Published: Sat, June 03, 2017
Science | By Hubert Green

Massive craters formed by methane blow-outs from the Arctic sea floor

Massive craters formed by methane blow-outs from the Arctic sea floor

Methane exploded from beneath the sea-floor here thousands of years ago.

New technology showed that the craters are covering a much larger area than previously thought.

Scientists worry that ice sheets will continue to retreat in Greenland and Antarctica, leaving those areas vulnerable to a release of long-pent-up reservoirs of methane that could have the potential to make the Earth even warmer.

Like the craters observed in the Norwegian study, there are "pockmarks" that are actively releasing gas in areas of the Beaufort Sea, which stretches across the coasts of the Northwest Territories and Yukon Territory, Dallimore said.

Craters as wide as 12 city blocks on the Arctic seafloor were put there by giant eruptions of underground methane gas. But researchers estimate that it is nothing compared to the methane blowouts right after the melting of ice.

The methane-filled craters were originally detected in 1990s but they were few and far between.

She knew the research team would find some craters on the seafloor when they began the study in the Barents Sea, however, she didn't realize just how many craters the team would find or how massive many of them turned out to be.

Regarding the size of these giant craters, Prof. During a recent expedition to the area, Andreassen's team documented well over a hundred of these craters, which measured between 300 and 1,000 meters (980 to 3,280 feet) wide. "But there are also many hundred smaller ones, less than 300 meters wide that is".

In comparison, two "huge" blowout craters on land on Siberian peninsulas Gydan and Yamal, are fifty to ninety meters across. While researchers are not sure, they speculate that some of the explosions may have sent methane into the atmosphere. These pingos are lumps of methane hydrate, or methane gas frozen within a lattice of water molecules. Still, because methane hydrates do still exist in the region - and conditions in the Arctic are rapidly changing, thanks to the climate change - it's a scenario deserving of continued research.

Some 2000 metres of ice loaded what now is ocean floor with heavy weight. Methane gas from deeper hydrocarbon reservoirs made their way up, under the ice - however, they could not escape. The hydrates were stable under ice sheet's high pressure and extreme cold conditions. "We got seismic data showing the structure underneath, and the links with deeper hydrocarbon sources".

There are several hundred craters in the area the study looked at. These mounds were over-pressured for thousands of years, and then the lid came off. Warming induced by either human activity or past cycles in the Earth's orbit, thaws some of these hydrates, releasing methane.

Did methane blowouts reach the atmosphere?

Major methane eruptions seem to be rare, which makes them hard to analyze and measure.

More work is clearly needed to understand the nature and power of these historical blowouts, and to assess their environmental impacts. To this day, methane and other hydrocarbons continue to slowly vent from the seafloor - and probably have been since the explosion occurred, Andreassen said. Any large-scale release of methane to the atmosphere is expected to speed up the greenhouse effect.

"We do estimate that an area of hydrocarbon reserves twice the size of Russian Federation was directly influenced by ice sheets during past glaciation". Grasby, the Natural Resources Canada scientist, recently published a separate paper describing a cluster of rocky mounds in the Canadian Arctic that researchers believe were also caused by an ancient methane explosion, although much further in the past. These scours indicated that the eruptions happened as the ice sheet was retreating, but while there was still ice in the area, the researchers said. At the end, as the ice sheet finally retreated, the gas would have concentrated into mounds on the seafloor.

"Our study provides the scientific community with a good past analogue for what may happen to future methane releases in front of contemporary, retreating ice sheets" concludes Andreassen.

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