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yexuqing木蟲之王 (文學(xué)泰斗)
太陽(yáng)系系主任
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[交流]
永久凍土減緩了北極河岸的侵蝕
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永久凍土減緩了北極河岸的侵蝕 ▲ 作者：Emily C. Geyman, Madison M. Douglas et al. ▲ 鏈接： https://www.nature.com/articles/s41586-024-07978-w ▲ 摘要： 在此，我們開發(fā)了新的計(jì)算方法，可以在比衛(wèi)星圖像像素尺寸小5—10倍的長(zhǎng)度尺度上檢測(cè)河岸侵蝕情況。這一創(chuàng)新使得在河流經(jīng)歷水溫和流量最大變化的次月時(shí)間尺度上量化侵蝕變成可能。 我們使用這些高頻觀測(cè)來約束河岸侵蝕在多大程度上受到熱條件限制的程度——這一要求將在永久凍土融化時(shí)消失——并與有足夠水流以運(yùn)輸構(gòu)成河岸的沉積物的力學(xué)條件進(jìn)行對(duì)比，后者是所有河流都會(huì)經(jīng)歷的情況。對(duì)阿拉斯加科尤庫(kù)克河高分辨率數(shù)據(jù)的分析表明，永久凍土的存在使侵蝕率降低了47%。 通過我們的觀測(cè)，我們校準(zhǔn)并驗(yàn)證了一個(gè)可以應(yīng)用于不同北極河流的數(shù)值模型。該模型預(yù)測(cè)，永久凍土完全融化可能導(dǎo)致北極河流的遷移率增加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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