British academy

From crocodiles to gerbils and back: palaeoclimate change in the Libyan Fazzan

Dr Nick Drake (King’s College London) and Dr Kevin White (University of Reading) on behalf of the Society for Libyan Studies

The climate of the central Sahara has experienced significant changes in the last 750,000 years, with a succession of humid and arid phases that are likely to have had a significant impact on human evolution and migration through the region; at times rainfall was enough to form a lake the size of England in this now hyper-arid region.

This project was facilitated by the Society for Libyan Studies, and has been funded by the Society for Libyan Studies, the Leverhulme Trust, The National Geographic Society and the Libyan Great Man Made River Project.

For further information, visit: www.britac.ac.uk/institutes/libya/

Summary

Digital elevation model of the Libyan Fezzan showing Lake Megafezzan in blue

Digital elevation model of the
Libyan Fezzan showing Lake Megafezzan in blue

The Fezzan is a large closed basin that contains a wealth of ancient lake deposits that can be dated using modern techniques to produce a chronology of climate change in the central Sahara. This chronology demonstrates evidence of relatively humid conditions in the Sahara during interglacial periods (times when planetary ice cover was at a minimum) spanning the last 750,000 years. From 750,000 to 420,000 years ago rainfall was high enough to produce a giant lake of about 130,000 km2, roughly the size of England, that we have called Lake Megafezzan. Later wet phases produced smaller lakes of a few thousand square kilometres. Most humid periods correspond to times of increased Saharan insolation, suggesting that they were caused by changes in the orbit of the Earth around the Sun. The last humid phase started at about 14,000 years ago, but was punctuated by brief and abrupt intensifications of aridity that are broadly synchronous with other arid events reported from surrounding regions and are probably linked to monsoon failure. Lake Megafezzan is but one of several giant lakes that once existed in the Sahara; their catchments link to form a corridor across the desert. This is a particularly important for palaeoecology and palaeoanthropology because the Sahara Desert is thought to provide a barrier for the movement of animals and hominids out of Africa. Though data are sparse, there is evidence for synchronous humid periods around 9,000 years ago, at 30,000 years ago and perhaps sometime between 40,000 and 50,000 years ago, suggesting that the Sahara is a more porous barrier to people and animals than previously thought.

Other contributors

Professor David Mattingly
Dr. Simon Armitage
Professor Ahmed al Hawat
Professor Mustafa Salem
Dr. Sue McLaren
Professor Robert Foley
Dr. Marta Mirazon Lahr