LAUSR

Better assessing the dynamic of stratosphere-troposphere exchange is a key point to improve our understanding of the climate dynamic in the East Antarctica Plateau, a region where stratospheric inputs are expected to be important. Although tritium (3H or T), a nuclide naturally produced mainly in the stratosphere and rapidly entering the water cycle as HTO, seems a first-rate tracer to study these processes, tritium data are very sparse in this region. We present the first high resolution measurements of tritium concentration over the last 50 years in three snow pits drilled at the Vostok station. Natural variability of the tritium records reveals two prominent frequencies, one at about 10 years (to be related to the solar Schwabe cycles) and the other one at a shorter periodicity : despite dating uncertainty at this short-scale, a good correlation is observed between 3H and Na+ and an anti-correlation between 3H and δ18O measured on an individual pit. The outputs from the LMDZ Atmospheric General Circulation Model including stable water isotopes and tritium show the same 3H- δ18O anti correlation and allow further investigation on the associated mechanism. At the interannual scale, the modelled 3H variability matches well with the SAM (Southern Annular Mode) index. At the seasonal scale, we show that modelled stratospheric tritium inputs in the troposphere are favored in winter cold and dry conditions.