Strong winds sweep across the Sahara, a tan cloud rises in the air, stretches between the continents, and ties together the desert and the jungle. It’s dust. And lots of it.
For the first time, a NASA satellite has quantified in three dimensions how much dust makes this trans-Atlantic journey. The above map shows a pictorial representation of dust making the journey.
Scientists have not only measured the volume of dust, they have also calculated how much phosphorus – remnant in Saharan sands from part of the desert’s past as a lake bed – gets carried across the ocean from one of the planet’s most desolate places to one of its most fertile.
This trans-continental journey of dust is important because of what is in the dust. Specifically the dust picked up from the Bodélé Depression in Chad, an ancient lake bed where rock minerals composed of dead microorganisms are loaded with phosphorus.
Phosphorus is an essential nutrient for plant proteins and growth, which the Amazon rain forest depends on in order to flourish. Nutrients – the same ones found in commercial fertilizers – are in short supply in Amazonian soils.
But some nutrients, including phosphorus, are washed away by rainfall into streams and rivers, draining from the Amazon basin like a slowly leaking bathtub. The phosphorus that reaches Amazon soils from Saharan dust, an estimated 22,000 tons per year, is about the same amount as that lost from rain and flooding.