title: Marine biogenic source of atmospheric organic nitrogen in the subtropical North Atlantic.
abstract: Global models estimate that the anthropogenic component of atmospheric nitrogen (N) deposition to the ocean accounts for up to a third of the ocean's external N supply and 10% of anthropogenic CO2 uptake. However, there are few observational constraints from the marine atmospheric environment to validate these findings. Due to the paucity of atmospheric organic N data, the largest uncertainties related to atmospheric N deposition are the sources and cycling of organic N, which is 20-80% of total N deposition. We studied the concentration and chemical composition of rainwater and aerosol organic N collected on the island of Bermuda in the western North Atlantic Ocean over 18 mo. Here, we show that the water-soluble organic N concentration ([WSON]) in marine aerosol is strongly correlated with surface ocean primary productivity and wind speed, suggesting a marine biogenic source for aerosol WSON. The chemical composition of high-[WSON] aerosols also indicates a primary marine source. We find that the WSON in marine rain is compositionally different from that in concurrently collected aerosols, suggesting that in-cloud scavenging (as opposed to below-cloud "washout") is the main contributor to rain WSON. We conclude that anthropogenic activity is not a significant source of organic N to the marine atmosphere over the North Atlantic, despite downwind transport from large pollution sources in North America. This, in conjunction with previous work on ammonium and nitrate, leads to the conclusion that only 27% of total N deposition to the global ocean is anthropogenic, in contrast to the 80% estimated previously.
authors.affiliation: Energy Research Centre, University of Cape Town, Cape Town 7701, South Africa; katye.altieri@uct.ac.za.
authors.forename: Katye E
authors.initials: KE
authors.lastname: Altieri
authors.affiliation: Department of Geosciences, Princeton University, Princeton, NJ 08544; Department of Oceanography, University of Cape Town, Cape Town 7701, South Africa;
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Fawcett
authors.affiliation: Bermuda Institute of Ocean Sciences, St. Georges GE01, Bermuda;
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Peters
authors.affiliation: Department of Geosciences, Princeton University, Princeton, NJ 08544;
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Sigman
authors.affiliation: Department of Earth, Environmental and Planetary Sciences and Institute at Brown for Environment and Society, Brown University, Providence, RI 02912.
authors.forename: Meredith G
authors.initials: MG
authors.lastname: Hastings
mesh_terms: D000336:Aerosols / Q000032:analysis*; D001267:Atlantic Ocean; D001272:Atmosphere; D009584:Nitrogen / Q000032:analysis*; D011891:Rain / Q000737:chemistry*; D012623:Seawater / Q000032:analysis*
chemical_list: D000336:Aerosols; D009584:Nitrogen
keywords: aerosol; atmospheric deposition; marine atmosphere; organic nitrogen; rain