Glacial lake drainage in Patagonia (13-8 kyr) and response of the adjacent Pacific Ocean

Abstract

Large freshwater lakes formed in North America and Europe during deglaciation following the Last Glacial Maximum. Rapid drainage of these lakes into the Oceans resulted in abrupt perturbations in climate, including the Younger Dryas and 8.2 kyr cooling events. In the mid-latitudes of the Southern Hemisphere major glacial lakes also formed and drained during deglaciation but little is known about the magnitude, organization and timing of these drainage events and their effect on regional climate. We use 16 new single-grain optically stimulated luminescence (OSL) dates to define three stages of rapid glacial lake drainage in the Lago General Carrera/Lago Buenos Aires and Lago Cohrane/Pueyrredón basins of Patagonia and provide the first assessment of the effects of lake drainage on the Pacific Ocean. Lake drainage occurred between 13 and 8 kyr ago and was initially gradual eastward into the Atlantic, then subsequently reorganized westward into the Pacific as new drainage routes opened up during Patagonian Ice Sheet deglaciation. Coupled ocean-atmosphere model experiments using HadCM3 with an imposed freshwater surface “hosing” to simulate glacial lake drainage suggest that a negative salinity anomaly was advected south around Cape Horn, resulting in brief but significant impacts on coastal ocean vertical mixing and regional climate.

The glacial geomorphology of the Lago Buenos Aires and Lago Pueyrredón ice lobes of central Patagonia

“…The most prominent lake shorelines occur east of LGC-BA and LC-P ( Figure 13) and rise to ∼300 m higher than contemporary lake levels. Previous shoreline mapping has enabled several reconstructions of proglacial lake evolution (Bourgois et al, 2016;Glasser et al, 2016;Turner et al, 2005). In comparison, we mapped a greater number of shoreline features, including very faint, closely spaced shoreline fragments located between the major wave-cut scarps.…”

“…These ice lobes advanced to the Argentine steppe (Caldenius, 1932), blocked regional river systems and caused a ∼200 km westward shift in the drainage divide towards the Patagonian cordillera, which diverted meltwater eastward to the Atlantic Ocean (Bell, 2008;Glasser et al, 2016;Turner, Fogwill, McCulloch, & Sugden, 2005). During deglaciation, large proglacial lakes developed in the basins between terminal moraines and the ice front (Bell, 2008;Turner et al, 2005).…”

“…Turner et al (2005), Bell (2008) and, more recently, Glasser et al (2016), mapped palaeoshorelines and raised lacustrine deltas formed at proglacial lake margins during glacier recession that contribute to a regional model of deglacial palaeolake development and drainage.…”

“…In contrast, Glasser et al (2012) proposed a regional stabilization of NPI outlet glaciers, including at this location, around the time of the European Younger Dryas, based on a suite of cosmogenic nuclide exposure ages of ∼11.0 to 12.8 ka, and supporting luminescence ages from local ice-contact deposits . These alternative chronologies have hampered attempts to develop a coherent regional model of ice lobe and palaeolake evolution that reconcile all dating evidence (Bourgois, Cisternas, Braucher, Bourlès, & Frutos, 2016;Glasser et al, 2016). New high-resolution mapping will enable refinements in the morphostratigraphic order of deglacial events and will contribute to resolving disparate retreat chronologies.…”

“…Flat-topped, sediment accumulations in the mouths of tributary valleys, and perched above modern lakes, represent raised lacustrine deltas (Figure 13; Bell, 2008Bell, , 2009Glasser et al, 2016;Hein et al, 2010;Turner et al, 2005). At LGC-BA, raised deltas are often flanked by beaches (Figure 13(D)).…”