N-alkane Distribution Patterns Research Articles

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.

Even carbon number predominance observed in C50-C110 n-alkanes and monocyclic alkanes in the highly mature source rock

Carbon number predominance of n-alkanes and monocyclic alkanes reveals essential geological information such as biological source, sediment maturity, and paleoenvironmental conditions. The carbon number range of the special distribution pattern is reported to lower than C40, prominantly in the range of C24-C34. Generally, this special distribution pattern fades away with the increase of maturity. However, these well-accepted beliefs are challenged by our investigations. In this work, C10-C125 n-alkanes and monocyclic alkanes were identified for the first time in the highly mature source rock of Well Luntan-1 in Tarim Basin (China). Both series exhibited significant even carbon number predominance observed in C50 and C110, but there was no carbon-number predominance observed before C50. The similar distribution patterns of n-alkanes and monocyclic alkanes indicated that they might have the same biological precursors. The discovery of higher alkanes with ultra-long carbon chains and their extraordinary display of carbon number predominance provided us with a new perspective, which may open up the era of macromolecular biomarkers exploration.

Maceral and Organic Geochemical Characteristics of the No. 6 Coal Seam from the Haerwusu Surface Mine, Inner Mongolia, China

Haerwusu Surface Mine of the Jungar Coalfield is a large coal mine. Its coal formation environments have not been reported in detail. In order to reconstruct the paleoenvironment of the peat formation, nine samples were collected, and were analyzed using microscope, column chromatography, gas chromatography (GC), and gas chromatography–mass spectrometry (GC–MS). According to the results of the microscopic analysis, the average random vitrinite reflectance ( Rr) is 0.73%, indicating a low rank bituminous coal. Vitrinite group is the predominant macerals with an average content of 54.54%, followed by inertinite group with an average of 35.99%. The higher inertinite contents indicate widespread wildfire events during the peat formation. The distribution pattern of n-alkanes, the cross plot between Pr/ n-C17 and Ph/ n-C18, the lower saturated/aromatic hydrocarbon ratios (0.22–0.68) and the presence of cadalene, retene, simonellite indicates that the organic matter is predominantly terrestrial higher plants with a small amount of aquatic organisms. The ternary diagram of Pr/Ph, Pr/ n-C17 and Ph/ n-C18 and the relative abundance of fluorene, dibenzofuran and dibenzothiophene indicate a continental–oceanic alternative facies. The higher contents of combustion-derived PAHs are also indicative of widespread wildfire events during peat formation.

Measurement and Distribution Pattern of n-alkanes in Size-Segregated Aerosols During Diwali Festival in Delhi, India

Measurement and Distribution Pattern of n-alkanes in Size-Segregated Aerosols During Diwali Festival in Delhi, India

Geochemical Characteristics and Significance of Organic Matter in Hydrate-Bearing Sediments from Shenhu Area, South China Sea.

Rock-Eval pyrolysis and the biomarker composition of organic matter were systematically studied in hydrate-bearing sediments from the Shenhu area, South China Sea. The n-alkane distribution patterns revealed that the organic matter in the sediments appeared to originate from mixed sources of marine autochthonous input, terrestrial higher plants, and ancient reworked organic matter. The low total organic carbon contents (average < 0.5%) and the low hydrogen index (HI, <80 mg HC/g TOC) suggested the poor hydrocarbon-generation potential of the deposited organic matter at a surrounding temperature of <20 °C in unconsolidated sediments. The abnormally high production index and the fossil-originated unresolved complex mixture (UCM) accompanied by sterane and hopane of high maturity indicated the contribution of deep hydrocarbon reservoirs. Preliminary oil-to-source correlation for the extracts implied that the allochthonous hydrocarbons in the W01B and W02B sediments might have originated from the terrestrial source rocks of mature Enping and Wenchang formations, while those of W03B seem to be derived from more reduced and immature marine source rocks such as the Zhuhai formation. The results of the organic extracts supported the previous identification of source rocks based on the isotopic composition of C2+ hydrate-bound gases. The biomarker of methanogens, squalane, was recognized in the sediments of this study, possibly suggesting the generation of secondary microbial gases which are coupled with the biodegradation of the deep allochthonous hydrocarbons.

