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Identifying and characterizing the spatial variability of supraglacial hydrological features on the western Greenland Ice Sheet King, Leonora Adele

Abstract

Glacier and ice sheet response to climate change is modulated in part by the temporal and spatial delivery of surface water to the subglacial system which can enhance ice sliding. Surface-to-bed connections are formed by near-vertical pathways through the ice called moulins. The mechanisms through which moulins form and the hydrological implications of their distribution are inadequately constrained. This thesis focuses on the southwest Greenland Ice Sheet, where surface melt and related features are abundant and where meltwater drainage through moulins has been empirically linked to ice speedup. In the first part, I employ flow routing over a high resolution digital elevation model to delineate supraglacial channels and catchments. I compare my results to an independent dataset and demonstrate that flow routing is an effective tool for delineating channels in high detail. Whereas multispectral methods provide instantaneous discharge estimates and flow routing derived catchments can be used to build hourly hydrographs, the two methods are temporally incongruous and produce discharge estimates in small catchments that differ by several orders of magnitude. In the second part of the thesis, I contribute empirical insight into where moulins form and the hydrological implications of the resultant spatial organization of catchments. Using remotely sensed data on supraglacial lake distribution, bed elevation, ice thickness, surface velocity and strain rate, I show that moulins form predominantly in low velocity, high strain rate ice with adverse bed slopes. Moulins formed near moulin-drained lakes are typically located down-ice of the lake. The spatial distribution of moulins affects the physical characteristics of supraglacial catchments, including elevation, size, elongation, drainage network configuration and slope. This in turn impacts the temporal delivery of meltwater to the subglacial network. I use synthetic unit hydrograph theory based on catchment morphometrics to show that catchment diurnal hydrograph lag times in the study area vary by up to 11 hours. The hydrological implications of subglacial meltwater supply vary according to the configuration of the subglacial catchments, which vary temporally based on subglacial water pressure. Considering this additional level of complexity is a necessary next step in constraining the relationship between melt and ice flow dynamics. Errata available at: http://hdl.handle.net/2429/70921

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