Palaeoecological Characteristics of a Subarctic Glacier Lake Based on Diatom Algae and Pigments from Bottom Sediments

The taxonomic composition of diatoms and the content of plant pigments were studied in a 40-cm sediment core from a postglacial oligotrophic lake of marine origin located on the shore of the White Sea (Lake Krivoe, Northern Karelia). Based on the content of chlorophyll a, pheopigments, and organic matter, the lake’s bottom sediments (sapropelites) correspond to the hypertrophic category throughout the evolution of the lake (marine lagoon, meromictic lake, freshwater lake). In the upper layers of the core (i.e., in freshwater conditions), the richness of planktonic diatoms (Pantocsekiella, Stephanodiscus, and Aulacoseira) was low, indicating stable pelagic conditions. Pennate diatoms, which are periphytic and benthic producers, were highly diverse and abundant. Pigment content dynamics show a trend toward decreasing productivity to date.