Ice sheets may be hiding vast reservoirs of powerful greenhouse gas

January 13, 2016, CAGE
Ice sheets can create, contain and maintain large amounts of gas hydrates, a frozen form of concentrated climate gas methane. The conservative estimate is that Barents Sea Ice sheet contained a 500-meter thick reservoir of gas hydrates. But it may have been over 800 meters thick -- the size of almost three Eiffel Towers stacked on top of each other. Credit: Illustration: Alexey Portnov/CAGE

The study indicates that under the frigid weight of Barents Sea Ice sheet, which covered northern Eurasia some 22 000 years ago, significant amounts of methane may have been stored as hydrates in the ground. As the ice sheet retreated, the methane rich hydrates melted, releasing the climate gas into the ocean and atmosphere for millennia.

This finding was published last week in Nature Communications in the paper "Ice-sheet-driven methane storage and release in the Arctic".

"Creation of gas hydrates requires high pressure; water; gas - mainly methane - and low temperatures. Nowadays we basically consider two environments suitable for this process to occur: subseabed along the world's continental margins, and permafrost areas on land and off shore. " Says principal author of the study, Dr. Alexey Portnov of CAGE - Centre for Arctic Gas Hydrate, Environment and Climate at UiT The Arctic University of Norway.

Ice sheets - a third process

But this is the first comprehensive study that shows that there is a third process that can create, contain and maintain large amounts of gas hydrates: ice sheets.

" They are heavy, can exert enormous pressure on the ground below. And they are cold, of course. With enough supply of gas and water from below and favorable geological setting you will likely have enormous amounts of contained under modern ice sheets as well".

Pockmarks are scars on the ocean floor, an evidence of gas release. These likely appeared as the ice sheet retreated from the western part of Svalbard, and the area began to submerge in seawater again. They prove that release of methane followed the retreat of the ice sheet. Credit: Alexey Portnov/CAGE

500-meter thick methane reservoir

The theory that this may be happening beneath the Antarctic has been published previously in Nature. CAGE-study is a more comprehensive take on that idea, and shows same processes taking place in the Arctic.

Scientists from CAGE have over time collected wide-ranging observational data offshore western Svalbard in the Arctic Ocean. This made it possible to create robust models for a scenario of subglacial evolution of gas hydrate reservoirs during and after Last Glacial Maximum, or last ice age in layman´s terms.

The results of the study indicate that even under conservative estimates of ice thickness a 500-meter thick gas hydrate stability zone existed beneath the ice sheet in the study area. This zone could have served as a methane sink-a reservoir containing immense amounts of the natural greenhouse gas. 1 m3 of gas hydrate contains almost 170 m3 of the greenhouse gas methane.

Rapid melt caused release of methane

During the last ice age the continental margin offshore western Svalbard, was land covered with ice, much as Greenland and Antarctica of today. But as the climate changed, the ice melted over a period of thousands of years, a rapid melt in geological terms.

The scientists have mapped over 1900 pockmarks - gas escape features - on what now is the seafloor in the study area. The age of these pockmarks has in previous studies been estimated as post-glacial, meaning that they appeared after the ice sheet had retreated.

"Pockmarks are evidence of gas release from the ground. We infer that the gas hydrate zone was stable as long as the climate was cold and the ice sheet was stable. Abrupt climate warming caused sheets to melt, decreasing the pressure on the ground and increasing the temperature. This destabilized the hydrates. Methane was released into rising seawater and possibly the atmosphere." says Portnov.

As the ice sheet retreated, the pressure lifted, steadily widening the corridor for major methane release.

Accelerating climate change

Rapid melting of the ice sheets due to global warming, and subsequent sea level rise has long been a concern to scientists.

Methane, being at least 20 times more potent greenhouse gas than CO2, can accelerate the global warming. If the same process of methane storage is occurring under the current ice sheets, there may be a new threat to take into the account when we are discussing ice sheet retreat in the future.

Modern ice sheets will not need thousands of years to melt., The Greenland ice sheet has been losing an estimated 287 billion metric tons per year, states NASA. The continent of Antarctica has been losing about 134 billion metric tons of ice per year since 2002, albeit its ice sheet tells a more complicated story.

