Integrating Carbon Flux Measurements with Hydrologic and Thermal Responses in a Low Centered Ice-Wedge Polygon near Prudhoe Bay, AK

Abstract:

Substantial attention is being devoted to soil organic carbon (SOC) dynamics in Polar Regions, given the potential impacts of CO₂ and methane (CH₄) release into the atmosphere. In this study, which is part of a broader effort to quantify carbon loss pathways in patterned Arctic permafrost soils, CH₄ and CO₂ flux measurements were recorded from a site approximately 30 km south of Deadhorse, Alaska and 1 km west of the Dalton Highway. Samples were collected in late July, 2014 using six static flux chambers that were located within a single low-centered ice-wedge polygon. Three flux chambers were co-located (within a 1 m triangle of each other) near the center of the polygon and three were co-located (along a 1.5 m line) on the ridge adjacent to a trough. Soil in the center of the polygon was 100% water saturated, whereas water saturation measured on the ridge ranged between 25-50%. Depth to ice table was approximately 50 cm near the center of the polygon and 40 cm at the ridge. Temperature depth probes were installed within the center and ridge of the polygon. Nine gas measurements were collected from each chamber over a 24 h period, stored in helium-purged Exetainer vials, shipped to a laboratory, and analyzed using gas chromatography. Measured cumulative methane fluxes were linear over the 24 h period demonstrating constant methane production, but considerable spatial variability in flux was observed (0.1 to 4.7 mg hr^-1 m^-2 in polygon center, and 0.003 to 0.36 mg hr^-1m^-2 on polygon ridge). Shallow soil temperatures varied between 1.3 and 9.8^oC in the center and 0.6 to 7.5^oC in the rim of the polygon. Air temperatures varied between 1.3 and 4.6^oC. CO₂ fluxes were greater than methane fluxes and more consistent at each co-location; ranging from 21.7 to 36.6 mg hr^-1 m^-2 near the polygon centers and 3.5 to 29.1 mg hr^-1 m^-2 in the drier polygon ridge. Results are consistent with previous observations that methanogenesis is favored in a water saturated active layer. The independence of CH₄ and CO₂ fluxes suggests that different mechanisms may affect their formation and transport. Ongoing work on DOC and acetate concentrations may further elucidate the source of CH₄ and CO₂ flux. Results will be used to benchmark vertical SOC transport and active layer dynamics models, and then integrated into a Lidar-based geomorphic model for ice wedge polygon terrain.