Middle Wisconsinan marine shells near Repulse Bay, Nunavut, Canada: implications for Marine Isotope Stage 3 ice-free conditions and Laurentide Ice Sheet dynamics in north-west Hudson Bay

摘要

Evidence suggesting a reduction of the Laurentide Ice Sheet (LIS) during Marine Isotope Stage 3 (MIS 3) is widespread but the boundaries of the ice sheet and the timing of minimum ice extent are still poorly constrained. Radiocarbon dating of glacially transported marine mollusks in Rae Isthmus ice stream till south of Repulse Bay, Nunavut, Canada, provides new evidence for MIS 3 deglaciation in the north-west part of Hudson Bay. Middle Wisconsinan finite C-14 ages varying between 31.7 and 39.2k C-14 a BP (similar to 35.0 and 43.7k cal a) indicate a marine event(s) for a minimum of similar to 8.7k cal years. Our findings suggest ice-free conditions in the ice stream source area in proto-Roes Welcome Sound, and therefore significant glacial recession of the LIS margin during the Middle Wisconsinan, much farther in the interior of the ice sheet than previously known. The marine incursion possibly occurred because of a calving bay developed from the north in the Gulf of Boothia - Committee Bay area following the recession and collapse of the ice stream. After the MIS 3 marine episode(s), the topographically controlled ice stream stemming from the eastern end of the Keewatin Ice Divide was re-activated, and maintained until deglaciation.