Not given to the dynamics of the cave or any local factors,but given that there seems to be an increase of CO2 in general then it could be (with the deluge and saturation of rainfall that we have experienced over the last 6 months)the levels of detritus(washed in) and from previously dry areas of caves that have become wet has kick started a reaction that involves dissolved carbon dioxide,this in turn reacts with water to form carbonic acid carbonic acid reacts with limestone which forms bicarbonates and carbonate ions.Bicarbonate is a resevoir for carbon dioxide(in breathing it is the bicarbonate ion that is responsible for the expeling of co2).How this carbon dioxide is then released is unknown to me but it could be down to increased bacterial/microorganism activity.Rehydration of archeobacteria?? :alien: