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Title: Understanding the effect of seasonal variability on the structure of ice shelves and meltwater plumes
Author: MacMackin, Christopher
ISNI:       0000 0004 7653 8544
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2018
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Ice shelves are important to the climate system as they control the release of fresh water from ice sheets into the ocean, with consequences for sea level rise and ocean dynamics. Channels modifying basal melt rates and structural integrity have been observed inscribed in the undersides of some ice shelves. Observations indicate that some channels run in a direction transverse to ice flow and it has been suggested that these form due to seasonal variations in ocean properties. This thesis analyses the effect of seasonal variability on ice shelves and meltwater plumes in the underlying ocean. A linear perturbation analysis on vertically integrated ice and plume models showed that seasonal forcing of subglacial discharge or ice flux can generate small ripples melted into the base of the ice shelf. These ripples did not develop into overdeepened channels, but the ripples caused by ice flux appear similar to basal terraces observed underneath some ice shelves. Code was developed to run 1-D nonlinear simulations with the vertically-integrated equations, producing similar results to the linear case. However, runs neglecting hydrostatic pressure gradients exhibited a feedback causing ice flux-generated ripples to grow into small proto-channels. A horizontally-integrated plume model was derived, incorporating the Coriolis force and transverse plume flow into a 1-D model which agreed well with a 3-D ocean simulation. Coupling this horizontally-integrated plume with a co-evolving ice shelf prevented proto-channels from forming. It appears unlikely that subglacial discharge or ice flux variations can give rise to observed transverse channels. A new approach was developed to predict the evolution of internal radar reflectors observed within ice shelves, using vertically-integrated models of ice flow. It is hoped this approach might have applications for inverse modelling and data assimilation.
Supervisor: Wells, Andrew Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Geophysical Fluid Dynamics ; Glaciology ; Physics ; Mathematical Modelling