Environmental studies urgently required before Ocean Carbon Capture can go large-scale, scientists warn

Scientists from Plymouth Marine Laboratory (PML) and the University of Exeter are urging caution in the upscaling of ocean carbon removal technologies until more detailed research can be carried out into the environmental impacts.

It follows a review of current research in addition to initial assessments made as part of the team’s SeaCURE project.

Published in Frontiers in Climate, the study, “Removal of dissolved inorganic carbon from seawater for climate mitigation: potential marine ecosystem impacts”, represents the first comprehensive review of the potential effects associated with Direct Ocean Carbon Capture and Storage (DOCCS).

Such technologies – including SeaCURE – work by electrochemically removing dissolved inorganic carbon from seawater, which can then be stored. The treated low-carbon, high pH seawater is then released back into the ocean where it will then naturally draw down more atmospheric CO₂, restoring the seawater to a normal pH and carbon concentrations.

It is thought that ocean or marine carbon dioxide removal (also known as mCDR or oCDR) – in addition to radical carbon emissions reductions – represents an important component in efforts to mitigate global warming.

But, as the new paper’s lead author Guy Hooper explains, this must not be done at commercial scales until the environmental effects are much better understood:

“It would be irresponsible to deploy DOCCS technology at commercial scales until we can more accurately understand how species and ecosystems will react.

The SeaCURE pilot plant has allowed us to begin to understand DOCCS technology in a limited, small-scale and controlled way. 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.

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.” 

The research identifies several potential impacts of DOCCS-treated seawater on marine life:

• Low carbon availability: The technology significantly reduces dissolved inorganic carbon in the treated seawater, which marine organisms need for photosynthesis (plankton, seaweeds) and shell-building (crabs, shellfish)
• High pH conditions: Low carbon seawater typically has a high pH, which could stress marine organisms.
• Unknown ecosystem effects: No published studies have directly investigated how marine ecosystems respond to the unique combination of low carbon and high pH conditions created by DOCCS

The team is currently carrying out environmental impact experiments, as well as engaging the public and other marine users to understand what they would like to see from marine carbon dioxide removal research. These findings will be released in the near future

Several priority areas have been highlighted for further investigation:

• Laboratory studies examining how key marine organisms respond to DOCCS discharge conditions
• Long-term ecosystem studies to understand chronic impacts on marine food webs
• Field experiments using controlled mesocosm studies before any large-scale deployments
• Chemical characterisation of how DOCCS discharge behaves in different ocean conditions.

The new study has significant implications for the emerging marine carbon removal industry and climate policy. Several companies are developing DOCCS technologies, with pilot projects already underway in the UK and elsewhere.

“The ocean’s vast carbon storage capacity makes marine carbon dioxide removal techniques like DOCCS potentially very exciting,” said co-author Professor Helen Findlay.

“However, these technologies manipulate the marine environment in ways we don’t yet fully understand. The environmental research must keep pace with technological development to ensure these promising potential ‘solutions’ don’t cause unintended harm.”

Co-author Professor Paul Halloran from the University of Exeter, who leads the SeaCURE project, alongside PML’s Professor Tom Bell, added:

“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”  

This study was supported by the UK Department for Energy Security and Net Zero and the UKRI NERC CO₂ Removal Hub.