Atmospheric deposition can supply obligate enzyme cofactors such as iron and zinc to promote the utilization of dissolved organic phosphorus (DOP), helping phytoplankton cope with phosphorus (P) stress in oligotrophic open oceans. In eutrophic coastal waters with higher metal stocks as well as prevailing P deficiency relative to nitrogen (N), the role of atmospheric deposition is still elusive. Using seven onboard microcosm experiments in China Coastal Seas (CCS) spanning oligotrophic-eutrophic statuses, we explored the pattern of the impacts of anthropogenic aerosol addition on DOP utilization in coastal waters. Aerosol addition could enhance alkaline phosphatase activities (APA), an indicator of DOP hydrolysis rate, and promote DOP utilization whether under the conditions of P limitation, NP co-limitation, or even N and no nutrient limitations. Combined with nutrient and trace metal treatments, we found aerosol addition primarily increased N:P ratio and then intensified P consumption to induce and/or stimulate APA in coastal waters, called “Atmospheric N:P Pump” (A-Pump_N:P), in contrast to the primary mechanism of supplying metal enzyme cofactors in oligotrophic open oceans. The A-Pump_N:P could enhance and even make DOP as the primary bioavailable P nutrient for phytoplankton growth. When the ratio of Chlorophyll a (Chl a) and dissolved inorganic P (DIP), i.e., Log₁₀(Chl a/DIP), was larger than 1.3±0.2 in seawater, APA was enhanced pronouncedly, suggesting the DIP and phytoplankton biomass joint control of aerosol-derived DOP utilization. Hence, atmospheric deposition can alter P bioavailability pronouncedly in meso-/eutrophic waters, although the direct DIP input is slight relative to seawater baseline stocks.

Atmospheric deposition,Dissolved organic phosphorus,coastal waters,Phytoplankton