CHEMICAL HYDROGRAPHY AND CHLOROPHYLL-A DISTRIBUTION IN THE EAST-CHINA-SEA IN SUMMER - IMPLICATIONS IN NUTRIENT DYNAMICS

A survey of the chemical hydrography and Chi a distribution in the mid dle and outer shelves of the East China Sea was carried out in July 19 92. Very high standing stock of Chi a (30-110 mg m(-2)) and supersatur ation of oxygen (up to 130%) were observed in the plume of the Changji ang Diluted Water, which was enriched in nitrate and silicate but depl eted in phosphate. Beneath the plume, a strong depletion in oxygen and an accompanied enrichment in nitrate as well as phosphate were eviden t. The rich phosphate in the subsurface water may have been crucial in supporting the rapid phytoplankton growth in the overlying water. The Taiwan Current Warm Water (TCWW) occupied most of the shelf to the so uth and to the east of the plume. The negative relationships between n itrate and temperature suggest that the nutrient-laden Kuroshio Subsur face Water from the slope was the main source of nutrients for the TCW W. The input of the slope water to the shelf was probably facilitated by countercurrents associated with the Kuroshio upwelling northeast of Taiwan and the mesoscale eddy at the shelf-break east of the Changjia ng river mouth. Yet another source of nutrients for the TCWW was revea led by the positive deviations from the mixing trend. These nutrients that may have originated from local remineralization accounted for up to 30% of the total nutrients in the bottom water on the middle shelf. Compared with the Changjiang river plume, the TCWW was relatively poo r in Chi a, except in the upwelling region off northern Taiwan where v ertical mixing was strong. The nutrients in the subsurface layer of th e TCWW further away from Taiwan were generally not available for phyto plankton uptake in the euphotic zone in summer. However, the reserved nutrients could have supported a phytoplankton bloom subsequent to str ong vertical mixing. Copyright (C) 1996 Elsevier Science Ltd.