Understanding lower temperature natural systems using stable isotopes

空气、水、生物群、岩石和沉积物主要由氧、氢、碳和氮组成。每种元素都以两种或三种稳定的同位素形式存在，例如氧-16、氧-17和氧-18。它们在水中、生物组织和矿物质中的相对丰度受环境条件的控制。例如，植物物质和贝壳可以代表沉积物中按时间顺序保存的过去环境。这些代用同位素组成可以转化为过去温度、干旱和有机生产力的记录。我的研究小组解码这些同位素信号以及控制或破坏其保真度的过程。我们“回到未来”，根据可靠的代理记录重建古代环境，并寻找可以作为未来风向标的模式。这里提出的方案侧重于淡水、有机物、次生壳壳物和泥灰岩碳酸盐岩作为过去一万年中大湖地区环境变化的代用物：(1)我们将测试一个新的模型，该模型表明“云内”过程驱动降水的氧和氢同位素变化，而不是60多年来的经典水源/蒸馏模型。五大湖地区受到不同来源气团的季节性影响。这种复杂性为“云内”假设提供了必要的测试。如果新模型得到验证，降水同位素组成可能成为气候相关水文转变的风向标。由此产生的范式转变也会影响代用同位素特征的解释；(2)我们将把重点放在过去3000年沉积的五大湖和较小的南安大略省湖泊沉积物中所含的代用物上。我们试图从人类活动的信号中检测和区分自然同位素的变化，并评估每种变化的相对贡献。首先，我们必须确定那些最能保存原始信息的代理和那些不总是可靠的过去证人（例如，散装有机物）。然后，以从“良好”代理获得的可靠的古气候记录为基础，我们可以帮助政策制定者预测这个人口稠密地区可能面临的气候、环境和水文变化，并更直接地确定哪些缓解人为影响将是最有效的。最后：(3)利用同一套工具对老页岩水的同位素特征进行了评价。如果这些成分反映了水源，这些数据就可以用来确定水的来源。如果水在捕获后与页岩粘土相互作用，原始同位素特征可能已经改变。知道哪种情况是正确的是很重要的。在加拿大，页岩是潜在的危险废物储存库；它们的孔隙水同位素特征通常被认为反映了水源，并用于确定这些岩石在很长一段时间内是渗漏的还是致密的。

Air, water, biota, rocks and sediments are dominated by oxygen, hydrogen, carbon and nitrogen. Each element occurs in two or three stable forms called isotopes, e.g., oxygen-16, oxygen-17 and oxygen-18. Their relative abundances in water, biological tissues and minerals are controlled by environmental conditions. Plant matter and shells, for example, can be proxies of past environments preserved in sediments in chronological order. These proxy isotopic compositions can be translated into records of past temperature, aridity and organic productivity. My research team decodes those isotopic signals and the processes that control or destroy their fidelity. We go "Back to the Future" to reconstruct ancient environments based on robust proxy records and seek patterns that can serve as bellwethers for the future. The program proposed here focuses on fresh water, organic matter and secondary shelly and marl carbonate as proxies for environmental change over the last 10,000 years in the Great Lakes region: (1) We will test a new model that suggests that `in-cloud' processes drive precipitation oxygen- and hydrogen-isotope variations, rather than the classical water-source/distillation model in place for more than 60 years. The Great Lakes region is seasonally affected by air masses of different origins. This complexity provides a needed test of the `in-cloud' hypothesis. If the new model is validated, precipitation isotope compositions could become a bellwether for climate-related hydrological transitions. The resulting paradigm shift would also affect interpretation of proxy isotopic signatures; and (2) We will focus on proxies contained in sediments of the Great Lakes and smaller southern Ontario lakes deposited during the last 3000 years. We seek to detect and distinguish natural isotopic variation from signals of human activities and to evaluate the changing relative contributions of each. First, we must identify those proxies that best preserve original information and those that are not always reliable witnesses to the past (e.g., bulk organics). Then, anchored by robust paleoclimate records obtained from `good' proxies, we can assist policy makers in anticipating shifts in climate, environment and hydrology that this highly populated region may face, and more immediately, in identifying what mitigation of anthropogenic effects will be most effective. Finally: (3) We are using the same tool kit to evaluate the isotopic signature of water trapped in old shales. If those compositions reflect water source, the data can be used to identify the water's origin. If the water has interacted with shale clays after entrapment, original isotopic signatures may have changed. Knowing which scenario is correct is important. Shales are potential repositories for hazardous wastes in Canada; their porewater isotopic signature is commonly assumed to reflect water source and used to determine whether these rocks have been leaky or tight over long periods of time.