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Wuite, JanSpatial and temporal dynamics of three East Antarctic outlet glaciers and their floating ice tongues
Doctor of Philosophy, The Ohio State University, 2006, Geological Sciences
Observations show that some glaciers in Greenland and Antarctica undergo rapid changes in flow velocity and thickness. There is concern about the implications for global sea levels and ocean circulation. Part of the changes has been ascribed to changes in glacier dynamics. Measuring velocity and velocity gradients are first steps in studying their dynamics and possible response to climatic changes. With the RADARSAT-1 Antarctic Mapping Project (RAMP) a great opportunity arose to derive flow velocity of Antarctica’s glaciers remotely. This study uses RAMP imagery to derive ice flow velocity and, in combination with other datasets, to study spatial and temporal fluctuations in velocity and stress fields of selected Antarctic glaciers. The derived high-resolution surface velocity maps form an important benchmark for gauging possible changes in velocity and dynamics. The maps are derived using pre-established feature tracking techniques that we improved and streamlined in order to extract as much velocity data as possible. To determine important flow governing forces we use force-budget theory. We include a detailed error analysis and investigate the implications of a recently established flow law on derived stresses. The investigations of our study areas suggest that flow has been rather constant over decadal timescales. Based on this we infer that stress fields have not changed significantly either, permitting combinations of various data sets to optimize the velocity field in order to study dynamics in greater detail then previously possible. We find that the relative contribution of side drag declines along the fjords, but demonstrate that, once they leave the valley walls, the glaciers are not immediately free floating ice shelves. Measurements show that ice tongues spread faster in the across flow direction than the along flow direction for a considerable length. In addition there appears to be some lateral drag, once a glacier leaves the coast, which could be associated with sub-surface valley walls or an adjacent ice shelf. This could lead to an increase in along flow creep if the ice tongue were to break off. Finally we conclude that ice tongues are important, because they can provide clues to past ice sheet behavior and fluctuations.

Committee:

Kenneth Jezek (Advisor)

Keywords:

Glaciology; Remote Sensing; Antarctica; Glacier dynamics

Walsh, Kaitlin M.Changes in the Marine-Terminating Glaciers of Central East Greenland, 2000-2010, and Potential Connections to Ocean Circulation
Master of Science, The Ohio State University, 2011, Geological Sciences
Outlet glaciers and ice caps on the periphery of the Greenland Ice Sheet have been observed to be extremely sensitive to climate. The limited studies conducted on the marine-terminating glaciers of eastern Greenland’s Geikie Plateau and Blosseville Coast suggest exceptionally rapid rates of mass loss and short-term variability in ice dynamics. This study is targeted at a region of central east Greenland for which GRACE mass-anomaly observations show substantial recent mass-loss since its launch in March 2002. Additionally, glaciers in this region terminate into Denmark Straight, which is a thermodynamic transition zone between the Arctic and North Atlantic oceans. Extensive glacial change has been more pronounced through the Denmark Straight and south of the straight, which supports the hypothesis that ocean dynamics, specifically the Irminger Current and East Greenland Current, are supporting increased melt at the ice-ocean interface. It is possible that an appreciable amount of melt and ice loss south of Kangerdlugssuaq is occurring as a result of warmer subpolar water flowing into glacial fjords. We present changes to 38 marine-terminating glaciers as observed using Landsat-7 ETM+ imagery to develop a time series of changing front positions and flow speeds of these glaciers from 2000 to 2010. ASTER DEMs were used to quantify elevation change and thinning. Additionally, we examine sea surface temperatures at five sites along the east Greenland coast to identify possible correlations between warming of the sea surface and increased melt at the glacier termini.

Committee:

Ian Howat, PhD (Advisor); Bryan Mark, PhD (Committee Member); Carolyn Merry, PhD (Committee Member)

Subjects:

Earth; Geophysical; Remote Sensing

Keywords:

