Assessing Shifts in 20th Century Carbon Stocks in NE Canadian Permafrost Peatlands

Abstract

<p>Recent and rapid changes in climate and permafrost thaw are affecting carbon dynamics in high-latitude peatlands. There is growing interest in evaluating the C sink potential of peatlands for conservation as nature-based climate solutions. However, rapid decadal-to centennial-scale changes are poorly understood, in part due to poor dating resolution in surface peat. Here, we evaluate the timing of vegetation shifts and rates of carbon accumulation for the past ~200 years peatlands for 100 cores from boreal and subarctic regions in Québec and Labrador (Eastern Canada). We used classical (Constant Rate of Supply - CRS) and Bayesian (Plum) approaches to model age-depth relationships from lead-210 (<sup>210</sup>Pb) and radiocarbon (<sup>14</sup>C) dates. Results highlight the important role of permafrost thaw in altering local peatland hydrological conditions, favouring Sphagnum growth and new peat addition in subarctic regions. While both models provide similar ages for the last century in complete cores, the CRS model tends to overestimate peat ages compared to Plum prior to ~1900CE. We recommend using Plum when constructing combined age-depth models, and importantly when if cores are incomplete. While <sup>210</sup>Pb activity profiles are a clear indicator of disturbance in the peat column from permafrost thaw, the addition of independent dating markers (e.g. postbomb <sup>14</sup>C dates) is especially important to validate age-depth models. The choice of age-depth model and user decisions can have important knock-on effects for interpreting timings of environmental shifts, as well as estimating the order of magnitude of C stocks for policy and conservation purposes.</p>