Understanding controls on soil formation: tracing and dating weathering transformations using U series disequilibria

点击翻译按钮获取中文摘要

Project summary Understanding controls on soil formation: tracing and dating weathering transformations using U-series disequilibria Soils are critically important natural resources at the interface of the biosphere, lithosphere, hydrosphere, and atmosphere. Soil formation has a profound impact on the chemistry of surface waters, the oceans, and the atmosphere, yet the rates and processes involved in soil formation are not well understood. U series isotope disequilibria has important potential for understanding soil formation and its associated geochemical fluxes, including the uptake of CO2 by soil formation, the supply of rock-derived nutrients to ecosystems, and the delivery of solutes and sediment to the oceans. This project investigates how soil formation rates change over time and as a function of climate. This project will provide the first thorough application of the U series disequilibria approach by examining previously well-characterized soil profiles of known parent material age that have experienced minimal erosion. This project will elucidate controls on soil formation rates and processes by examining variations across soils of different parent material ages, different landscape positions, and across precipitation gradients with identical parent material. The proposed research will take advantage of previously established soil research sites in Hawaii. Hawaii is the ideal natural laboratory to do this research because it is an environment where it is uniquely possible to study gradients where only one of the major soil forming factors varies while the others are held constant. Using detailed physical and chemical characterization already available for the Hawaii sites in combination with determinations of the weathering timescale and intensity based on U series disequilibria, I will test the hypotheses that soil formation rates are positively correlated with precipitation and erosion rate, and that soil formation rates decline by orders of magnitude over the lifetime of a soil. The Oxford host, Dr. Gideon Henderson, has extensive experience employing U series isotopes as tracers, and shares a mutual interest in understanding the fundamental controls on soil formation. Data collected and ideas developed in this study will provide a comprehensive examination of the role of age and climate in controlling soil formation and weathering rates. Better understanding of the controls on soil formation will improve global carbon cycle models and enhance our ability to predict effects of global change.