Revealing the fine-scale heterogeneity of Arctic terrestrial greenhouse gas fluxes

Abstract:

Arctic terrestrial greenhouse gas (GHG) fluxes of not only carbon dioxide (CO₂), but also methane (CH₄) and nitrous oxide (N₂O) can be key drivers of global climate change. However, these fluxes are rarely studied together and consequently, their relative importance in Arctic landscapes remains unresolved. Additionally, GHG fluxes are known to exert high fine-scale spatial variability, which is well documented at the plot scale, but not at the landscape scale. Here, we explore the contribution of net CO₂, CH₄, and N₂O fluxes to the landscape-scale terrestrial GHG budget during the peak season and investigate the fine-scale spatial variability of GHG fluxes. In a heterogeneous subarctic tundra landscape (5 km²), we measured chamber-derived GHG fluxes, together with in situ environmental data describing soil temperature, soil moisture, soil organic carbon stocks, and vegetation type from 101 points. Environmental data were first upscaled across the landscape with an ensemble of three machine learning models and high-resolution remote sensing imagery (3 m). Fluxes were then upscaled with these environmental layers across the study area with another set of ensemble models. Our results show that this region was a net GHG sink during the peak season. CO₂ fluxes were the largest flux, with meadows and deciduous shrubs having the highest net CO₂ uptake whereas N₂O fluxes were negligible. Although our upscaling revealed large CH₄ sources in wetlands, it also showed CH₄ uptake across the widespread mineral uplands, shifting this region to a net CH₄ sink at the landscape scale. These results demonstrate the dominant role of CO₂ fluxes across the tundra landscape, but suggest that CH₄ uptake might also play a significant role in the GHG budget. We provide high-resolution maps of GHG fluxes which reveal the fine-scale spatial heterogeneity of all three fluxes in an Arctic landscape. These maps, and the upscaling framework, can serve as a basis for future studies aiming to understand and upscale local changes in Arctic environmental conditions and biogeochemical cycles.