Size distributions of hydrocarbons in suspended particles from the Yellow River

Suspended particle samples from the Yellow River estuary were sorted into five grain size fractions to explore the effect of grain size distribution on organic matter content and composition. The n-alkanes and PAHs were determined for each size fraction. PAHs and n-alkanes were more abundant in the finer fractions and the loading decreases steadily with increasing of grain size. However, the total n-alkanes or PAHs normalized to organic C were lower in the smaller size fractions than those in the larger size fractions, suggesting n-alkanes or PAHs may be diluted by the addition of organic matter or gradually decreased by degradation in the smaller size fractions. The particulate n-alkanes in the Yellow River estuary consist of a mixture of compounds from terrigenous and riverine biogenic n-alkanes and more biogenic n-alkanes accumulate in finer particles. Particulate PAHs are related to combustion/pyrolysis processes of coal/wood, and the relative contribution of petrogenic PAHs increase with increasing grain size. The total particulate n-alkane and PAH discharges passing the Lijin Station are about 3.94 t d⁻¹ and 0.52 t d⁻¹, respectively. Fine particles (<32 μm) play a significant role in organic matter transfer.     

A compound-specific n-alkane δC and δD approach for assessing source and delivery processes of terrestrial organic matter within a forested watershed in northern Japan

We measured molecular distributions and compound-specific hydrogen (δD) and stable carbon isotopic ratios (δ¹³C) of mid- and long-chain n-alkanes in forest soils, wetland peats and lake sediments within the Dorokawa watershed, Hokkaido, Japan, to better understand sources and processes associate with delivery of terrestrial organic matter into the lake sediments. δ¹³C values of odd carbon numbered C₂₃-C₃₃n-alkanes ranged from −37.2‰ to −31.5‰, while δD values of these alkanes showed a large degree of variability that ranged from −244‰ to −180‰. Molecular distributions in combination with stable carbon isotopic compositions indicate a large contribution of C3 trees as the main source of n-alkanes in forested soils whereas n-alkanes in wetland soil are exclusively derived from marsh grass and/or moss. We found that the n-alkane δD values are much higher in forest soils than wetland peat. The higher δD values in forest samples could be explained by the enrichment of deuterium in leaf and soil waters due to increased evapotranspiration in the forest or differences in physiology of source plants between wetland and forest. A δ¹³C vs. δD diagram of n-alkanes among forest, wetland and lake samples showed that C₂₅-C₃₁n-alkanes deposited in lake sediments are mainly derived from tree leaves due to the preferential transport of the forest soil organic matter over the wetland or an increased contribution of atmospheric input of tree leaf wax in the offshore sites. This study demonstrates that compound-specific δD analysis provides a useful approach for better understanding source and transport of terrestrial biomarkers in a C3 plant-dominated catchment.     

The distribution, sources and toxicity risks of polycyclic aromatic hydrocarbons and n-alkanes in riverine and estuarine core sediments from the Daliao River watershed

The burial characteristics and toxicity risks associated with n-alkanes and polycyclic aromatic hydrocarbons (PAHs) in the riverine and estuarine sediments of the Daliao River watershed were investigated based on three sediment cores. The sum of the n-alkane and PAH concentrations, normalized to organic carbon (OC), ranged from 0.27 to 63.09 μg g^?1OC^?1 and 6.60 to 366.20 μg g^?1OC^?1, respectively. The features and the history of industrial activities, such as the oil and chemical industries and port activities near the river and estuary, resulted in different distributions and sources of hydrocarbons. The sources of pollution were identified based on n-alkane indexes and on diagnostic ratios of PAHs. The diagnostic ratios indicated that the n-alkanes were derived from both biogenic and petrogenic sources in different proportions and that the PAHs were derived primarily from petrogenic combustion sources. A hierarchical cluster analysis grouped the core samples into two clusters. The first cluster, river sediments, corresponded to industrial activities; the second cluster, estuarine sediments, corresponded to port shipping activities. The toxic potency of the PAHs in the cores was assessed in terms of toxic equivalents (TEQs) of dibenzo[a,h]anthracene and benzo[a]pyrene. The top layer of the sediment in the cores had a relatively high toxicity. The TEQ values for benzo(a)pyrene (TEQ_BaP) and dioxins (TEQ_TCDD) furnished a consistent assessment of the PAHs in the sediment cores.     

