Carbon Preference Index Values Research Articles

Sources of hydrocarbons and their risk assessment in seawater and sediment samples collected from the Nile Delta coast of the Mediterranean Sea

The aim of this work is to examine the levels, distribution, bases, and hazards of n-alkanes (n-C9 to n-C20) and PAHs in the seawater and sediments around oil production locations in the whole delta region. The variations in the levels of PAHs and n-alkanes in seawater and sediment of the Nile delta coast of the Mediterranean were investigated using GC–MS/MS. The Σn-alkanes residues ranged between 12.05 and 93.51 mg/L (mean: 50.45 ± 17.49 mg/L) and 4.70 to 84.03 µg/g (mean: 31.02 ± 27.995 µg/g) in seawater and sediments, respectively. Total PAHs concentrations ranged between 4.485 and 16.337 μg/L (average: 9.47 ± 3.69 μg/L) and 1.32 to 28.38 ng/g (average 8.61 ± 7.57 ng/g) in seawater and sediment samples, respectively. The CPI (carbon preference index) values fluctuated between 0.62 and 1.72 (seawater) and from 0.234 to 2.175 (sediment), proposing the variation sources of n-alkane in the studied area. PAHs concentrations were lower than the Effective Range Low (ERL) and Effective Range Median (ERM) levels. The Toxic Equivalent Quotient (TEQ) values oscillated between 0.002 and 6.84 ng/L and from 3.72 to 13.48 ng/g for the seawater and sediment samples, respectively. The Ant/(Ant + Phe) ratio in sediment and seawater samples indicated a pyrolytic source while the BaA/(BaA + Chry) ratio indicates petrogenic sources in most of the studied stations.

Intermittent hydrothermal alteration and silicification of black mudstones found in the Middle to Upper Miocene Yagen Formation, Shimokita Peninsula, Northeast Japan

AbstractOrganic geochemical processes in hydrothermal alteration system in terrestrial areas were investigated in the Shimofuro geothermal field, Northeast Japan. This study describes a continuous long mudstone outcrop of the Middle to Late Miocene Yagen Formation on the Shimokita Peninsula, Aomori Prefecture. The outcrop located near Mt.Hiuchi‐dake shows sequential alteration with a color change from black to white. Contents of total organic carbon (TOC) vary from 0.00% to 0.46% according to litho‐color change and become higher for black and lower for gray to white. TOC contents show a negative correlation with SiO2 concentration. These indicate that TOC contents in the outcrop strongly depend on silicification caused by hydrothermal alteration. The mineral assemblages are composed of alunite, kaolinite, illite and pyrite, and indicate distinct alteration zones with acidic to neutral hydrothermal activities. Composition of the minerals formed by the alteration suggests that the temperature of hydrothermal fluid ranged from 150 to 250°C in a high‐sulfidation hydrothermal system. Regarding the extracted hydrocarbons, particularly n‐alkane distributions are significant. Values of Carbon Preference Index (CPI) increase up to 2.8 with increasing alteration and with decreasing TOC contents. This can be explained by two processes, (1) at the site of highly hydrothermal alteration, thermal cracking of organic matter in black mudstone strongly occurred and produced low‐molecular gaseous hydrocarbons, and (2) at the site of inner rock with a distance from the hydrothermal alteration, thermal cracking moderately occurred and produced medium to long chain n‐alkanes which were overlapped with original n‐alkanes. Very low Tmax values were found at the hydrothermal zone. This implies that natural extraction, migration, and precipitation of bituminous organic matter were driven by hydrothermal fluid.

Distribution of Hydrocarbons in the Snow Cover of Natural and Urbanized Landscapes in the South of the Far East, Russia.

