Environmental and climatic aspects of the early to mid Holocene calcareous tufa and land mollusc fauna in southern Sweden

Abstract: Although deposition of freshwater calcium carbonates, tufa, has occurred in large areas with carbonate soil or bedrock in Sweden, no tufa formation has been observed in Sweden. To better understand the factors controlling tufa formation in southern Sweden, bio- and lithostratigraphical studies were carried out on (paludal) calcareous tufa deposits in the province of Skåne. The biostratigraphical methods include mollusc, pollen, plant macrofossil and insect analysis. These were supplemented by lithological and chemical analyses. An additional aim of the study was to provide new information on the postglacial immigration of terrestrial molluscs into Sweden. The chronology was based on pollen stratigraphical correlation and radiocarbon dating. Tufa formation was found to have occurred at several sites during the early Preboreal and Boreal 11,500-7,800 calibrated years BP (cal. BP). A tufa deposit was also recorded at one site dating to the Subboreal period (5,600-5,400 cal. BP). These periods were characterised by low lake levels in southern Sweden, suggesting that tufa deposition was favoured by drier conditions. The results thus indicate that Holocene tufa deposition in Skåne is likely to be controlled climate. Terrestrial molluscs proved to be potentially valuable as environmental indicators and were important in the palaeoenvironmental reconstructions. During the early Preboreal to early Boreal (11,500-7,800 cal. BP) the carrs remained open to semi-open. In the late Boreal (around 7,800 cal. BP) they became well shaded. A number of species were recorded that are rare in the region today. These include Vertigo genesii, Vertigo geyeri, Cochlicopa nitens and Vertigo moulinsiana, which are all on the national Red List of endangered species and included in the European Community’s habitat and species directory. Whereas Cochlicopa nitens and Vertigo moulinsiana seem to have been rare in Skåne during the early Holocene, which is also the case today, Vertigo genesii and Vertigo geyeri appear to have been common in the early Holocene. It was shown that the historical record is necessary to understand the full extent of the species biological requirements. An attempt to use carbon and oxygen stable isotope analysis of tufa and land molluscs to reconstruct palaeoclimatic conditions suggests that the method is worth testing in a full-scale investigation. Methodological and other questions related to the analysis of tufa deposits and malacology are also addressed.