Cap Ferret Research Articles

Un barrage contre l’Atlantique by Frédéric Beigbeder

Reviewed by: Un barrage contre l’Atlantique by Frédéric Beigbeder Alexander Hertich Beigbeder, Frédéric. Un barrage contre l’Atlantique. Grasset, 2022. ISBN 978-2-246-82655-2. Pp. 272. As his “du même auteur” page indicates, Beigbeder’s literary output can be fairly easily categorized: there are the “essais,” which are primarily compilations of previously published newspaper and magazine columns; short stories; the Marc Marronnier and Octave Parango “trilogies;” and the “romans de non-fiction,” which includes both works like Oona & Salinger, a historical novel relating the relationship between J.D. Salinger and Oona O’Neill; and more autobiographical texts, like his latest book, subtitled Un roman français, tome 2. As in the first volume, Beigbeder recounts his past while also examining his current life and contemporary society. But unlike the 2009 Prix Renaudot winner, this book is much more disparate in content and form. Most of the text is comprised of single sentences with a space between them—“Mes phrases respecteront la distanciation littéraire” (14)—which affords Beigbeder multiple opportunities for his trademark, winking aphorisms: “Certaines phrases se surestiment: elles se prennent pour des maximes, comme une instagrammeuse se prend pour une star” (39). This style also allows him to flow from one anecdote to the next, primarily from the 1980s, a sybaritic orgy of jetsetters, alcohol, drugs, sex, and outlandish pranks pulled across the party capitals of Europe—Paris, Venice, Ibiza—his “éducation sentimentale” (70). This era sharply contrasts with today’s pandemic-stricken world where individual rights, and for Beigbeder the hedonistic possibilities they allow, are curtailed: “Jamais je n’aurais pu imaginer que la fête serait prohibée en France sans la moindre protestation des citoyens” (169). Beigbeder, too, is in isolation. Barrage was composed at Benoît Bartherotte’s compound in Cap Ferret. Bartherotte, “le Sisyphe gascon” (40), le “Don Quichotte de la Pointa” (204), has been in the press most recently for his efforts to stop the erosion of Cap Ferret by building a 450-meter long seawall—whence the title, with a nod to Duras, flippant allusions being another Beigbeder specialty. While some see Bartherotte as a hero toiling tirelessly to save a landmark, others see him as an ultrarich rulebreaker who does whatever he wishes (he built both his house and the seawall without proper authorization). This portrait of his friend allows Beigbeder to ponder topics dear to him, such as iconoclasm, individual choice, and Western civilization. Like its predecessor, this autobiography builds to a crescendo of maudlin sentimentality. Even though Beigbeder repeatedly criticizes his father, by the end he recognizes that, in his own way, his father, stricken by Parkinson’s, loves him. Beigbeder reunites his extended family—his divorced parents, his adult daughter from a previous marriage, his young children and wife—for a dinner in Cap Ferret: “Il me suffit de me souvenir de cet instant, de le graver ici, sur cette page, et alors aucune de ces personnes ne disparaîtra jamais” (261). But given that his life story, as he admits, “est celle d’un homme qui a tellement tout tourné en [End Page 204] ridicule qu’il ne sait même plus comment retrouver le sérieux” (32), the reader may well have doubts. Beigbeder’s admirers and detractors will find much fodder here. [End Page 205] Alexander Hertich Bradley University (IL) Copyright © 2022 American Association of Teachers of French

Time-Lapse Camera Monitoring and Study of Recurrent Breaching Flow Slides in Cap Ferret, France

In this paper, we present a low-cost method designed to monitor recurrent breaching flow slides that impact the security of a beach. This beach, located in France at the inlet of Arcachon Bay, connects a sand spit to a tidal channel while ending at the toe of a coastal defense. Monitoring is based on capturing images and intends to add continuous information to intermittent direct observations so that triggering and influencing factors can be assessed more precisely. The method is based on time-lapse picture collection and processing. The field of view shows successive emerged manifestations of flow slide phenomena, as well as some possibly related environmental elements. On-site application for 576 days provides important indications and details on flow slide event progress and beach recovery. A simple but quantitative analysis of the influence of sand spit topographic changes is proposed as a preliminary approach of the method’s suitability for studies of environmental processes in conjunction with coast protection.

