TWIL #034 - The Sahara Desert Feeds the Amazon Rainforest
Every year, billions of tonnes of Saharan dust cross the Atlantic Ocean and land in the Amazon - delivering the phosphorus that the entire rainforest depends on.
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The Amazon rainforest is one of the most biodiverse places on Earth, but its soil is surprisingly poor. The constant tropical rainfall leaches minerals - particularly phosphorus - out of the ground faster than decomposition can replenish them. The rainforest should, in principle, be running a phosphorus deficit.
It isn't, because of the Sahara.
Every year, strong winds over the Sahara Desert loft enormous quantities of fine mineral dust into the upper atmosphere. A significant portion of this - estimated at around 22,000 tonnes of phosphorus annually - is carried west across the Atlantic Ocean by trade winds and deposited over the Amazon basin. The dust settles with the rain and becomes available to plants and soil organisms.
The specific source area is the Bodélé Depression in northeastern Chad - the remains of an ancient mega-lake called Lake Mega-Chad that dried up thousands of years ago. The lake bed is rich in diatom fossils whose silica shells contain high concentrations of phosphorus. As the surface erodes, this ancient biological material becomes Saharan dust.
NASA satellite data has tracked the dust transport path in detail. The same wind system also carries Saharan dust to the Caribbean, where it fertilises coral reef ecosystems.
Two ecosystems separated by 5,000 km, one of them a desert and one the most productive forest on Earth, connected by a river of ancient dust in the sky.