Model shows that rivers transmit high-frequency climate cycles to the sedimentary record

Abstract

Rivers are a major component of sediment routing systems that control the transfer of terrigenous sediments from source to sink. Although it is widely accepted that rivers are perturbed by millennial-scale climatic variability, the extent to which these signals are buffered or transferred down river systems to be recorded in sediments at or beyond the river mouth remains debated. Here, we employ a physically based numerical model to address this outstanding issue. Our model shows that river transport strongly amplifies high-frequency sediment flux variations arising from changing water discharge, due to positive feedback between discharge and the channel gradient. This behavior is distinctly different from short-period sediment flux signals (with constant water discharge) where the output sediment flux is strongly dampened within the river, due to negative feedback between the channel gradient and sediment concentration. We conclude that marine sedimentary basins may record sediment flux cycles resulting from discharge (and ultimately climate) variability, whereas they may be relatively insensitive to pure sediment flux perturbations (such as for example those induced by tectonics)

The distribution of rivers to terrestrial sinks: Implications for sediment routing systems

“…In addition, a millennial scale perturbation (tectonic or climatic) in source-derived sediment discharge may not necessarily increase the sediment discharge significantly of either system at the marine sink. However, a millennial scale perturbation in increased water discharge will likely increase sediment remobilization of stored terrestrial sink sediments (Simpson and Castelltort, 2012). A foreland setting with a large terrestrial sink will have a large surface area for the increased water discharge to remobilize sediment downstream.…”

“…As the preserved stratigraphy is composed of an incomplete record of infrequent but large magnitude events (Leeder et al, 1998;Corbett et al, 2014;Miall, 2014), the composition of sediments stored in the terrestrial sink can remobilize during larger millennial episodes that influence the entire system. Simpson and Castelltort (2012) showed numerical models indicating that while the terrestrial sink (N300 km) has the potential to diffuse millennial scale episodes (e.g., Castelltort and Van Den Driessche, 2003), an increase in sedimentation can occur at the marine environment due to an increase in water discharge remobilizing previously stored sediments.…”

“…22). Furthermore, the terrestrial sink is often understated even though it plays a vital role in understanding the dynamics of sedimentary delivery to the marine environment (see Van Den Driessche, 2003, Simpson andCastelltort, 2012;Romans et al, 2016).…”

Quantitative bounds on morphodynamics and implications for reading the sedimentary record

“…1). The latter far exceeds historical records of sediment flux (and its variability), and therefore our understanding of the role of morphodynamic feedbacks in environmental signal preservation is based largely on small-scale physical models 10,15 and numerical experiments 13,[15][16][17][18] . Nonetheless, upscaling results from analogue models to natural depositional systems incorporates uncertainties, and consequently, reconstructions of the sedimentary archives on both the Earth and the Mars routinely neglect any morphodynamic filtering (for example, Zhang et al 7 ).…”

“…Although sedimentary deposits have been shown to contain a rich archive of environmental (allogenic) conditions and their changes 7,13 (that is, tectonics, climatic, sea level, anthropogenic), there is increasing recognition of the role of self-organized (autogenic) dynamics of sediment-transport systems in obscuring or even obliterating the record of externally forced environmental signals [10][11][12]14 . Numerical and physical experiments [10][11][12][14][15][16][17][18] and field investigations 8,19 indicate that the primary signal in physical stratigraphy can in cases be the record of the nonlinear sediment-transport dynamics, played out through geologic time. Detangling autogenic dynamics from allogenic forcing in the sedimentary record is difficult, because we lack quantitative metrics to assess where environmental conditions may be preserved in depositional archives.…”