Three-dimensional acoustic monitoring and modeling of a deep-sea CO₂ droplet cloud

We show that release of 5 liters of liquid CO2 at 1000 m depth can be readily detected acoustically, and tracked for over 30 minutes, and 150 m of ascent, with both surface ship (38 kHz) and ROV (675 kHz) sonars. The released liquid broke up into droplets covered with a hydrate film. The remarkably sensitive acoustic response of the droplets may be attributed to the high sound speed contrast between CO2 (300 m/sec) and sea water (1500 m/sec), the near spherical shape of the droplets created by the hydrate shell, and the high compressibility of the liquid. The observed cloud conformed closely to models of CO2 disposal, allowing for reasonable predictions of larger scale processes. This offers a remarkably sensitive technique for examination in real time of engineered releases of CO2, volcanic sea floor liquid CO2 plumes, or leakage from geologic CO2 storage.