Interdisciplinary Research on Open Ocean Alkalinization

Adding fast-reacting alkaline substances directly to the open ocean is a promising pathway to achieving permanent carbon dioxide (CO2) removal at scales exceeding 1 gigaton (Gt) of CO2 per year. This approach, open ocean alkalinization (O-OAE), is projected to be achievable at relatively low costs and with low environmental impacts. However, further research is needed to address key scientific and engineering questions before large-scale implementation can be realized.

CSEi is building a comprehensive research program to investigate these key areas of O-OAE, spanning four broad topics:

1. Assessing the engineering requirements and economic feasibility of the large-scale production of calcium oxide (CaO) or magnesium oxide (MgO) + CaO mixtures produced by calcining limestone or dolomite with carbon capture and storage.
2. Assessing the engineering requirements and economic feasibility of transporting and distributing alkali hydroxides across the vast ocean surface.
3. Conducting ecological and geochemical studies to better understand the impacts of adding alkalinity to the ocean and its effectiveness in removing carbon from the atmosphere.
4. Exploring governance and economic mechanisms that could support responsible deployment of O-OAE at scale.

In addition to the individual research projects focused on O-OAE listed elsewhere on this site (e.g., Ocean Deacidification Project and Leading Indicators: Marine Microbial Community Gene Expression Responses to Ocean Alkalinity Enhancement), CSEi is initiating the following projects in 2025:

• Collaborating with engineering consultants and equipment vendors to develop studies on the engineering requirements and feasibility of producing alkali materials.
• Conducting laboratory experiments to evaluate the dissolution rates and sinking behavior of various alkali material candidates to inform effective and scalable strategies for O-OAE.
• Developing a global framework for identifying promising locations for large-scale alkalinity production by analyzing proximity to sedimentary rock, cost-effective energy, geologic CO₂ storage, and efficient ocean distribution infrastructure across major ocean basins.

View a flowchart of CSEi’s ongoing and planned ocean alkalinization projects

Project Update

On May 26, 2026, the project team published a report in Frontiers in Climate titled “Slaking quicklime with seawater for open-ocean alkalinity enhancement: technical feasibility and cost implications.”

The report is summarized below:

Looking at cheaper ways to do ocean alkalinity enhancement at scale

A promising way to remove carbon dioxide from the atmosphere is ocean alkalinity enhancement (OAE). The idea is to make seawater slightly more alkaline so it can store more carbon dioxide in a stable form by shifting seawater carbonate chemistry. To do OAE at scale, we would need to produce and move large amounts of alkaline material by ship.

One OAE approach, called open-ocean liming, involves adding lime-based materials to seawater. These include calcium oxide (CaO)—commonly known as quicklime—and calcium hydroxide (Ca(OH)2)—commonly known as hydrated lime.

Most studies of ocean liming assume that ships would transport hydrated lime. But quicklime may be a cheaper option; it is denser, easier to handle in bulk, and contains about 20% more alkalinity per unit mass. This would mean that ships could carry more alkalinity per trip.

The challenge is that quicklime must be slaked before use. Slaking is the process where quicklime is mixed with water to form hydrated lime. This is usually done on land with fresh water.

Our study simply looked at whether quicklime could be slaked onboard ships using seawater and what would be the costs savings of doing so.

We ran experiments using artificial seawater and compared the results with deionized water. Our results show that slaking quicklime with seawater is about as effective as with deionized water. Seawater slaking did produce small amounts of impurities (or secondary minerals), likely brucite and gypsum. However, these minerals are unlikely to significantly reduce OAE efficiency if alkalinity is distributed using recommended practices.

We also built a simple transport cost model. We found that transporting quicklime and slaking it onboard could reduce transport and port handling costs by up to 20% compared with transporting hydrated lime (slaked on land).

Overall, our results suggest that seawater slaking is technically feasible and could make open-ocean liming cheaper to deploy at scale.