Marine enhanced rock weathering (mERW) is proposed as a method to achieve ocean alkalinity enhancement, thus increasing the CO2 storage capacity of seawater. Deposition of minerals in shallow waters results in enhanced dissolution rates via the ‘benthic weathering engine’, thus inducing an additional alkalinity release from the seabed on top of the natural alkalinity efflux. However, the application potential of mERW as a carbon dioxide removal (CDR) technology remains uncertain. Here, we quantified the CDR potential via mERW through a spatially explicit model, using the coastal zone of France as a case study. We simulated the one-time addition of dunite (olivine-rich source rock) distinguishing between three sediment types: bedload, permeable, and cohesive seafloor environments. The average CO2 sequestration rate was estimated at 0.32 kg CO2 m–2 seafloor kg–1 dunite over 100 yr. The sediment type was identified as the most important factor governing the CO2 sequestration rate, as it critically constrains the olivine dissolution kinetics. Coarse sediments exposed to bedload transport provide the highest CO2 sequestration rates. The application area was restricted to the territorial seas of mainland France (12 nautical miles offshore), and we estimated that 45% of this zone is suited for mERW. This area is further reduced to 23% when nature conservation areas are excluded from application. Assuming a dunite (olivine-rich mineral) loading of 20 kg m–2 seafloor, the CO2 sequestration capacity over 100 yr for the entire mERW area in France is estimated to be 210 Mt. As such, mERW will not be able to cover the entire CDR need for a country like France but could be one technology in a larger portfolio of CDR techniques. Our model analysis identifies a number of uncertainties and knowledge gaps in the assessment of the mERW potential.

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