Reactive nitrogen biogeochemical cycling in the GFDL Earth System Models: Advancing understanding of atmosphere-land interactions under changing climate and land use

The goal of the project is to improve the representation of the formation, radiative properties, internal mixing, and heterogeneous sources and sinks of nitrate aerosol, to be incorporated into a new version of the GFDL atmospheric model, AM3N. In the land model, we plan to represent Nr loss through denitrification in soils under anoxic conditions, including an explicit treatment of microbial processes. Runoff of Nr and cycling in rivers will be represented globally. The model will use improved scenarios of historical and future land management practices. We propose to improve the characterization of the Nr emissions and deposition through online coupling between the atmosphere and land components of the GFDL ESM. Speciated Nr emissions (NH3, NO, N2O) from unmanaged ecosystems, managed agricultural lands, and biomass burning will be represented. Wet and dry deposition fluxes of Nr species from the atmosphere will be provided as sources to the land model. The proposal will leverage and extend ongoing observations of Nr exchange between soil and

atmosphere in managed ecosystems (feedlots, croplands) and to perform new observations in an unmanaged environment (forest or grassland). These detailed observations will provide important constraints for process-level evaluation of the coupled atmosphere-land Nr system in the ESM. Regional evaluation of AM3N will include comparison against ship-based, ground-based, mobile laboratory, airborne, and satellite measurements of Nr gases and aerosols.