(CN) — Beneath the frigid terrain of Svalbard, Norway, vast stores of methane gas are migrating below the archipelago’s thawing permafrost.
The discovery, published in Frontiers in Earth Science on Tuesday, is prompting Arctic geologists to warn that any substantial gas escape could trigger a feedback loop perpetuating climate change.
“Methane is a potent greenhouse gas,” said the study’s lead author Thomas Birchall in a statement. “At present the leakage from below permafrost is very low, but factors such as glacial retreat and permafrost thawing may ‘lift the lid’ on this in the future.”
Birchall, currently a principal geologist and petroleum engineer for Equinor, a Norwegian petroleum refining company, led the study with The University Centre in Svalbard to understand how much methane has accumulated below the region’s permafrost or ground that remains frozen for over two years.
The “cryospheric cap” of permafrost essentially consists of two layers, the first being the active layer on top that freezes and thaws annually. Everything below the base of the active layer stays frozen for several years, and the base of that layer starts above where the ground temperature rises above freezing.
In High Arctic areas like Svalbard, located between the northern Norwegian coast and the North Pole, permafrost is widespread, though not always uniform. Its mountainous islands experience sub-zero average air temperatures for eight months of the year, but its temperatures are also rising twice as fast as the rest of the Arctic, making it one of the most rapidly warming places on Earth.
The study authors explain that understanding the base of Svalbard’s permafrost is vital because of what is sealed beneath: fossil fuel sources that release methane in free-gas form or as natural gas hydrates. To find gas accumulations below permafrost base layers, the researchers analyzed historical data from commercial and research wellbores across Svalbard.
“I and my supervisor Kim looked through a lot of the historical wellbore data in Svalbard,” Birchall said. “Kim noticed that one recurring theme kept coming up, and that was these gas accumulations at the base of the permafrost.”
Starting with the identification of permafrost, the researchers documented temperature trends, ice formation within wellbores, shifts in background gas measurements and how drill cuttings change while drilling wellbores. To find the gas, they analyzed long-term wellbore monitors for signals of gas influxes and abnormal pressure measurements — signs often indicating where permafrost or the underlying geology traps methane.
What the researchers found was that not every signaled location yielded gas accumulations — including those with sources of hydrocarbons — leading them to suspect that the methane had already migrated away.
However, the researchers also note that the frequency of gas accumulation was higher than expected: Out of the 18 hydrocarbon exploration wells in Svalbard, eight showed evidence of permafrost and half of those struck gas.
“All the wells that encountered gas accumulations did so by coincidence,” Birchall said. “By contrast, hydrocarbon exploration wells that specifically target accumulations in more typical settings had a success rate far below 50%.”
Birchall added how the pattern appears to be common, citing a recent example from a wellbore near the airport in Longyearbyen.
“The drillers heard a bubbling sound coming from the well, so we decided to have a look, armed with rudimentary alarms designed for detecting explosive levels of methane, which were immediately triggered when we held them over the wellbore,” Birchall said.
Overall, the researchers concluded that the gas accumulations occur in intervals throughout the base of Svalbard’s permafrost, indicating the presence of ongoing hydrocarbon migration. How the gas migrates through the cryospheric cap, they write, occurs through permeable highlands with shallow permafrost or the region’s recent “major uplift over the last thousands to hundreds of thousands of years.”
Other natural pathways the authors cite include springs, warm-based glaciers, fjords or pingos, an observation reminiscent of an earlier study this year on how large stocks of methane are leaking from Svalbard’s groundwater springs.
What both studies have in common is a warning: the more gas that escapes, the faster that Earth’s temperatures will rise.
“Because methane is a potent greenhouse gas and the Arctic is warming faster than anywhere else on Earth, the release of sub-permafrost gas accumulations in Svalbard may contribute a positive climatic feedback effect,” the authors write.
Should Svalbard’s permafrost continue thawing at its current rate, the authors write that most trapped methane gas should remain “relatively stable.” However, they add that permafrost does not only thaw from above “but also laterally from the coastlines, in addition to having complex mechanical implications in the strata overlying these accumulations.”
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