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Remember those weird Siberian craters? Scientists say they may have an underwater version

Members of an expedition group explore a newly formed crater on the Yamal Peninsula, northern Siberia Nov. 8, 2014. (REUTERS/Vladimir Pushkarev/Russian Centre of Arctic Exploration)

A recent scientific paper may have just cast new light on mysterious happenings on the Yamal Peninsula in Siberia, where the appearance of numerous large craters in the permafrost has been attributed, at least by some, to the venting of large pockets of methane gas, possibly in a dramatic or sudden way.

Now, say Pavel Serov and colleagues from the Centre for Arctic Gas Hydrate, Environment, and Climate at the Arctic University of Norway, possibly related structures appear to exist offshore as well, embedded within the shallow continental shelf of the South Kara Sea. The researchers published their results in August in the Journal of Geophysical Research: Earth Surface, but they have recently gained more attention, thanks in part to a report in Siberian Times.

In particular, the researchers say, they have detected and measured several offshore “pingo-like formations,” large mounds rising from the seafloor. On land, pingos are gigantic icy mounds that form in some Arctic areas, with a huge wedge of ice protruding out of the ground, covered up by Earth so that it resembles a hill.

Subsea pingo-like formations have been studied as well – but in this case, the researchers say, they could involve much more than blocks of ice. Rather, the best explanation for at least one of them, the study suggests, appears to be a surge of methane from deep below the seafloor, creating a dome. They also suggest the formation  could be unstable and possibly subject to a future blowout.

The deep methane source, they further suggest, is a so-called methane “hydrate,” a frozen combination of methane and water that forms at high pressures and cold temperatures — i.e., deep beneath the ground or seafloor in the Arctic — but that can be destabilized by warming temperatures or by the Earth’s heat from below.

“In this area, there are no other sources of such an extensive and such a focused amount of methane on the seafloor than gas hydrates,” says Serov. “Plus we combined our observations with modeling results, and our modeling results show us that there could be gas hydrates inside the permafrost.”

Here’s where the research was conducted, and how the offshore locations relate to those onshore, which have already drawn so much attention:

The idea that climate change could destabilize methane hydrates, which contain enormous amounts of methane, has been frequently evoked as a kind of doomsday climate scenario, since methane packs a much greater warming punch than carbon dioxide, at least over a short time scale. But the researchers say their results do not support such alarmism – they may have detected the destabilization and upward migration of hydrate in one area, but not anything systematic or large scale enough to suggest a climate worry.

“I think those pingos are zones of focused discharge, but the total input of methane coming from pingos is not so significant,” says Serov.

The researchers report their results based on ocean measurements and marine core measurements surrounding several pingo-like formations in the region. Both were found in shallow waters of around 40 meters depth, bulging upward for a number of meters.

One very large group of pingo-like formations,  the largest of which was up to 1,000 meters in diameter, did not have noteworthy concentrations of methane in the seafloor sediments at its top. However, a smaller one had very high concentrations of methane in the sediment, greater than 120,000 parts per million.

The researchers go on to reason that in the case of the latter pingo, it might very well be the result of warmer waters further destabilizing submerged permafrost, and tapping into a methane hydrate that has started to melt. The pressure from the gas could have risen up and created the mound.

The results are “provocative,” says Carolyn Ruppel, who heads the gas hydrate program at the U.S. Geological Survey, in their implication that “one of these features may be storing and or expelling methane from deeper dissociating gas hydrates.”

Ruppel agrees that in this particular area, there could indeed be gas hydrates in subsea permafrost. Such hydrates are distinct from the most common type of hydrate, found in deeper ocean regions where there is less concern of destabilization or of methane actually venting to the atmosphere, rather than being dissolved in ocean water.

“I definitely find this more plausible that there could be gas hydrate in this area, just based on what I know about permafrost hydrates, and their very different distribution in the world than deep marine hydrates,” says Ruppel.

The complication, Ruppel adds, is that “there is no marker for methane that comes from dissociating gas hydrate.” So the authors can’t definitively prove that that is the actual source of the very high methane concentrations that they detected.

The worry that there could be a climatically significant methane “feedback” – in which warming destabilizes large amounts of methane that reach the atmosphere, driving more warming and more methane or carbon dioxide release — relies on a large number of assumptions and contingencies.

Nobody doubts that there are gigantic quantities of methane stored in gas hydrates around the world – one recent estimate is that hydrates contain between 1,600 and 1,800 gigatons, or billion metric tons, of carbon in the form of methane. That’s more than enough to cause very rapid warming if these were to be somehow tapped into and reach the atmosphere.

But there are many things preventing that from happening. The most important is depth: There would have to be significant amounts of methane hydrates lying beneath relatively shallow waters. That’s because for hydrates in deeper waters of about 100 meters or more, scientists think most or all of the methane released would be absorbed into the water column, rather than venting into the atmosphere in significant amounts.

Thus, the focus becomes hydrates located in permafrost on land or in permafrost beneath relatively shallow ocean waters. The latter are believed to be located in realms of so-called “relict permafrost” – areas that were once hard and frozen tundra, but that were flooded at the end of the last glacial maximum as ice sheets melted and sea levels rose. This process would have initiated a slow thawing of permafrost over thousands of years, and in turn, destabilization of hydrates. Global warming, meanwhile, could now be adding oomph to that process.

The question then becomes how much subsea permafrost is still left and how much hydrate it contains. The new study calls this question “controversial” and does not make any quantitative claims about the matter.

Ruppel herself has published a recent study suggesting that only about 1 percent of all hydrate methane is located in permafrost, corresponding to 20 gigatons worth of carbon. Subsea permafrost would be a fraction of that. However, the study also noted that this is a “conservative” estimate.

That’s why the new research, while it certainly does suggest one possible case of a hydrate dissociating from permafrost and creating a bulge on the seafloor, can’t necessarily be used to raise alarms about the methane climate feedback.

“It’s a difficult area to talk about because we have not much data conforming to or rejection the hypothesis,” says Serov. The new study does assert, though, that in the South Kara Sea, there are reasons to think there is still relict permafrost, and that it is still in a process of thaw.

There’s also a more immediate concern, Serov says – this is an area where there is much oil and gas development and the methane rich pingo-like formation could lead to a dangerous blowout. “It’s a very big geohazard,” he says. The paper notes that in the Pechora Sea, drilling into a pingo-like formation triggered an “emergency situation” for one vessel.

Finally, the analogy with the craters on land on the Yamal peninsula isn’t a certain one, simply because there is still debate over the origins of those. But there are definitely suggestions that they involve pingos and, possibly, methane releases.

“I think you’ve heard about the Yamal craters,” says Serov. “It might be more or less the same process, but going on onshore.”

The takeaway, then, is that we certainly have some evidence of odd happenings in permafrost regions in Siberia — some of which may involve methane. It’s not time to freak out about this. But the developments do underscore that when it comes to the rapidly changing Arctic, changes to permafrost could be one of the most important alterations to the Earth’s system, brought on by our own actions.