Is the North Atlantic in Sverdrup Balance?

Abstract

Evidence for the widespread assumption that Sverdrup balance describes the dynamics of the North Atlantic subtropical gyre is reviewed critically. If the balance were to hold up to the edge of the Gulf Stream system, then there is a serious conflict with existing estimates of the net meridional flux of heat. If a recirculation region near the Stream is excluded, then one loses numerical agreement between a geostrophic calculation of the interior mass flux and the opposite Gulf Stream transport. Our conclusion is that while the linear vorticity balance may well apply over much of the North Atlantic subtropical gyre, there is little evidence supporting the special version called Sverdrup balance even in the relatively quiescent region east of the Mid-Atlantic Ridge. To the contrary, simple order of magnitude estimates suggest that it is just as likely that the flows are dominated by bottom-induced vertical velocities as they are directly driven by the wind stress curl.