Pleistocene ice caps on the coastal mountains of the Adriatic Sea

Abstract

Ice caps once covered large areas of Mount Orjen (1894 m), on the Adriatic coast of Montenegro/Bosnia Herzegovina/Croatia. The largest ice cap covered an area of c. 165 km 2 and reached a maximum ice thickness of c. 450 m, in some areas reaching down to 500 m above modern sea level. U-series dating of secondary carbonates within moraines indicates that the most extensive glaciation occurred during the Middle Pleistocene, correlating with a major phase of glaciation in Greece to the south during MIS 12 (c. 480–430 ka). Later, less extensive, glaciations are also recorded in the cirques and valleys and correlate with glaciations during MIS 6 (190–130 ka) and MIS 5d-2 (110–11.7 ka). Each phase of glaciation would have required large amounts of snow accumulation. Under modern precipitation values, which at c. 5000 mm are some of the highest in Europe, mean annual temperatures would need to be only c. 5–6 °C lower in order to form similar sized glaciers today. A mean annual temperature depression of 12–13 °C would still require >1000 mm of snow accumulation (water equivalent) to balance ablation, suggesting sustained moisture supply during Pleistocene cold stages. Such sustained precipitation supply during Pleistocene cold stages is likely to have been facilitated by major temperature contrasts between the European landmass and the Mediterranean Sea, which are likely to have sustained lee-side vortices to the south of the Alps, in the Gulf of Genoa and Adriatic Sea, forming weak moisture-bearing depressions which tracked across the eastern Adriatic coastal mountains. Large ice caps on the Dinaric Alps would have blocked the inland penetration of these depressions, resulting in much drier conditions in the Balkan interior, creating favourable conditions for the deposition of thick accumulations of loess. The last glaciers on Orjen formed during the Younger Dryas (12.9–11.7 ka) and confirm the influence of North Atlantic Ocean circulation on Pleistocene climate change in this part of the Mediterranean.