Decadal Variations in Hydroxy Fatty Acids Over Chichijima Island in the North Pacific: Long-Term Seasonal Variability in Plant and Microbial Markers

To understand the sources and transport pathways of organic compounds associated with soil microbes and higher plant waxes in the East Asian outflow, we assessed source-specific tracers such as alpha-, beta- and omega-hydroxy fatty acids (FAs) in remote marine aerosols collected at Chichijima Island in the western North Pacific (WNP) during 2001-2003. Molecular distributions of hydroxy FAs are characterized by strong even-carbon numbered predominance, indicating biogenic sources. Hydroxy FAs showed a strong seasonality with higher loadings during winter/spring than summer/autumn. Cluster analysis of backward air mass trajectories, satellite-based fire counts and dust extinction data reveal an impact of the East Asian outflow over the WNP in winter/spring. In the spring, there are larger relative abundances of short-chain beta-hydroxy C-10-C-18 FAs (a proxy for soil microbes), consistent with the higher loadings of non-sea-salt Ca2+ (dust tracer). The molecular distributions of beta-hydroxy FAs in spring are in agreement with those of the reference materials of Chinese loess (CJ-1) and simulated Asian mineral dust (CJ-2), suggesting their probable sources in East Asia. A comparison of relative abundances of short-chain beta-hydroxy C-10-C-18 FAs and long-chain omega-hydroxy C-20-C-32 FAs (a proxy for higher plant metabolites) in Chichijima aerosols between this (2001-2003) and previous (1990-1993) studies have unveiled an increment of 20% and 30%, respectively. Such an increase was likely caused by the changes in source strength on a decadal-scale and warrants further investigation. Furthermore, cluster analysis of trajectories and the overall distributions of hydroxy FAs between both datasets have shown their similar provenance in winter/spring.