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Baltic Sea; Gotland Deep; North Central Basin; sediment; Cladocera; biostratigraphy; Baltic stages
Abstract:
Cladoceran remains were analysed in two sediment cores from the Gotland Deep and the North Central Basin which cover the period of the last 10,000 years. Cladoceran stratigraphy divided the profiles into three faunal zones: (1) The Ancylus stage was characterised by the co-occurrence of three taxa of freshwater planktonic cladocera, i.e. Bosmina longispina, Bosmina longirostris, and Daphnia sp. (2) During the Litorina stage foraminifers were present together with very low numbers of Bosmina longispina. (3) In the uppermost section of the cores a decrease in the foraminifers and a significant increase in Bosmina longispina occurred, possibly due to a drop in salinity (Limnaea stage ?). During the Ancylus stage the species Bosmina longispina is represented by a freshwater population while the specimens from the uppermost section belong to the brackish water race Bosmina longispina maritima. The conspicuous peaks in the frequencies of Bosmina longispina and B. longirostris observed at the end of the Ancylus stage seem to be a typical phenomenon in the Central Baltic of that time and have been previously reported from the Bornholm Basin and the Gdansk Bay.
