Inside the drilling tent at Skytrain Ice Rise, engineers and scientists separating the inner barrel of the drill from the outer barrel between drilling runs. Credit: University of Cambridge/British Antarctic Survey
Key points:
- Researchers have found the first direct evidence that the West Antarctic Ice Sheet shrunk suddenly and dramatically about 8,000 years ago.
- The team reached their conclusions after drilling and examining a 650-meter-long ice core from the West Antarctic Ice Sheet.
- The study data detailing the West Antarctic Ice Sheet’s past can help improve current models of projected ice loss and sea level rise due to climate change.
UK researchers have uncovered the first direct evidence that the West Antarctic Ice Sheet shrunk suddenly and dramatically at the end of the Last Ice Age, around 8,000 years ago. The evidence, contained within an ice core, shows that in one location the ice sheet thinned by 450 meters in just under 200 years.
For the study, published in Nature Geoscience, the researchers drilled a 651-meter-long ice core from Skytrain Ice Rise, which sits at the edge of the ice sheet, in 2019.
After transporting the ice cores back to the University of Cambridge, the researchers analyzed them to reconstruct the ice thickness. First, they measured stable water isotopes, which indicate the temperature at the time the snow fell. Then, they measured the pressure of air bubbles trapped in the ice. These measurements told the team that ice thinned rapidly 8,000 years ago.
“Once the ice thinned, it shrunk really fast,” said senior author Eric Wolff, a professor at Cambridge. “This was clearly a tipping point—a runaway process.”
Wolff and team think this thinning was probably triggered by warm water getting underneath the edge of the West Antarctic Ice Sheet, which normally sits on bedrock. This likely untethered a section of the ice from bedrock, allowing it to float suddenly and forming what is now the Ronne Ice Shelf. This then allowed neighboring Skytrain Ice Rise—no longer restrained by grounded ice—to thin rapidly.
When, how and why ice loss occurred in the past is crucial to our understanding of current conditions in the Antarctic under climate change. Model predictions suggest that a large part of the West Antarctic Ice Sheet could disappear in the next few centuries, causing sea levels to rise. Exactly when and how quickly is, however, uncertain.
One way to train models to make better predictions is to feed them with data on ice loss from periods of warming in Earth’s history. At the peak of Last Ice Age 20,000 years ago, Antarctic ice covered a larger area than today. As the planet thawed and temperatures slowly climbed, the West Antarctic Ice Sheet contracted to more or less its current extent.
“We already knew from models that the ice thinned at around this time, but the date of this was uncertain,” said Isobel Rowell, study co-author from the British Antarctic Survey. “Ice sheet models placed the retreat anywhere between 12,000 and 5,000 years ago and couldn’t say how quickly it happened. We now have a very precisely dated observation of that retreat, which can be built into improved models.”