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During the Last Glaciation a fast flowing glacier – an ice stream – flowed southwards down the Irish Sea.

The extent of ice cover over Britain and Ireland at the last glacial maximum is still debatable, though consensus is now turning towards ice having extended far offshore (red line). In Wales, only a few areas along the southern coastline remained permanently ice free. (Click for larger version)

The extent of ice cover over Britain and Ireland at the last glacial maximum is still debatable, though consensus is now turning towards ice having extended far offshore (red line).  (Click for larger version)

This was one of major outlet glaciers of the British-Irish Ice Sheet and extended all the way from its source in NW Scotland as far as the Isles of Scilly. It has been known for some time that this “furthest south” position was reached sometime between 18 and 25 thousand years ago, but new research involving C3W scientists published in the Journal of Quaternary Science has constrained the timing of ice advance and retreat with more precision. This indicates that retreat was very fast, in effect a rapid collapse of this part of the ice sheet.

This result is important because there are major concerns over the stability of ice sheets grounded below sea level, such as the West Antarctic Ice Sheet. The West Antarctic Ice Sheet contains enough ice to raise global sea level by around 6 metres, so if it were to collapse like the Irish Sea sector of the British-Irish Ice Sheet – with which it shares many common characteristics – there would be catastrophic consequences for society.

The Irish Sea Ice Stream reached the Isles of Scilly between 25,300 and 24,500 years ago and then retreated northwards into St Georges Channel by 23,000 years ago and Anglesey by 22,000 years ago, with retreat attaining rates as fast as 550 metres per year.

C3W contributors James Scourse and Katrien Van Landeghem (Bangor University) and Danny McCarroll (Swansea) are now developing the research as part of the NERC BRITICE-CHRONO Consortium – along with collaborators including C3W scientists Siwan Davies (Swansea), Geoff Duller, Mike Hambrey and Neil Glasser (Aberystwyth) – to constrain other parts of the Ice Sheet in a similar way and enable ice sheet models developed by the British Antarctic Survey to be tested against real data.

CHIVERRELL, R.C., THRASHER, I., THOMAS, G.S.P., LANG, A., SCOURSE, J.D., VAN LANDEGHEM, K.J.J., McCARROLL, D., CLARK, C., Ó’COFAIGH, C., EVANS, D.J.A. &  BALLANTYNE, C.K. 2013

Bayesian modelling the retreat of the Irish Sea Ice Stream  Journal of Quaternary Science 28, 200-209.