Submarine caves at Cape of Otranto, Southern Italy host eccentric stalactites, hanging from the ceil and protruding from lateral walls, towards the centre of each submerged hall. Only recently they have been recognised as completely biogenetic. Their composition varies from the entrance (where they are similar to coralligenous structures) toward the inner portion of the grottoes (where their composition appears to be mostly monospecific). The core of such speleothems is formed by calcareous tubules of Polychaeta Serpulidae. One of these stalactite (37 cm long), taken from a cave particularly rich of these structures, was longitudinally sectioned in order to allow a detailed description of the internal texture and to select samples for AMS radiocarbon dating. Preliminary investigations have been carried out in order to estimate the pre-bomb marine reservoir effect in the studied area (Southern Adriatic sea in the Mediterranean basin), determining a reservoir age of 320 ± 40 years corresponding, with comparison with the global MARINE04 calibration curve, to a R value of -45 ± 40 years. Modern organisms, of the same species found in the stalactite were sampled alive from the same cave and AMS 14C dated in order to asses the accuracy of the measurements carried out on the calcareous tubes, excluding the presence of effects which could fake the radiocarbon results such as the presence of sources of 14C-depleted carbonate in the organism diet . The measurements did not show anomalous 14C concentrations, while a difference in the Delta 14C value of only 5 ‰ was found between the centre and the terminal part of the same tube indicating for the organism a life cycle of 1-2 years. Different samples have been taken along the axis of the sectioned stalactite and prepared for AMS measurements by following standard procedures: mechanical cleaning, attack with hydrogen peroxide, conversion to carbon dioxide by orthophosphoric acid attack and a final catalytic reduction to graphite for the measurements of the carbon isotopic ratios in the accelerator mass spectrometer. The measurements has allowed to establish that the growing of the stalactite lasted about 5000 years from 6355 ± 85 cal BP to 1345 ± 75 cal BP with a non homogeneous growing rate progressively reducing from 1.5 cm per century in the first 1000 years to 0.4 cm per century in the last 2000 years.
See more of Poster Session II
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)