Orbital signatures and long-term vegetation patterns in the Mediterranean

An attempt is made to explore the relation between vegetation phases and or bital configurations by comparing long pollen sequences from the Mediterran ean region and astronomical curves on the basis of their independent chrono logies. Three recurring patterns emerge from this comparison: (i) all inter vals with perihelion passage occurring during northern winter were associat ed with significant contractions of tree populations; (ii) all temperate-st age expansions of certain Mediterranean vegetation elements occurred when p erihelion passage was in summer; and (iii) temperate-stage forests reached maximum extent at times of autumn perihelion. Of these patterns, the first corresponds to extreme dry/cold episodes culminating at times of March peri helion, and the second, to maximum summer temperature and evaporation regim es following June perihelion. The third, associated with the occurrence of September perihelion, appears to be more diffuse both in time and space, po ssibly reflecting local variations in hydrological regimes. The consistency of at least the first two cases provides some support for the notion that certain recurring vegetation patterns appear to be a result of climate chan ges linked to specific orbital signatures. This could eventually lead to th e development of improved terrestrial chronologies through astronomical tun ing. (C) 2000 Elsevier Science Ltd and INQUA. All rights reserved.