Geoscience Reference
In-Depth Information
The geologic deposits in the Baltic basin, as well as in the surrounding region, are
thus archives of its history. If these can be retrieved and “read” by geologists, we
will understand the background on which we shall base our interpretations of the
most recent history on, as well as plan for the future in a continuously changing
world. Therefore, we think it is appropriate to summarize some important, and for
the Baltic basin history decisive, aspects of its youngest geologic history. It should
be noted that this summary is from a slightly south Scandinavian perspective and
from the wealth of papers published on the subject we have chosen those considered
the most appropriate, i.e., with high quality of data and with a proper chronological
control.
The interglacial/glacial cycles and their recurring glaciations have had differ-
ent types of impacts on the Baltic basin and can be summarized into some main
categories:
•
Glacial and glaciofluvial erosion of the basin and its catchment, resulting in dis-
placement of clastic sediments (ground bedrock) from the surrounding land areas
to the basin floor.
•
Repeated cycles of downwarping of the lithosphere, as an effect of the glacial
expansion and loading, and uplift/unloading during phases of deglaciation or
thinning of the ice sheet.
•
Varying ice thicknesses during more or less extensive glaciations of the
Scandinavian ice sheet have resulted in highly different uplift rates (high in the
north and low in the south) during subsequent deglaciations.
•
The combination of glacially forced global sea level changes and regional iso-
static movements has resulted in changing water levels (depths) - in both time
and space - of the basin and of the critical threshold areas.
•
The above-mentioned processes have been the main salinity regulator for the
Baltic basin, allowing more or less saline water to enter the basin through more
or less broad and deep straits.
•
The setting of the Baltic Sea basin at the rim of the northeastern Atlantic means
that it is sensitive to changes in atmospheric and marine circulation patterns of
the region. These have caused large changes in both temperature and precipita-
tion/evaporation ratios. These have had a direct and also indirect impact on the
Baltic Sea; the latter through changing river and surface run-off from the huge
catchment area, four times as large as the basin itself.
4.2 History of the Baltic Sea Prior to the Last
Glacial Maximum (LGM)
4.2.1 130-70 ka BP
Deposits from the Last Interglacial, the Eemian (basically corresponding to Marine
Oxygen Isotope Substage (MIS) 5e) ca. 130-115 ka BP, have been described
