High Molecular Weight N-alkanes Research Articles

Sourcing sedimentary cherts with archaeological use through the combination of chromatographic and spectroscopic techniques

The nature and distribution of organic matter in geological cherts of archaeological use can serve to estimate the sources and origins of some remains of lithic industry. For example, organic and biomarker analysis can provide information to allow a deeper insight into source catchment areas, artefact displacement or the way in which the artefacts were employed. In this work, soluble (bitumen) and insoluble (kerogen) organic matter were isolated from several chert samples with different depositional history and analysed by means of gas chromatography–mass spectrometry (GC–MS) and spectroscopic techniques such as infrared and Raman spectroscopy. Chemometric treatment of the results allowed observation of differences between organic matter content on the basis of the depositional setting of the cherts. Samples with a continental deposition seemed to preserve more organic matter with little alteration. The hydrocarbon profiles of these samples were dominated by high molecular weight n-alkanes, alkylcyclohexanes and isoprenoid groups which allowed distinguishing them from the rest of the analysed samples.

A biomarker study of depositional paleoenvironments and source inputs for the massive formation of Upper Cretaceous lacustrine source rocks in the Songliao Basin, China

The abundance and composition of total organic carbon, aliphatic and aromatic hydrocarbons including biomarkers, and the δ13C composition of total organic matter and individual compounds in core samples of the Nenjiang Formation from the SK-1 borehole of the Songliao Basin provide information on the paleoenvironmental conditions of lacustrine sediments formed during the Upper Cretaceous. The distribution of n-alkanes, and their δ13C composition, and 4-methylsteranes and dinosteranes in the first member of the Nenjiang Formation (K2n1) indicate that the organic matter largely originated from algal organisms and is dominated by types I and II kerogen. The occurrence of gammacerane, aryl isoprenoids isorenieratane and low pristane/phytane and diasterane/sterane ratios further suggest a salinity stratified water column associated with anoxic bottom waters, as well as possible photic zone oxygen depletion conditions during major source rock deposition of the K2n1. The organic geochemical data also indicate significantly different depositional environments for the second member of the Nenjiang Formation (K2n2) sediments, which are interpreted to have been deposited under a uniform salinity (non-stratified) oxic water column. Consequently, although the organic matter in the K2n2 sediments was largely derived from algal and bacterial sources, the kerogen types are dominantly IIb and III due to the oxidative degradation of organic matter, combined with a gradual increase in land–plant input. Furthermore, the occurrence and shift of two saw-toothed distribution patterns of the δ13C composition of C29 to C33 n-alkanes, with “W” and “M” patterns being isotopically heavy odd- and even-numbered alkanes, respectively, is suggestive of organic input shift or an unknown mechanism of carbon uptake or isotopic fractionation. In particular, the heavy even carbon numbered high molecular weight n-alkanes is rare and needs further investigation.

Distribution of sedimentary organic matter in estuarine–inner shelf regions of the East China Sea: Implications for hydrodynamic forces and anthropogenic impact

The estuarine-inner shelf region of the East China Sea (ECS) is a major sink of the Yangtze River-derived fine-grained sediments and associated organic materials. In this work, surface sediment samples from a matrix of seventy-three sites that extend from the Yangtze River estuary (YRE) to the southern inner shelf were measured for their elemental, stable isotopic and molecular indices to provide a process-oriented study on the sources, distribution and fate of sedimentary organic matter (SOM) in this region. The results indicated that the re-suspension and alongshore transport of sediments could play a key role on the accumulation of SOM in the area. In addition to the physical reworking, the low C/N ratios and the enriched δ13C values could also be likely related to the presence of microorganism-derived organic matter (OM) and soil-derived OM. The composition and principal component analyses of the n-alkanes indicated that the majority of the riverine terrigenous SOM was primarily restricted within the mud deposits along the coastal ECS. The wide occurrence and southward increasing trend of high molecular weight n-alkanes along the coastal ECS suggest an effective preferential dispersal of the terrigenous organic components. However, the local supply of the marine-derived OM potentially promotes the subsequent degradation of these terrigenous OM, which are likely responsible for the decreasing trend of the carbon preference index (CPI25–33) from the northern YRE to the southern inner shelf. This indicates that the transported SOM from the YRE could become more homogenized as it moved toward the southern inner shelf. The presence of unresolved complex mixtures (UCM), lower Pr/Ph ratios and patterns of more stable geochemical biomarkers (hopanes and steranes) in the nearshore region reveals a petroleum contamination in the coastal environment.

