Seasonal and summer interannual variations of SeaWiFS chlorophyll a in the Yellow Sea and East China Sea

Seasonal variability in satellite chlorophyll a concentrations (SCHL) in the Yellow Sea and the East China Sea (YECS) was investigated using 10-year averages of monthly data collected between September 1997 and October 2006. Interannual variations were also assessed to help clarify the influence of Changjiang River discharge (CRD) during summer. The YECS was represented by 12 areas each with different seasonal variability in SCHL. SCHL were overestimated during winter due to re-suspension of sediment near the Changjiang Bank and near coastal areas. Increases of SCHL were observed over large areas of the YECS during spring, as would be expected with the occurrence of spring blooms. The spatial distribution of the summer maximum of SCHL shifted from the Changjiang River mouth to just east of Jeju Island from July to September. An eastward shift of the high SCHL water coincided with the movement of the Changjiang diluted water (CDW), taking approximately 2 months to move from Changjiang River mouth to Jeju Island. Summer SCHL between 1998 and 2006 in this region were positively correlated with CRD with a time lag of 0–2 months, suggesting that the interannual variation of SCHL was controlled by the interannual variation of CRD. SCHL during summer in the Yellow Sea gradually increased over the 10 years, indicating possible eutrophication.