Contrasted climate patterns during the Holocene in the central Mediterranean inferred from pollen data

In the central Mediterranean region, many studies suggest that the Holocene is characterized by complex and different climatic trends on either side of latitude 40°N. This particularity in the regional climate system has been highlighted by multiple proxies showing contrasting trends of climate variations. Chironomid temperature-based reconstructions indicate the presence of a thermal optimum in Italy (10,000-7,000 cal. BP), contradicting the pollen-inferred quantification of Europe. Those discrepancies point to the need for further investigation concerning the Holocene climate of the Mediterranean region. To date, various studies have attempted to quantify the climate signal through different approaches without being able to propose a consistent climate reconstruction between proxies and sites.In this context, and in the frame of the ANR project AUTUMNS-LAMBS, a multi-proxy method (brGDGTs and pollen) has been developed to quantify the Holocene climate in the central Mediterranean through a regional approach using multiple sites in Italy and Greece. We show here the results mainly based on pollen data, which is based on a collection of multiple sites, extracted from international pollen databases (NEOTOMA or European Pollen Database). The pollen-inferred climate is quantified by a multimethod approach, using four different methods (MAT, WAPLS, BRT and RF) and three modern databases (regional and global).This study highlights similar climatic trends and inter-regional differences in the central Mediterranean region. Results show that not all of Europe is marked by a thermal optimum and that a longitudinal climatic gradient (40°N) in the central Mediterranean may have been present through the Holocene. In Italy, pollen and brGDGTs show a thermal optimum in the northern and central regions for the early and mid-Holocene, which is coherent with other proxies such as chironomids. This thermal optimum is less marked in southern regions of Italy, highlighting the climatic differences on either side of latitude 40°N. The late Holocene shows a climate shift between the north and the south, with a central region colder than the northern and southern ones. Moreover, the spatial heterogeneity of the Holocene climate needs to be further investigated for a better understanding of the special and temporal specificity of this climate period