Title: Solute release during freeze-thaw sediment weathering in supraglacial ice, McMurdo Dry Valleys, Antarctica.

Abstract: In polar environments, glacier meltwater provides freshwater and essential nutrients to downstream ecosystems. The McMurdo Dry Valleys of Antarctica are the largest ice-free area in Antarctica. They have large expanses of exposed bedrock, a polar desert climate, and alpine glaciers descending from the valley walls. Meltwater produced on these cold-based glaciers flows through a supraglacial drainage network and off the terminus to pro-glacial streams that flow along the valley floor. The surface melt of these glaciers is the initial source of solutes in Taylor Valley ecosystems, but previous research focuses on cryoconite holes, isolated pockets of concentrated sediment, and not the main glacial ice. This leads to a lack of understanding how weathering dynamics of diffuse sediment within the main ice contribute solutes to the supraglacial and proglacial stream network. This research focuses on how solute concentrations change with increased freeze-thaw weathering. We will conduct an experiment on sediment from ice cores collected from the ablation zones of Canada, Commonwealth, Howard, Hughes, and Seuss glaciers. These samples were previously collected as part of a different project where the ice cores were divided into increments with depth and melted. The meltwater was filtered and the sediment was retained on glass fiber filters. We will group the filters by depth within ice and location on the glacier. Samples will undergo up to 60 free-thaw cycles and immediate filtration upon completion of the last cycle. We will analyze the filtrate for major ions using ion chromatography, and nutrients using colorimetric flow injection analysis. Initial results from freeze-thaw experiments on aeolian material and fresh bedrock samples indicate that solute concentrations increase with increased numbers of freeze-thaw cycles. Sediment grain size influences the concentrations of and when different solutes were released from sediment. The data collected from this study will improve our understanding of how cyclic freezing and thawing of supraglacial ice weathers solutes from sediment, an important contributor to meltwater chemistry in polar environments. 

Advisor: Anna Bergstrom

Committee: Ellyn Enderlin, Ruth Heindel, and Jim McNamara