Raw data of pCO2 measurements during Celtic Explorer cruise CE12010 at station 44ROV12 (Gas Release Experiment). The gas discharge of the gas release experiment was observed in situ during a 4 hour dive with GEOMAR's remotely operated vehicle ROV Kiel 6000 equipped with HD camera/video device and a sonar system. The spread of the dissolved CO2 plume was monitored geochemically using the commercial HydroC pCO2 sensor (S/N 0412-006, Kongsberg Maritime Contros GmbH) mounted to the front porch of the ROV. The sensor was calibrated for pCO2 signals up to 3,000 µatm (accuracy ~1% of reading resolution; resolution: <30 µatm) and was programmed to measure in 60 s intervals, which is equal to the sensor's response time.