Biogeochemical and Carbonate Chemistry Response to Natural and Anthropogenic Mineral‐Based Ocean Alkalinity Enhancement

Abstract

Ocean alkalinity enhancement, a marine carbon dioxide removal method, involves the addition of alkaline substances to seawater, thereby shifting the carbonate chemistry speciation toward carbonate ions. Ongoing research seeks to evaluate the efficacy and durability associated with these substances. Here, we investigate the alkalinity generation potential and response of carbonate chemistry speciations for three natural minerals—olivine, kaolinite, and dolomite, and two anthropogenic minerals—periclase and hydrated lime. Overall, no significant changes in alkalinity (), pH and dissolved inorganic carbon (DIC) were observed for the natural minerals, suggesting that these minerals have a lower efficiency in increasing . In contrast, the dissolution of anthropogenic minerals increased up to 18, representing more than 80 of the total added , and elevated pH up to 0.6 units. Additionally, we used the temporal changes in the DIC concentration and its isotopic composition (C) within the mesocosms to trace secondary carbonate precipitation, remineralization, photosynthesis, ingassing and outgassing. No clear alkalinity‐loss or secondary‐precipitation signal was detected over 9 days under the tested mesocosm conditions. As the loss of alkalinity via secondary precipitation diminishes the efficiency of the alkalinity enhancement, identifying the range of alkalinity levels that do not induce secondary precipitation is valuable for evaluating the effectiveness of this method.