The Global Overturning Circulation

In this article, I use the Estimating the Circulation and Climate of the Ocean version 4 (ECCO4) reanalysis to estimate the residual meridional overturning circulation, zonally averaged, over the separate Atlantic and Indo-Pacific sectors. The abyssal component of this estimate differs quantitatively from previously published estimates that use comparable observations, indicating that this component is still undersampled. I also review recent conceptual models of the oceanic meridional overturning circulation and of the mid-depth and abyssal stratification. These theories show that dynamics in the Antarctic circumpolar region are essential in determining the deep and abyssal stratification. In addition, they show that a mid-depth cell consistent with observational estimates is powered by the wind stress in the Antarctic circumpolar region, while the abyssal cell relies on interior diapycnal mixing, which is bottom intensified.