What will the West Antarctic Ice Sheet do in an increasingly warming world? It is a question that has occupied climate scientists around the world for decades. If the ice sheet melts completely, sea levels could rise an average of five meters. But no one understands exactly how the West Antarctic ice sheet responds to warming.
In the DNA of a small octopus from the Southern Ocean, researchers found evidence that a warming of roughly 1 to 1.5 degrees above pre-industrial levels is enough to cause the West Antarctic ice sheet to collapse. The group, led by evolutionary geneticist Sally Lau of Australia's James Cook University, published the analysis last month Science.
Of the three major ice sheets on Earth (Greenland and East and West Antarctica), West Antarctica is the most sensitive to warming of the air and oceans. The cap, more than 2,000 meters thick in some places, is in direct contact with warm ocean currents.
To learn something about what the ice sheet will do in the future, researchers look to the past. During the last interglacial (short break between two ice ages), 130,000 to 115,000 years ago, global temperatures averaged 1 to 1.5°C above pre-industrial levels. Due to melted glaciers, the sea level was then five to ten meters higher than it is now.
As short as a pencil
How much of that came from the melted West Antarctic Ice Sheet? To answer that, researchers study the canopy itself, sediments and use computer models. Various studies indicate that the West Antarctic ice sheet had completely collapsed, but much is uncertain.
Now Lau's team used a new dataset: 96 octopuses from different populations of the species Pareledone turqueti. These octopuses – with a body as short as a pencil – crawl across the seabed in the waters around Antarctica. With the exception of a few eggs carried along with the current, the octopuses do not wander far from home. The Ross Sea and Weddell Sea populations remain separated by the West Antarctic Ice Sheet.
But the DNA of the octopuses showed that the two populations once lived mixed. According to the researchers, this would suggest that the passage between the two seas was once open and the ice sheet had therefore melted. According to the researchers, the time of the mixing corresponds to the last interglacial.
“Interesting study,” responds Francesca Sangiorgi. She is an earth scientist at Utrecht University and conducts research into the melting of the West Antarctic ice sheet by analyzing fossil microalgae in drill cores, but is not involved in this study. “The researchers provide new evidence for what studies have previously suggested, but it is not yet enough. The researchers are trying to link a period to the melting of the ice sheet, and there is a lot of uncertainty. We will soon get more clarity about this with our analysis of sediments.”
The Earth has now warmed by about 1.2°C. It is impossible to say whether the same melt can occur again.
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