dust from Saharan desert

A Small World. How the Saharan Desert and the Amazon Rainforest are Linked

Dust from the Saharan desert in Africa helps replenish nutrients in the lush forests of the Amazon rainforest. Nutrients are hard to come by in the soil in the Amazon rainforest. Decomposing leaves and other organic matter are the primary source of nutrients. These are used up quickly by surrounding plants and trees after hitting the soil.

Some nutrients also wash away before the Amazon rainforest can use them all. One of them is phosphorus. This nutrient is essential for the Amazon basin to flourish. And, the Saharan desert is rich in it.

Saharan dust, and the phosphorus in it, is swept to the Amazon basin by strong winds. A new paper was published this week that provides the first satellite-based estimate of how much phosphorus flows from one of the most desolate places on Earth to one of the most lush.

Lead author Hongbin Yu, an atmospheric scientist at the University of Maryland who also works at NASA’s Goddard Space Flight Center, along with his colleagues examined dust picked up in the Sahara desert. Specifically, dust from the Bodélé Depression in Chad. This ancient lake bed has rock minerals composed of dead microorganisms that are rich with phosphorus.

“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. Understanding these effects requires answer two questions according to Yu. “How much dust is transported? And what is the relationship between the amount of dust transport and climate indicators?”

Using NASA’s Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation, or CALIPSO, researchers found that 182 million tons of dust is swept from the Saharan desert every year on average. 27 million tons of it reach the Amazon basin. The amount of phosphorus in this 27 million tons of dust comes to about 22,000 tons per year. This offsets the phosphorus loss from rain and flooding in the Amazon basin.

The team of researchers also found the amount of dust fluctuates quite a bit. Year by year data shows an 86% change between the highest amount of dust transported (2007) and the lowest (2011). Yu and his colleagues believe this variation is due to climate conditions in the Sahel, a long strip of semi-arid land on the southern border of the Sahara.

Researchers found that the amount of rainfall in the Sahal dictated how much dust would be transported the following year. Heavier rains mean lower amounts of dust and vice versa.

The precise mechanism behind this isn’t known. One possibility is the increase in rainfall leads to more vegetation and less soil exposed to strong winds. Yu believes the more likely explanation is the amount of rainfall is related to the circulation of winds.