Low Molecular Weight N-alkanes Research Articles

Measuring the Fate and Natural Attenuation Potential of a Viscous Marine Fuel on an Artificial Beach Mesocosm

Shoreline oiling poses a risk to coastal ecosystems and resources. Understanding the natural attenuation potential and impact of different sediment types is important for choosing appropriate intervention strategies and priority areas following a spill. Simulated IFO-40 oil spills on artificial beach mesocosms were carried out using different sediment types: sandy beach and sandy tidal flat, under low energy tidal cycles over a 5-day period. Chemical and biological analysis of leachate and sediment was conducted to understand the movement of oil through these mesocosms. Rapid oil movement from the oil slick to the surface sediment layer was observed in the sandy beach enclosures, while slower oil movement was observed in the sandy tidal flat enclosures. Increased hydrocarbon dissolution was observed in the sandy beach enclosures, marked by higher concentrations of low molecular weight n-Alkanes (C12 − 15) and naphthalenes (C0 − 3) in sandy beach leachate compared to sandy tidal flat samples. Despite the increase in hydrocarbons, there were no major shifts in microbial communities observed in the leachate and sediment compartments for either sediment type. Both prokaryote and microeukaryote communities differed between the two sediment types, with little overlap between dominant sequences. Our results indicate that limited oil penetration occurs within sandy tidal flat shorelines resulting in oil accumulation suggesting that sorbent or vacuuming could be used as emergency response to minimize the environmental and ecological impacts of spilled oil.

Investigating sources and health risk assessment of n-alkanes in atmospheric wet deposition in Indo-Gangetic Plain

The present study determines the levels of n-alkanes in atmospheric wet deposition at an urban site in the Indo-Gangetic Plain, Delhi, during monsoon and non-monsoon periods in 2021. The n-alkane homologs (C10–C33) were determined in wet deposition, which included wet-only and bulk samples. The average total n-alkanes were found to be 56.0 ± 16.7 and 439.4 ± 150.8 μg/L in wet-only samples, whereas, 149.6 ± 46.4 and 454.9 ± 108.4 μg/L in bulk samples during monsoon and non-monsoon periods, respectively. The low molecular weight n-alkanes (C10–C25) exhibited no odd-even predominance in wet-only and bulk depositions during monsoon and non-monsoon periods. However, the high molecular weight n-alkanes (>C25) showed odd-even predominance during the non-monsoon period. The molecular distribution patterns of n-alkanes indicated possible emissions from bacteria, fossil-fuel combustion, direct volatilization of unburnt fuels, biogenic sources, and other anthropogenic activities. A health risk assessment for n-alkanes revealed the higher susceptibility of children via dermal and oral exposure. The Hazard Index for the exposure of n-alkanes through atmospheric wet deposition was <1, i.e., within the acceptable limit. The Carbon Preference Index (CPI) and wax n-alkanes (WNA)%, supported the prevalence of mixed emission sources with higher contributions from anthropogenic activities. Five sources of n-alkanes were identified using the positive matrix factorization (PMF) model, i.e., gasoline vehicles + fuel evaporation, biogenic, biogenic + diesel exhaust, road dust, and mixed, contributing ∼30 %, 11 %, 26 %, 17 %, and 16 % respectively. The Concentration Weighted Trajectory (CWT) analysis revealed that n-alkanes in wet-only and bulk samples were contributed by different local, regional, and long-range transport of air pollutants.

Connecting molecular biomarkers, mineralogical composition, and microbial diversity from Mars analog lava tubes

Lanzarote (Canary Islands, Spain) is one of the best terrestrial analogs to Martian volcanology. Particularly, Lanzarote lava tubes may offer access to recognizably preserved chemical and morphological biosignatures valuable for astrobiology. By combining microbiological, mineralogical, and organic geochemistry tools, an in-depth characterization of speleothems and associated microbial communities in lava tubes of Lanzarote is provided. The aim is to untangle the underlying factors influencing microbial colonization in Earth's subsurface to gain insight into the possibility of similar subsurface microbial habitats on Mars and to identify biosignatures preserved in lava tubes unequivocally.The microbial communities with relevant representativeness comprise chemoorganotrophic, halophiles, and/or halotolerant bacteria that have evolved as a result of the surrounding oceanic environmental conditions. Many of these bacteria have a fundamental role in reshaping cave deposits due to their carbonatogenic ability, leaving behind an organic record that can provide evidence of past or present life. Based on functional profiling, we infer that Crossiella is involved in fluorapatite precipitation via urea hydrolysis and propose its Ca-rich precipitates as compelling biosignatures valuable for astrobiology.In this sense, analytical pyrolysis, stable isotope analysis, and chemometrics were conducted to characterize the complex organic fraction preserved in the speleothems and find relationships among organic families, microbial taxa, and precipitated minerals.We relate organic compounds with subsurface microbial taxa, showing that organic families drive the microbiota of Lanzarote lava tubes. Our data indicate that bacterial communities are important contributors to biomarker records in volcanic-hosted speleothems. Within them, the lipid fraction primarily consists of low molecular weight n-alkanes, α-alkenes, and branched-alkenes, providing further evidence that microorganisms serve as the origin of organic matter in these formations. The ongoing research in Lanzarote's lava tubes will help develop protocols, routines, and predictive models that could provide guidance on choosing locations and methodologies for searching potential biosignatures on Mars.

