Measurements of the land-atmosphere exchange of the greenhouse gases methane (CH4) andcarbon dioxide (CO2) in high Arctic tundra ecosystems are particularly difficult in the cold season, resultingin large uncertainty on flux magnitudes and their controlling factors during this long, frozen period. Weconducted snowpack measurements of these gases at permafrost-underlain wetland sites in ZackenbergValley (NE Greenland, 74∘N) and Adventdalen Valley (Svalbard, 78∘N), both of which also feature automaticclosed chamber flux measurements during the snow-free period. At Zackenberg, cold season emissionswere 1 to 2 orders of magnitude lower than growing season fluxes. Perennially, CH4fluxes resembledthe same spatial pattern, which was largely attributed to differences in soil wetness controlling substrateaccumulation and microbial activity. We found no significant gas sinks or sources inside the snowpack butdetected a pulse in the 13C-CH4stable isotopic signature of the soil’s CH4source during snowmelt, whichsuggests the release of a CH4reservoir that was strongly affected by methanotrophic microorganisms. In thepolygonal tundra of Adventdalen, the snowpack featured several ice layers, which suppressed the expectedgas emissions to the atmosphere, and conversely lead to snowpack gas accumulations of up to 86 ppm CH4and 3800 ppm CO2by late winter. CH4to C O2ratios indicated distinctly different source characteristicsin the rampart of ice-wedge polygons compared to elsewhere on the measured transect, possibly due togeomorphological soil cracks. Collectively, these findings suggest important ties between growing seasonand cold season greenhouse gas emissions from high Arctic tundra.