Marine Palynological Records From the Eastern Canadian Margin Suggest Multiple Meltwater Sources at the Time of the Younger Dryas

The sources and paths of meltwater drainage into the North Atlantic Ocean at the time of the Younger Dryas (YD) are still debated. The eastern route implied drainage from glacial Lake Agassiz and predecessor lakes along the southeastern edge of the Laurentide Ice Sheet to the North Atlantic Ocean, via the St. Lawrence River. A northern drainage route, along which meltwater reached the North Atlantic via the Arctic Ocean, is presently favoured, but alternate sources of freshwater (icebergs etc.) are also possible. We present evidence for meltwater drainage via the St. Lawrence valley from 8 sediment cores from Cabot Strait, Laurentian Channel, and from the Scotian, Northeast Newfoundland and Labrador Shelves at the time of the YD. Distinct dinoflagellate cyst assemblages are identified during the YD interval and we propose new biostratigraphic markers for the event. Dinoflagellage cysts are also used to reconstruct sea surface conditions. Reconstructions from cores along the eastern route contain strong evidence of lowered salinity within the YD interval, thereby re-establishing the St. Lawrence drainage system as a significant route for inflow of YD meltwater to the North Atlantic. This prompted us to re-examine original data and paleoceanographic interpretation of surface water conditions based on new analysis of dinoflagellate cyst zonation combined with an updated chronology supported by new radiocarbon dates and refined calibrations. Evidence for lowered salinity is also recorded in cores from the NE Newfoundland and Labrador Shelves. Geographical differences in the duration of cold, low salinity conditions associated with the YD event, west and east of Laurentian Channel, suggests another source of freshwater, possibly via the Labrador Current.