Pressure Pumping Effects on Fluxes and Release of Trace Gases From Soils

New evidence, obtained at the Glacier Lakes Ecosystem Experiments Site in the Rocky Mountains of southern Wyoming, is presented that supports the hypothesis that turbulent pressure fluctuations can affect the flux of CO₂ and other trace gases from soils and snowpacks. First, half-hourly measurements of CO₂ mole fraction taken between December 2000 and March 2001 at the soil/snowpack interface under a 1.1 m snowpack show significant variations with a dominant period of about 8 days and an amplitude of about 100 ppmV. These variations are strongly correlated with fluctuations in both wind speed and pressure. Second, simultaneous CO₂ fluxes, taken as part of the AmeriFlux network, increase with increasing wind speed and decreasing CO₂ mole fraction at the soil/snow interface. These eddy covariance fluxes are greater than purely diffusional fluxes through the snowpack. Third, an analytical model of CO₂ fluxes throught the snowpack is used to distinguish between the effects of low frequency barometric pumping and the relatively higher frequency turbulent pressure pumping and stationary pressure waves forced by topography. Comparison of the observations and the modeling results suggest that turbulent pressure pumping can significantly enhance purely diffusional CO₂ fluxes on a half-hourly basis and that the intensity of the turbulent pressure pumping is modulated by the low frequwncy synoptic scale.