Collaborative Research: The Role of Loess Weathering in Global Geochemical Cycles

这是由加州大学圣克鲁斯分校和阿拉斯加大学费尔班克斯分校的主要研究人员合作提出的一项建议。该奖项将由北极自然科学项目和地球科学部地质与古生物学项目共同资助。冰川产生了大量的细粒沉积物，使大量的矿物表面暴露在化学风化过程中。尽管冰川有巨大的潜力影响全球风化速率，从而影响大气中的二氧化碳水平，但这种影响尚未得到证实。冰川下的硅酸盐风化率较低，最近冰川消退的地形的风化率低于平均水平。该假说认为，黄土风化是冰川物理侵蚀与全球地球化学循环之间的关键联系。本项目旨在研究冰川黄土的硅酸盐风化通量，并评价其全球意义。黄土是一种粉质粘土大小的沉积物，由冰川河流的无植被辫状平原吹来，沉积在广阔的植被地区。细粒度和植被都使黄土沉积物极易受硅酸盐风化作用。这些沉积物有效地将冰川作用的影响扩展到比冰川冰的范围更大的地区。黄土的风化作用从未从对全球地球化学旋回的贡献角度进行过研究。该项目旨在回答两个问题：1)黄土沉积是否会增加土壤剖面的硅酸盐风化通量？ 2)黄土的风化速率是否会影响全球风化速率，从而影响全球二氧化碳水平？实验室实验、实地测量和建模将用于解决这些问题。研究地点位于阿拉斯加中部的三角洲河谷，这是一个冰川外冲系统，黄土沉积速率不断变化。实验室和野外工作的结果将综合成一个土壤风化通量的一维模型，该模型是黄土沉积速率、降水速率、有机质含量和粒度分布的函数。该模型将扩展到景观尺度，以评估黄土沉积对CO2消耗的全球意义。黄土的风化作用可能是一个重要的因素，但它仍然是碳循环的一个未被认识的组成部分。如果事实证明是这样的话，那么在大气CO2变化模式中，就必须考虑到比冰期持续时间长得多的时间尺度上的黄土形成和风化。

ABSTRACTAnderson OPP-0240676MannOPP-0240919This is a collaborative proposal by Principal Investigators at the Universities of California-Santa Cruz and Alaska -Fairbanks. This award will be jointly supported by the Arctic Natural Sciences Program and Geology and Paleontology Program in the Division of Earth Sciences. Glaciers produce large amounts of fine-grained sediment, exposing vast amounts of mineral surface area to chemical weathering processes. Despite the tremendous potential for glaciers to influence global weathering rates and hence atmospheric carbon dioxide (CO2) levels, this effect has not yet been demonstrated. Silicate weathering rates underneath glaciers are subdued, and rates in recently deglaciated terrain are below average. The hypothesis is that loess weathering provides the key link between the physical erosion done by glaciers and global geochemical cycles. This project is to study silicate weathering fluxes from glacial loess, and assess their global significance. Loess is a silt-clay sized sediment, transported by wind off unvegetated braid plains of glacier-fed rivers, and deposited over broad vegetated areas. Both the fine grain size and vegetation should render loess deposits highly susceptible to silicate weathering. These deposits effectively extend the impact of glaciation to a much broader area than the extent of glacier ice. Weathering of loess has never been examined from the perspective of contribution to global geochemical cycles. The project is designed to answer two questions: 1) does loess deposition increase the silicate weathering flux from a soil profile, and 2) does the weathering of loess occur at rates that can affect global weathering rates, and hence, global CO2 levels? Laboratory experiments, field measurements, and modeling will be used to address these questions. The field site is the Delta River valley in central Alaska, a glacial outwash system with on-going loess deposition at variable rates. Results from lab and fieldwork will be synthesized in a one-dimensional model of soil weathering fluxes as a function of loess deposition rate, precipitation rate, organic matter content, and grain size distributions. The model will be extended to the landscape scale to assess the global significance of loess deposition on CO2 consumption. Weathering of loess may be a significant, but it is still an unrecognized, component of carbon cycling. If this proves to be the case, then loess formation and weathering over timescales much longer than the duration of glaciation must be considered in models of atmospheric CO2 variation.