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1.
《Oceanologica Acta》1998,21(2):191-207
The Gironde estuary (France) discharges to the ocean an important amount of suspended particulate matter in the form of turbid plumes. The surface plume is more particularly studied from coastal oceanographic surveys and NOAA/AVHRR satellite data collected during a French programme of coastal oceanography (PNOC-Atlantic). The AVHRR reflectances are atmospherically corrected according to an algorithm based on the clear water concept. The comparison with suspended sediment concentrations are realised by direct and indirect calibrations. The correlations obtained show that at a same concentration the reflectance varies, probably because of varying particle (floc) size and composition. The shape and the surface measured from low resolution (4 km × 4 km) and high resolution (1 km × 1 km) AVHRR data are then compared to the forcings introduced by the fluvial output, the tide, neap and spring tide and the wind variations. The latter have an important effect on the orientation of the distal part of the turbid plume. 相似文献
2.
《Oceanologica Acta》1998,21(4):597-607
The hydrothermal environment is characterised, among other things, by a high metal concentration, related to the convective sea-water circulation inside the oceanic crust and its interaction with basaltic rocks. The biological communities associated with the hydrothermal system can survive in this toxic environment owing to their ability to regulate their intracellular metal levels by excretion or accumulation of metal ions in non-toxic forms. Various detoxification processes have been previously studied within an hydrothermal organism: immobilisation and precipitation of the metal in lysosomal systems, or binding to specific and soluble ligands such as metallothioneins. The later are heat stable and characterised by a high content of cysteine. The quantification of Fe, Zn, Cu, Mn, Cd, Ag, Ba and Sr in the tissues of the vent mussel Bathymodiolus sp. indicates a high accumulation of these metals in two target organs, the gill and the digestive gland. This accumulation is in relation with high concentrations of metallothioneins, but the subcellular distribution of metals indicates a higher contribution of the insoluble compartment for detoxification processes. These results are compared with the literature data about metal bioaccumlation in Bathymodiolus thermophilus collected at the Galapagos Rift. 相似文献
3.
《Oceanologica Acta》1998,21(5):695-708
This study deals with the colonisation of experimental Porites blocks by epilithic and endolithic algal community in two atoll lagoons and two high-island lagoons in French Polynesia, exposed to different environmental conditions during a 5-year period. A qualitative analysis of the community (cyanobacteria and micro-algae) was carried out, and the relationship between the epilithic and endolithic strata observed. HPLC analysis of chlorophyll pigments was used to quantitatively determine the plant biomass, which was then compared to that of the algal turf of neighbouring reefs. The results show that these blocks are colonised according to two factors: the reef structure (atoll or high-island) and the degree of human disturbance. The epilithic and endolithic population dynamics differ.The density of the epilithic algal community and the species diversity increase with the degree of eutrophication and the amount of borers (sea-urchins, parrotfish), while the proportion of endolithic species remains low (34 %–59 %). This is especially marked in the high-island lagoons, where leaching has caused enhanced nutrient levels. An extreme case is the station at Faaa, a highly polluted harbour, where increased sea-urchin levels (44 ind. m−2) meant that the blocks disappeared completely in less than five years due to bioerosion. In the oligotrophic waters of the atoll lagoons, the losses of CaCO3 by bioerosion do not exceed 35 % per block, and the algal community is made up mainly of endolithic species (66 %–85 %). The algal biomass is lowest in the Takapoto atolls (10–11 μg cm−2) and maximum in Tikehau atoll (23 and 56 μg cm−2). The first microborers to settle in the ecological succession of the community are the cyanobacteria. These are gradually replaced by Ostreobium (Chlorophyceae borers), which become dominant in the blocks exposed to the lowest bioerosion rate. The richness and the density of the algal turf reflect the convergence of many ecological factors: it seems that the covering of epilithic algae or the richness of endolithic flora could be used as a global indicator of the quality and the health of a reef. 相似文献
4.
