Collaborative Research: Testing Hypotheses of Global Warming during Three Major Mass Extinctions

大规模灭绝是地质学上的短暂事件，在此期间，大部分现存物种灭绝，并对生物圈，环境和全球地球化学循环产生深远的影响。一个巨大的天体与地球的撞击被认为是白垩纪末大规模灭绝的唯一或主要原因，人们普遍怀疑撞击会使地质记录中的大规模灭绝更深。另一种可能性是，大规模毁灭可能是地球环境的内源性变化的结果，包括大气温室气体和/或火山气溶胶的积累，大气氧含量的变化，或有毒硫化物化合物的生物圈生产。这些假设的“杀死机制”在预测的时间、幅度和表面和海洋温度变化的分布方面彼此不同。因此，高分辨率的温度记录可以区分这些相互竞争的假设，并可能扩大我们对伴随这些开创性事件的地球表面变化的理解深度。我们建议通过三个主要质量来检查大气和海洋表面的温度历史-灭绝事件使用一种新的地质测温技术的基础上'clumping'的13 C和18 O成键彼此在碳酸盐矿物晶格。我们的目标是获得第一个定量（约2摄氏度）和时间分辨记录的生长温度的大陆土壤碳酸盐和浅海碳酸盐化石的二叠纪/三叠纪和三叠纪/侏罗纪的边界，并进行比较，记录更好地了解白垩纪/古近纪的边界。考虑到气候变化在大规模灭绝的假设原因中的突出地位，以及在这些关键时期定量古温度测量的缺乏，我们相信，这些数据可能会使我们对质量守恒原因的理解取得突破性进展。我们方法的关键是，我们将使用的新的碳酸盐凝块同位素温度计是基于均匀平衡的（涉及单相成分的反应），因此可以严格限制温度，而无需任何关于碳酸盐生长的水的同位素组成的信息。因为我们可以使用这个温度计来独立地约束温度，我们也将能够解释古土壤碳酸盐和海洋化石的δ O 18值，作为它们生长的大气和海洋沃茨的δ O 18的替代物（即，因为我们将能够在独立已知的温度下“分离”碳酸盐-水分馏）。在土壤碳酸盐的情况下，我们将进一步补充我们的温度测量数据，估计pCO 2的基础上deltaC 13 measurement.This研究是加州理工学院和华盛顿大学之间的合作努力。这个项目的更广泛的影响是，它将支持一个博士生和三个夏季研究奖学金的本科生在加州理工学院。艾勒还将使用这笔赠款，以帮助支持高中生暑期实习。我们预计，这项研究将提供一个新的和广泛适用的方法来重建过去的气候模型，通过结合“聚集同位素”测温和传统的稳定同位素研究，从而将有助于仪器和方法的发展，地球化学。最后，我们的研究结果将说明气候变化和物种灭绝之间的关系，因此对预测现代全球变暖的可能后果具有相关性。

Mass extinctions are geologically brief episodes during which a large fraction of extant species became extinct, and have profound consequences for the biosphere, environment and global geochemical cycles. Impact of a large body with the earth is recognized as the singular or dominant cause of the best understood mass extinction at the end of the Cretaceous, and impacts generally are widely suspected of driving mass extinctions deeper in the geological record. Alternatively, mass extinctions might be consequences of endogenous changes in earth's environment, including build-up of atmospheric greenhouse gases and/or volcanic aerosols, variations in atmospheric oxygen content, or biospheric production of toxic sulfide compounds. These hypothesized 'kill mechanisms' differ from one another in the predicted timing, magnitude and distribution of surface and ocean temperature change. Therefore, high-resolution temperature records could discriminate among these competing hypotheses, and potentially expand the depth of our understanding of changes in the earth's surface that accompanied these seminal events.We propose to examine the temperature history of the atmosphere and surface ocean through three major mass-extinction events using a new geothermometric technique based on 'clumping' of 13C and 18O into bonds with each other in the carbonate mineral lattice. Our goal is to obtain the first quantitative (about 2 degrees C) and time-resolved records of growth temperatures of continental soil carbonates and shallow marine carbonate fossils across the Permian/Triassic and Triassic/Jurassic boundaries, and, for comparison, a record across the better-understood Cretaceous/Paleogene boundary. Given the prominence of climate change in hypothesized causes of mass extinctions and the dearth of quantitative paleothermometry at these key times, we believe these data could lead to a breakthrough in our understanding of the causes of mass extinctions.The key to our approach is that the new carbonate clumped-isotope thermometer we will use is based on a homogeneous equilibrium (a reaction involving components of a single phase) and so can rigorously constrain temperature without any information about the isotopic composition of water from which carbonate grew. Because we can use this thermometer to independently constrain temperature, we will also be able to interpret the deltaO18 values of paleosol carbonates and marine fossils as proxies for the deltaO18 of meteoric and ocean waters from which they grew (i.e., because we will be able to 'tease apart' the carbonate-water fractionation at an independently known temperature). In the case of soil carbonates, we will further supplement our thermometric data by estimating pCO2 of the atmosphere based on deltaC13 measurements.This research is a collaborative effort between Caltech and the University of Washington. Broader impacts of this project are that it will support one Ph.D student and three summer research fellowships for undergraduate students at Caltech. Eiler will also use this grant to help support high school student summer internships. We anticipate that this study will provide a model for a new and widely applicable approach to reconstructing past climates through combined 'clumped isotope' thermometry and conventional stable isotope studies, and thus will contribute to the development of instruments and methods for geochemistry. Finally, our results will speak to the relationship between climate change and extinction, and thus has relevance for predicting the possible consequences of modern global warming.