Biomarker and Stable Isotope Characterization of Coastal Pond Organic Matter, McMurdo Dry Valleys, Antarctica

Small coastal ponds containing photosynthetic microbial mat communities represent a potentially significant source of labile organic carbon within the McMurdoDryValleys, Antarctica. To distinguish coastal pond derived organic matter (CPDOM) from other sources of organic matter in the dry valleys, I investigated bulk organic carbon and nitrogen isotopic signatures and phospholipid fatty acid (PLFA) profiles of benthic microbial mats located at two sites, HjorthHillCoastand GarwoodValley. The average δ¹³C values at Hjorth Hill Coast and Garwood Valley are -10.91 ‰ and -10.19 ‰, respectively. The average δ¹⁵N values are 3.73 ‰ and -1.25 ‰, respectively. Microbial mats from all ponds are dominated by monounsaturated PLFAs, which are indicative of gram negative bacteria, and polyunsaturated PLFAs, which are indicative of microeukaryotes. Specific biomarkers for aerobic prokaryotes, eukaryotes, photoautotrophic microeukaryotes, and sulfur-reducing bacteria are present in all samples. Benthic mats atGarwoodValley are thicker, more laminated, have a higher biomass, and greater % C and % N, suggesting greater productivity than mats atHjorthHillCoast. Greater productivity is supported, as well, by greater dissolved oxygen contents likely derived from greater photosynthetic productivity. Higher productivity atGarwoodValley likely results from greater influx of terrestrial surface water and concomitant nutrient loading.