A radiometric dating revolution and the Quaternary glacial history of the Mediterranean mountains

Large glaciers and ice caps formed in the Mediterranean mountains during the cold stages of the Pleistocene and some small glaciers remain today. Here we review 157 outputs that include radiometric dates on glacial deposits or outwash in the Mediterranean published between 1975 and 2020. The last decade has seen a striking increase in the use of terrestrial cosmogenic nuclide (TCN) dating and this has revolutionised our understanding of the Late Pleistocene glacial record. Our meta-analysis of 1663 radiometric ages highlights much greater complexity in the timing of Pleistocene glaciation across the region than hitherto recognised. Evidence from multiple dating methods, in a range of depositional settings, confirms that the Mediterranean glacial record extends through all of the Late Pleistocene and deep into the Middle Pleistocene. Evidence of Early Pleistocene glacial activity has been recognised from outwash deposits in the Julian Alps of Slovenia. The most extensive glaciations occurred during the Middle Pleistocene: their ages have been established primarily by using 40Ar/39Ar in the Italian Apennines and U-series dating in the glaciokarst of the Balkans. The Late Pleistocene glacial geochronologies are based on optically stimulated luminescence (OSL), radiocarbon and TCN dating. TCN dating is now the dominant method for dating Late Pleistocene glacial landforms. It is now clear that glaciers were present throughout the Late Pleistocene and, in most parts of the Mediterranean, they were at or near their maximum extent before the global last glacier maximum (27.5–23.3 ka). The outwash record in river valleys downstream of the glaciated terrains confirms that glaciers were important agents of landscape change throughout this period. Deglaciation in the Mediterranean mountains was punctuated by glacier stabilisations as well as some readvances towards the very end of the Pleistocene. The deglacial trend has continued throughout the Holocene with rapid change in recent decades due to rising global temperatures. Some small glaciers remain today due to the influence of locally favourable topoclimatic factors. For much of the Quaternary Period conditions in the Mediterranean mountains involved much more extensive glaciation than recorded at any time in the Holocene.