Abstract

Quantifying the mixing and stirring caused by meso-scale eddies in the Southern Ocean remains an open problem in physical oceanography. Meso-scale eddies are of first-order importance to the meridional overturning circulation and to the transport of tracers such as heat, salt and CO2 . One of the obstacles to further understanding is the lack of observations of this region. Here I will present work from my PhD thesis which used a combination of satellite and in situ observations to diagnose two different eddy mixing measures.

The first is an effective diffusivity, derived for the whole Southern Ocean, using geostrophic surface velocities from satellite altimetry to advect a tracer in the offline MITgcm. We find that, as previously observed, there is a minimum in mixing in the core of the ACC . This is thought to be due to eddy – mean flow interactions, and we investigate alternate mixing parametrisations that try to account for this effect.

The second measure comes from comparing simulations of the DIMES tracer release with measurements taken on the DIMES cruises. Using a technique to assess the ‘roughness’ of a set of tracer values, we compare various simulations and assess the most appropriate diffusivity to match the observations. This leads to an estimate of the mixing experienced by the tracer, and shows an increasing diffusivity through the Drake Passage compared with upstream.