Quantification of the northern Italy Pliocene climate from pollen data – evidence for a very peculiar climate pattern.

International audienceA climatic reconstruction has been carried out on the Stirone pollen sequence (northern Italy), covering the Pliocene period from the Zanclean to the early Gelasian (~5.1 to ~2.2 Ma). Despite the existence of a number of hiatuses, the section provides a clear picture of the vegetation and climatic evolution during this time interval, which includes the first glacial-interglacial cycles of the Northern Hemisphere. The climate of this period has been quantified using the “Climatic Amplitude Method” developed for the Neogene, and five climatic parameters have been estimated. The results show that at the beginning of the Pliocene and during the interglacial periods, the climate was warm and humid (mean annual temperature from 16 to 20°C, mean annual precipitation from 1100 to 1500-1600 mm), similar to that found elsewhere in the Northwestern Mediterranean area. However, during the first glacial periods, the reconstructed climate differs from that found at other Mediterranean sites: the mean annual temperature, the temperature of the warmest and of the coldest months show lower values than those found during the lower Pliocene, but no marked reductions are observed in the annual precipitation, allowing the continual presence of a forested environment. These results are in agreement with the hypothesis that from at least the Upper Pliocene, the Po region has been a very particular region from the point of view of both vegetation and climate. The difference is particularly marked during the earliest glacial phases in northern Italy