Lipid geochemistry of a post-glacial lacustrine sediment

The post-glacial environmental history of Voua de la Motte, a small pond, was studied by the lipid geochemistry of a 6 m long core. Palynological studies show that the deepest part of the core goes back to 10,000 yr BP corresponding to the time of formation of the lake following the retreat of the Rhodanian glacier. Hydrocarbons, aldehydes, linear alcohols, sterols, monocarboxylic and monohydroxy fatty acids, were determined throughout the core both in the free and bound lipid fractions, as well as in the tightly bound fraction for the carboxylic acids. There is no clear evidence of a transformation from the unbound to the bound form, except perhaps for the α-hydroxy acids.Qualitative as well as quantitative fluctuations in the distributions of these lipid classes were observed upward in the core. An attempt is made to correlate these fluctuations with the bioenvironmental and climatological evolution of the Basin on the basis of information obtained from palynology.     

Marine and terrigenous lipids in coastal sediments from the Peru upwelling region at 15°S: Sterols and triterpene alcohols

The distributions of free 4-desmethyl sterols in sediments from the Peru coastal zone at 15°S have been determined. Major free sterols in the surface sediments include cholesterol, which is mainly derived from zooplankton, and two C₂₈ sterols: 24-methylcholesta-5,24(28)-dien-3β-ol and 24-methylcholesta-5,22E-dien-3β-ol both of which are derived fro diatoms. Their concentrations decrease by almost an order of magnitude in the top 20 cm of sediment depth, indicating that free sterols are rapidly degraded in this sedimentary environment. Lipids from higher plants were also detected: long chain fatty acids and alcohols and various triterpenoid alcohols, including taraxerol, lupeol and α- and β-amyrin. The concentrations of most terrigenous lipids varied by less than a factor of 3 over the same depth, and these changes were not correlated with changes in the concentrations of total organic carbon. Below 3 cm, lipids from higher plants predominated in the extractable lipid distributions due to the more rapid degradation of marine lipids. We postulate that there are significant marine sources of the higher plant sterols 24-ethylcholesterol, 24-ethylcholesta-5,22E-dien-3β-ol and 24-methylcholesterol in these sediments. A high proportion of many of the terrigenous lipids in these sediments are probably transported into the coastal zone by rivers, rather than from the atmosphere, and then redistributed by bottom currents.     

Biotransformation and assimilation of dietary lipids by Calanus feeding on a dinoflagellate

Stage V and adult females of the marine copepod Calanus helgolandicus were fed in the laboratory on the dinoflagellate Scrippsiella trochoidea at three concentrations calculated to represent pelagic ocean to ‘bloom’ conditions. The identification and quantification of sterols, fatty acids and alcohols present in the algal diet, copepods and their faecal pellets were then carried out using computerized gas chromatography- mass spectrometry (C-GC-MS). The grazing rates of animals were measured and the data then combined with those of lipid distributions in the diet and faecal pellets in order to determine quantitatively the fate of each lipid during its passage through the gut of Calanus. The results showed marked differences in the proportion of the three lipid classes removed, with highest values found for fatty acids and the lowest for sterols. Up to 97% of ingested algal fatty acids were removed by the copepod, with a preference towards the removal of polyunsaturated acids. Algal sterols were also removed by Calanus; the percentage composition and concentration of sterols in faecal pellets differing from the algal diet at all three food levels. Evidence that the removal of lipids from the diet represented assimilation by the copepods was provided by the further finding that during the feeding period (20 hr) all three lipid classes increased in animal tissues. Quantitative measurements of individual sterols revealed that significant amounts of 4-methyl and 4-desmethyl sterols having the 8(14) and 17(20) unsaturation were removed at all dietary levels. In contrast, ring-saturated stanols were not removed and appear to pass through the gut quantitatively.     

Microbial lipids of an intertidal sediment—I. Fatty acids and hydrocarbons

A detailed study has been made of the solvent extractable monocarboxylic, dicarboxylic and hydroxylated fatty acids and n-alkanes in a surface intertidal sediment, and the distributions compared to microorganisms cultured from the sediment. Diatoms are shown to contribute most of the monocarboxylic acids, particularly the significant amounts of polyunsaturated acids present, and a small proportion of the n-alkanes. Bacteria contribute between 11 and 14% of the monocarboxylic acids and markers for this, including trans-monounsaturated acids, are proposed. Detritus from the sea-grass Zostera muelleri is a major source of the α-hydroxy-, ω-hydroxy and α,ω-dicarboxylic acids in the sediment and a minor contributor of n-alkanes and long-chain fatty acids.     

