Measurements of the turbulent energy dissipation rate around the shelf break in the East China Sea

Using the micro-structure profiler, TurboMAP, large values for the turbulent energy dissipation rate epsilon were found just above the bottom of the shelf and around the thermocline near the continental shelf break in the East China Sea. The values found above the bottom are produced by the bottom stress due to tidal currents, resulting in a distinct bottom mixed layer where the vertical eddy diffusivity Kz is also large. Distinct maxima in the values of epsilon detected around the thermocline are located at the depth of the fine-scale shear maxima detected with the moored ADCP. The vertical profiles of epsilon were compared with those of the current velocity, and it was found that the maxima in epsilon appear to correspond to those of the shear with fine scale. The magnitude of the observed a coincided approximately with the epsilon calculated from the fine-scale shear and the buoyancy frequency according to the parameterization proposed by Gregg (1989), if the large-scale mean shear caused by the Kuroshio is subtracted. However, it is not clear whether the parameterization for the internal wave fields in the open ocean is applicable to the estimation of epsilon in the shelf break. Whereas the most predominant value of epsilon was found just above the bottom and around the thermocline, the maxima of epsilon could be found in the internal area. They could have been caused by the propagation of the vertically high wave number internal tides along the characteristic ray.