An international team has successfully hot-water drilled through 580 meters of Antarctic ice, collected numerous sediment cores from beneath Antarctica's Ross Ice Shelf, and gathered crucial experience in their mission to understand the West Antarctic Ice Sheet's past response to climate warming.

A team of twenty-seven, comprising scientists, drillers, and camp staff, worked together to set up camp. The camp was located on the Ross Ice Shelf along the Siple Coast, about 860 km from McMurdo Station and Scott Base. The team lived and worked there from late November through January as part of the SWAIS2C (Sensitivity of the West Antarctic Ice Sheet to 2ºC) project. The logistical support was provided by Antarctica New Zealand and the United States Antarctic Program.

Their mission was ambitious—to obtain a geological record in sediment layers hidden under the ice shelf at depths of up to 200 meters below the sea floor. To retrieve a sediment core this deep into an Antarctic seafloor requires a custom-designed drilling system (known as the AIDD – Antarctic Intermediate Depth Drill) and has never been attempted so far from an established logistics station, such as McMurdo Station or Scott Base.

"We're at the frontier, drilling through an ice shelf into the seafloor to acquire sediment samples that no one has previously been able to obtain. It's cutting-edge science and incredibly challenging work," says Richard Levy, SWAIS2C Co-Chief Scientist from GNS Science Te Pū Ao and Te Herenga Waka—Victoria University of Wellington.

The coveted core is expected to reach back hundreds of thousands of years, potentially even millions of years. Such a record could include the last interglacial period 125,000 years ago, a critically important time when Earth was around 1.5ºC warmer than pre-industrial temperatures—similar to the temperatures we are approaching this year due to climate change. 

"The West Antarctic Ice Sheet is currently losing mass at an unprecedented rate. It is one of the most vulnerable components in the Earth system to increasing warming. But we fundamentally do not know when and how fast it will disintegrate and raise global sea level by several meters," says Tina van de Flierdt, SWAIS2C Co-Chief Scientist from Imperial College London. "The sequence of rocks in the sediment should tell us how the West Antarctic Ice Sheet behaved when it was a bit warmer than today. If we find marine algae, it's likely the ice sheet retreated. This information will allow us to build a much better picture of how Antarctic ice will respond to future warming, which parts will melt first, and which parts will remain," says Levy.

To collect this sediment core, a hot water drill melted a 30-cm (12 inches) diameter borehole through 580 meters (1900 feet) of ice, breaking through the base of the ice shelf into the 55 m-thick (180 ft) ocean cavity lying between the ice and sea floor. Beneath the seafloor lies the ancient mud and rock with the clues to the influence a warmer world has on the West Antarctic Ice Sheet.

To even start drilling the sub-seafloor sediment, the AIDD required the drilling team to lower heavy equipment, including the drill string and glass-reinforced epoxy 'sea-riser' tubing, through the borehole. However, due to technical challenges, operations were halted, and the decision was made to retrieve the equipment and end deep-drilling operations for the season.

Levy says that having tested the deployment of the equipment in the field, the team now knows the modifications—a relatively simple fix—needed to improve the chance for success when they return next season.

"This year, we got tantalizingly close. With the knowledge we've gained from the samples collected and the technological experiments conducted, we have an excellent chance next year to recover the long sediment cores to provide the climate insights we're chasing."

An open borehole is an opportunity, and with the AIDD parked, the team got to work collecting shorter sediment cores using a simple-to-operate gravity corer. The gravity corer was successful in collecting numerous cores. A big success came once a larger corer, called the hammer corer, was deployed and "hammered" into the sediment to collect a 1.9m core.

"These samples offer a huge increase in the amount of material we have to help us understand the present-day environment beneath the ice shelf and the history those sediments represent. They also give us insight into the types of rock we will need to drill through to get those deeper records we're seeking," says Levy.

Principal Investigator at the Byrd Center's Polar Geomicrobiology Group, Assistant Professor Alex Michaud at The Ohio State University's School of Earth Sciences was thrilled with the samples collected because they contributed to understanding the marine ecosystem beneath the Ross Ice Shelf.

These samples help the drillers understand what they will drill into next season. They represent a rare chance to document and understand how a marine ecosystem functions beneath an ice shelf. The marine ecosystems beneath Antarctica's ice shelves are poorly studied and disappearing due to ice loss. These samples provide essential insight into life beneath an ice shelf. Much of this life is microscopic bacteria in the sediments and water column. Few samples are collected from beneath Antarctica's ice sheets with microbiology in mind, so the team's efforts for contamination-free sediment collection will provide data on how microbial activity in the sediments contributes to the marine system.

"Addressing the technological experiments carried out last year will only ensure success in reaching the scientific objectives associated with the SWAIS2C project at additional drilling locations," said Co-Chief Scientist Molly Patterson from Binghamton University.

Preparations are underway for the next season when SWAIS2C will return to the site armed with new knowledge and experience. "We are thrilled with what we've achieved. It's a massive step towards our ultimate goal to recover the sediment we need to answer the big questions crucial for humanity as we adapt and plan for sea-level rise," says van de Flierdt.

Related links:

• The fate of the West Antarctic ice sheet in a warming world, February 2024
• In Massive Project, Scientists to Probe Deposits Beneath West Antarctic Ice Sheet, November 2023
• Mission to drill further and deeper into West Antarctica for sea level secrets, November 2023
• Antarctic mission to offer glimpse into our planet’s climate change future, November 2023