A global rate of denudation from cosmogenic nuclides in the Earth’s largest rivers

Cosmogenic nuclide analysis in sediment from the Earth’s largest rivers yields mean denudation rates of the sediment-producing areas that average out 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, ²⁶Al/¹⁰Be ratios are significantly lower than these nuclides´ surface-production-rate ratio of 6.75. We explain these low ratio by a combination of slow erosion and shielding in the source area, and we provide estimates of the buffering timescales of sediment transport using paired nuclides. In the other 65% of studied rivers, ²⁶Al/¹⁰Be ratios are 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 (3.07 Gt/yr). By assuming that this sub-dataset is representative of the global land surface, we upscale to the total surface area for exorheic basins, thereby obtaining a global, millennial-scale denudation flux of 15.2 ± 2.8 Gt/yr. 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%.