Applications of chemical monitoring technologies for sub-sea CCS; Sensor assessment, baseline measurement and natural variability

• Evaluation of biogeochemical sensor for CCS MMV in Australia. • Tempo-spatial coverage of baseline biochemical signals for proposed CCS injection site. • Comparison and suitability of fixed and mobile platforms equipped with biogeochemical sensors for CCS monitoring. Sub-sea carbon dioxide (CO 2 ) storage on a commercial scale will require baseline measurements and ongoing monitoring of the biochemical signal of the water column above a storage complex to understand natural variation at the injection site and to be able to distinguish this from a potential leak from the storage structure. Here we discuss the performance of a suite of chemical sensors on various platforms and the observed biogeochemical signals within a near-shore dynamic environment in the Bass Strait, Gippsland, Australia. These sensors were deployed on seabed landers, surface moorings, Saildrone unmanned surface vehicle (USV) and a crewed vessel demonstrating reliable and high-quality, near real-time data return. We discuss the baseline signal and natural variability of the biochemical parameters at the study site and its relevance in the context of CCS monitoring.