Validating passive acoustic methods for gas flux quantification, offshore Panarea, Mediterreanean Sea

With the expected large scale adoption of carbon capture storage, a growing importance has been placed on developing methods for the detection and quantification of underwater gas releases in order to provide long term monitoring systems and assurance. Passive acoustic methods have strong potential, as a bubble larger than a few micrometers escaping from sediment into the water column produces a distinct acoustic signature, characterised by the Minnaert frequency. Building on this principle, Leighton and White (2012) devised a method for inverting the acoustic signature of a gas seep to determine its flux rate. However, until now little has been done to validate that passive acoustic gas inversion provides estimates that are consistent with other techniques, i.e., physical and optical measurements, in the field. A specialist acoustic-optical seabed lander was designed and deployed at a series of natural CO2 seep sites in offshore Panarea with the objective of comparing simultaneous flux estimates. Our results show that not only are acoustic estimates reliably consistent with all other methods but are also far more efficient.