Asymmetric Phytoplankton Responses to El Niño Diversity in the China Seas Mediated by the Western North Pacific Subtropical High

The increasing frequency of Central Pacific (CP) El Niño events under global warming necessitates a reassessment of ENSO's impact on marine carbon cycles. Although the canonical Eastern Pacific (EP) El Niño is well studied, the ecological imprint of El Niño diversity remains poorly resolved in marginal seas. Using a 25‐year satellite record, we reveal contrasting phytoplankton responses in the China Seas to EP and CP El Niño. This asymmetry is not uniform across the region. EP events suppress primary productivity primarily in the South China Sea via a stratification‐dominated pathway: a shallower winter mixed layer limits nutrient supply, followed by summer warming and stratification driven by a strengthened and westward‐displaced Western North Pacific Subtropical High (WNPSH), exacerbating nutrient limitation. Conversely, CP events promote phytoplankton growth, particularly in the Yellow Sea and East China Sea, via a mixing‐dominated pathway: by deepening the winter mixed layer, enriching nutrients, and subsequently through a northeastward WNPSH retreat that cools surface waters and weakens stratification in these northern sub‐basins. These findings reveal that the WNPSH acts as a critical “atmospheric switch,” toggling the ecosystem between opposing metabolic states. Our study highlights the necessity of distinguishing El Niño flavors to accurately predict the trajectory of shelf sea productivity and biological carbon pump efficiency in a warming climate.