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Methane bubbling up off the East Coast

NEW YORK — Scientists have discovered methane gas bubbling from the seafloor in an unexpected place: off the East Coast of the United States where the continental shelf meets the deeper Atlantic Ocean.

The methane is emanating from at least 570 locations, called seeps, from near Cape Hatteras, N.C., to the Georges Bank southeast of Nantucket.

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In a paper published online Sunday in the journal Nature Geoscience, the scientists, including Adam Skarke of Mississippi State University and Carolyn Ruppel of the US Geological Survey, reported evidence that the seepage had been going on for at least 1,000 years.

They said the depths of the seeps suggested that in most cases the gas did not reach the atmosphere but rather dissolved in the ocean, where it could affect the acidity of the water, at least locally.

But methane is a potent, if relatively short-lived, greenhouse gas, so the discovery should aid the study of an issue of concern to climate scientists: the potential for the release of huge stores of methane on land and under the seas as warming of the atmosphere and oceans continues.

Methane seeps occur in many places, but usually in areas that are tectonically active, like off the West Coast of the United States, or connect to deep petroleum basins, as in the Gulf of Mexico.

Ruppel said that at about 40 of the seeps — those in water depths exceeding 3,300 feet — the methane may be migrating up through the sediments from deeper reservoirs of the gas. Further studies would be needed to confirm this, she said.

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