This study analyzed total organic carbon (TOC), petroleum products (PP), suspended materials (SM), volatile aromatic hydrocarbons (toluene, o-xylene, etc.) and n-alkanes in the snow cover of Bol'shekhekhtsirsky, Zeysky state natural reserves and Khabarovsk, on 4, 5 and 9 stations in the south of the Russian Far East in March 2020. In Bol'shekhekhtsirsky reserve, the concentrations of TOC, PP, and SM in snow samples were in the range of 1.5-2.4, 0.06-0.11, and 11.4-1.9mg/L, 1.4-1.9, 0.02-0.05, and 11-23mg/L in Zeysky reserve, while in Khabarovsk were 1.7-23.7, 0.12-1.26, and 25-294mg/L, respectively. In addition, the benzene, toluene, and o-xylene concentrations of snow samples ranges from not detected (ND) to 2.4, ND-3.1, and 1.1-2.7µg/L in Khabarovsk, ND-1.3, ND-2.1, and ND-2.7µg/L, respectively in Bol'shekhekhtsirsky reserve. Carbon preference index values of n-alkanes were consistent with anthropogenic sources for stations 7, 8 and 2 in Khabarovsk (Heat Power Plants 1, 2 and city roads). The snow of the Zeysky Reserve is not contaminated with organic pollutants, and can be used as a conditional background for the south of the Russian Far East.

Effect of salinity on the preservation of plant-derived n-alkyl compounds in the terrestrial-aquatic interface

In sediments, plant biomolecules (n-alkanes and fatty acids) serve as robust proxies in paleoenvironmental studies. Although the factors controlling preservation and isotopic composition of plant biomolecules are understood in soil systems, the effect of changes in depositional environments in land-sea interfaces, especially in hypersaline environments, is not so well constrained. In this study, we observed that in bed sediments, the plant biomolecules are preserved with carbon preference index (CPI) values > 1 in high molecular weight (HMW) n-alkanes in the hypersaline, metahaline, and euhaline regions of the Pulicat lagoon, India. However, in sub-surface sediments (up to 70 cm depth), the CPI values are consistently < 1 in the hypersaline region, but > 1 in the euhaline and metahaline regions. In the hypersaline region, the alteration of plant biomolecules possibly results from halophilic bacterial degradation and fatty acid to n-alkane reduction in anaerobic conditions (pristane/phytane values < 1), during the weaker northeast monsoon (44–60 cm sub-surface). Prolonged hypersaline conditions and associated anoxia resulted in a higher isotopic difference between fatty acids and n-alkanes (δ13CFA-ALK value) in the hypersaline region (3.1 ± 1.5‰) compared to metahaline (2.2 ± 1.0‰) and euhaline (1.5 ± 1.0‰) regions. Although in the hypersaline region the HMW fatty acids have CPI values > 1, the higher δ13CFA-ALK value also suggests the alteration of fatty acids. This study suggests that if plant-derived n-alkanes are altered, the δ13C values and distribution patterns of plant-derived fatty acids should be critically evaluated before using it as an alternative proxy in coastal environments.

Gas chromatography‐mass spectrometry in assessment of road run‐off sediment quality parameters

Surface sediment samples were collected in the Banja Luka city area, near heavy traffic roads and the Vrbas river basin, in order to determine the origin of the organic substance. For this purpose, soluble organic substances were extracted by the Soxhlet method, and extracts were fractionated by the method of column chromatography into a group of saturated hydrocarbons, aromatic hydrocarbons, and polar compounds. The total amount of soluble organic substance was in the range of 1185–3050 μg/kg. Fractions were analyzed by gas chromatography-mass spectrometry method using a non-polar HP-5 ms stationary phase with a He 99.999% flow rate of 1 ml/min. Based on the chromatograms characteristic for n-alkanes m/z 71, steranes m/z 217, and terpenes m/z 191, the specific n-alkanes range was determined (n-C14–n-C39). n-Alkanes domination of odd/even C-number and carbon preference index values ranged from 1.12–2.48. The calculated parameters showed that the organic substance in the samples is of sedimentary origin with a significant anthropogenic input. In addition, based on the analysis of aromatic fractions and the detected unresolved complex mixture, the microbiological degradation of organic substance was determined.

Source Indication and Geochemical Significance of Sedimentary Organic Matters from the Xisha Area, the South China Sea.

