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Ocean Floor Offers Clues ro Arid Southern African Climate

August 27, 1997
To better understand the climate of Southern Africa (which includes one of the driest areas on Earth, the Namib desert) scientists will collect and study sediment and rock samples from beneath the seafloor during an Ocean Drilling Program (ODP) expedition off the coastline between Congo and the Cape of Good Hope. Precipitation in the south is greatly influenced by the ocean currents offshore. The Namib owes its existence to the upwelling of cold, subsurface ocean waters which produce a high air pressure region that blocks moist winds from entering the African continent.

The scientists seek to understand changes in the wind fields over the past several millions of years, and the effects on African climate. "The intensity of upwelling directly reflects the intensity of winds, and the precipitation in western Africa," explains co-chief scientist Dr. Gerold Wefer of the University of Bremen (Germany). "And, in turn, the winds drive the mighty Benguela Current, the strongest in the South Atlantic."

"The powerful hurricanes in the Caribbean are caused by the surface-current transfer of heat from the South to the North Atlantic via currents such as the Benguela, and that's why there are no hurricanes in the South Atlantic," says Dr. Wolf Berger of Scripps Institution of Oceanography, the other co-chief scientist. "We need to reconstruct the history of this heat transfer to understand what controls it and how sensitive it is to climate change. There are indications that human activity is changing the climate. We wish to know how resilient the natural system is to such modifications."

Upwelling of ocean water also releases carbon dioxide to the atmosphere and intensifies the biological abundance of the area, bringing to the surface nutrient-rich waters which fuel high productivity of plankton and other marine life. Twenty-five ODP scientists aboard the world's largest scientific drill ship JOIDES Resolution will examine the links among climate, carbon dioxide, and productivity during their cruise, which began August 12 and continues to October 10.

"These sediments contain the remains of plankton which feed whales and fish," says Berger. When sinking out of the sunlit zone, the organic plankton remains carry carbon from the surface layer of the ocean into the sediment. This transfer, or "biological pump" of carbon to the ocean bottom, modifies the level of carbon dioxide in the atmosphere, an important control of climate. Another focus is on the ultimate fate of the organic material.

"The accumulation of organic matter in the sediments is the first step towards the genesis of oil and gas," says Berger. "The oil fields now producing off Congo and Angola owe their existence to the accumulation of plankton remains some 100 million years ago, when the South Atlantic was in the early stages of opening up, through continental drift."

The Ocean Drilling Program, an international partnership of scientific institutions and governments, explores the history and evolution of Earth's crust. The Ocean Drilling Program is funded principally by the National Science Foundation, with substantial contributions from its international partners. These include the Federal Republic of Germany, France, Japan, and the United Kingdom. Australia, Canada, Chinese Taipei, and Korea hold a joint partnership. Another partner is the European Science Foundation, consisting of Belgium, Denmark, Finland, Iceland, Italy, The Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, and Turkey. The program is managed by Joint Oceanographic Institutions, a consortium of 10 U.S. institutions, with Texas A&M; University responsible for science operations. Lamont-Doherty Earth Observatory is the operator for downhole logging.

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Dr. Wolfgang H. Berger
Scripps Institution of Oceanography, University of California, San Diego
Work: (619) 534-1829
Fax: (619) 534-0784

Dr. Gerold Wefer
Fachbereich Geowissenschaften
Universität Bremen, Germany
Work: (49) 421-218-3389
Fax: (49) 421-218-3116

Dr. Carl Richter
Ocean Drilling Program
Texas A&M; University
Work: (979) 845-2522
Fax: (979) 845-0876

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