A late-glacial lake-effect climate regime and abundant tamarack in the Great Lakes Region, North America.

A unique regional climate progression, ca 14.2-11.5 cal ka BP, in the eastern Great Lakes region of North America is suggested by subfossil logs, high-resolution 14C dates, and established proxy records in New York, USA. The progression began with a northern boreal-type climate ca. 14.2-13.1 ka coeval with the expansion of Lake Iroquois, a transition to a southern boreal-type climate 13.1-12.9 ka that coincided with the transition of Lake Iroquois into progressively lower lake levels, and a continuation of the southern boreal-type climate 12.9-11.5 ka. These conditions and changes are evident in the tree rings and relative dominance of tamarack (Larix laricina) and spruce species (Picea spp.) plus the presence of black ash (Fraxinus nigra) as the only thermophilous species. Together they suggest variations in atmospheric moisture levels, surface winds, temperature extremes, and/or an enhanced seasonality over time. Here we propose that the evolution of the glacial Great Lakes and their interactions with ice sheets, meltwater, winds, and regional topography created a regional glacial lake-effect climate, 14.2-11.5 cal ka BP, that was opposite to the established warming Bølling-Allerød-cold Younger Dryas climate progression. [ABSTRACT FROM AUTHOR]