U and Th isotope constraints on the duration of Heinrich events H0‐H4 in the southeastern Labrador Sea

The duration and sequence of events recorded in Heinrich layers at sites near the Hudson Strait source area for ice‐rafted material are still poorly constrained, notably because of the limit and uncertainties of the 14C chronology. Here we use high‐resolution 230Th‐excess measurements, in a 6 m sequence raised from Orphan Knoll (southern Labrador Sea), to constrain the duration of the deposition of the five most recent Heinrich (H) layers. On the basis of maximum/minimum estimates for the mean glacial 230Th‐excess flux at the studied site a minimum/maximum duration of 1.0/0.6, 1.4/0.8, 1.3/0.8, 1.5/0.9, and 2.1/1.3 kyr is obtained for H0 (∼Younger Dryas), Hl, H2, H3, and H4, respectively. Thorium‐230‐excess inventories and other sedimentological features indicate a reduced but still significant lateral sedimentary supply by the Western Boundary Undercurrent during the glacial interval. U and Th series systematics also provide insights into source rocks of H layer sediments (i.e., into distal Irminger Basin/local Labrador Sea supplies).