LABRADOR SEA SEDIMENTS INDICATE ASYNCHRONOUS DISCHARGE FROM THE HUDSON STRAIT AND CUMBERLAND SOUND ICE STREAMS, NE LAURENTIDE ICE SHEET

Despite nearly two decades of research since the significance of Heinrich layers was recognized, questions concerning the cause of iceberg discharges to the North Atlantic remain unanswered. One of the more persistent questions is whether external climate effects rather than internal glaciological forces initiated the export of icebergs, meltwater and sediment from Hudson Strait during the Late Pleistocene. This study attempts to shed light on the cause of Hudson Strait-sourced Heinrich events by comparing their timing with that of rapid ice/sediment discharge events from the Cumberland Sound ice stream, a few hundred km north of Hudson Strait.

Detrital carbonate-rich (DC) layers corresponding to Hudson Strait-sourced Heinrich events 0 – 5 are identified based on lithostratigraphic parameters, stable isotopic analyses and radiocarbon dates on planktonic foraminifera in a 12-m core from the upper continental slope off southeastern Baffin Island. In addition to Hudson Strait-sourced DC layers, the core contains numerous dark gray, DC-poor diamict layers enriched in total organic carbon (TOC). These dark gray diamicts are traced to a former ice stream source in Cumberland Sound based on provenance data from bulk Sr-Nd-Pb isotopic compositions and U-Pb ages of detrital zircons. These provenance indicators also identify and differentiate Hudson Strait-derived sediment. Stratigraphic relationships between the TOC-rich diamicts and DC-layers show that increases in ice discharge and sediment flux from Cumberland Sound occurred at different times and more frequently than those from Hudson Strait. Glacial reconstructions illustrate that the flow through Cumberland Sound drained a smaller, more northerly portion of the NE Laurentide Ice Sheet, so its glaciological response is expected to differ from that of the Hudson Strait ice stream. These observations support the idea that glaciological factors within the Laurentide Ice Sheet strongly influenced the dynamics of these two ice streams, and further imply that marine effects on the margins such as sea-level change or ice shelf collapse did not solely control the timing of Heinrich events from the NE Laurentide ice sheet.