Sources of 24-ethylcholest-5-en-3β-ol in Japan Sea sediments over the past 30,000 years inferred from its carbon isotopic composition

Abstract

Carbon isotopic analyses of 24-ethylcholest-5-en-3β-ol in a marine sediment core (KH-79-3, C-3) covering the last 30,000 years, using gas chromatography/isotope ratio mass spectrometry (GC/IRMS), are presented. The source of 24-ethylcholest-5-en-3β-ol is unclear from the abundances for marine and terrestrial biomarkers. However, the carbon isotope results for this sterol exhibit a clear indication of the sources. The carbon isotopic composition (δ 13C) of 24-ethylcholest-5-en-3β-ol in the C-3 core ranges from −23.3 to −32.0‰ over the past 30,000 years. After the last glacial period (10–73 cm section; 2–9 ka), 24-ethylcholest-5-en-3β-ol is derived from marine algae (−24.2±1.1‰ on average). However, in the last glacial stage (140–274 cm section; 15–29 ka), it is likely that the value indicates a terrestrial higher plant origin (−30.5±0.9‰ on average). The trend in the isotopic composition of 24-ethylcholest-5-en-3β-ol is nearly consistent with paleoclimatic changes around the Japan Sea over the past 30,000 years.