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By S. Crivellari


The Baltic Sea can be considered the European largest estuary. At present, it has restricted exchange with the North Sea and strong latitudinal and vertical temperature and salinity gradients. During the Holocene, the Baltic hydrogeological conditions have changed dramatically: after the onset of the present interglacial and the “Baltic ice-lake period”, a lake phase (from 10 cal kyrs BP to 8.5 cal kyrs BP) was followed by a phase in which a connection with the sea took place at ~ 8 kyrs BP. The opening of a wide and deep strait in the south allowed for extensive salty water inflow causing an increase in the salinity of the Baltic water to values higher than today, reaching the maximum during the transgression at the Holocene Climatic Optimum. This study aims to investigate major environmental trends focusing on salinity and productivity/anoxia shifts in the Baltic Sea during the Holocene by using dinoflagellate cyst (dinocyst) assemblages and other brackish to freshwater palynomorphs. At first, a survey of present-day dinocyst assemblages from surface sediments has been performed. Dinocysts show remarkable changes in the assemblages, which can be related to salinity. A strong salinity gradient from the Danish strait to the Baltic Proper basin occurs. Samples closer to the Danish strait and influenced by North Sea water are dominated by marine taxa such as Operculodinium centrocarpum, Lingulodinium machaerophorum, Spiniferites spp. and Brigantedinium spp. dominate. Samples from the Baltic Proper are dominated by brackish-freshwater dinocyst species such as Pyxidinopsis psilata along with the massive presence of freshwater algae and acritarchs. The results obtained from surface sediment samples assemblages were used to reconstruct Holocene salinity trends in core LL19 (Gotland Basin). Dinocyst and other palynomorph assemblages are useful to target the lake to sea transition and the salinity maximum. In particular Gonyaulax apiculata and Ataxodinium choane are good indicators for the lake-sea transition and for targeting the salinity maximum, respectively. Based on freshwater indicators and the presence of Ataxodinium choane, reconstructed salinity values may have been higher than previously thought (Gustafsson, 2002) during the salinity maximum. We argue that salinity could have reached 20-22 psu

Topics: Baltic Sea, Holocene, dinoflagellate cysts, Salinity
Year: 2012
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