Collaborative Research: Microbially Mediated Anaerobic Carbon Cycling in Limnologically Contrasting Perennially Ice-Covered Antarctic Lakes

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Intellectual Merit: Anaerobic microbial processes mediate organic carbon mineralization in anoxic soils, sediments, and aquatic systems. The lakes of the McMurdo Dry Valleys (MCM) are perennially ice-covered and are the primary refuge for life in this hyperarid polar desert. The focus of the proposed research is on anaerobic microbially mediated carbon cycling in the bottom water and sediments of two geochemically contrasting Dry Valley lakes, Fryxell (FRX) and Vanda (VAN). Previous studies and preliminary data indicate that the key anaerobic processes of sulfate reduction and methanogenesis are distinct these lakes. In VAN, anaerobic metabolism is dominated by sulfate reduction while methanogenesis dominates in FRX. The research plan will study in detail a globally relevant biogeochemical process, the anaerobic oxidation of methane (AOM), which is almost certainly supported by a metabolically novel mechanism in FRX; the potential for AOM in Lake Vanda is unknown. The research program will address the following overarching questions: What factors control terminal carbon metabolism in anoxic and highly stable polar lake waters and sediments? What novel microbial communities are responsible for AOM and which electron acceptor(s) support AOM in these unique lakes? Specifically, the work will determine (1) The rates and/or mechanisms of anaerobic carbon and sulfur cycling in anoxic bottom waters and sediments; (2) The role of sulfate in driving anaerobic carbon/sulfur cycling in FRX and VAN; (3) The mechanism of AOM in the anoxic sulfate-depleted bottom waters and sediments of FRX; (4) The existence and mechanism of AOM in the sulfate-rich bottom waters and sediments of VAN; (5) The identity and diversity of the microorganisms involved in AOM and other methane- and sulfur-cycling processes in these lakes. Broader Impacts: The project will employ post-doctoral, graduate, and undergraduate students, and will complement existing NSF-funded projects, the MCM Long Term Ecological Research (LTER) and Microbial Observatory (MO) projects. The PIs will provide a focused, hands-on research experience in biogeochemistry and microbiology to students and staff while simultaneously advancing our understanding of microbiology and biogeochemistry in perennially ice covered lakes. Data distribution and outreach will be accomplished via a dedicated web site linked to the PI's home page and to the MCM LTER web site, press releases, presentations at national and international conferences, and publication in peer-reviewed