Holocene climate variability and periodicities in south-central Sweden, as interpreted from peat humification analysis

Analysis of the decomposition of peat has been used to identify climatic shifts over the last 10 000 years in two raised bogs, Stomyren and Kortlandamossen, south-central Sweden. Age-depth curves have been constructed using radiocarbon dates and tephra layers. Peat humification data have been subjected to spectral analyses using the Lomb-Scargle Fourier method and reveal a periodicity of c. 250 years in both records. Cycles of c. 200 yr and c 400 yr were found at Stomyren and at Kortlandamossen, respectively. These periodicities could correspond to changes in solar activity levels. A test estimating the possible level of noise has been applied to the spectral analyses. The humification indices indicate prominent shifts to wetter conditions at c. 7500, 4300-4200, 3700-3500 and 2800-2400 cal. yr BR The most distinct drier phases start at c. 4500 and 3250 cal. yr BP.