Sea ice, convection and the Greenland Sea

Abstract

The region where deep open-ocean convection occurs in the Greenland Sea corresponds to that where a sea ice winter feature, the Odden, usually forms. The role of sea ice in modifying the surface waters to overturn to depth is evaluated through the combination of in siu measurements, satellite imagery, meteorological measurements and drifting buoy data. Results suggest local meteorological and oceanographic conditions govern the ice conditions over the region. The high ambient wave energy precludes the formation of ice beyond the frazil-pancake stage; the changing surface pressure field, due to passing storm systems, influences the daily shape and extent of the Odden and enables pancake ice to expel brine at an increased rate. Finally, the analysis of drifting buoy data reveal that the ice is in free drift. t
These characteristics suggests the Odden may be regarded as a large scale latent heat polynya, with the predominately northerly winds blowing newly formed sea-ice constantly southward such that it melts in a different area from that of its formation. This salt separation process whereby the majority of brine is deposited where the ice was formed, and a smaller amount being released, through brine drainage, as the ice drifts with the prevailing wind has important consequences for the spatial and temporal distribution of the salt flux and hence surrounding hydrography. This is clearly demonstrated through the development of a salt flux model, which involves brine drainage and drift. A simple one-dimensional mixed layer model, driven by results of the salt flux model, predicts a strong density enhancement and deepening of the mixed layer over time. It is therefore envisaged that the formation of sea ice, brine drainage and drift are fundamental in eroding the pycnocline between the surface waters and those below. Sea ice should therefore be viewed as a preconditioning activity to deep overturning of the waters of the central Greenland Sea.

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