Trace Metal Fractional Solubility in Size‐Segregated Aerosols From the Tropical Eastern Atlantic Ocean

Alex R. Baker,Rosie Chance,Mingpei Li

doi:10.1029/2019gb006510

Alex R. Baker, Rosie Chance + Show 1 more

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https://doi.org/10.1029/2019gb006510

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Abstract

AbstractSoluble and total trace metals were measured in four size fractionated aerosol samples collected over the tropical eastern Atlantic Ocean. In samples that were dominated by Saharan dust, the size distributions of total iron, aluminum, titanium, manganese, cobalt, and thorium were very similar to one another and to the size distributions of soluble manganese, cobalt, and thorium. Finer particle sizes (< ~3 μm) showed enhanced soluble concentrations of iron, aluminum, and titanium, possibly as a result of interactions with acidic sulfate aerosol during atmospheric transport. The difference in fine particle solubility between these two groups of elements might be related to the hyperbolic increase in the fractional solubility of iron, and a number of other elements, during the atmospheric transport of Saharan dust, which is not observed for manganese and its associated elements. In comparison to elements whose solubility varies during atmospheric transport, the stability of thorium fractional solubility should reduce uncertainties in the use of dissolved concentrations of this element in seawater as a proxy for dust deposition, although this topic requires further work.

Highlights

Atmospheric deposition of mineral dust is an important source of trace elements to the remote surface ocean
The difference in fine particle solubility between these two groups of elements might be related to the hyperbolic increase in the fractional solubility of iron, and a number of other elements, during the atmospheric transport of Saharan dust, which is not observed for manganese and its associated elements
Separation of two Saharan dust aerosol samples collected over the tropical Atlantic Ocean into multiple size fractions has demonstrated that the two groups of dust‐associated trace metals (Fe, Al, Ti and Mn, Co, Th) show very different solubility characteristics in the particle size range 0.61–3.3 μm

Summary

Introduction

Atmospheric deposition of mineral dust is an important source of trace elements to the remote surface ocean. Similar hyperbolic relationships between solubility and atmospheric concentration have been reported for many other dust‐associated elements, for example, aluminum (Al), silicon (Si), P, titanium (Ti), and lead (Pb) (Baker & Jickells, 2006; Prospero et al, 1987; Shelley et al, 2018) Attempts to understand this solubility behavior have focused largely on Fe (Aguilar‐Islas et al, 2010; Baker & Jickells, 2006; Sedwick et al, 2007; Sholkovitz et al, 2012; Spokes et al, 1994), because of its major role as a limiting nutrient over large regions of the global ocean (Jickells et al, 2005). The fractional solubility of these tracer elements in dust is a key uncertainty in these calculations (Anderson et al, 2016; Hsieh et al, 2011; Measures et al, 2010)

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