Tides and Turbulent Mixing in the North of Taiwan Island

Abstract

Microstructure and hydrological profiles were collected along two cross-shelf sections from the deep slope to the shallow water in the north of Taiwan Island in the summer of 2006. While the tidal currents on the shelf were dominated by the barotropic tide with the current ellipse stretched across the shelf, significant internal tides were observed on the slope. The depth-mean turbulent kinetic energy (TKE) dissipation rate on the shelf was 10−6 W kg−1, corresponding to a diapycnal diffusivity of 10−2 m2 s−1. The depth-mean TKE dissipation rate on the slope was 1×10−7 Wkg−1, with diapycnal diffusivity of 3.4×10−4 m2 s−1. The shear instability associated with internal tides largely contributed to the TKE dissipation rate on the slope from the surface to 150 m, while the enhanced turbulence on the shelf was dominated by tidal or residual current dissipations caused by friction in the thick bottom boundary layer (BBL). In the BBL, the Ekman currents associated with the northeastward Taiwan Warm Current were identified, showing a near-bottom velocity spiral, which agreed well with the analytical bottom Ekman solution.