Why the Sahara Is Intricately Tied to the Amazon

The Sahara's dust is full of phosphorus and other fertilizers that end up in the Amazon's soils. cosmo_71 [CC by 2.0]/Flickr

On the surface, the Sahara Desert and Amazon rain forest don't seem to have much in common. One is dry and mostly filled with sand. The other is lush, green and one of the best examples of biodiversity on the planet. And yet, according to new research, the Sahara plays a critical role in the health of the Amazon by delivering millions of tons of nutrient-rich dust across the Atlantic, replenishing the rain forest’s soil with phosphorus and other fertilizers.

Researchers revealed in a paper published in the journal Geophysical Research Letters that about 22,000 tons of phosphorus get blown across the Atlantic Ocean. And it's a good thing, considering that number mirrors the estimated amount of phosphorus the Amazon loses each year due to rain and flooding.

This finding about the Sahara’s role in the health of the Amazon’s soil is just one data point in research pondering the bigger picture. Scientists are trying to better understand how dust affects the 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 lead author, Hongbin Yu.

Between 2007 and 2013, the scientists used NASA’s Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite to study the movement of dust on its journey from the Saharan to across the Atlantic Ocean and into South America and then beyond to the Caribbean Sea. This is believed to be the largest transport of dust on Earth.

Using samples from Chad's Bodélé Depression, a lake bed filled with dead and phosphorus-rich microorganisms, and from areas in Barbados and Miami, scientists were able to calculate how much phosphorus ends up in the Amazon basin.

While 22,000 tons of phosphorus sounds like a lot, it’s actually just 0.08 percent of the 27.7 million tons of dust that end up in the Amazon each year.

Amazon rain forest
The Amazon rain forest owes some of its lushness to the dust of the Sahara. Egon Zitter/Shutterstock

The scientists acknowledge that seven years is too short a time to draw conclusions about long-term trends in the transportation of dust, but the findings are a great start to learning more about how dust and other windborne particles move across the ocean and interact with faraway climates.

NASA scientist Chip Trepte, who was not involved in the study but who works with CALIPSO, said, "We need a record of measurements to understand whether or not there is a fairly robust, fairly consistent pattern to this aerosol transport.”

Right now, the numbers gathered vary widely from year to year, the largest change found between 2007 and 2011 where there was an 86 percent difference between the lowest and highest amount of transported dust recorded.

The researchers believe that the variations can be attributed to the amount of rainfall that takes place in the semi-arid land that borders the Sahara. Years when rainfall was higher were followed by lower years of dust transport. In the press release, they speculated that rain could lead to more vegetation causing less soil to be exposed to wind erosion. Another theory is that the amount of rainfall could impact the wind circulation patterns that cause dust to get brought across the ocean.

Whatever the reason behind the changes from year to year, Yu concludes, "This is a small world, and we're all connected together.”