Palaeohydrography and marine conditions in the south-western part of the Vänern basin during the Younger Dryas and Early Preboreal

Abstract

A clay-sequence from Lake Götesjön in the south-western part of the Lake Vänern basin has been investigated with respect to the foraminiferal and ostracod faunas and δ18Oc and δ13Cc. The sequence covers the middle/late Younger Dryas and the early part of the Preboreal chronozones. The conditions were severe during the Younger Dryas due to sea ice cover and a proximal position to the ice. The faunal assemblages indicate arctic glaciomarine conditions with a reduced salinity and the marine conditions ceased at c. 9700 14C-years BP. In the late Younger Dryas an increased ice retreat raised the salinity of the bottomwater. This was due to the formation of reaction currents with marine water entering the basin at the bottom as a response to a surface freshwater flowing out from the basin. A period with improved marine conditions is recorded in the Early Preboreal. The transition from the Younger Dryas to the Preboreal is recorded as a lowering in the δ18Oc due to increased input of meltwater and higher δ13Cc as a consequence of a more intensive mixing of water masses and a less extensive sea ice cover. The Vedde Ash is found in the lower part of the sequence and AMS radiocarbon datings of bivalves suggest a marine reservoir age in the area of 800–900 years during the Younger Dryas. The final drainage of the Baltic Ice Lake had only limited effects on the marine environment in the south-western part of the Vänern basin.