The glacial geomorphology of the Firth of Forth

Abstract

It is important to understand how past ice sheets both responded to and perturbed the ocean-climate system in order to help predict how current ice sheets will respond to future changes and, in particular, warming of the atmosphere and oceans. Ice streams are an important component of ice sheet dynamics and are a mechanism through which ice sheets can rapidly lose mass in response to external forcing. The British Irish Ice Sheet (BIIS) is thought to be a valuable analogue for future changes in ice sheets and has been extensively studied. Several palaeo-ice streams have been identified, but the inventory of palaeo-ice streams is unlikely to be complete. This thesis is aimed at identifying the likelihood of palaeo-ice streaming in the Firth of Forth region, south-east Scotland, where previous work and numerical modelling has hypothesised ice stream activity. However, and perhaps surprisingly, the glacial geomorphological evidence for ice stream has not yet been studied in detail. In this study, the glacial geomorphology of the Forth region has been examined and characterised using remote sensing imagery from the NEXTMap digital elevation model. Over 10,000 individual landforms have been identified, categorised and manually digitised in to a Geographic Information System (GIS). Established criteria has been used to test whether the Firth of Forth was the location of an ice stream and the subglacial landsystem has been examined to determine the relative roles of bedrock geology and topography. Both soft and hard bed signatures have been considered when analysing the subglacial landsystem, which is shown to be highly complex. The chronology and glacial history of the Forth has then been reconstructed using available dates in the area and through analysis and consideration of the subglacial landform and landsystems identified. The influence of the Forth region on regional ice sheet history has also been considered. Results reveal five different types of landform; flow traces, drumlins, intermediate forms, crag-and-tails and streamlined bedrock ridges. However, it is argued that they lie along a continuum that reflects the influence of underlying bedrock geology and drift thickness. It is concluded that the diverse collection of landforms identified indicates that the Forth imprint represents a mixed bed onset zone of a palaeo-ice stream that extended offshore and operated around 19 ka – 15 ka. This paper is the first to present evidence and formally identify the Forth area as a palaeo-ice stream, which was the largest terrestrial onshore imprint of a palaeo-ice stream identified on the east coast of the BIIS.