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

了解土壤形成的控制因素：利用铀系不平衡性追踪和测定风化作用的年代土壤是生物圈、岩石圈、水圈和大气层交界处极为重要的自然资源。土壤的形成对地表沃茨、海洋和大气的化学性质有着深远的影响，但人们对土壤形成的速率和过程还没有很好的了解。铀系同位素不平衡对于理解土壤形成及其相关的地球化学通量具有重要的潜力，包括土壤形成对CO2的吸收、岩石来源的营养物质对生态系统的供应以及溶质和沉积物向海洋的输送。该项目研究土壤形成率如何随时间和气候变化而变化。该项目将提供第一次全面应用的U系列不平衡的方法，通过检查已知的母质年龄，经历了最小的侵蚀以前很好的特点土壤剖面。该项目将通过研究不同母质年龄、不同景观位置和相同母质的降水梯度的土壤变化，阐明对土壤形成速率和过程的控制。拟议的研究将利用以前在夏威夷建立的土壤研究地点。夏威夷是进行这项研究的理想自然实验室，因为它是一个环境，在那里只有一个主要的土壤形成因素发生变化，而其他因素保持不变，才有可能研究梯度。使用详细的物理和化学表征已经提供的夏威夷网站结合U系列不平衡的基础上的风化时间尺度和强度的测定，我将测试的假设，土壤形成率与降水和侵蚀速率呈正相关，土壤形成率下降的数量级在土壤的寿命。牛津大学的主持人吉迪恩亨德森博士拥有使用铀系列同位素作为示踪剂的丰富经验，并在了解土壤形成的基本控制方面有着共同的兴趣。在这项研究中收集的数据和想法将提供一个全面的检查年龄和气候在控制土壤形成和风化速率的作用。更好地了解土壤形成的控制因素将改善全球碳循环模型，提高我们预测全球变化影响的能力。

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.