Methyl ketones in high altitude Ecuadorian Andosols confirm excellent conservation of plant-specific n-alkane patterns

To reconstruct past shifts in the upper forest line (UFL) in the Northern Ecuadorian Andes we are studying the applicability of plant-specific patterns of lipids preserved in soils as proxies for past vegetation along an altitudinal transect. Longer chain length n-alkanes, (C₁₉–C₃₅) were previously found to occur in plant-specific patterns in the dominant vegetation in the area as well as in preliminary soil samples, and may serve as such a proxy. In the present study, we assessed the preservation of n-alkane patterns with depth in soils from five excavations along an altitudinal transect 3500–3860 m above sea level (m.a.s.l) in the area. We used the carbon preference index (CPI) as well as chain length distributions of n-alkanes and their most likely degradation products, n-methyl (Me) ketones, n-alcohols and n-fatty acids. Clear n-alkane patterns were found in all the soils and at all depths, while a clear relationship with the observed patterns of n-Me ketones identified them as the primary degradation product of the former. Very low average n-Me ketone/n-alkane ratio values were found, ranging from 0.03 to 0.15 at the top of the mineral soil, to 0.05–0.20 at the interface with an underlying palaeosol several thousand years old. The concurrent high CPI values indicate very limited degradation of n-alkanes with depth. Except for C₃₃, the shifts in n-Me ketone/n-alkane values were similar for all chain lengths investigated, signifying an absence of preferential degradation of individual n-alkanes. With one exception, all the soils showed a similar increase in n-Me ketone/n-alkane values with depth, indicating that the degradation rates were not influenced by altitude. This means that, even if the total concentration of n-alkanes decreases over time, the characteristic pattern remains intact, conserving their potential as a biomarker for past vegetation reconstruction in the area, as well as for investigation of degradation processes of soil organic carbon.     

Experimental design approach to the optimisation of hydrocarbons extraction from the sediment: Method development and application

Extraction and analysis of organic pollutants from matrices such as sediment constitute an essential step in environmental research. However, the extraction for quantitative analysis can turn out to be difficult because these compounds are present in trace levels and can be strongly bound to the sorbent matrix. Consequently, accuracy of environmental analyses mainly depends on the efficiency and the robustness of the extraction step. In this work, a sequential ASE extraction procedure was applied to the extraction of polycyclic aromatic and aliphatic hydrocarbons (PAHs, Me-PAHs and n-alkanes) in sediment samples. The extraction protocol was developed for 26 PAHs, including the 16 PAHs of the United-States Environmental Protection Agency (EPA) priority list, for 17 alkylated PAHs homologues and for 29 n-alkanes (from n-C₁₂ to n-C₄₀). A set of 30 experiments was carried out for the determination of the optimal extraction conditions. The four parameters studied were pressure, temperature, extraction time and nature of the solvent. Extracts were analyzed by gas chromatography (GC-MS and GC-FID) after clean-up and concentration. The optimal extraction conditions selected for pressure, temperature, extraction time and nature of solvent were respectively 14 MPa, 160 °C, 24 min and hexane/acetone (1/1 v/v). The analytical procedure was validated by comparing predicted and experimental values of sediment samples and by analyzing standard reference material. The validated method was then applied to establish a depth profile contamination in the sediment of the Deûle River in Northern France.     

Significant seasonal variation in the hydrogen isotopic composition of leaf-wax lipids for two deciduous tree ecosystems (Fagus sylvativa and Acerpseudoplatanus)

