Sediment export in marly badland catchments modulated by frost-cracking intensity, Draix-Bléone Critical Zone Observatory, SE France

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 collected in the sparsely vegetated, steep marly badland catchments of the Draix-Bléone Critical Zone Observatory (CZO), SE France, allow analysing potential climatic controls on long-term regolith dynamics and sediment export. Although widely accepted as a first-order control, rainfall variability does not fully explain the observed inter-annual variability in sediment export, suggesting that regolith production and its controls may 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 frost weathering 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 a predictive model of sediment export from these badlands under a changing climate.

Phenomenological model of suspended sediment transport in a small tropical catchment

“…Its elevation ranges from 850 to 1250 m a.s.l, and the annual rainfall rate is about 900 mm yr −1 , with heavy rainfall events during spring and summer, and less intense but longer rainfalls in autumn. Besides, this catchment can also experience snowfalls during winter (Ariagno et al, 2022). Unlike Capesterre, vegetation covers only 32% of the Laval catchment (Carriere et al, 2020) (Fig.…”

“…7a). The latter is underlain by easily erodible Middle Jurassic black marls, leading to the formation of steep badlands slopes within the catchment (Ariagno et al, 2022). A gauging station operated by the Draix-Bléone Critical Zone Observatory monitors the concentration of suspended sediment and the water level in the stream.…”