Abstract
Two ∼4 m vertical sequences of basal ice were collected from tunnels dug into the northern lateral margin of Taylor Glacier, McMurdo Dry Valleys, Antarctica. In both cases the basal sequences exhibit two contrasting ice facies groups; clean (debris-free) and banded dispersed (debris-rich). Debris-rich ices exhibit elevated CO
2
and depleted O
2
concentrations compared to the clean facies. Bacterial cell numbers, respiration rates, and nutrient concentrations are highest in debris-rich layers. Together, our geochemical and biological data indicate that microbial heterotrophic respiration is likely occurring in situ within the basal ice matrix at ambient temperatures near −15°C. This implies that the basal ice zone of polar glaciers and larger ice sheets is a viable subglacial microbial habitat and active biome of significant volume that has not previously been considered.