The evolution and dynamic behaviour of the Northern Uummannaq Ice Stream System, West Greenland

Abstract

This thesis considers the evolution and dynamic behaviour of the northern Uummannaq Ice Stream System (UISS), a large ice stream which extended to the Greenland shelf edge during the Last Glacial Maximum (LGM). The Uummannaq region has been shown to be dominated by areas of selective linear erosion (SLE) and areal scour. Over multiple glacial cycles, enhanced by favourable geology and uplift, SLE controlled the formation of a confluent fjord system which triggered the onset and development of the UISS. At the LGM, northern UISS ice thicknesses reached 1400-1968 m a.s.l., comparable to data from the southern UISS. However, in the north, thicknesses were not sufficient to overtop fjord confines, with ice flow remaining topographically controlled.
The presence of thick, fast ice flowing ice in the onset zone suggests that subglacial conditions within the study area were characterised by intense basal sliding. The evolution of bedforms (roches moutonnées and whalebacks) was influenced by basal ice dynamics, but bedrock type, joints and bedding were also critical controls on bedform morphometry.
Deglaciation following the LGM began on the outer shelf by 14.9 kyr, with increased air temperature, rising relative sea-level and bathymetric over-deepening driving the UISS to the outer edge of coastal fjords by 11.4-11.0 kyr. Geochronological data demonstrate that the retreat rate of the northern and southern UISS became highly asynchronous during the early-Holocene. In the south, topographic constrictions stabilised the ice from 11.0-9.3 kyr, before it retreated beyond its present ice margin at 8.7 kyr. Ice in the north became pinned at the mouth of Rink-Karrat Isfjord between 11.6-6.9 kyr, remaining stable through the Holocene Thermal Maximum, demonstrating the ability of topography to override climate and sea-level drivers.
Geomorphological and sedimentological evidence has demonstrated that the Svartenhuk Peninsula in the northern Uummannaq region, previously cited as an LGM ice-free enclave, was overrun by ice during the LGM. Ice was sourced from the Svartenhuk interior, and expanded radially to the present coastline. This is contrary to existing work, and suggests there may be a need to reassess the evidence for interstadial, high sea-level conditions throughout Greenland.