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Saturday, 23 April 2011

A History of Holocene Sea-level change in SW Britain

 I have posted this before, but here it is again....

This is the overall pattern of eustatic sea-level rise at the end of the Devensian Glaciation, as agreed by most experts from a wide range of disciplines:

Around 14,500  years ago, sea-level stood around -100 m, but a rapid rise of 40 m occurred up to 13,000 BP at a rate of 3.7 m per century.  A second major melting phase at 11,000 BP raised eustatic sea-level to around – 40 m by the beginning of the Holocene (10,000 BP) at a rate of 2.5 m per century, by which time global ice volumes had been reduced by over 50%.

Holocene sea-level then rose in the Bristol Channel area from -35 m OD at 9,500 BP to 2-5 m OD at 5,000 BP.  The rate of sea incursion gradually declined.  Around 7,000 years BP sea-level was around 8 - 10 m lower than it is today, depending on whose curve you are using (there is generally assumed to be a margin of error of + or - 1m)

After around 6,000 BP the marine incursion into coastal areas of northwest Europe took place more slowly.  In Neolithic times, the sea was at c -6m OD, and in Bronze Age times about -4m OD.  About 2,000 years ago (the time of the Romans in the UK) sea-level was probably about 2m below that of today -- but it may have been higher.  

The configuration of the British coastline around the time of Christ was similar to that of the present day, except that it was more indented due to the drowning of wetlands and estuaries which have subsequently silted up.  As mentioned in earlier posts, the evidence is difficult to interpret in some estuarine and fenland environments because of the effects of storm surges, changes of coastal configuration resulting from the breaching of dune barriers or pebble beaches, and from the compaction of sediments.

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