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 10_Be/36_Cl 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).

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.