The vast West Antarctic Ice Sheet holds enough ice to raise global sea level by 4-5 m if it melts completely. It is protected on one side by the Ross Ice Shelf, the world’s largest floating ice mass, that serves as a buttress slowing the flow of glaciers and ice streams towards the sea. As our climate warms, the Ross Ice Shelf is becoming increasingly vulnerable, but there is uncertainty around what global temperature increase will trigger unsustainable melting of the shelf, and the subsequent loss of the West Antarctic Ice Sheet.

Retrieving a geological record to provide direct evidence of this temperature tipping point is the challenge driving the SWAIS2C (Sensitivity of the West Antarctic Ice Sheet to 2°C) project, a collaboration between 10 countries (New Zealand, the United States, Germany, Australia, Italy, Japan, Spain, Republic of Korea, the Netherlands, and the United Kingdom) involving more than 120 scientists. Earth Sciences New Zealand, Te Herenga Waka – Victoria University of Wellington and Antarctica New Zealand are at the helm leading project management, drilling operations, and logistics.

An ‘on-ice’ team of 29 scientists, drillers, engineers and Antarctic field specialists have embarked on the project’s third attempt to drill for a 200 m sediment core – a series of cylindrical samples of mud and rocks – from the bedrock deep beneath 500 m of ice at the Crary Ice Rise on the Ross Ice Shelf.

Along with a relatively recent geological record, the core is expected to contain layers of sediment laid down within the past 23 million years, containing periods in Earth’s history when temperatures were warmer than they are today.

“We’ll analyse the samples to collect environmental data about how the Ross Ice Shelf responded in these past times of warmth. This record from the past will help us build a much clearer picture of what temperature will trigger the retreat of the West Antarctic Ice Sheet and significant sea-level rise,” says Molly Patterson, SWAIS2C Co-Chief Scientist from Binghamton University, USA.

They’ll search for tiny microfossils of marine algae in the sediment, organisms that need light to survive. Their presence suggests open ocean conditions and the retreat of the Ross Ice Shelf.

No one has ever successfully obtained such a deep sediment core so far from a base and so close to the centre of the West Antarctic Ice Sheet. SWAIS2C has spent the past two Antarctic summers attempting to drill at KIS3, a site around 260 km from Crary Ice Rise, but both attempts were thwarted by technical issues with the custom-designed drilling system.

“This is Antarctic frontier science, and what we’re trying to do is complex and hugely challenging, from an engineering and logistical perspective as well as being world-leading science. We’ve made great progress towards our goal over the first two seasons and have modified the drilling system for success this year,” says Huw Horgan, SWAIS2C Co-Chief Scientist from Te Herenga Waka – Victoria University of Wellington and ETH Zurich, Switzerland.

Crary Ice Rise is a ‘pinning-point’ for the Ross Ice Shelf, a place where the seabed below the floating ice shelf is elevated and meets the base of the ice, anchoring the ice shelf and resisting the flow of the ice away from the continent. The researchers will analyse the sediment to learn more about the recent history of the ice rise and the role it plays in stabilising the ice shelf. There are indications that the ice at this site has become pinned and unpinned over the past 1100 years.

“Pinning points can play a critical role in stabilising the ice shelf. By examining the underlying geology, we can better understand how this pinning point might behave in the future. This is particularly key as our climate continues to warm, and the ice shelf becomes more at risk of retreating inland,” says Patterson.

SWAIS2C’s third season is underway with an even greater sense of urgency. 2024 was the first calendar year in which the average increase in Earth’s annual surface temperature exceeded the 1.5°C target of the Paris Agreement.

“We are well on track to permanently cross this warming threshold in the next 5 to 10 years unless we curb global emissions. The information we’re seeking about when and how much of the West Antarctic Ice Sheet we will lose is vital to help the world better adapt and prepare for sea-level rise, especially for the 680 million people living in low-lying coastal areas,” says Horgan.

An extreme polar road trip followed by eight weeks living in tents on the snow

Drilling in the deep field so far from the nearest base requires a large amount of equipment, both for the drilling itself and the operations of the camp, which must be set-up from scratch.

The six member Antarctica New Zealand traverse crew departed New Zealand’s Scott Base on 8 November – operating a convoy of PistenBully polar vehicles towing the load of fuel, science and drilling equipment, and supplies to sustain the camp for the approximately eight-week season. Their 1100 km journey over the Ross Ice Shelf required the use of a Ground Penetrating Radar to help them detect and avoid treacherous crevasses.

Arriving at Crary Ice Rise, the traverse team created a ‘skiway’ on the ice for ski-equipped aircraft, allowing the drillers and scientists to fly in (700 km ‘as the crow flies’). The team will live in tents on the snow, and work in shifts around the clock to make the most of the limited time at this hard-to-reach location.