In Situ Calibration of Optode-Based Oxygen Sensors

Eleven optode-based oxygen sensors were used for shipboard hydrographic casts in the North Pacific. Oxygen data from the optode sensors were compared with high-quality oxygen data obtained with discrete water samples, and the performance of the sensors was evaluated. The response of the sensing foil of the optode decreases with increasing ambient pressure, and this pressure effect was found to decrease the response by 3.2% ( 1000 dbar)(-1). A new calibration equation for the optode sensors was proposed. On the basis of oxygen data from water samples, the optode sensors were calibrated so that the reproducibility was less than 1%. High-quality oxygen profiles from the optode were obtained for fast-profiling conductivity temperature-depth ( CTD) observations, by compensating for the temperature-dependent delay in the optode data due to the slow response time of the optode.