Scientists have long been concerned that the massive West Antarctic Ice Sheet could collapse if global temperatures keep climbing. Should this happen, sea levels are predicted to rise by as much as five metres.
Now genetic evidence obtained from an Antarctic octopus reveals such an event may have happened in the not-too-distant past – possibly as recently as 200,000 years ago. This suggests that scientists' concerns about the state of today's ice sheet could be justified.
An international team of researchers analysed the genes of the Turquet's octopus, which lives in the Southern Ocean surrounding Antarctica. During the Census of Antarctic Marine Life from 2005 to 2010 and the International Polar Year, teams of scientists collected Turquet's octopuses from all around the continent.
They were able to take advantage of the many more samples than had been collected from Antarctica before. This presented the team a unique opportunity to study genetic differences between octopuses from different parts of the ocean.
Adult Turquet's octopuses only move to escape from predators so they tend to stay in a single locality and not travel around – which why the researchers expected octopuses from different regions to be genetically quite dissimilar.
Surprisingly, however, they found that the genes from octopuses taken from the Weddell and Ross Seas on opposite sides of Antarctica were startlingly similar, even though the two seas are completely separate and about 10,000 kilometres apart.
In a paper published in Molecular Ecology, the researchers say that when the climate was much warmer, sea levels would have been substantially higher, because less water would have been locked up as ice; in that event, the Ross and Weddell Seas could have been connected.
They note that ocean currents would have facilitated but also hindered the flow of genes, although the Antarctic Circumpolar Current almost certainly would not have facilitated so much dispersal by octopuses as to cause the two populations to have almost identical genetics.
They conclude that this could only have happened had the West Antarctic Ice Sheet collapsed. And, in contrast to the octopuses in the two seas, those from other parts of Antarctica showed the level of genetic differences expected.
“The octopus do not go any deeper than 1,000 metres, so populations on areas of the continental shelf that are separated by deep water are very effectively isolated,” said Dr Phill Watts from the University of Liverpool’s Institute of Integrative Biology.
A previous study, two years ago, provided the first evidence of a trans-Antarctic seaway connecting the Ross and Weddell seas, but the researchers say this is the first genetic evidence of such a connection.
Of the world's three major ice sheets, scientists believe the West Antarctic is most vulnerable to changes in climate. Because it is inherently unstable and is likely to collapse fairly quickly, it could make a substantial contribution to sea-level rise.
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