One hundred to one thousand times the normal atmospheric levels of the greenhouse gas methane (CH4), a greenhouse gas 25 times as powerful as CO2 at warming the earth, were found this summer over the Siberian shelf in the Arctic Ocean. The Siberian shelf contains enormous amounts of methane - 13 times the total carbon content of the earth's atmosphere.
The findings come from measurements of carbon fluxes around the north of Russia, led by Igor Semiletov from the University of Alaska at Fairbanks.
"Methane release from the East Siberian Shelf is underway and it looks stronger than it was supposed [to be]," he said.
A vast shallow sea lies north of Siberia. One quarter of the world's continental shelves are found in the Arctic. Seven great rivers pour carbon rich sediment onto the Arctic shelves. During the ice ages the very shallow and very vast east Siberian sea was above sea level causing deep permafrost to sequester the carbon at negative 17 Celsius. Enormous amounts of methane were trapped as methane hydrate ice.Rapid warming of the Arctic is now destabilizing the methane ice in parts of the east Siberian sea.
Fairbanks, Alaska—A team led by International Arctic Research Center scientist Igor Semiletov has found data to suggest that the carbon pool beneath the Arctic Ocean is leaking.
The results of more than 1,000 measurements of dissolved methane in the surface water from the East Siberian Arctic Shelf this summer as part of the International Siberian Shelf Study show an increased level of methane in the area. Geophysical measurements showed methane bubbles coming out of chimneys on the seafloor.
"The concentrations of the methane were the highest ever measured in the summertime in the Arctic Ocean," Semiletov said. "We have found methane bubble clouds above the gas-charged sediment and above the chimneys going through the sediment."
The new data indicates the underwater permafrost is thawing and therefore releasing methane.
Continental shelves hold most of the methane hydrate
Terrestrial permafrost is estimated to contain 400 gigatonnes of methane hydrates, while sub-sea continental shelf reservoirs are estimated to contain 10,000 gigatonnes of methane hydrates. For comparison, all recovered and non-recovered fossil fuels (coals, oil and natural gas) are estimated to contain about 5,000 gigatonnes of carbon. Since the arctic continental shelf makes up 25 per cent of the entire area of the world’s oceanic continental shelves (7 million square kilometres of the ocean’s area, 28.8 million square kilometres), it is estimated to contain 2,500 gigatonnes of carbon in the form of methane hydrates, which is more than 3 times greater than the amount of carbon currently stored in the atmosphere and more than 600 times greater than the current atmospheric content of methane. Release to the atmosphere of only 0.5 per cent of the methane stored within arctic shelf hydrates could cause abrupt climate change.
Submergence of the Arctic shelves at the end of the last ice age began the slow process of warming the deep permafrost. That process has accelerated recently because the extensive loss of summer sea ice has allowed solar heat to warm shelf water.
Permafrost on the East Siberian Arctic Shelf was predicted to be stable from the coast to a water depth of 70 metres, which encompasses more than 90 per cent of the shelf area. However, recent observational data obtained in the East Siberian Arctic Shelf showed that extensive methane release from the sea floor is occurring at depths ranging from 6 to 70 metres, emerging as huge clouds of bubbles rising through the water column. This bubbling release of gas is called ebullition.
Oxidation in the water column usually prevents methane released from oceanic hydrates in deep ocean waters from reaching the atmosphere. However, because the East Siberian Arctic Shelf is extremely shallow (more than 75 per cent of its entire area of 2.1 million square kilometres is shallower than 40 meters; the majority of the methane gas released from the East Siberian Arctic Shelf sea floor avoids oxidation in the water column and is released to the atmosphere.
Researchers are uncertain about the potential for rapid, explosive release of large bursts of methane. However, they have determined that destabilization of the methane ice has begun.
Multi-year observational data obtained in the East Siberian Arctic Shelf suggest that, contrary to modelling results, more than 80 per cent of bottom water and 50 per cent of surface water in the study area is supersaturated with methane by a factor of 10 to 1,000 relative to the background level of 3.5 nanomoles. That means that very likely more than 5 to 10 per cent of the East Siberian Arctic Shelf area is already affected by sub-sea permafrost destabilisation.