Ecosystem Scale Implication of Soil CO2 Concentration Dynamics During Soil Freezing in Alaskan Arctic Tundra Ecosystems

The rates, processes, and controls on Arctic cold period soil carbon loss are still poorly understood. To understand one component of winter CO2 loss in the atmosphere, continuous measurements of soil (CO2) were made and compared to ecosystem scale CO2 fluxes. Measurements of soil (CO2) were made near Utqiagvik, Alaska from the beginning of soil thaw in summer 2005 to spring 2007. In the summer, soil (CO2) rose with increased soil temperature, reaching value orders of magnitude higher than the 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 doubled than that was 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 (EC) measurements showed variable but continued emissions of CO2 to the atmosphere during freezeup. The disconnect between soil (CO2) and landscape level fluxes may be attributed to the spatiotemporal heterogeneity in release of high concentrations of soil (CO2) to the atmosphere during the fall; and when integrated over the area of the EC tower footprint, do not frequently result in detectable emission events. Continued monitoring of fall and winter soil (CO2) and ecosystem fluxes will be vital for further understanding the variability of interannual Arctic CO2 emissions.

Automated summary

Research on Arctic cold period soil carbon loss is still limited, and this study focused on continuous measurements of soil (CO2) near Utqiagvik, Alaska. The study found that soil (CO2) concentrations increased in summer with rising soil temperature, reaching values much higher than atmospheric CO2. Complex changes in biological activity led to doubling of soil (CO2) concentrations in fall and winter, with peak concentrations in November before steep decreases. Eddy covariance measurements showed continued CO2 emissions to the atmosphere during freeze-up, highlighting the need for further monitoring of Arctic CO2 emissions.