The Sahara Desert and the Amazon rainforest seem to inhabit separate worlds. The former is a vast expanse of sand and scrub stretching across the northern third of Africa, while the latter is a dense green mass of humid jungle covering northeast South America. And yet, they are connected: every year, millions of tons of nutrient-rich Saharan dust cross the Atlantic Ocean, bringing vital phosphorus and other fertilizers to depleted Amazon soils. For the first time, scientists have an accurate estimate of how much phosphorus makes this trans-Atlantic journey. A new paper, accepted for publication Feb. 24, 2015 in the journal Geophysical Research Letters, puts the number at about 22,000 tons per year, which roughly matches the amount that the Amazon loses from rain and flooding.

This phosphorus accounts for just 0.08% of the 27.7 million tons of Saharan dust that settles in the Amazon every year. The finding is part of a bigger research effort to understand the role of dust 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," said lead author Hongbin Yu, an associate research scientist at the Earth System Science Interdisciplinary Center (ESSIC), a joint center of the University of Maryland and NASA's Goddard Space Flight Center.