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by both archaeological and geological evidence and based on a consistently cali-
brated
14
C-AMS data set, much clearer conclusions can be drawn about sea-level
fluctuations than before.
Backed by a comprehensive borehole data set, the existing ideas about the
Holocene coastal evolution in the southern Baltic were critically evaluated. It
could be shown that the sediments underlying the barriers belong to a complex
fluvio-lacustrine drainage system of Late Glacial Age. Also, the large flat sand/silt
deposits of Usedom and Zingst were primarily built in the Late Glacial period and
were reshaped only slightly during the main Littorina transgression phase. This
underlines the importance of the sea-level rise rate for coastal erosion processes.
Higher rates cause flatter shoreface profiles which deflect from a Bruun-like equi-
librium. When the rise rate decreases, the shoreface profiles tend to rebuild an
equilibrium which leads primarily to higher erosion due to deeper profile mould-
ing, but to decreasing erosion (and sediment supply) with ongoing approach to
equilibrium.
All data from the Fischland in the west to the Usedom Island in the east point
to the existence of an interconnected Late Glacial fluvio-lacustrine system which
can be related to a level of -8 to -12 m found below all West Pomeranian barriers.
During the Littorina transgression the flat surface of these deposits was inundated
very rapidly and its small inclination is assumed to be the reason that less volu-
minous beach ridges/barriers developed and migrated with the transgressing sea.
Only at locations of steeper ground could small coastal features like spits grow, but
they were eroded or overstepped when the hinge points drowned. After the sea-
level rise became slower at c. 7,800 year cal BP, the sediment supply exceeded the
growth of the accommodation space. Large beach ridge systems began to accu-
mulate at higher elevated islands and promontories and developed into barriers.
Progradation started and in bays with closed sedimentary systems, barriers were
shaped to perfectly swash aligned beaches. The sediment volume finally incorpo-
rated in the barriers corresponded to a 1-2-km retreat of the feeding cliffs. Shore
profiles became equilibrated due to the very slow rise rate and the cliff retreat rates
decreased.
An important alteration in the sediment dynamics occurred with the onset of
the Late Subatlantic transgression which started at about 1,200 year cal BP. Former
progradation changed into retrogradation which was connected with sediment mobi-
lization and faster shoreline erosion leading to elongation of spits, more frequent
inundation and overwash and the development of transgressive dune fields. On the
back barriers, peat accumulation started. After an interruption of the rise due to the
Little Ice Age, the higher dynamic mode in coastal behaviour continues after about
1850.
Acknowledgements
This study was possible due to the financial support provided by the
Deutsche Forschungsgemeinschaft, which is gratefully acknowledged (FO 488/1). We thank all
members of the SINCOS Research Group for valuable data and discussions, and students and
staff from Greifswald University for their help in the field and laboratories. We acknowledge
the recommendations of three anonymous reviewers and the editors which helped to improve the
chapter.
