40 Die Küste, 74 ICCE (2008), 31-44 
depths of 5-15 m. These sediments result directly from the abrasion of the underlying till 
deposits. Material with grain sizes within the range of sand is removed by wave and current 
action, leaving the coarser components behind (Swift et ah, 1971; Tauber et ah, 1999). Lag 
deposit areas are often found to be surrounded by well-sorted fine to medium sands. Except 
for areas in the immediate proximity of the coast and abrasion platforms, these sand layers 
are relatively thin, for example only 0.5 to 2 m in Kiel Bight (Seibold et ah, 1971) and the 
inner Mecklenburg Bight. Significant amounts of marine sediments are found in the deeper 
basins and channels of the Baltic Sea, where fine-grained, organic-rich sediments (mud) ac 
cumulate (Werner et ah, 1987; Lemke, 1998; Harders et al., 2005). Depending on the water 
depth, the grain-size decreases from coarse to fine silt while the content of organic matter 
increases to 10-15 % (Winterhalter at ah, 1981). 
Comparison of two sonar images (mosaics) in the Pommeranian Bight confirm the rela 
tively stable pattern of seabed sediments of several years on the lower shore-face (Tauber and 
Emeis, 2005). Even bottom currents with maximum velocities of 30 cm s _1 could not mobilize 
the sand. However, a significant portion of fine-grained material (mud, fluff) has evidently 
been advected in the bottom boundary layer under moderate hydrodynamic conditions. 
Ziervogel and Bohling (2003) observed that the erosion behaviour of mud in the 
Mecklenburg Bight was dominated by the fluffy surface material, whereas the underlying silt 
fraction showed a higher erosion threshold due to its cohesive behaviour. Their comparison 
of near-bottom hydrodynamic forcing and experimentally derived critical shear velocities 
indicates a storm-controlled particle (mud and fine sand) transport in the bight. Based on 
statistical analysis of sedimentological parameters and hydrodynamic modelling, Bobertz 
and Harff (2004) found evidence that the preferred transport pathways for clastic material 
in the south-western Baltic Sea are based on the direction of the average current vectors. An 
exception represents the Pommeranian Bight, where sediments have not been accumulated 
under present-day conditions. According to Wehner (1990, in Bobertz and Harff, 2004), 
they are of glacio-fluviatile genesis during the late Pleistocene. 
3.2 Nearshore Zone 
Typical features in shallow waters are nearshore bars which are highly dynamic morpho 
logical structures depending on wave climate and sediment availability (Short, 1999; 
Schwarzer, 2003). They occur mainly in front of lowlands where several nearshore bars ex 
ist down to 6 m below sea level. Seawards of active cliffs these nearshore bars are often miss 
ing or exhibit only one long-shore bar. Their thickness seldom exceeds 2.5 m in the south 
western Baltic Sea. However, these morphological features have a significant influence on 
coastal stability as waves are breaking and energy is dissipated around these bars. 
Wave conditions and sediment transport in shallow coastal waters depend upon expo 
sure to the main wind and wave direction. Within this context, the coastline of the southern 
Baltic Sea is exposed to both north-easterly and westerly winds. For comparison, within the 
south-western Baltic Sea (Germany and Denmark) where fjords and bays are common, the 
most effective wind direction inducing coastal currents and sediment mobilisation varies 
considerably; it includes all directions, even south for some stretches of islands. 
Schwarzer et al. (2003) could demonstrate that waves are the main controlling factor of 
seasonal variations of the upper shore-face. Morphological changes induced by storm events 
remain on a decadal scale, whereas the lower shore-face shows a more stable sedimentologi 
cal and morphological behaviour; changes are only measureable on centennial and millen