Free,esterified and residual bound sterols in Black Sea Unit I sediments

Detailed compositional data for the sterols isolated from a surface, Unit I, sediment from the Black Sea are reported. A procedure based on digitonin precipitation has been used to separate the more abundant free sterols from those occurring in esterified forms. Saponification of the solvent extracted sediment residue liberated only a small quantity of residual bound sterols in contrast to studies of other sediments. 4-Methylsterols are much more abundant than 4-desmethylsterols in both the free and esterified sterol fractions which we attribute to a major dinoflagellate input, as in deeper Unit II sediment. The desmethylsterol fraction appears to derive from a variety of sources including dinoflagellates, coccolithophores, diatoms, terrigenous detritus and perhaps invertebrates. 5α(H)-Stanols are particularly abundant in the free sterol fraction. An analysis of the stanol/stenol ratios suggests that the 4-desmethyl-5α(H)-stanols are the result of specific microbial reductions of Δ⁵-sterols and/or the reflection of a contribution of stanol containing source organisms.     

Esters of acyclic and polycyclic isoprenoid alcohols: Biochemical markers in lacustrine sediments

Esters of phytol or related isoprenoid acids and fatty acid esters of pentacyclic triterpenoid alcohols and sterols have been isolated from lacustrine sediments varying in age from contemporary to c. 50,000 years old. The esters were analysed by C-GC-MS and identified by GC retention data and mass spectral interpretation based on comparison with authentic compounds.In surface sediment of a productive lake, phytyl and steryl esters are biochemical markers of input from algal and Zooplankton sources. Esters of pentacyclic triterpenols detected in an older, peat-derived sediment may reflect constituents of peat-forming plant species. In sediments derived mainly from terrestrial organic matter, steryl esters containing the same acyl group showed a lower stanol/Δ⁵-stenol ratio than did the corresponding free sterols.     

南海北部油气缓释环境沉积物脂类化合物组成特征

认识沉积环境有机碳留存状况是阐述油气形成过程中有机碳早期成岩的关键内容。以南海珠江口盆地及其邻近海域为背景,通过研究表层沉积物中脂类化合物的形态组成,认识脂类有机碳的来源和留存状态,阐述特征脂类分子的早期成岩特征。结果表明,研究区域表层沉积物有机碳含量为0.22%～0.66%,有机碳稳定同位素分布在-20.88‰～-22.93‰之间,表现为显著的海源特征。沉积物中共检测出21种脂肪酸、6种脂肪醇、8种甾醇和植醇;总脂肪酸、脂肪醇、甾醇和植醇含量分别为12.57～40.27μg/g、5.35～8.98μg/g、0.15～3.75μg/g和0.01～3.99μg/g干重,总体表现为靠近珠江口和台湾海峡略高。脂类化合物的存在形态以游离态(FR)和碱性水解态(BH)为主,酸性水解态(AH)贡献较低;其中植醇和甾醇呈现显著的BH优势,植醇中未检出AH组分的贡献。脂类化合物主要来自于海洋现场生产,海洋微藻和细菌的相对贡献率分别为21.18%～33.78%和11.02%～15.64%,陆源高等植物贡献低于5%。来源于硫酸盐还原菌的支链脂肪酸在靠近珠江口海域高达1.79～2.62μg/g,占总脂肪酸的5.14%～6.50%,并与硫酸盐还原过程相关的古菌分布相一致。     

The importance of atmospheric input of terrestrial organic material to deep sea sediments

The concentrations of lipids were determined in atmospheric particle, gas and rain samples collected from the tropical North Pacific to assess lipid sources, transport mechanisms and fluxes to the ocean surface. Four lipid compound classes (aliphatic hydrocarbons, fatty alcohols, fatty acid esters, and salts) all unequivocally show a terrestrial vascular plant source. These aerosol lipids originate from wind erosion of Asian and American soils and direct emission from vegetation. The major fluxes result from rain rather than dry deposition. These fluxes are large enough to have a major potential impact on the inventory of terrestrially derived lipid material found in deep-sea sediments. This has been showm for n-alkanes, fatty alcohols, fatty acids, total lipids and for organic carbon. By comparing atmospheric and sediment trap fluxes with sediment accumulation rates, it is suggested that some biogenic terrestrial material is more protected from degradation than marine-derived material.     

