Winter conditions in the Irminger Sea observed with profiling floats

Temperature/salinity profiles collected between 1994 and 2003 with profiling floats in the North Atlantic subpolar gyre are analyzed to investigate the hydrographic conditions in winter in the Irminger Sea. The salinity data can be calibrated against accurate profiles from ships obtained mostly during summer months and the resulting float profile salinity accuracy is of the order of 0.015. Between 1997 and 2003, when the North Atlantic Oscillation (NAO) index was generally low, the potential temperature and salinity of the Labrador Sea Water (LSW) core observed by the floats showed a positive trend, an indication of little or no deep convection. The float data show that in the Irminger Sea the thermal energy of the water column reaches the lowest values south and southwest of Cape Farewell, a place where deep convective events are likely to occur. The geostrophic velocity field at 15 m computed from drifting buoys and satellite measurements of sea level shows, for the same area, mean currents below 0.1 m s(-1) and low levels of eddy kinetic energy. These factors, together with recent estimates of winter air-sea heat fluxes as high as 500 W m(-2) for this region, are exploited to explore the evolution of the surface mixed layer using several one-dimensional models. The results suggest that the typical thickness of the surface mixed layer at the end of winter is of the order of 400 m. This is similar to observed values from floats.