Carbon isotope analyses of n-alkanes in dust from the lower atmosphere over the central eastern Atlantic

Enno Schefuß*, Volker Ratmeyer, Jan Berend W. Stuut, J. H.Fred Jansen, Jaap S. Sinninghe Damsté

*Corresponding author for this work

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Atmospheric dust samples collected along a transect off the West African coast have been investigated for their lipid content and compound-specific stable carbon isotope compositions. The saturated hydrocarbon fractions of the organic solvent extracts consist mainly of long-chain n-alkanes derived from epicuticular wax coatings of terrestrial plants. Backward trajectories for each sampling day and location were calculated using a global atmospheric circulation model. The main atmospheric transport took place in the low-level trade-wind layer, except in the southern region, where long-range transport in the mid-troposphere occurred. Changes in the chain length distributions of the n -alkane homologous series are probably related to aridity, rather than temperature or vegetation type. The carbon preference of the leaf-wax n-alkanes shows significant variation, attributed to a variable contribution of fossil fuel-or marine-derived lipids. The effect of this nonwax contribution on the δ13C values of the two dominant n-alkanes in the aerosols, n-C29 and n-C31 alkane, is, however, insignificant. Their δ13C values were translated into a percentage of C4 vs. C3 plant type contribution, using a two-component mixing equation with isotopic end-member values from the literature. The data indicate that only regions with a predominant C4 type vegetation, i.e. the Sahara, the Sahel, and Gabon, supply C4 plant-derived lipids to dust organic matter. The stable carbon isotopic compositions of leaf-wax lipids in aerosols mainly reflect the modern vegetation type along their transport pathway. Wind abrasion of wax particles from leaf surfaces, enhanced by a sandblasting effect, is most probably the dominant process of terrigenous lipid contribution to aerosols.

Original languageEnglish
Pages (from-to)1757-1767
Number of pages11
JournalGeochimica et Cosmochimica Acta
Issue number10
Publication statusPublished - 15 May 2003


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