Africa and South America are separated by an ocean. Yet every year, winds lift dust from North Africa high into the air, and some of it settles on the Amazon rainforest.
Inside that dust is phosphorus, a nutrient plants need. That much is real. The neat story about what happens next is where it gets interesting.
The Atlantic is no wall to dust.
NASA's CALIPSO satellite has tracked the plumes leaving the western edge of the Sahara and crossing about 2,600 km (1,600 miles) of ocean. Some of that dust settles over the Amazon, mostly between December and May.
Why would that matter?
Phosphorus is scarce in old, heavily weathered tropical soils. In a 2022 experiment in the central Amazon, on low-phosphorus soil typical of about 60% of the basin, forest productivity rose only when phosphorus was added.
In 2015, a satellite put a number on it.
Using CALIPSO data from 2007 to 2013, a NASA-led team estimated that about 28 million tonnes (31 million US tons) of African dust settled on the Amazon basin a year.
For the phosphorus, they used a value measured in dust from the Bodélé Depression in Chad, a dried ancient lake bed. That doesn't mean all the dust came from there. The result: roughly 22,000 tonnes (24,000 US tons) of phosphorus a year, similar to what the basin was estimated to lose as water washes it out.
That created the famous picture of Africa topping up the Amazon's losses. The paper was more careful: dust may help prevent phosphorus depletion over decades to centuries, and the forest recycles 60 to 180 times more through falling leaves.
Then a later study found far less dust.
In 2020, a team including a 2015 co-author paired 15 years of daily dust measurements in Cayenne, French Guiana, with a model. Their estimate: about 8–10 million tonnes (9–11 million US tons) a year, mostly over northern South America, with low rates in central Amazonia. The authors said this raises questions about dust's effect on Amazon soil fertility.
That doesn't make either study simply wrong. They used different data, methods and study areas, and direct measurements across the forest are scarce.
Not all of Africa's phosphorus arrives as dust.
A 2019 study at Cayenne found dust supplied most of the phosphorus in spring, when dust peaks. In autumn, smoke from southern African fires brought more of the soluble kind. A model suggested this smoke supplies up to half of the phosphorus deposited on the Amazon each year from African aerosols: half of Africa's airborne delivery, not of the forest's phosphorus.
African dust really does carry phosphorus across an ocean to the Amazon. How much, and how much it matters to the forest, is still being worked out.
On a map, the Atlantic separates Africa from the Amazon. In the air, it's more of a corridor, even if nobody yet knows how much travels along it.
Sources checked 13 October 2026·5 sources ↓