The nonlinear nature of barotropic currents in oceans

The structure of the barotropic component of oceanic currents is discussed. First, we present observational evidence against the absence of the vertical shear of horizontal velocity in barotropic flows . We then discuss the Taylor-Proudman theorem, which we base our presumption on. We show that this theorem crudely neglects nonlinear terms of fluid motion equations either through geostrophic approximation or directly through a scale analysis of the vorticity transport equation. However, these terms serve as a mechanism allowing for the vertical shear of horizontal velocity.