Phytoplankton physiology controls global ocean biogeochemistry (and climate)

The similarity of the average nitrogen-to-phosphorus ratios (N:P) in marine dissolved-inorganic and particulate-organic matter indicates tight links between those pools in the World Ocean. Here we analyse the sensitivity of marine biogeochemistry to variations in phytoplankton N and P subsistence quotas in an optimality-based ecosystem model coupled to the UVic Earth system model. Our results reveal distinct feedbacks between changes in the N and P quotas, N₂ fixation, and denitrification that loosen the coupling between dissolved and particulate N:P.  We demonstrate the importance of particulate N:C and P:C for regulating dissolved N:P on the global scale, with oxygen concentration being an important mediator. Our analysis also reveals a potential interdependence between phytoplankton stoichiometry and global equilibrium climate conditions.