Doctor of Philosophy (PhD)
The abundance of liquid water found beneath the Antarctic Ice Sheet (AIS) is thought to provide a suitable habitat for microbial life. However, the thick ice sheet has posed a significant obstacle to accessing this isolated system and as a consequence, little data exists to infer ecosystem processes occurring beneath ice sheets. To address this deficit, data generated through 16S rRNA (genes and molecules) and metagenomic sequencing was used to evaluate the diversity and potential metabolic function of communities inhabiting Subglacial Lake Whillans (SLW) and the ocean basin into which it discharges (Whillans Ice Stream grounding zone; WIS-GZ). The analysis of SLW was found to be dominated by bacterial and archaeal species with little evidence for active eukaryotic organisms. The abundance of taxa related to chemolithoautrophic species (e.g., Thiobacillus, Sideroxydans, Nitrosospira, and Candidatus Nitrosoarcheaum) suggested that reduced sulfur, iron, and nitrogen compounds were important in fueling primary production in the permanently dark lake. Consistent with this, genes involved in inorganic carbon fixation, sulfide oxidation, and ammonia oxidation were also identified and taxonomically affiliated with species of Thiobacillus and Nitrosospira. Furthermore, the abundance of sequences related to Methylobacter¬ combined with the detection of methanogenic taxa provided evidence for methane cycling beneath the AIS. Although organic carbon and nutrients generated in SLW are transported to the WIS-GZ and may help support the diverse community found there, the prevalence of chemolithoautotrophic taxa (e.g., Thioprofundum and Thiohalophilus) suggests primary production coupled to the oxidation of reduced sulfur compounds may also provide a source of new fixed carbon to the system. The WIS-GZ community was distinct from those of SLW and the Ross Ice Shelf edge, signifying that it is structured based on the combined influences of input from the subglacial and marine systems. Collectively, these studies show that diverse microbial assemblages exist beneath ice sheets that are largely sustained through chemosynthesis and the weathering of bedrock minerals.
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Achberger, Amanda Marie, "Structure and Functional Potential of Microbial Communities in Subglacial Lake Whillans and at the Ross Ice Shelf Grounding Zone, West Antarctica" (2016). LSU Doctoral Dissertations. 4453.