An estimated 22,000 tonnes of phosphorus, an essential nutrient for plant proteins and growth, is carried by the dust from Sahara Desert to the Amazon rain forest every year, a new study has found.
A NASA satellite has quantified how much dust makes the trans-Atlantic journey from the Sahara Desert to the Amazon rain forest.
Scientists have measured the volume of dust and 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.
The study is the first satellite-based estimate of this phosphorus transport over multiple years, said lead author Hongbin Yu, an atmospheric scientist at the University of Maryland who works at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
This trans-continental journey of dust is important because of what is in the dust, Yu said.
Specifically the dust picked up from the Bodele 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 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 said.
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, satellite from 2007 through 2013.
The data show that wind and weather pick up on average 182 million tonnes of dust each year and carry it past the western edge of the Sahara. This volume is the equivalent of 689,290 semi trucks filled with dust.
The dust then travels 2,574 km across the Atlantic Ocean, though some drops to the surface or is flushed from the sky by rain.
Near the eastern coast of South America, 132 million tonnes remain in the air, and 27.7 million tonnes - enough to fill 104,908 semi trucks - fall to the surface over the Amazon basin.
About 43 million tonnes of dust travel farther to settle out over the Caribbean Sea.
