HOT-75 COMMEMORATIVE SCIENCE SYMPOSIUM

A Potentiostatic, Solid-state Oxygen Sensor for Oceanic CTDs

Marlin Atkinson

Hawaii Institute of Marine Biology, SOEST, PO. Box 1346, Kaneohe, HI 96744

A non-membrane, potentiostatic oxygen sensor has been developed for oceanic CTDs and field-tested at Station ALOHA. The cathode of the sensor is a bundle of 1000, 3-µm diameter platinum-tipped carbon fibers that are recessed in epoxy. The sensor calibrates directly to oxygen concentration (not partial pressure as do membrane sensors), has a very small pressure effect and relatively fast response. These sensors, however, have a long-term decay of output, making them poor for moorings. The long-term drift does not preclude attainment of excellent calibrated oxygen profiles. For hydrocasts at Station ALOHA, the mean error of predicting oxygen concentrations of 19 bottles was not significantly different than the mean error in sampling of Niskin bottles (1.01 µM; mean r² of 10 deep casts was 0.9994.) This level of error in calibrations can be achieved using only three Winkler determinations on a cast. These potentiostatic, solid-state oxygen sensors are excellent for determining the fine-structure of oxygen in the ocean.

HOT program data have also been used to develop new oxygen calibration equations for membrane oxygen sensors. The high quality oxygen profiles were used to verify a temperature effect on the pressure term.