Browsing by Author "Rosenheim, Brad E."

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Biogeochemical and historical drivers of microbial community composition and structure in sediments from Mercer Subglacial Lake, West Antarctica
(Springer Science and Business Media LLC, 2023-01) Davis, Christina L.; Venturelli, Ryan A.; Michaud, Alexander B.; Hawkings, Jon R.; Achberger, Amanda M.; Vick-Majors, Trista J.; Rosenheim, Brad E.; Dore, John E.; Steigmeyer, August; Skidmore, Mark L.; Barker, Joel D.; Benning, Liane G.; Siegfried, Matthew R.; Priscu, John C.; Christner, Brent C.; Barbante, Carlo; Bowling, Mark; Burnett, Justin; Campbell, Timothy; Collins, Billy; Dean, Cindy; Duling, Dennis; Fricker, Helen A.; Gagnon, Alan; Gardner, Christopher; Gibson, Dar; Gustafson, Chloe; Harwood, David; Kalin, Jonas; Kasic, Kathy; Kim, Ok-Sun; Krula, Edwin; Leventer, Amy; Li, Wei; Lyons, W. Berry; McGill, Patrick; McManis, James; McPike, David; Mironov, Anatoly; Patterson, Molly; Roberts, Graham; Rot, James; Trainor, Cathy; Tranter, Martyn; Winans, John; Zook, Bob
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). 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. 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. 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. The most abundant taxa are related to chemolithoautotrophs capable of oxidizing reduced nitrogen, sulfur, and iron compounds with oxygen, nitrate, or iron. Concentrations of dissolved methane and total organic carbon together with water content in the sediments are the strongest predictors of taxon and community composition. δ¹³C values for EPS (−25 to −30‰) are consistent with the primary source of carbon for biosynthesis originating from legacy marine organic matter. 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.
Scientific access into Mercer Subglacial Lake: scientific objectives, drilling operations and initial observations
(Cambridge University Press, 2021-06) Priscu, John C.; Kalin, Jonas; Winans, John; Campbell, Timothy; Siegfried, Matthew R.; Skidmore, Mark; Dore, John E.; Leventer, Amy; Harwood, David M.; Duling, Dennis; Zook, Robert; Burnett, Justin; Gibson, Dar; Krula, Edward; Mironov, Anatoly; McManis, Jim; Roberts, Graham; Rosenheim, Brad E.; Christner, Brent C.; Kasic, Kathy; Fricker, Helen A.; Lyons, W. Berry; Barker, Joel; Bowling, Mark; Collings, Billy; Davis, Christina; Gagnon, Al; Gardner, Christopher; Gustafson, Chloe; Kim, Ok-Sun; Li, Wei; Michaud, Alex; Patterson, Molly O.; Tranter, Martyn; Venturelli, Ryan; Vick-Majors, Trista; Elsworth, Cooper
The Subglacial Antarctic Lakes Scientific Access (SALSA) Project accessed Mercer Subglacial Lake using environmentally clean hot-water drilling to examine interactions among ice, water, sediment, rock, microbes and carbon reservoirs within the lake water column and underlying sediments. A ~0.4 m diameter borehole was melted through 1087 m of ice and maintained over ~10 days, allowing observation of ice properties and collection of water and sediment with various tools. Over this period, SALSA collected: 60 L of lake water and 10 L of deep borehole water; microbes >0.2 μm in diameter from in situ filtration of ~100 L of lake water; 10 multicores 0.32–0.49 m long; 1.0 and 1.76 m long gravity cores; three conductivity–temperature–depth profiles of borehole and lake water; five discrete depth current meter measurements in the lake and images of ice, the lake water–ice interface and lake sediments. Temperature and conductivity data showed the hydrodynamic character of water mixing between the borehole and lake after entry. Models simulating melting of the ~6 m thick basal accreted ice layer imply that debris fall-out through the ~15 m water column to the lake sediments from borehole melting had little effect on the stratigraphy of surficial sediment cores.