[1] Pattern and origins of Kuroshio branches in the bottom water of southern East China Sea (ECS), were carefully examined by numerical simulations based on the Regional Ocean Modeling System (ROMS) together with observations. Model results show that in the bottom water of ECS, the intrusion pattern of Kuroshio is mainly composed of an Offshore Kuroshio Branch Current (OKBC) which, bifurcated from the Kuroshio northeast of Taiwan, flows nearly along the isobath of $100 m, and a Nearshore Kuroshio Branch Current (NKBC) which, originated from the Kuroshio northeast of Taiwan, upwells northwestward gradually from $250 m to $60 m, then turns to northeast around 27.5°N, 122°E, thereafter flows northeastward along the isobath of $60 m, and finally reaches at 30.5°N where it turns to east. Furthermore, we found that the NKBC mostly originated in the Kuroshio subsurface water (120-250 m) east of Taiwan, whereas the OKBC mainly stemmed from the Kuroshio water (60-120 m) east of Taiwan. This pattern and origins of OKBC and NKBC well addressed the observational phenomena that off the coast of Zhejiang province, China, there were colder, less saline, and more phosphate-rich bottom water near the isobath of $60 m rather than near the isobath of $100 m in August 2009. Finally, it is proposed that on southern ECS continental shelf, Kuroshio exhibits its intrusion branches by an anticyclonical stair structure: bottom stair NKBC, middle stair OKBC, and top stair Kuroshio surface branch (KBC).

[1] Using the Regional Ocean Model System, the ocean circulation on the East China Sea (ECS) shelf was examined by a fine-resolution model which was nested in a coarseresolution Pacific Ocean model. The high-resolution simulation shows an accurate volume transport of 2.70 Sv (Sv ≡ 10 6 m 3 s −1 ) through the Tsushima Strait, which is more consistent with the previous 5.5 year observation value (2.64 Sv) than former model results. For the Taiwan Strait it also shows a close volume transport (1.03 Sv) to a recent estimate (1.20 Sv). At the same time the model results reproduced almost all of the known circulation structure on the ECS shelf. In addition, the hindcast of 2009 shows a Kuroshio Bottom Branch Current to the northeast of Taiwan (KBBCNT). The KBBCNT is confirmed by the observational bottom high-salinity water (from 15 August to 2 September 2009) whose distribution is also reproduced by the model results. Tracer and particle experiments were carried out to elucidate the formation of the high-salinity water and the pathway of the KBBCNT. In light of the field observation and numerical experiments, a new pathway of the KBBCNT is proposed: bifurcated from the subsurface water of Kuroshio northeast of Taiwan, it upwells northwestward gradually from 300 to 60 m, then turns to northeast in the region around 27.5°N, 122°E, and finally reaches 31°N off the mouth of the Changjiang River along ∼60 m isobaths, forming the bottom saline water off the coast of Zhejiang province, China.

To better understand seasonal variation in phytoplankton community structure in the East China Sea (ECS), 4 research cruises were carried out between August 2009 and June 2011 over the continental shelf. Phytoplankton community structure and ambient seawater physicochemical parameters were examined. The phytoplankton community in the ECS was mainly composed of diatoms and dinoflagellates, with 242 taxa in 70 genera of diatoms and 104 taxa in 26 genera of dinoflagellates. Several species of Chlorophyta, Chrysophyta, and Cyanophyta were also observed. Chain-forming diatoms were the most dominant phytoplankton group throughout the year, except in spring when dinoflagellates dominated in coastal waters. Monsoon-induced turbulence played a significant role in regulating the dominance of dinoflagellates among seasons, with calm water favoring the growth of dinoflagellates and turbulent water inhibiting them. Phytoplankton abundance was always higher in coastal than offshore waters, mainly determined by nutrient availability. A Prorocentrum dentatum bloom and a Chaetoceros debilis bloom were observed in the Yangtze River estuary in spring 2011 and fall 2010, respectively. The blooms differed greatly in community diversity and cell abundance distribution, potentially affecting organic carbon export. In general, 3 different hydrographic water systems (coastal water, shelf mixed water, and Kuroshio water) were identified from a temperature−salinity plot of the ECS, and phytoplankton abundance showed spatially and temporally different distribution patterns in these 3 water systems. The nutrient N:P ratio, but not the Si:N ratio, played a significant role in regulating the phytoplankton community structure and the formation of the spring coastal dinoflagellate bloom in the ECS.