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A global rate of denudation from cosmogenic nuclides in the Earth's largest rivers
Earth-Science Reviews ( IF 12.1 ) Pub Date : 2020-05-01 , DOI: 10.1016/j.earscirev.2020.103147
H. Wittmann , M. Oelze , J. Gaillardet , E. Garzanti , F. von Blanckenburg

Abstract Cosmogenic nuclide analysis in sediment from the Earth's largest rivers yields mean denudation rates of the sediment-producing areas that average out the local variations commonly found in small rivers. Using this approach, we measured in situ cosmogenic 26Al and 10Be in sand of >50 large rivers over a range of climatic and tectonic regimes covering 32% of the Earth's terrestrial surface. In 35% of the analyzed rivers, we find 26Al/10Be ratios significantly lower than these nuclides´ surface-production-rate ratio of 6.75 in quartz, indicating radioactive decay over periods exceeding 0.5 Myr. We invoke a combination of slow erosion, shielding in the source area, and sediment storage and burial during long-distance transport to explain these low ratios. In the other 65% of studied rivers we find 26Al/10Be ratios within uncertainty of their surface production-rate ratio, indicating cosmogenic steady state. For these rivers, we obtain a global source area denudation rate of 141 t/km2×yr (54 mm/kyr of rock-equivalent) that translates to a flux of 3.07 ± 0.56 Gt/yr. By assuming that this sub-dataset is representative of the global land surface, we upscale this value to the total surface area for exorheic basins, thereby obtaining a global denudation flux of 15.2 ± 2.8 Gt/yr that integrates over the past 11 kyr. This value is slightly lower than published values from cosmogenic nuclides from small river basins (23 (+53/−16)) Gt/yr) upscaled using a global slope model, and also lower than modern sediment and dissolved loads exported to the oceans (24.0 Gt/yr). Our new approach confirms an estimate of global dissolved and solid matter transfer that converges to an encouragingly narrow range of within 35%; whereas the use of paired nuclides in large rivers provides estimates of the buffering timescales of sediment transport.

中文翻译:

地球上最大河流中宇宙成因核素的全球剥蚀速率

摘要 地球上最大河流沉积物中的宇宙成因核素分析得出产沙区的平均剥蚀率,平均了小河流中常见的局部变化。使用这种方法,我们在覆盖地球陆地表面 32% 的一系列气候和构造状况的超过 50 条大河流的沙子中原位测量了宇宙成因 26Al 和 10Be。在 35% 的分析河流中,我们发现 26Al/10Be 的比率明显低于这些核素在石英中的 6.75 的表面生产率比率,表明放射性衰变超过 0.5 Myr。我们援引缓慢侵蚀、源区屏蔽以及长途运输过程中的沉积物储存和掩埋的组合来解释这些低比率。在其他 65% 的研究河流中,我们发现 26Al/10Be 比率在其表面生产率比率的不确定性范围内,表明处于宇宙成因稳定状态。对于这些河流,我们获得了 141 t/km2×yr(54 mm/kyr 的岩石当量)的全球源区剥蚀率,转化为 3.07 ± 0.56 Gt/yr 的通量。通过假设该子数据集代表全球陆地表面,我们将该值放大到外流盆地的总表面积,从而获得 15.2 ± 2.8 Gt/yr 的全球剥蚀通量,该通量对过去 11 kyr 进行了积分。该值略低于使用全球坡度模型放大的小流域宇宙成因核素 (23 (+53/−16)) Gt/yr) 的公布值,也低于输出到海洋的现代沉积物和溶解负荷( 24.0 公吨/年)。我们的新方法证实了对全球溶解和固体物质转移的估计,该估计收敛到 35% 以内的令人鼓舞的狭窄范围;而在大河中使用成对核素可以估计沉积物运输的缓冲时间尺度。
更新日期:2020-05-01
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