EGU25-19618, updated on 15 Mar 2025
https://doi.org/10.5194/egusphere-egu25-19618
EGU General Assembly 2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
CO2 Dissolution as Bicarbonate in Seawater: Potential Co-benefits for Net Primary Production
Arianna Azzellino1, Daniela Basso2, Eleonora Barbaccia1, Mario Gabualdi1, Francesco Pietro Campo3, Giovanni Cappello3, Stefano Cappello3, Stefano Caserini4, Federico Comazzi3, Selene Varliero1, Pietro Macchi1, Samira Alamooti1, and Guido Raos1
Arianna Azzellino et al.
  • 1Politecnico di Milano DICA Civil and Environmental Engineering Department, Piazza Leonardo da Vinci, 32, 20133 Milano, MI, Italy
  • 2Department of Earth and Environmental Sciences, University of Milano–Bicocca, CoNISMa Research Unit of Milano–Bicocca, Milan, Italy
  • 3Limenet s.r.l., Galbiate (LC), Italy
  • 4Department of Engineering and Architecture, Università di Parma

The dissolution of CO2 in seawater as bicarbonate ions (HCO₃⁻) offers a promising alternative to geological storage, provided the process ensures long-term stability and avoids harming marine ecosystems. Storing CO2 in the form of bicarbonate ions could remain effective for geologic timescales, potentially up to 10,000 years [1–3]. This approach involves treating natural seawater by mixing it with pre-equilibrated seawater solutions produced from the reaction of CO2 with Ca(OH)2, adjusted to maintain the same pH as seawater. Recent research [4] has shown that the resulting bicarbonate-rich solution is stable, but concerns persist regarding its potential environmental impacts. While alkalinity itself does not directly affect marine biology, its increase significantly alters pH and the concentrations of key ions and molecules, such as those in the carbonate system, which can directly influence biological processes. The extent of modifications to seawater carbonate chemistry depends on the amount of alkalinity added per unit volume and the rate at which this volume mixes with surrounding waters. The rate at which perturbed seawater equilibrates with the atmosphere is also a critical factor. Seagrasses, marine angiosperms that evolved from terrestrial plants and returned to the sea during the Cretaceous period (approximately 140 to 100 million years ago), play a vital role in marine ecosystems. Seagrass meadows are among the most productive ecosystems on Earth, with an average primary productivity ranging from 394 to 1200 g C m⁻² y⁻¹. These meadows provide numerous essential ecosystem services. Seagrasses are thought to benefit from ocean acidification, as they can utilize both CO₂ and HCO₃⁻ for photosynthesis, although they have a higher affinity for CO₂ and are often carbon-limited [6–7]. Additionally, evidence from natural volcanic CO₂ vents at Ischia, Panarea Islands, and Basiluzzo Islet—where conditions of natural acidification occur—indicates a correlation between increased dissolved inorganic carbon (DIC) and enhanced net primary production [8]. Building on existing literature, this analysis will explore the potential co-benefits of increased bicarbonate concentrations for seagrasses, aiming to assess how these benefits could enhance seagrass health and growth. It will also evaluate the opportunity to integrate this technology with Nature-Based Solutions, such as seagrass restoration, to maximize ecosystem resilience and climate mitigation efforts.

References

[1] Renforth & Henderson. (2017). Assessing Ocean Alkalinity for Carbon Sequestration. Rev. Geophys. 

[2] Middelburg et al. (2020). Ocean Alkalinity, Buffering and Biogeochemical Processes. Rev. Geophys. 

[3] Eisaman et al. (2023). Assessing the Technical Aspects of Ocean-Alkalinity-Enhancement Approaches. State Planet, 2-oae2023, 1–29.

[4] Varliero et al. (2024). Assessing the Limit of CO2 Storage in Seawater as Bicarbonate-Enriched Solutions. Molecules. 29, 4069.

[5] Duarte et al. (2005). Major role of marine vegetation on the oceanic carbon cycle. Biogeosciences 2, 1–8.

[6] Invers et al. (2001). Inorganic carbon sources for seagrass photosynthesis: an experimental evaluation of bicarbonate use in species inhabiting temperate waters, J. Exp. Mar. Biol. Ecol., 265, 203–217, 2001.

[7] Koch et al. (2013). Climate change and ocean acidification effects on seagrasses and marine macroalgae, Glob. Change Biol., 19, 103–132.

[8] Guilini et al. (2017). Response of Posidonia oceanica seagrass and its epibiont communities to ocean acidification. PLoS ONE 12 (8): e0181531

How to cite: Azzellino, A., Basso, D., Barbaccia, E., Gabualdi, M., Campo, F. P., Cappello, G., Cappello, S., Caserini, S., Comazzi, F., Varliero, S., Macchi, P., Alamooti, S., and Raos, G.: CO2 Dissolution as Bicarbonate in Seawater: Potential Co-benefits for Net Primary Production, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19618, https://doi.org/10.5194/egusphere-egu25-19618, 2025.