BATHYMETRY, VOLUME, AND DYNAMICS OF GLACIAL LAKE AGASSIZ: 11,000 TO 7700 14C YR BP

Lake Agassiz was the largest of the proglacial lakes that formed in central North America during retreat of the Laurentide Ice Sheet. In this research, computer-based bathymetric models of Lake Agassiz were generated for 13 different lake stages that together span the 4000-year history of the lake (~11,700 to 7700 ¹⁴C yr BP). Each model was generated by subtracting a stage-specific database of interpolated isobase values from a geographically corresponding database of modern topography. The models were used to further define the size and geographic extent of the lake through time, and to calculate the volumes of several catastrophic outbursts of water from the lake that were caused by the opening of new (lower) lake outlets as the southern margin of the Laurentide Ice Sheet retreated.

The area and volume of Lake Agassiz varied considerably over its history. Its early stages generally had areas and volumes of up to about 170,000 km² and 13,000 km³, respectively (about the volume of modern Lake Superior). The largest of the middle stages of the lake had areas and volumes of about 250,000 km² and 23,000 km³ (about the total volume of the modern Great Lakes). The latest stages of Lake Agassiz were much larger than all preceeding stages, as a result if the lake's merger with glacial Lake Ojibway. Just prior to the final catastrophic release of its waters into the Tyrrell Sea (Hudson Bay), the area and volume of the combined Lake Agassiz-Ojibway had grown to 841,000 km² and 163,000 km³. At this time, the lake's volume was about seven times the total volume of the modern Great Lakes.

Among the largest catastrophic outbursts of fresh water from Lake Agassiz into the North Atlantic Ocean were those at 10,900 ¹⁴C yr BP (9500 km³), 10,100 ¹⁴C yr BP, (9300 km³), and 7700 ¹⁴C yr BP (163,000 km³). These outbursts coincide with the start of the Younger Dryas, Preboreal Oscillation, and 8.2 ka cal yr event, suggesting that outbursts from Lake Agassiz may have repeatedly influenced hemispheric climate by affecting ocean circulation and North Atlantic Deep Water production.