Phytoplankton variable stoichiometry modifies key biogeochemical fluxes and the functioning of the ocean biological pump

Ocean biota absorb carbon at the surface and export some to the ocean interior via the biological pump, affecting surface carbon, air-sea CO₂ exchange, and climate. Marine phytoplankton growth is often limited by nutrients (nitrogen, phosphorus, iron, silicon). The efficiency of carbon export is therefore constrained by nutrient availability and the nutrient/carbon ratios in the biota (stoichiometry). Field observations suggest widespread variability in phytoplankton stoichiometry (C/N/P/Fe/Si). Incorporating variable stoichiometry in marine biogeochemical models alters the magnitude and spatial patterns of carbon export by the biological pump and key nitrogen cycle fluxes, while fixed-stoichiometry models underestimate ocean carbon uptake and overestimate atmospheric CO₂. Thus, Earth System Models need to include dynamic plankton stoichiometry to enable more accurate projections of the carbon cycle and climate.