Geomorphology and 10Be chronology of the Last Glacial Maximum and deglaciation in northeastern Patagonia, 43°S-71°W

In southern South America, well-dated glacial geomorphological records constrain the last glacial cycle across much of the former Patagonian Ice Sheet, but its northeastern sector remains comparatively understudied and unconstrained. This knowledge gap inhibits our understanding of the timing of maximum glacier extent, the duration of the glacial maximum, the onset of deglaciation, and whether asynchronies exist in the behaviour of the former ice sheet with latitude, or with location (east or west) relative to the ice divide. Robust glacial reconstructions from this region are thus required to comprehend the mechanisms driving Quaternary glaciations at the southern mid-latitudes. We here present Be-10 surface exposure ages from five moraine sets along with Bayesian age modelling to reconstruct a detailed chronology of Last Glacial Maximum expansions of the Rio Corcovado glacier, a major former ice conduit of northern Patagonia. We find that the outlet glacier reached maximum expansion of the last glacial cycle during the global Last Glacial Maximum at similar to 26.5-26 ka, and that at least four subsequent advances/stillstands occurred over a 2e3 ka period, at similar to 22.5e22 ka, similar to 22-21.5 ka, similar to 21-20.5 ka and 20-19.5 ka. The onset of local ice sheet deglaciation likely occurred between 20 and 19 ka. Contrary to several other Patagonian outlet glaciers, including from similar latitudes on the western side of the Andes, we find no evidence for MIS 3/4 advances. Exposure dating of palaeo-shoreline cobbles reconstructing the timing of proglacial lake formation and drainage shifts in the studied region indicate three glaciolacustrine phases characterised by Atlantic-directed drainage. Phase one occurred from 26.4 +/- 1.4 ka, phase two between similar to 21 and similar to 19 ka and phase three between similar to 19 ka and similar to 16.3 ka. Exposure dating of icemoulded bedrock in the interior of the cordillera indicates local disintegration of the Patagonian Ice Sheet and the Atlantic-Pacific drainage reversal had occurred by similar to 16.3 ka. We find that local Last Glacial Maximum glacier expansions were coeval with Antarctic and southern mid-latitude atmospheric and oceanic cooling signals, but out of phase with local summer insolation intensity. Our results indicate that local Patagonian Ice Sheet deglaciation occurred 1-2 ka earlier than northwestern, central eastern and southeastern Patagonian outlet glaciers, which could indicate high regional Patagonian Ice Sheet sensitivity to warming and drying during the Varas interstade (similar to 22.5-19.5 ka). (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study reveals a detailed chronology of the Last Glacial Maximum expansions of the Rio Corcovado glacier in northern Patagonia, showing that the glacier's expansion was coeval with global Last Glacial Maximum and climatic signals, but out of phase with local summer insolation intensity. Additionally, it is observed that local ice sheet deglaciation occurred 1-2 ka earlier than other regions.