Organic matter has accumulated as peat in bogs since the last glacial retreat and its anaerobic decay by microbial communities produces methane (CH₄). CH₄ released from northern Boreal peat currently represents a significant proportion of the global budget but their contribution under future climates is uncertain. It is the surface peat 0-500 mm below the water table that is most important for emissions. This study aims to describe the vertical distribution of the gases CH₄, CO₂, O₂ and Ar and their fine scale (0.6 mm) variability in surface peat cores from a rain-fed bog using Quadrupole Mass Spectrometry (QMS). Direct links between the physical structure of peat and distribution of microbial communities have been investigated to identify the determinants of gas distribution.