Compound specific hydrogen isotope ratios (δD) of long chain sedimentary n-alkanes, which mostly originate from the leaf waxes of higher terrestrial plants, are increasingly employed as paleoclimate proxies. While soil water is the ultimate hydrogen source for these lipids and the isotopic fractionation during biosynthesis of lipids is thought to remain constant, environmental parameters and plant physiological processes can alter the apparent hydrogen isotopic fractionation between leaf-wax lipids and a plant’s source water. However, the magnitude and timing of these effects and their influence on the isotopic composition of lipids from higher terrestrial plants are still not well understood. Therefore we investigated the seasonal variability of leaf-wax n-alkane δD values for two different temperate deciduous forest ecosystems that are dominated by two different tree species, Beech (Fagus sylvatica) and Maple (Acerpseudoplatanus).We found significant seasonal variations for both tree species in n-alkane δD values of up to 40‰ on timescales as short as one week. Also, the isotopic difference between different n-alkanes from the same plant species did vary significantly and reached up to 50‰ at the same time when overall n-alkane concentrations were lowest.Since δD values of soil water at 5 and 10 cm depth, which we assume represent the δD value of the major water source for the investigated beech trees, were enriched in autumn compared to the spring by 30‰, whereas n-alkane δD values increased only by 10‰, we observed variations in the apparent fractionation between beech leaf derived n-alkanes and soil water of up to 20‰ on a seasonal scale. This observed change in the apparent fractionation was likely caused by differences in leaf water isotopic enrichment. Based on mechanistic leaf water models we conclude that changes in the isotopic difference between water vapor and soil water were the most likely reason for the observed changes in the apparent fractionation between n-alkanes and soil water.The large variability of n-alkane concentrations and δD values over time implies a continuous de novo synthesis of these compounds over the growing season with turnover times possibly as short as weeks. The signal to reach the soil therefore represents an integrated record of the last weeks before leaf senescence. This holds true also for the sedimentary record of small catchment lakes in humid, temperate climates, where wind transport of leaf-wax lipids is negligible compared to transfer through soil and the massive input of leaves directly into the lake in autumn.     

Use of biomarkers indices in a sediment core to evaluate potential pollution sources in a subtropical reservoir in Brazil

The presence of PAHs, n-alkanes, pristane, and phytanes in core sediment from the Vossoroca reservoir (Parana, southern Brazil) was investigated. The total concentration of the 16 PAHs varied from 15.5 to 1646 μg kg⁻¹. Naphthalene was present in all layers (3.34–74.0 μg kg⁻¹). The most abundant and dominant n-alkanes were n-C₁₅ and n-C₃₆, with average concentrations of 198.1 ± 46.8 and 522.9 ± 167.7 μg kg⁻¹, respectively. Lighter n-alkanes were distributed more evenly through the layers and showed less variation, specially n-C₉, n-C₁₂, and n-C₁₈, with average concentrations of 14.6 ± 3.0, 31.6 ± 1.9, and 95.0 ± 5.2 μg kg⁻¹, respectively; heavier n-alkanes were more unevenly distributed.     

Chemical characteristics and pollution sources of petroleum hydrocarbons and PAHs in sediments from the Beiluohe River,Northern China

To determine the degree of hydrocarbon contamination and the contribution of local petroleum industries to contaminant loadings in sediments from the Beiluohe River, China, 12 surface sediment samples were collected for geochemical analysis in 2005. Sediment samples were extracted by organic solvents, separated by silica gel column chromatography and the profiles of n-alkanes, biomarkers and polycyclic aromatic hydrocarbons (PAHs) in sediments were analyzed by gas chromatography with flame ionization detector and gas chromatography/mass spectroscopy. Concentrations of total hydrocarbons in the sediments varied from 12.1 to 3,761.5 μg g⁻¹ dry wt, indicating that most sediments in Beiluohe River was only slightly to moderately contaminated by hydrocarbons. Concentrations of PAHs for six samples (sum of 16 isomers) varied from 17.7 to 407.7 ng g⁻¹ dry wt and at present low levels of PAHs did not cause adverse biological effects in Beiluohe River sedimentary environment. PAH compositions, n-alkanes and biomarker profiles all suggested that there were different sources of contaminations in studied areas. n-Alkanes reflect two distinct sources: a fossil n-alkane series from crude oil at sites S40, S43, S87 and plantwax n-alkanes at sites S39 and S45. Judged by their PAH ratios, the sediments at site S15 were pyrolytic, sediments at S17 and S43 were petrogenic, and sediments at S39, S40 and S64 had a mixture source of pyrolytic and petrogenic.     

