Atmospheric deposition of anthropogenic inorganic nitrogen in airborne particles and precipitation in the East Sea in the northwestern Pacific Ocean

The atmospheric deposition of anthropogenic nitrogen is an increasingly important new source of nitrogen to the ocean. Coastal areas east of the Korean Peninsula are suitable for the investigation of the effects of atmospheric anthropogenic nitrogen on the ocean nutrient system because of the low riverine discharge rates and the prevailing influence of the East Asian outflow. Thus, we measured the concentrations of nitrate (NO₃ ⁻) and ammonium (NH₄ ⁺) in airborne particles and in precipitation from March 2014 to February 2016 at a coastal site (37.08°N, 129.41°E) on the east coast of Korea. The dry deposition of NO₃ ⁻ (27–30 mmol N m⁻² yr⁻¹) was far greater than that of NH₄ ⁺ (6–8 mmol N m⁻² yr⁻¹). The greater rate of dry NO₃ ⁻ deposition was associated with air masses traveling over northeastern China and central Korea. In contrast, the rates of wet deposition of NO₃ ⁻ (17–24 mmol N m⁻² yr⁻¹) and NH₄ ⁺ (14–27 mmol N m⁻² yr⁻¹) were comparable and were probably associated with in-cloud scavenging of these ions. The results indicate that the total deposition of NO₃ ⁻ and NH₄ ⁺ combined could contribute to ~2.4% and ~1.9% of the primary production in the coastal areas east of the Korean Peninsula and in the East Asian marginal seas, respectively, which would be a lower bound because the dry deposition of reactive nitrogen gas was not included. Our study shows that the atmospheric input of anthropogenic NO₃ ⁻ and NH₄ ⁺ may substantially increase phytoplankton biomass in the coastal waters of the East Sea near the Korean Peninsula.