Octopus DNA reveals a secret about the polar ice cap

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An octopus from Turquet (Archive photo)

Agence France-Presse

To study the past evolution of the Antarctic ice cap, scientists looked at the genes of an octopus living in these polar waters, discovering that part of this gigantic glacier could melt more quickly than previously estimated.

A study published in the journal Science (New window) (in English) reveals that today isolated populations of octopuses from Turquet, which live in the depths of Antarctica, were mating freely 125,000 years ago, implying that the western part of the continent was ice-free at the time.

This discovery suggests that this part of the ice sheet, called the West Antarctic Ice Sheet, could melt much more quickly than previously thought.

The threat: seeing sea levels rise by more than three meters if the world fails to meet the goal set out in the Paris Agreement of not exceeding 1.5°C of global warming.< /p>

Such a rise in sea levels would significantly transform global geography, submerging islands and coastal territories.

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Evolutionary biologist Sally Lau of James Cook University in Australia, lead author of the study, told AFP that Turquet's octopuses were ideal candidates to study the West Antarctic ice sheet, particularly due to their presence all around the ice continent.

Additionally, basic information is already known about this invertebrate, such as its lifespan and the fact that it has been around for around four million years.

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About 15 cm long without tentacles and weighing around 600 grams, it lays small quantities of large eggs on the sea floor. This means that octopuses must ensure that their offspring hatch, forcing a lifestyle that prevents them from straying too far.

Their freedom of movement is also limited by ocean currents.

Sally Lau and her team carried out DNA sequencing of 96 samples collected usually inadvertently by fishermen and then left in museum archives. Their research also demonstrates the former existence of maritime passages connecting the Amundsen, Ross and Weddell seas.

Genetic mixing found in the samples indicates that the West Antarctic Ice Sheet melted twice. First in the middle of the Pliocene, 3 to 3.5 million years ago, a melting that scientists already strongly suspected. Then during an era of warming, during the last interglacial period, 116,000 to 129,000 years ago.

That was the last time the planet was about 1.5°C warmer than pre-Industrial Revolution levels, says Sally Lau.

Human activity, mainly the burning of fossil fuels, has so far increased global temperatures by 1.2°C compared to those of the late 18th century.

A few studies before this one already suggested that the West Antarctic ice sheet had once melted, but their conclusions were far from conclusive due to the absence of precise geological or genetic data. /p>

This study provides empirical evidence that the West Antarctic Ice Sheet collapsed when the global average temperature was similar to today, suggesting that the tipping point A future collapse of the West Antarctic ice sheet is near, write the authors.

Authors of an accompanying article publication in Science, Andrea Dutton, of the University of Wisconsin-Madison, and Robert DeConto, of the University of Massachusetts, Amherst, United States, described the #x27;s study as a pioneer, adding that it poses intriguing questions about the possibility of history repeating itself.

They raise the fact, however, that several questions remain unanswered, notably as to whether previous ice sheet collapses were caused by increasing temperatures alone or whether #x27;Other variables, such as changing ocean currents and the complex relationships between ice and land, were factors in these melts.

Uncertainty also remains as to whether sea level rise would occur over several millennia or occur in more rapid leaps.

Such uncertainties are no excuse for inaction against global warming, argue Andrea Dutton and Robert DeConto, and this piece of evidence from octopus DNA adds a new element to an already rickety house of cards.