wiki:GroupActivities/CodeAvalaibilityPublication/ORCHIDEE_gmd-2018-14C

Version 1 (modified by bguenet, 6 years ago) (diff)

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ORCHIDEE_gmd-2018-14C

This version of ORCHIDEE has been used in publication The use of radiocarbon 14C to constrain soil carbon dynamics in the land surface model ORCHIDEE by Marwa Tifafi, Marta Camino-Serrano, Christine Hatté, Hector Morras, Lucas Moretti, Sebastián Barbaro, Sophie Cornu, Bertrand Guenet as manuscript gmd-2018-XX << Reference to be added as soon as the manuscript is open for review >>.

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, current LSMs generally represent soils in a very simplified way that can induce a misrepresentation of the deep dynamics of soil carbon and thus, large uncertainties in predictions of soil carbon response to climate change. In this study, we will present a new version of the IPSL-Land Surface Model called ORCHIDEE-SOM, incorporating the 14C dynamic in the soil. ORCHIDEE-SOM, first, simulates carbon dynamics in the soil column down to 2 m-depth, partitioned in 11 layers. Second, the concentration of dissolved organic carbon (DOC) in each layer and transport between layers are modeled. Finally, soil organic carbon (SOC) decomposition is considered taking into account the amount of fresh organic matter as a way of accounting for 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) from four sites with different vegetation covers. The model managed to reproduce the soil organic carbon stocks and the F14C along the vertical profiles at the four sites. However, an overestimation of the total carbon stock throughout the profile 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 diminution of the soil carbon stock overestimation, especially at the surface and an improvement of the estimates of the carbon age. This assumes that model improvements should focus more on a depth dependent parameterization, mainly for the diffusion, in order to improve the representation of the global carbon cycle in LSMs, thus helping to constrain the predictions of the future soil organic carbon response to global warming.

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