Isopycnal diffusivities from floats in the DIMES experiment

The Meridional Overturning Circulation (MOC) of the ocean is a critical regulator of the Earth's climate processes. Climate models have been shown to be highly sensitive to the representation of lateral eddy mixing in the southern limb of the MOC, within the Antarctic Circumpolar Current latitudes, although the lack of extensive in situ observations of Southern Ocean mixing processes has made evaluation of mixing somewhat difficult. We will present new in-situ estimates of lateral mixing across the Antarctic Circumpolar Current in the sector upstream of Drake Passage. Close to one hundred isopycnal floats were deployed along an isopycnal at 1300m depth as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean. The two year long trajectories are analyzed to quantify the cross-current lateral eddy diffusivity. The eddy diffusivity is estimated to be close to 700m^2/s with an rms error of 200 m^2/s. These values are smaller than previous estimates, because we had sufficient statistics to capture the suppression of mixing by the Antarctic Circumpolar Current. The implications of our results for climate models will be discussed.