Natural seabed gas leakage -- variability imposed by tidal cycles

Abstract

The likelihood of leakage from sub-seabed Carbon Capture and Storage (CCS) sites has been debated since geological storage was proposed as an effective option to remove greenhouse gas emissions from the climate system. Within the marine environment, passive acoustics has been presented as a feasible way for detecting and quantifying any such leakage. When determining estimates of gas escape across the seabed, the influence of dynamic environments, introducing natural variations in seepage rates must be considered, including tidal cycles. Panarea, Sicily, is the location of a series of natural marine CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas seeps and provides an excellent test bed to investigate variations of natural seabed gas leakage across a tidal cycle. A multivariate statistical approach was used to recognize the relationship when gas leakage is dominated by natural forcing. We show that the tidal height correlates negatively with the bubble sound power spectral density, the gas flux, and the bubble size. The strength of the correlation can vary significantly for different investigated time periods of observation, showing sensitivity of tidal influence. Our results corroborate evidence that natural migration of CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> through the seabed is moderated by tidal cycles.