Alkyl Diols Research Articles

East Asian winter monsoon controlling phytoplankton productivity and community structure changes in the southeastern South China Sea over the last 185 kyr

The South China Sea (SCS) is one of the largest marginal seas in the world and it plays an important role in regional climate change and carbon cycles. However, mechanisms of glacial–interglacial phytoplankton productivity changes remain under-studied, especially for the southeastern SCS. In this study, the productivity record for the southeastern SCS (core MD972142) over the last 185kyr was generated using multiple biomarkers, including C37 alkenones (C37:2+C37:3), brassicasterol, dinosterol, and alkyl diols (C30+C32) as productivity proxies for haptophytes, diatoms, dinoflagellates, and eustigmatophytes (and diatoms), respectively. All biomarker contents indicate higher individual as well as total phytoplankton productivities during peak glacials than during interglacials. Our records afford a better constraint on spatial pattern of glacial productivity changes, which suggest that both the southeastern and northern SCS glacial productivity increases were controlled by the stronger East Asian winter monsoon (EAWM), which brought more nutrients to the surface through stronger mixing of nutrient-rich deep waters. Biomarker ratios reveal a relatively stable phytoplankton community structure (PCS), but relative diatom productivity was higher during glacials. The PCS record is consistent with stronger EAWM forcing during glacials, which supplied nutrients to the surface with relatively stable composition. The decrease of C37 alkenones during the last 120kyr is likely a global phenomenon, which could be related to the evolution of the haptophytes. In the SCS, this trend was also likely caused by changes of subsurface nutrient supply to the SCS, which significantly modulated the PCS by a gradual decrease of haptophyte contribution to total phytoplankton in the northern and southeastern SCS since MIS 5.

Sources and proxy potential of long chain alkyl diols in lacustrine environments

Long chain 1,13- and 1,15-alkyl diols form the base of a number of recently proposed proxies used for climate reconstruction. However, the sources of these lipids and environmental controls on their distribution are still poorly constrained. We have analyzed the long chain alkyl diol (LCD) composition of cultures of ten eustigmatophyte species, with three species from different families grown at various temperatures, to identify the effect of species composition and growth temperature on the LCD distribution. The results were compared with the LCD distribution of sixty-two lake surface sediments, and with previously reported LCD distributions from marine environments. The different families within the Eustigmatophyceae show distinct LCD patterns, with the freshwater family Eustigmataceae most closely resembling LCD distributions in both marine and lake environments. Unlike the other two eustigmatophyte families analyzed (Monodopsidaceae and Goniochloridaceae), C28 and C30 1,13-alkyl diols and C30 and C32 1,15-alkyl diols are all relatively abundant in the family Eustigmataceae, while the mono-unsaturated C32 1,15-alkyl diol was below detection limit. In contrast to the marine environment, LCD distributions in lakes did not show a clear relationship with temperature. The Long chain Diol Index (LDI), a proxy previously proposed for sea surface temperature reconstruction, showed a relatively weak correlation (R2=0.33) with mean annual air temperature used as an approximation for annual mean surface temperature of the lakes. A much-improved correlation (R2=0.74, p-value <0.001) was observed applying a multiple linear regression analysis between LCD distributions and lake temperatures reconstructed using branched tetraether lipid distributions. The obtained regression model provides good estimates of temperatures for cultures of the family Eustigmataceae, suggesting that algae belonging to this family have an important role as a source for LCDs in lacustrine environments, or, alternatively, that the main sources of LCDs are similarly affected by temperature as the Eustigmataceae. The results suggest that LCDs may have the potential to be applicable as a palaeotemperature proxy for lacustrine environments, although further calibration work is still required.

