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Resume De 1885 a 1967, la temperature de l’eau de mer a ete quotidiennement mesuree a Marseille. Ces mesures servaient a corriger les enregistrements du maregraphe totalisateur utilise comme reference au nivellement national. Ces mesures (pres de 30 000) sont conservees sous forme manuscrites a l’Institut geographique national, ou nous les avons retranscrites et enregistrees sous forme de fichiers informatiques. L’etude de cette longue serie de temperatures, souvent evoquee, mais non examinee jusqu’a ce jour dans son integralite, pouvait etre tres utile, compte tenu des preoccupations actuelles sur le changement climatique et de la rarete de telles archives historiques pour le milieu marin. Par comparaison avec d’autres series pluriannuelles recentes de temperature de l’air et d’eau de mer de surface, il apparait que les minima hivernaux sont respectivement trop faibles, de 2 °C en moyenne, que ceux des eaux mediterraneennes, mais trop eleves par rapport a ceux actuels de l’air pour la region. Ce biais est consecutif au lieu ou etaient vraisemblablement realisees ces mesures de temperature : le puits du flotteur du maregraphe, c’est-a-dire en eau de mer confinee et non libre. Mais le fait que toutes ces donnees aient ete acquises selon le meme protocole pendant 83 ans autorise leur comparaison au cours du temps. Cette comparaison fait apparaitre une tendance au rechauffement de l’ordre de 0,66 °C en 100 ans pour les moyennes annuelles et de 0,76 °C pour les mois les plus chauds (juin a septembre).

Resume Entre juin 1999 et octobre 2002, des profils thermiques d'eaux cotieres ont ete realises (au moins mensuellement) en deux points de la Mediterranee, un dans le bassin oriental (Batroun, Liban ; 0–100 m) et un autre dans le bassin occidental (Marseille, France ; 0–55 m). Dans les deux sites, saisonnalite des traces thermiques et formation de la thermocline sont tres semblables. En revanche, a profondeur comparable, les temperatures sont plus elevees au Liban de 4 a 5 °C, et la thermocline estivale est plus longue (au moins six mois), permanente et plus profonde (40–50 m) qu'a Marseille (20–30 m), ou elle disparait frequemment en saison chaude, lors des refroidissements brusques consecutifs aux vents de nord-ouest. Cette specificite est due principalement aux differences entre les regimes de vents dominants sur les deux cotes. Documentant l'evolution temporelle d'eaux cotieres representatives au niveau regional des bassins mediterraneens, perennisee, cette observation couplee peut contribuer a apporter des enseignements sur des tendances a long terme et leurs consequences dans le cadre du rechauffement global de la Mediterranee. Pour citer cet article : M. Abboud-Abi Saab et al., C. R. Geoscience 336 (2004).

