Development of a chemical sensor for the measurement of dissolved inorganic carbon in seawater
The thesis presents the development of a novel, autonomous DIC sensor for seawater measurements. The work details a stepwise sensor development process from a bench-top prototype to a fully submersible system. Both versions operate on a conductometric detection principle in combination with a gas diffusion sequential injection analysis : (i) a custom-made four-hollow brass electrode detection cell, and (ii) a custom-made gas exchange unit with a “Tube In A Tube” configuration.
The bench-top analyzer was validated through laboratory experiments and tested in multiple field trials. Each measurement required 15 minutes. It achieved an analytical precision of measurement of ± 4.9 and 9.7 μmol kg-1 in laboratory and field deployments, respectively, meeting ‘Weather Quality’ standards for ocean carbonate measurements. Based on the success of the bench-top analyzer, an in-situ version was developed, retaining the core architecture. It featured a compact and pressure-resistant housing suitable for shallow water deployments. The in-situ sensor was deployed in multiple field trials and demonstrated an analytical precision of measurement of < 20 μmol kg-1, with each measurement completed in 20 minutes.
The high-frequency DIC data collected during field deployments in the North Sea and the Kiel Fjord provided new insights into the short-term variability and environmental drivers of carbonate system dynamics in coastal and estuarine systems. These data resolved high spatial and temporal resolution which overcomes the limitations of traditional discrete sampling method and demonstrated the potential of the analyzer to enhance carbonate system monitoring.
Overall, the work in this thesis showed the development of a novel, cost-effective, and autonomous DIC analyzer with an aim to address a critical technological gap in marine biogeochemical research.
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