The Litorina transgression in the Helsinki region, southern Finland: new evidence from coastal mire deposits

Sediment profiles were obtained, from the basal sections of two mire basins located above the highest Litorina shore in the Helsinki region, for pollen, diatom and Cladocera analyses and radiocarbon dating with the aim of exploring the relative sea-level changes during the Litorina stage of the Baltic Sea. Both profiles provided indications of 'long-distance effects' of the Litorina transgression around 7500–6100 BP, in the form of eutrophication, inundation, increased Pediastrum abundances, declined chydorid diversity and the presence of saline water diatoms. The results support the idea that sea level rose during the Litorina stage in the Helsinki region and suggest that this transgressive event had considerable effects on natural conditions in the coastal ecosystems. The findings contradict earlier accounts of a shore level stillstand during the Littorina stage in the Helsinki district.