《Oceanologica Acta》1998,21(6):861-870
Nitrate and ammonium uptake rates were measured in spring and summer in deep and shallow wellmixed waters of the English Channel during different cruises between 1986 and 1994. In the deep waters, nitrate uptake was relatively low during phytoplankton development and ammonium uptake represented more than 70 % of the total uptake irrespective of the season. In the shallow waters, nitrate uptake during spring phytoplankton growth was high and represented about 75 % of the total uptake. Ammonium uptake became substantial towards the end of spring and summer. The high contribution of ammonium to the nitrogenous nutrition of phytoplankton over the whole of the well-mixed waters is related to a high rate of recycling of nitrogen in the water column. Ammonium regeneration by microheterotrophs can satisfy between 62 % and the totality of the phytoplankton nitrogen requirements. The high primary production in deep well-mixed waters is not supported by allochthonous nitrogen supply but by an intense in situ regeneration of nitrogen. The situation is similar in shallow well-mixed waters, except during the spring bloom. 相似文献
5.
《Oceanologica Acta》2002,25(3-4):119-124
The comparative effect of the uptake of fresh and degraded detritus of halophytic plants, harvested from salt marches of the Mont Saint-Michel Bay (France), on the growth of a juvenile population of the annelid polychaete N. diversicolor (L.) was studied under experimental conditions in summer 1993. Fresh and degraded detritus of Spartina anglica, Halimione portulacoides and Salicornia europeae, as well as the green algae Enteromorpha sp. were distributed separately to homogenous set of juveniles for a 75 d period. The highest growth rate was obtained for worms fed with Enteromorpha sp. Administration of fresh detritus of a given halophyte species to N. diversicolor juveniles always leads to a significantly higher growth rate than did degraded detritus. This is probably due to a great microbial biomass occurring on the fresh detritus, which is moreover, much better assimilated than the detritus they colonize. 相似文献
6.
A sampling survey in the Ligurian Sea and north of the Balearic Islands (Mediterranean Sea) brought back samples containing the following elements: (1) lithified Quaternary crust and deep-lying corals; (2) Early Pliocene marls corresponding to reflector level M in some cases; (3) red sediments tentatively assimilated with the Messinian continental equivalent; (4) rocks coming from the basement; (5) volcanic rocks.For the first time, basalts with olivine were discovered in the Algero-Provencal Abyssal Plain.A volcano 500 m high was sampled by dredging north of Minorca. 相似文献
7.
《Oceanologica Acta》1998,21(6):923-935
As part of the Programme National d'Océanographie Côtière, the nutrient dynamics of the Bay of Seine were studied between 1992 and 1994 in order to complement work on ecological modelling. Firstly, the River Seine's nutrient fluxes were established: 80 000–130 000 t a−1 of dissolved inorganic nitrogen, 6 400–8 4001 a−1 of dissolved phosphorus and 20 000–77 000 t a−1 of dissolved silicium. Estuarine processes were taken into account. Consequences of nutrient loading for the bay were then evaluated at the pelagic level (nutrient and chlorophyll enrichments) and the benthic level (distribution of various phosphorus fractions in superficial sediments). The large continental inputs always induce concentration gradients in the water from the mouth of the river to the northwest of the bay. The northward spreading of fine particulate matter controls the distribution of adsorbed phosphate and iron-aluminium bound phosphate in sediments. In contrast, calcium bound phosphate, the main fraction in sediments, is not affected by river inputs. Organic phosphorus in sediments is related to phytoplankton blooms, with increasing concentrations during productive periods; afterwards the fast recycling prevents sedimentary accumulation. The nutrient depletions observed beyond the turbid plume during spring 1992 enabled the calculation of nutrient uptake rates, and the comparison of these rates with phytoplankton biomass (chlorophyll a + phaeopigments). Ratios of nutrient consumption to pigment concentration were estimated at 1 μmol μg−1 for nitrogen, 0.05 for phosphorus and 0.5 for silicate. These values, as N/P and Si/N uptake ratios (respectively 17.5 and 0.4), were similar to usual values. 相似文献
8.
