Continental Paleoclimate Reconstruction Through Analysis of Oxygen Isotopes in Iron Oxides

科赫9627953为了了解气候变化对生物群进化和生态组织的影响，详细记录过去温度、降水、风速和各种其他特征的替代数据是必不可少的。虽然海洋气候记录可以从广泛的替代物中重建，但在高度多变的大陆领域分析古气候变化已被证明更加困难。适用于极端古代的主要指标是基于树叶形状、动物群分布和自生矿物和化石的同位素化学分析。矿物的氧同位素组成由其形成的温度和沉淀出的水的同位素组成决定。在这个项目中，将利用土壤和地表水中的铁氧化物来重建大气水的氧同位素组成，该组成与现代中高纬度地区的年平均温度密切相关。这项提案有四个部分。首先，我们将测定现代土壤和地表水系统中各种不同气候下相对纯净的铁氧化物场地的氧化铁和大气水的氧同位素组成，以确定铁氧化物是否与大气水形成氧同位素平衡。第二，合成实验测定的赤铁矿-水分馏与理论计算的赤铁矿-水分馏存在差异。如果计算正确，则赤铁矿-水的分馏对温度不敏感，赤铁矿的氧同位素组成将仅反映大气降水成分的变化。提出了一系列合成实验来解决这一差异，并阐明了自然形成机制。最后，古土壤赤铁矿中的氧同位素将被用来研究过去1亿年来地球气候中最重要的两个转变，即古新世/始新世界线的急剧变暖和始新世末期向较凉爽气候的逐步转变。对古代气候的研究将集中在北美西部，那里有来自相同地层剖面的动物和植物变化的良好记录，这将为同位素研究提供血液。这些研究将有助于解决当地和全球气候变化在大陆动物群和植物群演化中所起的作用，并将提供一个机会，详细研究变暖和变冷对生物群的影响之间的对比。

Koch 9627953 To understand the influence that climate change has on the evolution and ecological organization of the biota, detailed records of proxy data for past temperature, precipitation, wind speed, and a variety of other features are essential. While the marine climate record can be reconstructed from a wide range of proxies, analysis of paleoclimatic change in the highly variable continental realm has proven more difficult. The chief proxies that are applicable to extremely ancient periods are analyses based on leaf shape, faunal distributions, and the isotope chemistry of authigenic minerals and fossils. The oxygen isotope composition of a mineral is determined by the temperature at which it forms and the isotope composition of the water from which it precipitates. In this project, iron oxides in soils and surface waters will be used to reconstruct the oxygen isotope composition of meteoric water, which is strongly correlated to mean annual temperature in modern mid- to high-latitude regions. This proposal has four sections. First, we will determine the oxygen isotope compositions of iron oxides and meteoric waters from sites with relatively pure iron oxides under a variety of different climates in modern soils and surface water systems to determine if iron oxides are forming in oxygen isotope equilibrium with meteoric water. Second, there are discrepancies between the hematite-water fractionation as a determined by synthesis experiments and by theoretical calculation. If the calculation is correct, then the hematite-water fractionation is insensitive to temperature, and the oxygen isotope composition of hematite will reflect solely change in the composition of meteoric water. A series of synthesis experiments are proposed to resolve this discrepancy and shed light on natural formation mechanisms. Finally, oxygen isotopes in ancient soil hematites will be used to study two of the most significant transitions in the earth's climate in the last 100 million years, the dramati c warming at the Paleocene/Eocene boundary and the stepwise transition to cooler climates at the end of the Eocene. The study of ancient climates will focus on western North America, where there are excellent records of faunal and floral change from the same stratigraphic sections that will supply hematities for the isotopic study. These studies will help resolve the roles played by local versus global climate changes in the evolution of continental faunas and floras, and will provide an opportunity to examine in detail the contrast between the effects of warming versus cooling on the biota.