Between 1996 and 2000, 79 cruises have been achieved following always the same transect between Marseilles and the Rhone river's mouth. While cruising, salinity, temperature and fluorescence of surface waters (1.5 m) were recorded every minute, in association with precise GPS position. The whole set of data. (i.e. 128 measured points per cruise) constitutes the Sorcom series whose synthetic results ate presented here. Despite the high spatial and temporal. variability encountered between two successive cruises, the regularity and duration of the sampling strategy permitted to define coherent spatial zonation and temporal evolutions. In the Cape Couronne vicinity the dynamic of the eastern extension of the dilution plume clearly changes. Westward, waters are frequently under its influence, but more sporadically to the east, with a less pronounced gradient. In few cases, salinity lowering has been measured up to the gulf of Marseilles. In these two areas, which can be divided in two sub zones, seasonal evolutions are different. In the eastern area (Cape Couronne-Marseilles), the classical rhythm prevailing over marine waters is observed but with earlier phytoplanktonic bloom than usually reported. In the western part, and as getting closer to the Rhone river mouth, a weaker seasonal variability is observed for the phytoplanktonic biomass then salinity and temperature differences remain high. The better knowledge of the eastern dilution plume is of important socio-economical concern due to the numerous population living on this coast and the presence of pollutants in the river waters., Entre 1996 et 2000, toujours selon le même trajet entre Marseille et l’embouchure du Rhône, soixante dix neuf missions ont été conduites. Le navire en route, toutes les minutes sont réalisées dans les eaux de surface (1,5 m) des mesures de salinité, température, fluorescence ainsi qu’un positionnement GPS. L’ensemble de ces données (soit 128 points de mesure par sortie) constitue la série Sorcom dont la synthèse de ces résultats est présentée ici. Malgré la forte variabilité spatiale et temporelle pouvant se manifester d’une sortie à l’autre, la stratégie de l’étude et sa durée permettent de dégager une zonation spatiale et des évolutions temporelles. C’est au voisinage du Cap couronne que se situe un changement net dans la dynamique d’extension, vers l’est, de l’influence du Rhône. A l’ouest, les eaux sont en quasi-permanence sous cette influence et plus sporadiquement vers l’est, avec un gradient moins marqué, mais dans certains cas une dessalure peut être détectée jusqu’à Marseille. Dans ces deux parties, chacune pouvant être découpée en deux sous zones, les évolutions saisonnières sont différentes. Si dans la partie est (cap Couronne–Marseille) on retrouve le rythme classique des eaux marines (avec une première poussée phytoplanctonique plus précoce que ce qui est reporté habituellement), la partie ouest (cap Couronne–Rhône) voit se mettre en place, au fur et à mesure que l’on se rapproche de l’embouchure, une plus faible variabilité inter saisonnière pour la biomasse phytoplanctonique alors que les écarts de salinité et surtout de température restent importants. La connaissance de la branche est de dilution des eaux du Rhône, sans doute moins étudiée car ne correspondant pas à la direction privilégiée du panache, revêt une importance socio-économique particulière du fait de la population qui vit sur cette côte et de la présence, dans les eaux du fleuve, d’un cortège de polluants amenés par le drainage du bassin versant.

Marine microorganism activities are commonly assessed by bulk methods and assigned to the total cell count. The presence in significant amounts of ghost, dead, and damaged cells makes such as assignment a non-correct one. A Nucleic Acid Double Staining protocol (NADS) of fresh water bacteria (Barbesti et al., Cytometry 40 (2000) 214-218) has been adapted to resolve viable, damaged and dead cells in marine environments (Gregori et al., Appl. Environ. Microbiol. 67 (2001) 4662-4670). The present reports the first in situ application of this approach, conducted in the Bay of Marseilles in winter and spring periods at two sites with contrasted features.

For one month photographic records of the sea surface were taken (every five minutes) in a coastal area and used with records of wind speed and direction to determine the frequency of formation and spatial extent of slicks. The analysis of photographic records showed that slick sizes and occurrence frequencies decrease as a direct function of the wind speed. When the weather is under the influence of local winds (heat flux exchanges between the sea and the continent), a periodic rhythm occurs for a 24-h period: in the morning and late afternoon slicks are generally large (coverage ~35%) and frequent) (occurrence frequency ~65%), but in the middle of the day, when the winds increase to maximum velocity, slicks are small (coverage ~12%) and rare (occurrence frequency < 40%). During the night, a high slick coverage (39%) can be deduced from wind conditions. The comparison of the present data to the results of a previous experiment conducted in another coastal area, and the fact that meteorological conditions which have prevailed during this study were not particular, allow us to extend our conclusions to the larger coastal zones. In situ sampling in the surveyed area has shown higher concentrations of anionic detergents and hydrocarbons in slicks as compared to the surrounding rough surface waters (Garabetian et al., 1993). Thus, this daily rhythm of slick formation may have some important consequences for the dynamics of pollutant dispersion.