Although various geochemical and geophysical investigations have already indicated a great resource potential in the Xisha area of the South China Sea, the origin of organic matter and molecular evidence for tracing the migration of hydrocarbons from deep petroleum reservoirs are still lacking. In this study, systematic organic geochemical analyses, including bulk organic matter parameters and lipid biomarkers were performed for deep sediments from two cores. The C/N ratios and δ13C and δ15N values of organic matter in most of the samples, together with the maxima of short-chain n-alkanoic acids and mid-chain n-alkanols, high abundances of monounsaturated fatty acids C18:1ω9 and C22:1ω13, jointly indicate the dominance of marine organic matter. n-Alkanes in sediments from core GMGS4-XH-W06B are characterized by small unresolved complex mixture (UCMs) humps, high odd/even predominance (OEP) and carbon preference index (CPI) values, clearly exhibiting characteristics of modern sediments. However, the sediments for core GMGS4-XH-W03B are featured with big UCMs, associated with OEP and CPI values around 1.0, showing signatures of petroleum hydrocarbons from high maturity sources. Considering the geologic background, the biomarker signatures are solid evidence for indicating the existence of underlying petroleum reservoirs, and may provide the valuable information for assessing the hydrocarbon resources in the Xisha area.

Organic geochemical characteristics and shale oil potential of the middle Eocene early-mature shale in the Nanpu Sag, Bohai Bay Basin, Eastern China

The decline of proven conventional petroleum resources in the shallow portions of the Nanpu sag has shifted attention to the exploration of deep unconventional oil and gas resources there, especially the shale oil resources in the middle Eocene shales of the Shahejie Formation (MES shales). In this study, to assess the oil potential of the MES shales, we carried out a systematical geochemical and basin modeling characterization. The results show that the MES shales have low maturity and are at the early stage of hydrocarbon generation, with a mean vitrinite reflectance of 0.64% and low ratio of C27 18α(H)-22, 29, 30-trisnorneohopane to C27 17α(H)-22, 29, 30-trisnorhopane (0.44–1.18). The MES shales contain abundant organic matter (OM), with an average total organic carbon content of 2.21 wt %. Biomarker analyses show that the OM in the MES shales derived mainly from floating macrophyte and aquatic algae, microalgae and bacteria. The sapropelinite group in the MES shales is predominant in the organic macerals, and the kerogen is sapropelic and dominated by types I and II1. Biomarker analyses also reveal that the MES shales were deposited in the stratified water column as suggested by the presence of gammacerane, under relatively warm and wet climatic conditions. The anoxic conditions built up in the water column facilitated the OM preservation, although slight microbial degradation resulted in relatively high carbon preference index values. Modeling results based on geochemical data and basin analyses show that considerable quantities of hydrocarbons remain in the low-maturity MES shales. The preliminary estimate of the quantity of shale oil resources in the Gaoliu area of Nanpu sag is approximately 1.78 × 108 t. Nanpu sag have good shale oil potential, and shale oil exploration may be more feasible for MES shales, especially in the context of in-situ heating technology.

The Composition and Distribution of Volatile Organic Compounds in Sediments of the East Taijinar Salt Lake in Northern Qinghai-Tibet Plateau

The main objective of this study was to explore the composition and distribution of volatile organic compounds (VOCs) and the factors that affect their distribution in the salt lake sediments. Thirteen sediment samples were collected from a depth profile in the East Taijinar Lake, China. VOCs of different samples were extracted by headspace solid phase microextraction. Gas chromatography-ion mobility spectrometry, gas chromatography-mass spectrometry, and X-ray diffraction were used to analyze the VOCs, n-alkanes, and minerals present in samples. Thirty-four VOCs were identified and classified into seven types, including terpenes, furans, esters, aldehydes, ketones, alcohols, and acids, apart from six contaminants. It was found that 24 of the most prevalent compounds in clay were on average 101.45% higher than those in sandstone and halite because of the sedimentary environment, while the remaining ten (2-acetylfuran, 2-pinene D, etc.) were on average 13.27% higher in sandstone and halite sediments than in clay. This can be attributed to their different biological sources, porosity, and higher salinity. Based on the Q-cluster analysis, the 13 sediment samples were split into two groups, including the group according to composition and the group based on distribution of VOCs. In this study, it was found that the VOCs correlate positively with detrital minerals, with Group I exhibiting a high content of detrital minerals (&amp;gt;25%), while Group II showed the opposite characteristics. The consumption of organic matter (OM) by microorganisms leads to the formation of VOCs in sediment. The values of carbon preference index and n-alkane further demonstrate that the organic matter of the two groups came from different sources, exogenous and endogenous. Pr/Ph ratios, Pr/C17, and Pr/C18 also suggest that the OM in all sediments was strongly affected by microorganisms in an anoxic environment. Together, these results demonstrate that the OM from different biological sources and microbial activities played a critical role in deciding the composition and distribution of VOCs in the sediment. This study also shows that the proportion of VOCs in halite was discernably higher than that in clay and sandstone and that the content of VOCs should be considered when studying OM in salt lake sediments.

