Scientists have long wondered whether the West Antarctic Ice Sheet is a ticking time bomb when it comes to sea level rise. New evidence from the DNA of a small octopus living in the Southern Ocean suggests that the ice sheet is indeed in danger of collapsing, according to study published Thursday in the journal Science.
The research 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 even less, could be a tipping point for the ice sheet. Earth is close to that temperature level now.
Several distinct populations of the Pareledone turquet, commonly known as the Turquet’s octopus, live in the waters around Antarctica today. These octopuses crawl on the sea floor and generally do not stray far from home. A few individuals or their eggs may occasionally drift in currents to neighboring groups, but populations in the Ross Sea and Weddell Sea are separated by the impassable West Antarctic Ice Sheet.
And yet, genetic analysis of octopuses from different locations around Antarctica shows that these two populations were mixing and exchanging DNA around 120,000 years ago. This was a period in Earth’s history called the Last Interglacial, 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 did not exist at the time and relatively open sea lanes across the continent allowed octopuses to travel freely between the Ross and Weddell Seas, according to the researchers.
Scientists know that the sea level was several meters higher then. But whether the extra water came from West Antarctica is “the question the geoscience community has been trying to answer for almost 50 years,” said Sally Lau, a postdoctoral researcher at James Cook University in Townsville, Australia, and lead author of the new study. .
Today, the global average temperature is about 1.2 degrees Celsius higher than it was from 1850 to 1900, when burning fossil fuels began to warm the climate. During the last Interglacial, the global average temperature was similarly about 0.5 to 1.5 degrees Celsius higher than this pre-industrial baseline, but sea levels were five to 10 meters higher than today. If climate change completely melts the West Antarctic ice sheet, sea levels could rise on average by as much as five meters, or 16 feet. (The East Antarctic Ice Sheet has even more frozen water, but is considered more stable.)
The researchers did not specifically say whether today’s temperatures had already committed the planet to a complete collapse of the western ice sheet. “We’re not yet in a position to say for sure, but that’s certainly the conclusion,” said Nicholas Golledge, a 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 can melt range from 200 to 2,000 years. “Our actions from this point forward will continue to change the rate at which we get there,” Dr. Golletz said.
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 consequent changes in the amount of sunlight the planet received. These cycles occur gradually over tens of thousands of years. Our current greenhouse gas emissions are causing similar changes in temperature, 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 today’s climate change, said Roger Creel, a postdoctoral researcher at Woods Hole Oceanographic Institution. He was not involved in the study published Thursday, but he contributed sea level estimates during this period.
“It’s such strong evidence from a completely different vantage point than the climate community often has,” said Dr. Creel for the new study.
Some of the octopus specimens studied by Dr. Lau were collected more than 30 years ago, by fishing boats and scientific expeditions, and kept in museums. Because DNA in dead animals degrades over time, this type of research using museum specimens was not possible until very recently with advances in genetic sequencing.
Other scientists have shown that the population genetics of land animals coincided with earlier melting of the West Antarctic Ice Sheet. ONE Study 2020 for springssmall ground-dwelling invertebrates, also suggested that ice in the Ross Sea region had melted during warm periods over the past 5 million years, including 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, an agency that monitors polar regions and author the study of springs.
“As biologists, we know that these patterns exist across populations,” he said. The challenge for biologists is to explain these observed patterns, while a challenge for geoscientists studying Antarctica has been to gather enough observational, physical evidence to validate their models.
“They have something to offer us,” Dr. Hogg said. “And we have something we can provide them.”