Characterizing and Quantifying African Dust Transport and Deposition to South America: Implications for the Phosphorus Budget in the Amazon Basin

Soils in the Amazon Basin are deficient in phosphorus, essential to soil fertility. Previous studies suggested that African mineral dust deposited to Amazonian soils served as an important source of phosphorus that enhances soil fertility. These studies lacked the quantitative measurements essential to validate estimates. Here we present daily measurements of mineral dust and PM(10)carried in the trade winds at Cayenne, French Guiana, during 2002-2017. MERRA-2 model dust concentrations showed excellent agreement with measurements over this period. Consequently, we used MERRA-2 to estimate temporal and spatial deposition rates to Amazonia. Our annual deposition rate, 8-10 Tg dust, is substantially lower than previous estimates. Deposition rates are greatest over the northern and northeastern regions of South America. In contrast, rates are low in central Amazonia. Our results raise questions about the impact of African dust on soil fertility in Amazonia. However, African aerosol transport carries other aerosol species that could play a role in soil fertility, including biomass-burning products known to contain substantial concentrations of phosphorus. Our study highlights the need for more measurements of aerosol and precipitation chemistry over wider expanses of South America in order to better characterize aerosol chemical and physical properties, to identify aerosol sources, and to constrain model estimates. We show that over 2002-2017 dust transport to South America was negatively correlated to rainfall over the Sahel in North Africa. Long-term monitoring is needed to capture changes in transport from Africa that might occur as a result of climate change.