Seasonal variation of chlorophyll a in the South China Sea from 1997-2010

This study aims to document the seasonal cycle of chlorophyll a interannual variability and to determine the dynamic framework for understanding the mechanisms that produce it. We investigated the variation in sea surface chlorophyll a concentration from autumn 1997 to summer 2010 in the South China Sea using the Sea-Viewing Wide Field-of-View Sensor products. Using the Season-Reliant Empirical Orthogonal Function method, we revealed the interannual and seasonal variations and their dependency on climate variability. The time coefficient of the first mode shows a sudden drop in 2007. Corresponding season-reliant empirical orthogonal function (spatial pattern) is the largest in the southern centre in the autumn, which can be explained by a large increase in chlorophyll a concentration during which Typhoon Hagibis passed through. The second mode reflected an anomalous event of low phytoplankton biomass in the western center of the sea during the summer of 1998 and 2010 due to an El Nino event. Time coefficient is negatively related with the Multivariate El Nino-Southern Oscillation Index. The third mode revealed an interannual variability of chlorophyll a in the region to the northwest of Luzon Islands, which appeared from autumn to the next spring. To better understand the chlorophyll a variation off the South Vietnam coast, we analyzed the summer chlorophyll a variability in this local region solely using the Empirical Orthogonal Function method.