Deep in the DNA of an Antarctic octopus, scientists may have discovered a big story about the future fate of the continent’s ice sheet – raising fears that global warming could soon reverse its meltdown.
Climate scientists have struggled to determine whether the ice sheet collapsed completely during the most recent “interglacial” period around 125,000 years ago, when global temperatures were similar to today.
The ice sheet holds enough water to raise sea levels by 3 to 4 meters and there are concerns that global warming could soon push it towards a catastrophic melt that would send sea levels rising over centuries.
With an ingenious approach, a team of 11 scientists – including biologists, geneticists, glaciologists, computer scientists and ice sheet modellers – looked at the genetics of the Turquet octopus – a species that has been living around the Antarctic continent for about 4m years.
Genetic samples were taken from 96 octopuses collected over decades across the continent.
Octopus DNA has a memory of the past, including how and when different populations moved and mixed together, exchanging genetic material.
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Scientists say they detected clear signs that, around 125,000 years ago, several octopus populations on the other side of the West Antarctic Ice Sheet had mixed together, and that the only likely route was a sea route between the southern Weddell Sea and Ross Sea.
“That could only happen if the ice sheet had completely collapsed,” said Dr Sally Lau, a geneticist at James Cook University who led the research.
The research is under peer review at a journal but has been made publicly available, Lau said, because she wanted the scientific community to have early access and because of the urgent nature of the results.
She said information on the changes in the octopus’s DNA can be used as a clock, allowing her to pinpoint the period when octopuses in the southern Weddell Sea and Ross Sea intermingled.
Professor Nick Golledge, co-author of the research from Victoria University of Wellington in New Zealand, said it was a major concern that the melting would become “self-sustaining” once the ice sheet reaches a tipping point and continue for centuries or longer. .
He said the route believed to have been used by the octopuses is about 1,500 to 2,000 meters below the top of the current ice sheet. That channel would be about 1,000 meters deep, but shallower closer to the edge.
“It’s a large segment of ocean and a significant seaway for organisms to cross,” he said.
He said over the past two decades the rate of ice loss from west Antarctica had been increasing.
According to the latest UN climate assessment, temperatures during the last interglacial were between 0.5C and 1.5C warmer than the period immediately preceding the industrial revolution. Sea levels were between 5 and 10 meters higher than today.
The authors of the octopus research say that even under 1.5C global warming – the most ambitious goal under the global Paris climate agreement – the West Antarctic Ice Sheet could be consigned to collapse.
Professor Nathan Bindoff, an oceanographer and expert on the Antarctic at the University of Tasmania, told sea levels that scientists strongly suspect that the melting of the West Antarctic Ice Sheet has contributed to rising sea levels.
Bindoff, who was not involved in the research, said using octopus DNA was “the last way I would think of having evidence of major sea level changes resulting from the collapse of the West Antarctic Ice Sheet”.
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“Losing that ice sheet would have real consequences for the entire planet. If this [octopus research] right, so there are sensitivities in the Earth system that lead to sea level rise on a planetary scale.”
In the United Nations’ latest climate report, Bindoff said one area of greatest uncertainty is how high sea levels might relate to the West Antarctic Ice Sheet.
He said there were currently about 670 million people living in low-lying areas around the world, and another 65 million 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 is crucial to how we think about the future.”
Professor Richard Alley, a leading ice sheet expert at Penn State University, said that although there was evidence that the ice sheet had collapsed millions of years ago, “we are still not sure whether the ice sheet declined during the interglacial most recent”.
He described the octopus research as “interesting and important” and said it strengthened the arguments that the ice sheet was lost during the last interglacial period.