 17 O-excess seasonal cycle, and strong anticorrelation between d-excess and δ 18 O, with d-excess variations up to 20%. The d-excess and 17 O-excess variations can be explained by the influence of kinetic fractionation at very low temperatures. The comparison with simple isotopic models confirms this explanation, but cannot explain the link between 17 O-excess, d-excess and temperature without (1) a particular relationship between condensation and surface temperature and/or (2) seasonal changes in the climatic conditions of the source regions.
