Observed and Simulated Lateral Eddy Diffusivity Upstream of the Drake Passage

Estimates of lateral eddy diffusivity in the Southern Ocean are poorly constrained due to lack of observations. We present the first direct estimate of isopycnal eddy diffusivity upstream of the Drake Passage. The estimate is computed from a point tracer release as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). The DIMES dataset is extrapolated using a data-constrained, 1/20th of a degree simulation of the Drake Passage region. We estimate a diffusivity of about 700m^2/s at 1500m depth upstream of the Drake Passage, consistent with an independent estimate based on float trajectories in the same region. The model is then used to discuss the vertical variations of the eddy diffusivity, which is suppressed at the surface and enhanced at deep steering levels.