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High resolution mapping of offshore and onshore glaciogenic features in metamorphic bedrock terrain, Melville Bay, northwestern Greenland
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
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Number of Authors: 7
2015 (English)In: Geomorphology, ISSN 0169-555X, E-ISSN 1872-695X, Vol. 250, 29-40 p.Article in journal (Refereed) Published
Abstract [en]

Geomorphological studies of previously glaciated landscapes are important to understand how ice sheets and glaciers respond to rapidly changing climate. Melville Bay, in northwestern Greenland, contains some of the most sensitive but least studied ice sheet sectors in the northern hemisphere, where the bathymetric knowledge previously was restricted to a few sparsely distributed single beam echo soundings. We present here the results of high-resolution, geomorphological mapping of the offshore and onshore landscapes in Melville Bay using multibeam sonar and satellite data, at 5- and 10-m resolutions respectively. The results show a similar areally-scoured bedrock-dominated landscape with a glacially modified cnoc-and-lochan morphology on the inner shelf (150-500 m depth) and on the nearby exposed coast. This is manifested by the presence of U-shaped troughs, moutonee-type elongated landforms, stoss-and-lee forms, and streamlined features. The submarine landscape shows features that are characteristic of bedrock in folded, faulted, and weathered metamorphic terrain, and, to a lesser extent, glacially molded bedforms; while coastal landforms exhibit higher relief, irregular-shaped basins, and more subdued fracture valleys. Although generally similar, the onshore and offshore landscapes contain examples of distinctly different landform patterns, which are interpreted to reflect a longer exposure to long-term deep weathering as well as to more recent periglacial weathering processes on land. The spatial variability in the distribution of landforms across the landscape in both study areas is mostly attributed to differences in lithological properties of the bedrock. The lack of sediment cover on the inner shelf is likely a result of a capacity for sediment erosion and removal by the West Greenland Current flowing northward over the area in combination with limited sediment supply from long sea ice-cover seasons. The distribution and orientation of the landforms in the offshore part indicate ice movement toward the NW, and suggests that this area acted as a tributary or onset region for the major paleo ice stream that formed the present day Melville Bay Trough.

Place, publisher, year, edition, pages
2015. Vol. 250, 29-40 p.
Keyword [en]
Melville Bay, northwest Greenland, Glacial erosional landforms, High-resolution mapping, Combined onshore-offshore mapping
National Category
Earth and Related Environmental Sciences
Research subject
Marine Geology
Identifiers
URN: urn:nbn:se:su:diva-124161DOI: 10.1016/j.geomorph.2015.08.011ISI: 000364266800003OAI: oai:DiVA.org:su-124161DiVA: diva2:889248
Available from: 2015-12-22 Created: 2015-12-15 Last updated: 2016-02-26Bibliographically approved
In thesis
1. High Arctic submarine glaciogenic landscapes: their formation and significance
Open this publication in new window or tab >>High Arctic submarine glaciogenic landscapes: their formation and significance
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is focused on studies of glacial and slope morphology in the high Arctic of western Greenland shelf and the Molloy Hole seafloor spreading area, based on high-resolution acoustic methods and other geophysical data. The main purpose is to improve our understanding of glacial dynamics and associated processes in the marginal region of a large marine-terminating ice sheet. Newly acquired data, together with existing datasets have been compiled to create bathymetric models, which were used to study the seafloor landscape and its preserved record of glacial and sedimentary processes. The new bathymetric models were used with novel processing tools combined with seismic profiles, sub-bottom profiles and overlays of geological- and gravimetric maps to describe the observed landforms and interpret causal relationships. The main conclusions are:

1)   The underlying geology is an important control on the cross-shelf trough (CST) dimensions in western Greenland. This is likely due to the influence of underlying geology to the frictional resistance of the ice flow over the basement rock. Our observations show that ice streaming in areas with basaltic bed-types cause minimal over-deepening of the main trunk of the trough, which also has weaker lateral boundaries allowing the ice stream to shift flow direction more easily. CSTs on the Cenozoic-Mesozoic sedimentary basins indicate a stronger eroding and more focused paleo-ice streams.

2)   Bedrock lithology has an important part in controlling the location of the head-to-trough transition in CSTs of western Greenland. The areas where the head’s network of channels converges to form the main trunk of the trough are mostly located on the boundary from crystalline to sedimentary bedrock. These areas are also marked by distinct over-deepenings.

3)   Preglacial conditions such as faults/fractures and lithological properties of the basement rocks in western Greenland served as an important control on the erosional potential of the glacial processes, particularly on a local scale. Faults and fractures have led to the topographic steering of the ice flow that causes further excavation and erosion of the bed, while uneven erosion patterns, based on differences in glacial morphological features, is observed between areas of adjacent bedrocks with different lithology.

4)   The occurrence of trough mouth fans is suggested to be controlled mainly by the shelf width, which governs the glacial flow length along available sediment sources. It is also controlled by the continental slope steepness, which may be too steep for sediment fans to accumulate, or may cause slope failure which eventually transports the sediments to the deep basin.

5)   The maximum ice extent in west Greenland extended towards the shelf edge. Geomorphological evidence of ice margin standstills and slow retreat (grounding zone wedges and transverse moraines) in some areas reveal a multi-stage deglaciation process.

6)   The view of a highly dynamic paleo-Greenland ice sheet is supported by the presence of a large number of CSTs which hosted ice streams, and evidence of ice stream flow-switching throughout one or several glaciations.

7)   The influence of glacial sedimentary processes extends into the deepest areas of the Arctic Ocean. A submarine landslide, here termed the Molloy Slide, has been described in the Molloy Hole in the Davis Strait between Greenland and Svalbard. This slide was likely caused by massive glacial sediment deposition along the west Svalbard margin.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2016. 34 p.
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 360
Keyword
High Arctic, GrIS, marine geophysics, glaciogenic landscapes, ice streams, submarine slides
National Category
Geology
Research subject
Marine Geology
Identifiers
urn:nbn:se:su:diva-127165 (URN)978-91-7649-367-0 (ISBN)
Public defence
2016-04-20, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: Manuscript.

Available from: 2016-03-28 Created: 2016-02-26 Last updated: 2016-04-08Bibliographically approved

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