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1.
《Oceanologica Acta》1998,21(2):345-351
A recapitulation of the records of tropical fishes from European Atlantic waters shows that 67.6% were fishes caught from the upper slope, between approximately 200 and 600 m; 19.8% were fishes caught from the continental shelf; and 13.5% were specimens caught from the middle slope, between 700 and 1 300 m. Since 1963, the upper slope species have made regular northward range extensions off of south Portugal to north-western Ireland (about 55° 30′N), more and less rapidly, about 30 years for Cyttopsis roseus and only 6 years for Sphoeroides pachygaster. The continental shelf species, observed from 1969 but mostly from 1981, have a northward range to south-eastern Ireland (about 52° N), but 65.2% of them have been caught off the south of the Bay of Biscay. The middle slope species, recorded only from 1991 according to the development of the deep fishery, were caught between 48° N and 60° N. The northward range extension of upper slope species and the higher frequency of records of continental shelf species from the southern part of the Bay of Biscay coincide with the investigations on the warming of the south-north current in the upper slope of northern Spain and of the south French Atlantic continental shelf.  相似文献   

2.
Dissolved cadmium and copper species were measured in the Loire estuary and the North Biscay Bay continental shelf (France) in spring 2002. Metal behaviours along the salinity gradient, metal fluxes from the Loire system and surface distributions on the continental shelf were described and compared with the ones obtained at a period of higher discharge (i.e., winter 2001). Vertical distributions at different stations were also examined with the aim to assess whether the Loire inputs affect the Cu and Cd speciation over the continental shelf. In the Loire estuary, different metal behaviours were observed from winter. Cu and its various species mostly followed a theoretical dilution line whereas a Cd addition composed of chloro- and organic complexes was observed. According to our estimations, the Cu flux was composed, as in winter, of 40% hydrophobic organic complexes. On the other hand, Cd organic complexes accounted for less in the total dissolved metal flux than they did in winter (55 and 78% for spring and winter, respectively). On the continental shelf, a C18Cu-to-TDCu ratio of 40% was observed in the stratified area under Loire influence. For Cd, the organic fraction was relatively important in the surface waters near the mouth of the estuary and decreased deeper and seaward. Thus, the Cu and Cd speciation on the North Biscay Bay continental shelf are firstly determined by the extent of the estuarine plume. Beyond the estuarine influence, biological processes appeared to be the origin of the observed variations.  相似文献   

3.
《Oceanologica Acta》1998,21(2):233-241
The western Atlantic continental margin of the Bay of Biscay is characterised by a combined macro-tidal and a high energy environment. These conditions are responsible for the essentially sandy sedimentary cover along with well-defined fine deposit zones observed on the shelf. The main continental sources are the Loire, Gironde and Adour Rivers. It is estimated that 2.4 to 2.5 million tons of fine sediments are supplied annually to the ocean from these rivers of the French Atlantic coast. The Gironde and the Loire contribute with 84 % and the Gironde with 60 % of this amount. Previous studies of the distribution of the clay mineral assemblages and of oligo-elements have distinguished two provinces (north and south Biscay areas) according to these riverine sources. The use of an inductively coupled plasma-mass spectrometry (ICP-MS) technique allowed us to analyse both heavy metals and rare earth elements (REE), thus permitting an effective characterisation of continental sources. On the basis of these results, it has been possible to better identify the respective contributions of the Loire and the Gironde Rivers to the fine-grained sedimentation on the inner shelf.  相似文献   

4.
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5.
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6.
Numerous oceanographic cruises (with hydrology, water sampling, drift current measurements) carried out since 1980 on the continental shelf of the Bay of Biscay, together with available NOAA/AVHRR infra-red images, form the basis of a proposed explanation for the processes responsible for the distribution of suspended sediments on the shelf. The seasonal hydrographic structure of continental shelf waters is of paramount importance in sediment distribution. In summer, there is an horizontal stratification of water masses, and suspended sediment distribution is closely related to the thermo-haline structure. A fresher water mass with less suspended material lies on a thicker and more turbid homogeneous layer. During winter, when sediment discharge from the rivers often reaches its annual maximum, an oceanic thermo-haline wedge occurs on the shelf at around −100 m. As a result, winter turbidity values on the outer continental shelf are low (comparable to summer values), and a permanent nepheloı̈d layer is never observed. The wedge, which lasts for several months, may act as a filter, preventing transport to the slope. High turbidities on the external shelf and the continental slope are only measured in spring, when the thermo-haline wedge disappears. It seems possible that during winter time, suspended materials brought by rivers are deposited in the “Grande Vasière” (the “large mud patch”). It is postulated that the position of this mud patch is linked to the long-term stable location of the thermo-haline front that separates oceanic waters from the colder and less salty coastal waters.  相似文献   

