Glacial rebound of the British Isles-II. A high-resolution, high-precision model

Abstract

S U M M A R Y Observations of ice movements across the British Isles and of sea-level changes around the shorelines during Late Devensian time (after about 25 000 yr BP) have been used to establish a high spatial and temporal resolution model for the rebound of Great Britain and associated sea-level change. The sea-level observations include sites within the margins of the former ice sheet as well as observations outside the glaciated regions such that it has been possible to separate unknown earth model parameters from some ice-sheet model parameters in the inversion of the glaciohydro-isostatic equations. The mantle viscosity profile is approximated by a number of radially symmetric layers representing the lithosphere, the upper mantle as two layers from the base of the lithosphere to the phase transition boundary at 400 km, the transition zone down to 670 km depth, and the lower mantle. No evidence is found to support a strong layering in viscosity above 670 km other than the high-viscosity lithospheric layer. Models with a low-viscosity zone in the upper mantle or models with a marked higher viscosity in the transition zone are less satisfactory than models in which the viscosity is constant from the base of the lithosphere to the 670 km boundary. In contrast, a marked increase in viscosity is required across this latter boundary. The optimum effective parameters for the mantle beneath Great Britain are: a lithospheric thickness of about 65 km, a mantle viscosity above 670 km of about (4-5) lo2" Pa s, and a viscosity below 670 km greater than 4 x lo2' Pas.

Eskers in a complete, wet-based glacial system in the Phlegra Montes region, Mars

“…1). The response of RSL to glaciation in Ireland, including across its continental shelf (Scourse et al, 2009), was regionally and temporally complex due to GIA (Lambeck, 1993a(Lambeck, , 1993bBradley et al, 2009;Brooks et al, 2011). Consequently, the hydraulic geometries of terrestrial glaciofluvial channels that developed within existing river valleys have been affected by both the magnitude of glaciofluvial discharge and variation in RSL (Gallagher, 2002;Gallagher et al, 2004).…”

Asymmetric ice-sheet retreat pattern around northern Scotland revealed by marine geophysical surveys

“…However, a more precise age and their 22 relationship with seabed moraines to the north and south remain unclear, though seismic-23 stratigraphic evidence indicates that their deposition pre-dates the moraines of the Otter Bank 24 Formation, which rest with angular discordance on the MacDonald Formation (Stoker and Holmes,25 1991; Stoker et al, 1993). Despite this stratigraphic discordance, subsequent large-scale shelf-wide 26 seabed geomorphological mapping and the resulting reconstructions have tentatively correlated 27 these outer Hebrides Shelf moraines with others on outer West Shetland Shelf, ~150 km to the NE 28 (Bradwell et present (Lambeck, 1991(Lambeck, , 1993Peltier and Fairbanks, 2006). The relative sea level picture at this 7 time offshore western Scotland was complex and is not well constrained on the NW continental 8…”

“…A 18 similar setting is envisaged in Shetland where no raised shorelines have been identified (Sissons, 19 1987) and relative sea levels are thought to have risen continuously (if not smoothly) from 20 deglaciation to the present day (Lambeck, 1991;Shennan et al, 2006). During Late Weichselian ice 21 sheet deglaciation (~18-16 ka BP), modelled seawater depths across much of the continental shelf 22 around northern Scotland, between the Flannan Isles and Shetland, were 40 to 80 m lower than the 23 present day (Lambeck, 1991(Lambeck, , 1993. However, as previously mentioned this sea level scenario varied 24 considerably with distance away from the centre of isostatic depression, with contemporaneous 25 relative sea level at the coastline (Cape Wrath, ~18-16 ka BP) being at or around the present-day 26 marine limit; whilst ~180 km further S in Skye and Arisaig, nearer the maximum isostatic depression, 27 relative sea levels were probably 20-40 m higher than present during the same time period 28 (Lambeck, 1991;Shennan et al, 2006).…”

“…The overall pattern depicted in Figure 18 is subdivided into 10 key stages outlined below: 9 constrained, but numerical glacio-isostatic models place them ca. 100 m below present on 30 the mid to outer shelf (Lambeck, 1991(Lambeck, , 1993). The implication is that the ice sheet margin at Taken collectively, the carefully reconstructed Stage 9 ice margins represent a considerable 10 reconfiguration during overall ice-sheet decay when the northern sector of the British-Irish 11…”

Ivestigating Glacial Isostatic Adjustement in Scotland with INSAR and GPS observation

“…On the one hand, geological evidence from palaeoshorelines and undisturbed isolation basins has been used to reconstruct long-term Holocene RSL change [5,6]. This information derived from sea-level index points has been employed to inform empirical isobase models of the uplift in Scotland using trend surface analyses [7,8], as well as to calibrate theoretical GIA models that rely on Earth mantle rheology and ice-sheet history [2,[9][10][11][12]. The latter approach faces a common modelling problem, namely a trade-off between Earth mantle parameters that leads to non-uniqueness of the solutions [13,14].…”