Spatial distribution of n-alkanes in the catchment and sediments of Lake Lugu, Southwest China: Implications for palaeoenvironment reconstruction

n-Alkanes have been widely used to reconstruct palaeoenvironmental variations in lacustrine environments. However, for robust reconstructions, improving the understanding of the origin of n-alkanes and their distribution within the lake is essential. Therefore, we examined the distribution pattern of n-alkanes in the aquatic plants within Lake Lugu (a deep alpine lake on the southeastern margin of the Tibetan Plateau, southwest China), and terrestrial plants and topsoils in the catchment, to unravel the origin of sedimentary n-alkanes and further investigate the spatial distribution of n-alkanes from surface sediments in this lake. The aquatic plants are dominated by mid-chain C23 and C25, terrestrial plants and soils by long-chain C29, and 76% of the surface sediment samples show C29 predominance. The average chain length (ACL) and the aquatic plant proxy (Paq) values of surface sediments are between those of aquatic and terrestrial plants and soils. Thus, n-alkanes from autochthonous (aquatic plants) and allochthonous (terrestrial plants and soils) sources were apparent in the surface sediments. A substantial spatial distribution of n-alkanes exists within Lake Lugu: the n-alkane concentrations of total, aquatic, and terrigenous origins are concentrated in the northwestern portion of the lake's north basin, which may be attributed to the underwater topography and increased human-induced soil erosion in this area. Similarly, the clear spatial heterogeneity of ACL21–33 and Paq may suggest that the sedimentary n-alkanes comprise a mixture contribution of autochthonous and allochthonous production, which might be the major source of n-alkanes in the lakeshore, and a higher proportion of autochthonous n-alkanes is present in deep water. However, there is no significant correlation between the Paq of sediments and water depth in Lake Lugu; thus, the application of Paq as a lake-level indicator should be used with caution in deep-water lakes similar to Lake Lugu.

Geochemical Characterization of the Eocene Coal-Bearing Source Rocks, Xihu Sag, East China Sea Shelf Basin, China: Implications for Origin and Depositional Environment of Organic Matter and Hydrocarbon Potential

Eocene coal-bearing source rocks of the Pinghu Formation from the W-3 well in the western margin of the Xihu Sag, East China Sea Shelf Basin were analyzed using Rock-Eval pyrolysis and gas chromatography–mass spectrometry to investigate the samples’ source of organic matter, depositional environment, thermal maturity, and hydrocarbon generative potential. The distribution patterns of n-alkanes, isoprenoids and steranes, high Pr/Ph ratios, abundant diterpanes, and the presence of non-hopanoid triterpanes indicate predominant source input from higher land plants. The contribution of aquatic organic matter was occasionally slightly elevated probably due to a raised water table. High hopane/sterane ratios and the occurrence of bicyclic sesquiterpanes and A-ring degraded triterpanes suggest microbial activity and the input of microbial organisms. Overwhelming predominance of gymnosperm-derived diterpanes over angiosperm-derived triterpanes suggest a domination of gymnosperms over angiosperms in local palaeovegetation during the period of deposition. The high Pr/Ph ratios, the plot of Pr/n-C17 versus Ph/n-C18, the almost complete absence of gammacerane, and the distribution pattern of hopanes suggest that the samples were deposited in a relatively oxic environment. Generally, fluctuation of redox potential is coupled with source input, i.e., less oxic conditions were associated with more aquatic organic matter, suggesting an occasionally raised water table. Comprehensive maturity evaluation based on Ro, Tmax, and biomarker parameters shows that the samples constitute a natural maturation profile ranging from marginally mature to a near peak oil window. Hydrogen index and atomic H/C and O/C ratios of kerogens suggest that the samples mainly contain type II/III organic matter and could generate mixed oil and gas.

