Indiana University-Purdue University Indianapolis (IUPUI) / 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.
| Identifer | oai:union.ndltd.org:IUPUI/oai:scholarworks.iupui.edu:1805/27242 |
| Date | 12 1900 |
| Creators | Arnardóttir, Eiríka Ösp |
| Contributors | Licht, Kathy, Graly, Joseph, Bird, Broxton, Gilhooly, William |
| Source Sets | Indiana University-Purdue University Indianapolis |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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