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Hydrology and Bed Topography of the Greenland Ice Sheet: Last known surroundings
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The increased temperatures in the Arctic accelerate the loss of land based ice stored in glaciers. The Greenland Ice Sheet is the largest ice mass in the Northern Hemisphere and holds ~10% of all the freshwater on Earth, equivalent to ~7 metres of global sea level rise. A few decades ago, the mass balance of the Greenland Ice Sheet was poorly known and assumed to have little impact on global sea level rise. The development of regional climate models and remote sensing of the ice sheet during the past decade have revealed a significant mass loss. To monitor how the Greenland Ice Sheet will affect sea levels in the future requires understanding the physical processes that govern its mass balance and movement. In the southeastern and central western regions, mass loss is dominated by the dynamic behaviour of ice streams calving into the ocean. Changes in surface mass balance dominate mass loss from the Greenland Ice Sheet in the central northern, southwestern and northeastern regions. Little is known about what the hydrological system looks like beneath the ice sheet; how well the hydrological system is developed decides the water’s impact on ice movement. In this thesis, I have focused on radar sounding measurements to map the subglacial topography in detail for a land-terminating section of the western Greenland Ice Sheet. This knowledge is a critical prerequisite for any subglacial hydrological modelling. Using the high-resolution ice thickness and bed topography data, I have made the following specific studies: First, I have analysed the geological setting and glaciological history of the region by comparing proglacial and subglacial spectral roughness. Second, I have analysed the subglacial water drainage routing and revealed a potential for subglacial water piracy between adjacent subglacial water catchments with changes in the subglacial water pressure regime. Finally, I have looked in more detail into englacial features that are commonly observed in radar sounding data from western Greenland. In all, the thesis highlights the need not only for accurate high-resolution subglacial digital elevation models, but also for regionally optimised interpolation when conducting detailed hydrological studies of the Greenland Ice Sheet.

Abstract [sv]

De ökade temperaturerna i Arktis påskyndar förlusten av landbaserad is lagrad i glaciärer och permafrost. Grönlands inlandsis är den största ismassan på norra halvklotet och lagrar ca 10% av allt sötvatten på jorden, vilket motsvarar ca 7 meter global havsnivåhöjning. För ett par decennier sedan var inlandsisens massbalans dåligt känd och antogs ha liten inverkan på dagens havsnivåhöjning. Utvecklingen av regionala klimatmodeller och satellitbaserad fjärranalys av inlandsisen har under de senaste decenniet påvisat en betydande massförlust. För att förutse vilken inverkan inlandsisen har på framtida havsnivåhöjningar krävs en förståelse för de fysikaliska processerna som styr dess massbalans och isrörelse. I de sydöstra och centrala västra delarna av inlandsisen domineras massförlusten av dynamiska processer i isströmmar som kalvar ut i havet. Massförlusten i de centrala norra, sydvästra och nordöstra delarna domineras av isytans massbalans. Ytterst lite är känt om hur det hydrologiska systemet ser ut under inlandsisen; hur väl det hydrologiska systemet är utvecklat avgör vattnets påverkan på isrörelsen. I denna doktorsavhandling har jag använt markbaserade radarmätningar för att kartlägga den subglaciala topografin för en del av den västra landbaserade inlandsisen. Denna kunskap är en viktig förutsättning för att kunna modellera den subglaciala hydrologin. Med hjälp av rumsligt högupplöst data över istjockleken och bottentopografin har jag gjort följande specifika studier: Först har jag analyserat de geologiska och glaciologiska förhållandena i regionen genom att jämföra proglacial och subglacial spektralanalys av terrängens ytojämnheter. Sedan har jag analyserat den subglaciala vattenavrinningen och påvisat en potential för att avrinningsområdena kan ändras beroende på vattentryckförhållandena på botten. Slutligen har jag tittat mer i detalj på englaciala radarstrukturer som ofta observerats i radardata från västra Grönland. Sammanfattningsvis belyser avhandlingen behovet av inte bara noggranna rumsligt högupplösta subglaciala digitala höjdmodeller, utan även regionalt optimerad interpolering när detaljerade hydrologiska studier ska utföras på Grönlands inlandsis.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 59 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1265
Keyword [en]
climate change, Greenland Ice Sheet, radio-echo sounding, digital elevation models, ice thickness, bed topography, spectral analysis, roughness, subglacial hydrology, water piracy, englacial features, drainage catchments, meltwater runoff, ice dynamics
Keyword [sv]
klimatförändringar, Grönlands inlandsis, markbaserad radar, digitala höjdmodeller, istjocklek, bottentopografi, spektralanalys, subglacial hydrologi, englaciala strukturer, avrinningsområden, isdynamik
National Category
Physical Geography
Identifiers
URN: urn:nbn:se:uu:diva-259076ISBN: 978-91-554-9280-9 (print)OAI: oai:DiVA.org:uu-259076DiVA: diva2:843111
Public defence
2015-09-11, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2015-08-20 Created: 2015-07-26 Last updated: 2016-02-12
List of papers
1. High-resolution ice thickness and bed topography of a land-terminating section of the Greenland Ice Sheet
Open this publication in new window or tab >>High-resolution ice thickness and bed topography of a land-terminating section of the Greenland Ice Sheet
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2014 (English)In: Earth System Science Data, ISSN 1866-3508, E-ISSN 1866-3516, Vol. 6, no 2, 331-338 p.Article in journal (Refereed) Published
Abstract [en]

