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Investigating the impacts of marine aerosols on phytoplankton in the northeast Pacific Ocean Fitz-Gerald, Wylee


Marine, Asian-derived aerosols are composed of macronutrients, trace metals, organic compounds and microbes that collectively, can have interactive effects on primary productivity upon deposition in the Fe-limited, high-nutrient low-chlorophyll surface waters of the northeast Pacific Ocean. Previous amendment studies have only focused on individual (e.g., addition of iron) or event-specific (e.g., addition of desert dust) aspects of aerosols to evaluate their effects on phytoplankton in this region. In this study, we determined how aerosols collected seasonally in the NE Pacific, representative of short-term deposition timelines, impacted phytoplankton physiology and community structure in the laboratory and field. In August 2021, we conducted an incubation experiment at an Fe-limited open-ocean station using the indigenous phytoplankton population, as well as aerosols collected in previous summers (August 2019 and 2020). In the laboratory, we conducted numerous experiments using a model diatom species, Thalassiosira oceania, cultured in Fe-limited open-ocean waters with aerosols collected in late winter (March 2022), spring (May 2021) and summer (August 2019, 2020 and 2021). During the field incubation, in response to one of the added aerosols, we observed a typical Fe-enriched shift in phytoplankton community composition, promoting the growth of pennate diatoms. However, in laboratory experiments, the input of aerosol metals did not fully explain Thalassiosira oceania growth trends. Rather, we hypothesized that aerosol-derived organic ligands significantly controlled aerosol-induced phytoplankton responses. Our results suggest that the overall effect of aerosols in the northeast Pacific on phytoplankton physiology and community composition is complex, and depends on numerous interacting factors, including aerosol trace metal and organic ligand composition, trace metal solubility, and initial metal concentrations in open-ocean waters.

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