7.
《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   

8.
Keppel Bay is a macrotidal embayment on a tectonically stable, tropical coast, which links the Fitzroy River with the Great Barrier Reef continental shelf. Estuaries and deltas act as conduits between catchments and inner shelf environments. Therefore, understanding sediment transport pathways in these complex systems is essential for the management of ecosystems such as coral-reefs that are potentially vulnerable to enhanced river sediment loads. Furthermore, the morphology and sediment dynamics of subtidal sand ridges and dunes are relatively poorly characterised in macrotidal estuaries, particularly in turbid, episodic systems such as the Fitzroy River and Keppel Bay. Our sedimentological analysis of seabed samples, shear-stress modelling and three-dimensional acoustic imaging reveals that Keppel Bay is a mixed wave- and tide-dominated estuarine system. Areas of sediment starvation and shoreward transport characterise the offshore zone, whereas a complex of both active and relict tidal sand ridges, and associated subaqueous dunes, dominate the relatively protected southern Keppel Bay. Transport within this region is highly dynamic and variable, with ebb-dominated sediment transport through tidal channels into the outer bay where there is a switch to wave-dominated shoreward transport. Ultimately, bedload sediments appear to be reworked back inshore and to the north, and are gradually infilling the bedrock-defined embayment. Our characterisation of the Keppel Bay system provides a detailed example of the physiography of the seaward portion of a tide-dominated system, and shows that sediment transport in these areas is influenced by a variable hydrodynamic regime as well as relict channels and bedrock topography.  相似文献   

9.
Under present-day conditions, rivers are the main source of fine sediments dispersed to the Bay of Biscay. They deliver about 2.5×106 t yr−1 of continental fine sediments, 60% of which is derived from the Gironde estuary. Of this flux, 65% is believed stored on the shelf. Two kinds of mud fields can be found in the Bay of Biscay: coastal mud and shelf mud belts. The total mass of fine sediments stored during the past 2000 years is 3.2×109 t. Consequently, about 0.9×106 t yr−1 could reach the shelf edge and eventually the open sea. From this amount of displaced material and the deposition surface areas, an evaluation of sediment fluxes across the margin during the late Holocene period is discussed. This evaluation is compared with results obtained from ECOsystéme du canyon du cap-FERret (ECOFER) data from sediment traps and surficial box cores.  相似文献   

10.
Sixteen rock samples were collected from the continental shelf and slope between Napier and Cape Turnagain, southern Hawkes Bay, most coming from offshore anticlinal ridges. Nine of the samples have a foraminiferal fauna of Upper Miocene and Pliocene age. The remainder cannot be dated, but most are probably of similar age. The foraminiferal. faunas are considered to have lived at depths ranging down to at least 1600 m deeper than the depth from which they were collected. Thus, the post‐depositional history of the samples includes tectonic uplift of similar magnitude since Upper Tertiary times. Because most of the samples arc very fine grained, unlike Recent sediments from ridges, it is suggested that the present regime of folding is largely post‐Pliocene in age.  相似文献   

11.
In order to investigate the parameters controlling the heterotrophic protists (nano-microzooplankton) on the continental shelf of the southern Bay of Biscay, plankton communities and their physico-chemical environment were studied 4 times in February, April, June and September–October 2004 at three stations in the euphotic zone in the Bay of Biscay. The abundance and carbon biomass of heterotrophic protists (ciliates, heterotrophic dinoflagellates and nanoflagellates) as well as all the others groups of plankton (picoplankton, nanophytoplankton, diatoms, autotrophic dinoflagellates, metazoan microzooplankton and mesozooplankton), the environmental parameters and the primary and bacteria production were evaluated at each sampling period. Microzooplankton grazing experiments were undertaken at the same time. Ciliates and heterotrophic dinoflagellates accounted for the main major component of nano- and microzooplankton communities in term of biomass. The total carbon biomass of heterotrophic protists was highest in spring and lowest at the end of summer. The development of heterotrophic protists started after a winter microphytoplankton bloom (principally large diatoms), the biomass was lower in June and was low in September (through inappropriate prey). The carbon requirement of microzooplankton ranged from 50 to more than 100% of daily primary, bacterial and nanoflagellate production. The heterotrophic protist community was predominantly constrained by bottom-up control in spring and at the end of summer via food availability and quality.  相似文献   

