Towards Autonomous Observing Platforms for Use in Ocean Tracer Release Experiments

Observing platform physical characteristics (e.g. speed, endurance, range, etc.) as well as, sensor/analyzer attributes (e.g. sampling frequency, response time) control the space and time resolutions at which observations of chemical tracers are made in the ocean. The in situ measurement of a large number of dissolved gases (e.g. nitrogen, noble gases, halocarbons, chlorofluorocarbons, etc.) from fixed or mobile platforms remains a challenge for chemical oceanographers (see Fassbender et al. 2017). We describe a fully automated, high-sensitivity and high-speed gas chromatography (GC) system which facilitates measurement of dissolved gas species which have conventionally been measured only through discrete sampling and in-laboratory analysis. Examples of underway measurements of transient tracers CCl₃F and CCl₂F₂, as well as, halocarbons CH₃I and CH₃Cl made in the Eastern Tropical South Pacific are described. Coincident measurements of SF₆ and a suite of volatile tracers made during a series of deliberate tracer release experiments in the Western Baltic Sea are also described. Tracer distributions measured during these campaigns are interpreted together with a suite of physical observations (including vessel-mounted ADCP, density fields) and remotely-sensed fields (sea surface height, chlorophyll α and particulate inorganic carbon). Considerable progress toward integrating the trace gas analyzer with the unmanned surface vehicle Dorado has been made. The combined system’s planned use for the detection of a deliberate tracer during a USV- or AUV-supported tracer release experiment (TRE) is described. The tool set will be used during such a TRE to validate circulation model -based representations of the dispersion of contaminants/pollutants.