While the Sahara Desert and the rainforests of the Amazon seem a world apart -- or at least continents apart -- Earth's largest temperate desert is largely responsible for the lushness of its largest tropical rainforest, a study shows.

Each year, many millions of tons of dust rich in nutrients from the Sahara's huge expanse of scrub and sand cross over the Atlantic Ocean, carrying phosphorus and other vital fertilizers to the depleted soils of the Amazon's dense mass of humid jungle, scientists say.

While the intercontinental link has been known for some time, researchers have now been able estimate for the first time just how much phosphorous makes the globe-spanning journey.

Around 22,000 tons of Sahara phosphorous ends up in the Amazon each year, roughly the same amount the South American jungle soils lose annually to rain and resulting flooding, the researchers report in the journal Geophysical Research Letters.

Of the 27.7 million tons of desert dust carried across the Atlantic to the Amazon each year, the phosphorous accounts for just 0.08 percent of that mass.

The researchers studied the fertilizing components of the dust as part of a larger research effort aimed at understanding what role dust plays in the environment and in climate, both globally and locally.

"We know that dust is very important in many ways," says study leader Hongbin Yu, a research scientist at the Earth System Science Interdisciplinary Center, a collaboration of the University of Maryland and NASA's Goddard Space Flight Center.

"It is an essential component of the Earth system," Yu says. "Dust will affect climate and, at the same time, climate change will affect dust."

Yu and his research colleagues focused on dust that is picked up by winds in the Bodélé Depression in Chad, a prehistoric lake bed containing massive sediments of dead microorganisms loaded with phosphorus.

Phosphorous and other nutrients are exactly what Amazon soils are always in need of, as flooding caused by the jungle basin's frequent heavy downpours continually washes them away.

Saharan dust conveyed across the Atlantic Ocean to South America is the largest transport of dust on the planet, the researchers explain.

The researchers studied 7 years' worth of data on samples of dust from the Bodélé Basin and from soils in South America.

Because the year-to-year pattern proved highly variable, the data record is too short to make firm conclusions about long-term trends, Yu says, but represents a vital step in understanding how the dust behaves as it moves halfway around the world, bringing sustenance to the Amazonian rainforests.

"This is a small world, and we're all connected together," he says.