Researchers reporting in the journal Climate of the Past have identified regions of Antarctica they say could record the past 1.5 million years of Earth’s climate history.
This map of Antarctica shows potential oldest ice study areas. Image credit: Van Liefferinge and Pattyn.
A 3.2-km-long ice core drilled about 10 years ago at Dome Concordia in Antarctica revealed 800,000 years of climate history, showing that greenhouse gases and temperature have mostly moved in lockstep.
Now, the scientists want to know what happened before that. At the root of their quest is a climate transition that marine-sediment studies reveal happened some 1.2 million years to 900,000 years ago.
“The Mid Pleistocene Transition is a most important and enigmatic time interval in the more recent climate history of our planet. The Earth’s climate naturally varies between times of warming and periods of extreme cooling over thousands of years. Before the transition, the period of variation was about 41 thousand years while afterwards it became 100 thousand years. The reason for this change is not known,” explained lead author Prof Hubertus Fischer from the University of Bern.
Researchers suspect greenhouse gases played a role in forcing this transition, but they need to drill into the ice to confirm their suspicions.
“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, it is compacted by the weight of new snow falling on top of it and is transformed into solid glacier ice over thousands of years. The weight of the upper layers of the ice sheet causes the deep ice to spread, causing the annual ice layers to become thinner and thinner with depth. This produces very old ice at depths close to the bedrock.
However, drilling deeper to collect a longer ice core does not necessarily mean finding a core that extends further into the past.
“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. This is what happens at Dome Concordia and limits its age to 800,000 years.”
“To constrain the possible locations where such 1.5 million-year old – and in terms of its layering undisturbed – ice could be found in Antarctica, we compiled the available data on climate and ice conditions in the Antarctic and used a simple ice and heat flow model to locate larger areas where such old ice may exist,” said study co-author Dr Eric Wolff from the University of Cambridge.
The scientists concluded that 1.5 million-year old ice should still exist at the bottom of East Antarctica in regions close to the major Domes, the highest points on the ice sheet, and near the South Pole, as described in the new Climate of the Past study. They also found that an ice core extending that far into the past should be between 2.4 and 3-km long, shorter than the 800,000-year-old core drilled in the previous expedition.
The next step is to survey the identified drill sites to measure the ice thickness and temperature at the bottom of the ice sheet before selecting a final drill location.
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Bibliographic information: Fischer H et al. 2013. Where to find 1.5 million yr old ice for the IPICS “Oldest-Ice” ice core, Clim. Past, 9, 2489-2505; doi: 10.5194/cp-9-2489-2013
