The Sahara is a favorite subject for astronauts aboard the International Space Station, who frequently snap photos of the desert's vast expanse and impressive dust storms from 260 miles above Earth.
While the trails of dust migrating over the Atlantic Ocean are beautiful, they're also important for scientists looking to understand Earth's climate and the ecology of South America's equally impressive Amazon. For the first time, the dust's annual journey from North Africa across the ocean to South America has been modeled in three dimensions, using seven years of NASA data.
The space agency's CALIPSO satellite measured the amount of dust that travels from an ancient lake bed in Chad known as the Bodélé Depression to the Amazon. I also calculated the amount of phosphorous in the dust, a crucial nutrient for Amazon soils.
For the first time, a NASA satellite has quantified in three dimensions how much dust makes the trans-Atlantic journey from the Sahara Desert to the Amazon rainforest. Among this dust is phosphorus, an essential nutrient that acts like a fertilizer, which the Amazon depends on in order to flourish. (Video via NASA/Goddard)
They found that an average of 182 million tons of dust leaves Chad each year. About 27.7 million tons of it — enough to fill more than 100,000 semi trucks — makes it to the Amazon, bringing with it an estimated 22,000 tons of phosphorous, roughly equivalent to the amount that rain removes from the soil by washing it into waterways.
But the amount of dust varied significantly from year to year, largely depending on the rainfall along the Sahara's southern border. That could be due to changes in vegetation and soil erosion, the relationship between rainfall and wind circulation, or some other factor as yet unidentified by researchers.
Unravelling the intricacies of this relationship could produce an important contribution to the field of aerosol research, which studies how tiny particles in the atmosphere, like dust and pollutants, affect cloud formation and other aspects of Earth's climate system. Because wind currents vary at different altitudes, studying dust patterns in three dimensions could help improve aerosol models.
"Dust will affect climate and, at the same time, climate change will affect dust," Hongbin Yu, an Earth scientist at NASA's Goddard Space Flight Center, said. "To understand what those effects may be, first we have to try to answer two basic questions. How much dust is transported? And what is the relationship between the amount of dust transport and climate indicators?"
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