Researchers in Antarctica suspect there are regions of the continent where ice core samples could provide climate data from as many as 1.5 million years ago, nearly doubling the look back in time afforded by the oldest ice core drilled to date.

The researchers are seeking to understand more about past climate, including a climate transition which marine sediments samples indicate took place between 1.2 million and 900,000 years ago. Presently, the oldest Antarctic ice core samples contain about 800,000 years of climate data history.

"Ice cores contain little air bubbles and, thus, represent the only direct archive of the composition of the past atmosphere," said Hubertus Fischer, an experimental climate physics professor at the University of Bern in Switzerland and lead author of the study published in the journal Climate of the Past.

"The Mid Pleistocene Transition is a most important and enigmatic time interval in the more recent climate history of our planet," said Fischer, referring to the ancient climate transition. Before the Mid Pleistocene Transition, the period of natural variation between ice ages was about 41,000 years, but afterward it became closer to 100,000 years.

"The reason for this change is not known," Fischer said, adding that it is suspected that greenhouse gasses played a role in the transition, but that the ice will need to be drilled for confirmation.

"The information on greenhouse-gas concentrations at that time can only be gained from an Antarctic ice core covering the last 1.5 million years. Such an ice core does not exist yet, but ice of that age should be in principle hidden in the Antarctic ice sheet."

As snow falls and settles on the surface of an ice sheet over thousands of years, it forms a solid glacier. The weight of the ice at the upper layers pushes down on lower layers, causing it to spread out, thinning the annual layers of ice deeper down. This process produces very old ice at depths close to the bedrock. But researchers must take care that the deep ice is not being melted by geothermal heat, which would contaminate their data.

"If the ice thickness is too high the old ice at the bottom is getting so warm by geothermal heating that it is melted away," Fischer explained. "This is what happens at Dome C and limits its age to 800,000 years."

Finding deep, undisturbed ice could be done with the help of a simple ice and heat flow model using available climate and ice conditions. The researchers contend that a 1.5 million-year-old ice sheet could exist deep beneath East Antarctica in regions close to the the major Domes, or high points on the ice sheet. They expect the ice core to be about 3 kilometers long.

The research team is in the process of identifying potential drill sites.

"A deep drilling project in Antarctica could commence within the next 3-5 years," Fischer said. "This time would also be needed to plan the drilling logistically and create the funding for such an exciting large-scale international research project, which would cost around 50 million Euros."