Talk by Kerim H. Nisancioglu (Bjerknes Centre for Climate Research, Bergen, Norway)

A Conceptual Model of D-O Events

Dansgaard-Oeschger (D-O) events are abrupt warmings that occurred intermittently throughout much of the last glacial period. The detailed mechanism behind D-O events remains unclear despite several decades of research on the topic. In this talk a complete conceptual model of D-O cycles is presented based on new high resolution marine proxy records from the Nordic Seas combined with results from a coupled ocean-atmosphere-sea ice model of intermediate complexity.

The climate model demonstrates that a freshwater discharge into the Nordic Seas from the Fennoscandian ice sheet creates a surface freshwater lens, accompanied by extensive sea ice, and a weak Atlantic meridional overturning circulation (AMOC). The resulting climate state is comparable to the cold stadials of D-O cycles recorded in proxy records. As the subsurface of the Nordic Seas is isolated from the atmosphere above, heat accumulates under the freshwater lens and expanded sea ice cover. Once there is enough heat to destabilize the water column, the freshwater lens is rapidly eroded together with the overlying sea ice, exposing the relatively warm ocean surface to the atmosphere above. As a result, Greenland experiences a warming similar to the rapid warming observed at the onset of a D-O event in Greenland ice cores.