Climate-related changes in peatland carbon accumulation during the last millennium

Abstract

Peatlands are a major terrestrial carbon store and a persistent natural carbon sink during the Holocene, but there is considerable uncertainty over the fate of peatland carbon in a changing climate. It is generally assumed that higher temperatures will increase peat decay, causing a positive feedback to climate warming and contributing to the global positive carbon cycle feedback. Here we use a new extensive database of peat profiles across northern high latitudes to examine spatial and temporal patterns of carbon accumulation over the past millennium. Opposite to expectations, our results indicate a small negative carbon cycle feedback from past changes in the long-term accumulation rates of northern peatlands. Total carbon accumulated over the last 1000 yr is linearly related to contemporary growing season length and photosynthetically active radiation, suggesting that variability in net primary productivity is more important than decomposition in determining long-term carbon accumulation. Furthermore, northern peatland carbon sequestration rate declines over the climate transition from the Medieval Climate Anomaly (MCA) to the Little Ice Age (LIA), probably because of lower LIA temperatures combined with increased cloudiness suppressing net primary productivity. Other factors including changing moisture status, peatland distribution, fire, nitrogen deposition, permafrost thaw and methane emissions will also influence future peatland carbon cycle feedbacks, but our data suggest that the carbon sequestration rate could increase over many areas of northern peatlands

Recent acceleration of carbon accumulation in a boreal peatland, south central Alaska

“…Supporting this hypothesis is a clear relationship between degree-days, mean annual temperature and long-term peat C accumulation in Finland and Canada [Clymo et al, 1998]. Similarly, photosynthetically active radiation (PAR), growing season length, and peat C accumulation rates over the last millennium were positively correlated throughout the northern hemisphere [Charman et al, 2012]. Modern Sphagnum NPP also correlates with PAR and growing season length, as shown on the basis of a meta-analysis that includes 142 Sphagnum plants from 52 high-latitude peatlands [Loisel et al, 2012].…”

Moving beyond bioclimatic envelope models: integrating upland forest and peatland processes to predict ecosystem transitions under climate change in the western Canadian boreal plain

“…Furthermore, the combination of drought and high temperatures can result in reduced productivity or mortality of the upper living layer of moss, limiting the replacement of peat lost to decomposition (Gignac et al, 2000;Bragazza, 2008). Conversely, if a peatland remains well hydrated, then any increase in the rate of decomposition resulting from higher temperatures is likely to be offset by an increase in the rate of production (Moore, 2002;Charman et al, 2012;Loisel and Yu, 2013). Furthermore, several studies have concluded that decomposition within deeper layers of peat is limited by the accumulation of phenolic breakdown products, not necessarily low temperature (Beer and Blodau, 2007;Beer et al, 2008;Morris and Waddington, 2011).…”

Northern peatland carbon stocks and dynamics: a review

“…210 Pb and post-bomb AMS 14 C dating and carbon analysis of recent peat cores are needed to fill this important data gap (e.g., Wieder, 2001;Turetsky et al, 2004;Malmer and Wallén, 2004). Datasets used in a recent data synthesis of the last millennium peat carbon dynamics (Charman et al, 2012) can be further explored for deriving net carbon balance at 100-yr intervals for the last 1000 yr. Also, as pointed out by Roulet et al (2007), we "need more replications across a diverse set of ecoclimatic regions and other peatland types" for contemporary NECB measurements, and I argue that measurements from sites in colder boreal and subarctic climates would fill an important data and knowledge gap (Fig. 2).…”