Ice-ocean interactions during shallow convection under conditions of steady winds: three-dimensional numerical studies

A three-dimensional hydrodynamic ocean model coupled to a thermohydrodynami c model for young sea ice is applied to study shallow haline convection in the central Greenland Sea, with an emphasis on sub-mesoscale ice-ocean inte ractions. Two types of young sea ice are distinguished; i.e., frazil and pa ncake ice, both acting different on surface heat, salt, and momentum fluxes . Two scenarios are considered: (a) continued frazil-ice production during steady winds, and (b) the same scenario but with the intermittent formation of pancake ice during a short intervening period of low winds. Brine relea se due to new-ice production creates shallow convection in both cases. Unde r conditions of continued frazil-ice production, ice streaks develop at the sea surface, finally becoming oriented roughly parallel to the wind. These streaks are the result of convective plumes that induce organized patterns of convergent and divergent surface currents. Frazil-ice is herded into co nvergence zones where it becomes as thick as 6 m within 24 h. The studies s uggest a strong relationship between streak spacing and the penetration dep th of convection, given by an aspect ratio in the range of 2-3. After panca ke ice has been formed, however, the organized ice streaks vanish, developi ng into complex patterns of pancake ice. This finding is in agreement with recent field observations in the Greenland Sea Is-Odden ice tongue. With th e existence of pancake ice, moreover, the surface-averaged buoyancy flux de creases and is determined from the integral of local sub-mesoscale ice-ocea n interactions. (C) 1999 Elsevier Science Ltd. All rights reserved.