London, September 23 : Scientists have discovered that massive deposits of subsea methane are bubbling to the surface as the Arctic region becomes warmer and its ice retreats.
According to a report in The Independent, this is the first evidence that millions of tons of a greenhouse gas 20 times more potent than carbon dioxide (CO2) is being released into the atmosphere from beneath the Arctic seabed.
Underground stores of methane are important because scientists believe their sudden release has in the past been responsible for rapid increases in global temperatures, dramatic changes to the climate, and even the mass extinction of species.
Scientists aboard a research ship that has sailed the entire length of Russia's northern coast have discovered intense concentrations of methane - sometimes at up to 100 times background levels - over several areas covering thousands of square miles of the Siberian continental shelf.
In the past few days, the researchers have seen areas of sea foaming with gas bubbling up through "methane chimneys" rising from the sea floor.
They believe that the sub-sea layer of permafrost, which has acted like a "lid" to prevent the gas from escaping, has melted away to allow methane to rise from underground deposits formed before the last ice age.
They have warned that this is likely to be linked with the rapid warming that the region has experienced in recent years.
Methane is about 20 times more powerful as a greenhouse gas than carbon dioxide and many scientists fear that its release could accelerate global warming in a giant positive feedback where more atmospheric methane causes higher temperatures, leading to further permafrost melting and the release of yet more methane.
The amount of methane stored beneath the Arctic is calculated to be greater than the total amount of carbon locked up in global coal reserves; so there is intense interest in the stability of these deposits as the region warms at a faster rate than other places on earth.
At some locations, methane concentrations reached 100 times background levels.
These anomalies have been seen in the East Siberian Sea and the Laptev Sea, covering several tens of thousands of square kilometres, amounting to millions of tons of methane, according to Orjan Gustafsson of Stockholm University in Sweden.
"The conventional thought has been that the permafrost 'lid' on the sub-sea sediments on the Siberian shelf should cap and hold the massive reservoirs of shallow methane deposits in place. The growing evidence for release of methane in this inaccessible region may suggest that the permafrost lid is starting to get perforated and thus leak methane," he said.