Diatom community responses to late-Holocene climatic variability, Baffin Island, Canada: a comparison of numerical approaches

A high-resolution diatom stratigraphy from the late-Holocene sediments of a small Arctic lake on Baffin Island (Nunavut, Canada) has been analysed by several numerical methods and considered in relation to independent palaeoclimatic proxies to enable an objective assessment of the response of freshwater diatom communities to climatic change. Diatom relative frequencies and absolute abundances were subjected to several manipulations, including application of a weighted-averaging transfer function for summer water temperature, conversion of valve concentrations to cell biovolumes, biostratigraphic rate-of-change, and taxonomic richness estimated by rarefaction analysis. The major directions of variability within the derived diatom data were explored using principal components analysis. Diatom-inferred lakewater temperatures and indices of diatom palaeoproductivity declined during late-Holocene cooling, and they faithfully record post-'Little Ice Age' warming. Between similar to2000 cal. BP and the 'Little Ice Age', which includes the coldest intervals of the Neoglacial, diatom assemblages diversified and destabilized, reflecting a state of intermediate disturbance. Together, these results examine different methods of interpreting freshwater diatom stratigraphic data with the objective of gaining palaeoclimatic insights from fossil assemblages.