Browsing by Subject "Greenland Ice Sheet"
Now showing 1 - 2 of 2
- Results Per Page
- Sort Options
Item Geometric controls on the inland extent of dynamic thinning for Greenland Ice Sheet outlet glaciers(2018-08-03) Felikson, Denis; Bettadpur, Srinivas Viswanath, 1963-; Catania, Ginny A.; Bui, Tan; Dawson, Clinton; Chen, JingyiThe Greenland Ice Sheet has been losing mass at an accelerating rate since 2003, in part due to changes in ice sheet dynamics. As ocean-terminating outlet glaciers retreat, they initiate thinning that diffuses inland, causing dynamic mass loss from the ice sheet interior. Although outlet glaciers have undergone widespread retreat during the last two decades, the inland extent of thinning and, thus, the mass loss is heterogeneous between glacier catchments. There remains a lack of a unifying explanation of the cause of this heterogeneity and accurately projecting the sea-level rise contribution from the ice sheet requires improvement in our understanding of what controls the upstream diffusion of thinning, initiated by terminus retreat. In this dissertation, I use observations and modeling to identify limits to the upstream diffusion of dynamic thinning for ocean-terminating glaciers draining the Greenland Ice Sheet. I start by using diffusive-kinematic wave theory to describe the evolution of thinning and I calibrate a metric that identifies how far upstream a thinning perturbation can diffuse from glacier termini. This metric is calculable from the observed glacier bed and surface topography and I use it to predict inland thinning limits for the majority of Greenland's outlet glaciers. I find that inland thinning limits often coincide with subglacial knickpoints in bed topography. These are steep reaches of the bed that are located at the transition between the portion of the bed that is below sea level and the upstream portion that is above sea level. I use the predicted thinning limits to help identify individual glaciers that have the largest potential to contribute to sea-level rise in the coming century. Finally, I use higher-order numerical modeling to validate the predicted thinning limits from the first-order kinematic wave model, and to investigate the timing and magnitude of glacier mass loss over the coming century. I find that glaciers that have small ice fluxes but are susceptible to thin far into the interior of the ice sheet have the potential to contribute as much to sea-level rise as their higher-flux counterparts. These lower-flux glaciers are often not discussed in literature but will be significant contributors to sea-level rise by 2100.Item Spatial and temporal evolution of the glacial hydrologic system of the western Greenland ice sheet : observational and remote sensing results(2015-12) Andrews, Lauren Cristy; Catania, Ginny A.; Cardenas, Meinhard Bayani; Hoffman, Matthew J.; Jackson, Charles S.; Mohrig, DavidThe Greenland Ice Sheet is losing mass at an accelerating rate due to a combination of increased surface melting and changes in dynamical behavior, both of which are associated with changing climate. In the ablation zone, seasonal melting results in a dynamic ice-sheet response as supraglacial meltwater reaches the ice–bed interface via moulins and crevasses. Meltwater delivery to the bed increases subglacial water pressure and decreases basal traction, leading to regional ice acceleration. However, these processes and their future evolution are poorly constrained. An improved understanding of the complex relationship between the glacial hydrologic system and ice velocity will ultimately improve predictions of ice-sheet mass change. In this dissertation, I use a suite of techniques to quantify the response of the glacial hydrologic system to changes in melt supply on daily to inter-decadal timescales. Moulins represent the primary englacial connection between the ice surface and its bed. As such, they play a critical role in determining the location of subglacial channels in the ablation zone. I observe inter-decadal persistence in moulin locations, which can result in positive feedbacks that allow for rapid growth at the onset of the melt season and encourage persistence of subglacial channels. These observations suggest that inter-decadal variability in the relationship between supraglacial melt production and ice velocity is caused by altering the rate at which efficient subglacial drainage pathways develop. Further, my observations indicate that daily changes in ice velocity are mirrored by moulin water levels, but this pattern does not hold at seasonal timescales. This relationship suggests that the channelized portion of the subglacial hydrologic system adjusts rapidly to the available meltwater; therefore, long-term trends in ice velocity are the result of increasing hydrologic connectivity of poorly connected regions of the bed, lowering regional subglacial water pressure. Finally, the subglacial hydrologic system experiences variability on multiple timescales, some of which are not accounted for in existing models of this system. By modeling the mechanisms causing both diurnal to seasonal and changes in moulin water level, I further constrain the physical processes impacting mass change in land-terminating regions of the Greenland Ice Sheet.