Impact of Different El Nino Types on Spring Chlorophyll‐a Concentrations in the Yellow and East China Seas

Abstract Phytoplankton biomass dynamics are strongly influenced by the El Niño‐Southern Oscillation (ENSO); however, the specific mechanisms through which different El Niño types regulate phytoplankton variability remain poorly understood. This study integrates satellite remote sensing, oceanic profile observations, and multi‐source reanalysis data sets to investigate how Eastern Pacific (EP) and Central Pacific (CP) El Niño events during the spring decay phase modulate chlorophyll‐a (Chl‐ a ) concentrations in the Yellow and East China Seas. The results revealed a significant decline in Chl‐ a concentrations across the study region during EP events, whereas a notable increase occurred during CP events. This contrasting response was driven by a cascading atmospheric circulation‐ocean mixing‐light availability mechanism. During EP events, a significantly intensified western North Pacific subtropical high (WNPSH) weakens the winter monsoon and elevates sea surface temperatures (SST), resulting in a shallower spring mixed layer depth (MLD). These conditions suppress vertical mixing and reduce surface phosphate concentrations. Simultaneously, decreased photosynthetically active radiation (PAR) also leads to a substantial reduction in spring Chl‐ a concentrations. In contrast, CP events are associated with a slightly intensified WNPSH and enhanced winter monsoon, which together deepen the winter MLD and facilitate upward phosphate flux from deeper waters, where phytoplankton growth is typically phosphate‐limited. Under favorable light and thermal conditions in spring, this nutrient enrichment drives a pronounced increase in Chl‐ a concentrations. These findings provide a conceptual framework for predicting ecological responses in marginal seas under future climate change scenarios.