SeaCURE research in Weymouth - can the ocean help us tackle climate change?

Do we need to remove excess Carbon Dioxide from the atmosphere?

Carbon dioxide (CO₂) traps heat and warms our planet. The most important thing we must do is drastically cut our use of fossil fuels, so we don't keep rapidly increasing the amount of CO₂ in the atmosphere. But even if we reduce emissions a lot, there will still be some we can't avoid, such as from flying and farming (learn more). Removing some CO₂ from the air can help balance these leftover emissions. This is called Net Zero. The animation below shows how this works.

Why the ocean?

The ocean acts like a sponge, absorbing a large share of human-made CO₂. Carbon is over 100 times more concentrated in seawater than it is in air. Capturing carbon from seawater or increasing the capacity of the water to hold carbon, could therefore be more practical than capturing carbon from air. Doing this would also minimise competition for space on land, which limits how much carbon we can remove from the atmosphere by approaches like tree planting. The ocean already absorbs a lot of human CO₂ — it acts like a sponge. There is 100 times more carbon in seawater than in air, so removing carbon from seawater can be easier than removing it from air. It also helps avoid using large areas of land needed for things like forests (why land matters).

How can seawater help remove CO₂ from the atmosphere?

The ocean is where human-emitted CO₂ will ultimately go, but this natural process of carbon removal takes tens of thousands of years. We can speed things up in two different ways. If we think of the ocean as a sponge for CO₂, we can:

• (Option 1) 'squeeze out the sponge', taking carbon out of seawater, so it can refill with CO₂ from the atmosphere. This is known as Direct Ocean Carbon Capture;
• (Option 2) 'make the sponge more absorbant', increasing the capacity of seawater to hold carbon, therefore more rapidly drawing CO₂ out of the atmosphere. This is known as Ocean Alkalinity Enhancement.

For a more detailed explanation of the process and the chemistry, click here.

The 'sponge can be squeezed' either by engineered or biological approaches. Biological approaches like growing marine plants or algae sound promising, but face a major hurdle, a lack of nutrients in the ocean. As the ocean's nutrients are already in short supply, growing more marine plants or algae in one spot often just limits growth elsewhere, leading to little or no extra carbon being removed. At large scales, biological approaches also present a risk to biodiversity because they rely on large monoculture (e.g. vast seaweed farms). The SeaCURE project is therefore focused on the engineered approaches, which we believe are less risky and more scalable.

What is SeaCURE?

The SeaCURE team built a Weymouth pilot plant which can look at both of the engineered approaches to ocean carbon removal described above (Option 1 and 2). As the only publicly funded facility of its kind outside a laboratory, and the 1st pilot plant outside of the USA, the Weymouth plant is uniquely positioned to provide an independent and objective look at both the promise and the challenges of ocean carbon removal.

To-date our work has been focused on developing and testing the 1st approach - capturing CO₂ from seawater and returning lower-carbon water to the ocean, so that it absorbs more CO₂ from the air. The small amount of CO₂ removed in our tests is currently released back to the air, but in commercial-scale operation the CO₂ would be stored deep underground or used industrially in processes that lock it away.

SeaCURE is based at SEA LIFE Weymouth. SEA LIFE have a strong commitment to marine science and sustainability, and a pumped seawater system and space for trialling technology. Together with the wealth of data available on the English Channel's biology and chemistry, these factors made Weymouth an exceptional location.

What have we done so far?

Over a two-month trial, the team demonstrated that the SeaCURE technology removes carbon. The team also examined:

• Potential marine impacts and how to safeguard the marine environment.
• How to prove the technique actually removes CO₂ from the air.
• How much energy it might take at scale and what it might cost.
• What large-scale operation might look like, and what barriers would need to be overcome.

The project has been led and run by the University of Exeter, with the Plymouth Marine Laboratory, Brunel University of London and Eliquo Hydrok.

What about impacts on marine life?

At the small scale of our pilot plant, we are confident it poses no risk to marine life, because the released low-carbon seawater dilutes very quickly returning to normal ocean carbon levels within meters of where it enters the sea. Fish cannot be sucked into the seawater intake pipe, which is buried beneath the beach. This intake also supplies the SEA LIFE.

The research team works closely with Defra and the Environment Agency, and operate within our Environment Agency Permit. We have automated controls to prevent water being released above a pH of 9.5 (for context, this is the upper pH limit for UK drinking water) to ensure we don't breach this permit.

Commercial scale plants would release more water, which would take longer to dilute. We need to understand how this might affect local ecosystems. We ran laboratory experiments with marine plankton (the tiny plants and animals in the ocean) and blue mussels to begin testing this. When the low-carbon seawater was mixed with at least an equal amount of with normal seawater most species showed only small changes in how fast they grew or how active they were. However, when low-carbon seawater was mixed with only small amounts of normal seawater, some organisms appeared not to be able to grow, or significantly reduced their activity - emphasising the importance of further research.

For more information about the SeaCURE marine impact experiments click here.

For information on the potential environmental impact of increasing the capacity of seawater to hold carbon (Option 2), which has been studied in greater detail, click here.

What's next?

We want to continue our work in Weymouth. Our next priorities are to:

• Understand how marine life and ecosystems would react to commercial scale carbon removal

  Some effects can't be captured in a lab, so experiments in larger on-shore tanks, and potentially at-sea floating tanks, can be used to see how different marine organisms respond over time to the released seawater.

• Demonstrate unequivocally that removing CO₂ from seawater leads to CO₂ being removed from the air.

  This could be investigated by tracking the water and simultaneously measuring and modelling how it changes.

• Broaden our research to look at increasing the capacity of seawater to hold CO₂

  We want to expand our research to look at 'making the sponge more absorbent' (Option 2). To do this, we would run the pilot plant in a different configuration, to study potential long-term effects on the ocean, challenges, and how well the process removes CO₂.

Click here for more details about the kind of activity that could happen from SEA LIFE over the coming years.

Who is funding this?

The initial project was funded by the UK Government's Department for Energy, Security and Net Zero from 2021 to May 2025 under the Greenhouse Gas Removal Innovation Programme.

Since May we have been supported by the University of Exeter, and the Carbon to Sea Initiative (a non-profit that funds scientists and engineers around the world who are evaluating ocean carbon dioxide removal). Carbon to Sea have funded workshops to understand the interest and thoughts of the local community.

Local community views on the pilot will inform future funding bids, aiming to support the site as a global research hub.

Conclusion

We've shown from a two-month trial that we can remove carbon from seawater, but there is a lot more to be done. The ocean is complex and changes with tides, seasons and between years. Building a full understanding will take time and effort.

Meanwhile, we're keeping an open mind. It's too early to know which methods will work best, and we may need a mix to tackle CO₂ effectively.

The facility in Weymouth is globally unique. Continued research here helps us gather real world evidence responsibly. This evidence will help the public and policymakers decide whether ocean-based carbon removal can—and should—play a part in tackling climate change, and how we might best do this.