Enhancing alkalinity for ocean-based carbon dioxide removal

Project duration: July 2023–June 2026

Project lead

Team

Richard Matear, Mathieu Mongin, Sharon Hook, Cathryn Wynn-Edwards and Craig Neill, together with external collaborators Matt Eisaman, Lennart Bach and Philip Boyd. 

Opportunity

Successful carbon dioxide removal (CDR) needs to combine carbon capture with carbon storage, however, finding suitable locations to store carbon at the gigaton scale required to make CDR useful in reducing atmospheric carbon dioxide (CO₂) concentrations is challenging.

The oceans, covering more than 70% of the earth’s surface, are one obvious option. Ocean-based CDR holds great potential due to its durability and huge storage capacity. To utilise the oceans for long-term carbon storage, however, requires the development of novel approaches to increase ocean storage with minimal adverse impacts.

Ocean alkalinity enhancement (OAE) using electrochemical approaches has great potential for reducing atmospheric CO₂ concentrations and surface warming while addressing ocean acidification. Large-scale modelling simulations have already shown OAE to be effective, but to move it from a concept to a viable option requires addressing fundamental knowledge gaps around its feasibility, scalability, efficacy, risks and social acceptance. Several recent reports describe potential economic and societal benefits, and the CDR literature is full of various options for OAE, but there are no examples of a rigorous assessment. This provides an opportunity to develop the necessary infrastructure to facilitate rigorous investigation of OAE options for CDR and advance our understanding of its potential. Should OAE prove feasible for CDR, it would yield large-scale, permanent, CO₂ removal. 

Goal

We aim to develop a flexible, mobile, modular testbed system to explore a range of OAE options for ocean-based CDR.

We’ll use modelling to evaluate site selection, optimise dispersal and dilution of modified seawater and subsequent capture of CO₂, while the testbed will enable us to demonstrate the ability to add alkalinity to the ocean, track it, and assess its biological and chemical impacts. A suite of observational methods and novel autonomous sensors will be used to quantify changes in ocean chemistry.

We also plan to develop a framework for monitoring, reporting and verification. The ultimate goal is to gain the required scientific understanding and experience to enable a large-scale demonstration of OAE for CDR. 

Barriers

The key challenge to adopting OAE at scale is overcoming public perception of the environmental risks posed by alkalinity addition to the ocean. Potential ecological impacts, and how to monitor for them, especially for short duration exposures, are a current knowledge gap. Much of the current scientific literature assesses potential impacts of ocean acidification, not alkalinisation. By undertaking small-scale field experiments that demonstrate our ability to simulate and track the plume of alkaline-rich seawater and assess its biological and chemical impacts, we’ll build public confidence and social acceptance for larger-scale experiments and contribute valuable information on the ecological impacts of increasing pH.

There may also be some initial barriers when it comes to scaling up, including minimising energy requirements and cost, access to the infrastructure required for large volumes of seawater, and the storage and use of byproducts (such as hydrochloric acid). We intend to pursue a lifecycle analysis of the OAE options to address these issues. The research is inherently risky. We may not gain public acceptance or find suitable options for large-scale CDR. The flexible testbed, however, means that we can pivot to investigate new options as they emerge. The risk associated with not undertaking this work is that we miss an important opportunity to identify a suitable CDR option for Australia to meet its net zero goals.

 

References

Lenton, A., Matear, R. J., Keller, D. P., Scott, V., & Vaughan, N. E. (2018). Assessing carbon dioxide removal through global and regional ocean alkalinization under high and low emission pathways. Earth System Dynamics, 9(2), 339-357.

Kitidis, V., Rackley, S. A., Burt, W. J., Rau, G. H., Fawcett, S., Taylor, M., … & Fileman, T. (2024). Magnesium hydroxide addition reduces aqueous carbon dioxide in wastewater discharged to the ocean. Communications Earth & Environment, 5(1), 354.

Ebb Carbon. https://www.ebbcarbon.com