Short Communication: Earth is (mostly) flat, but mountains dominate global denudation: apportionment of the continental mass flux over millennial time scales, revisited

Abstract. Carbon dioxide consumption by silicate mineral weathering and the subsequent precipitation of carbonate sediments sequesters CO₂ over geologic timescales. The rate of this carbon sequestration is coupled to rates of continental erosion, which exposes fresh minerals to weathering. Steep mountain landscapes represent a small fraction of continental surfaces but contribute disproportionately to global erosion rates. However, the relative contributions of Earth's much vaster, but more slowly eroding, plains and hills remain the subject of debate. Recently, Willenbring et al. (2013) analyzed a compilation of denudation rates and topographic gradients and concluded that low-gradient regions dominate global denudation fluxes and silicate weathering rates. Here, we show that Willenbring et al. (2003) topographic and statistical analyses were subject to methodological errors that affected their conclusions. We correct these errors, and reanalyze their denudation rate and topographic data. In contrast to the results of Willenbring et al. (2013), we find that the denudation flux from the steepest 10% of continental topography nearly equals the flux from the other 90% of the continental surface combined. This new analysis implies global denudation fluxes of ∼23 Gt yr⁻¹, roughly five times the value reported in Willenbring et al. (2013) and closer to previous estimates found elsewhere in the literature. Although low-gradient landscapes make up a small proportion of the global fluxes, they remain important because of the human reliance, and impact, on these vast areas.