The effect of lamina and lithofacies assemblage on molecular maturity of oil in a shale source-rock reservoir

This paper discusses the effect of the source rock–reservoir assemblage and the assemblage–induced variability in hydrocarbon expulsion and the subsequent molecular composition as well as molecular thermal maturity within a hybrid shale system. The characterization work was conducted on lithofacies and microlamina scales using core samples from the Chang 73 sub-member of the Triassic Yanchang Formation in the Ordos Basin, China. Samples were collected from a narrow interval with a depth range of less than 15 m, and the main characterization work was performed by Rock-Eval pyrolysis and GC–MS analysis. The results show that chemical fractionation of preferential expulsion and migration of the saturated fraction exists in the source rock–reservoir assemblages at both the lithofacies and lamina scales. However, the molecular composition behaves differently at the lithofacies and lamina scale's source rock–reservoir assemblages, in which ∑C21−/∑C22+ is higher in lamina scale reservoir but lower in lithofacies scale reservoir. It is assumed that the low-molecular weight n-alkanes also follow molecular fractionation. The lithofacies reservoir has a lower ∑C21−/∑C22+ because of the strong storage capacity of the laminated micro-reservoir within shale, which prevents the newly generated lighter oil from being charged into the lithofacies reservoir. The variation trends of thermal maturity indices Ts/hopane, the relative pregnane content, and TA(I)/TA(I + II) ratios, which have the same chemical basis with ∑C21−/∑C22+, carry the same maturity signature as ∑C21−/∑C22+. The above profile of the molecular composition and molecular-derived thermal maturity parameters indicate that within the short interval of a shale system where no differences in thermal maturity are expected, chain scission reactions and their derived thermal maturity indicators are very sensitive to source rock and reservoir. In addition, within a shale system, oil is more easily to expel out from the organic-rich lithofacies that are interbedded with organic-lean lithofacies. Oil expulsion may promote both chain cracking of oil and subsequently kerogen decomposition. This may provide geological evidence to explain why the frequent-stacking assemblage of source rock and reservoir lithofacies in a hybrid shale system is an ideal target for shale oil exploration.

The enhanced presence of tricyclic terpanes in the lacustrine rock extracts of the Upper Triassic Yanchang Formation, Qingcheng area, Ordos Basin, China

The predominance of tricyclic terpanes over hopanes was observed for the first time in the lacustrine rock extracts of the Upper Yanchang Formation collected from Well CYX in the Qingcheng area, Ordos Basin, China. Specifically, hopanes are dominant terpanes in the Chang 7-2 member, while tricyclic terpanes ranging from C19 to C39 predominate over hopanes in the Chang 7–3 and Upper Chang 8-1 member. The distributions of terpanes, steranes, as well as n-alkanes vary significantly in these thermally mature rock extracts, however, are closely correlated in each sample. Generally, rock extracts comprising more abundant tricyclic terpanes and their lower molecular weight homologues are characterized by having lower Pr/n-C17 ratios and by containing more abundant low molecular weight n-alkanes (n-C21-) and short-chain C21-22 steranes. Furthermore, among the Chang 7–2 and Chang 7-3 samples, black shales contain more abundant low molecular weight tricyclic terpanes and n-alkanes (n-C21-), and short-chain C21-22 steranes when compared with siltstones and mudstones, which comprise more abundant hopanes, diasteranes and regular C27-29 steranes. The similar geochemical characteristics could also be found in other rock extracts that have variable abundances of tricyclic terpanes and hopanes, especially in the East Berlin Formation (Hartford Basin, Connecticut, U.S.A), which suggests that the causes for the variable distributions of terpanes, steranes and n-alkanes in these strata are similar.On the one hand, it is determined by the proportion of aquatic versus terrigenous source input and depositional environment. The predominance of tricyclic terpanes over hopanes and short-chain C21-22 steranes over regular C27-29 steranes in the Chang 7-3 member, especially in black shales, could be resulted from algal bloom and possibly associated microbial metabolic process in stable or stratified water column, which may be triggered by plentiful nutrients provided by runoff, volcanic or hydrothermal events. On the other hand, high hydrocarbon-generation intensity and petroleum expulsion efficiency for source rocks, especially for black shales, may be another significant driving force for the enrichment of tricyclic terpanes. In such cases, significant oils have been generated and expelled, an early or faster rate of generation/expulsion of hopanes relative to tricyclic terpanes may occurred, which is evidenced by the extended hopanes are depleted in all the studied rock extracts. Furthermore, to our knowledge, the predominance of tricyclic terpanes over hopanes has not been observed in source rocks of the Yanchang Formation in other regions of the Ordos Basin. The observation of the enhanced presence of tricyclic terpanes in the current study may suggest that the hydrocarbon-generating intensity and petroleum expulsion efficiency of source rocks in the Qingcheng area are higher than that of other regions in the basin. Thus, the Qingcheng area has tremendous potential for petroleum resources and is an important area for future exploration.

