Extent and Dynamics of the Western Patagonian Ice Sheet Between 16 and 42 kyr cal BP

During the Last Glacial Maximum, the Patagonian Ice Sheet (PIS) was the second-largest ice mass in the Southern Hemisphere after Antarctica, extending across the southern Andes from ~38°S to 55°S. Today, only 5% of this ice mass remains. Here, we present a continuous reconstruction of the extent and dynamics of the western PIS between 16 and 42 kyr cal BP, derived from marine sediment core MD07-3119. The core was analysed using a multiproxy inorganic approach, including grain size, ice-rafted debris (IRD), inorganic geochemistry, and bulk mineralogy, to reconstruct sediment provenance and transport processes. These results are compared with moraine-based chronologies from the eastern PIS. Variations in bulk mineralogy, IRD content, and inorganic geochemistry indicate that the western PIS, which was land-terminating until 37 kyr cal BP, experienced five distinct Ice Expansion Intervals between 16 and 37 kyr cal BP. Data indicate that each Ice Expansion Interval is associated with enhanced sediment input from the coastal metamorphic unit. Our record indicates periods of high sediment discharge of predominantly Patagonian batholith origin corresponding to melting phases between these advances. The longest advance, at 37–31 kyr cal BP, lasted nearly 6 kyr. Variations in provenance proxies imply that PIS outlet glaciers retreated at least 65 km inland between successive advances. Our reconstruction indicates a complex temporal relationship between the western and eastern PIS margins. Overall, most ice retreat intervals in MD07-3119 match terrestrial exposure ages from the eastern side of the PIS, but the eastern PIS often appears to start shrinking earlier than its western side.