Golfe Du Lion Research Articles

Hydrography and nepheloid structures in the Grand-Rhoˆne canyon

Hydrographic and nephelometric data were gathered in the vicinity of the Grand-Rhoˆne canyon on the Golfe du Lion continental margin. These are used to describe the hydrographic structures and the suspended matter distribution. The results highlight the influence of wind-forced processes and current-canyon interaction on the dynamics in the canyon. These processes control the shelf-slope suspended matter exchanges, which are characterized by cross-canyon advection and near-bottom transfer along the axis of the canyon.

Copepod Distribution in Relation to Seasonal Hydrographics and Spatial Structure in the North-western Mediterranean (Golfe du Lion)

Copepod abundance and hydrography from the upper 50 m in the Golfe du Lion (NW Mediterranean) were studied during 1986-88. Seasonal distributions of eight genera and 35 species at 87 stations were analysed by means of numerical classification. An obvious distinction can be observed between near-coastal/neritic stations and oceanic stations. Most abundant copepods were epipelagic and non-migrating like: Clausocalanidae, Oithonidae, Paracalanus parvus, Oncaeidae, Centropages typicus and Temora stylifera. Inverse analysis demonstrated (1) High densities for the epipelagic, non-migrating Clausocalanidae and Oithonidae over many clustered station groups. Paracalanus parvus and C. typicus were abundant during the summer sampling periods whereas T. stylifera was abundant in September. Common were some vertical migrators like: Calanus helgolandicus, Pleuromamma gracilis, Candacia armata and Euchaeta marina. (2) Rare, bathypelagic species were collected during the February and July sampling periods in the upper 50 m. In February this synchronized with vertical mixing of the water column, in July with locally upwelled deep intermediate water, remaining below the thermocline. Relatively high mean subsurface temperatures were measured in December and February. Salinities showed a considerable variation in Rhône influence between the different seasons. Species with mainly herbivorous feeding habits were more abundant than those of more diverse omnivorous or carnivorous feeding habits.

Sex Ratio of Calanoid Copepods in Relation To Population Composition in the Northwestern Mediterranean

The population composition of the most abundant pelagic calanoids: Paracalanus parvus (Claus, 1863), Clausocalanus spp., Centropages typicus Kroyer, 1849, Temora stylifera (Dana, 1849), Acartia clausi Giesbrecht, 1889, Pleuromamma gracilis Claus, 1863, and Calanus helgolandicus (Claus, 1863), was studied from the upper 50 m in the northwestern Mediterranean (Golfe du Lion). The adult sex ratios were studied for these species and for three additional, less abundant, migrating species: Euchaeta marina Prestandrea, 1833, E. acuta Giesbrecht, 1892, and Candacia armata Boeck, 1872, from two different, partly overlapping water layers: the upper 50 m and the upper 200 m. In general the samples were composed of late copepodid stages, females and males in decreasing percentages. Maximum population densities were observed during different sampling periods for the different species. In most species the male-to-female ratio was highest during the periods of lowest female abundance. A pronounced dominance of females over males (>80%) was found throughout the year in the potentially herbivorous species Clausocalanus spp., P. parvus, A. clausi and C. helgolandicus. In the potentially and obligate carnivorous copepods P. gracilis, E. acuta, E. marina and C. armata female dominance was less striking, but seasonal variability was high. In the mixed feeders T. stylifera and C. typicus sexes were about equally represented throughout the year. Some species showed deeper male distributions during different periods. In the potentially herbivorous species the low male-to-female ratio is suggested to be related to swarming behaviour, which increases the encounter probability, facilitates the mating process, and serves as an adaptation to a limited food supply (leaving females a greater share). The migrating carnivorous species, which are not known to perform swarming behaviour, showed higher male proportions.

Seasonal variation in copepod abundance in relation to other zooplanktonic groups in the northwestern Mediterranean

Abundance of adult copepods and late copepodid stages from the upper 50 m in the Golfe du Lion (N.W. Mediterranean) was studied by the author in 1986, 1987, and 1988 for each season. Altogether 87 stations at 22 fixed locations were sampled in the frame of the multidisciplinary French/Spanish programme Pélagolion/Leopel in the near-coastal region (≤ 25 m bottom depth), the Rhone dilution zone, the neritic region (≤ 200 m bottom depth), and the oceanic region (200–2000 m bottom depth). Abundance of other zooplanktonic groups was estimated and total zooplankton biomass was determined for the upper 50 m. Copepod abundance was highest during September 1986 (all regions) and July 1987 (neritic). Total biomass was highest during July 1987 and May/June 1988, caused by high abundance of many other zooplankters.

