Climate and carbon accumulation in northern peatlands during the last 1000 years

We used published and new data from a network of 89 northern hemisphere sites to identify patterns of total carbon (C) accumulated and high-resolution changes in C accumulation rate over time in C-rich peatlands relative to climate and climate variation. Belowground C accumulated over the last 1000 years varied from 3 to 60 kg C m-2 and is related positively to contemporary growing season length and photosynthetically active radiation, suggesting that variability in net primary productivity is a dominant control on long-term soil C storage in these systems. C accumulation rates were derived by flexible Bayesian age-depth models and accounted for long-term C turnover and ecosystem maturity. Rates varied significantly within sites and from site to site, but overall declined over the climate transition from the Medieval Climate Anomaly (MCA) to the Little Ice Age (LIA), suggesting that lower LIA temperatures and possibly increased cloudiness suppressed net primary productivity. Spatial coherence of the C response to the MCA-LIA climate transition was observed in some regions and absent in others, showing the complex spatial character of climate anomalies and ecosystem function over the last millennium. Although it is has been assumed that increasing Arctic temperatures may boost soil respiration and CO2 flux to the atmosphere, our observations suggest a small but negative C-cycle feedback to climate warming from undisturbed peatland ecosystems has occurred in the recent past.