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Volume 19 Issue 9 (September 2009)

GSA Today

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Article, pp. 52-53 | Full Text | PDF (861KB)


Late Holocene relative land- and sea-level changes: Providing information for stakeholders

Ian Shennan1, Glenn Milne2, Sarah Bradley3

1 Sea Level Research Unit, Dept. of Geography, Durham University, Durham DH1 3LE, UK
2 Dept. of Earth Sciences, University of Ottawa, Ottawa K1N 6N5, Canada
3 Dept. of Earth Sciences, Durham University, Durham DH1 3LE, UK

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Throughout history, human societies dependent upon coastal environments have adapted to changes in sea level. Drowned peat layers on the North Sea continental shelf contain artifacts of Mesolithic communities that had no alternative than to migrate or drown as sea level rose up to 10 mm a–1. At the same time, those in western Scotland prospered, as illustrated by analyses of Mesolithic shell middens, when the rate of sea-level rise declined to zero at a mid-Holocene highstand (Shennan et al., 2006). We can explain these contrasts by the process of glacial isostatic adjustment (GIA), which results in variable relative sea-level change around the British Isles. This geological process, driven by the build-up and retreat of the last great ice sheets, continues in and around previously glaciated regions.

The combination of contrasting relative sea-level changes around the British Isles and a large database of paleo–sea-level reconstructions provides a rigorous test for quantitative GIA models. These models offer a spatial picture not easily inferred from field research at individual sites. Two studies demonstrate the recent advances: Brooks et al. (2008) and Shennan et al. (2006). Their model predictions show good agreement with the majority of the geological evidence of relative sea-level change since 16 ka B.P., but unlike Shennan and Horton (2002), did not include a map summarizing current rates.

The approaches outlined here are applicable to the coastlines of other previously glaciated countries where the processes controlling long-term coastal change, ranging from glacial isostatic adjustment to localized sediment consolidation, are similar to the British Isles (Peltier, 1998; Törnqvist et al., 2008). We also present a map showing our best estimates of current relative sea-level change around the British Isles.

Manuscript received 20 March 2009; accepted 27 April 2009.

doi: 10.1130/GSATG50GW.1