Kiden P., Denys L. and Johnston P. 2002. Late Quaternary sea-level change and isostatic and tectonic land movements along the Belgian-Dutch North Sea coast: geological data and model results.ABSTRACT: Early and middle Holocene sea-level data from Belgium plot ca. 2 m above data from the western Netherlands, reflecting differential tectonic and isostatic movements. The total uplift rate of Belgium relative to the western Netherlands decays gradually from 0.66 m kyr −1 at 7500 cal. yr BP to less than 0.25 m kyr −1 since 5000 cal. yr BP. The tectonic component of this relative movement, inferred from Eemian sea-level data, is in the order of 0.06 to 0.16 m kyr −1 . The isostatic component of the uplift is related to the last phase of the collapse of a peripheral bulge under The Netherlands and the Dutch and German sectors of the North Sea, and to hydroisostatic subsidence of the North Sea basin caused by water loading as sea-level rose. Comparisons with isostatic rebound models show that they predict well the Holocene isostatic movement between Belgium and the western Netherlands, and that the predictions are improved when the tectonic component is removed from the observations. Preliminary evaluation of sea-level data from the Dutch sector of the North Sea shows that glacio-hydroisostatic subsidence relative to Belgium was significantly greater than for the western Netherlands coastal area, and spatially highly variable.

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Although the Netherlands has a long tradition of sea-level research, no Holocene relative sea-level curve is available for the north of the country. Previous studies hypothesized that the relative sea-level reconstruction for the western Netherlands is also valid for the northern part of the country. However, glacial isostatic adjustment (GIA) models predict a lower and steeper relative sea-level curve because of greater postglacial isostatic subsidence. Long-term data of relative sea-level change are important to inform GIA models and understand postglacial vertical land motion related to the rebound of Fennoscandia and neotectonic activity. We compiled and evaluated a set of basal peat radiocarbon dates to reconstruct the Holocene relative mean sealevel rise in the Dutch Wadden Sea area. For the early Holocene, this reconstruction is lower than the western Netherlands curve. After 6400 cal a BP, the curve for the Wadden Sea is statistically indistinguishable from that for the western Netherlands, a result that conflicts with GIA model results. It remains to be investigated whether the problem lies with the GIA model predictions or with the quality of the available data. Additional basal peat radiocarbon dates from suitable sites should be collected to further resolve this problem.