(GRGC) Oxygen and Hydrogen Isotope Geochemistry of Soil Minerals: Implications for Paleoclimatology and Pedology.

9418970 Savin拟议的工作是对土壤矿物和土壤水的氧和氢同位素地球化学正在进行的研究的继续。这项工作的主要直接目标是了解不同成壤矿物(特别是粘土矿物和氧化物)的同位素组成与风化环境气候之间的关系。这项研究的一个主要长期目标是将这些关系应用于根据古土壤中矿物的同位素组成重建古代大陆气候。另一个目标是更深入地了解土壤矿物的形成和修饰过程。拟议的研究是独一无二的，因为它将土壤成因矿物的同位素组成的测量与土壤水和降水的同位素组成联系起来。对土壤矿物的研究始于非常仔细的野外、岩石学和矿物学检查，然后进行相分离以进行同位素分析。这些研究将包括已完成的亚马逊红土高岭石氧同位素组成工作的延伸。来自相同剖面的相同成土相的其他土壤矿物(特别是三水铝石、钛氧化物和铁氧化物)将被分析为~(18)O。对土壤矿物的研究还将包括对在弗吉尼亚州山前火成岩上形成的各种腐泥岩的分析，并将与喷气推进实验室和加州理工学院的同事协作，调查在科哈拉半岛(夏威夷)玄武岩上形成的土壤矿物的稳定同位素系统学，以及气候梯度(随着海拔从每年20厘米增加到每年150厘米)的变化。将在所研究的每一土壤剖面(巴西、弗吉尼亚州皮埃蒙特、夏威夷)用一年的时间监测土壤水的同位素地球化学，并在可能的情况下监测降水。关于土壤水的同位素地球化学的工作将侧重于分析非饱和带中的液态水相(而不是以前的大多数研究中的总水)。当土壤水同位素数据要与成壤矿物的同位素组成相关联时，这是重要的区别。将使用的分析技术是在本赠款期间开发的。这是一项基于实验室的二氧化碳平衡技术。还计划开展其他工作，在分析土壤二氧化碳和土壤水被分成液态和其他成分(如吸附水)时发生的同位素分馏的基础上，开发和核实一种原位技术。

9418970 Savin The proposed work is a continuation of ongoing research into the oxygen and hydrogen isotope geochemistry of soil minerals and soil water. The primary immediate goal of the work is to understand the relationships between the isotopic compositions of different pedogenic minerals (especially clay minerals and oxides) and the climate of the weathering environment. A major long term goal of the research is to apply those relationships in the reconstruction of ancient continental climates from the isotopic compositions of minerals in paleosols. An additional goal is to obtain increased insight into the processes involved in the formation and modification of soil minerals. The proposed study is unique in that it will relate measurements of the isotopic composition of pedogenic minerals to the isotopic composition of soil waters and precipitation. Studies of soil minerals begin with very careful field, petrologic and mineralogic examination prior to separation of phases for isotopic analysis. These studies will include an extension of completed work on the oxygen isotopic compositions of Amazonian lateritic kaolinites. Other soil minerals (especially gibbsite, titanium oxides, and iron oxides) from the same pedogenic facies of the same profiles will be analyzed for 18O. All hydrogen-containing phases will be analyzed for D. Studies of soil minerals will also include analysis of a variety of saprolites developed on igneous rocks in the Virginia Piedmont and , in collaboration with colleagues at JPL and Caltech, investigation of the stable isotope systematics of soil minerals developed on basalt on the Kohala Peninsula (Hawaii) along a climatic gradient (rainfall increasing with altitude from 20 cm to 150 cm per year. The isotope geochemistry of soil water and, where possible, precipitation, will be monitored over the course of a year at each of the soil profiles which are studied (Brazil, Virginia Piedmont, Hawaii). Work on the isot ope geochemistry of soil water will focus on the analysis of the liquid water phase (rather than total water as in most previous studies) in the unsaturated zone. This is important distinction when the soil water isotopic data are to be related the isotopic compositions of pedogenic minerals. The analytical technique to be used was developed in the current grant period. It is a laboratory-based CO2 equilibration technique. Additional work is planned on the development and verification of an in situ technique based upon the analysis of soil CO2 and upon the isotopic fractionations that occur when soil water is partitioned into a liquid phase and other components (e.g., adsorbed water).