Deglaciation dynamics of the Rio Cisnes palaeo-outlet glacier (~45°S), former Patagonian Ice Sheet

The former Patagonian Ice Sheet (PIS) expanded and contracted multiple times during the Quaternary, preserving a well-defined geomorphological and sedimentological record of ice extent and dynamics. Influenced by both regional (e.g. Southern Westerly Winds) and interhemispheric climate forcing mechanisms, reconstructions of PIS extent and dynamics through time may yield unique insights into Southern Hemisphere (palaeo-)climate and (palaeo-)glacier dynamics.

An increasing number of palaeoglaciological reconstructions in Patagonia have highlighted spatial asynchrony in the timing of local glacial maxima and deglaciation. This offset in the timing of ice advance/retreat implies that dynamic controls, such as topography or calving mechanisms, played a part in regulating the structure and pace of deglaciation. Assessing the role of these mechanisms is complicated by a general lack of glacial landsystems work in Patagonia, particularly north of the Northern Patagonian Icefield (46 – 47.5 °S).

Here we aim to understand the timing, structure, and style of deglaciation in the Rio Cisnes valley, an eastern outlet glacier of the former Patagonian Ice Sheet. We combine glacial geomorphological mapping, field sedimentology, Uncrewed Aerial Vehicle (UAV) photogrammetry, and a new chronology based on cosmogenic nuclide surface-exposure age dating. These data informed a refined deglacial ice and palaeolake reconstruction. The new ¹⁰Be exposure ages constrain the timing of palaeolake level drop to ~16 ka, which indicates that icefield outlet glaciers were retreating back from their zone of confluence in the Cisnes valley into their respective valleys by this time, leaving the main Cisnes valley ice free.