Thursday, 8 June 2017

Evidence of ice sheet retreat leading to methane release in last Ice Age

New Study: Ice Sheet Retreat Led to Rapid Methane Hydrate Release at End of Last Ice Age


7 June, 2017

Andreassen et al. found evidence of large craters embedded within methane-leaking subglacial sediments in the Barents Sea, Norway. They propose that the thinning of the ice sheet at the end of recent glacial cycles decreased the pressure on pockets of hydrates buried in the seafloor, resulting in explosive blow-outs. This created the giant craters and released large quantities of methane into the water above. — Science

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At the end of the last ice age, a warming world released a portion of its carbon stores into the atmosphere. The result was, ultimately, an increase in atmospheric CO2 by around 100 parts per million and in increase in atmospheric methane by around 300 parts per billion.

This increase in greenhouse gasses was a direct response to the Earth warming by approximately 4 degrees Celsius over the course of about 10,000 years. Under a present human-forced warming that is currently 1.2 C above late 19th Century averages and that is predicted to reach between 3.3 and 7 C warming this Century if fossil fuel burning continues, it is important to consider what additional carbon forcing the Earth System will produce under such an extreme and short-term temperature departure.

A new study recently published in Science indicates that these massive craters in the sea bed off Svalbard formed as methane hydrate erupted from the sea bed when ice sheets retreated at the end of the last ice age. Many of these craters are over a kilometer wide. Image source: K. Andreassen/CAGE.

One subject of concern is the behavior of methane hydrate deposits under warming conditions. It is estimated that upward of trillions of tons of hydrate exist in various frozen deposits around the world. And that even a fractional release from these deposits could contribute to the increasing greenhouse gas overburden in our atmosphere and further exacerbate warming. A potential for such a release in the short term would add risk of increased warming this Century on top of planned emissions from human fossil fuel burning — adding urgency to already necessary rapid emissions cuts (and a related swift transition to renewable energy based economies).
Paleoclimate Evidence of Massive Hydrate Release

This past week, a new study entitled — Massive blow-out craters formed by hydrate-controlled methane expulsion from the Arctic seafloor — lends credence to concerns regarding hydrate release as a potential amplifier to human warming. The study found that as ice sheets retreated and as pressure was relieved from the sea floor near Svalbard 12,000 years ago, pockets of methane hydrate rapidly migrated toward the surface as they turned to gas. This newly gasified methane formed large, high-pressure, mounds on the sea floor. Such mounds were unstable. Sensitive to changes in the local environment, they generated explosive outbursts which released considerable volumes of methane into the ocean and ultimately also added heat-trapping carbon to the Earth’s atmosphere.

The lead author of the study, Karin Andreasson, a professor at the CAGE Centre for Arctic Gas Hydrate, Environment and Climate noted in Phys.org last week that:
As [the] climate warmed, and the ice sheet collapsed, enormous amounts of methane were abruptly released. This created massive craters that are still actively seeping methane.
Though the methane craters formed off Svalbard around 12,000 years ago as the ice sheet retreated, they are linked to deeper methane pockets and are still leaking gas into the ocean today. Image source: Andreia Plaza Faverola/CAGE.

The researchers characterized these blow-out mounds as similar to those that have recently been forming in the Russian permafrost in places like Yamal and Yakutia. And their research indicates that a process like the one that occurred off Svalbard at the end of the last ice age may be at play as permafrost thins and as gas beneath this cap of frozen soil more rapidly migrates toward the surface — creating unstable blow-out mounds. Researchers also indicated that places presently locked in surface ice — like Greenland and Antarctica — could generate further methane blow out risk as ice sheets melt, withdraw and remove pressure from the methane deposits beneath them.

Conditions in Context

These are important findings due to the fact that paleoclimate evidence of past large-scale hydrate release provides a study-identified mechanism for how permafrost hydrates and gas deposits are being liberated due to present warming, how such warming may increase their rate of liberation in the future, and how ice sheet withdrawal could contribute to this hydrate liberation trend. 
What remains highly uncertain is the ultimate volume of hydrate response to a given level of warming over a given period and how significantly such releases would contribute to the already very considerable heat forcing provided by human emissions. That said, the new study does add to serious concerns regarding the potential for future warming and greenhouse gas levels — which will tend to be higher than present model studies indicate due to generally not accounting for these kinds of Earth System carbon feedbacks.
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Hat tip to TodaysGuestIs
Hat tip to Andy in San Diego



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