Seasonal variations of chlorophyll a concentration in the northern South China Sea

Monthly climatology of chlorophyll a concentration (chl a) based on nine years of SeaWiFS data is used to illustrate seasonal variations and spatial structures in the northern South China Sea (SCS). Chl a starts to increase in September at the northern coast of Luzon Island, continues to increase in the autumn, and reaches its maximum in December or January. Maximum chl a is centered in the northern SCS off the northwestern coast of Luzon Island. Chl a starts to decrease gradually in February, and its values become very low from June to August. The region of elevated chl a during the winter bloom season is funnel shaped, with the narrow end at the northern coast of Luzon Island, where the chl a value is highest and opening toward the northwest. The sea surface temperature (SST) in this funnel-shaped region is significantly colder than SST in surrounding regions of the same latitude. The present study indicates that the winter blooms indicated by higher chl a and colder SST in the northern SCS are linked strongly to the local winter monsoon. The initial data exploration and analysis presented in this study was carried out using Giovanni, a state-of-the-art Web-based data analysis and visualization tool.