Methane emission from northern wetlands in Europe during Oxygen Isotope Stage 3

Interstadials during the last glacial show a rapid rise of the atmospheric methane concentration at the onset of climatic warming. This is explained by reaction of (northern) wetlands to climate change, or by catastrophic release of methane from sea floor methane clathrates. The wetland hypothesis usually assumes expansion of wetlands, which is a slow process and difficult to reconcile with the rapid rise of the atmospheric methane concentration. Here it is demonstrated by modeling that wetland methane fluxes may have reacted rapidly on climatic warming by its direct effect on methane production, without the assumption of wetland expansion. A bottom-up modeling of methane fluxes in northern Europe during Oxygen Isotope Stage 3 is presented. This study combines paleodata on wetland ecology, climate model output, a process-based methane flux model, and GIS-based modeling of wetland areal distribution. The resulting methane flux during interstadials is twice as high as during stadials. This is attributed to higher bacterial metabolic rates, a longer frost-free period, and a higher ecosystem primary production providing more substrate for methanogenesis.