What is Ocean Alkalinity Enhancement?
Ocean Alkalinity Enhancement (OAE) is a carbon removal technology that takes inspiration from the Earth’s natural weathering process, which removes excess carbon dioxide from the atmosphere. Weathering is a geological process that removes carbon dioxide from the atmosphere and durably stores it in the ocean.
The weathering cycle begins when carbon dioxide dissolves in rainwater, forming carbonic acid. As rain falls, this acid reacts with minerals in rocks, forming stable, dissolved bicarbonate ions. These ions are then carried by rivers to the ocean, where the carbon dioxide is securely stored for tens of thousands of years.
This natural weathering process takes place over thousands of years and is too slow to have a significant impact on the climate on human-relevant timescales. OAE speeds up the weathering cycle by adding minerals directly to the ocean, accelerating a natural process into a powerful tool that can benefit the climate now.
How does Ocean Alkalinity Enhancement work?
The ocean is the world's largest store of carbon—it holds fifty times more than the atmosphere. Carbon dioxide naturally dissolves into the surface of the ocean through a process called equilibration, where the ocean tries to match the concentration of carbon dioxide in the atmosphere. Much of this dissolved carbon dioxide forms carbonic acid.
In OAE, powdered rocks or minerals are added to the surface layer of the ocean. In another approach, seawater can also be electrochemically split to produce an alkaline and an acidic stream—with the alkaline stream being released back into the surface ocean.
These minerals—or the alkaline water stream in the case of electrochemical OAE—react with carbonic acid in seawater to form stable bicarbonate ions. The bicarbonate ions are then durably stored deep in the ocean for tens of thousands of years.
When the bicarbonate ions are formed, the amount of carbon dioxide dissolved in the seawater decreases. Due to equilibration, the surface of the ocean then absorbs more carbon dioxide from the atmosphere to maintain a balance. This is when carbon removal takes place.
How does Ocean Alkalinity Enhancement help address ocean acidification?
The ocean has absorbed nearly a quarter of all human-caused carbon emissions, which has dramatically increased the levels of carbonic acid in seawater. As the amount of carbonic acid rises, the ocean steadily becomes more acidic—known as ocean acidification—which can harm marine life, such as coral and shellfish.
In OAE, the materials added to the surface of the ocean are alkaline. These alkaline materials can help balance the pH of the ocean, locally reducing ocean acidification.
What are the advantages of Ocean Alkalinity Enhancement?
Significant scalability and durability
The ocean is the world’s largest store of carbon dioxide. This means that OAE is not limited by storage capacity like some other carbon dioxide removal technologies. Additionally, the carbon dioxide removed from the atmosphere can be durably stored in the ocean for thousands of years.
Minimal land use
OAE does not require significant areas of land for deployment, so it does not compete for land like other carbon removal technologies. Additionally, OAE can make use of existing coastal infrastructure—such as water and wastewater facilities—for deployment, reducing the need for additional infrastructure.
Improving marine ecosystems
Alongside removing carbon dioxide from the atmosphere, OAE can also have significant additional benefits. Primarily, OAE can locally reduce ocean acidification, which can benefit marine life like coral and shellfish, supporting local ecosystems.
How much does Ocean Alkalinity Enhancement cost?
Today, OAE is one of the more expensive carbon dioxide removal technologies, primarily because it is in the early stages of development and deployment. The typical average cost of OAE is approximately $850 per tonne.
