New constraints on elemental and Pb and Nd isotope compositions of South American and Southern African aerosol sources to the South Atlantic Ocean

A Bory,S Dong,S Strekopytov,P Cid-Agüero,R Khondoker,V Bout-Roumazeilles,D Weiss,M Rehkämper,B.J Coles,P Smichowski,F Monna,T Van De Flierdt,E Humphreys-Williams,K Kreissig,R Losno,M Babinski

doi:10.1016/j.chemer.2018.05.001

Abstract

Improving the geochemical database available for characterising potential natural and anthropogenic aerosol sources from South America and Southern Africa is a critical precondition for studies aimed at understanding trace metal controls on the marine biogeochemical cycles of the South Atlantic Ocean. We here present new elemental and isotopic data for a wide range of sample types from South America and Southern Africa that are potentially important aerosol sources. This includes road dust from Buenos Aires and lichen samples from Johannesburg, soil dust from Patagonia, volcanic ash from the Andean volcanic belt, and aerosol samples from São Paulo. All samples were investigated for major (Al, Ca, Fe, Mg, Na, K, Mn) and trace element (Cd, Co, Cr, Cu, Ni, Pb, REE, Sc, Th, Y, V, Zn) concentrations and Nd and Pb isotopic compositions. We show that diagrams of 208Pb/207Pb vs. εNd, 208Pb/207Pb vs. Pb/Al, 1/[Pb], Zn/Al, Cd/Al, Cu/Al, and εNd vs. Pb/Al, and 1/[Nd] are best suited to separate South American and South African source regions as well as natural and anthropogenic sources. A subset of samples from Patagonia and the Andes was additionally subjected to separation of a fine (<5 μm) fraction and compared to the composition of the bulk sample. We show that differences in the geochemical signature of bulk samples between individual regions and source types are significantly larger than between grain sizes. Jointly, these findings present an important step forward towards a quantitative assessment of aeolian trace metal inputs to the South Atlantic Ocean.

Highlights

The atmosphere is a major pathway for delivering elements essential for primary production to surface waters (e.g., Boyd et al, 2000; Mahowald et al, 2005)
We observe generally higher 1/[Nd] values for the aerosols compared to natural sources (Fig. 2) as well as low εNd values of between −14.1 and −15.3 (Fig. 3). These results suggest that the aerosols derived from re-suspension of soils generated by the alteration of old Archean to Neoproterozoic rocks; supporting that the Nd values have been observed in re-worked particulates such as road dusts which can contain anthropogenic materials
This study significantly expands the elemental and isotopic (Pb and Nd isotope) data that is available to characterise and discriminate between important South American and South African aerosol sources to the South Atlantic Ocean. This was achieved by analysing a wide range of natural and anthropogenic samples, including road dust from Buenos Aires, aerosols from São Paulo, soil dust from Patagonia, and volcanic deposits from the Andean volcanic belt as well as various lichen from urban and rural areas of South Africa

Summary

Introduction

The atmosphere is a major pathway for delivering elements essential for primary production to surface waters (e.g., Boyd et al, 2000; Mahowald et al, 2005). Atmospheric modelling and satellite mapping indicate that Patagonia and the Puno-west Argentinian region are the main natural dust sources from South America to supply aerosols to the South Atlantic Ocean (Prospero et al, 2002; Gasso and Stein, 2007). Large arid regions such as the Namib, Sossusvlei and Kalahari deserts in South Africa are major dust sources on the other side of the South Atlantic (Chin, 2009).

Objectives

Methods

Results

Conclusion