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As winds sweep eastward into the Atlantic off the northwest African coast, a remarkable thing happens: plumes of aeolian dust particles are swept off the surface of the Sahara. They will meander along the varied paths of the easterly trade winds, only to settle again in places as remote from each other as they are from the source: North America, the Caribbean, the Amazon Basin, the southern Mediterranean, eastern Europe, and occasionally even the chilly southern shores of Scandinavia.
Where does the dust come from? Total Ozone Mapping Spectrometer (TOMS) suggest two major source areas: the Bodélé depression at the southern edge of the Sahara and an area covering eastern Mauritania, Western Mali and southern Algeria.
A little bit of dust blowing around shouldn’t be anything for meteorologists to bother about. This dust, however, is anything but inconsequential- in the Caribbean alone, an estimated 20 million tones are deposited annually. It is the primary source of several essential trace elements, such as calcium and magnesium, to island rain forests whose soils have been leached through tens of thousands of years of erosion. Saharan dust enters the Amazon basin in bursts accompanying major wet season rains, feeding the soil with nutrients that the forest depends on. In fact, scientists now believe the Amazon to be so dependent on aeolian dust inputs that efforts are underway to model long-term expansions and contractions of the world’s largest rain forest in relation to the size of the Sahara over geologic time.
Dust not only nourishes the forests, it moderates their climates. African mineral dust is now considered the dominant light scattering aerosol throughout the tropical and subtropical Atlantic. The ability of airborne dust particles to scatter light decreases the amount of direct solar radiation hitting earth’s surface around the equator.
The dependence of major ecosystems across the world on Saharan dust underscores the deep connectivity of the biosphere, atmosphere, lithosphere and hydrosphere.
1.Goudie, A. & Middleton, N. Saharan dust storms: nature and consequences. EARTH-SCIENCE REVIEWS 56, 179-204 (2001).
2. SWAP, R., GARSTANG, M., GRECO, S., TALBOT, R. & KALLBERG, P. SAHARAN DUST IN THE AMAZON BASIN. TELLUS SERIES B-CHEMICAL AND PHYSICAL METEOROLOGY 44, 133-149 (1992).