Australian scientists have drilled 400 metres into the Antarctic ice sheet, to retrieve ice that formed at the end of the last ice age, over 13,100 years ago, when woolly mammoths and sabre-toothed cats roamed the Earth.
The milestone marks the end of the second drilling season for the Million Year Ice Core (MYIC) project at Dome C North, about 1200 km from Casey research station and high on the Antarctic plateau.
As temperatures at the drilling site plummet below -45°C, scientists and a supporting traverse team have winterised the inland station that was home for nine weeks.
They've now departed with their treasure - ice cores containing a record of past climate.
MYIC Science Lead, Dr Joel Pedro, said the team had achieved everything they hoped for this year, in their multi-year quest to retrieve ice cores with a 1-2 million year climate archive, contained in air bubbles and impurities trapped in the ice.
This timeframe overlaps a period in Earth's history when there was a change in the timing and intensity of ice age cycles, with accompanying long-term changes in temperature and greenhouse gas levels in the atmosphere.
"We ticked off our big things this season, which were to set up our new deep drill system that we designed and built at the Australian Antarctic Division, and drill to 400.68 metres," Dr Pedro said.
"We also did a geophysical survey of the ice properties right down to bedrock, 3000 metres below, which will help us refine estimates of the age of the ice as we drill deeper into the climate record."
After a month of setting up the deep drilling system - which included the eight metre drill 'sonde' that descends into the ice sheet to drill cores, a four tonne winch, and the drill's electrical power, control and communication systems - the team broke ice with the new drill on Boxing Day.
"It was the first time we'd drilled ice cores with the new system, after seven years of preparation, and we managed to drill quite a nice core, so it was a very happy moment," Dr Pedro said.
"You can put a huge amount of planning into these sorts of things and still be astounded when it actually happens."
Two teams of four people - two drillers and two core processors - worked in eight-hour shifts to extract the cores, and then clean, cut and package them into one-metre lengths for storage and transport back to Australia.
They were assisted by traverse members in drilling, processing, and troubleshooting mechanical and electrical issues.
"We drilled from 7am through to 11pm, but we chose not to drill through the night because people get tired and little mistakes can make big problems," Dr Pedro said.
"It was -15 to -25°C in the drill tent, but if we had to go into the six-metre-deep drill trench it was -55°C, so we needed to work quickly and get out."
Setting up for success
The successful season was made possible in part by an early start to the traverse, on 1 November, thanks to the pre-positioning of equipment via a C-17 airdrop, and deployment of the 10-person traverse team to Casey on RSV Nuyina in October.
This early start, and the delivery of the large winch by French traverse, maximised the time the scientific team had available to drill, before the weather-window closed.
Traverse Leader, Damien Beloin, said the traverse took 17 days to travel between Casey and Dome C North, at about 80 km/day, carrying 47 tonnes of fuel and 67 tonnes of cargo.
"The total weight of the traverse was 640 tonnes, which is the heaviest to date, with two snow groomers and six tractors carrying kitchen and amenities vans, a new generator van to power the whole inland station, a water service container, and water," Mr Beloin said.
"The conditions were quite challenging to start with because we had four days of blizzard and poor visibility. After then it cleared up and the drive was very enjoyable."
He said one of the highlights of the whole experience was the group dynamics at the inland station.
This was enhanced by weekly games of volleyball, birthday celebrations, and visits to and from the French/Italian Concordia station, 10 km away.
"Some of us did not know each other before we go there, but within a few weeks we'd formed a very solid and experienced group in the middle of Antarctica," Mr Beloin said.
"Its impressive to be living in such a comfortable and enjoyable camp in the middle of nowhere with 18 others."
The ice cores will be flown back to Hobart for further research, while Dr Pedro and his team prepare for a third drilling season later this year.
"Our target next year is to drill down to over 1000 metres, which will take us deep into the Pleistocene epoch and the last ice age," Dr Pedro said.
Drilling through time
The MYIC team study the internal layers of ice as they drill down into the Antarctic ice sheet, to understand how the ice flows. This information is used in models to determine the age of the ice at different depths. Ice between 1-2 million years old is expected close to bedrock, at about 3000 metres.
So far the team have drilled through human history:
- 90 m (~2,000 years ago): The global human population stands at ~170 million
- 150 m (~4,000 years ago): The Bronze Age (ca. 3300-1200 BC)
- 200 m (~6,000 years ago): Cunieform writing (ca. 2900 BC); development of the potters' wheel; end of the Stone Age; Australian indigenous knowledge recalls sea levels rising to their current position from at least 6000 ya.
- 300 m (~9000 years ago): Early agriculture and farming
- 364 m: Drilling out of the current geological epoch (Holocene) into the preceding epoch (Pleistocene); rising seas flood Bass Strait, making Tasmania an island (12,000-10,000 ya)
- 400 m (13,100 years ago): end of the last ice age
