Mixing in the Southern Ocean

Southern Ocean mixing helps to establish properties of the global ocean both by blending waters from the northern basins and through local water-mass formation. Air-sea fluxes of heat, momentum, freshwater, and gas are responsible for mixing and transformation of water properties at the ocean surface. Transient storms and submesoscale motions influence the timing and magnitude of upper-ocean mixing and exchange with the interior. In the Southern Ocean, along-isopycnal stirring by eddies connects the ocean surface with the mid-depth to deep interior. Interior mixing is largely adiabatic, but spatially heterogeneous in both vertical and horizontal directions, with eddy diffusivities estimated to vary by a factor of four or more, from roughly 700 to 2800 m2 s−1. Regions of strong stirring and strain are concentrated above and downstream of major bathymetric features. Small-scale turbulent mixing in the ocean interior is driven by internal waves, generated through flow–topography interactions, and turbulent mixing is enhanced in the bottom boundary layer. The marginal ice zones around Antarctica and processes on the Antarctic shelf are mixing regimes unique to the Southern Ocean that remain frontiers of current research.