Article By: Becky Oskin of LiveScience
In an unexpected discovery, 100s 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.
Btwn North Carolina’s Cape Hatteras & Massachusetts’ Georges Bank, 570 methane seeps cluster in about 8 regions, according to sonar & video gathered by the National Oceanographic & Atmospheric Administration ship Okeanos Explorer between 2011 & 2013. The vast majority of the seeps dot the continental slope break, where the seafloor topography swoops down toward the Atlantic Ocean basin. The Okeanos Explorer used sound waves to detect the methane bubbles & map the seafloor. The technique, called multibeam sonar, calculates the time & distance it takes for sound waves to travel from the ship to the seafloor & back. The sonar can also detect the density contrast btwn gas bubbles & 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 w/Jason, a remotely operated vehicle, finding them teeming w/crabs, fish & 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, & possibly all the world’s oceans.
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 & water that appears when deep ocean pressures & cold temperatures force methane to solidify. Any type of methane gas can form hydrates. While methane vents are common around the world, only 3 natural gas seeps — where methane escapes from seafloor sediments — had been found off the East Coast before 2012.
“It was a surprise to find these features,” Skarke said. “It was unexpected bc many of the common things associated w/methane gas do not exist on the Atlantic margin.” The East Coast is a passive margin, & methane isn’t expected to come out of this environment. The margin hasn’t been squeezed or pulled by plate tectonic activity for tens of millions of years, & that means a lack of escape routes for methane. “I usually describe passive margins as cold, old & boring,” said study co-author Carolyn Ruppel, chief of the U.S. Geological Survey gas hydrates project in Woods Hole, Massachusetts.
Also missing from the Atlantic Coast are layers of salt, which are responsible for the Gulf of Mexico’s oil & gas. W/out more exploring, the researchers can’t say for sure why there are so many methane plumes along the Atlantic coastline. “It’s a huge research area that needs to be pursued,” Ruppel said. If the East Coast could hide 100s of bubbling methane pits, then it’s likely there are nearly 30,000 more awaiting discovery in the world’s oceans, the researchers said. “These processes may be happening in places we didn’t expect them,” Skarke said.
There’s also a good chance more methane vents will be found off the East Coast, but that doesn’t mean 1 should expect new drilling platforms popping up offshore to extract the gas, the researchers said. “We have no evidence to suggest this material would be a recoverable resource,” Skarke told Live Science. “There is no evidence whatsoever that there are conventional deep-seated oil & gas reservoirs underneath the Atlantic margin.” The more likely scenario: A fleet of research ships hurries to claim the seeps. The methane seeps are near ports where many of the U.S. research ships dock. The ease of access has set off an exploration stampede, w/several new projects in planning stages or already funded. “We’re setting the stage for a decade of discovery,” Ruppel said. Interest is running high bc the seeps could be a laboratory for studying how methane hydrates respond to climate change.
At present, scientists think the East Coast seeps don’t contribute much methane to climate change. Most of the methane gas dissolves in the ocean before reaching the surface, Ruppel said. The total amount of gas is also much smaller than sources on land, such as cows or gas drilling. “It’s probably on the order of a feedlot of methane,” Valentine said. However, some shallow-water seeps could vent methane to the surface, and researchers expect that future surveys will uncover even more shallow seeps. These regions only received a cursory look during the survey. Even though the methane may not escape to the atmosphere, the gas still adds to the ocean’s overall carbon budget — which is still a wildly uncertain #. “It’s not a huge #, but it’s an important # for us to know,” Ruppel said.
View full article at: http://news.msn.com/science-technology/hundreds-of-methane-plumes-erupting-along-east-coast
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