Observation of atmospheric aerosols at Mt. Hua and Mt. Tai in central and east China during spring 2009 – Part 2: Impact of dust storm on organic aerosol composition and size distribution

Abstract. PM10 and size-resolved particles (9-stage) were simultaneously collected at Mt. Hua and Mt. Tai in central and east China during the spring of 2009 including a massive dust storm occurring on 24 April (named as DS II), and determined for organic compounds to investigate the impact of dust storm on organic aerosols. High molecular weight (HMW) n-alkanes, fatty acids, and fatty alcohols and trehalose sharply increased and almost entirely stayed in coarse particles when dust storm was present, suggesting that high level of organic aerosols in the mountain atmospheres during the event largely originated from Gobi desert plants. However, most anthropogenic aerosols (e.g. PAHs, and aromatic and dicarboxylic acids) during the event significantly decreased due to a dilution effect, indicating that anthropogenic aerosols in the mountain atmospheres during the nonevent period largely originated from local/regional sources rather than from long-range transport. Trehalose, a metabolism product enriched in biota in dry conditions, was 62 ± 78 and 421 ± 181 ng m−3 at Mt. Hua and Mt. Tai during DS II, 10–30 times higher than that in the nonevent time, indicating that trehalose may be a tracer for dust emissions from Gobi desert regions. Molecular compositions of organic aerosols in the mountain samples demonstrate that domestic coal burning is still the major source of PAHs in China. n-Alkanes and fatty acids showed a bimodal size distribution during the nonevent with a major peak in fine mode (<2.1 μm) and a small peak in coarse mode (>2.1 μm). The coarse mode significantly increased and even dominated over the whole size range when dust was present. Glucose and trehalose were also dominant in the coarse mode especially in the DS II time. PAHs and levoglucosan concentrated in fine particles with no significant changes in size distribution when dust storm occurred. However, phthalic and succinic acids showed bimodal size distribution pattern with an increase in coarse mode during the event, because both are formed via a gas phase oxidation and a subsequent condensation/adsorption onto aerosol phase. In contrast, terephthalic and malic acids are mostly emitted from combustion process as fine particles, thus both showed a fine mode pattern during the whole campaign with a minor peak in coarse mode caused by an increased coagulation with dust during the event. Geometric mean diameters (GMDs) of the organic aerosols above are in general larger at Mt.~Hua than at Mt. Tai during the nonevent period. We found that during the event GMD of the fine mode organics that derived mostly from the local/regional sources rather than Gobi desert became smaller while GMD of them in coarse mode became larger. Such a splitting in sizes during the event is most likely caused by decreased fine particle coagulation due to dilution and increased adsorption/coagulation with dust.

Application of magnetite catalyzed chemical oxidation (Fenton-like and persulfate) for the remediation of oil hydrocarbon contamination

The chemical oxidative degradation of oil hydrocarbons was investigated by magnetite catalyzed Fenton-like (FL) and activated persulfate (AP) oxidation. An artificial soil composed of silica sand and magnetite was synthesized and characterized by XRD and Mössbauer spectroscopy. This magnetite rich sandy soil (MRS) was then spiked with (i) an organic extract from a soil contaminated by weathered oil (WO) and (ii) a fresh crude oil (CO) and was subjected to oxidation in batch slurry system at circumneutral pH. Experimental results indicate that approximately 70–80% of WO removal was achieved by both FL and AP treatments after one week. Moreover significant CO abatement was also observed by both oxidants (80–90%). Non-selective degradation was evaluated for FL while AP showed less reactivity towards higher molecular weight n-alkanes. Experiments were also conducted with soluble FeII as catalyst instead of magnetite and only 10–15% of degradation was achieved for oxidation experiments with or without soluble FeII addition. Whatever the treatment (FL and AP), no by-products were observed after oxidation experiments which indicate the complete degradation of oil hydrocarbons. Results of this study suggest that magnetite can be used as iron source to activate both Fenton and persulfate oxidation at circumneutral pH. This study has important implications in the remediation of oil polluted soils by FL or AP oxidation.

