Much of the bed of the central and eastern sectors of the Laurentide Ice Sheet was underlain by Paleozoic carbonates. We propose that pulses of detrital carbonate-rich sediments in two cores from the northwestern Labrador Sea reflect episodes when an ice stream from the Hudson Strait extended to the shelf break and delivered sediment onto the slope and deep-sea plain. Atomic mass spectroscopy 14C dating of planktonic foraminifera in cores HU75-009-IV-55 (2.4 km water depth) and HU87-033-009 (1.4 km water depth and 150 km north-northwest), indicates that the youngest event occurred between ca.14 and 15 ka and another occurred between 19 and 21 ka.
The two carbonate intervals in northwestern Labrador Sea cores are coeval with Heinrich events 1 and 2 in the eastern North Atlantic (lat 45°-50°N, long 20°W), where they are associated with an increase in lithic fragments and a drastic reduction in the numbers of foraminifera. These changes have been linked with the massive production of icebergs associated with ice-sheet surges. Our evidence indicates that Heinrich events 1 and 2 are associated with the dynamics of the Hudson Strait ice stream and denote considerable glaciological instability.