Palaeobotanical and biomarker evidence for Early Permian (Artinskian) wildfire in the Rajmahal Basin, India

This study provides a combined analysis on the palynology, fossil charcoal and biomarkers of the subsurface coal deposits from a borehole RMB #2 drilled at the Dhulia Coal Block, Rajmahal Basin, India, in attempts to establish the chronology of sedimentation and to propose palaeobotanical as well as geochemical evidence for the occurrence of wildfires in these sediments. The palynological investigation suggests a Scheuringipollenites barakarensis palynoassemblage from the lower Barakar Formation, dated as Artinskian (Early Permian) in age. This assemblage reveals the dominance of Glossopteridales and sub-dominance of taxa belonging to Cordaitales and Coniferales. Fossil charcoal in sediments is usually recognized as a direct indicator for the occurrence of palaeo-wildfires. More data involving the anatomical features of fossil charcoal analyzed by Field Emission Scanning Electronic Microscope broaden our knowledge on Early Permian wildfires from the peninsula of India. The studied macroscopic charcoal fragments exhibit anatomical details such as homogenized cell walls, uniseriate simple and biseriate alternate pitting on tracheid walls and rays of varying heights pointing to a gymnospermous wood affinitity. The excellent preservation of charcoal fragments, shown by their large sizes and almost unabraded edges, suggests a parautochthonous origin. The embedded biomarker study performed for charcoal sediments and its characterization demonstrate the presence of n-alkanes, isoprenoids, terpenoids and aromatic compounds. A bimodal distribution pattern of n-alkanes with a Cmax at n-C25 is identified. Diterpenoids and pentacyclic terpenoids are identified, indicating the input of an early conifer vegetation and bacterial activity, respectively. The identified polyaromatic hydrocarbon (PAH) compounds, together with the charcoal fragments, clearly suggest that repeated wildfire events occurred during the deposition of these Artinskian sediments in the Rajmahal Basin.

Early Palaeogene Climate Variability Based on n-alkane and Stable Carbon Isotopic Composition Evidenced from the Barsingsar Lignite-bearing Sequence of Rajasthan

The assessment of variations and the reconstruction of palaeoclimate, based on the distribution of n-alkanes and stable carbon isotope data, during early Palaeogene have been made on the Barsingsar lignite-bearing sequence associated with Palana Formation (Bikaner-Nagaur basin). The distribution pattern of various n-alkanes and the derived indices/ratios have widely been used as palaeoclimate indicators in several depositional realms. The distribution of n-alkanes in the studied sequence varies from C13 to C34. The values of calculated n-alkane parameters range from 26.20–28.39 (aliphatic chain length (ACL) index); 0.32–7.21 (low-to-higher molecular weight (L/H) ratio); 0.42–0.85 (Proxy wax (Pwax)); 0.20–0.67 (Proxy aqueous (Paq)); 0.28–5.22 (terrigenous/aquatic ratio (TAR)); 0.16–0.79 (C23/C29 ratio); 1.14–6.31 (C27/C31 ratio) and 1.47–7.02 (C29/C31 ratio). The δ13C varies from −24.8 to −26.1‰ and the TOC varies from 9.6 to 69.5 wt.%. All these variations indicate the changes in palaeoclimate from dry and warm to cool and wet conditions during the deposition of this lignite-bearing sequence. Further, it is also suggested that the climatic condition was cooler than that of the Palaeocene-Eocene thermal maximum (PETM) event.

Pollen and lipid analysis of coprolites from Yuhuicun and Houtieying, China: Implications for human habitats and diets

Sixteen coprolites from the Chinese Neolithic sites of Yuhuicun and Houtieying, Anhui Province, were analysed for pollen and lipid biomarkers. Steroid compounds provide evidence that the excrements originated from dogs and humans. Distribution patterns of n-alkanes and n-fatty alcohols indicate three sources: microorganisms, animal fats and plant wax lipids, further related to intestinal microbes, animal- and plant-derived food. Extremely high frequencies of Quercus pollen may refer to seasonal habitat for hunting activities with the assistance of dogs. High proportions of miliacin point to the consumption of millets.

