Using Observational Data to Inform Physically Based Models of Subsurface Thermal Hydrology Properties and Active Layer Thickness at the Barrow Environmental Observatory, Alaska

Abstract:

Climate change is profoundly impacting permafrost regions and reshaping carbon rich tundra ecosystems from carbon sinks to potential carbon sources triggering a positive feedback to climate change. The annual maximum depth of ice-free soil with above 0°C temperatures, which is known as the active-layer thickness (ALT), determines the volume of carbon-rich stores available for decomposition and therefore potential greenhouse gas release into the atmosphere. Despite the increased vulnerability of permafrost regions to climate change, predictive tools and precise parameterization of physical characteristics to estimate projected ALT in tundra ecosystems have been developed slowly and often are not adequately representing natural systems due to the complex nature of corresponding atmospheric-surface-subsurface hydrological and energy interactions undergoing freeze-thaw dynamics. A model-observation-experiment process (ModEx) is employed to generate three 1D models representing characteristic micro-topographical land-formations, which are capable of simulating present ALT from current climate conditions. Observational soil temperature data from a tundra site located near Barrow, AK is used to calibrate thermal properties of moss, peat, and sandy loam soil to be used in the multiphysics Arctic Terrestrial Simulator (ATS) models. In the process of calibration and model formulation key physical processes and appropriate model parameters are identified, which showcases the importance of correctly representing physical processes and reformulating models based on observational data. Iterative execution of the ModEx concept identified key processes that control thermal propagation into the subsurface: 1) physical representation of thermal conduction, 2) liquid, ice, and gas partitioning in the subsurface, 3) snowpack distribution and dynamics, and 4) precipitation delivery of water to the surface/subsurface. This work was supported by LANL Laboratory Directed Research and Development Project LDRD201200068DR and by the The Next-Generation Ecosystem Experiments (NGEE Arctic) project. NGEE-Arctic is supported by the Office of Biological and Environmental Research in the DOE Office of Science.