The Cosquer Cave on Cape Morgiou, Marseilles

The discovery of Palaeolithic wall paintings and engravings in a cave whose entrance lies below the present sea-level near Marseilles has created considerable interest – and no little controversy. The paper describes and analyses the remarkable find, with special attention to its authenticity.During the Pleistocene there were large variations in sea-level under the influence of glaciations and inter-glacial warm episodes. During the Late Wurm glaciation in the Upper Palaeolithic the sea-level dropped to 110–120 m below its present level (Lumley 1976: 311). At that time the Lerins islands, the Hyeres islands and the Frioul archipelago and the islet of Planier off Marseilles were linked with the coast, and much of the Golfe du Lion was occupied by a vast plain.

The sand dunes and their vegetation along the Mediterranean coast of France. Their likely response to climatic change

The Golfe du Lion is mainly bordered by low and narrow sand dunes. Since about four decades, 1/3 of its shoreline has been receding, while 1/3 has been prograding and another 1/3 is stable. Several types of dunes may be described mainly depending on storms, high wind frequencies and sand grain size. Vegetation on dune system is distributed along a primary gradient according to sand stability and soil development, and a secondary gradient along slope of dune according to a seasonal cycle of fresh and salt phreatic water level.

Observations with Moored Acoustic Doppler Current Profilers in the Convection Regime in the Golfe du Lion

In the Golfe du Lion, south of France, favorable conditions for deep winter convection exist and were documented by the MEDOC experiments during 1969–75. A renewed investigation of that regime with upward-looking moored acoustic Doppler current profilers (ADCPs) was carried out during 24 January–5 March 1987, to record the three-dimensional currents associated with the deep mixing. While in the earlier studies initial deep convection did not begin until fairly late in the winter season, a very strong Mistral around 10 January 1987 had already generated a 1arge deep-mixed patch, homogeneous down to around 2000 m at deployment time. Three ADCPs, two working at 150 kHz and one at 75 kHz, were moored in a triangle of 15 km sidelength at 550–780 m depth. Full records at 1-hour ensemble time intervals, 400 pings per ensemble, 8 m bin lengths were obtained by the 75 kHz and one of the 150 kHz ADCPs. In mid-February, a second Mistral hit the region. With the onset of strong winds and surface cooling the occurrence of short-period current fluctuations, in the period range of hours, was observed which lasted for the duration of the negative heat flux. The vertical currents recorded by the ADCPs during this period included downward events of 5–10 cm s−1 velocity with weaker upward motion in between. These events appeared to occur simultaneously over the depth range of several 100 m covered by the ADCPs. An interpretation of these events as frozen structures, advected by with the mean current, yielded a horizontal scale estimate of only order 1 km. The mean vertical velocity during the Mistral week due to the integrated effect of these events was of order 1 cm s−1 downward.

Arguments for the pre‐rift uplift and rift propagation in the Ligurian‐Provencal Basin (northwestern Mediterranean) In the light of Pyrenean Provencal Orogeny

The Cenozoic Provencal orogeny and the subsequent opening of the Ligurian‐Provencal basin were caused by a geodynamic mechanism that originated in the Cretaceous. It is evident from the arguments presented that (1) regional doming preceded rifting of the continental margin and this uplift widened and/or migrated during the ensuing opening of the Ligurian‐Provencal basin; (2) clastic sedimentation on the Provencal platform was initiated during the early Cenomanian; (3) deformation in the Provencal block, which varies from Late Cretaceous to Miocene, reflects a migration of the north‐south compression from west to east accross the block; (4) the Languedoc‐Provencal fold belt was initiated during the Eocene as a result of tectonic uplift and sinistral displacement of the Paleozoic basement toward the north. Significant geologic features of the region associated with these events include (1) similarities in shape of the Languedoc virgation and the Provencal thrust front with the shape of geophysical features over the Golfe du Lion; (2) the unusual width of the young, stretched continental margin in the Golfe du Lion; (3) the distinctive V‐shaped form of the Ligurian oceanic crust; and (4) the concordance in age of the earliest post‐rift deposits, which increasingly young toward the east, and magnetic anomalies that parallel the basin axis. These events and structures are attributed to the uplift of a Paleozoic block situated to the south in the Golfe du Lion and previously buried under the Mesozoic cover. The development of this crustal uplift since upper Aptian, and its northeastwards migration and/or gradual widening account for both sedimentary events and tectonic deformation that occurred on the Provencal platform until upper Eocene, and the later stage of rifting and formation of the Provencal margin. In the Ligurian‐Provencal basin, the synthesis of marine data as well as relevant terrestrial data indicates that rifting propagated towards the Gulf of Genoa, while the Corsica‐Sardinia block rotated to the southeast.

