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<p>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.</p>

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High frequency in situ total alkalinity measurement for monitoring ocean alkalinity enhancement field trials

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年4月22日

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  • Alireza Zabihihesari,
  • Will Burt,
  • Colin Sonnichsen,
  • Shahrooz Motahari,
  • Alex Whitworth,
  • Robert Izett,
  • Caroline Fradette,
  • Douglas Wallace,
  • Vincent Sieben

摘要

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.