Theme 1: Greenhouse Gases and the Oceans

Bange, H.W., Mongwe, P., Shutler, J.D., et al. (2024). Advances in understanding of air–sea exchange and cycling of greenhouse gases in the upper ocean. Elem. Sci. Anth., 12 (1): 00044. https://doi.org/10.1525/elementa.2023.00044

Lachkar, Z., Cornejo-D'Ottone, M., Singh, A., et al. (2024). Biogeochemistry of greenhouse gases in coastal upwelling systems: Processes and sensitivity to global change. Elem. Sci. Anth., 12(1): 00088. https://doi.org/10.1525/elementa.2023.00088

Resplandy, L., Hogikyan, A., Müller, J.D., et al. (2024). A synthesis of global coastal ocean greenhouse gas fluxes. Global Biogeochem. Cycles, 38: e2023GB007803. https://doi.org/10.1029/2023GB007803

Tian, H., Pan, N., Thompson, R. L., et al. (2024). Global nitrous oxide budget (1980–2020). Earth Syst. Sci. Data, 16: 2543–2604. https://doi.org/10.5194/essd-16-2543-2024

van Doorn, E., Marandino, C.A., Peters, A.J., Keywood, M. (2024). Science, international law, and policy across the air–sea interface. Elem. Sci. Anth., 12(1): 00047. https://doi.org/10.1525/elementa.2023.00047

To better quantify oceanic GHG budgets and air-sea fluxes and improve understanding of associated processes, we highly recommend detailed analyses of GHG fluxes and processes in key regions. These include the eastern boundary upwelling systems (EBUS), western boundary current systems, Southern Ocean, Arctic Ocean, land-ocean aquatic continuum and oceanic Oxygen Minimum Zones (OMZs). Recommended approaches include (i) novel observing tools and methods (e.g., remote sensing technology, in situ biogeochemical sensors, isotope, and tracer methods), and (ii) diverse platforms, including ships, autonomous profiling platforms (e.g., Argo floats, gliders), moorings, Saildrones and drones. Sustained time-series observations at fixed sites are also necessary to characterise the seasonal and interannual variability and long-term trends in regional GHG fluxes. Key principles of the Findable, Accessible, Interoperable, and Reusable (FAIR) protocols should guide data curation.

Improved quantification of ocean-atmosphere CO₂, N₂O and CH₄ fluxes has been achieved by combining surface ocean measurements with a range of mapping methods including spatial interpolation, multivariate regression and neural network analyses, as well as machine-learning and global biogeochemical models. While these approaches are valuable tools and continue to be employed, continuation of long-term observational efforts and increased temporal coverage are crucial for improving the representation of GHG fluxes in global models, thereby reducing the current emission uncertainties.

 

The good agreement between bottom-up and top-down (inverse modelling) air-sea fluxes estimates of GHGs suggests the potential benefits of incorporating coastal, land-based GHG observatories as tools for increasing monitoring capabilities in coastal regions.

 

Existing methodologies should strive for widespread incorporation of data quality-control and reporting  standards to ensure inter comparability. Furthermore, combined measurements of CO₂, N₂O and CH₄ (whenever possible) are recommended to facilitate a comprehensive quantification of the GHG role in the oceans'net radiative balance.

Significant questions remain in predicting how future oceanic GHG fluxes will evolve in response to the combined impacts of multiple environmental stressors (e.g., ocean warming, eutrophication, deoxygenation, and acidification) and the reduction in CO₂ emissions. Successful prediction of future GHG evolution requires the development of ocean biogeochemical models able to represent the key physical, chemical, microbiological and ecosystem processes and their interactions, in order to reliably estimate the impacts of anthropogenic pressures and environmental changes on the ocean GHG fluxes. Relevant biogeochemical and ecosystem component models should also be incorporated into Earth System Models (ESMs) employed for climate prediction to enable accurate quantification of the important GHG-climate feedbacks.

The community-led Surface Ocean CO₂ Atlas (www.socat.info) is used for quantification of ocean CO₂ uptake and ocean acidification and for evaluation of climate models and sensor data. SOCAT has an annual public release of quality-controlled in situ surface ocean fCO₂ (fugacity of CO₂) measurements for the global ocean and coastal seas. The value chain based on in situ inorganic carbon measurements of the ocean, of which SOCAT is part, provides policy makers with vital information in climate negotiations.

Following on from the successes of the previous SOLAS/IMBER Carbon group (SIC), the Integrated Ocean Carbon Research Group has been formed. This initiative is jointly sponsored by IOC, IMBER, SOLAS, IOCCP, GCP, CLIVAR, and WCRP. The group will identify the key research needs for ocean carbon science for the next decade, develop strategies to address these needs, and address the links to societal and policy applications. An initial expert group workshop was held at the International Oceanographic Commission, Paris, in October 2019; The group has published the report: "Integrated ocean carbon research: a summary of ocean carbon research, and vision of coordinated ocean carbon research and observations for the next decade" in 2021.

The MEMENTO (MarinE MethanE and NiTrous Oxide) database (https://memento.geomar.de/) hosts the largest compilation of dissolved N₂O and CH₄ concentrations of the global ocean. Observational products derived from MEMENTO quality-controlled data are currently used to constrain the global ocean sources- sinks of both gases and assess their relative role in the ocean's radiative balance (in close connection with SOCAT data).    

The overall aim of RECCAP2 is to support the Global Carbon Project and the stocktaking of greenhouse gases (CO₂, CH₄, N₂O) by providing a reliable scientific basis for the transport of carbon between land, ocean and atmosphere. The RECCAP2 initiative is a bottom-up effort by the global research community and driven by the Global Carbon Project with partner groups. It builds from existing global and regional projects, and voluntary contributions.

A dedicated special issue in AGU Global Biogeochemical Cycles is available here:

https://agupubs.onlinelibrary.wiley.com/doi/toc/10.1002/(ISSN)2169-8961.RECCAP2

Data from the project:

https://www.bgc-jena.mpg.de/geodb/projects/Data.php

• The 11th International Carbon Dioxide Conference (ICDC11), 29 July – 2 August 2024, Manaus, Brazil. Website
• Integrated Carbon Observation System (ICOS) Science Conference 2024, 10-12 September 2024, Versailles, France. Website
• SOLAS Open Science Conference, session "Greenhouse gases and the oceans", 10-14 November 2024, Goa, India. Website
• 2024 American Geophysical Union (AGU) Fall Meeting, 9-13 December 2024, Washington, D.C., USA. Website

Related sessions:

OS004 - Advancing our Understanding of Ocean Carbon and the Air-Sea Carbon Flux

OS023 - Improving the Understanding of Multiscale and Cross-scale Air-Sea Interaction with Observations from Autonomous Platforms

B028 - Carbon Monitoring Systems Research and Applications