Massive 12,000-Year-Old Methane Blowout Craters In Arctic Ocean Still Venting Methane, Research Finds
Enormous methane expulsions from the Arctic Ocean’s seafloor some 12,000 years ago created hundreds of kilometers-wide craters in the region — which are apparently still to this day leaking large amounts of methane — according to new research published in the journal Science.
While the existence of some of these craters was first inferred back in the 1990s, the scale and area covered by them is far greater than was first thought — as revealed by the new research.
“The crater area was covered by a thick ice sheet during the last ice age, much as West Antarctica is today. As climate warmed, and the ice sheet collapsed, enormous amounts of methane were abruptly released. This created massive craters that are still actively seeping methane” stated Karin Andreassen, first author of the study and professor at CAGE Centre for Arctic Gas Hydrate, Environment and Climate at UiT The Arctic University of Norway.
The key part of that statement is probably the reference to the current state of West Antarctica — current climate models more or less don’t take into account the possible release of massive amounts of methane from the Arctic and Antarctic regions as the climate continues warming and the ice sheets and shelves collapse, even though there’s probably nothing that could be done at this point to prevent that eventual reality. Methane is, of course, a potent greenhouse gas.
While there are still at least 600 gas (methane) flares identifiable around these craters, “that is nothing compared to the blow-outs of the greenhouse gas that followed the deglaciation. The amounts of methane that were released must have been quite impressive.”
Commenting on the new work, Andreassen stated: “We have focused on craters that are 300 meters to 1 kilometre wide, and have mapped approximately 100 craters of this size in the area. But there are also many hundred smaller ones, less than 300 meters wide that is.”
The press release provides more:
“In comparison, the huge blow-out craters on land on the Siberian peninsulas Yamal and Gydan are 50-90 meters wide, but similar processes may have been involved in their formation.
“The Arctic ocean floor hosts vast amounts of methane trapped as hydrates, which are ice-like, solid mixtures of gas and water. These hydrates are stable under high pressure and cold temperatures. The ice sheet provides perfect conditions for subglacial gas hydrate formation, in the past as well as today.
“Some 2000 metres of ice loaded what now is ocean floor with heavy weight. Under the ice, methane gas from deeper hydrocarbon reservoirs moved upward, but could not escape. It was stored as gas hydrate in the sediment, constantly fed by gas from below, creating over-pressured conditions.”
“As the ice sheet rapidly retreated, the hydrates concentrated in mounds, and eventually started to melt, expand and cause over-pressure. The principle is the same as in a pressure cooker: 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. They just collapsed releasing methane into the water column” explained Andreassen.
Commenting on the way that such massive prehistoric methane release events can be hard to identify and find evidence of, Andreassen continued: “Despite their infrequency, the impact of such blow-outs may still be greater than impact from slow and gradual seepage. It remains to be seen whether such abrupt and massive methane release could have reached the atmosphere. We do estimate that an area of hydrocarbon reserves twice the size of Russia was directly influenced by ice sheets during past glaciations. This means that a much larger area may have had similar abrupt gas releases in the overlapping time period.”
So, to go over earlier points again, this work matters because as the Arctic and Antarctic regions continue warming, the likelihood of such events reoccurring keeps growing.
“Our study provides the scientific community with a good past analogue for what may happen to future methane releases in front of contemporary, retreating ice sheets,” concluded Andreassen.
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