Source: Radio New Zealand
Co-chief scientist Molly Patterson with a core sample all packaged up for transportation back from the Crary Ice Rise campsite. Supplied / Ana Tovey (SWAIS2C)
An Antarctic sediment sample dating back millions of years shows evidence that a major ice sheet partially or totally collapsed during a previous warm period.
The sediment core was retrieved by a New Zealand-led research team from beneath half a kilometre of ice, during a record-breaking mission in a remote part of Antarctica.
It will now help answer the question of when, and how drastically, the West Antarctic ice sheet might melt as the climate keeps warming – releasing up to five metres of sea level rise as it goes.
Previously, the largest samples retrieved from that deep beneath an Antarctic ice sheet were only about 10 metres in length.
Camping on the ice, 1100 kilometres from the nearest permanent base, the team used a huge drill rig to extract a 228-metre sample of mud and rock, three metres at a time.
It dates back an estimated 23 million years – giving climate researchers an enormous geological record to examine.
“It still feels a little bit unreal, to be honest,” expedition co-chief scientist Molly Patterson said.
“I can’t imagine anything else in my professional life scaling that experience up.”
Co-chief scientists on the ice, Molly Patterson (left) and Huw Horgan, with the first core of sediment collected during the expedition. Supplied / Ana Tovey (SWAIS2C)
Collecting the sample was crucial to confirming models of what might happen to the West Antarctic Ice Sheet as the temperature warms by 2°C or more.
At the moment, the ice sheet is protected by ice shelves – floating layers of ice formed by the ice sheet flowing off the Antarctic continent.
Without them, the flow of ice into the ocean will accelerate, meaning the potential collapse of the entire ice sheet.
Some of the smaller shelves could collapse within years, but the Ross Ice Shelf, the largest of them, is still stable – for now.
However, early analysis of the sample confirms what the researchers already suspected from previous modelling – that there was a period in history when, instead of thick ice in that part of Antarctica, there was open ocean.
Patterson’s fellow co-chief, Huw Horgan, said from about the 200-metre mark, they started finding diatoms in the sample – small photosynthetic creatures that can only exist when there’s light.
“When there’s a thick ice shelf, no light gets through, so these organisms can’t live in the presence of the ice above them.
“So, they really tell you that there was open ocean, that there was no ice shelf, that there was no ice sheet there at the time they were deposited. So, it’s a very direct indicator of open ocean conditions at the site.”
The core was loaded carefully into polystyrene boxes for transport back to Scott Base and then on to New Zealand. Supplied / Ana Tovey (SWAIS2C)
The core has been transported safely to New Zealand and the next step is to accurately date it, Horgan said.
“Being able to then take that and relate it to what the temperature was in the past, what global temperatures were in the past, that’s really strong evidence for what we can expect the ice sheets to do in the future.”
That would also help to determine the rate at which any melting might occur.
All of that information would be fed into models of sea-level rise, which is expected to affect one billion people by the end of this century – within the lifetimes of children alive today.
“No one’s going to put their hand up and say, I want an unstable West Antarctica, I want four to five metres of sea level [rise],” Horgan said.
“But for me, any trepidation in finding out that result, finding out that there’s the absence of ice in these places is tempered by the fact that now we’re informed and better informed is better prepared.”
Third season lucky
The sediment was collected from a location where the Ross Ice Shelf and the West Antarctic Ice Sheet meet, called Crary Ice Rise.
There is no permanent base there.
Instead, an advance team transported equipment 1100km across the ice shelf from Scott Base, so the expedition could camp out for weeks while they set up the drill rig and got to work.
The 2026 camp and drill site at Crary Ice Rise on the edge of the West Antarctic ice sheet. Supplied / Ana Tovey (SWAIS2C)
It was the third attempt, after equipment failures during the 2024 and 2025 Antarctic summer seasons.
Head driller Tony ‘TK’ Kingan has been travelling to Antarctica for nearly 30 years to work on drilling projects.
This expedition was more technically difficult than most, because the ice was directly touching the bedrock – meaning the ground beneath the ice was also frozen, he said.
Before they could even start extracting sediment, the drilling team used a hot water drill to get through the 500 metres of ice sitting on top of it.
They then lowered a ‘riser’ – essentially a long pipe – through the hole in the ice so the drill could pass through it to the ground below.
“Whenever we stopped drilling in the ground itself, the hole would want to start freezing,” Kingan said.
To stop that happening, the drilling team had to keep the riser moving, and hot water circulating around the clock.
“Right to the bitter end, it was pretty full-on, pretty stressful. We’re running 24 hours in that instance over the drilling period,” he said.
“You can’t really relax until all the gear is out of the hole and the project’s done and we haven’t hurt anyone or lost any gear.”
Head driller Tony Kingan carefully collects a sediment core as it’s extruded from the drill pipe. Supplied / Ana Tovey (SWAIS2C)
Patterson said the first piece of core came up while she was off-duty – but she made sure to be there.
“I was working the night shift and it was during the day shift, but I just, I wouldn’t have been able to sleep or stay away. I just personally wanted to witness it.”
There was “a huge sense of relief” that the expedition had succeeded, Patterson said.
“Just because [of] the past two seasons, the challenges we’ve had, and also recognising how technologically difficult all this was.”
Horgan said the drilling team had managed the scientists’ expectations about what the first core might look like.
“There’s often nothing in it, and if there is, it might just be what they call drilling mud, which is just the fluid they put down to lubricate everything,” he said.
“And when the first core came up, it was actual core, and it was rock. And that was a fantastic feeling.”
The process of extracting the core had several stages, each with different technical challenges, made more difficult by the harsh Antarctic conditions the team was working in. Supplied / SWAIS2C
There were brief celebrations when the first core came up, and again at landmark depths – 50m, 100m and 200m.
“There’s definitely a pat on the back and a hug,” Horgan said.
“And the geologists are great. They’ll celebrate different rock types. So you get a core which has a different rock type, and suddenly a message will whip around the camp, and everyone’s coming and running to see the core.”
The science team is now finalising plans for a full analysis, so they can begin working on the results.
Horgan said there will also be discussions about future expeditions, including to the site of their previous failed attempts.
“We’re going to want to acquire more data in different places, sampling different parts of the geological record and looking at different ice sheet processes.
“We’ve got this incredible capability now, and I think it would be wise to use it.”
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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand
LiveNews: https://nz.mil-osi.com/2026/02/18/antarctic-expedition-collects-evidence-that-ice-sheet-melted-during-previous-warm-period/
