Powell, Ross D.
M.S. (Master of Science)
Department of Geology and Environmental Geosciences
Sediment transport--Antarctica; Ice sheets--Antarctica; Glaciers--Antarctica; Chemical weathering--Antarctica
Subglacial sediment from the Whillans Ice Stream, West Antarctica was studied in order to investigate the primary subglacial sediment transportation agent, ice stream dynamics, and chemical weathering under Whillans Ice Stream (WIS). Scanning electron microscopy on quartz sand grains, gravel form, roundness, and textural and compositional analyses were performed on sediment samples from cores recovered from three subglacial sites including Upstream Whillans (UpB) from 1988-93, Subglacial Lake Whillans (SLW) in 2012-13, and Whillans Grounding Zone (WGZ) in 2014-15. This study is part of the Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project that uses in situ samples to document the subglacial processes that constrain current dynamics and stability of the West Antarctic Ice Sheet (WAIS), to recover records of past dynamics of the ice sheet, and to prove the existence of and then document subglacial biological communities, their structure and ecosystem energies. The subglacial drainage network under WIS is known to increase ice flow velocity during periods when it "floods" out of one lake and into another and specifically, as SLW drains to the Ross Sea. This study concludes the subglacial sediment coarser than mud is not fluvially transported during these SLW drainage events, but rather the sediment is glacially transported in a weak deformation till. Furthermore, there is no evidence of changes in sand and gravel provenance either spatially from site-to-site or temporally at both SLW and WGZ; however, there is evidence at WGZ that the grounding line has been dynamic through the Holocene. Sediment stratigraphy at WGZ shows one prior grounding line fluctuation and a quite recent grounding line retreat that most likely indicates modern instability of the grounding zone. These conclusions support a previous study's findings that sediment flux to the grounding line may be insufficient to stabilize the ice stream against both rising and warming oceans by sediment accumulation in the grounding-zone wedge. Sediment transfer in the weak deformation till is too slow of a process compared with sediment transported in stiffer till or by more normal river floods. Finally, surface dissolution etching and mineral precipitation on freshly crushed surfaces of quartz sand grains provides evidence of microbially mediated chemical reactions occurring subglacially at all sites. Such changes on grain surfaces are thought uncommon in polar subglacial settings due to low chemical energies and thus, for the reactions to occur, they are most likely driven by microbes. The microbial activity discovered at SLW may not be limited to the subglacial lake, but is likely pervasive throughout the subglacial hydrologic network as well as the subglacial till. This finding points to the need for further spatial sampling to confirm the inferences of the broad distribution of subglacial microbial activity that would have the potential for releasing nutrients and organic matter to the Southern Ocean.
Puttkammer, Rebecca A., "Subglacial sediment transport, ice stream dynamics, and chemical weathering of the Whillans Ice Stream inferred from particle surface texture, form, and composition" (2016). Graduate Research Theses & Dissertations. 5130.
viii, 58 pages
Northern Illinois University
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