Theses and Dissertations at Montana State University (MSU)
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Item Geochemical characterization of shallow sediments from the grounding zone of the Whillans Ice Stream(Montana State University - Bozeman, College of Agriculture, 2019) Roush, Kimberly Anne; Chairperson, Graduate Committee: John C. Priscu and John Dore (co-chair); John Priscu, Mark Skidmore, Alex Michaud and the WISSARD Science Team were co-authors of the article, 'Signatures of subglacial water in shallow sediments of the Whillans grounding zone and overlying water column' which is contained within this thesis.; John Priscu, John Dore, Wei Li, Tristy Vick-Majors and the WISSARD Science Team were co-authors of the article, 'Sediment porewater organic matter content' which is contained within this thesis.The research presented in this thesis focused on subglacial flow beneath the West Antarctic Ice Sheet (WAIS) and its potential influence near the grounding zone. Antarctic grounding zones are of specific scientific interest because they can impact the stability of the continental ice sheet and its breakup, potentially resulting in significant sea level rise. My major objective was to determine whether there was influence of subglacial water at the Whillans Grounding Zone (WGZ) on the Siple Coast of the WAIS. A gravity corer was used to collect a 70 cm sediment core through 780 m of ice borehole drilled using a hot water clean access drilling system. The core was collected in a marine embayment adjacent to the WGZ beneath a 10 m water column. I used a combination of geochemical, isotopic and organic matter analyses to characterize the benthic sediments, porewater and water column. The geochemical and isotopic data showed the influence of subglacial freshwater on sediment porewater at specific depths in the 70 cm core. Vertical gradients of chloride and sulfate between surficial sediment and the overlying water column indicated ion diffusion from porewater to the column water. Dissolved organic matter concentration of sediment porewater and the overlying water column also indicated upward diffusion occurs from porewater to the overlying seawater. Sediment particulate carbon and nitrogen data showed that benthic sediments were more depleted in nitrogen than the overlying seawater. Sediment particulate carbon and nitrogen data showed that benthic sediments were more depleted in nitrogen than the overlying seawater. Geochemical, isotopic and organic matter data supports the influence of subglacial freshwater at the WGZ.Item Long-term perspectives on northern Rockies climatic variability from tree rings in Glacier National Park, Montana(Montana State University - Bozeman, College of Agriculture, 2004) Pederson, Gregory Thomas; Chairperson, Graduate Committee: Lisa J. Graumlich.Instrumental climate records reveal fluctuations in summer moisture anomalies and winter snowpack in Glacier National Park, Montana, on decadal and multidecadal timescales. However, because climate records for the region are limited to the 20th century, studies on the impacts of long-duration variations in climate on physical and ecosystem processes were limited. Therefore, a reconstruction of summer moisture variability (June - August) spanning A.D. 1540-2000 was created from a multi-species network of tree-ring chronologies sampled in Glacier National Park. The reconstruction shows decadal-scale shifts between drought and pluvial events with a pronounced cool/wet period spanning the end of the Little Ice Age (A.D. 1770-1840). The single most exceptional drought event occurred over the 20th century (A.D. 1917-1941) and was associated with the most spatially consistent drought regime throughout the northern Rockies and Pacific Northwest over the past ~500 yrs. Among a wider spatial network of hydroclimatic reconstructions arrayed along a north-south Rocky Mountain transect, trends at Glacier National Park were found to be most similar to those in the Canadian Rockies and the Pacific Northwest.Item Microbial ecology of an Antarctic subglacial environment(Montana State University - Bozeman, College of Agriculture, 2005) Mikucki, Jill Ann; Chairperson, Graduate Committee: John C. Priscu.The research presented in this dissertation focused on the microbial ecology of the subglacial discharge from the Taylor Glacier in the McMurdo Dry Valleys, Antarctica. The major objectives of my research were to 1) define the biogeochemistry of the subglacial outflow 2) describe the microbial diversity of the subglacial outflow and 3) examine the impact of subglacial outflow on the geochemistry and biology of the west lobe of Lake Bonney, a lake that abuts the glacier. The subglacial outflow from the Taylor Glacier is known as Blood Falls owing to a visible accumulation of iron-oxides at the point where it flows from the snout of the glacier. The subglacial reservoir is thought to originate from the Pliocene Epoch (~5 Mya) when the dry valleys were fjordlands. The episodic release of subglacial water at Blood Falls provides a sample of what is believed to be ancient seawater trapped in the upper Taylor Valley and eventually covered by the Taylor Glacier as it advanced. Biogeochemical measurements, culture-based techniques, and molecular analysis (based on 16S rDNA sequences), were used to characterize microbes and chemistry associated with the subglacial outflow.