Mega palaeolake in southern Sahara reduced to desert in just a few hundred years

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Researchers from Royal Holloway, Birkbeck and Kings College, University of London used satellite images to map abandoned shore lines around Palaeolake Mega-Chad, and analysed sediments to calculate the age of these shore lines, producing a lake level history spanning the last 15,000 years.

Mega palaeolake in southern Sahara reduced to desert in just a few hundred years
Fossilized fish: The drying of Lake Mega-Chad reveals a story of dramatic climate change
 in the southern Sahara, with a rapid change from a giant lake to desert dunes
 and dust, due to changes in rainfall from the West African Monsoon 
[Credit: University of Royal Holloway London]

At its peak around 6,000 years ago, Palaeolake Mega-Chad was the largest freshwater lake on Earth, with an area of 360,000 km2. Now today’s Lake Chad is reduced to a fraction of that size, at only 355 km2. The drying of Lake Mega-Chad reveals a story of dramatic climate change in the southern Sahara, with a rapid change from a giant lake to desert dunes and dust, due to changes in rainfall from the West African Monsoon. The research, published in the journal Proceedings of the National Academy of Sciences confirms earlier suggestions that the climate change was abrupt, with the southern Sahara drying in just a few hundred years.

Part of the Palaeolake Mega-Chad basin that has dried completely is the Bodele depression, which lies in remote northern Chad. The Bodele depression is the World’s single greatest source of atmospheric dust, with dust being blown across the Atlantic to South America, where it is believed to be helping to maintain the fertility of tropical rainforests. However, the University of London team’s research shows that a small lake persisted in the Bodele depression until about 1,000 years ago. This lake covered the parts of the Bodele depression which currently produce most dust, limiting the dust potential until recent times.

“The Amazon tropical forest is like a giant hanging basket,” explains Dr Simon Armitage from the Department of Geography at Royal Holloway. “In a hanging basket, daily watering quickly washes soluble nutrients out of the soil, and these need to be replaced using fertiliser if the plants are to survive. Similarly, heavy washout of soluble minerals from the Amazon basin means that an external source of nutrients must be maintaining soil fertility. As the World’s most vigorous dust source, the Bodele depression has often been cited as a likely source of these nutrients, but our findings indicate that this can only be true for the last 1,000 years,” he added.

Source: University of Royal Holloway London [June 29, 2015]

1 COMMENT

  1. Thanks a lot for this. The savanna idea of human evolution is based on the belief that human ancestors became bipedal when the environment in Africa became more open & dry, e.g. Raymond Dart 1925: ‚Äú‚Ķ It is generally believed by geologists that the climate has fluctuated within exceedingly narrow limits in this country since Cretaceous times ‚Ķ For the production of man a different apprenticeship was needed to sharpen the wits and quicken the higher manifestations of intellect ‚Äď a more open veldt country where competition was keener between swiftness and stealth …" (google e.g. econiche Homo).
    We now know that our Pleistocene ancestors did not run after antelopes (the "endurance-running" hypothesis), but followed African & Eurasian coasts & rivers (beach-combing, diving & wading bipedally for littoral, shallow aquatic & waterside foods), and the existence of mega-lake Chad (360,000 km2 c 6 ka) is another illustration of how far-fetched the traditional view of human evolution (running bipedally over water-poor plains, sweating water + salt) is, google e.g. researchGate marc verhaegen.