Spatial distribution characteristics and the environmental regulation mechanisms of phytoplankton chlorophyll a in the Bohai Sea and the Yellow Sea.

To comprehensively analyze the relation between the environmental factors and chlorophyll a (Chl-a) in the Bohai Sea (BS) and the Yellow Sea (YS), three investigations were conducted during April and October of 2019, and July of 2020. The distribution of Chl-a demonstrated pronounced regional and seasonal variability. The horizontal distribution of Chl-a was notably heterogeneous, generally exhibiting higher concentrations near the shoreline and diminishing values towards the central regions of the sea. Meanwhile, the vertical distribution of Chl-a concentrations also illustrated significant variations with depth and regional differences. The relationship between Chl-a concentration and environmental factors varied significantly across seasons. In the BS and the YS, seasonal variations in temperature and salinity were the principal drivers of the seasonal fluctuations in Chl-a concentrations. Additionally, variations in nutrient concentrations, which were influenced by temperature, contributed significantly to the seasonal variability of Chl-a concentrations.