Direct observation of permafrost degradation and rapid soil carbon loss in tundra

Abstract

Evidence suggests that 5–15% of the vast pool of soil carbon stored in northern permafrost ecosystems could be emitted as greenhouse gases by 2100 under the current path of global warming. However, direct measurements of changes in soil carbon remain scarce, largely because ground subsidence that occurs as the permafrost soils begin to thaw confounds the traditional quantification of carbon pools based on fixed depths or soil horizons. This issue is overcome when carbon is quantified in relation to a fixed ash content, which uses the relatively stable mineral component of soil as a metric for pool comparisons through time. We applied this approach to directly measure soil carbon pool changes over five years in experimentally warmed and ambient tundra ecosystems at a site in Alaska where permafrost is degrading due to climate change. We show a loss of soil carbon of 5.4% per year (95% confidence interval: 1.0, 9.5) across the site. Our results point to lateral hydrological export as a potential pathway for these surprisingly large losses. This research highlights the potential to make repeat soil carbon pool measurements at sentinel sites across the permafrost region, as this feedback to climate change may be occurring faster than previously thought.

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Fig. 1: Annual maximum thaw depth (active layer) of permafrost soils in response to ambient (control) and experimental warming.
Fig. 2: Pools of ambient (control) and warmed permafrost soils.
Fig. 3: Changes in 13C NMR spectra of ambient (control (left)) and experimentally warmed (right) permafrost soils after five years of treatment.

Data availability

All the data and metadata associated with this manuscript are deposited in the Long Term Ecological Research (LTER) Network Information System Data Portal at https://portal.lternet.edu/nis/home.jsp (https://doi.org/10.6073/pasta/894ec9847bc365347775d3aaba44a50210.6073/pasta/894ec9847bc365347775d3aaba44a502, https://doi.org/10.6073/pasta/f502d8fe1a2e1d6c6b035c198af04f3e and https://doi.org/10.6073/pasta/b559d2650efe99ccabb2a58d9d8819ab).

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Acknowledgements

This work was based in part on support provided by the following programs: US Department of Energy, Office of Biological and Environmental Research, Terrestrial Ecosystem Science (TES) Program, Award nos DE-SC0006982 and DE-SC0014085; National Science Foundation CAREER program, Award no. 0747195; National Parks Inventory and Monitoring Program; National Science Foundation Bonanza Creek LTER program, Award no. 1026415 and National Science Foundation Office of Polar Programs, Award no. 1203777. In addition, this project received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska Curie grant agreement 654132. We thank L. Barrios (CSIC) and the NAU statistical consulting lab for assistance with the data analysis.

Author information

E.A.G.S. conceived and designed the study. E.A.G.S. and S.M.N. implemented the field experiment. R.B., G.C., K.G.C., J.A.H., M.M., S.M.N., C.P., C.E.H.P., E.P., C.S., E.A.G.S., V.G.S. and E.E.W. performed the field research and/or data analysis. K.G.C., J.A.H., C.P., E.P., M.M., S.M.N. and V.G.S. conducted the laboratory research. C.P., G.C. and M.M. carried out data analyses. C.P., E.A.G.S. and E.P. wrote the article. All authors substantially discussed the results and contributed to editing the manuscript.

Correspondence to Edward A. G. Schuur.

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Supplementary descriptions, Supplementary Figs. 1–9 and Supplementary Tables 1–5

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