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Secrets of the Ice

Bubbles of air in a thin section of ice core.
Bubbles of air in ice cores contain a record of atmospheric gas composition. Tas van Ommen

Around one million years ago, when Homo erectus walked the Earth and Australia was home to giant megafauna, snow was falling high on the Antarctic plateau. That snow carried with it atmospheric gases, aerosols and dust that represented the weather, climate and composition of the atmosphere at the time.

Greenhouse gases like carbon dioxide (CO2), methane and nitrous oxide, particles from volcanic eruptions, and salts blown inland by storms over the Southern Ocean, were preserved in ice and air bubbles, as the snow compressed to ice under the weight of new snowfall.

Over the centuries, layers of climate records accumulated each year, like the pages of a book, just waiting to be read.

Now, the Australian Antarctic Division is leading one of the most ambitious and challenging scientific projects undertaken in Antarctica – the quest to drill an ice core containing over a million years of Earth’s climate and atmospheric history.

This continuous climate record will help solve a long-standing mystery about the timing and duration of past ice ages, detected in marine sediment cores.

These sediment cores showed that 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.

A leading theory is that declining atmospheric CO2 levels were the cause of the longer, colder ice ages. The million year ice core record will provide the essential CO2 record to test this theory.

In 2016 the Australian Government identified the drilling of a million year ice core and interpretation of its climate data to be a high priority for the Australian Antarctic Program. The government committed to the project through the Australian Antarctic Strategy and 20 Year Action Plan.

By greatly extending the detailed record of Earth’s climate history, the million year ice core will help:

  • Understand the natural variability that has led to our current climate and ice age cycles.
  • Place current changes in climate and greenhouse gas concentrations into a deeper context.
  • Advance understanding of long-term global climate, ice sheet and sea level stability and their sensitivities to past and future changes in atmospheric CO2.
  • Provide new data to test global climate models.

In the video below hear from Dr Joel Pedro, the Scientific Lead for the Million Year Ice Core Project, about why a climate record of more than one million years is so important. Then scroll down to learn more or jump to sections using the menu at top right.

Climate history
A man lying beside two ice cores in the snow, taking notes.
Ice cores contain a record of climate history in the layers of snow and ice deposited over thousands of years - much like the pages of a book. (Photo: Jo Chandler)

Reading the ice

Since the 1950s, ice cores have been drilled from the Greenland and Antarctic ice sheets and glaciated areas around the world.

The current longest continuous ice core record extracted from Antarctica, at Dome C (about 1200 km from Australia’s Casey station), extends back 800,000 years (the EPICA ice core).

By studying these cores scientists have been able to reconstruct past temperatures and snowfalls, define the chemistry and gas composition of the atmosphere, and identify the timing of volcanic eruptions, solar variability, ocean productivity and forest fires.

Location of deep ice cores with a climate history extending back over 10,000 years. (WAIS - West Antarctic Ice Sheet; EDML - EPICA Dronning Maud Land). AADC map based on Johnson, J. S. et al. Review article: Existing and potential evidence for Holocene grounding line retreat and readvance in Antarctica, The Cryosphere, 16, 1543–1562, https://doi.org/10.5194/tc-16-1543-2022, 2022.

Ice cores taken by the Australian Antarctic Program, from Law Dome in East Antarctica, show that since the mid-1800s CO2 concentrations have increased by over 30 per cent, from a pre-industrial concentration of about 280 parts per million (ppm) to today’s 422 ppm.

In the video below Dr Joel Pedro explains how the information contained in ice cores informs our understanding of past and future climate states.

Information in the ice

In the graph below, data from a composite of six Antarctic deep ice cores reveals past changes in Antarctic temperature and CO2 over the past 800,000 years.

Prior to the 1800s (left of the 0 on the time scale), CO2 concentrations fluctuated in a semi-regular pattern every 100,000 years, for at least the past 800,000 years, in time with past ice age cycles. Temperature and CO2 are closely coupled throughout the ice age cycles, which have about a 100,000 year periodicity.

You can see that the modern rise in CO2 is outside the bounds of natural variability over this period.

Chart of CO2 values recorded at Cape Grim from 800,000 years ago to the present
Data sources: Cape Grim CO2 (Cape Grim Baseline Air Pollution Station, Australian Bureau of Meteorology, and CSIRO Oceans and Atmosphere); Law Dome CO2 ( Rubino et al. 2019); Antarctic ice core composite CO2 (Bereiteret al. 2015); Antarctic temperature change (Jouzelet al. 2007). Image: Law Dome ice core (J. Pedro @MillionYearIce).

In the interactive version of the graph (below), hover over the graph to see the temperature and CO2 concentration change over time. Click, hold and drag your mouse to select a section of the graph for closer inspection. Zoom in or out (+ and - buttons) to expand or contract parts of the graph, and use the hand icon to move backwards or forwards through time. The home icon will return you to the original graphic.

One end of an ice core protruding from a steel drill barrel.
A freshly extracted ice core in the barrel of the drill, containing layers of climate information. (Photo: Joel Pedro)
Kerry Steinberner

X marks the spot

After many years of preparation, Million Year Ice Core Project Leader, Dr Joel Pedro, is excited to set foot on the site where he and his team will begin drilling for the world’s oldest ice.

