Modelling the transition zone of marine ice sheets.
An investigation of the flow in the transition zone of marine ice sheet is con ducted, and is motivated by recent satellite observations of rapid changes in the West Antarctic Ice Sheet. This region may undergo prolonged retreat as a consequence of changes in sea level or climate. To gain insight in...
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| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
| Published: |
University of London
2007
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| Online Access: | https://discovery.ucl.ac.uk/id/eprint/1445726/1/U593050%20Redacted.PDF https://discovery.ucl.ac.uk/id/eprint/1445726/ |
| Summary: | An investigation of the flow in the transition zone of marine ice sheet is con ducted, and is motivated by recent satellite observations of rapid changes in the West Antarctic Ice Sheet. This region may undergo prolonged retreat as a consequence of changes in sea level or climate. To gain insight into ice flow from a grounded ice sheet into a floating ice shelf, this thesis uses scale anal ysis and perturbation methods to solve analytically idealized ice sheet and ice shelf flows. In the transition zone, this 'shallow ice' approximation does not hold and cannot be used to simplify the governing equations. This transition zone problem does not appear to have an analytical solution, so a numeri cal analysis is necessary for gaining an understanding of the behavior of this region. The thesis presents a numerical model developed to solve the full steady-state Stokes equations on a two-dimensional domain, and to evaluate the position of the free surfaces. In the finite element model, ice density and temperature are treated as spatially homogeneous, ice rheology is considered linear, and the position of the flotation point is fixed. The hypothesis for ma rine ice sheet instability rests upon sea level controlling mass discharge at the flotation point. To test this hypothesis, we seek steady-state solutions for a range of mass fluxes, sea levels, and flow constrictions or back pressure. We demonstrate that for a given sea level, the number of steady-state solutions can be restricted by verifying that the simulations satisfy two contact inequal ities. The contact conditions reflect that for physically acceptable solutions, the compressive normal stress at the base of the grounded ice should exceed water pressure, and that the shelf surface should not get into contact with the bedrock. Violation of either conditions would result in grounding line migra tion. We find that when ice slides over the bedrock and for a given sea level, only one combination of mass flux, grounding line thickness and back pressure, satisfy the ... |
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