The surface waters of the Arctic Ocean may be releasing "significant" amounts of methane into the atmosphere, researchers reported yesterday in the journal Nature Geoscience.

Scientists flying a specially equipped plane over the region detected high concentrations of the heat-trapping gas close to the ocean surface during research flights in 2009 and 2010.

During flights in the high Arctic, above 82 degrees north latitude, the research jet's instruments detected methane that seemed to be coming from the ocean surface below. The signal was strongest when the plane was flying at low altitudes, sometimes just 500 feet above the water.

"We were surprised to see these enhanced methane levels over the Arctic at low altitudes," said lead author Eric Kort, a postdoctoral fellow at the California Institute of Technology's Jet Propulsion Laboratory. "It was surprising to find that it was probably coming out of the sea."

The signal was strongest over areas where sea ice was cracked or broken up.

The study's authors didn't have enough data to estimate the total amount of methane coming from the Arctic Ocean in a day or a year. But they do have measurements of methane flux -- how much of the gas is emitted from a specific area in a specific time frame.

In the portion of the Arctic Ocean they monitored, the daily methane flux was 2 milligrams per square meter -- roughly on par with emissions from the eastern Siberian Arctic shelf.

"It's not a particularly large number if you compare it to a high-latitude wetland that's really going in the summer," Kort said.

But the size of the Arctic Ocean that may be emitting methane could make it a significant source of the heat-trapping gas. One key question for scientists, Kort said, is how shrinking Arctic sea ice will affect those emissions.

The new study is one of the first analyses based on data collected by a recently concluded research program, "HIPPO," that sought to track the movement of greenhouse gases through the atmosphere using a Gulfstream V jet outfitted with scientific instruments and sensors.

The aircraft flew five long-haul journeys between the Earth's poles, swooping from low to high altitude and back again to allow the scientists to sample the composition of different layers of the atmosphere (ClimateWire, Sept. 8, 2011).

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500