Fatty Acid Signatures from Bacteria at the Freshwater/Seawater Boundary of the Krka Estuary in Winter, Spring and Autumn

Distribution of fatty acids was determined at the halocline and in adjacent brackish and marine waters in the Krka Estuary, on the East coast of the Adriatic Sea, in winter 1987, spring 1988 and fall 1990. Particulate matter (> 0.7 pm) was extracted and analyzed for fatty acids by gas chromatography and gas chromatography/mass spectrometry. Different groups of fatty adds were examined: branched and monounsaturated (vaccenic). Bacterial signatures were highly variable in the estuary, depending on season and the extent of accumulation of organic matter at the halocline. Imprint of branched fatty acids, probably representative for the largest bacterial populations, varied by three orders of magnitude. This imprint was generally low at marine stations with an exception of fall 1990, and high in river/brackish waters. Bacterial signatures were interpreted in terms of relationship between their occurrence and growth conditions expressed as suspended matter, organic carbon and chlorophyll a concentrations, as well as nature of organic matter in various water types, fresh, brackish and marine

n-Alkanes, PAHs and surfactants in the sea surface microlayer and sea water samples of the Gerlache Inlet sea (Antarctica)

Sea surface microlayer (SML) and sea water samples (SSW) collected in the Gerlache Inlet Sea (Antarctica) were analysed for n-alkanes and polycyclic aromatic hydrocarbons (PAHs). The SML is a potential enrichment site of hydrophobic organic compounds compared to the underlying water column. Total concentration ranges of n-alkanes and PAHs (dissolved and particulate) in subsurface water (−0.5 m depth) were 272– 553 ng l−1 (mean: 448 ng l−1) and 5.27–9.43 ng l−1 (mean: 7.06 ng l−1), respectively. In the SML, the concentration ranges of n-alkanes and PAHs were 353–968 ng l−1 (mean: 611 ng l−1) and 7.32–23.94 ng l−1 (mean: 13.22 ng l−1), respectively. To evaluate possible PAH contamination sources, specific PAH ratios were calculated. The ratios reflected a predominant petrogenic input. A characterisation of surface active substances was also performed on SML and SSW samples, both by gas bubble extraction, and by dynamic surface tension measurements. Results showed a good correlation between n-alkanes, PAHs and refractory organic matter

Food habits of the farmer damselfish Stegastes nigricans inferred by stomach content, stable isotope, and fatty acid composition analyses

The territorial damselfish, Stegastes nigricans, maintains algal farms by excluding invading herbivores and weeding unpalatable algae from its territories. In Okinawa, Japan, S. nigricans farms are exclusively dominated by Polysiphonia sp., a highly digestible filamentous rhodophyte. This study was aimed at determining the diet of S. nigricans in Okinawa and its dependency on these almost-monoculture algal farms based on stomach content and chemical analyses. Stomach content analyses revealed that all available food items in the algal farms (i. e., algae, benthic animal inhabitants, trapped detritus) were contained in fish stomachs, but amorphous organic matter accounted for 68% of the contents. Therefore, carbon and nitrogen stable isotope ratios and fatty acid (FA) compositions were analyzed to trace items actually assimilated in their bodies. Stable isotope analyses showed that benthic animals were an important food source even for this farmer fish. Two essential fatty acids (EFAs), 20:4n6 and 20:5n3, which are produced only by rhodophytes among available food items, were rich in the muscle tissue of S. nigricans as well as in algal mats and detritus, suggesting that algal mats contribute EFAs to S. nigricans directly and indirectly through the food web. In conclusion, S. nigricans ingested algal mats, detritus, and benthic animals maintained within its farm. Algae and detritus were original sources of EFAs, and benthic animals, which were much more abundant in the farms than in outside territories, provided a nitrogen-rich dietary source for the fish

