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Arctic and sub-arctic lake sediment sequences from the Pleistocene are uncommon due to multiple glacial–interglacial cycles and the associated advances and retreats of Pleistocene ice sheets. Pleistocene strata are preserved in a 9-m-long sediment core recovered from Pingualuit Crater Lake, Nunavik, northern Quebec (Canada). In addition to tychoplanktonic Aulacoseira species, the Pleistocene planktonic flora comprises representatives from the thalassiosiroid genera Cyclotella, Discostella and Puncticulata, of which most species are extant in perennially ice-free sub-arctic and arctic lakes. One Cyclotella species, C. pingualuitii is described as new and is characterized by a small central area, multiple central and scattered marginal fultoportulae with triangular satellite pore covers, a single large submarginal rimoportula and alveolate striae of unequal length. Cyclotella pingualuitii is the most prominent species during the oldest diatom-rich interval (DR3) recovered, which was deposited during the Lat...

Knowledge of the composition and ecological preferences of diatom assemblages in northern regions is important for paleoenvironmental reconstructions of variables related to climate and/or anthropogenic disturbances. Relatively little is presently known about diatoms from circumpolar treeline areas, especially for lakes located in northern Russia. Our study set included lakes in the Siberian tundra, forest-tundra, and boreal forest regions close to Norilsk, of which nine sites were subject to anthropogenic disturbances, such as mining and housing developments. We enumerated surficial sediment diatom assemblages and used multivariate statistical techniques to investigate which environmental variables were important in explaining the variation in diatom assemblages within our lake set. Deeper lakes were associated with higher abundances of planktonic centric taxa, such as Cyclotella Kutzing species. Warmer, higher conductivity forested lakes were associated with higher abundances of planktonic pennate taxa,...

La presente etude a permis de determiner la flore diatomifere de quatre sources thermales situees au Canada (Iles de la Reine-Charlotte en Colombie Britannique et Takhini au Yukon), au sud-ouest de l'Islande et au Japon (mont Hakone). La composition en especes des assemblages de chaque echantillon est decrite et appuyee par des illustrations originales. Certains assemblages sont constitues d'especes dominantes, telles que Diadesmis gallica W. Smith pour l'echantillon de Takhini, Brachysira microcephala (Grunow) Compere et Achnanthes minutissima Kutzing pour l'Islande et Pinnularia sp. [aff. anglica (Cleve) Krammer] pour le Japon. La majorite des taxons repertories sont des formes alcaliphiles et circumneutrales selon leur affinite pour le pH, et de formes oligohalobes, mesohalobes et euryhalobes selon la salinite. La comparaison de la microflore entre les quatre sources echantillonnees nous amene a la conclusion qu'on ne peut ici etablir de flore diatomifere specifique aux sources thermales. L'eloignement...