Interannual variability in the thermodynamics of subduction over the NorthAtlantic

Subduction requires a buoyancy input into the mixed layer, which over the g yre scale can either be achieved by an atmospheric input or a wind-induced Ekman redistribution of buoyancy. The buoyancy budget for subduction is dia gnosed over the North Atlantic using monthly fields from 1950 to 1992. The climatological-mean budget suggests that subduction over the subtropical gy re occurs through an Ekman redistribution of buoyancy from the Tropics, rat her than a surface buoyancy flux from the atmosphere. In contrast, interann ual variations in subduction are controlled by the variations in the surfac e buoyancy flux, which are generally greater than the variations in the Ekm an redistribution of buoyancy. However, over the Tropics and southern part of the subtropical gyre, there is a partial cancellation in the opposing co ntributions from the surface and Ekman buoyancy fluxes, which acts to reduc e the interannual variations in subduction.