Collaborative Research: Linking loess landforms and eolian processes

该项目由2009年美国复苏和再投资法案（Public Law 111-5）资助。该项目将调查北美、北方中国和中欧厚黄土（由风吹尘埃沉积形成的沉积物）地区发生的大型惊人地貌的起源。 这些地貌可能延伸数十公里，并与盛行风保持一致，在美国内布拉斯加州特别发达，研究将在那里进行。 本文将检验两种关于黄土地貌发育的假说，每一种假说都对沙尘在初始沉降后的稳定性作出了明显不同的假设。一种假说认为，除非被风吹来的沙粒通过跃移（在地面附近的短距离跳跃）移动，否则沉降的尘埃不会被重新移动。另一种假说认为，形成大多数厚黄土沉积物的粗粒灰尘很容易被风重新移动，许多黄土地貌是在初始积累后通过侵蚀形成的。利用最近开发的便携式原位风蚀实验室（PI-SWERL），将对黄土沉积物在风的作用下（有或没有跃移的沙子）的可能性进行研究。 此外，这两种假设导致不同的预测黄土粒度和沉积速率的空间格局，以及这些属性将如何随着时间的推移而变化。 这些预测将通过风的尘埃运输的定量模型进行改进，然后将使用黄土剖面的粒度分析和光释光（OSL）测年进行测试，这直接确定了黄土最初沉积的时间。该项目将提供关于黄土沉积物在哪里以及如何成为气候或土地使用变化的灰尘来源的新见解。 如果第二个假设是正确的，例如，过去黄土的风蚀足以雕刻出大片的地貌，可能产生大量的灰尘。在中国北方等厚黄土地区，沙尘是一种常见的环境危害，在20世纪30年代和50年代的大平原也是一种危害，但历史观测可能并不代表潜在的风蚀和沙尘产生的全部范围。 厚的黄土沉积物也是过去气候变化的重要信息来源，在数千年到数百万年之间。 通过记录影响黄土沉积和长期稳定性的复杂过程，该项目的结果应能更好地评估气候因素。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This project will investigate the origin of large, striking landforms that occur in areas of thick loess (sediment formed by deposition of wind-blown dust), in North America, northern China, and central Europe. These landforms may extend for tens of kilometers and are aligned with prevailing winds, and they are especially well-developed in Nebraska, USA, where the research will be conducted. Two hypotheses on loess landform development will be tested, each of which makes distinctly different assumptions about the stability of dust after its initial deposition. One hypothesis assumes that settled dust will not be remobilized unless it is disturbed by wind-blown sand moving by saltation (short hops near the ground surface). The other hypothesis assumes that the coarse-grained dust forming most thick loess deposits is readily remobilized by the wind, and many loess landforms are formed by erosion after initial accumulation. The potential for loess deposits to be set in motion by the wind, with or without saltating sand, will be investigated using the recently developed Portable In Situ Wind Erosion Laboratory (PI-SWERL). In addition, the two hypotheses lead to different predictions about the spatial patterns of loess grain size and deposition rate, and how these properties would have changed over time. These predictions will be refined through quantitative modeling of dust transportation by wind, and will then be tested using grain size analysis and optically stimulated luminescence (OSL) dating of loess sections, which directly determines the time since the loess was originally deposited. This project will provide new insight on where and how loess deposits can become sources of dust in response to climatic or land-use change. If the second hypothesis is valid, for example, past wind erosion of loess was sufficient to carve out large landforms, potentially producing enormous quantities of dust. Dust is a common environmental hazard today in some areas of thick loess such as northern China, and was a hazard in the Great Plains in the 1930s and 1950s, but historical observations probably do not represent the full range of potential wind erosion and dust production. Thick loess deposits are also an important source of information on past climate change, over thousands to millions of years. The results of this project should allow a better assessment of climate factors, by documenting the complex processes that influence the deposition and long-term stability of loess.