Monthly climatology of chlorophyll concentration (chl ) based on nine years of SeaWiFS data is used to illustrate seasonal variations and spatial structures in the northern South China Sea (SCS). Chl 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 is centered in the northern SCS off the northwestern coast of Luzon Island. Chl starts to decrease gradually in February, and its values become very low from June to August. The region of elevated chl during the winter bloom season is funnel shaped, with the narrow end at the northern coast of Luzon Island, where the chl 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 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.