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

Abstract

High-resolution bathymetric data have been central to recent advances in the understanding of past dynamics of the former British–Irish Ice Sheet (BIIS). As approximately two-thirds of the former BIIS was probably marine-based during the Last Glacial Maximum (LGM) ( c. 29–23 ka), geomorphic observations of the seabed are required increasingly to understand the extent, pattern and timing of past glaciation. Until recently, glacial reconstructions for the Inner Hebrides, offshore of western Scotland, have been based primarily on terrestrial observations. Previous workers have proposed generalized reconstructions in which the Inner Hebrides are located within a significant former ice-sheet flow pathway that drained the western Scottish sector of the BIIS, feeding the Barra Fan during the LGM and earlier glaciations (Fig. 1). Results from numerical ice-sheet modelling suggest that former ice-flow velocities within the region were on the order of hundreds to thousands of metres per year, but yield further insight by demonstrating how dynamic binge/purge cycles may have affected ice-sheet mass balance over time (Hubbard et al. 2009). Following the LGM, ice-sheet retreat through the area is estimated to have been in the order of 20 m per year (Clark et al. 2012). Here we present swath-bathymetric data from the Inner Hebrides that provide in situ constraints on ice-sheet flow and subsequent retreat dynamics from within this important sector of the BIIS. Fig. 1. Swath-bathymetric images. ( a ) Inner Hebrides, Scotland (acquired with both multibeam (e.g. Kongsberg EM3002D) and interferometric systems for the Maritime and Coastguard Agency's UK Civil Hydrography Programme © Crown copyright. Grid-cell size 5 m). ( b ) Superimposed flow sets of streamlined landforms. Landforms associated with black flow arrows post-date features associated with white arrows. ( c ) Convergence zone of two ice-stream tributaries overlain by a series of recessional moraines, indicating later ice margin retreat to the NE. Inset shows interpreted glacigenic-landform map highlighting …