Palaeoenvironmental reconstruction of the Konin Basin (central Poland) during lignite accumulation linked to the mid-Miocene climate optimum

We reconstruct palaeoenvironmental conditions during the formation of the first Mid-Polish Lignite Seam (MPLS-1) of the Konin Basin of central Poland, which is of mid-Miocene age. In terms of macropetrography, the MPLS-1 comprises different lithotype associations, predominantly xylodetritic lignite, and represents the peat deposits of mires most likely inhabited by Myricaceae-Cyrillaceae shrubs. Palynological assemblages obtained from the MPLS-1 at the Adamów Lignite Opencast Mine indicate the existence of wetland/palustrine and mesophytic vegetation during the accumulation of the peat. Applying the Coexistence Approach to the palynological assemblages, climate is inferred to have been warm temperate and humid with a mean annual temperature (MAT) of 15.7–18.0 °C with plant communities similar to modern pocosins developed on coastal plains in southeastern USA. The palynological assemblages from the MPLS-1 at Jóźwin IIB Lignite Opencast Mine show palaeofloristic cyclicality. In the studied section, five cycles were identified, dominated by swamp forests (Taxodium/Glyptostrobus–Nyssa) similar to modern forests in southeastern USA and China. The climate at that time was warm temperate and humid (MAT = 15.7–20.5 °C) based on CA application. This is consistent with the significant contribution of warm temperate plants, typical of mixed mesophilous forests, which grew in the vicinity of the swamp forests. The results of geochemical analyses are generally in agreement with palaeobotanical studies, indicating angiosperm dominated the peat-forming vegetation. However, the geochemically-derived average temperature ranges of ca. 24.2–25.0 °C, based on the carbon preference index (CPI), is significantly higher. These differences between palynologically- and geochemically-derived MATs can be explained by the influence of changes in vegetation on the CPI values. The periodic contribution of algae and microorganisms to the biomass while the water table was raised is indicated by elevated abundances of short-chain n-FAs. In contrast, under acidic conditions, bacterial activity was limited, as indicated by ββ/(ββ + αβ) hopane ratios and low sulfur content. Based on sedimentological data, the MPLS-1 was mainly formed either proximal (Jóźwin IIB, Tomisławice) or more distal (Adamów) to the river channels as evidenced by the presence or absence of siliciclastic partings within the MPLS-1. In summary, the MPLS-1 accumulated mostly as low-lying mires under freshwater conditions, corresponding to the last peak of the Mid-Miocene Climatic Optimum and to the period thereafter when the climate showed a cooling trend. Our findings are placed in the context of palaeotectonics and palaeoclimates at regional and global scales.

