Scientists have successfully recorded the sound of methane bubbles from the seafloor, opening the door to using acoustics to identify and measure this important greenhouse gas in the ocean.
The next step, researchers say, is to fine-tune their ability to detect the acoustic signature of the bubbles so they can use the sounds to estimate the volume of methane in the offshore reservoirs.
“The bubbles in the streams make sound, and the frequency of the sound is related to the size of the bubble,” said Robert Dziak, an acoustics scientist with the National Oceanic and Atmospheric Administration and lead author on the study. “The smaller the bubble, the higher the pitch. And the larger the bubble, the lower the sound pitch, but the more methane it contains.
“Our ultimate goal is to use sound to estimate the volume and rate of methane gas exiting these seafloor fields,” added Dziak.
In recent years, scientists have found hundreds of bubble streams emanating from methane deposits off the Pacific Northwest coast, but they have no way to determine how much methane is stored there. Methane is found both as an icy hydrate deposit and in a gas phase within the sediments of the continental margins.
It potentially could be a new energy source, or it could pose a serious environmental threat as a greenhouse gas.
Passive acoustic records of seafloor methane bubble streams on the Oregon continental margin R.P.Dziak et al, Deep Sea Research Part II: Topical Studies in Oceanography Volume 150, Pages 210-217