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. 2007 Jul 6;317(5834):111-4.
doi: 10.1126/science.1141758.

Ancient Biomolecules From Deep Ice Cores Reveal a Forested Southern Greenland

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Ancient Biomolecules From Deep Ice Cores Reveal a Forested Southern Greenland

Eske Willerslev et al. Science. .
Free PMC article

Abstract

It is difficult to obtain fossil data from the 10% of Earth's terrestrial surface that is covered by thick glaciers and ice sheets, and hence, knowledge of the paleoenvironments of these regions has remained limited. We show that DNA and amino acids from buried organisms can be recovered from the basal sections of deep ice cores, enabling reconstructions of past flora and fauna. We show that high-altitude southern Greenland, currently lying below more than 2 kilometers of ice, was inhabited by a diverse array of conifer trees and insects within the past million years. The results provide direct evidence in support of a forested southern Greenland and suggest that many deep ice cores may contain genetic records of paleoenvironments in their basal sections.

Figures

Fig. 1
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 insert 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 (in meters below 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.
Fig. 2
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 using alternative activation energies, models of racemization behavior, and basal temperature histories (AAR); age estimate from 10Be/36Cl measurements in silty ice; minimum ages based on single grain luminescence results (OSL). The time span covered by all dating methods (450-800Ka) is marked in gray. LIG = Last Interglacial. Stippled lines represent the results of less likely models. It should be noted that the maximum age estimate for the invertebrate COI sequences is based on an unlikely slow substitution rate. For details see main text and (6).

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