Remote Sensing Of Ocean Color For Seasonal Variation Of Phytoplankton Community Structure In The South China Sea

The phytoplankton plays an important role in the ocean biogeochemical cycles as the main primary producers in marine ecosystems. The oceanic carbon cycle is partly controlled by phytoplankton community composition. The two inversion algorithms were used in this paper to retrieve the data about the seasonal distributions of the dominant phytoplankton groups and the size-fractionized phytoplankton in the South China Sea (SCS) by using the remote sensing data with high spatial and temporal resolution.Based on the strong spectral dependence on the major dominant phytoplankton function types, the data of nanoeucaryotes, Prochlorococcus, Synechococcus and diatoms were inversed from the satellites ocean color data using the PHYSAT algorithm. The technique is run on the 13-year NASA Sea viewing Wide Field of view Sensor (SeaWiFS) data series in the South China Sea. The results show that nanoeucaryote is the dominant species in the South China Sea all year long, and Prochlorococcus, Synechococcus, diatoms in turn. Nanoeucaryotes, Prochlorococcus and Synechococcus contributions exhibit a stronger seasonal variability. In winter, large blooms of nanoeucaryotes occur. The contribution of Nanoeucaryotes-dominated waters to the biomass in the South China Sea is 88%, and Prochlorococcus 10% and Synechococcus 1% respectively. In contrast to winter, spring large blooms of Prochlorococcus occur. The contribution of Nanoeucaryotes-dominated waters to the biomass in the South China Sea is 40%, Prochlorococcus 50% and Synechococcus 13%. The differences between summer and autumn are small. Synechococcus seasonal distribution is bimodal, with peaks occurring in spring(13%) and autumn(14%). Diatoms is mostly observed in northern coast waters. Diatoms seems to be more abundant in autumn(3%) than that in the other seasons(from 1 to 2%).The seasonal distributions of three size-fractionized phytoplanktons, that is, Micro, Nano and Pico in the SCS were inversed from the 10 years average MODIS chlorophyll data using the Uitz algorithm. The results show that the seasonal variations in the relative contribution of each of the three size classes are great. The contribution of the Picoplankton to the chlorophyll concentration is maximum in the South China Sea. The relative abundance of Nanoplankton is much greater than that of Microplankton. In winter, the contribution of Picoplankton(25-50%) to biomass firstly increased and then decreased from north to south. In contrast to Picoplankton, Nanoplankton(40 ～ 50%) and Microplankton(10-30%) are decreased. In spring, phytoplankton behave differently, and appear to be ubiquitous with a rather stable contribution everywhere, Picoplankton (40-45%)>Nanoplankton (15-20%)>Microplankton (10-15%). In summer, due to the influence of a jet leaving the coast of Vietnam, the proportion of Nanoplankton and Microplankton are increased than elsewhere in the northeast of Vietnam and Picoplankton is decreased. Nanoplankton is the dominant group. Except this area, Pico(45～ 50%)>Nano(40-45%)>Micro(10-15%). The distribution in autumn is similar to that in winter, but the relative abundance in the east is larger than that in the west of South China Sea.