An 11,000‐yr record of diatom assemblage responses to climate and terrestrial vegetation changes, southwestern Québec

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Abstract A high‐resolution diatom sequence was developed from continuously laminated lake sediments in southwestern Québec, which spanned the Holocene (~11,000 yr). General and species‐specific changes in the diatom record were synchronous with patterns of vegetation succession inferred from regional palynological studies, demonstrating significant influences of terrestrial ecosystems on lake water chemistry and aquatic biota. Principal components analysis was used to identify three major diatom biostratigraphic zones corresponding broadly to early, mid‐, and late Holocene climate intervals. Benthic alkaliphilus diatom taxa were abundant when the landscape was a Picea‐dominated woodland in the early Holocene (11.1–8.0 ka), and when climate conditions were inferred as relatively cool and dry. In the mid‐Holocene (8.0–3.6 ka), warmer temperatures resulted in a stabilization of soils and forests in the catchment area. Shade‐tolerant tree species (Tsuga, Fagus, and Betula) increased during this time, and planktonic diatom taxa (Discostella stelligera and Fragilaria tenera) were abundant in the lake. The well‐known decline in Tsuga across eastern North America between 6.0 and 5.0 ka corresponded to a shift toward more nutrient‐rich lake conditions for several centuries, indicated by an increase in benthic diatom taxa and a lower ratio of chrysophytes relative to diatoms. Neoglacial cooling in the late Holocene (3.6 ka to present) triggered an initial decline in D. stelligera, which later recovered as a result of nutrient inputs that were associated with increased abundances of hardwood, deciduous species (Betula and Alnus) in the catchment. In addition to providing a high‐resolution record of lake ontogeny for the region, the full Holocene record from this lake adds a new perspective on the spatial extent of regional aridity during the Medieval Warm Period (1.2–0.8 ka).

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