Tundra meets atmosphere : Seasonal dynamics of trace gas exchange in the High Arctic

Abstract: Arctic environments have experienced strong warming in recent decades, which is affecting the carbon cycle of tundra ecosystems.Degrading permafrost, diminishing snow cover, and changing hydrology are examples of ongoing processes that affect the land-atmosphere interactions and seasonal ecosystem dynamics.Since a number of the affected processes involve the exchange of atmospheric greenhouse gases, such as the trace gases methane (CH4) and carbon dioxide (CO2), there is a potential for these interactions to lead to climate feedbacks.The impact this feedback could have on the global climate is currently not well known due to gaps in our knowledge about the involved processes.One reason for this mismatch is the scarcity of direct, continuous and comparable measurements of CH4 and CO2 fluxes in the high Arctic tundra.The relatively remote, harsh, and low-flux conditions dominating these environments for most of the year pose challenges for flux measurement techniques that have proven to work well at lower latitudes.The present study is, therefore, not only aiming to advance our understanding of trace gas exchanges in the Arctic tundra, but also trying to improve commonly-used flux measurement techniques to yield new insights.The two main study sites of this work are located in permafrost-underlain wetlands in Adventdalen, Svalbard and Zackenberg, NE Greenland.These sites show distinctly different processes that govern the trace gas exchange throughout the different seasons:The snow-free season is characterized by high CH4 emissions, which seem to follow predictable spatial and temporal patterns. Large CO2 uptake by photosynthesis and release by respiration give rise to a large amplitude of net ecosystem exchange during the growing season.The autumnal freeze-in period can feature the highest gas emissions, most likely due to physical mechanisms connected to the soil freezing that release a part of the soil gas reservoir.During winter and spring a low level of microbial activity is sustained but the gas transport capability of the frozen soil is relatively low. Still, snowpack gas concentrations indicate consistent emissions of CH4 and CO2 from the soil.Around the snowmelt period, emissions of stored gases in the snowpack and soil are superimposed on the fast increase of biological activity. The flooded and heterogeneous conditions make the representative flux estimation extremely challenging around this time of year.The diverse range of processes governing the seasonal flux dynamics at these two study sites exemplifies the complexity and possibilities of predicting the resilience and vulnerability of Arctic tundra ecosystems to climate change.