AFRICA/S.AMERICA – Smoke from fires in southern Africa is the largest contributor of phosphorus — an important agricultural fertilizer — to the Amazon rainforest, Tropical Atlantic and Southern oceans, according to new research published in the Proceedings of the National Academy of Sciences.
Nutrients found in atmospheric particles are transported by winds and deposited to the ocean and on land where they stimulate the productivity of marine phytoplankton and terrestrial plants leading to the sequestration 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 Dr. Cassandra Gaston, a researcher in the Rosenstiel School of Marine and Atmospheric Sciences at the University of Miami and senior author of the study.
“Our findings reveal that biomass burning emissions transported from Africa are potentially a more important source of phosphorus to these ecosystems than dust.”
Dr. Gaston’s team analyzed aerosols collected on filters from a hilltop in French Guiana, at the northern edge of the Amazon basin, for mass concentrations of windborne dust and their total and soluble phosphorus content.
They then tracked the smoke moving through the atmosphere using satellite remote sensing tools to understand the long-range transport of smoke from Africa during time periods when elevated levels of soluble phosphorus were detected.
They were then able to estimate the amount of phosphorus deposited to the Amazon basin and the global oceans from African biomass burning aerosols using a transport model.
The analysis concluded that the smoke from widespread biomass burning in southern Africa, mostly the result of land clearing, brush fires and industrial combustion emissions, is potentially a more important source of phosphorus to the Amazon rainforest and Tropic Atlantic and Southern oceans than dust from 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 study first author Anne Barkley, a graduate student at the University of Miami.
Anne E. Barkley et al. African biomass burning is a substantial source of phosphorus deposition to the Amazon, Tropical Atlantic Ocean, and Southern Ocean. PNAS, published online July 29, 2019; doi: 10.1073/pnas.1906091116