Late Quaternary glacial maxima in Southern Patagonia: insights from the Lago Argentino glacier lobe

Abstract

Abstract. Determining the timing and extent of Quaternary glaciations around the globe is critical to understanding the drivers behind climate change and glacier fluctuations. Despite synchronous ice-volume and extent change across hemispheres, evidence from the southern mid-latitudes indicates that local glacial maxima occurred earlier in the glacial cycle, preceding the global Last Glacial Maximum (LGM), implying that feedbacks in the climate system or ice dynamics played a role beyond the underlying orbital parameters. To shed light on these processes, we investigated the glacial landforms shaped by the Lago Argentino glacier (50° S), an outlet lobe of the former Patagonian Ice Sheet in southern Argentina, during the last two glacial cycles. We mapped geomorphological features on the landscape and dated moraine boulders and outwash sediments using 10Be cosmogenic nuclides and feldspar infrared stimulated luminescence (IRSL) to constrain the chronology of glacial advance and retreat. We, therefore, provide the first published age constraints on the middle-to-late Pleistocene glaciations at Lago Argentino, and report that this outlet lobe expanded during Marine Isotope Stage 6, at 153.0 ± 14.7 ka, and during Marine Isotope Stage 3, culminating at 44.5 ± 8.0 ka and at 36.6 ± 1.0 ka. Our results indicate that the most recent was its most extensive advance during the last glacial period, and hypothesize that this was a result of longer and colder winters, as well as increased precipitation delivered by a northward migration of the Southern Westerly Winds belt, highlighting the role of local and regional climate feedbacks in driving ice mass changes in the southern mid-latitudes.