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Multiple sea-ice states and abrupt MOC transitions in a general circulation ocean model

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Ashkenazy, Y. , Losch, M. , Gildor, H. , Mirzayof, D. and Tziperman, E. (2012): Multiple sea-ice states and abrupt MOC transitions in a general circulation ocean model , Fourth Kaplan Symposium, Jerusalem-Ein Gedi, Israel, 4 March 2012 - 7 March 2012 .
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Abstract:

Sea ice has been suggested, based on simple models, to play an important role in past glacial-interglacial oscillations via the so-called ``sea-ice switch'' mechanism. An important part of this mechanism is that multiple sea-ice extents exist under the same land ice configuration. This hypothesis of multiple sea-ice extents is tested with a state-of-the-art ocean general circulation model coupled to an atmospheric energy-moisture-balance model. The model includes a dynamic-thermodynamic sea-ice module, has a realistic ocean configuration and bathymetry, and is forced by annual mean forcing. Several runs with two different land ice distributions represent present-day and cold-climate conditions. In each case the ocean model is initiated with both ice-free and fully ice-covered states. The present- day runs converge approximately to the same sea-ice state for the northern hemisphere while for the southern hemisphere a difference of about three degree latitude between the sea-ice extents of the different runs is observed. The cold climate runs lead to meridional sea-ice extents that are different by up to four degrees in latitude in both hemispheres. While approaching the final states, the model exhibits abrupt transitions from extended sea-ice states and weak meridional overturning circulation, to less extended sea ice and stronger meridional overturning circulation and vice versa. These transitions are linked to cooling and warming of the North Atlantic high-latitude deep water. Such abrupt changes may be associated with the Dansgaard-Oeschger events, as proposed by previous studies.

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