Permafrost and peatland carbon sink capacity with increasing latitude

The permafrost zone covers approximately 50% of the Canadian landmass, and ranges in distribution from continuous coverage in the arctic to sporadic coverage further south in the boreal zone. At its southern limit in the mid-boreal, permafrost is found almost exclusively in ombrotrophic peatlands. Carbon accumulation (g Cm-2 yr(-1)) in frozen peatlands at the southern limit (mean annual air temperature (MAAT) = 0 to -2degreesC) approaches that of unfrozen peatlands, though permafrost-affected peatlands have lower vertical growth rates (cm yr(-1)) compared to adjacent peatland types. Further north in the high boreal and low subarctic zones (MAAT = -3 to -6degreesC), permafrost-affected peatlands sequester carbon at rates approximately half that of adjacent unfrozen peatlands. In the continuous permafrost zone (MAAT < -7degreesC), peatland carbon sequestration is currently minimal as evidenced by old near-surface radiocarbon dates. Decreasing mean annual air temperatures with increasing latitude appear to decrease rates of carbon accumulation as peat, resulting in a gradient of carbon sink capacity concurrent with increasing permafrost distributions. Permafrost controls on peat accumulation must be understood to predict the fate of soil carbon with climate warming.