Marine phytoplankton are the most important primary producers, responsible for approximately half of the global carbon fixation. Through the biological carbon pump, they can also transport surface CO2 to the deep ocean, playing a crucial role in the global carbon cycle. Since the industrial era, the surface ocean has been absorbing amounts of atmospheric CO2, leading to a rise in surface ocean pCO2 and the concentration of hydrogen ion, known as 'ocean acidification' (OA). Phytoplankton living in the euphotic layer are likely affected by OA. Therefore, figuring out responses of phytoplankton to OA on a global scale and changes in the ocean carbon flux is essential for predicting the future global carbon cycle.

Our study expands the default three phytoplankton function types (PFTs) in the Marine Biogeochemistry Library (MARBL) of the Community Earth System Model (CESM-2.1.3) to eight. These include three pico-phytoplankton (diameter between 0.2-2 μm), Prochlorococcus, Synechococcus, pico-eukaryotes; two diazotrophs, Trichodesmium, Crocosphaera; one calcifier, coccolithophores; other nanophytoplankton (2-20 μm) and diatoms. Moreover, we integrated the experimental results about acidification effects on different phytoplankton species to derive species-specific acidification coefficients. These coefficients were incorporated into the growth equations of autotrophs in the model, allowing us to explore how the distribution patterns of different phytoplankton types may shift in an acidified ocean, as well as the potential changes in biogeochemical fluxes.

CESM,Ocean acidification,phytoplankton