Submarine geomorphology and glacial history of the Sea of the Hebrides, UK

Abstract

The Sea of the Hebrides is an island-studded region of complex bathymetry on the UK continental shelf, west of the Scottish mainland. An extensive area (2200 km2) of recently collected multibeam bathymetry data, combined with seismic reflection profiles reveal this part of the shelf to have been extensively modified by both glacial and modern processes. Our new geomorphological evidence strongly supports the contention that an ice stream drained ice from western Scotland and the Inner Hebrides towards the Barra Fan at the continental shelf break at the height of the last glaciation (Marine Isotope Stage 2-3). Convergent seabed glacial lineations and other subglacially streamlined features eroded in bedrock around the Islands of Canna and Rum preserve the direction of ice sheet movement, and strongly suggest the onset of ice streaming in a southwesterly direction on the continental shelf in the Sea of the Hebrides region. This fast-flow zone formed part of a larger convergent ice stream system draining much of western Scotland and the north of Ireland-the southern part of which has been postulated already. A number of rock basins, linear troughs and deeps west and south of Muck, kept sediment-free by the dominant modern tidal regime, are interpreted as being at least partly subglacial in origin. Similarly, a large complex of buried deeps between Eigg and Arisaig are interpreted as an overdeepened glacial drainage network. It is suggested that intense bedrock erosion by focused subglacial abrasion and subglacial meltwater discharge over multiple glacial advance and decay cycles led to significant modifications of the pre-Quaternary bedrock surface. Other features such as moraines are only found in shallower water (typically < 50 m), west of Canna, west of Rum and south of Skye. Their relative paucity indicates that the modern tidally dominated environment of the area may have removed much of the localised geomorphological evidence of offshore glacial limits within the Sea of the Hebrides, or alternatively that the ice sheet margin was floating and retreated predominantly by calving leaving little geomorphological evidence of its retreat

Deglacial landform assemblage records fast ice-flow and retreat, Inner Hebrides, Scotland

“…1a). As originally proposed by Howe et al (2012), landforms attributed to this 'onset zone' are distributed across a geographically-controlled area, semi-independent of the region's complex bedrock geology (Dove et al 2015).…”

“…), Howe et al (2012) used high-resolution swath bathymetry to identify the first direct evidence relating to subglacial processes and fast ice-flow on the inner shelf. These data have been compiled together with newer bathymetry, as well as terrestrial airborne radar data, to form a near-continuous offshore-onshore digital elevation model (DEM) (horizontal resolution -5 m) that covers the majority of the Inner Hebrides region (Dove et al 2015).…”

Submarine glacial landforms record Late Pleistocene ice-sheet dynamics, Inner Hebrides, Scotland

“…363 8) (Benn and Evans, 2014). In the northern part of the study area, several groups of moraines were 364 previously described by Howe et al (2012), and indicate 'pinned' glacial retreat along the coastlines 365 of Skye and Rum. Farther south, moraines are found on a bedrock platform between Tiree and Mull 366 (Fig.…”

Seabed Characterization: Developing Fit for Purpose Methodologies

“…Mapping, via direct digitizing and building on the work of Howe et al (2012), has revealed an extensive array of well-preserved glacigenic landforms on the seabed associated with key stages of ice flow and retreat of the BIIS following the Last Glacial Maximum. On multiple submarine rock platforms and within overdeepened troughs, diverse assemblages of glacially streamlined landforms are present, forming a geomorphic continuum between rock drumlins and mega-flutes ( Figure 1b).…”