Seasonal survey of the composition and degradation state of particulate organic matter in the Rhône River using lipid tracers

International audienceLipid tracers including fatty acids, hydroxyacids, n-alkanols, sterols and triterpenoids were used to determine the origin and fate of suspended particulate organic matter (POM) collected in the Rhône River (France). This seasonal survey (April 2011 to May 2013) revealed a year-round strong terrestrial higher-plant contribution to the particulate organic matter (POM), with significant algal inputs observed in March and attributed to phytoplanktonic blooms likely dominated by diatoms. Major terrigenous contributors to our samples are gymnosperms, and more precisely their roots and stems, as evidenced by the presence of high proportions of ω-hydroxydocosanoic acid (a suberin biomarker). The high amounts of coprostanol detected clearly show that the Rhône River is significantly affected by sewage waters. Specific sterol degradation products were quantified and used to assess the part of biotic and abiotic degradation of POM within the river. Higher-plant-derived organic matter appears to be mainly affected by photo-oxidation and au-toxidation (free radical oxidation), while organic matter of mammal or human origin, evidenced by the presence of co-prostanol, is clearly more prone to bacterial degradation. Despite the involvement of an intense autoxidation-inducing ho-molytic cleavage of peroxy bonds, a significant proportion of hydroperoxides is still intact in higher plant debris. These compounds could affect the degradation of terrestrial material by inducing an intense autoxidation upon its arrival at sea

Identification of di- and triterpenoid lipid tracers confirms the significant role of autoxidation in the degradation of terrestrial vascular plant material in the Canadian Arctic

publisher: Elsevier articletitle: Identification of di- and triterpenoid lipid tracers confirms the significant role of autoxidation in the degradation of terrestrial vascular plant material in the Canadian Arctic journaltitle: Organic Geochemistry articlelink: http://dx.doi.org/10.1016/j.orggeochem.2017.03.011 content_type: article copyright: © 2017 Elsevier Ltd. All rights reserved

Analyse expérimentale du sifflement d'un riser industriel

International audienceLe champ acoustique induit par un écoulement dans un tuyau corrugué est étudié depuis longtemps. Un regain d'intérêt s'est manifesté en lien avec le développement de l'exploitation de gisements de gaz en haute mer utilisant de grandes longueurs de riser pour le transport gazier. Sur de telles installations, le phénomène peut entraîner une défaillance de l'équipement adjacent aux risers. Dans ce cadre, un test a été effectué dans un tuyau flexible de 6 pouces de diamètre interne et de 18 mètres de longueur. Ce riser était équipé de manchettes en amont et en aval sur lesquelles étaient fixés des capteurs de vitesse par fil chaud, des capteurs de température, des capteurs de pression ainsi que des microphones. Une série d'essais a été conduite pour des pressions internes et des vitesses d'écoulements variées. Nous avons observé que les signaux mesurés en condition de sifflement présentaient des fluctuations significatives tant temporelles que fréquentielles. Nous avons pu montrer que ces dernières étaient liées à la géométrie du riser. En outre, ces analyses ont permis de montrer que le sifflement observé existait aux fréquences acoustiques transverses du riser tout en se propageant à la vitesse de convection de l'écoulement

Oxidation products of alpha- and beta-amyrins: potential tracers of abiotic degradation of vascular-plant organic matter in aquatic environments

International audienceIn order to fulfil the current need for stable and specific tracers to monitor vascular- plant organic matter degradation in aquatic environments, alpha-amyrin (urs-12-en-3 beta-ol) and beta-amyrin (olean-12-en-3 beta-ol) were oxidised in vitro and their abiotic degradation products quantified in environmental samples from the Rhone River in France. Although they appear inert to photooxidation, they are clearly affected by autoxidation and the tracer potential of the resulting products was confirmed. Autoxidation of alpha- and beta-amyrins produces urs or olean-12-en-3-one, 3 beta-hydroxy-urs or olean-12-en-11- one, urs or olean-12-en-3 beta, 11 alpha-diol and urs or olean-12-en-3,11-dione. 3 beta-Hydroxy-urs-12-en-11-one and 3 beta-hydroxy- olean-12-en-11-one, the main oxidation products detected, were selected as autoxidation tracers. These compounds, specific to autoxidation, were detected in dry leaves of Smilax aspera and in suspended particulate matter samples collected in the Rhone River and evidenced the importance of autoxidation in the degradation of organic matter of terrestrial origin

QUANTITATIVE INVESTIGATIONS ON MACROBENTHOS COMMUNITIES OF THE SOUTHEASTERN WEDDELL SEA SHELF BASED ON MULTIBOX CORER SAMPLES.

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Temporal patterns among meiofauna and macrofauna taxa related to changes in sediment geochemistry at an abyssal NE Atlantic site

Two major size classes of the sediment community, meiofauna and macrofauna, and four classes of lipid compounds, fatty acids, alkanes, alcohols and sterols, were investigated using multicorer and USNEL boxcorer samples, collected during six cruises over a two year period (September 1996 to September–October 1998), at the Porcupine Abyssal Plain (~ 48° 50?N 16° 30?W, 4850 m depth) within the framework of the MAST 3 BENGAL project. This site was known to be subject to seasonality in the input of organic matter to the seafloor. Results are given for each faunal size class in terms of taxonomic structure at the level of phylum, class or order, depending on the taxon, and for the dominant faunal components in terms of density and vertical distribution. For each lipid compound class, results are given in concentration and vertical distribution. The taxonomic structure of each size class did not change within the study period. Total meiofaunal and macrofaunal densities were particularly high, probably reflecting the high quantity and quality of organic matter inputs to the site. The dominant components of the two size classes presented different temporal patterns in their responses to changes in their environment. Populations of meiofaunal species, a foraminiferan and an opheliid polychaete, which inhabit the surface or sub-surface of sediment and feed on phytodetritus, responded with a rapid increase in abundance to a pulse of organic input in summer 1996. The macrofaunal polychaetes showed a lagged response to the same event by slowly increasing in density. Other components of the sediment community, that can live deeper in the sediment, moved down the sediment column, in response to 1) the impoverishment and bioturbation of the surface layer, and 2) the downward mixing of organic matter in the sediment by larger organisms. In this study, different temporal patterns were demonstrated for the first time in different size classes of the sediment community, and in the biological and environmental parameters that were studied simultaneously

