Air-sea PV flux: observations and implications for the dynamics of the Atlantic overturning

In the Northern Hemisphere, both surface cooling and mechanical forcing by the wind tend to remove potential vorticity (PV) from dense isopycnal layers. In the Southern Hemisphere, however, mechanical (westerlies) and buoyancy forcing (heating) have opposite effects on surface PV fluxes for that same class of isopycnals. By estimating the various components of the air-sea PV flux from observed surface climatologies, we discuss quantitatively the PV budget of these dense isopycnals involved in the Atlantic overturning cell.