Crude Oil Classification Based On Age And Provenance From The Southern Iraq: A Review

A collection of 165 crude oils, 12 oil seeps, and 24 extracts and recovered samples from 25 oil exploratory wells and 6 oil seeps in the Southern Mesopotamian Basin were studied. Biomarker configurations and other organic geochemistry parameters were used to discover the depositional environments and to classify the oil samples as provenance groups. Petroleum liquids were geochemically classified into four groups. The first group of oils, Middle Jurassic Zagros Fold Belt, is located in the Maysan, Basra, and Thi qar provinces of the basin that has pristane/phytane (Pr/Ph) proportions ≤0.97 and contains sufficient gammacerane. Methylphenanthrene index 1 (MPI 1) values show that the first group of oils is mature. Oils from Group 2, Upper Jurassic–Lower Cretaceous Sulaiy/Yamama, by disparity have Pr/Ph proportions between 0.72 and 1.12 and relatively moderate C28/C29 steranes, 0.52-0.88. Ts/Tm ratios indicate thermal maturity for Group 2 oils. Unlike oils from other groups, the oils from Group 3, Cretaceous to Tertiary oils, in Subba Field hold the highest canonical variable (CV) values that range between 0.43 and –2.30. The fourth group, Late Triassic-Middle Jurassic oil seeps, is the oldest among all groups. This group holds an average carbon isotope ratio –28.25‰ and –28.10‰ for saturates and aromatics respectively, which are the lowest values among all oils in the studied region. The Tithonian-Berriasian Sulaiy/Yamama oils further divided into three subgroups. The first subgroup, A, has carbon preference index (CPI) values of ≤1.08 (average 0.86) and C28/C29 sterane of 0.56-1.13 with an average of 0.65. Second subgroup, B, holds CPI ≤1.18 (average 0.99) and C28/C29 sterane 0.55-0.82 with an average of 0.63. The last subgroup, C, has CPI values ≤0.93 (average 0.85) and high C27 and C29 steranes (average 46.5% and 39.61%, respectively). In the same way, the Group 3 can be further subdivided into two subgroups based on values of carbon isotopes for saturates and aromatics. The oils from this group are heterogeneous and can be further divided into Tertiary Subgroup and Cretaceous Subgroup.

Variation of the Distribution of Atmospheric n-Alkanes Emitted by Different Fuels’ Combustion

This study presents the emission profiles of n-alkanes for different vehicular sources in two Brazilian cities. Atmospheric particulate matter was collected in São Paulo (Southeast) and in Salvador (Northeast) to determine n-alkanes. The sites were impacted by bus emissions and heavy and light-duty vehicles. The objective of the present study is to attempt to differentiate the profile of n-alkane emissions for particulate matter (PM) collected at different sites. PM concentrations ranged between 73 and 488 µg m−3, and the highest concentration corresponded to a tunnel for light and heavy duty vehicles. At sites where diesel-fueled vehicles are dominant, the n-alkanes show a unimodal distribution, which is different from the bimodal profile observed in the literature. Carbon preference index values corresponded to anthropogenic sources for most of the sites, as expected, but Cmax varied comparing to literature and a source signature was difficult to observe. The main sources to air pollution were indicated by principal component analysis (PCA). For PCA, a receptor model often used as an exploratory tool to identify the major sources of air pollutant emissions, the principal factors were attributed to mixed sources and to bus emissions. Chromatograms of four specific samples showed distinct profiles of unresolved complex mixtures (UCM), indicating different contributions of contamination from petroleum or fossil fuel residues, which are unable to resolve by gas chromatography. The UCM area seemed higher in samples collected at sites with the abundance of heavy vehicles.

Sources and Distribution of n-Alkanes in Borneo Peat Core, Sarawak, Malaysia

This work reported the n-alkanes contents in a 10 m peat core collected at Timbarap, Sarawak. Different biomarker proxies were used to understand the predominance of sources present in the tropical peatland of Borneo. The total concentrations of n-alkanes in selected depths of Timbarap peat core ranged between 0.01 and 12.60 μg/g with an average of 1.58 μg/g. The presence of strong odd-to-even predominance from higher molecular weight n-alkanes homologues with high values of carbon preference index (CPI) provide clear evidences of the terrestrial plant wax assemblages. Increment of low-molecular-weight n-alkanes provide an indicator of biogenic-aquatic organic materials. The ratios of isoprenoids (pristane and phytane) have shown that the peat core was under anaerobic and reducingdepositional conditions, which could result the predominance source that alternated between aquatic-biogenic and terrestrial-derived materials.

