Theme 3: Atmospheric deposition and ocean biogeochemistry

Atmospheric deposition is an important nutrient source for marine ecosystems, with consequences on local, regional, and global biogeochemical cycles, as well as on the climate system. Theme 3 focuses on the relationships between natural and anthropogenic atmospheric inputs, the marine carbon and nitrogen cycles, and feedbacks to climate. The fundamental processes driving aerosol emissions, transportation, chemical reaction, and deposition may change atmospheric fluxes and surface mixed layer turnover times. In turn, microbial communities respond to changing atmospheric inputs, which may result in significant effects on the marine carbon and nitrogen budgets, as well as on atmospheric carbon dioxide uptake.

Theme 3 team

Team leaders

Santiago Gassó (United States, santiago.gasso@nasa.gov)

Maria Kanakidou (Greece, mariak@uoc.gr)

Team members

Alex Baker (United Kingdom, Alex.Baker@uea.ac.uk)

Ying Chen (China, yingchen@fudan.edu.cn)

Peter Croot (Ireland, peter.croot@nuigalway.ie)

Douglas Hamilton (United States, dshamil3@ncsu.edu)

Akinori Ito (Japan, akinorii@jamestec.go.jp)

Yoko Iwamoto (Japan, y-iwamoto@hiroshima-u.ac.jp)

William Landing (United States, wlanding@fsu.edu)

Maurice Levasseur (Canada, maurice.levasseur@bio.ulaval.ca)

Joan Llort (Spain, joan.llort@bsc.es)

Natalie Mahowald (United States, mahowald@cornell.edu)

Stelios Myriokefalitakis (Greece, steliosm@noa.gr)

Jun Nishioka (Japan, nishioka@lowtem.hokudai.ac.jp)

Morgane Perron (Australia, morgane.perron@utas.edu.au)

Alessandro Tagliabue (United Kingdom, a.tagliabue@liverpool.ac.uk)

Processes and impacts/stressors associated with long-lived greenhouse gases.

Main sources, cycling, processes, and species relating to Core Theme 3 (processes are indicated in italics).

Research questions

Key questions to be addressed within this theme are:

How do biogeochemical and ecological processes interact in response to natural and anthropogenic material input from the atmosphere across coastal and open ocean regions?
How do global warming, ocean acidification, and other anthropogenic stressors synergistically alter the uptake of atmospheric nutrients and metals by marine biota in different oceanic regions?
What are the large-scale impacts of atmospheric deposition to the ocean on global elemental cycles (e.g., C, P, and N) and climate change feedbacks in major marine biomes?

Priorities

Global key areas

Focus on key regions where atmospheric depositions and their impacts are important to marine primary production and biogeochemistry. These regions include coastal and open ocean regions such as the Southern Ocean, the Arctic Ocean, the Tropical Atlantic, the North Pacific, the Mediterranean Sea and the Indian Ocean.

Recent science highlight

- Increasing evidence of ecosystem stimulation by large atmospheric events

Studies report observed evidence that indicate atmospheric induced ocean phytoplankton blooms, such as a massive phytoplankton bloom following the eruption of volcano, and smoke from a major wildfire enhance the ocean productivity (Tang et al., Nature, 2021; Liu et al., Nat. Commun., 2022; Barone, et al., Geophys. Res. Lett., 2022).

- Importance of changing Fe chemistry during transport in the atmosphere

Recent studies clearly indicate importance of chemical reaction during the atmospheric transport such as the changing atmospheric acidity as a modulator of nutrient and Fe speciation, the influence of strong iron-binding ligands on cloud water (Baker et al., Sci. Adv., 2021; Gonzalez et al., Sci. Total Environ., 2022; Sakata et al., Atmos. Chem. Phys., 2022).

- Increasing importance of anthropogenic/combustion in iron emission

Recent studies have brought up a great deal of attention to Fe in combustion aerosols as an important source of Fe in the surface ocean, and the amount of Fe emitted globally from combustion sources has been estimated for many oceanic basins (Hamilton et al., Annu. Rev. Mar. Sci., 2022, Kurisu et al., Atmos. Chem. Phys., 2021; Ito et al., Sci. Adv., 2019).

- Progress in Fe isotope and modeling study approach

Measurements of Fe isotope in the ocean and associated modeling studies have been increasing in the last two years and indicate that the Fe isotope can be used as a fingerprint of anthropogenic input, only when evaluated with a model that accounts for other sources and biological iron cycling (König et al., Geophys. Res. Lett., 2022).