12.
The intermediate water masses in the eastern Atlantic Ocean between 31°N and 53°N were studied by analysis of the distributions of potential temperature, salinity, dissolved nutrients and oxygen. Sub-surface salinity minima are encountered everywhere in the area. At the northern and southern boundary they are connected with the presence of Sub-Arctic Intermediate Water and Antarctic Intermediate Water, respectively, but towards the European ocean margin the sub-surface salinity minima shift to shallower density levels. The sub-surface salinity minima observed west of the Iberian Peninsula represent a water mass formed by winter convection in the Porcupine Sea Bight and the northern Bay of Biscay. These minima gain salt by diapycnal mixing with the underlying Mediterranean Sea Outflow water and with the overlying permanent thermocline. The core of Antarctic Intermediate Water appears to contribute to the formation of Mediterranean Sea Outflow Water since it becomes entrained into the overflow near Gibraltar. This entrainment gives rise to an enhanced concentration of the nutrients in the Mediterranean water in the North Atlantic. The deep salinity minimum, due to the presence of Labrador Sea Water, is restricted mainly to the Porcupine Abyssal Plain. In the Bay of Biscay this water type is strongly modified by enhanced diapycnal mixing near the continental slope. At all intermediate levels the continental slope in the Bay of Biscay seems to be a focal point for water mass modification by diapycnal mixing. Below the core of the Mediterranean Sea Outflow Water the Labrador Sea Water is also strongly modified. Its salinity is strongly enhanced by diapycnal mixing with the overlying core of Mediterranean Sea Outflow Water. An analysis of the oxygen and nutrient data indicates that the large spatial concentration differences at the level of the Labrador Sea Water are caused mainly by ageing of the water. The youngest water is observed at 52°N, and, especially in the Bay of Biscay and off south-west Portugal, the water at levels of about 1700 dbar are strongly enriched in nutrients and depleted in oxygen.  相似文献   

13.
In the 2000 and 2001 springtime periods, mesozooplankton samples were systematically taken during research cruises devoted to the study of the distribution and abundance of small pelagic fishes in the French part of the Bay of Biscay, NE Atlantic, continental shelf. Simultaneous activities of three enzymes were measured in these mesozooplankton samples, to characterize the main features of ecosystem function at a regional scale. The aim was to assess assimilation rates of carbohydrates, through pyruvate kinase activity, and protein, through trypsin activity, by the mesozooplankton community and the resulting overall productivity, through aspartate transcarbamylase activity. The highest influence on the pelagic environment was the strong difference in the freshwater outflow rates from the two main large rivers, the Loire and the Gironde, which was principally responsible for the inter-annual fluctuations of the nutrients in the Bay. This overall influence of river flow results in a characteristic pattern of sea-surface salinity, which was reflected by the phytoplankton biomass distribution. Mesozooplankton enzyme activities showed high variations between the two years. The contrast in the dynamics of the pelagic food web processes between the two consecutive years, with higher activity in 2001, affected the nutritional condition of the zooplanktivorous breeding anchovy Engraulis encrasicolus.  相似文献   

14.
Spatio-temporal changes in totally and enzymatically hydrolyzable amino acids (THAA and EHHA) and EHAA/THAA ratios of superficial sediments were assessed during 1997-1999 in three areas (i.e., the Gulf of Lions, the Bay of Biscay, and Central Chile) differing in their primary productivity. In all three areas, and even off Central Chile where a strong El Niño event took place during 1997-1998, spatial changes were always much greater than temporal ones. The factors affecting the spatial distributions of amino acid concentrations differed among areas. In the Gulf of Lions, sediment granulometry was apparently the most important driving force of THAA, EHAA, and EHAA/THAA, and there was no marked difference between stations located on the open slope and those in submarine canyons. Conversely, in the Bay of Biscay, there were clear differences between the stations located off Cap-Breton, on the open slope, and those in the Cap-Ferret canyon; the latter two featuring lower EHAA and THAA but higher EHAA/THAA. This pattern is likely to result from the predominance of different sources of organic matter and especially from the importance of continental inputs to the Cap-Breton canyon. Off Central Chile, amino acid concentrations and ratios were both maximal around 100 m depth, probably reflecting the interaction between the primary productivity gradient and the presence of an oxygen minimum zone (OMZ) reducing the degradation of sedimentary organics. When comparing the average values collected in the three areas studied, THAA and EHAA were highest in Central Chile, intermediate in the Bay of Biscay and lowest in the Gulf of Lions. EHAA/THAA ratios were also highest in Central Chile but were lowest in the Bay of Biscay. Differences between the Gulf of Lions and the Bay of Biscay could have been affected by sampling design. In Central Chile, the use of labile organic carbon to total organic carbon (C-LOM/TOC) and EHAA/THAA as indices of organic matter lability led to very similar results. This was not the case in the Bay of Biscay. It is therefore argued that the use of C-LOM/TOC should be restricted to highly productive areas.  相似文献   