Anthropogenically driven differences in n-alkane distributions of surface sediments from 19 lakes along the middle Yangtze River, Eastern China.

During the past few decades, the Yangtze River basin has undergone massive anthropogenic change. In order to evaluate the impacts of human interventions on sediment n-alkanes of lakes across this region, the aliphatic hydrocarbon fractions of 19 surface sediment samples collected from lakes along the middle reaches of the Yangtze River (MYR) were analyzed using gas chromatography-mass spectrometry. The n-alkanes extracted from the sediments contained a homologous series from C15 to C34, with a notable predominance of odd carbon compounds except for sediments from the more intensively industrialized Lake Daye, in which > C21 n-alkanes showed no odd/even predominance, and carbon preference index (CPI) approached unity. Abundance values of middle-chain (C21, C23, and C25) and long-chain (C27, C29, C31, and C33) n-alkanes in Lake Daye were approximately 4 to 3 times greater than the average for other lakes, reaching 272.4 and 486.3μg/g TOC, respectively, in the study. Short-chain n-alkanes (C15, C17, and C19) in the sediments varied in abundance from 10.0 to 76.2μg/g TOC across the study and showed a moderate correlation with total phosphorus (TP) concentrations in the overlying water. The results indicated anthropogenic eutrophication enhanced the accumulation of short-chain n-alkanes in sediments because the primary producers in which they are synthesized are highly susceptible to nutrient forcing. Middle-chain n-alkane abundances were less affected by eutrophication and generally enriched in macrophyte lakes, while long-chain n-alkanes tend to be low in sediments from more eutrophic water. In the case of Lake Daye, direct discharges of petroleum products from heavy industry have introduced quantities of petroleum n-alkanes (> C21), far exceeding the amounts of biogenic input, and the sediment > C21 n-alkanes detected in this study showed typical characteristics of petroleum source. In other lakes, inputs of petroleum products from surface runoff of vehicle/traffic emissions associated with urbanization and economic growth contributed comparatively few n-alkanes to sediments, resulting in declines in CPI for > C21 n-alkanes, most obviously in Lakes Huanggai, Donghu, and Futou. Calculated CPI values suggest that a major proportion of the n-alkanes present in these lakes are derived from biogenic input. The results of this study provided evidences that n-alkane profiles of lake sediments respond sensitively to human-induced eutrophication and different sources of petroleum pollution.

Discriminating sources and preservation of organic matter in surface sediments from five Antarctic lakes in the Fildes Peninsula (King George Island) by lipid biomarkers and compound-specific isotopic analysis

Lakes are important paleoenvironmental archives retaining abundant information due to their typical high sedimentation rates and susceptibility to environmental changes. Here, we scrutinize the organic matter (OM) composition, origin and preservation state in surface sediments from five lakes in a remote, warming-sensitive, and poorly explored region partially covered by the retreating Collins Glacier in King George Island (Antarctica), the Fildes Peninsula. Lipid biomarkers of terrestrial origin (i.e. high-molecular weight n-alkanes, n-alkanoic acids, and n-alkanols; β-sitosterol, campesterol, and stigmasterol) were detected in the five Fildes Lakes, with the smallest basin (i.e., Meltwater) showing a particularly strong moss imprint. Aquatic source indicators such as low C/N and terrestrial over aquatic ratios (TAR), or less negative δ13C values were preferentially found in the mid-sized lakes (i.e., Drake and Ionospheric). Sedimentary carbon in the larger lakes (i.e., Uruguay and Kitezh) displayed a largely biogenic origin (i.e., values of carbon preference index, CPI, ≫1), whereas the three lakes close to Collins Glacier (i.e., Drake, Meltwater, and Ionospheric) showed certain contribution from petrogenic sources (CPI ~ 1). The results suggest that the geochemical signature of the surface sediments in the five Fildes lakes is determined by factors such as the distance to the retreating Collins Glacier, the proximity to the coast, or the lake depth. This study illustrates the forensic interest of combining lipid biomarkers, compound-specific isotopic analysis, and bulk geochemistry to reconstruct paleoenvironments and study climate-sensitive regions.

