Deep CO 2 soil inhalation / exhalation induced by synoptic pressure changes and atmospheric tides in a carbonated semiarid steppe Pérez Sánchez-Cañete, Enrique Kowalski, Andrew Serrano Ortiz, Penélope Pérez-Priego, O. Domingo Poveda, Francisco Knowledge of all the mechanisms and processes involved in soil CO2 emissions is essential to close the global carbon cycle. Apart from molecular diffusion, the main physical component of such CO2 exchange is soil ventilation. Advective CO2 transport, through soil or snow, has been correlated with the wind speed, friction velocity or pressure (p). Here we examine variations in subterranean CO2 molar fractions (χc) over two years within a vertical profile (1.5 m) in a semiarid ecosystem, as influenced by short-timescale p changes. Analyses to determine the factors involved in the variations in subterranean χc were differentiated between the growing period and the dry period. In both periods it was found that variations in deep χc (0.5–1.5 m) were due predominantly to static p variations and not to wind or biological influences. Within a few hours, the deep χc can vary by fourfold, showing a pattern with two cycles per day, due to p oscillations caused by atmospheric tides. By contrast, shallow χc (0.15 m) generally has one cycle per day as influenced by biological factors like soil water content and temperature in both periods, while the wind was an important factor in shallow χc variations only during the dry period. Evidence of emissions was registered in the atmospheric boundary layer by eddy covariance during synoptic pressure changes when subterranean CO2 was released; days with rising barometric pressure – when air accumulated belowground, including soil-respired CO2 – showed greater ecosystem uptake than days with falling pressure. Future assessments of the net ecosystem carbon balance should not rely exclusively on Fick's law to calculate soil CO2 effluxes from profile data. 2014-06-16T12:49:31Z 2014-06-16T12:49:31Z 2013 info:eu-repo/semantics/article Sánchez-Cañete, E.P.; et al. Deep CO 2 soil inhalation / exhalation induced by synoptic pressure changes and atmospheric tides in a carbonated semiarid steppe. Biogeosciences, 10: 6591-6600 (2013). [http://hdl.handle.net/10481/32265] 1726-4170 1726-4189 http://hdl.handle.net/10481/32265 10.5194/bg-10-6591-2013 eng info:eu-repo/grantAgreement/EC/FP7/244122 http://creativecommons.org/licenses/by-nc-nd/3.0/ info:eu-repo/semantics/openAccess Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License Copernicus Publications; European Geosciences Union (EGU)