Modelling the contribution of wind waves to Cap Ferret's updrift erosion

Wind waves breaking at an angle with the shoreline force the drifting of littoral sediments, which is known for contributing to the formation and growth of barrier spits. Intriguingly, increased rates of longshore wave power have also been associated with the erosion of some barrier spits on the updrift margin of tidal inlets. Therefore, a numerical experiment was designed and is presented here, which investigates the possible links between the longshore wave power and the shortening of these elongated coastal barriers. Based on a process-based model, the experiment provides new insights into the forces at play in the redistribution of sediments between a sandspit and its adjacent inlet, respectively the Cap Ferret and the Bay of Arcachon's tidal inlet, in SW France. More particularly, model scenarios were defined that show how combined waves and tide create gradients of residual sediment transport responsible for a sediment deficit at the spit – inlet boundary. The deficit was also found to deepen with increasing longshore wave energy, as if the transfer of sediment from the spit to inlet shoals was accelerated. This physically explains the previously observed retreat of the spit's distal end during periods dominated by the positive phase of North Atlantic Oscillation (NAO) in winter. Indeed, according to model results, higher and/or more oblique waves associated with the positive phase of the NAO are expected to increase the transfer and storage of the drifting sediments to and by the inlet shoals, and this at the expense of the spit. While these conclusions remain valid, we noticed that the sensitivity of model results to the bottom friction enhanced the importance of accurately representing the spatio-temporal distribution of bed roughness when investigating the morphodynamic interactions between real-world tidal inlets and their margins.

Bathyal cumacean assemblages from the southern margin of the Cap Ferret Canyon (SE Bay of Biscay)

The structure of the cumacean assemblages from the southern margin of the Cap Ferret Canyon was studied at 13 stations ranging from 346 to 1099 m depth with a modified Macer-GIROQ suprabenthic sledge (four superimposed nets; 0.5 mm mesh size). A total of 1885 specimens were collected and classified into 5 families and 42 species. The total abundances fluctuated between 2.8 ind./100 m2 (station TS04; 484-485 m) and 55.8 ind./100 m2 (station TS08; 714-708 m). The highest values of species richness and diversity were recorded at station TS13 (1097-1099 m): S=25 species; H’(log2)=4.05. The near-bottom vertical distribution of the cumacean fauna showed the same pattern at all stations: at least 60% of the individu­als were sampled by the lower net of the sledge and a drastic abundance decrease occurred between the two lowermost water layers sampled by the sledge. The multivariate analysis carried out on abundance data discriminated three main groups of stations distributed across depth (TS09 excluded): group Ia (346-485 m) characterized by the dominance of Nannastacidae (57.2%) at family level and Campylaspis sulcata, Leptostylis macrura at species level; group Ib (522-714 m) characterized by the dominance of Nannastacidae (66.1%) at family level and Campylaspis squamifera, C. laevigata and Leptostylis ma­crura at species level; and group II (790-1099 m) characterized by the dominance of Diastylidae (40.3%) at family level and Makrokylindrus (Adiastylis) josephinae, Leucon (Epileucon) pusillus and Diastyloides serratus at species level. According to this analysis, the main faunal change occurs between group I and II between 714 and 790 m, in relation to changes in the texture of surficial sediments. Although bathyal cumacean assemblages appear to be less abundant than those studied on continental shelves, they are significantly more diverse. However, such results could be in part related to the use of different sampling methods.

Eusirus bonnieri sp. nov. (Crustacea: Amphipoda: Eusiridae), a new deep speciesfrom the southeastern Bay of Biscay (NE Atlantic Ocean).