《Oceanologica Acta》1998,21(6):939-950
The release of enteric pathogenic bacteria in aquatic environments poses the problem of the fate of these bacteria under the effects of environmental factors (solar radiation, salt concentration, temperature, nutrient level, pH, competition). Frequently, these bacterial cells, potentially pathogenic, enter into a non-culturable state on routine bacteriological plating media. However, the use of direct detection methods DAPI stained cells allows the visualization of these Viable but Non Culturable cells VNC. But, beyond the characterization of the viability of the cells electron transport activity, metabolic activity, membrane integrity, structure and/or quantity of DNA, what happens with the virulence of these cells? This problem was experimentally investigated according to the bacterial model Salmonella Typhimurium. The virulence of this strain, which is the agent of the murine typhoid, was evaluated on a mouse model. Experimentally, the effects of some environmental factors on the survival and on the maintenance of virulence of Salmonella Typhimurium were measured in microcosms exposed to UV radiation (four germicidal lamps 8 mW s−1 cm−2, wave length: 254 nm, salt concentration (Sea Salt Sigma, 37, nutrient starvation. The microcosms were simultaneously submitted to these three factors, with variable exposure times. For each of those times, the viability of the nonculturable cells which became nonculturable because of the exposure to the three factors was measured through different physiological states notable in the cells, after using different fluorescent dyes. The stained cells were observed by epifluorescence microscopy and analysed by image cytometry. So, the cellular populations are characterised by enumeration of respiring bacteria CTC, [39], metabolising bacteria YEK, [22] modified, bacteria owning an undamaged cytoplasmic membrane LD, Live/Dead BacLight Viability Kit. Molecular Probes Inc.; we also determined the quantity and/or structure of DNA of the cells fluorescence level of DAPI stained cells), After exposure to the three factors for one hour 13.56 J cm−2, while the plate count cell density rapidly decreased from #107 cells mL−1 to0.1 cell mL−1, physiological states of these viable but non-culturable cells are similar to those of non-exposed cells. On the other hand, after exposure for three hours, only 10 % of the cells deposit a CTC formazan-crystal and 20 % are substrate responsive cells enlarged cells in presence of Yeast Extract and Cephalexin: YEC. Half of the cellular population presents an undamaged cytoplasmic membrane and the level of fluorecence of DAPI stained cells is close to 85 %, which shows that the DNA of these cells is weakly damaged. After exposure to the three experimental factors for24 hours 315 J cm−2, weak replies to the physiological tests used in this study to characterize the viability of the non-culturable cellular population are observed CTC: 4 %; YEC: 2 %; LD: 11.8 % while the fluorescence level of DAPI stained cells remains firm at 80 %. At the same time, the virulence expression of VNC cells of Salmonella Typhimurium, evaluated by intraperitoneal injection to the mouse route which excludes uncontrolled parameters, unlike the per os route does not seem to be correlated with the cellular viability such as it has been evaluated in this study. A 30 min exposure (6.73 J cm−2) to the three environmental factors, leading to the non-culturability of almost the entire exposed cell population 0.08 culturable cell mL−1 whereas the level of viability of those culturable cells is closed to the one of non-exposed cells. The injection of 1000 of those cells 0.001 culturable cells in 100 μL inoculated into the mouse a group of ten mice does not cause any mortality four weeks post-inoculation, whereas the injection of the same dose of non-exposed cells leads to the death of all mice in the group one week post-inoculation. According to our preliminary experiments on Salmonella Typhimurium, the loss of the state of culturability and the loss of virulence towards mice by intra-peritoneal route, because of the exposure to associated effects of UV irradiation 254 nm, salinity 37 and nutrient starvation, seem to be concomitant. 相似文献
9.
