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 declined 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 in a warmer future

Experimental warming differentially affects microbial structure and activity in two contrasted moisture sites in a Sphagnum-dominated peatland

“…Other studies indicated that climate change can further diminish C sequestration by promoting the growth of vascular plants which, in turn, depress the productivity of peat mosses (Breeuwer et al, 2009;Bragazza et al, 2013). In contrast to these studies, Loisel and Yu (2013) and Charman et al (2013) indicated that the C accumulation rate of many northern peatlands could increase in response to a warmer climate in the future, as long as moisture is not a limiting factor. These examples illustrate the ongoing debate on the fate of C in peatlands in response to climate change.…”

Transient Earth system responses to cumulative carbon dioxide emissions: linearities, uncertainties, and probabilities in an observation-constrained model ensemble

“…Modern peat carbon stocks are not in equilibrium with the current climate and boreal peatlands still sequestered about 0.1 Gt C yr −1 during the last millennium (Charman et al, 2013;Yu et al, 2010). Peat carbon distribution for our transient simulations is initialized with the output from a transient simulation starting at the Last Glacial Maximum as described in Spahni et al (2013).…”

Carbon dioxide flux and net primary production of a boreal treed bog: Responses to warming and water-table-lowering simulations of climate change

“…Warm and dry conditions in peatlands can promote CO 2 uptake by enhancing GPP, diminish uptake by limiting moisture (Roulet et al, 2007;Charman et al, 2013) or accelerate CO 2 release by enhancing R (Hanson et al, 2000;Davidson and Janssens, 2006;Lund et al, 2010;Ise et al, 2008;Cai et al, 2010). In a dwarf-shrub pine bog, Pihlatie et al (2010) found that the CO 2 flux peak followed the increase in air and soil temperature closely, being higher (uptake) on warm and lower (emission) on cold days.…”