A micro-hole potentiostatic oxygen sensor for oceanic CTDs

Abstract A non-membrane, micro-hole, potentiostatic oxygen sensor was designed and tested for use on an oceanic CTD. The sensor consists of three electrodes: a carbon-fiber cathode, a Ag/ AgC1 reference and a platinum anode; all are mounted in a plexiglass flow duct. The carbon-fiber cathode is a bundle of 1000 carbon fibers recessed in epoxy and electroplated with platinum. The sensor calibrates to oxygen concentration (0 2 ), not partial pressure. The effect of temperature on sensor output can be modelled with an activation energy term. Pressure decreases current output of these sensors 5% over 5000 dbar. Ten calibration casts were performed as part of the Hawaii Ocean Time Series (HOTS) sampling program in the Pacific Ocean north of Oahu, Hawaii. Vertical profiles of O 2 were calibrated using 18–23 Winkler determinations from each cast. The coefficient of determination ( r 2 ) for the calibrations ranged from 0.9979 to 1.0000. The standard deviation of the unexplained error between predicted O 2 and Winkler OZ ranged from 0.49 to 3.6 μM, with a mean value of 1.3 μM.