Browsing by Author "Graly, Joseph"

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    A Glacier through a Grain of Sand: Sediment Micromorphology from a Land-Terminating Glacier in West Greenland
    (2024-10) Woodie, Kayla Pearl; Licht, Kathy; Gilhooly, William P., III; Graly, Joseph
    Isunnguata Sermia is a land terminating glacier in West Greenland with prominent upwellings of subglacial water in the outwash plain. Sediment that is suspended in the upwelling water is preserved in ice, creating a window into the subglacial environment. The presence of certain established microtextures, such as those caused by fluvial or high-stress processes, is indicative of a grain’s impact and transport history. Scanning electron microscopy (SEM) imaging of quartz sand grains is used to analyze this micromorphology. Across sand grains collected from different glacial depositional environments and the frozen subglacial water of Isunnguata Sermia, the microtexture distributions are extremely similar despite their different transport processes. While this may represent the limitations of microtexture analysis, it also suggests a high degree of sediment recycling in a basin that includes both the subglacial and the proglacial environment.
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    Meteoric 10Be as a Tracer for Subglacial Chemical Weathering in East Antarctica
    (2021-12) Arnardóttir, Eiríka Ösp; Licht, Kathy; Graly, Joseph; Bird, Broxton; Gilhooly, William
    Subglacial chemical processes in Antarctica are potentially significant contributors to global geochemical cycles, but current understanding of their scale and nature is limited. A sequential chemical extraction procedure was developed and tested to investigate the utility of meteoric 10Be as a tracer for chemical weathering processes beneath the East Antarctic Ice Sheet. Subglacial meltwater is widely available under the Antarctic Ice Sheet and chemical constituents within it have the potential to drive geochemical weathering processes in the subglacial environment. Meteoric 10Be is a cosmogenic nuclide with a half-life of 1.39×106 years that is incorporated into glacier ice, therefore its abundance in the subglacial environment in Antarctica is meltwater dependent. It is known to adsorb to fine-grained particles in aqueous solution, precipitate with amorphous oxides, and/or be incorporated into authigenic clay structures during chemical weathering. The presence of 10Be in weathering products derived from beneath the ice therefore indicates chemical weathering processes in the subglacial environment. Freshly emerging subglacial sediments from the Mt. Achernar blue ice moraine were subject to chemical extractions where these weathering phases were isolated and 10Be concentrations therein quantified. Optimization of the phase isolation was developed by examining the effects of each extraction on the sample mineralogy and chemical composition. Experiments on 10Be desorption revealed that pH 3.2-3.5 was optimal for the extraction of adsorbed 10Be. Vigorous disaggregation of the samples before grain size separations and acid extractions is crucial due to the preferential fractionation of the nuclide with clay-sized particles. 10Be concentrations of 2-22×107 atoms g-1 measured in oxides and clay minerals in freshly emerging sediments strongly indicate subglacial chemical weathering in the catchment of the Mt. Achernar moraine. Sediment-meltwater contact in the system was calculated to be on the order of thousands of years, based on total 10Be sample concentrations, local basal melt rates, and 10Be ice concentrations. Strong correlation (R = 0.96) between 10Be and smectite abundance in the sediments indicate authigenic clay formation in the subglacial environment. This study shows that meteoric 10Be is a useful tool to characterize subglacial geochemical weathering processes under the Antarctic Ice Sheet.