Deep in the Antarctic ice, scientists have unearthed a geological archive, a discovery that could reshape predictions of future sea level rise. The research team drilled through 523 meters of ice in the Crary Ice Rise on the edge of the West Antarctic Ice Sheet and successfully extracted a 228-meter-long mudstone sediment core. These sediments record key evidence of environmental changes during previous warm periods in Earth's history and help estimate how quickly the region's ice sheets are melting under global warming.
If the West Antarctic Ice Sheet completely collapses, global sea levels are expected to rise by 4 to 5 meters. Previous predictions have relied mainly on satellite data and sedimentary records near the ice edge, under floating ice shelves, in sea ice, and in the Ross Sea and Southern Ocean. This core provides direct and detailed evidence of previous warm periods at the edge of the ice sheet.
This drilling belongs to the international SWAIS2C project (Sensitivity of the West Antarctic Ice Sheet to 2°C Warming) and was located in the Cleary Ice Dome on the inner edge of the Ross Ice Shelf. Unlike previous records, this core directly reveals the behavior of the ice sheet.
Preliminary analysis shows that the core sediments cover the past 23 million years, including a period when global average temperatures were more than 2°C higher than pre-industrial times. This will provide key insights into predicting the response of the West Antarctic Ice Sheet and the Ross Ice Shelf to warming above 2°C.
Preliminary dating estimates were made at the drilling site by identifying marine microbial fossils preserved in sedimentary layers, and SWAIS2C project researchers from 10 countries will conduct further detailed analysis to confirm the timeline.
As the drilling progressed, the team extracted core sections up to 3 meters long, showing a remarkable diversity of sediments, ranging from fine mud to compact gravel containing large rocks. Some of the deposits are similar to ice sheet deposits beneath the current Cleary Ice Dome, but there are also signs of typical open ocean, floating ice shelf-covered ocean, or ice shelf margin calving of icebergs.
Shell fragments and the remains of light-demanding marine life indicate that the area was once covered by open ocean rather than ice, confirming long-standing speculation that the Ross Ice Shelf has partially or completely retreated and that parts of the West Antarctic Ice Sheet may have collapsed.
Determining the exact timing of these recessions and the environmental conditions that trigger them is a primary goal of the SWAIS2C team.
Extracting the core was not only a scientific milestone but also an engineering feat. The 29-person team, including scientists, drillers, engineers and polar experts, faced huge uncertainty after two previous attempts failed due to technical failures. Previously, the longest sediment core under the ice sheet was less than 10 meters, but they exceeded the 200-meter target. This is cutting-edge Antarctic science.
The team used a special drilling system to work in continuous shifts. They first used hot water to drill the 523-meter deep hole, and then lowered more than 1,300 meters of "risers" and "drill pipes" to reach the sediments below. Each section of core was carefully recorded, photographed, X-ray scanned and sampled.
"It feels great when the first section of core comes up, but then you worry about the next section until it's over," said SWAIS2C co-lead scientist Huw Horgan of Victoria University Wellington, ETH Zurich and WSL. "We have learned from previous challenges and successfully extracted this geological record that will help the world combat the impacts of climate change."
Molly Patterson, another co-chief scientist and professor of geology at Binghamton University in the United States, said: "Our multidisciplinary international team has begun to work together to unlock the climate secrets in the cores. The drilling system has withstood the harsh Antarctic test, and we plan to continue drilling in the future to gain a deeper understanding of the sensitivity of the West Antarctic ice sheet to global warming."