New record: 4.6 million-year-old ice found in Antarctica | Polarjournal
The COLDEX team found the oldest ice to date in the blue ice of the Allan Hills. Photo: Julia Marks Peterson

The record for the oldest ice found in Antarctica has been broken by a US research team: In the Allan Hills, they discovered 4.6 million-year-old ice from before the ice age.

At this year’s General Assembly of the European Geosciences Union (EGU) last week in Vienna, the team from the Center for Oldest Ice Exploration (COLDEX) reported on the astonishing discovery: In the Allan Hills near the coast, not far from the Ross Ice Shelf, the researchers found ice dating back 4.6 million years to the late Pliocene before the ice age – by far the oldest ice ever found in Antarctica.

The aim of the US research initiative COLDEX is to find climate records from the last 5 million years. These can only be found in so-called blue ice areas, where the very old ice emerge at the surface, as Dr. Frédéric Parrenin, senior scientist at the Institute of Environmental Geosciences for the French CNRS and French manager of the Beyond EPICA project, who was not involved in the study, explains in an email to Polar Journal.

The drilling site in the Allan Hills is located near the coast in East Antarctica. In 2004, the oldest continuous ice core was recovered near Dome C, dating back 800,000 years. Nearby, at Little Dome C, the Beyond EPICA project is drilling for 1.5 million-year-old ice. Map: Julia Hager / GoogleEarth

The Allan Hills are one of these blue ice areas. This is where the ice stream, which has been flowing from the interior of Antarctica to the edges of the continent for millions of years, meets a barrier and the lowest, oldest layers of ice are transported upwards. This creates folds in the ice that mix up the layers of different ages. As a result, the oldest ice is not always the deepest and the layers of the ice cores are not in the correct chronological order. The advantage, however, is that drilling does not have to be as deep.

Back in 2017, some of the researchers from the current COLDEX team found the oldest ice to date in the Allan Hills, dating back 2.7 million years. The team was able to extract numerous samples that are between 1 and 3 million years old from the new ice cores from the past 2023/2024 field season, according to the presentation abstract by Edward Brook, Professor of Earth, Ocean and Atmospheric Sciences at Oregon State University and director of the COLDEX project. One of the samples contains ice dating from the late Pliocene, 4.6 million years ago.

The researchers hope to gain insights into the atmospheric composition at that time from the trapped air bubbles. Initial results are already available, which the team also presented in Vienna. According to this, the atmospheric CO2 content was below 350 ppm (parts per million) in the Pliocene about 3.1 million years ago, when temperatures were about 3°C higher than pre-industrial levels or 1.5°C higher than today. Todays CO2 levels are at 427 ppm.

“The study shows that the CO2 concentrations from 2.7 Myr were not as high as we thought before, although the climate was a lot warmer. It is important because it shows that a moderate increase of CO2 concentrations can lead to a large warming,” says Dr. Parrenin.

The air bubbles contain coveted information about the climate of times long past. In blue ice, however, they are often deformed and less well preserved. Photo: Austin Carter

However, in contrast to ice from the Antarctic interior, which contains well-preserved ice in chronological sequence and on which the Beyond EPICA project, for example, focuses, the results from the analysis of air bubbles in blue ice are somewhat less reliable. These could also contain CO2 from organic matter on the glacier bed.

“Of course, these results should be taken with caution since the ice from blue ice areas might not be well preserved, but it is an important element in our understanding of these old climates from the late Pliocene,” Dr. Parrenin continues.

In the upcoming 2024/2025 field season, the COLDEX team plans to continue drilling and ideally obtain longer ice cores that show chronological layering over a longer period of time – modeling predicts that a 1250-meter-long ice core with a continuous stratigraphy over 1 million years could be possible in the region.

Julia Hager, Polar Journal AG

Links to the presentation abstracts:

Brook, E. and the Center for Oldest Ice Exploration Allan Hills Research Team: Plio-Pleistocene ice cores from the Allan Hills Blue Ice Area, Antarctica: recent results and prospects for future work, EGU General Assembly 2024, Vienna, Austria, 14-19 Apr 2024, EGU24-4497, https://doi.org/10.5194/egusphere-egu24-4497, 2024.

Marks Peterson, J., Shackleton, S., Severinghaus, J. et al: Late Pliocene and Early Pleistocene CO2 and CH4 from ice cores from the Allan Hills, Antarctica, EGU General Assembly 2024, Vienna, Austria, 14-19 Apr 2024, EGU24-6781, https://doi.org/10.5194/egusphere-egu24-6781, 2024.

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