Arctic leads are thought to play an important role in the air-sea heat exchange at high latitudes. The evolution of the local ice-ocean-atmosphere coupled system, when a lead opens up and immediately begins to refreeze, is of considerable interest in terms of the heat exchanged by the ocean to the atmosphere, as well as the amount of salt extruded into the oceanic mixed layer. Here we will present a coupled model of the ice-ocean system that provides a quantitative description of a refreezing lead, especially the evolution of the ice cover and the mixed layer below. The model is applied and compared with what has been learned from the Lead Experiment (LEADEX) observations in the April of 1992 in the Beaufort Sea. The results suggest that Arctic leads, especially during winter, are, in general, close to a state of free convection. Strong convection driven by the extruded brine in a refreezing lead drives vigorous mixing in the mixed layer immediately below, irrespective of the advective velocity of ice. Turbulence intensities reach quite high values during the initial phases of refreezing but weaken gradually with a half-life time of about 2 days. Inertial oscillations are superimposed on the resulting currents and are especially vigorous below the mixed layer. The ice builds up to a thickness of over 12 cm in the first 24 hours in a refreezing lead, in accordance with LEADEX observations, with a significant contribution coming from frazil ice formation in the supercooled water below.

Not surprisingly, since the water below is at or close to freezing, advection of water masses past the lead due to ice motion or prevailing currents does not alter the refreezing rate substantially, even though the frazil ice contribution shows a significant increase. Advection does affect the local properties in the mixed layer immediately below and downstream of the lead. For example, the increase in salinity, an indicator of the intensity of the refreezing process in a lead, depends very much on the motion of ice cover relative to the underlying water. For large advective velocities the salinity increase is an order of magnitude smaller than the purely convective situation and the turbulence is dominated by that generated by shear underneath the rough ice, upstream of the lead which tends to mask that generated by convection in the lead itself. For a stationary lead, refreezing gives rise to an inward jet underneath the ice and outward flow at the base of the mixed layer. Vertical motion is in the form of convective cells centered at the lead edges. ¿ American Geophysical Union 1995