Unravelling heterogeneity in erosion-weathering feedbacks and critical zone architecture

Abstract:

Weathering – erosion feedbacks play a fundamental role in regulating regolith cover, mineral residence times, solute and sediment fluxes, and Critical Zone architecture. However, existing conceptual models for Critical Zone evolution and architecture may become limited in their applicability for steep landscapes at the extreme end of the erosional spectrum. In these systems, complex morphologies and stochastic but rapid erosion add complexity and heterogeneity to regolith weathering and cover. Here, we use global compilations of riverine and soil-derived weathering fluxes and insight from new research in diverse mountain belts to highlight this complexity and explore its underlying controls. Regolith in rapidly eroding landscapes often records rapid and surprisingly intense chemical weathering, even as soils thin and/or becomes increasingly isolated. At the same time, data show that local regolith weathering rates become poor predictors of landscape-wide fluxes in these bedrock-dominated systems. The transition to kinetically-limited weathering can help to explain some complexity of regolith structure and function in these systems as weathering fluxes become sensitive to multiple controls including hydrology, moisture availability, and fluid and mineral residence times. However, grand challenges persist in both quantifying this complexity and understanding its implications and controls within the critical zone.