Modelling the Impact of Multiple Environmental Drivers on Marine Diazotrophy

Marine nitrogen fixation, or diazotrophy, is a major source of new nitrogen to the ocean, supporting primary production in the nitrogen-limited tropical ocean. The response of nitrogen fixation to climate change will therefore interact with projected changes to physical nitrogen supply to regulate the response of tropical ocean primary production. Experimental evidence suggests that the ecological niche of diazotrophs may be altered by warming, ocean acidification and changes to nutrient supply which will impact the spatial pattern of nitrogen fixation. Here, we coupled a new model of nitrogen fixation based upon observed diazotroph energetics of growth and limitation to a global model of phytoplankton physiology and ocean biogeochemistry, which accounts for variable phytoplankton stoichiometries and cellular resource trade-offs. We use our model to investigate the influence of different environmental drivers on the response of diazotrophy to climate change under the RCP8.5 scenario. Understanding how climate will impact diazotrophy is essential in order to gain insight into how patterns of nutrient limitation and primary production are likely to change in the future.