This Antarctic Octopus warns of rising sea levels
Scientists have long wondered whether the West Antarctic Ice Sheet is a ticking time bomb in terms of sea level rise. New evidence from the DNA of a small octopus living in the Southern Ocean suggests that the ice sheet is indeed at risk of collapsing. a study published Thursday in the journal Science.
The research doesn’t predict when this could happen, but it indicates that 1.5 degrees Celsius of global warming above the pre-industrial global average, or perhaps even less than that, could be a tipping point for the ice sheet. The Earth is now close to that temperature level.
Several separate populations of Pareledone turqueti, commonly known as Turquet’s octopus, live in the waters around Antarctica today. These octopuses crawl across the seabed and generally don’t stray far from home. A few individuals or their eggs occasionally drift on the currents to neighboring groups, but the populations in the Ross Sea and the Weddell Sea are separated by the impassable West Antarctic Ice Sheet.
And yet genetic analysis of octopuses from various locations around Antarctica shows that these two populations intermingled and exchanged DNA about 120,000 years ago. This was a time in Earth’s history called the Last Interglacial Period, before the most recent Ice Age, when temperatures were similar to today.
The observed patterns in the octopus gene pool would only be possible if the West Antarctic Ice Sheet was not there at the time and relatively open seaways across the continent allowed the octopuses to travel freely between the Ross and Weddell Seas, according to the researchers.
Scientists know that the sea level was several meters higher at that time. But whether the extra water came from West Antarctica is “the question the geoscience community has been trying to answer for almost 50 years,” says Sally Lau, a postdoctoral researcher at James Cook University in Townsville, Australia, and lead author of the new research. study.
Today, the average temperature on Earth is about 1.2 degrees Celsius higher than it was between 1850 and 1900, when the burning of fossil fuels began to warm the climate. During the last interglacial, Earth’s average temperature was about 0.5 to 1.5 degrees Celsius warmer than that pre-industrial baseline, but sea levels were five to ten meters higher than today. If climate change completely melts the West Antarctic ice sheet, sea levels could rise by an average of five meters. (The East Antarctic Ice Sheet contains even more frozen water, but is considered more stable.)
The researchers did not explicitly state whether current temperatures had already forced the planet into a complete collapse of the western ice sheet. “We still can’t say for sure, but that’s certainly the implication,” said Nicholas Golledge, professor of glaciology at Victoria University of Wellington in New Zealand and another author of the study.
If the ice sheet has already reached a tipping point, estimates of how quickly it could melt range anywhere from 200 to 2,000 years. “Our actions from this point on will still change the speed at which we get there,” said Dr. Golledge.
Unlike today, the Last Interglacial was part of an ongoing natural cycle of changes in the tilt of the Earth’s axis and its orbit around the sun, and resulting changes in the amount of sunlight the planet receives. These cycles occur gradually over tens of thousands of years. Our current greenhouse gas emissions are causing similar temperature changes, but at a much faster rate.
Although the reasons behind past and current warming are different, the Last Interglacial is still one of the best analogs for current climate change, says Roger Creel, a postdoctoral researcher at the Woods Hole Oceanographic Institution. He was not involved in the study published on Thursday, but did contribute to it estimates of sea level during that period.
“It’s such strong evidence from a very different point of view than the climate community often has,” said Dr. Creel on the new study.
Some of the octopus specimens that Dr. Lau studied, were collected more than thirty years ago on fishing boats and scientific expeditions, and preserved in museums. Because DNA in dead animals degrades over time, this type of research using museum specimens was not possible until recently thanks to advances in genetic sequencing.
Other scientists have shown that population genetics of terrestrial animals are consistent with the past melting of the West Antarctic Ice Sheet. a 2020 springtail researchsmall bottom-dwelling invertebrates also suggested that the ice in the Ross Sea area had melted away during warm periods over the past 5 million years, including during the last interglacial.
Geoscientists can use mathematical models to reconstruct past ice sheets and sea levels, but emerging biological evidence can help confirm these reconstructions, says Ian Hogg, a researcher at Polar Knowledge Canada, an agency that monitors polar regions, and author of the book the study of springtails.
“As biologists, we know that these patterns exist among populations,” he said. The challenge for biologists is explaining these observed patterns, while a challenge for geoscientists studying Antarctica is gathering enough observational, physical evidence to validate their models.
“They have something that they offer us,” said Dr. Hogg. “And we have something we can offer them.”