Response of the Carbonate System to Ocean Alkalinity Enhancement: A Mesocosm-Scale Experiment

We assessed two dosage regimes through repeated additionslow (20 μmol L^–1 alkalinity increase per addition, reaching a total theoretical alkalinity increment of 120 μmol L^–1) and high (180 μmol L^–1 per addition, reaching a total theoretical increment of 1080 μmol L^–1)comparing against control mesocosms over 14 days, monitoring the pH, total alkalinity, dissolved inorganic carbon, and solid precipitates.

The results for the treated mesocosms show that the low dosage effectively increased the total alkalinity and maintained it over the duration of the experiment, unlike the high dosage mesocosms, where the alkalinity dropped within a few days due to the secondary precipitation of carbonates and degassing. In particular, the final net changes of alkalinity were +110 μmol L^–1 for low dosages (close to the theoretical limit) but amounted to about −330 μmol L^–1 for the high ones.