Ancient Biomolecules from Deep Ice Cores Reveal a Forested Southern Greenland

doi:10.1126/science.1141758

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Ancient Biomolecules from Deep Ice Cores Reveal a Forested Southern Greenland

Eske Willerslev¹^*, Enrico Cappellini², Wouter Boomsma³, Rasmus Nielsen⁴, Martin B. Hebsgaard¹, Tina B. Brand¹, Michael Hofreiter⁵, Michael Bunce⁶^,7, Hendrik N. Poinar⁷, Dorthe Dahl-Jensen⁸, Sigfus Johnsen⁸, Jørgen Peder Steffensen⁸, Ole Bennike⁹, Jean-Luc Schwenninger¹⁰, Roger Nathan¹⁰, Simon Armitage¹¹, Cees-Jan de Hoog¹², Vasily Alfimov¹³, Marcus Christl¹³, Juerg Beer¹⁴, Raimund Muscheler¹⁵, Joel Barker¹⁶, Martin Sharp¹⁶, Kirsty E. H. Penkman², James Haile¹⁷, Pierre Taberlet¹⁸, M. Thomas P. Gilbert¹, Antonella Casoli¹⁹, Elisa Campani¹⁹ and Matthew J. Collins²

¹ Centre for Ancient Genetics, University of Copenhagen, Denmark.
² BioArch, Departments of Biology and Archaeology, University of York, UK.
³ Bioinformatics Centre, University of Copenhagen, Denmark.
⁴ Centre for Comparative Genomics, University of Copenhagen, Denmark.
⁵ Max Planck Institute for Evolutionary Anthropology, Germany.
⁶ Murdoch University Ancient DNA Research Laboratory, Murdoch University, Australia.
⁷ McMaster Ancient DNA Center, McMaster University, Canada.
⁸ Ice and Climate, University of Copenhagen, Denmark.
⁹ Geological Survey of Denmark and Greenland, Denmark.
¹⁰ Research Laboratory for Archaeology and the History of Art, University of Oxford, UK.
¹¹ Department of Geography, Royal Holloway, University of London, UK.
¹² Department of Earth Sciences, University of Oxford, UK.
¹³ Paul Scherrer Institut (PSI)/Eidgenössische Technische Hochschule (ETH) Laboratory for Ion Beam Physics, Institute for Particle Physics, ETH Zurich, Switzerland.
¹⁴ Swiss Federal Institute of Aquatic Science and Technology (EAWAG), Switzerland.
¹⁵ GeoBiosphere Science Center, Lund University, Sweden.
¹⁶ Department of Earth and Atmospheric Sciences, University of Alberta, Canada.
¹⁷ Ancient Biomolecules Centre, Oxford University, UK.
¹⁸ Laboratoire d'Ecologie Alpine, CNRS Unité Mixte de Recherche 5553, Université Joseph Fourier, Boîte Postale 53, 38041 Grenoble Cedex 9, France.
¹⁹ Dipartimento di Chimica Generale e Inorganica, Università di Parma, Italy.

Fig. 1. Sample location and core schematics. (A) Map showing the locations of the Dye 3 (65°11'N, 45°50'W) and GRIP (72°34'N, 37°37'W) drilling sites and the Kap København Formation (82°22'N, W21°14'W) in Greenland as well as the John Evans Glacier (JEG) (79°49'N, 74°30'W) on Ellesmere Island (Canada). The inset shows the ratio of D– to L–aspartic acid, a measure of the extent of protein degradation; more highly degraded samples (above the line) failed to yield amplifiable DNA. (B) Schematic drawing of ice core/icecap cross section, with depth [recorded in meters below the surface (m.b.s.)] indicating the depth of the cores and the positions of the Dye 3, GRIP, and JEG samples analyzed for DNA, DNA/amino acid racemization/luminescence (underlined), and ¹⁰Be/³⁶Cl (italic). The control GRIP samples are not shown. The lengths (in meters) of the silty sections are also shown. [View Larger Version of this Image (66K GIF file)]

Fig. 2. Summary of dating results for the silty ice from Dye 3. From top to bottom, the bars indicate: maximum likelihood estimates for the branch length of the invertebrate COI sequences (COI); amino acid racemization results with the use of alternative activation energies, models of racemization behavior, and basal temperature histories (AAR); age estimate from ¹⁰Be/³⁶Cl measurements in silty ice; and minimum ages based on single-grain luminescence results (optically stimulated luminescence or OSL). The time span covered by all dating methods (450 to 800 ka) is marked in gray. Stippled lines represent the results of less likely models. The maximum age estimate for the invertebrate COI sequences is based on an unlikely slow substitution rate [for details, see text and (6)]. [View Larger Version of this Image (23K GIF file)]