A new bathyal eusirid, Eusirus bonnieri sp. nov., is described from the SE Bay of Biscay, mainly characterized by its strongly deflexed rostrum (not mentioned for any other known Eusirus species) and by a long spiniform process at the posterodistal corner of pereopods 5-7 merus. It was sampled with a suprabenthic sledge between 370 and 1099 m on southern margin of the Cap Ferret Canyon and within the Capbreton Canyon. It was relatively scarce on the open slope and its maximum abundance was registered within the upper part of the Capbreton canyon. Beside some ecological/biological data, an identification key is provided for all known species in this genus.

Imprints of wave climate and mean sea level variations in the dynamics of a coastal spit over the last 250 years: Cap Ferret, SW France

AbstractIn coastal areas, sea level rise (SLR) and changing wave climates are expected to be the main oceanic drivers of shoreline adjustments. These drivers have been shown to vary on a wide spectrum of spatial and temporal scales. Nonetheless, a general rule about how this variability impacts global shorelines remains to be articulated. Here, we discuss the impacts of wave climate changes and SLR on the evolution of a barrier spit–inlet system over the last 250 years. The distal end of the Cap Ferret barrier spit, SW France, has undergone large‐scale oscillations that were well correlated with variations of the decadal average of the winter North Atlantic Oscillation (NAO) index. The local wave climate hindcast supports that increased alongshore wave energy fluxes associated with the positive phase of the NAO were responsible for the updrift retreat of the spit. By opposition, the spit has elongated downdrift when waves were less energetic and more shore normal, as during the negative phase of the NAO. In addition, lower rates of SLR appeared to be necessary for the spit to develop, as higher rates of SLR very likely forced the adjacent inlet to enlarge, at the expense of the spit. These results should help to predict and detect coastal adjustments driven by climate change and by climate variability. © 2019 John Wiley & Sons, Ltd.

Corridor Mapping of Sandy Coastal Foredunes with UAS Photogrammetry and Mobile Laser Scanning

Recurrent monitoring of sandy beaches and of the dunes behind them is needed to improve the scientific knowledge on their dynamics as well as to develop sustainable management practices of those valuable landforms. Unmanned Aircraft Systems (UAS) are sought as a means to fulfill this need, especially leveraged by photogrammetric and LiDAR-based mapping methods and technology. The present study compares different strategies to carry UAS photogrammetric corridor mapping over linear extensions of sandy shores. In particular, we present results on the coupling of a UAS with a mobile laser scanning system, operating simultaneously in Cap Ferret, SW France. This aerial-terrestrial tandem enables terrain reconstruction with kinematic ground control points, thus largely avoiding the deployment of surveyed ground control points on the non-stable sandy ground. Results show how these three techniques—mobile laser scanning, photogrammetry based on ground control points, and photogrammetry based on kinematic ground control points—deliver accurate (i.e., root mean square errors < 15 cm) 3D reconstruction of beach-to-dune transition areas, the latter being performed at lower survey and logistic costs, and with enhanced spatial coverage capabilities. This study opens the gate for exploring longer (hundreds of kilometers) shoreline dynamics with ground-control-point-free air and ground mapping techniques.

Large-scale bedforms induced by supercritical flows and wave–wave interference in the intertidal zone (Cap Ferret, France)

The Cap Ferret sand spit is situated along the wave-dominated, tidally modulated Atlantic coast of western France, characterized by a semidiurnal macrotidal range. It displays peculiar dome-like bedforms that can be observed at low tide across the intertidal zone. These bedforms exhibit a wavelength of ca. 1.2 m and an elevation of ca. 30 cm. They occur only when the incident wave heights reach 1.5–2 m. The internal stratifications are characterized by swaley-like, sub-planar, oblique-tangential, oblique-tabular, as well as hummocky-like stratifications. The tabular and tangential stratifications comprise prograding oblique sets (defined as foresets and backsets) that almost always show variations in their steepness. Downcutting into the bottomsets of the oblique-tangential stratifications is common. The sets of laminae observed in the bedforms share common characteristics with those formed by supercritical flows in flume experiments of earlier studies. These peculiar bedforms are observed at the surf–swash transition zone where the backwash flow reaches supercritical conditions. This type of flow can explain their internal architecture but not their general dome-like (three-dimensional) morphology. Wave–wave interference induced by the geomorphology (i.e. tidal channel) of the coastal environment is proposed as explanation for the localized formation of such bedforms. This study highlights that the combination of supercritical flows occurring in the surf–swash transition zone and wave–wave interferences can generate dome-like bedforms in intertidal zones.