Biodegradation of dissolved organic matter and sedimentary organic matter in high arsenic groundwater system: Evidence from lipid biomarkers and compound-specific carbon isotopes

Organic matter plays important roles in arsenic mobility. Whether sedimentary or dissolved organic matter is the predominant electron donors is still on debate. To fill this gap, both sediments and groundwater were collected from the Hetao Basin, a typical arid-semiarid area hosting high arsenic groundwater, to characterize diagnostic biomarkers and compound-specific carbon isotopes of lipids in dissolved organic matter (DOM) and its depth-matched sedimentary organic matter (SOM). Results showed that SOM in both clay and sand layers were mainly sourced from terrestrial higher plants, but sand SOM had additional sources from microbial and petroleum OM. Compound-specific carbon isotope compositions of DOM and SOM showed that δ13C of low molecular weight (LMW) n-alkanes (δ13CL) were more positive than those of high molecular weight (HMW) n-alkanes (δ13CH). The δ13CH in groundwater (δ13CH-DOM) and sediments (δ13CH-SOM) fall in the range of C3 plants, indicating that DOM and SOM had similar origins. More positive δ13CL than δ13CH suggests preferential degradation of LMW compounds in both sediments and groundwater. In comparison with SOM, more microbial-derived OM was observed in groundwater DOM, especially in high‑arsenic groundwater. High arsenic groundwater was accompanied by the low ratio of n-alkanes to hopanes in depth-matched SOM, and the great difference between δ13CL and δ13CH and low terrestrial/microbial ratios (TAR) in groundwater DOM. This indicates that SOM and DOM should be utilized by indigenous bacteria to fuel the reductive dissolution of Fe oxides for arsenic release into groundwater. Furthermore, more abundant LMW compounds and weaker odd-to-even predominance in DOM than those in SOM support that DOM encountered stronger biodegradation. This study highlights that preferential biodegradation of DOM (especially LMW components and petroleum sourced OM) would provide electrons for the reductive dissolution of arsenic-bearing Fe/Mn oxides and thus induce arsenic enrichment in groundwater.

Baseline levels and characterization of hydrocarbons in surface marine sediments along the transportation corridor in Hudson Bay: A multivariate analysis of n-alkanes, PAHs and biomarkers

Hudson Bay is a small arctic inland shelf sea which receives large amounts of freshwater from riverine discharges, with marine flow from the north and the Atlantic. A warming climate has resulted in an expanded open water season which will result in an increase in shipping of fuel oil and petroleum to communities and mines on the western shore, increasing the risk of hydrocarbon releases. To evaluate the status of hydrocarbons, surface sediments were collected at 34 locations in the transportation route and offshore and analysed for several types of hydrocarbons. Total hydrocarbons varied by over 25 times between sites, reaching a maximum of 1116 μg/g OC (organic carbon basis) in Hudson Strait due to low molecular weight n-alkanes from marine primary production. The gross mean for all sites was 344 μg/g OC (GSD = 173–682), roughly equivalent to other remote sites in the Canadian Arctic with no known local hydrocarbon source. n-alkanes accounted for >90 % of residues. Diagnostic ratios (e.g., Carbon Preference Index (CPI), Odd-Even Predominance (OEP)) indicated mixed sources of n-alkanes, likely due to the input from vascular plants and ombrotrophic peat in northern and western watersheds, and primary production within the Bay. The elevated proportion of high molecular weight n-alkanes at deep water sites is consistent with lotic particulate organic matter deposited in the nearshore environment and redeposited offshore. Ʃ36PAHs were a small fraction (1.9 %) of hydrocarbons, with a gross mean of 5.68 μg/g OC (GSD = 3.30–9.79). PCA separated deep water sediments from nearshore and community samples due to 4 alkylated naphthalenes which usually indicate a petrogenic source but probably indicates a natural source due to the lack of other petrogenic markers. Priority PAHs (i.e., Ʃ16PAH) varied from 31.5 % to 56.6 % of the Ʃ36PAH residues. The concentrations of individual PAHs were well below the Interim Sediment Quality Guidelines recommended by the Canadian Council of Ministers of the Environment.

