Measurements of the turbulent energy dissipation rate ε and an evaluation of the dispersion process of the Changjiang Diluted Water in the East China Sea

[ 1] The large amount of fresh water discharged from Changjiang spreads over the East China Sea continental shelf as low salinity water, particularly in the summer season. To understand the primary production in the East China Sea, it is necessary to clarify the dispersion process of the Changjiang Diluted Water (CDW), since the high production area appears to cover the CDW. In this study, the dispersion process of the CDW was evaluated through the estimation of the turbulent energy dissipation rate epsilon in the CDW and calculation of the divergence in the CDW using satellite-tracked drifters. A large value of e was observed just above the bottom and in the surface layer, whose magnitude was sometimes greater than 10(-7) W kg(-1). On the other hand, a small value of epsilon, less than 10(-8) W kg(-1), was found just beneath the CDW. The small value of epsilon leads to a small value of the vertical eddy diffusivity of less than 10(-5) m(2) s(-1). The vertical advection of the bottom water is likely to be a major process for increasing the salinity, since the horizontal diffusion would not play a significant role if the usual magnitude of the horizontal diffusivity is assumed. Calculation of divergence in the surface layer, using the drifters' data, also suggests that upward velocity of O(10(-5)) m s(-1) over the CDW area is expected. The vertical transport from the bottom layer could increase the salinity of the CDW, and also carry the nutrients into the euphotic zone resulting in biological production.