Widespread release of old carbon across the Siberian Arctic echoed by its large rivers

Abstract. Over decadal-centennial timescales, only a few mechanisms in the carbon-climate system could cause a massive net redistribution of carbon from land and ocean systems to the atmosphere in response to climate warming. The largest such climate-vulnerable carbon pool is the old organic carbon (OC) stored in Arctic permafrost (perennially frozen) soils. Climate warming, both predicted and now observed to be the strongest globally in the Eurasian Arctic and Alaska, causes thaw-release of old permafrost carbon from local tundra sites. However, a central challenge for the assessment of the general vulnerability of this old OC pool is to deduce any signal integrating its release over larger scales. Here we examine radiocarbon measurements of molecular soil markers exported by the five Great Russian-Arctic Rivers (Ob, Yenisey, Lena, Indigirka and Kolyma), employed as natural integrators of carbon release processes in their watersheds. The signals held in estuarine surface sediments revealed that average radiocarbon ages of n-alkanes increased east-to-west from 6400 yr BP in Kolyma to 11 400 yr BP in Ob. This is consistent with westwards trends of both warmer climate and more degraded organic matter as indicated by the ratio of high molecular weight (HMW) n-alkanoic acids to HMW n-alkanes. The dynamics of Siberian permafrost can thus be probed via the molecular-radiocarbon signal as carried by Arctic rivers. Old permafrost carbon is at present vulnerable to mobilization over continental scales. Climate-induced changes in the radiocarbon fingerprint of released permafrost carbon will likely depend on changes in both permafrost coverage and Arctic soil hydraulics.

Anaerobic Biodegradation of Longer-Chain n-Alkanes Coupled to Methane Production in Oil Sands Tailings

Extraction of bitumen from mined oil sands ores produces enormous volumes of tailings that are stored in settling basins (current inventory ≥ 840 million m(3)). Our previous studies revealed that certain hydrocarbons (short-chain n-alkanes [C(6)-C(10)] and monoaromatics [toluene, o-xylene, m-xylene]) in residual naphtha entrained in the tailings are biodegraded to CH(4) by a consortium of microorganisms. Here we show that higher molecular weight n-alkanes (C(14), C(16), and C(18)) are also degraded under methanogenic conditions in oil sands tailings, albeit after a lengthy lag (~180 d) before the onset of methanogenesis. Gas chromatographic analyses showed that the longer-chain n-alkanes each added at ~400 mg L(-1) were completely degraded by the resident microorganisms within ~440 d at ~20 °C. 16S rRNA gene sequence analysis of clone libraries implied that the predominant pathway of longer-chain n-alkane metabolism in tailings is through syntrophic oxidation of n-alkanes coupled with CO(2) reduction to CH(4). These studies demonstrating methanogenic biodegradation of longer-chain n-alkanes by microbes native to oil sands tailings may be important for effective management of tailings and greenhouse gas emissions from tailings ponds.

Hydrogen isotope ratios of leaf wax n-alkanes in grasses are insensitive to transpiration