15.
Sediment samples were collected to delineate the distribution of contaminants along the central California coast. Sampling included a variety of Canyons and shelf/slope areas to evaluate contaminant transport patterns and potential delivery to Canyons and the continental slope to a depth of 1200 m. Sediments were collected and analyzed for organic contaminants using standard techniques of the NOAA National Status and Trends Program (NS&T). DDT is distributed on the shelf within a zone of fine-grained sediments between Half Moon and Monterey Bays. DDT was found at higher concentrations in Ascension, A?o Nuevo, and Monterey/Soquel Canyons than in Pioneer and Carmel Canyons, the Gulf of the Farallones, or the continental slope. The Monterey Bay watershed appears to be the primary source of DDT. In contrast, PAHs and PCBs on the shelf appear to be derived primarily from San Francisco Bay. DDT appears to be delivered to the deep ocean via the Canyons more than from cross-shelf sediment transport. Sediment budget estimates for the continental shelf north of Monterey Bay need further refinement and more data to account for the movement of material from Monterey Bay onto the shelf.  相似文献   

16.
The Bay of Biscay (North-East Atlantic) has long been subjected to intense direct and indirect human activities that lead to the excessive degradation and sometimes overexploitation of natural resources. Fisheries management is gradually moving away from single-species assessments to more holistic, multi-species approaches that better respond to the reality of ecosystem processes. Quantitative modelling methods such as Ecopath with Ecosim can be useful tools for planning, implementing and evaluating ecosystem-based fisheries management strategies. The aim of this study was therefore to model the energy fluxes within the food web of this highly pressured ecosystem and to extract practical information required in the diagnosis of ecosystem state/health. A well-described model comprising 30 living and two non-living compartments was successfully constructed with data of local origin, for the Bay of Biscay continental shelf. The same level of aggregation was applied to primary producers, mid-trophic-levels and top-predators boxes. The model was even more general as it encompassed the entire continuum of marine habitats, from benthic to pelagic domains. Output values for most ecosystem attributes indicated a relatively mature and stable ecosystem, with a large proportion of its energy flow originating from detritus. Ecological network analysis also provided evidence that bottom-up processes play a significant role in the population dynamics of upper-trophic-levels and in the global structuring of this marine ecosystem. Finally, a novel metric based on ecosystem production depicted an ecosystem not far from being overexploited. This finding being not entirely consistent over indicators, further analyses based on dynamic simulations are required.  相似文献   

17.
A fisheries research cruise conducted in 2000 offered a first opportunity to take simultaneous measurements of the activities of three enzymes in mesozooplankton samples collected at a regional scale over the continental shelf of the Bay of Biscay in the NE Atlantic, with the aim of characterizing main aspects of the functioning of the biotic environment of small pelagic fish populations. The activity of the digestive endopeptidase trypsin was selected to characterize the assimilation rate of proteins, whereas pyruvate kinase (PK) was chosen as an indicator of carbohydrate assimilation and aspartate transcarbamylase (ATC) provided an overall assessment of mesozooplankton productivity. The Bay of Biscay region is subject to various strong physical driving forces that directly affect the primary structure of the pelagic food web. On our cruise, the phytoplankton biomass distribution reflected these different physical influences: diatoms dominated the nutrient-enriched coastal water; picoplankton dominated the northern-central part where nutrients were depleted; and nanoplankton were abundant at the shelf break where internal waves provided an input of nutrients. These and other results (on bacteria, particulate organic carbon distribution, among others) illustrate the differences that exist in the microbial food webs of different sectors of the bay. The living matter produced was characterized by the quality and quantity of the smallest prey items that were available to higher trophic levels. Variations in mesozooplankton enzyme activities may agree well not only with classically expected results, but also present unexpected special features: high ATC specific activities were measured around the mouth of the Gironde, in the nutrient-rich desalted water of the plume, but surprisingly not in front of the Loire river. PK specific activities reflected preponderantly the balance between phytoplankton cells sizes and the related bacterial abundance resulting from nutrient limitation (mainly P), that induces varying carbohydrates production potential. Trypsin specific activities were moderately variable, except in a restricted area where a highly abundant protein content characterized the particulate matter and in the plume of water flowing out of the Gironde. It is concluded that the presented approach of the metabolism of mesozooplankton communities may provide novel views on crucial processes occurring at the mesoscale, which fits in generally well with the scales of ecological factors mostly influential on small pelagic fish populations.  相似文献   

