Seafloor glacial features reveal the extent and decay of the last British Ice Sheet, east of Scotland

Abstract

Three-dimensional (3D) seismic datasets, 2D seismic reflection profiles and shallow cores provide insights into the geometry and composition of glacial features on the continental shelf, offshore eastern Scotland (588 N, 1-28 W). The relic features are related to the activity of the last British Ice Sheet (BIS) in the Outer Moray Firth. A landsystem assemblage consisting of four types of subglacial and ice marginal morphology is mapped at the seafloor. The assemblage comprises: (i) large seabed banks (interpreted as end moraines), coeval with the Bosies Bank moraine; (ii) morainic ridges (hummocky, push and end moraine) formed beneath, and at the margins of the ice sheet; (iii) an incised valley (a subglacial meltwater channel), recording meltwater drainage beneath former ice sheets; and (iv) elongate ridges and grooves (subglacial bedforms) overprinted by transverse ridges (grounding line moraines). The bedforms suggest that fast-flowing grounded ice advanced eastward of the previously proposed terminus of the offshore Late Weichselian BIS, increasing the size and extent of the ice sheet beyond traditional limits. Complex moraine formation at the margins of less active ice characterised subsequent retreat, with periodic stillstands and readvances. Observations are consistent with interpretations of a dynamic and oscillating ice margin during BIS deglaciation, and with an extensive ice sheet in the North Sea basin at the Last Glacial Maximum. Final ice margin retreat was rapid, manifested in stagnant ice topography, which aided preservation of the landsystem record.

Sensitivity of the North Atlantic circulation to break-up of the marine sectors of the NW European ice sheets during the last Glacial: A synthesis of modelling and palaeoceanography

“…Recent evidence strongly supports the existence of grounded ice cover in this area (also Larsen et al, 2009), from a combination of micromorphological evidence (Carr et al, 2006), 3D seismic evidence for mega-scale glacial lineations (Lonergan et al, 2006;Graham et al, 2007), tunnel valleys (Lonergan et al, 2006) and ice margin and sub-glacial geomorphology (Graham et al, 2009). Some of this evidence suggests sub-glacial freshwater drainage to the north (Lonergan et al, 2006;Graham et al, 2009) and overland drainage to the south (Toucanne et al, 2010) from a southern North Sea lake. The existence of this lake was raised as a possibility by Clark et al (2004).…”

Middle to Late Devensian glaciation of north‐east Scotland: implications for the north‐eastern quadrant of the last British–Irish ice sheet

“…Mega-scale glacial lineations (MSGL) imaged on 3D seismic datasets at the unconformable top of the uppermost glacigenic unit represent the signature of fast-flow within a grounded ice sheet (Graham et al, 2007;Graham et al, 2009;Graham et al, 2010). Their presence and general SE-NW orientation are compatible with a major ice stream (Witch Ground Ice Stream; WGIS) draining the northern North Sea Basin fed by coalescent British and Scandinavian ice sheets.…”

Quaternary glaciations of northern Europe

“…Well-developed seismic, geomorphological and sedimentological evidence now exists for the coalescence of both the Scandinavian and British ice sheets in the northern North Sea (Carr et al, 2006;Bradwell et al, 2007;Graham et al, 2007Graham et al, , 2009Bradwell et al, 2008c) (Figure 3) with ice reaching its maximum extent at the continental margin around 29 ka BP (Sejrup et al, 2009). Separation of the two ice sheets is considered to have occurred by 25 ka BP (Sejrup et al, 1994;Bradwell et al, 2008c;Sejrup et al, 2009, Clark et al, 2012 with numerous ice-marginal oscillations occurring during retreat (Bradwell et al, 2008c, Clark et al, 2012.…”