Freshwater outbursts to the oceans from glacial Lake Agassiz and their role in climate change during the last deglaciation

Abstract

Lake Agassiz was the largest lake in North America during the last deglaciation. As the Laurentide Ice Sheet (LIS) retreated, large volumes of water stored in this proglacial lake were episodically released into the oceans. These waters were variably routed to the Gulf of Mexico, Arctic Ocean, North Atlantic Ocean, and Hudson Bay. During this period, the three largest cooling events in the Northern Hemisphere closely followed 4 of the 5 largest outbursts from Lake Agassiz: (1) the Younger Dryas, which was preceded by a release of 9500 km 3, (2) the Preboreal Oscillation, preceded by releases of 9300 km 3 and 5900 km 3, and (3) the “8.2 ka cold event”, preceded by a 163,000 km 3 outburst; these are, respectively, fluxes of 0.30 Sv, 0.29 Sv, 0.19 Sv, and 5.2 Sv if released in 1 year. Because the influx of freshwater reaching the North Atlantic Ocean can inhibit thermohaline circulation, partly depending on whether the ocean was in a glacial, interglacial, or transitional mode of circulation, we believe that at least these large outbursts from Lake Agassiz may have provided the triggers for changes in ocean circulation and, in turn, for widespread climate change.