Arctic ecosystem functioning is not only critically affected by climate change, but also has the potential for major positive feedbacks on climate. There is however relatively little information available on the role, patterns, and vulnerabilities of CO2 fluxes during the non-summer seasons. Presented here is a year-around study of CO2 fluxes in an Alaskan Arctic tussock tundra ecosystem. Also presented are key environmental controls on CO2 fluxes as well as possible impacts of likely changes in season timing. This is aided by a new empirical quantification of seasons in the Arctic based on net radiation, which can help describe seasonal responses to greenhouse gas fluxes under climate change. The fluxes were computed using standard FluxNet methodology and corrected using standard WPL density terms, adjusted for influences of instrument surface heating. The results showed that the non-summer season comprises a significant source of carbon to the atmosphere. The summer period was a net sink of 10.83 g C m-2 yr-1, while the non-summer seasons released more than four times the CO2 uptake observed in the summer, resulting in a net annual source of 37.6 g C m-2 yr-1 to the atmosphere. This shows a change in this region of the Arctic from a long-term annual sink of CO2 from the atmosphere to an annual source of CO2 from the terrestrial ecosystem and soils to the atmosphere. The results presented here demonstrate that nearly continuous observations may be required in order to accurately calculate the annual NEE of Arctic ecosystems, and to build predictive understanding that can be used to estimate, with confidence, Arctic fluxes under future conditions.