Previous research had found methane bubbling out of melting permafrost—frozen soil—in Arctic wetlands and lakes.

But the permafrost lining the deep, cold seas was thought to be staying frozen solid, holding in untold amounts of trapped methane.

"It's not the case anymore," said study leader Natalia Shakhova, a biogeochemist at the University of Fairbanks, Alaska. "The permafrost is actually failing in its ability to preserve this leakage."

(Related: "Methane Bubbling Up From Undersea Permafrost?")

In fact, Shakhova and colleagues estimate that roughly eight million tons of methane are leaking into the atmosphere each year from the East Siberia Sea (map),