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Modelling calving and sliding of Svalbard outlet glaciers: Spatio-temporal changes and interactions
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.ORCID iD: 0000-0002-0128-3386
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Future sea level rise associated to global warming is one of the greatest societal and environmental challenges of tomorrow. A large part of the contribution comes from glaciers and ice sheets discharging ice and meltwater into the ocean and the recent worldwide increase is worrying. Future predictions of sea level rise try to encompass the complex processes of ice dynamics through glacier modelling but there are still large uncertainties due to the lack of observations or too coarse parameterisation, particularly for processes occurring at the glacier interfaces with the bed (sliding) and with the ocean (calving). This thesis focuses on modelling these processes from two marine-terminating glaciers in Svalbard, Kronebreen and Tunabreen. By inverting three years of high temporal resolution time-series of surface velocities on Kronebreen, basal properties are retrieved with the ice flow model Elmer/Ice in Paper I. Results suggest that surface melt during the summer greatly influences the dynamics of the following season and that sliding laws for such glaciers should be adapted to local and global processes changing in space and time. The subglacial drainage system, fed by the surface melt, is modelled in Paper II during two melting seasons. Results show different configurations of efficient and inefficient drainage systems between years and the importance of using a sliding law dependent on spatio-temporal changes in effective pressure. The interaction with the ocean is incorporated in Paper III by combining a series of models, including an ice flow model, a plume model and a particle model for discrete calving and compares the output with observations. Results show the importance of glacier geometry, sliding and undercutting on calving rate and location. However, more observations and analytic methods are needed. Time-lapse imagery placed in front of Tunabreen have been deployed and a method of automatic detection for iceberg calving is presented in Paper IV. Results show the influence of the rising plume in calving and the front destabilisation of the local neighbourhood.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. , p. 82
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1606
Keywords [en]
cryospheric science, glacier modelling, time-lapse imagery, undercutting, sliding inversion, discrete particle model, calving model, subglacial hydrology, sliding law, automatic detection method, calving events size and frequency, ocean interaction, melt water runoff, ice dynamics, ice flow model
National Category
Geosciences, Multidisciplinary
Research subject
Earth Science with specialization in Physical Geography
Identifiers
URN: urn:nbn:se:uu:diva-334787ISBN: 978-91-513-0170-9 (print)OAI: oai:DiVA.org:uu-334787DiVA, id: diva2:1160673
Public defence
2018-01-24, Hambergsalen, Villavägen 16, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-12-22 Created: 2017-11-27 Last updated: 2018-03-08
List of papers
1. Basal dynamics of Kronebreen, a fast-flowing tidewater glacier in Svalbard: non-local spatio-temporal response to water input
Open this publication in new window or tab >>Basal dynamics of Kronebreen, a fast-flowing tidewater glacier in Svalbard: non-local spatio-temporal response to water input
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2017 (English)In: Journal of Glaciology, ISSN 0022-1430, E-ISSN 1727-5652, Vol. 63, no 242, p. 1012-1024Article in journal (Refereed) Published
Abstract [en]

We evaluate the variability in basal friction for Kronebreen, Svalbard, a fast-flowing tidewater glacier. We invert 3 years (2013–15) of surface velocities at high temporal resolution (generally 11 days), to estimate the changing basal properties of the glacier. Our results suggest that sliding behaviour of Kronebreen within a year is primarily influenced by changes in water input patterns during the meltwater season and basal friction is highly variable from a year to another. At present, models usually employ parameterisations to encompass the complex physics of glacier sliding by mathematically simulate their net effect. For such ice masses with strong seasonal variations of surface melt, the spatio-temporal patterns of basal friction imply that it is neither possible nor appropriate to use a parameterisation for bed friction that is fixed in space and/or time, at least in a timescale of a few years. Basal sliding may not only be governed by local processes such as basal topography or summer melt, but also be mediated by factors that vary over a larger distance and over a longer time period such as subglacial hydrology organisation, ice-thickness changes or calving front geometry.

Keywords
Arctic glaciology, glacier modelling, ice dynamics, ice velocity, subglacial processes
National Category
Physical Geography
Research subject
Earth Science with specialization in Physical Geography
Identifiers
urn:nbn:se:uu:diva-334293 (URN)10.1017/jog.2017.69 (DOI)000418852500007 ()
Available from: 2017-11-22 Created: 2017-11-22 Last updated: 2018-02-05Bibliographically approved
2. Modelled subglacial hydrology and basal sliding at Kronebreen, a tidewater glacier in Svalbard
Open this publication in new window or tab >>Modelled subglacial hydrology and basal sliding at Kronebreen, a tidewater glacier in Svalbard
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(English)Manuscript (preprint) (Other academic)
National Category
Geosciences, Multidisciplinary
Research subject
Earth Science with specialization in Physical Geography
Identifiers
urn:nbn:se:uu:diva-334778 (URN)
Available from: 2017-11-27 Created: 2017-11-27 Last updated: 2017-11-27
3. Effects of undercutting and sliding on calving: a global approach applied to Kronebreen, Svalbard
Open this publication in new window or tab >>Effects of undercutting and sliding on calving: a global approach applied to Kronebreen, Svalbard
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2018 (English)In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 12, p. 609-625Article in journal (Refereed) Published
Abstract [en]

In this paper, we study the effects of basal friction, sub-aqueous undercutting and glacier geometry on the calving process by combining six different models in an offline-coupled workflow: a continuum-mechanical ice flow model (Elmer/Ice), a climatic mass balance model, a simple sub-glacial hydrology model, a plume model, an undercutting model and a discrete particle model to investigate fracture dynamics (Helsinki Discrete Element Model, HiDEM). We demonstrate the feasibility of reproducing the observed calving retreat at the front of Kronebreen, a tidewater glacier in Svalbard, during a melt season by using the output from the first five models as input to HiDEM. Basal sliding and glacier motion are addressed using Elmer/Ice, while calving is modelled by HiDEM. A hydrology model calculates subglacial drainage paths and indicates two main outlets with different discharges. Depending on the discharge, the plume model computes frontal melt rates, which are iteratively projected to the actual front of the glacier at subglacial discharge locations. This produces undercutting of different sizes, as melt is concentrated close to the surface for high discharge and is more diffuse for low discharge. By testing different configurations, we show that undercutting plays a key role in glacier retreat and is necessary to reproduce observed retreat in the vicinity of the discharge locations during the melting season. Calving rates are also influenced by basal friction, through its effects on near-terminus strain rates and ice velocity.

National Category
Natural Sciences Geosciences, Multidisciplinary
Research subject
Earth Science with specialization in Physical Geography
Identifiers
urn:nbn:se:uu:diva-334771 (URN)10.5194/tc-12-609-2018 (DOI)000425729800002 ()
Available from: 2017-11-27 Created: 2017-11-27 Last updated: 2018-05-02Bibliographically approved
4. Automatic detection of calving events from time-lapse imagery at Tunabreen, Svalbard
Open this publication in new window or tab >>Automatic detection of calving events from time-lapse imagery at Tunabreen, Svalbard
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(English)Manuscript (preprint) (Other academic)
National Category
Geosciences, Multidisciplinary
Research subject
Earth Science with specialization in Physical Geography
Identifiers
urn:nbn:se:uu:diva-334776 (URN)
Available from: 2017-11-27 Created: 2017-11-27 Last updated: 2017-11-27

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Citation style
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