Getting to this moment has required a collaborative international effort over more than a decade, including extensive ground and aerial geophysical surveys of the ice sheet and bedrock below, to help narrow the location of ice that is likely to contain a climate record of more than one million years.

An initial drilling site was chosen in 2021 in a region known as Little Dome C. Radar data and ice flow modelling indicated a record of up to 1.4 million years could be recovered from this site. However recent advances in ice flow modelling and the interpretation of radar data, has enabled identification of a new location with older ice – potentially reaching two million years – about 45 kilometres south-west of the original site, at Dome Concordia North (Dome C North).

Existing cargo cached at Little Dome C was moved to Dome C North to commence drilling in January 2025.

An aircraft with radar antennas beneath its wings, flying over ice.
A Basler aircraft equipped with ice-penetrating radar, used to conduct geophysical surveys of Antarctica’s ice sheet and bedrock. Jack Holt

Dome C North may hold Antarctica’s oldest continuous ice core record. The site features excellent properties for the preservation of ancient ice including:

  • 3100 metre-thick ice above bedrock
  • undisturbed and continuously preserved layers, with a smooth and minimal ice flow path to the site
  • a maximum modelled age of up to two million years, preserved at a time resolution of better than 20,000 years per metre.

The image below shows an approximately 80 kilometre-long slice of the ice sheet from ice penetrating radar over the Dome C region. The distance across the ice sheet is shown on the horizontal axis and elevation on the vertical axis.

The deepest visible ‘mountainous’ line shows the continental bedrock. Everything above that line is ice. The wavy lines are internal reflections from within the ice.

Red labels show the locations where the radar line passes near the target million year ice core (MYIC) site at Dome C North, as well as the current 'Beyond EPICA Oldest Ice' (BE-OI) European ice core drilling project, and the EPICA Dome Concordia (EDC) ice core, which was completed in the 1990s and reaches 800,000 years.

Glaciologists can trace the internal layers within the ice sheet and date them where they cross the existing EDC ice core. The traced layers, in combination with ice modelling, indicate a maximum age of up to two million years at the Dome C North site.

Airborne radar data from the ICECAP-EAGLE project (‘International Collaborative Exploration of the Cryosphere through Airborne Profiling' and ‘East Antarctic Grounding Line Experiment’), using POLARIS radar with support from the Danish Technical University and European Space Agency. Figure Ailsa Chung.

“The potential to recover an ice core extending well past the Mid-Pleistocene Transition, when the cycle of ice ages shifted, and potentially spanning up to two million years, is a very exciting prospect for the Australian Antarctic Program and ice core science,” Dr Pedro said.

“It’s the culmination of many years of collaborative work involving Australian, European and US science teams, collecting and sharing radar imagery from extensive ground and aerial surveys of the ice sheet, along with modelling expertise."

A man in warm clothing stands beside a tall metal tube. The Australian flag is flying from a raised platform behind.
Million Year Ice Core Project Lead, Dr Joel Pedro, at Dome C North. (Photo: Derryn Harvie)

Drilling season

In their first drilling season (2024-25) at Dome C North, the science team have set up their 27 metres-long by 7 metres-wide drill shelter.

This substantial structure needs to be in place for an expected five summer seasons of ice core drilling required to reach the base of the ice sheet, some 3100 metres below.

Six people stand inside the frame of a large cylindrical tent.
Before leaving for Antarctica, the Million Year Ice Core project team did a test build of their new drill tent, including defining where the drill will fit (pink lines). (Photo: Dan Broun)
A cylindrical metal frame, about 27 metres long, rises above a compacted snow floor, in Antarctica. People stand on one side preparing to haul a tarpaulin over the structure using ropes.
Construction of the drill shelter at Dome C North, almost complete, in January 2025. (Photo: Joel Pedro)

With the tent up, the team can begin chainsawing a 6 metre-deep x 1 metre-wide x 6 metre-long drill slot into the ice and setting up the drill and associated equipment.

“At a depth of only a few metres the mean temperature in the drill slot is −55°C. It feels like you could be in space, it’s so foreign,” Dr Pedro said.

Once the drill is set up, the team will drill a pilot hole, about 140 metres-deep, and widen the borehole using a series of drill fittings called ‘reamers’. 

In the following season the team will insert a fibreglass borehole casing that will help keep the borehole open for the duration of the project.

An ice core drill in its drilling slot. (Photo: Joel Pedro)

Once deep drilling gets underway, ice core drilling and core handling teams of six to eight people will work in shifts through the field season.

The team expect to drill 100 to 150 metres per week. Over a field season of six to eight weeks they could drill between 600 and 1,200 metres of ice core. This will produce between four and 8.5 tonnes of ice core a year.

Ice exceeding one million years old is expected in the few hundred metres above the bedrock. The team expect to drill this very oldest ice around 2027–28.

In the video below Dr Joel Pedro describes how he expects drilling will progress.

Drilling sequence
0 m
Bedrock

At 0 metres deep, the ice is 0 years old. A single metre of ice represents 49 years.

