Establish the metrological traceability of seawater acidification measurements

Since the beginning of the industrial revolution, the concentration of carbon dioxide (CO₂) in the atmosphere has increased by 50% due to human activities. Each year, the ocean absorbs 26% of CO₂ emissions. However, this absorption leads to ocean acidification and changes in the carbonate system. This, by affecting the stability of calcium carbonate mineral forms, affects marine biodiversity. Oceanographic measurements are essential for observing the oceanic carbonate system, supporting decision-making regarding mitigation and adaptation strategies. Monitoring acidification relies on accurate measurements of variables such as pH_T and total alkalinity (TA). To ensure data quality, international recommendations and best practice guidelines have been established, such as those from the Global Ocean Acidification Observing Network (GOA-ON), which sets data quality objectives.

The thesis work aims to support oceanographers with metrological tools to ensure the comparability of pH_T and TA measurement results. Metrology, including traceability, validation of measurement procedures, and uncertainty assessment, is crucial for obtaining reliable and comparable results, enabling the evaluation of long-term trends in ocean acidification.

For both parameters, reference materials have been developed and tested in inter-laboratory comparisons, allowing the evaluation of the precision and trueness of measurement methods. The uncertainty budgets of pH_T and TA measurements have also been studied using two approaches of uncertainty quantification.

Finally, improvements to the metrological traceability chains are presented.

ocean acidification, carbonate system, total pH, total alkalinity, metrology, traceability

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