| Summary: | Due to the heterogeneity of the Arctic tundra, general current understanding of net carbon (C) uptake in these ecosystems is poorly developed. This study investigates the dependency of carbon dioxide (CO 2 ) fluxes on environmental, meteorological and vegetation properties in high, low and subarctic tundra sites for the purpose of exposing the environmental, meteorological and vegetation factors, especially season length, that drive CO 2 fluxes in disparate tundra environments. Partitioning CO 2 fluxes and redefining seasons in the same manner improved our interpretation of the factors affecting flux variability. An improved understanding of the control of ancillary variables on net ecosystem exchange (NEE), gross primary production (GPP) and ecosystem respiration (R e ) will improve the accuracy with which CO 2 exchange seasonality in Arctic tundra ecosystems is modelled. Fluxes were measured with the eddy covariance technique at three Arctic tundra sites in Greenland (74.47 °N), Canada (64.52 °N) and Sweden (68.33 °N). Our results show that the variations in CO 2 fluxes were driven by varying factors at each site with the growing season length controlling at least one flux component at Zackenberg and Daring Lake. Growing season NEE correlated mainly to cumulative radiation and temperature-related variables at Zackenberg, while at Daring Lake the same variables showed significant correlations with the partitioned fluxes (GPP and R e ). Stordalen was temperature dependent during the growing season. This study emphasizes the inherent need for a standardized year round measurement and analytical routine of CO 2 fluxes and ancillary variables, and investigations into the interconnectedness of ancillary variables in the Arctic tundra.
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