A latest Pleistocene palynologic record from western New York
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Understanding the geographic extent of past large-scale abrupt climate change is essential for predicting outcomes of contemporary climate change, as climate models that are used to assess future climate scenarios rely on paleoclimate data. Therefore, tracing the geographic extent of past climate oscillations is essential for understanding the impacts of future change. The relatively warm Bølling-Allerød (B-A; 14,700-12,900 cal yr BP) and relatively cold Younger Dryas (YD; 12,900-11,700 cal yr BP) periods are well-documented climate events during the latest Pleistocene that were likely triggered or amplified by changes in Atlantic Meridional Overturning Circulation (AMOC). While these climate oscillations have been well-documented around the Northern Hemisphere, their spatial distribution is poorly understood in the eastern Great Lakes region of the United States. The B-A and YD have strong paleoclimate signals in the northeastern US, but those signals become more difficult to interpret farther west from the Atlantic and towards the Great Lakes. This thesis assesses impacts of late Pleistocene climate events in the eastern Great Lakes region. There is a lack of paleoclimate records that extend into the late Pleistocene. Existing records that capture the B-A and YD often offer mixed signals, especially regarding impacts of the YD. A 6.3 meter-long sediment core with a basal age of 15,190 ± 200 cal yr BP was extracted from Dragonfly Kettle, western New York. A vegetation reconstruction via pollen analysis was created from a two meter long section of the core, covering ~15,000-11,400 cal yr BP. Loss-on-ignition, moisture content, and magnetic susceptibility were measured at a 0.5 cm interval, giving a ~20 year resolution. Fossil pollen assemblages were analyzed at a 4 cm interval, giving a ~90 year resolution. The results reveal vegetation shifts that are coincident with the timing of the B-A and the YD boundaries, and vegetation types consistent with these warm and cold climate intervals. The study site was characterized by high amounts of grasses and pioneer plants such as birch and willow, implying a geomorphically unstable landscape and cold conditions at the end of the Oldest Dryas (~15,000 cal yr BP). The appearance of temperate broad leaf deciduous trees and the decrease in grasses during the B-A (14,700-12,900 cal yr BP) are a strong indicator of warmer growing conditions and greater moisture availability. However, the coexistence of trees such as oak, ironwood, fir, and spruce contain elements of a plant community with no modern analogue, making climate interpretations difficult. Additionally, high charcoal concentrations during the B-A suggest that the landscape may still have been prone to large disturbances. The sudden disappearance of the temperate trees, accompanied by an increase in boreal forest trees, indicates a return to stadial-like conditions during the YD (12,900-11,700 cal yr BP). A peak in pine percentages, a decline in ragweed, and the reappearance of walnut trees during the early Holocene suggest a more stable landscape, characterized by drier and warmer conditions. The vegetation reconstruction implies that western New York, although geographically far from the Atlantic Ocean, was affected by latest Pleistocene large-scale climate oscillations associated with AMOC disturbances.