Antarctic Octopus Holds Secrets of Prehistoric Ice Loss in its Genome

As the climate crisis continues, sooner or later the great West Antarctic Ice Sheet will collapse. An unsuspecting octopus just gave scientists an important clue as to how quickly that can happen

Turquet octopuses can be found all over Antarctica crawling on the ocean floor.

Scientists trying to understand Antarctica’s past face a daunting challenge. Ice does not fossilize, so there is no direct evidence to show how far the southern continent’s glaciers have been for a long time. That’s a problem because it makes predicting Antarctica’s future in a warming world more difficult.

Enter Turquet’s octopus (Pareledone turqueti). This tiny creature floats on the sea floor around Antarctica, and in new research, scientists have used its genetics to argue that a large ice sheet in Antarctica completely collapsed at some point in the past when the temperatures just one degree Celsius warmer than preindustrial times. Called the West Antarctic Ice Sheet, the ice sheet has returned to contain 770,000 cubic miles of ice today, but if it collapses again, its meltwater will raise sea levels by more than 10 feet worldwide.

“This is really the first biological evidence used for a past collapse, and I think that’s the really special and amazing thing about this paper,” said Ryan Venturelli, a paleoglaciologist at the Colorado School of Mines, which are not included in the new research. “I think it’s incredible that we can use octopus populations to teach us about the history of the Antarctic ice sheet.”

This type of research is not possible in any species, says Sally Lau, an evolutionary geneticist at James Cook University in Australia and co-author of the new research, published on December 21 in Science. “We need a species that is distributed throughout Antarctica but [that] FOR the most part [does] stay in one place,” he said. “If it swims a lot and moves constantly around Antarctica, then any historical signatures of migration and exchange of genetic material will be destroyed how quickly. [it is] acting quickly.”

Turquet’s octopuses fit the bill because they are found all over Antarctica and crawl along the ocean floor instead of swimming far, Lau said. For the new study, he and his colleagues analyzed nearly 100 DNA samples from octopuses found in museum collections or accidentally caught by fishing boats.

When they looked at the animals’ genetic material, Lau and his colleagues noticed geographic trends. For example, the octopuses found around Shag Rocks and South Georgia, two island clusters off the eastern tip of South America, are pretty similar—as you might expect because these populations are closer to each other. than different populations.

When it came to populations around the West Antarctic Ice Sheet, however, what the researchers found was even more surprising. Modern octopuses living in the Ross Sea, tucked into the nook on one side where the West Antarctic Ice Sheet meets the rest of Antarctica, share genetic material with animals located around the coast of the mainland—but with also with octopuses on the opposite side. at the connecting point of the continental ice sheet in the South Weddell Sea. Now the Turquet octopus has to swim countless miles around the jutting peninsula that points to South America to pass between these two oceans, an impossible feat for these non-enthusiastic swimmers, Lau said.

However the researchers argue that the genetic similarity between these two populations is a relic of a time when the West Antarctic Ice Sheet completely melted, leaving shallow seas connecting the Ross and Weddell Seas. And genetic analysis suggests that these two populations began to mix more than three million years ago and separated between 139,000 and 54,000 years ago. That time line matches previous suspicions that the West Antarctic Ice Sheet completely collapsed during the Last Interglacial, a warm period that occurred 130,000 to 115,000 years ago.

Until now, however, glaciologists and geologists have had limited tools to try to understand whether the sheet has completely collapsed or is simply subsiding. Their most helpful technique so far has been the analysis of sediment cores—long cylinders of layered sediment laid down over years and even centuries—which often come from beyond the ice sheet itself. “We have, for a long time, been approaching this question from the same old tricks,” Venturelli said. Analyzing the genetics of modern animals marks a completely different approach to add to the tool kit.

And understanding the history of the West Antarctic Ice Sheet may sound arcane, but that couldn’t be further from the truth, said Ted Scambos, a polar scientist at the University of Colorado Boulder, who was not involved in the new research. . The fragility of this ice sheet will shape the fate of people around the world, he said, making any insight valuable, even from an unlikely source like an octopus.

With the new findings, he said, scientists can better predict the timeline of future human-driven ice sheet collapse—whether its loss will occur in the next century or two or take 400 or 500 years. From there, scientists can more accurately calculate the pace of sea level rise and give societies the time they need to act on land.

“This is the most uncertain and difficult to predict threat of sea level rise in the next two or three centuries,” Scambos said. “It’s not hard to understand how warmer ocean temperatures or warmer air temperatures will ultimately affect this. The question is: How fast can it separate?

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