Is the removal of atmospheric CO2 via Ocean Alkalinity Enhancement feasible for climate mitigation?

Ocean alkalinity enhancement (OAE) is an approach for the deliberate removal of CO₂ from the atmosphere. This emerging technology relies on human intervention to increase the alkalinity of seawater which, in turn, induces a net flux of atmospheric CO₂ into the ocean. OAE is considered comparatively scalable and promises to deliver durable carbon removal but, to the best of our knowledge, a detailed feasibility study has not been undertaken. Key aspects to consider in such an analysis are: 1) how much alkalinity can be added at coastal outfall sites before breaching regulatory and geochemical constraints on seawater pH and carbonate saturation state, and 2) whether delivery of alkalinity can be achieved with a sufficiently low carbon footprint. We present results addressing both questions using the coast of Nova Scotia in eastern Canada as a test case. The first operational deployment of OAE started in Halifax Harbour, Nova Scotia, in October 2023.  By October 2025, the climate-tech company Planetary Technologies had retired carbon credits for the removal of 1,800 tons of CO₂. We ask what it would take to scale up from an annual net carbon removal of 1000 t/y of CO₂ to 1 Gt/y, which is commonly considered the threshold for a carbon removal technology to be scalable. Specifically, we analyze the maximum CDR capacity of individual outfalls since this will meaningfully influence deployment strategies for OAE. Our results are based on a suite of simulations using a coupled circulation-biogeochemical model for Halifax Harbour that has been used to support OAE field work and verification of OAE credits and a prospective Life Cycle Analysis conducted for this site.