Understanding the long-term Tidal Modulation on Methane Bubble Emissions using Acoustics, Southern Hydrate Ridge, Cascadia

Abstract

Carbon output from methane hydrate in the seafloor reservoir likely plays an important role in global warming and is not well quantified. Our study investigates the temporal discontinuity of methane bubble emissions at Southern Hydrate Ridge (SHR), developing a proxy for the presence of bubble plumes based on a 3.5-month record of acoustic Doppler current profiler echo intensity from the Ocean Observatories Initiative Cabled Array. We find significant tidal modulation of bubble emissions, consistent with the promotion or inhibition of hydraulic fracturing by hydrostatic pressure changes in the water column. The bubbling behaviour at SHR is best explained by a tidally modulated dynamic equilibrium regulated from above by water column hydrostatic pressure and below by changes in pore fluid pressure at the base of the methane hydrate stability zone.