40 Seafloor Gas Seeps Found Off US East Coast

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Two different perspectives of the seeps, made by bouncing sound waves off rising plumes of gas. CREDIT: NOAA

Content provided by Douglas Main, OurAmazingPlanet

A research cruise has discovered 40 previously unknown gas seeps on the

seafloor off the U.S. East Coast. The plumes of gas are almost

certainly methane, also known as natural gas, according to government

scientists.

Methane is a potent greenhouse gas

due to its ability to absorb heat, but the released gas is not likely

to reach the ocean surface in significant quantities and affect the

climate, said Carolyn Ruppel, a researcher with the U.S. Geological

Survey, which collaborated in the research. Neither is the amount of gas

likely to warrant commercial interest, she said.

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The seeps were found in four clusters, three of them about 100 miles

(160 kilometers) southeast of Nantucket, Mass. The other cluster,

consisting of 17 of the seeps, was mapped about 90 miles (147

kilometers) east of Cape Henry, Va., according to a release from the

National Oceanographic and Atmospheric Administration, which led the

expedition.

Methane seeps are important to find and study since they involve the

transfer of carbon from the ground to the atmosphere, which is important

for getting an accurate picture of climate change in terms of how much

gas is emitted naturally and how much is emitted by humans, Ruppel told

OurAmazingPlanet. Methane also can oxidize in water and contribute to ocean acidification, she said. (Video: Humans Hit the Oceans Hard)

The NOAA ship Okeanos Explorer mapped the locations between Nov. 2 and

Nov. 20 using multibeam sonar, which produces detailed images of the

seafloor by calculating the amount of time and distance it takes for

sound waves to travel from the ship to the seafloor and back. During

that time the ship and its instruments mapped 5,970 square miles (15,460

square kilometers) of seafloor, an area larger than Connecticut,

according to the NOAA release. The mapping was primarily done along the

continental slope, where the North American continent ends and drops

into the Atlantic Ocean basin. Sound waves were also used to visualize

the rising plumes of gas.

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It's unclear exactly where the gas is coming from, Ruppel said. Methane

either can arise from microbial activity in shallow deposits of organic

material, or it can come from more deep-seated processes involving oil

formation. Probably both processes are at work in these different seeps,

she said.

A mere generation ago, methane seeps were virtually unheard of off the East Coast. Since the early 1980s, however, several seeps have been found.

"With advanced multibeam sonar, it may become routine to discover seeps

while we systematically explore our poorly known ocean," NOAA scientist

Stephen Hammond said in the statement.

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