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Abstract Northern peatlands have been a carbon sink since their initiation. This has been simulated by existing process‐based models. However, most of these models are limited by lacking sufficient processes of the N cycle in peatlands. Here, we use a peatland biogeochemistry model incorporated with N‐related processes of fixation, deposition, gas emission, loss through water flow, net mineralization, plant uptake and litterfall to project the role of the peatlands in future radiative forcing (RF). Simulations from 15‐ka BP to 2100 are conducted driven by CMIP5 climate forcing data of IPSL‐CM5A‐LR and bcc‐csm1‐1, including warming scenarios of RCP 2.6, RCP 4.5 and RCP 8.5. During the Holocene, northern peatlands have an increasing cooling effect with RF up to −0.57 W m⁻². By 1990, these peatlands accumulate 408 Pg C and 7.8 Pg N. Under warming, increasing mineral N content enhances plant net primary productivity; the cooling effect persists. However, RF increases by 0.1–0.5 W m⁻²during the 21st century, mainly due to the stimulated CH₄emissions. Northern peatlands could switch from a C sink to a source when the annual temperature exceeds −2.2 to −0.5°C. This study highlights that the improved N cycle causes higher CO₂‐C sink capacity in northern peatlands. However, it also causes a significant increase in CH₄emissions, which weakens the cooling effect of northern peatlands in future climate. 

Abstract As Arctic regions warm rapidly, it is unclear whether high‐latitude soil carbon (C) will decrease or increase. Predicting future dynamics of Arctic soil C stocks requires a better understanding of the quantities and controls of soil C. We explore the relationship between vegetation and surface soil C in an understudied region of the Arctic: Baffin Island, Nunavut, Canada. We combined soil C data for three vegetation types—polar desert, mesic tundra, and wet meadow—with a vegetation classification to upscale soil C stocks. Surface soil C differed significantly across vegetation types, and interactions existed between vegetation type and soil depth. Polar desert soils were consistently mineral, with relatively thin organic layers, low percent C, and high bulk density. Mesic soils exhibited an organic‐rich epipedon overlying mineral soil. Wet meadows were consistently organic soil with low bulk density and high percent C. For the top 20 cm, polar desert contained the least soil C (2.17 ± 0.48 kg m⁻²); mesic tundra had intermediate C (8.92 ± 0.74 kg m⁻²); wet meadow stored the most C (13.07 ± 0.69 kg m⁻²). Extrapolating to the top 30 cm, our results suggest that approximately 44 Tg C is stored in the study region with a mean landscape soil C stock of 2.75 kg m⁻²for non‐water areas. Combining vegetation mapping with local soil C stocks considerably narrows the range of estimates from other upscaling approaches (27–189 Tg) for soil C on South Baffin Island. 

Abstract Northern peatlands are a large C stock and often act as a C sink, but are susceptible to climate warming. To understand the role of peatlands in the global carbon‐climate feedback, it is necessary to accurately quantify their C stock changes and decomposition. In this study, a process‐based model, the Peatland Terrestrial Ecosystem Model, is used to simulate pan‐Arctic peatland C dynamics from 15 ka BP to 1990. To improve the accuracy of the simulation, spatially explicit water run‐on and run‐off processes were considered, four different pan‐Arctic peatland extent data sets were used, and a spatially explicit peat basal date data set was developed using a neural network approach. The model was calibrated against 2055 peat thickness observations and the parameters were interpolated to the pan‐Arctic region. Using the model, we estimate that, in 1990, the pan‐Arctic peatlands soil C stock was 396–421 Pg C, and the Holocene average C accumulation rate was 22.9 g C·m⁻² yr⁻¹. Our estimated peat permafrost development history generally agrees with multi‐proxy‐based paleo‐climate data sets and core‐derived permafrost areal dynamics. Under Anthropocene warming, in the freeze‐thaw and permafrost‐free regions, the peat C accumulation rate decreased, but it increased in permafrost regions. Our study suggests that if current permafrost regions switch to permafrost‐free conditions in a warming future, the peat C accumulation rate of the entire pan‐Arctic region will decrease, but the sink and source activities of these peatlands are still uncertain. 

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. 

