Geoscience Reference
In-Depth Information
early Medieval times, the bay was still separated from the Wismar Bight by the
remains of a ground moraine that formed a natural barrier. The moraine was then
cut through by just a small inlet, thus connecting the Wismar Bight with the bay
to create outstanding conditions for its use as a natural harbour. Given the above-
mentioned rising sea level in the Wismar Bight, the ground moraine was gradually
completely eroded over the last 1,200 years and the shoreline of the harbour bay
displaced by about 80 m towards the coast so that the former waterfront area and
harbour basin are now completely submerged. Observations made on the site indi-
cate that the sea level in the eighth century AD was 80-100 cm lower than the
present sea level. It seems possible that the gradual erosion of the ground moraine
as a result of the rising sea level finally led to the loss of the harbour's natural pro-
tection, which could also be a reason for abandoning the trading centre already at
the beginning of the ninth century AD.
The Haithabu trading centre can be regarded as the economic successor of
reric
/Groß Strömkendorf (Jöns
1999
). It existed from the eighth to the eleventh
century AD and was situated at the head of the Schlei fjord - a narrow, navigable
inlet flowing into the Baltic Sea. During the ninth and tenth centuries AD, Haithabu
was the most important trading centre on the southern Baltic rim and a link between
the North Sea and Baltic trade routes (for a summary see Carnap-Bornheim and
Hilberg
2006
).
The history of the Schlei fjord has recently been reconstructed by Labes
(
2002
/
03
) with regard to the sea-level changes from the Bronze Age to modern
times. Her research is mainly based on a number of radiocarbon-dated tree stumps
and data from several archaeological sites that were originally located on the banks
of the Schlei. The data prove that the sea level around 2,500 cal. BC was approxi-
mately 2 m lower than today and that it rose during the second millennium BC up
to 1 m below the present sea level. By around the beginning of the first millennium
AD, the sea level is thought to have reached almost the present level. A regression
to a level 1 m below the present sea level has been reconstructed for the first millen-
nium AD, followed by repeated transgression phases during the second millennium
AD until the present level was reached. These data were, in general, confirmed by
the recently completed evaluation of the excavations in the harbour area of Haithabu
(Kalmring
2010
). In his conclusion, this author has assumed a sea level in the tenth
century AD at 80 cm below the present level.
The most important trading centre in the central Baltic area was undoubtedly
Birka, located on Björko island in Lake Mälaren (for a summary see Gräslund
2001
).
Trade and exchange, between the western and eastern Baltic as well as to the eastern
Mediterranean via the Russian rivers, was organized from here between the eighth
and tenth centuries AD (Noonan
1997
).
The main harbour area of Birka has also been at least partially excavated and
yielded evidence of several jetties at different levels between 5 and 6 m above
the present sea level and at various distances from the present shore (Fig.
15.17
).
Considerable shore displacement and a fall in sea level during the Viking period is
obvious (Ambrosiani and Clarke
1998
). Numerous typologically datable artefacts,
found in direct association with the jetties, could be used to adjust the regional