Organic molecular evidence of seafloor hydrocarbon seepage in sedimentary intervals down a core in the northern South China Sea

The hydrocarbons in sedimentary organic matter (OM) at Site 4B in the Pearl River Mouth Basin (PRMB), northern South China Sea (SCS) were analyzed. The odd/even predominance (OEP) of long chain n-alkanes (>n-C24) with CPI (carbon preference index) values from 1.62 to 3.80 and n-C29/n-C31 being the two most abundant in most of the samples are strongly indicative of a terrestrial higher plant source, and the even/odd predominance (EOP) distribution of mid-chain n-alkanes (n-C16–22) suggests a marine bacterial input, probably chemical autotrophic bacteria. However, the biomarker distributions at the 65–70 cm, 80–85 cm and 85–90 cm intervals show a similar to those of crude oils, which were characterized by a dominance of an unresolved complex mixture (UCM) in the n-C20+ region, low CPI values (<1.5) of long chain n-alkanes, low values of ββ/(αβ + ββ + βα)-C30 hopane (<0.15), and high values (>9) of total tricyclic terpanes/αβ-C30 hopane. These features are typical characteristics of mature OM that has experienced catagenesis and metagenesis, suggesting that outside hydrocarbons migrated into these three intervals. In terms of petroleum systems developed in the PRMB, hydrocarbon seepage from deep source rocks via a diaper structure and fault system is proposed to be responsible for the occurrence of this mature OM.

Temperature effect on abundance and distribution of leaf wax n-alkanes across a temperature gradient along the 400 mm isohyet in China

Long chain n-alkanes are plant wax biomarkers that are widely used in paleoenvironmental reconstructions. Temperature is an important influence on the composition of leaf wax n-alkanes. However, to date, understanding of changes in the abundance and distribution of leaf wax n-alkanes with temperature remains unclear. The main reason is that the interference of precipitation on leaf wax n-alkanes has not been effectively removed in most investigations of natural ecosystems. We sampled 357 plants across a temperature gradient along an isohyet in China to minimize the influence of precipitation and evaluate the effect of temperature on the abundance and distribution of leaf wax n-alkanes. Most plant functional groups showed similar distributions in total n-alkane concentration (∑alk), carbon preference index (CPI) and average chain length (ACL). CPI values were not sensitive to temperature change. ∑alk values were negatively correlated with summer mean temperature (TJJA, June to August) for most plant functional groups. ACL values were always positively related to temperature, especially TJJA. However, large variability in ∑alk and ACL occurred within plants from the same site. Therefore, this study suggests that ∑alk and ACL can indicate relative environmental temperature, but they should not be used as quantitative proxies of paleo-temperature.

Concentrations and Composition of Sphagnum Peat Lipids Depending on Temperature in the Climatic Zones of Western Siberia

The composition of n-alkanes; sesqui-, di-, and triterpenoids; steroids; carboxylic acids; and tocopherols of sphagnum peat from the southern, middle, and northern taiga and forest-tundra of Western Siberia was studied by gas chromatography–mass spectrometry. It was shown that the latitudinal shift to the north leads to the preservation of the peat lipid components and sufficiently high values of carbon preference index (CPI) close to those of mire plants. This can be caused by a decrease in microbiological activity due to a decrease in the mean annual temperature. Towards the north, the total concentrations of n-alkanes, steroids, pentacyclic triterpenoids, squalene, and tocopherols increased, and a ratio of the total concentration of steroids to the concentrations of pentacyclic triterpenoids and hopanes decreased.

