Octopus DNA Reveals Clues to When the West Antarctic Ice Sheet Last Collapsed

Understanding the ice sheet’s past could help researchers shed light on its future melting

An octopus
Turquet’s octopus David Barnes via the University of Western Australia

In the sea surrounding Antarctica, small cephalopods called Turquet’s octopuses have been crawling along the ocean floor for some four million years. The six-inch-long creatures (excluding arms) are unassuming, but researchers have recently discovered that the animals’ DNA may help solve a longstanding scientific mystery: When did the West Antarctic Ice Sheet last collapse? 

The West Antarctic Ice Sheet (WAIS) holds enough water to raise global sea levels by more than 16 feet if it were to melt entirely, an inundation that would flood Washington, D.C. and many coastal U.S. cities. In recent years, global ocean warming—fueled by high levels of greenhouse gas emissions from burning fossil fuels—has left the ice sheet in a precarious situation. An October study found that even under best-case emissions scenarios, the sheet’s melting is inevitable. Still, learning more about its past could help us understand what’s to come.  

“What makes the WAIS important is that it is also Antarctica’s current biggest contributor to global sea level rise,” Jan Strugnell, director of the Center for Sustainable Tropical Fisheries and Aquaculture at James Cook University in Australia, says in a statement. “Understanding how the WAIS was configured in the recent past when global temperatures were similar to today will help us improve future sea-level rise projections.” 

So, Strugnell and her colleagues turned to the Turquet’s octopus (Pareledone turqueti) for answers. While these animals live all around the icy continent, their populations in the Ross Sea and Weddell Sea are separated by the impassable WAIS and rarely move far from where they live. If researchers could determine how recently the two populations interbred, that might give some clues to when the ice sheet last melted. 

In a study published Thursday in Science, the team sequenced the DNA of 96 Turquet’s octopuses from all around the continent that were either accidentally caught by fishers or stored in museum collections. Though their oldest specimen was from the 1990s, genetic analysis could provide a glimpse millions of years back in the octopus family tree, per CNN’s Katie Hunt.  

“It’s like doing a 23andMe on the octopus,” lead study author Sally Lau, a researcher at James Cook University, tells the publication. “This information gets passed down from parents to children and grandchildren and so on.”

The genetic analysis revealed that the Weddell Sea and Ross Sea octopuses interbred between about 54,000 and 139,000 years ago, during a period known as the Last Interglacial—a conclusion that matched with scientists’ suspicions that a collapse had occurred during that time.

“This is really the first biologic evidence that’s being used for past collapse, and I think that that is the really special and surprising thing about this paper,” Ryan Venturelli, a paleoglaciologist at the Colorado School of Mines who was not involved in the research, tells Meghan Bartels of Scientific American. “I think it’s just incredible that we can use populations of octopus to teach us about the history of the Antarctic ice sheet.”

Global average temperatures currently hover around 1.2 degrees Celsius higher than pre-industrial averages. During the Last Interglacial, the Earth was about 0.5 to 1.5 degrees Celsius warmer than pre-industrial averages, yet sea levels were about 16 to 33 feet higher than they are now, reports Delger Erdenesanaa for the New York Times. While it’s still unclear exactly when the WAIS melted, or how long it took, scientists say the study is a stark warning for the planet. 

“This is telling us that we need to take this bigger picture seriously,” Andrea Dutton, a geologist at the University of Wisconsin–Madison who studies ancient sea levels but was not involved in the study, tells Science’s Erik Stokstad. “We can’t just kick the can down the road and wait to make emissions cuts for another five years, another ten years. It really demands that we do it now.”

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