Impact of physical processes on the phytoplankton blooms in the South China Sea: an eddy-resolving physical-biological model study

Abstract. An eddy-resolving coupled physical-biological ocean model has been employed to investigate the physical influences on phytoplankton blooms in the South China Sea during 2000–2007. The model captures the seasonal and interannual variability of surface chlorophyll distribution associated with mesoscale eddies, ocean circulation and upwelling generated by the monsoon winds. The model also reproduces the high chlorophyll distributions in two coastal upwelling regions: the northwestern Luzon in winter and the eastern coast of Vietnam in summer. To the northwest of Luzon, the monsoon driven-upwelling, anticyclonic eddies, and the intrusion of the Kuroshio have a large impact on the winter phytoplankton bloom. The model shows the winter phytoplankton bloom is induced by the shallow nutricline depth under the northeast monsoon. Strong vertical motions at the edge of anticyclonic eddies enhance the phytoplankton bloom and produce the filamentary structure. Off the eastern coast of Vietnam, the monsoon-driven upwelling and anticyclonic circulation control the high chlorophyll distribution in summer. During the southwest monsoon, strong offshore Ekman transport and upwelling occur and increase the surface chlorophyll. The high chlorophyll is advected from the coast to open ocean by the strong offshore circulation.