Geomorphology of the Avilés Canyon System, Cantabrian Sea (Bay of Biscay)

The Avilés Canyon System (ACS) is a complex, structurally-controlled canyon and valley system constituted by three main canyons of different morphostructural character. They are, from east to west: La Gaviera Canyon, El Corbiro Canyon and Avilés Canyon. In addition to this ACS, a new canyon has been surveyed: Navia Canyon.We present for the first time a high resolution multibeam map showing with great detail the morphological and structural complexity of this segment of the Cantabrian margin.ACS presents a tectonic imprint marked by NW–SE, NNE–SSW and E–W structures. The morphology of their reaches as well as their single mouth, in addition to some rock dredges in their major valleys, demonstrates active down-slope flushing.The continental shelf shows a flat, uniform slope with local and well defined rock outcrops south of Aviles Canyon head. Sedimentary zones are limited, showing thin unconsolidated sedimentary cover.Strong continental margin water dynamics avoid thicker sediment deposition, being littoral sedimentary dynamics responsible for transport to the canyons heads and conduit to the Biscay Abyssal plain.Biscay Abyssal Plain shows evidence of a strong westward current affecting the surveyed strip of this more than 10km wide plain. Presence of two parallel deep sea channels, erosive scarps, and erosion of gully divides on the lower slope, may indicate that this is part of the distal fan at the termination of the large turbiditic system fed by Cap Ferret, Capbreton and other large canyons (Santander, Torrelavega, Lastres and Llanes) to the west of ACS.

Rare and new cumaceans (Crustacea, Peracarida) from the southern margin of the Cap Ferret Canyon (Bay of Biscay)

A new cumacean genus and species, Ithyleucon sorbei gen. et sp. n., was described from material collected in the southern margin of the Cap Ferret Canyon (Bay of Biscay, NE Atlantic). Although the new genus resembles Pseudoleucon Zimmer, 1903, in terms of the general aspect of the carapace and the pseudo-rostrum position, it shows important differences in the uropod structure and in the size of the antenna 1 accessory flagellum. In addition, some comments regarding the morphology of certain rare species (Mesolamprops denticulatus Ledoyer, 1983, Hemilamprops normani Bonnier, 1896 and Schizocuma spino-culatum (Jones, 1984)) are also provided.

Eddies in the Bay of Biscay: A numerical approximation

The results of numerical modelling in the Bay of Biscay have been used to investigate eddy dynamics. The modelling has been carried out using mean climatological and atmospheric forcing as input for hydrodynamic simulations with the ROMS model (Regional Ocean Modeling System). The most significant regional circulation features have been simulated in a mesoscale model configuration, with 6.6 km horizontal resolution. Eddy characteristics (horizontal and vertical structure, origins and migration) have been analysed. During winter, jet-like extensions of the slope current off northern Spain (mainly in the vicinity of Cape Ortegal) and France (near Cap Breton, Cap Ferret and Audierne canyons) developed into anticyclonic and cyclonic eddies, with an upper core of slope water. Most of the eddies identified in the model area were anticyclonic, with diameters at sea surface of between 60 and 130 km and significant effects below 500 m in depth. After their generation, the eddies moved slowly westward, with a mean migration speed of less than 2 cm s −1; they dissipated later in the year in the deep basin of the Bay of Biscay. The mean annual surface kinetic energy, estimated with the model, was around 34 cm 2 s −2. Both the kinetic energy and vorticity variability in the study area depend upon changes (magnitude and direction) in the wind stress, which have effects on the development of: the slope poleward current; the Galician upwelling; and the eddy generation and migration.

