Browsing by Author "Hawkings, Jon R."

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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.
Enhanced trace element mobilization by Earth’s ice sheets
(Proceedings of the National Academy of Sciences, 2020-11) Hawkings, Jon R.; Skidmore, Mark L.; Wadham, Jemma L.; Priscu, John C.; Morton, Peter L.; Hatton, Jade E.; Gardner, Christopher B.; Kohler, Tyler J.; Stibal, Marek; Bagshaw, Elizabeth A.; Steigmeyer, August; Barker, Joel; Dore, John E.; Lyons, W. Berry; Tranter, Martyn; Spencer, Robert G. M.
Trace elements sustain biological productivity, yet the significance of trace element mobilization and export in subglacial runoff from ice sheets is poorly constrained at present. Here, we present size-fractionated (0.02, 0.22, and 0.45 µm) concentrations of trace elements in subglacial waters from the Greenland Ice Sheet (GrIS) and the Antarctic Ice Sheet (AIS). Concentrations of immobile trace elements (e.g., Al, Fe, Ti) far exceed global riverine and open ocean mean values and highlight the importance of subglacial aluminosilicate mineral weathering and lack of retention of these species in sediments. Concentrations are higher from the AIS than the GrIS, highlighting the geochemical consequences of prolonged water residence times and hydrological isolation that characterize the former. The enrichment of trace elements (e.g., Co, Fe, Mn, and Zn) in subglacial meltwaters compared with seawater and typical riverine systems, together with the likely sensitivity to future ice sheet melting, suggests that their export in glacial runoff is likely to be important for biological productivity. For example, our dissolved Fe concentration (20,900 nM) and associated flux values (1.4 Gmol y−1) from AIS to the Fe-deplete Southern Ocean exceed most previous estimates by an order of magnitude. The ultimate fate of these micronutrients will depend on the reactivity of the dominant colloidal size fraction (likely controlled by nanoparticulate Al and Fe oxyhydroxide minerals) and estuarine processing. We contend that ice sheets create highly geochemically reactive particulates in subglacial environments, which play a key role in trace elemental cycles, with potentially important consequences for global carbon cycling.