Thermokarst Lake Methane Ebullition and Diffusion in Arctic Alaska: Flux Partitioning, Seasonal Dynamics, and Climate Feedback Sensitivity From 3-Year Eddy Covariance and Chamber Measurements

This study investigates methane ebullition and diffusion flux partitioning, seasonal dynamics, and climate feedback sensitivity from three thermokarst lakes on the Alaskan North Slope measured by eddy covariance and static chambers over 3 years within the context of arctic biogeochemistry and climate science, an area of growing scientific importance given its implications for Arctic CH4 flux parameterization in Earth system models, thermokarst lake expansion feedback quantification, and permafrost carbon vulnerability assessment. Using floating eddy covariance (LI-COR LI-7700 CH4, 10 Hz) for total CH4 flux, static stainless-steel chambers (n=48, 1-hour deployment) for diffusion, ebullition by difference, sediment temperature and talik depth probes, and radiative forcing calculation using IPCC AR5 GWP100, we examine methane produced by methanogenesis in anoxic lake sediments and underlying talik (thawed permafrost), released by ebullition (bubble seeps) dominating warm-period flux and diffusion dominating shoulder seasons; ebullition rate sensitive to sediment temperature and lake bed pressure with 2.4x amplification per 3 C sediment warming in 3 lakes x 3 open-water seasons (June-September 2013-2015) = 9 lake-years; 48 chamber deployments per lake per week during open water (total 3,456 chamber measurements); eddy covariance at 30-min flux intervals drawn from Toolik Field Station, North Slope Alaska (68.6 N, 149.6 W); 3 thermokarst lakes varying in age (8, 24, and 84 years since formation), area, and talik depth. Results indicate that mean total CH4 flux 84.2 mg CH4/m2/day open water; ebullition 68.4% of total (58.4-78.4% across lakes); oldest lake (84-yr) emits 2.84x young lake; radiative forcing 0.48 W/m2 lake-area-averaged; flux doubles per 3 C sediment warming (Q10=2.4) (p < 0.001), with ebullition 68.4% of flux; 84-yr lake 2.84x young lake; Q10=2.4; RF=0.48 W/m2 as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to arctic biogeochemistry and climate science and carry actionable implications for the design of programs and policies targeting Arctic CH4 flux parameterization in Earth system models, thermokarst lake expansion feedback quantification, and permafrost carbon vulnerability assessment.