Large-scale atmospheric circulation changes in the northern Mediterranean realm during the Younger Dryas: new insights from Lago Grande di Monticchio (Italy)

The Mediterranean region is recognized as a climate change hotspot, where temperatures increase faster than the global average. Modelling experiments suggest that such rapid and drastic changes will induce droughts and extreme rainfall events in this vulnerable region. Records of past climatic changes are useful to determine the speed and mode of regional responses and climatic sensitivities. We examine here the response of southern European hydroclimate to large-scale oceanic disturbances and rapid climatic changes during the Younger Dryas (YD) interval (e.g., 14-11 ka BP). We present new results from Lago Grande di Monticchio (Italy) that allow us to explore the dynamics of precipitation at high temporal resolution. By combining multiple tracers (hydrogen isotope ratios of leaf waxes, X-ray fluorescence scanning, microfacies analyses, tephrochronology), we were able to determine both rainfall dynamics and sedimentary and environmental responses. We identified a pronounced positive shift in hydrogen isotope ratios (expressed as δD values) during the YD cold period of ca. 20 ‰ between 12.6 and 11.5 ka BP. We interpret this to reflect to a decrease in the input of north Atlantic moisture (a significant contributor to annual rainfall at present) and lower overall precipitation amount. This coincides with an increase in the varve thickness and occurrence of organic-clastic microfacies. The presence of marker tephra layers in the record (esp. the Neapolitan Yellow Tuff and Pomici Principali) provides important temporal tie-points that enable us to compare local hydroclimatic responses across the wider region. In particular, the observed drying trend at Monticchio is in striking contrast to more humid conditions north of the Alps in western, central and eastern Europe, potentially reflecting the southward migration of synoptic climatic systems (westerlies) and the presence of sea-ice in the moisture source region.