Input of nutrients and suspended matter into the Golfe du Lion by the River Rhone

Input of nutrients and suspended matter into the Golfe du Lion by the River Rhone

Environmental structures and variation in coastal vegetation of the Golfe du Lion (France)

Environmental structures and variation in coastal vegetation of the Golfe du Lion (France)

Holocene evolution of the Canet‐St Nazaire lagoon (Golfe du Lion, France) as determined from a study of sediment properties

ABSTRACTThe sedimentation in the lagoons of the Golfe du Lion coast (Mediterranean Sea, France) records their post‐Holocene evolution. The Canet‐St Nazaire lagoon provides an example of such an evolution.Eight cores (ranging from 13.5 to 19.7 m in length) from a transect of the lagoon provide a cross‐section of the late Quaternary stratigraphy. The sedimentary sequence comprises mud and sand layers. The two sand formations are identified as parts of two distinct shelf‐sedimentary prisms. Stratigraphic analysis defines three stages in the recent, muddy infilling, corresponding to the last divisions of the Holocene.Sedimentation rates of the muds, related to climatic and palaeogeomorphological events, largely determine their geotechnical and geochemical properties. It appears, indeed, to be the most important factor in determining the compressibility index, the saturated bulk density and the organic and water contents of the deposits. Subboreal muds, poorly consolidated and rich in organic matter, correspond to a high rate of deposition. In the Subatlantic muds, in contrast, the sedimentation rate is lower whilst there is a decrease in the organic matter and an increase in the degree of cohesion.

Sediment entrainment on a wave-graded shelf, Roussillon, France

The sands of the inner shelf off the Roussillon coast of the microtidal Golfe du Lion display a seaward-fining texture and merge, in water deeper than 20–30 m, with midshelf muds. There is a qualitative correspondence between the textural gradient and the seaward-attenuating, annual (surface gravity) wave power expended by tangential stress on the shelf surface. Various equations, used to quantify the relation of sediment texture to fluid energy, predict the trend of the observed textural gradient, but overestimate its value. An empirical threshold equation (Komar and Miller, 1975a, b) and a theoretical null point equation (Johnson and Eagleson, 1966) give comparable results, implying that both may be describing the same state. There is a disparity between the predictions of an incipient motion equation (Johnson and Eagleson, 1966) and the threshold equation, probably because static instability of grains occurs prior to dynamic instability of grains in an increasing fluid velocity field. Theory forecasts that, in water shallower than 30 m, the sands are frequently entrained by shoaling waves, particularly during the winter months; the threshold of movement of sands in 5 m of water is exceeded for more than 40% of the year. Hence the grain size of the shallow-water sands does not reflect the maximum energy level of the environment.

Faunistique et écologie des métazoaires parasites de Boops boops linnaeus (1758) (teleosteen sparidae) dans le golfe du Lion

A global study of the Metazoan parasites of Boops boops (L., 1758) have been made in the "golfe du Lion". Fourteen different species (eight Platyhelmintha, one Nematoda and five Crustacea) have been inventorized. Their respective localisation on the hosts, globals and specifics corresponding prevalences as well as their variations according to the size of the fish, and their abundance have been precised. Parasitics associations have also been examined.

Étude paléoécologique des formations du Quaternaire terminal du plateau continental du Golfe du Lion

The Foraminifera associations and their sedimentological setting have been studied in cores located on a transect off the Rhone delta (Golfe du Lion). A cross-section of the recent Quaternary sediments of the shelf is described with particular emphasis on environmental characteristics of the deposits. A paleoecological and paleogeographical reconstitution is attempted.

