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This perspective piece on aerosol deposition to marine ecosystems and the related impacts on biogeochemical cycles forms part of a larger Surface Ocean Lower Atmosphere Study status-of-the-science special edition. A large body of recent reviews has comprehensively covered different aspects of this topic. Here, we aim to take a fresh approach by reviewing recent research to identify potential foundations for future study. We have purposefully chosen to discuss aerosol nutrient and pollutant fluxes both in terms of the journey that different aerosol particles take and that of the surrounding scientific field exploring them. To do so, we explore some of the major tools, knowledge, and partnerships we believe are required to aid advancing this highly interdisciplinary field of research. We recognize that significant gaps persist in our understanding of how far aerosol deposition modulates marine biogeochemical cycles and thus climate. This uncertainty increases as socioeconomic pressures, climate change, and technological advancements continue to change how we live and interact with the marine environment. Despite this, recent advances in modeling techniques, satellite remote sensing, and field observations have provided valuable insights into the spatial and temporal variability of aerosol deposition across the world’s ocean. With the UN Ocean Decade and sustainable development goals in sight, it becomes essential that the community prioritizes the use of a wide variety of tools, knowledge, and partnerships to advance understanding. It is through a collaborative and sustained effort that we hope the community can address the gaps in our understanding of the complex interactions between aerosol particles, marine ecosystems, and biogeochemical cycles., This publication resulted in part from support from the U.S. National Science Foundation (Grant OCE-1840868) to the Scientific Committee on Oceanic Research. DSH acknowledges that this work was supported by North Carolina State University. ARB was funded by the UK Natural Environment Research Council (grant NE/V001213/1). JL was funded by the European Space Agency—LPF (No. 4000135579/21/I-DT-lr) and the Barcelona Supercomputing Centre. SM acknowledges support by the project “PANhellenic infrastructure for Atmospheric Composition and climatE change” (MIS 5021516) implemented under the Action “Reinforcement of the Research and Innovation Infrastructure,” which is funded by the Operational Programme “Competitiveness, Entrepreneurship and Innovation” (NSRF 2014–2020) and cofinanced by Greece and the European Union (European Regional Development Fund) and the National Infrastructures for Research and Technology S.A. (GRNET S.A.) in the National HPC facility ARIS for computational time granted under project ID 010003 (ANION). MMGP acknowledges that this work was supported by the Interdisciplinary graduate school for the blue planet (ISBlue, ANR-17-EURE-0015) and cofunded by a grant from the French government under the program “Investissements d’Avenir” embedded in France 2030., Peer Reviewed, Postprint (published version)

Atmospheric iron (Fe) deposition to the open ocean affects net primary productivity, nitrogen fixation, and carbon uptake. We investigate changes in soluble Fe (SFe) deposition from the pre-industrial period to the late 21st century using the EC-Earth3-Iron Earth System model. EC-Earth3-Iron considers various sources of Fe, including dust, fossil fuel combustion, and biomass burning, and features comprehensive atmospheric chemistry, representing atmospheric oxalate, sulfate, and Fe cycles. We show that anthropogenic activity has changed the magnitude and spatial distribution of SFe deposition by increasing combustion Fe emissions and atmospheric acidity and oxalate levels. We report that SFe deposition has doubled since the early industrial era, using the Coupled Model Intercomparison Project Phase 6 emission inventory. We highlight acidity as the main solubilization pathway for dust-Fe and oxalate-promoted processing for the solubilization of combustion-Fe. We project a global SFe deposition increase of 40% by the late 21st century relative to present day under Shared Socioeconomic Pathway (SSP) 3–7.0, which assumes weak climate change mitigation policies. Conversely, SSPs with stronger mitigation pathways (1–2.6 and 2–4.5) result in 35% and 10% global decreases, respectively. Despite these differences, SFe deposition increases over the equatorial Pacific and decreases in the Southern Ocean (SO) for all SSPs. We further observe that deposition over the equatorial Pacific and SO are highly sensitive to future changes in dust emissions from Australia and South America, as well as from North Africa. Future studies should focus on the potential impact of climate- and human-induced changes in dust and wildfires combined., This work was funded by the European Research Council under the Horizon 2020 research and innovation programme through the ERC Consolidator Grant FRAGMENT (grant agreement no. 773051), the AXA Research Fund through the AXA Chair on Sand and Dust Storms at BSC, the Spanish Ministerio de Economía y Competitividad through the NUTRIENT project (CGL2017-88911-R), the European Union's Horizon 2020 research and innovation programme under grant agreement no 821205 (FORCeS), and ESA through the DOMOS project (ESA AO/1-10546/20/I-NB). We acknowledge the EMIT project, which is supported by the National Aeronautics and Space Administration Earth Venture Instrument program, under the Earth Science Division of the Science Mission Directorate. RLM received additional support from the NASA Modeling, Analysis and Prediction Program (NNG14HH42I). We also acknowledge the resources obtained on the Marenostrum4 supercomputer at BSC, granted through the PRACE project eFRAGMENT2 and RES project AECT-2020-3-0020, along with the technical support provided by BSC and the Computational Earth Sciences team of the BSC Earth Sciences Department., Peer Reviewed, Postprint (published version)

