Regional and local patterns of peat humification in three raised peat bogs in Varmland, south-central Sweden

摘要

Peat humification in five cores from three ombrotrophic bogs in Varmland, south-central Sweden, was analysed in an attempt to investigate local and regional responses to climate changes during the Holocene. The chronology of the five peat sequences was constrained by means of AMS radiocarbon dates and tephrochronology. Four tephras were geochemically correlated with the Askja AD 1875, Hekla-3, Kebister and Hekla-4 tephras. A further tephra, the Stomyren tephra, dated by interpolation to 2200-2100 cal yr BP was found in one bog. A composite record of peat humification changes show several periods of wetter bog conditions. These occur during the later part of the Holocene, corresponding to known climate changes in the North Atlantic region, especially around 4500-4000, 3700-3200, 3000-2700 and 1700-700 cal yr BP. Wet shifts are inferred from individual peat cores and the composite record at c. 5500, 4200, 3700, 3500, 2900, 1700, 850, 650, 500 and 250 cal yr BP. Development of composite records could be a powerful tool to smooth the palaeohydrological records in order to reduce the influence of local fluctuations in the proxy data and to extract the regional climatic signal.