A new study led by researchers at the Rosenstiel School of Marine and Atmospheric Sciences at the University of Miami (UM) has found that smoke from fires in Africa may be the most important source of phosphorus, a key nutrient that acts as a fertilizer in the Amazon rainforest, the tropical Atlantic and the southern oceans.
The nutrients found in atmospheric particles, called aerosols, are transported by winds and deposited in the ocean and on land, where they stimulate the productivity of marine phytoplankton and terrestrial plants that lead to the ‘containment’ of atmospheric carbon dioxide.
“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,” said the study’s senior author Cassandra Gaston, an assistant professor in the Department of Atmospheric Sciences at the UM Rosenstiel School.
The researchers’ findings reveal that “biomass burning emissions transported from Africa are potentially a more important source of phosphorus for these ecosystems than dust,” explains Gaston.
To carry out the study, the researchers analyzed the aerosols collected in the filters of a hill in French Guiana, at the northern end of the Amazon basin, in search of massive concentrations of dust carried by the wind and its total and soluble phosphorus content. The researchers then tracked the smoke that moved through the atmosphere using satellite remote sensing tools to understand long-range smoke transport from Africa during periods when high levels of soluble phosphorus were detected.
Then they were able to estimate the amount of phosphorus deposited in the Amazon basin and the global oceans from African aerosols that burn biomass using a transport model.
The study concluded that smoke from widespread biomass burning in Africa, primarily the result of land clearing, forest fires, as well as industrial combustion emissions, is potentially a more important source of phosphorus for the Amazon rainforest and the tropical Atlantic and the southern oceans that the dust of the Sahara Desert.
“To our surprise, we discovered that phosphorus associated with smoke from southern Africa can be blown all the way to the Amazon and, potentially, out over the Southern Ocean where it can impact primary productivity and the drawdown of carbon dioxide in both ecosystems,” said UM Rosenstiel School graduate student Anne Barkley, lead author of the study.
“Aerosols play a major role in Earth’s climate, however, there is a lot that we don’t understand regarding how they affect radiation, clouds, and biogeochemical cycles, which impedes our ability to accurately predict future increases in global temperature,” said Gaston. “These new findings have implications for how this process might look in the future as combustion and fire emissions in Africa and dust transport patterns and amounts change with a changing climate and an increasing human population.”