Coastlines of the Baltic Sea – Zones of Competition Between Geological Processes and a Changing Climate: Examples from the Southern Baltic

Abstract

Relative sea level change is, besides the geological buildup and hydrographic parameters, the main controlling factor in shaping the coastlines on the centennial timescale and beyond. Vertical displacement of the earth’s crust and eustasy serve as main components driving the relative sea level (RSL) change during the Quaternary. Whereas the eustatic change mirrors mainly climatic factors, the vertical displacement of the earth’s crust has to be regarded in former glaciated areas as a result of glacio-isostatic adjustment superimposed by the regional tectonic regime or land subsidence due to local factors. A simple model is applied to reconstruct the palaeogeographic development of a coastal area and to generate future projections as coastline scenarios. For the hindcast relative sea level curves have to be compared with recent digital elevation models. For future projections data of vertical crustal displacement received from gauge measurements and eustatic changes based on climate scenarios have to be superimposed. The model has been applied to the Baltic Basin, considered as a natural laboratory for coastal research as it is extending from the uplifting Fennoscandian Shield to the subsiding southern Baltic lowlands. Subsidence, climatically driven sea level rise, and meteorologically induced coastal flooding provoke permanent coastal retreat at the southern sinking coasts. Predictions of coastal hazards are made with the model by using neotectonical data and long-term sea level change data superimposed with extreme sea level data measured during the storm surge in November 1872.