Compound specific δD values of long chain n-alkanes derived from terrestrial higher plants are indicative of the δD of meteoric waters: Evidence from surface soils in eastern China

The stable carbon and hydrogen isotope composition of higher plant-derived long chain n-alkanes (δ¹³C_n-alkanes and δD_n-alkanes) from 45 surface soil samples (within well characterized vegetation zones) from eastern China (18°N–50°N) are reported. The weighted average δD_n-alkanes value for n-C₂₇, n-C₂₉ and n-C₃₁ in the samples and the annual average δD of meteoric water recorded at 12 weather stations proximal to the sampling sites show similar spatial variations. The δD of n-alkanes shows a gradual depletion in value with increasing latitude. The results demonstrate that, on a large spatial scale, the δD values of long chain n-alkanes derived from higher plants have the potential to record the δD of meteoric water, although many other factors can also influence the isotope values. There appears to be no apparent relationship between the δD of the n-alkanes extracted from the surface soil and the overlying vegetation type (i.e. forest/grassland or C₃/C₄ composition). Therefore, palaeoenvironmental studies utilizing δD_n-alkanes from higher plant-derived material in geological samples have the potential to provide additional information with regard to the past hydrological cycle.     

地质样品正构烷烃组分分离纯化的部分问题探究

用实验室自配的标准正构烷烃样品分别经硅胶或氧化铝柱层析后发现,等量溶剂洗脱的情况下硅胶对长链正构烷烃无吸附而氧化铝具有一定吸附性。进一步通过用植物样品测试4种层析柱填充方法,发现不论是只用氧化铝填充还是上部硅胶下部氧化铝和上部氧化铝下部硅胶,都会对长链正构烷烃产生一定的吸附,且这种吸附效果随着碳链的增长而增强。在实验条件下,当碳链加长到C36时,用硅胶加氧化铝填充层析柱的吸附量已达到20%左右,而只用氧化铝填充层析柱的吸附量则高达50%。故建议对研究高碳数正构烷烃的地质样品组分提取时用单一的硅胶柱层析方法。同时,实验显示对于一些杂质多的正构烷烃样品经过尿素络合后比络合前"干净"得多。18个黄土-古土壤和植物样品平均回收率为50%左右,经过尿素络合后的样品正构烷烃各组分相对含量基本不会发生改变,也不会产生明显的同位素分馏效应。因此在进行非正构组分干扰较大的正构烷烃各组分相对含量或同位素分析时,可以选择尿素络合的方法来将其纯化。     

Characterisation of n-alkanes and their hydrogen isotopic composition in sediments from Lake Qinghai, China

The distributions of n-alkanes and their hydrogen isotopic composition (δD) in surface and core sediments from the saline Qinghai Lake were measured to assess whether or not biological source information was recorded in the δD values of n-alkanes. The results indicate that the n-alkane distributions between shallow water surface and core sediments were similar, and closer to those of terrestrial herbaceous plants from the Qinghai Lake surrounding areas, rather than the aquatic plants living in the lake. The n-alkanes in the surface and core sediments had similar mean δD values, ranging from −185‰ to −133‰ and −163‰ to −142‰, respectively. The mean δD values of n-alkanes in the sediments showed that the even n-alkanes were heavier in D compared with the odd homologues.     

Different source of n-alkanes and n-alkan-2-ones in a 6000 cal. yr BP Sphagnum-rich temperate peat bog (Roñanzas,N Spain)

The most widely accepted origin of n-alkan-2-ones in peats is the microbial oxidation of the related n-alkanes and/or oxidative decarboxylation of fatty acids derived from plant input. The distributions of n-alkanes and n-alkan-2-ones in 48 samples from the Roñanzas 6000 cal. yr BP peat bog profile (N Spain) do not justify a single source. The n-alkan-2-ones typically dominate the n-alkanes, maximizing at C₁₉ or C₂₅/C_27, whereas the n-alkanes maximized either at C₂₃ or at C₃₁/C₃₃. The averaged δ¹³C values of the n-alkanes ranged from −32.3‰ to −33.1‰, but those of the n-alkan-2-ones were consistently higher (−29.2‰ to −29.9‰), suggesting a different, probably bacterial, source for the ketones.     

