Underwater Permafrost Is a Big, Gassy Wild Card for the Climate

researcher pulling robot mapping device from water - Photograph: Charlie Paull/MBARI

Underwater Permafrost Is a Big, Gassy Wild Card for the Climate
WIRED, March 21, 2022
By Matt Simon

“You’ve probably heard of permafrost, the frozen carbon-rich land. But it’s also thawing under the sea, burping up planet-warming gases.”


Around 20,000 years ago, the world was so frigid that massive glaciers sucked up enough water to lower sea levels by 400 feet. As the sea pulled back, newly exposed land froze to form permafrost, a mixture of earth and ice that today sprawls across the far north. But as the world warmed into the climate we enjoy today (for the time being), sea levels rose again, submerging the coastal edges of that permafrost, which remain frozen below the water.


It’s a huge, hidden climate variable that scientists are racing to understand. They know full well that the destruction of terrestrial permafrost is a significant source of carbon entering the atmosphere. As it thaws, microbes munch on the organic matter it contains, releasing carbon dioxide (if the material is fairly dry) and methane (if the melted ice forms a pond). This can form a feedback loop, in which more permafrost thaw produces more emissions, which heat the planet to thaw even more permafrost. That’s an extra-big problem because the Arctic is now warming four times as fast as the rest of the planet.


Yet submarine permafrost is largely unstudied, owing to its inaccessibility—renting out time on a research vessel is not cheap anywhere, much less in the Arctic, and it’s much harder to reach for drilling samples. Now, in an alarming paper published last week in the Proceedings of the National Academy of Sciences, an international team of scientists give us a rare look at what’s going on down there. The team used oceanic robots, which look like torpedoes, off the coast of northern Canada and mapped the seafloor with sonar. The scientists repeated this several times over the course of nine years to get a sense of how the topology of the seafloor might be changing and found that it’s undergoing massive upheaval.


The result is the worrisome image shown above [see online article]—a massive sinkhole indicating that the subsea permafrost has thawed and collapsed. This sinkhole is a giant among dozens of pockmarks the researchers found on the seafloor. Scientists have already documented this violent phenomenon, called thermokarst, on land. Because permafrost is made of soil suspended in a matrix of frozen water, when it thaws the land shrinks, gouging massive holes across the Arctic landscape. And as these images of the seafloor show, it’s also happening underwater.


“I think it’s just absolutely remarkable that there are places on the seafloor where changes of this scale are happening at this rate,” says Monterey Bay Aquarium Research Institute marine geologist Charlie Paull, a coauthor on the paper. The entire survey covered an area that’s half the size of Manhattan and tallied 40 holes. (You can see a portion of the area in the image below. [see online article]) The giant one, he says, “is equivalent to a whole New York City block composed of six-story apartment buildings.”

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About the Author:

Matt Simon is a science journalist at WIRED, where he covers biology, robotics, cannabis, and the environment. He’s also the author of Plight of the Living Dead: What Real-Life Zombies Reveal About Our World—And Ourselves, and The Wasp That Brainwashed the Caterpillar, which won an Alex Award.