Ecosystem scale implication of soil carbon dioxide (CO2) concentration dynamics during soil freezing in Alaskan Arctic tundra ecosystems 2005-2007

The rates, processes, and controls on Arctic cold period soil carbon loss are
still poorly understood. To understand one component of winter CO2 loss to the atmosphere, continuous
measurements of soil [CO2] (concentration of CO2) were made and compared to ecosystem scale CO2 fluxes. Measurements of soil [CO2]
were made near Utqiaġvik, Alaska from the beginning of soil thaw in summer 2005 until spring 2007. In the
summer, soil [CO2] rose with increased soil temperature, reaching values orders of magnitude higher than
atmospheric [CO2]. Soil [CO2] initially decreased at the end of summer and beginning of fall but then
increased subsequent to soil freezing. Due to complex changes in biological activity, storage, and
transport processes, soil [CO2] was then approximately double that observed in the summer. After reaching
peak concentrations in November, soil [CO2] steeply decreased over a couple of weeks, suggesting a substantial
release of CO2 into the atmosphere and movement within the soil column. Eddy covariance measurements showed
variable but continued emissions of CO2 to the atmosphere during freeze-up. The disconnect between soil
[CO2] and landscape level fluxes may be attributed to the spatio-temporal heterogeneity in releases of high
concentrations of soil [CO2] to the atmosphere during the fall; and when integrated over the area of the eddy
covariance tower footprint, do not frequently result in detectable emission events. Continued monitoring of
fall and winter soil [CO2] and ecosystem fluxes will be vital to further understanding the variability of
inter-annual Arctic CO2 emissions.