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Ancient biomolecules from deep ice cores reveal a forested southern Greenland

5 July 2007

Using about 50g of melted ice, we extracted and amplified DNA from the plant chloroplasts, and insect mitochondria...

James Haile

Ancient DNA recovered from the base of the Greenland ice cap shows a climate very much warmer than today’s, according to an international team of scientists. Oxford University researchers were part of the team providing the first direct evidence in support of the theory that southern Greenland was once forested, as published in this week’s Science. The research also suggests that deep ice cores may contain genetic records of past environments.

The scientists were able to identify DNA in the ice that originated from a diverse array of conifer trees and insects that may date back more than 450,000 years. However, the mere presence of temperate flora and fauna in the ice, more than 2,000 metres below the surface, is of little value without a temporal context. As no single established method for dating old ice exists, the team used a variety of dating techniques.

One technique was the dating of mineral particles entombed within the deep ice using optically stimulated luminescence (OSL), a method which enables the researchers to determine when certain minerals were last exposed to light. Dr Jean-Luc Schwenninger and Roger Nathan, from the Luminescence Dating Laboratory at Oxford’s Research Laboratory for Archaeology and the History of Art, and Dr Cees-Jan de Hoog, from the University’s Department of Earth Sciences, were able to measure the amount of trapped charge which accumulated inside each sand-sized grain over time. By further determining the precise concentration of radioactive elements and by applying radiation-modelling techniques, they calculated dose rates and age estimates.

About 10 per cent of the world is covered by ice sheets and glaciers and given that further polar drillings are planned, this new approach could be extended to other sites which may contain an archive of genetic and environmental data that is even older.

Dr Jean-Luc Schwenninger said: ‘The dating of deep ice can be immensely challenging and problematic, but we managed to develop new methodologies which offer the prospect of extending the age range of luminescence-dating in ice to several million years provided future samples are collected under more stringent light-proof conditions.’

Researcher James Haile, from the Henry Wellcome Ancient Biomolecules Centre at Oxford University, said: ‘To get a glimpse into the past in this way is very exciting, especially as fossils from the arctic are very sparse and are normally buried below kilometres of ice. Using about 50g of melted ice, we extracted and amplified DNA from the plant chloroplasts, and insect mitochondria, and used the resulting sequence of bases to determine what family the organisms belonged too. We even obtained DNA from butterflies and moths, which are exceptionally rare in the fossil record.’

For more information and photographs, please contact the Press Office at the University of Oxford on 01865 280534 or press.office@admin.ox.ac.uk

Notes to editors

  • The paper ‘'Ancient Biomolecules from Deep Ice Cores Reveal a Forested Southern Greenland' by Eske Willerslev et al will bepublished in Science on Friday 6 July 2007.
  • The team was led by Professor Eske Willerslev, Director of the Centre for Ancient Genetics, University of Copenhagen, Denmark.
  • Professor Willerslev is also a Visiting Researcher at the Henry Wellcome Ancient Biomolecules, Oxford University, where he was based before taking up the appointment at the University of Copenhagen.
  • The Oxford University team included four scientists from the Research Laboratory for Archaeology and the History of Art, Department of Earth Sciences, and Ancient Biomolecules Centre.
  • The international team was made up of scientists from Denmark, the UK, Germany, Australia, Canada, Switzerland, Sweden, France and Italy.
  • The correspondence author is ewillerslev@bi.ku.dk

Further information