Deep intense vertical mixing in the Bussol' Strait

Abstract

To reveal the intensity of deep mixing in the Bussol' Strait, we performed the direct observations of turbulence for the first time. Vigorous vertical mixing with a turbulent energy dissipation rate ε above 10 −6 W/kg and diapycnal diffusivity K ρ above 10 3 cm 2 /s were observed at depths of 600–1300 m (potential densities of 27.0–27.5 σ θ ) at the western gap of the Bussol' Strait, possibly affecting water‐mass transformation and thermohaline circulation. The strong vertical mixing with a diurnal period occurred when the diurnal tidal current flowed toward the Okhotsk Sea, corresponding to a period of enhanced shear consisting of the mean flow with a two‐layered structure and the large‐amplitude diurnal tidal current with a vertical structure explained by a low‐vertical mode topographically trapped wave. The empirical relationship of ε = 10 −1.46±1.91 × S 2.16±0.72 is obtained between ε and the shear S reconstructed from the 50‐m‐scale mean, diurnal, and semi‐diurnal tidal currents.