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Thursday, 7 February, 2002, 14:48 GMT
Ancient lake's climate secrets
Lake Malawi is one of the most important lakes on Earth
By BBC News Online science editor Dr David Whitehouse

Scientists are planning to drill into what could be the longest and richest archive of Earth's past climate. It could provide a year-by-year continuous record going back millions of years in a part of the world where it is thought humans first evolved.

Using a newly developed drilling system, researchers will, for the first time, obtain sediments from the bottom of Lake Malawi.

Situated at the southern end of the East African rift valley, Lake Malawi, is 750 metres (2,460 feet) deep and possibly seven million years old.

Researchers say that the data they could obtain about past climatic variations might provide the environmental background needed to understand human origins and evolution.

"Our goal is to get something on the order of a half-million to a million-year record on past climate and environment, taking advantage of the fact that these lake sediments are frequently annually layered," said Professor Andrew Cohen of the University of Arizona, US.

Short and unforgiving

From previous studies, scientists know that each annual layer of Lake Malawi sediment consists of a black zone - the sediment runoff from land deposited during the rainy season - and a light-coloured layer of single-celled algae that grow in abundance each dry season.

Malawi Drilling Project
The lake has been extensively surveyed
The composition and variation in the layers can be used to infer climatic conditions - temperature, precipitation, etc - in the distant past. Because this information is not a direct record of climate behaviour, scientists refer to it as proxy data.

Old trees, glaciers, even fossilised plankton shells hold clues to what the Earth's climate was up to millions of years ago.

Andrew Cohen said: "A big question has always been whether the global climate engine has been driven by the advance and retreat of glaciers at high latitudes or by circulation patterns at the tropics.

"It has long been assumed that Earth's climate engine was driven by the ice sheets themselves. But there is good reason to believe the tropics may be driving the global climate system. So, one of the first things we want to address is the question of whether the climate history of the tropics leads or lags behind the climate of the polar regions."

Ultimate goal

Preparations for Lake Malawi drilling will take place during the summer, with the actual drilling starting in December or January 2003. The project will take 70 days.

Malawi Drilling Project
Seismic traces of the lake's sediments
"This is a risky scientific expedition, to be sure," said David Verardo, of the US National Science Foundation's Earth System History program. "We are moving a new drilling system into a technologically challenging environment."

This is because Lake Malawi is deep and the weather window for drilling operations is short and unforgiving.

Scientists say that their ultimate goal is to obtain sediment cores at Lake Tanganyika.

Andrew Cohen said: "At Tanganyika, there is potential for getting much longer records than from Malawi. Lake Malawi is 750 meters deep. Tanganyika is around 1,500 meters deep. We suspect that Lake Malawi dried up sometime during the Pleistocene, whereas Lake Tanganyika held water."

See also:

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