Atmospheric deposition is a major pathway through which natural and anthropogenic aerosol particles are transferred from the atmosphere to marine ecosystems, supplying surface waters with nutrients, trace metals, and organic pollutants, influencing phytoplankton productivity, community composition, and marine biogeochemical cycling. As interactions among atmospheric chemistry, marine ecosystems, and climate are expected to intensify under future climate change, understanding how aerosols from different emission sources affect marine primary producers has become increasingly important. However, the contributions of individual aerosol components and the species-specific responses of phytoplankton to source-dependent atmospheric deposition remain poorly constrained.
This study investigated physiological and biochemical responses of marine phytoplankton to contrasting aerosol sources through controlled laboratory incubation experiments. The effects of ambient biomass-burning aerosols and a model black carbon material were assessed by examining the growth of representative phytoplankton spanning different size classes, including Gephyrocapsa huxleyi, Cylindrotheca closterium, Melosira nummuloides and Synechococcus sp. In addition, the effects of anthropogenic aerosol deposition were evaluated using laboratory cultures of the nanophytoplankton Coccolithus braarudii and the cyanobacterium Synechococcus sp. The experiments demonstrated that atmospheric deposition elicits distinct, source-dependent and species-specific responses. Exposure to biomass burning aerosols altered growth and photosynthetic performance, highlighting the importance of aerosol composition in determining phytoplankton sensitivity. Anthropogenic aerosols, enriched in dissolved inorganic nitrogen, stimulated the growth of larger phytoplankton, whereas trace metals and organic pollutants, including polycyclic aromatic hydrocarbons and nitrogen-containing aromatic compounds, exerted proportionally stronger effects on the smaller cyanobacterial cells, likely due to their higher nutrient and contaminant uptake rates. Atmospheric inputs also induced marked changes in the biochemical composition of phytoplankton-derived organic matter, increasing lipid production relative to carbohydrates and proteins, which suggests adaptive metabolic adjustments to atmospheric stressors. These findings demonstrate that the ecological impacts of atmospheric deposition depend on both aerosol source and phytoplankton species, with potential consequences for community composition, nutrient cycling, carbon export, and air–sea carbon exchange. By elucidating the mechanisms through which atmospheric deposition influence marine primary producers, this study advances understanding of atmosphere–ocean interactions and their role in shaping coastal marine ecosystems under a changing climate.
This work was supported by Croatian Science Foundation projects IP-2024-05-6224 ADRIAirBURN and IP-2018-01-3105 BiREADI.

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