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

The measurement of low-level dissolved CO(2) using a fiber-optic sensor is described. The sensor, based on the Severinghaus CO(2) electrode principle, consists of a CO(2)-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 pCO(2) 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 pCO(2) in surface seawater.