Ideas and perspectives: A framework for understanding efficiency losses of Ocean Alkalinity Enhancement

Abstract. Ocean alkalinity enhancement (OAE) is a proposed carbon dioxide removal (CDR) approach in which seawater alkalinity is increased to facilitate both the enhanced uptake of atmospheric CO₂ and long-term storage in the ocean’s dissolved inorganic carbon pool. Carbonate system thermodynamics provide a stoichiometric upper bound on the amount of CO₂ that can be taken up per unit of alkalinity added, but realized uptake can be lower due to dynamic physical and (bio)geochemical processes that evolve over time. This Perspective presents a structured framework for understanding these potential efficiency losses. We identify loss pathways across four categories: incomplete mineral dissolution, loss of alkalinity to solid phases, incomplete air–sea exchange, and indirect impacts on ocean biogeochemical cycles. The potential significance of each loss varies across OAE approaches and across spatial and temporal scales. We highlight that substantial knowledge gaps persist across all of these processes, and we suggest targeted research priorities to improve fundamental understanding and reduce uncertainty. By providing a common structure and definitions, this framework aims to support coordination across oceanographic disciplines and to improve assessments of OAE efficiency at both the project and global scale.