The Experts below are selected from a list of 114 Experts worldwide ranked by ideXlab platform
Karen A Cameron - One of the best experts on this subject based on the ideXlab platform.
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meltwater export of prokaryotic cells from the greenland ice sheet
Environmental Microbiology, 2017Co-Authors: Karen A Cameron, Marek Stibal, Jon R Hawkings, A B Mikkelsen, Jon Telling, Tyler J Kohler, Erkin Gozdereliler, Jakub D Zarsky, Jemma L Wadham, Carsten S JacobsenAbstract:Summary Microorganisms are flushed from the Greenland Ice Sheet (GrIS) where they may contribute towards the nutrient cycling and community compositions of downstream ecosystems. We investigate meltwater microbial assemblages as they exit the GrIS from a large outlet glacier, and as they enter a downstream river delta during the record melt year of 2012. Prokaryotic abundance, flux and community composition was studied, and factors affecting community structures were statistically considered. The mean concentration of cells exiting the ice sheet was 8.30 × 104 cells mL−1 and we estimate that ∼1.02 × 1021 cells were transported to the downstream fjord in 2012, equivalent to 30.95 Mg of carbon. Prokaryotic microbial assemblages were dominated by Proteobacteria, Bacteroidetes, and Actinobacteria. Cell concentrations and community compositions were stable throughout the sample period, and were statistically similar at both sample sites. Based on our observations, we argue that the Subglacial Environment is the primary source of the river-transported microbiota, and that cell export from the GrIS is dependent on discharge. We hypothesise that the release of Subglacial microbiota to downstream ecosystems will increase as freshwater flux from the GrIS rises in a warming world.
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understanding of silicate weathering in Subglacial Environment by inverse modeling of west greenland glacial meltwater
AGU Fall Meeting Abstracts, 2012Co-Authors: L Liu, Karen A Cameron, Brent C Christner, Birgit Hagedorn, R S Sletten, Kyla Choquette, Markus Dieser, Z Harrold, Karen JungeAbstract:The acceleration of chemical weathering due to physical processes in glaciers has been studied in various systems. In our study we consider the potential role of microbes in addition to physical weathering to enhance weathering in runoff from the Greenland Ice sheet (GrIS). Sub- and supra- glacial weathering products in bulk meltwater are used to determine reaction processes and assess solute provenance. Most current models estimate that 80-100% of the dominant ion Ca2+ is derived from weathering of trace carbonates. The potential for significant silicate-derived Ca2+ is not generally considered. We hypothesize that seasonal changes in Subglacial water routing and water residence times have a large impact on the weathering of lithologies with differing geochemical reactivity. This study deconvolutes the solute chemistry in runoff from the GrIS using PHREEQCi, a computer-based speciation mass-balance model. The model utilizes a mass balance approach and allows multiple alternative weathering scenarios under different hydrological conditions to be tested simultaneously. It is parameterized using seasonal chemical and mineralogical field data from Thule (76°N, 68°W), West Greenland. Hypothetical geochemical weathering scenarios suggest Ca-feldspar dissolution is an important solute source and silicate weathering is likely to be dominated by Ca-feldspar weathering in GrIS, due to their relatively high dissolution rates. The proportion of silicate dissolution decreases with increasing discharge on the seasonal timescale, and this reflects the seasonal expansion of the channelized system. At places where the development of channelized system is limited and most waters are routed through a distributed system, silicate minerals, which are more abundant but less reactive than carbonates, have sufficient time to dissolve and may have a greater contribution, approximately equal amounts of Ca2+ as carbonates, to the major solutes.
Mark L Skidmore - One of the best experts on this subject based on the ideXlab platform.
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a microbiologically clean strategy for access to the whillans ice stream Subglacial Environment
Antarctic Science, 2013Co-Authors: John C Priscu, Amanda M Achberger, Joel Cahoon, Brent C Christner, Robert L Edwards, Warren L Jones, Alexander B Michaud, M R Siegfried, Mark L Skidmore, Robert H SpigelAbstract:The Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project will test the overarching hypothesis that an active hydrological system exists beneath a West Antarctic ice stream that exerts a major control on ice dynamics, and the metabolic and phylogenetic diversity of the microbial community in Subglacial water and sediment. WISSARD will explore Subglacial Lake Whillans (SLW, unofficial name) and its outflow toward the grounding line where it is thought to enter the Ross Ice Shelf seawater cavity. Introducing microbial contamination to the Subglacial Environment during drilling operations could compromise Environmental stewardship and the science objectives of the project, consequently we developed a set of tools and procedures to directly address these issues. WISSARD hot water drilling efforts will include a custom water treatment system designed to remove micron and sub-micron sized particles (biotic and abiotic), irradiate the drilling water with germicidal ultraviolet (UV) radiation, and pasteurize the water to reduce the viability of persisting microbial contamination. Our clean access protocols also include methods to reduce microbial contamination on the surfaces of cables/hoses and down-borehole equipment using germicidal UV exposure and chemical disinfection. This paper presents experimental data showing that our protocols will meet expectations established by international agreement between participating Antarctic nations.
