Orbital signatures and long-term vegetation patterns in the Mediterranean

An attempt is made to explore the relation between vegetation phases and orbital configurations by comparing long pollen sequences from the Mediterranean region and astronomical curves on the basis of their independent chronologies. Three recurring patterns emerge from this comparison: (i) all intervals with perihelion passage occurring during northern winter were associated with significant contractions of tree populations; (ii) all temperate-stage expansions of certain Mediterranean vegetation elements occurred when perihelion 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 perihelion, and the second, to maximum summer temperature and evaporation regimes following June perihelion. The third, associated with the occurrence of September perihelion, appears to be more diffuse both in time and space, possibly 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 changes linked to specific orbital signatures. This could eventually lead to the development of improved terrestrial chronologies through astronomical tuning. (C) 2000 Elsevier Science Ltd and INQUA. All rights reserved.