Hydrographic thresholds in the western Baltic Sea: Late Quaternary geology and the Dana River concept

Since the final Weichselian deglaciation the water exchange between Kattegat and the Baltic Sea and hence the palaeogeographical development of the (western) Baltic has been controlled by a number of sills. Major thresholds are found at the southern entrance of the Great Belt and in the Darss Sill area. The easternmost of these structures is formed by Late Weichselian sands at a level of 24 m below present sea level (bsl) at the Falster-Rügen sand plain. A second threshold consisting of till was found within the Kadet Channel at a level of 23-24 m bsl. Thus, we exclude water exchange between Mecklenburg Bay and the Arkona Basin at levels below 24 m since the end of the Pleistocene. A high resolution sediment echosounder survey at the triple junction area of Langeland Channel, Vejsnaes Channel and Winds Grave Channel showed outcropping glacial deposits. Narrow channels incised at a level below 25 m bsl are filled partly with fine grained organic rich late- and postglacial sediments. Assuming no substantial crustal movements in this area in the Holocene no Ancylus Lake drainage at a level deeper than 25 m bs1 is likely to have occurred here.