OPTIMIZING THE ANTARCTIC ICE CORES TIME SCALES WITH A MODELING APPROACH

Ice cores from central Antarctica provide invaluable records of the Quaternary climate because 1) they contain direct samples of the past atmosphere and provide estimates of temperature change above Antarctica, 2) these records are long (several climatic cycles) and 3) their resolution is accurate (10-100 years). One of the challenges is to obtain an accurate and unique time scale for these Antarctic ice cores. The chronology for these ice cores is generally obtain thanks to the use of a glaciological model, representing the accumulation above the ice sheet during time and the thinning of the ice layers during their burying. However, such a model cannot be used solely, because of bad known parameters, such as sliding and melting at the base of the ice sheet, or such as the ice isotopes of snow - surface temperature relationship. These parameters have thus to be constrain using independent chronological and physical information, such as comparison with a dated paleoclimatic record or such as the measure of temperature in the deep borehole. To constrain this glaciological model with these independent informations, we propose to use an inverse method based on the Metropolis-Hastings algorithm. This method allows not only to obtain a optimal chronology, but also to evaluate its confidence interval. We applied this inverse method to the Vostok, Dome Fuji and Dome C ice cores. We analyzed the difference between the resulting optimal chronologies and the problem we face to improve the accurary. In a last step, we will propose a synthetic Antarctic temperature record, using the isotopic records and the chronologies of the three ice cores.