Why western boundary currents in realistic oceans are inviscid : A link between form stress and bottom pressure torques

It is shown that wind stress curl is balanced by bottom pressure torque in a zonal integral over any strip wide enought o smooth out the effect of nonlinear terms (typically about 3degrees of latitude). The derivation is completely general as long as the zonal wind stress is balanced by form stress at each latitude, as is known to be the case in the ocean.