INTERGLACIAL VEGETATION PATTERNS AT THE EARLY-MIDDLE PLEISTOCENE TRANSITION: A POINT OF VIEW FROM THE MONTALBANO JONICO SECTION (SOUTHERN ITALY)

Abstract

The Montalbano Jonico succession (southern Italy) represents a rich stratigraphic archive of the Early to Middle Pleistocene environmental and climatic changes in the central Mediterranean. Pollen analyses associated to multivariate statistical methods (principal component and cluster analyses) have been carried out in the sedimentary portion including Marine Isotope Stages (MIS) 21 to 17 (~200 kyrs and ~190 m). The pollen ratio between mesotherm and steppic taxa (Pollen Temperature Index), used as a proxy of temperature, permits to precise consecutive warmer and cooler phases associated, respectively, to interglacials/interstadials and glacials/stadials (substages 21.3 to 18.3 plus stage 17). Pollen data suggest major expansions of mixed oak forests during warm phases, whereas open vegetation typically marks cool to cold phases. The statistical processing puts in evidence both analogies and differences among the successive interglacials/interstadials. Mid- to high-altitude trees and Mediterranean taxa appear to expand slower than hydrophytes plus deciduous oaks and other herbs, which conversely act like pioneers. Moreover Tsuga, Cedrus plus steppic plants and Poaceae are inversely related to Mediterranean xerophytes and mesotherm deciduous taxa, possibly due to the different tolerance to temperature decreases. On this basis, three main vegetation patterns seem to occur during warm periods. The 1st pattern (including MIS 21.3, 19.3 and 17) shows a tripartite structure with a middle warm phase including higher abundances of slow-spreading taxa, sandwiched between cooler intervals (at the beginning and the end of the sub-stage) with the increase of faster-expanding taxa. The 2nd pattern (in MIS 21.1 and 19.1) shows a complex structure characterized by rapid changes in proportions between fast- and slow-spreading taxa as well as among plants with different tolerance to temperature decrease. The 3rd pattern (in two interstadials within MIS 18), is characterized by relatively high abundances of fast-spreading taxa and low abundances of warmth-demanding taxa. This work represents a first attempt for a better understanding of interglacial vegetation dynamics during the Early-Middle Pleistocene Transition; deeper investigations are in progress with the specific aim to better characterize the observed multiple patterns and possibly to define their causes.