February 25, 2015
NASA: Amazonian rain forest highly dependent on Saharan dust
The Amazonian rain forest and the Sahara desert are both very distant and very different from each other. However, the South American rain forest just might be highly dependent on dust it gets from the Sahara that is swept across the Atlantic by global winds.[VIDEO: Satellite tracks Saharan dust to Amazon in 3D]
According to a new study published Geophysical Research Letters, about 27.7 million tons of Sahara dust is transported to the Amazon each year. The study’s findings are based on several years worth of three-dimensional models showing dust clouds streaming across the equatorial Atlantic.
"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 study author Hongbin Yu, an atmospheric scientist at the University of Maryland.
"First we have to try to answer two basic questions,” Yu added. “How much dust is transported? And what is the relationship between the amount of dust transport and climate indicators?"
The researchers gathered data for their models from NASA's Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite. The team used data from 2007 though 2013 and found that more than 180 million tons of dust each year leaves the western edge of the Sahara. Most of the dust journeys 1,600 miles across the Atlantic and almost 28 million tons makes it all the way to the Amazon basin. Approximately 43 million tons of dust journey farther and drop over the Caribbean.
The study team said they are particularly interested in the amount of phosphorus, an essential nutrient, being deposited to the Amazon. To determine ratio of phosphorus in Saharan dust, the study team collected dust samples from ground stations on Barbados and in Miami. This approximation is used to determine how much phosphorus gets lodged in the Amazon basin from the Sahara.
While the length of the study is too short to understand long-term trends, it does show – for the first time ever – how dust and other aerosols move across the ocean. The team did see that the system is quite variable, with an 86 percent change between the highest point in 2007 and the low point in 2011. They said rainfall in the Sahel, a strip of semi-arid land along the southern border of the Sahara, might be a factor in that variation.
Though the use of CALIPSO data, the researchers were able to visualize the "curtains" of dust layers across a range of altitudes in the atmosphere. The study team said the data could be also useful in seeing how the dust interacts with Earth's climate-generating factors.
"Wind currents are different at different altitudes," noted Chip Trepte, a CALIPSO scientist at NASA's Langley Research Center who was not involved in the study. "This is a step forward in providing the understanding of what dust transport looks like in three dimensions, and then comparing with these models that are being used for climate studies."