Thermokarst lakes, formed in permafrost‐thaw depressions, are known sources of atmospheric methane but the location of gas production in a thermokarst‐lake environment is not well constrained. This study compares methane production potentials of samples collected from various depths along a 5.5‐m deep lake sediment core and an adjacent 40‐m deep undisturbed permafrost profile, allowing for direct determination as to where methane is originating within an active thermokarst‐lake landscape.
Vault Lake and Vault Creek Permafrost Tunnel are located approximately 40 km north of Fairbanks, Alaska in a region characterized by yedoma permafrost. The Vault Lake sediment core, collected in the center of a ~4000 sq. m lake, captured the surface lake sediments, talik (thaw bulb), and the permafrost actively thawing beneath the lake for comparison to parallel permafrost soil samples from the Vault Creek Permafrost Tunnel. Samples were analyzed for bulk density, ice and water content, organic and inorganic carbon content, C:N ratios, and water‐soluble organic C (WEOC). Initial soil organic matter (SOM) composition was characterized using pyrolysis‐gas chromatography/mass spectrometry (py‐GC/MS). WEOC qualities and composition were characterized using spectrofluorometry. Methane production potentials from 21 depths along the lake core and 16 depths along the permafrost tunnel were measured in anaerobic laboratory incubations. Preliminary results suggest methanogenesis is highest in the top 1 m of the Vault Lake core and at the base of the talik, which is the permafrost thaw
front beneath the lake.