Ferromanganese nodule fauna in the Tropical North Pacific Ocean: species richness, faunal cover and spatial distribution

The poorly known ferromanganese nodule fauna is a widespread hard substratum community in the deep sea that will be considerably impacted by large-scale nodule mining operations. The objective of this study was to analyze the spatial distribution of the fauna attached to nodules in the Clarion-Clipperton Fracture Zone at two scales; a regional scale that includes the east (14°N, 130°W) and the west (9°N, 150°W) zones and a local scale in which different geological facies (A, B, C and west) are recognizable. The fauna associated with 235 nodules was quantitatively described: 104 nodules from the east zone (15 of facies A, 50 of facies B and 39 of facies C) and 131 nodules from the west zone. Percent cover was used to quantify the extent of colonization at the time of sampling, for 42 species out of the 62 live species observed. Fauna covered up to 18% of exposed nodule surface with an average of about 3%. While species richness increased with exposed nodule surface, both at the regional and at the facies scales (except for facies A), total species density decreased (again except for facies A). When all nodules were included in the statistical analysis, there was no relation between faunal cover and exposed nodule surface. Nevertheless, faunal cover did decrease with exposed nodule surface for the east zone in general and for both facies B and C in particular. Species distributions among facies were significantly different but explained only a very small portion of the variance (5%). We identified two groups of associated species: a first group of two species and a second group of six species. The other species (34) were independently distributed, suggesting that species interactions play only a minor role in the spatial distribution of nodule fauna. The flux of particulate organic carbon to the bottom is the only major environmental factor considered to vary between the two zones within this study. We conclude that the higher species richness and higher percent faunal cover of the east zone can be partially attributed to greater food availability derived from surface inputs. Moreover, the surfaces of facies B and C nodules had a complex, knobby micro-relief, creating microhabitat heterogeneity that may also have contributed to the greater species richness observed in the east zone

Evidence for episodic recruitment in a small opheliid polychaete species from the abyssal NE Atlantic

The abundance and size spectra of an infaunal opheliid polychaete species was followed over a two year period (September 1996-October 1998) in meiofaunal-(32 µm-1 mm) and macrofaunal -(> 250 µm) samples collected at an abyssal site (4850 m depth) in the NE Atlantic. The site, situated on the Porcupine Abyssal Plain (PAP), is characterised by the episodic deposition of aggregated phytodetritus. The response of the fauna to this seasonal food supply was addressed by time-series sampling within the MAST-III BENGAL programme. In autumn 1996, small opheliid juveniles (mean length: 281 µm in September and 254 µm in October) were sampled only in the meiofauna samples. In March 1997, juvenile specimens of the opheliid, which were on average nearly twice as large (mean length: 480 µm) as those collected in 1996 were sampled in both both meio- and macrofaunal samples. The occurrence of only small juvenile individuals in 1996 suggests that a synchronous recruitment event had taken place earlier during that year. Small juveniles (mean length: 252 µm) were also abundant in a sample collected at the PAP site in May 1991, immediately following the deposition of a pulse of phytodetritus. The opheliid population structure in 1997 and 1998 indicates the slow progression of the settled cohort, possibly supplemented by a further, but relatively minor recruitment event in March 1998. Size spectra analysis implies that either growth was slow or that immigration of larger juveniles had augmented the population. The PAP opheliid may be an opportunist, which waits for optimal conditions before converting its slowly accumulated energy into reproduction. In addition, this species can apparently maintain a stable pool of developing juveniles if the organic pulse fails to materialise. The present study also shows that a more holistic approach is necessary to investigate the life cycles of some organisms, which lie close to the boundary between the meiofauna and macrofauna

Analyse expérimentale du sifflement d'un riser industriel

International audienceLe champ acoustique induit par un écoulement dans un tuyau corrugué est étudié depuis longtemps. Un regain d'intérêt s'est manifesté en lien avec le développement de l'exploitation de gisements de gaz en haute mer utilisant de grandes longueurs de riser pour le transport gazier. Sur de telles installations, le phénomène peut entraîner une défaillance de l'équipement adjacent aux risers. Dans ce cadre, un test a été effectué dans un tuyau flexible de 6 pouces de diamètre interne et de 18 mètres de longueur. Ce riser était équipé de manchettes en amont et en aval sur lesquelles étaient fixés des capteurs de vitesse par fil chaud, des capteurs de température, des capteurs de pression ainsi que des microphones. Une série d'essais a été conduite pour des pressions internes et des vitesses d'écoulements variées. Nous avons observé que les signaux mesurés en condition de sifflement présentaient des fluctuations significatives tant temporelles que fréquentielles. Nous avons pu montrer que ces dernières étaient liées à la géométrie du riser. En outre, ces analyses ont permis de montrer que le sifflement observé existait aux fréquences acoustiques transverses du riser tout en se propageant à la vitesse de convection de l'écoulement