Severe drought-influenced composition and δ13C of plant and soil n-alkanes in model temperate grassland and heathland ecosystems

Drought events are predicted to increase under future climate change. In temperate ecosystems, plants are capable of resisting drought due to their hydrophobic wax layer, in which n-alkanes are important constituents. In soils, plant-derived n-alkanes are comparatively resistant to degradation. To improve understanding of the significance of n-alkanes in plant-soil systems during a severe drought period (104 days), we investigated bulk organic carbon (Corg) concentration, total lipid extract (TLE) concentration, and n-alkane molecular ratios such as average chain length (ACL), carbon preference index (CPI) and chain length ratios of different n-alkane compounds, in addition to the compound-specific isotope composition (δ13C) of n-alkanes in model temperate grassland and heathland plant-soil systems. Although plant communities of two (heathland) and four (grassland) species were available, only one representative species per biome was accessible for the current study.Heathland plants and soil revealed significantly higher concentrations of Corg and TLE compared with grassland. TLE and alkane composition responded quickly during the first drought phase (0–40 days). This indicates that plants were actively utilizing C and produced more n-alkanes in order to withstand drought, which was confirmed by increased (2–3‰) δ13C values for n-alkanes in shoot biomass. However, during later drought phases all the parameters remained constant for plants and soils. This suggests limited change in biosynthesis and cycling of plant lipids such as n-alkanes during intense drought. Surprisingly, during the first drought phase, increased ACL and CPI values in soil demonstrated a rapid input of plant-derived long chain n-alkanes to soil, which was not expected due to the decadal residence time of alkanes in soil. The study enabled tracing of plant metabolic response in terms of alkane biosynthesis under different phases of drought and rapid cycling of alkanes in the plant-soil system.

Occurrence and sources of aliphatic hydrocarbons in soils within the vicinity of hot mix asphalt plants in Obigbo and Igwuruta Areas of Rivers State, Nigeria

This study investigated the occurrence and sources of aliphatic hydrocarbons (AHCs) in soils within the vicinity of hot mix asphalt (HMA) plants. Soil samples were collected from two HMA plants and analysed with gas chromatography - flame ionisation detector (GC-FID). Sample collection was from both surface (0-15 cm) and subsurface (15-30 cm) soils at an increasing distance of 10 m from the HMA plants while the control samples at both depths were collected at 1 km away from the plants. The AHCs concentration (nC9-nC38) in soils from both HMA Plants ranged from 8.16 - 433.04 mg/kg and 5.91-177.83 mg/kg for surface and subsurface soils respectively while the concentration in the control samples ranged from 5.97 - 23.95 mg/kg and 2.52 - 13.31 for surface and subsurface soil respectively. The sources of the AHCs were determined using isoprenoid ratios, carbon preference index (CPI) and maximum carbon chain (Cmax). The isoprenoid ratios and CPI values of the samples closer ( 20 m from the HMA plants showed mixture of both anthropogenic and biogenic sources. Keywords : Asphalt Plants; Soil; Aliphatic hydrocarbons; Pristane; Phytane.

Molecular Paleoclimate Reconstructions over the Last 9 ka from a Peat Sequence in South China.

To achieve a better understanding of Holocene climate change in the monsoon regions of China, we investigated the molecular distributions and carbon and hydrogen isotope compositions (δ13C and δD values) of long-chain n-alkanes in a peat core from the Shiwangutian (SWGT) peatland, south China over the last 9 ka. By comparisons with other climate records, we found that the δ13C values of the long-chain n-alkanes can be a proxy for humidity, while the δD values of the long-chain n-alkanes primarily recorded the moisture source δD signal during 9–1.8 ka BP and responded to the dry climate during 1.8–0.3 ka BP. Together with the average chain length (ACL) and the carbon preference index (CPI) data, the climate evolution over last 9 ka in the SWGT peatland can be divided into three stages. During the first stage (9–5 ka BP), the δ13C values were depleted and CPI and Paq values were low, while ACL values were high. They reveal a period of warm and wet climate, which is regarded as the Holocene optimum. The second stage (5–1.8 ka BP) witnessed a shift to relatively cool and dry climate, as indicated by the more positive δ13C values and lower ACL values. During the third stage (1.8–0.3 ka BP), the δ13C, δD, CPI and Paq values showed marked increase and ACL values varied greatly, implying an abrupt change to cold and dry conditions. This climate pattern corresponds to the broad decline in Asian monsoon intensity through the latter part of the Holocene. Our results do not support a later Holocene optimum in south China as suggested by previous studies.