CHANGES IN CARBON-ISOTOPE DISCRIMINATION IN GRAIN CEREALS FROM DIFFERENT REGIONS OF THE WESTERN MEDITERRANEAN BASIN DURING THE PAST 7 MILLENNIA - PALEOENVIRONMENTAL EVIDENCE OF A DIFFERENTIAL CHANGE IN ARIDITYDURING THE LATE HOLOCENE

Carbon isotope discrimination (Delta) was determined for kernels of si x-row barley and durum wheat cultivated in the western Mediterranean b asin during the last seven millennia. Samples came from different arch aeological sites in Catalonia (north-east Spain) and in the south-east of Spain (mainly eastern Andalusia). Samples from the present were al so analysed. Mean values of Delta for barley and durum wheat grains de creased slightly from Neolithic (7000-5000 BP) to Chalcolithic-Bronze (5000-3000 BP) and Iron ages (3000-2200 BP) both in Catalonia and in s outh-east (SE) Spain. Values were consistently lower in SE Spain than in Catalonia throughout these five millennia, which suggests that Cata lonia was less arid than SE Spain in this period. Within a given regio n, current discrimination values for kernels of the same cereal specie s cultivated under rainfed conditions were lower than those of archaeo logical grains, which implies more arid conditions at present. Further more, an empirical relationship between Delta of mature kernels and to tal precipitation (plus irrigation where applicable) during grain fill ing (r(2) = 0.73, N = 25) was established for barley, currently cultiv ated at different locations in the western Mediterranean basin in Spai n. The resulting relationship was applied to the Delta data for barley kernels from 10 archaeological sites in Catalonia and 10 sites in SE Spain, to estimate the precipitation during grain filling at the time the kernels were produced. For both regions, current climatic conditio ns are consistently more arid than those inferred for the Neolithic, B ronze and Iron ages. In addition, although Catalonia was estimated to have had consistently wetter conditions (about 20% more precipitation) than SE Spain throughout these millennia, differences in precipitatio n between these two regions have recently increased, with 79% more pre cipitation in Catalonia. Results indicate a more rapid increase in ari dity in SE Spain than in Catalonia, probably produced during the last few centuries, and due to anthropogenic causes.