"It is difficult to study this processes in modern polar environments. The ice sheets of Greenland and Antarctica are several kilometers thick and examining the ground beneath them is challenging and expensive, nonetheless. But the circumstances that were present in formation of hydrate zones in the past are also present today. We need to take that into the account when we are considering the impacts that the rapid melt of the modern ice sheets will have on our future climate" says Portnov.

Explore further: Retreat of the ice followed by millennia of methane release

More information: Alexey Portnov et al. Ice-sheet-driven methane storage and release in the Arctic, Nature Communications (2016). DOI: 10.1038/ncomms10314

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2 / 5 (8) Jan 13, 2016
"Modern ice sheets will not need thousands of years to melt. The Greenland ice sheet has been losing an estimated 287 billion metric tons per year, states NASA..."

Good grief. The Greenland ice sheet has a mass of about 2,613,000 Gt, so if it lost ice at a rate of 287 Gt of ice per year it would take 9100 years to melt.

361.8 Gt of melted ice is required to raise sea-level by one millimeter, so 287 Gt of ice is just 0.8 mm of sea-level rise.

What's more, that's probably high. This recent paper estimates a current rate of Greenland ice loss of just 186.4 +/- 18.9 Gt/yr:

Moreover, there's been no increase in the globally averaged rate of sea-level rise in at least 85 years, so mankind's greenhouse gas emissions don't seem to be affecting overall ice melt.
4 / 5 (4) Jan 14, 2016

I think you need to integrate here and not just do a linear extrapolation. Ice loss will accelerate as the world warms and feed-backs kick in.
Also you say "..there's been no increase in the globally averaged rate of sea-level rise in at least 85 years."

That's not what the science says.....

3.2 / 5 (5) Jan 14, 2016
runrig wrote:
Ice loss will accelerate as the world warms and feed-backs kick in."

Most feedbacks don't "kick in." They simply amplify or attenuate forcings.

Some (like Eschenbach tropical cloud feedback) are non-linear, but even they don't "kick in" at some time in the future, and most climate feedbacks are "negative" (attenuating).

runrig also wrote:
you say "..there's been no increase in the globally averaged rate of sea-level rise in at least 85 years" [but] That's not what the science says"

Actually, that IS what the scientific measurements show. You apparently misread that article. It uses the word "unabated," not "accelerated."

Sea-level is rising in some places and falling in others, but the average is a slight rise. It is rising no faster now, with CO2 at 400 ppmv, than it was 85 years ago, with CO2 at ~305 ppmv.

Here's an illustrative graph of historical sea-level measurements:

3 / 5 (4) Jan 14, 2016
Here are some more graphs of historical sea-level measurements:




As you can see, even though CO2 levels have increased dramatically, that has not caused any measurable increase in the rate of sea-level rise.

No wonder even the Obama Administration has trouble finding reliable climate alarmists to promote The Cause. Dr. Steven Koonin was Obama's Undersecretary for Science in the Energy Department 2009-2011. After he left that position, he admitted the inconvenient truth:

"Even though the human influence on climate was much smaller in the past, the models do not account for the fact that the rate of global sea-level rise 70 years ago was as large as what we observe today."
4 / 5 (4) Jan 15, 2016
As you can see, even though CO2 levels have increased dramatically, that has not caused any measurable increase in the rate of sea-level rise.

Because system response is slower than the few decades?

Recent sea level rise has spiked to nearly 1 cm/yr
3 / 5 (4) Jan 16, 2016
dart2000, if you bothered to click on any of the links I gave you, you can see that coastal sea-level rise has not "spiked" at all, let alone to 1 cm/yr. Sea level is rising no faster now than it was 85 years ago.

Nor is there any physical basis for the notion that the climate system takes more than 2/3 century ("the few decades") to respond to CO2's forcing.

Other forcings affect temperature almost immediately (less than a year). The effect of volcanic aerosols on global temperatures is very clear. In fact, Pinatubo cooled the oceans so much that it greatly increased their CO2 uptake for 2-3 years, measurably reducing the rate of CO2 increase, as you can see here:

The only explanation for the lack of measurable effect of CO2 levels on coastal sea-level rise is simply that atmospheric CO2 levels have very little effect on the rate of coastal sea-level rise.
2.3 / 5 (3) Jan 18, 2016
Excellent rebuttals, ncdave. I wish there were ten or twenty more of you on physorg, though.
1 / 5 (1) Jan 18, 2016
Thank you, HannesAlfven. You are very kind.

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