A chronology of environmental changes in the Lake Vattern basin from deglaciation to its final isolation

During and after deglaciation, Lake Vattern developed from a proglacial lake situated at the westernmost rim of the Baltic Ice Lake (BIL), into a brackish water body connecting the North Sea and the Baltic Sea, and finally into an isolated freshwater lake. Here we present geochemical and mineralogical data from a 70-m composite sediment core recovered in southern Lake Vattern. Together with a radiocarbon age model of this core, we are able to delineate the character and timing of the different lake stages. In addition to a common mineralogical background signature seen throughout the sediment core, the proglacial sediments bear a calcite imprint representing ice-sheet transported material from the limestone bedrock that borders the lake basin in the northeast. The proglacial fresh to brackish water transition is dated to 11480 +/- 290cal. a BP and is in close agreement with other regional chronologies. The brackish period lasted c.300years and was followed by a c.1600year freshwater period before the Vattern basin became isolated from the Initial Littorina Sea. Decreasing detrital input, increasing C-13 values and the appearance of diatoms in the upper 15m of the sediment succession are interpreted as an overall increase in biological productivity. This mode of sedimentation continues until the present and is interpreted to mark the final isolation of the lake at 9530 +/- 50cal. a BP. Consequently, the isolation of Lake Vattern was not an outcome of the Ancylus Lake regression, but rather because of ongoing continental uplift in the early Littorina period.