Biomarkers of novel ecosystem development in boreal forest soils

Novel ecosystem development is occurring within the western boreal forest of Canada due to land reclamation following oil sand surface mining. Sphagnum peat is the primary organic amendment used to reconstruct soil in these novel ecosystems. We hypothesised that ecosystem recovery would be indicated by an increasing similarity in the biomolecular characteristics of novel soil organic matter (SOM) derived from peat to those of natural boreal ecosystems. We evaluated the use of the homologous series of long chain (⩾ C₂₁) n-alkanes with odd/even predominance to monitor the re-establishment of boreal forest on these anthropogenic soils. The lipids were extracted from dominant vegetation inputs and SOM from a series of natural and novel ecosystem reference plots. Twice the concentration of n-alkanes was extracted from natural than from novel ecosystem SOM (p < 0.01). We observed unique n-alkane signatures for the source vegetation, e.g. peat material was dominated by C₃₁, and aspen (Populus tremuloides Michx.) leaves by C₂₅. The n-alkane distribution differed between the two systems (p < 0.001) and reflected the dominant vegetation input, i.e. peat or tree species. Our results indicate that further research is required to clarify the influence of vegetation or disturbance on the signature of n-alkanes in SOM; however, the use of n-alkanes as biomarkers of novel ecosystem development is a promising application.     

Effect of leaf litter degradation and seasonality on D/H isotope ratios of n-alkane biomarkers

During the last decade, compound-specific hydrogen isotope analysis of plant leaf-wax and sedimentary n-alkyl lipids has become a promising tool for paleohydrological reconstructions. However, with the exception of several previous studies, there is a lack of knowledge regarding possible effects of early diagenesis on the δD values of n-alkanes. We therefore investigated the n-alkane patterns and δD values of long-chain n-alkanes from three different C3 higher plant species (Acer pseudoplatanus L., Fagus sylvatica L. and Sorbus aucuparia L.) that have been degraded in a field leaf litterbag experiment for 27 months.We found that after an initial increase of long-chain n-alkane masses (up to ∼50%), decomposition took place with mean turnover times of 11.7 months. Intermittently, the masses of mid-chain n-alkanes increased significantly during periods of highest total mass losses. Furthermore, initially high odd-over-even predominances (OEP) declined and long-chain n-alkane ratios like n-C₃₁/C₂₇ and n-C₃₁/C₂₉ started to converge to the value of 1. While bulk leaf litter became systematically D-enriched especially during summer seasons (by ∼8‰ on average over 27 months), the δD values of long-chain n-alkanes reveal no systematic overall shifts, but seasonal variations of up to 25‰ (Fagus, n-C₂₇, average ∼13‰).Although a partly contribution by leaf-wax n-alkanes by throughfall cannot be excluded, these findings suggest that a microbial n-alkane pool sensitive to seasonal variations of soil water δD rapidly builds up. We propose a conceptual model based on an isotope mass balance calculation that accounts for the decomposition of plant-derived n-alkanes and the build-up of microbial n-alkanes. Model results are in good agreement with measured n-alkane δD results. Since microbial ‘contamination’ is not necessarily discernible from n-alkane concentration patterns alone, care may have to be taken not to over-interpret δD values of sedimentary n-alkanes. Furthermore, since leaf-water is generally D-enriched compared to soil and lake waters, soil and water microbial n-alkane pools may help explain why soil and sediment n-alkanes are D-depleted compared to leaves.     

Hydrothermal alteration of organic matter in sediments of the Northeastern Pacific Ocean: Part 2. Escanaba Trough,Gorda Ridge

