Observations of methane net sinks in the upland Arctic tundra

This study focuses on direct measurements of CO2 and CH4 turbulent eddy covariance fluxes in tundra ecosystems on the Svalbard islands over a 2-year period. Our results reveal dynamic interactions between climatic conditions and ecosystem activities such as photosynthesis and microbial activity. During summer, pronounced carbon uptake fluxes indicate increased photosynthesis and microbial methane consumption, while during the freezing seasons very little exchange was recorded, signifying reduced activity. The observed net summertime methane uptake is correlated with the activation and aeration of soil microorganisms, and it declines in winter due to the presence of snow cover and because of the negative soil temperature which triggers the freezing process of the active layer water content but then rebounds during the melting period. The CH4 fluxes are not significantly correlated with soil and air temperature but are instead associated with wind velocity, which plays a role in the speed of soil drying. Non-growing-season emissions accounted for about 58% of the annual CH4 budget, characterized by large pulse emissions. The analysis of the impact of thermal anomalies on CO2 and CH4 exchange fluxes underscores that high positive (> 5 °C) thermal anomalies may contribute to an increased positive flux in both summer and winter periods, effectively reducing the net annual uptake. These findings contribute valuable insights to our understanding of the dynamics of greenhouse gases in tundra ecosystems in the face of evolving climatic conditions. Further research is required to constrain the sources and sinks of greenhouse gases in dry upland tundra ecosystems in order to develop an effective reference for models in response to climate change.