The first 150 metres of a planned 3000 metre-long Antarctic ice core has been safely returned to Australia after a successful drilling season for the Million Year Ice Core (MYIC).
The ice core, in one metre-lengths, contains a record of the past 4000 years of climate history.
The core was drilled at a deep field camp at Dome C North, about 1200 km "up the hill" from Australia's Casey research station.
It's just the start of an ambitious Australian Antarctic Program drilling effort to extract the world's oldest, continuous ice core record of up to two million years.
MYIC science lead, Dr Joel Pedro, said the full-length ice core is expected to extend the current ice core climate record well beyond 1.2 million years, and help solve a climate mystery.
"About one million years ago the cycle of ice ages shifted from a regular 41,000 year glacial-interglacial cycle, to a cycle every 100,000 years," Dr Pedro said.
"An ice core record of over one million years can help us answer why that shift in the climate state occurred, and that will provide really important information to test models and better predict climate in the future."
After a few years of weather and Covid-related delays to drilling, Dr Pedro said the science team, alongside a supporting tractor-traverse team, were relieved to achieve everything they had hoped for this season, thanks to a joint, multi-skilled, team effort.
"Our number one priority was to progress the pilot drilling for the MYIC borehole, but to do that we first had to set up the drill shelter," Dr Pedro said.
"We joined forces with the traverse team and were able to get the shelter constructed in 10 days - half the time we expected - and our drill built and tested in parallel.
"Then we split in to two shifts to run the drill 16 hours a day, with the traverse team joining us in drilling and core processing.
"After so much effort by so many people, and so much planning and time, it was a very special moment for me to pull out that first ice core - to the point that I had a tear in my eye."
Independent living
Traverse Field Leader, Chris Gallagher, led a team of mechanics, electricians, a carpenter and a doctor, that towed equipment and supplies to the drill site.
Using snow-groomers, and tractors towing sleds carrying 600 tonnes of gear, the team travelled 18 days through blizzards and heavy snow, via a route established last year.
Once at Dome C North they set up the scientists' accommodation modules, ready for their arrival by air.
"Over the next few years the traverse will bring up the rest of the inland station so that it can operate independently of the traverse's 'sustainability train'," Mr Gallagher said.
Drill skills
The traverse team were as keen to start drilling ice as the scientists, and put their skills to use.
"Setting up the drill tent was quite complicated, with underground trenches and cabling that had to be installed, including the drill trench itself, which was six metres deep," Mr Gallagher said.
"Our diesel mechanics used their skills with chainsaws, battery drills, dumpy levels and other construction techniques, to help our carpenter build the tent, and then the scientists helped finish it off.
"Once the drilling started, the mechanics assisted the drill engineers to help ensure the drill kept running properly, and other traverse team members took core measurements and wrapped and packed the cores.
"It was fascinating."
Boring anxiety
The science team drilled to 150 metres and then progressively widened the borehole from 130 mm wide at the bottom, to 260 mm wide at the top, using a series of 'reaming' attachments.
Next season the widest part the borehole will be fitted with a fibreglass bore casing.
This will seal off the porous ice near the surface and allow drill fluid to be added to prevent the borehole closing under pressure, as they drill deeper.
It was a nail-biting time for Dr Pedro.
"We had to go back down the borehole three times to expand it, so we effectively drilled about 520 metres," he said.
"Every time you put something down the borehole there's a chance it will get stuck, and there are a number of boreholes in Antarctica that have had reamers or drills stuck in them, and they've had to move and start again.
"When we got the last reamer out, I quickly shut the trap door on the hole and I knew we were safe."
The ice core sections were then loaded into an insulated box for transport back to Casey on the traverse and back to Australia on a C17 aircraft.
The team will begin analysing the cores in coming months. This includes measuring water isotopes for temperature, and greenhouse gases such as methane and carbon dioxide trapped in air bubbles in the ice, which reflect changes in climate over time. They'll also look for impurities that provide information on storms, sea-ice processes and volcanic activity.
Next season
Dr Pedro said the science team is now well set up for the 2025-26 drilling season.
"A lot of the work will involve setting up our bigger drill that can get to 3000 metres," he said.
"We'll add the bore casing and drill fluid handling system and the aim is to drill to 400 metres. After that the target is to drill 1000 metres per year, which will put us on track to reach bedrock by 2029."
Mr Gallagher said it had been a remarkable season of achievements.
"Thanks to our highly motivated and skilled teams the inland station is well established and the drill tents are up and ready to go," he said.
Read more about the MYIC project in this season's Drilling Diary and our special feature Secrets of the Ice.
