Summary/Abstract
Carbon storage in the ocean as bicarbonate ions (by increasing ocean alkalinity) has received very little attention. Yet recent work suggests sufficient capacity to sequester copious quantities of CO2. It may be possible to sequester hundreds of billions to trillions of tons of C without surpassing postindustrial average carbonate saturation states in the surface ocean. A range of technologies have been proposed to increase ocean alkalinity (accelerated weathering of limestone, enhanced weathering, electrochemical promoted weathering, and ocean liming), the cost of which may be comparable to alternative carbon sequestration proposals (e.g., $20–100 tCO2−1). The aim of this paper is to review all aspects of the inorganic C sink in the ocean, including the function of alkalinity in the natural oceanic C cycle (section 2), the changes in ocean chemistry imposed by artificial alkalinity changes (section 3), the stability of increased alkalinity in the ocean (section 4), technologies for increasing ocean alkalinity (sections 5 and 6), and the potential environmental impact (sections 6 and 7). This builds on existing general discussions of geochemical C sequestration, which ocean carbon storage is introduced in the context of other removal schemes. Alkalinity storage in the ocean raises issues around environmental impact, quantification, monitoring, governance, and longevity, all of which will be explored in detail in this review.