Evaluation of long chain 1,14-alkyl diols in marine sediments as indicators for upwelling and temperature

Long chain alkyl diols form a group of lipids occurring widely in marine environments. Recent studies have suggested several palaeoclimatological applications for proxies based on their distributions, but have also revealed uncertainty about their applicability. Here we evaluate the use of long chain 1,14-alkyl diol indices for reconstruction of temperature and upwelling conditions by comparing index values, obtained from a comprehensive set of marine surface sediments, with environmental factors such as sea surface temperature (SST), salinity and nutrient concentration. Previous studies of cultures indicated a strong effect of temperature on the degree of saturation and the chain length distribution of long chain 1,14-alkyl diols in Proboscia spp., quantified as the diol saturation index (DSI) and diol chain length index (DCI), respectively. However, values of these indices for surface sediments showed no relationship with annual mean SST of the overlying water. It remains unknown as to what determines the DSI, although our data suggest that it may be affected by diagenesis, while the relationship between temperature and DCI may be different for different Proboscia species. In addition, contributions from algae other than Proboscia diatoms may affect both indices, although our data provide no direct evidence for additional long chain 1,14-alkyl diol sources. Two other indices using the abundance of 1,14-diols vs. 1,13-diols and C30 1,15-diols have been applied previously as indicators for upwelling intensity at different locations. The geographical distribution of their values supports the use of 1,14 diols vs. 1,13 diols [C28+C30 1,14-diols]/[(C28+C30 1,13-diols)+(C28+C30 1,14-diols)] as a general indicator for high nutrient or upwelling conditions.

Long-chain branched/cyclic alkanes in recent sediment of Lake Fuxian and their environmental implications

Lake Fuxian is a large, deep, and oligotrophic freshwater lake. In recent sediment of this lake, a series of branched and cyclic alkanes, including branched alkanes with one or two quaternary carbon atoms (C2n compounds), alkylcycloheptane, and alkylcyclohexane, were detected in high abundance. For each homolog of long-chain branched/cyclic alkanes, molecules with only an odd or even carbon number were present in the sediment. The abundance variation of each compound homolog corresponded to those of other compound homolog in the section, indicating the same origin of these compounds. The concentrations of long-chain branched/cyclic alkanes in the sediment profile exhibited variations similar to those of phytoplankton biomarkers, such as 3-methyl-alkanes, short-chain odd carbon n-alkanes, hopene, polyunsaturated fatty acids, phytol, sterols, and long-chain alkyl diols, but slightly different from those of long-chain odd carbon n-alkanes, which are ubiquitous biomarkers for higher plants. Therefore, the C2n compounds and long-chain cyclic alkanes in the lake sediment were most likely produced by algae and bacteria in the water, primarily, by the heterotrophic bacteria in the moderately oxygenated waters, which flourishing might be the results of specific water environments in Lake Fuxian.

Potential biological sources of long chain alkyl diols in a lacustrine system

Long chain alkyl diols (LCDs) have been detected in a range of marine and lacustrine environments, as well as in several algal cultures. However, the identity of the producers, their preferred ecological niche and seasonality are uncertain. We applied a gene-based approach to determine the identity and abundance of Eustigmatophyceae 18S rRNA genes and compared the data with the distribution of LCDs in the water column of Lake Challa (East Africa). Gene-based analysis revealed three known and two novel Eustigmatophyceae groups. Maxima in the number of gene copies and LCD concentration coincided at 9m water depth, signifying Eustigmatophyceae as important producers of LCDs. In addition, seasonal changes in LCD abundance in sedimenting particles revealed several blooms of LCD producers over the annual cycle.

Enlarged helical twisting power in chiral cyclic dimers based on conventional chiral alkyl diols

We prepared a homologous series of chiral cyclic liquid crystal (LC) dimers containing two biphenyl mesogens linked by two alkyl spacers, one of which was based on a R-enantiomeric chiral diol. In solution, the circular dichroism spectra of all the R-enantiomeric dimers showed the first negative and second positive Cotton effects, which indicated that the two biphenyl mesogens were located in a skewed overlapping alignment with counter-clockwise helicity. The helical twisting power (HTP) of these cyclic dimers was confirmed by the cholesteric LCs in mixtures with the nematic host. The induced cholesteric LCs in all mixtures had the same counter-clockwise helical sense as the skewed conformation of the two biphenyl mesogens. Furthermore, HTP values and Cotton effect amplitudes were linearly correlated, indicating direct induction of cholesteric twisting by the skewed biphenyl moieties. The induced HTP values were quite large, irrespective of the use of conventional chiral diols; the largest HTP value exceeded 100 μm−1 and was obtained in the cyclic dimer based on the R,R-1,2-diphenylethane diol.

