The work assesses the availability and localizations of different raw materials suitable for ocean alkalinity enhancement (OAE), like limestone, olivine, magnesite and brucite, since several billion tons of rocky materials are needed to achieve meaningful results for carbon sequestration through OAE. Resources of carbonates are immense and widespread around all continents. Availability of pure carbonates is still very large (outcrop area 4.1 million km²) and is not a constraint for the large‐scale development of OAE. Outcrops of pure carbonates within 10 km from the coastline and below bare ground or scrub/shrub, preferred for the logistics of exploitation, account for about 70,000 km², and could provide about 5,000 Gt of limestone. These values increase by a factor of 3 and 8 within 50 and 100 km from the coastline, respectively. Potential resources of olivine, less easily identifiable from the geological data, are estimated in the order of a few hundred billion tons and could provide only a minor contribution to ocean‐based carbon removal strategies. A comparison with the current level of world extraction of mineral raw materials is also provided. The annual production of limestone, estimated to be more than 6.6 Gt from deposits scattered all around the world, is about 9% of the world production of mineral raw materials (around 44 Gt yr⁻¹), and is of the same order of magnitude as coal (7.3 Gt yr⁻¹). The annual productions of magnesite (29 Mt yr⁻¹), olivine (8.4 Mt yr⁻¹) and brucite (1.5 Mt yr⁻¹) are two orders of magnitude lower.

Proposals to increase ocean alkalinity may make an important contribution to meeting climate change net emission targets, while also helping to ameliorate the effects of ocean acidification. However, the practical feasibility of spreading large amounts of alkaline materials in the seawater is poorly understood. In this study, the potential of discharging calcium hydroxide (slaked lime, SL) using existing maritime transport is evaluated, at the global scale and for the Mediterranean Sea. The potential discharge of SL from existing vessels depends on many factors, mainly their number and load capacity, the distance traveled along the route, the frequency of reloading, and the discharge rate. The latter may be constrained by the localized pH increase in the wake of the ship, which could be detrimental for marine ecosystems. Based on maritime traffic data from the International Maritime Organization for bulk carriers and container ships, and assuming low discharge rates and 15% of the deadweight capacity dedicated for SL transport, the maximum SL potential discharge from all active vessels worldwide is estimated to be between 1.7 and 4.0 Gt/year. For the Mediterranean Sea, based on detailed maritime traffic data, a potential discharge of about 186 Mt/year is estimated. The discharge using a fleet of 1,000 new dedicated ships has also been discussed, with a potential distribution of 1.3 Gt/year. Using average literature values of CO₂ removal per unit of SL added to the sea, the global potential of CO₂ removal from SL discharge by existing or new ships is estimated at several Gt/year, depending on the discharge rate. Since the potential impacts of SL discharge on the marine environment in the ships' wake limits the rate at which SL can be applied, an overview of methodologies for the assessment of SL concentration in the wake of the ships is presented. A first assessment performed with a three-dimensional non-reactive and a one-dimensional reactive fluid dynamic model simulating the shrinking of particle radii, shows that low discharge rates of a SL slurry lead to pH variations of about 1 unit for a duration of just a few minutes.