| Summary: | Arctic ecosystems represent an important component in the global terrestrial exchange of greenhouse gases and energy with the atmosphere. In the changing climate, which is most pronounced in the Arctic, the possible scenarios of greenhouse gas exchange response should be seriously considered in predictive climate modelling efforts. As a prerequisite for this, detailed studies of key processes affecting greenhouse gas exchange in the Arctic are important, as well as monitoring of its current dynamics. However, the number of such studies, carried on in high Northern latitudes is significantly smaller than for lower latitudes, and within the existing studies there is a bias towards studying the growing season. The main aim of this study was to improve our process understanding of greenhouse gas exchange in the Arctic terrestrial ecosystems, including the processes taking place at low temperatures and outside the growing season. In order to achieve this some development in measurement techniques, such as automatic closed and flow-through chambers, adapted for monitoring CH4 and CO2 exchange under Arctic conditions, membrane diffusion probes to study subsurface profiles of these gases, laboratory techniques of low-temperature incubation and gas exchange studies on permafrost samples. During the studies, some novel results were obtained, such as on detailed multiseasonal CH4 emission dynamics in a high Arctic fen, on late-season bursts of CH4 and CO2 at Greenland and Svalbard, and in relation to respiration and its origin in old permafrost. Four years of CH4 emission monitoring data have shown that the exchange of this greenhouse gas under truly Arctic conditions is having some very special dynamics and different dominating controlling factors compared with conventional knowledge from lower latitudes. The patterns of growing season CH4 emission are highly dependent on the snow melt date. The greatest variations in fluxes between the study years was observed during the first 30-40 days after snow melt. This variability ...
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