Uncertainties in modeling CH<sub>4</sub> emissions from northern wetlands in glacial climates: effect of hydrological model and CH<sub>4</sub> model structure
Abstract. Methane (CH4) fluxes from northern wetlands may have influenced atmospheric CH4 concentrations at climate warming phases during the 800 000 years and at present global warming. Including these CH4 fluxes in earth system models is essential to understand feedbacks between climate and atmospheric composition. Attempts to model CH4 fluxes from wetlands have been undertaken previously using various approaches. Here, we test a process-based wetland CH4 flux model (PEATLAND-VU) which includes details of soil-atmosphere CH4 transport. The model has been used to simulate CH4 emissions from continental Europe in different glacial climates and the present climate. This paper displays results on the sensitivity of modeling glacial terrestrial CH4 fluxes to basic tuning parameters of the model, to different approaches in modeling of the water table, and to model structure. For testing the model structure, PEATLAND-VU has been compared to a simpler modeling approach based on wetland primary production estimated from a vegetation model (BIOME). The tuning parameters are the CH4 production rate from labile organic carbon and its temperature sensitivity. The modelled fluxes prove comparatively insensitive to hydrology representation, and sensitive to microbial parameters and model structure. Glacial climate emissions are also highly sensitive to assumptions on the extent of ice cover and exposed seafloors. Wetland expansion on low relief exposed seafloor areas, may have compensated for a decrease of wetland area due to continental ice cover.