This Antarctic Octopus Has a Warning About 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 in danger of collapsing, according to a study published Thursday in the journal Science.

The research does not predict when this will happen, but it does indicate that 1.5 degrees Celsius of global warming over the preindustrial global average, or perhaps less than that, would be a tipping point for the ice sheet. The Earth is close to the current temperature level.

Several distinct populations of Pareledone turqueti, commonly known as Turquets octopus, live in the waters around Antarctica today. These octopuses crawl on the sea floor and usually do not stray from the house. Some individuals or their eggs sometimes drift with currents to neighboring groups, but the Ross Sea and Weddell Sea populations are separated by the impassable West Antarctic Ice Sheet.

However, genetic analysis of octopuses from different locations around Antarctica shows that these two populations mixed 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, where the temperature is similar to today.

The observed patterns in the octopus gene pool could only be possible if the West Antarctic ice sheet was not there at the time and relatively open oceans 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 in the past. But whether more water is coming from West Antarctica is the question the geoscience community has been trying to answer for nearly 50 years, says Sally Lau, a postdoctoral researcher at James Cook University in Townsville, Australia, and lead author. in a new study.

Today, the global average temperature is about 1.2 degrees Celsius higher than in 1850 to 1900, when the burning of fossil fuels began to warm the climate. During the Last Interglacial, the global average temperature was about 0.5 to 1.5 degrees Celsius warmer than the preindustrial base line, but the sea level was five to 10 meters higher than today. If climate change melts the entire West Antarctic ice sheet, sea levels could rise by an average of up to five meters, or 16 feet. (The East Antarctic Ice Sheet has more frozen water, but it is considered more stable.)

Researchers have not clearly stated whether the current temperatures have turned the planet into a complete collapse of the western ice sheet. Still can’t say for sure, but that’s 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 reached a tipping point, it is estimated how quickly it will melt from 200 years to 2,000 years. Our actions from this point will still change the rate at which we get there, Dr. Golledge 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 the resulting 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 faster rate.

Although the causes behind past and present warming are different, the Last Interglacial is still one of the best analogs for climate change today, said Roger Creel, a postdoctoral scholar at the Woods Hole Oceanographic Institution. . He was not involved in the study published Thursday but contributed to the estimate of sea levels at the time.

Such strong evidence comes from a completely different point of view than the climate community has always had, said Dr. Creel about the new study.

Some of the octopus specimens studied by Dr. Lau was collected more than 30 years ago, from fishing boats and scientific expeditions, and held in museums. Because the DNA of dead animals degrades over time, this type of research using museum specimens has not been possible until now with advances in genetic sequencing.

Other scientists have shown that the genetics of land animal populations is in line with past melting of the West Antarctic Ice Sheet. A 2020 study of springtails, small land-dwelling invertebrates, also suggests that ice in the Ross Sea region has been melting during warm periods over the past 5 million years, including the Last Interglacial.

Geoscientists may use mathematical models to reconstruct ice sheets and sea levels in the past, but emerging biological evidence is helping to confirm these reconstructions, said Ian Hogg, a research scientist at Polar Knowledge Canada, an agency that monitors the polar regions, and an author of the springtails study.

As biologists, we know these patterns exist in populations, he said. The challenge for biologists is to explain these observed patterns, while a challenge for geoscientists studying Antarctica is to gather enough observational, physical evidence to validate their models.

They have something they gave us, said Dr. Hogg. And we have something to give them.

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