Advancing mechanistic understanding of phytoplankton and oxygen responses to Pacific warming

Pacific warming is accelerating ocean deoxygenation and threatening phytoplankton diversity. However, detecting warming-induced phytoplankton and oxygen trends and understanding phytoplankton adaptive responses to warming remain largely unexplored, particularly over long-term observations. Herein, we established a Bayesian-mechanistic model and incorporate a unique phytoplankton vertical migration mechanism to assess the countervailing effects of Pacific warming on phytoplankton migration potential and oxygen dynamics and associated rigorous uncertainties. Our study reveals that commonly used light exposure calculations by considering surface radiation but do not integrate the phytoplankton-specific underwater light regime considerably overestimate chlorophyll-a concentrations because of missing interactions among phytoplankton migration, light, and nutrient, unresolved transport processes, or unaccounted for variations in phytoplankton vertical migration. Our results indicate the subtropical phytoplankton present weak migratory responses, while tropical taxa have engaged in dive migration strategy to mitigate photoinhibitory-induced declines in production. Moreover, physical mixing, rather than thermally-driven changes in oxygen solubility, predominantly drives Pacific deoxygenation. Our work promises a robust mechanistic understanding between climate change and marine ecosystems.