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It is one of the most unlikely links on Earth.

A new Nasa satellite has revealed the stunning link between the Sahara desert and the Amazon rainforest. 

For the first time it showed vast dust clouds travelling high in the atmosphere.

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Nasa's Calipso collects 'curtains' of data that show valuable information about the altitude of dust layers in the atmosphere.

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 is a small world,' said 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.

'And we're all connected together.'

A new paper published Feb. 24 in Geophysical Research Letters, a journal of the American Geophysical Union, provides the first satellite-based estimate of this phosphorus transport over multiple years.

A second paper published online by Yu and colleagues Jan. 8 in Remote Sensing of the Environment provided the first multi-year satellite estimate of overall dust transport from the Sahara to the Amazon.

It is the first time a Nasa satellite has quantified in three dimensions how much dust makes this trans-Atlantic journey.

This trans-continental journey of dust is important because of what is in the dust, Yu said. 

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. 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. 

The data show that wind and weather pick up on average 182 million tons of dust each year and carry it past the western edge of the Sahara at longitude 15W.

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, Yu said. 

The finding is part of a bigger research effort to understand the role of dust and aerosols in the environment and on local and global climate. 

'We know that 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,' said Yu.  

This volume is the equivalent of 689,290 semi trucks filled with dust.

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 though 2013. 

Yu and colleagues focused on the Saharan dust transport across the Atlantic Ocean to South America and then beyond to the Caribbean Sea because it is the largest transport of dust on the planet.

Dust collected from the Bodélé Depression and from ground stations on Barbados and in Miami give scientists an estimate of the proportion of phosphorus in Saharan dust. 

THE CALIPSO SATELLITE

CALIPSO collects 'curtains' of data that show valuable information about the altitude of dust layers in the atmosphere.

CALIPSO sends out 20 laser pulses every second, and each is only 20 billionths of a second long. 

Knowing the height at which dust travels is important for understanding, and eventually using computers to model, where that dust will go and how the dust will interact with Earth's heat balance and clouds, now and in future climate scenarios. 

This estimate is used to calculate how much phosphorus gets deposited in the Amazon basin from this dust transport. 

Looking at the data year by year shows that that pattern is actually highly variable. 

There was an 86 percent change between the highest amount of dust transported in 2007 and the lowest in 2011, Yu said. 

NASA reveals how dust from the Sahara fertilizes the AMAZON

'Wind currents are different at different altitudes,' said Trepte. 

'This is a step forward in providing the understanding of what dust transport looks like in three dimensions, and then comparing with these models that are being used for climate studies.'

Climate studies range in scope from global to regional changes, such as those that may occur in the Amazon in coming years. 

In addition to dust, the Amazon is home to many other types of aerosols like smoke from fires and biological particles, such as bacteria, fungi, pollen, and spores released by the plants themselves.

In the future, Yu and his colleagues plan to explore the effects of those aerosols on local clouds – and how they are influenced by dust from Africa.