Theme 3: Atmospheric deposition and ocean biogeochemistry

It aims to evaluate the impact of aerosols from fires on ocean biogeochemistry. The initiative is led by SOLAS researchers D. Hamilton, M.Perron and J.Llort and its first achievement was the successful organisation of the Fire science Learning AcRoss the Earth system (FLARE) workshop which brought together researchers from all disciplines related to fire. The workshop led to the publication of a white paper (Hamilton et al, 2024) that set the priorities of multidisciplinary research on fire-atmosphere-ocean interactions. Legacy from the workshop includes the publication of the first volume of a series of annual reviews on the "State of Wildfire".

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/).

Addressing underlying key questions related to how far atmospheric deposition of soluble iron and other trace element (TE) contained in aerosol – from different sources with different properties – modules marine biological activity and carbon dioxide (CO₂) sequestration requires the interdisciplinary focus and international expertise. And this is the purpose of this SCOR Working Group 167, “RUSTED”. Furthermore, to predict how ocean ecosystems will respond to future changes in soluble TE fluxes, models must 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 and atmospheric biogeochemistry communities; (2) a set of Reference Procedures for the most frequently used aerosol leaching schemes used for the estimation of TE solubility; (3) The creation of a web-hosted comprehensive data research tool for existing atmospheric TE measurements 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/

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 in the name of the RUSTED working group and will be held again in July 2025 next year. The SCOR working group (RUSTED) really embodies this link between SOLAS and GEOTRACES as many SOLAS theme 3 people are involved.

SOLAS Theme 3 members are also involved in workshops organised by the joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) working group 38 with the example of the  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 workshop in South Africa and the upcoming 2025 workshop in Crete”.

One of the main scientific research topics under the theme 3 is "understand atmospheric nutrient (Fe, N, P) deposition and its influence on ocean biological production". In order to predict changes in nutrients supply 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. Within the UN Decade, SOLAS scientists will play a role by producing the scientific knowledge necessary to fisheries, stakeholders, etc. and contribute to UN SDG 14 "Life below Water".