The structure of Langmuir films of long diols on mercury

Surface-specific X-ray methods and surface tensiometry are used to study the structure of Langmuir films of alkyl diols with 15 ≤ n ≤ 24 carbons supported on a liquid mercury subphase. Phases of either mono- or bi-layers of surface-parallel molecules are found, depending on surface pressure. Although both ends of the diol molecule can form hydrogen bonds, as do corresponding-length α,ω-alkyldiacids, the consequent 2D order occurring in diacids is not observed here. Instead, one-dimensional order along the chain-normal direction is established for the longer diols, exhibiting two length scales, corresponding both to the molecular width, and differing by ∼3%. The reasons for, and molecular interactions leading to, this structure are discussed.

Hydrophilic modification of silica–titania mesoporous materials as restricted-access matrix adsorbents for enrichment of phosphopeptides

A new nano-scale restricted-access matrix (RAM) SiO2 (MCM-41) with relatively high Ti-content (Ti/Si=0.1), but superior surface area (1129m2/g), was successfully synthesised for the enrichment of phosphopeptides. The TiO2 was incorporated into the Si-MCM-41 via a hydrothermal process and the external surface was modified with alkyl diol by the successive hydrolysis of γ-(glycidyloxypropyl) trimethoxysilane (GPTMS). Scanning electron microscopy, transmission electron microscopy, N2 adsorption and Fourier transform infrared spectroscopy were used to characterise the alkyl diol-Ti-MCM-41. The appropriate pore diameter (2nm) coupled to the marshy weeds-like hydrophilic external surface result in an efficient size-exclusion effect for the adsorption of standard cytochrome c with a molecular weight (MW) of ca. 12.4kDa. At the same time, the strong affinity interaction between the incorporated titanium in the framework and the phosphoryl groups of phosphopeptides demonstrated a selective extract of phosphopeptides from the tryptic digestion. The detection sensitivity for phosphopeptides, determined by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) was as low as 5fmol for standard tryptic digest of β-casein. Therefore, this alkyl diol-Ti-MCM-41 mesoporous material can be used as a potential adsorbent for applications in MS-based phosphoproteomics.

Short scale (6 h) temporal variation of sinking fluxes of planktonic and terrigeneous lipids at 200 m in the NW Mediterranean Sea

Abstract. Drifting sediment trap measurements were carried out at high temporal frequency in the northwestern Mediterranean Sea in the course of the DYNAPROC 2 campaign, during the transition between late summer to autumn conditions. Molecular biomarkers were analyzed in selected subsets of consecutive samples collected for 6 h at 200 m depth. Fluxes of n-alkanes, long-chain alkenones, sterols and steroid ketones show high variability between consecutive 6-h samples, comparable in range to seasonal variability. n-Alkane export ranges from 1.4 to 29.7μg m−2 d−1, fluxes of C37 alkenones varies from 0 to 14.2 μg m−2 d−1. Fluxes of sterols, steroid ketones and C30 alkane diol respectively range from 31 to 377, 2.2 to 46 and 0.3 to 9.3 μg m−2 d−1. Biomarker flux ranges are coherent with the relatively low primary production and the low export ratio encountered during the study. Molecular characteristics of biomarker composition is consistent with reworked algal and zooplanktonic organic matter. Lipid biomarker composition points to the dominance of haptophytes over dinoflagellates in the exported material, and to a minor contribution of diatoms and eustigmatophytes. The intrusion of coastal water at the study site was recorded by an enhanced imprint of higher plant n-alkanes. Two processes can be responsible for the pulses in biomarker flux: changes in the magnitude of particle flux (dry weight mass flux) and changes in the concentration of biomarkers in the particles. Concurrent variability in fluxes, significant Pearson correlations between fluxes of biomarkers of haptophytes, dinoflagellates, eustigmatophytes, zooplankton activity and higher plants (alkenones, dinosterol, alkyl diols, dehydrocholesterol, steroid ketones, p&lt;0.01, n=31, suggest that the short term temporal variability of biomarker export fluxes depends primarily on the intensity of particle dry weight flux. Biomarker concentrations vary on a relatively narrower range than biomarker fluxes, indicating that changes in particle composition (due to degradation or change in source apportionment) has a weaker influence on flux variability. Thus, particle aggregation and sinking are key processes to explain the dynamic of biomarker export at a temporal scale of 6 h. None the less, abrupt changes of OC-normalized concentrations of biomarkers, in the time scale of 6 h, indicate that the exported particles composition also show short-time variability. Highest biomarker flux values recorded by the trap samples from 27 to 29 September correspond to highest values of zooplankton biomass integrated between the surface and 200 m. The decrease in primary production after the October wind events is echoed by minima in biomarker flux values. Despite these correspondences, the coupling between primary production and biomarker export is complex.

