Cryoturbation Rates and Depths in Arctic Permafrost from Cosmogenic Nuclides


Arctic Research Initiative
2008 Funded Project


Permanently frozen ground, permafrost, dominates high latitude terrestrial landscapes and represents a crucial reservoir of greenhouse gases.  The potential impacts of warming on Arctic permafrost include the release of large quantities of methane and CO2 to the atmosphere, nutrients to the Arctic oceans, and changes to Arctic ecosystems.  Cryoturbation, which refers to soil movement caused by the forces of freezing and thawing, is an important landscape process in polar permafrost regions.  The zone of cryoturbated soil movement closest to the air surface, referred to as the “active layer”, is one of the key feedbacks between atmospheric temperature and chemical fluxes from the permafrost.   Despite the importance of cryoturbation and the response of permafrost systems to global climate change, the chronology of soil formation and the rates of cryoturbation are poorly known.  This proposal seeks funds to use in situ produced cosmogenic nuclide measurements to determine Arctic cryoturbation rates.  In situ cosmogenic nuclide methodologies are well established, but have rarely been applied to soils, and have never been applied to Arctic permafrost.  The abundance of cosmic ray produced nuclides decreases exponentially with depth in undisturbed bedrock; any soil or bedrock movement will cause a deviation from this exponential behavior.  Simple models suggest that these deviations can be used to understand the nature of Arctic soil convection and quantitatively estimate the convection rates.  Sharp changes in the depth profiles will reveal the maximum depth of the active layer, averaged over long time periods (i.e.  ~ 20 Ka), which is a key parameter for estimating fluxes.  We will measure the depth profiles for 3He, 21Ne, or 10Be at two locations in the Alaskan Arctic: Toolik Lake and Barrow Stations, both of which are within regions of continuous permafrost and are readily accessible.  Cryoturbation is generally manifested by patterned ground; our sampling strategy is to target patterned ground of several different ages from each of these two locations.  These two sites are ideal because there are preliminary maps of surficial geology and a wide range of exposed surficial ages, most of which are glacially deposited.  Barrow Station, which is on the northern-most coast, should be representative of the permafrost regions that deliver most of the material flux to the Arctic Ocean.  The results will be interpreted within the context of field data and soil advection-diffusion models, allowing evaluation of permafrost models and cryoturbation rates.