Bioclimatic signification of marker taxa of the Mediterranean Pliocene
Résumé
The climatic reconstruction of the Pliocene, based on pollen data, requires a new method of quantification because of the presence in pollen spectra, of temperate, warm-temperate but also subtropical plants. As no modern pollen spectra contain all these taxa, the best analogues method is inappropriate for this period. So, a new method is proposed: it corresponds to a climatic amplitude method modified to partially take into account some taxa abundances. The first step in this new method is to determine the present-day distribution of a few subtropical plants and some taxa still existing in the Mediterranean region with a good climatic signal. Then, the climatic parameters of the corresponding areas are defined, either by a climatic atlas or by personal knowledge. A test on a few pollen spectra, corresponding to different localities but of almost the same age (about 3.4 Ma) is realised. The first results of climatic estimation confirm an increasing latitudinal gradient for annual temperatures from North to South, which is estimated as today, even if the temperatures were higher (about 2 to 6 degrees C more). We may confirm the same for the precipitations which were more important to the North than to the South of the Mediterranean. These latitudinal gradients are quantified.