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

Nicola A Wiseman , J. Keith Moore, Adam C Martiny, Robert Letscher

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.