Subterranean CO2 ventilation and its role in the net ecosystem carbon balance of a karstic shrubland

Recent studies of carbonate ecosystems suggest a possible contribution of subterranean ventilation to the net ecosystem carbon balance. However, both the overall importance of such CO2 exchange processes and their drivers remain unknown. Here we analyze several dry‐season episodes of net CO2 emissions to the atmosphere, along with soil and borehole CO2 measurements. Results highlight important events where rapid decreases of underground CO2 molar fractions correlate well with sizeable CO2 release to the atmosphere. Such events, with high friction velocities, are attributed to ventilation processes, and should be accounted for by predictive models of surface CO2 exchange. Key Points Subterranean ventilation contributes greatly to the NECB in karstic ecosystems Models of CO2 surface exchange should account for subterranean ventilation Subterranean ventilation is driven mainly by the friction velocity