Carbon and peat accumulation rates over the past 1200 yr were measured in relation to permafrost aggradation, maturity, ground fires, and degradation in a peatland with discontinuous permafrost near Fort Simpson, N.W.T., Canada. The White River volcanic ash layer, deposited 1200 yr ago, was used as a chronostratigraphic marker to compare peat and carbon accumulation among peat cores collected along transects over a consistent period of time. The aggradation of permafrost results in a change from unfrozen bog to forested peat plateau, and approximate decreases of 50 and 65% in carbon and vertical peat accumulation rates, respectively. Carbon and peat accumulation continue to decrease significantly with both increasing permafrost maturity and the number of ground fires. The transition from peat plateau to collapse bog through internal permafrost degradation results in up to a 72 and 200% increase in carbon and vertical peat accumulation rates, respectively. Permafrost degradation at the margins of a peat plateau can result in the formation of collapse fens, in which vertical peat accumulation increases significantly yet the carbon accumulation rates remain similar to the peat plateau. A warming climate may result in a shift towards higher carbon accumulation rates in peatlands associated with bog vegetation following peat plateau collapse, yet warmer peat temperatures, greater soil aeration, greater rates of peat decomposition, and an increase in burning may provide limits to the increase.