A New Process-Based Soil Methane Scheme:Evaluation Over Arctic Field Sites With the ISBA Land Surface Model

• Published in: Journal of Advances in Modeling Earth Systems
• Main Authors: Morel, X., Decharme, B., Delire, C., Krinner, G., Lund, M., Hansen, B. U., Mastepanov, M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2019
• Subjects: arctic ecosystem; carbon cycling; methane emission; modeling; Arctic; Greenland; Nuuk; permafrost; Zackenberg; Siberia
• Online Access: https://curis.ku.dk/portal/da/publications/a-new-processbased-soil-methane-scheme(87f698d0-f1ba-4834-99c5-0a7eaa4e52cd).html; https://doi.org/10.1029/2018MS001329; https://curis.ku.dk/ws/files/213499584/A_New_Process_Based_Soil_Methane_Scheme.pdf

Permafrost soils and arctic wetlands methane emissions represent an important challenge for modeling the future climate. Here we present a process-based model designed to correctly represent the main thermal, hydrological, and biogeochemical processes related to these emissions for general land surface modeling. We propose a new multilayer soil carbon and gas module within the Interaction Soil-Biosphere-Atmosphere (ISBA) land-surface model (LSM). This module represents carbon pools, vertical carbon dynamics, and both oxic and anoxic organic matter decomposition. It also represents the soil gas processes for CH 4 , CO 2 , and O 2 through the soil column. We base CH 4 production and oxydation on an O 2 control instead of the classical water table level strata approach used in state-of-the-art soil CH 4 models. We propose a new parametrization of CH 4 oxydation using recent field experiments and use an explicit O 2 limitation for soil carbon decomposition. Soil gas transport is computed explicitly, using a revisited formulation of plant-mediated transport, a new representation of gas bulk diffusivity in porous media closer to experimental observations, and an innovative advection term for ebullition. We evaluate this advanced model on three climatically distinct sites : two in Greenland (Nuuk and Zackenberg) and one in Siberia (Chokurdakh). The model realistically reproduces methane and carbon dioxide emissions from both permafrosted and nonpermafrosted sites. The evolution and vertical characteristics of the underground processes leading to these fluxes are consistent with current knowledge. Results also show that physics is the main driver of methane fluxes, and the main source of variability appears to be the water table depth.