An international research team co-led by a researcher from ETH Zurich has recovered the longest sediment core ever drilled from beneath an ice sheet in West Antarctica. The core preserves evidence of climate changes spanning millions of years and will help improve predictions of how the West Antarctic Ice Sheet may respond to ongoing global warming.
In Brief
- Beneath the ice of West Antarctica lie natural records of past climate variability, containing sediments deposited during warmer periods when the region was partly or entirely ice-free.
- An international team co-led by a researcher from ETH Zurich and the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) has now retrieved the longest sediment core ever drilled from beneath an ice sheet, using a custom-designed drilling system.
- The 228metre-long core contains geological evidence and fossils of marine organisms that indicate a previously open, ice-free ocean. This archive provides new insights into how sensitive the West Antarctic Ice Sheet is to a warming climate.
Some 700 kilometres from the nearest Antarctic stations, researchers drilled through 523 metres of ice at Crary Ice Rise, on the margin of the West Antarctic Ice Sheet. They extracted a record-breaking sediment core measuring 228 metres in length, composed of layers of mud and rock. This geological archive documents environmental conditions during earlier warm periods in Earth's history - information that is crucial for estimating how quickly the region's ice might melt in a warmer future.
If the West Antarctic Ice Sheet were to melt completely, global sea level would rise by four to five metres, according to scientific estimates. Until now, projections of how the ice sheet might respond to further warming relied mainly on satellite observations and geological records collected next to the ice sheet, below floating ice shelves, sea ice and in the open Ross Sea and Southern Ocean.
Comprehensive record of past warm periods
The new sediment core, drilled as part of the international SWAIS2C project (Sensitivity of the West Antarctic Ice Sheet to 2°C), was recovered at Crary Ice Rise - an ice dome grounded at the inner margin of the Ross Ice Shelf. For the first time, it provides direct and comprehensive evidence of how the ice-sheet margin behaved during earlier warm intervals.
"This record will give us critical insights about how the West Antarctic Ice Sheet and Ross Ice Shelf is likely to respond to temperatures above 2°C. Initial indications are that the layers of sediment in the core span the past 23 million years, including time periods when Earth's global average temperatures were significantly higher than 2°C above pre-industrial," says SWAIS2C Co-Chief Scientist Huw Horgan of Te Herenga Waka - Victoria University of Wellington, ETH Zurich and WSL.
Preliminary dating of the sediment carried out in the field was based on identification of tiny fossils of marine organisms found in some of the layers. A wider team of scientists from the 10 countries collaborating in the SWAIS2C project will now refine and confirm the age of the records.
Where thick ice lies today, there was once open ocean
As the team drilled down through the layers of sediment deep below the ice sheet, pulling up the core in lengths up to three metres long, they encountered a striking variety of sediment types from fine-grained muds through to firmer gravels with larger rocks embedded within.
"We saw a lot of variability. Some of the sediment was typical of deposits that occur under an ice sheet like we have at Crary Ice Rise today. But we also saw material that's more typical of an open ocean, an ice shelf floating over ocean, or an ice-shelf margin with icebergs calving off," says Co-Chief Scientist Molly Patterson, Professor of Geology at Binghamton University, USA.
Shell fragments and remains of marine organisms that require light to survive indicate that parts of the region must once have been ice-free open ocean. It is already thought that the region experienced past periods of open water, indicating partial or complete retreat of the Ross Ice Shelf, and potential collapse of the West Antarctic Ice Sheet.
However, the timing of these periods has remained uncertain. Determining when the ice retreated and which environmental factors drove the changes is now a central focus of the SWAIS2C team, according to Molly Patterson.
Record-breaking drill success on the third attempt
The recovery of the sediment core marks a significant scientific and technical achievement. For the 29 scientists, drillers, engineers and polar specialists, success was far from guaranteed. Two earlier drilling attempts had been thwarted by technical challenges. This was not unexpected given that no one had earlier drilled geological records from such depths beneath an ice sheet and so far away from any main base of resources.
"To our knowledge, the longest sediment cores previously drilled under an ice sheet are less than ten metres. We exceeded our target of 200 metres. This is Antarctic frontier science," says Patterson.
The 29‑member team worked around the clock in shifts using a custom‑designed drilling system (details are published external page here ). To access the elusive sediment, the team had to first use a hot-water drill to melt a hole through 523 m of ice, then lowered more than 1300 m of 'riser' and 'drill string' pipe down the hole. Once the core was pulled up, the scientists described, photographed and x-rayed the tubes of sediment, and took samples.
Looking ahead to further drilling
"It was a great feeling when that first core came up, but then you start worrying about the next core and the next core after that. So, it's stressful right up until the end. We're thrilled to have learnt from our previous challenges and to have successfully retrieved this geological record that will help the world prepare for the impacts of climate change," says Horgan.
The researcher is already looking ahead: "Our multi-disciplinary international team is already collaborating to unravel the climate secrets hidden in the core. With our drilling system having been put to the test under these tough Antarctic conditions and passing with flying colours, we're looking ahead to plan future drilling to continue our mission to learn more about the sensitivity of the West Antarctic Ice Sheet to global warming," says Horgan.
Image Gallery
This article is a slightly shortened and editorially adapted version of an external page English media release produced as part of the SWAIS2C project.
