Astrobiology August 2007, 7(4): 645-661
Small coastal ponds that contain photosynthetic microbial mat communities represent an extreme environment where a potentially significant source of labile organic carbon can be found within the McMurdo Dry Valleys, Antarctica. To distinguish coastal pond-derived organic matter from other sources of organic matter in the Dry Valleys, bulk organic carbon, nitrogen, and sulfur isotope signatures and phospholipid fatty acid (PLFA) profiles of benthic microbial mats located at two sites—Hjorth Hill coast and Garwood Valley—were investigated. The average isotope values at Hjorth Hill coast and Garwood Valley are, respectively, −10.9% and −10.2% for δ13 C, 3.7% and −1.3% for δ15N, and 8.1% and 16.7% for δ34S. Microbial mats from all ponds are dominated by monounsaturated PLFAs (indicative of Gramnegative bacteria) and polyunsaturated PLFAs (indicative of microeukaryotes). Biomarkers specific to aerobic prokaryotes, eukaryotes, and photoautotrophic microeukaryotes, as well as sulfur-reducing bacteria, are present in all samples. Benthic mats at Garwood Valley are thicker and more laminated, have a higher biomass, and have a greater carbon and nitrogen content, which suggests greater productivity than mats at Hjorth Hill coast. Greater productivity is supported, as well, by higher dissolved oxygen contents likely derived from heightened photosynthetic productivity. More productivity at Garwood Valley likely results from a larger influx of terrestrial surface waters together with a concomitant nutrient loading.