Abstract Permafrost dynamics can drastically affect vegetation and soil carbon dynamics in northern high latitudes. Vegetation has significant influences on the energy balance of soil surface by impacting the short-wave radiation, long-wave radiation and surface sensible heat flux, affecting soil thermal dynamics, in turn, inducing vegetation shift, affecting carbon cycling. During winter, snow can also significantly impact soil temperature due to its insulative effect. However, these processes have not been fully modeled to date. To quantify the interactions between vegetation, snow, and soil thermal dynamics and their impacts on carbon dynamics over the circumpolar region (45–90° N), we revise a sophisticated ecosystem model to improve simulations of soil temperature profile and their influences on vegetation, ecosystem carbon pools and fluxes. We find that, with warmer soil temperature in winter and cooler soil temperature in summer simulated with the revised model considering vegetation shift and snow effects, the region will release 1.54 Pg C/year to the atmosphere for present-day and 66.77–87.95 Pg C in 2022–2100. The canopy effects due to vegetation shift, however, will get more carbon sequestered into the ecosystem at 1.00 Pg C/year for present day and 36.09–44.32 Pg C/year in 2022–2100. This study highlights the importance to consider the interactions between snow, vegetation shift and soil thermal dynamics in simulating carbon dynamics in the region. 

Abstract. Northern peatlands have been a large C sink during the Holocene,but whether they will keep being a C sink under future climate change isuncertain. This study simulates the responses of northern peatlands tofuture climate until 2300 with a Peatland version Terrestrial EcosystemModel (PTEM). The simulations are driven with two sets of CMIP5 climate data(IPSL-CM5A-LR and bcc-csm1-1) under three warming scenarios (RCPs 2.6, 4.5 and8.5). Peatland area expansion, shrinkage, and C accumulation anddecomposition are modeled. In the 21st century, northern peatlands areprojected to be a C source of 1.2–13.3 Pg C under all climate scenariosexcept for RCP 2.6 of bcc-csm1-1 (a sink of 0.8 Pg C). During 2100–2300,northern peatlands under all scenarios are a C source under IPSL-CM5A-LRscenarios, being larger sources than bcc-csm1-1 scenarios (5.9–118.3 vs.0.7–87.6 Pg C). C sources are attributed to (1) the peatland water table depth(WTD) becoming deeper and permafrost thaw increasing decomposition rate; (2) net primary production (NPP) not increasing much as climate warms becausepeat drying suppresses net N mineralization; and (3) as WTD deepens,peatlands switching from moss–herbaceous dominated to moss–woody dominated,while woody plants require more N for productivity. Under IPSL-CM5A-LRscenarios, northern peatlands remain as a C sink until the pan-Arctic annualtemperature reaches −2.6 to −2.89 ∘C, while this threshold is −2.09to −2.35 ∘C under bcc-csm1-1 scenarios. This study predicts anorthern peatland sink-to-source shift in around 2050, earlier than previousestimates of after 2100, and emphasizes the vulnerability of northernpeatlands to climate change. 

Abstract. Wetlands and freshwater bodies (mainly lakes) are the largestnatural sources of the greenhouse gas CH4 to the atmosphere. Great effortshave been made to quantify these source emissions and their uncertainties.Previous research suggests that there might be significant uncertaintiescoming from “double accounting” emissions from freshwater bodies andwetlands. Here we quantify the methane emissions from both land andfreshwater bodies in the pan-Arctic with two process-based biogeochemistrymodels by minimizing the double accounting at the landscape scale. Twonon-overlapping dynamic areal change datasets are used to drive the models.We estimate that the total methane emissions from the pan-Arctic are 36.46 ± 1.02 Tg CH4 yr−1 during 2000–2015, of which wetlands andfreshwater bodies are 21.69 ± 0.59 Tg CH4 yr−1 and 14.76 ± 0.44 Tg CH4 yr−1, respectively. Our estimation narrows thedifference between previous bottom-up (53.9 Tg CH4 yr−1) andtop-down (29 Tg CH4 yr−1) estimates. Our correlation analysisshows that air temperature is the most important driver for methane emissionsof inland water systems. Wetland emissions are also significantly affected byvapor pressure, while lake emissions are more influenced by precipitation andlandscape areal changes. Sensitivity tests indicate that pan-Arctic lakeCH4 emissions were highly influenced by air temperature but less bylake sediment carbon increase. 

Abstract Atmospheric concentrations of methane, a powerful greenhouse gas, have strongly increased since 2007. Measurements of stable carbon isotopes of methane can constrain emissions if the isotopic compositions are known; however, isotopic compositions of methane emissions from wetlands are poorly constrained despite their importance. Here, we use a process-based biogeochemistry model to calculate the stable carbon isotopic composition of global wetland methane emissions. We estimate a mean global signature of −61.3 ± 0.7‰ and find that tropical wetland emissions are enriched by ~11‰ relative to boreal wetlands. Our model shows improved resolution of regional, latitudinal and global variations in isotopic composition of wetland emissions. Atmospheric simulation scenarios with the improved wetland isotopic composition suggest that increases in atmospheric methane since 2007 are attributable to rising microbial emissions. Our findings substantially reduce uncertainty in the stable carbon isotopic composition of methane emissions from wetlands and improve understanding of the global methane budget.