ABRUPT Arctic Climate Change

During the last glacial, a series of abrupt climate change events took place. Over Greenland, atmospheric temperature shifts of about 10±5°C, from cold to relatively warm, occurred within decades. A link is seen between changes in the sea ice extent in the southern Nordic Seas and these climate shifts. However, it is still not known how far north the sea ice cover disappeared when it broke up in the southern Nordic Seas. Or how different the timing and duration of the events were in the northernmost Nordic Seas relative to the southern Nordic Seas, how the stability of the water column was impacted, or what may have initiated abrupt changes in the full ocean basin. Through ABRUPT, we will provide reconstructions of sea ice, ocean and climate conditions in the Fram Strait over a couple of these abrupt events. These reconstructions, and reconstructions from other parts of the Nordic Seas, will be used in combination with climate model data to investigate the abrupt climate changes that took place, and why. Furthermore, the ice-covered Nordic Seas of the cold glacial periods share some characteristics with the present-day Arctic Ocean; a cold, fresh water layer that stabilize the sea ice cover and the underlying layer of Atlantic water that brings warm and salty water masses to the interior of the ocean basin, where it recirculates underneath the cold, fresh water mass. Over the last decades, abrupt warming has occurred around the Fram Strait, comparable to the rapidity of the glacial temperature changes that occurred over Greenland during the glacial. ABRUPT will evaluate if understanding the abrupt glacial climate changes may be of relevance for understanding the risk of similar changes in the future Arctic.

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 General Circulation Model (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.