Raney nickel (RN) desulfurization is widely applied to access sulfur-bound biomarkers, yet its quantitative reliability remains poorly constrained. Here we systematically evaluate RN desulfurization through parallel (reproducibility) and mass-gradient (linearity) experiments on polar fractions of a Tertiary crude oil. Results demonstrate exceptional reproducibility of biomarker ratios and strong linearity (R2 > 0.8) between product yields and reactant masses (10–20 mg), establishing a firm methodological foundation for quantitative desulfurization analysis. Importantly, carbon-number dependent yields of n-alkanes reveal molecular selectivity of natural sulfurization, validating RN desulfurization as a robust quantitative tool for tracing genuine biosignatures and calibrating paleoenvironmental reconstruction derived from sulfur-bound biomarker pools.
Intramolecular isotope analysis is a powerful tool for tracing molecular origins and formation pathways by characterizing isotope distributions among distinct molecular moieties. This study presents an on-line gas chromatography–hydropyrolysis–gas chromatography–isotope ratio mass spectrometry method for methyl- and phenyl-moiety-specific carbon isotope analysis of toluene. The key innovation of this method is the introduction of an on-line hydropyrolysis step. First, optimal hydropyrolysis conditions for toluene were determined through systematic experimentation: a pyrolysis temperature of 880 °C, an H2 pressure of 0.15 MPa, and a carrier gas flow rate of 0.8 mL/min. Under these optimized conditions, methane and benzene were identified as the main pyrolytic fragments, and no appreciable amounts of other carbon-containing compounds were detected. Subsequently, an isotope-dilution experiment showed that methane was derived predominantly from the methyl carbon of toluene. Together with the near 1:1 M ratio of methane to benzene, this result indicates that benzene carbon is mainly derived from the remaining phenyl moiety and that secondary reactions are negligible within analytical uncertainty during hydropyrolysis. Finally, the results demonstrate that isotopic fractionation during pyrolysis is stable and reproducible at a given temperature. Therefore, the δ13C value of the methyl carbon and the average δ13C value of the phenyl moiety can be calculated by applying the fractionation factors of the hydropyrolysis process to the measured δ13C values of the pyrolytic fragments. This work establishes a simple, rapid, and sensitive intramolecular carbon isotope method for determining the δ13C value of the methyl carbon and the average δ13C value of the phenyl moiety of toluene.
This study examines the distribution, sources, and toxicity of polycyclic aromatic hydrocarbons (PAH) in two peatlands of the Pechora region (Komi Republic, Russia). Physicochemical properties, botanical composition, and the contents of 15 PAH and retene were determined in peat cores (1.2–1.4 m deep). Total PAH concentrations in the organic peat layers range from 88 to 763 ng/g (mean 340 ng/g), falling within the range typical of background peatlands. Differences in organic matter genesis were observed: the SP-1 profile is enriched in recalcitrant wood-derived organic matter, whereas SP-2 consists primarily of herbaceous and mossy vegetation. Maximum PAH accumulation occurs in the middle and deep horizons (40–120 cm), indicating historical accumulation rather than recent surface contamination. Low molecular weight PAH (predominantly naphthalene and phenanthrene, up to 95%) predominated in both profiles; however, the SP-1 sample at 40–80 cm exhibited simultaneously elevated levels of high molecular weight PAH and retene, pointing to a local input of pyrogenic products. Two possible mechanisms of PAH formation are discussed: diagenetic (polymerisation and polycondensation of organic transformation products) and pyrogenic (natural fires in past epochs). Diagnostic PAH isomer ratios also indicate a mixed diagenetic and pyrogenic origin. Toxic equivalent (TEQ) values were low (0.3–13.1 ng/g) in most horizons; however, in the middle layers of SP-1 (40–80 cm), they reached 30.7–130.7 ng/g, exceeding the Russian soil standard (20 ng/g). The results demonstrate a close link between historical PAH accumulation, vegetation succession, organic matter transformation, and past fires. Elevated TEQ values indicate a potential long-term risk of remobilisation of the historical PAH pool under changing climatic and hydrological conditions.
3-Hydroxy fatty acids (3-OH-FAs), lipid biomarkers primarily derived from Gram-negative bacteria, have recently been proposed as proxies for temperature and pH. Existing studies focus on terrestrial environments and marginal seas, leaving their applicability in deep ocean settings inadequately explored. In this study, we investigated the presence of 3-OH-FAs in 13 surface and 29 core sediment samples from four hadal trench regions: the Mariana, New Britain, Atacama, and Kermadec trenches, covering water depths ranging from 2560 to 10,085 m. 3-OH-FAs were detected in all trench sediment samples, with carbon chain lengths varying from C10 to C18, and total concentrations ranging from 16 to 2411 μg/g dry weight sediment. Consistent with other marine sediments, trench sediments exhibited a significantly higher abundance of anteiso homologues compared to terrestrial samples. Reconstructed sea surface temperatures (SST) based on established RANs (ratio of anteiso (a-) to normal (n-) isomers of 3-OH-FAs) calibrations were substantially lower than the observed values, with cold biases of −20.2 ± 2.7 °C for RAN13 (ratio of a- to n- isomers for C13 homologues) and −6.7 ± 3.0 °C for RANs, indicating that these calibrations are not directly applicable to trench sediments. Analysis of 16S rRNA gene sequencing data uncovered diverse bacterial communities in trench sediments, encompassing several major phyla dominated by Gram-negative taxa. This finding suggests a potential benthic source of sedimentary 3‑OH‑FAs. We observed strong correlations between sediment oxygen concentration and 3-OH-FAs indices, suggesting that oxygen availability may play a crucial role in controlling 3-OH-FAs distributions in trench environments. Consequently, the signatures of deep-trench 3-OH-FAs are likely influenced by benthic processes, underscoring the need for further investigation into whether 3-OH-FA indices can serve as indicators of benthic conditions in the deep ocean.
This study presents the first region-specific calibrations of 3-hydroxy fatty acids (3-OH-FAs),and branched glycerol dialkyl glycerol tetraethers (brGDGTs) for reconstructing temperature and hydroclimate across mainland Southeast Asia. Surface sediments and soils from forty-eight lakes and thirty catchments spanning tropical Thailand to temperate Yunnan, China, were analyzed to establish empirical relationships between biomarker indices and mean annual air temperature (MAAT). Among the 3-OH-FA indices, RAN13 and the newly proposed RIN15 exhibit the significant correlations with MAAT in lake sediments (slope = −0.026, R2 = 0.63, p < 0.001 and slope = −0.162, R2 = 0.63, p < 0.001, respectively), while RAN15 performs best in soils (slope = −0.06, R2, = 0.83, p < 0.001). For brGDGTs, the MBT′5ME index shows robust correlations with MAAT in lakes (slope = 0.026, R2 = 0.71, p < 0.001), whereas the relationship is notably weaker in soils (slope = 0.013, R2 = 0.28, p < 0.01), although it still outperforms MBT′6ME. pH-related indices (e.g., BR, RIN, CBT′ and IR6ME) display weaker relationships, reflecting limited pH variability across sites. Together, these results highlight distinct bacterial contributions to lipid assemblages and demonstrate that 3-OH-FA- and brGDGT-based temperature proxies respond systematically to regional thermal gradients. The new calibrations provide a robust framework for reconstructing, past temperature and hydroclimatic variability across Southeast Asia′s monsoon region.
