Continental fens in western Canada as effective carbon sinks during the Holocene

Abstract

Here, we present results of Holocene carbon accumulation from seven new peat cores at four fen sites from Alberta, western Canada. Along with two other published fen records in the same region, we provide a regional synthesis of carbon accumulation patterns, as well as peat property data in this continental climate. On the basis of >3000 peat sample measurements at 1-cm intervals, organic matter content in peat samples is on average at 91.0% (±9.3% in SD) and ash-free bulk density at 0.141 g/cm³ (±0.045 g/cm³ in SD) with a range of 0.018–0.381 g/cm³. On the basis of 109 radiocarbon age determinations from these cores, the overall mean carbon accumulation rate at these fens since 9 kyr (1 kyr = 1000 cal. yr BP) is 32.5 g C/m²/yr, which is much higher than the northern peatland average of 18.6–22.9 g C/m²/yr from large-scale syntheses. The ‘instantaneous’ apparent carbon accumulation rates from all these individual measurements at mostly 1-cm intervals are highly variable throughout the Holocene, ranging from 6 to 504 g C/m²/yr. The carbon accumulation rates appear to show peak values at 8.3, 6.8, 5.3, 3.8, 2.7, and 1.1 kyr, suggesting a ~1500-year periodicity in carbon accumulation, possibly in response to Holocene climate change. Furthermore, carbon accumulation shows a gradual declining trend from 7 to 2 kyr, reaching a minimum at 2 kyr, likely in response to neoglacial climate cooling during the later part of the Holocene in the high-latitude regions. Overall, these fens accumulated and store on average 264 kg C/m² during the Holocene, among the highest soil carbon storage reported from terrestrial ecosystems. Our results, along with previous global and regional syntheses, suggest that in contrast to conventional wisdom, fens in continental climates accumulate peat at similar or greater rates than do bogs in oceanic climates.