Samples from the Ocean Drilling Program Leg 169 in Escanaba Trough, Gorda Ridge, NE Pacific Ocean, were analyzed to study maturation by accelerated diagenesis and/or by catagenesis of the sedimentary organic matter to hydrothermal petroleum. At Site 1038 the hydrothermal petroleums have migrated after generation to shallower horizons. The n-alkane maturation was indicated by the strong even C number preference (i.e., CPI <1.0) as in the case of Middle Valley. All samples contained admixed organic matter of terrigenous and marine components as indicated by the distributions of the biomarkers. The biological precursors were catagenetically altered to their equivalent mature compounds. The presence of high molecular weight PAHs in some sediment sections at Site 1038 reflected the high temperature alteration and reworking of organic matter into mature hydrothermal petroleum. At Site 1037, the reference hole in the Escanaba Trough, the n-alkanes with a strong predominance of odd C number homologs reflected immature non-marine lipid components essentially throughout the hole. Maturation of organic matter was only observed below 450 mbsf with n-alkanes showing a CPI <1.0. The strong even C number predominance in those intervals was attributed to initial maturation by high heat flow during the early rifting process.     

Hydrocarbons and fatty acids in the Evergreen Shale,Surat Basin,Queensland, Australia

Alkane hydrocarbon and n-fatty acid distributions have been examined in cores taken over a 550 ft thickness through the lower Jurassic, largely non-marine Evergreen Shale, Surat Basin, Queensland, Australia. No depth trends in compound abundances or carbon preference indices are discernible. There is no evidence for significant generation of n-alkanes from kerogen nor for cracking of long-chain n-alkanes. The present distribution patterns of the biochemicals probably reflect closely the nature of the original organic matter. The general strong dominance of long-chain (C₂₀₊) n-alkanes; the lack of evidence for diagenetic change; and the absence of correlation between abundances of n-alkanes and n-fatty acids (among both the longer- and shorter-chain compounds), lead to the conclusion that at least the long-chain n-alkanes were largely deposited as such in the sediment, having originated in land-plant material, remains of which are abundant in the samples. In the upper 170 ft. (possibly marine), n-alkanes with chain lengths below C₂₀ become important, suggesting greater significance of aquatic life as a source of organic matter at the time of deposition, a conclusion which is in general accord with the geological history of the basin, although this history is not well known.     

Characterization of the hydrogen isotopic composition of individual n-alkanes in terrestrial source rocks

In order to characterize the H isotopic compositions of individual lipid compounds from different terrestrial depositional environments, the δD values of C-bound H in individual n-alkanes from typical terrestrial source rocks of the Liaohe Basin and the Turpan Basin, China, were measured using gas chromatography–thermal conversion–isotope ratio mass spectrometry (GC–TC–IRMS). The analytical results indicate that the δD values of individual n-alkanes in the extracts of terrestrial source rocks have a large variation, ranging from −140‰ to −250‰, and are obviously lighter than the δD of marine-sourced n-alkanes. Moreover, a trend of depletion in ²H(D) was observed for individual n-alkanes from different terrestrial depositional environments, from saline lacustrine to freshwater paralic lacustrine, and to swamp. For example, the δD values of n-alkanes from a stratified saline lacustrine environment vary from −140‰ to −200‰, δD for n-alkanes from swamp facies range from −200‰ to −250‰, while those from freshwater paralic lacustrine–lacustrine environments fall between the δD values of the end members. The shift toward lighter δD from saltwater to freshwater environments indicates that the source water δD is the major controlling factor for the H isotopic composition of individual compounds. In addition, H exchange between formation water and sedimentary organic matter may possibly be important in regard to the δD of individual n-alkanes. Therefore, other lines of geochemical evidence must be considered when depositional paleoenvironments of source rocks are reconstructed based on the H isotopic composition of individual n-alkanes.     

Ambient distribution of particulate- and gas-phase <Emphasis Type="Italic">n</Emphasis>-alkanes and polycyclic aromatic hydrocarbons in the Tibetan Plateau

