Absolute dating of deep ice cores with argon and krypton isotopes.

In the search for very old ice, finding the age of the ice is a key parameter necessary for its interpretation. Most ice core dating methods are based on chronological markers that require the ice to be in stratigraphic order. However, the oldest ice is likely to be found at the bottom of ice sheets, where the stratigraphy is disturbed, or in ablation areas, where the classical methods cannot be used. Absolute dating techniques have recently been developed to provide new constraints on the age of old ice. In particular, ⁸¹Kr measurements provide strong dating constraints for the old ice cores. Still, these measurements are limited in deep ice cores because of the large sample size required (5-6 kg). In addition to ⁸¹Kr dating, we discuss here the analytical performances of a new technique for ⁴⁰Ar dating, which allows us to provide a reliable age with 80g of ice rather than 800g, as previously published. Finally, we present two applications for the ⁸¹Kr and ⁴⁰Ar dating on the bottom of the TALDICE and Dome C ice cores.