Greenland; glacier dynamics

Enderlin, Ellyn MaryObservations and Modeling of Greenland Outlet Glacier Dynamics
Doctor of Philosophy, The Ohio State University, 2013, Geological Sciences
Increased mass loss from the Greenland Ice Sheet due to rapid changes in tidewater outlet glacier dynamics has the potential to substantially increase sea level within this century, yet the external factors triggering these changes and the internal controls that govern the glaciers' dynamic response are poorly understood. The observational and numerical modeling studies presented herein focus on the tidewater outlet glaciers that drain the Greenland Ice Sheet with the aim of improving the current understanding of regional variability in dynamic change. Using remotely-sensed observations of glacier surface elevations and speeds, we find that dynamic thinning initiated near the termini of the majority of the glaciers draining the northwestern portion of the Greenland Ice sheet prior to the detection of regional mass loss acceleration by GRACE and GPS in ~2005. The timing and magnitude of thinning varied widely between glaciers such that no clear regional signal could be discerned. The lag in the detection of regional mass loss acceleration is likely due to the time required for dynamic changes to propagate out of the narrow outlets and across the broad ice sheet interior. Although it is likely that dynamic acceleration of tidewater outlet glacier throughout Greenland are triggered by changes in oceanographic conditions, temporal changes in submarine melt rates beneath the floating tongues of 13 glaciers located throughout Greenland were uncorrelated with dynamic changes observed between 2000 and 2010. Our first-order estimates indicate, however, that submarine melt rates reached values of up to ~3 m/d and accounted for 5-85% of the volume lost from the floating ice tongues during the study period. In order to determine whether variations in glacier shape can at least partially explain the observed variability in glacier dynamics, we simulate the transient behavior of 9 glaciers with idealized geometries using a width- and depth-integrated numerical ice flow model (i.e., 1D flowline model). The modeling results indicate that for glaciers draining the same interior catchment, wider glaciers and those that overlie deeper basal depressions are more likely to undergo rapid, unstable retreat years after the onset of an applied perturbation. These results not only indicate that shape differences may help explain intra-regional variability in glacier behavior but also that uncertainty in glacier shape can strongly influence predictions of future dynamic change. Confidence in prognostic ice flow modeling is further limited by the influence of parameter uncertainty on predictions of future dynamic change. Model simulations performed using a non-unique combination of ice rheology and basal sliding parameter values can reproduce similar steady-state glacier configurations; however, once perturbed, the response of the simulated glaciers varies widely. Taken together, the results of our studies indicate that although the observed dynamic changes are likely triggered by changes in external forcing, the dynamic response of each glacier is largely determined by internal controls (i.e., shape, rheology, basal sliding, etc.). Thus, uncertainty in the parameterizations of these internal controlling factors will strongly limit our ability to confidently predict future dynamic change in the absence of improved observational constraints.

Committee:

Ian Howat (Advisor); Lonnie Thompson (Committee Member); W. Berry Lyons (Committee Member); Michael Durand (Committee Member)

Subjects:

Climate Change; Geophysics; Remote Sensing

Keywords:

glacier dynamics; Greenland; tidewater glaciers; ice flow modeling; submarine melting; dynamic sensitivity

Markus, Julie T.Flow Dynamics of a Soft-Bedded Glacier in Southeast Iceland During Basal Sliding Events
Master of Science, The Ohio State University, 2011, Geological Sciences
The purpose of this study is to determine how glacier motion and stresses vary spatially and temporally in order to clarify weaknesses in current understanding of soft-bedded glacier motion using data collected from Breiðamerkurjökull, Iceland. The dynamics of ice motion are the most substantial source of uncertainty in current models of future ice sheet mass-loss and resulting sea level rise. Currently, there is a general lack of quantitative understanding of how glacial basal conditions, such as the hydrology and till rheology at the bed, control ice motion. This study focuses on the examination of high spatial and temporal resolution surface velocities retrieved from a 12-station GPS grid in the melt seasons of 2009 and 2010 to evaluate the variation of glacial motion and strain rates over time on Breiðamerkurjökull. The first specific objective is to identify any short-term velocity variations. The second is to use the surface motion data to calculate strain rates and other components of the force budget. The third objective is to explain the variations in velocity and force budget components while taking into account glaciomorphic features of the bed. Results reveal five distinct periods of increased surface motion, termed sliding events, corresponding to periods of rainfall and/or increased temperatures during the 2009 and 2010 melt seasons. Along-flow strain rates show extension upglacier and compression downglacier during sliding events. The force budget solution indicates that upglacier, basal drag decreases substantially during speed-up events and cannot resist the local driving stress, most likely indicating pressurization of a distributed subglacial drainage system. The excess driving stress is then transferred downglacier, through gradients in longitudinal stress, to a more efficiently draining terminus where water pressures are lower and basal drag is sufficient to support the excess stress. The results demonstrate that the till at the terminus accommodates the excess stress, possibly through extensive grain bridging and dilatant hardening or by a relocation of stress to bedrock bumps during sliding events. This buttressing role of the till-bedded margin in resisting increased upglacier sliding, likely over bedrock, is novel and counter to the prevailing view of soft beds, with implications for simulating the evolution of past and current ice masses.

Committee:

Dr. Ian Howat (Advisor); Dr. Dorota Grejner-Brzezinska (Committee Member); Dr. Michael Bevis (Committee Member)

Keywords:

glacier dynamics; force budget; glacier sliding events; soft-bedded glacier