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

Abstract

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.

The importance of Northern Peatlands in global carbon systems during the Holocene

“…In particular, it is believed that the age of the Hudson Bay Lowlands may be younger than other peatlands, which will shift the overall C uptake into a later time in the Holocene. Second, even with well-constrained basal dates, the bulk C accumulation rates may be varying with climatic and biogeographic conditions (Yu et al, 2003;Belyea and Malmer, 2004;Yu et al, 2009), although Gorham et al (2003) indicated a relative constant long-term C accumulation rate. Third, we have neglected the radiative forcing of methane (CH 4 ) emitted from the NP development, which has been estimated at roughly 0.05-0.1 W/m 2 through the Holocene (Frolking and Roulet, Fig.…”

“…Those changes are, in turn, a function of external climatic influences and/or allogenic controls (Hilbert et al, 2000;Roulet, 2000;Charman, 2002;Frolking and Roulet, 2007). For example, in an 8-ka core from a Western Canadian fen, Yu et al (2003) found that the C accumulation rate increased during the wet Holocene periods. A recent study of Yu et al (2009) shows that the estimated C accumulation at 8 ka BP is about 73-98 PgC, which is similar to our study and previous estimates (29-58 PgC by MacDonald et al, 2006; 92 PgC by Adams and Faure, 1998).…”

National circumstances in the international circumboreal community

“…Boreal soils have more C than those of any other biome. Much of the C is contained in organic soils (10-40%) and much of it is labile and can easily oxidise (Neff and Hooper 2002) through fire or decomposition, both of which are expected to increase in the near future due to climate change (Yu et al 2003, Turetsky et al 2006. This would, in turn, release more C into the atmosphere and further exacerbate the affect of climate change.…”

“…These disturbances resulted in the establishment of large cohorts of young forest stands in the early (Kurz and Apps 1999). This current rejuvenation process may be due to a combination of both natural disturbance cycles and natural/anthropogenic climate change (e.g., Royama 1984, Yu et al 2003, Campbell et al 2004, Gray and MacKinnon 2006, Soja et al 2007). …”

“…Finland's forest has a baby-boom-like demographic wave reflecting the impact of the Second World War on its forest industry (Andersson and Östlund 2004). In Canada, there was a high rate of natural disturbances in the late 1800s due to the Little Ice Age that altered species ranges and disturbances regimes, and restructured ecosystems (Campbell andMcAndrews 1993, Bergeron et al 2004). There was also a high rate of accidental anthropogenic forest fire associated with the construction of the cross-continental railway in the late 1800s (e.g., Johnson et al 1990).…”