Holocene climate variability and long-term diatom community dynamics in a small lake on Victoria Island, Northwest Territory, Canada

A lake sediment core spanning 9900 years, collected from a small lake on western Victoria Island, provides a high-resolution record of diatom community dynamics over the Holocene. Ten radiocarbon dates and 210Pb dating provided the core chronology. Loss-on-ignition (LOI) gradually increased over the Holocene whereas carbonate content and magnetic susceptibility showed an inverse trend. Biogenic silica content had apparent cyclicity over ~1500 year periods. Major shifts in diatom assemblages at 8100-8000 calendar years before present (cal yrs BP), 5800-5700 cal yrs BP, and 3800-3500 cal yrs BP occurred simultaneously with millennial-scale climate changes reported from the region. There is evidence of diatom community response to centennial scale variations such as the 'Medieval Warm Period' (~1000-700 calendar years before present, cal yrs BP), 'Little Ice Age' (~800-150 cal yrs BP) and recent warming. Variations of the taxa within the genera Staurosira, Pseudostaurosira, Fragilaria, and Staurosirella, usually combined into one genus in Arctic lake sediment studies, suggest these taxa may be more useful in paleolimnological studies than previously believed. Although recent changes in diatom community composition, production and species richness were apparent they were surpassed at other periods throughout the Holocene. The rate of community compositional change in the last few centuries was rapid, however it was not exceptional in the lake history.