A global rate of denudation from cosmogenic nuclides in the Earth's largest rivers
A global rate of denudation from cosmogenic nuclides in the Earth's largest rivers
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DOI：
10.1016/j.earscirev.2020.103147
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发表时间：
2020-05
影响因子：
12.1
通讯作者：
H. Wittmann;M. Oelze;J. Gaillardet;E. Garzanti;F. Blanckenburg
中科院分区：
文献类型：
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作者：
H. Wittmann;M. Oelze;J. Gaillardet;E. Garzanti;F. Blanckenburg
对地球最大河流沉积物中的宇宙成因核素分析得出沉积物产生区的平均剥蚀率，该平均剥蚀率消除了小河流中常见的局部变化。使用这种方法，我们测量了覆盖地球陆地表面 32% 的一系列气候和构造状况下超过 50 条大河沙子中的 26Al 和 10Be。在 35% 的分析河流中，我们发现 26Al/10Be 比率显着低于这些核素在石英中的表面生成率比率 6.75，表明放射性衰变的周期超过 0.5 Myr。我们结合缓慢侵蚀、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范围内，表明宇宙成因稳态。对于这些河流，我们获得的全球源区剥蚀率为 141 t/km2×yr（54 mm/kyr 岩石当量），换算成通量为 3.07 ± 0.56 Gt/年。通过假设该子数据集代表全球陆地表面，我们将该值升级为放流盆地的总表面积，从而获得过去 11 kyr 积分的 15.2 ± 2.8 Gt/年的全球剥蚀通量。该值略低于使用全球斜率模型放大的小河流域宇宙成因核素的公布值 (23 (+53/−16)) Gt/年)，也低于现代沉积物和输出到海洋的溶解负荷 (24.0 Gt/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，该估计收敛于 35% 以内的令人鼓舞的狭窄范围；而在大河流中使用配对核素可以估计沉积物迁移的缓冲时间尺度。
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 measuredin situcosmogenic26Al and10Be 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 find26Al/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 find26Al/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.