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

Carbon isotopic analyses of 24-ethytlcholest-5-en-3 beta -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-3 beta -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 (delta C-13) Of 24-ethylcholest-5-en-3 beta -ol in the C-3 core ranges from -23.3 to -32.0 parts per thousand over the past 30,000 years. After the last glacial period (10-73 cm section; 2-9 ka), 24-ethylcholest-5-en-3 beta -ol is derived from marine algae (-24.2+/-1.1 parts per thousand 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 parts per thousand on average). The trend in the isotopic composition of 24-ethylcholest-5-en-3 beta -ol is nearly consistent with paleoclimatic changes around the Japan Sea over the past 30,000 years. (C) 2001 Elsevier Science Ltd. All rights reserved.