Drag the slider down the ice core to explore how the ice ages

Based on data from Ailsa Chung, Université Grenoble Alpes

Designer drill

Australia’s ice core drill has been built by Australian Antarctic Division scientists, engineers and instrument technicians, using and adapting drawings provided by American colleagues, based on a Danish design.

The design was tweaked to suit Australia’s needs and experience, and the operating conditions at the site. These include temperatures as low as -55°C and pressures up to 300 kilograms per square centimetre at the full drill depth.

To cope with these stressors, components for the 8.4 metre-long drill were machined from specialised stainless steel, aluminium, bronze and titanium, and temperature and pressure tested in the laboratory.

A cylindrical metal component of the drill pump.
A component for the ice drill’s pump, which keeps drill fluid circulating and helps clear ice chips. Jessica Fitzpatrick

The main part of the drill system is the ‘drill sonde’.

This consists of the spinning drill head that cuts into the ice, a three-metre-long barrel to collect the cores, a motor, gearbox, and electronics package to drive and control the drill, and an anti-torque section to stop everything that shouldn't spin, from spinning.

The electronics package contains a range of sensors to ensure drilling progresses in a perfectly straight line.

Circular cutting end of an ice drill
The cutting end of the ice core drill. (Photo: AAD)

To add to the complexity, the drill sonde must work with a winch, cable and drill tower, which moves the drill from horizontal to vertical.

Once drilling begins, drill fluid is pumped into the hole to lubricate the drill, prevent ice chips jamming it, and to equalise the pressure in the hole to stop it closing.

Two people inside an ice core drill tent working an ice drill with a long, steel barrel.
An example of an ice core drill used by Australia, showing the drill sonde attached to a winch and drill tower. (Photo: Tony Fleming)

Watch the video below to see the drill sonde being lowered into a drill hole.

Lowering the drill

International effort

Australia is part of a larger international effort of cooperation through the International Partnerships in Ice Core Sciences, to recover multiple ice cores extending back at least 1.2 million years.

As part of this, Australia and a European team (Beyond EPICA Oldest Ice) are each leading a drilling operation on the Antarctic plateau, about 45 kilometres apart.

Each team has built ice core drills to suit the conditions they will face and their operational methods and experience.

Fourteen pyramid tents and four cylindrical tents set up on snow.
An ice core drilling camp at Aurora Basin. Work here helped narrow the location for the million year ice core drilling site. Tony Fleming

The teams will recover independent ice cores, which is particularly important for joint replication and verification of the data from the very oldest ice near the bedrock.

“The properties of the ice close to bedrock at the two sites are expected to be different, based on the radar data and modelling,” Dr Pedro said.

“Modelling indicates ice at the Australian site may be older, however it is notoriously difficult to predict the age of ice so close to bedrock, and only time will tell what the deepest ice holds.”

Deep field traverse

To get to the drill site, Australia has assembled a high-powered, heavy-duty, tractor traverse, capable of towing a mobile station, camp infrastructure and equipment.

In November 2024, members of the 10-person traverse team flew to Casey to get the 18-day traverse underway.

The traverse team used two snow groomers and six tractors to tow 62 tonnes of equipment to the drill site, including accommodation modules and drill equipment.

The science and drilling team flew to Casey in late November, and then on to the nearby Dome Concordia Station skiway by Basler on 31 December. 

After a day acclimatising to the 3000 metres of altitude, they ‘hailed’ a snow groomer to travel the final nine kilometres to the drill site, and rendezvoused with the tractor traverse team.

Together, the traverse and scientific teams set up the drill camp, drill tent and equipment.

Two men construct a wooden frame in the snow, with shipping container vans that provide accommodation and mess facilities for the campsite in the distance.
Setting up the drill tent site at Dome C North. The camp's accommodation vans and blue and white mess tent are visible behind. (Photo: Joel Pedro)
A collection of red and green shipping containers and a large cylindrical tent, on a flat, white, ice plateau
The Dome C North campsite on 9 January 2025, showing the covered drill shelter and accommodation and living vans. (Photo: Joel Pedro)

“The traverse team has been invaluable in getting the support and infrastructure in place to get our science underway," Dr Pedro said.

"Time is critical, as we have a weather window of only three to four weeks to get as much of the camp set up and drilling done as possible."

In future years, traverses will bring in supplies and equipment at the start of each season, and set up the campsite and aircraft skiway, before the drill team flies in for six to eight weeks of work.

Read more about the modern inland traverse capability.

Watch an animation of the traverse and ice core drilling below.

Quest for a million year ice core
A team of 16 men and women standing around a long metal drill and drilling trench.
The scientific drilling and traverse teams at Dome C North. Joel Pedro

The ice cores will be transported by traverse to Casey research station in insulated containers for the journey back to Tasmania on a Royal Australian Air Force C-17 Globemaster, or Australia’s Antarctic aircraft.

Many years of careful laboratory work at the Australian Antarctic Division, and with national and international partners, will be undertaken to measure the gasses and trace chemicals in the cores.

Competing theories on the cause of the ice age cycle change will then be tested by the cold hard data!

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