Detection of transience in eroding landscapes
Detection of transience in eroding landscapes
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检测侵蚀景观中的瞬态现象
DOI：
10.1002/esp.3923
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发表时间：
2016
影响因子：
3.3
通讯作者：
Mudd S
中科院分区：
文献类型：
--
作者：
Mudd S
过去气候和构造的变化导致了许多景观在空间和时间上变化的侵蚀率。在这方面的贡献，我检查方法检测和量化的性质和时间的瞬态侵蚀景观。在一个单一的地点，宇宙成因核素可以检测到的瞬时删除材料或加速侵蚀率在千年的时间尺度使用成对的核素。只有当其中一种核素的半衰期明显短于另一种核素时，才有可能检测到。目前，唯一可行的方法是使用cosmogenicin situcarbon-14（14 C）和寿命更长的核素，如铍-10（10 Be）。山坡信息可以补充或代替宇宙成因信息：在土壤覆盖的景观中，通过比较地形和山脊曲率，可以在增加后的数千年内检测到增加的侵蚀率。只要最终的侵蚀速率大于初始速率的两倍，这种技术就可以工作。在景观尺度上，瞬变可以根据通道剖面或脊顶的不平衡来检测，但瞬变对瞬变强迫的性质很敏感。在强迫是周期性的，景观表现出不同的行为，如果强迫是由基准面下降率的变化与变化的效率，无论是渠道或山坡侵蚀（如气候变化驱动）。基准面下降的振荡导致流域平均侵蚀率反映了长期的平均侵蚀率，尽管当地侵蚀率具有很强的空间异质性。这种平均反映在河流沉积物中的10 Be浓度。坡面泥沙输运系数的变化会导致流域平均侵蚀速率的大幅波动，这也反映在10 Be浓度中。侵蚀速率的变化在景观中的泥沙输移和通道可蚀性系数的变化是由坡面输移系数的变化占主导地位。版权所有© 2016约翰威利父子有限公司.
Past variations in climate and tectonics have led to spatially and temporally varying erosion rates across many landscapes. In this contribution I examine methods for detecting and quantifying the nature and timing of transience in eroding landscapes. At a single location, cosmogenic nuclides can detect the instantaneous removal of material or acceleration of erosion rates over millennial timescales using paired nuclides. Detection is possible only if one of the nuclides has a significantly shorter half‐life than the other. Currently, the only practical way of doing this is to use cosmogenicin situcarbon‐14 (14C) alongside a longer lived nuclide, such as beryllium‐10 (10Be). Hillslope information can complement or be used in lieu of cosmogenic information: in soil mantled landscapes, increased erosion rates can be detected for millennia after the increase by comparing relief and ridgetop curvature. This technique will work as long as the final erosion rate is greater than twice the initial rate. On a landscape scale, transience may be detected based upon disequilibria in channel profiles or ridgetops, but transience can be sensitive to the nature of transient forcing. Where forcing is periodic, landscapes display differing behavior if forcing is driven by changes in base level lowering rates versus changes in the efficiency of either channel or hillslope erosion (e.g. driven by climate change). Oscillations in base level lowering lead to basin averaged erosion rates that reflect a long term average erosion rate despite strong spatial heterogeneity in local erosion rates. This averaging is reflected in10Be concentrations in stream sediments. Changes in hillslope sediment transport coefficients can lead to large fluctuations in basin averaged erosion rates, which again are reflected in10Be concentrations. The variability of erosion rates in landscapes where both the sediment transport and channel erodibility coefficients vary is dominated by changes to the hillslope transport coefficient. Copyright © 2016 John Wiley & Sons, Ltd.