Subglacial lakes were discovered beneath the Antarctic Ice Sheet in the 1970’s and, given the presence of liquid water and saturated sediments, it has been debated whether or not these deep, cold biosphere habitats harbor active microbial communities. Subglacial Lake Whillans (SLW) was cleanly sampled in January 2013 with the goal of establishing the habitability and presence of life beneath the Antarctic Ice Sheet. The aim of this graduate fellowship project was to further characterize the SLW carbon cycle, in particular, chemolithoautotrophic microbial processes through geochemical and microbiological methods. Geochemical analyses showed that sulfide oxidizing bacteria were active and contribute to mineral weathering in the surficial sediments of SLW. Long water residence times beneath the West Antarctic Ice Sheet (WAIS) create a mineral weathering regime in SLW that is distinctly different from subglacial habitats of mountain glaciers. Concentration and stable isotope measurements of methane confirm a reservoir of methane formed by methanogenic archaea beneath the WAIS. The modeling results show that this biological methane provides a source of energy to an active methane oxidizing population at the sediment-water interface. The methane also is modeled to be an important source of carbon for biomass synthesis in the methane oxidizing population, with rates of biomass incorporation similar to that of ammonia oxidizing archaea in the SLW water column. These results provide evidence that the sub ice sheet environment provides favorable conditions and substrates to support an active microbial ecosystem, thus expanding the extent of the biosphere to include the area beneath the WAIS and, possibly, the entire Antarctic Ice Sheet.