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yexuqing木虫之王 (文学泰斗)
太阳系系主任
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[交流]
永久冻土减缓了北极河岸的侵蚀
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永久冻土减缓了北极河岸的侵蚀 ▲ 作者：Emily C. Geyman, Madison M. Douglas et al. ▲ 链接： https://www.nature.com/articles/s41586-024-07978-w ▲ 摘要： 在此，我们开发了新的计算方法，可以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情况。这一创新使得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变成可能。 我们使用这些高频观测来约束河岸侵蚀在多大程度上受到热条件限制的程度——这一要求将在永久冻土融化时消失——并与有足够水流以运输构成河岸的沉积物的力学条件进行对比，后者是所有河流都会经历的情况。对阿拉斯加科尤库克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%。 通过我们的观测，我们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%。 ▲ Abstract： 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. |
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