Update on the Dynamics of the Late Wisconsinan Northwestern Laurentide Ice-Sheet

Abstract:

Ice streams draining ice from major ice divides over Keewatin, New-Quebec and Foxe Basin-Baffin Island areas constitute a key feature of the Last Glacial Maximum (LGM) Laurentide Ice Sheet (LIS). They put constraints on the topographic evolution, volume and stable isotope contents of LIS, thus on LGM ocean volume and isotopic composition. Here, we re-visit field-based information about Laurentide Ice Sheet (LIS) dynamics in the Hudson Bay and Strait area, from the LGM to its final decay, and confront this information with deep-sea core records from Baffin Bay and the Labrador Sea. Core HU08-029-004 raised off Hudson Strait points to continuous in Hudson Strait throughout the whole interval, with acceleration during Heinrich (H) events 2 and 1, possibly triggered (at least for H1) by a delayed LGM-glacio-isostatic response. Streaming sediment supplies from Hudson Strait are recorded by fine detrital carbonates, without evidence of Foxe Basin sediment sources, thus suggesting streaming from the Ungava Peninsula and southern Baffin Island. Later on, in southern Hudson Bay, the Cochrane surges (~8.7 ka BP) illustrate fast ice streaming southwards, mostly from the Keewatin ice-divide, into Lake Agassiz-Ojibway. Ice-thinning in the Bay and the Foxe Basin areas led to the lake final drainage through Hudson Strait, and its replacement by the Tyrrell Sea (~8.3 ka BP). In Baffin Bay, out of phase surgings, mostly from the Inuitian and Greenland ice sheets, are similarly recorded. These new data and re-interpretation of earlier information corroborate the concept of a dynamic (ice-stream prevalent) North American Ice complex during the Late Wisconsin as evident in recent glaciological reconstructions. This along with recent data-calibrated glaciological reconstructions for the other major ice sheets result in a global shortfall of at least 10m compared to far field relative sea-level records.