Multi-isotope investigation of paleozoic climate an environment: a new approach using redox sensitive stable isotope tracers

在过去的5.4亿年里，海平面比现在高得多，导致古大陆的大片地区被淹没。如果大陆在赤道附近被淹没，石灰岩就会沉积下来。海洋早已从大陆上退去，但石灰岩依然存在。在石灰岩中有以同位素指纹的形式存在的地球化学线索，我们可以用它来了解地球过去的环境和气候的本质。通过测量古代海洋石灰岩的地层序列，我们可以追踪地球环境和气候随时间的演变。同位素指纹图谱告诉我们古代碳循环和温室效应、海平面和陆表海的海水循环模式、海水的温度和盐度。这类信息有助于我们对过去气候与海平面环流模式或气候与大陆风化率之间关系的思考和模型。它还涉及到关于人为二氧化碳对当代全球变暖的影响的争论。我的工作重点是通过时间来完善对碳同位素记录的解释，发展古代碳循环模型，并推进同位素示踪剂（如钕）的应用，我发现它与过去的海平面变化有关。新的研究将大大增加这一同位素工具库；其中首次包括古代海水中溶解氧水平的替代指标——铀和铬的稳定同位素变化。铀和铬同位素的行为将首先在现代环境中进行研究。这将包括采样海水，沿海海域的分层水，甚至是一个底部没有溶解氧的现代分层湖。这些现代研究将描述现代系统中铬和铀同位素分馏的范围，以及控制同位素分馏的过程。这些发现将揭示古代海洋沉积物中铀和铬同位素指纹的效用，作为追踪地球浅海和海洋中随时间变化的氧含量的工具。

In the past 540 million years, sea level has been much higher than today, causing large areas of the paleocontinents to be submerged. If submergence occurred when a continent was near the equator, limestones were deposited. The seas have long since retreated from the continents, but the limestones remain. Inside the limestones there are geochemical clues in the form of isotopic fingerprints that we can use to understand the nature of the Earth's past environment and climate. By making our measurements in stratigraphic successions of ancient marine limestones we can track the evolution of the Earth's environment and climate over time. The isotopic fingerprints tell us about the ancient carbon cycle and greenhouse effect, sea level, and seawater circulation patterns in epicontinental seas, temperature, and salinity of marine waters. This type of information informs our thinking and models on the relationship between climate and sea level circulation patterns, or climate and continental weathering rates in the past. And it bears on the debate regarding the impact of anthropogenic carbon dioxide on contemporary global warming. My work is focused on refining interpretations of carbon isotope records through time, developing models of ancient carbon cycling, and advancing the application of isotope tracers like neodymium, which I have found to be related to sea level changes in the past. New research will add significantly to this repertoire of isotopic tools; including, for the first time, a proxy indicator of dissolved oxygen levels in ancient seawater-stable isotope variations of uranium and chromium. The behavior of uranium and chromium isotopes will be first studied in modern environments. This will involve sampling ocean waters, stratified waters in coastal seas, and even a modern stratified lake with no dissolved oxygen in the bottom waters. These modern studies will characterize the range of chromium and uranium isotope fractionation in modern systems, and the processes that control the isotope fractionations. These findings will inform on the utility of uranium and chromium isotope fingerprints in ancient marine sediments as tools for tracking changing oxygen levels in the earth's shallow seas and oceans over time.