A HOLOCENE RECORD OF CLIMATE CHANGE FROM SOUTHERN ONTARIO DEVELOPED USING GEOCHEMICAL ANALYSIS OF MARL LAKE SEDIMENTS

Several paleoclimate records from the eastern Great Lakes region reveal an abrupt shift to cold and dry conditions across the mid- to late-Holocene transition ~ 5,500 to ~4,000 years ago. The shift in climate has often been attributed to a change in atmospheric circulation linked to the Jet Stream and its influence on moisture delivery to the mid-continent. However, the precise timing of the shift in climate and spatiotemporal patterns of change across the broader region are yet resolved, because in part of the application of disparate proxies that provide different suites of paleoclimate information and different sampling strategies that yield variable resolution proxy datasets. In this study, we present new geochemical data from sediment cores collected from a small alkaline lake situated on the Niagara Escarpment in southern Ontario. Overlapping sediment cores were collected from an intermediate water depth (~ 8.6 meters) site of the lake in May of 2019. A composite 3.9-meter length core was developed by matching visible stratigraphic markers common to adjacent drives. We characterized the sediments via smear-slide mineral analysis, imaged the cores, and measured visible reflectance along with measurement of dry bulk density, loss-on-ignition for organic and carbonate content, and powder X-ray Diffraction for mineral phase identification. Our preliminary results show the composite core consists of mixed organic and calcareous (single phase calcite) sediment with no evidence of disconformities. Ongoing work includes carbonate stable isotope analysis for quantitative paleoclimate reconstruction and radiocarbon dating of terrestrial macrofossils to provide age control, all of which will provide a regional perspective to the evolution of mid- to late-Holocene climate change in the eastern Great Lakes region.