2018 CSDMS meeting-056
Transient relationships between chemical and physical erosion rates in regolith-mantled topography
Chemical erosion of regolith is of wide interest due to its role in Earth’s topographic evolution, the supply of nutrients to soils and streams, and the global carbon cycle. Theory and experiments suggest that chemical erosion rates (W) should be strongly controlled by physical erosion rates (E), which affect W by removing weathered regolith and regulating mineral supply rates to the regolith from its underlying parent material. A global compilation of field measurements reveals a wide range of relationships between W and E, with some sites exhibiting positive relationships between W and E, some exhibiting negative relationships, and others exhibiting a flat relationship within uncertainty. Here we apply a numerical model to explore the variety of W-E relationships that can be generated by transient perturbations in E in well-mixed regolith.
Our modeling results show that transient relationships between W and E during erosional perturbations can strongly deviate from steady-state relationships. These deviations ultimately result from the time lag in changes in W following imposed changes in E. As a consequence of the lag, a hysteresis develops in plots of W versus E during transients in E. This yields a positive relationship between W and E at some times during a transient perturbation, a flat relationship at other times, and a negative relationship at other times. The shape and duration of these transient hystereses can be modulated by climate and lithology, as the lag time increases linearly with a characteristic regolith production time and decreases with a characteristic mineral dissolution time, both of which are affected by climatic and lithologic factors. Our results show that even in the absence of variations in climate and lithology, however, a range of W-E relationships can be generated by a single perturbation in E. To the extent that these model results capture the behavior of chemical and physical erosion in natural landscapes, these results may aid interpretation of field measurements of W and E.