Hundreds of Methane Plumes Erupting Along East Coast
Becky Oskin, Senior Writer
In an unexpected discovery, hundreds of gas plumes bubbling up from the seafloor were spotted during a sweeping survey of the U.S. Atlantic Coast.
Even though ocean explorers have yet to test the gas, the bubbles are almost certainly methane, researchers report today (Aug. 24) in the journal Nature Geoscience.
"We don't know of any explanation that fits as well as methane," said lead study author Adam Skarke, a geologist at Mississippi State University in Mississippi State.
Surprising seeps
Between North Carolina's Cape Hatteras and Massachusetts' Georges Bank, 570 methane seeps cluster in about eight regions, according to sonar and video gathered by the National Oceanographic and Atmospheric Administration ship Okeanos Explorer between 2011 and 2013. The vast majority of the seeps dot the continental slope break, where the seafloor topography swoops down toward the Atlantic Ocean basin. [Gallery: Amazing images of Atlantic Methane Seeps]
The Okeanos Explorer used sound waves to detect the methane bubbles and map the seafloor. The technique, called multibeam sonar, calculates the time and distance it takes for sound waves to travel from the ship to the seafloor and back. The sonar can also detect the density contrast between gas bubbles and seawater.
Huge canyons etched in the shallow continental shelf also hide bubble plumes, as well as diverse ecosystems that are based on methane-loving bacteria. In 2013, researchers explored a handful of these seeps with Jason, a remotely operated vehicle, finding them teeming with crabs, fish and mussel beds. In Norfolk canyon off the coast of Virginia, researchers from the University of North Carolina at Wilmington discovered the largest methane seep ever found in the Atlantic Ocean, and possibly all the world's oceans. [Photos: Unique Life Found at East Coast Gas Seep]
Most of the methane seeps are in water less than 1,640 feet (500 meters) deep. Most of these shallow methane seeps seem to arise from microbes blurping out methane, the researchers said. The researchers did find some deeper methane vents, at which the ROV Jason glimpsed patches of methane hydrate. This is the icy mix of methane and water that appears when deep ocean pressures and cold temperatures force methane to solidify. Any type of methane gas can form hydrates.
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