Numerical reconstructions of the Patagonian Ice Sheet: Growth and demise through the Late Quaternary

Glacial geomorphological and geochronological studies suggest that the Patagonian Ice Sheet (PIS) stretched from 38°S to 55°S during the Marine Isotope Stages (MIS) 2-3. While its western margin reached the Pacific Ocean, the easternmost sectors of the PIS were characterized by terrestrial lobes that fed large paleo glacial lakes after its maximum extension towards the end of the MIS 3. An ice-marginal stabilization occurred throughout the global Last Glacial Maximum followed by a rapid deglaciation after 18,000 yr before present.

Here we present an ensemble of transient numerical simulations of the PIS that have been carried out to provide information on its thickness and extents through the MIS 3 and MIS 2. Our aim here is to determine the range of climate conditions that matches the field-derived ice sheet geometries and the timing of local deglaciation, while bracketing the spread in possible ice volumes and sea level contributions originating from uncertainties in the internal parameters and external forcings. The model ensemble makes use of the new higher-order version of the ice sheet model SICOPOLIS forced by combination of present-day atmospheric conditions from the ERA5 reanalysis and outputs from the Paleoclimate Modeling Intercomparison Project (PMIP) and new Community Earth System Model (CESM) experiments. Our results indicate that the regional climate conditions required to reproduce a realistic growth and demise of the PIS through the Late Quaternary are not captured by coarse-resolution global climate models, implying the necessity of high spatial-resolution regional modeling. Our results also suggest that in order to realistically simulate the evolution of the PIS in agreement with geological archives, the MIS3 should have witnessed colder regional temperatures in and around Patagonia than those shown by global climate models for the MIS 2.