The scientists examined 17 ‘dirty ice’ samples from the bottommost 12 metres of a 3,000- metre ice core extracted from Summit, Greenland, in 1993, looking at the concentration of a rare form of beryllium, which accumulates in soil when it’s exposed to the air.
Because they assumed that most of the soil would have been derived from glacier-scoured bedrock, they expected to find only tiny amounts of the beryllium. However, they found that the silt had very high concentrations of the isotope, indicating that rather than scraping the landscape, the ice sheet has been frozen to the ground.
The team also measured levels of nitrogen and carbon in the sample that could have been left by plant material. ‘The fact that measurable amounts of organic material were found indicates that soil must have been present under the ice,’ said one of the study’s authors, Andrea Lini of the University of Vermont. The material’s composition suggested that the pre-glacial landscape may have been a partially forested tundra.
To confirm their findings, the researchers also measured beryllium levels in a modern permafrost tundra soil from Alaska. ‘The values were very similar, which made us more confident that what we found under Greenland was tundra soil,’ said the study’s lead author, Paul Bierman, also of the University of Vermont.
Taken together, the results provide strong evidence that the Greenland Ice Sheet has persisted much longer than previously thought, surviving several past periods of global warming. ‘It’s likely that it did not fully melt at any time,’ Bierman said.
This story was published in the June 2014 edition of Geographical Magazine