Paleolimnological Assessment of Algal Production During the Holocene Thermal Maximum from the Sediment Record of a Boreal Lake in Northeastern Ontario
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The Holocene Thermal Maximum (HTM) was a period of enhanced warmth during the early-to- mid Holocene period largely caused by enhanced solar insolation. In northwestern Ontario, the HTM was characterized by a lower abundance of Picea pollen and an increase in Cupressaceae and Ambrosia pollen. Pollen-based inferences suggest HTM temperatures were elevated by approximately 2-3°C, and lake levels were regionally lower than today, suggesting warmer and more arid conditions than today. This warming resulted in increased algal production and associated cyanobacteria blooms in lakes in northwestern Ontario. In northeastern Ontario, climate projections suggest the HTM was 2-3°C warmer. However, to date, there has been little research on the impact of the HTM on boreal lakes in northeastern Ontario, creating a gap in our understanding of the effects of climate change on aquatic ecosystems. A pollen study conducted previously suggests the HTM was warm and wet in northeastern Ontario, and his pollen framework is used to infer past changes in climate for this study. In this thesis a paleolimnological approach is used to assess how algal assemblages changed over the Holocene from a sediment core from Charland Lake, a boreal lake in northeastern Ontario near Timmins, and if the proxy data supports a conclusion of higher levels of algal production during the warmer HTM. A carbon-dated sediment core taken from the deep-water flat central basin of Charland Lake was examined for sedimentary pigments, diatom assemblages, and percent organic matter. Statistical analysis revealed diatom and pigment assemblages and concentrations varied throughout the Holocene, broadly coinciding with changes in the regional climate as inferred from past research. Lake-water production was low after deglaciation and through the HTM, potentially attributable with an unstable landscape and associated contributions of fine clastic material to the lake. Lake-water production was highest during the post-HTM period (~4460-2590 cal yr BP), but before the onset of modern conditions. The results also suggest that the last ~4500 years had higher levels of lake-water production, than during the HTM, likely related to interactions that depend on location and landscape characteristics. In comparison to northwestern Ontario, changes in the proxies of production were not very large.