Sahara Dust: Rainforest Fertilizer Comes From Tiny Source
More than half of the dust that falls in the Amazon rainforest and provides much-needed minerals comes from a single small region in the Sahara. It has now been located by a team led by Ilan Koren from the Israeli Weizmann Institute in Rehovot using satellite image analysis.
Although the responsible Bodélé Depression in Chad makes up only 0.2 percent of the world's largest desert, it is its most prolific source of dust, averaging 700,000 tons of fines per dust storm day. The emission process is particularly active during the winter and spring months, while the weather in large parts of the rest of the Sahara is rather calm during this time.
According to Koren, a special combination of geographical location and the prevailing weather conditions causes this productive fine material transport. The Bodélé depression is located at the exit of a crater-like valley between the Tibesti and Ennedi mountains, which narrows towards the end of the valley, thereby focusing the wind currents and increasing their speed. When the strong desert winds known as harmattan then blow closer to the southern border of the Sahara to the Sahel in winter, strong gusts also occur in nearby Bodélé, which whirl up dust grains up to higher atmospheric levels, where they can be transported west with trade winds.
They provide the tropical rainforest of Amazonia with urgently needed nutrients, as large parts of the ecosystem grow on very old and correspondingly poor soil. Some scientists even suspect that without this external supply of minerals, the rainforest would be replaced by vegetation with a much lower species population.