Holocene environmental history of the Gotland Basin (Baltic Sea)-a micropalaeontological model

Organic microfossils of a well-dated sediment core from Gotland Basin were analysed and used for the ecological interpretation of the Holocene history of this area. To avoid confusion with corrected and uncorrected 14C ages, only calendar years BP are used. In the lowermost part organic microfossils are rare, but few marine dinoflagellate cysts between 11 300 and 11 000 years BP indicate the marine Yoldia Phase. At 9800 years BP a significant environmental change is indicated by the rapid increase of freshwater dinoflagellates and pine pollen. At the end of the freshwater stage an enormous abundance increase of cladoceran remains indicates an eutrophication event between 7600 and 7400 years BP. First permanent brackish water conditions of the surface water were established at 7400 years BP and the increasing salinity reached its maximum between 6700 and 6400 years BP. Further changes in the brackish surface water ecosystem of the Gotland Basin can be found at 5500, 4400, 3000, 1000, and 800 years BP, which are thought to be mainly climatically induced.