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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/esurf-2017-29
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
15 May 2017
Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Earth Surface Dynamics (ESurf) and is expected to appear here in due course.
Model predictions of long-lived storage of organic carbon in river deposits
Mark A. Torres1, Ajay B. Limaye2, Vamsi Ganti3, Michael P. Lamb1, A. Joshua West4, and Woodward W. Fischer1 1Division of Geological & Planetary Sciences, California Institute of Technology, USA
2Department of Earth Sciences, University of Minnesota, 2 SE 3rd Ave., Minneapolis, MN 5541, USA
3Department of Earth Science & Engineering, Imperial College, UK
4Department of Earth Sciences, University of Southern California, USA
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 CO2 and O2. 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 as well as the effects of POC cycling. We specifically target rivers because sediment transport defines 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 ameliorates 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.


Citation: Torres, M. A., Limaye, A. B., Ganti, V., Lamb, M. P., West, A. J., and Fischer, W. W.: Model predictions of long-lived storage of organic carbon in river deposits, Earth Surf. Dynam. Discuss., https://doi.org/10.5194/esurf-2017-29, in review, 2017.
Mark A. Torres et al.
Interactive discussionStatus: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version      Supplement - Supplement
 
RC1: 'Torres et al. (E-Surf Disc.): review', Anonymous Referee #1, 14 Jun 2017 Printer-friendly Version 
 
RC2: 'Review of Torres et al.', Jim Pizzuto, 05 Jul 2017 Printer-friendly Version 
 
AC1: 'Author responses and changes made in revision', Mark Torres, 02 Aug 2017 Printer-friendly Version Supplement 
Mark A. Torres et al.
Mark A. Torres et al.

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Short summary
In this manuscript, we describe a new model for the storage times of sediments and organic carbon (OC) in river deposits. Comparisons between our model predictions and field data show good agreement, which suggests that our model accurately captures the relevant time and space scales. An implication of our model is that OC is stored in river deposits over geologic timescales and, as a result, we propose that fluvial storage plays a larger role in the carbon cycle than previously recognized.
In this manuscript, we describe a new model for the storage times of sediments and organic...
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