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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.
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Large stocks of peatland carbon and nitrogen are vulnerable to permafrost thaw
Northern peatlands have accumulated large stocks of organic carbon (C) and nitrogen (N), but their spatial distribution and vulnerability to climate warming remain uncertain. Here, we used machine-learning techniques with extensive peat core data ( n > 7,000) to create observation-based maps of northern peatland C and N stocks, and to assess their response to warming and permafrost thaw. We estimate that northern peatlands cover 3.7 ± 0.5 million km 2 and store 415 ± 150 Pg C and 10 ± 7 Pg N. Nearly half of the peatland area and peat C stocks are permafrost affected. Using modeled global warming stabilization scenarios (from 1.5 to 6 °C warming), we project that the current sink of atmospheric C (0.10 ± 0.02 Pg C⋅y −1 ) in northern peatlands will shift to a C source as 0.8 to 1.9 million km 2 of permafrost-affected peatlands thaw. The projected thaw would cause peatland greenhouse gas emissions equal to ∼1% of anthropogenic radiative forcing in this century. The main forcing is from methane emissions (0.7 to 3 Pg cumulative CH 4 -C) with smaller carbon dioxide forcing (1 to 2 Pg CO 2 -C) and minor nitrous oxide losses. We project that initial CO 2 -C losses reverse after ∼200 y, as warming strengthens peatland C-sinks. We project substantial, but highly uncertain, additional losses of peat into fluvial systems of 10 to 30 Pg C and 0.4 to 0.9 Pg N. The combined gaseous and fluvial peatland C loss estimated here adds 30 to 50% onto previous estimates of permafrost-thaw C losses, with southern permafrost regions being the most vulnerable.
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- PAR ID:
- 10189494
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 117
- Issue:
- 34
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- 20438 to 20446
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1073/pnas.1916387117
