Environmental factors regulating winter CO₂ flux in snow-covered black forest soil of Interior Alaska

Abstract

High latitude winter soil CO₂ emission is an important component of the annual carbon budget at regional and global scales. Here, continuous monitoring of winter CO₂ flux-measurement in black spruce forest soil of interior Alaska was performed using non-destructive infrared (NDIR) CO₂ sensors at 10, 20, and 30 cm above the surface during the snow-covered period of 2006/7. To analyze the effects of environmental factors in the CO₂ flux, the dataset was clustered based on major meteorological patterns. Periods were selected based on atmospheric pressure corresponding to well-identified synoptic large scale patterns: ambient pressure larger than 1000 hPa (HP: high pressure), atmospheric pressure is in the range between 985 and 1000 (IP: intermediate pressure), and cases in which the atmospheric pressure was below 986 hPa (LP: low pressure). Furthermore, the dataset corresponding to the snowmelt period (MP) was treated independently for all values of ambient pressure. Winter CO₂ fluxes were 0.20 ± 0.02, 0.23 ± 0.02, 0.29 ± 0.03, and 0.17 ± 0.02 gC m^–2 d^–1 for the HP, IP, LP, and MP phases, respectively. Atmospheric and soil temperature at 5 cm depth, modulated by atmospheric pressure, were significant factors in regulating winter soil-originated CO₂ emission and fluctuation. We found that changes in CO₂ fluxes during the snow-covered period can be as much as 35% on the average. These results are significant, as wintertime CO₂ emissions represent ~20% of annual soil-originated emissions.