New research from the University of Miami's Rosenstiel School of Marine shows that African wildfires supply the Amazon with vital nutrients.
The team reports that winds blow nutrient-rich aerosol (i.e. smoke) from Africa that keep the Amazon Basin fertile. These aerosols are estimated to deposit around one half of the phosphorus that plant life in the Basin consumes. In effect, this makes the African continent a key player in the Amazonian ecosystem.
Airmail nutrients
"It had been assumed that Saharan dust was the main fertilizer to the Amazon Basin and Tropical Atlantic Ocean by supplying phosphorus to both of these ecosystems," says the study's senior author Cassandra Gaston, an assistant professor in the Department of Atmospheric Sciences at UM's Rosenstiel School.
"Our findings reveal that biomass burning emissions transported from Africa are potentially a more important source of phosphorus to these ecosystems than dust."
Previous research has shown that dust blown over from the Sahara and other desert regions in Africa act as sources of nutrients for South America. The role of smoke in this, however, was still unknown.
Besides seeding the Amazonian Basin with phosphorus -- enabling its wealth of biodiversity and productivity to sequester significant amounts of atmospheric carbon dioxide -- the team also found that these aerosols fertilize the Tropical Atlantic and Southern oceans (TAO), sustaining the phytoplankton that is the basis of the marine ecosystem in the region.
The findings are based on measurements of windborne dust, phosphorus and soluble phosphorus Amazon's northeastern coast. The team also tracked winds from the African continent using satellite data.
Wind-borne dust wasn''t very rich in phosphorus. The team reports that it actually acts as the area's main supply of low-solubility phosphorus (P) in February through April contributing around 5%. September through November, however, the team recorded high levels of soluble P originating from biomass fires in Southern Africa. This also coincided with the season when dust deposits are lower.
The team crosschecked their findings by identifying aerosols from Africa on high-soluble-P measurement days using satellite imagery. They also traced back all high-soluble-P aerosols in air masses that had passed over the Sahara and the Sahel where biomass burning was active.
The team says their findings offer a new perspective on biomass-burning emissions, which are considered primarily destructive in terms of air quality. While such events are known to promote new growth in their wake, it's exciting to see how it can affect developments on a whole other continent.
It also helps explain how the Amazon Basin manages to retain its immense biodiversity and productivity despite heavy, year-round rainfall, which drains the soil of nutrients. It dentifies an important nutrient source for marine ecosystems in the region.
The paper "African biomass burning is a substantial source of phosphorus deposition to the Amazon, Tropical Atlantic Ocean, and Southern Ocean" has been published in the journal PNAS.