Influence of plant growth form, habitat and season on leaf-wax n-alkane hydrogen-isotopic signatures in equatorial East Africa

Abstract Leaf-wax n-alkanes are produced by terrestrial plants, and through long-term preservation in sediments their stable hydrogen-isotopic signature (δ2Hwax) provides useful information on past hydrological variation for paleoclimate reconstructions. However, gaps remain in our understanding of the relationships between the isotopic signatures of leaf waxes and the plants’ source water. In this study, we investigated the influence of plant growth form, habitat and season on the distribution patterns and δ2Hwax values of 14 plant species (among which are two grasses, five trees and seven shrubs) sampled during four successive dry and wet seasons in three distinct habitats around Lake Chala in equatorial East Africa. Variation in δ2Hwax was analyzed with linear mixed-effect models and compared with the associated values of xylem water (δ2Hxylem), leaf water (δ2Hleaf) and biosynthetic hydrogen fractionation (ebio). Our results show that plant growth form was the most important driver of modern-day δ2Hwax variability in the study area, and that differences in δ2Hwax among habitats to a large extent reflect how each major growth forms is represented in those habitats. Individual plant species appear to express substantial species-specific isotopic fractionation that cannot be attributed to the tested external factors but rather seem to depend on intrinsic (e.g., plant phenological and biosynthesis-related) factors. For the purpose of calibrating δ2Hwax signatures against vegetation types, it is thus crucial to analyze representative samples of the plant communities present in the study area. Our results further indicate that paleohydrological studies in regions receiving rain from multiple moisture sources must take into account possible seasonal bias in the δ2Hwax signature relative to annual rainfall, due to unequal use of those moisture sources by the plants. Finally, the strong influence of plant growth form on δ2Hwax values argues for δ2Hwax variation in paleo-records being evaluated in conjunction with independent proxy data on changes in vegetation composition. Differences in n-alkane distribution patterns among trees, shrubs and grasses (e.g., average chain length, carbon preference index and C31/(C29 + C31) ratio) may provide such proxies, and can be produced from the same leaf-wax n-alkane dataset used to determine δ2Hwax.

Use of n-alkanes to trace erosion and main sources of sediments in a watershed in southern Brazil

Erosive processes can transport sediments containing nutrients, heavy metals and contaminants of organic and inorganic origin into bodies of water, therefore affecting the local ecosystem and the population that benefits from the water sources. In order to better understand the origin of sediment sources and establish mitigation measures, the use of the sediment fingerprinting technique has been highlighted. Thus, the present work had as objective to apply n-alkanes in order to trace and understand the main sources of organic matter in sediments and associate the results with land and soil occupation. The study area is located in the municipality of Rio Negrinho - Brazil, in the Saci river basin. Soil samples were collected and classified according to their use and occupation, as well as and samples of local vegetation to be used as reference. The distribution of n-alkanes in the sediments was compared with the distribution found in the vegetation and soil. Previously, a distribution pattern of n-alkanes had been identified in all major vegetation used to trace the source of organic matter and hence the soil. The concentrations of total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP) and granulometry were also analyzed in the soil and sediment samples. Indexes between n-alkanes were used and applied to assess the source together with statistical analysis (PCA). In sum, the results showed that the sediments are mainly composed of Pinus taeda reforestation soils, as well as soil from the abandoned roads used to transport the cut trees, while the contribution of autochthonous sediments was found to be minimal. In this way, the fingerprint technique served as an auxiliary tool in order to establish measures for the good management of a river basin, bringing important information about the contributing sources of sediment to water bodies.

