As decarbonization efforts accelerate, scientists are exploring the ocean’s unique role as a carbon sink to remove greenhouse gases more efficiently. Direct Ocean Capture (DOC) technologies extract dissolved inorganic carbon from seawater and return it to the ocean after processing, leveraging natural exchange with the atmosphere to draw down additional CO2. Early UK-based pilots are now operating at public-facing sites, testing real-world logistics, energy use, and scalability.
Why seawater capture matters
Roughly a quarter to a third of anthropogenic CO2 ends up in the ocean as dissolved carbon species, making it a vast reservoir for engineered removal. DOC systems exploit this chemistry, using electrochemical or pH-shift processes to pull carbon from water streams, then allowing the ocean to equilibrate by absorbing more CO2 from the air. Because seawater has high carbon content and is continuously replenished, DOC could complement direct air capture in a potentially more energy-efficient way.
The SeaCURE pilot in the UK
A leading pilot, SeaCURE, is located at the Weymouth Sea Life Centre and targets processing thousands of liters per minute, aiming to remove on the order of 100 tons of CO2 annually in its demonstration phase. The collaboration spans universities and industry partners and is funded to surface technical bottlenecks such as fouling, energy needs, and carbon accounting. By placing the pilot at an operational facility with existing water circulation, the team studies integration with real marine infrastructure.
Engineering approaches and energy use
DOC methods include electrochemical separation, alkalinity enhancement, and membrane-based capture, each with differing energy profiles and byproducts. Key questions include long-term durability in corrosive marine environments, verification of net carbon removal, and the fate of captured carbon—whether mineralized, utilized, or stored. Comparative studies assess when DOC outperforms air capture and how renewable power can minimize lifecycle emissions.
Environmental and governance concerns
Some researchers caution that large-scale marine manipulation must be carefully monitored to avoid unintended ecological impacts. Independent reviews call for transparent MRV (measurement, reporting, and verification), public engagement, and precautionary regulation as pilot projects scale. As with other carbon removal, critics warn that removal is not a substitute for rapid emissions cuts but a complement for hard-to-abate sectors.
What it means
DOC is emerging as a promising tool in the carbon removal portfolio, with pilots beginning to quantify real-world performance and constraints. If robust MRV and low-carbon energy inputs are achieved, seawater capture could become a practical lever to draw down atmospheric CO2 alongside aggressive emission reductions.
