A nutrient sensor suite for autonomous ocean vehicles

We report a comprehensive suite of miniaturised automated chemical nutrient analysers and their integration into a fleet of autonomous underwater and surface vehicles. Combining these technologies creates a system capable of conducting multi-parameter automated in situ chemical measurements on spatial and temporal scales that were not previously possible.

The suite consists of lab-on-chip (LOC) analysers for phosphate, nitrate, nitrite, ammonia, silicic acid, iron(II) an d total dissolved iron, while the fleet consists of a long range AUV (Autosub Long Range, developed at NOC), underwater gliders (Teledyne Slocum and Kongsberg Seagliders) and a surface vehicle (Liquid Robotics Waveglider).

The LOC nutrient analysers perform reagent-based (wet chemical) colorimetric, fluorimetric or chemiluminescence measurements on polymer microfluidic chips. Microfluidics (i.e. manipulating fluids 10-100 µL) is key to minimising physical size, reagent usage and power consumption, leading to miniaturised systems with increased endurance. This enables multiple units to be integrated into a single mobile platform. Analytical performance of the LOC sensors is, for most parameters, comparable laboratory-based seawater analysis techniques. While they do create liquid chemical waste, this is stored onboard the vehicle until recovery and not expelled into the environment.

The sensor suite connects to the vehicle via hub that provides a common interface and logger designed to be easily transferable to other platforms in future. For several platforms the sensor data is also telemetered via the vehicle for near real-time data.

We present novel chemical datasets from the sensor suite and vehicles that would be impossible or difficult to collect using traditional techniques of ship-based surveys and manually collected water samples.