Scientists have long wondered whether the West Antarctic Ice Sheet is a ticking time bomb in terms of sea level rise. New DNA evidence from a tiny Southern Ocean octopus suggests the ice sheet is indeed in danger of breaking up. A study released Thursday in the journal Science.
The study does not predict when that might happen, but suggests that 1.5 degrees Celsius of global warming above the pre-industrial global average, or perhaps less, could be the tipping point for the ice sheet. Earth is now close to this temperature level.
Several distinct populations of Pareledone turqueti, commonly known as Turquet's octopus, live in the waters around Antarctica today. These octopuses crawl on the bottom of the sea and usually do not stray far from home. Some individuals or their eggs may drift from time to time to neighboring groups, but the Ross Sea and Weddell Sea populations are separated by the impassable West Antarctic Ice Sheet.
And yet, genetic analysis of octopuses from different locations around Antarctica showed that the two populations intermingled and exchanged DNA around 120,000 years ago. This was a time in Earth's history called the last interglacial period, before the last ice age, when temperatures were similar to today.
The observed patterns in the octopus gene pool would only have been possible if the West Antarctic Ice Sheet had not existed at the time and the continent's relatively open seas had allowed octopuses to move freely between the Ross and Weddell Seas, the researchers said.
Scientists know that the sea level was several meters higher then. But whether the extra water came from West Antarctica is “a question the geoscience community has been trying to answer for almost 50 years,” said Sally Lau, a postdoctoral fellow at James Cook University in Townsville, Australia, and lead author of the new study. learning.
Today, the global average temperature is about 1.2 degrees Celsius warmer than it was between 1850 and 1900, when the burning of fossil fuels began to warm the climate. During the last interglacial period, global average temperatures were about 0.5 to 1.5 degrees Celsius warmer than the pre-industrial baseline, but sea levels were 5 to 10 meters higher than today. If climate change completely melts the West Antarctic Ice Sheet, sea levels could rise by an average of five meters, or 16 feet. (The East Antarctic Ice Sheet holds even more frozen water, but it is considered more stable.)
Researchers have not definitively said whether today's temperatures have led to the complete collapse of the Western Ice Sheet. “We still can't say for sure, but it's definitely a sign,” said Nicholas Golledge, a professor of glaciology at Victoria University of Wellington, New Zealand, and another author of the study.
If the ice sheet has already reached its tipping point, estimates of how quickly it could melt range from 200 to 2000 years. “Our actions from now on will change the pace at which we get there,” Dr Golledge said.
Unlike today, the last interglacial was part of the ongoing natural cycle of tilting the Earth's axis and changing orbit around the Sun, and the 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 causes of past and present warming are different, the last interglacial is still one of the best analogies for today's climate change, said Roger Kriel, a postdoctoral fellow at the Woods Hole Oceanographic Institution. He was not involved in the study released Thursday, but contributed Estimates of sea level for this period.
“This is such strong evidence from a very different vantage point than the climate community often has,” Dr Kriel said of the new study.
Some of the octopus specimens studied by Dr. Lau were collected more than 30 years ago, from fishing boats and scientific expeditions, and stored in museums. Because the DNA of dead animals degrades over time, this type of research using museum specimens was not possible until recently with advances in genetic sequencing.
Other scientists have shown that population genetics of land animals are consistent with past melting of the West Antarctic Ice Sheet. A 2020 study of spring tailsSmall soil-dwelling invertebrates also suggest that ice in the Ross Sea region has been melting 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 those reconstructions, said Ian Hogg, a researcher at Polar Knowledge Canada, the agency that monitors the polar regions, and author of the Spring Tails study.
“As biologists, we know these patterns exist between populations,” he said. The challenge for biologists is to explain these observed patterns, and for geoscientists studying Antarctica to collect enough observational, physical evidence to validate their models.
“They have something that they're giving us,” Dr. Hogg said. “And we have something we can give them.”