Interannual Variability in the Thermodynamics of Subduction over the North Atlantic

Abstract

Subduction requires a buoyancy input into the mixed layer, which over the gyre scale can either be achieved by an atmospheric input or a wind-induced Ekman redistribution of buoyancy. The buoyancy budget for subduction is diagnosed over the North Atlantic using monthly fields from 1950 to 1992. The climatological-mean budget suggests that subduction over the subtropical gyre occurs through an Ekman redistribution of buoyancy from the Tropics, rather than a surface buoyancy flux from the atmosphere. In contrast, interannual variations in subduction are controlled by the variations in the surface buoyancy flux, which are generally greater than the variations in the Ekman redistribution of buoyancy. However, over the Tropics and southern part of the subtropical gyre, there is a partial cancellation in the opposing contributions from the surface and Ekman buoyancy fluxes, which acts to reduce the interannual variations in subduction.