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

量化气候如何影响风化、侵蚀和土壤发育的长期速率

• 批准号: 0000999
• 负责人: James Kirchner
• 金额: $ 27.5万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-09-01 至 2003-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0000999&HistoricalAwards=false
• 关键词: Quantifying; how; Climate; Affects; Long

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.

James W.Kirchner EAR-0000999物理侵蚀和化学风化是相互依存的过程，塑造了山区景观，调节了土壤成分，将沉积物和溶质输送到水生生境，并在很长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的速度都很难衡量。因此，关于侵蚀和风化如何影响景观、土壤、水生生境和气候的演变，目前还没有明确的共识。最近的进展使人们能够从流域侵蚀沉积物的化学成分中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侵蚀速率。化学风化速率可以通过比较岩石和土壤中的不溶性元素(如Zr和Nb)的浓度来推断，这反映了化学风化所占的侵蚀比例。该项目将测量化学风化速率如何随气候和物理侵蚀速率的变化而变化。初步结果表明，气候对风化速率的影响比侵蚀影响要小。然而，当侵蚀的影响被明确考虑时，气候影响是可以测量的。为了扩大这些结果，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摄氏度；降雨量为10至420厘米/年)。为了尽量减少基岩风化敏感性变化的影响，这项研究将只集中在花岗岩基岩上。在这6个地点，每个地点将选择5个小流域，并收集水系沉积物、基岩和山坡土壤样本进行分析。水系沉积物中的宇宙源核素浓度将被用来测量长期侵蚀率。化学风化所占的侵蚀比例，比通过比较土壤和基岩的整体化学成分来推断的比例要小。该项目将量化长期风化和侵蚀速率如何随气候变化，同时首次明确测量化学风化和物理侵蚀之间的相互关系。这些结果应有助于更好地建立营养循环和长期气候演变模型，更准确地评估沉积物和溶质向水生生态系统的输送，以及更定量地了解土壤发育和地形演变。