Recent changes in measured wind in the NE Atlantic and variability of correlation with NAO

Abstract. The paper deals with wind measurements, recorded since the 1950s, at twelve meteorological stations along a transect near the westernmost European border, between 64° and 44° N. Extreme wind speed tends to decrease sharply near the northern boundary (at Reykjavick), near the middle of the study area (at Shannon and Valentia) and near the southern boundary (at Brest and Cap Ferret), to increase at Thorshavn, with less significant trends at the other stations. Average wind speeds confirm the above tendencies, with an additional increasing speed at Lerwick, Kirkwall, Malin Head, Belle-Ile and Cap Ferret. To compare changes in wind activity, the data have been subdivided into three periods: until 1975, 1976–1992 and 1993–2008. Frequencies have been computed also for the "winter" (October to March) period, per quadrants, and for occurrences exceeding the speed of 15 m s−1. At Reykjavick a recent increase in the frequency of strong winds has occurred from various directions. Between 62° N (Thorshavn) and 59° N (Kirkwall) strong wind has been increasing since 1975. Minor changes can be observed at Stornoway, whereas at Malin Head the greatest increase for southerlies and westerlies is observed during the 1976–1992 period. At Belmullet, the frequency of strong southerlies has almost doubled since 1992, while at Shannon and Valentia it remains quite low. Finally at Brest and Belle-Ile, westerlies are predominant among winds >15 m s−1. Important changes in time and latitude appear in the correlation with the NAO (North Atlantic Oscillation) index. The highest correlation coefficients, calculated with monthly or seasonal means between the early 1950s and 1975, are observed from between 58° N (Stornoway) and Iceland, whereas low positive coefficients are reported more south. During the period 1976–1992, when increasing NAO index is predominant, positive correlation improves southwards as far as 54° (Belmullet) with some improvement also at Shannon and Valentia, while it remains low or even negative near the French Atlantic coast. Finally in the 1993–2008 period, correlation improves for all the stations south of 54° N (Belmullet), while it weakens more north.

Formation and evolution of paleo-valleys linked to a subsiding canyon, North Aquitaine shelf (France)

High resolution seismic data display four channel sets in front of the Lake of Hourton and the Lake of Lacanau covering a faulted and folded unit (U2) deposited during a high sea level at the end of the Burdigalian. The next unit (U3-1) shows sigmoid to oblique reflections (U3-1) but without apparent channels. However, during the sea level fall at the end of the Langhian, chaotic seismic facies and channels developed. The explanation should be the tectonic phase of the Aquitaine margin with an uplift of the North Aquitaine shelf. This induced the deformation of the unit U2 and provoked the creation of an alluvial plain on the North Aquitaine shelf with the formation of distributary channels (U3-2). The three following sea level falls during the Serravalian could explain the formation of the three other sets of channels (U3-3, U3-4 and U4). The last channels have a reduced mobility and correspond downstream to small paleo-canyons joining southwards the canyon of Cap Ferret. These channels disappear suddenly at the boundary at the Basin of Parentis.

Morphosedimentary features and recent depositional architectural model of the Cantabrian continental margin

Multibeam bathymetry, high (sleeve airguns) and very high resolution (parametric system-TOPAS-) seismic records were used to define the morphosedimentary features and investigate the depositional architecture of the Cantabrian continental margin. The outer shelf (down to 180–245 m water depth) displays an intensively eroded seafloor surface that truncates consolidated ancient folded and fractured deposits. Recent deposits are only locally present as lowstand shelf-margin deposits and a transparent drape with bedforms. The continental slope is affected by sedimentary processes that have combined to create the morphosedimentary features seen today. The upper (down to 2000 m water depth) and lower (down to 3700–4600 m water depth) slopes are mostly subject to different types of slope failures, such as slides, mass-transport deposits (a mix of slumping and mass-flows), and turbidity currents. The upper slope is also subject to the action of bottom currents (the Mediterranean Water — MW) that interact with the Le Danois Bank favouring the reworking of the sediment and the sculpting of a contourite system. The continental rise is a bypass region of debris flows and turbidity currents where a complex channel-lobe transition zone (CLTZ) of the Cap Ferret Fan develops. The recent architecture depositional model is complex and results from the remaining structural template and the great variability of interconnected sedimentary systems and processes. This margin can be considered as starved due to the great sediment evacuation over a relatively steep entire depositional profile. Sediment is eroded mostly from the Cantabrian and also the Pyrenees mountains (source) and transported by small stream/river mountains to the sea. It bypasses the continental shelf and when sediment arrives at the slope it is transported through a major submarine drainage system (large submarine valleys and mass-movement processes) down to the continental rise and adjacent Biscay Abyssal Plain (sink). Factors controlling this architecture are tectonism and sediment source/dispersal, which are closely interrelated, whereas sea-level changes and oceanography have played a minor role (on a long-term scale).

