Are ice-rafted debris in cores indicative of past climate fluxes or ice sheet instability?
Ice-rafted debris (IRD) found within oceanic cores from mid latitudes of the North Atlantic has generally been thought to result from “Heinrich events” (HEs), intermittent instabilities in the Laurentide Ice Sheet, associated with a buildup of subglacial meltwater beneath the ice sheet. Several times during the last glacial cycle, the ice sheet surged over this lubricated base, transporting glacially-scoured continental detritus into the ocean. Marshall and Koutnik suggest that Dansgaard-Oeschger (D-O) cycles also generated ice-rafted debris, separate from ice sheet surges. D-O climate oscillations caused ice sheet extent to fluctuate. During cold periods of these cycles, ice sheets advanced onto the continent shelf, calved icebergs, and deposited glacially-scoured material into the oceans. Based on a model of ice sheet formation and advance, the authors note that peak iceberg fluxes associated with Dansgaard-Oeschger cycles occurred about 500 years after the inception of cooling. Howe
