Climate and ice sheet dynamics in Patagonia during the Last Glacial Maximum
Abstract. During the Last Glacial Maximum (LGM, ~ 23,000 to 19,000 years ago), the Patagonian Ice Sheet (PIS) covered the central chain of the Andes between ~ 38° S to 55° S. Existing paleoclimatic evidence – mostly derived from glacial landforms – suggests that maximum ice sheet expansions in the Southern and Northern Hemispheres were not synchronized. However, large uncertainties still exist in the timing of the onset of regional deglaciation as well as its major drivers. Here we present an ensemble of numerical simulations of the PIS during the LGM. Our aim is to assess the ability of paleoclimate model products to reproduce the range of atmospheric conditions needed to enable the ice sheet growth in concordance with geomorphological and geochronological evidence. The resulting ensemble is then used as a guideline for the evaluation of the PMIP3 and PMIP4 model performance across different sectors of the former PIS. Our analysis suggests a strong dependence of the PIS geometry on near-surface air temperature forcing. All the ensemble members driven by PMIP products are not able to reproduce the reconstructed ice cover in the northern part of Patagonia. In contrast, the modelled PIS tends to expand beyond its constrained boundaries in south-eastern Patagonia. We largely attribute these discrepancies between the model-based ice geometries and geological evidence to the low resolution of paleoclimate models. We conclude that among all tested climate forcings, the PMIP4 climate models INM-CM4-8 and MPI-ESM1-2-LR produce the necessary conditions for ice sheet growth across Patagonia. It should be kept in mind that this analysis is based only on the evaluation of the modelled ice sheet extent because geological constraints on the former ice thickness are still lacking. Nevertheless, our analysis suggests that a realistic PIS geometry at the LGM can be reproduced only if the complex topographic features of the Andes are properly resolved by climate models.
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