EFFECTS OF TRANSIENT PERTURBATIONS IN PHYSICAL EROSION RATES ON CHEMICAL EROSION RATES (Invited Presentation)

Understanding the controls on regolith chemical erosion rates is of wide interest due to the central role that chemical erosion plays in driving landscape evolution, supplying nutrients to soils and streams, and modulating the global carbon cycle. One of the strongest controls on chemical erosion rates (W) has long been thought to be physical erosion at a rate E, which removes weathered material from the regolith and modulates rates of fresh mineral supply to the regolith by regulating regolith thickness. Measured relationships between W and E, however, vary substantially around the globe, with some sites exhibiting positive relationships between W and E, some exhibiting negative relationships, and others exhibiting no relationship. Here we explore the response of W to transient perturbations in E with a numerical model for mineralogy in a 1-D regolith column.

This model predicts that changes in W lag changes in E by a time that scales linearly with a characteristic regolith production time and inversely with a characteristic mineral dissolution time. As a consequence of the lag between W and E, a hysteresis develops in plots of W versus E during transients in E, which results in a positive relationship between W and E over some periods of time, a flat relationship at other times, and a negative relationship at other times. To the extent that this reflects the behavior of chemical erosion rates in nature, this implies that a variety of relationships between W and E can be generated by a single perturbation in E, even in the absence of changes in other factors that affect W, such as climate, biota, or lithology. This behavior may aid interpretation of measurements of W and E based on regolith geochemistry and fluxes of fluvial sediment and solutes.