Permafrost Thaw Depth and Active Layer Carbon Flux in Subarctic Alaska: Evidence From a Decade-Long Eddy Covariance Network

This study investigates permafrost thaw depth trends and net ecosystem carbon exchange across subarctic Alaskan tundra sites within the context of arctic biogeochemistry and ecosystem ecology, an area of growing scientific importance given its implications for Arctic carbon cycle modeling, permafrost-climate feedbacks in Earth system models, and climate policy. Using eddy covariance flux towers with continuous CO2 and CH4 monitoring combined with annual frost probe active layer depth measurements, we examine warming-induced active layer deepening accelerating soil organic carbon decomposition and net greenhouse gas release in 16 eddy covariance monitoring sites spanning the Seward Peninsula and Alaska Range foothills (2013-2023) drawn from subarctic Alaskan tundra spanning a 400-km latitudinal gradient from 61 to 67 degrees N. Results indicate that active layer depth has increased by a mean of 8.4 cm per decade across monitoring sites, converting three sites from net carbon sinks to net carbon sources since 2018, with annual NEE shifting from -48 to +36 g C/m2/yr (p = 0.001), with 8.4 cm per decade active layer deepening rate 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 ecosystem ecology and carry actionable implications for the design of programs and policies targeting Arctic carbon cycle modeling, permafrost-climate feedbacks in Earth system models, and climate policy.