Late Pleistocene glaciers and climate in the High Atlas, North Africa

Extensive glaciers covered the High Atlas mountains in Morocco during the late Pleistocene. On the northern escarpments of the Marrakech High Atlas a series of cirques perched at ~3000 to 3500 m fed their valley glaciers which in some cases extended to as low as 2000 m. Cosmogenic exposure dating with 10Be and 36Cl has shown that at least three phases of glaciation are preserved in glacial deposits over the last glacial cycle at 50, 22 and 12 ka which appear to correlate with marine isotope stage (MIS) 3, the global last glacial maximum (LGM) and the Younger Dryas chronozone. This geochronological framework is sufficiently robust to allow for time-constrained glacier-climate reconstructions. The glaciers associated with these 3 phases of advance had ELAs of 2761 m (~50 ka), 2919 m (~22 ka), and 3213 m (~12 ka). Glacier-climate modelling suggests that all of these phases were driven by both colder temperatures and wetter conditions than today. The dominant moisture supply to these glaciers in all phases would have been sourced from Atlantic depressions. The influence of an extended and enhanced West African monsoon on glacier development during African Humid Periods is unlikely to have been a significant influence on glacier dynamics. The climate conditions associated with the three glacier phases indicates sustained moisture supply to the highest mountain areas when records from other areas such as the Middle Atlas lakes, and also marine sediment cores offshore, indicate marked aridity.