Huge mounds, pingos, are discovered on the seabed offshore Siberia. They are forming because of the thawing of subsea permafrost and high accumulation of methane.Text: Maja Sojtaric

“Pingos are intensively discussed in the scientific community especially in the context of global climate warming scenarios. They may be the step before the methane blows out.” says Serov.

A recent study by Pavel Serov, PhD at Centre for Arctic Gas Hydrate, Environment and Climate (CAGE) has documented pingo (“Pingos are spectacular landforms associated with permafrost in the Arctic. They are circular or elliptical formations protruding from the level ground of the tundra, and can be up to 60 meters high. In essence, they are huge lumps of ice covered with soil. Similar structures are now found strewn on the ocean floor in the Arctic shallow seas." like features have been discovered in the thawing of the subsea permafrost off the South Kara Sea Shelf in Siberia.

FishOutofWater has frequently written about the Siberian land craters that were discovered in the Siberian permafrost back in 2014. This new study focused on two subsea pingos that were identified offshore the very same area of the mysterious Yamal peninsula craters.

Serov and colleagues focused on two subsea pingos that were identified offshore the very same area of the mysterious Yamal peninsula craters. The study shows how important methane accumulation is for the formation of subsea pingos. The study area lies in the shallow South Kara Sea, at approximately 40-meter water depth. Serov and colleagues, present in their paper a range of scenarios for the formation of the mounds, leading to potential blowouts of methane. “Our question was: Are these mounds submerged terrestrial pingos? Or are they something different forming under marine conditions? One of the South Kara Sea pingos was leaking a lot of methane but where was the methane coming from?”

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As permafrost extends into the ocean so do the pingos. They even appear in geographical proximities to the ones observed on land. An early study suggested that these pingos formed on land during the glacial period, and are therefore relics from the ice age, just like the Arctic subsea permafrost. “The average ocean temperature is much warmer than Siberia, initially suggesting that the formation of subsea pingos could not be recent, as anticipated for pingos in cold Siberian environments. “ says CAGE director, prof. Jürgen Mienert, a co-author on the paper.



The study found that the sub sea pingos are much larger than those on land and they suggest that "the mound formed more recently, moving material physically upwards.”



On land pingos are mainly formed when the water freezes into an ice core under soil, because of the chilling temperatures of permafrost. However, subsea pingos, may be formed because of the thawing of relict subsea permafrost and dissociation of methane rich gas hydrates. Gas hydrates are ice-like solids composed of among other things methane and water. They form and remain stable under a combination of low temperature and high pressure. In permafrost the temperatures are very low and gas hydrates are stable even under the low pressure, such as on shallow Arctic seas. Thawing of permafrost leads to temperature increases, which in turn leads to melting of gas hydrates, therefore, releasing the formerly trapped gas. “ The methane creates the necessary force that pushes the remaining frozen sediment layers upward, forming mounds.” says Serov. Quiet explosions beneath the Arctic shallow seas Subsea pingos can potentially blow out, without massive attention, as was the case with the highly visible Yamal craters, but with massive expulsions of methane into the ocean. For petroleum companies these areas may pose a geohazard. Drilling a hole into one of these subsea pingos, can be not only expensive but also catastrophic. During a geotechnical drilling in the close by Pechora Sea, an industry vessel unknowingly drilled a hole into one of these mounds. It triggered a massive release of gas that almost sunk the vessel. “We don´t know if the methane expelled from the subsea pingos reaches the atmosphere, but it is crucial that we observe and understand these processes better, especially in shallow areas, where the distance between the ocean floor and the atmosphere is short.” says Serov.



The Siberian Times also reported on the underwater pingo’s with an emphasis on the risks of oil drilling in this area.



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