September 20, 2017

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Large Uncertainty in Permafrost Carbon Stocks Due to Hillslope Soil Deposits

Soil sampling and geophysical imaging efforts that target hill toe deposits can help constrain uncertainty.

The Science

The gradual and ongoing transport of soil and soil organic carbon (SOC) down hillslopes results in deposits at the base of hills. Limited sampling of these deposits leaves the quantity of carbon buried on hills poorly quantified. This study’s analysis suggests that accounting for carbon in these deposits could significantly alter present estimates of carbon stored in permafrost.

The Impact

Quantifying the amount of carbon frozen and stored in permafrost soils is a critical challenge in the attempt to estimate the possible feedback that thawing permafrost may have on the global carbon cycle. Given the widespread distribution and potential for deposits thicker that one meter, hillslope deposits of soil carbon could be a significant, but presently unaccounted-for, store of carbon in permafrost regions. Greater study should be focused on these depositions to better constrain estimates of permafrost SOC stores.

Summary

This study combined topographic models with soil profile data and topographic analysis to evaluate the quantity and uncertainty of SOC mass stored in perennially frozen hill toe soil deposits. The study shows that in Alaska this SOC mass introduces an uncertainty that is >200% the current state-wide estimates of SOC stocks 77 petagrams of carbon (Pg C) and that a similarly large uncertainty may also pertain at a circumpolar scale. The SOC content of permafrost hill toe deposits can meaningfully change current estimates of permafrost SOC. SOC stored in hill toe deposits is likely sensitive to climate change–induced erosion and deposition. Soil sampling and geophysical imaging efforts that target hill toe deposits can help constrain this large uncertainty.

Principal Investigator

Joel Rowland
Los Alamos National Laboratory
jrowland@lanl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

This research is supported by the Next-Generation Ecosystem Experiments (NGEE)–Arctic project of the Office of Biological and Environmental Research within the U.S. Department of Energy (DOE) Office of Science. Contributions of U. Mishra were supported under Argonne National Laboratory Contract No. DE-AC02-06CH11357.

References

Shelef, E., J. C. Rowland, C. J. Wilson, and G. E. Hilley, et al. "Large uncertainty in permafrost carbon stocks due to hillslope soil deposits". Geophysical Research Letters 44 (12), 6134–6144  (2017). https://doi.org/10.1002/2017GL073823.