Spatiotemporal distribution of chlorophyll-a concentration in the south China sea and its possible environmental regulation mechanisms.

In this paper, the spatial and temporal distribution of chlorophyll-a (Chl-a) concentration in the South China Sea (SCS) and its major environmental regulator mechanisms were studied by using satellite remote sensing data sea surface temperature (SST), sea surface wind (SSW), and aerosol optical depth (AOD) spanning from January 2000 to December 2022. The results show that Chl-a in the SCS exhibit notable spatio-temporal variations: they peak in winter (∼0.234 mg m^-3) and autumn (∼0.156 mg m^-3), and decline in spring (∼0.144 mg m^-3) and summer (∼0.136 mg m^-3). Spatially, Chl-a near the coast and in upwelling areas are generally higher than those in offshore areas. A monthly average time series correlation analysis across the entire SCS shows that Chl-a significantly correlate with SST (R = -0.78, P < 0.01) and SSW (R = 0.78, P < 0.01), and moderately correlate with AOD (R = 0.29, P < 0.01). The regulator of environmental factors also shows seasonal differences: during the winter monsoon period, Chl-a has the highest partial correlation with SSW (R = 0.73, P < 0.01), followed by SST (R = -0.55, P < 0.01), and no significant partial correlation with AOD (R = 0.14, P > 0.05); during the summer monsoon period, Chl-a has the highest partial correlation with SST (R = -0.63, P < 0.01), followed by AOD (R = 0.40, P < 0.01), and no significant partial correlation with SSW (R = 0.12, P > 0.05). A comprehensive analysis indicates that the mixing and upwelling processes regulated by the winter monsoon and SST exert a greater influence on nutrient variations. The enhanced mixing caused by the winter monsoon and the cold environment promote the growth of phytoplankton, leading to higher Chl-a concentrations in winter compared to other seasons. In contrast, the increased temperature in the summer monsoon period significantly weakens the mixing effect of wind speed and nutrients influx from deep layers to surface layers. Consequently, the external nutrient sourced from aerosol becomes crucial in determining Chl-a distribution, especially in oligotrophic regions near the southern SCS and the basin. However, in regions where other nutrient sources significantly contribute, such as the coastal areas influenced by seasonal upwelling, the contribution of aerosols is negligible.