WIDESPREAD FOSSIL CO2 IN THE ANSANTO VALLEY (ITALY): DENDROCHRONOLOGICAL, 14C, AND 13C ANALYSES ON TREE RINGS

The Ansanto Valley (southern Italy) is characterized by vents and boiling mud lakes that emit typical volcanic exhalations (mostly fossil CO2). This fossil dilution spreads over the Ansanto Valley and its impact on local trees is investigated in this study. Six trees at increasing distance from the emitting sources and 2 aliquots of gas were sampled. Dendro-chronological analysis was performed on tree cores in order to check the accuracy of the tree-ring sequences; the results indicate no anomalies in the curves of the analyzed trees. delta C-13 and radiocarbon (C-14) analyses were performed on the alpha-cellulose extracted from some selected tree rings. The main aim of delta C-13 analysis was to gain information about the origin of CO2 arising from the source; the results support the hypothesis of a carbonatic origin, with respect to a volcanic origin. C-14 analysis was performed to evaluate the influence and to quantify the percentage of fossil dilution characterizing the local atmosphere and affecting the trees at different distances from the source during the years. The results show the presence of a strong fossil dilution affecting the trees, increasing toward the sources (from similar to 6% at 80 m distance to similar to 30% at 20 m from the nearest vent) with quite stable values over the examined period.