Quantifying responses of CO2 and CH4 fluxes in a subarctic dry tundra ecosystem to summer warming and snow accumulation

The Arctic is experiencing rapid warming and changing precipitation regimes. However, the overall impact of climate change on greenhouse gas fluxes remains uncertain in subarctic dry tundra ecosystems, which frequently experience drought. Since 2012, field experiments manipulating summer warming and snow accumulation have been conducted in a dry tundra in western Greenland. Here, we combined long-term experimental observations with process-based models (CoupModel and an analytical reaction-based model) to assess the impacts of summer warming and snow accumulation on CO₂ and CH₄ fluxes.

Model simulations successfully reproduced the observed seasonal and interannual variability of CO₂ and CH₄ fluxes. The ecosystem functioned as a net CO₂ source and a net CH₄ sink from 2014 to 2020. Over the studied period, summer warming enhanced CH₄ uptake and reduced net CO₂ emissions, leading to a decrease in the overall carbon balance. These responses were mainly driven by increased soil temperature and reduced soil moisture during the growing season. In contrast, increased snow accumulation has an adverse impact on the carbon balance, primarily due to the cooler and wetter soil during the early growing season. Importantly, drought suppressed the cooling effect induced by warming and amplified carbon losses associated with enhanced snow accumulation. This study suggests that future drought could undermine carbon sequestration and methane uptake under a warmer and wetter climate, thereby strengthening positive climate-carbon feedback.