Four years' observations of terrestrial lipid class compounds in marine aerosols from the western North Pacific

Abstract

In order to understand the long‐range atmospheric transport of terrestrial organic matter over the open ocean, marine aerosol samples were collected on a biweekly basis from 1990 to 1993 in a remote island, Chichi‐Jima, in the western North Pacific. The samples were analyzed for lipid class compounds using a capillary gas chromatography (GC) and GC/mass spectrometry (GC/MS). A homologous series of n‐alkanes (C 20‐C 40), alcohols (C 13‐C 34), fatty acids (C 9‐C 34) and α,ω‐dicarboxylic acids (C 7‐C 28) were detected in the aerosol samples. Distributions of n‐alkanes (0.17–14 ngm−3, average 1.7 ngm−3) are characterized by a strong odd‐carbon number predominance (CPI ratios, average 4.5) with a maximum at C 29 or C 31, indicating that n‐alkanes are mainly derived from terrestrial higher plant waxes. Fatty alcohols (0.19–23 ngm−3, average 2.0 ngm−3) show an even‐carbon number predominance with a maximum generally at C 26 or C 28, again indicating a contribution from terrestrial higher plants. On the other hand, fatty acids (2.5–38 ngm−3, average 14 ngm−3) show a bimodal distribution with two maxima at C 16 and C 24 or C 28. Lower molecular weight fatty acids (generally <C 20) that are mainly derived from marine organisms showed higher concentrations in summer. In contrast, higher molecular weight fatty acids (C 21‐C 34) derived from terrestrial higher plants, together with C 25‐C 35 alkanes, C 20‐C 34 alcohols and C 20‐C 28 dicarboxylic acids, generally showed higher concentrations in winter to spring seasons. This seasonal trend is most likely interpreted as atmospheric transport of terrestrial organic matter from Asian continent in winter/spring, when westerly winds dominate over the western North Pacific. Backward trajectory analyses supported the long‐range atmospheric transport of higher plant‐ and soil‐derived organic matter from the Asian continent over the Pacific Ocean. This study also suggested that the atmospheric transport is the main pathway for the terrestrial lipid compounds that are abundantly present in the deep‐sea sediments in the Central Pacific.