the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Jun 2023
Modelling detrital cosmogenic nuclide concentrations during landscape evolution in CIDRE V2.0
Abstract. The measurement of cosmogenic nuclide (CN) concentrations in riverine sediment has provided breakthroughs in our understanding of landscape evolution. Yet, linking this detrital CN signal and the relief evolution is based on hypotheses that are not easy to verify in the field. A model would help to better understand the statistics of CN concentrations in sediment grains. In this work, we present a coupling between the landscape evolution model Cidre and a model of the CN concentration in distinct grains. These grains are exhumed and detached from the bedrock and then transported in the sediment to the catchment outlet with temporary burials and travel according to the erosion-deposition rates calculated spatially in Cidre. The concentration in the various CN can be tracked in these grains. Because the CN concentrations are calculated in a limited number of grains, they provide an approximation of the whole CN flux. Therefore, this approach is limited by the number of grains that can be handled in a reasonable computing time. Conversely, it becomes possible to record part of the variability in the erosion-deposition processes in the grain-by-grain distribution of the CN concentrations by tracking the CN concentrations in distinct grains using a Lagrangian approach. We illustrate the robustness and limits of this approach by deriving the catchment-mean erosion from the 10Be mean concentration of grains leaving a synthetic catchment uplifting at different rates and by comparing this derived erosion rate to the actual one calculated by Cidre.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(5586 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(5586 KB) - Metadata XML
- BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-1113', Carole Petit, 20 Jul 2023
The approach used here consists of coupling a Lanscape Evolution Model (LEM) developed by the 1st author with well-known cosmogenic nuclide (CN) production and decay laws, in order to track individual particles (grains) journey from their source to their sink (here, when they leave the model grid). This allows the authors to evaluate statistically how the 10Be signal carried by a population of grains in riverine sands is representative of the average denudation rate of the upstream catchment. For now, I guess the aim of the authors is to demonstrate the model’s ability to achieve the desired goal (i.e., to retrieve denudation rate variations with a limited number of grains and a reasonable computational time), not to address very specific questions on real or synthetic cases. To this respect, this paper is extremely interesting and the Lagrangian approach used here allows to account for the large variability in individual grains histories. The effect of grid size, resolution, time step, and number of grains are tested and the results seem extremely robust. It may however reach its limits for a larger landscape (here the grid is only 10km x 10km, except for fig 7 where it is 20km x 20km), and/or with low denudation rates, for which a large number of grains would be needed.
I only have some minor to moderate comments. There are some points that are unclear to me concerning the LEM itself, independently of the CN part. Some sentences are not very clear and may need to be rephrased. Finally, I think that some outcomes deserve a deeper discussion: the influence of the grains’ origin (Quartz source located close or far from the outlet) and the strong amplitude reduction of the 10Be-derived erosion rate for short period precipitation oscillations.
See detailed comments in the pdf file.
- AC1: 'Reply on RC1', Sebastien Carretier, 25 Aug 2023
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RC2: 'Comment on egusphere-2023-1113', Rebekah Harries, 31 Jul 2023
Carretier et al. present a timely development of their Cidre model that supports the rapidly developing field of new lab techniques for sampling cosmogenic concentrations in individual sediment grains. The model allows the numerical exploration of the landscape processes that influence the residence time of sediment grains in mountain catchments and the impact these processes have on the population statistics of cosmogenic concentrations in exported sediment. This is very useful for generating hypotheses that are becoming increasingly testable with field data.
One uncertainty that I have relates to the relationship between relief and CN production in the model and how erosion rate is defined relative to the topographic surface. It would be great if there was a figure clarifying the coordinate system for the attenuation path of cosmic rays emulated together with the surface lowering/mass removal processes. Are the rays attenuated vertical or perpendicular to the topographic surface in the model? Is this important if the model is to be applicable to topographies steeper than those modelled in the paper (>30O)? I am thinking that steeper slopes do not lower their surface uniformly, so if cosmic rays are attenuated vertically, how might the production rates vary depending on the hillslope model used? E.g. non-linear hillslope diffusion model vs Cidre’s model where detachment rates are proportional to slope and mass removal is modelled with non-local effects above a threshold. Some clarification would be great for us visual learners.
Other minor comments are included in the pdf attached.
- AC2: 'Reply on RC2', Sebastien Carretier, 25 Aug 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-1113', Carole Petit, 20 Jul 2023
The approach used here consists of coupling a Lanscape Evolution Model (LEM) developed by the 1st author with well-known cosmogenic nuclide (CN) production and decay laws, in order to track individual particles (grains) journey from their source to their sink (here, when they leave the model grid). This allows the authors to evaluate statistically how the 10Be signal carried by a population of grains in riverine sands is representative of the average denudation rate of the upstream catchment. For now, I guess the aim of the authors is to demonstrate the model’s ability to achieve the desired goal (i.e., to retrieve denudation rate variations with a limited number of grains and a reasonable computational time), not to address very specific questions on real or synthetic cases. To this respect, this paper is extremely interesting and the Lagrangian approach used here allows to account for the large variability in individual grains histories. The effect of grid size, resolution, time step, and number of grains are tested and the results seem extremely robust. It may however reach its limits for a larger landscape (here the grid is only 10km x 10km, except for fig 7 where it is 20km x 20km), and/or with low denudation rates, for which a large number of grains would be needed.
I only have some minor to moderate comments. There are some points that are unclear to me concerning the LEM itself, independently of the CN part. Some sentences are not very clear and may need to be rephrased. Finally, I think that some outcomes deserve a deeper discussion: the influence of the grains’ origin (Quartz source located close or far from the outlet) and the strong amplitude reduction of the 10Be-derived erosion rate for short period precipitation oscillations.
See detailed comments in the pdf file.
- AC1: 'Reply on RC1', Sebastien Carretier, 25 Aug 2023
-
RC2: 'Comment on egusphere-2023-1113', Rebekah Harries, 31 Jul 2023
Carretier et al. present a timely development of their Cidre model that supports the rapidly developing field of new lab techniques for sampling cosmogenic concentrations in individual sediment grains. The model allows the numerical exploration of the landscape processes that influence the residence time of sediment grains in mountain catchments and the impact these processes have on the population statistics of cosmogenic concentrations in exported sediment. This is very useful for generating hypotheses that are becoming increasingly testable with field data.
One uncertainty that I have relates to the relationship between relief and CN production in the model and how erosion rate is defined relative to the topographic surface. It would be great if there was a figure clarifying the coordinate system for the attenuation path of cosmic rays emulated together with the surface lowering/mass removal processes. Are the rays attenuated vertical or perpendicular to the topographic surface in the model? Is this important if the model is to be applicable to topographies steeper than those modelled in the paper (>30O)? I am thinking that steeper slopes do not lower their surface uniformly, so if cosmic rays are attenuated vertically, how might the production rates vary depending on the hillslope model used? E.g. non-linear hillslope diffusion model vs Cidre’s model where detachment rates are proportional to slope and mass removal is modelled with non-local effects above a threshold. Some clarification would be great for us visual learners.
Other minor comments are included in the pdf attached.
- AC2: 'Reply on RC2', Sebastien Carretier, 25 Aug 2023
Peer review completion
Journal article(s) based on this preprint
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Sebastien Carretier
Vincent Regard
Youssouf Abdelhafiz
Bastien Plazolles
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(5586 KB) - Metadata XML