OUTBURSTS FROM GLACIAL LAKE AGASSIZ DURING THE LAST DEGLACIATION AND THEIR POSSIBLE IMPACT ON THERMOHALINE CIRCULATION

During the last deglaciation, the Laurentide Ice Sheet (LIS) retreated downslope in Canada, impounding water along its margin. The area and volume of these proglacial lakes varied substantially through time as a result of the changing location of the ice margin, topography of the newly deglaciated surface, elevation of the overflow outlet from the lake, and differential isostatic rebound. Glacial Lake Agassiz was the largest of these lakes from 11.7 to 7.7 ¹⁴C ka BP and, although it varied dramatically in size and volume, throughout most of its life it covered >150,000 km² and contained >10,000 km³ of water. On many occasions Lake Agassiz abruptly released large volumes of water through newly opened outlets, drawing down the level of the lake. We reconstructed the bathymetry of the lake for ten lake stages by subtracting interpolated isobase data from a database of modern elevations; these bathymetric models were then used to quantify changes in lake volume through time, and to estimate the volumes of catastrophic releases of water from the lake. Releases from Lake Agassiz ranged from 1600 to 9500 km³ (0.05-0.31 Sv, if released in one year). After Lake Agassiz merged with glacial Lake Ojibway in the southern Hudson Bay Lowland about 8 ¹⁴C ka BP, the size of this ice-marginal lake expanded to 841,000 km². When the Lake Agassiz-Ojibway superlake was finally drained into the Hudson Bay basin and out to the North Atlantic Ocean about 7.7 ¹⁴C ka BP, the two-stage burst released 123,000 km³ (3.9 Sv) and then 49,900 km³ (1.6 Sv). Several catastrophic bursts, plus associated baseline diversions which averaged about 0.034-0.05 Sv, may have influenced North Atlantic Deep Water formation and linked climate during deglaciation, notably at (1) 11 ¹⁴C ka BP (at the start of the Younger Dryas) when 9500 km³ were added to a baseline flow of 7432 km³/year and at (2) 7.7 ¹⁴C ka BP.