Silicate weathering of soil-mantled slopes in an active Alpine landscape
Silicate weathering of soil-mantled slopes in an active Alpine landscape
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DOI：
10.1016/j.gca.2010.06.019
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发表时间：
2010-09
影响因子：
5
通讯作者：
K. Norton;F. Blanckenburg
中科院分区：
文献类型：
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作者：
K. Norton;F. Blanckenburg
尽管位于瑞士中央阿尔卑斯山的高、陡、活跃的隆起和以前的冰川斜坡上，但罗纳河谷上游的土壤相对于其母岩的阳离子消耗高达50%。这种消耗是由基于Zr作为难熔元素的质量损失平衡确定的。全新世风化率和物理侵蚀率的这些斜坡出乎意料的低，作为测量cosmogenic10Be衍生剥蚀率。化学损耗分数CDF的范围为0.12至0.48，而平均土壤化学风化速率为33±15tkm−2yr−1。宇宙成因核素的剥蚀率和模型计算表明，这些土壤已达到风化稳定状态，因为冰消期15万年前。风化信号随海拔和山坡形态而变化。此外，化学风化速率随海拔升高而降低，表明温度可能是这些高阿尔卑斯盆地风化的主要控制因素。模型计算表明，化学风化速率是有限的反应动力学，而不是新鲜材料的供应率。我们比较山坡和集水区的风化通量与现代流阳离子通量，并表明，高浮雕，裸露的岩石斜坡表现出低得多的化学风化率，尽管较高的物理侵蚀率。岩石的低风化通量，迅速侵蚀的斜坡允许更广泛的含义，即山区建设，而提高整体剥蚀率，可能不会导致增加山坡上的化学风化率。为了使这些沉积物风化，需要中间储存，例如在洪泛区。
Despite being located on high, steep, actively uplifting, and formerly glaciated slopes of the Swiss Central Alps, soils in the upper Rhone Valley are depleted by up to 50% in cations relative to their parent bedrock. This depletion was determined by a mass loss balance based on Zr as a refractory element. Both Holocene weathering rates and physical erosion rates of these slopes are unexpectedly low, as measured by cosmogenic10Be-derived denudation rates. Chemical depletion fractions, CDF, range from 0.12 to 0.48, while the average soil chemical weathering rate is 33±15tkm−2yr−1. Both the cosmogenic nuclide-derived denudation rates and model calculations suggest that these soils have reached a weathering steady-state since deglaciation 15ky ago. The weathering signal varies with elevation and hillslope morphology. In addition, the chemical weathering rates decrease with elevation indicating that temperature may be a dominant controlling factor on weathering in these high Alpine basins. Model calculations suggest that chemical weathering rates are limited by reaction kinetics and not the supply rate of fresh material. We compare hillslope and catchment-wide weathering fluxes with modern stream cation flux, and show that high relief, bare-rock slopes exhibit much lower chemical weathering rates despite higher physical erosion rates. The low weathering fluxes from rocky, rapidly eroding slopes allow for the broader implication that mountain building, while elevating overall denudation rates, may not cause increased chemical weathering rates on hillslopes. In order for this sediment to be weathered, intermediate storage, for instance in floodplains, is required.