We analyzed hydrogen isotope ratios of high-molecular weight n-alkanes ( δD l) and oxygen isotope ratios of α-cellulose ( δ 18O C) for C 3 and C 4 grasses grown in the field and in controlled-environment growth chambers. The relatively firm understanding of 18O-enrichment in leaf water and α-cellulose was used to elucidate fractionation patterns of δD l signatures. In the different relative humidity environments of the growth chambers, we observed clear and predictable effects of leaf-water enrichment on δ 18O C values. Using a Craig–Gordon model, we demonstrate that leaf water in the growth chamber grasses should have experienced significant D-enriched due to transpiration. Nonetheless, we found no effect of transpirational D-enrichment on the δD l values. In field samples, we saw clear evidence of enrichment (correlating with relative humidity of the field sites) in both δ 18O C and δD l. These seemingly contrasting results could be explained if leaf waxes are synthesized in an environment that is isotopically similar to water entering plant roots due to either temporal or spatial isolation from evaporatively enriched leaf waters. For grasses in the controlled environment, there was no enrichment of source water, whereas enrichment of grass source water via evaporation from soils and/or stems was likely for grass samples grown in the field. Based on these results, evaporation from soils and/or stems appears to affect δD l, but transpiration from leaves does not. Further evidence for this conclusion is found in modeling expected net evapotranspirational enrichment. A Craig–Gordon model applied to each of the field sites yields leaf water oxygen isotope ratios that can be used to accurately predict the observed δ 18O C values. In contrast, the calculated leaf water hydrogen isotope ratios are more enriched than what is required to predict observed δD l values. These calculations lend support to the conclusion that while δ 18O C reflects both soil evaporation and transpiration, δD l appears to only record evaporation from soils and/or stems. Therefore, the δD of n-alkanes can likely be used to reconstruct the δD of water entering a leaf, supporting the soil-enrichment model of Smith and Freeman (2006). In both the field and controlled studies, we found significant photosynthetic pathway effects on n-alkane δD suggesting that biochemical pathways or plant phylogeny have a greater effect on leaf wax δD than leaf-water enrichment in grasses.

Palaeoenvironmental changes in the Padul Basin (Granada, Spain) over the last 1 Ma based on the biomarker content

The n-alkane components of sediments were measured in 530 samples taken from a 107 m-long core in the Padul Basin (Andalusia, Spain) covering from the Lower Pleistocene ( ca. 1 Ma) to the mid-Holocene ( ca. 4.5 ka B.P.). We show that the relative percentages of the high molecular weight n-alkanes (C 27, C 29 and C 31) are useful tools to reconstruct the ancient vegetation and palaeoclimatological evolution of this basin. On the basis of these proxies, we distinguished twelve long-term climatic periods linked to alternating dry/humid scenarios: 6 Dry Episodes alternating with 5 Humid Episodes were interpreted in the Pleistocene record, together with a final Episode covering the Holocene. Dry scenarios produced the recession of forests and the development of grasses, whereas the inverse pattern was interpreted during humid phases. The good correlation with the Guadix-Baza Basin record showed that, in most cases, dry periods coexisted with warm conditions, while humid ones were linked to temperate-colder conditions. Only during the last long-term Dry Episode of the Pleistocene, which coincided with the end of the Last Glacial Period, did low temperatures concur. The relative percentages of the high molecular weight n-alkanes also indicate rapid changes in vegetation produced by short-scale arid cycles during the last Glacial Period (< 100 ka B.P.), which are linked to the Heinrich Events and Younger Dryas. This interpretation has been confirmed by previous pollen analysis performed in the Padul Basin. Likewise, a correlation was observed with Marine Isotope Stages (MIS). These results show that vegetation responds to long-term cycles (orbital scale) and millennial-scale global cycles. Therefore, climatic variations in the Padul Basin responded to global climatic changes, although with local climatic effects. Good correspondence was also observed with elemental, isotopic and other molecular organic proxies, thereby amplifying the palaeoclimatological knowledge of the Padul Basin during the Pleistocene, especially in some spans that were previously unclear.

Variation in solvent-extractable lipids and n-alkane compound-specific carbon isotopic compositions with depth in a southern China karst area soil

