Stanol to sterol ratios in late Quaternary sediments from southern California: An indicator for continuous variability of the oxygen minimum zone

In this study, we analyzed 5α(H)-stanol/Δ5-sterol ratios in offshore marine sediments using offline tetramethylammonium hydroxide thermochemolysis (TMAH) gas chromatography-mass spectrometry (GC-MS). Data were used to reconstruct redox events recorded in a southern California marine sediment core (Ocean Drilling Program, Leg167, Hole 1017E). The 24-nordehydrocholestanol/24-nordehydrocholesterol and diatomstanol/diatomsterol ratios clearly recorded oxygen minimum zone (OMZ) fluctuations in southern California during the last 40 kyr. In particular, two ratios corresponding to Marine Isotope Stage 3 (MIS3) varied significantly at the OMZ, exhibiting millennial-scale fluctuations related to Dansgaard-Oeschger shifts of warming and cooling intervals. In contrast, other ratios (cholestanol/cholesterol, campestanol/campesterol, sitostanol/sitosterol, and 22-dehydrocholestanol/22-dehydrocholesterol) showed no significant trends, possibly reflecting the influence of stanol-creating organisms. Our results show that 5α(H)-stanol/Δ5-sterol ratios obtained using the TMAH GC-MS method are useable tracers of water column and surface sediment redox conditions in southern California marine sediments.