Two peat cores from two mires with different characteristics, but both containingpermafrost features and located in the eastern part of the Tavvavuoma mire complex innorthernmost Sweden, were analysed for macrofossils and geochemical properties. Local vegetationsequences and changes in geochemical properties of peat were used to reconstruct development ofthe studied mires during the Holocene. The study includes measurements of water/ice content, bulkdensity, loss-on-ignition and C/N ratio. Radiocarbon dates for peatland inception and permafrostaggradation are available. The main purpose of the study is to verify permafrost history in thepeatlands. The results of the macrofossil analysis and values of C/N ratio indicate nutrient poor tointermediate fen environments in both studied mires until recently. Signs of permafrost upheavalwhich caused formation of xerophilic peat can be proved only since late 1950’s. The study resultscorroborate with other studies from Northern Fennoscandia and infer peatland initiation soon afterthe deglaciation of the area and permafrost-free conditions throughout entire Holocene untilrecently.

A paleoecological study was carried out on a 4.7 m peat core from Anderson Fen on central Vancouver Island, using a multi-proxy approach. Pollen, non-pollen palynomorphs, and physicochemical analyses were used to document past vegetation, peatland developmental history, and carbon and nitrogen accumulation rates over the last 14,000 years. Lake sediment and aquatic plant remains at the base of the core indicate a shallow pond was present at the site after deglaciation. By ~11,700 calendar years before present (cal yr BP), the shallow pond became a herb-dominated wetland (marsh) through terrestrialization. Bog formation started around 10,500 cal yr BP with decreasing water levels, as indicated by high C:N, Sphagnum and fungal remains, and testate amoebae such as Archerella flavum and Heleopera. A fen developed by ~9400 cal yr BP with fluctuating water levels through the rest of Holocene. Carbon accumulation rates were highest towards the surface and during the early Holocene warm period, with an overall mean rate of 12.9 g/m2/cal yr, which is low compared to continental and northern peatlands. Pollen analysis reveals that non-arboreal communities dominated by Salix prevailed soon after deglaciation before the expansion of Pinus forests 13,200 cal yr BP. Pseudotsuga menziesii dominated forests between ~10,700 and 8400 cal yr BP under warm and dry conditions. Tsuga heterophylla rainforest was established by ~7000 cal yr BP under increasingly cool and wet conditions. Overall, Anderson fen and the surrounding area experienced major and rapid changes in environmental conditions and vegetation in response to climate change during the late glacial and early Holocene, while mid- to late Holocene changes have been more subtle and relatively gradual. / Graduate / 2020-10-25