The El Niño-Southern Oscillation (ENSO) profoundly influences marine ecosystems by reshaping phytoplankton community structures through environmental changes. However, because of limited field observations, the impact of ENSO on phytoplankton communities in the northwestern Pacific has been unclear. Through a comprehensive analysis combining field observations, satellite data, and reanalysis data, we obtained robust evidence of distinct patterns of the impact of El Niño and La Niña events on phytoplankton communities in the northwestern tropical Pacific, particularly within the region of the Mindanao eddy. These patterns contradicted expectations based on studies in the tropical eastern Pacific. During El Niño events, the relative concentrations of diatoms and haptophytes showed a notable increase, whereas during La Niña events, Prochlorococcus was the most abundant phytoplankton. Our analysis also revealed that the Pacific Decadal Oscillation amplified ENSO's impact on phytoplankton communities. This study highlighted the contrasting mechanisms between climate oscillations and marine ecosystem dynamics.
 

phytoplankton,climate change,western Pacific,ENSO,PDO