COUPLED ICE-OCEAN VARIABILITY IN THE GREENLAND SEA

A major surface feature of the Greenland Sea during winter is the freq uent eastward extension of sea ice south of 75-degrees-N and an associ ated embayment to the north. These features are nominally connected wi th the East Greenland Current, and both the promontory and the embayme nt are readily apparent on climatic ice charts. However, there are sig nificant changes in these features on time-scales as short as a few da ys. Using a combination of satellite microwave images (SSM/I) of ice c over, meteorological data and in situ velocity, temperature and salini ty records, we relate the ice distribution and its changes to the deve loping structure and circulation of the upper ocean during winter 1988 -1989. Our measurements illustrate the preconditioning that leads to c onvective overturn, which in tum brings warmer water to the surface an d results in the rapid disappearance of ice. In particular, the surfac e was cooled to the freezing point by early December and the salinity then increased through ice formation (about 0.016 m d-1) and brine rej ection. Once the vertical density gradient was sufficiently eroded, a period of high heat flux (>300 W m-2) in late January provided enough buoyancy loss to convectively mix the upper water column to at least 2 00 m. We estimate vertical velocities at about 3 cm s-1 downward durin g the initial sinking. The deepening of the thermocline raised surface temperatures by over 1-degrees-C resulting in nearly 1.5 x 10(5) km2 of ice-melt within two days. Average rates of ice retreat are about 11 km d-1 southwestward, generally consistent with a wind-driven flow. C omparison of hydrographic surveys from before and after the overturnin g indicate the fresh water was advected out of the area, possibly to t he south and east of our moorings.