Antarctic octopus genome holds secrets of prehistoric ice loss

Megan Bartels

Scientists trying to understand Antarctica’s past face daunting challenges. Ice does not fossilize, so there is no direct evidence of how far the southernmost continent’s glaciers extended in the distant past. That’s a problem because it makes it harder to predict Antarctica’s future in a warming world.

Enter the Tequite Octopus (Paredon Tuquiti). The little creature moves quickly along the seafloor around Antarctica, and in new research, scientists used its genetics to show that one of Antarctica’s major ice sheets completely collapsed in the past, when temperatures were just one degree Celsius warmer than pre-industrial times. The swath of ice known as the West Antarctic Ice Sheet has now grown back to cover 770,000 cubic miles of ice, but if it collapses again, its meltwater will raise sea levels by more than 10 feet around the world.

“This is really the first biological evidence for past subsidence, and I think that’s what’s really special and surprising about this paper,” said Ryan Venturelli, a paleoglaciologist at the Colorado School of Mines who was not involved in the work. research. New research. “I think it’s incredible that we can use octopus populations to understand the history of the Antarctic ice sheet.”

This kind of research does not apply to any species, said Sally Lau, an evolutionary geneticist at James Cook University in Australia and co-author of the new study, which was published in the journal Nature on December 21. superior. science. “We need a species that is distributed across Antarctica, but [that] Generally speaking [does] Stay in one place,” she said. “If it swims around Antarctica too much and moves too frequently, any historical signature of migration and exchange of genetic material will be eroded by the speed. [it is] Move now. “

The tequita octopuses fit that bill because they are found throughout Antarctica and crawl along the seafloor rather than swimming long distances, Liu said. In the new study, she and her colleagues analyzed DNA samples from nearly 100 of these octopuses, which were either found in museum collections or accidentally caught by fishing boats.

When Liu and her colleagues looked at the animals’ genetic material, they noticed geographic trends. For example, the octopuses found around Shag Rock and South Georgia, two island groups east of the tip of South America, are very similar, as you would expect since these populations are closer together than different populations. .

However, when it came to the populations surrounding the West Antarctic Ice Sheet, the researchers saw something even more surprising. Tucked away in a corner on one side of where the West Antarctic Ice Sheet meets the rest of Antarctica, modern octopuses living in the Ross Sea share genetic material with animals around the continent’s coast, but also with octopuses on the other side of the ice sheet and Antarctica. Weddell Sea continental junction. Today, Liu said, Tequite octopuses would need to swim countless miles around a jutting peninsula pointing toward South America to pass between the two oceans, an impossible feat for these less adventurous swimmers.

Instead, the researchers believe the genetic similarities between the two groups are remnants of a time when the West Antarctic ice sheet completely melted, leaving behind shallow sea lanes connecting the Ross Sea and the Weddell Sea. Genetic analysis shows that the two groups began to mix three million years ago and separated between 139,000 and 54,000 years ago. The timeline is consistent with previous suspicions that the West Antarctic Ice Sheet completely collapsed during the last interglacial, a warm period that occurred between 130,000 and 115,000 years ago.

Until now, however, glaciologists and geologists have had limited tools to try to understand whether the ice sheet collapsed completely or simply shrank. Their most useful technique so far is the analysis of sediment cores, long cylinders of layered sediment deposited over the past few years or even centuries, often from outside the ice sheet itself. “We’ve been using the same old tricks to solve this problem for a long time,” Venturelli said. Analyzing the genetics of modern animals marks a completely different approach to add to the toolbox.

Ted Scambos, a polar scientist at the University of Colorado Boulder who was not involved in the new study, said understanding the history of the West Antarctic Ice Sheet may sound mysterious, but that’s far from the truth. . The fragility of this ice sheet will determine the fate of humans around the world, he said, making any insights valuable, even from unlikely sources like octopuses.

With the new findings, he said, scientists can better predict the timeline of future human-driven collapse of the ice sheet — whether its disappearance occurs in the next century or two, or takes 400 or 500 years. From there, scientists can more accurately calculate the rate at which sea levels are rising and provide the time it will take for societies to move inland.

“This is the most uncertain and difficult to predict threat from sea level rise over the next two to three centuries,” Scambos said. “It’s not hard to understand how rising ocean temperatures or rising air temperatures will ultimately affect it. The question is: How quickly will it break down?”