Bingham, Robert

Hulton, Nick

Davies, Damon

Natural Environment Research Council (NERC)

2018-07-23T10:34:46Z

2018-07-23T10:34:46Z

2018-07-03

Ice streams are fast flowing outlet glaciers through which over 90% of the ice stored within the Antarctic Ice Sheet drains. The dynamic behaviour of ice streams is therefore crucial in controlling the mass balance of the ice sheet. Over the past few decades, Antarctica has been losing mass. Much of this mass loss has been focussed around coastal regions of the Antarctic Ice Sheet. Some of the most dramatic changes such as grounding-line retreat, acceleration and surface elevation change have been observed in Pine Island Glacier (PIG) and its neighbouring ice streams. This is of particular concern because these ice streams account for 10% of the discharge from the west Antarctic Ice Sheet and therefore have the potential to contribute significantly to global sea-level rise. One of the key challenges in accurately forecasting this future sea-level rise is improving understanding of processes occurring at the beds of ice streams. This requires detailed knowledge of the properties and dynamics of the bed. This thesis aims to address this knowledge gap by investigating the spatial and temporal characteristics of the bed of PIG using high-resolution geophysical data acquired in its trunk and tributaries and beneath the ice shelf. The thesis begins by analysing radar-derived high-resolution maps of subglacial topography. These data show a contrasting topography across the ice-bed interface. These diverse subglacial landscapes have an impact on ice flow through form drag, controlled by the size and orientation of bedrock undulations and protuberances. The next chapter provides a quantitative analysis of these landscapes using Fast Fourier analysis of subglacial roughness. This analysis investigates the roughness signature of subglacial bedforms and the how the orientation and wavelength of roughness elements determine their correlation with ice dynamic parameters. The slow-flowing inter-tributary site is found to have a distinct signature comparable to “ribbed” patterns of modelled basal shear stress and transverse “mega rib” bedforms. Roughness oriented parallel to ice flow with wavelengths approaching mean ice thickness are found to have the highest correlation with ice dynamic parameters. The temporal stability of PIG is analysed using repeat radar measurements. No significant change is observed over a period of 3-6 years with no evidence of rapid erosion or the evolution of subglacial bedforms as observed in previous repeat measurements of ice-stream beds elsewhere in Antarctica. This suggests that the widespread deforming till layer detected in extensive seismic reflection surveys is in steady state. Lastly, the thesis explores geomorphological evidence of twentieth-century grounding-line retreat beneath PIG Ice Shelf using high-resolution geophysical data acquired from autonomous underwater vehicle surveys. Evidence of erosion, deposition, meltwater flow and post-glacial modification is observed in fine detail. The observed distribution of sediment supported previous surveys indicating a geological transition coinciding with the ridge that acted as a former stable grounding-line location. Metre-scale resolution images of recently deglaciated ice stream beds were found to reveal bedforms that are not detectable with traditional offshore bathymetric surveys. Together these findings reveal the role of short wavelength topography as both an influence on, and product of fast ice stream flow. It also highlights the spatial diversity of subglacial environments and the need to focus future research on tying detailed observations of ice-stream beds with knowledge of basal properties over time.

http://hdl.handle.net/1842/31399

en

The University of Edinburgh

The University of Edinburgh. College of Science and Engineering

Bingham, R.G., Vaughan, D.G., King, E.C., Davies, D., Cornford, S.L., Smith, A.M., Arthern, R.J., Brisbourne, A.M., De Rydt, J., Graham, A.G., Spagnolo, M., Shean, D.E (2017). Diverse landscapes beneath Pine Island Glacier influence ice flow. Nature communications, 8(1), doi:10.1038/s41467-017-01597-y

Davies, D., Bingham, R. G., King, E. C., Smith, A. M., Brisbourne, A. M., Spagnolo, M., Graham, A. G. C., Hogg, A. E., and Vaughan, D. G. (2017). How dynamic are ice-stream beds?, The Cryosphere, 12, pp.1615-1628 https://doi.org/10.5194/tc-12-1615-2018.

Davies, D., Bingham, R.G., Graham, A.G.C., Spagnolo, M., Dutrieux, P., Vaughan, D.G., Jenkins, A. and Nitsche, F.O., (2017). High-resolution sub-ice-shelf seafloor records of twentieth century ungrounding and retreat of Pine Island Glacier, West Antarctica. Journal of Geophysical Research: Earth Surface, 122(9), pp.1698-1714.

Brisbourne, A. M., A. M. Smith, D. G. Vaughan, E. C. King, D. Davies, R. G. Bingham, E. C. Smith, I. J. Nias, and S. H. R. Rosier (2017), Bed conditions of Pine Island Glacier, West Antarctica, Journal of Geophysical Research: Earth Surface, 122(1), 419–433, doi: 10.1002/2016JF004033, 2016JF004033.

glaciology

geophysics

geomorphology

radar

Antarctica

ice-sheet

subglacial

Nature and dynamics of ice-stream beds: assessing their role in ice-sheet stability

Thesis or Dissertation

Doctoral

PhD Doctor of Philosophy