Radionuclide profiles and net soil carbon accrual in moist acidic tundra near Toolik Lake, Alaska
Date
2018
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Publisher
University of Delaware
Abstract
The response of the Arctic terrestrial carbon cycle to climate change is one of the largest uncertainties affecting climate change predictions and research. Current models give a wide, varying estimate of the fate of currently frozen permafrost organic carbon with warming of the high-latitude climate. This study is an investigation of permafrost soil cores taken in 2012 and 2016 from a snow fence experiment installed in 1994 at Toolik Lake, AK. Data was acquired for depth profiles of radionuclides (7Be, 137Cs and 210Pb), organic carbon contents, and carbon stable isotope ratios of permafrost active layer cores taken at locations that had different winter snow depths. Be-7 activities were measurable only in the top 1-3 cm, corresponding to the canopy thickness of current-year growth. Profiles of excess 210Pb were normalized to cumulative dry mass vs. depth to obtain mass accumulation rates of the organic-rich horizon under a set of assumptions regarding initial 210Pb activity in the accumulating material. The resulting age profiles were compared to the depth of the 137Cs peak that was deposited in 1963, yielding agreement in some but not all cases. Previous studies have shown that 210Pb deposition and accumulation is correlated with precipitation amounts, and also may be affected by local topography. Therefore, standard 210Pb models do not accurately represent the conditions at the Toolik Lake snow fence site because of large variations in winter snow depth over a small distance. Normalization of the 210Pb activities to the organic carbon content of the cores gives historical information on the rate of net carbon uptake of the permafrost active layer, and an improved accounting of the response of the soil carbon system to changing snow depth that includes winter C loss, as a proxy for climate warming. Results from this method indicate substantial increases in rates of soil organic carbon accumulation following snow fence installation in the region of increased snow depth. Based on these results, increased winter precipitation in the Alaskan Arctic Continuous Permafrost Zone may be expected to cause increases in soil insulation, growing season, vegetation growth, and active layer thickness.This ultimately will lead to an increased organic carbon availability and general permafrost degradation with time. These changes may contribute positive feedback to the carbon cycle, and therefore promote the effects of current climate change predictions.
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Keywords
Earth sciences, Alaska, Arctic, Climate change, Geochemistry, Radioactive isotopes, Radionuclide