《Oceanologica Acta》2002,25(1):23-30
The colonization of a fringing reef of Reunion Island by fish larvae takes place essentially from August to February with two peaks, in August-September, when the water temperatures are coldest, and in February when they are at a maximum. The number of fishes, as well as the number of sampled species, present similar values over two consecutive years with, nevertheless, a strong variation in the species involved. In Reunion Island, the number of post-larvae which colonise the reef is one hundred to four hundred times lower than on larger and more structured reefs. This phenomenon could be explained by the geographical characteristics of the island. The stock control of the adult fish in Reunion could largely be the result of the arrival of post-larvae on reefs and would correspond to the model of “recruitment limitation”. 相似文献
10.
《Oceanologica Acta》1999,22(2):179-191
The grain size of mature coastal sands changes rapidly in response to the variation of the energy regime which provokes either erosion or deposition of fractions of the textural assemblage. Whatever the dynamic conditions, questions of paramount importance such as the size of grain populations transported simultaneously, the most common size of the grains in movement and the grain-size range of the sediment fraction involved are still poorly understood. The present paper deals with an attempt to describe this fraction without any consideration of the processes responsible for the observed changes. A major problem results from the fact that the distribution of the mobilized fraction cannot be known and described by direct comparison between the initial and the final grain-size curves. The only way to characterize the mobile fraction between two subsequent grain-size states is to simulate various kinds of removal or deposition. The first question is to express the shape of the actual distributions of the sediments mathematically. The simple Gaussian approximation being irrelevant, distributions can be expressed using advanced computer programmes which can provide mathematical expressions for all distributions. The cubic-spline approximation was chosen. The mobile fraction was assumed to have a Gaussian distribution. Various tests were made in order to simulate qualitative phenomena observed in nature (bimodality, grain-size parameter changes…) and to assess the three parameters which define the characteristics of the fraction deposited or removed: modal value, dispersion of the mobile population and relative amplitude of the change. An application was carried out on the Senegalese coast offshore from the Senegal delta and on the Mediteranean coast in the Gulf of Lions. It suggests that the dynamic agents have a great selectivity. Further developments are considered. 相似文献
11.
《Oceanologica Acta》1998,21(2):209-221
Coastal waters are generally a product of mixing between continental and oceanic originated water masses. Near river mouth areas, as in the Gironde estuary, oceanic waters are modified by the influence of freshwater discharge that introduces suspended and dissolved substances, including pollutants. Within PNOC (Programme National d'Oceanographie Côtière) our objective is to determine the extent of the influence of the Gironde estuary on to the Aquitanian continental shelf. Several cruises for collecting hydrological data have been carried out in this area. The data of every cruise were coupled with a NOAA-11 satellite passage. The recorded images have been analysed and were compared with the results given by a 3D mathematical model. The interaction among different dynamical factors (density, wind-driven and tidal circulation) controls the mixing and the transport of low salinity waters. 相似文献
12.
Bathyscaph dives off Madeira permitted discovering at a depth of about 1200 m, a morphologic feature interpreted as a volcanic crater or a small caldera. Between 900 m and 1700 m deep, volcano-sedimentary formations, interpreted as hyaloclastites of explosive origin, were observed. It is assumed that these formations were initially deposited at shallower depths and may reflect the subsidence of the Madeira archipelago owing to the great thickness of its volcano-sedimentary series (more than 6000 m). 相似文献
13.