Understanding how multiphase processes affect the iron-containing aerosol cycle is key to predicting ocean biogeochemistry changes and hence the feedback effects on climate. For this work, the EC-Earth Earth system model in its climate–chemistry configuration is used to simulate the global atmospheric oxalate (OXL), sulfate (SO), and iron (Fe) cycles after incorporating a comprehensive representation of the multiphase chemistry in cloud droplets and aerosol water. The model considers a detailed gas-phase chemistry scheme, all major aerosol components, and the partitioning of gases in aerosol and atmospheric water phases. The dissolution of Fe-containing aerosols accounts kinetically for the solution's acidity, oxalic acid, and irradiation. Aerosol acidity is explicitly calculated in the model, both for accumulation and coarse modes, accounting for thermodynamic processes involving inorganic and crustal species from sea salt and dust. Simulations for present-day conditions (2000–2014) have been carried out with both EC-Earth and the atmospheric composition component of the model in standalone mode driven by meteorological fields from ECMWF's ERA-Interim reanalysis. The calculated global budgets are presented and the links between the (1) aqueous-phase processes, (2) aerosol dissolution, and (3) atmospheric composition are demonstrated and quantified. The model results are supported by comparison to available observations. We obtain an average global OXL net chemical production of 12.615 ± 0.064 Tg yr−1 in EC-Earth, with glyoxal being by far the most important precursor of oxalic acid. In comparison to the ERA-Interim simulation, differences in atmospheric dynamics and the simulated weaker oxidizing capacity in EC-Earth overall result in a ∼ 30 % lower OXL source. On the other hand, the more explicit representation of the aqueous-phase chemistry in EC-Earth compared to the previous versions of the model leads to an overall ∼ 20 % higher sulfate production, but this is, Stelios Myriokefalitakis, Evangelos Gerasopoulos, and Maria Kanakidou acknowledge support by the project “PANhellenic infrastructure for Atmospheric Composition and climatE change” (MIS 5021516) implemented under the Action “Reinforcement of the Research and Innovation Infrastructure”, which is funded by the Operational Programme “Competitiveness, Entrepreneurship and Innovation” (NSRF 2014–2020) and cofinanced by Greece and the European Union (European Regional Development Fund). This work was supported by computational time granted from the National Infrastructures for Research and Technology S.A. (GRNET S.A.) in the National HPC facility – ARIS – under project ID 010003 (ANION). Elisa Bergas-Massó, María Gonçalves-Ageitos, and Carlos Pérez García-Pando gratefully acknowledge the computer resources at Marenostrum4 granted through the PRACE project eFRAGMENT3 and the RES project AECT-2020-3-0020, as well as the technical support provided by the Barcelona Supercomputing Center (BSC) and the CES team of the Earth Sciences Department. Their work was supported by the ERC Consolidator Grant FRAGMENT (grant agreement no. 773051) and the AXA Chair on Sand and Dust Storms at BSC funded by the AXA Research Fund, both of which are led by Carlos Pérez García-Pando, who also acknowledges the Ramon y Cajal program (grant no. RYC-2015-18690) of the Spanish Ministry of Science, Innovation and Universities and the ICREA program. The research leading to these results has also received funding from the Spanish Ministerio de Economía y Competitividad as part of the NUTRIENT project (CGL2017-88911-R) and the H2020 GA 821205 project FORCeS. Support for this research was provided to Akinori Ito by the JSPS KAKENHI (grant no. 20H04329) and the Integrated Research Program for Advancing Climate Models (TOUGOU) (grant no. JPMXD0717935715) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. Twan van Noije, Philippe Le Sager, Maria Kanakidou, and Stelios Myr, Peer Reviewed, Postprint (published version)

Understanding how multiphase processes affect the iron-containing aerosol cycle is key to predicting ocean biogeochemistry changes and hence the feedback effects on climate. For this work, the EC-Earth Earth system model in its climate-chemistry configuration is used to simulate the global atmospheric oxalate (OXL), sulfate (SO42-), and iron (Fe) cycles after incorporating a comprehensive representation of the multiphase chemistry in cloud droplets and aerosol water. The model considers a detailed gas-phase chemistry scheme, all major aerosol components, and the partitioning of gases in aerosol and atmospheric water phases. The dissolution of Fe-containing aerosols accounts kinetically for the solution's acidity, oxalic acid, and irradiation. Aerosol acidity is explicitly calculated in the model, both for accumulation and coarse modes, accounting for thermodynamic processes involving inorganic and crustal species from sea salt and dust. Simulations for present-day conditions (2000-2014) have been carried out with both EC-Earth and the atmospheric composition component of the model in standalone mode driven by meteorological fields from ECMWF's ERA-Interim reanalysis. The calculated global budgets are presented and the links between the (1) aqueous-phase processes, (2) aerosol dissolution, and (3) atmospheric composition are demonstrated and quantified. The model results are supported by comparison to available observations. We obtain an average global OXL net chemical production of 12.615 ± 0.064 Tg yr-1 in EC-Earth, with glyoxal being by far the most important precursor of oxalic acid. In comparison to the ERA-Interim simulation, differences in atmospheric dynamics and the simulated weaker oxidizing capacity in EC-Earth overall result in a ∼ 30 % lower OXL source. On the other hand, the more explicit representation of the aqueous-phase chemistry in EC-Earth compared to the previous versions of the model leads to an overall ∼ 20 % higher sulfate production, but this