Researchers have drilled the deepest Antarctic sediment core ever, uncovering 23 million years of climate history beneath the ice sheet.
After two failed attempts to collect the deepest and most remote samples, researchers with the Sensitivity of the West Antarctic Ice Sheet to 2°C (SWAIS2C) project have finally succeeded in their mission. The samples reveal new insights into Earth’s ancient climate and provide clues to Antarctica’s resilience amid the current global climate crisis.
Below the Antarctic Ice
This is SWAIS2C’s first drilling attempt, but unfortunately, the previous two endeavors ended in failure due to technical issues. However, this is the deepest and most remote Antarctic drilling ever attempted, so challenges were to be expected. The ice was pierced with a hot-water drill before the team lowered a drill string down the hole to collect the sediment core. Working around the clock due to limited time on-site, researchers then described, photographed, and x-rayed the samples.
“To our knowledge, the longest sediment cores previously drilled under an ice sheet are less than 10 m,” said Molly Patterson, co-chief scientist and associate professor of earth sciences at Binghamton University. “We exceeded our target of 200 m, and undertook this 700 km from the nearest base – this is Antarctic frontier science.”
Beneath 523 meters of ice, the team drilled another 228 meters into the mud and rock, which records climate fluctuations across the Earth’s history. This sediment core provides researchers with crucial information to predict the melting of Antarctic ice in a warming global climate.
Scientists estimate that if the West Antarctic Ice Sheet were to melt completely, it would cause a four- to five-meter rise in global sea level. Fears of such an occurrence are well-founded, as satellite observations indicate that the ice sheet is disappearing at an accelerating rate. Still, exactly what the minimum temperature is to catalyze a rapid melt of the entire sheet remains uncertain.
New Antarctic Insights
Previous work in this area used geological data collected near the ice sheet, but never from directly below it. SWAIS2C finally rectified this by taking the deepest Antarctic core sample ever retrieved.
“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,” said co-chief scientist Huw Horgan from Victoria University of Wellington. “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.”
While the team drilled over 200 meters below the ice, they had to remove the core in pieces only three meters long. In these short sections, composed of sediment ranging from fine muds to rough gravels, researchers combed for clues about the ancient climate. Tiny marine fossils discovered in the sediment allowed the researchers to make a preliminary dating estimate of the sediment. While there is evidence for an initial age of 28 million years, an international team of scientists will conduct further work to determine the age of the climate records stored in the sediment.
“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,” said Patterson. “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.”
Understanding a Warmer Antarctic
Intriguingly, the samples included evidence of a remote period when the Antarctic was ice-free, including shell fragments and marine fossils. Scientists have previously theorized that the region was likely ice-free at some point, but this is among the first solid pieces of evidence for exactly when that period occurred.
“This new record provides sequences of environmental conditions through time, and ground truths the presence of open ocean in this region,” Patterson explained. “In addition to pinning down the time when this occurred and the corresponding global temperature, analysis will help us quantify the environmental factors that drove the ice sheet retreat, such as determining what the ocean temperatures were at that time.”
Presently, the core is at Scott Base, still in Antarctica, ahead of its journey to New Zealand and then to researchers across the globe.
“Our multi-disciplinary international team is already collaborating to unravel the climate secrets hidden in the core,” Horgan concluded. “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.”
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.