The Devensian glaciation gets bigger and bigger.....

This research has been around for a long time now -- we did a post on it back in 2011.  The work by Daniel Praeg and colleagues was published in 2015, and it is rather relevant to my observations on the Scilly Isles of a couple of years ago.

This is quite convincing research, suggesting that the ice limit suggested by Scourse and others (white line on the map) was far too conservative, and that the actual outermost ice edge during the Devensian was about 150 km further south, right on the edge of the shelf roughly coinciding with the -150m contour.  The authors have not yet worked out the interactions of eustatic sea-level positions, ice margin oscillations, and isostatic effects -- but no doubt that will come.......

What interests me particularly is the presence of the elongated sea floor ridges which are not thought to have anything to do with tidal scour or sea bed currents.  They are best interpreted as glacial streamlining features, created by a rapidly moving Irish Sea Glacier shaping or deforming very soft bed sediments.  But look at the alignment of these ridges off the tip of Brittany.  They run broadly NNE to SSW.  Ice cannot have created these features if the Devensian Irish Sea Glacier had  skidded to a halt along the north coasts of the Isles of Scilly.  The ice must have wrapped itself around the western coasts of Scilly as well, exactly as I am proposing as a result of my field observations in 2016.


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Ice sheet extension to the Celtic Sea shelf edge at the Last Glacial Maximum (2015)
by Daniel Praeg, Stephen McCarron, Dayton Dove, Colm O Cofaigh, Gill Scott, Xavier Monteys,
Lorenzo Facchin, Roberto Romeo, Peter Coxon

Quaternary Science Reviews 111 (2015) 107e112

http://dx.doi.org/10.1016/j.quascirev.2014.12.010



Abstract

Previous 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: over- consolidated 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.

Quote:
Our results thus support previous interpretations linking IRD flux in deep-sea cores to a short-lived advance and retreat of the Irish Sea Ice Stream (Scourse and Furze, 2001; Scourse et al., 2009a,b). However, they further indicate that the BIIS extended across the Celtic Sea to the Irish-UK continental shelf edge, up to 150 km seaward of previously proposed limits (Fig. 1). We infer a rapid (2 ka) purging of the ice sheet, involving a cycle of ISIS advance and its collapse during HE2. Our results add to regional evidence of a highly dynamic BIIS drained by marine-based ice streams (Clark et al., 2010). Further field data and modelling studies are required to test our findings, which have linked im- plications for the maximum volume and thickness of the BIIS, for the dynamics of the ISIS in interaction with changing sea levels, as well as for the age and origin of the seabed ridges.