《Marine environmental research》1987,21(2):95-107
The sewage originated by the city of Marseilles (more than 1 M inhabitants) is entering the sea water at surface level in the calanque of Cortiou (6–8 km east of the city). In the 6 km 2 basin concerned with the polluted flux, bacterial communities demonstrate some behavorial analogies with other plankton. In spite of organic and mineral enrichments, both bacterial and phytoplanktonic densities are similar to those of the oligotrophic surrounding sea water. As for zooplanktonic species, which are able to resist in polluted environments, bacteria show capabilities to grow in various cultural conditions. No effect of the annual temperature cycle is noted on bacterial numbers. But, considering the bacterial community dynamics, the mechanisms leading to these similarities are quite different for bacteria. Heterotrophic bacteria mineralize the exogenous organic matter far from the ‘point source’, as demonstrated by the good correlation between N-NH4 and viable counts (r=0·98). The fluctuations of the numbers of viable heterotrophs and total coliforms (incubated at 37°C) are similar (r=0·98 for n=60) showinga low selective effect of the temperature and the capability for the same bacteria to grow both on selective or not selective medium. The biomass production resulting is shown by high values of the frequency of dividing cells and is due to heterotrophic bacteria. Bacterial production is more important in the more polluted part of the basin (N-NE), but, the bacterial density is regulated by factors varying in relation to the distance to the source of sewage. Near the mouth of the outlet sedimentation, dispersion, zooplanktonic grazing of particles with attached bacteria and bacterial predators grazing on free-living bacteria are the major causes of bacterial disappearance. In the west and south areas, where pollutants and organic material are diluted, the amount of substrate necessary for energy maintenance also plays a role. On the other hand, in these areas, no attempt was made to detect viable but not active cells in direct counts. 相似文献
14.
A detailed mapping and data from borings support the conclusion that there is a late lava flow inside the Papenoo valley, the main valley of Tahiti island. This last volcanic manifestation which took place 400,000 years ago came after the phase of erosion corresponding to the Illinoian glacial period. It is one of the four phases of erosion followed by filling observed in the cross section of the Papenoo valley. 相似文献
15.
《Oceanologica Acta》1998,21(5):645-654
Intensity and spectral characteristics of the fluorescence of water samples collected along the transect Cherbourg-Isle of Wight during four cruises for excitations at 370, 313 and 270 nm have been investigated within the framework of the FluxManche II program. Seasonal and spatial differences appeared to reflect on the one hand, variations in terrestrial inputs, and on the other hand, waters masses structuring. The observed linear variation of the fluorescence intensity with salinity indicates a gradual dilution of the continental humic material in going from the coasts to the central part of the English Channel. The largest signal was observed for the English coastal waters in agreement with important terrestrial inputs from the Solent river. While the fluorescence intensity was not found to be correlated with the DOC, it shows a good correlation with the nutrients. This result could indicate both a supply from terrestrial inputs and an almost simultaneous autochtonous regeneration. As similarly reported for waters in the eastern part of the French coastal zone, excitation at 313 nm gives evidence for the presence of two classes of fluorescent dissolved organic matter. These two fluorescent components are indicative of the simultaneous presence of continental humic substances and substances whose assignment to marine humic substances or to heterotrophic related substances are still an open question. As compared to the eastern part of the Channel along the French coasts, excitation at 270 nm indicates a lower content of protein-like compounds which may be related to a lower biological activity along the transect or may be due to the fact that the samplings were made out of the phytoplanktonic bloom period (April–May 1995). 相似文献
16.
《Oceanologica Acta》1998,21(2):371-381
Regular flights over the Bay of Biscay by the French Customs Air Service, have enabled us to record more precisely, from 1989 to 1995, the geographical locations of French and other European Community (EU) fishing boats. Data showed three main ‘métiers’ within the Bay of Biscay fishing fleet: French and Spanish bottom trawlers (61 %), French gill-netters and Spanish longliners. More than 80 % of gill-netters worked inside the territorial sea (12 nautical miles) and 60 % of them worked south of Noirmoutier (47°N). Longliners moved according to the seasons, from the edge of the continental shelf to the 50–100 m sounding lines. Since they work at night, only few pelagic trawlers have been recorded (records being made in daylight). The potters, liners and other small ‘métier’ boats of the bay were only located along the coast. The position of the French boats' positions according to their registration district showed that most boats worked close to their landing ports and that the overlap is small between the areas of two neighbouring fleets. Further analysis of the spatial distribution of boats in the French EEZ showed that Spanish boats were mainly recorded in the southern part of the Bay of Biscay, and that most were Basque. Belgian and Dutch beam trawlers fished their quota of sole off the ‘Pertuis Charentais’, the Gironde estuary and the ‘bassin d'Arcachon’. The 100 m sounding line appeared to constitute a demarcation line between the major fraction of the French fleet and other EU fishing boats. Although some fishing areas were only visited by boats practising a particular ‘métier’, others were coveted by everybody and, consequently, were areas with the most serious risk of conflicts. 相似文献
17.
