Palaeontology Department Seminar
Quantifying Holocene sea-level change in the UK
Dr. Tom Hill
Department of Palaeontology, NHM
THURSDAY 15th March
Neil Chalmers Seminar Room, DC2,
16:00 - 17:00
When comparing mid twentieth century measurements of annual sea-level rise (c. 1.8mm/yr) to the current observed rate of c. 3.3mm/yr, there is clear evidence for rising sea levels in response to human-induced global warming. But as tide gauge records are only available for the last few centuries, how do we know such changes are indeed human-induced or in fact simply part of natural cycles of sea-level change that have prevailed for hundreds and thousands of years?
Biostratigraphic analyses of Holocene coastal sediments from around the UK offer one route through which the elevation of past sea level can be quantified. In southwest England, extensive sequences of interbedded estuarine silts and freshwater peats have accumulated within the Severn Estuary basin, suitable for sedimentary coring and subsequent laboratory analyses. Preserved in abundance are diatoms, unicellular microscopic algae that live in all subaqueous environments, requiring specific environmental conditions to survive. By analysing the diatom assemblages at different depths within the sediment cores and relating the species abundance and diversity encountered to those present along the contemporary Severn Estuary coastline, it was possible to quantify the palaeo-elevation at which the estuarine sediments were deposited, relative to past sea level. Such information yields an insight into the way sea level has changed during the last 10,000 yrs and complements other, more traditional techniques of sea-level reconstruction.
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