IceLab · Ice-ocean interactions during Heinrich Events in the Labrador Sea

Ice-ocean interactions during Heinrich Events in the Labrador Sea

Under the influence of ongoing climate warming, melting of the Greenland ice sheet is accelerating. The release of freshwater from the ice sheet into the surrounding ocean has important implications for the global sea level and the ocean circulation, driven by the balance of heat and salt. Climate model projections for future sea level rise under different warming scenarios, however, are associated with significant uncertainty, partly due to the lack of understanding of the interactions of the ice sheet with the surrounding ocean and other components of the climate system, including sea-ice. The objective of the Marie Skłodowska-Curie Action Fellowship IceLab was to improve our understanding of sea-ice/ocean interactions and their implications for the melting of ice sheets by investigating periods in the geological past characterized by the collapse of an ice sheet or rapid ice sheet retreat. One specific objective was to study sea-ice extent and subsurface temperatures in the outer Labrador Sea during so-called Heinrich events between 30 and 60 thousand years before present (ka BP). These are events of ice-sheet collapse during the last ice age, associated with the release of vast amounts of icebergs from Hudson Strait into the Labrador Sea and adjacent North Atlantic. One possible mechanism that might have triggered the collapse of the Hudson Strait ice sheet is melting induced by warmer ocean temperatures. A warmer ocean in turn might have been caused by the formation of a ‘sea-ice lid’ (an extensive sea-ice cover) in the Labrador Sea, which prevented the release of heat from the surface ocean to the atmosphere. Sea-ice and subsurface temperatures can be reconstructed using different geochemical methods applied to marine sediment cores. Sediment core U1302/03 from the outer Labrador Sea, investigated during IceLab, was taken as part of the International Ocean Discovery Program (IODP). The original research plan for IceLab also included the reconstruction of sea-ice extent in the northern Baffin Bay and on the Faroe Banks for the same interval from 30-60 ka BP. This would allow to understand the variability of sea-ice extent in both space and time. Different challenges with the available sediment cores, however, meant that this objective could not be implemented. Instead, sea-ice conditions were reconstructed from the northern Baffin Bay and the southern Lincoln Sea, based on four sediment cores (two from each region), covering approximately 20 and 12 ka BP, respectively. These time periods cover the transition from the last ice age to the current warm period and the onset of the current warm period, characterized by pronounced ice sheet retreat. Thus, although not part of the original research plan of IceLab, the sediment cores from the northern Baffin Bay and southern Lincoln Sea are able to inform the main objective of IceLab; to understand the interactions of sea-ice and the ocean with ice sheets in the past.

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