By Sid Perkins
Northwestern Africa has always been a prodigious source of airborne dust. But dust supplies really took off when commercial agriculture came to the region in the 19th century, a new analysis suggests.
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Climate exerts a strong influence on African dust emissions: When precipitation is lower than normal, atmospheric concentrations of dust increase. But new data gleaned from sediments deposited on the North Atlantic seafloor suggest that since the mid-1800s, human activity — especially agriculture along the southern fringe of the Sahara, a region known as the Sahel — has played a big role too, says Stefan Mulitza, a paleoclimatologist at the University of Bremen in Germany. He and his colleagues report their findings in the July 8 Nature.
To reach their conclusion, the researchers analyzed two sediment cores taken from the seafloor about 30 kilometers from the mouth of the Senegal River. That material contains both fine-grained, iron-rich sediment carried there by the river and silicon-rich dust blown to the site by prevailing winds, says Mulitza. One core, which measures more than 5 meters long, covers the last 3,200 years, the team’s radiocarbon dating suggests. The other core, only 43 centimeters long, provided a high-resolution look at sediment that accumulated in recent years.