Latitudinal difference in the molecular distributions of lipid compounds in the forest atmosphere in China

Lipids are important biogenic markers to indicate the sources and chemical process of aerosol particles in the atmosphere. To better understand the influences of biogenic and anthropogenic sources on forest aerosols, total suspended particles (TSP) were collected at Mt. Changbai, Shennongjia, and Xishuangbanna that are located at different climatic zones in northeastern, central and southwestern China. n-Alkanes, fatty acids and n-alcohols were detected in the forest aerosols based on gas chromatography-mass spectrometry. The total concentrations of aliphatic compounds ranged from 15.3 ng m−3 to 566 ng m−3, and fatty acids were the most abundant (44–95%) followed by n-alkanes and n-alcohols. Low molecular weight- (LFAs) and unsaturated fatty acids (UnFAs) showed diurnal variation with higher concentrations during the nighttime in summer, indicating the potential impact from microbial activities on forest aerosols. The differences of oleic acid (C18:1) and linoleic acid (C18:2) concentrations between daytime and nighttime increased at lower latitude, indicating more intense photochemical degradation occurred at lower latitude regions. High levels of n-alkanes during daytime in summer with higher values of carbon preference indexes, combining the strong odd carbon number predominance with a maximum at C27 or C29, implied the high contributions of biogenic sources, e.g., higher plant waxes. In contrast, higher concentrations of low molecular weight n-alkanes were detected in winter forest aerosols. Levoglucosan showed a positive correlation (R2 > 0.57) with high- and low molecular weight aliphatic compounds in Mt. Changbai, but such a correlation was not observed in Shennongjia and Xishuangbanna. These results suggest the significant influence of biomass burning in Mt. Changbai, and fossil fuel combustion might be another important anthropogenic source of forest aerosols. This study adds useful information to the current understanding of forest organic aerosols at different geographical locations in China.

Characteristics of hydrocarbons in hydrothermal products of the Clam hydrothermal field from the Okinawa trough

The hydrothermal products of the Clam hydrothermal field from the Okinawa Trough were analyzed by gas chromatography–mass spectrometry to determine abundances of hydrocarbons. The n-alkanes in the hydrothermal products conformed to a bimodal distribution and exhibited an odd-to-even predominance of high molecular weight and an even-to-odd predominance of low molecular weight n-alkanes with maxima at C16 and C18. The total concentration of n-alkanes in hydrothermal sediment was much higher than that in hydrothermal sulfide and altered rock. The carbon isotopic value of individual n-alkanes in hydrothermal sediment was slightly higher than that in pelagic sediment. The concentrations and individual carbon isotopic compositions of n-alkanes suggest that the n-alkanes in hydrothermal products may be mainly the result of the metabolic activity of submarine microorganisms. Additionally, the present results suggest that the abiogenic contribution to source of hydrocarbons in hydrothermal products of the Clam hydrothermal field from the Okinawa Trough should not be ignored.

Parent and methyl polycyclic aromatic hydrocarbons and n-alkanes emitted by construction machinery in China

Construction machinery emits considerable quantities of organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs) and n-alkanes, which significantly affect air quality, human health, and climate change. However, actions to reduce the pollution caused by these pollutants are insufficient due to a lack of comprehensive studies. Therefore, 16 United States Environmental Protection Agency (EPA) priority control PAHs (pPAHs), nine methyl PAHs (mPAHs), and 27 n-alkanes (C12-C38) in particulate matter (PM2.5) emitted by 20 construction machines of different types and emission standards, operated under three modes, were measured in this study. The results showed that (1) the total fuel-based emission factors of pPAHs, mPAHs, and n-alkanes for construction machinery were in the ranges 0.033–1.43, 0.027–1.37, and 1.32–87 mg/kg fuel, respectively. (2) The average emission factors of pPAHs, mPAHs, and n-alkanes in excavator and bulldozer emissions were higher than those in loader and forklift emissions, which can be attributed to machine type, operation mode, emission standards, and engine power. (3) Pry, Phe, C18-C22, 1-mNaP, and mFluo emissions were significantly dominant. Some diagnostic ratios of PAHs (e.g., Ant/(Ant + Phe), Flu/(Flu + Pry), BaA/(BaA + Chry), and IP/(IP + BghiP)) were consistent with those emitted by liquid fossil fuel combustion, whereas the ratios of low molecular weight n-alkanes (C ≤ 24) to high molecular weight (C > 24) n-alkanes from construction machines were higher than those for on-road gasoline vehicles, diesel vehicles, and vessels. (4) The benzo(a)pyrene equivalents (BaPeq) and lifetime cancer risk (LCR) values of PAHs from bulldozer and forklift emissions were higher than those from excavator and loader emissions, especially under working modes. Furthermore, the BaPeq and LCR values of PAHs from construction machineries were higher than that specified by GB3095-2012 and 10^−4, respectively, thereby indicating that PAHs emitted from construction machines pose high health risks.