Twenty-nine sea-surface microlayer samples, associated with their related bulk water, were collected in coastal waters of the northwestern Mediterranean Sea, and examined for the concentration and composition of their particulate sugar fraction. The monosaccharide content was assayed by high-performance liquid chromatography (HPLC) and fluorescence detection after dansylhydrazine precolumn derivatization. Samples were collected in both marine areas influenced by fresh water. As compared with bulk waters, accumulation of particulate organic matter in the surface microlayer was higher in marine than in brackish waters (about three-fold higher for particulate organic carbon (POC) and ten-fold higher for sugars). However, in brackish bulk waters, the concentrations of organic compounds (POC, particulate organic nitrogen (PON), chlorophyll a and sugars) were higher than in marine bulk waters. In all the samples the sugar content appeared to be directly linked to POC. All the surface microlayers were enriched in bacteria but phytoplanktonic pigments were less represented in microlayers than in other particulate organic fractions. In brackish waters, chlorophyll a concentrations were correlated with the percentage of monosaccharide carbon in POC, but the microbiomass could explain only a small part (5–10%) of the sugar concentrations recorded in surface microlayers. In all cases, glucose was the major monosaccharide form. In brackish waters, no change was noted in monosaccharide composition of the sugar fraction in surface microlayers as compared with their related bulk waters. In marine samples, a slight but significant depletion of glucose was recorded in the microlayers, and three forms (mannose, arabinose and rhamnose) exhibited higher percentages (+4%, +4% and +15%, respectively) in marine sea-surface microlayers. During mild acid hydrolysis of the particulate organic matter, the release of the ·Dubois-reactive compounds’ was faster in marine microlayer samples than in related bulk waters, and the relative concentration of glucose increased with time of hydrolysis in the two types of water. When hydrolysis was not complete, a compound which eluted at the beginning of the chromatogram and remained at a constant level throughout the hydrolysis, was detected.

Surface microlayer samples were collected with a rotating device at eight stations in a coastal area, and examined, with their related bulk waters, for their organic matter composition. At each station, sampling operations were conducted inside and outside slicks. With the exception of pigments, all the examined groups of compounds, particularly hydrocarbons and anionic detergents, exhibit accumulation in surface microlayer; enrichment is higher in samples collected inside slicks than outside. A decrease of the surface tension measurements is linked to the accumulation of organic matter in the slicks. In surface microlayers, the major part of the identified organic fraction, consists of carbohydrates and proteinaceous compounds rather than lipids. As far as could be deduced from an estimation of lipid, sugar- and protein-carbon, half the recorded particulate organic carbon weight is of an unidentified complex form. The study of hydrolysis kinetics of the carbohydrate particulate fraction shows that the organic matter is in a less condensed form in surface microlayers than in bulk water samples. A close relationship appears between pollutant accumulation and the lowering of surface tension in slicks. This has a direct consequence: the dampening effect on waves which smooths the surface of the sea, making slicks observable features of pollutant accumulation.

The respective roles of regular echinoids and scarid fishes in the transformation of turf algae, the main food resource for reef herbivores, were investigated on French Polynesian coral reefs. The role of one species of parrotfish (Scarus sordidus) was compared with that of four species of echinoids. The degree and ways of degradation of the algal matter were determined by the organic matter percentage, the composition of the sugar fraction, and the concentration and composition of chlorophylltype pigments as assayed by HPLC analysis. Chemical analyses were performed on anterior and posterior intestines for scarids, intestinal contents and faeces for echinoids, and on fresh algal turf as a control of initial food quality. A decrease in mean percentage of organic matter in gut content was observed from intestine (9.7%) to faeces (7%) in sea urchins, but not in parrotfishes. The total sugar fraction decreased from fresh algal turf (32% of total organic matter) to echinoid (28%) to scarid (18%) gut contents. The ratio of insoluble to soluble sugars (I/S ratios) was higher in echinoids (2.6) than in scarid gut contents (1.0). A decrease in the total pigment concentration was measured from fresh algal turf to echinoid and it was found to be even lower in scarid gut contents. Chromatograms showed that the composition of chlorophyll-type pigments in scarid intestines was very similar to fresh algal turf, with a dominance of native forms, mainly chlorophyll a and b. On the contrary, degraded pigment forms dominated in echinoids. The main degraded products were pheophorbides in sea urchins, and chlorophyllides in parrotfishes. These results provided evidence for differentiation in digestive processes occurring in the two types of grazers. Echinoids released higher degraded algal material than did scarids. Thus, these two types of grazers play different roles in the recycling of organic matter on coral reefs.

