Relationship between the lipid compositions of marine aerosols, the sea surface microlayer, and subsurface water

Aerosols, surface microlayer, and subsurface water samples have been collected during the ‘Midlante’ cruise of the R/V Jean Charcot (May 1974) in the northeastern tropical Atlantic, taking all possible precautions against shipboard contamination. The concentrations of n alkanes, total hydrocarbons, and fatty acids (C12 to C32 were obtained by gas-liquid chromatography in these aerosol samples as well as for the dissolved and particulate fractions of the microlayer and subsurface waters. The aqueous phase fatty acids are of obvious planktonic origin, but an anthropogenic source cannot be definitely discounted for the aqueous phase n alkanes. On average, fatty acid lipids, n alkanes, and total hydrocarbons are all enriched in the microlayer by factors of 2–5. The three aerosol samples show a strong similarity in composition, and all differ from the corresponding aqueous samples in having lauric acid C12 as the dominant acid instead of C16, typical of planktonic lipids, as found for the water samples. The hydrocarbon distributions of the aerosols, which resemble petroleum-derived materials, are characteristically different from those of the subsurface and microlayer, which are similar and appear to have a marine origin. The overlying n alkane distributions of all three sample types are similar, however, being generally regular without predominance of n alkanes with n even or odd, and are also quite different from distributions characteristic of terrigenous dust containing hydrocarbons derived from higher plants.