Because literatures about the lipid compositions of modern soils in karst areas are scarce, we have studied the soil horizons overlying the Heshang (和尚) Cave that has provided paleoclimate records from speleothem lipid contents. Our analysis reveals a series of n-alkanes, free fatty acids, n-alkanols and n-alkan-2-ones distribution and relative abundance changing with the depth, and in which the ratios of the lower molecular weight to higher molecular weight n-alkanes, free fatty acids, n-alkanols and n-alkan-2-ones have a peak at a subsurface depth of 5 to 10 cm. An accompanying peak in 17β(H), 21β(H)-hop-22(29)-ene (diploptene) and a shift to less negative n-alkane carbon isotopic values also identify this layer in the karst soil. This pattern indicates the existence of a subsurface soil layer in which the microorganisms that produce these compounds are especially abundant. The carbon isotopic values of individual plant wax n-alkanes are about 3‰ greater at the base of the 30- to 40-cm soil profile than in the surface layer, probably as a result of selective microbial degradation of n-alkanes from different primary sources. The lipids and carbon isotopic values of individual plant wax n-alkanes study of the overlying soil show a strong microbial activity in this karst soil and help in interpreting the lipid compositions and specific carbon isotopic value of n-alkanes of the stalagmites of the Heshang Cave for paleoenvironmental reconstructions.

Distribution of high-molecular-weight n-alkanes in paraffinic crude oils and asphaltene-resin-paraffin deposits

Paraffinic and high-paraffin oils and asphaltene-resin-paraffin (ARP) deposits of Samara oblast have been investigated by differential scanning calorimetry (DSC) and GLC techniques. High-paraffin oils have been found to contain n-alkanes with the number of carbon atoms of C15-C60 and higher forming a crystalline phase with the mp ∼30–40°C. The ARP deposits from high-paraffin oils almost do not contain highmolecular-weight n-alkanes with the number of carbon atoms >55. This is due to the peculiarities of the crystallization and cocrystallization processes of high polydispersity n-alkanes in crude oils.

Organic Molecular Compositions and Size Distributions of Chinese Summer and Autumn Aerosols from Nanjing: Characteristic Haze Event Caused by Wheat Straw Burning

Size-segregated aerosol samples were collected in urban Nanjing, China during summer and autumn of 2007 including a period of hazy days during June 1-5. Organic aerosols in the haze event were characterized by elevated concentrations of levoglucosan, high molecular weight (HMW) n-alkanes, and HMW fatty acids due to the emissions from field burning of wheat straw. In contrast, organic aerosols on nonhazy days were characterized by a predominance of fossil fuel combustion products. Levoglucosan (4030 n g m(-3)), n-alkanes (1520 ng m(-3)), fatty acids (2629 ng m(-3)), and PAHs (57 ng m(-3)) in the haze samples were 3-40 times more abundant than those in nonevent samples. Approximately 30-90% ofthe organics during the haze period can be attributed to wheat straw burning. Concentrations of particulate material (PM) mass, n-alkanes, and low molecular weight (LMW) PAHs showed a unimodal size distribution, peaking at 0.7-1.1 microm during the hazy days, and a bimodal distribution, peaking at 0.7-1.1 microm and 4.7-5.8 microm during nonhazy days. The geometric mean diameters (GMDs) of organic aerosols are larger in the fine mode (<2.1 microm) during the hazy days, suggesting aerosols emitted from the wheat straw burning are larger than those from fossil fuel combustion, and fine particle coagulation and organic compound repartitioning were enhanced.

Hydrogen isotopic ratios of plant wax n-alkanes in a peat bog deposited in northeast China during the last 16 kyr

Based on paleoclimatic reconstructions using various proxies, the Holocene Climate Optimum (10.5–6ka) has been characterized as a warmer and wetter period in most of East Asia. The summer monsoons associated with the East Asian Monsoon evidently intensified and extended further inland from the Pacific Ocean, a source region of moisture. A notable exception to this general pattern exists in northeast China, where less wet conditions are recorded. We determined molecular compositions of individual plant wax hydrocarbons and their hydrogen isotope compositions (δD values) in a radiocarbon-dated peat core recovered from the Hani marsh in Jilin Province (China) and confirmed that the temperature-dependent effective precipitation in northeast China decreased during the Holocene Climate Optimum. A combination of Paq, an indicator of the relative contribution of aquatic to terrestrial plants, and the difference in δD between low (C23, C25 and C27) and high molecular weight (C31) n-alkanes in the Hani peat bog indicates a dramatic change in vegetation from the deglaciation to the Holocene. No significant differences were observed between the δD values of low and high molecular weight n-alkanes with relatively high δD values and low Paq during the early Holocene, indicating that all n-alkanes were produced by evapotranspiration-sensitive terrestrial plants during that time. However, lower δD values of mid-chain n-alkanes (C23, C25 and C27) relative to the long chain n-alkane (C31), together with higher Paq values during the deglaciation (14–11ka), suggest an increase in the contribution of aquatic plants and a higher water level during the period. The study demonstrates that northeast China was under a markedly wetter climate condition during the late deglaciation. For the 16kyr record in the Hani peat sequence, we infer that moisture delivery by the East Asian Monsoon was relatively invariable in northeast China, but increased evaporation during the warmer Holocene Climate Optimum reduced the effective precipitation, defined by the balance between precipitation and evaporation.