Leaf wax &amp;lt;i&amp;gt;n&amp;lt;/i&amp;gt;-alkane distributions record ecological changes during the Younger Dryas at Trzechowskie paleolake (northern Poland) without temporal delay

Abstract. While of higher plant origin, a specific source assignment of sedimentary leaf wax n-alkanes remains difficult. In addition, it is unknown how fast a changing catchment vegetation would be reflected in sedimentary leaf wax archives. In particular, for a quantitative interpretation of n-alkane C and H isotope ratios in terms of paleohydrological and paleoecological changes, a better understanding of transfer times and dominant sedimentary sources of leaf wax n-alkanes is required. In this study we tested to what extent compositional changes in leaf wax n-alkanes can be linked to known vegetation changes by comparison with high-resolution palynological data from the same archive. We analyzed leaf wax n-alkane concentrations and distributions in decadal resolution from a sedimentary record from Trzechowskie paleolake (TRZ, northern Poland), covering the Late Glacial to early Holocene (13 360–9940 yr BP). As an additional source indicator of targeted n-alkanes, compound-specific carbon isotopic data have been generated in lower time resolution. The results indicated rapid responses of n-alkane distribution patterns coinciding with major climatic and paleoecological transitions. We found a shift towards higher average chain length (ACL) values at the Allerød–Younger Dryas (YD) transition between 12 680 and 12 600 yr BP, coevaled with a decreasing contribution of arboreal pollen (mainly Pinus and Betula) and a subsequently higher abundance of pollen derived from herbaceous plants (Poaceae, Cyperaceae, Artemisia), shrubs, and dwarf shrubs (Juniperus and Salix). The termination of the YD was characterized by a successive increase in n-alkane concentrations coinciding with a sharp decrease in ACL values between 11 580 and 11 490 yr BP, reflecting the expansion of woodland vegetation at the YD–Holocene transition. A gradual reversal to longer chain lengths after 11 200 yr BP, together with decreasing n-alkane concentrations, most likely reflects the early Holocene vegetation succession with a decline of Betula. These results show that n-alkane distributions reflect vegetation changes and that a fast (i.e., subdecadal) signal transfer occurred. However, our data also indicate that a standard interpretation of directional changes in biomarker ratios remains difficult. Instead, responses such as changes in ACL need to be discussed in the context of other proxy data. In addition, we find that organic geochemical data integrate different ecological information compared to pollen, since some gymnosperm genera, such as Pinus, produce only a very low amount of n-alkanes and for this reason their contribution may be largely absent from biomarker records. Our results demonstrate that a combination of palynological and n-alkane data can be used to infer the major sedimentary leaf wax sources and constrain leaf wax transport times from the plant source to the sedimentary sink and thus pave the way towards quantitative interpretation of compound-specific hydrogen isotope ratios for paleohydrological reconstructions.

Assessing environmental changes in Lake Shihwa, South Korea, based on distributions and stable carbon isotopic compositions of n-alkanes

We investigate historical environmental changes in an artificial lake, Lake Shihwa in South Korea, based on bulk (TOC, TN, C/N ratio, δ13CTOC, and δ15NTN) and molecular (concentrations and δ13C of n-alkanes) parameters, by analyzing riverbank sediments (n = 12), lake surface sediments (n = 9), and lake core sediments (n = 108). Although the bulk organic parameters showed similar characteristics for all lake surface sediment samples, the distribution pattern and δ13C of n-alkanes revealed distinct differences between 2009 samples and 2012/2016 samples. This change of sedimentary organic matter characteristics can be attributed to operation of the tidal power plant that began in 2011, which improved lake water circulation and thus changed the lake sedimentary environment from anoxic to more oxic conditions. The vertical profiles of bulk and molecular lake sediment core records collected in 2009, especially at the site closest to the dike, showed a drastic shift around 1987, indicating that stronger anoxic sedimentary conditions prevailed after 1987. This is linked to sea dike construction in 1987, which prohibited sea-lake water exchange and thus deteriorated water quality in Lake Shihwa. We conclude that Lake Shihwa has experienced severe environmental changes due to human activities.

