Continuing Decrease in Nitrogen Fixation in the North Atlantic Ocean Associated with Dissolved Inorganic Carbon

Biological nitrogen fixation is closely linked to marine primary productivity and the nitrogen balance. Traditional Earth system models and geochemical estimation methods are subject to high uncertainties in nitrogen fixation evaluation. We employed a comprehensive global nitrogen fixation rate data set (2590 in situ measurements) and projected 20-year global oceanic nitrogen fixation data. In conventional process-based modeling calculations, the nitrogen fixation flux was overestimated by 75.92% in the North Atlantic. A significant decrease of 14.12% in the North Atlantic has occurred over the past two decades. In contrast to iron, which is well documented, dissolved inorganic carbon (DIC) is strongly associated with the process of the significant 20-year decrease in nitrogen fixation fluxes in the North Atlantic. Under the future low-emission scenario, a continued increase in DIC could further reduce the nitrogen fixation rate by 64.01%, which could pose significant challenges for marine nitrogen budgets.