Atmospheric forcing during active convection in the Labrador Sea and its impact on mixed-layer depth

Abstract

Hydrographic data from the Labrador Sea collected in February–March 1997, together with atmospheric reanalysis fields, are used to explore relationships between the air-sea fluxes and the observed mixed-layer depths. The strongest winds and highest heat fluxes occurred in February, due to the nature and tracks of the storms. While greater numbers of storms occurred earlier and later in the winter, the storms in February followed a more organized track extending from the Gulf Stream region to the Irminger Sea where they slowed and deepened. The canonical low-pressure system that drives convection is located east of the southern tip of Greenland, with strong westerly winds advecting cold air off the ice edge over the warm ocean. The deepest mixed layers were observed in the western interior basin, although the variability in mixed-layer depth was greater in the eastern interior basin. The overall trend in mixed-layer depth through the winter in both regions of the basin was consistent with that predicted by a 1-D mixed-layer model. We argue that the deeper mixed layers in the west were due to the enhanced heat fluxes on that side of the basin as opposed to oceanic preconditioning.