Abstract
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 language | English |
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Pages (from-to) | 1757-1767 |
Number of pages | 11 |
Journal | Geochimica et Cosmochimica Acta |
Volume | 67 |
Issue number | 10 |
DOIs | |
Publication status | Published - 15 May 2003 |
Funding
We gratefully appreciate the effort of R. R. Schneider to enable the dust sampling. H. D. Schulz is thanked as chief scientist of RV Meteor cruise 41/1. Peer Helmke (University of Bremen) generously supplied the satellite composite picture. Special thanks are given to Ulrike Wyputta for substantial support during trajectory analysis and preprocessing of windfield data. The Dutch scientific funding organization (NWO) is thanked for financial support to E.S. (project no. 75019617) and the Deutsche Forschungs-Gemeinschaft (DFG) for financial support to V.R. The comments by two anonymous reviewers significantly improved an earlier version of the manuscript. This is NIOZ publication no. 3614. Associate editor: N. E. Ostrom