MODELLING CONSTRAINTS ON THE CONTINENTAL GLACIATION OVER ANTARCTICA AT THE EOCENE-OLIGOCENE TRANSITION AND ON THE POSSIBLE EXISTENCE OF HIGH-LATITUDES ICE SHEETS DURING THE MIDDLE-LATE CRETACEOUS AND EARLY CENOZOIC

Waxing and waning of relatively small ephemeral ice sheets is thought to have occurred periodically during the warm world of the Middle-Late Cretaceous and Early Cenozoic. These alternating episodes culminated in the Eocene-Oligocene transition (34 – 33.5 Ma) during which a sudden and massive glaciation occurred over Antarctica. Since a decade, modeling studies have put forward the primary role of CO₂ in the initiation of this glaciation (e.g., DeConto and Pollard 2003), which is constituted of two ≈ 50 kyrs glacial events separated by a ≈ 200 kyrs plateau. In this study, we investigate the impacts of CO₂ and orbital parameters on the evolution of the ice sheet during the 500 kyrs of the E-O transition using a new tri-dimensional interpolation method. This latter accounts for atmospheric CO₂ concentrations, precise orbital variations and ice sheet feedbacks and is implemented within a set of asynchronously coupled GCMs – ISM. Our results show for the first time a precise reconstruction of the two-stepped ice sheet evolution, the timing and amplitude of which are well correlated with the δ¹⁸O steps and sea-level fall events seen in the data (e.g., Coxall et al. 2005, Houben et al. 2012). We conclude that orbital parameters are key to initiate the first step of the glaciation but that atmospheric CO₂ remains the major driver that enables the continental coverage of Antarctica with ice.

However, the presence of ice sheets over the Earth remains unclear for most of the Cretaceous and early Cenozoic. There still exists a vivid debate concerning the possible existence of short-lived ice sheets at the poles during a period, which is acknowledged to be one of the warmest in Earth’s history (e.g., Bornemann et al. 2008, MacLeod et al. 2013). We will also present some of our latest results concerning potential ice sheet glaciation thresholds for different paleogeographies of the Middle-Late Cretaceous (115 Ma, 95 Ma and 70 Ma) and the Early Cenozoic (55 Ma, 42 Ma).