The role of eddies for the deep water formation in the Labrador Sea

The Labrador Sea is one of a few sites of the world ocean where open ocean deep convection occurs. Previous ocean general circulation models of the North Atlantic tend to show large deficits in simulating observed characteristics of deep water formation in the Labrador Sea. It is shown that three key processes lead to significant improvements: 1) an adequate representation of the freshwater exchange with the Nordic Seas; 2) an efficient representation of eddy fluxes between the boundary currents and the interior of the Labrador Sea; 3) low (numerical) diapycnal mixing. Based on these results, a refined eddy resolving model of the North Atlantic is developed and analyzed with respect to the important aspects of the deep water formation and its variability in the Labrador Sea. The dominant eddy kinetic energy signal is associated with the generation of well stratified ”Cape Desolation Eddies” which are not a direct result of the deep water formation process. These eddies are able to suppress deep convection in the interior of the Labrador Sea. A second type of rather unstratified ”rim current eddies” are formed during the deep convection process. Both types contribute to the restratification after convection and are important for this process to occur on observed timescales. Beside the well known correlation between surface heat flux changes and Labrador Sea Water formation, the model suggests two novel mechanisms of convection variability related to wind stress: 1) in case of enhanced wind stress the eddy kinetic energy at Cape Desolation increases. The resulting higher generation of well stratified Cape Desolation eddies leads to significantly lower Labrador Sea Water formation; 2) wind stresses parallel to the coast west of Greenland causes Ekman transports of relatively fresh and cold water off the coast towards the interior. This buoyant water at the surface stratifies the water column on the Greenland side of the Labrador Sea and suppresses deep convection