Effects of phytoplankton physiology on global ocean biogeochemistry and climate.

The similarity of the average ratios of nitrogen (N) and phosphorus (P) in marine dissolved inorganic and particulate organic matter, dN:P and pN:P, respectively, indicates tight links between those pools in the world ocean. Here, we analyze this linkage by varying phytoplankton N and P subsistence quotas in an optimality-based ecosystem model coupled to an Earth system model. The analysis of our ensemble of simulations discloses various feedbacks between changes in the N and P quotas, N fixation, and denitrification that weaken the often-hypothesized tight coupling between dN:P and pN:P. We demonstrate the importance of particulate N:C and P:C ratios for regulating dN:P on the global scale, with marine oxygen level being an important control. Our analysis provides further insight into the potential interdependence of phytoplankton physiology and global climate conditions.