Long-term morphological modeling of a tidal inlet: the Arcachon Basin, France

The Arcachon Lagoon on the French Atlantic coast is a triangular shaped lagoon of 20 km on a side connected to the ocean by a 3-km wide inlet between the mainland and an elongated sand spit. This tidal inlet exhibits a particularly active morphology due to locally strong tidal currents and rough wave conditions. During the past 300 years, minimum and maximum spatial extents of the Cap Ferret sand spit have varied by 8 km while one or two channels have alternately allowed circulation between the lagoon and the ocean. These impressive morphological changes have never prevented regular flushing of the lagoon, eventhough the spit came as close as 300 m from the coast during the 18th century. According to Bruun's concept of tidal inlet stability [Theory and Engineering (1978), 510 pp.], the balance between longshore littoral transport and the tidal prism ensures the perpetuity of the inlet. Process modeling was believed to give better insight into the respective roles of tides and waves in driving the long-term morphological changes of the inlet. A two-dimensional horizontal morphodynamic model was therefore developed, combining modules for hydrodynamics, waves, sediment transport and bathymetry updates. The use of process models at a scale of decades requires a schematization of the input conditions. We defined representative mean annual wave and tide conditions with respect to sediment transport, i.e. conditions that induce the same annual transport as measured in the field. Driven by these representative conditions, simulations run from the 1993 bathymetry show that the tide is responsible for the opening of a new channel at the extremity of the sand spit (where tidal currents are the strongest), while waves induce a littoral transport responsible for the longshore drift of sand bodies across the inlet. One particular simulation consisted in running the model from a hypothetical initial topography where the channels are filled with sand and the entire inlet is set to a constant depth (3 m). The results show the reproduction of a channel and bar system comparable to historical observations, which supports the idea that the lagoon is unlikely to be disconnected from the ocean, provided tide and wave conditions remain fairly constant in the following decades.

Seismic patterns of a muddy contourite fan (Vema Channel, South Brazilian Basin) and a sandy distal turbidite deep-sea fan (Cap Ferret system, Bay of Biscay): a comparison

The aim of this paper is to discriminate the depositional facies, geometries and mechanisms of deposition of contouritic fans from those of turbidite distal fans, with a view to provide better resolution of reservoir prediction. Two examples are analysed: the Vema contouritic drift in the South Brazilian Basin and the Cap Ferret turbiditic fan in the Bay of Biscaye. The Vema contourite fan is a Neogene mud-rich accumulation (200–400 m thick), fed by Antarctic Bottom Water bottom currents and located downstream of the Rio Grande Rise. It forms one single-mound fan-shaped body in between two major channels, and where the main part of the deep circulation is funnelled into. As a result of the morphological and hydrological background, the comourite drift progrades mostly downstream. The accumulation was built as several depositional units (‘channel-levee’ systems) bounded by widespread discontinuities showing erosional patterns. This resulted from episodes of strong and/or unstable current activity producing the discontinuities, alternating with periods of relatively weak and stable currents and major deposition. The Pliocene-Quaternary Cap Ferret distal deep-sea fan is a thick (500 m) sand-rich turbiditic accumulation fed directly by an uplifting mountain range. The accumulation is developed downstream of a main turbiditic feeder channel and the volume of sediment involved is much higher than for the Vema contourite fan. It shows a complex network of shallow channels and low-relief levees which merge downstream into thin, sandy, sheet-like deposits. Several depositional units are stacked vertically. Each unit is built by the lateral migration of a ‘channel-levee’ system. The stacking pattern of the successive units is prograding towards the basin. The presence of major discontinuities cutting throughout a whole accumulation, and the fairly irregular geometry of the ‘channel-levee’ deposits (absence of any obvious migrating trend), appear to be the most distinctive features of a contourite fan. On the other hand, the lateral migration of the ‘channel-level’ geometries and the presence of erosional surfaces of limited extent and restricted to the channels, are the main diagnostic features of a distal turbidite fan. Otherwise the seismo-facies are fairly similar in both sedimentary bodies.