La contraception chez la femme diabétique

The abundance and composition of total organic carbon, aliphatic and aromatic hydrocarbons including biomarkers, and the δ13C composition of total organic matter and individual compounds in core samples of the Nenjiang Formation from the SK-1 borehole of the Songliao Basin provide information on the paleoenvironmental conditions of lacustrine sediments formed during the Upper Cretaceous. The distribution of n-alkanes, and their δ13C composition, and 4-methylsteranes and dinosteranes in the first member of the Nenjiang Formation (K2n1) indicate that the organic matter largely originated from algal organisms and is dominated by types I and II kerogen. The occurrence of gammacerane, aryl isoprenoids isorenieratane and low pristane/phytane and diasterane/sterane ratios further suggest a salinity stratified water column associated with anoxic bottom waters, as well as possible photic zone oxygen depletion conditions during major source rock deposition of the K2n1. The organic geochemical data also indicate significantly different depositional environments for the second member of the Nenjiang Formation (K2n2) sediments, which are interpreted to have been deposited under a uniform salinity (non-stratified) oxic water column. Consequently, although the organic matter in the K2n2 sediments was largely derived from algal and bacterial sources, the kerogen types are dominantly IIb and III due to the oxidative degradation of organic matter, combined with a gradual increase in land–plant input. Furthermore, the occurrence and shift of two saw-toothed distribution patterns of the δ13C composition of C29 to C33 n-alkanes, with “W” and “M” patterns being isotopically heavy odd- and even-numbered alkanes, respectively, is suggestive of organic input shift or an unknown mechanism of carbon uptake or isotopic fractionation. In particular, the heavy even carbon numbered high molecular weight n-alkanes is rare and needs further investigation.

Differential transport and degradation of bulk organic carbon and specific terrestrial biomarkers in the surface waters of a sub-arctic brackish bay mixing zone

Detailed organic geochemical analyses were performed on surface water particulate samples of the lower Kalix River and northern Bothnian Bay collected during the spring flood of 2005. Both bulk geochemical and molecular biomarker analyses indicated a predominance of terrestrially-derived particulate organic matter (POM), both of higher plant and Sphagnum origin in the low salinity zone (LSZ) of the Kalix River estuary, with an increasing contribution of marine-derived POM in the offshore Bothnian Bay basin. Two-dimensional box modeling of the mixed surface layer in the LSZ indicated that 65% of the particulate organic carbon (POC) and between 73 and 93% of the terrestrial biomarker classes analyzed (high molecular weight n-alkanes, n-alkanoic acids and n-alkanols as well as sitosterol) were degraded in the course of their weeklong transit through the inner LSZ during the spring flood. This corresponds to field-based degradation rate constants for the biomarkers of 0.5 and 2.5 day − 1 , which are similar to results reported from mesocosm experiments for related compounds. The degradation rate constant for terrestrial POC of 0.38 day − 1 was about 20 times larger than for DOC and suggests that POC mineralization stands for 44% of the total mineralization, which is much larger than previously considered. This sub-arctic river-export regime has a geochemistry resembling that of neighboring western Russian Arctic Rivers, suggesting that a large part of the OM coastally exported from northernmost Eurasian soils may be degraded within the vicinity of the river mouths and putatively be released as carbon dioxide. The 65% degradation of terrestrial POC in the coastal surface water of this sub-arctic recipient is substantially larger than a global-average of 35% used in recent budget estimates of the fate of terrestrially-exported POC on the pan-arctic shelves. Considering ongoing and predicted changes in the Arctic Region due to global warming a more efficient degradation of river-exported terrestrial POC may have far-reaching consequences for the large-scale biogeochemical cycling of carbon in the pan-arctic region and beyond.

