In the North Atlantic we define H-O as a Heinrich-like event which occurred during the Younger Dryas chron. On the SE Baffin shelf prior to 11 ka, surface water productivity was reasonably high, as measured by the numbers of diatom and planktic foraminifera per gram, but an abrupt increase in detrital carbonate (DC-O event) (from approximately 15% up to 50% carbonate by weight) occurred at 11+/-C-14 ka and continued to circa 10 ka. These deposits, 2-6 m thick, are dominated by detrital calcite and silt- and clay-sized sediments. During this event (DC-O/H-O), ice extended onto the inner shelf but did not reach the shelf break and probably originated from a center over Labrador-Ungava. As a consequence, the pattern of ice-rafted debris and sediment provenance shown by H-O in the North Atlantic is different from that during H-l (14.5 ka) or H-2 (20 ka) when the ice sheet extended along the axis of Hudson Strait and may have reached the shelf break; for example, there is no concrete evidence for DC-O is cores on the floor of the Labrador Sea due east of Hudson Strait (HU75-55,-56), but H-O has been noted in cores off Newfoundland and west of Ireland. A coeval carbonate event to DC-O, but this one dominated by dolomite, occurs in HU82-SU5 on the west side of Davis Strait with a source either from northern Baffin Bay or Cumberland Sound. Although other sources for North Atlantic detrital carbonate cannot be totally excluded, our evidence suggests that H-O represents the expression of glaciological instability of the Laurentide Ice Sheet within the general region of Hudson Strait and probably to the north (Cumberland Sound and northernmost Baffin Bay). There is one younger DC event, dated circa 8.4 ka, present in sediments along the Labrador margin and in Hudson Strait, which represents the final collapse of the ice sheet within Hudson Strait and Hudson Bay.
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