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OSUG - Terre Univers Environnement

An ice flow multi-model approach to locate a 1.5 million yr-old ice archive

Soutenance de thèse d’Olivier Passalacqua, 13 octobre 2017

by Brice Boudevillain - 14 September 2017

Abstract

Antarctic ice is an exceptional archive of the ancient atmospheric composition. The oldest available ice archive (800 ka) is not old enough to study a main climatic transition that occurred between 1.2 Ma and 0.9 Ma (mid-Pleistocene transition). Locating a future old-ice drill site is now one of the main goal of the ice-core community. In the region of Dome C (East Antarctica), several old-ice targets have required characteristics, from a thermal and mechanical point of view, to hosts very old ice. The goal of this work is to precisely locate suitable coring sites, using several glaciological models. First a 1D heat model to constrain the local geothermal flux, that make us confident that bedrock heights have been free of basal melting for at least the last 800 ka. It is very likely that such sites are able to host a 1.5 Ma ice archive. Second, a 3D ice flow model, to describe the ice trajectories from the ice surface to the bed. Drilling less than 10 km from the surface ridge mimimizes the risks of stratigraphic disturbance, and drilling on the flanks of the bed relief - and not on its top - is mandatory to ensure a sufficient age resolution. Third, a 1D dating model constrained by isochrones let us describe the distribution of basal ages and age resolutions compatible with observed isochrones, and assess the risk of success or failure of the drilling. With currently available data and modelling tools, a few drilling sites are proposed that are located 37 km from Dome C, at which 1.5 Ma-old ice is very likely to be archived in required conditions and with sufficient resolution.