How Saharan Dust Fertilizes Amazon Rainforest

You would think that the Saharan Desert and Amazon rainforest are worlds apart. The African Sahara is a vast expanse of hot sand and arid air, while the Amazon is miles of lush, humid jungle covering northeast South America. But despite their stark contrasts, they are intimately connected. New research shows that each year, millions of tons of nutrient-rich Saharan dust crosses the Atlantic Ocean and fertilizes the Amazon rainforest.

This trans-Atlantic journey, described in the journal Geophysical Research Letters, provides insight into the role dust plays in the environment and its effects on local and global climate.

"We know that dust is very important in many ways. It is an essential component of Earth system. Dust will affect climate and, at the same time, climate change will affect dust," study lead author Hongbin Yu said in a press release.

Yu and his colleagues focused on dust picked up from the Bodélé Depression in Chad in particular. This ancient lake bed contains huge deposits of dead microorganisms that are loaded with phosphorus - a vital nutrient that the Amazon lacks. Phosphorus and other important nutrients get washed away from Amazonian soils by frequent and heavy rainfall each year.

Saharan dust, it turns out, is key to replenishing these lost nutrients.

To determine how much phosphorus dust in the Sahara contains, the researchers used satellites to study samples from the Bodélé Depression and from ground stations on Barbados and in Miami - since the dust travels across the Atlantic Ocean to South America and beyond.

They came up with the most accurate estimate of trans-Atlantic dust to date. A whopping 22,000 tons of phosphorus makes its way to the Amazon each year - that's roughly the equivalent of how much the Amazon loses from rain and flooding.

What's more, this phosphorus accounts for just 0.08 percent of the 27.7 million tons of Saharan dust that annually settles in the Amazon basin.

However, exactly how much dust makes the trip varies from year to year. For example, there was an 86 percent change between the highest amount of dust transported in 2007 and the lowest in 2011.

Yu and his colleagues have yet to understand the underlying mechanism behind this correlation, but this new study shows just how interconnected the world really is.

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