Sea ice dynamics in the Labrador Sea across Heinrich events during MIS 3

The most prominent events of ice-sheet collapse in the recent geological past are so-called Heinrich events observed during millennial-scale climate oscillations of the last glacial period. They are characterized by the dispersal of ice(berg) rafted debris and freshwater across the North Atlantic, with the Hudson Strait suggested as the predominant source region. One potential mechanism triggering iceberg release invokes cryosphere-ocean interactions, where subsurface warming destabilizes the Laurentide ice sheet. In this scenario, the build-up of a subsurface heat reservoir is caused by an extensive sea ice cover in the Labrador Sea in combination with a reduced overturning circulation in the North Atlantic, preventing the release and downward mixing of heat in the water column.

Here we present high-resolution reconstructions of sea ice dynamics in the outer Labrador Sea between 30 ka and 60 ka at IODP Site U1302/03, located on Orphan Knoll. Sea ice reconstructions are based on a suite of sympagic and pelagic biomarkers, including highly branched isoprenoids and sterols. These results suggest a transition from reduced/seasonal to extended/perennial sea ice conditions preceding the onset of iceberg rafting associated with Heinrich event 3, 4, 5, and 5a by a couple of hundred to a thousand years. Our preliminary results thus support the importance of sea ice in the Labrador Sea for triggering Heinrich events. Future results from the same core will have to confirm the timing and extent of subsurface warming and ocean circulation dynamics.