RADIONUCLIDE PROFILES AND CARBON ACCRUAL IN PERMAFROST SOIL AT TOOLIK LAKE, ALASKA

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 carbon as the high-latitude climate warms. This study is investigating permafrost soil cores taken in 2016 from a 22-year snow fence experiment in Toolik, AK and will compare the radionuclide isotope depth profiles (⁷Be, ¹³⁷Cs and ²¹⁰Pb), carbon contents, and carbon stable isotope ratios of cores taken at different locations beneath varying winter snow depths. Be-7 activities were measurable only in the top 1-3 cm, corresponding to canopy thickness of current-year growth. Profiles of excess ²¹⁰Pb were normalized to cumulative dry mass vs. depth to obtain accumulation rates of organic horizons assuming constant initial ²¹⁰Pb concentration (i.e. CIC model) in the accumulating material. The resulting age profiles were compared to the depth of the ¹³⁷Cs peak that was deposited in 1963, yielding perfect agreement in some but not all cases. Results indicate nearly constant mass accumulation rates within each core profile, but different rates depending on snow depth. Previous studies have shown that ²¹⁰Pb deposition is determined by the daily fluctuations in precipitation and by its concentration in ground-level air, with the annual deposition flux being driven by weather variations. Local topography may also play a significant role in the ²¹⁰Pb accumulation variability. Therefore, the CIC model may not accurately represent the conditions at the Toolik Lake site. Work in progress will involve normalizing the ²¹⁰Pb activities to the organic carbon content of the samples to better understand the response of the soil carbon system to changing snow depth as a proxy for climate warming.