AbstractThe reconstruction of past ice sheet dynamics can shed a light on long-term ice sheet activity, and in turn provide constraints on the response of modern ice sheets to climate change. The Hebrides Ice Stream (HIS) flowed across part of the western Scottish shelf to the shelf-break during the last glacial cycle and drained a large portion of the northern sector of the British Irish-Ice Sheet (BIIS). This area has not received much attention in past studies.
This thesis aims to examine how the HIS evolved and interacted with the changing climate and the underlying landscape after 27 ka. The work is subdivided into: a) investigation of modern high-resolution bathymetry data coupled with seismic data with the aim of reconstructing deglacial dynamics; b) analysis of Pb isotopic composition in sediment cores on the shelf in order to locate the sources of glacial sediment; c) study of shelf cores’ sedimentology and microfaunal assemblage to reconstruct Lateglacial paleoenvironmental changes.
A three-stage deglacial pattern, where topography played a critical role, is defined: i) ice stream margin retreat punctuated by standstills, ii) topography-controlled fjordic retreat, with evolution from a coherent ice-sheet to separate fjord tidewater glaciers, and iii) stabilisation at the transition from tidewater to land-based ice margins. Between 21 and 15 ka, fine sediments transported by meltwater plumes were the product of erosion of Neoproterozoic basement, while the coarse fraction was instead dominated by island igneous rocks. These results indicate prevailing sediment input from NW Scotland. Lateglacial sediment deposition was strongly influenced by shelf currents and shows wide variation. Therefore, the seismic and sedimentological interpretations need to be considered only on a local scale. Glacimarine sandy deposits in the Muck Deep region support a prolonged glacial occupancy until the latest stages of GS-1, and are at odds with recent studies indicating earlier glacial retreat.
The thesis demonstrates the complex interactions between BIIS evolution, subglacial landscape and ocean dynamics. Some of the outcome of this research can be useful to inform future numerical reconstructions.
|Date of Award||5 Oct 2017|
|Supervisor||John Howe (Supervisor), K.C. Crocket (Supervisor), Colm O'Cofaigh (Supervisor) & dayton dove (Supervisor)|