Octopus DNA reveals long history of Antarctic ice sheet

Scientists have used octopus DNA to discover that the West Antarctic Ice Sheet (WAIS) likely collapsed during the Last Interglacial period around 120,000 years ago – when global temperatures were similar to today.

A new analysis published Thursday in Science finds that geographically-isolated populations of the eight-limbed sea creatures mated freely around 125,000 years ago, signaling an ice-free corridor during a period when global temperatures were similar to today.

The findings suggest the WAIS is closer to collapse than previously thought, threatening 3.3 to 5 meters of long term sea level rise if the world is unable to hold human-caused warming to the 1.5 degrees Celsius target of the Paris Agreement, said the authors. 

Turquet's octopus made an ideal candidate for studying WAIS, because the species is found all around the continent and fundamental information about it has already been answered by science, such as its 12-year-lifespan, and the fact it emerged some four million years ago. 

About 15 centimeters long excluding the arms and weighing around 600 grams, they lay relatively few, but large eggs on the bottom of the seafloor. This means parents must put significant effort into ensuring their offspring hatch – a lifestyle that prevents them traveling too far away.

They are also limited by circular sea currents, or gyres, in some of their modern habitats.

The team compared the genetic profiles of Turquet's octopus found in the Weddell, Amundsen, and Ross seas and found genetic connectivity dating back to the Last Interglacial.

The history of genetic mixing indicated WAIS collapsed at two separate points - first in the mid-Pliocene, 3 to 3.5 million years ago, which scientists were already confident about, and the last time in a period called the Last Interglacial, a warm spell from 129,000 to 116,000 years ago.

"This was the last time the planet was around 1.5 degrees warmer than pre-industrial levels," said the lead author Sally Lau of James Cook University in Australia. Human activity, primarily burning fossil fuels, has so far raised global temperatures by 1.2 degrees Celsius compared to the late 1700s. 

"This study provides empirical evidence indicating that the WAIS collapsed when the global mean temperature was similar to that of today, suggesting that the tipping point of future WAIS collapse is close," the authors wrote.