Mixing processes at the southwestern entrance to the Japan/East Sea

Abstract

Abstract Small-scale processes at the southwestern boundary of the Ulleung Basin (UB) in the Japan/East Sea (JES) were examined using combined ship-based and moored observations along with model output. Model results show baroclinic semidiurnal tides are generated at the shelf break and corresponding slope connecting the Korea/Tsushima Strait with the UB, and propagate into the UB with large barotropic to baroclinic energy conversion over the slope. Observations show high-frequency internal-wave packets and indicate strong velocity shear and energetic turbulence associated with baroclinic tides in the stratified bottom-layer. Solitary-like waves with frequencies 0.2 N to 0.5 N (buoyancy frequency, N ) were found at the edge of the shelf break with supercritical flow. For subcritical flow, a hydraulic jump formed over the shelf break with weakly-dispersive internal lee waves with frequencies varying from 0.5 N to N . These high-frequency lee waves were trapped in the stratified bottom-layer, with wave stress similar to the turbulent stress near the bottom. The power loss due to turbulent bottom drag can be an important factor for energy loss associated with the hydraulic jump. Turbulent-kinetic-energy dissipation rates of ~10 −4 W kg −1 were found. Large downward heat and salt fluxes below the high-salinity core mix warm/salty Tsushima Current Water with cold/low-salinity JES intermediate water. Mixing over the shelf break could be very important to the JES circulation since the calculated diapycnal upwelling (1-6 m d −1 ) at the shelf break and slope is substantially greater than the basin-averaged estimate from chemical tracers and modeling studies.