Organic matter sources in an enclosed coastal inlet assessed using lipid biomarkers and stable isotopes

The sources of organic matter (OM) in surface sediments from Wilson Inlet, an enclosed and seasonally barred inlet in Western Australia, have been determined using a combination of lipid biomarkers (including fatty acids, sterols, phytol, long chain alcohols, alkyl diols, tetrahymanol and C 32 hopanol) and stable carbon and nitrogen isotope data for bulk OM and δ 13C data for n-alkanols. The organic composition of sediments from the inflowing rivers was used as a proxy for terrestrial inputs of higher plant OM, since these sediments contained only small amounts of carbon from microalgae (mostly diatoms), bacteria and cyanobacteria. The relative proportions of “marine” and “terrestrial” OM in the sediments could be estimated using the stable carbon isotope signature of the bulk organic carbon. The sediments from Wilson Inlet showed similar lipid compositions and isotope values, and the sterol and fatty acid distributions showed the complexity typical of marine ecosystems. Relative contributions from algal (phytoplankton and microphytobenthos), bacterial, terrestrial plants and seagrass sources were estimated using biomarker/organic carbon ratios in the different source terms. Microalgae and bacteria are the most important source of OM within the inlet (over 80% in most sediments) and most of the algal material originates from the water column, except in sandy shallow sediments at the eastern end of the inlet where a contribution from microphytobenthos can be discerned. The distributions, abundances and δ 13C isotope values of long chain n-alkanols proved to be useful in quantifying the contributions from terrestrial plants and the seagrass Ruppia megacarpa. The latter is a relatively small contributor (< 10%) to the OM in the sediments, despite the presence of large seagrass beds around the edges of the inlet and the presumed importance of seagrass as a source of carbon in the foodwebs of the inlet. Nonetheless, seagrass is a significant contributor of the “higher plant” marker 24-ethylcholesterol (sitosterol) in the sediments.

Biomarker Evidence of Relatively Stable Community Structure in the Northern South China Sea during the Last Glacial and Holocene

High-resolution molecular abundance records for several marine biomarkers during the last glacial and Holocene have been generated for core MD05-2904 (19°27.32’N, 116°15.15’E, 2066 m water depth) from the northern South China Sea. The UK(subscript k1)37 SST record indicates a 4.4°C cooling during the Last Glacial Maximum for this site, consistent with previous reconstructions. The contents of C37 alkenones, dinosterol, brassicasterol, and C30 alkyl diols are used as productivity proxies for haptophytes, dinoflagellates, diatoms, and eustigmatophytes, respectively. These records reveal that both individual phytoplankton group and total productivity increased by several factors during the LGM compared with those for the Holocene, in response to increased nutrient supply. However, the community structure based on biomarker percentages remained relatively stable during the last glacial-Holocene transition, although there were short-term oscillations.

Restricted access materials for sample clean-up in the analysis of trace levels of tetracyclines by liquid chromatography: Application to food and environmental analysis

Restricted access materials (RAM) based on alkyl diol silica (ADS) porous particles were evaluated for the sample clean-up in tetracyclines analysis in milk and water samples by liquid chromatography. RAM with C 4, C 8 and C 18 bonded to the inner pore surfaces were tested, with C 8 providing the best performance. A switching column LC system which combines an ADS C 8 RAM column and an analytical C 18 column connected to a fluorimetric detector was used for tetracyclines analysis. The RAM clean-up removed large peaks that otherwise appeared in the initial time window of the chromatograms, attributed to proteins in milk samples and humic substances in water samples. Thus, quantification of analytes in real samples, especially of the most polar compounds such as oxytetracycline and tetracycline, was clearly improved.