Organic geochemical studies of a recent Inner Great Barrier Reef sediment—I. Assessment of input sources

The concentration of solvent-extractable (SE) and bound hydrocarbons, ketones, alcohols, sterols, monocarboxylic acids, hydroxyacids and α,ω-dicarboxylic acids of a surface sample (0–2.5 cm) from a recent carbonate tropical sediment taken at 60ft (18m) depth north-west of the Low Isles, North Queensland, are reported in detail. n-Alkanes are a minor constituent in the SE and bound hydrocarbon fractions with the major component being unresolved complex hydrocarbon material which is not an anthropogenic input. 6,10,14-Trimethylpentadecan-2-one derived from chlorophyll, as well as phytol, were identified as major components of the ketone and alcohol constituents. No chlorophyll pigments or pigmented degradation products were present, implying degradation before incorporation into the sediment. This conclusion is consistent with evidence for higher-plant input in which all sensitive lipids have been degraded before incorporation. SE and bound fractions have been studied in detail and show considerable differences probably arising from the importance of viable biomass in the SE fraction. Inputs to the sediment are determined as higher plants, algae, bacteria, fungi and meiofauna in descending order of importance.     

Organic geochemistry of Walvis Bay diatomaceous ooze—I. Occurrence and significance of the fatty acids

Diatomaceous ooze of the shelf off Walvis Bay (S.W. Africa) was analysed for lipid material. The lipids from the sediment consist of a mixture of hydrocarbons, alcohols, ketones, fatty acids, sterols, carotenoid pigments and chlorophylls. The total fatty acid mixture has been analysed by capillary gas chromatography mass spectrometry and shown to consist of straight chain, iso-, anteiso- and isoprenoid acids. The environmental setting of the S.W. African shelf (Walvis Bay) makes it possible to discuss these fatty acids as markers for the fate of organic matter. The acids in the sediment point to a generation during passage of algal lipids through levels of microbial activity either on or slightly above the burial surface.     

δC and δD identification of sources of lipid biomarkers in sediments of Lake Haruna (Japan)

Organic materials in lacustrine sediments are from multiple terrestrial and aquatic sources. In this study, carbon (δ¹³C) and hydrogen isotopic compositions (δD) of phytol, various sterols, and major n-fatty acids in sediments at Lake Haruna, Japan, were determined in their solvent-extractable (free) and saponification-released forms (bound). The δ¹³C-δD distributions of these lipid molecules in sediments are compared with those of terrestrial C3 and C4 plants, aquatic C3 plants, and plankton to evaluate their relative contributions. δ¹³C-δD of free phytol in sediments is very close to that of phytol in plankton samples, whereas δ¹³C-δD of bound phytol in sediments is on a mixing line between terrestrial C3 plant and plankton material. Unlike phytol, no significant δ¹³C-δD difference between free and bound forms was found in sterols and n-fatty acids. δ¹³C-δD values of algal sterols such as 24-methylcholesta-5,22-dien-3β-ol in sediments are close to those of plankton, whereas δ¹³C-δD of multiple-source sterols such as 24-ethylcholest-5-en-3β-ol and of major n-fatty acids such as n-hexadecanoic acid in sediments are between those of terrestrial C3 plants and plankton samples. Thus, δ¹³C-δD distributions clearly indicate the specific source contributions of biomarkers preserved in a lacustrine environment. Free phytol and algal sterols can be attributed to phytoplankton, and bound phytol, multiple source sterols, and major n-fatty acids are contributed by both terrestrial C3 plants and phytoplankton.     

Lipid geochemistry of sediments from Upton Broad,a small productive lake

Major lipid classes isolated from 3 sections of the sediment profile of Upton Broad, a shallow lake formed about 500 yr ago, were correlated with input and with changes attributable to early diagenesis. Surficial sediment contains lipids characteristics of the known recent algal and microbial input; preservation of chlorophyll pigments and absence of appropriate markers suggest that diagenesis is minimal. Older deposits from the eutrophic phase of the lake's history contain higher levels of bacterial lipids and diagenetic products. The earliest sediment contains lipids characteristic of terrigenous input subjected to more extensive diagenesis than the younger sediment. Recognition of early diagenesis in anoxic sediment suggests that distributions of the shorter-chain homologous free n-alkanes, alkanols and alkanoic acids result from microbial synthesis using material initially deposited at the sediment surface, rather than partial preservation of the lipids of primary source organisms.     

