Lake Chad once the largest lake in the World

Here we wrote that dust from Bodélé depression blows across the Atlantic to help fertilise the rainforests of the Amazon. The Bodélé depression was once an enormous lake called Mega Lake Chad in what is now the Sahara desert.

To analyse Mega Chad’s decline, researchers from Royal Holloway, Birkbeck and Kings College, University of London used satellite images to map abandoned shore lines[1]. They also analysed lake sediment to calculate the age of these shore lines, producing a lake level history spanning the last 15,000 years.

Mega Lake Chad was once the biggest freshwater lake on earth covering 360,000 square kilometers of Central Africa and rapidly shrunk to a its present size just 1,000 years ago.

A reconstructed lake level history for the ancient Lake Mega-Chad, suggests that a North African humid period, with increased precipitation in the Sahara region, started about 15,000 years ago and ended abruptly around 5,000 years ago. The lake’s Bodélé basin, now a large source of atmospheric dust, may not have dried out until about 1,000 years ago. Prior to that time dust output from the northern basin must have been limited, and suggestions that this dust plays an important role in fertilizing Atlantic and Amazonian ecosystems are either overstated or only true for the last thousand years.

The researchers found that the change took place in just a few hundred years – much more quickly than previously considered. The end of this humid period also forced people to the only habitable region in northern Africa: the Nile. That in turn resulted in the rise of the Egyptian civilisation.

All that remains now is Lake Chad, which at 355 square kilometers is still quite large, but is just a fraction of its former glory. The lake, which crosses the borders of Chad, Niger, Nigeria and Cameroon, has been further reduced in size by humanity siphoning off fresh water from it.

[1] Armitage et al: West African monsoon dynamics inferred from abrupt fluctuations of Lake Mega-Chad in Proceedings of the National Academy of Sciences – 2015