Geoscience Reference
In-Depth Information
The transition from the Baltic Ice Lake to its successor, the Yoldia Sea (9,700-
8,800 cal. BC), was marked by a rapid fall in the water level, about 25 m, caused
by a newly opened strait through central Sweden to the Kattegat that allowed Baltic
water to flow out into the North Sea. For a short period around 9,600 cal. BC, salt
water also entered the Baltic through this strait and created a brackish environment.
As a consequence of the decline in the water level the environmental conditions
changed rapidly, especially in the southern and the western parts of the Baltic. It
also led to an extension of the land bridge connecting northern Germany, Denmark
and Sweden.
The transition from the Baltic Ice Lake to the Yoldia Sea occurred during the
Younger Dryas stadial, which was characterized by a radical fall in the average
annual temperature throughout the whole southern Baltic area, to a level even lower
than that during the Meiendorf interstadial: the ice margin, which had moved far to
the north during the Allerød, was now located in the area that is now central Sweden
and southern Norway (Eriksen
2002
). This climate change turned the open wood-
land into wide-spread tundra again: the reindeer herds, and with them the hunter
communities, therefore returned to the southern parts of the Baltic area for the period
from 10,800 to 9,600 cal. BC (Terberger
2006a
). They ranged over an area stretch-
ing from Russia to England and central Germany (Eriksen
2002
). A few sites with
typical Ahrensburgian artefacts from central Sweden and western Norway indicate
(Fuglestvedt
2008
) that in that period a few communities also moved to the north.
According to Terberger et al. (
2004
), this expansion can be seen as evidence of a
climatic amelioration already before the periglacial climate finally ended during the
Preboreal.
The similarities in some of their equipment and in their hunting techniques indi-
cate that the communities living in this wide-spread area were culturally closely
related but, due to the differences in their material culture, they are terminologically
divided into different regional groups, e.g. the Ahrensburgian group in north-
western Germany and southern Scandinavia (Eriksen
2002
), the Fosna-Hensbacka
in south-western Norway (Fuglestvedt
1999
,
2008
) and western Sweden (Kindgren
1996
, Schmitt et al.
2006
,
2009
), and the Swiderian or Eastern Ahrensburgian group
in Poland and the eastern Baltic (Zagorska
1999
).
While the shores of the last phase of the Baltic Ice Lake and Yoldia Sea in the
south-western part of the Baltic rim were still far from the present coastline, the
eastern part experienced the emergence of new land as a result of the strong isostatic
land uplift caused by deglaciation. Recently, the ancient shoreline of the Baltic Ice
Lake on the territory of Latvia was observed at 55-12 m above the present sea
level (Eberhards and Zagorska
2002
). Palynological investigations have shown that
this development took place in five phases during the Older Dryas, Allerød and
Younger Dryas periods. As a result of this development, former ice-margin basins
developed into lakes and the beds of the Daugava and Lielupe rivers - originally
formed by glacial meltwater during the early stage of the Baltic Ice Lake - became
the drainage system for the area (Zagorska
2007a
). The subsequent banks of these
rivers were partly formed as a vertical sequence of wide terraces. Specific artefacts