Lipid biomarker investigation of the origin and diagenetic state of sub-arctic terrestrial organic matter presently exported into the northern Bothnian Bay

Predicted climate warming and observed increases in river discharge in the vulnerable Arctic region can lead to alterations in the flux and composition of terrestrial organic matter (terrOM) transported into high latitude coastal waters. A benchmarking of the current sources, transport and degradation dynamics of sub-Arctic terrOM exported into the northernmost Baltic Sea was detailed with lipid biomarkers and bulk geochemical proxies along a transect extending from the unregulated Kalix River to the central Bothnian Bay. Bulk δ 13C and molecular biomarkers suggested a predominance of terrOM throughout both the estuary and the open bay. Terrestrial biomarkers were abundantly present in surface sediments with high molecular weight (HMW) n-alkanes, n-alkanoic acids and n-alkanols between 190 and 960 μg/gOC and β-sitosterol between 120 and 1500 μg/gOC, which is comparable to Russian Arctic estuaries. A relatively large contribution of the n-alkane C 23 and C 25 homologs (as shown by P aq values of 0.57–0.62) indicated a high contribution of Sphagnum-derived OM to the surface sediments. Loss of functionality of lipid biomarkers (e.g., decreasing ratios of HMW n-alkanoic acids to HMW n-alkanes, and stanols to sterols) between surface water particles and surface sediments, and in the offshore direction for both surface water particles and surface sediments, suggested ongoing and rapid degradation of terrOM throughout the coastal system. Comparison of terrestrial biomarker signatures (e.g., n-alkane carbon preference index and C 23 / (C 23 + C 29) values) and bulk δ 13C in terrOM released from Kalix River and the Russian Arctic Rivers shows that Kalix River extends the east–west trends of many molecular-level terrOM source indicators and delivers a Sphagnum-impacted terrestrial signal that resembles that of the River Ob.

The dispersal of sedimentary terrestrial organic matter in the East China Sea (ECS) as revealed by biomarkers and hydro-chemical characteristics

Terrestrial organic matter (TOM) in surface sediments from the lower Yangtze River and adjacent East China Sea (ECS) shelf was characterized using elemental, stable carbon isotope and molecular analysis. The results show that it is heterogeneous and derives from various sources in the lower river transect (RC transect) and inner shelf transect (ZJ transect), but is more homogeneous and presumably derives from a single source in the cross-shelf transect (PN transect). The trends in sedimentary TOM abundance indicated by high molecular weight n-alkane abundances and distributions, lignin-derived products, δ 13C values of total organic carbon ( δ 13C TOC) and ratio of TOC to total nitrogen (C/N) suggest a southward (off-estuary) transport mode of TOM along the inner shelf transect while, counter intuitively, the opposite or no trend in TOM off-estuary transport occur along the cross-shelf transect. We therefore suggest that Yangtze-discharged OM is transported southwards along the Zhejiang-Fujian coast (ZJ transect) and enters the Southern Okinawa Trough via near bottom currents, from where it is ultimately delivered back upslope to the middle shelf by the Kuroshio invading water, consistent with the hydro-chemical characteristics of the ECS.

