Diapycnal Mixing and Double Diffusion over the Continental Slope in the Northern Sea of Japan in the Warm Half-Year

Abstract

This study investigates double diffusion processes responsible for diapycnal mixing in the Primorye current in the northern Sea of Japan. The results of processing and analysis of a long time series of data from regular Aqualog-profiler measurements of thermohaline characteristics and current velocity over the continental slope between the horizons of 60 and 420 m from April to October 2015. Using the Osborne-Cox parameterization (1972) and Gregg’s (1989) parameterization, we estimated heat and salt diffusivities, as well as the buoyancy flux. To reveal the processes of double diffusion, the Turner angle was estimated. We estimated contributions of diffusive convection and salt fingers into the buoyancy flux. Due to double diffusion, the intense vertical mixing covered the layer from 80 to 170 m. From mid-spring to early May, diffusive convection penetrated to a horizon of 250 m, and then a process like salt fingers played a leading role. Shear instability caused by the weakly nonlinear interaction of internal waves prevailed in the underlying layers.