Latitudinal Difference in the Molecular Distributions of Lipid Compounds in the Forest Atmosphere in China

Lipids are important biological markers to indicate the sources and chemical process of aerosol particles in the atmosphere. To better understand the influences of biological and anthropogenic sources on forest aerosols, total suspended particles (TSP) were collected at Mt. Changbai, Shennongjia, and Xishuangbanna that are located at different climatic zones in northeastern, central and southwestern China. n-Alkanes, fatty acids and n-alcohols were detected in the forest aerosols based on gas chromatography-mass spectrometry. The total concentrations of aliphatic compounds ranged from 33.2 ng m-3 to 520 ng m-3, and fatty acids were the most abundant (44-95%) followed by n-alkanes and n-alcohols. Low molecular weight- (LFAs) and unsaturated fatty acids (UnFAs) showed diurnal variation with higher concentrations during the nighttime in summer, indicating the potential impact from microbial activities on forest aerosols. The differences of oleic acid (C18:1) and linoleic acid (C18:2) concentrations between daytime and nighttime increased at lower latitude, indicating more intense photochemical degradation occurred at lower latitude regions. High levels of n-alkanes during daytime in summer with higher values of carbon preference indexes, combining the strong odd carbon number predominance with a maximum at C27 or C29, implied the high contributions of biological sources, e.g., higher plant waxes. In contrast, higher concentrations of low molecular weight n-alkanes were detected in winter forest aerosols. Levoglucosan showed a positive correlation (R2>0.57) with high- and low molecular weight aliphatic compounds in Mt. Changbai, but such a correlation was not observed in Shennongjia and Xishuangbanan. These results suggest the significant influence of biomass burning in Mt. Changbai, and fossil fuel combustion might be another important anthropogenic source in Northeast China. This study adds useful information to the current understanding of forest organic aerosols at different geographical locations in China.

Contrasting compositions and sources of organic aerosol markers in summertime PM2.5 from urban and mountainous regions in the North China Plain

Although the chemical compositions and sources of organic aerosols (OAs) have been extensively investigated at the summit of Mt. Tai in the North China Plain (NCP), their vertical distributions and characterizations in the Mt. Tai region is not well known. To better understand the vertical variations of OAs in the urban and mountainous atmosphere, PM2.5 samples were collected simultaneously on a daytime/nighttime basis at two sites of different altitudes (Taian urban site: 20 m above ground; the summit of Mt. Tai: 1534 m a.s.l.) during the summer of 2016. The concentrations of all the determined chemical compounds (e.g., OC, EC, inorganic ions, saccharides, n-alkanes, PAHs and hopanes) except for biogenic secondary organic aerosol (BSOA) tracers decreased with the increase in sampling height, indicating the relatively larger contribution of anthropogenic pollutants to OAs at the lower heights. The relatively low concentration levels of biomass burning tracers (e.g., levoglucosan, galactosan and mannosan) and the insignificant correlations of levoglucosan with carbonaceous species demonstrated a negligible effect of biomass burning on the mountaintop atmosphere. The enhanced concentrations of BSOA tracers were observed with the increase of height, largely due to the more intensive secondary oxidation of volatile organic compounds (VOCs) under the stronger radiation conditions at the summit. The daytime concentrations of carbonaceous species, primary sugars, sugar alcohols, PAHs and low molecular weight n-alkanes were significantly higher than those in nighttime at Mt. Tai, suggesting that these chemical compounds at the summit of Mt.Tai aerosols were transported from the ground surface by valley breezes in daytime. There was no correlation between BSOA tracers and relative humidity (RH) or liquid water content (LWC) at both the sites, because both the high RH and LWC can suppress the acid-catalyzed formation of BSOA due to the dilution of the aerosol acidity.

