Assessment of the potential of different alkaline minerals to mitigate ocean acidification and sequester CO2

Ocean alkalinity enhancement is a novel and upcoming approach to removing CO2 from the atmosphere while mitigating ocean acidification simultaneously. We employed different concentrations of a silicate mineral, olivine (Mg2SiO4), as well as of several calcium-based minerals, including dolomite (CaMg(CO3)2), calcite (CaCO3), chalk (CaCO3), and limestone (CaO) on artificial and North Sea seawater over an experimental runtime of 98 days to monitor their impact on seawater carbon chemistry and their potential to counteract ocean acidification. We systematically analyzed the major and trace metals of the minerals. Olivine contained the highest concentrations of the potentially ecotoxic trace metals nickel (Ni) and cobalt. Dolomite and olivine showed both the highest concentrations of iron, which might be beneficial for phytoplankton communities in the ocean, as those are often iron-limited. Dissolution efficiencies of the different minerals varied and reflected the general challenge of achieving a useful proportion of dissolved minerals for ocean alkalinity enhancement (OAE). Our results showed further a comparatively high potential of olivine and dolomite to increase and stabilize seawater pH, while the Ca2+ based minerals regularly lead to opposite effects, reducing the pH. Alkalinity could be increased by olivine, albeit comparatively less by dolomite and the other minerals, confirming olivine as an ideal candidate for OAE. The promising outcomes for olivine and dolomite warrant further applicability assessments, especially considering the Ni sensitivity of local natural communities; dolomite emerges as a suitable alternative for more sensitive environments in the context of mineral-based OAE.