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

气候模型预测，由于气候变暖，北美洲破坏性热带飓风和中纬度气旋风暴的频率将增加。然而，现有的过去风暴事件（<150年）的历史记录太短，无法评估气候模式的预测。NSERC资助的研究将采用湖泊沉积物的物理和地球化学性质的测量，以更好地了解过去8000年来五大湖下游风暴事件的频率。在大风暴事件期间，风暴波越过顶部桑迪海滩屏障，在沿海泻湖中沉积独特的过冲砂层。河流的泄洪也会使风暴层沉积在湖泊中。这些沉积物（风暴岩）可以根据其沉积特征（粒度、微型动物、磁性）和地球化学成分，在从湖床提取的沉积物岩心中识别。风暴事件层的放射性碳测年提供了一个详细的风暴和极端天气事件的年代记录，在全新世气候既温暖和干燥（高温）和凉爽和潮湿（小冰河时代）比现在。博伊斯和研究团队（1名博士，2名硕士，5名B.Sc.学生）将调查三个安大略湖沿海泻湖（皮克林的法国人湾;爱德华王子县的沙洲）和米湖（彼得伯勒）风暴沉积层的地球化学和沉积特性。研究人员将通过使用麦克马斯特ITRAX设施中的微X射线荧光（micro-XRF）核心扫描技术测量核心沉积物中元素的丰度，对风暴沉积物进行地球化学“指纹”。ITRAX岩心扫描仪使用X射线束测量岩心样品中各种元素的丰度，包括可诊断风暴沉积的元素（如Ti、K、Si、Rb、Zr）。扫描仪还记录岩芯磁化的变化，并产生高分辨率彩色和X射线图像，可用于确定沉积物粒度和组成的变化。利用这些综合特性，可以探测到非常薄的风暴事件层（<0.2 mm），从而获得过去风暴事件的高度详细记录。通过对湖泊沉积物中花粉的放射性碳测年，将获得过去全新世（<8 Ka）风暴事件和气候变化的详细年代学。210-Pb测年。高分辨率的湖泊沉积物记录将使麦克马斯特研究人员能够评估过去大风暴事件的频率是否不同，以及风暴的变化是否与气候变量有关，例如过去的温度和降水变化。这些数据对于评估风暴频率的预测变化至关重要，并将有助于为面临恶劣天气风险的五大湖人口稠密地区制定应急和基础设施规划。

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.