《Marine environmental research》1987,22(1):19-32
This work describes a complete procedure to simplify pre-analytical operations and to reduce problems of contamination during nutrient analysis which prove the importance of the various potential contaminations: fingerprints, atmosphere, particulate matter. For instance, on a fingerprint there is enough urea to bring about 80 μmol litre− to an autoanalyzer cup, i.e 150 times the mean value in seawater. Atmospheric contact increases the ammonia concentration by about 1·5 μmollitre− per hour. The overestimation due to the interference of particulate matter reaches 15–80% of dissolved phosphate in summer in coastal seawater.In order to minimize tese contaminations, the sample is never poured out of its sampling flask. Thus, when the level of suspended matter is too high, centrifugation of the sample is performed directly in the vial, just before Analysis, instead of the usual filtration. Moreover, a Technicon Sampler IVhas been modified to receive vials up to 125 ml. In this way any filling of cups is avoided and atmospheric contamination is greatly reduced because of the larger volume of sample.The results show the improvement induced by our modifications: with reduced handling results are expected to be more reliable and representative. 相似文献
18.
P. Weydert 《Marine Geology》1974,16(3):39-45
The outline of the Pleistocene coastal geomorphology in the Tuléar area (Madagascar) can be redrawn from the analysis of the setting and characteristics of present-day coral reefs. Initial outer reef tracts, which grew in Tatsimian times (according to Battistini's terminology), followed in their development the river pattern, since they settled upon the divides between valleys instead of growing uniformly on the outer shelf. These primary reef chains coalesced subsequently. Inner reefs and coral banks also followed, although not so closely, the river pattern. 相似文献
19.
20.
Françoise Bourrouilh 《Marine Geology》1974,16(4):213-235
A geomorphological study of the east coast of Andros (Fresh Creek area) shows the existence of a paleotopography represented by low-altitude hills (few metres). This paleotopography is protected by the presence of a calcitic Quaternary crust which covers Pleistocene calcarenite.In the western part of the area, there are long woody axes, oriented NE-SW, parallel to the channels of the creek. They end at two kilometres from the coast, along which is a second kind of lower hills, orthogonal to the first.The first axes can be interpreted as megaripples as seen at the present time on modern deposits (on the Great Bahama Bank) and fossilized by the upper crust. The second direction is made by accretion ripples along the coast.The surface of the Bahamian calcarenite has been studied. The Bahamian karst presents two topographical forms: “blue holes” like those outside the island, which are 60–80 m in diameter and both sparse and deep; and “washtub” dolines; these are numerous and shallow, and, from low altitude, exhibit a honeycombed aspect on the surface. This karstic topography with dolines and blue holes is also seen through the water of the Creek the hard bottom of which is covered only here and there with a few centimetres of sediments. Hence, there is a submerged karstic topography, made of the same elements as the aerial karst, but submerged by the Holocene transgression. The present karstic relief, in relation with the different eustatic levels of the Quaternary, has begun 120,000 years ago, according to the isotopic ages, and might be composed by different steps, difficult to show now, in the topography.The blue holes in the interior of the island of young and little evolved karst, were formed more by solution than by collapse of the karstic caves, because of the absence of a real river to drain the Andros shelf at the time of low sea levels. Blue holes of the inside of the island, as they are called, with submarine openings, have the same salinity as the water of the creek (17.5 g/l). The dolines with very low salinity (0.7 g/l to 3.8 g/l) are filled with stromatolites and charophytes, slowly forming sediments made up essentially of high-magnesian calcite.It seems that the Andros Island karst can be compared with that of the Yucatan, where there are round and deep open pits, called cenote, of which the Bahamian equivalent would be the blue holes which were drowned by the Holocene transgression. 相似文献