Ocean carbon capture raises concerns over marine stress, say UK scientists

CAPTURING CO2 directly from seawater could negatively impact marine organisms and put them under stress, according to research from the University of Exeter and Plymouth Marine Laboratory.

The study is part of the researchers’ joint SeaCURE project, which uses electrodialysis to extract inorganic carbon from seawater for storage, before returning the treated water back into the ocean.

Earlier this year, the SeaCURE project launched its first pilot plant for Direct Ocean Carbon Capture and Storage (DOCCS) at the Sea Life Centre in Weymouth, UK. The plant can process 3,000 L of seawater per minute and remove around 100 t/y of CO2.

The new study raises concerns about scaling the technology to commercial levels, citing a lack of research into its potential impact on marine ecosystems.

Guy Hooper, the lead author of the study, said: “Our ongoing work shows that DOCCS technology is potentially a very powerful tool, but further investigation on the biological effects is now urgently needed in order to understand when and where they might occur and how they can be mitigated.”

Stressful waters

In the DOCCS process, seawater is acidified to release CO2 that is then captured and stored. The treated seawater is then neutralised with alkaline chemicals and returned to the sea.

The study identified several potential impacts of DOCCS-treated seawater on marine life, including reduced availability of dissolved inorganic carbon, which plankton and seaweeds require for photosynthesis, and shellfish and crustaceans need for shell formation. The elevated pH of treated seawater may also place physiological stress on certain marine organisms.

Hooper explained: “It’s clear from our lab-based experiments that returning treated decarbonised and high pH seawater to the ocean, without sufficient dilution, could place stress on certain marine organisms.”

Further research

The SeaCURE team has identified further areas of investigation, including lab studies on how specific marine organisms respond to DOCCS discharge conditions, and the long-term impacts of DOCCS on marine food webs.

Paul Halloran, another co-author of the study, said: “Understanding potential environmental risks is crucial not only for protecting marine ecosystems but also for supporting licensing applications, developing mitigation strategies, and ensuring public acceptance of these technologies.”

The team is now conducting environmental impact studies and engaging with the public and other marine users to understand expectations around marine CO2 removal research.