Large-scale alkalinization of the open ocean is a promising method for removing gigatons of carbon dioxide (CO₂) from the atmosphere each year. This approach—known as open-ocean alkalinity enhancement (O-OAE)—involves adding alkaline materials (such as lime or quicklime) into surface ocean waters. Once added, these materials dissolve and release substances that increase seawater alkalinity, which promotes greater CO₂ uptake from the atmosphere by the ocean.
The effectiveness of O-OAE depends on two factors:
- How much alkalinity a material can release
- How quickly a material dissolves before sinking below the surface layer of the ocean.
To remove CO₂ from the atmosphere, alkaline materials must dissolve in the ocean’s surface layer, where chemical reactions drive atmospheric CO₂ uptake. Despite growing interest in O-OAE, little is known about how fast these materials dissolve or how quickly they sink. Both behaviors must be understood for large-scale O-OAE deployment.
This project will use laboratory experiments to measure the dissolution rates and sinking speeds of various candidate alkaline materials. The results will help identify the ideal material properties (such as composition and particle size) for effective O-OAE deployment. The findings will also support ongoing work on the large-scale production of carbon-neutral alkaline materials for ocean-based CO₂ removal.
Video: trajectories of sinking particles captured using a Real-Time Sinking Speed Visualizer (RTSSV) and analyzed with machine learning-based image processing.
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.
