Your DNA isn’t just a blueprint of who you are—it’s an archive of where you came from. Same goes for the DNA of all life on Earth, including the mollusks—snails, slugs, clams, and cephalopods—wriggling around on the Southern Ocean’s seafloor. It was only a matter of time before someone realized the genetic code of these squishy bottom-dwellers may hold clues to the history (and future) of Antarctica’s most vulnerable ice sheet.
That, at least, is the suggestion of a fascinating new paper, which proposes using marine invertebrates living around West Antarctica to reconstruct the ice sheet’s history. The idea is that if a warming climate caused the ice sheet to retreat dramatically in the past, it would have opened a trans-Antarctic seaway connecting populations of animals living in the Weddell, Amundsen, and perhaps Ross Seas. Signatures of any trans-Antarctic fraternizing should be recorded in the genetic code of any tentacled descendants alive today.
In other words, mollusk sex could tell us exactly what climate conditions could cause a vast Antarctic ice sheet to collapse. Go figure.
There certainly hasn’t been a better time for outside-the-box thinking on the West Antarctic Ice Sheet (WAIS), which contains enough frozen water to raise sea levels by up to fifteen feet. A growing body of evidence suggests portions of the ice sheet are exceptionally vulnerable to collapse in a warming world. Warm water is chewing away at the floating ice shelves that ring the ice sheet, and one of its buttressing glaciers, Pine Island, is thinning. Models suggest that Pine Island, and its larger neighboring glacier Thwaites, could experience rapid retreat if warming trends continue.
But there’s still a lot of uncertainty regarding how quickly the WAIS could collapse, and how much warming is required to trigger such an event.
In the new paper, which appears in Quaternary Science Reviews, Jan Strugnell of James Cook University and his colleagues specifically call out the last interglacial period, 130,000-116,000 years ago. At the time, global temperatures were about 2 degrees Celsius higher than they are today, and sea levels were 5.5 to 9 meters (18 to 30 feet) higher.
Lower estimates for sea level rise during the last interglacial can be accounted for by melting the Greenland ice sheet and smaller mountaintop glaciers worldwide. But in order to get 30 feet of sea level rise, you’ve also got to melt a good chunk of West Antarctica.
A partial collapse of the WAIS would have opened a seaway between the Weddell and Amundsen seas. A more complete melt would have linked up the Ross Sea, too. According to the authors, the opening of one or both of these two seaways—or neither of them—could, in theory, be distinguishable in the genetic structure of populations whose ancestors lived and migrated across the Southern Ocean during that time.
“Examination of the genomic signatures of bottom-dwelling marine species using the latest methods can provide an independent window into the integrity of the WAIS more than 100,000 years ago,” the authors write. “Periods of connectivity facilitated by trans-Antarctic seaways could be revealed by dating coalescent events recorded in DNA.”
The authors write that the ideal candidate would be an organism found across the Southern Ocean, one whose DNA contains some degree of “phylogeographic structure,” meaning populations that are geographically separated are also genetically different. Strugnell told Earther he’s already begun some work on Turquet’s octopus (Pareledone turqueti), a seafloor-dwelling species found all around Antarctica.
David Barnes, an ecologist with the British Antarctic Survey who was not involved with the study, told Earther that the paper’s proposed approach “has a lot of merit.”
“Indeed I can’t think of a better one,” he said, while cautioning that it will likely be difficult to obtain samples from areas around the Antarctic seaway gates. “Nevertheless we should be aspirational and we make ever more considerable leaps in polar research all the time,” Barnes added.
Mike MacFerrin, a glaciologist at the University of Colorado Boulder who also wasn’t involved, thought the paper offered “a really cool approach and a wicked idea to try.” He noted that the methods scientists use to determine the last time Greenland was ice-free—which involve counting rare isotopes deposited on exposed bedrock—don’t work so well around the edges of West Antarctica, where most of the bedrock lies below sea level.
“If the approach works, it would give us the first conclusive evidence of the last time [West Antarctica] was uncovered,” he said.
Hopefully, scientists interested in pursuing this approach can start collecting samples soon—before climate change reshapes Antarctica’s seafloor communities yet again.