Thickness diffusivity in the Southern Ocean

Thickness diffusivity (kappa) 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 k. Zonally averaged near surface values of kappa remain smaller than 200 m(2)/s poleward of the polar front, increases between 60 - 45 degrees S to about 600 m(2)/s and peak between 45 - 35 degrees S at almost 3000 m(2)/ s. kappa stays high in the upper 500 m but decreases with depth and is essentially zero below 2500 m. In addition to the thickness diffusion (kappa) there is eddy-induced eastward ( westward) advection of isopycnal thickness at the poleward (equatorward) flank of the ACC pointing toward strong anisotropic lateral mixing.