Flow characteristics of the Northeast Greenland Ice Stream

In recent years, increasing global temperatures have been shown to be causing the widespread shrinking of ice sheets and glaciers. In particular, rates of ice mass loss from the Greenland Ice Sheet have been accelerating, with around 50% of this mass imbalance being attributed to the dynamical discharge of fast-flowing ice streams and outlet glaciers to the ocean. In order to quantify and predict the future changes of ice sheet mass loss, the accurate representation of ice dynamics in ice sheet models is required. Specifically, the subglacial processes which underpin the fast flow of ice streams are poorly understood, in addition to the temporal and spatial stability of ice streams, which are central factors of the dynamic behaviour of past, present, and future ice sheets. This thesis explores the impacts of subglacial topography and basal conditions on the ice flow dynamics of Greenland’s largest ice stream (the Northeast Greenland Ice Stream; NEGIS), through the analysis of radio-echo sounding data. My focus is on the interactions between subglacial geomorphology and ice flow dynamics, to provide deeper insight into the processes which govern this fast-flowing outlet of the Greenland Ice Sheet and its evolution, as well as the formational processes of subglacial topography on multiple spatial scales. Here, I find that the basal conditions and subglacial geomorphology of the NEGIS evolve spatially downstream, and are more heterogenous than previously thought, which gives insight into the topographic and geologic controls on the NEGIS and provides new constraints on the subglacial geology. The change from upstream regions of softer sediment to rougher, hard bedrock downstream, as well as a trough channelling the ice flow, is likely to enable its propagation so far into the interior of the ice sheet. In addition, the finding of mega-scale glacial lineations (MSGLs) at the onset of the NEGIS was made possible with swath radar imaging, which produces an unprecedentedly high-resolution Digital Elevation Model of the subglacial bed. The presence of MSGLs beneath relatively slow ice flow velocities (<60 m yr-1), also places a new boundary condition on their formational processes, and raises questions surrounding their use as an indicator of very high (>100 m yr-1) ice flow velocities when reconstructing palaeo-ice sheets. This illustrates the importance of high-resolution mapping of the ice base, in order to understand both past ice flow, and the in-situ formation of subglacial landforms.