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 (δ13C) 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.