Understanding lower temperature natural systems using stable isotopes

点击翻译按钮获取中文摘要

Oxygen, hydrogen, carbon and nitrogen are among the most abundant elements making up Earth's atmosphere, biosphere, hydrosphere and lithosphere. The atoms of each of these elements occur naturally in two or three forms - known as stable isotopes. Their relative abundances (e.g., oxygen-18 vs. oxygen-16, carbon-13 vs. carbon-12, nitrogen-15 vs. nitrogen-14, and hydrogen-2 vs. hydrogen-1) in rocks, minerals, water, plants and animals are determined by the source of the element (freshwater, seawater, atmosphere, biosphere, shallow or deep Earth) and the conditions (temperature, aridity, photosynthetic pathway, diet) under which each substance developed. The objective of my research is to improve our ability to measure stable isotopic compositions in Earth materials, and to interpret these ratios in terms of the processes that created them. To what purpose, you ask? On one hand, we are using the stable isotopic compositions of rocks and minerals to identify the sources and types of fluids that swept through Earth's crust over a vast area of very old (760 - 510 million years) rocks now comprising parts of New Brunswick, mainland Nova Scotia, Cape Breton Island, Newfoundland and Massachusetts. Our goal is to learn the cause and timing of this large-scale interaction between rock and hot water, and its consequences for creation or destruction of economic mineral deposits. On the other hand, we are using the signatures of environmental conditions captured in the isotopic compositions of freshwater, plant tissues (organic matter), shelly fauna, and teeth and bones (e.g., mammoths and mastodons) to track changing climatic/ecosystem conditions over time. Ancient soils and sediments contain many such proxy materials, which can be dated. An immediate goal is to determine the pathways of glacial meltwater in the Great Lakes region at the end of the last Ice Age. A longer range objective is to increase our understanding of North American climatic conditions over the last ~15,000 years. Better understanding of the rate of past climate change in this now heavily populated mid-continental region should lead to better predictive capabilities for its future behaviour.