References

Baker, A., Kanakidou, M., Nenes, A., et al., (2021). ‪Changing atmospheric acidity as a modulator ‪of nutrient deposition and ocean biogeochemistry. Sci. Adv., 7, eabd8800. https://doi.org/10.1126/sciadv.abd8800

Barone, B., Letelier, R.M., Rubin, K.H. and Karl, D.M. (2022). Satellite detection of a massive phytoplankton bloom following the 2022 submarine eruption of the Hunga Tonga-Hunga Haʻapai volcano. ESS Open Archive, May 18, 2022. https://doi.org/10.1002/essoar.10511402.1

González, A.G., Bianco, A., Bouton, J., et al., (2022). Influence of strong iron-binding ligands on cloud water oxidant capacity. Sci. Total Environ., 829, 154642. https://doi.org/10.1016/j.scitotenv.2022.154642

Hamilton, D.S., Perron, M.M.G., Bond, T.C., et al., (2022). Earth, wind, fire, and pollution: A review on aerosol nutrient sources and impacts on ocean biogeochemistry. Annu. Rev. Mar. Sci., 14, 303-330. https://doi.org/10.1146/annurev-marine-031921-013612

Ito, A., Myriokefalitakis, S., Kanakidou, M., et al., (2019). Pyrogenic iron: the missing link to high iron solubility in aerosols. Sci. Adv., 5(5), eaau7671. https://doi.org/10.1126/sciadv.aau7671

König, D., Conway, T.M., Hamilton, D.S. and Tagliabue, A. (2022). Surface ocean biogeochemistry regulates the impact of anthropogenic aerosol Fe deposition on the cycling of iron and iron isotopes in the North Pacific. Geophys. Res. Lett., 49(13), e2022GL098016. https://doi.org/10.1029/2022GL098016

Kurisu, M., Sakata, K., Uematsu, M., et al., (2021). Contribution of combustion Fe in marine aerosols over the northwestern Pacific estimated by Fe stable isotope ratio. Atmos. Chem. Phys., 21(20), 16027–16050. https://doi.org/10.5194/acp-21-16027-2021

Liu, D., Zhou, C., Keesing, J.K., et al., (2022). Wildfires enhance phytoplankton production in tropical oceans, Nat. Commun., 13, 1348. https://doi.org/10.1038/s41467-022-29013-0

Sakata, K., Kurisu, M., Takeichi, Y., et al., (2022). Iron (Fe) speciation in size-fractionated aerosol particles in the Pacific Ocean: The role of organic complexation of Fe with humic-like substances in controlling Fe solubility. Atmos. Chem. Phys., 22, 9461–9482. https://doi.org/10.5194/acp-22-9461-2022

Tang, W., Llort, J., Weis, J., et al., (2021). Widespread phytoplankton blooms triggered by 2019–2020 Australian wildfires. Nature, 597, 370-375. https://doi.org/10.1038/s41586-021-03805-8

Observational studies and modelling

While the impact of aerosol deposition has been documented in several instances, it is also true that there is conflicting evidence from incubation and satellite studies showing a toxic impact or no biome response. This illustrates the complexity to understand a phenomenon that encompasses so many time scales and disciplines. This is why more comprehensive studies are needed, both to verify evidence that nutrient inputs from the atmosphere are affecting biological production. This can only be achieved through combination of in situ observations using ships and satellites, and numerical models representing atmospheric nutrient deposition and ocean biogeochemistry, including chemical models of the atmosphere.

Future visions

Progress in the quantitative understanding of deposition rates for elements (Fe, N, P) and other species to the surface ocean is moving forward but slow. The first ideas of the role of aeolian nutrient deposition were put forward in the late 80s/early 90s and since then significant knowledge (as well technological improvements) have enabled the discovery of the mechanisms and processes at play. However, there are no clear answers in the horizon as the limitation of the current approaches and tools are still apparent. For example, efforts are scattered all over the world focusing on different marine ecosystems. It would be worth to start to ask for more focused studies in selected areas. Also, major phenomena are just poorly understood or entirely missing in modeling efforts: the mineral dust, pyrogenic, anthropogenic aerosol transportation scale, importance of extreme events, deposition area (where), the turnover time and residence time in surface water, dissolution rate, and fraction of bioavailable Fe (chemical speciation, including transformation during transport that depends in part of the in situ conditions where the deposition occurs), under natural conditions. We still need information on controlling factors of Fe speciation (acidity, ligands, temperature, etc) and its evolution in time. Therefore, we will continue to advocate for initiatives that addressed these subjects.

