The Potential of Carbon Storage in the Ocean as Bicarbonate

Bicarbonate (HCO₃^-) and carbonate (CO₃^2-) ions in the ocean are a fundamental component of the global carbon cycle. The oceans contain approximately 38,000 billion tonnes of C as HCO₃^- and CO₃^2- (40x the C content of the atmosphere) with fluxes between different parts of this reservoir on the order of <1 GtC per year. Eventually, most of anthropogenic CO₂ emitted to the atmosphere will be incorporated into this sink because of mineral weathering. Intentionally storing additional CO₂ as HCO₃^- in the ocean has been suggested since the mid-90s (e.g., ocean liming, accelerated weathering of limestone, enhanced weathering), but estimates on storage potential, environmental impact, and technical feasibility remain poorly constrained. Our recent modelling estimate that trillions of tonnes of CO₂ can be stored as bicarbonate in the ocean with marginal changes in ocean chemistry when the impact is distributed globally. The changes could be more acute around the points of addition and may vary with each technology. While the global decadal scale-up of such an operation to impact the climate is not unprecedented, it raises questions regarding environmental and social acceptability.