Seasonality is critical to understanding the controls and budget of annual CO2 exchange in Arctic tundra ecosystems

Background/Question/Methods Positive feedback cycles make the Arctic a critical area for understanding climate change and controls on carbon exchange. Although research has been ongoing for decades, there is still a paucity of research on carbon dynamics in the non-summer seasons. Here, we analyze a year-long eddy covariance dataset in the Alaskan Arctic tundra ecosystem, and determine the importance of non-summer seasons to the annual carbon budget. In addition, we look at the controls on carbon flux, which change throughout the year. To systematically address the changes, we also define the seasons using available energy, which can adapt to shifting seasons, as is seen in the Arctic.

Results/Conclusions

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.