Ocean Ammonia Outgassing: Modulation by CO 2 and Anthropogenic Nitrogen Deposition

• Published in: Journal of advances in modeling earth systems Vol. 12; no. 10
• Main Authors: Paulot, Fabien, Stock, Charles, John, Jasmin G., Zadeh, Niki, Horowitz, Larry W.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01.10.2020
• Subjects: Acidification; Acidity; Air-sea interaction; Ammonia; Anthropogenic factors; Atmosphere; Biogeochemistry; Carbon dioxide; Coastal zone; Cobalt; Emissions; Fluid dynamics; Hydrodynamics; Ice cores; Light; Nitrates; Nitrogen; Nitrogen deposition; Nitrogen enrichment; Oceans; Regions; Respiration; Simulation
• ISSN: 1942-2466; 1942-2466
• DOI: 10.1029/2019MS002026

Abstract The imprint of anthropogenic activities on the marine nitrogen (N) cycle remains challenging to represent in global models, in part because of uncertainties regarding the source of marine N to the atmosphere. While N inputs of terrestrial origin present a truly external perturbation, a significant fraction of N deposition over the ocean arises from oceanic ammonia ( NH 3 ) outgassing that is subsequently deposited in other ocean regions. Here, we describe advances in the Geophysical Fluid Dynamics Laboratory's (GFDL) Earth System Model 4 (ESM4.1) aimed at improving the representation of the exchange of N between atmosphere and ocean and its response to changes in ocean acidity and N deposition. We find that the simulated present‐day NH 3 outgassing (3.1 TgN yr −1 ) is 7% lower than under preindustrial conditions, which reflects the compensating effects of increasing CO 2 ( −16 % ) and N enrichment of ocean waters ( +9 % ). This change is spatially heterogeneous, with decreases in the open ocean ( −13 % ) and increases in coastal regions ( +15 % ) dominated by coastal N enrichment. The ocean outgassing of ammonia is shown to increase the transport of N from N‐rich to N‐poor ocean regions, where carbon export at 100 m increases by 0.5%. The implications of the strong response of NH 3 ocean outgassing to CO 2 for the budget of NH 3 in the remote marine atmosphere and its imprint in ice cores are discussed. Key Points Development of an interactive representation of N exchange between ocean and atmosphere in the GFDL ESM4.1, including ammonia outgassing Little change in the ocean NH 3 outgassing over the historical period due to compensation between acidification and increasing N deposition Ocean NH 3 outgassing increases carbon export at 100 m in N‐limited regions by 0.5%