Towards Autonomous Observing Platforms for Use in Ocean Tracer Release Experiments

John Christopher L'Esperance, Dalhousie University, Oceanography, Halifax, NS, Canada, Toste S Tanhua, Helmholtz Centre for Ocean Research Kiel, GEOMAR, Kiel, Germany and Douglas Wallace, Dalhousie University, Department of Oceanography, Halifax, NS, Canada
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.