Sea-level curves of northwest Europe: Evidence for isostatic subsidence of the German North Sea coast

Report of the project:

• North Sea

Sea-level curve Source: BGR

A thorough understanding of the causes and effects of differential relative sea-level (RSL) rise in the southern North Sea area since the end of the Last Glacial Maximum is important to help predict future morphological development along the intensively utilised German coastal zone. Several reliable post-glacial RSL curves from coastal regions of northwest Europe, based mainly on the analysis of dated basal peat layers, have been published in the past few decades, e.g. for Belgium (Denys and Baeteman, 1995), the southern Netherlands (Kiden, 1995), the western and northern Netherlands (van de Plassche, 1982), the central Netherlands (Makaske et al., 2003; van de Plassche et al., 2005) and northwest Germany (Behre, 2003). A comparison of these curves on a common time-depth scale and after correction to mean sea level (MSL) shows that RSL varies in magnitude and form between these regions, revealing a complex pattern of differential crustal movement which is attributed mainly to the variable effects of tectonic and isostatic subsidence. The Belgian RSL curve shows the best general fit with the eustatic sea-level curves of Fleming et al. (1998), Peltier (2002) and Milne et al. (2005), showing that crustal movements have had their smallest net effect on the altitude and position of the Belgian coastal plain. However, the RSL curves of the Netherlands and northwest Germany lie significantly lower than the Belgian RSL curve between 9 and 4 cal. kyr BP and diverge progressively back in time. By subtracting the maximum tectonic component, which can be roughly estimated using the depth of Eemian highstand deposits in each sub-region, an approximation of the minimum glacio- and hydro-isostatic component relative to Belgium is obtained (Kiden et al., 2002). This component had a greater effect on the position of northwest Germany than on the Netherlands between 9 and 4 cal. kyr BP and is considerably greater than was previously assumed for the German coast. The subsidence is at least in part associated with the post-glacial uplift of Scandinavia and the concurrent collapse of the peripheral regions.

Sea-level curve Source: BGR

The RSL data have been compared to geodynamic Earth and ice models in order to (i) infer the lithosphere thickness and radial viscosity structure of the Earths mantle underneath northwest Europe, as isostatic adjustment is mainly controlled by variations in these factors, and (ii) predict sea-level curves and palaeocoastlines in regions where we have no empirical data (Vink et al., 2007). The model results generally confirm earlier findings from Great Britain and Scandinavia and help to refine current palaeo-ice models as well as to determine a geodynamically-consistent viscosity distribution for the mantle. Furthermore, the comparison of model and empirical data allows the identification of the effects of local-scale factors such as compaction, past changes in tidal range or (neo)tectonic activity. 

In comparison to the relatively well-analysed continental areas, only very little information is available on the early Holocene RSL and palaeocoastline development in the deeper parts of the present North Sea. Thus, one of the aims of our North Sea project is to obtain more RSL data from the southern North Sea in order to

(i) constrain the approximate zone of maximum post-glacial isostatic subsidence, and

(ii) acquire preliminary data on the approximate rates of present tectonic subsidence in the southern North Sea (e.g. Vink et al., 2007). 

 

 

Project/research partners:

• Holger Steffen – Institute of Geodesy, Leibniz University Hannover
• Georg Kaufmann – Institute of Geological Sciences, FU Berlin
• Steffen Wolters; Felix Bittmann – Lower Saxony Institute for Historical Coastal Research (NIhK), Wilhelmshaven
• Manfred Frechen –Leibniz Institute for Applied Geosciences (GGA), Hannover
  

Literature:

• Behre, K.-E., 2003. Eine neue Meeresspiegelkurve für die südliche Nordsee: Transgressionen und Regressionen in den letzten 10.000 Jahren. Probleme der Küstenforschung im südlichen Nordseegebiet 28, 9-63.
  
  
• Denys, L., Baeteman, C., 1995. Holocene evolution of relative sea level and local mean high water spring tides in Belgium – a first assessment. Marine Geology 124, 1-19.
  
  
• Fleming, K., Johnson, P., Zwartz, D., Yokoyama, Y., Lambeck, K., Chappell, J., 1998. Refining the eustatic sea-level curve since the Last Glacial Maximum using far- and intermediate-field sites. Earth and Planetary Science Letters 163, 327-342.
  
  
• Kiden, P., 1995. Holocene relative sea-level change and crustal movement in the southwestern Netherlands. Marine Geology 124, 21-41.
  
  
• Kiden, P., Denys, L., 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. J. Quat. Sci. 17, 535-546.
  
  
• Makaske, B., van Smeerdijk, D.G., Peeters, H., Mulder, J.R., Spek, T., 2003. Relative water-level rise in the Flevo lagoon (The Netherlands), 5300–2300 cal. yr BC: an evaluation of new and existing basal peat time-depth data. Netherlands Journal of Geosciences 82, 115-131.
  
  
• Milne, G.A., Long, A.J., Bassett, S.E. (2005). Modelling Holocene relative sea-level observations from the Caribbean and South America. Quat. Sci. Rev. 24, 1183-1202.
  
  
• Peltier, W.R. (2002). On eustatic sea level history: Last Glacial Maximum to Holocene. Quat. Sci. Rev. 21, 377-396.
  
  
• Van de Plassche, O., 1982. Sea-level change and water-level movements in the Netherlands during the Holocene. Mededelingen Rijks Geologische Dienst 36(1), 1-93.
  
  
• Van de Plassche, O., Bohncke, S.J.P., Makaske, B., van der Plicht, J., 2005. Water-level changes in the Flevo area, central Netherlands (5300–1500 BC): implications for relative mean sea-level rise in the Western Netherlands. Quaternary International 133-134, 77-93.
  
  
• Vink, A., Steffen, H., Reinhardt, L., Kaufmann, G., 2007. Holocene relative sea-level change, isostatic subsidence and the radial viscosity structure of the mantel of northwest Europe (Belgium, the Netherlands, Germany, southern North Sea). Quaternary Science Reviews, eingereicht.