Methane Is Bubbling Up From Hundreds of Places Along the U.S. East Coast Seafloor

August 26, 2014

At hundreds of places deep beneath the ocean surface along the U.S. Atlantic coastline, scientists have discovered plumes of bubbles streaming toward the surface that may contain methane, a heat-trapping gas many times more powerful than carbon dioxide.

The discovery, published Sunday in the scientific journal Nature Geoscience, of about 570 methane-leaking sites between North Carolina and Massachusetts shows that methane seeps -- the name for the sites where methane is bubbling up -- are far more common than previously believed.

“Widespread seepage had not been expected on the Atlantic margin," Adam Skarke, the study’s lead author and a professor at Mississippi State University, said in a news release. "It is not near a plate tectonic boundary like the U.S. Pacific coast, nor associated with a petroleum basin like the northern Gulf of Mexico."

It's also a powerful greenhouse gas, more than 20 times more potent than carbon dioxide, so scientists also are concerned about how these seeps might contribute to GHG concentrations in the atmosphere as the planet continues to warm.

“It highlights a really key area where we can test some of the more radical hypotheses about climate change,” John Kessler, a professor at the University of Rochester who was not involved in the research, told the New York Times.

Only three seeps had been found by scientists before in this region, Nature reported. “I’m not that surprised that people haven’t seen these things before,” said Tim Minshull, an oceanographer at the U.K.-based University of Southampton, who was not involved in the study. “These features are quite narrow, sometimes just a few [yards] across, and the ocean’s a big place.”

These seeps -- known as cold seeps to distinguish them from hydrothermal vents, which bring hot liquids from beneath the ocean floor -- have yet to be sampled, but the scientists involved in the study believe they contain methane, based on their location and what scientists already know about the geology of the region.

While methane from reservoirs deep in the ground is tapped for natural gas at drilling sites around the world, the methane at these sites is produced by microbes in shallow settlements -- not the kind that's suitable for drilling.

Methane has likely been seeping from these sites for at least 1,000 years, the scientists who conducted the survey said. Because of their depths, the methane also is probably not reaching the atmosphere, but rather is dissolving into the ocean.

Warmer ocean temperatures in the water column above the seeps is believed to contribute to their release of methane, which forms ice-like crystals known as gas hydrates when subjected to temperature and pressure conditions deeper than about 1,640 feet.

“Warming of ocean temperatures on seasonal, decadal or much longer time scales can cause gas hydrate to release its methane, which may then be emitted at seep sites,” Carolyn Ruppel, chief of the U.S. Geological Survey Gas Hydrates Project and a co-author of the study, said in a news release. 

“Such continental slope seeps have previously been recognized in the Arctic, but not at mid-latitudes," she added. "So this is a first.”

Read the full story at Nature, or see the full study at Nature Geoscience.

MORE: Methane Ice Bubbles

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