Decadal carbon balance and its response to 2 degree warming among heterogenous Arctic landscapes

The large amounts of carbon (C) stored in the Arctic region can strongly interact with the climate system through the exchange of carbon dioxide (CO₂) and methane (CH₄) under the unmitigated environmental changes. Currently, there are still large uncertainties in the C exchange and the subsequent C-climate feedbacks between the land and atmosphere across the Arctic region, to which the highly heterogeneous landscapes make a key contribution. However, our knowledge on the present and future ecosystem C balance jointly considering the exchange of CO₂ and CH₄ in the Arctic region with heterogeneous landscapes is still limited. In this study, a process-based biogeochemistry model was calibrated and validated using the empirical data on concurrently measured CO₂ and CH₄ exchange observed using eddy covariance, automatic and manual chamber methods and associated climate, soil and plant data derived from several heterogeneous landscapes in the Kaamanen region. With the validated model, decadal C balance during 2005-2018 and its response to 2 ^oC warming were evaluated for the constituent land cover types (LCTs). Our results showed that most LCTs were a sink for atmospheric CO₂ and a source of CH₄ during 2005-2018. Under the 2 ^oC warming scenario, most ecosystems continued to be CO₂ sinks and CH₄ sources. Moreover, the CO₂ budget in most LCTs did not change significantly as the two major fluxes of gross primary productivity (GPP) and total ecosystem respiration (TER) increased simultaneously thus maintaining similar rates of net ecosystem exchange (NEE) in response to warming, while a significant increase in CH₄ emission from most LCTs was evident. Our results presented here provide us a better understanding and prediction of C dynamics and the inherent C-climate feedbacks in the Arctic region.