Abstract
Abstract. At the interface between the lithosphere and the atmosphere, the critical zone records the complex interactions between erosion, climate, geologic substrate, and life and can be directly monitored. Long data records (30 consecutive years for sediment yields) collected in the sparsely vegetated, steep, and small marly badland catchments of the Draix–Bléone Critical Zone Observatory (CZO), SE France, allow analyzing potential climatic controls on regolith dynamics and sediment export. Although widely accepted as a first-order control, rainfall variability does not fully explain the observed interannual variability in sediment export. Previous studies in this area have suggested that frost-weathering processes could drive regolith production and potentially modulate the observed pattern of sediment export. Here, we define sediment export anomalies as the residuals from a predictive model with annual rainfall intensity above a threshold as the control. We then use continuous soil temperature data recorded at different locations over multiple years to highlight the role of different frost-weathering processes (i.e., ice segregation versus volumetric expansion) in regolith production. Several proxies for different frost-weathering processes have been calculated from these data and compared to the sediment export anomalies, with careful consideration of field data quality. Our results suggest that frost-cracking intensity (linked to ice segregation) can explain about half (47 %–64 %) of the sediment export anomalies. In contrast, the number of freeze–thaw cycles (linked to volumetric expansion) has only a minor impact on catchment sediment response. The time spent below 0 ∘C also correlates well with the sediment export anomalies and requires fewer field data to be calculated than the frost-cracking intensity. Thus, frost-weathering processes modulate sediment export by controlling regolith production in these catchments and should be taken into account when building predictive models of sediment export from these badlands under a changing climate.
Highlights
Landscape erosion and its associated hazards, such as torrential floods and rockfalls, are some of the visible consequences of the complex interaction between the critical zone and climate (e.g., Anderson et al, 2012)
Based on our analysis of sediment yield records and soil temperature data from the Draix–Bléone Critical Zone Observatory (CZO) and accounting for the inevitable uncertainties in our dataset, we show that frost-weathering processes modulate sediment export by controlling sediment production in these marly catchments
The annual hysteresis cycle (Fig. 4) shows an anticlockwise pattern in the first half of the year (February–July) and a clockwise pattern later in the year (August–December), suggesting a spring–early summer transport-limited regime followed by a supply-limited regime during late summer and autumn in these catchments
Summary
Landscape erosion and its associated hazards, such as torrential floods and rockfalls, are some of the visible consequences of the complex interaction between the critical zone and climate (e.g., Anderson et al, 2012). Over the last 35 years, several small catchments in these marly badlands have been monitored in the framework of the Draix–Bléone Critical Zone Observatory (CZO), leading to a quantification of weathering and erosion through repeated measurements of sediment yield at the event scale (Mathys et al, 2003). As an example, during one flood event on 17 June 2014, 6390 t km−2 was exported and the suspended sediment concentration reached 440 g l−1. Such sediment-laden floods can potentially cause significant damage to downstream infrastructure. Landscape changes are and rapidly observable in the Draix–Bléone catchments, but improved identification and understanding of the weathering processes in these marls are required to more accurately predict exported sediment volumes
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