Nature 493, 489–494 (24 January 2013) doi:10.1038/nature11789
ReceivedAccepted 13 November 2012 Published online 23 January 2013
Extracting a record of the Eemian was a challenge: the core’s lowest layers had been deformed and folded by the constant movement of the ice sheet. “Of course we had hoped for a purer record,” says Dorthe Dahl-Jensen, a palaeoclimatologist at the University of Copenhagen who led the NEEM project. “But it is a fantastic record even so, and it does have all the information we needed to reliably reconstruct the Eemian climate and ice-sheet history.”
She and her colleagues painstakingly compared and synchronized the disturbed parts of their core, layer by layer, with other well-dated ice cores from Greenland and Antarctica to tease out the story. “I am very sure that we have got the picture right,” says Dahl-Jensen.
The results confirm the warmth of the Eemian climate: ratios of oxygen and nitrogen isotopes in the core show that some 6,000 years after the onset of the Eemian, local temperatures reached about 8 °C above the present-day annual average of roughly −25 °C.
But the ice sheet at the NEEM site did not get much thinner than its present 2.5 kilometres, according to the air content in the core that the team correlated with elevation.