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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.

During summer 1999, a massive mortality of attached benthic invertebrates was reported at several points along the French Mediterranean coast, east of the Rhone River. Such a wide geographical extension suggested the occurrence of a climatic anomaly as a direct or an indirect cause of this phenomenon. The systematic observations of surface water temperature (1 record/30 min) and vertical thermal structure from 0 to 55 m (semi-monthly frequency) performed by the service of observation of centre d’oceanologie de Marseille since 1994 in the Gulf of Marseilles (northwestern Mediterranean) compared with historical data obtained for the summer periods (June till October) indicates a thermal anomaly during summer 1999. Although the surface temperatures do not strictly show exceptional values, the stability during long periods of high temperatures (24.1 °C ± 0.5 in September, n = 1 018) and the thermal structure of the water column are remarkable. The vertical temperature profiles of 1999 reflect a general warming of 2–3 °C in the water layer overlying the thermocline, accompanied by its deepening (up to 30–40 m). This situation can be explained by the scarcity of NW winds with a marked drop of their relative frequency during July and October 1999 (13–27 % versus 42 %, mean value calculated from the previous 12 years) and the short duration of these windy periods (between 30 min and 5 h as a mean). Parallel to this, a large number of no wind registrations (125–250 h/month as a mean) were observed during this period. A similar thermal stratification, of lesser amplitude, associated with comparable meteorological conditions was also observed in 1997. The hypothesis that this summer 1999 temperature anomaly could constitute a partial explanation for the recorded massive mortality is discussed.

International audience; This article presents a comparison between simulated and in situ temperature data. The aim is to test the reliability of the Symphonie model on the short coastal area, few kilometres wide (~ 20 km) with a strait configuration. The in situ data comes from records collected by the team of the marine park of Strait of Bonifacio (South of Corsica). The results show a difference between the two sets of data in winter and in summer, where the variation of temperature is the most extreme.

International audience; The dynamics of Bonifacio strait (south of Corsica) are investigated in a comprehensive study at long term from two set of data. First, by moored ADCP put in middle of the strait during six weeks (4 November 2004 to 7 January 2005), at a depth of 40 m and at few Kilometers from coast. Second, by velocity profiles obtained with a 314.4 kHz Acoustic Doppler Current Profiler (ADCP) during seven cruises (Cyrce) covering entirety strait. From moored ADCP data, a study is made on time correlation between wind stress and current. Shipboard ADCP data permits to obtain a general view in totality of strait and mostly to observe spatial variability. This study shows that the circulation is governed both by wind stress and by general circulation of Mediterranean Sea.

13 pages, 7 figures, 3 tables, Two large-scale mass mortality events (MMEs) of unprecedented extent and severity affecting rocky benthic communities occurred during the summers of 1999 and 2003 along the coasts of the NW Mediterranean Sea. These mortality outbreaks were associated with positive thermal anomalies. In this study, we performed an analysis of inter-regional and inter-annual differences in temperature (T) conditions associated with MMEs of the red gorgonian Paramuricea clavata by analyzing high resolution T time series (hourly records for 3 to 8 years) from four regions of the NW Mediterranean with differing hydrological conditions and biological impacts. High resolution records allowed a detailed analysis using classical and new descriptors to characterize T anomalies. We were able to determine that the MMEs were triggered by two main types of positive thermal anomalies, with the first type being characterized by short periods (2 to 5 days) with high Mean T reaching more than 27°C in some regions and being associated with high intra-day and intra-period variability, while the second type of anomaly presented long duration (near one month) at warm T (24°C) with low intra-period variability. Inter-regional patterns arose; some regions displayed both types of anomalies, while others exhibited only one type. The results showed that T conditions should be considered as the main factor that explains the observed inter-regional and inter-annual differences in mortality impacts. In explaining these differences, the late timing of T anomalies, in addition to their magnitude was found to be determinant. Finally, by combining thermotolerance experimental data with the maximal T stress conditions observed in the four regions, we were able to determine the differential risk of mass mortality across regions. We conclude that expanding high resolution T series is important for the development of sound management and conservation plans to protect Mediterranean marine biodiversity in the face of climate change, Funding: This work was supported by the Alßan Program (C. Crisci doctoral fellowship, fellowship code: E06D103213UY; www.programalban.org); Parc National de Port-Cros; The IFB Foundation (Institut Français de la Biodiversite´ ); Agence Nationale pour la Recherche (ANR) (MEDCHANGE Project (http://www.agencenationale-recherche.fr; http://sudek.esil.univmed.fr/medchange/spip); Ministry of Science and Innovation (Biorock project ref. CTM2009-08045). These funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Dr. Nathaniel Bensoussan is employed by IPSO-FACTO SARL; he contributed to the analysis of the data and the writing of the manuscript

14 pages, 3 figures, 4 tables, Late in summer 2003, extensive mass mortality of at least 25 rocky benthic macro-invertebrate species (mainly gorgonians and sponges) was observed in the entire Northwestern (NW) Mediterranean region, affecting several thousand kilometers of coastline. We were able to characterize the mortality event by studying six areas covering the main regions of the NW Mediterranean basin. The degree of impact on each study area was quantified at 49 sites by estimating the proportion of colonies affected in populations of several gorgonian species compared with reference data obtained in years without mortality signs. According to these data, the western areas (Catalan coast and Balearic Islands) were the least affected, while the central areas (Provence coast and Corsica-Sardinia) showed a moderate impact. The northernmost and eastern areas (Gulf of Genoa and Gulf of Naples) displayed the highest impact, with almost 80% of gorgonian colonies affected. The heat wave of 2003 in Europe caused an anomalous warming of seawater, which reached the highest temperatures ever recorded in the studied regions, between 1 and 3 °C above the climatic values (mean and maximum). Because this exceptional warming was observed in the depth ranges most affected by the mortality, it seems likely that the 2003 anomalous temperature played a key role in the observed mortality event. A correlation analysis between temperature conditions and degree of impact seems to support this hypothesis. Under the present climate warming trend, new mass mortality events may occur in the near future, possibly driving a major biodiversity crisis in the Mediterranean Sea, This research was partly supported by the IFB Foundation (Institut Français de la Biodiversité), the environmental department of TOTAL-Fina-Elfgroup, an 'Action Concertée Iniciative' (ACI) program 'Jeunes chercheus 2003' (number JC5360) from French Research Ministry, research grants CTM2006-01463 and CGL2007-66757

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.

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 (Grégori 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.

Chlorophyll and its breakdown product contents were determined by both high pressure liquid chromatography (HPLC) and the fluorimetric method in surface microlayer and related bulk water samples collected in the western Mediterranean Sea. Differences in chlorophyll α measurements between the two methods are enhanced in highly loaded organic matter water samples such as surface microlayers. In several samples, pheophytins, which are commonly reported to be present in surface microlayers, were detected by the fluorimetric method, but not by HPLC. In most cases, the accumulation processes of pigments can be recorded in surface microlayers, but with small differences in pigment composition when compared with that of related bulk waters. Enrichment factors for chlorophyll are often higher than those of its degradation products. On the other hand, the low reported values of phytoneustonic productivity provide evidence for an inhibition of phytoplankton organisms transported to the sea-air interface; these organisms should be stressed but alive. These results also support the hypothesis that pigments could be actively photo-oxidized by the high level of solar radiation prevailing in surface microlayers.

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.