| Summary: | Glaciers are of critical importance in the global hydrological cycle and the implications of their recent rapid decline are still poorly understood. Subglacial processes impact glacial hydrology through nutrient production, water chemistry, and aquifer recharge, but are inaccessible to direct observation. Furthermore, understanding the impact current subglacial melt processes have on surrounding environments may provide insight to changes that likely occurred on glacial-interglacial timescales. In my work, I combine multiple elemental and isotopic systems to understand glacial hydrology, including the subglacial environment. First, I have developed a Bayesian Monte Carlo isotope-mixing model that incorporates stable isotope, δ18O and δD, measurements to extrapolate relative contributions of ice and snowmelt to the glacial system. This model can also be applied to other earth surface systems with distinct end member isotopic compositions. Second, I have combined the melt fractions from my isotope-mixing model with a radioactive uranium-series (U-series) isotope age model to quantify the average residence time and storage length of subglacial melt. By combining these two isotopic systems, I provide unique insights on the size of the subglacial meltwater reservoir and its potential impacts on glacial sliding and meltwater nutrients. Third, I investigate the influence of the U chemistry of current glacial meltwater from the Greenland Ice Sheet on adjacent seawater as a proxy to reconstruct the potential influence of glacial melt on global seawater U chemistry over glacial-interglacial timescales using a simple seawater U budget box model. The models presented here are applied to a broad geographic range to investigate the universality of climate-melt relationships and the impact of glacial melt on the chemistry of both freshwater and seawater reservoirs. PhD Earth and Environmental Sciences University of Michigan, Horace H. Rackham School of Graduate Studies ...
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