Liquid chromatographic determination of enrofloxacin in nasal secretions and plasma of healthy pigs using restricted access material for on-line sample clean-up

A new fully automated method was developed for the quantitative analysis of an antibacterial drug, enrofloxacin (ENRO), in both nasal secretions and plasma samples of healthy pigs. The method is based on the use of a pre-column packed with restricted access material (RAM), namely RP-18 ADS (alkyl diol silica), for on-line sample clean-up coupled to a liquid chromatographic (LC) column containing octadecyl silica. The only off-line sample preparation was the 50-fold dilution of nasal secretions and plasma samples in the washing liquid composed of 25 mM phosphate buffer of pH 7.4. A 10 μl diluted sample volume was injected directly onto the pre-column and washed for 7 min. By rotation of a switching valve, the analyte of interest was eluted in the back-flush mode with the LC mobile phase which consisted in a mixture of 25 mM phosphate buffer of pH 3.0 and acetonitrile according to a segmented gradient elution. By a new rotation of the switching valve, the pre-column and the analytical column were equilibrated for 3 min with the initial mobile phases. The flow-rate was 0.8 ml min −1 for the washing liquid and 1.5 ml min −1 for the LC mobile phase. ENRO was detected by fluorescence at excitation and emission wavelengths of 278 and 445 nm, respectively. Finally, the developed method was validated using an original strategy based on total measurement error and accuracy profiles as a decision tool. The limits of quantitation of ENRO in plasma and in nasal secretions were 30.5 and 91.6 ng/ml, respectively. The validated method was then applied successfully to the determination of ENRO in healthy pigs treated by intramuscular injection at different doses (2.5, 10 and 30 mg/kg bodyweight) for a pilot study. This method could be also used for the simultaneous analysis of ENRO and its main metabolite, ciprofloxacin (CIPRO).

Coordinated 1,3‐Diyne Diols as Organometallic Building Blocks for Large Macrocycles Containing Oxygen and Unsaturated Donor Units

AbstractThe acid‐catalysed reaction of [{Co2(CO)6(μ‐η2‐HOCH2C2‐)}2] (1a) with a range of alkyl diols has been examined as means of preparing large crown‐type macrocycles (up to twenty eight‐membered) containing at least one coordinated 1,3‐diyne unit, multiple oxygen atoms and a variety of soft donor units. Thus, interaction of 1a with HOCH2(CH2)nCH2OH, allows access to the monomeric cyclised complexes [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2OCH2(CH2)nCH2O}] (3a: n = 2, 3b: n = 3, 3c: n = 4) along with the dimeric cyclised species [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2OCH2(CH2)nCH2O}]2 (4a: n = 2, 4b: n = 3, 4c: n = 4). Introduction of additional oxygen donor atoms into the macrocycle can be achieved by reaction of 1a with the glycols, HO(CH2CH2O)nH, to afford exclusively monomeric [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2O(CH2CH2O)n}] (5a: n = 3, 5b: n = 4). On the other hand, treatment of 1a with the 1,3‐diyne‐linked alkyl diols, HOCR2C≡CC≡CCR2OH, furnishes the more rigid monomeric [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2OCR2C2C2CR2O}] [6a: R = H, 6b: R = Me] and dimeric macrocycles [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2OCR2C2C2CR2O}]2 [7a: R = H, 7b: R = Me], whereas the use of the alkynyl‐ or aryl‐linked alkyl diols, HOCH2(L)CH2OH, affords the unsymmetrical dimeric [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2}2O{OCH2(L)CH2O}] [8a: L = –C≡C–, 8b: L = 1,4‐C6H4] and symmetrical dimeric species [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2OCH2(L)CH2O}]2 [9a: L = –C≡C–, 9b: L = 1,4‐C6H4]. Also isolated as a by‐product from all the above reactions is the self‐dimerised macrocycle [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2O}]2 (2) which can itself be synthesised more directly by treating 1a with catalytic quantities of HBF4·OEt2. Single crystal X‐ray diffraction studies have been performed on 2, 3a, 5a, 7a, 8a, 8b and 9a. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)

Characterization of Alkane Diol-CD Complexes. Acid Denitrosation of N-Methyl-N-Nitroso-p-Toluenesulphonamide as a Chemical Probe