Bulk and molecular composition variations of gold-tube pyrolysates from severely biodegraded Athabasca bitumen

Gold-tube pyrolysis experiments were performed on two Athabasca oil sand bitumens at 300 °C to 525 °C with 2 °C/h rate and 25 °C step under 50 MPa. Pyrolysis temperature of 425 °C is critical for weight loss of bulk bitumen and hydrocarbon generation and destruction. Polar compounds are the main source of saturated and aromatic hydrocarbon, gas and coke fractions. Molecular compositions in pyrolyzates vary systematically with increasing pyrolysis temperatures. High molecular weight n-alkanes (C26+) are gradually destructed during pyrolysis due to thermal cracking. Moderate molecular weight n-alkanes (C21–C25) show the highest thermal stability in designed pyrolysis temperatures. The loss of low molecular weight n-alkanes (C20−) might be caused by volatilization during pyrolysis, which may alter commonly used molecular parameters such as ∑n-C20−/∑n-C21+, Pr/n-C17 and Ph/n-C18. Aromatic hydrocarbons were generated from 300 to 425 °C, then condensation and dealkylation have been initiated at 425 °C as evidenced by decreased summed alkylnaphthalenes to alkylphenanthrenes ratios and increased unsubstituted aromatics to substituted homologs ratios in higher temperatures. The occurrence of anthracene and benz[a]anthracene in pyrolysates indicates pyrogenic origin, while fluoranthene shows unexpected behaviors during pyrolysis. Ratios derived from them are not always reliable for pyrogenic source input diagnosis in environmental samples.

Biotransformation of chemically dispersed diesel at sub-zero temperatures using artificial brines

ABSTRACT The biotransformation of hydrocarbon compounds in seawater at sub-zero temperature has gained research interest in recent years with the most focus placed on temperatures around 0°C. In this study, biotransformation of dispersed diesel at sub-zero temperatures (−2°C to −6°C) in artificial brines, prepared by adding Instant Ocean salt to natural seawater to increase salinity, is examined. The oil was pre-mixed with dispersant Finasol 51 to prepare the dispersed oil at 2 mg l−1. The native microorganisms in sub-arctic seawater were able to adapt to high salinity and lower temperature in the sea ice brine at tested temperatures and were capable of biotransforming hydrocarbon compounds. Complete depletion of low and middle-range molecular weight n-alkanes, 2/3 ring PAHs and their alkylated compounds was observed after 123 days at −2°C. The depletion extents of hydrocarbon compounds were reduced at −6°C in comparison with −2°C, especially for PAHs and alkylated hydrocarbons. This study suggests that: there is a potential for biodegradation of dispersed oil in sea ice brine at temperatures between −2°C and −6°C. However, for oil with high pour point, the biodegradation process will be more affected by low temperature. Therefore, to predict the fate of dispersed oil at low temperature, the biodegradation rate should be established for each individual oil type and at a specific temperature.

High daytime abundance of primary organic aerosols over Mt. Emei, Southwest China in summer

Organic molecular composition of fine aerosols in the free troposphere is poorly understood. Here, PM2.5 (particles with aerodynamic diameters ≤ 2.5 μm) samples were collected at the summit of Mt. Emei (3080 m a.s.l.) in the Southwestern China on a daytime and nighttime basis during summer 2016 (June–July). The samples were analyzed by solvent-extraction followed by derivatization and gas chromatography/mass spectrometry (GC/MS). Four classes of organic compounds, i.e. n-alkanes, fatty acids, saccharides and lignin/resin acids were measured quantitatively. Fatty acids were found to be the most abundant species with an average concentration of 401 ± 419 ng m−3 (range 25.7–1490 ng m−3) in the daytime, similar to the average concentration at night (399 ± 447 ng m−3, 19.6–1970 ng m−3). However, the concentrations of biomass burning tracers (e.g., levoglucosan), primary biological aerosol tracers (e.g., mannitol and arabitol) and low molecular weight n-alkanes derived from fossil fuel combustion in daytime samples were obviously higher than those in nighttime samples. The results suggest that valley breezes transported a large number of aerosols and their precursors from the ground surface to the summit of Mt. Emei in the daytime. Estimated with tracer-based methods, the contributions of biogenic primary sources (plant debris, fungal spore, and biomass burning) to organic carbon was in the range of 3.28–83.5% (22.0 ± 17.5%) in the daytime and 3.45–37.4% (10.9 ± 8.97%) at night. As the largest contributor, biomass burning was an important anthropogenic/natural source of aerosol particles in the free troposphere over Mt. Emei. CapsuleValley/mountain breeze is an important constraint to the temporal variations in organic aerosols over Mt. Emei.

Changes of composition and content of tricyclic terpane, hopane, sterane, and aromatic biomarkers throughout the oil window: A detailed study on maturity parameters of Lower Toarcian Posidonia Shale of the Hils Syncline, NW Germany

