  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.
