The Tibetan Plateau(TP)and Arctic permafrost constitute two large reservoirs of organic carbon,but pro-cesses which control carbon accumulation within the surface soil layer of these areas would differ due to the interplay of climate,soil and vegetation type.Here,we synthesized currently available soil carbon data to show that mean organic carbon density in the topsoil(0-10 cm)in TP grassland(3.12±0.52 kg C m-2)is less than half of that in Arctic tundra(6.70±1.94 kg C m-2).Such difference is primarily attrib-uted to their difference in radiocarbon-inferred soil carbon turnover times(547 years for TP grassland versus 1609 years for Arctic tundra)rather than to their marginal difference in topsoil carbon inputs.Our findings highlight the importance of improving regional-specific soil carbon turnover and its control-ling mechanisms across permafrost affected zones in ecosystem models to fully represent carbon-climate feedback.