Diverse responses of coupled mountain-basin system to periodic climate change

Fluvial erosion and deposition rates are influenced by channel slope, upstream water discharge, and sediment flux. In mountain belts, fluvial processes primarily generate sediment through the incision of bedrock, with the eroded material being transported downstream by the fluvial discharge. As sediment reaches the low-gradient foreland basin, the reduced channel slope significantly diminishes the river's transport capacity, resulting in part of sediment being deposited in the basin, while the remainder is transported further through the basin's drainage network, eventually reaching more distant locations such as oceans or large lakes. The processes of sediment generation, transfer, and preservation are highly sensitive to precipitation rate change. Therefore, variations in sediment flux within rivers and changes in basin sediment thickness can provide insights into past climate conditions. 

Using a fluvial erosion-deposition landscape evolution model, we investigate how erosion-dominated regions (mountain belts) and deposition-dominated areas (foreland basins) respond to periodic variations in precipitation rates. The model results indicate that landscape response is highly sensitive to the ratio of forcing period (P) to response time (τ). Mountain regions typically respond to medium- to high-frequency signals in the form of fluctuations in sediment flux, which can be amplified through sedimentation processes. As the forcing period increases, peak sediment flux and peak precipitation rates may become in-phase, lag, or lead. These differences result from variations in the migration distance of knickpoints, as demonstrated by river elevation profiles and χ-plots. In contrast, basins are more responsive to low-frequency signals in the form of changes in sediment thickness, with basin elevation adjustments consistently lagging behind the forcing. Our work provides insights into understanding the response of the mountain-basin system to precipitation rate variations on different time scales and offers explanations for their different responses to precipitation rate change.