Modelling the asynchronous maximum extent of the last Patagonian Ice Sheet

Understanding the controls, timing and extent of the former Patagonian Ice Sheet (PIS) is a long-standing challenge. The geochronology developed over the last 3 decades shows asynchrony in the timings of the ice maxima during the last glacial cycle. In general terms, northern and southern Patagonia reached their maximum ice extent at different moments during MIS 3, whereas central Patagonia during early MIS 2, almost contemporaneous with the Last Glacial Maximum. It has long been proposed that this asynchrony is related to either a latitudinal shift or northwards expansion of the moisture-bearing Southern Westerly Winds belt (SWWs), but modelling efforts aiming to test these scenarios have been limited so far. Here we use a numerical ice sheet model to assess the influence of a range of possible SWWs patterns in controlling the evolution and maximum extent of the PIS. We find that to reproduce full glacial conditions consistent with mapped extents along Patagonia the SWWs expanded to northern latitudes and that this northern precipitation pattern evolved through the last glacial cycle. Our modelling suggests that ice surface mass-balance feedbacks exaggerate the asynchrony in the timing of maximum extent by making the central region harder to retreat but easier to grow in comparison to the North and South. As a consequence, we explain the asynchrony through a combination of SWWs evolution and differences in the topography along the PIS, that enable differential preservation of evidence of the pre-MIS 2 glacial advances in the North and South and exclusively MIS 2 in Central Patagonia.