The Effects of Talik Formation on Non-Growing Season Carbon and Nitrogen Cycling in Permafrost Ecosystems

High-latitude warming is expected to increase talik (an unfrozen zone in the subsurface) formation in permafrost ecosystems across the arctic. Perennially unfrozen taliks can strongly affect subsurface hydrology and thus influence carbon and nitrogen cycling, especially during the winter months. In this study, we use an integrated ecosystem model, ecosys , to investigate how the presence or absence of a talik affects the connectivity and dependency of key hydrological controls on non-growing season carbon and nitrogen cycling in permafrost ecosystems. Our work focuses on a watershed along the Teller road on the Seward Peninsula in Alaska that has been extensively characterized and monitored by the Next-Generation Ecosystem Experiment (NGEE-Arctic). First, we apply a Morris global sensitivity analysis to explore how the observed variation in topography, soil properties, and meteorological inputs across the watershed affect modeled soil temperatures. We then split the simulations into groups based on modeled near and deep subsurface thermal regimes and apply a Bayesian network approach to interpret the complex and interrelated model outputs. Separate Bayesian networks are developed based on the groups of runs using a constraint-based hill-climbing algorithm. Differences in the network structure are used to interpret how the relationships between key variables for wintertime soil carbon and nitrogen transformations and the exports changes under the talik formation. We found that the heterogeneity of biogeochemical fluxes has increased over the past century, driven primarily by increased heterogeneity in near-surface thermal and hydrological states which can primarily be attributed to variations in parameters associated with topography and soil drainage.