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.
