During cold phases in the D-O cycle, Nordic seas are covered by ice, the authors suggest. Warm Atlantic subsurface water flowing into the region, trapped beneath the sea ice and a freshwater cap, warms the subsurface. Eventually, this warming breaks the halocline, a barrier to vertical mixing caused by sharp differences in salinity, allowing the warm water to rapidly melt the sea ice cap and vent the heat to the atmospherethe warming spike of a D-O event. The high temperatures melt water from the nearby Fennoscandian ice sheet, rebuilding the freshwater cap, promoting sea ice formation, and resetting the mechanism. The authors note that their hypothesis avoids ad hoc freshwater forcings that other hypotheses rely on and is supported by observations from high-resolution marine sediment cores.
The authors suggest that a similar mechanism could be active in the Arctic right nowthe observed subsurface warming of Arctic waters could drive a sudden burst of warming, rapidly pushing the Arctic into an ice-free state and heating the surrounding area.
Source: Paleoceanography, doi:10.1002/palo.20042, 2013 http://onlinelibrary.wiley.com/doi/10.1002/palo.20042/abstract
Title: Dansgaard-Oeschger cycles: interactions between ocean and sea ice intrinsic to the Nordic Seas
Authors: Trond M. Dokken: UNI Research AS, Allegaten 55, 5007 Bergen, Norway and Bjerknes Centre for Climate Research, 5007 Bergen, Norway;
Kerim H. Nisancioglu: Department of Earth Science, University of Bergen, 5007 Bergen, Norway and UNI Research AS, Allegaten 55, 5007 Bergen, Norway and Bjerknes Centre for Climate Research, 5007 Bergen, Norway;
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American Geophysical Union