18.
Primary production (PP), calcification (CAL), bacterial production (BP) and dark community respiration (DCR) were measured along with a set of various biogeochemical variables, in early June 2006, at several stations at the shelf break of the northern Bay of Biscay. The cruise was carried out after the main spring diatom bloom that, based on the analysis of a time-series of remotely sensed chlorophyll-a (Chl-a), peaked in mid-April. Remotely sensed sea surface temperature (SST) indicated the occurrence of enhanced vertical mixing (due to internal tides) at the continental slope, while adjacent waters on the continental shelf were stratified, as confirmed by vertical profiles of temperature acquired during the cruise. The surface layer of the stratified water masses (on the continental shelf) was depleted of inorganic nutrients. Dissolved silicate (DSi) levels probably did not allow significant diatom development. We hypothesize that mixing at the continental slope allowed the injection of inorganic nutrients that triggered the blooming of mixed phytoplanktonic communities dominated by coccolithophores (Emiliania huxleyi) that were favoured with regards to diatoms due to the low DSi levels. Based on this conceptual frame, we used an indicator of vertical stratification to classify the different sampled stations, and to reconstruct the possible evolution of the bloom from the onset at the continental slope (triggered by vertical mixing) through its development as the water mass was advected on-shelf and stratified. We also established a carbon mass balance at each station by integrating in the photic layer PP, CAL and DCR. This allowed computation at each station of the contribution of PP, CAL and DCR to CO2 fluxes in the photic layer, and how they changed from one station to another along the sequence of bloom development (as traced by the stratification indicator). This also showed a shift from net autotrophy to net heterotrophy as the water mass aged (stratified), and suggested the importance of extracellular production of carbon to sustain the bacterial demand in the photic and aphotic layers.  相似文献   

19.
海平面变化及其海岸响应   总被引：4，自引：0，他引：4  
第四纪气温的大幅度冷暖变化，导致全球海平面的变化，引起陆架海侵扣海退。海岸上的各种地貌如海滩、沙坝、三角洲扣陆架沙脊等响应海平面升降而发生新的演化扣变异。东海陆架古岸线、围绕古岸线发育的陆架沙脊、陆架深切河谷扣河谷充填沉积以及冰后期海进型扣海退型沙坝的形成乖演化等沉积事件都是响应海平面升降的结果。近百年来特别是近30年全球海平面普遍上升，引起风暴潮的频度扣幅度的增大。近岸波能增强，越滩浪增多，导致海滩侵蚀，岸线后退。Bruun法则扣其他一些模型能够说明海滩随海平面上升而蚀退的规律，但在预测速率时仍存在很多问题。使用时应注意海平面变化的区域性、海滩发育的滞后性和海滩蚀退因素间的权重关系。  相似文献   

20.
Seismic reflection profiles and vibracores have revealed that an inner shelf, sand-ridge field has developed over the past few thousand years situated on an elevated, broad bedrock terrace. This terrace extends seaward of a major headland associated with the modern barrier-island coastline of west-central Florida. The overall geologic setting is a low-energy, sediment-starved, mixed siliciclastic/carbonate inner continental shelf supporting a thin sedimentary veneer. This veneer is arranged in a series of subparallel, shore-oblique, and to a minor extent, shore-parallel sand ridges. Seven major facies are present beneath the ridges, including a basal Neogene limestone gravel facies and a blue-green clay facies indicative of dominantly authigenic sedimentation. A major sequence boundary separates these older units from Holocene age, organic-rich mud facies (marsh), which grades upward into a muddy sand facies (lagoon or shallow open shelf/seagrass meadows). Cores reveal that the muddy shelf facies is either in sharp contact or grades upward into a shelly sand facies (ravinement or sudden termination of seagrass meadows). The shelly sand facies grades upward to a mixed siliciclastic/carbonate facies, which forms the sand ridges themselves. This mixed siliciclastic/carbonate facies differs from the sediment on the beach and shoreface, suggesting insignificant sediment exchange between the offshore ridges and the modern coastline. Additionally, the lack of early Holocene, pre-ridge facies in the troughs between the ridges suggests that the ridges themselves do not migrate laterally extensively. Radiocarbon dating has indicated that these sand ridges can form relatively quickly (1.3 ka) on relatively low-energy inner shelves once open-marine conditions are available, and that frequent, high-energy, storm-dominated conditions are not necessarily required. We suggest that the two inner shelf depositional models presented (open-shelf vs. migrating barrier-island) may have co-existed spatially and/or temporally to explain the distribution of facies and vertical facies contacts.  相似文献   

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