Paleoenvironmental record of Holocene storm event frequency in the lower Great Lakes

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Climate models predict an increase in the frequency of destructive tropical hurricanes and mid-latitude cyclonic storms in North America as a consequence of climate warming. The available historical record of past storm events (<150 years), however, is too short to evaluate climate model predictions. The NSERC-funded research will employ measurements of the physical and geochemical properties of lake sediments to better understand the frequency of storm events in the lower Great Lakes over the past 8000 years. During large storm events, storm waves over top sandy beach barriers depositing distinctive overwash sand layers in coastal lagoons. Storm layers are also deposited in lakes by the flood discharge of rivers. These deposits (tempestites) can be identified in sediment cores extracted from the lake bed based on their sedimentary characteristics (grain size, microfauna, magnetic properties) and geochemical composition. Radiocarbon dating of storm event layers provides a detailed chronological record of storms and extreme weather events during periods when Holocene climate was both warmer and dryer (the Hypsithermal) and cooler and wetter (Little Ice Age) than present. Boyce and research team (1 Ph.D., 2 M.Sc., 5 B.Sc. students) will investigate the geochemical and sedimentary properties of storm sediment layers in three Lake Ontario coastal lagoons (Frenchman's Bay, Pickering; Sandbanks, Prince Edward County) and in Rice Lake (Peterborough). The researchers will geochemically "finger-print" storm deposits by measuring the abundance of elements in core sediments using micro-X-ray-florescence (micro-XRF) core scanning technology available in the McMaster ITRAX facility. The ITRAX core scanner uses an X-ray beam to measure the abundance of a wide range of elements in core samples, including elements (e.g. Ti, K, Si, Rb, Zr) that are diagnostic of storm deposition. The scanner also records changes in the magnetization of the core and produces a high-resolution colour and X-ray images that can be used to identify changes in sediment grain size and composition. Using these combined properties, it is possible to detect very thin storm event layers (<0.2 mm), yielding highly-detailed records of past storm events. A detailed chronology of past Holocene (<8 Ka) storm events and climate variability will be obtained by radiocarbon dating of pollen in lake sediments. and 210-Pb dating. The high-resolution lake sediment record will allow McMaster researchers to assess whether the frequency of large storms events has been different in the past, and whether variability in storminess is linked to climate variables, such as past changes in temperature and precipitation. These data are critical for evaluating predicted changes in storm frequency and will assist in the development of emergency and infrastructure planning for heavily populated areas of the Great Lakes that are at risk from severe weather.