TEMPERATURE EVOLUTION OF THE UPPER OCEAN IN THE GREENLAND SEA JANUARYTO MARCH 1989

Tomographic data obtained during early 1989 in the Greenland Sea have been analyzed at 4-8 hour resolution to give the range-averaged vertic al temperature evolution in the upper 500 m for a 106 km path. The tom ographic inversions used both ray travel time data and normal mode gro up velocity data in order to maximize near-surface resolution. Two maj or events are apparent in the results. The first is the warming of a c old (-1.9 degrees C) 100 m thick surface layer, and the second, 10 day s later, is the cooling of a relatively warm (-0.9 degrees C) subsurfa ce layer between 300 m and 500 m depth. This warm subsurface layer is a critical source of salinity and buoyancy for deep convection. The su rface layer warming is consistent with a mixed layer deepening over a portion of the path, bringing up water from below. Special Sensor Micr owave Imager (SSM/I) ice data indicate that the local ice field disapp ears 3-4 days after the surface warming. The cooling of the warm 300 m to 500 m layer is also consistent with a vertical process. There is n o ice cover at this time, and so surface heat fluxes are large. A nort herly wind event occurs at the onset of the cooling of the 300-500 m l ayer, suggesting that wind-induced mixing may have played a role in in itiating the process. There is evidence of southward flow advecting wa rm water into the area both before and after the two events studied in detail here.