THERMAL EVOLUTION OF THE GREENLAND SEA GYRE IN 1988-1989

Slice inverses of temperature and heat content from the 1988-1989 Gree nland Sea Tomography experiment and other observations, including stan dard conductivity-temperature-depth stations, moored thermistors, surf ace meteorological variables, and surface ice cover are combined to be tter understand the thermodynamics of the Greenland Sea Gyre. Thermal evolution of the gyre center seems to divide naturally into the follow ing three periods: a preconditioning phase (November-January), during which surface salinity is increased by brine rejection from ice format ion and by entrainment but in which the mixed layer deepens only slowl y to a depth of some 150-200 m; a deep mixing phase (February-March) d uring which the surface mixed layer deepens rapidly to approximately 1 500 m in the gyre center purely under the influence of local surface c ooling; and a restratification phase during which the products of deep mixing are replaced by Arctic Intermediate Water flowing in from the gyre edges. The onset of the deep mixing phase occurs after ice format ion in the gyre center stops, resulting in an area of open water where large heat fluxes can occur. In surrounding regions, including the Od den region to the south, ice is still being formed. To the north and w est, closer to the steep topography of the continental shelf, the inve rse results show significant variability due to advection, and large t emperature and heat content fluctuations with a period of about 50 day s are seen.