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Thursday, 16 December 2010

Modelled ice extent over Southern England

This is one of the "extreme" glacial models for the Last Glaciation Limit created by Dr Alun Hubbard et al.  This model requires quite heavy precipitation over southern Ireland in order to "force" the ice of the Irish Sea Glacier across SW England.  Note that the authors suggest that the ice may only have been present over Cornwall, Devon and Somerset for around 1,000 years.....

In two of the three experiments presented, the modelled ISIS
does not advance across the Isles of Scilly, despite the fact that all
three indicate ice advancing across Pembrokeshire onto the north
Devon coast. Here, the model is not consistent with the recent
evidence. We would not at all wish to claim ascendancy or to
question the important work on the southern limits of the ISIS and,
in particular, the glaciation of the Isles of Scilly (Scourse and Furze,
2001). However, despite all the shortcomings and limitations of the
modelling approach utilised in this study, it does have a consistent
internal logic based on contemporary glaciological principles that
seems to suggest that the Irish Sea Basin story is not yet resolved.

Without preconditioning certain large but critically limited zones
of the Irish Basin to a priori streaming, it is difficult to achieve
a single ‘surge-advance’ south to the Scilly Isles without a broad
piedmont type-lobe impinging onshore across much of SW
England. The reconstruction inferred in the E109b2 experiment
with a high precipitation scenario across western Britain may be
exaggerating the case somewhat but this simulation does tantalisingly
still meet all of the available ice-directional and RSL
constraints. Further enhancing precipitation rates across SW Eire
up to and exceeding present day values would yield a considerably
more western dominated Irish Sea ice-mass that would bring
modelled ice limits, especially those associated with the ISIS in SW
England, into line. However, there is little palaeo-climatic evidence
nor GCM modelling to support a wetter LGM than present across
southern Eire. Within the limitations of this study, we do not
pursue this though further investigation is clearly required.

The experiments presented also indicate significant excursions
of wet-based ice into areas of southern England, where little
evidence of recent glaciation has been found.  This may not present
such a major problem given that our model indicates ice was at this
extended limit for less than 1 ka. The experiments also provide
support for a possible glacial mechanism for the movement of
Preseli erratics as a transport trajectory which overrides parts of
northern Pembrokeshire and was subsequently deflected southeastwards
across the Bristol Channel into SW England, cannot be
completely discounted.


Dynamic cycles, ice streams and their impact on the extent, chronology
and deglaciation of the British–Irish ice sheet

Alun Hubbard , Tom Bradwell , Nicholas Golledge, Adrian Hall, Henry Patton, David Sugden,
Rhys Cooper, Martyn Stoker

Quaternary Science Reviews 28 (2009) 759–777


Robert Langdon said...

Excellent model!

The Scilly Isles is a 'Big Issue' as clear evidence has been found.

Is it possible that the ice sheet spread down to the English Channel - which would solve the Scilly mystery and the evidence is at the bottom of the sea?

Get your snorkel Brian!


BRIAN JOHN said...

There is certainly a big debating point over the Scilly Isles -- the question is not whether the ice reached the Scilly Isles (it clearly did, because there is till there) but WHEN. James Scourse has C14 dates that show the ice was there in the Devensian -- but he wants a strange ice lobe running down the centre of the Celtic Sea from St George's Channel without impinging on the coasts of Devon and Cornwall. as the authors of this paper say, that is glaciologically implausible.

Kellaway wanted ice in the English Channel -- it's in one of his papers. Personally, I don't think that's at all likely. I don't think either the glaciological modelling or the field evidence points that way.