Diagenesis of organic matter in suspended particles and sediments in the Cariaco Trench

Suspended particulate materials and bottom sediments from the Cariaco Trench were analysed for lipid content to investigate the diagenesis of organic matter in an anoxic water column and sediment. Distributions of fatty acids, sterols, and the acyclic isoprenoid hydrocarbons, lycopane and 2,6,10,15,19-pentamethyleicosane, support the hypothesis that alteration of organic matter usually attributed to sedimentary diagenesis occurs in the water column. Typical indicators of diagenetic processes, including preferential loss of unsaturated fatty acids, increased abundances of branched fatty acids, stenol-to-stanol conversion, and abundant acyclic isoprenoids, were observed in the water column across the oxic/anoxic interface in the Cariaco Trench. Lipid distributions in the sediment were remarkably uniform with depth. We conclude that organic material delivered to the sediment has been extensively altered in the water column, but that which is buried is preserved without much additional alteration.     

The lipid chemistry of sediments from the St Lawrence estuary. Acyclic unsaturated long chain ketones,diols and ketone alcohols

Long chain unsaturated ketones (C₃₇C₃₉) and two limited series of alkan-1,15-diols and alkan-15-one-1-ols (chain lengths of 30, 31 and 32 carbon atoms) have been isolated from extracts of sediments from the Gulf of St Lawrence and an associated continental slope sample. The detection of these compound classes in these sediments further extends the range of environments within which these compound classes occur. Differences in the absolute abundance of these lipid classes are probably due to variations in the abundances of E. huxleyi or related algae (in the case of the unsaturated ketones). These lipid components were below the limits of detection, however, in all sediments collected from a third, estuarine sampling site. This observation is one feature distinguishing the lipid distribution and thus differences in the contributing biota at the three sites. These data highlight the use of the biological marker approach for assessing the spatial distribution of a contributing organism to sediments within an open estuarine system. The absolute abundance of long chain ketones, diols and ketone alcohols decreased with depth in Gulf sediments (≈2.3 to less than 0.001 μg/g for long chain ketones).     

Diagenesis of free and bound lipids in terrestrial detritus deposited in a lacustrine sediment

Recent sediments from an oligotrophic lake (Loch Clair) having uniform organic input for 2000 yr show changes in lipid abundance and composition, with increasing depth, attributed to diagenesis. Stability of free lipids decreases in the order n-alkanes, alkan-2-ones, sterols, n-alkanoic acids, n-alkanols, n-alkenoic acids. Diagenetic loss of shorter-chain homologues is complete within 400 yr. Stabilisation of bound relative to free lipids increases the proportion of the former with sediment age and reduces loss of shorter-chain bound homologues.In an eutrophic lake (Cross Mere), shorter-chain free and bound sedimentary lipids show increased abundance compared with Loch Clair. The relative importance of higher input of shorter-chain lipids derived from aquatic detritus, and slower initial diagenesis due to the anoxic hypolimnion, as causative factors for this difference between lake types cannot yet be assessed.     

Sterols of a contemporary lacustrine sediment

C₂₆, C₂₇, C₂₈ and C₂₉ sterols, including Δ⁵-, Δ²²- and Δ^5,22-sterols and both 5α- and 5β-stanols, have been identified in the contemporary lacustrine sediment of Rostherne mere (Cheshire, England). Amounts of total sterols decrease from ca. 400 ppm extracted sediment dry weight for the 0–7 cm sediment section to ca. 40 ppm for the corresponding 18–30 cm section. 5α-stanols are of far greater abundance than the 5α-stanol isomers. The carbon number distributions of unsaturated and saturated sterols and the increase in stanol: Δ⁵-sterol ratio with sediment depth provide indirect evidence for the operation of a sterol hydrogenation process. C₂₉ sterols preponderate at lower sediment depths, suggesting a predominantly higher plant input, whereas C²⁷ sterols are more abundant in the surface sediment.     

Lipid biogeochemistry of Phormidium and Microcoleus mats

A study on the predominant sources of organic matter and the main diagenetic processes in two different cyanobacterial mats from evaporite-controlled environments was performed. Fatty acids, hydrocarbons, alcohols, ketones and aldehydes were anlyzed in selected millimetre and submillimetre core sections. The changes in lipid composition were evaluated by comparison with the vertical distributions of the populations observed by optic microscopy and with the lipid patterns of enrichment cultures of species such as cyanobacteria, diatoms, purple bacteria, sulphate-reducers and methanogens obtained from the mats.The cyanobacteria Phormidium valderianum and Microcoleus chthonoplastes are the predominant primary producers, and occur almost as monocultures in the respective top layers. However, these mat-forming organisms only leave minor features in the solvent-extractable lipid sedimentary record. The predominant fatty acid distributions parallel the composition observed in the enrichment cultures of purple bacteria and appear mixed with acids characteristic of heterotrophic eubacteria such as sulphate-reducers. The concentrations of these lipids are, however, 5–10 times lower than the cyanobacterial acids from the top layer. De novo heterotrophic eubacterial synthesis is also observed in cases such as the highly branched isoprenoid eicosenes, the major hydrocarbon in the deep layers (>2 mm) of the Phormidium mat. Other major diagenetic changes involve dehydration and hydrogenation. These two processes take place concurrently under anoxic conditions and have been observed among the sterols and the isoprenoid alcohols. Significant amounts of 5ß(H)-stanols were observed in the more reducing sections where molecular indicators of methanogenic bacteria were also found.     

