Methane Bubbling Up From Undersea Permafrost?

Mason Inman in San Francisco, California
for National Geographic News
December 19, 2008

The East Siberian Sea is bubbling with methane, a powerful greenhouse gas, being released from underwater reserves, according to a recent expedition.

This could be a sign that global warming is thawing underwater permafrost, which is releasing methane that has been locked away for many thousands of years.

If these methane emissions from the Arctic speed up, it could cause "really serious climate consequences," said expedition member Igor Semiletov of the University of Alaska, Fairbanks.

(Related: "Global Warming Feedback Loop Caused by Methane, Scientists Say" [August 29, 2006].)

Semiletov and colleagues have traveled along the Siberian coast—this year they covered 13,000 miles (22,000 kilometers)—while monitoring methane concentrations in the air and observing the seas.

"According to our data, more than 50 percent of the Arctic Siberian shelf is serving as a source of methane to the atmosphere," Semiletov said.

This vast shelf is about 750,000 square miles (2 million square kilometers)—about the same size as Greenland or Mexico—and about 80 percent of it is covered with permafrost, Semiletov said.

He presented the findings from his group at an American Geophysical Union meeting in San Francisco this week.

Not-So-Permanent Permafrost

Permafrost is basically dirt that's been permanently frozen for hundreds or thousands of years, much of it since the last ice age.

Sea levels back then near the Siberian coast were about 325 feet (100 meters) lower than today, and the exposed ground froze solid down to 1,600 to 2,300 feet (500 to 700 meters) deep.

Over the past 10,000 years, sea levels rose to cover some of this permafrost, and in recent years those seas have seen increases in average temperatures.

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