Quantifying how Climate Affects Long-Term Rates of Weathering, Erosion, and Soil Development

James W.物理侵蚀和化学风化是相互依存的过程，塑造了山区景观，调节土壤的组成，将沉积物和溶质输送到水生栖息地，并在很长一段时间内帮助调节全球气候。 直到最近，长期的侵蚀和化学风化率一直难以测量。 因此，目前还没有明确的共识，侵蚀和风化如何影响景观，土壤，水生栖息地和气候的演变。 最近的进展现在允许从流域侵蚀沉积物的化学成分推断出物理侵蚀和化学风化的长期平均速率。 宇宙成因核素（26Al和10Be）的浓度可以用来测量长期的侵蚀速率。 通过比较岩石和土壤中不溶性元素（如Zr和Nb）的浓度，可以从侵蚀速率推断出化学风化速率，这反映了化学风化造成的侵蚀部分。该项目将测量化学风化率如何随气候和物理侵蚀率而变化。 初步结果表明，气候对风化率的影响比侵蚀作用小。 然而，如果明确考虑到侵蚀的影响，气候影响是可以测量的。 为了扩展这些结果，选择了六个地点，这些地点跨越了广泛的气候范围（温度为4至24 ℃;降水量为10至420厘米/年）。 为了尽量减少基岩风化敏感性变化的影响，本研究将专门集中在花岗岩基岩。 在六个地点中的每一个，将选择5个小流域，并收集河流沉积物、基岩和山坡土壤样本进行分析。 河流沉积物中的宇宙成因核素浓度将用于测量长期侵蚀率。 通过比较土壤和基岩的整体化学成分推断出的化学风化所占的侵蚀比例。 该项目将量化风化和侵蚀的长期速率如何随气候变化而变化，同时首次明确测量化学风化和物理侵蚀如何相互关联。 这些结果应有助于更好的营养循环和长期气候演变的模型，更准确的评估沉积物和溶质输送到水生生态系统，以及更定量的了解土壤发育和地貌演变。

James W. KirchnerEAR-0000999 Physical erosion and chemical weathering are interdependent processes that sculpt mountainous landscapes, regulate the composition of soils, deliver sediment and solutes to aquatic habitats, and, over long timescales, help regulate global climate. Until recently, long-term rates of erosion and chemical weathering have been difficult to measure. As a result there is presently no clear consensus about how erosion and weathering affect the evolution of landscapes, soils, aquatic habitats, and climate. Recent advances now permit long-term average rates of physical erosion and chemical weathering to be inferred from the chemical composition of eroding sediment in watersheds. The concentrations of cosmogenic nuclides (26Al and 10Be) can be used to measure long-term rates of erosion. Chemical weathering rates can be inferred from erosion rates by comparing the concentrations of insoluble elements (such as Zr and Nb) in rocks and soils, which reflect the fraction of erosion that is accounted for by chemical weathering. This project will measure how chemical weathering rates vary with climate and physical erosion rates. Preliminary results show that climatic effects on weathering rates are small compared to erosional effects. However, the climatic effects are measurable, when the effects of erosion are explicitly accounted for. To expand on these results, six sites have been selected that span a wide range of climates (4 to 24 C in temperature; 10 to 420 cm/yr in precipitation). To minimize effects of variations in bedrock weathering susceptibility, this study will focus exclusively on granitic bedrock. At each of the six sites, 5 small watersheds will be selected, and samples of stream sediment, bedrock, and hillslope soils will be collected for analysis. Cosmogenic nuclide concentrations in the stream sediment will be used to measure long-term erosion rates. The fraction of erosion that is accounted for by chemical weathering than will be inferred by comparing the bulk chemical composition of soil and bedrock. This project will quantify how long-term rates of weathering and erosion vary with climate while, for the first time, explicitly measuring how chemical weathering and physical erosion interrelate. These results should contribute to better models of nutrient cycles and long-term climatic evolution, more accurate assessments of sediment and solute delivery to aquatic ecosystems, and a more quantitative understanding of soil development and landform evolution.