Vegetation and climate changes during the OIS 9-8 from Compositional Data Analysis and Modern Analogues Technique of the high resolution pollen record of Acerno (southern Italy)

The Acerno lacustrine basin is a tectonic palaeolake formed during the Middle Pleistocene. Pollen analysis and tephrostratigraphy performed on the lacustrine succession (about 100 m thick) allowed the vegetation history to be reconstructed and correlated with OIS 9 and 8 on the basis of the presence of the Lower WTT (297 ka) marker level (Russo Ermolli, 2000; Munno et al., 2001). Compositional data analysis pointed out the vegetation dynamics during the different phases of the climatic cycle. Constrained cluster analysis (Grimm, 1987; Di Donato et al., 2008) allowed identification of four pollen zones corresponding to as many vegetation phases. Relative Variation Biplots (Aitchison and Greenacre, 2002) got insight on the compositional changes in the pollen assemblages and on the relationship among taxa. The main source of variability, accounting for 41% of total variance, relies on the opposition between arboreal and herbaceous taxa along the first axis of biplots. This means a relatively high standard deviation of corresponding logratios. A secondary source of variability is related to the opposition between Betula and Pinus. The first taxon characterising the phases of climate amelioration preceeding the interglacial conditions while Pinus closing the forest succession before entering the glacial period. The position within the biplots of samples corresponding to each of the four pollen zones, identified through CCA, pointed to the vegetation cover variation along the Acerno cycle. The MAT (Hutson, 1979) was applied to the Acerno pollen record by using a modern pollen database of 7664 spectra. The reconstructed temperatures pointed out a series of oscillations that can be correlated to the OIS 9 substages. Precipitation shows a drastic decrease towards the top of the sequence corresponding to the onset of the OIS 8 glacial period.