AN INCREASE IN SUMMER TEMPERATURES AT THE START OF THE YOUNGER DRYAS: EVIDENCE FROM THE ALLEGHENY PLATEAU AND LOWLANDS OF THE LAKE IROQUOIS - MOHAWK RIVER VALLEY IN EAST-CENTRAL NEW YORK, USA

The Mohawk River Valley in east-central New York is recognized as the drainage route of meltwater from the Laurentide Ice Sheet via both glacial Lakes Algonquin and Iroquois from 14.5 until around 13.0 kyr cal BP. The drainage route was southeast out of Lake Iroquois and received both meltwater and winds off of the lake system. During that time, the Allegheny Plateau was close to the shores of the glacial Laurentian Great Lakes, southwest of the St. Lawrence Valley and south of the southernmost margin of the LIS. The region received the brunt of any heat exchange between surface winds and the lakes, meltwater, and the LIS, combined with cold winds south of glacial anticyclonic circulation. All features likely prohibited any interaction with warmer climatic conditions to the south.

The end of Mohawk Valley meltwater drainage is estimated to be at the opening of the St. Lawrence Valley, ca 13.0 kyr cal BP. Here we show that just before 12.9 kyr cal BP, the onset of the Younger Dryas chronozone elsewhere, the glacial impact along the newly-exposed lowlands and Mohawk Valley was removed for at least the summer months. Tree-rings in logs found along the Lake Ontario and Mohawk Valley lowlands indicate significantly better growing conditions than up on the plateau before 13.1 kyr cal BP. Despite the better summer conditions, however, boreal climatic conditions continued during the rest of the year, likely from sustained freeze-over of the glacial lakes, until ca. 11.5 kyr cal BP.