Distribution and variability of n-alkanes in waxes of conifers

Epicuticular waxes have vital roles in the growth and development of plants and in defense. Conifers have a considerable amount of waxes on their cones and leaves. Here we characterized the n-alkane composition of Iranian conifers, including Juniperus oblonga, J. foetidissima, J. sabina, J. communis subsp. hemisphaerica, J. excelsa, Cupressus sempervirens, Platycladus orientalis from Cupressaceae and Taxus baccata from Taxaceae for the first time using GC-FID analyses. In the waxes, 25 n-alkane homologs with chain lengths ranging from C7 to C32 were identified. Short-chain n-alkanes were dominant in almost all samples with some exceptions. Complementary studies to elucidate complete wax constituents of Iranian conifers and n-alkane distribution pattern as a function of geographical and bioclimatic variables are recommended.

The fate of plant wax lipids in a model forest ecosystem under elevated CO2 concentration and increased nitrogen deposition

Atmospheric CO2 concentration and nitrogen (N) deposition have been altered by anthropogenic activity and they affect global biogeochemical cycles. It is still not clear how these environmental changes influence the storage and cycling of organic matter (OM) in soils, although this plays a key role in the biogeochemistry of terrestrial ecosystems. Here, we used n-alkanes as biomarkers for plant-derived OM in specific soil fractions. We investigated the effect of elevated CO2 concentration and increased N deposition on the molecular and isotopic (δ13C) composition of n-alkanes in above-ground and below-ground tree biomass (beech and spruce) and soil density fractions.The n-alkane distribution patterns of spruce needles and root biomass were well reflected in those of particulate soil OM. Long chain (C27–34) n-alkanes were preserved in soil by association with soil minerals, while mid-chain (C20–27) n-alkanes from plant biomass and particulate soil OM were ultimately degraded due to lack of physical protection. Renewal of n-alkanes was lower in roots and spruce needles than in beech leaves. Similar low renewal of n-alkanes in soil reflected the low input of n-alkanes from plant biomass to the soil n-alkane pool. n-Alkane biosynthesis in beech leaves was modified under high N deposition and similar effects were observed for n-alkanes in mineral soil fractions and bulk soil. Here, different biosynthesis of n-alkanes in beech leaves under high N deposition consequently led to a modified input of n-alkanes from plant biomass to soil, with a relatively low proportion of new (experimentally-derived) n-alkanes bound to soil minerals.

Geochemical characterisation of Tithonian–Berriasian Chia Gara organic-rich rocks in northern Iraq with an emphasis on organic matter enrichment and the relationship to the bioproductivity and anoxia conditions

Tithonian–Berriasian Chia Gara organic-rich rocks, located in Kurdistan (northern Iraq), were analysed based on inorganic and organic geochemistry to define the origin, type of organic matter, and the influencing factors of organic matter (OM) enrichment, including the OM input and preservation, and their relationship to the paleoenvironment conditions.The δ13Corg values of the Chia Gara rocks range from −29.99‰ to −26.93‰, with average values of approximately −28.8‰, indicating that the organic matter has a predominantly marine origin. Enhanced biological productivity within the photic zone of the water column during deposition of the Chia Gara Fm. is indicated by consistently high organic carbon content in most samples (average 3wt.%), as well as by bulk geochemical and biomarker characteristics. Major contributions by aquatic algae and microorganisms with a minor terrigenous organic matter contribution are indicated by the n-alkane distribution patterns and the composition of the hopanoids, steroids, and tricyclic terpenoids. Strongly reducing bottom water is indicated by low pristane/phytane ratios, homohopane distribution patterns, and the redox-sensitive trace elements geochemistry. Salinity stratification with alkaline bottom waters is indicated by high Sr/Ba ratios and the presence of gammacerane in the analysed Chia Gara samples. These data indicate that OM enrichment in the Tithonian–Berriasian Chia Gara rocks results from the combination of enhanced biological productivity and salinity stratification with anoxic bottom water conditions, which favoured OM preservation.