Sources of neutral lipids in a temperate intertidal sediment

The compositions of sterol, alcohol and ketone fractions from an oxic intertidal surface sediment from Corner Inlet. Victoria, Australia, have been examined by capillary gas chromatographymass spectrometry and related to the lipids of diatoms cultured from the sediment and to lipids of the sea-grass Zostera muelleri. Of the more than thirty sterols in the sediment most appear to derive from diatoms, including the major sterol 24-methylcholesta-5.22E-dien-3β-ol. Small amounts of 24-ethylcholesterol probably derive from Zostera, with a minor diatom contribution. 5α-stanols, both fully saturated and with a side-chain double bond, represented ca. 14% of the total sterols: a significant proportion of these are probably derived from marine invertebrates. These organisms also contribute C₂₆ sterols. most of the cholesterol and possibly small amounts of Δ-sterols. The data suggest that in situ biohydrogenation of stenols was not a major process in sterol transformation in the surface oxic sediment. Alcohols ranged from C₁₂ to C₃₀ and showed an unusual abundance of unsaturated components with Δ⁹-16:1 being the major constituent. The long-chain alcohols probably originate largely from Zostera but the shorter-chain. C₁₂-C₂₀. alcohols are at least partly derived from wax esters of unknown origin. Diatoms do not contribute significant amounts of alcohols. Ketones were not major constituents of the sediment and consisted mainly of 6.10.14-trimethylpentadecan-2-one and a series of n-alkan-2-ones ranging from C₁₆ to C₃₃. The latter showed a similar distribution to that of the n-alkanes but the correspondence was not sufficient to substantiate a product-precursor relationship. Very long-chain C₃- C₃₉ unsaturated methyl and ethyl ketones, which may originate from the marine unicellular alga Emiliania huxleyi. were present in low concentration.     

The identification of organic input sources of sediments from the santa catalina basin using factor analysis

Individual neutral lipids, including hydrocarbons, ketones, alcohols, sterols, keto-ols and diols have been analysed from eight horizons in a sediment core taken from the Santa Catalina Basin, Calif. Variations in the concentration of individual lipid components between sites are studied using factor analysis to determine their inputs. Several sources of organic material are postulated from the composition of hypothetical factors, including methanogenic bacteria, higher plants and algae including coccolithophores, dinoflagellates and diatoms. Sources for long chain keto-ols and diols and a C₃₅ bicyclic alkene are suggested as methanogenic bacteria and algae respectively.     

Lipids of aquatic organisms as potential contributors to lacustrine sediments—II

The relationship between the lipid composition of organisms in the water column of an eutrophic lake and the lipid composition of underlying sediments, previously examined for n-alkanols and steroids, is now reported for hydrocarbons, ketones and carboxylic acids.The n-C₇ alkane and alkenoic acids from two primary sources are rapidly metabolized in the water column and surficial sediment. Bacterial biomarkers, including hopenes and fatty acids, were detected in the photosynthetic bacterial layer occurring just above the sediment-water interface.Within the sediment the apparent conversion of free n-alkanes, alkan-2-ones and ω-hydroxy acids to the corresponding bound form is noted; microbiological oxidation of n-alkanes to alkan-2-ones is supported by the detection of the intermediate alkan-2-ols with a distribution similar to that of the ketones. The geochemistry of sediment deposited c. 1900, prior to biological study of the site, was interpreted from stable biomarkers and the diagenetic changes recognised in the study of contemporary deposition. A qualitative difference in algal input to the older sediment is inferred from the low Δ⁷-sterol content and presence of 2,6,10-trimethyl-7-(3-methylbutyl)-dodecane. However, there was still significant dinoflagellate input, as indicated by the presence of 4α-methylsterols. A difference in higher-plant input to the older sediment, indicated from the n-alkane, alkene and triterpenoid ketone distributions, is consistent with the recent development of tree cover.