High-resolution paleoenvironmental record of Late Holocene storm activity in coastal lagoons

飓风和强烈的“后热带”气旋是加拿大东部恶劣天气的主要原因。气候模型预测，由于气候变暖，未来破坏性飓风的频率将增加。一些模型表明，这可能与人类引起的气候变暖和温室气体的产生有关。然而，北美过去风暴事件的可用记录（< 150年）太短，无法评估长期趋势。 NSERC资助的研究将采用湖泊和沿海泻湖沉积物的地球化学和磁性测量，以更好地了解过去5000年来大型风暴事件的频率。在大风暴事件期间，风暴波越过桑迪海滩屏障，在湖底沉积独特的“过冲”沙层。暴雨沉积层也会因河流的泄洪而沉积在湖泊中。从湖床提取的沉积物岩心中可以识别出风暴过冲和洪水沉积物，并通过对风暴事件层的测年，可以确定过去风暴事件的频率。然而，仅根据沉积物的可见特征来识别风暴层可能是困难的。为了获得过去风暴频率的更详细和可靠的记录，博伊斯和研究小组（1博士，2名硕士，5名B.Sc.学生）将调查沿海泻湖风暴沉积层的地球化学和磁性。通过确定风暴事件携带的独特元素和磁性矿物的丰度，研究人员将能够对风暴沉积物进行地球化学“指纹”。为了获得风暴事件的详细记录，研究人员将在麦克马斯特使用新的ITRAX核心扫描设备。ITRAX岩心扫描仪使用X射线束非常精确地测量岩心样品中各种元素的丰度。该扫描仪还记录岩芯磁化的变化，并产生高分辨率彩色图像，可用于确定沉积物结构和颜色的变化。利用这些综合特性，可以探测到非常薄的风暴事件层（小于2/10毫米），从而获得过去风暴事件的非常详细的记录。利用这种新技术，研究人员将详细记录安大略湖和加拿大大西洋沿岸（新斯科舍省，纽芬兰）过去的风暴事件。ITRAX设施产生的风暴事件的详细长期记录将使麦克马斯特研究人员能够评估过去风暴的频率是否不同，以及风暴的变化是否与其他气候变量有关，例如过去的温度和降水变化。这些数据对于评估气候模型预测的风暴频率的未来变化至关重要，并将有助于为加拿大东部人口稠密地区制定适当的应急计划，这些地区面临恶劣天气的风险。

Hurricanes and intense "post-tropical" cyclones are a major cause of severe weather in eastern Canada. Climate models predict that there will be an increase in the frequency of destructive hurricanes in the future due to climate warming. Some models suggest possible linkages with human-induced climate warming and the production of greenhouse gases. However, the available record of past storm events in North America (< 150 years) is too short to evaluate long-term trends. The NSERC-funded research will employ measurements of the geochemical and magnetic properties of sediments in lakes and coastal lagoons to better understand the frequency of large storm events over the last 5000 years. During large storm events, storm waves overtop sandy beach barriers depositing distinctive “overwash” sand sheets on the lake floor. Storm sediment layers are also deposited in lakes by the flood discharge of rivers. Storm overwash and flood deposits can be identified in sediment cores extracted from the lake bed and by dating of the storm event layers, the past frequency of storm events can be determined. Identification of storm layers can be difficult, however, based on the visible characteristics of the sediments alone. In order to obtain more detailed and reliable records of past storm frequency, Boyce and research team (1 Ph.D., 2 M.Sc., 5 B.Sc. students) will investigate the geochemical and magnetic properties of storm sediment layers in coastal lagoons. By determining the abundance of distinctive elements and magnetic minerals carried by storm events, the researchers will be able geochemically “finger-print” the storm deposits. In order to obtain a detailed record of storm events, researchers will employ the new ITRAX core scanning facility at McMaster. The ITRAX core scanner uses an X-ray beam to measure very precisely the abundance of a wide range of elements in core samples. The scanner also records changes in the magnetization of the core and produces a high-resolution colour image that can be used to identify changes in sediment texture and colour. Using the combined properties, it is possible to detect very thin storm event layers (less than 2/10 of a millimetre), yielding a very detailed record of past storm events. Using this new technique, the researchers will develop a detailed history of past storm events in Lake Ontario and on the Atlantic coast of Canada (Nova Scotia, Newfoundland). The detailed long-term record of storm events produced with the ITRAX facility will allow McMaster researchers to assess whether the frequency of storms has been different in the past, and whether the variability in storminess is linked to other climate variables, such as past changes in temperature and precipitation. These data are critical for evaluating future changes in storm frequency predicted by climate models and will assist in the development of appropriate emergency planning for heavily populated areas of eastern Canada that are at risk from severe weather.