Pollen analysis of the ship site of Pisa San Rossore, Tuscany, Italy: the implications for catastrophic hydrological events and climatic change during the late Holocene

Abstract

In 1998, an ancient shipping wharf was brought to light in Pisa, Italy. The shipwrecks found there showed human activity from the Etruscan to the late Roman Empire periods. Sandy sediments burying the ships and related materials show four main periods of catastrophic floods separated by thin muddy layers pointing to phases between flooding episodes. Pollen analyses in these fine grained deposits showed: 1) significant percentages of Abies and Fagus during the pre-Roman period; 2) elements of mixed oak woodland together with hygrophilous plants in pollen spectra dominated by herbs, in the Roman interflood deposits. On the whole, the pollen data show a vegetational change which may be attributed to different climatic conditions, supporting the hypothesis that the Roman period was warmer, even though a significant human influence cannot be excluded. Numerous fresh water genera suggest that the area was a poorly drained alluvial plain. Integration between pollen and sedimentological analyses allows some inferences on the dynamics of the warm Roman period and indicates that the warm climate was punctuated by century-scale hydro-climatic crises triggering catastrophic floods.