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Shallow waters

In their latest study, Shakova and her colleagues reported thousands of measurements of methane bubbles taken in summer and winter, between 2003 and 2012.

But the team also sampled seawater temperature and drilled into the ocean bottom, to see if the sediments are still frozen. Most of the survey was in water less than 100 feet (30 meters deep).

The shallow water is one reason so much methane escapes the Siberian shelf — in the deeper ocean, as methane-eating microbes digest the gas before it reaches the surface, Shakova said. But in the Laptev Sea, "it takes the bubbles only seconds, or at least a couple of minutes, to escape from the water column," Shakova said.

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Massive burst

But other researchers think the permafrost warming started only recently. "This is the first time in 12,000 years the Arctic Ocean has warmed up 7 degrees in the summer, and that's entirely new because the sea ice hasn't been there to hold the temperatures down," said Peter Wadhams, head of the Polar Ocean Physics Group at the University of Cambridge in the U.K., who was not involved in the study. The summer ice melt season has lasted longer since 2005, giving the sun more time to warm the ocean. (10 Things You Need to Know About Arctic Sea Ice)

"If we do have a methane burst it's going to be catastrophic," Wadhams said. Earlier this year, Wadhams and colleagues in Britain calculated that a mega-methane release from the Siberian shelf could push global temperatures up by 1 degree Fahrenheit (0.6 degrees Celsius). The suggestion, published in the journal Nature, was widely debated by climate researchers. Climate change experts and international negotiators have said that keeping the rise in Earth's average temperature below 2 degrees Celsius (3.6 degrees Fahrenheit) is necessary to avoid catastrophic climate change.

Shakova said much more research is needed to understand the factors that control how much methane is released from the entire East Siberian Arctic Shelf, which covers 772,000 square miles (2 million square kilometers), or nearly one-fifth the size of the United States.

"Ten years ago we started from zero knowledge in this area," Shakova said. "This is the largest shelf in the world's oceans. That's why it's very challenging to understand the natural processes behind the methane emissions in this area."


http://m.livescience.com/41476-more-arctic-seafloor-methane-found.html