Earth
Does dust from the Sahara feed the Amazon rainforest?
The short answer
Yes. A NASA satellite measured about 27.7 million tons of Saharan dust blowing across the Atlantic to the Amazon basin each year, carrying roughly 22,000 tons of phosphorus. That is about the amount of phosphorus the rainforest loses every year to rain and floods, so the desert is topping up the jungle.
It sounds like a children's story: the driest place on one continent keeps the lushest place on another alive. But the physics is plain. Wind lifts fine dust off the Sahara, trade winds carry it 5,000 kilometres west over the Atlantic, and rain washes it out over South America.
NASA's CALIPSO satellite used a laser to measure the dust plume in three dimensions over seven years. The average was 182 million tons leaving Africa annually, about 27.7 million tons of which settled over the Amazon basin. The rest fell into the sea or carried on to the Caribbean.
The important ingredient is phosphorus, a nutrient plants cannot do without and which Amazon soils are chronically short of because the rain keeps washing it away. Much of the dust comes from an ancient dried-up lake bed in Chad, the Bodélé Depression, whose floor is made of the remains of microscopic organisms, rich in exactly that mineral. The rainforest is being fed by a lake that evaporated thousands of years ago, on another continent.