Some of the ideas discussed in this blog are published in my new book called "The Stonehenge Bluestones" -- due for publication on June 1st 2018. After that, it will be available by post and through good bookshops everywhere. Bad bookshops might not have it....
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Thursday, 23 February 2012

More on the Early Devensian

Oxygen isotope records for the Devensian -- assumed to be a reasonable representation of temperature oscillations and of glacial and non-glacial conditions in the mid-latitudes.  Note that in the bottom graph the time scale runs in the opposite direction!

Further to my last post, we now have a multitude of environmental reconstructions to work off, many of them based on oxygen isotope records from Greenland and Antarctica, and others from deep sea cores etc.  It seems that there was a very distinct cooling around 60,000 - 70,000 years ago -- a period conventionally labelled "Oxygen isotope stage 4."

The key question is this:  was that cooling episode prolonged enough, and was it characterized by sufficient precipitation in the form of snow, to trigger off a true glacial episode in the UK uplands?  

In an interesting paper called "The Last Glacial Stage (the Devensian) in Northwest England" (NW Geog, 2003, vol 3 (1)) Catherine Delaney suggests that in OI Stage 4 there was a sharp temperature reduction, a drop in sea level to -60m and a number of short-term cooling events.  She suggests that the British - Irish ice sheet was in existence at this time and that there was an ice stream in the Irish Sea basin.  Some authorities think that the ice was restricted to northern Britain, but Prof David Bowen and others have argued for an ice cover in Ireland at the time as well.  There were valley glaciers in the Lake District at this time, as indicated by lake sediments.  In these circumstances it is inconceivable that there was NOT a Welsh ice cap at this time.  But was it big enough to expand beyond the present coastline?

Henry Patton's work suggests that for the development of a sizeable Welsh ice cap you need quite a prolonged period of low temperatures -- ie a degree of climatic stability.  How long does this stable cold period need to be?  Around 15,000 years?    Watch this space.....

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