Towards an Anglian glacial model

Model from Patton et al 2016

As readers of this blog will know,  there are now many modelled reconstructions of what the LGM ice sheet looked like in the British Isles and Ireland.  There are huge doubts about dating (the LGM might have occurred around 21 ka or around 27 ka, depending on which paper you are reading) -- but gradually things are moving towards a consensus on extent -- ie where the ice edges were actually located.  The discussions about the Celtic Sea lobe will go on for some time, I expect.

But as I was mulling over all this, I came across this message from Henry Patton, who has given much valuable advice over the years:

Based only modelling carried out so far it seems that your Anglian flowline reconstruction for ice impingement into SW England, travelling up the Bristol Channel, is reasonable and consistent with our data. The model results associated with the L.Weichselian are of course at odds with the growing empirical evidence from this region, but it raises the question of how important S. Irish ice was in glaciating the Celtic Sea. To match L.Weichselian limits on the SW coastline it is logical to assume that S. Irish ice was the more dominant force in the area dictating/nudging the flow of Irish Sea ice, based on distances from ice divides but also in a manner to reconcile ice extension to the Scilly Isles and beyond without encroaching onshore Devon/Cornwall etc.

Based on observations of ice extension far west onto Porcupine Bank it sounds feasible that a thick ice cap probably existed in S. Ireland, so glaciologically it makes sense that ice was also flowing south/southeast too. However, reconstructing the subtle interactions of these two ice masses in the Celtic Sea would require more detailed attention and model resolution. In particular I think the climate forcing would be key to testing these hypotheses. In our reconstruction the Irish climate is already quite maritime in order to grow ice on relatively subdued terrain, but the area is also very sensitive to summer ablation. I would therefore presume any major extension into the Celtic Sea from Ireland was short lived and deglaciated fast.

The "Anglian" style reconstruction produced by our model appears to suggest that the relative dominance of the Irish Sea ice stream was much greater relative to Irish ice further west during this stage, probably driven by greater build-up of ice over northern Britain and Scotland.

The lower map is from the British Geological Survey -- the orange dashed lines represent Anglian ice movement directions.  The blue arrows show the movement of valley glaciers and outlet glaciers from the Welsh Ice Cap in both the Anglian and Devensian glaciations.

I'm sure Henry won't mind me reproducing his points here.  What he is saying is that he sees no problem with the flowlines suggested for the Anglian glaciation, with ice pressing all the way up the Bristol Channel and into Somerset (and maybe Wiltshire) as long as there is adequate eastwards pressure from a thick ice cap over Southern Ireland.  The flowlines -- based on what we know about erratic distributions, striations etc -- are precisely in tune with the models, even though they were created for a different glaciation!  Ice in unconstrained situations will always flow perpendicularly to the ice edge -- a fact apparently ignored by some of the geomorphologists who are working in this field at the moment.

Ice thickness and extent model from Edwards et al 2017

Another map from Patton et al -- a Devensian model that appears to more accurately represent the Anglian glacial situation

One of the maps from the modelling exercise by Hubbard et al for the Devensian.  This is another "maximum" model, created to show the number of years each location was ice-covered, but there is ab obvious correlation with ice surface altitude and ice extent.  Again, this map has relevance for our understanding of the Anglian Glaciation, around 500,000 years ago.