An Autonomous Sensor and Telemetry System for Low-Level pCO2 Measurements in Seawater

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Abstract
The measurement of low-level dissolved CO2 using a fiber-optic sensor is described. The sensor, based on the Severinghaus CO2 electrode principle, consists of a CO2-sensitive bicarbonate buffer solution containing the pH-sensitive fluorescent dye carboxy-SNAFL-1 immobilized at the end of an optical fiber using a gas-permeable membrane. The sensor is used in a ratiometric mode and has a reversible working dynamic range between 200 and 1000 ppm pCO2 and a sensitivity ±1 ppm. Results are presented for the sensor calibration, effects of temperature, and response time characteristics. An integrated measurement system with electrooptic and data acquisition modules coupled to a satellite transmission system was tested in Vineyard Sound, MA, and data are presented that demonstrate continuous monitoring of pCO2 in surface seawater.