Glacial lake evolution and Atlantic-Pacific drainage reversals during deglaciation of the Patagonian Ice Sheet

Abstract

Modelling experiments of drainage events from proglacial lakes of the Río Baker catchment (central Patagonia, 46–48 ⁰S) indicate that Atlantic-Pacific drainage reversals may have caused freshwater forcing of regional climate. However, much of the region remains unmapped in detail and available geochronological data is equivocal, leading to multiple published palaeolake evolution models. We evaluate these models through new geomorphological mapping from the Baker valley; cosmogenic dating of moraine boulders that demonstrates an Antarctic Cold Reversal ice readvance that blocked drainage through the Río Baker; an altitudinal-based review of published geochronology; and regional analysis of shoreline glacio-isostasy and palaeolake levels. We use these datasets to present a new regional palaeolake evolution model underpinned by Bayesian age modelling. We demonstrate that 103 km3 of freshwater was released to the Pacific over at least 6 drainage events from before 15.3–15.0 cal yr BP to the early Holocene. The final stages of lake drainage involved catastrophic flooding along the Baker valley, evidenced by high magnitude flood landforms such as boulder bars, likely caused by failure of large valley floor moraine dams. We place these drainage events in the context of Late Quaternary meltwater pathways associated with advance/retreat of the Patagonian Ice Sheet and early human occupation across the region. Although broad patterns of ice retreat and lake formation may be similar across Patagonia, driven by Southern Hemisphere palaeoclimate, regional topographic settings likely resulted in spatial and temporal heterogeneity of Atlantic-Pacific drainage reorganisation across southernmost South America.