Analysis of organic matter by flash pyrolysis-gas chromatography–mass spectrometry in the presence of Na-smectite: When clay minerals lead to identical molecular signature

Different studies have already pointed out the influence of clays during the analysis of pure organic compounds (especially alkanols, alkanoic acids) as well as macromolecules (humic acids) by flash pyrolysis-gas chromatography–mass spectrometry (PyGC–MS). Especially, the occurrence of clay minerals favors the generation of aromatic units such as alkylbenzenes and polycyclic aromatic hydrocarbons. So as to better identify the nature of the organic compounds which are sensitive to the presence of clays during flash pyrolysis, a humic acid mixed in variable proportions of a Na-homoionic clay was tested. The smectite/humic acid mixtures containing from 10% to 100% humic acid allowed us to identify the progressive disappearance or appearance of specific compounds after PyGC–MS. n-Alk-1-enes disappear when the clay proportion is higher than 67%. For higher contents of Na-smectite, n-alkanes become less and less abundant with a preferential consumption of high molecular weight n-alkanes, whereas the aromatic hydrocarbon proportion increases. Moreover, the distribution of each aromatic hydrocarbon family (alkylbenzenes and alkylnaphthalenes) has been investigated. The pyrogram of pure humic acid exhibits a specific distribution of alkylbenzenes and alkylnaphthalenes reflecting the structure of the organic macromolecule. With the increase in clay proportion, these distributions are modified and lead to other distributions with a preferential predominance of thermally stable isomers. Pyrograms of humic acid and undecanoic acid in the presence of 90% of Na-smectite are similar, especially concerning alkylbenzene and alkylnaphthalene distributions. Therefore, clays (Na-smectite in our experiments) in high proportion modify initial organic products by recombination reactions and lead to the generation of new compounds of very similar distribution, whatever the nature of the initial organic matter. Such results underline the very important catalytic properties of clay minerals on functionalized organic matter during flash pyrolysis.

Impact of a highly contaminated river on a more important hydrologic system: Changes in organic markers

The Fensch River is a tributary of the Moselle River. It is a highly contaminated river that drains an industrial area. The objective of this preliminary study is to determine its impact on the Moselle River by analysing the extractable organic matter (EOM) coming from the sediments at the molecular scale. EOM is described in term of aromatic hydrocarbons, aliphatic hydrocarbons and polar compounds. EOM coming from Fensch River sediments is mainly composed of anthropogenic molecules. Aromatic hydrocarbons are dominated by parent Polycyclic Aromatic Hydrocarbons (PAHs) underlining the pyrogenic origin of this fraction. Aliphatic hydrocarbons consist of diagenetic hopanes and a broad UCM that are characteristics of thermal mature organic matter. Upstream the confluence the EOM of the Moselle River is mainly from vegetal origin. It is composed of high molecular weight n-alkanes with an odd over even predominance, degredation products of phytol and stigmasterol. The occurrence of PAHs and diagenetic hopanes underlines that the Moselle River is already contaminated before the confluence. The Fensch River input drastically changes the EOM of the Moselle River. Amount of PAHs is doubled and the fingerprints of both aliphatic hydrocarbons and polar compounds highlight the combination of both natural and anthropogenic sources.

Characterisation of organic matter in a shallow, reducing, arsenic-rich aquifer, West Bengal

Elevated arsenic in groundwaters extensively exploited for irrigation and drinking water in West Bengal and Bangladesh is causing serious impacts on human health. A key mechanism for the genesis of arsenic (As) in these waters is microbially mediated reductive transformation of arsenic-bearing Fe(III) hydrated oxides. The role of organic C in this process, whether from in situ organic matter (OM), i.e. OM from within the sediment, or from other sources, is widely recognised. Despite this, there is a paucity of data about the characteristics of OM in these As-rich aquifers. Extraction and analysis of the polar and apolar fractions from seven different sediments from a known groundwater As “hotspot” in West Bengal revealed OM characteristic of the original terrestrial depositional environment. However, this was overprinted by abundant hydrocarbons with thermally mature (e.g. petroleum) distributions. These hydrocarbons included abundant high molecular weight n-alkanes and unresolved complex mixtures (UCMs), as well as thermally mature distributions of hopanes and steranes. Additionally, at certain depths (surface sands: 8 and 13 m, deeper sands: 25 m) the OM appeared to be biodegraded, with the preferential removal of petroleum-sourced n-alkanes, suggesting that indigenous microbes within the aquifer can utilise this carbon source. The presence of this previously unreported source of bioavailable organic carbon is of importance as it has the potential to promote microbial activity and subsequent As release in the aquifers.