Ice sheet extension to the Celtic Sea shelf edge at the Last Glacial Maximum

Abstract

a b s t r a c tPrevious reconstructions of the BritisheIrish Ice Sheet (BIIS) envisage ice streaming from the Irish Sea to the Celtic Sea at the Last Glacial Maximum, to a limit on the mid-shelf of the Irish-UK sectors. We present evidence from sediment cores and geophysical profiles that the BIIS extended 150 km farther seaward to reach the continental shelf edge. Three cores recently acquired from the flank of outer Cockburn Bank, a shelf-crossing sediment ridge, terminated in an eroded glacigenic layer including two facies: overconsolidated stratified diamicts; and finely-bedded muddy sand containing micro-and macrofossil species of cold water affinities. We interpret these facies to result from subglacial deformation and glacimarine deposition from turbid meltwater plumes. A date of 24,265 ± 195 cal BP on a chipped but unabraded mollusc valve in the glacimarine sediments indicates withdrawal of a tidewater ice sheet margin from the shelf edge by this time, consistent with evidence from deep-sea cores for ice-rafted debris peaks of Celtic Sea provenance between 25.5 and 23.4 ka BP. Together with terrestrial evidence, this supports rapid (ca 2 ka) purging of the BIIS by an ice stream that advanced from the Irish Sea to the shelf edge and collapsed back during Heinrich event 2.

New age constraints for the limit of the British–Irish Ice Sheet on the Isles of Scilly

“…This has been considered the maximum extent of ice advance across the Celtic shelf, but the recent evidence reported by Praeg et al . () places the Scilly ice limit in a new context (Fig. ); does it represent a lateral ice limit to the ISIS, flowing southwards from the north to the west, or does it represent a terminal limit to a larger ice body on the Irish shelf to the west with driving stresses from the north‐west?…”

“…Solid line is the ice limit after Scourse et al . (), and dashed line is an inferred limit based on the interpretation that the ISIS reached the shelf edge (Praeg et al ., ). The core site (VC‐64) on which this interpretation is based is also shown.…”

“…Bayesian analysis of the existing geochronological ( 14 C, OSL, TCN) data combined with the prior knowledge of ice retreat for the entire ISIS have been used to reduce the uncertainties inherent to the individual techniques, and model ice impingement on to the Isles of Scilly at 23.3–24.0 ka (Chiverrell et al ., ). The timing of this advance was accompanied by an associated increase in ISIS‐sourced ice‐rafted detritus (IRD) flux to the adjacent deep ocean (Scourse et al ., ) and agrees with recent 14 C dating of an arctic bivalve recovered from glacigenic sediments cored close to the shelf break in the Irish sector of the Celtic Sea (Praeg et al ., ).…”

Ice margin oscillations during deglaciation of the northern Irish Sea Basin

“…Average retreat rates then slowed to 13–20 m a −1 when the ice margin oscillated northwards across the northern Isle of Man and lowland Cumbria and experienced both limited and large‐scale (>1–2 km) retreat–readvance cycles before retreating northwards into the Galloway Hills in south‐west Scotland. Surface exposure ages obtained for high ground on the Isle of Man (18.9 ± 1.0 ka) and western Cumbrian Mountains (21.5 ± 0.8 ka) overlap with the rapid retreat of ice from maximum limits in the Celtic Sea (Praeg et al ., ; Smedley et al ., ) with ice margins retreating across the Llŷn Peninsula from 23.9 ± 1.6 to 21.1 ± 0.6 ka (Smedley et al ., ) and the Isle of Man from 20.8 ± 0.7 to 18.3 ka. The rapid advance of the ISIS to and subsequent retreat from maximum limits when associated with unambiguous evidence for ice streaming in the central ISB (Van Landeghem et al ., ) provides a context for significant drawdown of the ice stream surface.…”

The Whittard Canyon – A case study of submarine canyon processes

“…20-13 ka) resulted in a significant increase in the fluvial flux to the Grande Sole drainage basin, and hence the Whittard Canyon, with terrigenous input prolonged until 7000 years ago by glacio-hydroisostatic uplift of the British Isles (Bourillet et al, 2003;Lambeck, 1996). The linear tidal sand ridges that developed on the outer continental shelf of the Celtic Sea (Praeg et al, 2015) between 20 and 12 ka years ago (Scourse et al, 2009) are also proposed as a sediment source to the Celtic deep-sea fan through strong tidal transport of sediments into the canyon heads Scourse et al, 2009). However, recent current measurements and oceanographic modelling results suggest an opposite sediment transport direction (see below, and also in Cunningham et al, 2005).…”