Contrasting chlorophyll-a seasonal patterns between nearshore and offshore waters in the Bohai and Yellow Seas, China: A new analysis using improved satellite data

The seasonal cycles of sea surface Chlorophyll-a (Chl-a) concentration in the Bohai and Yellow Seas (BYS) were examined using new remotely sensed Chl-a products derived using a regional algorithm. Based on objective clustering analysis, two contrasting Chl-a seasonal patterns were delineated: 1) A nearshore pattern with a long-lasting Chl-a peak from spring to autumn, coinciding with sufficient nutrient supply and high light availability, and lower Chl-a values in winter due to the light-limitation as a consequence of low solar irradiance and high diffuse attenuation coefficient of light for the water column; 2) An offshore pattern with a strong spring bloom triggered by alleviated light limitation and abundant nutrients coinciding with high water column stability. A weak autumn peak induced by new nutrient replenishment from bottom re-suspension and horizontal transportation, a low Chl-a trough in winter mainly attributed to light-limitation, and a Chl-a trough in summer due to nutrient scarcity were observed. The linkages between the province-specific Chl-a seasonal patterns and the seasonal cycles of the corresponding environmental variables as well as other potential influencing factors are comprehensively delineated and discussed