Characterization of unusual sterols and long chain diols, triols, keto-ols and n-alkenols in El Junco Lake, Galápagos

A variety of lipid biomarkers were identified in sediments from El Junco Lake, Galápagos and their sources investigated for potential use in paleoclimate applications. A series of unusual sterols was also found, including 4α-methylgorgostanol, reported in only four species of dinoflagellates to date. We also tentatively assigned 22,23-methylene-4α-methyl-24-ethylcholest-5-en-3β-ol, the mass spectrum of which matched a sterol found in resting cysts of the dinoflagellate Peridinium umbonatum. In addition, we identified the novel sterol 4α,22,23,24-tetramethyl-5α-cholest-22E-en-3β-ol. Based on the unique sterol distribution, we hypothesize that a dinoflagellate from the genus Peridinium was the primary source of dinosterol and the novel sterols throughout the sediment record. The source specificity and abundance throughout the 3.7 m of recovered sediment make dinosterol an excellent target for hydrogen isotope analysis for use as a paleohydrological proxy in future studies. The abundant C30 and C32 1,ω20-diols and keto-ols, C29 9,10-diol and C29 1,ω9,ω10-triol likely derive from the ferns Azolla microphylla and Cyathea weatherbyana, while sources of the C30 1,ω16-diol and keto-ol, C32 1,ω18-diol and keto-ol, and the C30-C32n-alken-1-ols are likely limited to aquatic microalgae. Due to their source specificity, these diol, triol, keto-ol, and n-alkenol biomarkers present further tools for studying past environmental and climatic change.