A study was carried out on the acid denitrosation of N-methyl-N-nitroso-p-toluenesulfonamide (MNTS) in mixed systems made up of linear (geminal and terminal) alkyl diols and β-cyclodextrin (CD). The alkyl diols used allowed us to vary the length of the hydrocarbon chain from 2 to 6 carbon atoms. The observed rate constant, kobs, decreases in the presence of CD. The inhibition profile decreases as the as the number of carbons in the chain is increased. This behaviour can be interpreted as a consequence of a balance between the complexation processes of MNTS and the alkyl diols by the CD. At a constant CD concentration and increase in the diols concentration decreases the concentration of free cyclodextrin available to complex with MNTS molecules and therefore produces an increases in the observed rate constant. The results were interpreted in terms of two different models; trough the presupposition and non-presupposition of a stoichiometry for the CD-diols complex. Both models agreed quite well and allow us to determine the uncomplexed cyclodextrin concentration in each case as well as the stoichiometry of the complexes. The binding constant for both types of alkane diols increase with increasing the number of carbon in the chain. Besides, the binding constant of the α,ω-alkane diols is higher than for the analog α,β-alkane diols. One of the main consequences of this study is that the acid denitrosation of MNTS can be use to obtain the stochiometry of the CD-diol complexes and to monitor the free cyclodextrin concentration.

Fast assay of angiotensin 1 from whole blood by cation-exchange restricted-access solid-phase microextraction

A novel restricted-access material with cation-exchange properties was evaluated for the extraction of the peptides angiotensin 1 (Ang1) and angiotensin 2 (Ang2) from whole blood. The ion exchange diol silica (XDS) material revealed enhanced efficiency for extraction of peptides when compared with the conventional alkyl diol silica (ADS) with reversed phase extraction centers. The outer surface of XDS particles contains diol groups while the internal surface has sulphonic acid moieties with strong cation-exchange properties toward compounds with low molecular weight. This new coating for solid-phase microextraction (SPME) offers the possibility to combine all initial sample preparation steps into a single one, even for complex biological samples such as whole blood or plasma. The XDS material was immobilized on a stainless steel wire with a binding agent; the reproducibility of the procedure was determined to be 5.56%. Compounds extracted from whole blood were separated by narrow-bore liquid chromatography (LC) and Ang1 was quantified by electrospray mass spectrometry, with good linearity over the range of 25–500 pM. Total analysis time was less than 90 min. The detection limit for Ang1 from whole blood was determined to be 8.5 pM. A single fiber could be used more than 150 times before a noticeable decrease in extraction capacity was observed. Although the limit of quantification is not as low as that of radioimmunoassay techniques, this method is much faster, less expensive and still provides enough sensitivity at physiological levels of Ang1.

Automated method for the determination of a new matrix metalloproteinase inhibitor in ovine plasma and serum by coupling of restricted access material for on-line sample clean-up to liquid chromatography

A fully automated liquid chromatographic method was developed for the determination of Ro 28-2653, a new synthetic inhibitor of matrix metalloproteinases (MMPs), in ovine serum and plasma. The method was based on the coupling of a pre-column packed with restricted access material, namely LiChrospher RP-8 ADS (alkyl diol silica), for sample clean-up to an analytical column containing octyl silica stationary phase. One hundred μl of biological sample, to which 2-propanol was automatically added, were injected onto the ADS pre-column, which was then washed with a washing liquid consisting of a mixture of 25 mM phosphate buffer (pH 7.0) and acetonitrile (90:10; v/v) for 10 min. By rotation of the switching valve, the analyte was then eluted in the back-flush mode with the LC mobile phase composed of a mixture of acetonitrile and 25 mM phosphate buffer (pH 7.0) (57:43; v/v). The UV detection was performed at 395 nm. The main parameters likely to influence the sample preparation technique were investigated. The method was then validated over a concentration range from 17.5 to 1950 ng/ml, the first concentration level corresponding to the lower limit of quantitation. At this concentration level, the mean bias and the R.S.D. value for intermediate precision were −2.4% and 4.2%, respectively.

