Quantitative bounds on morphodynamics and implications for reading the sedimentary record

Ganti, Vamsi; Lamb, Michael P.; McElroy, Brandon

doi:10.1038/ncomms4298

Cited by 79 publications

(96 citation statements)

References 55 publications

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“…Therefore the distance travelled assuming a flow velocity of 1 km h −1 and an elevation of suspension of 1 m is roughly 3 km. Using a similar argument the travel distance of a sediment grain typical of the Bengal Fan is estimated to be ∼ 10 4 m (Ganti et al, 2014). This suggests that rapid transport of sediment across a continent is possible.…”

Section: Erosion Within a Single Dimension Systemmentioning

confidence: 77%

“…This hypothesis is somewhat backed up by the analysis of response times for the transport model, as the response time increases with system length (Table 2) unlike the stream power model, which has a response that is only slightly modified by system length (Whipple, 2001;Baldwin et al, 2003). To date, physical constraints on landscape and sediment flux response times to climate changes in the geologic past are relatively scarce (Ganti et al, 2014;Romans et al, 2016;Temme et al, 2017) because real systems are complex. They include internal dynamics, such as vegetation and autogenic behaviour, which are often omitted from model studies, and because of the need for stratigraphic archives to be complete with well-established chronologies Forman and Straub, 2017).…”

Section: Response Times As a Function Of Model Choicementioning

confidence: 99%

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Numerical modelling of landscape and sediment flux response to precipitation rate change

et al. 2018

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Abstract. Laboratory-scale experiments of erosion have demonstrated that landscapes have a natural (or intrinsic) response time to a change in precipitation rate. In the last few decades there has been growth in the development of numerical models that attempt to capture landscape evolution over long timescales. However, there is still an uncertainty regarding the validity of the basic assumptions of mass transport that are made in deriving these models. In this contribution we therefore return to a principal assumption of sediment transport within the mass balance for surface processes; we explore the sensitivity of the classic end-member landscape evolution models and the sediment fluxes they produce to a change in precipitation rates. One end-member model takes the mathematical form of a kinetic wave equation and is known as the stream power model, in which sediment is assumed to be transported immediately out of the model domain. The second end-member model is the transport model and it takes the form of a diffusion equation, assuming that the sediment flux is a function of the water flux and slope. We find that both of these end-member models have a response time that has a proportionality to the precipitation rate that follows a negative power law. However, for the stream power model the exponent on the water flux term must be less than one, and for the transport model the exponent must be greater than one, in order to match the observed concavity of natural systems. This difference in exponent means that the transport model generally responds more rapidly to an increase in precipitation rates, on the order of 10 5 years for post-perturbation sediment fluxes to return to within 50 % of their initial values, for theoretical landscapes with a scale of 100 × 100 km. Additionally from the same starting conditions, the amplitude of the sediment flux perturbation in the transport model is greater, with much larger sensitivity to catchment size. An important finding is that both models respond more quickly to a wetting event than a drying event, and we argue that this asymmetry in response time has significant implications for depositional stratigraphies. Finally, we evaluate the extent to which these constraints on response times and sediment fluxes from simple models help us understand the geological record of landscape response to rapid environmental changes in the past, such as the Paleocene-Eocene thermal maximum (PETM). In the Spanish Pyrenees, for instance, a relatively rapid (10 to 50 kyr) duration of the deposition of gravel is observed for a climatic shift that is thought to be towards increased precipitation rates. We suggest that the rapid response observed is more easily explained through a diffusive transport model because (1) the model has a faster response time, which is consistent with the documented stratigraphic data, (2) there is a high-amplitude spike in sediment flux, and (3) the assumption of instantaneous transport is difficult to justify for the transport of large grain sizes as an alluvi...

