The role of cave ventilation in the triple oxygen and hydrogen isotope composition of condensation waters in Altamira Cave, northern Spain

•Water condensation can compromise the preservation of cave rock art.•Cave ventilation controls the sources of moisture for water condensation.•External water vapor condenses mostly in summer close to the cave entrance.•The inmost cave sectors are not affected by external water vapor.•Autochthonous vapor sources water condensation in the inner cave sectors.