The last bits of glacial ice and permafrost as remains of the late Holocene Mediterranean glaciations. New discoveries from Mount Olympus periglacial zone

Despite the existence of numerous glaciers on the Mediterranean mountains during the Little Ice Age (LIA), many of these disappeared during the 20^th century. However, periglacial conditions are sustained in the formerly glaciated alpine zones, preserving relicts of the late Holocene glacial record. The present climate of the Mediterranean mountains is hostile to glaciation and projected climate trends suggest that the Mediterranean cryosphere will be shrinking with immediate impacts on the water budget of the lowlands. Here we show preliminary results of an extensive fieldwork campaign that focuses on the Holocene reconstruction of the climate and alpine critical zone environmental conditions of Mount Olympus (2918 m) in Greece. A well-preserved sequence of late Holocene glacial moraines dating to ⁓2.5 and ⁓0.6 ka BP, respectively, suggest that the small cirque glaciers were geomorphologically active during the LIA, whereas 30 m deep glacial ice found in a perennial ice cave opens a new window of local and regional continuous climate reconstructions. The extensive snowfields of the mid-20^th century have shrunk dramatically but have survived the warmest summers of the 21^st century. Below these perennial snowfields a 15 m thick permafrost layer has been discovered during our campaign through 3 Electrical Resistivity Tomography (ERT) profiles, in a location where the mean annual air temperature (MAAT) of the last 10 years is above 0^oC, but in agreement with permafrost occurrence in other mountains of the Southern Balkan peninsula. The base horizon of postglacial alpine soils overlying glacial till deposited in a glaciokarstic plateau below the summit, appears cryoturbated whereas the soils are characterized by translocation of clay from the upper to the lower horizon. These observations along with occasional early summer soil freeze and subsequent waterlogging, suggest that the periglacial activity on Mount Olympus continues in a rapidly warming Mediterranean environment. However, regional warming and anomalous early summer convective rainfall that has caused a dramatic reduction in the volume of the perennial ice cave deposits and the near extinction of the perennial snowfields (even after winters with very high snow accumulation) over the past 10 years also threatens this periglacial activity. Altogether these observations show the general decreasing trend of the Mediterranean cryosphere and periglacial activity, and they highlight immediate impacts on karstic aquifer water recharge and water availability in the piedmont and coastal zone of Mount Olympus, especially during the summer season when water demand is very high due to agricultural and touristic activities.