Carbon and nitrogen fixation experiments were conducted on mats collected from 10 of the ponds on the McMurdo Ice Shelf near Bratina Island. Nitrogen fixation was determined via reduction of acetylene gas and gas chromatography. Carbon fixation was measured via oxygen evolution and dissolved inorganic carbon uptake. Raw data for carbon fixation was collected in the field and was corrected for biomass (chlorophyll a) and surface area before comparing results between ponds. Two of the ponds differed in type of microbial mat present. One was a benthic mixed community microbial mat while the other was a lift-off mat comprised almost exclusively of the nitrogen fixing bacteria Nostoc. Species composition and community structure were also determined.