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Characterization of Coarse-Mode, Iron-Containing Aerosols Transported to South America: Implications for Biogeochemical Cycles and Radiative Balance
ANNE BARKLEY, Nicole Olson, Joseph M. Prospero, Alexandre Gatineau, Kathy Panechou, Nancy Maynard, Patricia Blackwelder, Swarup China, Andrew Ault, Cassandra Gaston, University of Miami
Abstract Number: 207
Working Group: Aerosols, Clouds and Climate
Abstract
The long-range transport and subsequent deposition of nutrients associated with African aerosol to South America fertilizes nutrient-depleted ecosystems, such as the Amazon and Tropical Atlantic Ocean (TAO). Quantifying the physio-chemical properties of long-range transported aerosols is important both for nutrient delivery and the radiative properties. In this work, we collected African aerosol at a coastal site on the northeast coast of the Amazon Rainforest in South America from February to March 2016. Using scanning electron microscopy (SEM) coupled to energy dispersive X-ray spectrometry (EDX), we detected a wide diversity of iron (Fe) containing, coarse-mode particles including mineral dust, freshwater diatoms (FDs), primary biological aerosol particles (PBAPs), and biomass burning aerosols. Number size distributions for FDs peaked between 7.6 and 10 μm and PBAPs peaked between 10.0 and 17.7 μm. Additionally, we show that with increasing particle size, FDs and PBAPs made up a larger percentage of particles. These findings highlight that long-range transported aerosols can be larger than predicted by gravitational settling. We also found that the FDs, likely from paleo-lakes within the Saharan, often contained inclusions of mineral dust within the holes in their frustules and were more aspherical than mineral dust particles. Using elemental mapping, we show that these FDs with mineral dust contain small “hotspots” of Fe. We propose that FDs facilitate increased nutrient transport because they are more easily kept aloft due to their large aspect ratios, light density, and high surface area-to-volume ratios. Thus, these FDs could be vectors for increased nutrient transport to the Amazon and western TAO. Our findings contribute to the growing literature that show coarse and super-coarse mode aerosol are globally important aerosols and need to be included in global biogeochemical and radiative balance models.