From the Southern Ocean to the North Atlantic in the Ekman Layer?

JANUARY 2004 AMERICAN METEOROLOGICAL SOCIETY | T he idea that the southern winds might be important to the rate of the deep water formation in the North Atlantic was first put forward by Toggweiler and Samuels (1995). They analyzed the results of a global circulation model (GCM) and showed that the rate of North Atlantic Deep Water (NADW) formation increased when the strength of the southern winds was increased. Since a zonal integration of the geostrophic pressure associated with the interior (i.e., the domain below the top Ekman layer and above bottom topography) over the Southern Ocean vanishes, and since there can be no local transformation of Ekman water to deep water, they concluded that the transformation must take place in the North Atlantic via the NADW. In this scenario, the Ekman flux in the Southern Ocean must somehow find its way to the Northern Hemisphere where, through cooling, it sinks to the bottom. We shall show here that, although the mass flux of water crossing the equator is indeed equal to the Ekman flux in the Southern Ocean, the crossing waters do not originate in the southern Ekman layer but rather in the southern Sverdrup interior.