Quantifying subglacial roughness and its link to glacial geomorphology and ice speed
The shape of subglacial bed topography, termed its roughness, is a recognised control on basal ice-flow. Although glaciologists have observed patterns of variations in ice speed over beds with different roughness values, the strength of this relationship has rarely been quantified, and measurements...
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| Format: | Thesis |
| Language: | unknown |
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2013
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| Online Access: | http://etheses.dur.ac.uk/7746/ http://etheses.dur.ac.uk/7746/1/prescottpw.pdf |
| Summary: | The shape of subglacial bed topography, termed its roughness, is a recognised control on basal ice-flow. Although glaciologists have observed patterns of variations in ice speed over beds with different roughness values, the strength of this relationship has rarely been quantified, and measurements of roughness are based on just a few methods. Moreover, the shape of topography can vary in a number of ways, but how this influences roughness and the quantification of roughness is largely unknown. This project investigates methods of measuring roughness, and how such measurements might be related to spatial patterns in ice speed in both contemporary and palaeo-settings. Roughness of ice-sheet beds has traditionally been summarised using spectral analysis. The first part of this projected was aimed at reviewing this method. The influence of the number of data points was explored by developing a new technique for re-digitising radio-echo sounding records, which remain the most extensive source of bed data from Antarctica. This yielded measurements with a resolution (c.250 m) eight-times higher than those used in previous work, and allowed assessment of roughness over short window lengths. Significantly, subjective decisions about, for example, the choice of window length can lead to differing results using spectral analysis. The second part of this project was, therefore, to identify and evaluate 36 alternative methods of quantifying roughness, many of which had never before been used to analyse subglacial beds. The project looked at the broader approach to quantifying roughness, exploring the benefits of 2D versus 3D techniques for investigating subglacial data. The relationship between roughness and ice speed was tested using these alternative techniques in isolation, but also in a combination. Indeed, the use of generalised linear models (GLMs) allowed the strength of this relationship to be quantified for the first time, and permitted the roughness variables most related to ice speed to be identified. Testing the ... |
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