Ocean alkalinity enhancement increases seawater alkalinity to boost carbon dioxide uptake. We report the first field deployment of an autonomous Lab-on-a-Chip total alkalinity analyzer during an ocean alkalinity enhancement trial using magnesium hydroxide slurry. In 2023, the analyzer-co-deployed with pH, salinity, and temperature sensors 60 m from the discharge-performed 314 total alkalinity and 52 onboard certified reference material measurements over 40 days, totaling ~3300 optical readings. High-frequency alkalinity measurements revealed stronger semi-diurnal tidal coherence prior to dosing, followed by reduced coherence and more variable phase relationships as dosing progressed. Over the deployment, total alkalinity relative to a baseline alkalinity-salinity relationship significantly increased by ~40 µmol/kg after ~210 tonnes of alkaline addition and did not return to baseline between dosing intervals, indicating a system memory effect with cumulative alkalinity retention. This autonomous in situ approach captures high-resolution variability relevant to monitoring and verifying alkalinity-based carbon dioxide removal, which is challenging to achieve using discrete bottle sampling.
Zabihihesari et al. (Wed,) studied this question.