On the edge of faraway Antarctica, the majestic ice sheets are undergoing an irreversible change. One of the earth’s most precious freshwater reserves lies beneath this vast expanse of ice. The West Antarctic Ice Sheet (WAIS), although not the largest on the continent, bears pressures of great concern. Long-term monitoring data reveal that from 1979 to 2017, the WAIS has been losing an average of approximately 160 billion tons of ice per year. Should this ice sheet completely melt, the global sea level will rise by several meters, a potential threat that cannot be ignored.
Climate change poses unprecedented challenges to the WAIS, and many researchers are exploring what this change means for the future. To answer this question, our focus turns to the last interglacial period between 129,000 and 116,000 years ago when the Earth’s climate was overall milder, experiencing slight fluctuations. Studies indicate that the global temperature during that period was 0.5 to 1.5 degrees Celsius higher than pre-industrial levels, sharing similarities with the temperature levels of current climate change. The sea level at that time was 5 to 10 meters higher than today, and how much of this was due to changes in the WAIS is still being explored by paleoclimatologists.
Although we cannot travel back in time to that era, we can reveal the secrets of the ancient climate robustly through the Earth’s sedimentological and ice core evidence. In this exploration, the genetics of the Antarctic octopus provide important clues.
The Turquet octopus (Pareledone turqueti) has inhabited the icy Antarctic waters for approximately 4 million years. These creatures are not capable of long-distance swimming; their breeding grounds are fixed to the seabed, ensuring the survival of their offspring with low reproductive rates and relatively large eggs. Therefore, their gene flow is greatly restricted, rarely mixing with distant populations, making them ideal subjects for studying their migration history.
In a new study published in the journal Science, a research team analyzed DNA samples from 96 Turquet octopuses, unearthing crucial clues about the past living trajectories of these creatures. The oldest samples in this study date back to the 1990s, providing valuable information about the historical activity of the WAIS.
Researchers matched octopus specimens with their capture locations, aiming to disclose the substantial genetic differences among populations from different places. Scientists found that by analyzing the genetic material of the octopuses, they could observe a trend closely connected to geographical distribution. For instance, the genetic similarity between octopus populations captured around neighboring Shag Rocks Island and South Georgia Island was far higher than that of populations from other areas. This is evidently reasonable, given the closer proximity between these populations and, consequently, more frequent genetic exchange between them.
However, scientists studying octopus populations around the WAIS made some unexpected findings. Octopuses from the Ross Sea, living on the border adjacent to other Antarctic regions, not only had genetic exchanges with neighboring sea populations but also exchanged genes with populations from the South Weddel Sea located across the WAIS. This phenomenon is astonishing because the South Weddel Sea populations are separated by the entire WAIS. Similarly, octopus populations from the Amundsen Sea, on the opposite side of the WAIS, exhibited similar patterns of genetic exchange.
“Under current Antarctic topographical conditions, if these octopuses want to encounter each other, they would need to travel countless kilometers around the West Antarctic ice sheet. For these creatures, which are not fond of adventure, this task is nearly impossible to complete,” explains Sally Lau, co-author of the research report, “unless they find a shortcut.”
So, does such a shortcut exist? In fact, beneath the West Antarctic ice sheet lies a potential passageway. The West Antarctic land itself is shaped like a large basin, with a central depression that even dips below sea level in some areas. This unique topography also makes the ice sheet more susceptible to contact with the warm waters beneath, thus accelerating the ice sheet’s fragile state. And when the West Antarctic ice sheet disappeared in the past, what seems today to be an insurmountable continental shelf was transformed into an inland sea, allowing populations to exchange genes.
Researchers used models to simulate the impact of different states of the West Antarctic ice sheet on the octopus genome during the last interglacial period. These models considered the ice sheet being relatively intact, partially collapsed, and scenarios where only two populations could engage in genetic exchange. After thousands of simulations, the results suggest that only when the West Antarctic ice sheet completely disappeared could it best correspond to the genetic patterns currently observed in the octopus genome. Through scientific analysis, researchers infer that hybridization among these octopus populations occurred sometime between approximately 139,000 and 54,000 years ago.
In other words, this finding serves as incontrovertible evidence that points to the complete disintegration of the Antarctic ice sheet during the last interglacial period hundreds of thousands of years ago. Researchers realize that such a discovery is extremely rare in other studies. The organisms making this discovery possible must have an appropriate genetic model, provide ample samples, and most crucially, they need to have a widespread distribution in Antarctica and lack strong migratory abilities.
“This is the first biological evidence confirming past collapses of the ice sheet, which I believe makes this study incredibly unique and remarkable,” stated a paleoglaciologist from the Colorado School of Mines in the United States, although not involved in the research, “Using octopus populations to decode the history of the Antarctic ice sheet is truly unbelievable.”
The uncertain future of the West Antarctic ice sheet is intertwined with the fate of people globally. In December 2023, a report called ‘The Global Tipping Point Report’ was released at the 28th Conference of the Parties of the United Nations Framework Convention on Climate Change, pointing out that the world is at risk of breaching five major climate tipping points, one of which is the disappearance of the West Antarctic ice sheet. If this “tipping point” is breached, it will mark large-scale, irreversible losses of Antarctic ice. Unlike the last interglacial period, which was caused by natural planetary cycles involving the tilt of Earth’s axis and variations in solar orbits, the crisis we now face is due to greenhouse gas emissions, proceeding at a speed far exceeding natural variations. Even in the most optimistic predictions of climate models, the smallest degree of warming is enough to trigger the collapse of the West Antarctic ice sheet, leading to rising sea levels — this climate tipping point is indeed on the brink of danger.
However, numerous critical issues remain unresolved. For example, whether the disintegration of past ice sheets was caused solely by global warming or was influenced by a broader range of factors, such as changes in ocean currents or the complex interactions between the ice layers and the solid earth. Once these questions are answered, we ultimately need to confront a fundamental question: How much time do we have left to take action?
