Desert roamed during Ice Age

March 24, 2000

Scientists have tracked the shifting sands of the Kalahari through 180,000 years of history to gain an unprecedented glimpse at how climate shifts have affected the evolution of a desert.

Research by scientists from the universities of Luton, Oxford and Sheffield into the age of sand dunes has revealed the desert's past in unprecedented detail.

It has also provided an approach to studying climate change that has previously been inaccessible to science.

In the largest survey of its kind ever attempted, the team has taken samples from 50 sites across 1 million km2 of the Kalahari Basin, covering Botswana, South Africa, Zimbabwe, Zambia and Namibia.

Paul Shaw, head of the department of environment, geography and geology at the University of Luton, will present his latest results at a conference in South Africa in July.

"This is the first systematic study of sand dune age over an entire region, giving us a palaeoclimatic record from a whole desert," he said.

The team is using optically stimulated luminescence (OSL) dating, a technique suited to arid conditions where lack of organic matter precludes the use of radiocarbon dating.

OSL dating measures the quantity of radiation, derived from the decay of natural radio-isotopes, that is stored as electrons in the structure of quartz crystals.

The electrons accumulate over time after a sand grain is buried, but are "bleached out" on exposure to sunlight, effectively resetting the "clock".

Samples taken from different depths in the desert were analysed at the University of Sheffield to measure the electron content of the grains and hence the time since they were last at the surface.

Much of the Kalahari is today stabilised by vegetation.

Through the OSL dating, however, the scientists have identified a series of episodes when the dunes were able to move, exposing their sand to the light.

This would have been due to either particularly dry spells, which would have killed the binding vegetation, or more wind.

The spatial and temporal pattern of these changes, particularly during the last ice age, has been found to be much more complex than previously thought.

The team is now studying sand grains taken from dry lake beds in the Kalahari to investigate times when the climate was wetter than at present.

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