Compte rendu ornithologique camarguais pour les années 1978 et 1979

This bird report covers the years 1978 and 1979 and completes a period of 30 years of observations by a contingent of resident and visiting ornithologists in the Rhône delta and neighbouring Crau and Alpilles. It presents not only observations of rare species or unusual numbers of birds, but also indicates the results of several long term monitoring programmes concerning in particular, waterfowl and allied species. A climatological report summarizes the most important meteorological phenomena of the two years, the most striking of which were the very wet spring of 1978 and the dry summer of 1979. The winter of 1978-1979 must surely be remembered in northern and central Europe as one of the most severe this century. In the Mediterranean, however, it was much less severe and, fortunately, had none of the disastrous effects of the previous hard winters of 1956 and 1962-1963. “ La Crau ”, a unique stony desert area and former delta of the River Durance, is suffering seriously from the spread of industry and from agricultural reclamation. Some of the first census work to be carried out here shows just how important the area is for breeding Stone Curlews, Little Bustards and Pin-tailed Sandgrouse in particular. The sandgrouse population is an isolated one, the species occurring elsewhere in Europe only in parts of Spain. Observations of sea birds are not carried out systematically and more thorough sea-watching would probably show that many of the species mentioned here are regularly wintering in the “ Golfe du Lion ”. Unusually high numbers of Black-necked Grebes appear each autumn in the saline “ Etang de Lavalduc ” (up to 4,500), which makes it an internationally important site for this species. Whilst the herons as a group maintain their numbers, several notable changes have taken place in recent years. The reed-nesting Grey Heron continues to increase whilst the Purple clearly shows the opposite trend. The Cattle Egret, occuring only as an accidental visitor less than 15 years ago, appears now to have reached the peak of colonisation with the numbers of breeding pairs levelling off. Autumn roost counts show the total of individuals at close to 2,000. The first indications of roughly how many Bitterns breed in the Camargue are given whilst the second only record of White Storks breeding in the delta involved one semi-captive male and a wild female carrying a ring. This was a chick transplanted from Morocco to a nest in Alsace as part of a reintroduction programme in 1975. The flamingos again had two successful breeding seasons and the summer population for the south coast of France peaked at over 35,000 birds both years. Particularly interesting data are being gathered from the sightings of “ Darvic-ringed ” birds, 1858 of which have thus been marked over the past three years. 24 % of these have already been read outside France. Amongst the Anseriiformes, the wintering Bewick’s Swan population was the highest yet recorded with a maximum of 85 in January 1979. During this same period four species of geese were present with Greylags and Bean’s both reaching one hundred or more individuals. Counts of Shelducks have shown how important the salines are both as a breeding area and winter quarters, and a ringing programme has thrown some light on their movements. For other ducks the overall wintering population has been quite high with a peak of 122,000 in January 1979. In general the number of diving ducks was below average but this was compensated for by several of the surface feeders being present in large numbers, in particular Teal, Gadwall and Shoveler. The list of raptor observations is as impressive as ever and includes a second estimate of the breeding Marsh Harrier population with results slightly superior to those obtained ten years earlier. The eighth complete census of breeding Laro-limicoles was carried out in the brackish and salt water zone of the greater Camargue area. All species are maintaining their numbers and attention is drawn to the increasing populations of Mediterranean and Slender-billed Gulls. Nearctic waders already observed in the delta included sightings of Buff-breasted Sandpiper and Wilson’s Phalarope whilst the Pectoral was only the second reported. Eagle Owls in “ Les Alpilles ” appear to be increasing with 30 pairs recorded. Passerines have not been ignored entirely ; the continued increase of breeding Stonechats is encouraging whilst the successful nesting of a pair of Bed-billed Quelea in the Camargue adds an exotic flavour to this report.

Spatial structure of surface currents in the Golfe du Lion: Fieux, M., S. Garzoli and J. Gonella, 1978. J. Rech. océanogr., 3(4): 13–26

Spatial structure of surface currents in the Golfe du Lion: Fieux, M., S. Garzoli and J. Gonella, 1978. J. Rech. océanogr., 3(4): 13–26