Constraints on Ocean Alkalinity Enhancement: Limited Olivine Dissolution and Secondary Precipitation During Periclase Addition to Seawater

Abstract

Ocean alkalinity enhancement (OAE) is a proposed carbon dioxide removal strategy. Although several methods have been proposed for OAE, a systematic assessment of the mineral‐based alkalinity generation potential, along with the associated carbonate chemistry and biogeochemical responses to alkalinity additions, is not fully constrained. Previous studies indicate a high alkalinity generation potential of periclase and limited dissolution of olivine. We conducted a 9‐day mineral‐based mesocosm experiment to evaluate the potential of periclase and olivine for OAE across a broader range of targeted alkalinity additions: periclase (P1: +500, P2: +1,000, P3: +1,500, and P4: +2,000 μmol ) and olivine (O1: +250, O2: +500, O3: +750, and O4: +1,000 μmol ). Olivine additions did not result in measurable changes in alkalinity or pH, likely due to high dissolved organic matter, high pH, and limited mixing over time. In contrast, for periclase treatments (P1–P4), alkalinity increased by ∼200, ∼450, ∼447, and ∼463 μmol , while pH increased by 0.31, 0.42, 0.60, and 0.59, respectively. Dissolved inorganic carbon (DIC) declined within the first 24 hr in P2, P3, and P4, with alkalinity decreasing subsequently after day one. This decline in DIC, together with the isotopic signature of DIC (), revealed that secondary precipitation dominated at alkalinity additions of 1,000 μmol for periclase. This suggests that the threshold for effective alkalinity enhancement lies between 500 and 1,000 μmol . We further conclude that temporal changes observed in the mesocosms were primarily driven by nutrient availability and biogeochemical processes rather than the alkalinity addition.