Predicted Vulnerability of Carbon in Permafrost Peatlands With Future Climate Change and Permafrost Thaw in Western Canada. Issue 5 (12th May 2021) - Treat, Claire C.
Abstract: Climate warming in high‐latitude regions is thawing carbon‐rich permafrost soils, which can release carbon to the atmosphere and enhance climate warming. Using a coupled model of long‐term peatland dynamics (Holocene Peat Model, HPM‐Arctic), we quantify the potential loss of carbon with future climate warming for six sites with differing climates and permafrost histories in Northwestern Canada. We compared the net carbon balance at 2100 CE resulting from new productivity and the decomposition of active layer and newly thawed permafrost peats under RCP8.5 as a high‐end constraint. Modeled net carbon losses ranged from −3.0 kg C m −2 (net loss) to +0.1 kg C m −2 (net gain) between 2015 and 2100. Losses of newly thawed permafrost peat comprised 0.2%–25% (median: 1.6%) of "old" C loss, which were related to the residence time of peat in the active layer before being incorporated into the permafrost, peat temperature, and presence of permafrost. The largest C loss was from the permafrost‐free site, not from permafrost sites. C losses were greatest from depths of 0.2–1.0 m. New C added to the profile through net primary productivity between 2015 and 2100 offset ∼40% to >100% of old C losses across the sites. Differences between modeled active layer deepening and flooding following permafrost thaw resulted in very small differences in net C loss by 2100, illustrating the important role of present‐day conditions and permafrost aggradation history in controlling net C loss. Plain Language Summary: The thawing of permafrost in tundra, fen, bog, and other peatland wetlands can enhance climate change through releasing carbon from the soil. Using a model for six sites in western Canada, we estimate how much carbon will be lost by 2100 under a high‐end emissions scenario. While these peatlands continue to accumulate carbon in the surface soil layers through enhanced vegetation growth, more carbon is lost from slightly deeper in the soil profile. As a result, most sites were projected to lose relatively small amounts of carbon compared to how much they contain (<5%). Little of the carbon lost was from newly thawed permafrost, while the largest carbon losses were from the permafrost‐free site. In sites where permafrost thawed, the carbon losses were related to peatland and permafrost history. Key Points: Simulated carbon balance in peatlands with and without permafrost using process‐based model from 8000 BP to 2100 CE Modeled decomposition losses from active layer peat (0.2–1.0 m) were the predominant carbon source, not deeper peat or newly thawed permafrost Modeled new peat accumulation offset a large fraction of C losses but future changes in vegetation productivity are poorly understood