A Data-Model Comparison of Ice Sheet Demise in Northern Patagonia During the Last Deglaciation

During the Last Glacial Maximum (26,000-19,000 years B.P.; Clark et al. 2009), the Patagonian Ice Sheet (PIS) formed a contiguous ice cap over the southern Andes from 38° to 55° S, with a sea level equivalent to 1.5 m (Davies et al., 2020). Despite recent progress in reconstructing the PIS configuration during the last glacial cycle (Davies et al., 2020), constraints on the timing of PIS retreat and thinning during the last deglaciation remain limited. In order to understand how the PIS responds to centennial and millennial scale changes in climate, we provide geologic constraints to reconstruct the timing of its past area and volume changes and apply numerical ice sheet models to test the sensitivity of the PIS to past climate change. To do this, we apply cosmogenic nuclide dating of exposed bedrock surfaces across the Southern Volcanic Zone in northern Patagonia to document the rates of ice sheet thinning during the last deglaciation. Our data are from elevations of 200-2000 m and span a ~400 km latitudinal transect. Transient model simulations of the PIS with the Ice Sheet and Sea-level System Model (ISMM) were performed to test the sensitivity of the northern PIS to changing climatological inputs driven by the Trace-21ka experiment (He, 2011). Our cosmogenic nuclide ages document the onset of rapid ice sheet thinning that initiated at ~18,000 years B.P. with accelerated and widespread deglaciation occurring after 15,000 years, which is in good agreement with our model simulations (Cuzzone et al. 2024). Together, our data and model simulations show that ice sheet thinning and retreat occurred earlier in the northern sector of the PIS than in the south (Cuzzone et al., 2024), which we attribute to a reduction in wintertime precipitation driven by a poleward migration of the westerly winds. Our work highlights the important, but often overlooked, role of precipitation in modulating both the timing of and magnitude of surface mass balance changes of mid-latitude ice sheets at the millennial-scale following the last glacial period.