Interaction between ice sheet instability and sea surface characteristics in the Labrador Sea during the last 50 ka

The study on the decay of ice sheets in the past provides important insights into the interaction between ice sheet behaviours and ocean characteristics, especially under a sustained warming climate. On the one hand, the ice sheet may affect the ocean environment; on the other hand, changes in sea surface conditions may affect the instability of the ice sheets. However, interactions between ice sheet dynamics and sea surface characteristics are still not fully understood. Thus, studies of carefully selected sediment cores representing both ice-sheet and ocean characteristics can help to better predict changes in ice sheets in the future. Here, we show sedimentary records from the eastern Labrador Sea, proximal to the Laurentide Ice Sheet (LIS) and the Greenland Ice Sheet (GrIS), representing the last 50 ka, i.e., the last glacial-deglacial-Holocene period. Our XRF and biomarker data document the outstanding collapse of the LIS/iceberg discharge during Heinrich Events (i.e., HE5, HE4, HE2, and HE1) and the occurrence of meltwater plumes from the LIS and GrIS during the deglaciation. Such meltwater discharge has caused surface water freshening in the Labrador Sea and, consequently, decreased sea surface temperatures and decreased primary productivity. Enhanced Irminger Current inflow might have triggered the retreat of ice sheets/meltwater discharge, as shown in our planktic foraminifera records. In contrast to dominantly relatively low primary productivity during the glacial period, both higher sea ice algae and phytoplankton production occurred during the Last Glacial Maximum (LGM), probably caused by a polynya in front of the GrIS reaching its maximum extent at that time. During the deglaciation to Holocene time interval, primary productivity shows an increasing trend probably related to decreased meltwater discharge, decreased sea ice extent, and increased insolation.