Attention has been paid for the levels, sources and health risks of atmospheric aliphatic and polycyclic aromatic hydrocarbons (n-alkanes and PAHs) in remote areas, however, few studies have focused on those in the Tibetan Plateau. In this study, 18 pairs of atmospheric samples were obtained during the period from August 2006 to July 2007 in Lhasa, the capital city of Tibet. Both gas-phase and particulate-phase n-alkanes and PAHs were measured. Concentrations of n-alkanes (gas + particulate phase, 99.1–480.9 ng/m³) and PAHs (gas + particulate phase, 11.4–72.5 ng/m³) in Lhasa are lower than those in many cities. The sources of n-alkanes related to biological and petroleum sources were 67 and 33%, respectively. According to the results of diagnostic ratios and principal component analysis, emission of traffic vehicles was one of the important PAH sources, and sources of benzo(a)pyrene was likely attributed to incense burning. Good simulations were obtained by traffic soot-based model for fluoranthene, pyrene and benzo(a)anthracene, while, wood soot-based model fitted the experimental results of benzo(a)pyrene better. This meant atmospheric fate of PAHs was mainly influenced by the adsorptive partitioning that occurred during traffic and incense burning procedures. In addition, the benzo[a]pyrene-equivalent carcinogenic power (BaPE) in the present study (0.1–1.6 ng/m³) is lower than those in other cities and also the air quality standard of China, suggesting that atmospheric PAHs caused low health risks.     

Latitudinal distribution of terrestrial lipid biomarkers and n-alkane compound-specific stable carbon isotope ratios in the atmosphere over the western Pacific and Southern Ocean

We investigated the latitudinal changes in atmospheric transport of organic matter to the western Pacific and Southern Ocean (27.58°N-64.70°S). Molecular distributions of lipid compound classes (homologous series of C₁₅ to C₃₅n-alkanes, C₈ to C₃₄n-alkanoic acids, C₁₂ to C₃₀n-alkanols) and compound-specific stable isotopes (δ¹³C of C₂₉ and C₃₁n-alkanes) were measured in marine aerosol filter samples collected during a cruise by the R/V Hakuho Maru. The geographical source areas for each sample were estimated from air-mass back-trajectory computations. Concentrations of TC and lipid compound classes were several orders of magnitude lower than observations from urban sites in Asia. A stronger signature of terrestrial higher plant inputs was apparent in three samples collected under conditions of strong terrestrial winds. Unresolved complex mixtures (UCM) showed increasing values in the North Pacific, highlighting the influence of the plume of polluted air exported from East Asia. n-Alkane average chain length (ACL) distribution had two clusters, with samples showing a relation to latitude between 28°N and 47°S (highest ACL values in the tropics), whilst a subset of southern samples had anomalously high ACL values. Compound-specific carbon isotopic analysis of the C₂₉ (−25.6‰ to −34.5‰) and C₃₁n-alkanes (−28.3‰ to −37‰) revealed heavier δ¹³C values in the northern latitudes with a transition to lighter values in the Southern Ocean. By comparing the isotopic measurements with back-trajectory analysis it was generally possible to discriminate between different source areas. The terrestrial vegetation source for a subset of the southernmost Southern Ocean is enigmatic; the back-trajectories indicate eastern Antarctica as the only intercepted terrestrial source area. These samples may represent a southern hemisphere background of well mixed and very long range transported higher plant organic material.     

Hydrocarbons generated by hydropyrolysis of suspended marine particulate organic matter: Relationship to the oceanography of the Black Sea and the Rhodes Gyre

The suspended particulate organic matter, SPOM, in the autumnal Black Sea has been characterised using catalytic hydropyrolysis (HyPy) of the total (bound plus free) lipid material. The technique, which generates maximum yields of volatile products from sediments, kerogens and phytoplankton, was followed using gas chromatography and gas chromatography/mass spectrometry. The generated alkanes were dominated by n-C₁₈, hypothesised to arise predominantly from unsaturated C₁₈ fatty acids. Steranes were generated from reductive conversion of free and bound sterols. The generation of branched alkanes and especially of hopanes provided formal evidence for the participation of bacteria in the mineralisation of the SPOM. Whereas similar distributions of n-alkanes were generated from SPOM sampled from different depths of the comparatively well-stirred Rhodes Gyre (eastern Mediterranean), mineralisation of the SPOM at each depth of the central Black Sea produced characteristic changes in the composition and concentration of the HyPy products. Depth profiles of the n-alkanes generated from SPOM in the region of the Rim Current were affected by the local hydrography. Polynuclear aromatic hydrocarbons (PAHs) of anthropogenic origin were present in the surface waters of the central Black Sea. Some methyl benzenes, thiophenes and pyrroles were also generated.