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

Photosynthetic Production Determines Bottom Water Oxygen Variations in the Upwelling Coastal South China Sea Over Recent Decades

“…Over the past few decades, an increasing number of DOrelated proxies based on biomarkers, elements (i.e., molybdenum and uranium), and foraminifer (i.e., Bulimina marginata and Quinqueloculina spp.) have been proposed and applied to reconstruct paleo-DO or paleo-redox conditions (e.g., Nakakuni et al, 2017;Nakakuni et al, 2018;Li et al, 2018;Naafs et al, 2019;Jacobel et al, 2020;Wakeham, 2020, and references therein). Among the biomarker-derived redox proxies, the 5α-stanol/Δ 5 -sterol ratios are widely used because eukaryotederived Δ 5 -sterols are ubiquitous in aquatic environments and can be anaerobically transformed to 5α-stanol counterparts without aerobic re-conversion (e.g., Gaskell and Eglinton, 1975;Wakeham, 1989;Wakeham, 2020;Berndmeyer et al, 2014;Nakakuni et al, 2017Nakakuni et al, , 2018.…”

“…have been proposed and applied to reconstruct paleo-DO or paleo-redox conditions (e.g., Nakakuni et al, 2017;Nakakuni et al, 2018;Li et al, 2018;Naafs et al, 2019;Jacobel et al, 2020;Wakeham, 2020, and references therein). Among the biomarker-derived redox proxies, the 5α-stanol/Δ 5 -sterol ratios are widely used because eukaryotederived Δ 5 -sterols are ubiquitous in aquatic environments and can be anaerobically transformed to 5α-stanol counterparts without aerobic re-conversion (e.g., Gaskell and Eglinton, 1975;Wakeham, 1989;Wakeham, 2020;Berndmeyer et al, 2014;Nakakuni et al, 2017Nakakuni et al, , 2018. Some other processes, such as in vivo production of 5α-stanols and preferential degradation of Δ 5 -sterols may also modulate the 5α-stanol/Δ 5 -sterol ratios and confound their applicability to reflect redox processes (e.g., Nishimura and Koyama, 1977;Wakeham, 1989;Arzayus and Canuel, 2004;Bogus et al, 2012).…”

Methyl Ether-Derivatized Sterols and Coprostanol Produced via Thermochemolysis Using Tetramethylammonium Hydroxide (TMAH)

“…Typically, 5 α (H)-stanols are produced under anoxic conditions via bacterial conversion from sterols [7,37,38]. Thus, the ratio of 5 α (H)-stanol/Δ 5 -sterol can be applied as a tracer for redox conditions in the field of organic geochemistry [5,6,39]. However, the 5 α (H)-stanol/Δ 5 -sterol ratio could be large due to the preferential degradation of sterols in terrestrial organic matters, even under oxic conditions [35].…”

“…Sterols exist in the membranes of eukaryotic organisms, including microorganisms and terrestrial plants [1,2]. Thus, sterols have been detected in various natural environments, such as in lake and ocean waters and in sediments [3,4,5,6,7]. These natural sterols can be used to estimate ecological sources because sterol structures differ depending on the types of microorganisms [1,8].…”

“…Upon the TMAH reaction, sterols are provided as sterol methyl ethers. The application of the TMAH method for sterols can produce different types of sterols, including cholesterol, sitosterol, brassicasterol, and stanols [5,6,29]. The efficiency of methylation in sterols reaches >90% [29], indicating that sterols are able to be stably analyzed.…”