Atmosphere-ice-ocean Interactions and Dansgaard-Oeschger Cycles

Abstract:

Millennial-scale climate flip-flops called Dansgaard-Oeschger (D-O) cycles punctuated the last ice age. In the Greenland ice cores, they appear as large, rapid warming (interstadial) and cooling (stadial) episodes unlike anything else recorded in the last 120 thousand years. Sea ice has long been thought to play an important role in D-O cycles because of its strong influence on regional temperature and its ability to grow and melt rapidly in response to relatively weak forcings. Although some observational evidence exists to support this idea, it is not sufficient to constrain the characteristics of or mechanisms behind sea ice displacements during D-O cycles. This presentation will provide an overview of modelling experiments and high-resolution marine proxy data from the North Atlantic aimed at resolving some of these open questions. The modelling results point to a role for seasonal sea ice displacements in the Nordic Seas for creating the observed Greenland signals associated with D-O cycles. The high-resolution proxy data support this idea, and further suggest that the sea ice displacements are part of a coupled, transient climate response associated with changes in the thermohaline structure and stratification of the Nordic Seas, the existence of an Arctic-like cold halocline in the region, and the accessibility of the subsurface ocean heat reservoir to the atmosphere.