Our results indicate that the non-summer season is a source of carbon, masking any uptake gained in the summer months. Specifically, summer was a net sink of 11.4 g C m-2 yr-1, but the non-summer seasons emitted 49.0 g C m-2 yr-1, yielding a net source of 37.6 g C m-2 yr-1. Seasons were defined as summer, spring, winter, and fall, and can be used Arctic-wide for inter-site and inter-year comparisons. Controlling factors changed according to season. Winter carbon exchange was controlled by air temperature, wind speed, and soil temperature. Spring carbon exchange was controlled primarily by net radiation. Summer factors on carbon exchange included soil and air temperature and net radiation, and fall carbon exchange was best explained by vapor pressure deficit.