Long-term Impacts of Permafrost Thaw on Carbon Storage in Peatlands: Deep Losses Offset by Surficial Accumulation

摘要

Peatlands in northern permafrost regions store a significant proportion of global soil carbon. Recent warming is accelerating peatland permafrost thaw and thermokarst collapse, exposing previously frozen peat to microbial decomposition and potential mineralization into greenhouse gases. Here, we show from a site in the sporadic-discontinuous permafrost zone of western Canada that thermokarst collapse leads to neither large losses nor gains following thaw, as deep carbon losses are offset by surficial accumulation. We collected peat cores along two thaw chronosequences, from peat plateau, through young (~30 years since thaw), intermediate (~70 years), and mature (~200 years) thermokarst bog locations. Macrofossil and ~(14)C analysis showed synchronicity of peatland development until recent thaw, with wetland initiation ~8,500 cal yr BP followed by succession through peatland stages prior to permafrost aggradation ~1,800 cal yr BP. Analysis and modeling of soil carbon stocks indicated 8.7 ± 12.4 kg C m~(-2) of carbon accumulated prior to thaw was lost in ~200 years post-thaw. Despite these losses, there was no observed increase in peat humification as assessed by Fourier transform infrared and C:N ratios. Rapid peat accumulation post-thaw (9.8 ± 1.6 kg C m~(-2) over 200 years) offset deeper losses. Our approach constrains the net carbon balance to be between uptake of 27.3 g C m~(-2) yr~(-1) and loss of 106.6 g C m~(-2) yr~(-1) over 200 years post-thaw. While our approach cannot determine whether thermokarst bogs in the sporadic-discontinuous permafrost zone act as long-term carbon sinks or sources post-thaw, our study better constrains post-thaw C losses and gains.