Browsing by Author "Carter, Sasha"

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A microbial ecosystem beneath the West Antarctic ice sheet
(Nature Publishing Group, 2014) Priscu, John C.; Christner, Brent C.; Achberger, Amanda M.; Barbante, Carlo; Carter, Sasha; Christianson, Knut; Michaud, Alexander B.
Liquid water has been known to occur beneath the Antarctic ice sheet for more than 40 years1, but only recently have these subglacial aqueous environments been recognized as microbial ecosystems that may influence biogeochemical transformations on a global scale2, 3, 4. Here we present the first geomicrobiological description of water and surficial sediments obtained from direct sampling of a subglacial Antarctic lake. Subglacial Lake Whillans (SLW) lies beneath approximately 800 m of ice on the lower portion of the Whillans Ice Stream (WIS) in West Antarctica and is part of an extensive and evolving subglacial drainage network5. The water column of SLW contained metabolically active microorganisms and was derived primarily from glacial ice melt with solute sources from lithogenic weathering and a minor seawater component. Heterotrophic and autotrophic production data together with small subunit ribosomal RNA gene sequencing and biogeochemical data indicate that SLW is a chemosynthetically driven ecosystem inhabited by a diverse assemblage of bacteria and archaea. Our results confirm that aquatic environments beneath the Antarctic ice sheet support viable microbial ecosystems, corroborating previous reports suggesting that they contain globally relevant pools of carbon and microbes2, 4 that can mobilize elements from the lithosphere6 and influence Southern Ocean geochemical and biological systems7.
Subglacial Lake Whillans microbial biogeochemistry: a synthesis of current knowledge
(2016-01) Mikucki, Jill A.; Lee, P.A.; Ghosh, D.; Purcell, A.D.; Mitchell, Andrew C.; Mankoff, K.D.; Fisher, A.T.; Tulaczyk, Slawek; Carter, Sasha; Siegfried, Matthew R.; Fricker, H.A.; Hodson, Timothy; Coenen, J.; Powell, Ross; Scherer, Reed; Vick-Majors, Trista J.; Achberger, Amanda M.; Christner, Brent C.; Tranter, Martyn
Liquid water occurs below glaciers and ice sheets globally, enabling the existence of an array of aquatic microbial ecosystems. In Antarctica, large subglacial lakes are present beneath hundreds to thousands of metres of ice, and scientific interest in exploring these environments has escalated over the past decade. After years of planning, the first team of scientists and engineers cleanly accessed and retrieved pristine samples from a West Antarctic subglacial lake ecosystem in January 2013. This paper reviews the findings to date on Subglacial Lake Whillans and presents new supporting data on the carbon and energy metabolism of resident microbes. The analysis of water and sediments from the lake revealed a diverse microbial community composed of bacteria and archaea that are close relatives of species known to use reduced N, S or Fe and CH4 as energy sources. The water chemistry of Subglacial Lake Whillans was dominated by weathering products from silicate minerals with a minor influence from seawater. Contributions to water chemistry from microbial sulfide oxidation and carbonation reactions were supported by genomic data. Collectively, these results provide unequivocal evidence that subglacial environments in this region of West Antarctica host active microbial ecosystems that participate in subglacial biogeochemical cycling.