Some of the abrupt climate changes that took place during the last glacial was associated with large freshwater fluxes to the North Atlantic. The fresh water entered the North Atlantic through melting of iceberg being released from the North American is sheet and transported with the ocean currents, crossing large parts of the North Atlantic while melting. This freshwater release impacted the ocean circulation and the climatic conditions over large areas. During these cold phases the Nordic Seas have been seen as totally covered by sea ice. Our preliminary results suggest, however, the existence of a polynya, a smaller area with open water, in the Northernmost Nordic Seas, the Fram Strait, through a parts of one of these cold intervals, despite the existence of a perennial sea ice cover further south. When the sea ice cover started to retreat in the southeastern Nordic Seas, it seems like a restricted corridor of open water existed for a short time in the eastern Nordic Seas, all the way north to the Fram Strait. However, while the southeastern Nordic Seas was ice free during the following warm phase, the sea ice cover quickly grew back in the Fram Strait, and the areas stayed sea ice covered during most of this warm interval.
The last glacial was characterized by a series of abrupt climate shifts between cold stadials and warm interstadials (DO-events). A link is documented between sea ice variability in the southern Nordic Seas and air temperature change over Greenland, with sea ice identified as a key determination factor for setting up these large, abrupt climate shifts. However, the spatial extent of the sea ice cover is still unknown and several unanswered questions remain, e.g.: When the sea ice cover broke up in the southern Nordic Seas during the stadial-to-interstadial transitions, how far north did it break up? How different were the timing and duration of the events in the northernmost Nordic Seas relative to the southern Nordic Seas? What were the magnitude and timing of changes in the vertical stability of the ocean? What triggered the abrupt, full basin scale changes? In ABRUPT we will reconstruct the sea ice conditions, hydrography and climate of the Fram Strait, with an unprecedented resolution for this area, over two targeted DO-events. These reconstructions and a regional data synthesis will be used in combination with multi-model output from four state-of-the art GCM glacial simulations, for an integrated analysis of the dynamics of abrupt Arctic climate change during the last glacial. Furthermore, the stadial Nordic Seas bear strong resemblance with the present Arctic Ocean, e.g. the existence of a strong halocline stabilizing the sea ice cover and a subsurface layer of Atlantic Water that bring warm and salty water masses into an interior basin, where it recirculates under the halocline. The rate of change seen for the warming around the Fram Strait over the recent decades, where Atlantic water meets the Arctic sea ice cover, is comparable to the rapidity of the DO-events. ABRUPT will evaluate the relevance of the DO-events for ongoing Arctic climate change to unravel mechanisms important for understanding the risk of similar changes in the future Arctic.
