Vertical mixing in the bottom mixed layer near the continental shelf break in the East China Sea

The strength of the vertical mixing in the bottom mixed layer near the continental shelf break in the East China Sea was directly measured with the Micro-Scale Profiler (MSP). It has been shown that there is no significant statistical relation between the turbulent energy dissipation ε and the degree of the stratification N². It seems that the vigorous turbulence occurs not constantly but intermittently in the bottom mixed layer so that a large variation of ε is found depending on the time. In contrast to ε, the coefficient of the vertical eddy diffusivity K_z is mostly determined by N such that K_z is large in the bottom mixed layer and small in the thermocline. Large value of K_z in the bottom mixed layer is also found in the time series of K_z estimated in terms of Richardson number calculated from the data obtained with electromagnetic current meters. The value of K_z more than 10 cm²s^-1 frequently occur in the layer of 20-25 m thick just above the bottom.