Carbon sequestration in western Canadian peat highly sensitive to Holocene wet-dry climate cycles at millennial timescales

A high-resolution fen peat record and 79 basal peat dates from paludified peatlands in continental western Canada provide evidence for cyclic change in moisture conditions and in peat carbon accumulation. The ash-free bulk density, a proxy for degree of peat decomposition and thus moisture conditions, shows periodicities at both millennial (from 1500 to 2190 yr, with a mean of 1785 yr) and century scales (386 yr and 667 yr). Wet periods of 200–600 yr in duration, especially at ~6900, 5500 and 4000 cal. BP, correlate with rapid peat accumulation, new peatland initiation and declines in the rate of increase of atmospheric CO₂ concentrations. The wet periods in western North America are coeval with warm periods in the North Atlantic, a phasing relationship that has been documented in other published palaeorecords for the glacial period and late Holocene, probably in response to variations in solar activity. These results indicate a strong connection between climate and the global carbon cycle at the millennial scale, mediated in part by peatland dynamics. This is the first demonstration that peatland carbon sequestration rates are highly sensitive even to minor climatic fluctuations, which are too small to produce detectable changes in major species in the peatland. That global atmospheric CO₂ concentrations have in the past responded to these changes in peatland dynamics implies a strong potential for peatlands to be a major player in affecting future global change.