African smoke is ‘fertilising the Amazon’


It may even have an impact in the Southern Ocean, new study finds.


A controlled burn in Burkina Faso, West Africa. The impact may have been felt far afield.

DE AGOSTINI PICTURE LIBRARY / GETTY IMAGES

Smoke from widespread biomass burning in Africa – mostly the result of land clearing, brush fires and industrial combustion emissions – may be the most important source of the phosphorus that fertilises the Amazon rainforest, new research shows.

Nutrients found in atmospheric particles, called aerosols, are transported by winds and deposited on land and sea, where they stimulate the productivity of marine phytoplankton and terrestrial plants leading to the sequestration of atmospheric carbon dioxide.

It has long been assumed that Saharan dust is the main fertiliser to the Amazon Basin and the Tropical Atlantic Ocean, says Cassandra Gaston from the University of Miami in the US, but her work with colleagues from UM and the ATMO Guyane in French Guiana suggests otherwise.

The findings are published in the journal Proceedings of the National Academy of Sciences.

The researchers analysed 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.

From this they were 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.

"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," says lead author Anne Barkley.

Gaston says there is a lot that we don't understand regarding how aerosols affect radiation, clouds and biogeochemical cycles, which “impedes our ability to accurately predict future increases in global temperature”.

"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."

  1. https://www.pnas.org/content/early/2019/07/23/1906091116
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