We present ice thickness and bed topography maps with a high spatial resolution (250–500 m) of a land-terminating section of the Greenland Ice Sheet derived from ground-based and airborne radar surveys. The data have a total area of ~12 000 km2 and cover the whole ablation area of the outlet glaciers of Isunnguata Sermia, Russell, Leverett, Ørkendalen and Isorlersuup up to the long-term mass balance equilibrium line altitude at ~1600 m above sea level. The bed topography shows highly variable subglacial trough systems, and the trough of Isunnguata Sermia Glacier is overdeepened and reaches an elevation of ~500 m below sea level. The ice surface is smooth and only reflects the bedrock topography in a subtle way, resulting in a highly variable ice thickness. The southern part of our study area consists of higher bed elevations compared to the northern part. The compiled data sets of ground-based and airborne radar surveys cover one of the most studied regions of the Greenland Ice Sheet and can be valuable for detailed studies of ice sheet dynamics and hydrology. The combined data set is freely available at doi:10.1594/pangaea.830314.

National Category
Physical Geography
Research subject
Earth Science with specialization in Physical Geography
Identifiers
urn:nbn:se:uu:diva-233536 (URN)10.5194/essd-6-331-2014 (DOI)000356933900005 ()
Available from: 2014-10-07 Created: 2014-10-07 Last updated: 2017-12-05Bibliographically approved
2. Spectral roughness and glacial erosion of a land-terminating section of the Greenland Ice Sheet
Open this publication in new window or tab >>Spectral roughness and glacial erosion of a land-terminating section of the Greenland Ice Sheet
2015 (English)In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 238, 149-159 p.Article in journal (Refereed) Published
Abstract [en]

Spectral roughness offers a significant potential for understanding the evolution of glaciated landscapes. Here, we present the first roughness study combining a high-resolution (250 to 500 m) DEM of a large land-terminating section (12,000 km2) of the Greenland Ice Sheet with the topography of the proglacial area. Subglacial roughness shows a directional dependence with consistently lower values in the ice flow direction compared to the across–flow direction. We find a correlation between low basal roughness, fast ice flow, and subglacial troughs. The northern part of the subglacial study area has an undulating topography with variable roughness, resembling the landscape in the proglacial area. In this area, there is a glacially eroded, overdeepened trough with bed elevations 510 m below sea level, consistent with warm ice and a well-lubricated bed. The southern part of the subglacial study area has higher bed elevations and higher roughness than the northern part, possibly because the bedrock consists of hard granitic gneiss as in the adjacent proglacial area. The subglacial troughs, which have been eroded to various extents, are aligned with geological weakness zones suggesting a preglacial origin. In general, there is a major geological control on the distribution of bed variability.

National Category
Geophysics Geology
Research subject
Earth Science with specialization in Physical Geography
Identifiers
urn:nbn:se:uu:diva-247641 (URN)10.1016/j.geomorph.2015.02.027 (DOI)000355036000013 ()
Available from: 2015-03-23 Created: 2015-03-23 Last updated: 2017-12-04Bibliographically approved
3. Subglacial water drainage, storage, and piracy beneath the Greenland Ice Sheet
Open this publication in new window or tab >>Subglacial water drainage, storage, and piracy beneath the Greenland Ice Sheet
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2015 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 18, 7606-7614 p.Article in journal (Other academic) Published
Abstract [en]

Meltwater drainage across the surface of the Greenland Ice Sheet (GrIS) is well constrained by measurements and modeling, yet despite its critical role, knowledge of its transit through the subglacial environment remains limited. Here we present a subglacial hydrological analysis of a land-terminating sector of the GrIS at unprecedented resolution that predicts the routing of surface-derived meltwater once it has entered the basal drainage system. Our analysis indicates the probable existence of small subglacial lakes that remain undetectable by methods using surface elevation change or radar techniques. Furthermore, the analysis suggests transient behavior with rapid switching of subglacial drainage between competing catchments driven by seasonal changes in the basal water pressure. Our findings provide a cautionary note that should be considered in studies that attempt to relate and infer future response from surface temperature, melt, and runoff from point measurements and/or modeling with measurements of proglacial discharge and ice dynamics.

Keyword
Greenland ice sheet; ice sheet hydrology; ice sheet dynamics
National Category
Physical Geography
Identifiers
urn:nbn:se:uu:diva-258786 (URN)10.1002/2015GL065393 (DOI)000363412400046 ()
Available from: 2015-07-20 Created: 2015-07-20 Last updated: 2017-12-04Bibliographically approved
4. Origin of englacial features in radio-echo sounding data from the Greenland Ice Sheet
Open this publication in new window or tab >>Origin of englacial features in radio-echo sounding data from the Greenland Ice Sheet
(English)Manuscript (preprint) (Other academic)
National Category
Geophysics Physical Geography
Identifiers
urn:nbn:se:uu:diva-258787 (URN)
Available from: 2015-07-20 Created: 2015-07-20 Last updated: 2015-10-01

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