A cosmogenic nuclide-derived chronology of pre-Last Glacial Cycle glaciations during MIS 8 and MIS 6 in northern Patagonia

The precise environmental mechanisms controlling Quaternary glacial cycles remain ambiguous. To address this problem, it is critical to better comprehend the drivers of spatio-temporal variability in ice-sheet evolution by establishing reliable chronologies of former outlet-glacier advances. When spanning multiple glacial cycles, such chronologies have the capacity to resolve conundrums on interhemispheric phasing of glaciations and climate events. In southern Argentina, reconstructions of this kind are achievable, as Quaternary expansions of the Patagonian Ice Sheet have emplaced a wellpreserved geomorphological record covering several glacial cycles. Moreover, robust ice-sheet reconstructions from Patagonia are powerful barometers of former climate change, as Patagonian glaciers are influenced by the Southern Westerly Winds and its coupled Antarctic Circumpolar Current. Former shifts in these circulation mechanisms are essential to better constrain, as they may have played a critical role in pacing regional and possibly global Quaternary climate change. Here, we present a new set of cosmogenic 10 Be and 26 Al exposure ages from pre-Last Glacial Cycle moraine boulder, glaciofluvial outwash cobble and bedrock samples. This dataset constitutes the first direct chronology dating pre-LGM glacier advances in northern Patagonia, and completes our effort to date the entire preserved moraine record of the Río Corcovado valley system (43°S, 71°W). We find the outermost margins of the study site depict at least three distinct pre-Last Glacial Cycle glaciations occurring at 284 ± 7 ka, 257 ± 7 ka, and 147 ± 4 ka. Combined with the local LGM chronology, we discover that a minimum of four distinct Pleistocene glaciations occurred during Marine Isotope Stages eight, six, and two in northern Patagonia. Evidence for stage four and three deposits were not found at the study site, which illustrates former longitudinal and latitudinal asynchronies in Patagonian Ice Sheet mass balance during these stages. We find the most extensive middle-to-lat