Removal of dissolved inorganic carbon from seawater for climate mitigation: potential marine ecosystem impacts

Electrochemical technology can be used to remove inorganic carbon from seawater and facilitate the removal of carbon dioxide (CO₂) from the atmosphere. Electrochemical ‘Direct Ocean Carbon Capture and Storage’ (DOCCS) is a marine carbon dioxide removal (mCDR) method that removes atmospheric CO₂ by releasing low-carbon seawater into the surface ocean, where it re-equilibrates with the atmosphere and stores atmospheric CO₂. At the point of release, DOCCS discharge has low concentrations of dissolved inorganic carbon (DIC) and high pH, potentially causing unintended marine environmental impacts; however, its chemistry moves progressively towards that of ambient seawater as it dilutes and re-equilibrates with the atmosphere. To date, there are no published studies that investigate the impact of DOCCS discharge on marine ecosystems. Research from relevant analogues, where biological responses to low-DIC and/or high-pH seawater are investigated, provides some insight into potential DOCCS impacts. Despite this, significant evidence gaps remain. These evidence gaps are discussed alongside DOCCS-specific recommendations for future environmental impact research. Understanding the potential risks/benefits to marine ecosystems from discharge of low-DIC and high-pH seawater is critical to: (i) support licensing applications; (ii) develop any necessary mitigating actions; (iii) determine the net benefit of mCDR approaches; and (iv) stimulate informed public discourse about the acceptability of such approaches.