Diatom assemblage shifts relative to changes in environmental and climatic conditions in the circumpolar treeline regions of the Canadian and Siberian Arctic

Measured water variables from 77 lakes exhibited clear differences among subpolar ecozones, reflecting strong changes in biome characteristics (e.g. vegetation, permafrost, climate) across the central Canadian treeline region. Similarly, diatom distributions from the surface sediments of these lakes were closely related to ecozonal catchment differences. Ordination analysis of the modern diatom assemblages from these calibration lakes suggested that dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and total nitrogen (TN) were important variables (all decreased with increasing latitude) for explaining diatom distributions. Weighted averaging regression and calibration techniques were used to develop inference models for these variables.; Post-glacial climatic and limnological conditions were inferred from diatom assemblage changes recorded in sediment cores from two tundra lakes (Slipper Lake and TK-20) in the Canadian arctic treeline region. Reconstructed values for DIC, together with qualitative diatom changes, indicated long-term, natural acidification throughout the earlier histories of both lakes. Radiocarbon dates revealed that treeline advanced to the south of TK-20 ca 7210 cal yr BP which coincided with the development of a more diverse diatom community consisting of higher abundances of planktonic taxa. Climate amelioration at this time likely resulted in more favourable growing conditions. Unlike studies of Holocene treeline changes from nearby lakes, diatom assemblage changes in TK-20 did not reflect an abrupt reversion back to prior conditions with climate cooling ca 3600 cal yr BP which is consistent with trees never becoming established in the catchment. Increases in planktonic Cyclotella taxa in the 19th century sediments of both lakes resulted in a decrease in diatom diversity. These diatom shifts may be related to changes in aquatic habitat as a result of 19th century arctic warming.; The potential application of diatoms and other siliceous microfossils to peatland studies was assessed by a stratigraphic analysis of an arctic peat core from north-central Siberia. Diatoms, protozoan plates, and chrysophyte cysts clearly inferred changes in hydrology and moisture. Increases in phytolith abundances tracked fire episodes (as inferred from charcoal) likely triggered by drier conditions. These proxies can provide paleoenvironmental information that can strengthen interpretations derived from other commonly used peat indicators.