The amount and timing of snow cover control the cycling of carbon (C), water, and energy in arctic ecosystems. The implications of changing snow cover for regional C budgets, biogeochemistry, hydrology, and albedo due to climate change are rudimentary, especially for the High Arctic. In a polar semidesert of NW Greenland, we used a~10 year old snow manipulation experiment to quantify how deeper snow affects magnitude, seasonality, and 14 C content of summer C emissions. We monitored ecosystem respiration (R eco ), soil CO 2 , and their 14 C contents over three summers in vegetated and bare areas. Additional snowpack, elevated soil water content (SWC), and temperature throughout the growing season in vegetated, but not in bare, areas. Daily R eco was positively correlated to temperature, but negatively correlated to SWC; consequently, we found no effect of increased snow on daily flux. Cumulative summertime R eco was not related to annual snowfall, but to water year precipitation (winter snow plus summer rain). Experimentally increased snowpack shortened the growing season length and reduced summertime R eco up to 40%. Soil CO 2 was older under increased snow. However, we found no effect of snow depth on the R eco age because older C emissions were masked by younger CO 2 produced from the litter layer or plant respiration. In the High Arctic, anticipated changes in precipitation regime associated with warming are a key uncertainty for understanding future C cycling. In polar semideserts, water year precipitation is an important driver of summertime R eco . Permafrost C is vulnerable to changes in snowpack, with a deeper snowpack-promoting decomposition of older soil C.