Ancient Atmospheric Pco2, Paleoclimates and the Stable Isotope Geochemistry of Low Temperature Iron Oxides

小行星9614265 地质记录表明，地球上气候变化的历史在很大的时间尺度上是一个复杂的历史。 因此，关于因果关系和自然系统通过地球的流体“球体”（大气层和水圈）媒介相互联系的方式的问题变得更加复杂。 寻找这些问题的答案需要关于大气“温室”气体丰度的新数据来源（例如，COO）和地球历史上不同时期的地表温度的相应信息。 氧同位素系统学的共同，低温铁羟基氧化物，针铁矿（a-FeOOH），使其成为一个宝贵的信息来源，环境温度和水在矿物形成的时间。 针铁矿在潮湿的氧化环境中形成，如土壤，可以保存大陆气候条件的定量记录。 研究发现，在针铁矿的晶体结构中有少量的CO2被“捕获”，因为来自古代土壤的针铁矿中的Fe（CO 3）OH可以用来确定地球大气中CO2的分压。 在过去的4.4亿年里，大气中的二氧化碳似乎有很大的波动，但地球的气候似乎并不总是以传统的预期方式做出反应。 建议继续努力获取和核实关于中生代气候和大气化学长期变化的资料。 土壤CO2的扩散混合模型将被应用到碳同位素数据从古代的鲕状铁矿石，以获得更多的信息，在地球的过去，特别是在两个有趣的和令人费解的时间在“恐龙时代”（中生代）的大气CO2压力。 在这些相同的样本中适当的矿物对的氧同位素数据将用于评估温度和水源，以寻找与Eart h大气中CO2含量的明显联系。 将对年轻、活跃的含针铁矿矿床进行碳、氢、氧同位素和元素分析，以进一步确定天然针铁矿（可能还有铁铁矿）的同位素系统学。 将分析这些年轻针铁矿中“难熔”有机碳的碳同位素组成，并将其与共存的“可获得”有机碳进行比较，作为研究这一新认识到的古代样品信息来源的一部分。 作为理解和利用低温铁氧化物同位素系统学在古环境研究中的一部分，我们将开展以下实验工作：（I）与CO_2在铁白云石上吸附有关的碳同位素效应的实验研究;（ii）评估混合的水铁矿干扰从新的自然系统中针铁矿的Fe（CO 3）OH组分回收CO2的可能性：（iii）在不同温度下，针铁矿内部Fe（CO 3）OH与针铁矿表面吸附CO2的碳同位素分馏（相对于气态CO2）的比较。 这样的实验是重要的，因为重要的作用，水铁矿作为常见的初始Fe（III）氢氧化物沉淀在自然系统中（因此，前体针铁矿），因为需要更好地了解的机制，其中Fe（CO 3）OH在针铁矿获得其碳同位素组成。

9614265 Yapp The geologic record reveals that the history of climatic change on the Earth is one of complexity on a wide range of time scales. As a result, questions about causality and the ways in which natural systems are linked through the media of the Earth's fluid "spheres" (the atmosphere and hydrosphere) have become more complex. The search for answers to such questions has required new sources of data on the abundance of atmospheric "greenhouse" gases (e.g., COO) and corresponding information on surfical temperatures at various times in the history of the Earth. The oxygen isotope systematics of the common, low temperature iron oxyhydroxide, goethite (a-FeOOH), make it a valuable source of information on ambient temperature and water at the time of mineral formation. Goethite forms in moist, oxidizing environments such as soils and can preserve a quantitative record of climatic conditions on the continents. It was discovered that there is a small amount of CO 2 "trapped" in the crystal structure of goethite as an Fe(CO3) OH in goethites from ancient soils can be used to determine the partial pressure of CO2 in the Earth's atmosphere. There appear to have been large fluctuations in atmospheric CO2 over the past 440 million years, but it seems that the Earth's climate has not always responded in a conventionally anticipated manner. A continuation of the efforts to acquire and verify information on long-term changes in climate and atmospheric chemistry during the Phanerozoic is proposed here. The diffusive mixing model for soil CO2 will be applied to carbon isotope data from ancient oolitic ironstones to obtain additional information on atmospheric CO2 pressures in the Earth's past-particularly at two interesting and puzzling times in the "age of the dinosaurs" (the Mesozoic era). Oxygen isotope data from appropriate mineral pairs in these same samples would be used to evaluate temperatures and sources of water in a search for apparent links with the CO2 content of the Eart h's atmosphere. Carbon, hydrogen and oxygen isotope and elemental analyses will be performed on young, active, goethite-bearing deposits to further define the isotopic systematics of natural goethites (and possibly ferrihydrites). The carbon isotope composition of "refractory" organic carbon in these young goethites will be analyzed and compared with coexisting "accessible" organic carbon as part of the study of this newly recognized source of information in ancient samples. As part of the overall effort to understand and utilize the isotopic systematics of low temperature iron oxides in studies of ancient environments, the following experimental work will be undertaken: (I) an experimental study of the carbon isotope effects associated with the adsorption of CO2 onto ferrihydrites; (ii) an assessment of the potential for admixed ferrihydrite to interfere with the recovery of CO2 from the Fe(CO3)OH component in goethites from young natural systems: and (iii) a comparison at various temperatures of the carbon isotope fractionation (relative to gaseous CO2) of the Fe(CO3)OH in the interior of goethite with that of CO2 adsorbed onto the surface of goethite. Such experiments are important, because of the important role of ferrihydrite as the common initial Fe(III) hydroxide precipitate in natural systems (and therefore a precursor to goethite), and because of a need to better understand the mechanisms by which Fe(CO3)OH in goethite acquires its carbon isotope composition.