What Determines the Change of Coastlines in the Baltic Sea?

Abstract

The change of coastline positions of the Baltic Sea is mainly determined by both the eustatic sea-level change and the glacio-isostatic adjustment (GIA). For changes on the Holocene time scale, the relative sea-level change can be reconstructed from paleo-coastline positions and correspondingly dated sediments and organic remains. On the decadal scale, tide gauge data are available. Both data sets display the relative value of sea-level change resulting from the superposition of climatically and meteorologically induced factors, vertical crustal displacement, and related gravitational forces. The isolation of the GIA signal from the compound relative sea-level change data plays a critical role for future projections of coastline changes within the frame of coastal zone management. To separate different components of sea-level data sets, statistical methods for the exploration of empirical water level, meteorological, and GPS data are combined with analytical methods to solve the sea-level equation. In the result, the pattern of vertical crustal movement can be displayed as maps covering the uplifting Fennoscandian Shield and its subsiding belt. Whereas along the uplifting coasts morphodynamic processes play a subordinated role, in the subsiding Southeast and South, Quaternary sediments are permanently exposed to coastal erosion, sediment transport, and re-deposition. This mainly wave-driven sediment dynamics together with aeolian processes depend on meteorological forcing of the in general west-east directed air-flow from the northern Atlantic Ocean to Eurasia. Regional coastal morphogenesis can generally be described by alongshore sediment transport pattern deduced from the integration of subregional to local models of transport capacities. For future projection, coastlines and the morphology of the adjacent zones have to be regarded a function of its position related to the vertical displacement of the Earth's crust, the regional climatic and meteorological conditions, and the geological setting. Results of climate modelling, the Earth’s visco-elastic response to the deglaciation, geological data and regional sediment transport capacities have to be interpreted comprehensively.