Understanding lower temperature natural systems using stable isotopes

使用稳定同位素了解低温自然系统

• 批准号: RGPIN-2014-05293
• 负责人: Longstaffe, Fred
• 金额: $ 6.48万
• 依托单位: University of Western Ontario
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=633867
• 关键词: Understanding; lower; temperature; natural; systems

Earth’s 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, for example oxygen-18, oxygen-17 and oxygen-16. Their abundances in low-temperature minerals, and in plant and animal tissues, are determined by environmental conditions. My research team and I will go “Back to the Future” based on the isotopic signatures of climatic and ecological conditions preserved in such proxy records over the last 100,000 years. We will search for patterns in these records that can serve as bellwethers for the future. Two areas in North America are of special interest, the Great Lakes region and the lost Beringian Pleistocene ecosystem in the Yukon. The modern Great Lakes region is sensitive to shifting air masses on seasonal, decadal and longer time-scales. Freshwater contains an isotopic record of these variations. For ~20 years, we have collected these data for the region. This record’s length will now allow testing for climatic trends, and can also serve a baseline for ancient conditions. Modern plants also retain ecosystem isotopic and molecular records, which we will use to interpret data for ancient vegetation. Using oxygen-17, we will also quantify the contribution of atmospheric nitrate to the threat posed by nitrogen deposition in the area. Leakage from bedrock wells from Ontario’s early petroleum boom also is a threat to drinking-water aquifers. We will define the isotopic and chemical fingerprints of specific bedrock brines, pinpoint contamination sources, and thus aid cost-effective plugging of the leaks. Further back in time, glacial meltwater outbursts from the retreating Laurentide Ice Sheet may have triggered global cooling by changing oceanic circulation patterns. One pathway to the Atlantic Ocean was through the Great Lakes. We will use shelly fauna and organic biomarkers (n-alkanes) contained in Great Lake sediments to track meltwater movement since ~15,000 years ago. These proxies also record post-glacial ecosystem changes in Great Lakes watersheds. We are especially interested in isotopic signals of climatic factors versus other processes that caused substantial drops in water level – and even hydraulic closure – of some Great Lakes. Megafauna tissues (bone, tooth) are also superb isotopic proxies for environmental change, recording seasonal variations in climate and forage (vegetation, prey). We will use such data to examine possible causes (climate, over-hunting) of Pleistocene megafauna extinctions in North America. By analyzing mammoth, mastodon and giant beaver, we will learn about the terrestrial ecosystem characteristics of the Great Lakes region at the end of the Pleistocene. Yukon’s Beringia also has a fascinating story to tell. Its species diversity (e.g., mammoth, horse, bison, camel, lion, short-faced bear) is much higher than the modern Arctic. Why were its tundra-steppe grasslands so productive, despite the cold and dry climate? Anomalous nitrogen-15 enrichment in mammoths is a special puzzle. This simple observation may signal that the nitrogen cycle in Beringia was quite different from today. To test this idea, we will grow Beringian grasses under Beringian climatic conditions in Beringian loess soils, analyze ancient Beringian vegetation from ~90,000 to 25,000 year-old ground squirrel nests extracted from permafrost, and compare the isotopic results – including individual amino acids – with the region’s modern vegetation and soil. In short, we will determine how two different landscapes responded to climate change at the end of the last glacial period. Why some mammals adapted while others became extinct holds important lessons for anticipating modern ecosystem responses to environmental change.

地球的空气、水、生物群、岩石和沉积物主要由氧、氢、碳和氮组成。每种元素都有两种或三种稳定的同位素形式，例如氧-18、氧-17和氧-16。它们在低温矿物质和动植物组织中的丰度取决于环境条件。我和我的研究小组将根据过去10万年来保存在这些代用记录中的气候和生态条件的同位素特征来“回到未来”。我们将在这些记录中寻找可以作为未来风向标的模式。北美有两个地区特别令人感兴趣，即五大湖地区和育空地区丧失的白令纪更新世生态系统。现代五大湖地区对季节性、十年期和更长时间尺度上的气团变化很敏感。淡水含有这些变化的同位素记录。大约20年来，我们一直在收集该地区的这些数据。这个记录的长度现在可以测试气候趋势，也可以作为古代条件的基线。现代植物还保留了生态系统的同位素和分子记录，我们将用这些记录来解释古代植被的数据。利用氧-17，我们还将量化大气硝酸盐对该地区氮沉积所构成威胁的贡献。安大略早期石油繁荣时期基岩威尔斯井的泄漏也对饮用水含水层构成威胁。我们将确定特定基岩卤水的同位素和化学指纹，查明污染源，从而帮助经济有效地堵塞泄漏。在更早的时间，冰川融水从后退的劳伦泰德冰盖爆发可能通过改变海洋环流模式引发了全球冷却。通往大西洋的一条途径是通过五大湖。我们将使用大湖沉积物中所含的贝壳动物群和有机生物标志物（正构烷烃）来追踪约15，000年前的融水运动。这些代用指标还记录了五大湖流域的冰后期生态系统变化。我们特别感兴趣的是气候因素与其他过程的同位素信号，这些过程导致一些五大湖水位大幅下降，甚至水力关闭。巨型动物的组织（骨骼、牙齿）也是环境变化的极好同位素替代物，记录了气候和饲料（植被、猎物）的季节性变化。我们将利用这些数据来研究北美更新世巨型动物灭绝的可能原因（气候，过度狩猎）。通过分析猛犸、乳齿象和巨型海狸，我们将了解更新世末五大湖地区的陆地生态系统特征。育空地区的白令吉亚也有一个迷人的故事要讲。其物种多样性（例如，猛犸、马、野牛、骆驼、狮子、短面熊）的数量比现代北极地区高得多。为什么在寒冷干燥的气候条件下，它的苔原草原如此高产？猛犸象中氮-15的异常富集是一个特殊的难题。这个简单的观察可能表明，白令吉亚的氮循环与今天大不相同。为了验证这一想法，我们将在白令气候条件下在白令黄土土壤中种植白令草，分析从永久冻土中提取的约90，000至25，000年的地松鼠巢中提取的古代白令植被，并将同位素结果（包括单个氨基酸）与该地区的现代植被和土壤进行比较。简而言之，我们将确定两种不同的景观如何在末次冰期结束时应对气候变化。为什么一些哺乳动物适应了环境，而另一些却灭绝了，这对预测现代生态系统对环境变化的反应具有重要意义。