Around 100,000 years ago, the vast western ice sheet of Antarctica disintegrated, forming canals between its three adjacent seas. Surprisingly, evidence supporting this theory comes from the DNA of Turquet's octopus (Pareledone turqueti), indicating that separated populations of these marine creatures were able to interbreed for millennia until the ice sheet's collapse. This story is documented in the genomes of these octopuses, shedding light on Antarctica's buried history and raising concerns about a potential rise in sea level.
The research, published in Science, employs a creative approach to uncovering Antarctica's past. Andrea Dutton, a geologist at the University of Wisconsin-Madison, commends the study for its innovative methodology. The investigation focuses on a brief interlude between 129,000 and 116,000 years ago known as the Last Interglacial,a milder period when the planet's average temperature was approximately 0.5°C higher than today. Climate estimates suggest a return to similar temperatures in the coming decades, potentially leading to a significant rise in sea levels.
The collapse of the West Antarctic Ice Sheet is believed to have contributed to elevated sea levels during the Last Interglacial. Geological evidence indicates that such collapses have occurred at least once in the past several million years. To explore this further, researchers examined the DNA of Turquet's octopus, a species kept apart by the ice sheet today.
Turquet's octopus, a mollusk about the length of a pencil that feeds on microscopic invertebrates, resides in waters as deep as one kilometer around Antarctica. Researchers collected small tissue samples from 96 octopuses caught by fishing vessels over 33 years. Through DNA analysis, evolutionary geneticist Sally Lau of James Cook University identified genetic markers called single-nucleotide polymorphisms (SNPs) to distinguish distinct octopus populations.
Lau constructed demographic models to simulate various scenarios of interbreeding between ancient octopuses, reflecting the changing conditions of the ice sheet. The models indicate that before the ice age, ocean currents connected four octopus populations in the Weddell Sea, Amundsen Sea, Ross Sea, and East Antarctica. As the West Antarctic Ice Sheet grew, these populations became isolated.
The findings are consistent with geological evidence of the ice sheet collapse, substantiated by sediment cores extracted from Iceberg Alley in 2019. The cores showed a surge in iceberg-carried debris during the Last Interglacial, corroborating the massive collapse hypothesis. The octopus genome data further supports this, indicating that interbreeding resumed between 139,000 and 54,000 years ago.
Claire Jasper, a graduate student at Columbia University, presented the findings at a meeting of the American Geophysical Union. The study warns about the potential consequences of continued ocean warming due to greenhouse gas emissions, which could destabilize the submerged portion of the West Antarctic Ice Sheet. To mitigate these risks, immediate action to reduce emissions is crucial, reinforcing the importance of understanding modern climate conditions and their impact on Antarctica.
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