This Antarctic octopus sounds warning about rising sea levels

Scientists have long wondered whether the West Antarctic ice sheet is a ticking bomb when it comes to sea level rise. New evidence from DNA from small octopuses in the Southern Ocean suggests the ice sheet is indeed in danger of collapse, according to a study published Thursday in the journal Science.

The study does not predict when this will happen, but it suggests that global warming of 1.5 degrees Celsius above the pre-industrial global average, and possibly even less, could become a tipping point for ice sheets. The Earth is now approaching this temperature level.

Today, several different groups of Pareledone turqueti (commonly known as Turquets octopus) live in the waters around Antarctica. These octopuses crawl along the seafloor, usually not straying too far from home. A few individuals or their eggs may occasionally drift on ocean currents to neighboring colonies, but populations in the Ross Sea and Weddell Sea are separated by the impassable West Antarctic Ice Sheet.

However, genetic analysis of octopuses from various locations across Antarctica suggests that the two groups began mixing and exchanging DNA about 120,000 years ago. This was a period in Earth’s history known as the last interglacial, before the most recent ice age, when temperatures were similar to today.

The researchers say the patterns observed in the octopus gene pool would only have been possible if the West Antarctic Ice Sheet did not exist and relatively open shipping lanes across the continent allowed octopuses to travel freely between the Ross and Weddell Seas. possible.

Scientists know that sea level was several meters higher at that time. But whether the extra water came from West Antarctica is a question the earth science community has been trying to answer for nearly 50 years, said Sally Lau, a postdoctoral researcher at James Cook University in Townsville, Australia, and lead author of the new study.

Today, global average temperatures are about 1.2 degrees Celsius higher than between 1850 and 1900, when the burning of fossil fuels began causing warming. During the last interglacial period, global average temperatures were also about 0.5 to 1.5 degrees Celsius higher 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 5 meters (16 feet). (The East Antarctic Ice Sheet holds more ice water, but it is considered more stable.)

The researchers did not specify whether today’s temperatures have caused the Earth’s western ice sheet to completely collapse. “We still don’t know for sure, but it’s certainly a hint,” said study co-author Nicholas Golledge, a professor of glaciology at Victoria University of Wellington in New Zealand.

If the ice sheet has reached a critical point, estimates of its melt rate range from 200 to 2000 years. Golic said our actions from now on will still change how quickly we get there.

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 Earth 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.

Roger Creel, a postdoctoral scholar at the Woods Hole Oceanographic Institution, said that although the causes behind past and current warming are different, the last interglacial period remains one of the best analogies for today’s climate change. He was not involved in the study published Thursday but contributed to sea level estimates for the period.

Creel said of the new study that it provides such strong evidence from a completely different perspective than is typical in the climate community.

Some of the octopus specimens studied by Liu were collected from fishing boats and scientific expeditions more than 30 years ago and kept in museums. Because DNA in dead animals degrades over time, such studies using museum specimens were only possible with recent advances in genetic sequencing technology.

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 springtails, small invertebrates that live in soil, also showed that ice in the Ross Sea region 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 These reconstructions. A study of springtails.

As biologists, he says, we know these patterns exist in human populations. The challenge for biologists is to explain these observed patterns, and the challenge for geoscientists studying Antarctica is to collect enough observational and physical evidence to validate their models.

‘They’re giving us something,’ Hogg said. We have something to offer them.