Effect of ventilation on karst system equilibrium (Altamira Cave, N Spain): An appraisal of karst contribution to the global carbon cycle balance

Abstract

Altamira cave air CO2 concentration, and both cave and air δ13C values seasonally vary indicating the cave behaves as a CO2 reservoir or source in winter and summer, respectively. During the ‘CO2-reservoir phase’ the δ13C of the cave air is lower, because it is influenced by the infiltration of soil-derived organic carbonrich waters. In the ‘CO2-source phase’ the δ13C of the cave air is heavier due to the ventilation of the cave and the mix with the air from the external atmosphere and soil. The13C/12C analyses confirmed the importance of the external soil as the CO2 source for the underground system as well as the effect of ventilation on system equilibrium.