Natural CO₂ Seeps Offshore Panarea: A Test Site for Subsea CO₂ Leak Detection Technology

Abstract

During RV Poseidon cruise POS469 (May 2014), the distribution of pCO₂ in the near field of submarine volcanic gas flares in shallow water depths down to 50 m below sea level was continuously monitored using three different and independent methodologies. In situ nondispersive infrared (NDIR) spectrometry, pH measurements, and onboard membrane inlet mass spectrometry (MIMS) were used to determine the fate of rising CO₂ bubbles and the dissolved CO₂ plume patterns in a 300 × 400-m working area. The In situ sensor carrier platform, a towed video-controlled water sampling rosette, equipped with CTD sensors, guaranteed excellent ground truthing of seafloor characteristics and bubble discharge. Sensor data and near-seafloor observations indicated that the gas bubbles (<9 mm in diameter, >97 vol.% of CO₂) dissolved very rapidly within the first 10 m above seafloor. Bottom water masses enriched with pCO₂ (up to 1,100 μatm) show low pH values (up to 7.80) and tend to spread rather downslope west than following the measured weak current in SSE-SSW direction. The 3-D evaluation of pCO₂ plume is a valuable tool to back-trace the origin of CO₂ leakage when compared with local current regimes, water column CTD data, and seafloor bathymetry. Seep sites offshore Panarea can be used for studying CO₂ leakage behavior and testing measuring strategies in shallow waters. Moreover, this area is a naturally designed laboratory to improve existing physicochemical and oceanographic transport models for subsea CO₂ leakage.