Abstract:

Anthropogenic climate warming and coastal eutrophication have restructured phytoplankton communities in the East China Sea; however, the centennial-scale dynamics of phytoplankton remain poorly understood. By systematically integrating 33 sediment cores, we reconcile the variations of primary productivity during the last century. The results revealed increased primary productivity during the past century, while the phytoplankton groups showed divergent eco-regional responses: river-dominated estuaries have partially mitigated the dominance of dinoflagellates (1980s) via Changjiang nitrate loading, while potential hypoxic regions shifted earlier (1960s) under thermal forcing and silicate concentration. Our novel hierarchical framework establishes nutrient stoichiometry as the primary driver in eutrophic zones versus temperature dominance in hypoxic regions. Generalized additive models project continued primary productivity increases under different warming scenarios, but with accelerating dinoflagellate proliferation elevating the risks of harmful algal blooms. These findings provide a mechanistic basis for the adaptive management of coastal ecosystems under intensifying anthropogenic pressures.