Microcosm experiments reveal source‐specific impacts of atmospheric aerosols on plankton communities and organic matter in the sea surface microlayer

Abstract The impact of atmospheric deposition on marine ecosystems requires consideration of the interfacial processes within the sea surface microlayer, the uppermost layer at the air–sea interface. This study examines the impact of anthropogenic and biomass burning aerosol particles on the plankton community structure and organic matter accumulation in the system derived from in situ‐collected microlayer compared to the underlying water through a 4‐day microcosm experiment conducted in August 2020 in the Central Adriatic area. Realistic aerosol additions (1 mg L −1 ) had different impacts on surface layers, revealing complex interactions between nutrient availability, toxicity, and plankton competition. A sudden nutrient supply, particularly of nitrogen, favored larger phytoplankton, while other aerosol constituents, such as trace metals and carbonaceous compounds, likely had a toxic effect, particularly on smaller species. The neuston in the microlayer showed greater sensitivity to pollutants, possibly due to higher UV exposure enhancing toxicity compared to the underlying water counterparts. Shifts in neuston diversity promoted the accumulation of organic carbon and surfactants in the microlayer, with potential implications for suppressing the air–sea CO 2 exchange.