EVIDENCE FOR YOUNGER DRYAS-AGE FRESHWATER ROUTING THROUGH THE ST. LAWRENCE ESTUARY

Glacial lake drainage is a hypothesized cause of deglacial abrupt climate change, but uncertainty surrounds the timing and duration of lake discharge events. Sediment cores recovered from the Lake Champlain Valley in New York State contain glacial lacustrine varved clays and marine silts and clays deposited during the transition from glacial Lake Vermont to the Champlain Sea. This transition is radiocarbon dated on wood at 11,050 ± 90 B.P. (12,845 – 13,192 calibrated B.P.) and thus appears to be near the beginning of the Younger Dryas. Microfaunal analyses and oscillations in δ¹⁸O values for the freshwater ostracode Candona and the marine foraminifer Cassidulina reniforme indicate complex hydrological changes occurring over less than 150 varve years during the lacustrine-marine transition. Our observed patterns are regionally robust and cannot be ascribed to mixing or transport of microfaunas. We will discuss possible explanations in terms of rapidly changing hydrography, source water, paleosalinity, and glacial lake drainage.