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

A three-dimensional hydrodynamic ocean model coupled to a thermohydrodynamic 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 interactions. Two types of young sea ice are distinguished; i.e., frazil and pancake 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 release due to new-ice production creates shallow convection in both cases. Under 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 convergence zones where it becomes as thick as 6 m within 24 h. The studies suggest a strong relationship between streak spacing and the penetration depth of convection, given by an aspect ratio in the range of 2–3. After pancake ice has been formed, however, the organized ice streaks vanish, developing into complex patterns of pancake ice. This finding is in agreement with recent field observations in the Greenland Sea Is-Odden ice tongue. With the existence of pancake ice, moreover, the surface-averaged buoyancy flux decreases and is determined from the integral of local sub-mesoscale ice–ocean interactions.