A novel electrochemical calibration setup for oxygen sensors and its use for the stability assessment of Aanderaa optodes

We present a laboratory calibration setup for the individual multi‐point calibration of oxygen sensors. It is based on the electrochemical generation of oxygen in an electrolytic carrier solution. Under thorough control of the conditions, i.e., temperature, carrier solution flow rate, and electrolytic current, the amount of oxygen is strictly given by Faradays laws and can be controlled to within ± 0.5 µmol L−1 (2 SD). Whereas Winkler samples can be taken for referencing with a reproducibility between triplicates of 0.8 µmol L−1 (2 SD), the calibration setup can provide a Winkler‐free way of referencing with an accuracy of ± 1.2 µmol L−1 (2 SD). Thus calibrated oxygen optodes have been deployed in the Southern Ocean and the Eastern Tropical Atlantic both in profiling and underway mode and confirm the validity of the laboratory calibrations to within few µmol L−1. In two cases, the optodes drifted between deployments, which was easily identified using the calibration setup. The electrochemical calibration setup may thus facilitate accurate oxygen measurements on a large scale, and its small size makes it possible to configure as a mobile, sea‐going, Winkler‐free system for oxygen sensor calibrations.