Extensive mountain glaciation in central Patagonia during Marine Isotope Stage 5

The timing and magnitude of glacial advances throughout a glacial cycle can give insight on the underlying drivers of climate change. Our knowledge of glacial activity early in a glacial cycle, however, is limited by incomplete preservation of the geomorphological record. Here, we present a -dated glacial chronology from early in the last glacial cycle from the Belgrano valley, east of Monte San Lorenzo in central Patagonia. Our chronology reveals the most extensive glacial advance of the last glacial cycle occurred at 75 ka, at the end of Marine Isotope Stage 5. A second, less-extensive advance occurred at 25 ka during the global Last Glacial Maximum. The topographic setting is such that ice growth would have initiated on and around the San Lorenzo massif at the start of the glacial cycle. We suggest reduced southern hemisphere summer insolation at the time played a significant role in driving this early advance. The comparatively smaller glacier extent during the global Last Glacial Maximum is likely a consequence of the build-up of the full Patagonian Ice Sheet, which would have caused ice-divide migration, ice-flow re-routing, and increased aridity on its lee side.