CONTINENTAL EROSION AT MILLENNIAL TIMESCALES

Since the last decade, in situ produced cosmogenic radionuclides (CRN) in fluvial sediments have been used to estimate basin-averaged erosion rates across Earth's surface. We have compiled approximately 565 of these measurements representing global-scale landscape denudation at timescales of 10^3-10^6 years. The total range of sampled erosion rates exceeds three orders of magnitude (0.0015-5.1mm/yr) for a collection of basins having mean elevations up to 4500 meters. Mean elevations were derived for each sampled basin from a single topographic source, SRTM. Four other physiographic metrics were also measured for each basin: maximum elevation, total relief, mean relief, and mean slope. At CRN timescales all five topographic indices are equally correlated with log-transformed basin-averaged denudation; each explain ~45% of the global erosion-rate variance. In contrast, linear relations between the topographic metrics and erosion rates have correlations of approximately r-square=0.26.

We suggest that mean elevation is the most appropriate predictor of denudation averaged over these scales and cast it as a proxy for convergence or divergence in sediment transport systems globally. The relation between elevation, E, and erosion rate, R, is given by R=20e^(0.00075E), with units of mm/yr and m, respectively. The precision associated with this elevation based prediction of CRN timescale, basin averaged denudation is half an order of magnitude. Additionally, the relation is paralleled by existing datasets of sediment yield to the world's oceans and similarly coincides with production rates required by Phanerozoic sediment volumes. From these relationships it is evident that the suite of erosion rates found across Earth's surface today has a range that far exceeds the possible secular variations for any individual basin at millennial timescales.