Tidally Driven Mixing “Hot Spot” at the Entrance of the Japan/East Sea

Abstract

Mixing at the southwestern boundary of the Ulleung Basin (UB) in the Japan/East Sea was examined using combined ship‐based, moored, and quasi‐autonomous observations. These observations revealed strong tidal currents, high‐frequency internal wave packets, and energetic turbulence over the sill connecting the Korea/Tsushima Strait and the UB, especially when a supercritical flow becomes subcritical over the sill. In addition, strong velocity shear associated with the semidiurnal baroclinic tide was found near the bottom, where the bathymetry slope was critical to the semidiurnal tide. Large temperature fluctuations were observed during the subcritical phase of the flow, as hydraulically controlled flow generated internal‐wave packets and energetic turbulence with a turbulent‐kinetic‐energy dissipation rate of ∼ $\sim $10−4 Wkg−1, and a diapycnal diffusivity of ∼ $\sim $10−2 m2s−1. Our analysis suggests that the sill is a hot spot of mixing, which in turn can play an important role in the Japan/East Sea circulation.

Shear-driven vertical mixing and turbulent exchange over the continental slope in the northwestern Sea of Japan

“…The intense turbulence patches under the mixed layer and the high vertical gradients of temperature and salinity often lead to the spots with enhanced vertical heat and salt exchanges. The increased vertical heat exchange was as large as 10 4 W m −2 with a 3-day averaged flux of about 300 W m −2 on the southwestern boundary of the Ulleung Basin in the Sea (Wijesekera et al, 2022), where vertical mixing was studied using combined ship-based, moored, and quasi-autonomous observations. Notice that Wijesekera et al (2022) highlighted the enhanced vertical mixing below the mixed layer.…”