Abstract: Using the MODIS remote sensing data from Jan. 2003 to Dec. 2019, and combining with the data of sea surface temperature(SST) and wind speed(WS), the chlorophyll concentrations distribution in the mid-western South China Sea and their controlling factors were discussed. The results showed the seasonal variations of the spatio-temporal distribution of chlorophyll concentration in the study area. EOF decomposition indicated that EOF1 probably reflected the impact of extreme weather such as typhoons on the concentration of chlorophyll, while EOF2 and EOF3 reflected influence of the coastal upwelling. The correlation analysis showed that the concentration of chlorophyll had good positive correlation with the WS (r=0.87, p<0.01), and negative correlation with SST (r=-0.59, p<0.05). In summer, the upwelling current formed along the southeastern coast of Vietnam under the influence of southwest monsoon, and it resulted in flourishing of phytoplankton and increase of chlorophyll concentration. In winter, the mixing of upper ocean layer became strong and the nutrient supply increased under the influence of strong northeast monsoon. It promoted the growth of phytoplankton and resulted in higher chlorophyll concentration than that in other seasons.

Key words: chlorophyll, mid-western South China Sea, EOF decomposition, sea surface temperature, sea surface wind field