Scientists looking at how Antarctica’s ice sheets retreated in the distant past have taken an unusual approach: analyzing the genomes of octopuses that live in its frigid seas.
According to a new study published Thursday in Science, geographically dispersed populations of the eight-limbed sea animals mated freely around 125,000 years ago, indicating an ice-free corridor during a time when global temperatures were similar to today.
According to the authors, the data indicate that the West Antarctic Ice Sheet (WAIS) is closer to collapse than previously anticipated, causing 3.3-5 meters of long-term sea level rise if the world fails to limit human-caused warming to the Paris Agreement’s 1.5 degrees Celsius target.
As an evolutionary biologist concentrating on marine invertebrates, lead author Sally Lau of Australia’s James Cook University told AFP, “I understand and then apply DNA and biology as a proxy of changes to Antarctica in the past.”
Turquet’s octopus was a perfect choice for investigating WAIS, she said, because the species is widespread all over the continent and key questions about it, such as its 12-year lifetime and the fact that it first appeared four million years ago, had previously been solved by science.
They lay relatively few, but huge eggs on the seafloor, measuring around half a foot (15 cm) long excluding the limbs and weighing roughly 1.3 pounds (600 kilos). This means that parents must exert considerable effort to ensure that their offspring hatch — a lifestyle that prevents them traveling too far away.
In parts of their modern environments, they are also constrained by circular sea currents known as gyres.
Lau and colleagues discovered evidence of trans-West Antarctic seaways that once connected the Weddell, Amundsen, and Ross seas by sequencing the DNA across genomes of 96 samples that were mainly captured mistakenly as fishing bycatch and then placed in museum storage over the course of 33 years.
WAIS collapsed at two distinct stages, the first in the mid-Pliocene, 3-3.5 million years ago, which scientists were already certain about, and the second in the Last Interglacial, a warm stretch from 129,000 to 116,000 years ago.
“This was the last time the planet was around 1.5 degrees warmer than pre-industrial levels,” he stated. Human activity, especially the use of fossil fuels, has boosted global temperatures by 1.2 degrees Celsius since the late 1700s.
“Tipping point of future WAIS collapse is close”
Before the recent Science publication, there were a few studies that suggested WAIS collapsed at some point in the past, but they were far from conclusive due to the considerably lower resolution genetic and geological evidence.
“This study provides empirical evidence indicating that the WAIS collapsed when the global mean temperature was similar to that of today, suggesting that the tipping point of future WAIS collapse is close,” the researchers said in a statement.
A 3.3-meter rise in sea level will radically alter the world map as we know it, burying low-lying coastal regions all over the place.
Andrea Dutton of the University of Wisconsin-Madison and Robert DeConto of the University of Massachusetts, Amherst characterized the new research as “pioneering,” noting that it raised intriguing issues about whether ancient history might repeat itself.
They did, however, point out that other critical concerns remained unsolved, such as whether the past ice sheet collapse was caused solely by rising temperatures, or if other factors like as altering ocean currents and intricate interactions between ice and solid Earth were also at work.
It’s also unclear whether the sea level rise would be gradual over millennia or come in more abrupt bursts.
Uncertainties like these, however, cannot be used as an excuse to do nothing about climate change, “and this latest piece of evidence from octopus DNA stacks one more card on an already unstable house of cards,” they added.
Recent Antarctic ice news
The research comes less than a month after scientists announced that the world’s largest iceberg was “on the move” after being trapped to the ocean floor for 37 years on Friday. According to the British Antarctic Survey, the iceberg, known as A23a, is currently traveling past the northern tip of the Antarctic Peninsula and toward the Southern Ocean.
The survey revealed spectacular video shot by the ship’s crew earlier this month, including drone footage of a pod of orcas swimming close to the huge iceberg.
According to estimates from the European Space Agency (ESA), the iceberg weighs about a trillion tons.
The iceberg, which covers over 4,000 square kilometers (or 1,500 square miles), broke away from the Antarctic shoreline in 1986 but became stranded in the Weddell Sea, according to the BBC.
Meanwhile, scientists announced in October that they had discovered a vast, hidden landscape of hills and valleys formed by ancient rivers that had been “frozen in time” beneath the Antarctic ice for millions of years.
“It is an undiscovered landscape — no one has seen it,” Stewart Jamieson, a glaciologist at the United Kingdom’s Durham University and the study’s principal author, told AFP.
According to Jamieson, the area beneath the East Antarctic Ice Sheet is less well known than the surface of Mars.
The 32,000 square kilometers (12,000 square miles) area was formerly home to trees, forests, and possibly animals.
But then the ice arrived, and it became “frozen in time,” according to Jamieson.