Variability in Laurentide ice sheet dynamics and global climate changes: a perspective fro mthe depositional record of the greater Hudson Bay region

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The location of Hudson-James Bay near the former geographic center of the Laurentide ice sheet (LIS) makes this region particularly important for the study of ice sheet dynamics. Numerous paleoclimate proxies have shown that the greater Hudson Bay region was at the origin of important climate changes during the last glacial cycle, notably through episodic and massive discharges of icebergs in the North Atlantic Ocean from the margin of a marine-based ice sheet. These so-called Heinrich events are significant in term of ice sheet dynamics because current glaciological model attribute Heinrich events to an abrupt collapse of a large ice dome centered over Hudson Bay. Field-based geological data, however, argue for a multi-dome configuration of the LIS. Sequences of shifting ice flow documented from multi-faceted and striated rock outcrops indicate important migrations of these ice domes that could be related to Heinrich-type drawdown episodes of certain sectors of the LIS. However, the timing of these ice flow shifts, as well as the exact ice flow paths associated with the disintegration of the LIS are inadequately constrained. As a result, numerical models currently disagree with available geological observations. This research program addresses these issues by studying various aspects of the Quaternary geomorphic and stratigraphic records of the Hudson-James Bay lowlands. This region is adjacent to the former zones of displacement of two of the most important ice domes of the LIS, located east and west of Hudson Bay. These sedimentary sequences should thus be sensitive to changes in ice sheet configuration and record information on the postulated collapse. The presence of several glacial units interbedded with nonglacial sediments offers an outstanding opportunity to sort out the chronology of ice movements. Dating of the nonglacial deposits will provide chronological constraints on the shifting sequences of ice flow. A long-term objective of the research program is to correlate the evolution and episodes of reorganizations of the LIS with global climate changes (e.g. Heinrich events) documented from deep-sea sediment records.