| Summary: | The rates, processes, and controls on Arctic cold period soil carbon loss are still poorly understood. To understand one component of winter carbon dioxide (CO2) loss to the atmosphere, continuous measurements of soil CO2 concentration, [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.
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