For 2 years photographic records of the sea surface were taken in a coastal area. These were used, in conjuction with records of the wind speed and direction, to determine the frequency of formation of slicks as an index of surface microlayer presence. Parallel collection of sea-surface samples provided evidence for a relation between the pictures and accumulation processes of organic matter in surface microlayers. Results show that slicks are present for more than 25% of the recording time; this frequency may reach more than 60%, depending on the hour and season. Slick formation is dependent on wind speed and slicks never exist at wind speeds greater than 7 m s −1 ; below this upper limit the highest probability of slick formation corresponds with wind speed values between 2 and 4 m s −1 , but in many cases, no slicks are formed under low wind speed conditions. (Slicks were found to require considerable time to form, following a decrease in wind speed, and to disperse, following an increase in wind speed. This dependence explains most of the seasonal and diurnal variations in slick occurrence.) Slicks are more frequent in the morning, and less frequent at midday and afternoon, because of wind induced by heat flux between the sea and continent in coastal areas. Despite the fact that it was not possible to take photographic records during the night, a high probability of slick formation during the night can be deduced from the recorded decrease in wind speed.

Changes in the composition and distribution of organic matter from the urban sewer of the City of Marseilles (France) were studied in superficial sediments (16 stations) and in suspended particulate matter collected by sewer sediment traps. Sugar and amino acid compositions were assayed by HPLC (high pressure liquid chromatography) analysis in parallel with determination of hydrolysis kinetics and the insoluble to soluble ratios. The organic matter from the sewage outlet and in sediments located near the outlet was more rapidly hydrolysed and exhibited lower I/S ratios than that of marine sediments. The monosaccharide composition and particularly the glucose/ribose, glucose/fucose and mannose/fucose ratios which varied strongly with increasing distance from the sewage outlet may constitute a fingerprint of the terrigenous matter in the marine environment. The variations in the amino acid spectra were comparatively smaller. Four major forms were dominant in the outlet itself, the superficial sediments and particle-traps and exhibited significant changes. Changes in the nitrogenous fraction could be attributed to changes in some minor or non-protein amino acids such as methionine and methionine sulfoxide.

Discriminating approach of various microplanktonic-stage contributions to whole electron transport system (ETS) measurements in sea-water sampless. b. Bacateria Data obtained from cultures of natural bacterial populations were applied to various water samples in order to determine both the phytoplanktonic and bacterial contributions to whole ETS water-sample measurements. The bacterial part was estimated both by cell enumerations and HPLC muramic-acid measurements and the phytoplankton contribution by enumeration and chlorophyll levels. An appropriate first-order equation is adequate to low carbon content samples but must be corrested for highly organic loaded samples in order to obtain a better adjustment between the sum of the “estimated” phytoplanktonic and bacterial ETS and the really-measured ETS concentrations in the water samples.

Influences of unsalted waters penetration, in the Gulf of Fos, are marked as much on the primary step structuration level as on the component cellular physiology one. At their outlet, the weak structuration and the considerable biomasses resulting from an intense eutrophication go with a strong mortality clearly shown as well as by ATP/chlorophyll ratio than these of ATP, ADP and AMP inside the adenylic nucleotides pool. The primary step acquires a larger maturity in the salt share of the south eastern area. Spectrum variations of the population specific cellular volumes in terms of population importance can in a certain measure explain the intracellular rate variations into biochemical components.

Discriminating Approach of Various Microplanktonic-stage Contributions to Whole ETS Measurements in Sea-water Samples. a. Phytoplankton Data obtained from algal cell cultures were applied to various sea water samples in order to estimate the specific contribution of phytoplanktonic organisms to whole ETS (electron transport system) measurements of these samples which have been collected at eleven stations in the northwest Mediterranean Sea. When the phytoplankton ETS contributions were quantified by cell enumerations or by other indirect-biomass-indicator measurements, the results are in good accordance to the recorded ETS measurement values of the sample. More specific of the phytoplankton stage is the index used for such an estimation (as chlorophyll a), and better is the relationship between both estimated and measured ETS values.