Decoding environmental regimes and spring phytoplankton bloom occurrence in the central Yellow Sea
摘要
Phytoplankton blooms, defined as a periods of high biomass, are key indicators of climate-driven ocean responses. Shifts in their timing and magnitude can substantially alter the marine ecosystem, yet the environmental regimes governing bloom development remain poorly constrained. We analyzed long-term environmental data (2003–2023) from the Central Yellow Sea (CYS) to decode the drivers of the spring phytoplankton bloom (SPB), which is defined into four developmental stages based on changes in chlorophyll-a (Chl-a). A machine-learning decision tree (DT) was employed to identify specific quantitative critical thresholds associated with each phase. Results show that the SPB initial stage represented low-light intensity in early-April. The peak stage was determined by strong-light intensity; thus, the Chl-a increased rapidly in mid-April. The decline stage corresponded to a high sea surface temperature (SST