||The overall objectives of this proposal are to provide a mechanistic understanding of how deep warming of peat and carbon dioxide (CO2) enrichment in a peatland affect carbon mineralization and methane (CH4) production, consumption, and transport and to incorporate that understanding into a biogeochemistry model, the Terrestrial Ecosystem Model (TEM). The proposed work will compliment ongoing DOE research at the Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE) experiment taking place in a black spruce-Sphagnum bog located at the Marcell Experimental Forest (MEF) in northern Minnesota. Porewater from all treatment plots will be collected monthly throughout the soil profile to determine seasonal depth dynamics of key electron donors and acceptors and fermentation products that together regulate anaerobic carbon mineralization and CH4 dynamics. We will also measure the stable isotope composition (δ13C and δD) in dissolved CH4, CO2 and acetate in porewater and in emitted CH4 and CO2 to explore, in situ, the dominant methanogenic pathway, the importance of recently fixed carbon in anaerobic carbon mineralization, and the degree of CH4 oxidation in the unsaturated zone. Periodic measurements of 14CH4 and 14 CO2 will be used to determine the age of respired carbon and to determine if deep, older peat is more heavily mineralized in response to warming. Initial laboratory experiments will explore the potential temperature response of carbon mineralization in shallow, relatively labile, and deep, relatively recalcitrant, peat soils as well as the importance of priming in regulating the temperature response of peatland carbon mineralization. This increased mechanistic understanding of the complex set of controls that regulate CH4 dynamics, and how they respond to key global changes, will be explicitly incorporated into TEM.