Model‐Based Assessment of the CO2 Sequestration Potential of Coastal Ocean Alkalinization

Abstract The potential of coastal ocean alkalinization (COA), a carbon dioxide removal (CDR) climate engineering strategy that chemically increases ocean carbon uptake and storage, is investigated with an Earth system model of intermediate complexity. The CDR potential and possible environmental side effects are estimated for various COA deployment scenarios, assuming olivine as the alkalinity source in ice‐free coastal waters (about 8.6% of the global ocean's surface area), with dissolution rates being a function of grain size, ambient seawater temperature, and pH. Our results indicate that for a large‐enough olivine deployment of small‐enough grain sizes (10 µm), atmospheric CO 2 could be reduced by more than 800 GtC by the year 2100. However, COA with coarse olivine grains (1000 µm) has little CO 2 sequestration potential on this time scale. Ambitious CDR with fine olivine grains would increase coastal aragonite saturation Ω to levels well beyond those that are currently observed. When imposing upper limits for aragonite saturation levels (Ω lim ) in the grid boxes subject to COA (Ω lim = 3.4 and 9 chosen as examples), COA still has the potential to reduce atmospheric CO 2 by 265 GtC (Ω lim = 3.4) to 790 GtC (Ω lim = 9) and increase ocean carbon storage by 290 Gt (Ω lim = 3.4) to 913 Gt (Ω lim = 9) by year 2100.