Long chain n-alkyl diols, hydroxy ketones and sterols in a marine eustigmatophyte, Nannochloropsis gaditana, and in Brachionus plicatilis feeding on the algae

Base-hydrolyzed sterols and long-chain alcohols of a marine eustigmatophyte, Nannochloropsis gaditana have been studied. Sterol composition of N. gaditana is similar to that of other member of this genus, with predominance of cholest-5-en-3β-ol and 24-ethylcholest-5-en-3β-ol. The C29:2 and C30:1 unsaturated aliphatic alcohols were predominant. Saturated and monounsaturated C28 to C36n-alkyl diols occurred as a mixture of positional isomers with ω16 predominating among the C28 alkyl diols, ω18 among C30, C32, C34 and C36 alkyl diols and ω17 for the odd chain alkyl diols. C28–C32 hydroxy ketones were identified for the first time in a marine organism, with a distribution parallelling the alkyl diol mixtures and suggesting a biosynthetic relation between both alcohol classes. N. gaditana was fed to Brachionus plicatilis and the distribution of alkyl diol positional isomers remained the same in the algae and the rotifer fecal pellets. However, digestion resulted in an increase in C30 diols relative to C32 diols and in an enrichment of unsaturated long-chain alcohols relative to alkyl diols.

Burial and reactivity of sedimentary microalgal lipids in bioturbated Mediterranean coastal sediments

The fate of microalgal lipid biomarkers in marine coastal sediments when acted on by natural bioturbation processes (Carteau Bay, Gulf of Fos, Mediterranean Sea) was studied under laboratory conditions. Both dead phytoplanktonic cells ( Nannochloropsis salina) and luminophores (inert fluorescent particulate tracers) were deposited at the surface of intact sediment cores which were then incubated for 22, 44 and 63 days. Sediment reworking and concentration profiles of specific lipid components of N. salina ( n-alkenes, alkyl diols, sterols and fatty acids) were determined as a function of time and depth. The results show that, in the sediment investigated, bioturbation occurs essentially as a biodiffusive process and that it has a rapid and significant impact on the qualitative and quantitative record of sedimentary lipids. Whereas most of the biomarkers were detected in the entire reworked layer (0–6 cm) after 22 days, n-alkenes were never detected below 3 cm due to their low concentration and their high reactivity. For each individual lipid, the comparison of the amounts obtained from the inventories of biomarkers in the reworked zone, with the amount deposited initially at the sediment surface, allowed the determination of its extent and rate of degradation. These ranged from 72% to 99% and from 0.010 to 0.047 day −1, respectively, depending on the biomarker considered, with polyunsaturated fatty acids (PUFAs) and alkenes being degraded faster than the other components. Comparison with previous work suggests that, in biologically reworked sediments, the apparent reactivity of lipids is: (i) positively correlated with the biological mixing coefficient ( D b) and, (ii) generally much higher than in non-bioturbated (anoxic) sediments. Our results also support the idea that degradation of lipids in reworked sediments involves the combined effects of aerobic and anaerobic degradation processes, but that biological mixing results in diagenetic properties more characteristic of completely oxidized conditions.

Biological markers and their carbon isotopes as an approach to the paleoenvironmental reconstruction of Nansha area, South China Sea, during the last 30 ka

Paleoenvironmental changes over the last 30 ka have been documented for the Nansha area, South China Sea, from the biomarkers and their carbon isotopic composition of 314 sediment samples from core 17962. The concentrations of marine lipids indicate that the paleoceanographic and paleoclimatic conditions were not stable in the Nansha area during the last glacial period. The accumulation rates of C 37 alkenones and C 30 alkyl diols show that marine paleoproductivity was higher during the last glaciation than in the Holocene, and correlate well with those of terrestrial biomarkers. Simultaneous variations in accumulation rates of marine biomarkers and terrigenous long-chain compounds during the last glacial period suggest that this enhancement of marine productivity was caused by an increase in terrestrial nutrient supply from the Sunda Shelf. The stable carbon isotopic composition of terrigenous long-chain compounds, such as n-alkanes ( δ 13C=−28.6∼−34.2‰), n-alkanoic acids ( δ 13C=−27.1∼−31.8‰) and n-alkanols ( δ 13C=−26.6∼−35.3‰), indicates that these compounds were derived from C 3 plants, and the surrounding area of southern South China Sea was not dry during the last glacial.