Sediment budget and transfer of suspended sediment from the Gironde estuary to Cap Ferret Canyon

A study of the particulate organic carbon content, the grain size of suspended sediment and turbidity in a transect between the Gironde estuary and Cap Ferret Canyon indicates that particles from the Gironde river are transferred to near the bottom of the canyon. The separation of turbid estuarine water into bottom and surface nepheloid layers takes place in the Gironde itself and in the nearshore zone. The development of these two separate turbid layers is due to vertical (a turbid surface plume) and horizontal (bottom layer) salinity gradients. The bottom nepheloid layer is caused primary by a horizontal supply of suspended sediment from the Gironde rather than from resuspension or vertical sedimentation as suggested by other workers. On the median and outer shelf the distribution of particles in the water column is influenced by thermal stratification. The thickness of the bottom nepheloid layer increases from the estuary towards Cap Ferret Canyon as a function of the thickness of the bottom waters. Detached nepheloid layers are observed at the shelf break coinciding with isopycnal surfaces due to the presence of cold waters in the Cap Ferret Canyon. Superimposed advective inputs from the northern part of the shelf and resuspension of particles from mud patches contribute to the supply of particles towards the canyon. Suspended sediment in transit over the shelf break represents 2–3% of the total discharge from the Gironde estuary. This is a considerable amount as 50% of the suspended sediment is trapped in the west Gironde mud patch and another undefined portion of the Gironde sediment load is transported along the coast by tidal currents.

Three anticyclonic slope water oceanic eDDIES (SWODDIES) in the Southern Bay of Biscay in 1990

Jet-like extensions of the slope current off northern Spain and France in the southern Bay of Biscay in the winter develop into anticyclonic eddies with an upper core of slope water. Three eddies were observed to develop in the winter of 1989/1990, subsequently named F90a, F90b and O90. F90a was an anticclonic eddy of radius 50–60 km, with a central core of mixed water of slope origin (from the slopes in the vicinity of Cap Ferret Canyon) and of volume ∼400 k 3. In the eddt centre, the mixed core extended from ∼70 to ∼280 m. Measurements at sea showed minimal changes in the core characteristics of F90a (potential temperature, 12.95°C, salinity, 35.74 psu) with time, and remote sensing studies demonstrated that these slope water core eddies can maintain their identities for about a year. Rotation rates in the central core of F90a were about 3 days and values of normalized relative vorticity were about −0.5. Maximummean azimuthal velocities were about 30 cm s −1 at a radius of 30 km. Hydrographic data showed that the presence of the core was felt to a depth of ∼1500m, resulting in an azimuthal transport of about 8 Sv. Both F90a and O90 moved westward across the deep (4800 m) Bay of Biscay, and the westward migration speed (2 cm s −1) seems in excess of simple theoretical estimates for the β-induced westward propagation speed (0.4 cm s −1) of anticyclonic eddies. If the latter figure is used for self-advection and the effects of topography and mutual influence are neglected, the observed westward movement suggests a clockwise mean circulation −2 cm s −1) for the oceanic water in the Bay of Biscay. By contrast, F90b remained nearly stationary near 4°W. Remote sensing studies indicate that the occurence of a 4°W eddy in the summer of any year miight be attributed to warm slope water inflow along the northern Spanish slope in the previous winter.