October 1, 2008
Sahara Desert Was Once Green
Reconstructing the climate of the past is an important tool for scientists to better understand and predict future climate changes that are the result of the present-day global warming. Although there is still little known about the Earth's tropical and subtropical regions, these regions are thought to play an important role in both the evolution of prehistoric man and global climate changes. New North African climate reconstructions reveal three "Ëgreen Sahara' episodes during which the present-day Sahara Desert was almost completely covered with extensive grasslands, lakes and ponds over the course of the last 120.000 years. The findings of Dr. Rik Tjallingii, Prof. Dr. Martin Claussen and their colleagues will be published in the October issue of Nature Geoscience.
Scientists of the MARUM "“ Center for Marine Environmental Research in Bremen (Germany) and the Alfred-Wegener-Institute in Bremerhaven (Germany) studied a marine sediment core off the coast of Northwest Africa to find out how the vegetation cover and hydrological cycle of the Sahara and Sahel region changed. The scientists were able to reconstruct the vegetation cover of the last 120.000 years by studying changes in the ratio of wind and river-transported particles found in the core. "We found three distinct periods with almost only river-transported particles and hardly any wind dust particles, which is remarkable because today the Sahara Desert is the world's largest dust-bowl," says Rik Tjallingii. He now works at Kiel University, researching within the cluster of excellence 'The Future Ocean'. The scientists explain these periods by an increase of the precipitation that resulted in a much larger vegetation cover resulting in less wind dust and stronger river activity in the Sahara region. The green Sahara episodes correspond with the changing direction of the earth's rotational axis that regulates the solar energy in the tropical Atlantic Ocean. Periods of maximum solar energy increased the moisture production while pushing the African monsoon further north and increasing precipitation in the Sahara.
Image 2: Dr. Rik Tjallingii investigates the Earth's climatic past by analyzing sediment cores from the sea floor; here at the Institute of Geosciences at Kiel University. Photo: CAU, J. Haacks
On the Net: