Going back in time to better understand the future is what scientists from Princeton University have done recently. They recovered 1 million years old ice samples from Antarctica. Ice that preserved ancient air and climate information in from of tiny bubbles. Their research results have been published last month in the journal PNAS (Proceedings of the National Academy of Sciences) providing a snapshot of the climate in the past.

Glacial ice is an extremely valuable climate archive, since it preserves tiny air samples in form of bubbles. These bubbles are like windows into Earth's former atmosphere. Gases such as carbon dioxide (CO2) and methane (CH4) got trapped and preserved inside the bubbles when the snow fell that formed the ice in the past. The longest continuous ice core record is going back 800,000 years (the EPICA ice core). Now scientists are aiming to find older and older ice to extend this record further back.

Geochemist John Higgins of Princeton University and his team recovered a million-year-old ice sample from the Allan Hills in Antarctica.  “It predates the oldest continuous atmospheric records by about 200,000 years,” Higgins said.

The ice was drilled from the "blue ice" region of the Allan Hills, one hour flight from the US base McMurdo. Blue ice forms where landmasses such as mountain ranges force glacial ice to flow upward, bringing old ice to the surface. Strong winds in the region also scour and remove snow and ice from the surface, further exposing the old ice.

Researchers obtained million-year-old ice cores from the area where the ice sheet is uplifted by contact with the Allan Hills, making old ice much easier to extract. (Graphic courtesy of John Higgins)
Researchers obtained million-year-old ice cores from the area where the ice sheet is uplifted by contact with the Allan Hills, making old ice much easier to extract. (Graphic courtesy of John Higgins)

Despite the superlative age of the ice, Higgins said the sample provides more of a “snapshot” of climatic conditions, though it doesn’t capture an uninterrupted sequence going back a full million years. “I would call them snapshots of what the atmosphere looked like at 1 million years ago,” Higgins said. “The most desirable thing would be to have a continuous record that went from 800,000 back to 1 million, but because of the nature of the type of ice that we’re looking at, it’s very unlikely that we’ll find these beautifully continuous – I call them layer cake – sequences.”

An example of a blue ice area, where old ice is forced to the surface and wind ablates the upper ice layers, while sun radiation melts a pattern into the ice. (Photo: Katja Riedel)
An example of a blue ice area, where old ice is forced to the surface and wind ablates the upper ice layers, while sun radiation melts a pattern into the ice. (Photo: Katja Riedel)

The findings from the ice cores suggest a strong link between carbon dioxide levels and glacial cycles for the past million years. In the oldest ice, levels of CO2 were about 30 parts per million (ppm) higher, at most, than more recent measurements from between 800,000 to 450,000 years ago Overall, the oldest ice fits the atmospheric CO2 relationships established across the past 800,000 years.

During warm spells between the ice ages, called interglacials, carbon dioxide levels never rose above about 300 parts per million during the past 800,000 years – until very recently. CO2 levels linked to human fossil fuel emissions are currently at about 400 ppm and rising.

“It suggests the style of variations we have seen over the last 800,000 years indeed carried back to 1 million years,” Higgins said. “The interesting new twist is that we do place new constraints on how high carbon dioxide might’ve gotten during interglacial warm periods prior to 800,000 years,” said Higgins.

“Carbon dioxide is definitely higher in the interglacials 1 million years ago than it was from 400,000 to 800,000 years ago. That’s probably the most robust conclusion,” he said.

Higgins said the find of million-year-old ice was made more extraordinary since the core was retrieved from the relatively shallow depth of 130 meters in a spot where ice is pushed upward by the landmass of the Allan Hills. He said that the million-year-old snapshot demonstrates the value of targeting similar ice cores as a cost-effective alternative to deeper excavation efforts, which can delve thousands of meters below the surface.

At the drilling site near the Alan Hills, old ice is here easily and comparatively cheap accessible compared to deep ice cores. (Photo: Katja Riedel)
At the drilling site near the Alan Hills, old ice is here easily and comparatively cheap accessible compared to deep ice cores. (Photo: Katja Riedel)

“There are lots of questions about how high was the carbon dioxide when it was this much warmer,” Higgins said. “It’s a way to try to look at getting some sort of sense for what the response of changes in atmospheric carbon dioxide are or what effects the changes in atmospheric carbon dioxide are going to have on the climate system.”

Source: Live Science and Climate Change