Temperature evolution of the upper ocean in the Greenland Sea January to March 1989

Abstract

Tomographic data obtained during early 1989 in the Greenland Sea have been analyzed at 4-8 hour resolution to give the range-averaged vertical temperature evolution in the upper 500 m for a 106 km path. The tomographic inversions used both ray travel time data and normal mode group velocity data in order to maximize near-surface resolution. Two major events are apparent in the results. The first is the warming of a cold (-1.9°C) 100 m thick surface layer, and the second, 10 days later, is the cooling of a relatively warm (-0.9°C) subsurface layer between 300 m and 500 m depth. This warm subsurface layer is a critical source of salinity and buoyancy for deep convection. The surface layer warming is consistent with a mixed layer deepening over a portion of the path, bringing up water from below. Special Sensor Microwave Imager (SSM/I) ice data indicate that the local ice field disappears 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 no ice cover at this time, and so surface heat fluxes are large. A northerly wind event occurs at the onset of the cooling of the 300-500 m layer, suggesting that wind-induced mixing may have played a role in initiating the process. There is evidence of southward flow advecting warm water into the area both before and after the two events studied in detail here. Copyright 1997 by the American Geophysical Union.