Evidence for meltwater drainage via the St. Lawrence River Valley in marine cores from the Laurentian Channel at the time of the Younger Dryas.

Debate is ongoing about the source(s) and paths of meltwater that drained into the North Atlantic Ocean at the time of the Younger Dryas (YD), especially the eastern route from glacial Lake Agassiz and predecessor lakes of the Laurentian Great Lakes located along the southeastern edge of the Laurentide Ice Sheet. Here, evidence is presented for meltwater drainage via the St. Lawrence eastern route from five new sediment cores from Cabot Strait, Laurentian Channel and Scotian Shelf at the time of the YD. Palynological analyses are used to reconstruct sea surface conditions based on dinoflagellate cyst records, and pollen data are used for additional correlation. The reconstructions show distinct drops in salinity and temperature and increased sea ice cover duration within the YD period. In addition to these new records, we present a re-examination of original data and paleoceanographic interpretation of surface waters based on a new analysis of dinoflagellate cyst zonation in combination with an updated chronology supported by new radiocarbon dates and refined calibrations. The results clearly define the YD core intervals which contain strong evidence of lowered salinity, thereby re-establishing the St. Lawrence drainage system as a significant route for inflow of YD meltwater to the North Atlantic. This inflow does not exclude the possibility for another source of freshwater, as suggested by geographical differences in the duration of cold, low salinity conditions west and east of Laurentian Channel associated with the YD climatic event. [ABSTRACT FROM AUTHOR]