Planned activities

Iron model intercomparison

With the increase of trace metal surveys in all ocean basins, we now have a better understanding of the nutrient and trace metals dynamics, and it is clear the importance of not only oceanic Fe sources but also those of atmospheric origin. Therefore, a coherent explanation for the biological response to input nutrients needs knowledge of both atmospheric and oceanic inputs of Fe. This subject is the core theme of SCOR Working Group 151 Iron Model Intercomparison Project (FeMIP) (https://scor-int.org/group/151/).

Reducing Uncertainty in Soluble aerosol Trace Element Deposition (RUSTED)

Addressing underlying key questions related to how far atmospheric deposition of soluble iron and other trace element (TE) aerosol – from different sources with different properties – modules marine biological activity and CO₂ sequestration requires the interdisciplinary focus and international expertise and this is the purpose of this SCOR Working Group. Furthermore, to predict how ocean ecosystems will respond to future changes in soluble TE fluxes, it is vital that models represent and reproduce current TE distributions. RUSTED has three key deliverables: (1) production of a glossary of terms addressing inconsistencies in the use of terminology used by the ocean biogeochemistry and atmospheric chemistry communities; (2) a set of Standard Operating Procedures for the most frequently-used aerosol leaching schemes used for the estimation of TE solubility; (3) The creation of a new, comprehensive database of atmospheric TE measurements following FAIR (Findable, Accessible, Interoperable, and Reusable) data principles aimed to facilitate easier evaluation and calibration of global models than is currently possible. SCOR Working Group 167: https://scor-int.org/group/reducing-uncertainty-in-soluble-aerosol-trace-element-deposition-rusted/

ACCEPTED: "Fire Land Atmosphere Ocean Workshop" in response to the European Space Agency (ESA) – Future Earth joint program open call for global research networks (GRNs): collaborative Earth observation (EO) activities 2022-2023. –> FLARE: Fire science Learning AcRoss the Earth system Workshop organised by SOLAS Early Career Researchers, Douglas Hamilton, Joan Llort and Morgane Perron aims at bringing land surface and wildfire researchers, remote sensing experts, atmospheric chemists, and biogeochemical oceanographers together to understand the future impacts of fires on the Earth system. The workshop will be an important contribution to SOLAS research, particularly to Core Theme 3, on Atmospheric deposition and ocean biogeochemistry, and the Cross-Cutting Theme on Science and Society.

COP27 event/discussion session at OSC22: to build a consortium (with GEOTRACE, IMBER and other large international programs: the goal is to propose a large project under the umbrella of the UN Ocean Decade with the general theme: present and future impact of fires on the ocean and feedbacks to society.

Research programmes

Current international research program "PEACETIME" which was endorsed by SOLAS has been completed. Its main results have been compiled in the published as “Atmospheric deposition in the low-nutrient-low-chlorophyll (LNLC) ocean: effects on marine life today and in the future (BG/ACP inter-journal SI); Editor(s): Christine Klaas, Cecile Guieu, et al.” in the Biogeosciences and Atmospheric Chemistry and Physics journal.

Relation to other global international programmes

In addition, progress quantitative understanding along with coherent explanations of the biological response at the ocean surface that incorporate the knowledge of both atmospheric and the oceanic Fe supplies has been slow. SOLAS will continue to advocate towards improving collaborations between ocean and atmospheric researchers by promoting more collaborative studies, symposium, workshop, and other activities with GEOTRACES project. SOLAS is working closely with GEOTRACES. The Iron at the air-sea interface workshop in 2022 continues to be conducted by Theme 3 members and will be held again next year. The above reference new SCOR working group (RUSTED)" really embodies this link between SOLAS and GEOTRACES as many SOLAS theme 3 people are involved.

Other workshops are also planned, including one to discuss nutrient deposition from the atmosphere to the oceans in the Indian Ocean “Potential role of atmospheric deposition in driving ocean productivity in the Southwest Indian Ocean, GESAMP WG38 with SOLAS SSC members, South Africa, 4-7 October 2022”.

SDGs, UN Ocean Decade

One of the main scientific research topics under the theme 3 is "understand atmospheric nutrient (Fe, N, P) deposition and its influence to ocean biological production". In order to predict changes in nutrients suppy from the atmosphere to the ocean surface in the future, understanding the material exchange process between the atmosphere and the ocean, which include atmospheric chemistry, quantitative estimation of the nutrient flux, and the amount of biological production produced by the nutrient deposition, is necessary. In order to achieve this, accurate numerical model research validated by observation data is required. SOLAS theme 3 studies will directly lead to an understanding of the role of the atmospheric nutrient deposition in the current and future oceanic biological production process and be related to human life. At UN Decade, SOLAS scientists will play a role as a producer of scientific knowledge required by fisheries, stake holders, etc. and contribute to UN SDG 14 "Life below Water".

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