Dynamics of Methane Bubbles in the Sediment in the Presence of Intense Internal Waves in a Stratified Ocean.

It is shown that the existence of intense (linear or nonlinear) internal waves in the ocean, in particular in shallow water, with gas saturated sediment can lead to remarkable temporal and spatial fluctuations of hydrostatic pressure at the seafloor and in turn to spatio-temporal variation of methanogenesis and spatial distribution and dynamics of methane bubbles. It is shown on the base of numerical modeling that for typical variations of hydrostatic pressure at the bottom about 500 Pa with the horizontal scale of variability about a few hundred meters and the time period from a few minutes and more, there are variations of velocity of moving bubbles, their concentrations and displacement of the gas layer’s horizon by about 10 cm and more per time period. Due to strong dependence of the sound speed in the sediment on gas bubbles concentration mentioned variations can be registered and estimated using acoustical methods. It can be done using for example multiple reflections of the sound pulse from the sea floor for different moments of time and sound propagation in shallow water waveguide in different areas in the presence of internal waves. The corresponding numerical modeling is carried out, experimental setup is discussed.