ABSTRACT: High-resolution paleoenvironmental reconstruction since the last outburst flood of Lake Agassiz in Hudson Bay and Strait.

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During the last two decades much effort has been put in the reconstruction of paleoenvironmental conditions of Hudson Bay and Strait as well as adjacent areas. However, those investigations mainly focused on seismic or geomorphologic studies distinguishing large scale variations of environmental change like glacial and interglacial conditions. Alternatively, continuous or high resolution studies focused on the last outburst flood of Lake Agassiz around 8.5 ka. Nevertheless, sediments of the Hudson Bay complex consisting of Foxe Bay, Hudson Bay and Hudson Strait hold the complete history of that area, i.e., the final stages of the Laurentide Ice Shield and the remaining Holocene.In combination with several radiocarbon dates, we present continuous and high resolution sedimentary records from the east coast of Hudson Bay, the central Hudson Bay area and Western Hudson Strait, enabling a deeper insight into the development of postglacial paleoenvironmental changes. Up to 4 m long sedimentary cores were collected as part of the ArcticNet program during the AMD0509 (CCGS Amundsen) expedition aiming for regions with high Holocene sedimentation rates. Sites were carefully selected using a 3.5 kHz subbottom profiler and multibeam sonar to avoid areas affected by mass wasting deposits or iceberg scouring.While the central area of Hudson Bay isgenerally characterised by stable depositional conditions after the outburst flood (i.e., no variations in grain sizes or color), Eastern Hudson Bay and Hudson Strait show a more diverse pattern. However, the general trend in those cores is a tendency towards increased terrestrial input with time. The highest sedimentation rates were observed in the center of the Hudson Bay complex (1.03-1.60 mm a-1 / mean: 1.13 mm a-1), i.e., the westernmost tip of Hudson Strait between Mansel Island and Nottingham Island. In this area thehighest total (in-)organic carbon and total nitrogen contents were also observed. Similar sedimentation rates, although slightly lower, were recorded in Nastapoka Sound (0.58-1.21 mm a-1 / mean: 0.86 mm a-1), southeastern Hudson Bay. As expected due to its distal position, sedimentation rates arelowest in the center of Hudson Bay (0.17 mm a-1). Even if age-control 20 km off the mouth of la Grande Rivière de la Baleine is less constrained, the general trend towards more minerogenic terrestrial input is also evident there. This isinferred from an increase in magnetic susceptibility, density and grain sizes as well as from CN analyses, suggesting a grater fluvial influence either due to a general increase in discharge, more extreme events due to the lack of waterstorage in the glacier or a closer proximity of the coast to the coring location due to isostatic rebound since the final flood of Lake Agassiz.

Bibliography of Canadian Geomorphology