To study the past evolution of the Antarctic ice cap, scientists examined the genes of an octopus living in these polar waters and found that part of this gigantic glacier may be melting faster than expected. Estimated so far.
A study published in the journal Science (New Window) (in English) shows that now isolated populations of turquet squid living in the depths of Antarctica mated freely 125,000 years ago, suggesting that this occurred in the western part The continent was then ice-free.
This discovery suggests that this part of the ice sheet, called the West Antarctic Ice Sheet, may be melting much faster than previously thought.
The danger: A rise in water levels of more than three meters if the world does not meet the Paris Agreement target of no more than 1.5°C of global warming.
Such sea level rise would dramatically alter global geography, submerging islands and coastal areas.
Evolutionary biologist Sally Lau of James Cook University in Australia, lead author of the study, told AFP that turquet octopuses were ideal candidates for studying the West Antarctic ice sheet, particularly given their presence across the ice continent.
In addition, basic information about this invertebrate is already known, such as its lifespan and the fact that it has existed for around four million years.
Measuring about 15 cm long without tentacles and weighing about 600 grams, it lays large eggs in small quantities on the seabed. This means that octopuses must ensure that their offspring hatch, forcing them to adopt a lifestyle that prevents them from straying too far away.
Their freedom of movement is also restricted by ocean currents.
Sequencing
Sally Lau and her team carried out DNA sequencing of 96 samples, usually collected accidentally by fishermen and then left in museum archives. Their research also demonstrates the earlier existence of sea passages connecting the Amundsen, Ross and Weddell Seas.
The genetic mix 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 before the Industrial Revolution, says Sally Lau.
Human activities, particularly the burning of fossil fuels, have so far increased global temperatures by 1.2°C compared to the late 18th century.
Some studies prior to this study had already suggested that the West Antarctic ice sheet had once melted, but their conclusions were far from conclusive due to the lack of precise geological or genetic data.
This study provides empirical evidence that the West Antarctic ice sheet collapsed when global average temperatures were similar to today, suggesting that the tipping point for future West Antarctic ice sheet collapse is near, the authors write.
History could repeat itself
The authors of an article accompanying the publication in Science, Andrea Dutton of the University of Wisconsin-Madison and Robert DeConto of the University of Massachusetts, Amherst, USA, called the study groundbreaking and added that it raises interesting questions about the possibility that history repeats itself.
However, they raise the fact that several questions remain unanswered, including whether previous ice sheet collapses were caused solely by rising temperatures or whether other variables, such as changing ocean currents and the complex relationships between ice and earth, were factors in this melting.
There remains uncertainty about whether sea level rise would occur over several millennia or in more rapid spurts.
Such uncertainties are no excuse for inaction on global warming, argue Andrea Dutton and Robert DeConto, and this evidence from octopus DNA adds another element to an already shaky house of cards.