Learning to Read the Chemistry of Regolith to Understand the Critical Zone

The base of the Critical Zone includes the mantle of altered soil and rock regolith-that changes in response to chemical, physical, and biological processes occurring at Earth's surface. These processes are recorded in the chemistry of the regolith, and this long-term record can often be deciphered. For example, on eroding ridgetops where flows are generally downward for water and upward for earth material, element concentrations vary with depth to constitute depletion, addition, depletion-enrichment, and biogenic profiles. Models can be used to explore the records of mineral dissolution, atmospheric input, coupled dissolution-precipitation, and biolifting documented in these profiles. These models enable interpretation of the effects of time, climate, rates of erosion, and human and other biotic impacts on the profile patterns. By testing quantitative models against the long-term record of information in regolith, we will learn to project changes arising from human and natural perturbations of the Critical Zone.