Understanding key assumptions in cosmogenic nuclide-derived catchment-average denudation rates

Basin-averaged erosion rates derived from cosmogenic nuclide concentrations are one of the most commonly used data for the study of landscape evolution histories across a wide range of tectonic and climatic regimes. Despite recent advances in global nuclide datasets and analytical techniques, methods for converting measured concentrations into denudation rates have progressed little.

Converting cosmogenic nuclide concentrations to denudation rates requires several key assumptions; however, one in particular is more difficult to assess, which is that denudation rates remain spatially and temporally constant over timescales comparable to the nuclide integration period. These assumptions rarely hold in nature, especially in mountain catchments with pronounced knickpoints propagating upstream, complicating the interpretation of a single mean concentration. Previous studies have often only evaluated how mean concentrations are affected when one or more assumptions are violated. However, minerals sampled from complex landscapes likely represent distinctly non-Gaussian populations that cannot be adequately characterized by a single mean value.

We present modelling results of cosmogenic nuclide concentration distributions in catchments experiencing spatially and temporally variable denudation rates under different tectonic and climatic forcings. Analysing concentration distributions rather than mean values alone reveals how assumption violations affect inferred denudation rates. Our model employs a detachment-limited stream power law and calculates nuclide accumulation from multiple production pathways using the Lifton-Sato-Dunai scaling scheme.

Preliminary results indicate that the presence of knickpoints does not significantly compromise the interpretation of cosmogenic nuclide concentrations except in cases with fast knickpoint retreat rates in high-relief catchments. However, we find that even moderate climatic changes (simulated by varying the erodibility constant), can yield significant errors in inferred versus real denudation rates. We propose that simple evaluations of cosmogenic nuclide distributions can enhance the reliability of denudation rate estimates in future applications.