Abstract
AbstractThe Camp Century, Greenland, ice core was recovered from a bore hole which extended 1 375 m from the surface of the Greenland ice sheet to the ice/sub-ice interface. The bottom 15.7 m of the core contain over 300 alternating bands of clear and debris-laden ice. The size of the included debris ranges from particles less than 2 μm in diameter to particle aggregates which are a maximum of 3 cm in diameter: the average debris concentration is 0.24ººby weight. The debris size, concentration, and composition indicate that the debris originates from the till-like material directly below the debris-laden ice. The total gas concentration averages 51 ml/kg ice compared to the average of 101 ml/kg ice for the top 1 340 m. The gas composition of debris-bearing ice has apparently been modified by the oxidation of methane as reflected by traces of methane, high CO2levels, and low O2levels with respect to atmospheric air. Argon, which is not affected by the oxidation, shows an enrichment in samples with lower gas concentrations. Both the low gas concentrations in the debris-laden zone and the argon enrichment may be explained by the downward diffusion of gases from bubbly glacier ice into an originally bubble-free zone of refrozen debris-laden ice. Ice texture and ice-fabric analyses reveal extremely fine-grained ice and highly preferred crystal orientation in the lowermost 10 m of the core, indicating a zone of high deformation.
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