Study on the Turbulent Mixing and Horizontal Transport of Shelf Water around the Continental Shelf Break

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Intensive observations around the continental shelf break in the East China Sea were carried out from 26 to 28 May, 1997, from 6 to 12 November, 1997, from 10 to 13 and from 22 to 26 May, 1998 and from 7 to 13 November, 1998. Vertical profiles of temperature, salinity and turbidity were obtained along a cross-shelf section near the continental shelf break. Time series of current velocity, temperature and turbidity were also obtained with moored instruments. Moreover, turbulent energy dissipation rate and vertical shear of current velocity were determined with Micro-Scale Profiler and Fine- and Micro- Scale Profiler. And dye experiments were carried out to evaluate vertical diffusion.Vertical profiles of turbidity show intrusion of relatively high turbid water from the bottom layer on the shelf into the intermediate layer of the Kuroshio. This offshore transport of the shelf water could be generated with ageostrophic component induced by vertical mixing around the shelf break. The results obtained in May, 1997 suggested that change of density structure around the thermocline could form offshore ageostrophic flow. Furthermore, direct measurement of velocity profile with FMSP in November, 1997 indicated offshore flow just around the thermocline and high turbid layer.Time series obtained with moored array in May, 1998 show frequent occurrence of short time scale internal waves, particularly those observed on May 12 would result in a change of stratification.Dye experiments carried out in November, 1997 and May, 1998 could catch some dye patches around the introduced layer, however, it was quite difficult to estimate an intensity of vertical diffusion because we were not able to catch whole shape of dye patches.