Spatial Distribution of Noise near Marine Hydrocarbon Seeps

摘要

Releases of gas in the form of methane bubbles from the ocean floor are known as gas plumes. Interest in this natural phenomenon has been provoked for the following reasons. First, the gas plume is a direct indicator of methane (generally, gas hydrate) deposits in the ocean floor. Second, the bubble mechanism of gas transfer into the atmosphere plays an important role. Gas plumes are rather easily detected by acoustic methods using even shipboard sonar. The present communication shows that the presence of gas bubbles results in a significant decrease of sound speed and that gas plumes are an effective acoustic waveguide. Hence, the spatial distribution of underwater noise near the gas plumes is characterized by a innhomogeneous (modal) pattern. The spectral density of the noise has maxima at frequencies corresponding to the eigenmode of collective oscillations of the bubble cloud governed by the gas plume size and the void fraction of the medium.