Summertime primary production in northwest South China Sea: Interaction of coastal eddy, upwelling and biological processes

The Northwest South China Sea (NWSCS) ecosystem is controlled by multiple physical processes in summer including the monsoon wind induced coastal upwelling, the cyclonic eddy off the eastern Leizhou Peninsular (ELP), and the Yuexi Coastal Current (YCC). Based on the high-resolution in situ and remote sensing data, this study examined in details the spatial patterns of phytoplankton biomass and primary production in the coast of NWSCS in summer and discussed the underline physical processes involved. The results suggested that the southwesterly monsoon wind induced coastal upwelling is the major mechanism for the relatively high phytoplankton biomass and primary production found in the coastal area. However, the waters off the ELP have relatively higher phytoplankton biomass than that off the eastern Hainan Island (EHI). This is probably due to the topography- and eddy-driven enhancement of nutrient supply and light availability along the ELP. A small but distinguishably high biomass/productivity area was found at the east side of the Qiongzhou Strait. This eddy-shaped feature appears to be separated from the larger high productivity area near the Qiongzhou Strait, and is likely caused by the interaction of multiple dynamical processes including coastal upwelling, topographically-induced double eddy circulation, the YCC and associated large-scale cold eddy, and possibly the tidal mixing in this area. The YCC tends to inhibit phytoplankton growth and thus depresses the surface phytoplankton biomass in the near-shore waters of the ELP, mainly through the stratification-induced nutrient limitation (primarily phosphorous limitation). Overall, the interaction of physical processes between wind-induced upwelling, coastal current and tidal-shoaling mixing as well as eddy upwelling are key drivers regulating the horizontal and vertical distribution of phytoplankton biomass and productivity in the NWSCS. (C) 2012 Elsevier Ltd. All rights reserved.