A total of 30 core samples of organic matter-rich Lower Toarcian shale (Posidonia Shale) were geochemically analyzed to study systematic changes in the quantitative and qualitative composition of specific biomarkers at different thermal maturities ranging from 0.48 to 1.45% vitrinite reflectance (VRr). The samples are derived from 5 wells (Hils Syncline, NW Germany) each representing a different level of maturation (0.48, 0.68, 0.73, 0.88, 1.45 %VRr). In NW Germany, Posidonia Shale was deposited under marine, oxygen-deficient bottom water containing initially high amounts of TOC (above 10%) and marine type I-II kerogen. Upon maturation, organic carbon has been lost and hydrogen index values have decreased. Biomarker ratios reflecting this maturation very well include ratios of short over long-chain n-alkanes, ratios of pristane and phytane over nC17 and nC18, Ts/(Ts + Tm), C29Ts/(C29Ts + C29H), ratios based on DMDBTs, and TA(I)/TA(I + II) ratios (triaromatic steroids). The evolution of different steroid-, hopane-, naphthalene-, phenanthrene- and dibenzothiophene-related parameters is documented and compared to literature.Concentrations of individual hydrocarbons were measured in order to obtain quantitative data on biomarker abundance and their evolution upon maturation. Whereas there is a general trend of increasing biomarker content from immature (0.48 %VRr) to early mature (0.68 %VRr) conditions and of decreasing biomarker content with maturation from 0.68 to 0.88 %VRr, there are some exceptions from this trend, especially at low levels of maturity. Almost no polycyclic biomarkers were detected at the highest maturity level of 1.45 %VRr in well Haddessen, where n-alkanes and aromatic hydrocarbons are predominant. The overall pattern of polycyclic biomarker abundance is not only determined by isomerization and aromatization processes, but mainly by preferential degradation of thermally less stable biomarkers leading to the observed modifications of biomarker maturity parameters.Furthermore, outer and inner sections from the 10 cm wide cores were compared in order to find out, whether 40 years of dry storage in a core repository affected the biomarker parameters. No significant and systematic differences have been observed, with exception of the most mature Haddessen well, where low molecular weight n-alkanes (<nC21) are more abundant in the outer part.

Geochemical features of bitumen shows in the Lower-Middle Devonian deposits of the Northern-Western part of Kotelny Island (Novosibirsk Island Archipelago) v

The work presents the results of organic matter (OM) study of rocks, the composition, chemical structure of chloroform bitumen (CB), their fractions and the nature of the hydrocarbon biomarkers distribution in samples taken from outcrops. The obtained results confirmed the existing idea of ​​the domanicoid nature of OM and the high oil and gas potential of the studied deposits. According to our data, the aquagenic type of OM is indicated by a high content of Corg, a high yield of CB, a high content of oils in the composition of synbitumoids, and the predominance of relatively low molecular weight n-alkanes with a maximum at nС15-18. A sufficient maturity of bitumen can be judged by CPI coefficients close to unity and low absorption coefficients of oxygen-containing groups and bonds in the CB, thus deposits entered the main oil generation zone and generated liquid hydrocarbons that could migrate and form clusters. According to the data of Chromato Mass Spectrometry, it is shown that a feature of the composition of CB from the Lower Devonian sediments is the presence of high concentrations of dibenzothiophenes, in contrast to the Middle Devonian, which may be associated with the formation of the initial OM in an environment with higher hydrogen sulfide contamination of sediments. It has been suggested that naphthides generated by aquagenic OM of the Lower Devonian deposits can be enriched with dibenzothiophenes. The studied bitumen shows are mainly syngenetic in nature and have been influenced by hypergenic oxidation (judging by the nature of the IR spectra of resinous components) and contact metamorphism. According to the characteristics of the distribution of saturated hydrocarbons, it was shown that, in the Middle Devonian, bitumen occurrences along with chemical oxidation were affected to a different degree of bacterial oxidation processes, in contrast to the Lower Devonian bitumen shows. The results can be used to assess the generation potential of oil source strata and to forecast the prospects of oil and gas potential in the shelf of the eastern sector of the Russian part of the Arctic.

Geochemical impacts of hydrothermal activity on surface deposits at the Southwest Indian Ridge

