Vertical heat transport in eddying ocean models

The effect of mesoscale eddies on the vertical heat transport of the ocean is examined using two eddy-resolving numerical models. The global heat transport by the mean flow and diffusion are both downwards and are balanced by an upward eddy heat flux. Mean and eddy advective heat fluxes dominate the subpolar regions, while diffusive flux is important primarily in the subtropics. In the subtropical abyss, the mean advective heat flux is balanced by a combination of eddy and diffusive fluxes and the classical Munk-type advective-diffusive heat balance must be modified. The Munk and Wunsch (1998) expression for the vertical turbulent diffusivity over-estimates the diffusivity by as much as a factor of four near the base of the main thermocline. This implies that the mixing required to close the meridional overturning circulation determined by Munk and Wunsch (1998) may be an over-estimate due to the neglect of mesoscale eddies.