[A-OS21] Coastal ocean circulation and material cycle

[AOS21-03] Enhanced vertical mixing and turbulent exchange by mesoscale eddies over the continental slope in the northwestern Sea of Japan

*Dmitry Stepanov¹, Yusuke Kawaguchi², Nadya Sachneva¹, Evgeniya Korshenko³ (1.Pacific Oceanological Institute, Far Eastern Branch, Russian Academy of Sciences, 2.The University of Tokyo, 3.N.N. Zubov State Oceanographic Institute)

Keywords:vertical mixing, Japan Sea, Thorpe scale, mesoscale eddy, fine-scale parameterization, sub-mesoscale activity

Vertical mixing is a leading mechanism for penetration of various scalars across isopycnals. Mesoscale eddies can modulate vertical mixing and diapycnal fluxes. Using the fine-structure measurements carried out using the Aqualog profiler moored over the continental slope in the northwestern Sea of Japan, the events of mesoscale eddies moving across the moored station were analyzed from April-October 2015. The fine-scale parameterization and Thorpe-scale method were used to quantify vertical mixing and diapycnal transfer of heat and salt near the flanks of moving mesoscale eddies. The enhanced diapycnal diffusivity was observed below the upper mixed layer, when the mesoscale eddy moved across the moored station. The diapycnal diffusivity sharply uplifted up to 0.001 m^2/s on the rear side of eddy’s periphery. In addition, the enhanced vertical mixing was observed near the bottom of the eddy’s core. The heat absorption of the intermediate layer was enhanced when mesoscale eddies moved across the moored station and vertical heat fluxes exceed the value of 1 W/m^2. In contrast, the salinity of the intermediate layer decreased when the mesoscale eddies moved across the moored station. Both double diffusion and shear instability can be responsible for the enhanced vertical mixing. Moreover, the submesoscale dynamics induced by the instability of the vorticity front near the flanks of the mesoscale eddy can enhance the vertical mixing below the upper mixed layer.