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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/gmd-2018-102
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Development and technical paper
29 May 2018
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This discussion paper is a preprint. It is a manuscript under review for the journal Geoscientific Model Development (GMD).
The use of radiocarbon 14C to constrain carbon dynamics in the soil module of the land surface model ORCHIDEE (SVN r5165)
Marwa Tifafi1, Marta Camino-Serrano2,3, Christine Hatté1, Hector Morras4, Lucas Moretti5, Sebastián Barbaro5, Sophie Cornu6, and Bertrand Guenet1 1Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France
2CREAF, Cerdanyola del Vallès, 08193, Catalonia, Spain
3CSIC, Global Ecology Unit CREAF-CSIC-UAB, Bellaterra 08193, Catalonia, Spain
4INTA-CIRN, Instituto de Suelos, 1712 Castelar, Buenos Aires, Argentina
5INTA-EEA Cerro Azul, 3313 Cerro Azul, Misiones, Argentina
6Aix Marseille Univ, CNRS, IRD, INRA, Coll France, CEREGE, Aix-en-Provence, France
Abstract. Despite the importance of soil as a large component of the terrestrial ecosystems, the soil compartments are not well represented in the Land Surface Models (LSMs). Indeed, soils in current LSMs are generally represented based on a very simplified schema that can induce a misrepresentation of the deep dynamics of soil carbon. Here, we present a new version of the IPSL-Land Surface Model called ORCHIDEE-SOM, incorporating the 14C dynamic in the soil. ORCHIDEE-SOM, first, simulates soil carbon dynamics for different layers, down to 2 m depth. Second, concentration of dissolved organic carbon (DOC) and its transport are modeled. Finally, soil organic carbon (SOC) decomposition is considered taking into account the priming effect.

After implementing the 14C in the soil module of the model, we evaluated model outputs against observations of soil organic carbon and 14C activity (F14C) for different sites with different characteristics. The model managed to reproduce the soil organic carbon stocks and the F14C along the vertical profiles. However, an overestimation of the total carbon stock was noted, but was mostly marked on the surface. Then, thanks to the introduction of 14C, it has been possible to highlight an underestimation of the age of carbon in the soil. Thereafter, two different tests on this new version have been established. The first was to increase carbon residence time of the passive pool and decrease the flux from the slow pool to the passive pool. The second was to establish an equation of diffusion, initially constant throughout the profile, making it vary exponentially as a function of depth. The first modifications did not improve the capacity of the model to reproduce observations whereas the second test showed a decrease of the soil carbon stock overestimation, especially at the surface and an improvement of the estimates of the carbon age. This assumes that we should focus more on vertical variation of soil parameters as a function of depth, mainly for diffusion, in order to upgrade the representation of global carbon cycle in LSMs, thereby helping to improve predictions of the future response of soil organic carbon to global warming.

Citation: Tifafi, M., Camino-Serrano, M., Hatté, C., Morras, H., Moretti, L., Barbaro, S., Cornu, S., and Guenet, B.: The use of radiocarbon 14C to constrain carbon dynamics in the soil module of the land surface model ORCHIDEE (SVN r5165), Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2018-102, in review, 2018.
Marwa Tifafi et al.
Marwa Tifafi et al.
Marwa Tifafi et al.

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Short summary
The role of soil carbon in the climate dynamics becomes one of the major uncertainties in the Land Surface Models. This work is a presentation of a new version of the Land Surface Model called ORCHIDEE incorporating the radiocarbon (14C) used as integrator of the soil carbon dynamics. It has been possible to highlight an underestimation of the age of carbon in the soil and that model improvements should focus more on a depth dependent parameterization mainly for the diffusion.
The role of soil carbon in the climate dynamics becomes one of the major uncertainties in the...
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