Microbial ecology of an Antarctic subglacial environment
Mikucki, Jill Ann.
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The research presented in this dissertation focused on the microbial ecology of the subglacial discharge from the Taylor Glacier in the McMurdo Dry Valleys, Antarctica. The major objectives of my research were to 1) define the biogeochemistry of the subglacial outflow 2) describe the microbial diversity of the subglacial outflow and 3) examine the impact of subglacial outflow on the geochemistry and biology of the west lobe of Lake Bonney, a lake that abuts the glacier. The subglacial outflow from the Taylor Glacier is known as Blood Falls owing to a visible accumulation of iron-oxides at the point where it flows from the snout of the glacier. The subglacial reservoir is thought to originate from the Pliocene Epoch (~5 Mya) when the dry valleys were fjordlands. The episodic release of subglacial water at Blood Falls provides a sample of what is believed to be ancient seawater trapped in the upper Taylor Valley and eventually covered by the Taylor Glacier as it advanced. Biogeochemical measurements, culture-based techniques, and molecular analysis (based on 16S rDNA sequences), were used to characterize microbes and chemistry associated with the subglacial outflow.Culture and molecular-based techniques, along with geochemical data, indicate the presence of a diverse chemoautotrophic and heterotrophic bacterial assemblage that utilizes iron and sulfur minerals for growth. 16S rDNA clone library phylotypes and cultured isolates were related to organisms that inhabit permanently cold environments. The biological and geochemical component of the ancient outflow changes as it travels from the subglacial environment to the moat of the west lobe of Lake Bonney and eventually into the saline deep water in the lake proper. The bottom water of the west lobe of Lake Bonney is geochemically similar to ancient subglacial outflow, but the microbial diversity in the two systems is distinct, and ancient subglacial brine does not appear to provide the microbial seed for the deep water of Lake Bonney. Collectively, my data indicate that the habitat beneath the Taylor Glacier harbors a functional microbial ecosystem that utilizes chemosynthetic and heterotrophic activity to obtain carbon and energy in the absence of light.