Modern sediment records of stanol to sterol ratios in Lake Suigetsu, Japan: An indicator of variable lacustrine redox conditions

摘要

We tested the usefulness of the 5 alpha(H)-stanol/Delta(5)-sterol ratios obtained by the tetramethylammonium hydroxide (TMAH) thermochemolysis gas chromatography-mass spectrometry (GC-MS) method used to reconstruct redox events in marine sediments as a redox tracer in lake sediments using cores from Lake Suigetsu, Japan. The lake was previously a freshwater lake and is now brackish owing to excavation works conducted during the 17th century. Other redox tracer analyses (e.g., based on farnesol) have shown that C26(nor-24)Delta(22)/C26(nor-24)Delta(5,22) (24-nordehydrocholestanol/24-nprdehydrpcholesterol), C-28(24Me)Delta(22)/C-28(24Me)Delta(5,22) (diatomstanoficliatomsteml), and C-27 Delta(22)/C-27 Delta(5,22) (22-dehydrocholestanol/22-de hydrocholesterol) ratios have risen (similar to 0.53) following strong anoxic conditions that formed in Lake Suigetsu (A.D. 1848 and 1935). This study is the first to show that 5 alpha(H)-stanol/Delta(5)-sterol ratios determined using the TMAH method could be useful as a redox tracer in lacustrine environments. In particular, the ratio of diatomsterol, which is detected in both brackish and fresh water in relatively high abundance, has the potential to be a very useful tracer of redox events. On the other hand, the other 5 alpha(H)-stanol/Delta(5)-sterol ratios (C-27 Delta(0)/C-27 Delta(5) [cholestanol/cholesterol], C-28(24me)Delta(0)/C-28(24me)Delta(5) [campestanol/campesterol], and C-29(24Et)Delta(0)/C-29(24Et)Delta(5) [sitostanol/sitosterol] ratios) showed no increasing trends, suggesting the influence of terrestrial inputs from degraded products. (C) 2018 Elsevier Ltd. All rights reserved.