Jun 2, 2017

Thawing Arctic Glaciers Released ‘Explosive’ Methane — and Could Do So Again

Massive craters on the floor of the Barents Sea were formed around 12,000 years ago, but are still seeping methane and other gases.
Millennia ago, as the great glaciers of the Ice Age receded, methane that had been frozen under the seafloor melted and burst forth, leaving massive craters that remain on the ocean bottom to this day.

Today, new research suggests humankind should be concerned that a similar release of methane, a potent greenhouse gas that can harm marine ecosystems, might happen again as global warming melts the ice in the Arctic, Greenland, and elsewhere.

“We provide a model for abrupt and explosive methane releases,” said Karin Andreassen, a professor at CAGE Centre for Arctic Gas Hydrate, Environment, and Climate and the lead author of a study on Arctic methane published in the journal Science.

Examining craters formed by methane eruptions 12,000 years ago, Andreassen and her colleagues determined that enormous amounts of methane in hydrate form — an ice-like mix of water and gas — must have dissolved as the 6,500-feet-thick ice sheets retreated from the Barents Sea north of what is now Scandinavia and western Russia.

They found more than 100 craters on the seafloor that ranged from around 1,000 to almost 3,300 feet wide — larger than any discovered before — as well as thousands of smaller pockmarks, according to their research.

“The principle is the same as in a pressure cooker,” she said. “If you do not control the release of the pressure, it will continue to build up until there is a disaster in your kitchen. These mounds were over-pressured for thousands of years, and then the lid came off.”

The study area is in Bjørnøyrenna close to the Arctic archipelago Svalbard.
It’s not clear how much of that methane reached the atmosphere, where it traps 84 times more heat in the atmosphere than carbon dioxide over a 20-year period, according to the Environmental Defense Fund.

Today, methane seepage is common throughout the oceans. Researchers believe bacteria consumes most of that methane, however, converting it into other chemicals like carbon dioxide that causes coral bleaching and other problems but also prevents it from reaching the surface to contribute to global warming.

The craters are connected to deeper gas chimneys, showing gas flow from deeper hydrocarbon reservoirs. Hundreds of gas flares are seen in the water above.
The large craters discussed in the study suggest methane blowouts could occur on a scale much larger than people have seen, especially as global warming worsens, Andreassen said.

It’s not clear what’s going on under glaciers that are melting now because studying them firsthand is difficult, she added.

“When we see what took place in the Barents Sea, this is also what we can expect to happen under today’s ice sheets,” she said.

Read more at Discovery News

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