Thickness diffusivity in the Southern Ocean

Thickness diffusivity (κ) according to the Gent and McWilliams parameterisation which accounts for eddy‐driven advection in the ocean, is estimated using output from an eddy‐resolving model of the Southern Ocean. A physically meaningful definition of rotational eddy fluxes leads almost everywhere to positive κ. Zonally averaged near surface values of κ remain smaller than 200 m2/s poleward of the polar front, increases between 60–45°S to about 600 m2/s and peak between 45–35° S at almost 3000 m2/s. κ stays high in the upper 500 m but decreases with depth and is essentially zero below 2500 m. In addition to the thickness diffusion (κ) there is eddy‐induced eastward (westward) advection of isopycnal thickness at the poleward (equatorward) flank of the ACC pointing toward strong anisotropic lateral mixing.