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

古代大气 Pco2、古气候和低温氧化铁的稳定同位素地球化学

• 批准号: 9614265
• 负责人: Crayton Yapp
• 金额: $ 22.48万
• 依托单位: Southern Methodist University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-02-01 至 2001-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9614265&HistoricalAwards=false
• 关键词: Ancient; Atmospheric; Pco2; Paleoclimates; Stable

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.

9614265地质记录表明，地球上气候变化的历史在广泛的时间尺度上是复杂性之一。 结果，有关因果关系的问题以及通过地球流体“球”（大气和水圈）的介质将自然系统联系在一起的方式变得更加复杂。 搜索此类问题的答案需要有关大气“温室”气体（例如COO）的新数据来源，以及在地球历史上不同时期的各个时候表面温度的相应信息。 普通的低温氧化铁（A-feOOH）的氧同位素系统学使其成为矿物质形成时环境温度和水的宝贵信息来源。 在潮湿，氧化环境（例如土壤）中形成的gothite形成，可以保留大陆气候条件的定量记录。 据发现，在古铁岩的晶体结构中，有少量的CO 2“被困”，作为Fe（Co3），在古代土壤中，可以用来确定地球大气中CO2的二氧化碳的部分压力。 在过去的4.4亿年中，大气二氧化碳的波动似乎很大，但似乎地球的气候并不总是以常规预期的方式做出反应。 这里提出了在Phanerozoic期间获得和验证有关气候和大气化学长期变化信息的努力的延续。 土壤二氧化碳的扩散混合模型将应用于古老的橄榄铁石的碳同位素数据，以在“恐龙时代”（中生时代）的两个有趣而令人困惑的时期获得有关地球过去的大气二氧化碳压力的其他信息。 在这些样品中，适当矿物对的氧同位素数据将用于评估水的温度和水源，以寻找与Eart H大气中的CO2含量的明显联系。 碳，氢和氧同位素和元素分析将对年轻，活跃的含谷子沉积物进行，以进一步定义天然Gothites的同位素系统（甚至可能是富铁岩）。 将分析这些年轻的Gothites中“难治性”有机碳的碳同位素组成，并将其与共存的“可访问”有机碳进行比较，这是对古代样品中新认识的信息来源的研究的一部分。 作为在古代环境的研究中了解和利用低温铁氧化物的同位素系统的总体努力的一部分，将进行以下实验工作：（i）对与二氧化碳对铁人物的吸附相关的碳同位素效应的实验研究； （ii）评估混合液体水溶液的潜力，干扰了幼年天然系统中的Fe（CO3）OH成分从Fe（CO3）OH组件中回收：（III）在碳同位素分馏的各种温度下进行比较，而co2 in Interior co2 in Interior the Interor the co2 co2 cop（co3）相对于fe（co3）的co2 co2）进行了比较。 这样的实验很重要，因为铁硫酸盐作为天然系统中常见的初始Fe（III）氢氧化物沉淀物（因此是Gothite的前体），并且由于需要更好地理解gothite在Gothite中获得其碳同位素组成的机制。