Evidence of enhanced double‐diffusive convection below the main stream of the Kuroshio Extension

Abstract

AbstractIn this study, a Navis‐MicroRider microstructure float and an EM‐APEX float were deployed along the Kuroshio Extension Front. The observations deeper than 150 m reveal widespread interleaving thermohaline structures for at least 900 km along the front, presumably generated through mesoscale stirring and near‐inertial oscillations. In these interleaving structures, microscale thermal dissipation rates χ are very high ( K2s−1), while turbulent kinetic energy dissipation rates ϵ are relatively low ( Wkg−1), with effective thermal diffusivity of ( m2s−1) consistent with the previous parameterizations for double‐diffusion, and, is two orders of magnitude larger than the turbulent eddy diffusivity for density . The average observed dissipation ratio Γ in salt finger and diffusive convection favorable conditions are 1.2 and 4.0, respectively, and are larger than that for turbulence. Our results suggest that mesoscale subduction/obduction and near‐inertial motions could catalyze double‐diffusive favorable conditions, and thereby enhancing the diapycnal tracer fluxes below the Kuroshio Extension Front.