The gradual and ongoing transport of soil and soil organic carbon 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. Our analysis suggests that accounting for carbon in these deposits could significantly alter present estimates of carbon stored in permafrost.
Quantifying the amount of carbon frozen and stored in permafrost soils is a critical challenge in the attempt to estimate the possible feedback 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 soil organic carbon stores.
We combined topographic models with soil profile data and topographic analysis to evaluate the quantity and uncertainty of soil organic carbon (SOC) mass stored in perennially frozen hill toe soil deposits. We show that in Alaska this SOC mass introduces an uncertainty that is >200% of the current state-wide estimates of SOC stocks (77 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.
Joel C. Rowland
Los Alamos National Laboratory, Los Alamos, NM
This research is supported by the DOE Office of Science, Office of Biological and Environmental Research, Next Generation Ecosystem Experiment, NGEE-Arctic project. Contributions of U. Mishra were supported under Argonne National Laboratory contract DE-AC02-06CH11357.
Shelef, E., J. C. Rowland, C. J. Wilson, G. E. Hilley, U. Mishra, G. L. Altmann, and C.-L. Ping. 2017. “Large Uncertainty in Permafrost Carbon Stocks Due to Hillslope Soil Deposits”, Geophys. Res. Lett., DOI:10.1002/2017GL073823.
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