美国加州理工学院Geyman Emily C.小组发现，永久冻土减缓了北极河岸的侵蚀。相关论文于2024年10月9日发表于国际顶尖学术期刊《自然》杂志上。

据介绍，河流迁移的速度影响北极基础设施和社区的稳定性，并调节碳、营养物和沉积物向海洋的通量。然而，迄今为止，在北极变暖的情况下预测河流迁移的速度将如何变化，一直受到相互矛盾的观察结果的阻碍，即冻土主要是减缓还是加速河流迁移。

研究人员开发了新计算方法，能够在比卫星图像像素尺寸小5-10倍的长度尺度上检测河岸侵蚀，这是一项创新，可以在河流经历水温和流量最大变化的次月时间尺度上量化侵蚀。研究使用这些高频观测来限制侵蚀的程度，这些侵蚀是由凝结河岸沉积物的孔隙冰融化的热条件所限制的，当永久冻土融化时，这一必要条件将会消失，相对于有足够的流量来运输构成河岸的沉积物的机械条件，这是所有河流都经历过的条件。

研究人员对阿拉斯加Koyukuk河高分辨率数据的分析表明，永久冻土的存在使侵蚀率降低了47%。经过观察，研究人员校准并验证了一个可以应用于不同北极河流的数值模型。该模型预测，永久冻土完全融化可能导致北极河流的迁移率增加30%至100%。

附：英文原文

Title: Permafrost slows Arctic riverbank erosion

Author: Geyman, Emily C., Douglas, Madison M., Avouac, Jean-Philippe, Lamb, Michael P.

Issue&Volume: 2024-10-09

Abstract: The rate of river migration affects the stability of Arctic infrastructure and communities and regulates the fluxes of carbon, nutrients and sediment to the oceans. However, predicting how the pace of river migration will change in a warming Arctic has so far been stymied by conflicting observations about whether permafrost primarily acts to slow or accelerate river migration. Here we develop new computational methods that enable the detection of riverbank erosion at length scales 5–10 times smaller than the pixel size in satellite imagery, an innovation that unlocks the ability to quantify erosion at the sub-monthly timescales when rivers undergo their largest variations in water temperature and flow. We use these high-frequency observations to constrain the extent to which erosion is limited by the thermal condition of melting the pore ice that cements bank sediment, a requirement that will disappear when permafrost thaws, versus the mechanical condition of having sufficient flow to transport the sediment comprising the riverbanks, a condition experienced by all rivers. Analysis of high-resolution data from the Koyukuk River, Alaska, shows that the presence of permafrost reduces erosion rates by 47%. Using our observations, we calibrate and validate a numerical model that can be applied to diverse Arctic rivers. The model predicts that full permafrost thaw may lead to a 30–100% increase in the migration rates of Arctic rivers.

DOI: 10.1038/s41586-024-07978-w

Source: https://www.nature.com/articles/s41586-024-07978-w