Geochemical variations in aeolian mineral particles from the Sahara–Sahel Dust Corridor

Abstract

The Sahara-Sahel Dust Corridor runs from Chad to Mauritania and expels huge amounts of mineral aerosols into the Atlantic Ocean. Data on samples collected from Algeria, Chad, Niger, and Western Sahara illustrate how corridor dust mineralogy and chemistry relate to geological source and weathering/transport history. Dusts sourced directly from igneous and metamorphic massifs are geochemically immature, retaining soluble cations (e.g., K, Na, Rb, Sr) and accessory minerals containing HFSE (e.g., Zr, Hf, U, Th) and REE. In contrast, silicate dust chemistry in desert basins (e.g., Bodélé Depression) is influenced by a longer history of transport, physical winnowing (e.g., loss of Zr, Hf, Th), chemical leaching (e.g., loss of Na, K, Rb), and mixing with intrabasinal materials such as diatoms and evaporitic salts. Mineral aerosols blown along the corridor by the winter Harmattan winds mix these basinal and basement materials. Dusts blown into the corridor from sub-Saharan Africa during the summer monsoon source from deeply chemically weathered terrains and are therefore likely to be more kaolinitic and stripped of mobile elements (e.g., Na, K, Mg, Ca, LILE), but retain immobile and resistant elements (e.g., Zr, Hf, REE). Finally, dusts blown southwestwards into the corridor from along the Atlantic Coastal Basin will be enriched in carbonate from Mesozoic-Cenozoic marine limestones, depleted in Th, Nb, and Ta, and locally contaminated by uranium-bearing phosphate deposits.

Iron oxide minerals in dust-source sediments from the Bodélé Depression, Chad: Implications for radiative properties and Fe bioavailability of dust plumes from the Sahara

“…Our results extend earlier research on the occurrences of iron-bearing minerals in Bodélé surface sediments and elsewhere in North Africa that aimed to establish linkages between dust mineralogy and potential environmental effects of dust (Lafon et al, , 2006Alfaro et al, 2004;Moreno et al, 2006;Mounkaila, 2006;Journet et al, 2008Journet et al, , 2104Chudnovsky et al, 2009;Lázaro et al, 2011;Maher, 2011;Shi et al, 2011;Moosmüller et al, 2012;Adetunji, 2014;Formenti et al 2014 a, b). These studies employed many methods for dust and soil mineralogy, including magnetic analyses, X-ray absorption analysis, X-ray diffraction, microscopy, elemental and isotopic chemistry combined with leaching experiments, as well spectroscopic techniques in the laboratory and applied to satellite retrievals.…”

Deciphering human–climate interactions in an ombrotrophic peat record: REE, Nd and Pb isotope signatures of dust supplies over the last 2500years (Misten bog, Belgium)

“…5). A similar range of Sc-normalised REE content is observed between the European soils (data from European soil geochemical atlas -http:// www.gtk.fi/publ/foregsatlas/) and the Saharan airbornes (Moreno et al, 2006): it therefore characterizes the range for natural, regional and distal dust sources. (2) During the Industrial Revolution, the Misten samples are enriched in REE (Fig.…”

Eolian dust input to the Subarctic North Pacific

“…The higher dust fractions along the western part of the Southern Transect could alternatively be the result of lower HREE concentrations in eolian dust at the deposition site compared to the source. Since important REE host minerals like zircon are relatively LREE depleted (Gromet et al, 1984;Moreno et al, 2006;Taylor and McLennan, 1985), this could argue for a compositional change during transport from the source to the depositional site. On the other hand, we would expect similar changes for 4 He and 232 Th.…”