The global overturning circulation and the importance of non-equilibrium
effects in ECCOv4r4
Abstract
We quantify the volume transport and watermass transformation rates of
the global ocean circulation using the Estimating the Circulation and
Climate of the Ocean version 4 release 4 (ECCOv4r4) reanalysis product.
Our results support large rates of intercell exchange between the
mid-depth and abyssal cells, in agreement with modern theory and
observations. However, the present-day circulation in ECCO cannot be
interpreted as a near-equilibrium solution. A dominant portion of the
apparent diapycnal transport of watermasses within the deep ocean is not
associated with irreversible watermass transformation. Instead up- and
down-welling is associated with isopycnal volume changes, reflecting
trends in the deep ocean density structure. Our results reveal
disagreement between ECCO’s representation of the overturning
circulation and associated watermass transformations, and prevailing
equilibrium theories of the overturning circulation.