A UNIQUE GLACIAL LAKE-EFFECT ENVIRONMENT IN THE GREAT LAKES BASIN

During the Late Glacial (LG) ice recession, 14.2-11.5ka cal BP, changing glacial lake outlets and differential isostatic rebound changed water sources, meltwater distribution, lake configuration and landscape in the Great Lakes basin. Changes in subfossil logs and other proxy data found downwind of the lakes suggest that the coupling of prevailing winds with the lakes created a unique glacial lake-effect environment, thus climate, within and downwind of the lakes.

Today, the Great Lakes affect air temperatures for ~50km and atmospheric moisture up to ~350km downwind of the lakes. During the LG and at least within that area, changes in prevailing winds altered the characteristics and spatial extent of the lake-effect climate. Over time, a site was successively exposed to easterly winds driven by the glacial anticyclone, turbulence at the wind interface, prevailing westerlies, and drier northwesterlies as the ice sheet receded. The greater seasonality of the LG interval was amplified by heat and moisture exchange between the winds and frozen vs. open glacial lakes.

A reconstruction of LG climate for the Great Lakes region differs from the accepted progression of the warm Bølling-Allerød to cold Younger Dryas climate. Rather, climate changes correlate with those in the lakes and surface winds as the ice receded. Ca 14.2- 13.1ka cal BP, sustained cold with increasing moisture coincided with the expansion of glacial Lake Iroquois and drainage of meltwater into New York State. A warming summer trend with decreasing moisture correlated with the demise of Lake Iroquois and end of meltwater flow in New York ca 13.1-12.9ka. The better summers continued and moisture increased with the expansion of glacial Lake Algonquin ca 12.9-12.5ka. A similar climate with higher variations and decreasing moisture coincided with extensive changes when drainage from Lake Algonquin was re-routed to the north ca 12.5ka-11.9ka. Drier conditions subsequently prevailed, 11.9-11.5ka. Changes in surface winds across the lakes coincided with changes in lake and landscape configuration and the position of the ice sheet.

A glacial lake-effect environment offers new insight into modifications of the ecosystems and landscape features downwind of the Great Lakes basin. This study suggests that the Great Lakes may influence climate change in the future.