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Past environmental and climatic changes related to tree-line shifts inferred from fossil diatoms from a lake near the Lena River Delta, Siberia

Kathleen M. Rühland

John P. Smol

Paleoecological Environmental Assessment and Research Laboratory (PEARL), Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6

Changes in diatom assemblages in a sediment core taken from a tundra lake near the Lena River Delta, northeastern Siberia, reflect climatic and environmental changes throughout the Holocene. Significant limnological changes occurred at the same time as trees advanced into the region c. 9100 cal. yr BP (8500 radiocarbon yr BP) and subsequently retreated c. 3800 cal. yr BP (3500 radiocarbon yr BP). Prior to this tree-line shift, diatom assemblages were dominated by small benthic Fragilaria species, and diatom-inferred alka linity values were high, suggesting that climatic conditions were cool and relatively dry, and that lake pro ductivity was probably low. Coincident with tree-line advance into the region c. 9100 cal. yr BP, inferred alkalinity decreased and remained low throughout the forested period, reflecting soil development and increased organic runoff associated with the shift in catchment vegetation. The establishment of a larch forest in the catchment corresponded with an initial period of limnological change between 9100 and 7700 cal. yr BP, suggesting that soil and forest development took place over approximately 1400 years. Between c. 7700 cal. yr BP (c. 7000 radiocarbon yr BP) and 3800 cal. yr BP, a stable diatom assemblage dominated by Achnanthes species and low diatom-inferred alkalinity indicate the influence of organic runoff associated with a fully developed forest. A return to cooler conditions and reversion to shrub tundra c. 3800 cal. yr BP coincided with a shift back to a Fragilaria-dominated diatom assemblage and an increase in diatom-inferred alkalinity. Recent conditions have been marked by declining alkalinity estimates and a minor change in diatom assemblages, most likely reflecting an influx of humic substances from catchment peats. The close correlation between trends in reconstructed alkalinity and catchment vegetation suggests that diatom-inferred alkalinity may provide a sensitive record of soil and forest development in unpolluted circumneutral or alkaline tree-line lakes.

Key Words: Palaeolimnology • tree-line • climatic change • Arctic lakes • alkalinity • diatoms • Siberia • Holocene

The Holocene, Vol. 9, No. 5, 547-557 (1999)
DOI: 10.1191/095968399675614733


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