Ice-rafted debris (IRD)

IRD has been found to be widely distributed in the entire subpolar North Atlantic. Glacial sedimentary records from this region display discrete IRD layers at time intervals of about 7,000 years named “Heinrich” layers that witness large-scale iceberg surging of the North American Laurentide Ice Sheet. This conclusion was made based on the lithology of the IRD involved, showing, among others, a large contribution of detrital dolomitic carbonate derived from the sedimentary rocks around Hudson Bay and Strait. Mineral studies have provided also evidence for IRD originating from European and Greenland glaciers. Asynchronous deposition of IRD from these various sources suggests a different stability regime of ice sheets west and east of the North Atlantic. Although several mechanisms may have played a role, increasing evidence arises which demonstrates that (sub)surface ocean warming and associated bottom melting of floating glaciers and ice shelves have been an important mechanism triggering large-scale iceberg calving (“Heinrich”) events, both under glacial climate and under present-day warming conditions.