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influence of bedrock mineral composition on microbial diversity in a Subglacial Environment
Geology, 2013Co-Authors: Mark L Skidmore, Andrew C Mitchell, Melissa J Lafreniere, Eric S BoydAbstract:Microorganisms in Subglacial Environments drive the chemical weathering of bedrock; however, the influence of bedrock mineralogy on the composition and activity of microbial assemblages in such Environments is poorly understood. Here, using a combination of in situ mineral incubation and DNA fingerprinting techniques, we demonstrate that pyrite is the dominant mineralogical control on Subglacial bacterial community structure and composition. In addition, we show that the abundance of Fe in the incubated minerals influences the development of mineral-associated biomass. The ubiquitous nature of pyrite in many common bedrock types and high SO 4 2– concentrations in most glacial meltwaters suggest that pyrite may be a dominant lithogenic control on microbial communities in many Subglacial systems. Mineral-based energy may therefore serve a fundamental role in sustaining Subglacial microbial populations and enabling their persistence over glacial-interglacial time scales.
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a microbial driver of chemical weathering in glaciated systems
Geology, 2013Co-Authors: Scott N Montross, Mark L Skidmore, Martyn Tranter, Annaliisa Kivimaki, John R ParkesAbstract:Glaciological processes under ice sheets provide sustainable ecosystems for microbes, forming an aquatic Environment through basal melting, and providing nutrients and energy from bedrock. Microbes facilitate solute production in most Earth surface Environments, but the balance of biotic and abiotic weathering in Subglacial Environment is presently unknown. This study demonstrates an up to eightfold increase in dissolved major cations in biotic relative to abiotic weathering experiments using glacial sediments and meltwater. This conclusion greatly expands our view of Earth's biogeochemically active weathering zone by incorporating the large wet-based portions of glaciated continents, both at present and during Earth's history. The profound Environmental significance is that microbial processes have the ability to maintain terrestrial chemical weathering rates in cooling climates during glacial advance.
Carsten S Jacobsen - One of the best experts on this subject based on the ideXlab platform.
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meltwater export of prokaryotic cells from the greenland ice sheet
Environmental Microbiology, 2017Co-Authors: Karen A Cameron, Marek Stibal, Jon R Hawkings, A B Mikkelsen, Jon Telling, Tyler J Kohler, Erkin Gozdereliler, Jakub D Zarsky, Jemma L Wadham, Carsten S JacobsenAbstract:Summary Microorganisms are flushed from the Greenland Ice Sheet (GrIS) where they may contribute towards the nutrient cycling and community compositions of downstream ecosystems. We investigate meltwater microbial assemblages as they exit the GrIS from a large outlet glacier, and as they enter a downstream river delta during the record melt year of 2012. Prokaryotic abundance, flux and community composition was studied, and factors affecting community structures were statistically considered. The mean concentration of cells exiting the ice sheet was 8.30 × 104 cells mL−1 and we estimate that ∼1.02 × 1021 cells were transported to the downstream fjord in 2012, equivalent to 30.95 Mg of carbon. Prokaryotic microbial assemblages were dominated by Proteobacteria, Bacteroidetes, and Actinobacteria. Cell concentrations and community compositions were stable throughout the sample period, and were statistically similar at both sample sites. Based on our observations, we argue that the Subglacial Environment is the primary source of the river-transported microbiota, and that cell export from the GrIS is dependent on discharge. We hypothesise that the release of Subglacial microbiota to downstream ecosystems will increase as freshwater flux from the GrIS rises in a warming world.
Andrew C Mitchell - One of the best experts on this subject based on the ideXlab platform.
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influence of bedrock mineral composition on microbial diversity in a Subglacial Environment
Geology, 2013Co-Authors: Mark L Skidmore, Andrew C Mitchell, Melissa J Lafreniere, Eric S BoydAbstract:Microorganisms in Subglacial Environments drive the chemical weathering of bedrock; however, the influence of bedrock mineralogy on the composition and activity of microbial assemblages in such Environments is poorly understood. Here, using a combination of in situ mineral incubation and DNA fingerprinting techniques, we demonstrate that pyrite is the dominant mineralogical control on Subglacial bacterial community structure and composition. In addition, we show that the abundance of Fe in the incubated minerals influences the development of mineral-associated biomass. The ubiquitous nature of pyrite in many common bedrock types and high SO 4 2– concentrations in most glacial meltwaters suggest that pyrite may be a dominant lithogenic control on microbial communities in many Subglacial systems. Mineral-based energy may therefore serve a fundamental role in sustaining Subglacial microbial populations and enabling their persistence over glacial-interglacial time scales.
Kenneth C Jezek - One of the best experts on this subject based on the ideXlab platform.
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evidence for Subglacial water transport in the west antarctic ice sheet through three dimensional satellite radar interferometry
Geophysical Research Letters, 2005Co-Authors: Laurence Gray, Ian Joughin, Slawek Tulaczyk, Vandy Blue Spikes, Robert Bindschadler, Kenneth C JezekAbstract:[1] RADARSAT data from the 1997 Antarctic Mapping Mission are used interferometrically to solve for the 3-dimensional surface ice motion in the interior of the West Antarctic Ice Sheet (WAIS). An area of ∼125 km2 in a tributary of the Kamb Ice Stream slumped vertically downwards by up to ∼50 cm between September 26 and October 18, 1997. Areas in the Bindschadler Ice Stream also exhibited comparable upward and downward surface displacements. As the uplift and subsidence features correspond to sites at which the basal water apparently experiences a hydraulic potential well, we suggest transient movement of pockets of Subglacial water as the most likely cause for the vertical surface displacements. These results, and related lidar observations, imply that imaging the change in ice surface elevation can help reveal the key role of water in the difficult-to-observe Subglacial Environment, and its important influence on ice dynamics.
