Deep within the DNA of an Antarctic octopus, scientists may have uncovered an important clue about the future fate of the continent’s ice sheet — sparking fears that global warming could soon trigger a runaway melt.
Climate scientists are struggling to work out whether the ice sheet collapsed completely during the most recent “interglacial” period, about 125,000 years ago, when global temperatures were similar to today’s.
The ice sheet is holding enough water to raise sea levels by 10 to 15 feet, with fears that global warming could quickly push it toward runaway melting, which would keep rising sea levels for centuries. held.
In an ingenious approach, a team of 11 scientists – including biologists, geneticists, glaciologists, computer scientists and ice sheet modelers – looked at the genetics of Turquet’s octopus – a species that has lived around the Antarctic continent for about 4 million years.
Genetic samples were taken from 96 octopuses collected across the continent over three decades.
The octopus DNA holds a memory of its past, including how and when different populations moved and mixed and exchanged genetic material.
Related: Could octopus DNA reveal the secrets of West Antarctica’s ice sheet collapse?
The scientists say they’ve discovered clear signs that about 125,000 years ago, some octopus populations on opposite sides of the West Antarctic Ice Sheet had mixed, with the only likely route being a seaway between the southern Weddell Sea and the Ross Sea.
“That could only have happened if the ice sheet had completely collapsed,” said Dr Sally Lau, a geneticist at James Cook University who led the research.
The study is undergoing peer review in a journal, but it was made public, Lau said, because she wanted the scientific community to have quick access to it and because of the urgent nature of the findings.
She said information about the changes in the octopus’s DNA could be used as a clock, helping her pinpoint the time period when octopuses in the southern Weddell Sea and Ross Sea mixed.
Prof Nick Golledge, a co-author of the study from New Zealand’s Victoria University of Wellington, said a major concern was that once the ice sheet reaches a tipping point, melting becomes “self-sustaining” and will continue for centuries or more. .
He said the route the octopuses would have taken is about 1,500 to 2,000 meters below the top of the current ice sheet. That channel would have been about 3,000 feet deep, but shallower closer to the rim.
“It’s a significant ocean segment and an important seaway for organisms to traverse,” he said.
He said the rate of ice loss from West Antarctica had increased over the past two decades.
According to the most recent UN climate assessment, temperatures during the last interglacial were between 0.5C and 1.5C warmer than in the period just before the industrial revolution. The sea level was between 5 and 10 meters higher than now.
The authors of the octopus study say their findings suggest that even 1.5°C of warming — the most ambitious target of the global Paris climate agreement — threatens the West Antarctic ice sheet to collapse.
Prof Nathan Bindoff, an oceanographer and Antarctic expert at the University of Tasmania, said with regard to sea levels, senior scientists strongly suspect that a melting West Antarctic ice sheet must have contributed to that rising sea level.
Bindoff, who was not involved in the study, said using octopus DNA was “the last way I would have thought to have evidence of major sea level changes due to the collapse of the West Antarctic ice sheet”.
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“The loss of that ice sheet would have very real consequences for the entire planet. If this [octopus research] is true, then there are sensitivities in the Earth system that lead to sea level rise on a planetary scale.”
In the most recent UN climate report, Bindoff identified an area of greatest uncertainty about how high sea levels may be related to the West Antarctic Ice Sheet.
He said there are currently about 670 million people living in low-lying areas around the world, with another 65 million living in small island states.
He said: “This paper is another piece of evidence that reduces that uncertainty about how this ice sheet evolved in the past and that’s crucial for how we think about the future.”
Professor Richard Alley, a leading expert on ice sheets at Penn State University, said that while there was evidence that the ice sheet had collapsed millions of years ago, “we still don’t know for sure whether the ice sheet decayed during the most recent interglacial “.
He described the octopus study as “interesting and important” and said it strengthened the case for the loss of the ice sheet during the last interglacial period.