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Section: Erosion Within a Single Dimension Systemmentioning

confidence: 77%

Section: Response Times As a Function Of Model Choicementioning

confidence: 99%

Numerical modelling of landscape and sediment flux response to precipitation rate change

et al. 2018

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“…Settling timescales are independent of the vigorousness of shear and turbulence for relatively large particles or modest turbulence. In such conditions, the adjustment timescale through settling depends on the settling velocity and the vertical section that needs to be re-equilibrated (Dorrell and Hogg, 2012;Ganti et al, 2014). In vigorous turbulent shear conditions, however, the mixing action of the turbulence induces a vertical dispersion flux that cannot be ignored.…”

Section: Summary Discussion and Conclusionmentioning

confidence: 99%

Physical theory for near-bed turbulent particle suspension capacity

2017

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Abstract. The inability to capture the physics of solid-particle suspension in turbulent fluids in simple formulas is holding back the application of multiphase fluid dynamics techniques to many practical problems in nature and society involving particle suspension. We present a force balance approach to particle suspension in the region near no-slip frictional boundaries of turbulent flows. The force balance parameter contains gravity and buoyancy acting on the sediment and vertical turbulent fluid forces; it includes universal turbulent flow scales and material properties of the fluid and particles only. Comparison to measurements shows that = 1 gives the upper limit of observed suspended particle concentrations in a broad range of flume experiments and field settings. The condition of > 1 coincides with the complete suppression of coherent turbulent structures near the boundary in direct numerical simulations of sediment-laden turbulent flow. thus captures the maximum amount of sediment that can be contained in suspension at the base of turbulent flow, and it can be regarded as a suspension capacity parameter. It can be applied as a simple concentration boundary condition in modelling studies of the dispersion of particulates in environmental and man-made flows.

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“…This mixing of variably aged biomarkers will act as a signal filter and modify the sedimentary expression of environmental changes preserved in the isotopic composition of these compounds (Douglas et al, 2014). While such "shredding" of environmental signals has been extensively considered for sediments (Jerolmack and Paola, 2010;Ganti et al, 2014;Pizzuto et al, 2017), here we extended this type of analysis to organic biomarkers.…”

Section: Interpretation Of Time-varying Environmental Signalsmentioning

confidence: 99%

Model predictions of long-lived storage of organic carbon in river deposits

et al. 2017

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Abstract. The mass of carbon stored as organic matter in terrestrial systems is sufficiently large to play an important role in the global biogeochemical cycling of CO 2 and O 2 . Field measurements of radiocarbon-depleted particulate organic carbon (POC) in rivers suggest that terrestrial organic matter persists in surface environments over millennial (or greater) timescales, but the exact mechanisms behind these long storage times remain poorly understood. To address this knowledge gap, we developed a numerical model for the radiocarbon content of riverine POC that accounts for both the duration of sediment storage in river deposits and the effects of POC cycling. We specifically target rivers because sediment transport influences the maximum amount of time organic matter can persist in the terrestrial realm and river catchment areas are large relative to the spatial scale of variability in biogeochemical processes.Our results show that rivers preferentially erode young deposits, which, at steady state, requires that the oldest river deposits are stored for longer than expected for a well-mixed sedimentary reservoir. This geometric relationship can be described by an exponentially tempered power-law distribution of sediment storage durations, which allows for significant aging of biospheric POC. While OC cycling partially limits the effects of sediment storage, the consistency between our model predictions and a compilation of field data highlights the important role of storage in setting the radiocarbon content of riverine POC. The results of this study imply that the controls on the terrestrial OC cycle are not limited to the factors that affect rates of primary productivity and respiration but also include the dynamics of terrestrial sedimentary systems.

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Quantitative bounds on morphodynamics and implications for reading the sedimentary record

Cited by 79 publications

References 55 publications

Numerical modelling of landscape and sediment flux response to precipitation rate change

Numerical modelling of landscape and sediment flux response to precipitation rate change

Physical theory for near-bed turbulent particle suspension capacity

Model predictions of long-lived storage of organic carbon in river deposits

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