A MICRO-HOLE POTENTIOSTATIC OXYGEN SENSOR FOR OCEANIC CTDS

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 (O-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 O-2 ranged from 0.49 to 3.6 mu M, with a mean value of 1.3 mu M.