Scholarship & Research
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Item Methane flux from recently exposed subglacial sediments, Robertson Glacier, Canada(Montana State University - Bozeman, College of Letters & Science, 2014) Spotts, Terra Marie; Chairperson, Graduate Committee: Mark L. SkidmoreMethane is over 20 times more effective than CO 2 as a greenhouse gas. Thus, its atmospheric concentration and the processes controlling it are important components of the global climate system. Recent research has shown methanogenesis in subglacial sediments. However, the net contribution from subglacial systems to the global methane budget is poorly understood due to a dearth of empirical data. Using measurements via the static chamber method, the flux of methane from recently exposed subglacial sediments at Robertson Glacier, Canadian Rockies was quantified. Methane concentrations were measured from surface gas flux chambers in transects both parallel and perpendicular to the glacier terminus. Over 300 measurements were made during the 2012 melt season (July to September) and used to determine both spatial and temporal variability in the gas fluxes. The chamber farthest from the glacier terminus, approximately 50 m down valley, had an average flux close to zero whereas the chambers nearest the terminus had the highest average fluxes. The average methane efflux from the sediment surface to atmosphere was 0.22 micromoles m -2 d -1. The highest methane efflux during the season, 11.0 micromoles m -2 d -1, was measured in close proximity to the glacier terminus. Shallow sediment cores were collected adjacent to the static chambers and vertical gas concentration profiles were measured from the cores. Within the profiles, methane concentrations were greater than atmospheric concentrations at all depths. Additionally, CO 2, CO and H 2 gas concentrations were analyzed in the cores to evaluate potential microbial metabolic pathways of methane production. Previous studies on methane fluxes from glacial sediments in Greenland and the Swiss Alps used single time point flux measurements during a melt season from multiple locations. This study concludes that such point measurements are unlikely representative for determining a net seasonal flux as they do not consider temporal variability. There was a two order of magnitude difference between the annual source contribution of methane based on the average melt season flux and the highest measured surface flux. This indicates that single sampling periods may significantly over or underestimate the net seasonal flux of methane from recently exposed glacial sediments to the atmosphere.Item Chemolithotrophic primary production in a subglacial ecosystem(2014-10) Boyd, Eric S.; Hamilton, Trinity L.; Havig, Jeff R.; Skidmore, Mark L.; Shock, Everett L.Glacial comminution of bedrock generates fresh mineral surfaces capable of sustaining chemotrophic microbial communities under the dark conditions that pervade subglacial habitats. Geochemical and isotopic evidence suggests that pyrite oxidation is a dominant weathering process generating protons that drive mineral dissolution in many subglacial systems. Here, we provide evidence correlating pyrite oxidation with chemosynthetic primary productivity and carbonate dissolution in subglacial sediments sampled from Robertson Glacier (RG), Alberta, Canada. Quantification and sequencing of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) transcripts suggest that populations closely affiliated with Sideroxydans lithotrophicus, an iron sulfide-oxidizing autotrophic bacterium, are abundant constituents of microbial communities at RG. Microcosm experiments indicate sulfate production during biological assimilation of radiolabeled bicarbonate. Geochemical analyses of subglacial meltwater indicate that increases in sulfate levels are associated with increased calcite and dolomite dissolution. Collectively, these data suggest a role for biological pyrite oxidation in driving primary productivity and mineral dissolution in a subglacial environment and provide the first rate estimate for bicarbonate assimilation in these ecosystems. Evidence for lithotrophic primary production in this contemporary subglacial environment provides a plausible mechanism to explain how subglacial communities could be sustained in near-isolation from the atmosphere during glacial-interglacial cycles.Item Biogeochemistry of basal ice from Taylor Glacier, Antarctica(Montana State University - Bozeman, College of Letters & Science, 2012) Montross, Scott Norman; Chairperson, Graduate Committee: Mark L. Skidmore; Mark Skidmore, Brent C. Christner, Denis Samyn, Jean Louis Tison, Reginald Lorrain, Shawn Doyle and Sean Fitzsimons were co-authors of the article, 'Debris-rich basal ice as a microbial habitat, Taylor Glacier, Antarctica' in the journal 'Journal of geophysical research- biogeosciences' which is contained within this thesis.; Mark Skidmore, Brent C. Christner, Shawn Doyle, Jean Louis Tison and Todd Sowers were co-authors of the article, 'Alteration of the composition of air trapped in debris-rich basal ice by in situ microbial respiration at -15°C' in the journal 'Nature geoscience' which is contained within this thesis.; Mark Skidmore was a co-author of the article, 'Biogeochemical weathering in debris-laden basal ice from Taylor Glacier, Antarctica' in the journal 'Journal of glaciology' which is contained within this thesis.The thesis addresses a topical and exciting question in cryospheric biology: are microorganisms capable of metabolism in debris-rich basal ice of a polar glacier? The research was carried out on debris-rich basal ice from a cold-based glacier, Taylor Glacier, McMurdo Dry Valleys, Antarctica. A key component of the research was the collection and analysis of large parallel samples of basal ice for analysis of sediment concentration and mineralogy, nutrient and ion chemistry, gas composition, isotopic gas composition, cell density and metabolic activity on individual ~1-2cm thick layers. The primary material for the thesis was from a 4 m high section of basal ice collected from a vertical shaft at the end of a 15m tunnel chainsawed into the northern margin of the Taylor Glacier. Some data was derived from ice samples collected from tunnels 500m upglacier and downglacier from the 2007 tunnel, excavated in 1999 and 2009 respectively. The main research findings presented in this dissertation are that (a) debris-rich basal ice is a viable habitat for microbial life, (b) in situ microbial heterotrophic respiration is a source of CO 2 in debris-rich basal ice, and (c) microbially-mediated weathering of entrained mineral debris is a source of solute in the ice. Geologic debris in basal ice is the key component for microbial activity since it leads to a higher fraction of liquid water in the ice and provides both organic and inorganic substrates to organisms in the ice. Microbial activity in the ice produces isotopic and geochemical signatures that could be used as biomarkers for exploration of other icy systems. The results of the thesis enforce the notion that the debris-rich basal ice environment is a viable microbial habitat that supports life at temperatures below 0°C. This has broader implications at the ice sheet scale since recent discoveries in East Antarctica, indicate significant basal ice up to 1100 m thick with approximately the same volume as the world's fourth largest freshwater lake, Lake Michigan-Huron.