A Convective Model for the Weddell Polynya

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Abstract
Mechanisms are considered which may induct the large (over 105 km2) area of open water, or polynya, which frequently occurs within the Weddell Sea winter sea-ice. We propose that when surface cooling and ice formation decrease the temperature and increase the salinity of the surface water (the latter by salt rejection during ice formation) in a preconditioned area, static instability with intense vertical mixing can occur. The upwelled warm, salty deep water can then supply enough heat to melt the ice, or prohibit its formation, even in the middle of winter. A simple two-level model is derived to test this theory and is found to agree well with observations. The process is found to be irregular due to different times of ice onset from one year to the next, and to a lesser extent from variations in surface heating and cooling. Further, it is shown that unless the freshwater input exactly balances the increased salinity from the overturn each year, the system will either gain or lose salt yearly an... Abstract Mechanisms are considered which may induct the large (over 105 km2) area of open water, or polynya, which frequently occurs within the Weddell Sea winter sea-ice. We propose that when surface cooling and ice formation decrease the temperature and increase the salinity of the surface water (the latter by salt rejection during ice formation) in a preconditioned area, static instability with intense vertical mixing can occur. The upwelled warm, salty deep water can then supply enough heat to melt the ice, or prohibit its formation, even in the middle of winter. A simple two-level model is derived to test this theory and is found to agree well with observations. The process is found to be irregular due to different times of ice onset from one year to the next, and to a lesser extent from variations in surface heating and cooling. Further, it is shown that unless the freshwater input exactly balances the increased salinity from the overturn each year, the system will either gain or lose salt yearly an...

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