The evolution of the Mecklenburg Bay environment in the Holocene in the light of multidisciplinary investigations of the sediment cores

Multi-proxy studies of the sediment cores and acoustic profiles from Mecklenburg Bay display a more detailed picture of the evolution of the environment in the Holocene. Studies of diatoms, geochemistry, grain size and radiocarbon dating clearly reveal the age and character of freshwater and marine transgressions and regressions. After the final regression of the Baltic Ice Lake, a local lake and swamp environment was recorded by peat gyttja sediments. This environment existed until the Ancylus Lake transgression dated ca 10,500 cal BP. During the Ancylus Lake period, the area remained a shallow-water lake, transitional isolated from the main Baltic Basin. The first slightly brackish marine inflows confirmed by the appearance of planktonic, mesohalobous and halophilous diatoms were identified at the beginning of the Initial Littorina Sea stage and dated ca 8800 cal BP. The boundary between the Ancylus Lake and the Initial Littorina Sea is marked by increasing contents of biogenic silica and iron. The Initial Littorina Sea stage was characterized by increasing mesohalobous and polyhalobous diatom forms and decreasing oligohalobous species. The Initial Littorina Sea environment was recorded as a slightly brackish reservoir sporadically affected by weak marine inflows. The Littorina transgression appeared in the Mecklenburg Bay at ca 7500–7700 cal BP and is reflected by the domination of polyhalobous diatoms, increasing mean grain size, biogenic silica, and calcium and magnesium contents. The Initial Littorina Sea was a 1500-year-long period in Mecklenburg Bay, existing until the Littorina transgression. The main Littorina transgression first appeared in Mecklenburg Bay around 7700 cal BP and after a few hundred years at around 7200 cal BP in the Arkona Basin.