On the interplay between downwelling, deep convection and mesoscale eddies in the Labrador Sea

(2019) Georgiou, S., van der Boog, C.G, Brüggemann, N., Ypma, S.L., Pietrzak, J.D. and C.A., Katsman. On the interplay between downwelling, deep convection and mesoscale eddies in the Labrador Sea, Ocean Model., 135, 56-70, https://doi.org/10.1016/j.ocemod.2019.02.004

Schematic showing the indirect link between convection and downwelling strength. The horizontal density gradient between the interior and the boundary current (red arrow) set by convection (blue cylinder) affects the instability of the boundary current. The eddy field and the buoyancy loss of the boundary current along the west Greenland coast govern the dynamics of the downwelling in this region.

In this paper, it is explored how changes in the surface heat fluxes affect the magnitude of the downwelling, the evolution of deep ocean convection in the Labrador Sea and their interplay through the eddy activity. The motivation of this study stems from the need to improve our understanding of the location where the downwelling takes place at high latitudes and its response to changes in the forcing conditions in light of a changing climate.

Both the convection and the eddy field are affected by the changes in the surface forcing. In response to a stronger (weaker) surface winter heat loss, convection is stronger and the temperature gradient between the interior and the boundary current increases (decreases). This directly impacts the eddy field; as the temperature gradient increases, the baroclinicity of the boundary current increases, and the boundary current becomes more unstable. While the generation of the eddies is known to be governed by local processes, their impacts are not restricted to their generation region since they propagate away towards the interior. As a result, the associated eddy heat transport from the boundary current towards the interior strengthens. This increases the heat loss of the boundary current, which in turn governs the magnitude of the downwelling, and at the same time provides a negative feedback on the convection depth. These idealized simulations thus highlight that complex interactions between the boundary current and interior are established via the eddy activity, and in concert determine the downwelling in the basin as well as the characteristics of convection (see Figure).