Microbial origin of excess greenhouse gases in glacial ice

Abstract

We report the discovery of methanogenic archaea that account for abrupt factor 10 increases in methane concentration found by E. Brook at depths of 2954 and 3036 m in the GISP2 (Greenland Ice Sheet Project 2) ice core. The total microbial concentration we measured with direct cell counts tracks the excesses of methanogens that we identified by their F420 fluorescence. The highly localized (<1 m thick) layers of methanogens suggest flow induced mixing of layers of microbe laden anaerobic basal ice with glacial ice. The metabolic rate we found for microbes at 2954 and 3036 m lies roughly on the Arrhenius line for microbes imprisoned in rock, sediment, and basal ice. Equating the loss rate of methane recently discovered in the Martian atmosphere to the production rate by possible methanogens, we estimate that their Martian habitat would be at a temperature of ~0 degrees C and that the concentration, if uniformly distributed in a 100 m thick layer, would be 0.04 cell per cubic centimeter.