Sources markers in aerosols, oceanic particles and sediments

This review presents some diagnostic criteria used for identifying and quantifying terrestrial organic matter inputs to the ocean. Coupled to the isotopic composition of total organic carbon, the analysis of stable biomarkers permits to trace higher plant contributions in aerosols, dusts, sedimenting particles and dissolved phase in the water column and ultimately in recent and ancient sediments and soils. Some applications are presented, based on the analysis of n-alkyl compounds by a combination of gas chromatography and mass spectrometry (n-alkanes, n-alkanols, n-alkanoic acids and wax esters). Another approach has been developed using the analysis of macromolecular compounds present in higher plants. Abundances of the phenolic compounds from lignin, benzene carboxylic acids obtained during cupric oxide oxidation, Curie pyrolysis are used to characterise terrestrial organic matter sources and inputs. Finally due to the importance of biomass burning in continent-ocean transfers, biomarkers are presented in the polycyclic aromatic hydrocarbon class and for monosaccharide derivatives from the breakdown of cellulose

Biogeochemical processes in the ocean and at the ocean-atmosphere interface

The ocean can be considered as a chemical reactor, whose energy sources are the various matter inputs originating from the continent and the ocean. Among various elements, carbon plays a key role as it is involved in both inorganic form as CO$_{2}$ and organic forms such as compounds synthesized through photosynthesis. Thus, the ocean is presently an active actor in climate change and ocean-atmosphere exchange processes. This review will present some insights into: 1) schematic representations of the carbon cycle, with emphasis on CO$_{2}$ exchange between the ocean and the atmosphere and to the organic parts of this cycle, 2) concepts relative to the biological pump of CO$_{2}$, with a detailed view on photosynthesis, 3) concepts leading to the existence of oceanic provinces and associated productivity for open sea and coastal areas, 4) addressing the question: what is the net efficiency of the biological pump of CO$_{2 }$in terms of exportation of organic carbon and sequestration in sediments and 5) specific aspects on biogeochemical processes occurring at the boundary between the ocean and the atmosphere

Stratégies d'échantillonnage et d'analyse appliquées à l'étude des polluants organiques dans les eaux côtières

Les hydrocarbures sont un danger majeur pour l'océan. Dans les eaux côtières ce type de contamination est exacerbé par les effets de synergie entre de multiples sources de pollution. Le développement de programmes permettant de dresser des bilans des différents apports et la nécessité de concevoir des modèles prédictifs permettant d'évaluer l'impact des hydrocarbures et des autres contaminants sur la qualité des eaux marines et sur les écosystèmes côtiers reposent sur la qualité des stratégies d'échantillonnage et d'analyse mises en place. Cette revue décrit certains points importants de ces stratégies, appliquées au delta du Rhône et au bassin Méditerranéen Nord-occidental. L'échantillonnage doit comprendre des prélèvements effectués aux étapes clés du fonctionnement du fleuve et des activités biologiques se développant dans les zones frontales, au large du fleuve. La stratégie d'échantillonnage comprend l'étude de la diffusion des eaux fluviales et de leurs polluants associés en milieu marin et I'étude des zones de création et d'accumulation de particules. L'échantillonnage s'intéresse à divers compartiments: eau, particules en suspension (y compris les organismes vivants), couches turbides se développant près du fond, sédiments superficiels. Après une couverture complète de paramètres clés, tels salinité, MES, Carbone organique, O2, pH, une étude détaillée et quantitative sera effectuée sur les hydrocarbures par combinaison de diverses techniques chromatographiques. Les empreintes obtenues peuvent être discutées en termes d'identification de diverses sources naturelles et anthropiques, de leur disponibilité pour les organismes vivants en fonction de leur répartition entre phases dissoute et particulaire, de transport, de dégradation et d'ultime dépôt dans les sédiments. Des exemples illustrent l'intérêt des analyses d'hydrocarbures aromatiques polycycliques dans les sédiments; ils signent des empreintes fidèles des divers types de contamination que l'on peut rencontrer en milieu marin côtier

Water-rock interaction : 1 : low temperature environments

L'origine et les processus de transformation de la matière organique dans les eaux interstitielles d'un récif corallien ont été étudiés en utilisant les hydrocarbures non-aromatiques comme biomarqueurs. L'origine de ceux-ci semble reliée à l'intense activité microbienne qui induit des transformations diagénétiques de la matière organique. La détection des 17 alpha, 21 Beta propanes indique que cette matière organique est mature. Sa présence dans la partie haute des récifs implique un mouvement ascendant des eaux interstitielles, ainsi que proposé par le modèle d'endo upwelling. (Résumé d'auteur