High Arctic submarine glaciogenic landscapes: their formation and significance

Time: April 20 2016, 10h00
Place: William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm,
http://su.diva-portal.org/smash/get/diva2:907168/FULLTEXT03.pdf

Supervisor: Richard Gyllencreutz
Co-supervisor: Martin Jakobsson

Opponent: professor Haflidi Haflidason, Department of Earth Science, University of Bergen, Norway

Examining committee:
Docent Boris Dorschel, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Tyskland
Professor Clas Hättestrand, Department of Physical Geography, Stockholm University
Docent Mona Henriksen, Department of Environmental Sciences, Norwegian University of Life Sciences, Norge

Reserve: Docent Thomas Andrén, School of Natural Science, Technology and Environmental Studies, Södertörn University, Stockholm

Abstract
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.

 

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