Release of nitrous oxide from the global coastal ocean: interactions with ecosystems and humans (NITRACTIONS)

Nitrous oxide (N₂O)—a strong greenhouse gas and a cause of ozone layer depletion—is released from land, seawater and its sediment into the atmosphere. This release is aggravated by the production and use of nitrogen fertilisers worldwide. About one third of N₂O emissions comes from the ocean, most of which is formed in the coastal ocean. The basic mechanisms of biochemical reactions of nitrogen compounds (also called reactive nitrogen, Nr) are largely known, but quantitative estimates and predictions of N₂O outflux diverge. We plan to improve the representation of the nitrogen cycle and get better flux estimates in the state-of-the-art ocean model BLOM/iHAMOCC (also a module of the Norwegian Earth System Model, NorESM). We will model the N₂O sources and sinks in the seawater and sediment porewaters, which will be the basis for simulating realistic N₂O fluxes. Hence, we will create a dataset of time-dependent maps of the amount of N₂O released from the sediment and seawater into the atmosphere, derived from the model simulations. This will be validated against observations. The release of N₂O is aggravated by the production and use of nitrogen fertilisers worldwide. Hence, the final objective in this proposal is to quantify the influence of the inflow of anthropogenic nitrogen compounds into the sea on N₂O fluxes from the sea. If much of the N₂O outflux can be attributed to Nr inflow, we can make recommendations for nutrient management in agriculture to the Norwegian government and other stake holders.This proposal was submitted to the Norwegian Research Council (NFR) in May 2020. In December 2020 it was rejected