What connects Earth's largest, hottest desert to its largest tropical rainforest? The answer is 22,000 tonnes of dust per year.
For the first time, a NASA satellite has quantified in three dimensions how much dust makes the trans-Atlantic journey from Sahara desert to the Amazon rainforest.
The Sahara desert is a near-uninterrupted brown band of sand and scrub across the northern third of Africa.
The Amazon rainforest is a dense green mass of humid jungle that covers northeast South America.
Scientists have not only measured the volume of dust, they 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," said lead author Hongbin Yu, atmospheric scientist at the University of Maryland who works at NASA's Goddard Space Flight Centre in Greenbelt, Maryland.
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Nutrients - the same ones found in commercial fertilisers - are in short supply in Amazonian soils.
Instead, they are locked up in the plants themselves.
Fallen, decomposing leaves and organic matter provide the majority of nutrients which are rapidly absorbed by plants and trees after entering the soil.
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 tonnes per year, is about the same amount as that lost from rain and flooding," Yu noted.
Dust is very important in many ways. It is an essential component of the Earth system.
"Dust will affect climate and, at the same time, climate change will affect dust," Yu pointed out.
The new dust transport estimates were derived from data collected by a lidar instrument on NASA's Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation, or CALIPSO, a satellite from 2007 though 2013, the US space agency said in a statement.