Rates of chemoautotrophy and methanotrophy were sufficient to support heterotrophic demand in the water column and agreed well with the inferred physiologies of dominant taxa identified, yet observed doubling times of ~200 days confirmed slow metabolisms with low growth efficiencies (8%). When SLW was accessed for study in 2013, its water column was under-saturated in oxygen ( ∼16% of air-saturated water), had relatively high dissolved organic carbon (DOC) concentrations (~221 μmol L −1), and contained a diverse and metabolically active community of bacteria and archaea. 1) is a component of that system beneath an 800 m thick portion of the West Antarctic Ice Sheet (WAIS) and was the first Antarctic subglacial lake directly sampled. Comparison of communities to those in lake sediments under an adjacent ice stream (Whillans Subglacial Lake) and near its grounding zone provide seminal evidence for a subglacial metacommunity that is biogeochemically and evolutionarily linked through ice sheet dynamics and the transport of microbes, water, and sediments beneath WAIS.ĭynamic subglacial water systems beneath the Antarctic ice sheet are modulated by hydrologically connected subglacial lakes that episodically fill and drain, transferring water and material between basins before eventually discharging to the ocean. δ¹☼ values for EPS (−25 to −30‰) are consistent with the primary source of carbon for biosynthesis originating from legacy marine organic matter. Concentrations of dissolved methane and total organic carbon together with water content in the sediments are the strongest predictors of taxon and community composition. The most abundant taxa are related to chemolithoautotrophs capable of oxidizing reduced nitrogen, sulfur, and iron compounds with oxygen, nitrate, or iron. Bacterial and archaeal communities in the surficial sediments are more abundant and diverse, with significantly different compositions from those found deeper in the sediment column. We examined microbial abundances, used 16S rRNA gene amplicon sequencing to assess community structures, and characterized extracellular polymeric substances (EPS) associated with distinct lithologic units in the sediments. A 2.06 m composite sediment profile was recently recovered from Mercer Subglacial Lake, a 15 m deep water cavity beneath a 1087 m thick portion of the Mercer Ice Stream. Ice streams that flow into Ross Ice Shelf are underlain by water-saturated sediments, a dynamic hydrological system, and subglacial lakes that intermittently discharge water downstream across grounding zones of West Antarctic Ice Sheet (WAIS).
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