Submarine hydrothermal circulation has attracted much scientific interest since seafloor hydrothermal activity was first observed in the 1970s; an area of particular interest is the impact of exported inorganic and organic materials from hydrothermal vent systems into the open ocean. In 2007, the first active hydrothermal vent field, with vent fluid temperatures up to 379 °C, was discovered at the ultraslow spreading Southwest Indian Ridge (SWIR), where active vents are much less abundant than fast spreading ridges, and the effect of hydrothermal extrusion on surface sediments is not fully understood. To explore how geochemical proxy signatures respond to hydrothermal activity, we investigated the distributions of elements, minerals and lipids in surficial normal marine sediments, metalliferous sediments and low-temperature hydrothermal deposits collected from the SWIR. The results showed different effects of hydrothermal activity on the surface deposits. The normal marine sediments were predominantly calcium carbonate characterized by > 42% CaO and > 90% calcite, with a significant autochthonous marine contribution to organic matter (OM) and a predominance of lower molecular weight alkanols and fatty acids; they were uninfluenced by hydrothermal activity but received some terrigenous input represented by abundant high molecular weight n-alkanes with an odd-over-even predominance. The near-field metalliferous sediments and hydrothermal deposits were very different. Some near-field metalliferous sediments were influenced by low-temperature hydrothermal activity, and their distributions of elements and minerals were similar to those of hydrothermal deposits, which were characterized by abundant Fe/Si and opal/nontronite. Other near-field metalliferous sediments were evidently influenced by mixing of high-temperature hydrothermal sulfides typically containing abundant Cu/Zn. With respect to the organic matter assemblages, near-field deposits contained little evidence for thermal maturation of organic matter and all were characterized by a strong microbial signature, including hopanoids, isoprenoidal and non-isoprenoidal dialkyl glycerol ether lipids, and low molecular weight n-alkanes with an even carbon number predominance. The far-field metalliferous sediments, despite the influence of non-buoyant plumes and slightly higher concentrations of hydrothermal-derived metals (e.g., Fe, Cu and Zn), had the same distribution of organic lipids and major mineral composition (> 90% calcite) as did normal marine sediments. Thus, the influence of non-buoyant plume inputs appears to have been minimal possibly due to the dilution of in situ microorganisms by normal marine organisms in sediment and seawater. Furthermore, these characteristics indicate inorganic indices based on abundant metal elements derived from the hydrothermal systems (such as Fe/Cu/Zn content, ∑REE/Fe, the ternary diagram of Fe, Cu×100 and Ca) are more sensitive, serving as better proxies than organic matter assemblages to differentiate the effects of diverse hydrothermal activity on surface deposits.

Distribution of n-alkanes from Lake Wanghu Sediments in Relation to Environmental Changes

Concentrations and distribution of n-alkanes (n-C14 to n-C33) in Lake Wanghu sediment core were analyzed to investigate the environmental changes in the lake during the past~100 years. Relatively higher concentrations of mid-and long-chain n-alkanes with a strong odd-over-even carbon number predominance indicated organic matter contributions dominated by aquatic macrophytes and terrestrial plants. The lower values of 2n-C31/(n-C27+n-C29) highlighted a type of landscape dominated by woody plants. The environmental changes that have been happening over the past 100 years in Lake Wanghu can be divided into three stages, based on the organic matter sources inferred from the changes in n-alkane parameters in the sediments. Before the 1950s, higher values of terrigenous/aquatic ratio (TAR) and high-/low-molecular weight n-alkanes (H/L) indicated vascular, plant-derived sediments deposited during a low-nutrient, clear-water phase with frequent water exchange between the lake and the Yangtze River. Between the 1950s and 1980s, decrease in values of H/L and TAR, and increase in the proportion of mid-and short-chain n-alkanes indicated a shift towards mid-and shorter-chain components likely associated with the increasing contribution of macrophytes and algae. Lower 2n-C17/(n-C23+n-C25) values indicated a relatively low algal abundance. In that stage, the lake trophic state increased slightly with the decreasing influence of the Yangtze River flow. After the 1980s,H/L and TAR values increased and then decreased, total n-alkane concentrations and 2n-C17/(n-C23+n-C25) increased significantly, especially after 2000s, suggesting the main contributor to high organic matter input most likely shifted to algae because of the eutrophication caused by anthropogenic activities.

Quantification of low molecular weight n-alkanes in lake sediment cores for paleoclimate studies

Organic biomarkers, such as n-alkanes, can be used as proxies in a range of paleoclimate and paleoenvironmental investigations. n-Alkanes accumulate in lacustrine sediments and can therefore be used to determine past terrestrial conditions by investigating chain length ratios and compound specific isotope signatures. Analytical methods for their quantification in sediments have been described previously; however, method validation has not been rigorously reported for the low molecular weight (LMW) n-alkanes, which have recently been gaining attention as useful proxies. Using spike and recovery experiments with a simple sand matrix, we found that LMW n-alkanes are prone to low recovery due to volatilization when following common protocols for quantification. This is alarming because low recovery can lead to misinterpretation of n-alkane results. On the other hand, we found that isotope fractionation was fortunately not observed even when volatilization loss was high. We addressed the problem of LMW n-alkane volatilization by developing an alternative extraction and sample preparation method. The optimized method, which employs pressurized liquid extraction, was tested by using it to extract n-alkanes from sediments from three Southern New Zealand lakes (Hinemoa, Ohau and Thomas) with different properties. Recovery of the C15-C40n-alkanes ranged from 32–66% for Lake Hinemoa, 54–85% for Lake Thomas and 61–89% for Lake Ohau. Variation in n-alkane recovery from the three lakes was attributed to differences in sediment properties, notably organic matter and particle size, and an approach for calculating ‘adjusted concentration’ with a sediment-specific adjustment factor for each n-alkane is suggested.