The Amazon rainforest is fertilized in part by phosphorus from a dry lake bed in the Sahara desert, researchers say in a new report that shows how different parts of our planet are connected in deep and surprising ways.
The findings were published Tuesday in Geophysical Letters.
Scientists have known for decades that great plumes of dust get lifted by winds and weather from the largest desert in the world and travel thousands of miles across the Atlantic Ocean, eventually coming to rest in the Amazon basin.
Each individual dust particle is just a fraction of the width of a human hair, but together they make up a vast tan dust cloud so large it can be seen from space.
In 2006 NASA launched the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation satellite, known as CALIPSO, to look at the vertical structure of clouds and airborne particles around the globe. Now, data collected from that satellite have revealed for the first time how much Saharan dust is moving across the Atlantic into South America.
In a paper published in the journal Remote Sensing of the Environment, University of Maryland atmospheric scientist Hongbin Yu, reported that an average of 182 million tons of dust get carried past the western edge of the Sahara each year, and 28.8 million tons of that dust settle in the Amazon basin.
That is the equivalent of 689,290 semi-trucks filled with the dust leaving the desert and the dumping of 104,908 dust-filled semi-trucks in the Amazon a year, according to a NASA release.
An even more recent paper also by Yu, published Tuesday in Geophysical Letters, provides the first satellite-based estimate of how much phosphorus is in that dust.
Phosphorus is an essential nutrient for plant growth, but previous research has shown that 90% of the soil in the Amazon is phosphorus-deficient. Scientists say that rain and rivers wash many of the nutrients, including phosphorus, right out of the forest.
However, across the Atlantic, the Sahara is loaded with phosphorus. Much of it comes from an ancient lake bed called the Bodele Depression in Chad.
After analyzing the satellite data, as well as dust samples collected from research stations in Chad, Barbados and Miami, the researchers concluded that 22,000 tons of phosphorus arrive in the Amazon from the Sahara each year -- roughly the same amount as gets washed away.
Of course, this is science, so it's not as neat and tidy as it sounds: The researchers also found major fluctuations in the amount of dust that gets swept across the Atlantic each year. There was an 86% difference between the largest dust plume seen, in 2007, and the smallest, in 2011.
They did find that the previous year's rainfall in the Sahel -- a strip of land on the Southern border of the Sahara -- may have something to do with it. When rainfall in the Sahel was higher, the amount of dust that got transported went down. However, they can't yet explain the correlation.
It's just another interconnection to explore.