Oxygen and Hydrogen Isotopes in Soils as Indicators of Continental Paleoclimates

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There is far less quantitative information about the evolution and history of climate on the continents than in the deep sea. Among the reasons for this is a scarcity of quantitative proxy indicators of continental climate. The work outlined is an effort to develop and apply techniques for using oxygen and hydrogen isotope ratios of minerals in soil profiles as indicators of climatic conditions during the soil-forming process. The initial stage of the research will consist of detailed studies of a series of active weathering profiles developed on a variety of parent materials in a variety of climatic regimes. Weathering profiles targeted for this study include lateritic soils in the Amazon Basin of Brazil, saprolites on the Virginia Piedmont, and weathering profiles developed on Hawaiian basalts under varying rainfall regimes. The approach combines careful field description, petrographic and mineralogical study, isotopic analysis of soil water and isotopic analysis of separated soil minerals. We expect this proposed study of modern weathering profiles to lead to an understanding of the climatic factors which control the isotopic compositions of soil minerals. In a later stage of the project we will apply the results of the initial stage of the work to the study of paleosols. The most important result expected from the proposed work is the development of new tools for the study of continental paleoclimates. When these tools are widely applied in this and later studies, the information obtained will be useful for global paleoclimatic reconstructions and the testing of climate models.