Eddy Stirring and Horizontal Diffusivity from Argo Floats: Global Patterns and Suppression by Strong Currents

Isopycnal stirring by mesoscale eddies is an important factor in determining the transport and distribution of tracers within the ocean. Salinity anomalies on isopycnal surfaces from Argo profiling floats are used to estimate isopycnal salinity variance and eddy mixing lengths. These eddy mixing lengths, along with eddy kinetic energy from the ECCO2 global state estimate, are used to estimate isopycnal diffusivity on 100 km scales in the upper 2000 m of the ocean with near-global coverage.

We will focus on the geographic patterns of isopycnal diffusivity, including horizontal and depth variability. The estimated diffusivity varies by over two orders of magnitude with location and depth. As expected, diffusivities are generally elevated in regions of strong mesoscale activity, including western boundary current (WBC) extensions, the equatorial region, and the Antarctic Circumpolar Current (ACC). In the ACC and WBC extensions, the maximum diffusivity often occurs at depths greater than 500 m. This suggests that strong currents may act to suppress eddy stirring in these regions. However, the apparent lack of suppression by strong currents near the equator suggests that existing theories for suppression of eddy diffusivity are incomplete. The diffusivity estimates presented here can be used to evaluate future diffusivity parameterizations used in numerical models.