GC-MS analysis of cuticular lipids in recent and older scavenger insect puparia. An approach to estimate the postmortem interval (PMI)

An analytical method was developed to characterize puparia cuticular lipids (hydrocarbons, waxes) and to compare the molecular distribution patterns in the extracts from either recent or older puparia. Acid-catalyzed transesterification and solvent extraction and purification, followed by combined gas chromatography coupled to mass spectrometry, were optimized for the determination of hydrocarbons and fatty acid ethyl esters from transesterified waxes, extracted from a single species of a fly scavenger (Hydrotaea aenescens Wiedemann, 1830). Comparison between recent (2012) or older (1997) puparia contents has highlighted significant composition differences, in particular, a general decrease of the chain length in the n-alkane distribution pattern and, on the contrary, an increase of the ester chain length. Both extracts contain traces of three hopane hydrocarbon congeners. Preliminary results evidence the change in puparia lipid composition over time, thus potentially providing new indices for estimating postmortem interval.

Consistency of plant-specificn-alkane patterns in plaggen ecosystems: A review

Plaggen soils, formed by various vegetational inputs during century-long plaggen (i.e. sod) application, comprise remarkably stable organic matter. Source identification could contribute to a better understanding of carbon stabilization mechanisms in soils and reconstruction of Holocene vegetation and land-use history. Cuticular-derived n-alkane distribution patterns as present in current vegetation are recognized as valuable tools to discriminate input sources, but an assessment of their consistency and variability is lacking to date. Therefore, this review synthesizes information on published n-alkane patterns of vegetation species and their various parts that contributed to plaggen soil formation (i.e. Calluna vulgaris, Betula pendula, Quercus robur, Pinus sylvestris, Lolium perenne, Deschampsia flexuosa, Molinia caerulea and Poa annua). This provided in addition valuable information on potential sources of systematic variation (e.g. geography/climate, environmental conditions, ontogeny and seasonality). Method of extraction/analysis showed no evident effects on n-alkanes. n-Alkanes showed predominantly distinct patterns for different plaggen vegetation species and parts in the range C17–36. Prominent n-alkanes C27, C29, C31and C33allowed clear distinction between input by shrubs, trees and grasses to plaggen soils. Nevertheless, systematic variability was indicated among n-alkane patterns. Unfortunately, the current limited data set of n-alkane patterns did not allow for exact quantification of the controls of variation. The need for more systematic studies and the setup of a reference data base for vegetation species is highlighted to (1) advance application of n-alkane patterns in source identification, (2) gain more insight into controls on, magnitude and timing of variations and (3) improve our knowledge concerning input sources, carbon dynamics and stabilization mechanisms in (plaggen) soils.

Red palaeosols development in response to the enhanced east asia summer monsoon since the mid-pleistocene in South China: Evidence derived from magnetic properties and molecular fossil records

Although Pleistocene red paleosols are widely distributed in South China, paleoenvironmental interpretation has proved difficult because of intense weathering. Here we combine data from molecular fossil and magnetic properties to reconstruct a record of changes in pedogenic intensity for red paleosols in Southeast China. Depth distribution pattern of magnetic properties indicates that lower (higher) χ but higher (lower) values of HIRM (hard isothermal remanent magnetization) and SIRM (saturation isothermal remanent magnetization)/χ has tight relationship with the intensity of pedogenesis, especially the occurrence of well-developed net-like veins, which is absolutely responsible for the presence of anti-ferromagnetic minerals at the cost of fine-grained SP (superparamagnetic)/SD (single domain) ferrimagnetic minerals. The carbon distribution pattern of n-alkanes, n-alkanols, and n-alkanoic acids reflects the predominant contributions of microorganisms to the organic matter during pedogenesis, which provide direct evidence for strong microbial activities in response to the extremely hot-humid condition while white coarse net-like veins occurrence. Our results demonstrate that the presence of the enhanced East Asia summer monsoon has played a key role in the oxide-dominated weathering regime, and pedogenesis, and microbial activities. Changes in molecular ratios and magnetic properties are used to show that red paleosols have undergone three stages of soil formation in striking response to the evolution of the East Asia summer monsoon: (1) the most effective since the Middle Pleistocene; (2) moderately effective since 270 ka or so; (3) least effective since the last glacial. Our research provides important evidence to understand how red paleosols espond to global change since the Middle Pleistocene.