The climate of the Wester Ross region of NW Scotland is particularly sensitive to fluctuations in the strength and latitude of the North Atlantic Gulf Stream. This was particularly apparent during the last deglaciation (14.7-12.9 ka), when overall climatic amelioration was interrupted by periods of cooling, the most significant being a 1.2 ka return to glacial conditions during the Younger Dryas (12.9-11.5 ka). Glacial readvances during these cooling episodes left behind numerous geomorphological features, which have been mapped and interpreted through a variety of methods, including fieldwork observations, aerial photography and digital elevation models, to form a detailed reconstruction of the style and timing of deglaciation. These methods were augmented by the study of 3D digital models, produced by combining 5cm resolution, Light Detection and Ranging (LiDAR) scans with colour photography, leading to the production of a detailed geomorphological map of a cirque formation in Torridon, Wester Ross, which was covered by an ice-sheet at the Last Glacial Maximum, and experienced localised ice flow during subsequent deglaciation and readvances. Six statistically comparable cosmogenic 10Be bedrock exposure ages give a Younger Dryas age for sites in Torridon and Applecross (Wester Ross), and have also been used to constrain the vertical extent of these ice fields. Reconstructions of these ice bodies revealed that the Torridon ice field (mean ELA, 482m) covered ~100km2, over twice the surface area covered by the Applecross ice field (~43km2). This could have resulted from the survival of ice in Torridon prior to the onset of the Younger Dryas cooling, and is tentativelty supported by pre-Younger Dryas cosmogenic 10Be exposure ages from this study and previous studies, which imply that ice existed close to the Wester Ross coastline and within central Torridon between 14-13ka. The Applecross ice field mean ELA (361m) was lowered by the presence of independent glaciers, which formed in low-lying troughs as snow was efficiently transferred to the NE by prevailing SW winds. Using empirical values from a global dataset, average annual Younger Dryas palaeoprecipitation values for the Torridon and Applecross ELAs are 2010 ± 266 and 2312 ± 534 mm a-1 respectively, suggesting a wetter climate than today. Palaeoprecipitation calculated using equations based on a climate model of NW Scotland, yield lower values between 1005 ± 67 mm a-1 and 1758 ± 118 mm a-1 for the Torridon ELA and 1205 ± 233 mm a-1 to 2109 ± 407 mm a-1 for the Applecross ELA, perhaps a more reliable estimate which reflect enhanced continentaility, promoted by the formation of sea ice on the NE Atlantic seaboard during the Younger Dryas.Despite the rapid warming observed in palaeotemperature proxies, studies of glacial geomorphology and basal shear stress suggest that initial deglaciation was slow, oscillatory and warm-based, leading to the formation of prominent retreat moraines in the lower valleys. This prolonged transition can be related to the northward migration of sea ice and the gradual reintroduction of a Gulf Stream-dominated maritime climate. Ice remaining in the central area down-wasted in-situ as the regional ELA increased, creating hummocky landscape. Finally, cosmogenic 10Be exposure ages indicate that glaciers (probably characerised by a polythermal regime) retreated into the high north-facing corries at approximately 11.8ka, depositing a series of flutes.
|Date of Award
|1 Aug 2012
- The University of Manchester
|Simon Brocklehurst (Supervisor)
- Cosmogenic dating