ORCHIDEE_SOM_r4859

This version of ORCHIDEE has been used in Using stable carbon isotopes as an observational constraint on the dynamics of soil carbon in the land-surface model ORCHIDEE by Marta Camino-Serrano, Marwa Tifafi, Jérôme Balesdent, Christine Hatté, Josep Peñuelas, Sophie Cornu, Bertrand Guenet. Submitted to Journal of Advances in Modelling Earth Systems

Abstract

Soil carbon is a crucial component of the terrestrial carbon cycle, but the uncertainty in simulations of soil-carbon stocks by Earth system models (ESMs) remains high, limiting the predictability of future climate change feedbacks. The turnover times of the modeled soil-carbon pools are key sources of uncertainty in the simulations of soil organic carbon (SOC). Studies have highlighted the utility of soil δ13C measurements for benchmarking SOC turnovers in global models. The use of δ13C as an observational constraint in global models, however, has not yet been possible, because these models do not explicitly represent soil δ13C. We used soil 13C as a tracer within a vertically discretized soil module of a land-surface model, ORCHIDEE-SOM. Our new module also represents some of the processes that have been hypothesized to lead to a 13C enrichment with soil depth: 1) the Suess effect, 2) the relative 13C enrichment of roots compared to leaves and 3) 13C fractionation associated with heterotrophic respiration. We then tested if the upgraded soil module was able to reproduce the δ13C signal at two temperate sites, a forest and a grassland, and the short-term change in the isotopic signal of soil after a shift in C3/C4 vegetation in two temperate experimental croplands. A comparison of modeled and measured δ13C indicated that the model performed better when simulating the shift in the isotopic signal due to short-term changes in vegetation cover from C3 to C4 than simulating the observed δ13C that represents a mixture of long-term processes. We also modeled each new process separately to assess its relative importance. The natural δ13C variability along the soil profile was in all cases higher than the variability identified by the various processes used in the model. Our results stress the importance of the long-term history of land cover for simulating vertical profiles of δ13C, particularly for deep soil (>1 m).

Code access

• See the version on the webinterface here : ​https://forge.ipsl.jussieu.fr/orchidee/browser/branches/publications/ORCHIDEE_SOM_13C_r4859
• Extract it on a terminal as follow, type anonymous as password:

  svn co --username anonymous svn://forge.ipsl.jussieu.fr/orchidee/branches/publications/ORCHIDEE_SOM_13C_r4859 ORCHIDEE
  

Metadata

DOI
Creator	Bertrand Guenet
Affiliation	CNRS
Title	ORCHIDEE_SOM_13C revision 4859
Publisher	Institut Pierre Simon Laplace (IPSL)
PublicationYear	2018
ResourceType	Software
Rights	This software is distributed under the CeCILL license
rightsURI	​http://www.cecill.info/
Subject	Land surface model, Soil organic matter, carbon isotopes
DataManager	Karim Ramage (IPSL)
DataCurator	Josefine Ghattas (IPSL)
ContactPerson	Bertrand Guenet (CNRS)
FundingReference	ANR-14-CE01-0004 DeDyCAS and European Research Council Synergy grant ERC- 2013-SyG-610028 IMBALANCE-P