Using Holocene sea-level data to improve sea-level predictions for the United Kingdom: a combined empirical and model-based approach

The thesis presents new sea-level data for north Wales and western Pembrokeshire. These data are used alongside the existing British sea-level database to assess current GIA models. The suitability of enclosed coastal back-barrier freshwater marshes as archives for Holocene sea level more generally is also evaluated. This work expands on the work by Gehrels and Anderson (2014) who first demonstrated the suitability of peat deposits in coastal freshwater peat-gravel back-barrier marshes for sea-level reconstructions. The suitability of the method is expanded to include peat-sandy gravel and peat-sand systems. Groundwater monitoring was used to show that the back-barrier water table is controlled by tide levels. Groundwater modelling experiments were conducted to test the controls of stratigraphy, peat permeability and marsh recharge on the link between groundwater and sea level. Hand-drilled coring was used to establish the stratigraphy of these sites. Sea-level index points were collected from basal Holocene peat that was dated by radiocarbon methods and is immune to sediment compaction. Presented here are two new compaction-free sea-level index points for north Wales and six for west Pembrokeshire. The new data show a c.5.2m sea-level rise in north Wales, between c.7400 and 1900 cal years BP. Whilst a mid Holocene highstand can not be ruled out, this data leaves little room for one to have occurred. In western Pembrokeshire sea level rose c.8.2m between c.7000 and 2900 cal years BP. Current GIA models are shown to over-predict sea level at both sites, possibly due to the under prediction of isostatic rebound. These misfits need to be addressed to improve future predictions of sea-level change for the UK.